OrcaFlex - Engineering Department

Dynamic analysis and control of offshore 

marine systems using OrcaFlex 

A presentation to the SUPERGEN 7 th 

Doctoral Training Programme Workshop 

‘Control of Wave and Tidal Energy Converters’ 

Lancaster University, LUREG, Room A74 Eng & Computer Rooms 

by Steve Dalton and Sarah Ellwood, Orcina Ltd 

26 th February 2010 

www.orcina.com Slide 1 of 40

OrcaFlex 

(latest release v9.3, Aug-09) 

Contents 

1. About OrcaFlex - Overview 

2. Capabilities for modelling offshore marine systems 

1. Companies using OrcaFlex to analyse marine RE systems 

2. Types of marine energy systems modeled 

3. Environmental modeling – waves, current etc 

4. Example models 

3. Current Problems and Some Solutions 

4. How OrcaFlex can support SUPERGEN2 Marine 

Consortium and other RTD into Marine Systems 

5. Way Forward 




1. About OrcaFlex 

Our main product OrcaFlex is the world's leading 

software package for the design and analysis of a 

wide range of marine systems, including all types of: 

– Riser systems: SCRs, TTRs, hybrids, flexibles, umbilicals, 

hoses, bend stiffeners, bend restrictors etc. 

– Mooring systems: spread, turret, SPM, jetty, etc. 

– Installation planning with capabilities across the full range of 

scenarios. 

– Towed systems: bundle dynamics, seismic arrays, towed 

bodies, etc. 

– Defence, marine renewables, seabed stability and many 

other types of system. 


OrcaFlex- Visualisation 

The GUI, visualisation and 

automation facilities of 

OrcaFlex are widely 

recognised as best-in-class, 

making OrcaFlex the most 

productive line dynamics 

environment to work with. 






2. Capabilities for analysing Offshore 

Marine RE Systems 

• Analysing the static and dynamic response of structures to simple to 

complex environments 

• Can import hydrodynamic data from diffraction (AQWA, WAMIT) 

• Modelling structures – vessels (RAOs/ QTFs), buoys, shapes, links, 

winches, lines (pipe chain & rope, wire moorings, umbilicals, risers) 

• 3D and 6D Buoys, Surface piercing, CALM, SPAR, Towed fish, wings. 

• Modelling the environment - seabed, sea, current, wind, waves 

• Full non-linear capabilities (material, geometric, loading regime, 

boundary conditions, friction, contact, release, buckling etc) 

• Modal analyses of lines (natural frequencies and mode shapes) 

• Time history and detailed fatigue analysis (regular & rainflow) options 

• Both Implicit and Explicit solvers are provided to solve most problems 




2.1 Companies and Academia using OrcaFlex 

to analyse marine RE systems 

• Some of our Clients that use OrcaFlex for the design 

and analysis of Marine Renewable Systems include:- 

– AWS Ocean 

– Aquamarine 

– Nemo Engineering 

– OceanLinx 

– Ocean Power Technologies 

– Pelamis Wave (formerly OPD) 

– Trelleborg (formerly CRP) 

– Wavegen 

– Several Universities (SuperGen Marine Programme) 

Edinburgh. University of Strathclyde , Herriot Watt. 




2.2 Types of marine energy systems modelled 

• Marine Renewable Devices include:- 

– Wave Energy Converters (WECs) 

– Energy harvesting Vehicles (e.g. Wave Glider, Wave Runner, 

SeaRaser) 

– Tidal Energy Converters (TECs) 

• Types of WEC devices include:- 

– BMD-Buoyant Moored device 

– HCD-Hinged Contour device 

– OWC-Oscillating Water Column 

• Types of TEC devices include:- 

– Tidal Stream Systems normally using Horizontal or Vertical axis 

devices. Others include oscillating (hydrofoils) or Venturi effects 

– Barrages making use of head (potential energy) 

– Tidal Lagoons (making use of potential and kinetic energy of tides) 




• Current Technologies 

Attenuators and Point Absorbers:- 

- BMD-Buoyant Moored Device. e.g. wavebob, 

wavehub, PowerBuoy (OPT), wave 

energy point absorber (OSU PMLG) 

- HCD-Hinged Contour Device . 

e.g. Pelamis, Waveroller 

(OPD), WRASPA, Oyster, AWS. 

- Heave, Pitch & Surge devices 

OWC-Oscillating Water Column:- e.g. 

Oceanlinx, Wavedragon, Orecon, 

Limpet, Wavegen Near-shore 

Overtopping devices e.g. (wavedragon) 

Submerged differential pressure – 

normally hydraulic 

Other types – e.g. wave rotor and flexible 

structures (shape/volume) 

Main Types of WECs 




2.3 Wave Resource in UK waters 

• The world ocean resource is 

massive (Scotland alone is 60GW) 

• Many studies carried out e.g Fugro 

OCEANOR, Orecon, APBmer (UK 

Marine RE Atlas), DTI, ETSU. 

• Significant work already done 

under SuperGen programme 

The physical consequences of 

energy extraction on marine 

resources are now much more 

quantifiable and resource 

assessment before and after 

device deployment can now be 

more effectively conducted, 

based upon firm scientific 

principles. 




Properties and Types of waves 


Spectral Density (m^2 / Hz) 

Spectral Density (m^2 / Hz) 



Modelling Waves in OrcaFlex 

Regular Waves (Hs & Tz) 

• Airy 

• Dean 

• Stokes 5 th 

• Cnoidal 

Irregular (Random) Waves 

Setting up a random sea-state 

• JONSWAP and ISSC Spectra, 

• Ochi-Hubble Spectrum, 

• Torsethaugen Spectrum, 

• Gaussian Swell, 

OrcaFlex 9.4a22: pretty Ochi.dat (modified 14:19 on 05/02/2010 by OrcaFlex 9.4a22) 

Spectral Density for Wave Train 'Wave1' 

40 

30 

20 

10 

OrcaFlex 9.4a22: default Jonsw ap.dat (modified 14:18 on 05/02/2010 by OrcaFlex 9.4a22) 

Spectral Density for Wave Train 'Wave1' 

140 

120 

100 

80 

60 

40 

20 

• User-Defined Spectrum. 

0 

0 

0.1 

0.2 

0.3 

0.4 

Frequency (Hz) 

0.5 

0.6 

0.7 

0 

0 

0.05 

0.1 

0.15 

Frequency (Hz) 

0.2 

0.25 




Wave Power Formula 

• In deep water where the water depth is larger than half the 

wavelength, the wave energy flux is 

• where 

– P the wave energy flux per unit wave crest length (kW/m); 

– H m0 is the significant wave height (meter), as measured by wave buoys and 

predicted by wave forecast models. By definition, H m0 is four times the 

standard deviation of the water surface elevation; 

– T e is the energy period (second); 

– ρ is the mass density of the water (kg/m 3 ), and 

– g is the acceleration by gravity (m/s 2 ). 

• The above formula states that wave power is proportional to the 

wave period and to the square of the wave height. When the 

significant wave height is given in meters, and the wave period 

in seconds, the result is the wave power in kilowatts (kW) per 

meter of wavefront length 




Wave Power Calculation - example 

• Example: Consider moderate ocean swells, in deep water, a few 

kilometers off a coastline, with a wave height of 3 meters and a 

wave period of 8 seconds. Using the formula to solve for power, 

we get 

- 

• meaning there are 36 kilowatts of power potential per meter of 

coastline. 

• In major storms, the largest waves offshore are about 15 meters 

high and have a period of about 15 to 20 seconds. According to 

the above formula, such waves carry about 1.7 MW/m of power 

across each meter of wavefront and can be very destructive. 

• An effective wave power device captures as much as possible 

of the wave energy flux. As a result the waves will be of lower 

height in the region behind the wave power device. 




Wave energy and wave energy flux 

• In a sea state, the average energy density per unit area of gravity waves on the 

water surface is proportional to the wave height squared, according to linear 

wave theory: 

– 

• where E is the mean wave energy density per unit horizontal area (J/m 2 ), the 

sum of kinetic and potential energy density per unit horizontal area. PE=KE both 

contributing half to the wave energy density E, as can be expected from the 

equipartition theorem. 

• As the waves propagate, their energy is transported. The energy transport 

velocity is the group velocity. As a result, the wave energy flux, through a 

vertical plane of unit width perpendicular to the wave propagation direction, is 

equal to:- 

• with cg the group velocity (m/s). Due to the dispersion relation for water waves 

under the action of gravity, the group velocity depends on the wavelength λ, or 

equivalently, on the wave period T. Further, the dispersion relation is a function 

of the water depth h. As a result, the group velocity behaves differently in the 

limits of deep and shallow water, and at intermediate depths. 




Some WECs being designed, developed and/ or tested 


Wave Energy Converters (WECs) 



• Over 80 companies globally developing different types of wave energy devices (see EMEC). 

• A number of wave energy devices have been built but few have yet been developed up into 

commercial scale WECs because this of the very challenging environment & technicalities. 

• A few devices have been built and tested at large scale and at least three types have been grid 

connected (Wavedragon, Pelamis, Oyster). These are still being optimised. 

• Most have not been fully successful due to cost, complexity, reliability and harsh environment 

• Major UK companies include the following covering the three main types of WEC device:- 

– Aquamarine (Oyster-HCD/OWC) 

– AWS Ocean (AWS-III-BMD) 

– Carnegie Corporation (CETO-BMD)) 

– Finavera Renewables (AquaBuoy and Wave Buoy-BMD) 

– Manchester Bobber (BMD) 

– OceanLInx (OWC) 

– OPT (Power Buoy-BMD) –Consortium with Japan 

– Pelamis wave, formerly OPD (Pelamis-HCD) 

– Protean Power (BMD) 

– Trident Energy (BMD) 

– WaveBob (BMD)) 

– Wave Dragon (floating slack moored OWC). 


Power take-off 1-2 Length (m) 

Power take-off 1-2 Tension (kN) 



Example 3: Simulation of Cockerell raft 

OrcaFlex 9.4a24: Cockerell raft.sim (modified 11:55 on 06/07/2004 by OrcaFlex 8.5a) 

Time History: Pow er take-off 1-2 Length 

12 

11.5 

11 

10.5 

10 

9.5 

-5 

0 

5 

Time (s) 

10 

15 

20 

OrcaFlex 9.4a24: Cockerell raft.sim (modified 11:55 on 06/07/2004 by OrcaFlex 8.5a) 

Time History: Pow er take-off 1-2 Tension 

150 

100 

50 

0 

-50 

-100 

-150 

-5 

0 

5 

Time (s) 

10 

15 

20 


Bow line 1 Effective Tension (kN) at End A 

Float 1 Moment (kN.m) 

Float 1 Velocity (m/s) 



Example 5: Operations on Articulated Jetty 

OrcaFlex 9.4a20: articulated jetty - RMI version.dat (modified 00:28 on 05/10/2001 by OrcaFlex 7.5a34) 

Time History: Float 1 Moment 

40000 

35000 

30000 

25000 

20000 

15000 

10000 

5000 

0 

-10 

0 

10 

Time (s) 

20 

30 


Time History: Bow line 1 Effective Tension at End A 

30 


Time History: Float 1 Velocity 

2.5 

20 

2 

10 

1.5 

0 

1 

-10 

0.5 

-20 

-10 

0 

10 

Time (s) 

20 

30 

0 

-10 

0 

10 

Time (s) 

20 

30 


Bow mooring Effective Tension (kN) at End B 

Link 1X Tension (kN) 

Example 6: Fish Model links 



OrcaFlex 9.4a24: Fish model links.sim (modified 14:27 on 05/11/2007 by OrcaFlex 9.1a) (azimuth=270; elevation=0) 

Time: 20.0000s 

5 m 

Z 

X 

OrcaFlex 9.4a24: Fish model links.sim (modified 14:27 on 05/11/2007 by OrcaFlex 9.1a) 

Time History: Bow mooring Effective Tension at End B 

1 

0.95 

0.9 

Z 

X 

0.85 

0.8 

0.75 

0.7 

0.65 

-5 

0 

5 

Time (s) 

10 

15 

20 

OrcaFlex 9.4a24: Fish model links.sim (modified 14:27 on 05/11/2007 by OrcaFlex 9.1a) 

Time History: Link 1X Tension 

20 

15 

10 

5 

0 

-5 

-10 

-5 

0 

5 

Time (s) 

10 

15 

20 


Horizontal distance in metres 

Axial load in tethers in kN 



Example 8: Simulation of Wave Glider UUV – 

wave powered device - Liquid Robotics Inc 

Distance covered by Wave Glider (model-9b) 

90 

80 

70 

60 

50 

40 

glider 

30 

20 

10 

0 

0 10 20 30 40 50 60 

Time in seconds 

Axial loads in tethers of Wave Glider (model-9b) 

0.5 

0.4 

0.3 

0.2 

0.1 

0 

0 10 20 30 40 50 60 

-0.1 

glider 

-0.2 

-0.3 

-0.4 

-0.5 

Time in seconds 




Wave Runner -A new propulsion system for 

boats ditches the diesel? 

Wave-powered boat finishes crossing 

• A Japanese adventurer has completed a 

three-month journey from Hawaii to 

Japan in a boat powered by the energy of 

ocean waves. 

The 4,800-mile voyage, which began in 

Honolulu in March, ended when Kenichi 

Horie's three-ton yacht docked in 

Wakayama in western Japan last night. 

"The sea was so calm, and the weather 

was so great throughout my journey. 

That's why it took me so long," he said. 

His boat, which relies on wave energy to 

move two fins at its bow and propel it 

forward, sailed at an average speed of 

1.5 knots - slower than humans walk. 




Tidal Resource in UK waters 

The key advantages of tidal 

Stream energy over other 

renewable forms of generation 

are: 

• High energy intensity smaller 

cheaper rotors for a given 

power 

• Predictable energy capture less 

project risk 

• Energy to a timetable greater 

revenue per MWh generated 

• Low environmental impact low 

development overheads 

• Simple decommissioning low 

back-end risk and cost 




Main Types of TECs 

• Current Technologies 

– HAD-Horizontal Axis Device. 

e.g. MCT, Open hydro, Torcado. 

– VAD-Vertical Axis Device. 

e.g.Kobold by pontediarchemede 

– Oscillating Hydrofoil Devices 

e.g. Pulse Tidal - Reduces water 

depth & size limitations over HAD 

– Venturi Effect 

– Other Designs 

– Barrage and Lagoons 

Using existing low head water 

turbine technology (Kaplan's) into 

large fixed, gravity of floating 

structures to generate electricity. 




Methods to secure TECs to the seabed 

There are several methods to securing TEC to the seabed (as defined on EMEC website): 

i) Seabed Mounted / Gravity Base: 

This is physically attached to the seabed or is fixed by virtue of its massive weight. In some cases there 

may be additional fixing to the seabed. 

ii) Pile Mounted: 

This principle is analogous to that used to mount most large wind turbines, whereby the device is attached 

to a pole penetrating the ocean floor. Horizontal axis devices will often be able to yaw about this structure. 

This may also allow the turbine to be raised above the water level for maintenance. 

iii) Floating: 

Flexible mooring: The device is tethered via a cable/chain to the seabed, allowing considerable freedom 

of movement. This allows a device to swing as the tidal current direction changes with the tide. 

Rigid mooring: 

The device is secured into position using a fixed mooring system, allowing minimal leeway. 

Floating structure: 

This allows several turbines to be mounted to a single platform, which can move in relation to changes in 

sea level. 

iv) Hydrofoil Inducing Downforce: 

This device uses a number of hydrofoils mounted on a frame to induce a downforce from the tidal current 

flow. Provided that the ratio of surface areas is such that the downforce generated exceeds the overturning 

moment, then the device will remain in position. 

ORCAFLEX can model most of these in simple up to complex sea states 


Z (m) 



Modelling Currents & Tides in OrcaFlex 

1. Multiple sets of current profiles can 

be used, e.g. for 100yr, 1yr and 

95% exceedance 

OrcaFlex 9.3c (azimuth=220; elevation=5) 

20 m 

Y 

Z 

X 

2. Current can be ramped during 

statics build-up 

3. Vertical current variation by 

Interpolation or power law 

4. Tide cycles modelled if important 

No Depth (m) 

factor Rot (deg) 

OrcaFlex 9.3c 

Vertical Current Profile 

0 

1 0 1 0 

-20 

2 20 0.8 10 

3 30 0.6 30 

-40 

4 55 0.4 -5 

-60 

5 85 0.3 40 

-80 

6 100 0.25 35 

-100 

0 

0.2 

0.4 

Speed (m/s) 

0.6 

0.8 

1 


Properties of Tides and Currents 



Energy calculations 

• Various turbine designs have varying efficiencies and therefore varying 

power output. If the efficiency of the turbine "ξ" is known the equation 

below can be used to determine the power output. 

• The energy available from these kinetic systems can be expressed as: 

• where: 

– ξ = the turbine efficiency 

– P = the power generated (in watts) 

– ρ = the density of the water (seawater is 1025 kg/m³) 

– A = the sweep area of the turbine (in m²) 

– V = the velocity of the flow 

• Relative to an open turbine in free stream, depending on the geometry 

of the shroud shrouded turbines are capable of as much as 3 to 4 times 

the power of the same turbine rotor in open flow. .[36] 


Tidal Energy Converters (TECs) 



• Over 30 companies globally developing different types of wave energy 

devices (see EMEC). 

• Companies involved in developing TEC devices include:- 

– Aquamarine (Oyster-HCD/OWC) 

– AWS Ocean (AWS-III-BMD) 

– Carnegie Corporation (CETO-BMD)) 

– Finavera Renewables (AquaBuoy and Wave Buoy-BMD) 

– Manchester Bobber (BMD) 

– OceanLInx (OWC) 

– OPT (Power Buoy-BMD) –Consortium with Japan 

– Pelamis wave, formerly OPD (Pelamis-HCD) 

– Protean Power (BMD) 

– Trident Energy (BMD) 

– WaveBob (BMD)) 

– Wave Dragon (floating slack moored OWC). 




Example 9: Preliminary modelling of Rotor 

energy take-off device- (tidal/current) 


Survey Vessel Z (m) 

Towfish X (m) 

Towfish Z (m) 



Example 10: Simulation of a Towed fish to 

demonstrate PID control (of elevation) 

OrcaFlex 9.4a20: E05 PID Controlled Tow ed Fish.dat (modified 14:25 on 04/12/2009 by OrcaFlex 9.2a24) 

Time History: Tow fish X 

-435 

-440 

-445 

-450 

-455 

0 

50 

100 

150 

Time (s) 

200 

250 

300 


Time History: Survey Vessel Z 

6 


Time History: Tow fish Z 

-85 

4 

-90 

2 

0 

-95 

-2 

-4 

-100 

-6 

0 

50 

100 

150 

Time (s) 

200 

250 

300 

0 

50 

100 

150 

Time (s) 

200 

250 

300 




3. Problems and Solutions 

Modeling wave power extraction devices will help 

engineers identify the best designs (MIT Dec 2009) 

PROBLEM 

• Ocean waves could theoretically generate an estimated 10 to 

100 megawatts of renewable energy per kilometer of coastline. 

Several pilot installations already harvest wave power, and the 

first commercial wave farm began operating off the coast of 

Portugal in 2008, but has since been put on hold. 

• Many wave-energy device designs involve floating buoys that 

bob in the waves to capture mechanical energy. The buoys’ 

bobbing motion acts like a piston, moving a magnet or activating 

a hydraulic system that generates electricity. Designs include 

large single-buoy units and arrays of units of many small buoys. 

• Determining which design extracts the most energy from a 

broad range of wave frequencies that vary widely in time, 

and finding the optimal spacing and deployment of units 

present major challenges to widespread development of 

wave-energy extraction devices. 




Modelling wave power – a solution? 

SOLUTION 

• MIT Professor Chiang Mei focuses on power extraction from 

short waves induced by wind, rather than from tides. To provide 

engineers with predictive tools, his team is developing 

theoretical models for both single-buoy units and arrays of 

smaller units. Most single-unit absorbers are designed to 

resonate in such a way that a given wave train produces the 

largest oscillation of the device to maximize energy extraction. 

• In normal sea waves, isolated buoys must be large in order to 

resonate, but they do so only within a narrow frequency range. 

Smaller buoys, if appropriately separated, do not resonate in 

normal sea waves and can only be activated to moderate 

amplitudes by waves across a broad bandwidth. 

• ORCAFLEX can do much of this and is an ideal tool for front 

end design, parametric studies and global analyses, but it does 

have a number of limitations to model WECs / TECs accurately. 




4. Application of OrcaFlex to Marine Research 

• Whilst most of the research themes and 13 work packages 

under Phase 1 of the SuperGen Marine Energy programme are 

complete, Phase 2 (SuperGen2) is now underway. 

• OrcaFlex can complement aspects on 8 of the 12 work 

packages under SuperGen2:- 

– WP1: Numerical and physical convergence 

– WP2: Optimisation of collector form and response 

– WP3: Combined wave and tidal effects 

– WP4: Arrays, wakes and near field effects 

– WP5: Power Take Off and Conditioning 

– WP6: Moorings and Positioning 

– WP7: Advanced Control (non-linear modelling of ocean waves) 

– WP8: Reliability 




Current state of Wave Energy Research 

• Hydraulic and hydrodynamic modelling using:- 

– CFD-FLOW-3D (WASPRA) 

– AQUABUOY –E2I-EPRI 

– SUPERGEN MARINE (CFD & WAMIT, MarinOPT)- HW/LANCS 

– ORCAFLEX 

• Hydraulic and hydrodynamic testing at various facilities using:- 

– Small to medium scaled models 

– Large scale and Full-scale devices being designed using offshore Oil & Gas 

standard codes & practice e.g. Oyster (Aquamarine Power) 

• Mooring systems (lines and anchors) are key to the design and 

implementation of most WEC’s 

• Most WEC devices will have to be deployed in a series of arrays 

• Most WEC’s are still small to modest scale prototypes which require 

much RTD, especially predictive modelling and harshness testing 

• Some larger scale projects due for deployment and pre-commercial 

testing at EMEC and elsewhere over the next 5 years 




UK Universities involved in WEC research 

• University of Bristol 

• University of Bath 

• University of Plymouth 

• University of Southampton (SOTON and SERG) 

• University of Loughborough 

• University of Manchester (UMIST) 

• Manchester Metropolitan University (MMI) 

• Robert Gordon University 

• University of Lancaster (LUREG) 

• University of Strathclyde 

• University of Edinburgh 

• University of Herriot-Watt 

• Queens University- Belfast 

• University of Newcastle 

• University of Glasgow 

These form the SuperGen 

Marine Consortium 




International Universities currently 

involved in WEC research 

• MIT (Energy Initiative) 

• University of Aalborg, Denmark (Wave Dragon) 

• University of Agder, Norway (Wave Dragon) 

• University of Uppsala, Sweden (Vattenfall) 

• Oregon State University, USA (OH Hinslade Wave Research Lab) 

• Ghent University 

• University of Patras 

• University of Delft 

• University of Stellenbosch, South Africa (CRSES) 

• University of Plymouth, Australia 

• University of South Australia 

• Kyushu University, Japan (wave powered impulse turbine) 

• + a quite a few others –many involved in Tidal Energy Research 




Other organisations & test facilities 

• Department of Energy and Climate Change (DECC) 

• Scottish Council for Development and Industry (SCDI) 

• UKERC 

• Supergen Consortium (5 UK Universities) 

• BWEA - Marine 

• Marine Institute 

• Powertech Labs Inc. 

• SWAY, Norway 

• IEA- Ocean Energy Systems 

• European Marine Energy Centre (EMEC) –Stomness, Orkney 

• New and Renewable Energy Centre (NaREC), Blyth 

• Wave energy tanks at PRIMaRE, University of Plymouth 

• Ocean Energy Test Site, Galway 

• Wave Energy Centre (WavEC), Lisbon, Portugal 

• Wave Energy Technology Test Facility, South Africa (Saneri) 

• Many more conferences and events being held e.g. ITE summit, ICMENE, 

BWEA, AWATEA, OTC, AE, OMAE, ISOPE, ICOE,REC, ICOE etc! 




Deep and shallow ‘coastal’ water 

characteristics and opportunities 

• Deep water corresponds with a water depth larger than half the 

wavelength, which is the common situation in the sea and ocean. 

• In deep water, longer period waves propagate faster and transport their 

energy faster. The deep-water group velocity is half the phase velocity. 

• In shallow water, for wavelengths larger than twenty times the water 

depth, as found quite often near the coast, the group velocity is equal to 

the phase velocity. 

• The regularity of deep-water ocean swells, where "easy-to-predict longwavelength 

oscillations" are typically seen, offers the opportunity for the 

development of energy harvesting technologies that are potentially less 

subject to physical damage by near-shore cresting waves. 

• ORCAFLEX can model complex irregular wave trains and perform nonlinear 

structural response and rainflow fatigue assessment to these 

waves. However limitations include:- 

– No capability to model detailed design of power take off (energy conversion) 

– No capability to model complex fluid-structure interaction 

– Breaking waves and local shore effects cannot be modelled easily 

– It does not allow for wave field or tide effects to be modified by the device 


Conclusions (1) 



• Marine renewables is clearly a very demanding and challenging field. 

The success or failure of devices being developed and commercialised 

relies on good design & analysis, robust engineering, deployment and 

rigorous testing. 

• A range of devices are being developed especially in UK, USA, 

Canada, Norway, Portugal BUT… 

• Several large wave energy devices have recently sunk during being 

towed out to sea or have been destroyed in the first few weeks of 

operation or have failed due to poor reliability and durability problems. 

(e.g. Trident, Osprey, Pelamis). Therefore… 

• More rigorous RTD (research, design, analysis, testing & development) 

is required to avoid these sort of problems. More Front End + Detailed 

Design/Analysis + Testing is essential! 

• There are a lot of similarities with modelling WECs and TECs 

compared to offshore marine systems e.g. coupled response, (as well 

as quite a few differences – energy extraction, wake effects etc). 


Conclusions (2) 



• Main Advantages of using OrcaFlex as a FEED analysis tool ! 

– Very effective tool for modelling offshore/marine systems 

– Simple to very complex modelling of the environment and the 

system 

– Rapid model building, analysis and simulations can be undertaken 

– Both Passive and Active (PID) control is provided – via algorithms 

and external functions. 

– Full non-linear modelling capability is provided 

– Very effective software tool for modelling FEED and for assessing 

and optimising the viability of global marine systems subjected to 

hostile environments 

• The software is widely used in the offshore industry and is well 

validated for this purpose 

• However there are some limitations with using OrcaFlex to 

simulate Marine RE systems 

– It does not model energy extracted from the sea by the device 

– Wake effects between devices are not easy to model 

– BUT improvements and new features are regularly being added! 


Questions and Answers 

Thanks for listening 



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OrcaFlex - Engineering Department

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