ANSYS Solutions? - Czech Technical University

Industry Spotlight: 

Chemical and 

Processing 

FEA is a valuable tool that 

aids doctors in orthopedic 

operations 

Researchers use ANSYS to 

develop micron-sized, selfpowered 

mobile mechanisms 

Quickly vary geometry even 

without parametric CAD

Take a look at the future of 

product development... 

...a process that's more automated, more integrated, 

more innovative and truer to life. That’s where ANSYS 

is taking engineering simulation. By combining technologies 

like industry-leading meshing, nonlinear analysis and 

computational fluid dynamics, you can reduce costs and 

drive products to market quicker. 

Bring your products and processes to life with ANSYS. 

Visit www.ansys.com/secret/6 or call 1.866.ANSYS.AI.

Contents 

Industry Spotlight 

Departments 

6 

Chemical and Processing 

A continuing series on the value 

of engineering simulation in 

specific industries 

Editorial -To Collaborate, 

You Need People 

Industry News -Recent Announcements 

and Upcoming Events 3 

2 

Features 

10 

14 

ANSYS for Virtual 

Surgery 

FEA is a valuable tool that 

aids doctors in orthopedic 

operations 

FEA in Micro-Robotics 

Researchers use ANSYS to 

develop micron-sized, selfpowered 

mobile mechanisms 

Software Profile -The New Face of 

ANSYS ICEM CFD 16 

CFD Update -Simulation Helps 

Improve Oil Refinery Operations 

Managing CAE Processes -Upfront 

Analysis in the Global Enterprise 

Simulation at Work - Analysis of 

Artificial Knee Joints 

Tech File -Demystifying Contact 

Elements 

Tips and Techniques-Contact 

Defaults in Workbench and ANSYS 

18 

25 

26 

33 

36 

Guest Commentary-Putting Quality 

Assurance in Finite Element Analysis 40 

28 

Design Insight for 

Legacy Models 

Quickly vary geometry even 

without parametric CAD 

Want to continue receiving 

ANSYS Solutions? 

Visit www.ansys.com/subscribe to update 

your information. Plus, you’ll have the chance 

to sign up to receive CFX eNews and email 

alerts when the latest electronic version of 

ANSYS Solutions becomes available! 

About the cover 

There are many examples 

of successful chemical and 

processing companies using 

ANSYS simulation technology 

to improve products and 

processes. Our cover article 

describes how Twister BV 

used ANSYS CFX to reduce 

costs by 70% compared 

to the conventional route 

without CFD in developing 

gas separator equipment. 

For ANSYS, Inc. sales information, call 1.866.267.9724, or visit www.ansys.com on the Internet. 

Go to www.ansyssolutions.com/subscribe to subscribe to ANSYS Solutions. 

Editorial Director 

John Krouse 

jkrouse@compuserve.com 

Designers 

Miller Creative Group 

info@millercreativegroup.com 

Ad Sales Manager 

Ann Stanton 

ann.stanton@ansys.com 

Editorial Advisor 

Kelly Wall 

kelly.wall@ansys.com 

Managing Editor 

Jennifer L. Hucko 

jennifer.hucko@ansys.com 

Art Director 

Paul DiMieri 

paul.dimieri@ansys.com 

Circulation Manager 

Elaine Travers 

elaine.travers@ansys.com 

CFD Update Advisor 

Chris Reeves 

chris.reeves@ansys.com 

ANSYS Solutions is published for ANSYS, Inc. customers, partners, and others interested in the field of design and analysis applications. 

The content of ANSYS Solutions has been carefully reviewed and is deemed to be accurate and complete. However, neither ANSYS, Inc., nor Miller Creative Group guarantees or 

warrants accuracy or completeness of the material contained in this publication. ANSYS, ANSYS DesignSpace, CFX, ANSYS DesignModeler, DesignXplorer, ANSYS Workbench 

Environment, AI*Environment, CADOE and any and all ANSYS, Inc. product names are registered trademarks or registered trademarks of subsidiaries of ANSYS, Inc. located in the 

United States or other countries. ICEM CFD is a trademark licensed by ANSYS, Inc. All other trademarks or registered trademarks are the property of their respective owners. 

POSTMASTER: Send change of address to ANSYS, Inc., Southpointe, 275 Technology Drive, Canonsburg, PA 15317, USA ©2004 ANSYS, Inc. All rights reserved. 

©2004 ANSYS, Inc. All rights reserved. 

www.ansys.com ANSYS Solutions | Summer 2004

Editorial 

2 

To Collaborate, You Need People 

Intellectual capital for creating innovative designs is lacking 

at manufacturers that skimp on jobs. 

By John Krouse 

Editorial Director 

ANSYS Solutions 

jkrouse@compuserve.com 

One of the most significant – 

and possibly least recognized 

– aspects of engineering 

simulation is that the technology 

can be a tremendously 

effective communication 

and collaboration tool in 

product development. By 

using virtual prototyping, 

what-if studies and a wide 

range of other analyses 

to show how proposed 

products will perform, 

engineering simulation can 

give people in multi-functional 

product development teams tremendous insight into 

designs. The technology also provides an effective way 

for team members to interact, with disciplines outside 

engineering able to see the impact of their various ideas, 

suggestions, feedback and 

input. In this way, teams can 

investigate even the most 

unconventional ideas, some 

of which can turn out to be 

the basis of ground-breaking 

new products. 

Collaborative product 

development is a growing 

trend in manufacturing industries, getting engineers and 

analysts working with others across the extended 

enterprise: manufacturing, testing, quality assurance, 

sales, marketing and service – even those outside the 

company such as suppliers, customers, consultants 

and partners. These people typically don’t know how to 

build meshes, define boundary conditions, run analyses 

or perform optimizations. But they can see the impact of 

what simulations show, and they can provide valuable 

feedback in spotting, evaluating and fixing potential 

problems. Marketing could suggest a different contour 

that would make a consumer product more saleable, for 

example, or procurement might suggest alternate 

suppliers for stronger and less expensive components 

to reduce excess stress. 

This multi-functional synergy is the basis for 

the creativity necessary to develop innovative products 

and processes that might not immediately occur to 

individuals working separately. Collaboration taps into 

the intellectual capital of the enterprise – the combined 

know-how and insight of workers about the company’s 

operation, its products and its customers. 

Companies need people for multidisciplinary 

collaboration. But, unfortunately, jobs at manufacturing 

firms are in steady decline. According to the National 

Association of Manufacturers, after peaking at 17.3 million 

in mid-2000, manufacturing employment has fallen 

by 2.8 million while employment in non-manufacturing 

sectors of the economy rose by 671,000 to 115 million. 

Data from the U.S. Bureau of Labor Statistics indicates 

there were 2,378 extended mass layoffs in 

manufacturing during 2002 alone, resulting in 454,034 

workers being removed from their jobs. 

Meanwhile, the overall economy is rebounding, 

with the Dow Jones Industrial Average undergoing 

a strong sustained rally and corporate profits up. 

Forecasters at the National Association for Business 

Economics predict that the U.S. economy will show a 

robust annual growth of 4.5% in 2004. 

Despite this strong economic growth, payrolls in 

manufacturing continue to go down as manufacturers 

operate with as few people 

as possible. Running these 

super-lean operations 

pumps up short-term 

profits. But manufacturers 

cannot sustain long-term 

growth based on savings 

from a barely adequate 

workforce being stretched 

to the limit. Product quality, customer service and brand 

image ultimately suffer, as do product innovations that 

spring from collaborative design. 

To collaborate, you need people: ones with enough 

time in the workday to apply their knowledge on creative 

projects. When manufacturers cut jobs indiscriminately, 

they’re not just getting rid of salaried bodies, they’re 

discarding the company’s most valuable asset – the 

wealth of intellectual capital in its workforce. Companies 

that fall into this trap risk being left behind in the market 

by astute competitors with enough sense to invest in 

their workers and the knowledge they bring to the 

collaborative processes necessary to develop winning 

products. ■ 

COLLABORATION TAPS INTO THE 

INTELLECTUAL CAPITAL OF THE ENTERPRISE – 

THE COMBINED KNOW-HOW AND INSIGHT OF 

WORKERS ABOUT THE COMPANY’S OPERATION, 

ITS PRODUCTS AND ITS CUSTOMERS. 


Industry News 

3 

Recent Announcements 

EASA 3.0 - The New Standard for Efficient 

Application Development 

EASA enables ultra-rapid creation and deployment 

of Web-enabled applications that can drive most 

applications, including ANSYS and CFX. EASA 

also can be used to integrate several tools, thus 

automating processes involving say CAD, FEA and 

even in-house codes. EASA is available as a software 

product to author and publish your own custom 

applications. Alternatively, several ASDs are now using 

EASA to create turnkey applications to your 

specification as a service. 

New features in EASA 3.0 include: 

• Connectivity to Relational Databases such as SQL 

Server and Oracle, and with database applications 

such as ERP, CRM and PLM systems. 

• Improved Security for Internet Use using Secure 

Socket Layer (SSL) technology, enabling you to host 

applications for use over the Internet. 

• Multi-Language EASAPs — create your app in your 

language, and users see it in their preferred 

language. Character sets supported include 

Roman, Chinese, Japanese, Russian and Arabic. 

• New parametric study and optimization capabilities 

• New API — EASA’s differentiator has always been to 

allow non-programmers to create professionalgrade 

Web-enabled applications around their 

underlying software. Now an API allows EASA 

authors who have programming skills to create 

applications at the next level by using custom code. 

For more information, visit www.ease.aeat.com. 

2004 International ANSYS Conference Hailed 

Success 

Engineering professionals from throughout the world 

gathered at the Hilton Pittsburgh in May for the 2004 

International ANSYS Conference to discover the true 

meaning behind what it is to Profit from Simulation. 

Vision and strategy set the theme for the general 

session. Kicking off the conference with a welcome 

address, ANSYS president and CEO, Jim Cashman, 

set the stage for keynote speaker, Brad Butterworth of 

Team Alinghi. As the cunning strategist aboard the 

Team Alinghi yachts, Brad shared his 

experience and discussed how the America’s Cup 

winner is using ANSYS’ integrated simulation 

solutions to defend its title in the 2007 competition. 

After the morning break, ANSYS presented its 

Technology Roadmap, the company’s successful, 

ongoing strategy for integrating the power of the entire 

ANSYS, Inc. family of products into the ultimate 

engineering simulation solution. Then, Bruce Toal, 

director of Marketing and Solutions, High Performance 

Technical Computing Division at Hewlett-Packard 

Company, spoke about the company’s Adaptive 

Enterprise for Design and Manufacturing. 

Following a day of technical and general sessions, 

and visiting exhibitor booths, attendees enjoyed a 

conference social sponsored by Hewlett-Packard 

Monday evening. Standing ovations and triumphant 

applause echoed throughout the ballroom during the 

social as ANSYS president and CEO, Jim Cashman, 

presented Dr. John Swanson, ANSYS founder, with an 

award for being the recipient of the 2004 AAES John 

Fritz Medal. 

ANSYS long-standing partners and its key customers 

took to the podium for the Tuesday general session. 

LMS International’s Tom Curry, executive vice 

president and chief marketing officer, spoke about the 

product creation process. Tom guides the company’s 

growth in predictive computer-aided engineering, 

physical prototyping and related services. 

Herman Miller’s Larry Larder, director of engineering 

services, discussed how they use ANSYS 

simulation technologies to experiment and innovate in 

the office furniture industry. 


Industry News 

4 

SGI’s director of product marketing, Shawn 

Underwood, presented future of high performance 

computing followed by Dr. Paresh Pattani, director of 

HPC and Workstation Applications at Intel 

Corporation who focused on the paradigm shift in high 

performance computing. 

of quality products to market, users have faced major 

challenges to realizing the full value. For example, 

hardware and software limitations have historically 

made realistic simulations elusive when realism 

involves highly detailed models and complex physical 

behavior. 

Jorivaldo Medeiros, technical consultant at 

PETROBRAS, offered his ANSYS success story 

on how the company drives development and 

innovation in equipment technology. 

In addition, ANSYS became the first engineering 

simulation company to solve a 111 Million Degrees of 

Freedom structural analysis model. After lunch, the 

Management Track addressed strategies on how to 

implement new technologies and explain the benefits 

of engineering simulation to management. 

ANSYS Breaks Engineering Simulation Solution 

Barrier 

ANSYS, Inc. has become the first engineering 

simulation company to solve a structural analysis 

model with more than 100 million degrees of freedom 

(DOF), making it possible for ANSYS customers to 

solve models of aircraft engines, automobiles, 

construction equipment and other complete systems. 

“Manufacturers are looking for more accurate, large 

system simulations to improve their time-to-money,” 

said Charles Foundyller, CEO at Daratech, Inc. “This 

announcement means that users now have a clear 

roadmap to improved productivity.” 

As hardware advances in speed and capacity, ANSYS 

is committed to being the leader in developing CAE 

software applications that take advantage of the latest 

computing power. This leadership provides customers 

with the best engineering simulation tools for their 

product development process to help achieve better 

cost, quality and time metrics. 

This powerful new offering from ANSYS speaks to its 

commitment to develop and deliver the best in 

advanced engineering solutions. In turn, ANSYS has 

entered into a three-year partnership with SGI 

to advance the capabilities of ANSYS in parallel 

processing and large memory solutions. 

In a joint effort with Silicon Graphics, Inc. (SGI), 

the 111 million DOF structural analysis problem was 

completed in only a few hours using an SGI ® Altix ® 

computer. DOF refers to the number of equations 

being solved in an analysis giving an indication of a 

model’s size. 

“ANSYS’ ability to solve models this large opens the 

door to an entirely new simulation paradigm. Prior to 

this capability, a simulation could be conducted only at 

a less detailed level for a complete model or only 

at the individual component level for a detailed model. 

Now, it will be possible to simulate a detailed, 

complete model directly; potentially shortening design 

time from months to weeks. Equally important, having 

a high fidelity comprehensive model can allow trouble 

spots to be detected much earlier in the design 

process. This may greatly reduce additional design 

costs and can provide an even shorter time to 

market,” said Jin Qian, senior analyst at Deere & 

Company Technical Center. 

According to Marc Halpern, research director at 

Gartner, although simulation accelerates the delivery 

Safe Technology Incorporates AFS Strain-Life 

Cast Iron Database in fe-safe 

Safe Technology Ltd has been granted a license to use 

the AFS cast iron database from the research report 

“Strain-Life Fatigue Properties Database for Cast Iron” 

in its state-of-the-art durability analysis software suite 

for finite element models, fe-safe. Safe Technology Ltd 

is a technical leader in the design and development 

of durability analysis software that pushes the 

boundaries of fatigue analysis software to ensure 

greater accuracy and confidence in modern fatigue 

analysis methods for industrial applications. The 

availability of the AFS database within fe-safe ensures 

that users will have access to the most up-to-date and 

accurate cast-iron materials data for their durability 

analyses. 

The AFS Ductile Iron and the Gray Iron Research 

Committees have developed a Strain-Life Fatigue 

Properties Database for Cast Iron. This database 

represents the capability of the domestic casting 

industry and is available as a special AFS publication. 

It is the culmination of a five-year effort in partnership 


with the DOE Industrial Technology Program. 

The scope of this information includes 22 carefully 

specified and produced castings from ASTM/SAE 

standard grades of irons, including Austempered Gray 

Iron (AGI) (specification is under development). Each 

grade is comprehensively characterized from an 

authoritative source with chemical analysis, 

microstructure analysis, hardness tests, monotonic 

tension tests and compression tests. This information 

is contained in user-friendly digital files on two 

CD-ROMs for importing into computer aided design 

software. AFS Publications are described online at 

www.afsinc.org/estore/. 

For more information, visit www.safetechnology.com 

Product Development Platform Will Simulate 

and Optimize Design Performance for Autodesk 

Inventor Professional Customers 

Autodesk will license ANSYS simulation technologies 

and package them as an integral part of the Autodesk 

Inventor Professional 9.0 product and future releases. 

Powered by ANSYS’ part-level stress and resonant 

frequency simulation technologies, Autodesk Inventor 

Professional 9.0 will enable design engineers to create 

more cost-effective and robust designs, based on how 

the products function in the real world, by facilitating 

quick and easy “what-if” studies right within the 

software’s graphical user interface. 

Upcoming Events 

“Autodesk is proud to be working with an industry 

innovator like ANSYS,” said Robert Kross, vice 

president of the Manufacturing Solutions Division at 

Autodesk. “This reinforces our commitment to deliver 

proven and robust technologies to manufacturers, in 

order to help them deliver better quality products and 

bring them to market faster. Inventor Pro 9.0 will make 

simulation (CAE) functionality available to a broader 

mechanical design community, while protecting 

customers’ business investment by seamlessly 

integrating with other high-end ANSYS offerings. Our 

customers will surely benefit from this relationship.” 

The total solution will help product development 

teams make more informed decisions earlier in the 

design process, allowing them to reduce costs and 

development time while designing better and more 

innovative products. 

“This new offering from Autodesk will be viewed very 

strategically by their customers. As they deploy 

simulation tools throughout their product design 

process, the Autodesk-ANSYS offering will be a 

key component to a customer’s overall simulation 

strategy,” said Mike Wheeler, vice president and 

general manager of the Mechanical Business Unit at 

ANSYS. “ANSYS is proud to be part of the design 

effort to create this next generation tool as part of our 

overall ANSYS Workbench development plan.” 

5 

Date Event Location 

August 29-September 3 ICAS 2004 Yokohama, Japan 

September 5-8 RoomVent 2004 Coimbra, Portugal 

September 6-9 17th International Symposium Bonn, Germany 

on Clean Room Technology 

September 7-8 European UGM for Automotive Neu-Ulm, Germany 

Applications Radtherm User Conference 

September 19-20 German Aerospace Congress 2004 Dresden, Germany 

September 21-22 Numerican Analysis and Simulation Troy, Michigan, USA 

in Vehicle Engeineering 

September 22-25 3rd International Symposium on Two-Phase Pisa, Italy 

Flow Modeling and Experimentation 

September 29-30 Calculation & Simulation in Vehicle Building Wurzburg, Germany 

September 29-30 Pump Users Intarnational Forum 2004 Karlsruhe, Germany 

September 28 - October 2 ASME DETC/CIE Conference Salt Lake City, Utah, USA 

October 4 2004 PLM European Event UK 

October 4-5 DaratechDPS Novi, MI 

October 12 ANSYS Multiphysics Seminar Sweden 

October 13 Construtec Conference Spain 

October 20 ANSYS 9.0 Update Seminar Sweden 

October 28-29 ANSYS User Conference Mexico 



6 

Industry Spotlight: 

Chemical and Processing 

A continuing series on the value of engineering 

simulation in specific industries. 

The chemical and processing industries provide the building blocks for many 

products. By using large amounts of heat and energy to physically or chemically 

transform materials, these industries help meet the world’s most fundamental 

needs for food, shelter and health, as well as products that are vital to such advanced 

technologies as computing, telecommunications and biotechnology. 

According to the American Chemical Society, chemical and processing industries account for 25% of 

manufacturing energy use. 

These industries consume fossil resources as both fuel and feedstock, and produce large amounts of 

waste and emissions. 

In turn, as exemplified by the U.S. Government’s 2020 Vision, these industries face major challenges to 

meet the needs of the present without compromising the needs of future generations in the face of 

increasing industrial competitiveness. This translates into the need to make processes much more energy 

efficient, safer and more flexible, and to reduce emissions to meet the many competitive challenges within 

a global economy. As well as the need to reduce design cycle times and costs, major challenges where 

simulation has an important role including: 

■ ‘Scale-up’, to extrapolate a process from laboratory and pilot plant scale, to the industrial plant 

scale, which may require many millions of dollars investment. 

■ Process intensification, to combine different processes into smaller compact and efficient units, 

instead of treating them as individual processes. 

■ Retrofitting, to upgrade a plant to become more efficient, within the many constraints of the existing 

footprint of the plant. 

This issue of ANSYS Solutions provides examples of these, in offshore oil 

production, waste water treatment and chemical processing, and many other 

examples which highlight the benefits to be obtained are to be found on the 

ANSYS CFX Website at www.ansys.com/cfx. 

These problems are inherently multi-scale, with the combination of different 

physical and chemical processes at the molecular level, and the macro-flow 

processes transporting a reacting fluid around the complex geometries of a large 

industrial chemical reactor. The recent advances in modeling capabilities, 

combined with the scalable parallel performance of low cost hardware, and the 

powerful geometrical and meshing tools in the ANSYS software modules open 

up many new opportunities to achieve major new benefits in the complex and 

demanding world of the chemical and process industries. 

Offshore platform 


Case-in-point: 

Integral Two-Phase Flow Modeling in 

Natural Gas Processing 

Customized version of CFX reduces costs 70% 

compared to the conventional route without 

CFD in developing gas separator equipment. 

By Marco Betting, Team Leader Twister 

Technology; Bart Lammers, Fluid 

Dynamics Specialist; and Bart Prast, 

Fluid Dynamics Specialist, Twister BV 

Natural gas processing involves dedicated systems 

to remove water, heavy hydrocarbons and acidic 

vapors from the gas stream to make it suitable for 

transportation to the end-customer. From a process 

engineering perspective, these systems are 

combinations of flashes, phase separations, flow 

splitters, and heat and mass exchangers exhaustively 

designed to achieve required export specifications. 

While the process engineer is concerned with 

finding the optimal system configuration using 

pre-defined process steps and equilibrium 

thermodynamics, the flow-path designer tries to 

optimize the performance of each individual process 

step in the system based on an understanding of both 

two-phase flow behavior and non-equilibrium 

thermodynamics. The fluid dynamics interaction 

between subsequent process steps is not always 

Normalized total C8 fraction in vortex section of 

Twister Supersonic Separator 

Uniform C8 

distribution 

❿ 

❿ 

❿ 

C8 separation 

taken into account to its full extent, even though this 

can strongly influence the total system performance. 

Developing and designing new equipment for the 

process industry is a time-consuming and expensive 

exercise. Twister BV (www.twisterbv.com) offers 

innovative gas processing solutions that can play 

an essential role in meeting these challenges. 

The team has been developing the Twister 

Supersonic Separator, which is based on a 

❿ 

Liquid 

Vapor 

7 

Expander 

Cyclone Separator 

Compressor 

Saturated 

Feed Gas 

100 bar, 20ºC 

Dry gas 

70 bar, 5ºC 

Laval Nozzle 

30 bar, -40ºC 

Supersonic Wing 

Mach 1.3 (500 m/s) 

Cyclone Aeparator 

(300,000 g) 

Liquids + Slip-Gas 

70 bar, 5ºC 

Diffuser 

In Twister, the feed gas is expanded to supersonic velocity, thereby creating a homogeneous mist flow. During the 

expansion, a strong swirl is generated via a delta wing, causing the droplets to drift toward the circumference of the tube. 

Finally a co-axial flow splitter (vortex finder) skims the liquid enriched flow from the dried flow in the core. The two flows 

are recompressed in co-axial diffusers resulting in a final pressure being approximately 35% less than the feed pressure. 

Twister separator 



8 

unique combination of known physical processes, 

combining aero-dynamics, thermo-dynamics and 

fluid-dynamics to produce a revolutionary gas 

conditioning process. The route from a new Twister 

tube concept to marketable hardware via several 

production field trials has been a major undertaking. 

Reducing costs in the cycle of designing, testing and 

redesigning of Twister prototypes for the challenging 

conditions involved in high-pressure sour natural gas 

processing is of great importance. The introduction 

of computational fluid dynamics in the Twister 

development four years ago resulted in a cost 

reduction of approximately 70% compared to the 

conventional route without CFD. 

Customized Version of CFX 

Twister BV and ANSYS CFX jointly have developed a 

customized version of CFX 5.6*, capable of modeling 

non-equilibrium phase transition in multi-component 

real gas mixtures. The consulting team at ANSYS was 

chosen to perform this work because of their 

understanding of the needs of the industry and the 

flexible nature of CFX-5, which made it suitable for 

implementing the specialized features required. The 

specific features of this customized two-phase CFD 

code are: 

• Full equations of state, including the effects of 

phase change 

• Multi-component gases with several 

condensable species 

• A homogeneous nucleation model to 

determine the droplet number density 

• A growth model, to allow for the change in size 

of the particles, through condensation and 

evaporation 

• Droplet coalescence models depending on 

droplet size, number density and turbulence 

intensities 

• Slip models to predict the separation of the 

droplets from the continuous phase 

• Accounts for turbulent dispersion 

• Aforementioned models are coupled via mass, 

momentum and energy equations 

• Energy is affected by release of latent heat 

during condensation/evaporation 

The development and validation of the 

customized CFX code was of paramount importance 

in maturing the Twister separator for commercial 

application in the oil & gas industry. 

This custom version of CFX-5 includes all 

first-order effects useful for determining the 

performance of liquid/gas separators proceeded by an 

expander or throttling valve. 

Twister and LTX separators 

G + L 

dispersed 

G + L 

stratified 

G + L 

dispersed 

L 

For a process engineer, the quality of the gas coming over the 

top of the separator is determined with the phase equilibrium 

after an isenthalpic flash, presuming a certain liquid carry-over. 

The flow-path designer is concerned with the reduction of the 

carry-over by optimizing the flow variables of the separator, 

based on a feed with presumed droplet sizes. 


Using the customized two-phase code, the flow path designer can study the 

influence of the geometry of a choke valve on the resulting droplet size 

distribution and better assess the performance of the separator based thereon. 

9 

P, T, flow, LGR composition 

P, T, flow, LGR, 

composition 

Mach number 

1.4 

1.2 

1.0 

0.8 

0.6 

0.4 

0.2 

0.0 

P, T, flow, LGR, 

droplet size, 

droplet number 

P, T, flow, 

composition 

LTX separator 

Improving Facility Performance 

Essential for the optimization of the separation 

performance of Twister is the prediction of droplet 

sizes. The droplet size is determined by both the vapor 

diffusion rate toward the droplets and the mutual 

agglomeration of these droplets. The size distribution 

mainly depends on the time interval of the nucleation 

pulse. The droplet size distribution determines the drift 

velocity of the liquid phase and hence determines the 

separation efficiency. Appropriate models for this have 

been implemented. 

This customized CFX code also enables the 

process engineer to better understand the relationship 

between the performance of subsequent process 

steps, e.g., the operation of a Low Temperature 

Separator (LTS) fed by a choke valve. 

Twister BV and ANSYS CFX have completed a 

powerful CFD code validated for natural gas processes. 

This unique CFD capability enables process engineers 

to optimize engineering practices, while increasing the 

performance of gas processing facilities. ■ 

*I.P. Jones et. al, “The use of coupled solvers for multiphase and reacting flows”; 3rd international conference of CSIRO, 10–12 December 2003, Melbourne, Australia. 


10 

ANSYS for Virtual Surgery 

FEA is a valuable tool that aids doctors in orthopedic operations. 

By András Hajdu and Zoltán Zörgö 

Institute of Informatics 

University of Debrecen, Hungary 

Analysis, imaging and visualization technologies 

are being applied increasingly in medical applications, 

particularly in evaluating different approaches to 

surgery and determining the best ways to proceed in 

the operation. In this growing field, one of the primary 

focuses of our work applies finite element analysis to 

orthopedic surgery: specifically, the specialized area of 

osteotomy, where bones are surgically segmented 

and repositioned to correct various deformities. We 

chose ANSYS for this work because of the reliability 

and flexibility of the software in handling the irregular 

geometries and nonlinear properties inherent in these 

materials. 

Medical imaging technologies such as CT, MRI, 

PET or SPECT deliver slice or projection images 

of internal areas of the human body. These tools are 

generally used to visualize configurations of bones, 

organs and tissue, but they also have the ability 

to export image data and additional information in 

commonly known medical file formats like DICOM. 

These files then can be processed by third-party 

computer programs for assessing and diagnosing 

the condition of the patient and planning surgical 

intervention, that is, how the surgical procedure will be 

performed. Other very promising fields include 

telesurgery, virtual environments in medical school 

education and prototype modeling of artificial joints. 

The goal of the research is to develop computer 

applications in the field of orthopedic surgery, 

especially osteotomy intervention procedures based 

on CT images. the team at the Institute of Informatics 

uses this simulation technology to examine theories 

underlying new types of surgeries as well as to aid 

doctors in treating individual patients undergoing hip 

joint correction. These two approaches have many 

common tasks: extracting image data from diverse 

medical image exchange format files, enhancing 

images, choosing the appropriate segmentation 

techniques, CAD-oriented volume reconstruction, 

data exchange with FEM/FEA tools, and geometric 

description of virtual surgery. 


11 

Building Orthopedic Models 

CT data files. The first step in building an 

orthopedic model is extracting an image file from 

medical data exchange formats. As CT images 

represent the X-ray absorption of a given crosssection, 

the intensity values of their pixels represent 

this 12-bit absorption rate, rather than common color 

ranges. Since the slice density is usually reduced to 

a minimum for in-vivo scanning, considerable 

information often is lost, especially in complex regions 

of the human body. For visualization purposes, this 

deficiency can be compensated with interpolation 

techniques, but no lost anatomical data can be 

recovered in this way. Using these files for FEA work 

thus often requires further enhancement. 

Image enhancement and segmentation. As 

given tissue structures have their own absorption rate 

intervals, a windowing technique might be sufficient 

for a simple visualization. However, because these 

intervals can overlap, other tissue parts that differ from 

our VOI (Volume Of Interest) remain in the image, after 

applying the intensity window. Some conventional 

procedures like morphological or spectral-space 

filtering must be applied, as well as specific 

techniques for CT segmentation. We found that other 

methods, such as region growing and gradient-based 

segmentation, achieved excellent results for bone 

structures. 

Volume reconstruction. The final goal of the 

project is to develop an application to be used in 

surgery planning on a routine basis by medical staff 

without experience in using CAD-related software. We 

wanted this application to be able to transfer structural 

data into a finite element modeling and analysis 

software. Thus, volumetric information must be 

represented in a geometrically appropriate way. There 

is a difference between simple surface rendering and 

geometrical volume reconstruction in CAD systems. 

Volumetric data has to be represented using solid 

modeling primitives, and reconstructed using related 

concepts: keypoints, parametric splines, line loops, 

ruled and planar surfaces, volumes and solids. 

When extracting contour points of ROIs (Regions 

Of Interest), we need to reduce the number of points 

to approximately 10-15% by keeping only points with 

rapidly changing surroundings. These points then can 

be interpolated with splines, splines assembled to 

surfaces and surfaces to solids. The major difficulty is 

that CAD-related systems are designed to work with 

regular-shaped objects, and bone structures are not 

like that. However, to be able to execute FEA, it is 

necessary to use this approach. Moreover, virtual 

surgery interventions have to be carried out on 

this representation, or in such a way that proper 

geometrical representation of the modified bone 

structure remains easy to regain. As is often the case, 

conversion problems may occur when exchanging 

data between CAD systems, so we perform the above 

volume reconstruction procedure directly in the FEM 

software using built-in tools provided in the package. 

After testing many FEM programs, we chose ANSYS 

software for this task. Figure 1 illustrates how they 

Figure 1. Steps of volume (bone) reconstruction in ANSYS. 


12 

Figure 2. Part of theoretical path and planar 

intersection of the cutting tool. 

reconstructed in ANSYS an 8-inch part of a femur 

(pipe-like bone) using the mentioned procedure. The 

entire reconstruction procedure was implemented in a 

simple ANSYS script file. 

A natural extension of this method seems to be 

suitable also for bones containing more parts, holes, 

etc. In this case, Boolean operations between solids 

provided by ANSYS gives us a powerful tool. Another 

challenging problem currently being investigated is the 

reconstruction of those parts of the bones where the 

CT slices contain varying topology (e.g., when 

reaching a junction in some special bones). 

Approaches to Virtual Surgery 

Planar approach. There are some cases when 

information from 2-D slices is sufficient for performing 

virtual surgery instead of 3-D solids. For example, 

the first subject of our project – human femur 

lengthening using helical incision – provided a good 

opportunity for experimenting with 3-D interventions 

performed in 2-D. By taking the intersection (dark 

section on Figure 2) of the theoretical cutting tool path 

(Figure 2 left) with the planes of the individual 

CT slices, we subtracted these profiles from the bone 

section profile (Figure 3). 

After the volume reconstruction using this 

technique, we obtained the modified bone structure 

without the need for further intervention. Another 

possibility is to use ANSYS to build up the geometric 

model of the bone and the cutting tool from their 

boundary lines, then to remove the solid defined by 

the path of the cutting tool. The team wrote an ANSYS 

script to obtain fast and automatic model creation. 

In the case of the hip joint correction, some 

intervention also might be simulated in 2-D, but 

designating and registering ROIs on the slice set is 

more difficult. However, handling volumes as a set of 

unsorted 3-D points with additional attributes serves 

as an intermediate solution. 

Three-dimensional approach. In the first subject, 

the 3-D approach adopted by us was the combination 

of the volume reconstruction technique and 

conventional CAD modeling. We reconstructed the 

middle part (diaphysis) of the human femur, and, in the 

same coordinate system, using the axis of the actual 

bone, we constructed the solid object representing the 

path of the cutting tool. This was achieved by applying 

helical extrusion along this axis on a rectangle, 

using the parameters of the actual osteotomy. By 

subtracting these solids from each other, they 

Figure 3. Subtraction of the cutting tool from a 

bone section profile in 2-D, and the 3-D outcome. 

Figure 4. Subtracting a helix from the diaphysis. 


13 

Figure 5. Tetrahedron mesh for GL visualization 

and FEA. 

Figure 6. Different bar hole types and variable 

helix paths to improve efficiency of lengthening. 

obtained the wanted solid object (Figure 4). This 

Boolean subtraction was also executed by ANSYS. 

As previously mentioned, they also work on 

pre-operative analysis and comparison of hip joint 

osteotomy. The 3-D reconstruction of this region 

is more difficult because of the information loss 

during the CT scanning procedure. There are many 

consecutive slice pairs with large differences. In this 

case, interpolation gives no satisfying results, and we 

specialize in general methods to reduce the level of 

user action required. 

Our interface for virtual surgery is GLUT-based, 

containing I/O tools for importing existing meshes and 

exporting the model into a FEM/FEA environment. 

Besides using similar scripts for building up the 

geometry as described above, we also take advantage 

of the mesh generator and manager capabilities of 

ANSYS in data exchange. That way, we can import a 

tetrahedron mesh used in OpenGL technology into 

ANSYS for FEA analysis, for example, and ANSYS 

geometry also can be exported as a tetrahedron mesh 

for visualizing purposes. Figure 5 shows an example of 

a tetrahedron mesh visualization in OpenGL. 

FEM/FEA results. Using the volume 

reconstruction approach, we needed only to translate 

our internal representation to the scripting language. 

Material types and parameters also can be defined 

using scripts. The bone material model we used is a 

linear isotropic one. After applying constraints and 

forces on the nodes of the solids, they have tested 

stress and displacement of the bone structure. Using 

the obtained results, a comparison can be made for 

the known osteotomy interventions of a certain type. 

For femur lengthening, our experience indicated that 

the highest stress values occurred around the starting 

and ending boreholes of the cut, so we also 

considered the usability of different borehole types 

and helix with variable pitches, as shown in Figure 6. ■ 

Dr. András Hajdu is an instructor with the Institute of 

Informatics at the University of Debrecen in Hungary and 

can be contacted at hajdua@inf.unideb.hu. His research is 

supported by OTKA grants T032361, F043090 and IKTA 

6/2001. Zoltán Zörgö (zorgoz@inf.unideb.hu) is in PhD studies 

at the Institute. 

References and Resources for Further Reading 

H. Abé, K. Hayashi and M. Sato (Eds.): Data Book on 

Mechanical Properties of Living Cells, Tissues, and 

Organs, Springer-Verlag, Tokyo, 1996. 

Z. Csernátony, L. Kiss, S. Manó, L. Gáspár and K. 

Szepesi: Multilevel callus distraction. A novel idea to 

shorten the lengthening time, Medical Hypotheses, 

2002, accepted. 

R. C. Gonzalez and R. E. Woods: Digital image 

processing, Addison-Wesley, Reading, 

Massachusetts, 1992. 

A. L. Marsan: Solid model construction from 3-D 

images (PDF, PhD dissertation), The University of 

Michigan, 1999. 

K. Radermacher, C. V. Pichler, S. Fischer and G. Rau: 

3-D Visualization in Surgery, Helmholtz-Institute 

Aachen, 1998. 

L. A. Ritter, M. A. Liévin, R. B. Sader, H-F. B. Zeilhofer 

and E. A. Keeve: Fast Generation of 3-D Bone Models 

for Craniofacial Surgical Planning: An Interactive 

Approach, CARS/Springer, 2002. 

M. Sonka, V. Hlavac and R. Boyle: Image processing, 

analysis, and machine vision, Brooks/Cole Publishing 

Company, Pacific Grove, California, 1999. 

Tsai Ming-Dar, Shyan-Bin Jou and Ming-Shium Hsieh: 

An Orthopedic Virtual Reality Surgical Simulator 

(PDF), ICAT 2000. 

Zoltán Zörgö, András Hajdu, Sándor Manó, Zoltán 

Csernátony and Szabolcs Molnár: Analysis of a 

new femur- lengthening surgery, IEEE IASTED 

International Conference on Biomechanics (BioMech 

2003) (2003), Rhodes, Greece, Biomechanics/34-38. 

Web Links to More Information 

http://graphics.stanford.edu/data/3-Dscanrep/ 

http://image.soongsil.ac.kr/software.html 

http://medical.nema.org 

http://www.ablesw.com/3-D-doctor/ 

http://wwwr.kanazawa-it.ac.jp/ael/imaging/synapse 

http://www.materialise.com 

http://www.nist.gov/iges 


14 

FEA in Micro-Robotics 

Researchers use ANSYS to develop micron-sized, self-powered 

mobile mechanisms. 

By Bruce Donald, Craig McGray, and Igor Paprotny of the Micro-Robotics Group, Computer Science Department, 

Dartmouth College; Daniela Rus, Department of Electrical Engineering and Computer Science, Massachusetts 

Institute of Technology; and Chris Levey, Dartmouth Thayer School of Engineering 

Mobile robots with dimensions in 

the millimeter to centimeter range 

have been developed, but the 

problem of constructing such 

systems at micron scales remains 

largely unsolved. 

The anticipated applications for mobile 

micro-robots are numerous: manipulation of biological 

cells in fighting cancer, for example, or stealth 

surveillance technology where clouds of flying 

micro-robots could monitor sites relatively undetected 

by sight or radar. Micrometer-sized robots could 

actively participate in the self-assembly of higherorder 

structures, linking to form complex assemblies 

analogous to biological systems. One could envision 

such self-assembly to take place inside a human 

body, growing prosthetic devices at their destination, 

for example, thus alleviating the need for intrusive 

surgery. 

Targeting these types of potential future 

micro-robotic applications, the Micro-Robotics Group 

at Dartmouth College has been developing a new 

class of untethered micro-actuators. Measuring less 

than 80 mm in length, these actuators are powered 

through a novel capacitive-coupled power delivery 

mechanism, allowing actuation without a physical 

connection to the power source. Finite element 

analysis using ANSYS allowed us to test the feasibility 

of the power delivery mechanism prior to actual 

fabrication of the device. 

The micro-actuators are designed to move in 

stepwise manner utilizing the concept of scratch-drive 

actuation (SDA). The functionality of a scratch-drive 

Figure 1. Concept behind scratch-drive actuation, which 

moves the micro-actuators in a stepwise manner. An electrical 

potential applied between the back-plate (1) and an 

underlying substrate (2) causes the back-plate to bend 

down, storing strain energy, while the edge of a bushing 

(3) is pushed forward. When the potential is removed from 

the back-plate, the strain energy is released and the backplate 

snaps back to its original shape, causing the actuator 

to move forward. 

actuator is shown in Figure 1. The actuation cycle 

begins when an electrical potential is applied between 

the back-plate and an underlying substrate. The 

back-plate bends downward, storing strain energy, 

while the edge of a bushing is pushed forward. When 

the potential is removed, the strain energy is released 

and the back-plate snaps back to its original shape. 

The actuation-cycle is now completed, and the 

actuator has taken a step forward. 

In contrast to traditional SDA power delivery 

schemes (such as using rails or spring tethers), our 

designs induce the potential onto the back-plate using 


a capacitive circuit formed between underlying 

interdigitated electrodes and the back-plate of the 

actuator. A circuit representation of the system as 

shown in Figure 2 indicated that the back-plate 

potential should be approximately midway between 

the potentials of the underlying electrodes. We 

validated the power delivery concept for the specific 

geometry of our design by modeling the system 

through electro-static analysis in ANSYS. Figure 3 

shows the volume model of the actuator and the 

electrode field. 

The results of the analysis are shown in Figure 4, 

indicating the electrical potentials of the conductive 

elements in the model. Additionally, a cut through the 

air element shows the electrical potential from the field 

propagating through it. The potential of the electrodes 

in this example was set to 0 V (blue) and 100 V (red), 

which represented the model boundary conditions. 

The required potential of the back-plate was solved to 

be approximately 50 V, validating the circuit-model 

approximation. We also discovered that the potential 

of the back-plate changes only slightly as a function of 

the orientation of the drive in relation to the electrode 

field. This indicates that the actuator can be powered 

regardless of its orientation, so long as the device 

remains inside the electrode field. 

Additionally, we used the ANSYS model to 

visualize the intensity of the electric field propagating 

through the bottom layer of the insulation material, as 

shown in Figure 5. We suspect charging of the device 

due to charge-migration in the direction of the field, 

and charges embedding in the insulating layer 

underneath the drive. We anticipate that these charges 

will cluster along the areas where the electric field is 

the strongest. In future experiments, attempt will be 

made to image this pattern using a scanning electron 

microscope. 

Following the finite element analysis, we have 

successfully fabricated and actuated an untethered 

scratch-drive actuator capable of motion at speeds of 

up to 1.5mm/s—good pace for such a tiny device. 

Our current work is focused on how to apply these 

actuators to create steerable autonomous 

micro-robotic systems. We anticipate further use of 

ANSYS to model the electrostatic and mechanical 

interaction of the system components to further 

shorten our development cycle. In particular, we plan 

to use the ANSYS coupled-physics solver to 

determine the snap-down and operational 

characteristics of our actuators. ■ 

Figure 2. Simplified capacitive-circuit representation 

of the system. 

Figure 3. Volume model of the actuator and the electrode 

field, prior to solving the model in ANSYS. 

Figure 4. Results of the electrostatic analysis, indicating the 

calculated potentials of the different model components 

after applying the boundary conditions. 

15 

Figure 5. Intensity of the electric field propagating through 

the bottom insulation layer of the actuator. 


Software Profile 

16 

The New Face of 

ANSYS ICEM CFD 

V5.0 represents a significant redesign for 

the market leader in mesh generation. 

Judd Kaiser, Technical Solution Specialist 

The new user interface for ANSYS ICEM CFD brings 

important benefits to all users and has undergone 

extensive testing, with earlier releases of 

AI*Environment and ANSYS ICEM CFD 4.CFX utilizing 

essentially the same interface. 

The learning curve for new users can be 

dramatically shortened by way of an updated layout 

consisting of tabbed panels, a hierarchical model tree 

and intuitive icons. 

Existing users can look forward to enhanced 

meshing technology in a single 

unified environment for shell, 

tet, prism, hex and hybrid mesh 

generation. Performance improvement 

highlights for these users 

include hotkeys (which provide 

one-click access to the most commonly 

used functions), selection 

filters and support for the Spaceball 

3-D motion controller. 

Getting Geometry In 

ANSYS ICEM CFD is well-known 

for its ability to get geometry from 

virtually any source: native CAD 

packages, IGES, ACIS or other 

formats. The package continues to 

be unique among mesh generators 

in its ability to use geometry in both CAD and faceted 

representations. Faceted geometry is commonly used 

for rapid prototyping (stereo lithography, STL), reverse 

engineering (where the STL geometry comes from 

techniques such as digital photo scan) and biomedical 

applications (where the geometry can come 

from techniques such as magnetic resonance 

imaging [MRI]). 

One major development is that V5.0 is the first 

version of ANSYS ICEM CFD capable of running 

within the ANSYS Workbench Environment. As the 

common platform for all ANSYS products, Workbench 

ANSYS ICEM CFD remains the clear 

choice for meshing complex geometry. 

Shown is a tet/prism mesh for a race 

car wheel and suspension. 

provides a common desktop for a wide range of CAE 

applications. With ANSYS Workbench V8.1 and 

ANSYS ICEM CFD V5.0 installed, ANSYS ICEM CFD 

meshing is exposed as the Advanced Meshing tab. 

Geometry can be transferred seamlessly from 

DesignModeler to ANSYS ICEM CFD. 

Fault-Tolerant Meshing 

Having the geometry in hand doesn’t do you any good 

if you can’t create a mesh. Fault-tolerant meshing 

algorithms remain the heart of the 

ANSYS ICEM CFD meshing suite. 

Using an octree-based meshing 

algorithm, ANSYS ICEM CFD Tetra 

generates a volumetric mesh of 

tetrahedral elements that are projected 

to the underlying surface model. This 

methodology renders the mesh 

independent of the CAD surface patch 

structure. This makes the meshing 

algorithm highly fault-tolerant – sliver 

surfaces, small gaps and surface 

overlaps cause no problem. The mesh 

has the ability to walk over small 

details in the model. Control is in the 

hands of the user, who has the flexibility 

to define which geometric details are 

ignored and which are represented 

accurately by the mesh. Tetra’s computation speed 

has been improved with V5.0. As an example, a test 

model of 250,000 elements and moderate geometry 

complexity required 32% less CPU time during 

meshing when compared with the previous version. 

The Delaunay tet meshing algorithm was added 

to the meshing suite in the previous version and has 

undergone numerous improvements, including 

support for density volumetric mesh controls. 

For viscous CFD applications, tet meshes can be 

improved by adding a layer of prism elements for 

improved near-wall resolution for boundary layer 


17 

Prism before 

Prism after 

Images showing a cut through a hybrid hex/tet mesh of a wind tunnel/missile configuration before and after adding a layer of prism elements 

on the wind tunnel walls. Note that the prism layer is included for both the hex and tet zones (new feature in V5.0). 

flows. ANSYS ICEM CFD Prism also has been 

improved for this release. Prism layers can now be 

grown from surface mesh without the need for an 

attached volume tet mesh. Perhaps more significant, 

prism layers can now be grown from both tri and quad 

elements. This means that it is now possible to grow a 

prism layer in a combined hybrid hex/tet mesh. 

Integrated Hex Meshing 

ANSYS ICEM CFD Hexa remains a leader in getting 

high-quality, all-hex element meshes on geometries, 

which most competitors wouldn’t even attempt a hex 

mesh. The key to the approach is a block structure 

that is generated independent of the underlying 

arrangement of CAD (or faceted) surfaces. Think of the 

block structure as an extremely coarse all-hex mesh 

that captures the basic shape of the domain. Each 

block is then a parametric space in which the mesh 

can be refined. For CFD meshes, the ability of this 

parametric space to be distorted to follow anisotropic 

physics makes it very efficient at capturing 

key features of the flow with the lowest possible 

element count. 

Dassault Systemes recognized the power and 

promise of this methodology, selecting ANSYS ICEM 

CFD technology as the only hex meshing solution to 

be offered integrated into CATIA V5. CAA V-5–based 

ANSYS ICEM CFD Hexa offers hex meshing that 

maintains parametric associativity to the native CATIA 

Design Analysis Model. 

New in V5.0, Hexa has been fully integrated into 

the new user interface. Hex meshing functions are 

housed in the blocking tab, and block structure 

entities are organized on the blocking branch of the 

model tree. In addition to reworking the user interface, 

several operations have been significantly streamlined. 

New methods of creating grid blocks have been 

added. The process of grouping curves and defining 

edge-to-curve projections has been made more 

efficient. Most operations now take advantage of 

multi-selection methods, such as box and polygon 

select. The addition of blocking hotkeys is a real 

time-saver, giving the user single-keystroke access to 

the most frequently used operations. 

For shell meshing, V5.0 offers unstructured 2-D 

blocks, combining the best of ANSYS ICEM CFD 

Hexa and the patch-based mesher formerly known as 

Quad. The creation of blocks for 2-D shell meshing 

has been automated, so that blocks can be created 

automatically for all selected surfaces. 

Mesh Editing 

ANSYS ICEM CFD offers maximum flexibility in its 

mesh editing tools, whether it’s via global smoothing 

algorithms or techniques to repair or recreate individual 

problem elements. These tools provide one last 

place to work around any bottlenecks. 

Noteworthy are new unstructured hex mesh 

smoothing algorithms, which strive for mesh smoothness 

and near-wall orthogonality while preserving 

mesh spacing normal to the wall. Two new quality 

metrics have been added in order to help quantify 

mesh smoothness: adjacent cell volume ratio and 

opposite face area ratio. 

Scripting Tools 

ANSYS ICEM CFD provides a powerful suite of tools 

for geometry creation, model diagnosis and repair, 

meshing and mesh editing. All of these tools 

are exposed at a command line level, providing a 

formidable toolbox for the development of vertical 

applications. Every operation performed can be stored 

in a script for replay on model variants. This power can 

be extended by using the Tcl/Tk scripting language, 

enabling the development of entire applications. 

These tools enable users to get around virtually 

any geometry or meshing bottleneck, getting the mesh 

you need using the geometry you have. ■ 


CFD Update: What’s New in Computational Fluid Dynamics 

18 

Blood Flow Analysis Improves Stent-Grafts 

Coupled ANSYS and CFX fluid structure simulations help 

researchers develop optimal surgical recommendations, 

improved stent designs and proper stent placement. 

By Dr. Clement Kleinstreuer, Professor and Director of 

the Computational Fluid-Particle Dynamics Laboratory 

and Zhonghua Li, Doctoral Student, Biomechanical 

Engineering Research Group, North Carolina State 

University 

One of the more intriguing challenges in modern 

medicine is the repair of abdominal aortic aneurysms 

using stent-grafts: tubular wire mesh stents 

interwoven with a synthetic graft material. The device 

is guided into place through a small incision in the 

groin and then propped open in the aorta, thus 

reinforcing the damaged area of the artery. For 

reasons that were not well understood until recently, 

however, some stent-grafts move out of place. This 

migration may again expose the weakened aortic wall 

to relatively high blood pressure, potentially leading to 

sudden aneurysm rupture and death. 

Developing an understanding of stent-graft 

migration and finding suitable solutions is our current 

work at the Biomechanical Engineering Research 

Group (BERG) of North Carolina State University in 

Raleigh. We are using a pairing of computational 

fluid dynamics (CFD) interactively coupled with 

computational structure analysis. Using coupled CFX 

and ANSYS Structural models in these fluid structure 

interactions (FSI), we are learning what goes on inside 

the aorta before and after a stent-graft is surgically 

inserted, and how the stent-graft might migrate or 

dislodge. 

Most studies assume that artery walls are stiff 

with regard to the pressure changes that come with 

each heartbeat, and that arterial wall thicknesses 

are constant both axially and circumferentially. Neither 

is usually true, especially for older patients with 

hypertension, a group that suffers most from 

aneurysms. 

LEFT: Representation of a cross-section of an abdominal aortic aneurysm 

(AAA) with a bifurcating stent-graft. RIGHT: Representation of an aortic artery 

aneurysm (bulge on left) between the renal artery (to the kidneys, top) and the 

iliac bifurcation (to the legs). Aside from the color shading chosen, this is 

what the surgeon would see before starting to implant the stent-graft. 

Studying Stent Migration 

The stent migration problem in abdominal aortic 

aneurysm (AAA) repairs is critical to the patient’s 

survival. When the stented graft slides out of place 

axially, the weakened or diseased artery wall is 

re-exposed to the high blood pressure of pulsating 

blood flow. That greatly increases the possibility of 

AAA-rupture, which is usually fatal. Easily overlooked, 

aortic aneurysms are the 13th leading cause of death 

in the United States. 

Wall displacements and pressure/stress levels for Resteady=1200, using CFX and ANSYS: (left) axisymmetric AAA, 

and (right) stented AAA, where the stent-graft clearly shields the weakened aneurysm wall from the blood flow 


Schematic representation 

of an axisymmetric AAA, 

including implanted stent-graft 

with relevant analytical data. 

19 

Using five case histories, CFX and ANSYS 

Structural were used to compute the incipient 

migration forces of a stented graft under different 

placement conditions. In the process, we modeled 

different artery neck configurations, variable arterial 

wall thicknesses, transient hemodynamics and 

multi-structure interactions. 

The actual stented AAA model in ANSYS 

consisted of a lumen or bulge in the artery wall, an 

endovascular graft shell, a cavity of stagnant blood 

and the AAA wall. 

Using iterative fluid structure interaction was an 

intense computational problem as ANSYS Structural 

and CFX exchanged coupled variations in wall flex and 

geometry, requiring several new flow and structure 

results at each time step. The ANSYS Structural 

problem centered around nonlinear, large deformation, 

contact and dynamic analyses. 

Insight into Physical Processes 

The CFX post-processor in conjunction with our 

programs gives us a great deal of insight into the 

physical processes. It helps us to spot critical areas 

where platelets or low-density lipoproteins (LDLs) may 

clump together, and, ultimately, it helps us with design 

optimization of stent-grafts and secure stent-graft 

placements. 

The coupled CFX and ANSYS results were 

validated with experimental data sets and with clinical 

observations. 

Surgeons and scientists know that forces 

triggering stented graft migration include blood 

momentum changes, blood pressure and artery wall 

shear stress, inappropriate configurations of the 

healthy aortic neck section, tissue problems in the 

aortic neck segment and biomechanical degradation 

of the prosthetic material. 

To set the model stent-graft into motion, an 

increasing pull force was applied with an APDL 

subroutine. Coulomb’s Law was used for each contact 

element’s friction coefficients, but the simulations 

revealed a nonlinear correlation in large displacements 

between the migration force needed to move the stent 

and the friction coefficients. The simulation also 

revealed that the risk of displacement rises sharply in 

patients with high blood pressure. 

Coupled ANSYS and CFX fluid structure 

simulations verified that a stent-graft can significantly 

reduce the risk of an aneurysm rupture even when 

high blood pressure is the fundamental cause. Clearly, 

these tools for blood-flow-stent-artery interactions are 

valid, predictive and powerful for optimal surgical 

recommendations, improved stent designs and proper 

stent placement. ■ 

For this study, CFX-4 was linked to ANSYS with 

Fortran to perform fluid-structure interaction. 

Presently, generalized, fully representative stented 

abdominal aortic aneurysm configurations are being 

analyzed, employing ANSYS and CFX-5. 

Cardiac cycle (time level of 

interest: t/T=0.32, Re=550) 

Velocity distribution in non-stented 

axisymmetric AAA model 

Wall stress and velocity distribution in stented 

axisymmetric AAA model 



20 

Simulation Helps Improve Oil 

Refinery Operations 

Analysis assists in reducing coke deposits while improving 

hydrocarbon stripping. 

By Dr. Peter Witt 

Research Scientist 

CSIRO Minerals 

During oil processing, heavier products are broken down by high 

temperatures into lighter products in cokers. This “cracking” 

process strips off lighter liquid hydrocarbon products such as 

naphtha and gas oils, leaving heavier coke behind. The challenge 

that CSIRO Minerals has been helping Syncrude resolve is how to 

best reduce coke deposits that build-up in their fluid coker stripper 

while maintaining or improving hydrocarbon stripping. 

Syncrude Canada Ltd. is the world’s largest 

producer of crude oil from oil sands and the largest 

single-source producer in Canada. CSIRO (Australia’s 

Commonwealth Scientific and Industrial Research 

Organisation) is one of the world’s largest and most 

diverse scientific global research organizations. 

CSIRO Minerals is a long time user of CFX and in 

collaboration with the Clean Power from Lignite CRC 

developed the fluidized bed model in CFX-4. Because 

of its robust multiphase capability and its ability to be 

extended into new application areas, CFX is used 

extensively by CSIRO Minerals in undertaking 

complex CFD modeling of multiphase, combustion 

and reacting processes in the mineral processing, 

chemical and petrochemical industries. 

In the past, physical modeling had been used to 

understand the flow of solids and gas in the stripper. 

This modeling is performed at ambient conditions, so 

scaling of both the physical size and materials is 

required to approximate the actual high temperature 

and pressure in the stripper. This scaling process can 

introduce some uncertainty in understanding the 

actual stripper operation. 

Maintenance work on a coker unit at Syncrude’s 

oil sands plant in Alberta, Canada. 


0.0 secs 

By using CFD modeling to complement the 

physical modeling programs, scaling is eliminated and 

the actual dimensions and operating conditions are 

used. Furthermore, CFX simulation provides much 

greater detail of the flows and forces in the stripper 

than can be obtained from physical models or from 

the plant. This is due to the difficulty in making 

measurements and visualizing the flow in complex 

multiphase systems. 

Syncrude senior research associates Dr. Larry 

Hackman and Mr. Craig McKnight explain that 

extensive cold flow modeling (but not CFD modeling) 

had previously been used to investigate the operation 

of the fluid bed coker stripper and the gas and solids 

behavior in the unit. McKnight notes this project with 

CSIRO Minerals resulted in detailed, high quality 

reports, which provide “a new understanding of the 

fluid coker stripper operation.” Hackman indicated, 

“By using CFX to gain a better understanding, it is 

anticipated that design changes will be identified to 

improve stripping efficiency, reduce shed fouling and 

optimize stripper operation.” 

To most efficiently perform the simulations and 

utilize the results, the two companies are leveraging 

the distance separating their facilities. When it is night 

in Edmonton, Alberta, Canada where Syncrude 

Research is located, CSIRO Minerals staff is hard at 

work in Australia performing analyses and posting 

results (including pictures and animations) on their 

extranet. The next morning, the group in Canada can 

view progress of the modeling work and provide 

feedback for a quick turnaround. 

In this way, CSIRO is utilizing CFX technology to 

assist Syncrude in determining how best to utilize their 

current plant to get maximum throughput and thus 

make the most of their capital investment. ■ 

5.0 secs 

9.0 secs 

13.0 secs 

21 

16.5 secs 

Three-dimensional fluidized bed model of the Syncrude fluid 

coker “stripper.” The model predicts the motion of bubbles (in 

purple) rising from injectors in the lower part of the bed and 

the complex flow behavior of coke particles. Flow simulations 

provide insights into the stripper 

operation, which are then used to 

improve the design. 

Gas Volume 

Fraction 

0.75 

0.68 

0.60 

0.52 

0.45 

20 secs 



22 

CFX-5.7 Brings Powerful Integrated 

Tools to Engineering Design 

Latest release enhances core CFD features and gives 

users greater access to ANSYS tools. 

By Michael Raw 

Vice President, Product Development 

ANSYS Fluids Business 

Released in April 2004, CFX-5.7 demonstrates 

the continuing development of core CFD technologies, 

plus leverages ANSYS technologies to provide 

an exciting new series of capabilities for CFX users. 

This latest version contains the most advanced 

CFD features available, representing a powerful 

combination of proven, leading-edge technologies 

that provide the accuracy, reliability, speed and 

flexibility companies trust in their demanding fluid 

simulation applications. 

bi-directional associative CAD interfaces to all major 

CAD packages. The CFX-5 mesher, called CFX-Mesh 

and based on the advancing front inflation tetra/prism 

meshing technology, has been implemented in 

Workbench as a native GUI application that is easy to 

use and closely integrated with DesignModeler. 

ANSYS ICEM CFD meshers, including the unique 

hexahedral element meshing tools, are also now 

available in Workbench. They provide meshes for the 

most demanding CFD applications and are well 

known for their robustness when applied to very large 

or complex industrial CAD models. The combination 

of ANSYS DesignModeler, CFX-Mesh and ICEM 

ANSYS Integration 

CFX customers are now gaining access 

to state-of-the-art geometry modeling 

software with ANSYS DesignModeler, a 

Workbench-based product that is our 

new geometry creation tool providing 

CFX data can be interpolated 

directly onto ANSYS CBD 

files, providing a flexible route 

to transfer CFX results to an 

existing ANSYS mesh. 


It is now possible to perform 

texture mapping in CFX-Post 

CFD meshing technology provides a comprehensive 

CAD-to-meshing solution for CFD applications. As this is 

often the most time-consuming stage of CFD simulation, 

this represents a genuine time-saving benefit to ANSYS 

CFX users. 

The latest release introduces a fluid structure 

interaction (FSI) capability for when the interaction of a 

fluid around the solid is important, such as fluids-induced 

stresses and heat transfer. A simple-to-use, one-way 

transfer of data from a CFX solution to ANSYS provides 

for seamless passing of thermal and loads information 

from fluids to structural analysis. This approach 

automatically interpolates the data into the ANSYS CBD 

file format. For more complex FSI situations, such as 

large-scale solid deformation or motions in which the 

two-way influences are important, CFX-5 can dynamically 

interact with ANSYS stress analysis. ANSYS Inc. has the 

unique distinction of offering the industry’s only native 

connection between such components, which means 

ease-of-use, flexibility and reliability. 

Core CFD Enhancements 

As our flagship CFD simulation product, CFX-5.7 has 

been significantly enhanced for this release in several 

modeling areas, including moving mesh capability, 

general grid interface support of conjugate heat transfer, 

advanced turbulence models, multiphase models, as well 

as pre- and post-processing improvements. These 

enhancements are briefly described in the sections that 

follow. 

When fluid flow simulations involve changing 

geometry (as in devices such as valves, pistons or gear 

pumps, for example), CFX-5 moving mesh options can be 

used. Several mesh movement strategies are available: 

prescribed surface movement with automatic mesh 

morphing, explicit 3-D mesh movement via user functions 

or multiple mesh files, remeshing with topology change 

and combinations of these strategies. These strategies 

cover almost every conceivable mesh movement needed. 

The Generalized Grid Interface (GGI) is now 

supported for Conjugate Heat Transfer (CHT), allowing the 

solid and fluid or the two solids to be created and meshed 

separately — and set up to reflect the needs of the 

physics in each zone independently. The heat transfer 

and/or radiation between the two objects can then be 

analyzed by connecting the two domains using GGI. 

CFX-5.7 adds two innovative turbulence models to 

its already comprehensive suite for turbulence analysis. 

Turbulence is present in most industrial flow, and 

accounting for this phenomenon appropriately can 

make a great difference in the accuracy of a 

simulation. CFX-5.7 will introduce the 

Transition Turbulence model, which helps 

to accurately predict the laminar-toturbulent 

scenarios often key for 

heat transfer prediction, e.g. in 

turbine blades. In addition, 

the detached eddy (DES) 

transient turbulence 

model has been 

Reacting particles are a feature of this release, including 

a fully featured coal combustion model. 

completed. Unique to CFX-5, this model combines the 

efficiencies of a Reynolds Averaged Navier Stokes (RANS) 

simulation in attached boundary layer regions with the 

ability to compute the large eddy transient structures using 

LES. 

Current multiphase capabilities have been extended, 

and an algebraic slip model (ASM) has been added. Using 

an algebraic approximation for the dispersed phase 

velocities, ASM is highly efficient even for a large number of 

dispersed phase size groups. A first implementation of the 

Multiple Size group model (MUSIG), accounting for a wide 

spectrum of particles sizes and shapes at every point in 

dispersed two-phase flows, has been added with access 

through the CFX Command Language (CCL). 

The material properties editor in CFX-Pre, the CFX-5 

physics pre-processor, allows users to select materials 

from groups to ensure proper interactions with their 

physical model set-up. This helps to avoid errors in 

selecting or combining materials. 

A multi-component, customizable particle model is 

now available as part of the Lagrangian Particle Tracking 

capability. Reacting particles features include evaporating, 

boiling and oil droplet models, as well as a fully featured 

coal combustion model. These models are often key to 

accurate simulations in the power generation industry. 

Some of the improvements now in CFX-Post include 

the ability to easily compare results between different 

simulation results or time steps, CGNS data support, 

surface streamlines, text labels that update automatically, 

surfaces of revolution, display of particle subset in particle 

tracking and texture mapping. 

Development is now focused on future releases, 

which will provide for a closer interface with the ANSYS 

Workbench Environment, including more enhancements 

to fluid-structure interaction capabilities as well as the 

continued investment in core CFD technology. ■ 

23 



24 

How many holes do we need 

to dig? Construction costs 

can exceed $1 million for a 

new 22m diameter tank at a 

water treatment plant. 

Improving Water Treatment Systems 

Engineers design compact, 

more efficient secondary 

clarifiers with the aid of CFX. 

By David J. Burt 

Senior Engineer 

MMI Engineering 

A secondary clarifier is the final treatment stage of a traditional 

activated sludge sewage works. It separates solid precipitate 

material from effluent water prior to discharge. Because of recent 

changes in environmental legislation, many treatment works in 

the UK are required to carry increased throughput or meet more 

stringent effluent quality limits. This means that more clarification 

capacity is needed. But with land in urban areas scarce and 

construction costs high, there is an increasing need to maximize 

the performance of existing units rather than build new ones. 

The standard technique for designing a final clarifier is mass 

flux theory. However, this method uses a one-dimensional settling 

model and cannot account for the ‘density current’ flow typical in 

a clarifier. Even if the clarifier external design satisfies mass flux 

theory it may still fail, or perform badly in practice because of the 

internal flow features. Often designers are forced to allow a for 

a 20% factor of safety in tank surface area to allow for the 

shortcomings of mass flux theory. With CFD modeling, it 

is possible to capture all of the flow processes to show 

short-circuiting, scouring of the sludge blanket and solids 

re-entrainment to effluent. This means it is possible to design 

more compact units or retrofit existing units with internal baffling 

to allow for higher loading. 

By augmenting the standard drift flux models in CFX, 

engineers at MMI have established a set of validated and verified 

models for clarifier performance. These models include settling 

algorithms and rheological functions for activated sludge 

mixtures. The models have recently been used at a number of 

UK sites to optimize final effluent quality for increased load. ■ 

Concentration profiles through a cross section of 

the clarifier approaching 8000 mg/l solids in the 

blanket. This tank features an Energy Dissipation 

Influent EDI, optimized stilling well diameter and 

additional Stamford baffling below the effluent 

weir. 

A useful post-processing idea is to track stream 

lines for the solid phase velocity field. In this 

case colored with G scalar to show where floc 

may experience greatest shear. 

MMI Engineering is a wholly owned subsidiary of GeoSyntec Consultants 

and provides a range of environmental, geotechnical, hydrological 

and civil engineering services. Further details can be found at 

www.mmiengineering.com and www.geosyntec.com. 


Managing CAE Processes 

Upfront Analysis 

in the Global 

Enterprise 

Early simulation is especially important when engineers at 

dispersed locations must collaborate in product development. 

25 

By Fereydoon Dadkhah 

Mechanical Analysis and Simulation 

Delphi Electronics and Safety 

Two important side effects of the continuing pressure 

to reduce product development time and development 

costs have been the increased use of analysis in the 

early stages of design and the development and 

manufacturing of many products at overseas sites. 

Upfront analysis has been identified by many 

companies as a critical stage of product development 

due to the many benefits it provides. Done properly, 

upfront analysis can shorten the design cycle of a 

product drastically by identifying problems early 

before substantial investment of time and material has 

been made in the product. In the earlier stages of 

design, engineers have more options at their disposal 

when changing a design to address problems 

uncovered by analysis. As a product’s design 

approaches completion, many design modification 

options are eliminated due to a variety of reasons 

such as manufacturability, cost, system integration, 

packaging etc. Therefore, problems that are 

discovered later in the process are generally more 

expensive to implement. Once a problem is 

discovered using upfront analysis, all the viable design 

options can also be evaluated by employing the same 

analysis techniques. As a result, when a prototype is 

finally built and tested, it is much more likely to pass 

the tests than if upfront analysis had not been used. 

Another fact of today’s global economic 

environment is that many companies have moved 

beyond establishing manufacturing-only facilities 

overseas to performing some of their product 

development activities at the overseas locations 

as well.This global footprint can lead to situations 

where a product is conceived and its performance 

requirements specified in country A, it is then designed 

and tested in country B and mass produced in country 

C. Therefore, development centers have to be flexible 

enough to respond to the needs of their local market 

as well as be able to develop products for 

different, distant markets. Once again, the shortened 

design schedules makes the use of CAE mandatory, 

especially in the early stages. Because of the 

distributed product development process, it is 

important that all the engineers and designers use the 

same processes 

and techniques. 

Using analysis as an 

integrated part of product 

development enables engineers 

from around the world to collaborate 

in unprecedented ways. 

Many of Delphi Corporation’s customers are 

global companies which market and sell their products 

around the world. It is therefore important for all of 

Delphi’s resources to be used to satisfy our customer’s 

needs regardless of where the need arises. Recent 

programs at Delphi Electronics and Safety (Formerly 

Delphi Delco Electronics Systems) have involved just 

such a scenario. Engineers from three different 

countries have been involved in the design process 

from the moment contracts are awarded. Even while 

some the system features are being finalized, 

the resources of the company around the world are 

mobilized to analyze and evaluate the component 

designs. Finite element analysis is used extensively to 

evaluate component performance. In many cases 

the early analysis indicates that modifications 

are necessary. The modifications are made and 

assessed until all problems are eliminated. Engineers 

responsible for making design modifications can use 

the local resources as well as those abroad to ensure 

the viability of their design. For example, many 

engineers at Delphi Electronics and Safety’s design 

centers around the world have been trained to use 

first-order analysis tools. These engineers are usually 

able to use analysis to eliminate many design flaws. 

However, often they need help in completing the 

picture, either because of shortage of time and other 

resources, or because they lack the specialty skills 

that are available at other sites. 

Finally, one of the most important reasons for 

performing upfront CAE is simply that many of 

our customers require it. In many cases, customers 

have developed extensive validation requirements 

that use simulation extensively in the concept 

approval phase. ■ 


Simulation at Work 

26 

Y 

Z 

X 

Analysis of Artificial 

Knee Joints 

ANSYS provides fast, accurate feedback 

on new orthopedic implant designs. 

Founded in 1895, DePuy is the oldest manufacturer 

of orthopedic implants in the United States, with a 

reputation for innovation in new product development. 

The company has patented a wide range of 

replacement knee systems, the first of which was 

developed more than 20 years ago. One of these 

types incorporates a state-of-the-art mobile bearing, 

which offers a wide range of options to allow the 

surgeon to match the implant to the patient’s anatomy. 

Figure 1 illustrates a typical replacement knee. 

In one recent application, two sizes of a 

replacement knee design were analyzed at different 

angles of articulation using ANSYS. Initially, finite 

element results were compared with known 

experimental measurements obtained on one of the 

two sizes at three angles of articulation. Once 

correlation had been achieved, the same methodology 

was used to analyze the other design at various angles. 

Meshing Critical Components 

The replacement knee design is composed of two 

components: the femoral component and the bearing. 

Figure 2 shows the solid geometry of the design 

in ANSYS after importation of the CAD model in 

Parasolid format. 

Both the femoral component and the bearing 

were meshed with 3-D higher order tetrahedral 

elements. The meshing of the two parts was made 

fully parameterized. The mesh on the underside of the 

femoral component was made sufficiently fine to 

ensure minimal loss of accuracy in the geometry of the 

curved contact surfaces. 

A coarser mesh was used in the interior and on 

the upper side of the femoral component, since 

its material was significantly stiffer than that of the 

bearing, and, consequently, very little structural 

deformation was expected. Another option was to 

mesh the contact surfaces of the femoral component 

with rigid target and the load applied to a pilot node. 

A similar approach was used for the bearing, 

as the size of the elements was more critical in the 

contact region than other non-contacting surfaces. 

However, a mesh density even finer than that on the 

contact surfaces of the femoral component was 

desirable in the bearing to ensure a good resolution of 

the contact area and stresses. 

An indiscriminate refinement of the mesh on all 

the upper surfaces of the bearing proved to be 

computationally too expensive, and a new meshing 

procedure was developed and tested by IDAC, a finite 

element analysis and computer-aided engineering 

consulting firm and the leading UK provider of ANSYS 

and DesignSpace software. 


27 

Figure 1. One of DePuy’s knee implants 

incorporates a mobile bearing that offers a 

wide range of options to allow the surgeon 

to match the implant to a patient’s anatomy. 

Figure 2. Solid geometry of orthopedic 

knee design in ANSYS after importation 

of the CAD model in Parasolid format. 

Figure 3. Analysis shows stress distribution 

in contact area between the bearing and 

the femoral component. 

Running the Analysis 

A preliminary contact analysis was first run with the 

original mesh density prescribed to the bearing, then 

the elements that were in contact with the femoral 

component were further refined for the subsequent 

solution. An example of this mesh is depicted in Figure 

3. The image illustrates the stress distribution in the 

contact area between the bearing and the femoral 

component. These stress distribution plots can be 

created in the ANSYS program for any point in time 

during the nonlinear solution. 

It was found that excessive geometric 

penetration at setup produced stress singularities and 

that, therefore, the contact pair should be checked 

prior to the solution. Localized peak contact stresses 

also could be produced by the discretization of 

the otherwise smooth contact surfaces. The mesh 

refinement level for the elements in the vicinity of 

contact after the preliminary contact analysis may be 

increased, but at the expense of a longer solution time. 

Apart from contact stresses, the total contact 

area was also an important aspect of the design being 

studied. The total contact area was obtained from 

summing the areas of all contact elements showing 

partial or full contact. This generally leads to an 

overestimation of the actual contact area (although it 

was considered insignificant given the high mesh 

density in the contact area). 

All analysis work described in this project was 

performed on Intel-based personal computers running 

the ANSYS program. DePuy are users of ANSYS and 

the parametric models created by IDAC have been 

supplied to DePuy for their engineers to perform 

further analyses and modifications in-house. 

Benefits: Speed and Accuracy 

“Following on from this study, and working with IDAC, 

a number of our own engineers have been able to do 

further comparisons of a new design against an 

existing product in various loading conditions,” says 

James Brooks, a senior mechanical design engineer at 

DePuy. “This has rapidly allowed us to get a good 

indication of the performance of the product before 

testing.” 

Fiona Haig, a mechanical designer at DePuy, 

reports additional benefits of the analysis solution. 

“IDAC’s macro allowed us to quickly and consistently 

replicate physical testing that would normally have 

taken weeks to undertake in our labs. In addition, it 

permitted us to gain detailed information on stress and 

deflection, which can be difficult to detect in physical 

tests. The macro has proved an invaluable tool in the 

comparison and validation of new implant designs as 

well as proving a highly effective learning aid for our 

core team of FEA users,” explains Haig. “The results 

achieved using IDAC’s analysis method closely 

correlated to the results of those physical tests 

previously undertaken in our labs. This validation 

has allowed us to extend the application of this 

methodology to the evaluation of a range of new 

implant designs, providing feedback accurately and in 

a short time frame.” ■ 


28 

More Design Insight, 

Faster... 

Quickly study the design impact of 

varying geometry, even without a 

parametric CAD model. 

By Pierre Thieffry, ParaMesh and Variational 

Technology Solutions Specialist and Raymond 

Browell, Product Manager, ANSYS, Inc. 

The combination of the ANSYS Workbench 

Environment and DesignXplorer VT provides ANSYS 

users with powerful tools for gaining significant insight 

into designs when working with a CAD system. 

Bi-directional parametric associativity with the parent 

CAD package, made possible by the ANSYS 

Workbench Environment, makes understanding 

the design impact of varying geometry easy and 

comprehensive. 

But what if this is an old design and the user 

cannot find the geometry files for the part? Or perhaps 

you have the geometry, but it is in a non-associative 

format such as IGES or Parasolid. Maybe the 

geometry is parametric and regenerates robustly, but 

the parameters created by the designer are not the 

ones that make sense for the analyst. For instance, the 

parameters’ definitions might be chained together so 

that it is impossible to vary one feature without 

changing others. Perhaps a consultant provided the 

user with only the FEA or “math model” and the 

original geometry used to create the model isn’t 

available, or it might take too much time to recreate. 

This is quite often the case with legacy models. 

Typically, this would be the end of the story. But with 

the combination of ParaMesh and DesignXplorer VT, it 

is just the beginning. 

Take an inside lok at how these tools can be used 

to study a legacy model like the engine torsional 

damper model shown in Figure 1. 

To optimize this engine damper, perform the 

following six-step procedure: 

1. From an existing ANSYS database write a 

“.cdb” file. 

2. Import the .cdb file into ParaMesh. 

3. Create the mesh morphing parameters within 

ANSYS ParaMesh. (Note the name of the 

parameters and their order of creation. This 

information will be mandatory in the next 

steps.) 

4. Declare the mesh morphing parameters by 

editing the ANSYS input file 

5. Perform the Parametric Solution using ANSYS 

DesignXplorer VT. 

6. Post-process with Solution Viewer, the 

DesignXplorer VT post-processor within the 

ANSYS Environment and, if desired, optimize 

the results. 

Figure 1. Sample model of engine torsional damper. 

Figure 2. Parameter definitions used for mesh morphing. 


Even for Legacy Models 

29 

Creating an ANSYS .cdb file is easy for ANSYS 

users, and importing the model into ParaMesh is no 

different than reading a file into any package, so skip 

to Step 3. Figure 2 shows the parameter definitions we 

will create in Step 3. 

The first parameter adjusts the inner diameter of 

the structure by moving the inner surface nodes and is 

named “inner_diam,” and it has a range of variation of 

–0.5 mm to +2 mm with an initial wall thickness of 

2mm. 

The second parameter adjusts the width of the 

slotted hole and is named “hole_diam,” which has a 

range of –2 to +2mm, with an initial value of 4 mm. 

The third parameter is the radial location of the 

slotted hole and is named “hole_position,” which has a 

range of –3 to +3 mm and has an initial value of 45mm. 

hole_position 

Minimum Value 

hole_position 

Maximum Value 

angle_position 

Minimum Value 

inner_diam 

Minimum Value 

angle_position 

Maximum Value 

inner_diam 

Maximum Value 

Figure 3. Extremes in part geometry obtained by varying mesh morphing 

parameters. 

Hole_diam 

Minimum Value 

Hole_diam 

Maximum Value 

The fourth parameter is the location of the start of 

the bevel angle bend and is named “Angle_position,” 

which has a range of –6 to +2mm with an initial value 

of about 20mm. 

Comparing the images in Figure 3 indicates the 

extremes of the part. The boundary conditions applied 

are: symmetry boundary conditions on the planar 

faces, structure is clamped on the central hole and an 

inward radial pressure applied on the external surface. 

For Step 4, edit the ANSYS input file (see Figure 

4) and declare the ParaMesh mesh morphing 

parameters so that DesignXplorer VT will know to 

solve for them. As seen in the sample file, the 

parameters’ definitions are straightforward. To access 

the ParaMesh parameters from within the ANSYS 

DesignXplorer VT solution, use the SXGEOM 

command. 


30 

… 

/SX 

SXMETH,,AUTO 

! Define the output results 

SXRSLT,disp,NODE,U,ALL,, 

SXRSLT,sigma,ELEM,S,ALL,, 

SXRSLT,mass,ELEM,MASS,ALL,, 

! Define the file where the parameters have been created 

SXRFIL,tor_spring,rsx 

Starting with a sensitivity histogram as shown 

in Figure 5, the sensitivity of maximum stress with 

respect to each of the mesh morphing parameters is 

evident. These values are interpreted such that for a 

change from the minimum value to the maximum 

value of the parameter hole_position, the maximum 

stress increases by 103MPa. For the hole_diam 

parameter, the maximum stress decreases as the 

parameter increases. 

! Declare the shape parameters 

SXGEOM,inner_diam 

SXGEOM,hole_diam 

SXGEOM,angle_position 

SXGEOM,hole_position 

FINISH 

/SOLU 

! Prepare for a DXVT solution 

STAOP,SX 

Figure 4. Sample section of the ANSYS input file. 

Figure 5. Sensitivity diagram. 

This brings us to Step 5, which is solving 

the model with the mesh morphing parameters using 

DesignXplorer VT. 

DesignXplorer VT uses a new and exclusive 

technique called Variational Technology. In a traditional 

finite-element analysis, each change of the value of 

any input variable requires a new finite element 

analysis. To perform a “what-if” study where several 

input variables are varied in a certain range, a 

considerable number of finite element analyses may 

be required to satisfactorily evaluate the finite element 

results over the range of the input variables. In other 

methods, it is important to remember that each design 

candidate requires a complete re-mesh and re-solve. 

The benefit of Variational Technology is that only 

one solution is required to make the same type of 

forecast that other methods provide. The “response 

surface” created by DesignXplorer VT is an explicit 

approximation function of the finite-element results 

expressed as a function of all selected input variables. 

Variational Technology provides more accurate results, 

faster. 

Now post-process the analysis using the Solution 

Viewer, the DesignXplorer VT post-processor within 

the ANSYS Environment. 

Figure 6. Histogram showing sensitivity of stress, displacement 

and mass with respect to morphing parameters. 

DesignXplorer VT’s Solution Viewer allows the 

user to view the sensitivity of multiple results to the 

input parameters. In the histogram shown in Figure 6, 

we see the sensitivity of the Maximum Von Mises 

Stress, Maximum Displacement, and the Model Mass 

with respect to all of the mesh morphing parameters. 

The above sensitivities are relative ones. The 

“angle_position” parameter has essentially no effect 

on the stress. 


With the initial structure, there is a maximum Von 

Mises Stress at 305MPa, a maximum displacement of 

0.06 mm and a mass of 116g. It is ideal to keep the 

maximum stress under 265Mpa and keep the mass as 

low as possible. To reach this objective, the above 

sensitivities give some ideas about the changes to be 

made. The parameter “hole_position” has the most 

influence on the stress and has to be lowered. 

Moreover, it does not affect the mass, so it is a critical 

parameter for stress reduction only. The same holds 

for the inner_diam parameter’s effect on the mass. It is 

the most influent on mass, and has little effect 

on stresses. To reach the objective, expect two 

parameters to be lowered. 

Note the complexity of the response of this 

torsional damper with respect to the input parameters. 

As seen in the design curves, all but one of the 

responses to the input parameters are nonlinear. The 

response of the stresses to the hole_diameter has a 

definitive kink in it. The reason for that is tht the 

maximum stress jumps from one location to another 

when the parameters are changing. Simple Design of 

Experiment (DOE) curve fitting of results to selected 

samples would not have typically discovered this. 

One of the unique features of DesignXplorer VT is 

the instant, real time availability to the entire finite 

element solution for anywhere in the parameter 

domain. Pick any combination of parameter values 

and see a contour display of the finite element results. 

This is directly available, unlike DOE, DesignXplorer VT 

already has the results available for the user. 

Figure 9 shows a contour of Von Mises Stress 

from directly inside the Solution Viewer, for the 

parameter hole_position at -3mm, 0 and 3mm. The 

color scheme is the same for all meshes, so we really 

see the evolution with the given parameter. 

31 

Figure 7. Design curves created by Solution Viewer. 

hole_position 

at -3mm 

Additionally, DesignXplorer VT’s Solution Viewer 

allows you to view your parametric response as 

either design curves such as those in Figure 7, or as 

response surfaces as shown in Figure 8. 

hole_position 

at 0 

hole_position 

at 3mm 

Figure 8. Response surface created by Solution Viewer. 

Figure 9. Stress plots created by Solution Viewer with respect to varying 

parameter hole_position. 


Software Highlights 

32 

DesignXplorer VT also includes powerful 

optimization and tolerance capabilities. Using the 

optimization capabilities built into the Solution Viewer, 

optimize the part. As stated before, minimize the mass 

of the part while keeping its maximum stress under 

265 MPa. 

The optimization needs in this case only 63 

iterations. These are achieved in 60 seconds – an 

amazingly short time considering the number of 

iterations. This is because, as mentioned earlier, 

DesignXplorer VT has the entire finite element solution 

for anywhere in the parameter domain. No additional 

solutions are required. 

The final maximum stress is 265Mpa. The final 

stress value is more than 10% below the initial stress 

value. The final mass has also been lowered to 101g, a 

saving of 13% which is a better solution in terms of 

both stress and the mass. 

The powerful combination of ParaMesh and 

DesignXplorer VT opens doors to analyses that never 

before existed. Previously, you had to guess, or 

optimize manually. Now parametric analysis is 

available, no matter what environment is being used: 

Workbench for those that have parameterized CAD 

models, and ParaMesh with DesignXplorer VT for 

those with models without parametric CAD. 

That is the value this powerful combination of 

ANSYS ParaMesh and ANSYS DesignXplorer 

provides: more design insight, faster...even for legacy 

models. ■ 

Procedure Overview 

1. From an 

existing 

ANSYS 

model, write 

a “.cdb” file 

(CDWRITE) 

Create 

an 


.cdb file 

2. Import the .cdb file into 

ANSYS ParaMesh 

ANSYS ParaMesh 

3. Create the mesh 

morphing parameters 

within ANSYS ParaMesh 

Start with an 


database 

4. Declare the mesh 

morphing parameters 

by editing the ANSYS 

input file (file.dat) 

(Be sure to have 

consistent names) 

file .rsx 

(or .van) 

Edit the input file 

(file.dat) by adding the 

following commands: 

SXGEOM, SXRFIL, 

SXMETH 

5. Perform the Parametric 

Solution by using ANSYS 

DesignXplorer VT 

ANSYS DX VT 

and SXPOST 

6. Post-process the 

parametric results and 

optimize the part 

Follow these six steps in using ParaMesh and DesignXplorer VT to optimize legacy models, even if you do not have geometry or if 

the geometry is non-associative. ParaMesh easily prepares these models so they can be studied with DesignXplorer VT to arrive at 

quick insight into the design impact of varying the geometry. 


Tech File 

33 

Demystifying Contact Elements 

Part 1 of 2: 

What they are, how they work and when to use them. 

By John Crawford 

Consulting Analyst 

If you analyze enough problems, 

chances are good that sooner or 

later you’ll run across one that 

requires the use of contact 

elements. Contact elements are 

used to simulate how one or 

more surfaces interact with each 

other. For most analysts, our first exposure to contact 

elements can be a little confusing because of the 

variety of elements and the multitude of special 

features that are available. 

We have to determine which contact elements 

are appropriate for our problem, resolve any 

convergence problems that might arise during 

solution, and check the results for reasonable and 

accurate answers. Let’s see if we can clear up some of 

the mysteries that surround the use of contact 

elements. We’ll begin by talking about the elements 

themselves. 

Node-to-Node Elements 

In the early days of finite element analysis, there was 

one type of contact element: the node-to-node variety. 

The early versions of node-to-node contact elements 

were CONTAC12 (2-D) and CONTAC52 (3-D). More 

recently, CONTA178 (2-D and 3-D) was introduced to 

encompass the capabilities of both of these elements 

and also introduce some new features, such as 

additional contact algorithms. Node-to-node contact 

elements are simple and solve relatively quickly. Their 

basic function is to monitor the movement of one node 

with respect to another node. When the gap between 

these nodes closes, the contact element allows load 

to transfer from one node to the other. What does this 

really mean and how does ANSYS know when the 

nodes are touching? 

Remember that an analysis is made up of one or 

more load steps, and each load step has one or more 

substeps. Within each substep there can be several 

nested layers of equilibrium iterations. The precise 

number and manner in which they are nested is 

dependent on the solver, how many nonlinear features 

are being used and several other things. Contact 

analyses are nonlinear and therefore require their own 

equilibrium iteration loop. At the end of each contact 

equilibrium iteration, ANSYS checks to see if the 

status of each contact element has changed. It also 

calculates a convergence value (usually force 

equilibrium) and compares it to the convergence 

criteria. If the element status has not changed and the 

convergence criteria has been met, ANSYS 

determines that the solution for this iteration has 

converged and moves on to the next outer iteration 

loop, the next substep or the next load step, or stops 

solving altogether if the analysis is now complete. 

If at this point you’re a little confused, don’t 

worry. The critical ideas to remember from this are 

the following: 

• Contact analyses are nonlinear in nature 

• ANSYS performs a special equilibrium 

iteration “loop” when doing a contact analysis 

• Contact elements have a “status” that 

indicates if they are open, closed, sliding, etc. 

• ANSYS checks the element status and the 

convergence criteria at the end of each 

contact equilibrium iteration to determine if 

equilibrium has been achieved 


Tech File 

34 

These characteristics are true for all types of contact 

elements. While they may seem a little primitive when 

compared with the newer contact elements, node-tonode 

contact elements have a lot going for them. 

They’ve been around long enough to have had their 

bugs worked out many years ago, and their extensive 

use over several decades means that there is a vast 

experience base to draw upon when setting up and 

debugging an analysis. CONTAC12 and CONTAC52 

can have nodes that are either coincident or non-coincident. 

While the majority of applications involve using 

non-coincident nodes, coincident nodes can be useful 

for certain analyses. If coincident nodes are used, 

the orientation of the contact “surface” that exists 

between the two nodes must be defined. The initial 

condition gap or interference can be provided by the 

user as being either positive (gap) or negative (interference), 

or automatically calculated from the relative 

positions of the nodes. 

Node-to-node contact is also available in 

COMBIN40. COMBIN40 is a rather unique element 

because it also includes a spring-slider, a damper 

(which works in parallel with the spring-slider) and 

a mass at each node. Any of these features can be 

used alone or simultaneously with any or all of the 

other features. 

While node-to-node contact elements are very 

useful, there are some limitations that must be kept in 

mind when using them. One limitation is that the 

orientation of the gap is not updated when large 

deflection analyses are performed. Another limitation 

is that these elements do not account for moment 

equilibrium. This does not present a problem when a 

line drawn between the nodes is normal to the contact 

surface because in this instance the moments are 

zero, but care should be taken in each analysis to 

recognize whether this is the case or not. If not, it is 

important to consider what effect this might have on 

the results. It is the responsibility of the analyst to 

recognize whether this condition is present and 

whether it introduces an unacceptable error that 

invalidates the usefulness of the analysis. 

Node-to-node elements can always be generated 

manually, and, depending on the model, you can often 

use the EINTF command to make them as well. 

Node-to-Surface Elements 

The next evolution in contact elements was the 

introduction of node-to-surface contact elements, 

such as CONTAC26 (2-D), CONTAC48 (2-D), 

CONTAC49 (3-D), and the recent addition of 

CONTA175 (2-D and 3-D). The major enhancement 

offered by node-to-surface contact elements is that 

they allow a node to contact anywhere along an edge 

(in 2-D) or a surface (in 3-D). Rather than a node being 

confined to contacting a specific node, a node can 

contact the edge of a certain element. This has 

significant benefits when objects translate or rotate 

relative to each other. Node-to-surface contact 

elements are capable of simulating large relative 

movements with accuracy. 

Because CONTA175 includes all the capabilities 

of the other node-to-surface contact elements and 

has other features that these elements do not have, 

CONTA175 will replace the other node-to-surface 

elements in future versions of ANSYS. Beginning in 

ANSYS 8.1, CONTAC26, CONTAC48 and CONTAC49 

will be undocumented, and they will eventually be 

removed from ANSYS. 

There are several ways to generate node-tosurface 

contact elements. They can be made 

manually, but this becomes impractical when making 

more than a few elements. GCGEN and ESURF are 

commands that are frequently used to generate 

node-to-surface contact elements, with GCGEN being 

the easiest and quickest way to make CONTAC48 and 

CONTAC49 node to surface contact elements, while 

ESURF is used to make CONTA175 node to surface 

elements. To use GCGEN, you make two components, 

one that contains the nodes from one of the contact 

surfaces, and another that contains the elements from 

the other contact surfaces, and then use GCGEN to 

automatically generate node-to-surface contact elements 

between every node and every element that are 

in these components. To use ESURF, you select the 

elements that the CONTA175 elements will be 

attached to and their nodes that are on the surface 

you wish to place the contact elements onto, making 

sure that you have the proper element attributes active 

(TYPE, REAL and MAT), and then issue the ESURF 

command. 

Last but not least, the Contact Wizard can be 

used to generate node-to-surface contact elements 

and is usually the easiest and quickest way of making 

them. 


Surface-to-Surface Elements 

The latest evolution of contact element technology has 

been in the area of surface-to-surface contact. This 

allows contact to take place between one or more 

edges in 2-D, or one or more surfaces in 3-D. There 

are several important characteristics that make 

surface-to-surface contact elements very different 

from their less sophisticated ancestors. 

• Surface-to-surface contact is not defined by a 

single element, but by two types of elements 

called targets and contacts. 

• Any number of target and contact elements 

can be identified as being a set or group. 

Contact can take place between any contact 

elements and any target elements that are in 

this group. 

• ANSYS uses the real constant number to 

identify the target and contact elements that 

are in a group. All target and contact elements 

in this group have the same real constant 

number. 

Two-dimensional contact problems can be 

simulated using either CONTA171 or CONTA172 with 

TARGE169, while three-dimensional problems would 

use either CONTA173 or CONTA174 with TARGE170. 

CONTA171 and CONTA173 are appropriate for edges 

and surfaces made from linear (no midside nodes) 

elements while CONTA172 and CONTA174 can be 

used with edges and surfaces made from quadratic 

(having midside nodes) elements. Both CONTA172 

and CONTA174 can be used in a degenerate form on 

surfaces made from linear elements. 

The introduction of surface-to-surface contact 

elements has brought about big improvements in 

solution efficiency and has also broadened the types 

of contact problems that can be modeled. They offer 

many new and improved features, such as the ability 

to contact and then bond two surfaces together, 

automatic opening or closing of gaps to a uniform 

value, and a variety of contact algorithms, to name just 

a few. 

You can generate surface-to-surface contact 

elements by using series NSEL, ESEL and ESURF 

commands. The Contact Wizard automates these 

steps and makes the generation of surface-to-surface 

contact elements quick and easy in both 2-D and 3-D. 

Now that we have been introduced to the contact 

elements that are at our disposal, we’ll follow up next 

time with some helpful hints on how to use them. ■ 

Part two of this article, to appear in the next issue of ANSYS 

Solutions, will discuss various aspects of using contact 

elements, including modeling tips and setting appropriate 

stiffness. 

35 

Want to continue receiving 

ANSYS Solutions? 

Visit www.ansys.com/subscribe/ 

to update your information. 

Plus, you’ll have the chance to sign 

up to receive CFX eNews and email 

alerts when the latest electronic 

version of ANSYS Solutions 

becomes available! 


Tips and Techniques 

36 

Contact 

Defaults in 

Workbench 

and ANSYS 

Intelligent default 

settings solve 

common problems 

fast with minimal 

user intervention. 

By ANSYS, Inc. Technical Support 

As every experienced FEA analyst knows, no two 

contact problems are exactly alike, so there is no 

silver bullet combination of KEYOPT and real 

constant settings that will successfully work for all 

problems. That explains the many features 

available today within the contact elements. It also 

explains, in part, the rationale behind the different 

default settings sometimes found in the different 

environments. As migration between Workbench 

and ANSYS environments progresses, it is 

important for analysts to recognize that, although 

the contact technology used in both of these 

environments is exactly the same, some of the 

default KEYOPT and real constant settings are not. 

Tables 1 and 2 summarize all surface-tosurface 

contact element (CONTA171–174) 

KEYOPTs and real 

constant properties 

with their respective 

default settings in each environment. Those that 

have different defaults in the different environments 

are highlighted in bold italic. 

KEYOPT(1): Select Degrees of Freedom (DOF) 

This option gives you the freedom to assign the 

contact DOF set consistent with the physics of the 

underlying elements. ANSYS surface-to-surface 

contact technology offers an impressive 

combination of structural, thermal, electric and 

magnetic capabilities. When building pairs through 

the ANSYS environment with traditional ANSYS 

Parametric Design Language (APDL), users must 

Table 1: 8.0 Default Contact KEYOPTs 

KEYOPTs Description ANSYS APDL Contact Wizard Workbench Workbench 

Default Linear Default Nonlinear 

(bonded, no sep) (standard, rough) 

1 Selects DOF manual automatic automatic automatic 

2 Contact algorithm Aug Lagrange Aug Lagrange pure penalty pure penalty 

3 Stress state when super element no super elem no super elem n/a n/a 

is present 

4 Location of contact detection point gauss gauss gauss gauss 

5 CNOF/ICONT adjustment no adjust no adjust no adjust no adjust 

6 (blank) 

7 Element level time increment control no control no control no control no control 

8 Asymmetric contact selection no action no action no action no action 

9 Effect of initial penetration or gap include all include all exclude all include all/ ramped 

10 Contact stiffness update btwn loadsteps btwn substps btwn loadsteps btwn loadsteps 

11 Beam/shell thickness effect exclude exclude exclude exclude 

12 Behavior of contact surface standard standard bonded n/a 


Table 2: 8.0 Default Contact Real Constants 

Real Constants Description ANSYS APDLContact Wizard Workbench 

No. Name 

1 R1 Target circle radius 0 n/a n/a 

2 R2 Superelement thickness 1 1 n/a 

3 FKN Normal penalty stiffness factor 1 1 Note 1 

4 FTOLN Penetration tolerance factor 0.1 0.1 0.1 

5 ICONT Initial contact closure 0 0 0 

6 PINB Pinball region note 2 note 2 n ote 2 

7 PMAX Upper limit of initial penetration 0 0 0 

8 PMIN Lower limit of initial penetration 0 0 0 

9 TAUMAX Maximum friction stress 1.00E+20 1.00E+20 1.00E+20 

10 CNOF Contact surface offset 0 0 0 

11 FKOP Contact opening stiffness 1 1 1 

12 FKT Tangent penalty stiffness 1 1 1 

13 COHE Contact cohesion 0 0 0 

14 TCC Thermal contact conductance 0 0 Note 3 

15 FHTG Frictional heating factor 1 1 1 

16 SBCT Stefan-Boltzmann constant 0 0 n/a 

17 RDVF Radiation view factor 1 1 n/a 

18 FWGT Heat distribution weighing factor 0.5 0.5 0.5 

19 ECC Electric contact conductance 0 0 n/a 

20 FHEG Joule dissipation weighting factor 1 1 n/a 

21 FACT Static/dynamic ratio 1 1 1 

22 DC Exponential decay coefficient 0 0 0 

23 SLTO Allowable elastic slip 1% 1% 1% 

25 TOLS Target edge extension factor note 4 note 4 note 4 

26 MCC Magnetic contact permeance 0 0 n/a 

Notes: 

1. FKN = 10 if only linear contact is active (bonded, no sep). If any nonlinear contact is active, all regions will have FKN = 1 (including bonded, no sep). 

2. Depends on contact behavior, rigid vs. flex target, KEYOPT (9) and NLGEOM ON/OFF. 

3. Calculated as a function of highest conductivity and overall model size. 

4. 10% of target length for NLGEOM,OFF. 2% of target length for NLGEOM,ON. 

37 

set this option manually. The default will always be 

KEYOPT(1) =0 (for UX,UY). When building contact 

pairs in the ANSYS environment using the contact 

wizard, KEYOPT(1) is set automatically according 

to the DOF set of the underlying element. In 

Workbench, this option also is set automatically, 

depending on the underlying element DOF set. 

KEYOPT(2): Contact Algorithm 

ANSYS contact technology offers many algorithms 

to control how the code enforces compatibility at a 

contacting interface. 

The penalty method (KEYOPT(2) =1) is a 

traditional algorithm that enforces contact 

compatibility by using a contact “spring” to 

establish a relationship between the two surfaces. 

The spring stiffness is called the penalty parameter 

or, more commonly, the contact stiffness. The 

spring is inactive when the surfaces are apart (open 

status), and becomes active when the surfaces 

begin to interpenetrate. 

The augmented Lagrange method (KEYOPT(2) 

= 0) uses an iterative series of penalty methods to 

enforce contact compatibility. Contact tractions 

(pressure and friction stresses) are augmented 

during equilibrium iterations so that final 

penetration is smaller then the allowable tolerance. 

This offers better conditioning than the pure penalty 

method and is less sensitive to magnitude of 

contact stiffness used, but may require more 

iterations than the penalty method. 

The Multi-Point Constraint (MPC) Method 

(KEYOPT(2) = 2) enforces contact compatibility by 

using internally generated constraint equations to 

establish a relationship between the two surfaces. 

The DOFs of the contact surface nodes are 

eliminated. No normal or tangential stiffness is 

required. For small deformation problems, no 


Tips and Techniques 

38 

iterations are needed in solving system equations. 

Since there is no penetration or contact sliding 

within a tolerance, MPC represents “true linear 

contact” behavior. For large deformation problems, 

the MPC equations are updated during each 

iteration. This method applies to bonded surface 

behavior only. It is also useful for building surface 

constraint relationships similar to CERIG and RBE3. 

MPC is available as a standard option when 

modeling bonded contact in both ANSYS and 

Workbench environments. 

The Pure Lagrange multiplier method 

(KEYOPT(2) = 3) adds an extra degree of freedom 

(contact pressure) to satisfy contact compatibility. 

Pure Lagrange enforces near-zero penetration with 

pressure DOF. Unlike the penalty and augmented 

Lagrange algorithms, it does not require a normal 

contact stiffness. Pure Lagrange does require a 

direct solver, can be more computationally 

expensive and can have convergence difficulties 

related to overconstraining, but it is a very useful 

algorithm when zero penetration is critical. It also 

can be combined with the penalty algorithm in the 

tangential direction (KEYOPT(2) = 4), when zero 

penetration is critical, and friction is also present. 

The ANSYS environment uses the augmented 

Lagrange by default. The Workbench environment 

currently uses the penalty method, but the default 

can be changed via the Options Menu at 8.1. MPC 

is available as a standard alternative in both 

environments. The Pure Lagrange options are 

available in ANSYS, but can be accessed in 

Workbench via the pre-processor command 

builder. At version 8.1, Pure Lagrange is available in 

the Workbench environment. Table 3 summarizes 

all the algorithms with pros and cons of each. 

KEYOPT(9): Effect of Initial Penetration or Gap 

Properly accounting for or controlling interferences 

and gaps can sometimes be the difference 

between success and failure in simulating a 

complicated contact relationship. There are several 

contact options available to control how the code 

accounts for initial interference or gap effects: 

(0) Include everything: Include an initial 

interference from the geometry and the 

specified offset (if any). 

(1) Exclude everything: Ignore all initialinterference 

effects. 

(2) Include with ramped effects: Ramp the 

interference to enhance convergence. 

(3) Include offset only: Base initial interference 

on specified offset only. 

(4) Include offset only w/ ramp: Base initial 

interference on specified offset only, and 

ramp the interference effect to enhance 

convergence. 

Table 3: Contact Algorithms 

Algorithm Pros Cons When to Use 

Pure Penalty Offers easiest convergence in least Requires contact stiffness and Helpful when contact convergence 

number of iterations allowance for some finite is a challenge and minimal penetration 

penetration 

is acceptable (Default in Workbench) 

Augmented Minimizes penetration; better Might require more iterations The default for surf-to-surf and nodeconditioning 

than penalty; less 

to-surf in ANSYS, as it has proven to 

sensitive to contact stiffness 

produce the best quality results in the 

most common applications 

(Default in ANSYS) 

Pure Lagrange Offers near-zero penetration; Might require more iterations; When zero penetration is critical 

zero elastic slip (no contact might also require adjustment to 

stiffness required) 

chatter control parameters unique 

to this algorithm; can produce 

overconstraints in model 

Pure Lagrange on Same as Pure Lagrange, plus Same as Pure Lagrange When zero penetration is critical 

Normal; Penalty simulation of friction is handled and friction is present 

on Tangent most efficiently 

Multipoint More efficient than traditional Can produce overconstraints Recommended for large bonded contact 

Constraint (MPC) bonded contact; offers contact in model models to enhance run time and for 

betweenmixed element types; 

contact between mixed element types 

offers CERIG RBE3 type constraints 

and surface constraint applications 


In ANSYS, the default KEYOPT(9) = 0 is to 

include everything. In Workbench, the default is to 

exclude everything (1) when linear contact (bonded, 

no separation) is defined and include with ramped 

effects (2) when nonlinear contact (frictional, 

frictionless, rough) is defined. 

KEYOPT(10): Contact Stiffness Update 

When using the penalty and/or augmented 

Lagrange method, contact stiffness has long been 

recognized as a critical property that influences 

both accuracy and convergence. Too high a 

stiffness will ultimately lead to convergence 

difficulty; too low a stiffness will result in 

over-penetration and an inaccurate assessment of 

surface pressures and stresses at the interface. 

In an effort to arrive at a good balance 

between these extremes, automatic stiffness 

updating between loadsteps (KEYOPT(10) = 0) and 

substeps (KEYOPT(10) = 1), or between iterations 

(KEYOPT(10) = 2) was introduced as an 

enhancement to traditional trial-and-error methods. 

In ANSYS, when contact is built via APDL, the 

default is to update stiffness between loadsteps. 

In ANSYS, when contact is built via the Wizard, the 

default has been changed to update between 

substeps. This is considered to produce the 

most robust contact simulation in most cases. 

In Workbench, the default behavior is still between 

loadsteps, but the default can be changed via the 

Option Menu at Version 8.1. These defaults may 

change in future releases as further enhancements 

are made. 

KEYOPT(12): Behavior of Contact Surface 

ANSYS contact technology offers a rich library of 

surface behavior options to simulate every possible 

situation. These options are as follows: 

(0) Standard: (Referred to as “Frictionless” or 

“Frictional” in Workbench) normal contact 

closing and opening behavior, with normal 

sticking/sliding friction behavior when 

nonzero friction coefficient is defined. 

(1) Rough: Normal contact closing and 

opening behavior, but no sliding can occur 

(similar to having an infinite coefficient of 

friction). 

(2) No Separation: Target and contact 

surfaces are tied once contact is 

established (sliding is permitted). This is not 

available as a standard option in Workbench, 

but can be accessed via the 

pre-processor command builder. 

(3) Bonded: Target and contact surfaces are 

“glued” once contact is established. 

(4) No Separation (always): (Referred to 

simply as “No Separation” in Workbench) 

Any contact detection points initially inside 

the pinball region or that come into contact 

are tied in the normal direction (sliding is 

permitted). 

(5) Bonded Contact (always): (Referred to 

simply as “Bonded” in Workbench) Any 

contact detection points initially inside the 

pinball region or that come into contact are 

bonded. (Design-space Default) 

(6) Bonded Contact (initial contact): Bonds 

surfaces ONLY in initial contact, initially 

open surfaces will remain open. This is 

not available as a standard option in 

Workbench, but can be accessed via the 

pre-processor command builder. 

The default surface behavior in ANSYS is 

nonlinear “standard” for simulating the most 

general normal contact closing and opening 

behavior, with normal sticking/sliding friction. 

In Workbench, the default behavior (which can be 

changed via the Options Menu at Version 8.1), set 

up with automatic contact detection to simulate an 

assembly, is linear Bonded Contact (Always). 

Real Constant(3): Normal Penalty Stiffness 

Factor (FKN) 

Users control the initial contact stiffness used by 

multiplying the calculated value by a factor, FKN. 

The default value for FKN used in ANSYS (APDL or 

Wizard) is 1.0. In Workbench, FKN = 10 if only linear 

contact is active (bonded or no separation). If any 

nonlinear contact is active, all regions will have FKN 

= 1 (including bonded and no separation). 

Real Constant(14): Thermal Contact 

Conductance (TCC) 

This constant dictates the thermal resistance 

across the interface of contacting bodies in 

applications involving thermal analysis. The default 

value in ANSYS for TCC is zero (perfect insulator). 

In Workbench, the default is automatically 

calculated as a function of the highest thermal 

conductivity of the contacting parts and the 

overall model sizethus essentially modeling perfect 

thermal contact. ■ 

39 


Guest Commentary 

40 

Quality 

Assurance 

Putting 

in Finite Element Analysis 

Part 2 of 2: 

Step-by-step ways to best implement a quality assurance program. 

By Vince Adams 

Director of Analysis Services 

IMPACT Engineering 

Solutions, Inc. 

The NAFEMS document 

“Management of Finite Element 

Analysis—Guidelines to Best 

Practice” states that a quality 

assurance program should be 

developed to serve an organization, not vice-versa. To 

address this concern and the barriers described in Part 

1 of this series, IMPACT Engineering Solutions has 

developed a suite of QA tools that can be customized 

and scaled to meet the needs of a wide-range of 

product development teams and industries. This suite 

of tools for QA includes: process audits, management 

education, user skill-level assessment, user education/ 

continuous improvement, pre- and post-analysis 

checklists, project documentation, data management, 

and analysis correlation guidelines. 

Process Audit 

The first step in establishing a QA program should be to 

document existing processes and company goals, 

including technical, organizational and competitive 

goals. Developing an understanding of how products 

are developed, what the historical issues and 

challenges have been, what interactions exist, and how 

simulation technologies can best impact a company’s 

bottom line should precede any recommendations. 

A process audit should evaluate not only the tools 

used by an engineering department but also identify 

additional state-of-the-art tools that can impact the 

design process or allow simulation activities to grow 

beyond current limitations. A process audit should help 

ensure that all groups involved in the design process 

are on the same page. Finally, the process audit should 

put some monetary values to typical tasks so that 

potential savings and opportunities for gains can be 

more readily identified. The report generated from the 

process audit should be a living document that 

allows periodic review of critical components and 

observations. 

Management Education 

A recent survey indicated that management, for various 

reasons, was the greatest barrier to success of FEA in 

product design by the users who responded. Helping 

managers set proper expectations regarding the 

capabilities and limitations of analysis is often the 

single most important step in improving the quality 

and value of simulation at a company. Management 

training should also include a discussion of the 

validity of assumptions and results, quality control 

concepts and an overview of the skills that they 

should expect their team members to possess to be 

productive with FEA. 

User Skill Level Assessment 

Skill level assessment may be the most difficult and 

controversial component of a QA program, and the 

one with the most far-reaching impact. Skill level 

assessment isn’t technically difficult as there are 

several areas of expertise that are fundamental to the 

successful use of analysis. The difficulty lies in the 

potential for perceived threat. Consequently, users 

must be shown that the program is not a test but a 

tool to help them better understand their skills and 

needs. The program we have developed is 

composed of four sections in which candidates: 

• Demonstrate a basic understanding of 

engineering mechanics (failure theory, stress 

concepts, material properties, etc.) 

• Show a working knowledge of finite element 

analysis (terminology, concepts, capabilities, 

meshing, boundary conditions, etc.) 

• Solve hands-on sample problems (using FEA 

tools that are to be part of their job) 

• Present a portfolio of past work they have 

performed (reports, screen shots, models, 

plots, etc.) 

The assessment report provided back to 

management should include not only performance 

results but also a plan for improvement for that 

individual (including courses and other support 

options, as well as special skills that might be shared 

with others in the organization. Finally, some sort of 

indication of a user’s level of competence and/or 

approved responsibility level should be noted, 

without negative connotations that could be 

misconstrued. 

User Education/Continuous Improvement 

A proactive and forward-thinking QA program should 

identify areas of growth and knowledge required to 


keep skills of users sharp. A company can’t be 

confident that users are state-of-the-art in their 

techniques and tools unless they are exposed to 

people and techniques outside of their familiar 

surroundings. The process audit conducted at the 

beginning of the program should identify critical 

skills and techniques that are needed to maximize the 

benefits of simulation, while the skills assessment 

should identify which users need work in those 

techniques. Employee growth should be planned, not 

expected to happen haphazardly. Knowledge and 

documentation of the next plateau for each user or 

group of users, with clear milestones, will help ensure 

that quality is maintained. It is also preferable to insist 

that all users at an organization go through a standard 

set of courses so that all are using the same language 

and have been exposed to the same data. 

Pre and Post-Analysis Checklists 

NAFEMS has developed an excellent starting point 

for companies looking to implement checklists as a 

quality control tool. We suggest taking these a step 

further and customizing them for a particular 

company’s tools and analysis environment. As part of 

a total QA program, clients should be able to access 

these forms online via an Intranet or the Internet, and 

they should be made available as part of the project 

documentation as described below. We’ve found that 

when these simple checking tools are bypassed, 

minor errors in data entry and interpretation can cause 

major problems in the decisions based on FE data. 

Project Documentation 

Too few companies have standard report formats for 

analysis while many companies don’t mandate reports 

at all. Despite the obvious loss of intellectual capital a 

company will experience when an analyst leaves the 

organization without documenting their work, a 

company loses one of the most important quality 

control tools in the analysis process when reports 

aren’t completed. A QA program for analysis must 

include a report format that transcends groups, 

specializations, or departments. Analysis data on 

seemingly unrelated components could still provide 

insight and prevent repetition of work. In addition to 

providing details of the recent work, a project report 

should include references to similar historical projects, 

test data and correlation criteria. A report should 

indicate the source of inputs and assumptions as well 

as comment on the validity of these assumptions. 

Additionally, a company would benefit from linking test 

and analysis reports, even to the point of using similar 

formats for the two related tasks. 

Data Management 

As companies begin to evaluate their PLM (product 

lifecycle management) structures, the organization of 

analysis or other product performance data must be 

included in the initial planning. D.H. Brown and 

Associates have investigated the needs of CAE data 

management and have found that structured PDM 

(product data management) systems may not be up to 

the task. PDM systems were typically developed to 

manage revisions and bill hierarchies, not the 

simplified geometries, results formats, and validation 

databases required for an analysis program. While 

every company must develop its own PLM and data 

management system that best fits within their 

organization, a QA program for analysis must tap into 

that system, formalize it if need be and provide means 

for policing the archiving of analysis data so that a 

company’s intellectual property and investment in 

simulation is secure. 

Analysis Correlation Guidelines. 

Unfortunately, companies rarely correlate their finite 

element data with physical testing. And when testing 

is used, set-ups are often inappropriate, proper 

procedures are not followed and sufficient data points 

not gathered. Therefore, thought should be given to 

multiple validation points to ensure that boundary 

conditions, material properties and geometry are all 

properly specified to provide consistent correlation. 

The analyst and the test technician should work 

closely together to devise a test intended to correlate 

the analysis modeling assumptions. Care should be 

taken to evaluate the validity of constraints in the 

model, especially fixed constraints, as these can lead 

to gross variations in stiffness when comparing test 

results to analysis results. A QA program for analysis 

should bridge the gap between test and analysis, and 

document procedures for correlating FE data. ■ 

Part 1 of this article in the previous issue of ANSYS Solutions 

discussed ways to overcome barriers to effective quality 

assurance in finite element analysis. 

Vince Adams is co-author of the book “Building Better 

Products with Finite Element Analysis” and the inaugural 

chairman for the NAFEMS North American Steering 

Committee. He currently serves as Director of Analysis 

Services at IMPACT Engineering Solutions, Inc. 

(www.impactengsol.com), a consulting firm providing design 

and analysis services and support to industrial clients in a wide 

range of industries around the world. Vince can be reached at 

vadams@impactengsol.com. 

Quality Doesn’t Happen by Accident 

Even if their product lines are similar, no two companies 

operate alike. Consequently, no QA program can be assumed 

valid for all companies without running the risk of forcing an 

engineering organization to cater to the needs of the system. 

In our training programs, we identify geometry, properties, 

mesh and boundary conditions as the key assumptions in any 

analysis and the most likely sources of error. If nothing else, a 

QA procedure for FEA must provide a crosscheck on these 

factors. Ideally, all users in an organization will possess all the 

skills required to competently perform analyses. However, as 

the technology proliferates further into the design process, as it 

should, the likelihood of that required ideal skill level becomes 

less and less. So management of engineering organizations 

need to foster a quality environment so that analysis can be 

used to its full potential. Remember, quality doesn’t happen by 

accident. Only with planning, standardization, education and 

diligent follow-through can a company truly feel confident that 

quality in FEA is assured. 


Unparalleled CAE performance and infrastructure 

The fastest CAE performance on the planet just got more versatile 

Choose between: 

■ Intel ® Itanium ® processor’s fastest floating point in the industry. 

■ The CAE software portfolio offered by HP-UX, Linux and 

Microsoft ® Windows ® . 

■ The cluster capability of HP Integrity servers. 

■ The value offered by HP ProLiant industry-standard servers. 

■ The pre/post processing power offered by HP Workstations. 

Whatever your choice, HP and our CAE partners deliver. 

www.hp.com/go/cae 

Screen images courtesy of (left to right): ANSYS ® ICEM CFD Cabin Modeler and 

ANSYS ® CFX ® 

Intel and Itanium are registered trademarks of the Intel Corporation 

in the United States and other countries. 

Microsoft and Windows are U.S. registered trademarks of Microsoft Corporation. 

© 2004 Hewlett-Packard Development Company, L.P.

ANSYS Solutions? - Czech Technical University

Create successful ePaper yourself

Delete template?

Save as template?