Space Grant Consortium - University of Wisconsin - Green Bay

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which involved dropping an increasing number of spheres modeled with rigid body frictional contacts in a box using two different multibody dynamic engines. The ‘LCP’ column denotes the program which exploits the improved formulation, while the ‘Penalty’ column uses the inefficient penalty-based method (Madsen, Pechdimaljian et al. 2007). The motivation for this research project stems from the fact that a majority of the virtual prototyping software used by industry today relies on simple, brute force methods to solve rigidbody frictional contact problems. This creates a limit on the number of frictional contacts that can be simulated efficiently. High-fidelity models with many contacts, such as tracked vehicles or vibration feeders, cannot be used in the design process because even small simulations can take hours to days to complete on a state-of-the-art desktop computer. The primary goal of this project is to be able to model and simulate real-life mechanisms by leveraging this new rigidbody frictional contact formulation. Simulations are expected to take much less time, but solution accuracy must be maintained if the new method is to be useful. The mechanism of choice is a tracked sub-system of a hydraulic excavator similar to the model used in a previous project (Madsen 2007). There are many rigid-body frictional contacts present in the model, and short simulations using industry grade software took many hours to complete. Table 1: Number of rigid spheres vs. CPU time using LCP and Penalty contact approaches Number of Max Number of LCP CPU time (seconds) Penalty CPU time (seconds) Spheres Mutual Contacts 1 1 0.7 0.41 2 3 0.73 3.3 4 14 0.73 7.75 8 44 0.76 25.36 16 152 0.82 102.78 32 560 1.32 644.4 The second goal of this research is to determine if the improved fixed-point iterative method will yield tracked vehicle simulation results that are accurate when compared to those from previously performed simulations. Concretely, the time evolution of the displacements, velocities, and accelerations of all bodies should be similar to the values previously obtained. This demonstrates that using the new fixed-point iterative method to solve the set of LCPs that arise from modeling frictional contacts as a set of unilateral constraints yields accurate results when compared to identical simulations carried out using proven methods. Because this new method enforces contact constraints on the velocity-level, there can be a drift in these constraint equations due to numerical errors (Studer and Glocker 2005). Also, the new formulation is not proven to have unique solution, although it has been shown to converge to a single solution under most circumstances (Anitescu 2006). Procedure The first step in the project was to select an appropriate model in which to apply the new multibody dynamic formulation. A hydraulic excavator model similar to that described in (Madsen 2007) was selected because the system contains many rigid-body frictional contacts. The computational model is described, and then the modeling procedure using two different multibody dynamic engines is discussed. The inefficient penalty based formulation for contact 18
forces is implemented in the popular industry-grade software MSC/ADAMS, while the new LCP contact formulation and fixed-point iterative solver are implemented in the research-grade Software Development Kit (SDK) ChronoEngine. Difficulty was encountered while porting the original model, which was built using MSC/ADAMS, to ChronoEngine using the SDK. Details about the differences of the multibody models in each dynamics engine will be presented. Original Computational Model. The original model is a tracked subsystem of a hydraulic excavator which consists of the following rigid bodies: a center block, five bottom rollers, one main idler, three top rollers, a drive sprocket and 45 track shoes. Each of the five bottom rollers are modeled identically with a revolute joint that is at a fixed location from the center block, allowing the roller to spin around its own center axis with one Degree of Freedom (DOF). Friction is present in these joints. There are also contact forces between each roller and all the individual shoe elements. The three support rollers are modeled in a similar fashion as the bottom rollers. The drive sprocket is composed of three parts: two identical gears and a drive wheel. Both gears are rigidly attached to the drive wheel, and each gear has contact forces specified with all 45 track shoes. The drive sprocket revolves around its central axis by a revolute joint which is a fixed distance from the center block. It is also where the driving torques and motions are applied. The front idler is modeled almost identically as the bottom rollers; it is constrained with a revolute joint and has contact forces specified with the track shoes. There is one main difference which is due to the presence of a simplified tensioning system. The revolute joint is not a fixed distance from the center block; it is constrained with a translational joint that represents the track tensioner system. This allows the idler to have an extra DOF so it can move forwards and backwards with respect to the center block. A single component horizontal force applied to the center of the idler keeps the shoes in tension. Each track shoe is connected to its neighboring shoes with revolute joints that rotate along the axis of the connecting pins. Contact forces are specified between each track shoe and all the running gear components, i.e. the rollers, idler and drive sprocket. There are also contact forces between the track shoes and the ground block, which is simply a large rectangle. Finally, the entire model is constrained to a single plane by applying a primitive joint to the center block which removes the ‘roll’ DOF of the vehicle. The assembled model as seen in MSC/ADAMS is shown in Figure 1. This type of tracked vehicle was originally selected because it has a simple suspension and low operating speeds (~2 km/h) which make its behavior easy to predict. There are also a total of 585 rigid body contact forces specified in the model, which is the computational bottleneck. The original model was tested under multiple conditions using the ground block, the type of propulsion method and the rate of the propulsion method as independent variables. However for this comparison, a straight-line quasi-steady state dynamic simulation was used for simplicity. The next step was to create a model in ChronoEngine that is as similar to the original as possible. 19
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Space Grant Consortium wisconsin UN
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THE CASSINI ENCOUNTER WITH THE GEM
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Th he proceedinngs of our 199th Ann
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Wisconsin Space Grant Consortium Un
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Part 3: NASA Reduced Gravity Progra
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EAA Women Soar - You Soar, Lee Siud
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Elijah High Altitude Balloon Projec
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Our experience with the HALO II lau
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which had been a problem in the pas
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Figure 6: 3-D GPS Generated Track o
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Results The seeds tested in the lab
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hour as we assumed the flight in th
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Experimental Results There are two
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A series of tests were done in a co
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380 360 340 320 23.3 Temp. (Celsius
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First Place, Non-Engineering: Schmi
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of the basis for fin designs came f
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ejection charge from the motor fire
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using rip-stop nylon cloth. To atta
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Post-flight recovery. A field searc
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Thus, it is believed that the main
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[2] Public Missiles Ltd. Frequently
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Design Features The chief requireme
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4. NASA JPL. MIRI FOCAL PLANE SYSTE
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Is Lake Superior a significant sour
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each grid cell at daily resolution.
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Figure 3. (a) Seasonal cycle of lak
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Figure 5. Model pCO2 at the surface
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Marshall, J., A. Adcroft, C. Hill,
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numerical weather prediction (NWP)
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High Resolution Radiometer (AVHRR)
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On the morning of 26 May 2008, ther
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References Behnke, C., 2005: Synopt
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Figure 3 Figure 3 contains base ref
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A Comparative Study of Type IIb Sup
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Fig. 3.— Cartoon Image of SN blas
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Fig. 4.— Light curve of SN 2008bo
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type IIn Supernova SN 1995N,” 200
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and then can spiral in to the black
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Understanding the Evolution of Supe
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Radio  measurements  of  supe
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In the equations on the p
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SN 2008ax in NGC 4490 SN2008ax is a
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References Chevalier, R. A., “Int
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Computational Fluid Dynamical Model
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context of the k − ɛ model invol
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Figure 3: Experimental results (•
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direction results in the terminal s
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121 (2000). [Blue Ridge Numerics, I
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concentrated our effort specificall
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density, and Ps is a pressure tenso
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Properties of the GEM problem Recon
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Figure 1: Increase in reconnection
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Figure 3: Examples of agreement of
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Reflection and Refraction of Vortex
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Experimental Procedure The left han
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frames in the upper left corner, wh
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Vortex ring reflection. Similarly,
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References L Bernal and J Kwon. Vor
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group started in 1997 with the goal
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I conducted five semi-structured in
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In the example of the guinea pig pr
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explain t his t rend. F rom t alkin
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Research. Washington, DC: Pan Ameri
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Our team has two goals: 1. To put S
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fluctuating humidity, drying winds,
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western border of the Arkansas Rive
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adjusted to less than .4millisecond
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Cacti Experiment 18 has produced 10
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13. What N decomposer's are needed
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Abstract Toxic Offgassing Analysis
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Tables 4 and 5 show offgassing comp
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there was no dichlorobenzene peak.
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eneficiation reagents. Ionic liquid
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Figure 3: Current versus voltage da
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Abstract New Initiatives in the Pro
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was noticed above the gel. A discol
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delicate structures (hairs). N o fu
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and A. Y. Rozanov, Eds., SPIE, Vol.
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Combining Writing Across the Curric
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But the study also reported a consi
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Educators’ Aerospace Workshop for
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2008-2009 Evaluation Educators’ A
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Some comments from participants 200
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The cost of a one credit graduate c
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EAA WOMEN SOAR - YOU SOAR Dr. Lee J
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� Incorporated the technology res
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Evaluation Results: At the conclusi
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Educational Standards: The National
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curriculum development, to provide
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and applications of GIS technology
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• A significant new outcome for t
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The design of this project and appl
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Activities at the workshop involved
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to give our students a series of PR
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In the past we have not focused on
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Providing High School Students with
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that th e current generations of s
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instruction a s pa rt o f t heir ow
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Wisconsin Space Grant Consortium &
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11:45-1:00 pm Lunch *** Concurrent
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Moderator: David B lock, A ssociate
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Second Place, E ngineering, Drew an
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Wisconsin Space Grant Consortium
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