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| 2. |
- Bodin, Kenneth, et al.
(författare)
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Constraint based particle fluids on GPGPU
- 2011
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- We present a fluid simulation method adapted for stream parallelism on general purpose graphics processingunits (GPGPU). In this method the equations of Navier and Stokes are discretized using particles and kernelfunctions as in Smoothed Particle Hydrodynamics (SPH), but rather than using penalty methods or solving for a divergence free velocity field, incompressibility is enforced using holonomic kinematic constraints [1]. We useone constraint for each smoothed particle stating that the local density should be kept constant. Other constraintsare used for boundary conditions and multiphysics coupling. We also present a viscosity model in which theshear rate at each pseudo particle is constrained to satisfy a given constitutive law. The computation of theconstraint forces, namely, the pressure and the stresses, requires the solution system of linear equations whichhave a sparse, saddle point structure. These are solved using the Uzawa method of preconditioned conjugate gradients (CG) applied directly to the symmetric indefinite matrix. The overall simulation method has its rootsin a discrete variational principle and the SPOOK time stepping scheme for constrained mechanical systems [2].The SPOOK method is second order accurate on the positions and constraints violations, and is stable at largetime-steps, thus often allowing several orders of magnitude larger timesteps in our method compared to intraditional SPH methods. The numerical implementation on GPGPU that is the main result of this paper consistsof the following components: particle neighbour searches based on spatial decomposition; summation of kernel densities; construction of Jacobians representing the constraints on the density, boundary conditions, viscosityand multiphysics couplings; a Uzawa CG solver for the system of linear equations; and finally, discrete timestepping of velocities and positions. The CG solver is particularly suitable for stream computing since it is basedon matrix-vector multiplications. The sparse system data is stored in a compressed matrix format and the algorithms operating on this data on GPGPU are implemented in CUDA and OpenCL. Our simulation resultsinclude performance measurements, and validation of the method for benchmark problems. We achieve up totwo orders of magnitude speed-up from the GPGPU over traditional processors and together with the increased timestep efficiency of our method we arrive at interactive performance for systems with up to two million fluidparticles representing an incompressible fluid.
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| 3. |
- Bodin, Kenneth, et al.
(författare)
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Constraint Fluids
- 2012
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Ingår i: IEEE Transactions on Visualization and Computer Graphics. - Los Alamitos, USA : IEEE Computer Society. - 1077-2626 .- 1941-0506. ; 18:3, s. 516-526
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Tidskriftsartikel (refereegranskat)abstract
- We present a fluid simulation method whereincompressibility is enforced through a holonomic constrainton the mass density. The method starts in aLagrangian particle formulation where the mass densityand other field quantities are represented by SmoothedParticle Hydrodynamics (SPH) kernel approximations.The density constraint is formulated as a regularizedmanybody constraint and is equivalent to very highsound speed. The system is integrated using a variationaldiscrete-time scheme, SPOOK, that includesconstraint regularization and stabilization. This constraintformulation of SPH enables systematic multiphysicsintegration, between rigid multibody physicsand fluids, where buoyancy falls out naturally. The fluidmodel results in a linear system of equations, whilemore general multiphysics systems result in a mixedlinear complementarity problem (MLCP) and we solvethese using iterative methods. The results demonstratenear perfect incompressibility, vastly improved stability,allowing for large time steps, and two orders of magnitudeimproved computational performance. Proof ofconcept is given for computer graphics applications andinteractive simulations.
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| 4. |
- Bodin, Kenneth, et al.
(författare)
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Method for simulating dynamic incompressible fluids using particle based spatial discretization and mass density constraints
- 2009
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Patent (populärvet., debatt m.m.)abstract
- Disclosed is a method of simulating dynamic fluids comprising a set of pseudo particles usedto represent physical quantities of the fluid, a fluid density computed from a weightedaverage over the pseudo particle, and a density constraint on the fluid density constraining itto be incompressible with the reference density of a real physical fluid that is modeled. Theconstraint stabilization forces of the density constraint govern the dynamics of the pseudoparticles and the simulated fluid. The method comprises a combined time stepping andconstraint stabilization and relaxation method that provides global conservation of physicalsymmetries and therefore robust physical and numerical stability under large constraintviolation, and substantial improvement in efficiency over other known methods.
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| 5. |
- Brembilla, Christian, 1983-, et al.
(författare)
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Investigation of thermal parameters addressed to a building simulation model
- 2015
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Ingår i: Energy, Science and Technology 2015. - Karlsruher, Germany : Karlsruher Institute of Technology (KIT). ; , s. 128-
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Konferensbidrag (refereegranskat)abstract
- Introduction The uncertainty of setting input parameters in a building model can have a major impact on the simulated output. The tolerance of thermal parameters is a necessary information that helps modeler to know the influence of eachfactors on the outcomes. This paper shows the allowable tolerance of thermal parameters in order to build anaccurate building model.
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| 6. |
- Brembilla, Christian, 1983-, et al.
(författare)
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Investigations of thermal parameters addressed to a building simulation model
- 2015
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Ingår i: Proceedings of BS2015. - India, Hyderabad : International Building Performance Simulation Association (IBPSA). ; , s. 2741-2748, s. 2741-2748
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Konferensbidrag (refereegranskat)abstract
- This paper shows the tolerance of thermal parameters addressed to a building simulation model in relation to the local control of the HVAC system. This work is suitable for a modeler that has to set up a building simulation model. The modeler has to know which parameter needs to be considered carefully and vice-versa which does not need deep investigations. Local differential sensitivity analysis of thermal parameters generates the uncertainty bands for the indoor air. The latter operation is repeated with P, PI and PID local control of the heating system. In conclusion, the local control of a room has a deterministic impact on the tolerance of thermal parameters.
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| 7. |
- Lacoursiere, Claude, et al.
(författare)
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A framework for data exchange and benchmarking of frictional contact solvers in multibody dynamics
- 2015
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Ingår i: Multibody Dynamics 2015. - : International Center for Numerical Methods in Engineering. - 9788494424403 ; , s. 1538-1547
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Konferensbidrag (refereegranskat)abstract
- We present an HDF5 layout specification to store and exchange the run-time kinematic data of simulations of contacting multibody systems subject to dry friction in descriptor form. This is intended to be used to test solvers on the incremental problem defined by one single configuration, allowing any mathematical formulation and friction law, and compatible with any numerical method. We also introduce metrics to measure the quality of a solution comprehensively, separating the errors from the different aspects of a given friction law. We started a public web site with a collection of problems, from simple stacking to full vehicle dynamics as well as grasping robots. We provide software to manipulate the data contained in the HDF5 files, assemble matrices needed for different formulations, and to interface with existing solvers. We also provide software to compute our metrics and generate plots which provide a global picture of performance and accuracy. As this is written in MATLAB and OCTAVE we believe our contributions will allow anyone wanting to write or test a solver to work with "real life" examples without any difficulty, and concentrate on the numerical methods themselves, and get results before writing a code suitable for integration with a full featured software package.
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| 8. |
- Lacoursiere, Claude
(författare)
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A parallel block iterative method for interactive contacting rigid multibody simulations on multicore PCs
- 2007
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Ingår i: Applied parallel computing. - Berlin : Springer Berlin/Heidelberg. - 9783540757542 ; , s. 956-965
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Konferensbidrag (refereegranskat)abstract
- A hybrid, asynchronous, block parallel method to approximately solve complementarity problems (CPs) in real-time on multicore CPUs is described. These problems arise from interactive real-time simulations of systems of constrained, contacting rigid bodies, which are useful in virtual operator training systems for instance. A graph analysis phase identifies components which are weakly coupled using simple heuristics. Each component is then solved in parallel using either a block principal pivot or a projected block Gauss-Seidel method running in separate threads. Couplings which generate forces between the subsystems are handled iteratively using a Gauss-Seidel process which communicates updates between the interacting subsystems asynchronously. Preliminary results show that this approach delivers good performance while keeping overhead small.
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| 9. |
- Lacoursiere, Claude, et al.
(författare)
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Direct Sparse Factorization of Blocked Saddle Point Matrices
- 2012
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Ingår i: Applied parallel and scientific computing. - 9783642281440 ; , s. 324-335
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Konferensbidrag (refereegranskat)abstract
- We present a parallel algorithm for the direct factorization of sparse saddle-point matrices of moderate size coming from real-time multibody dynamics simulations. We used the specific structure of these problems both for a priori construction of supernodes and to avoid all dynamic permutations during factorization. For the latter, we present a technique we call "leaf swapping" which performs permutations of the supernodes in the elimination tree without any reference to numerical values. The results compare favorably with currently available high performance codes on our problem sets because of the high overhead necessary to process very large problems on increasingly complex supercomputers.
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| 10. |
- Lacoursière, Claude, et al.
(författare)
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Fast and stable simulation of granular matter and machines
- 2010
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Konferensbidrag (refereegranskat)abstract
- We present mathematical models and numerical techniques designed to address thechallenges of real-time simulator training for earth moving equipment involving heavyvehicles and granular matter.
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