Publications old

Published in: Department of Physics, Umeå University, SE-90187 Umeå, Sweden
Authors: M. Servin, T. Berglund, and S. Ulin
Date: October 2020

Abstract

A multiscale model for real-time simulation of terrain dynamics is explored. To represent the dynamics on different scales the model combines the description of soil as a continuous solid, as distinct particles and as rigid multibodies. The models are dynamically coupled to each other and to the earthmoving equipment. Agitated soil is represented by a hybrid of contacting particles and continuum solid, with the moving equipment and resting soil as geometric boundaries. Each zone of active soil is aggregated into distinct bodies, with the proper mass, momentum and frictional-cohesive properties, which constrain the equipment’s multibody dynamics. The particle model parameters are pre-calibrated to the bulk mechanical parameters for a wide range of different soils. The result is a computationally efficient model for earthmoving operations that resolve the motion of the soil, using a fast iterative solver, and provide realistic forces and dynamic for the equipment, using a direct solver for high numerical precision. Numerical simulations of excavation and bulldozing operations are performed to validate model and measure the computational performance. Reference data is produced using coupled discrete element and multibody dynamics simulations at relatively high resolution. The digging resistance and soil displacements with the real-time multiscale model agree with the reference model up to 10-25%, and run more than three orders in magnitude faster.

KEYWORDS: deformable terrain; discrete element method; multibody dynamics;
multiscale; real-time simulation; soil mechanics

Read full paper: pdf
On web

Durchgängige Nutzong von Anlagenmodellen

Published in: ATP Magazin (6-7) 2018
Authors: Felix Auris, Daimler, Holger Zipper, Ifak e.V Michael Brandl, Algoryx Simulation, Subastian Süss, Sick, Christian Diedrich, Otto-von-Guericke Universität
Date: June 2018
ISSN: 2190-4111

Abstract

Über den gesamten Lebenszyklus von Produktionsanlagen

Der Beitrag konzentriert sich auf neue Konzepte zur durchgängigen, ganzheitlichen,
standardisierten und effizienten Simulation über den Anlagenlebenszyklus automatisierter
Montageanlagen im Automobilbau. Es wird gezeigt, wie durch die Nutzung
standardisierter Datenformate ein sogenanntes mechatronisches Anlagenmodell, oft
auch als digitaler Zwilling bezeichnet, implizit aus den Konstruktionsdaten generiert
werden kann und in allen folgenden Phasen des Anlagenlebenszyklus weiterverwendet
wird.
SCHLAGWÖRTER Engineeringbegleitende Simulation / Co-Simulation /
Physikalische Modelle / FMI / Durchgehendes Engineering

Holistic use of engineering models throughout the entire plant life cycle

The article focuses on new concepts for integrated, holistic, standardized and efficient
simulation of automated assembly systems in the automotive industry. By using
standardized data formats, a mechatronic plant model can be implicitly derived from
the 3D design data and can be used continuously in all subsequent phases of the
plant life cycle.

KEYWORDS simulation based engineering / co-simulation / physics based models /
FMI / continuous engineering

Read full paper: Contact us for a digital copy

Physics-based virtual environments for autonomous earthmoving and mining machinery

Published in: CVT2018 – 5th International Commercial Vehicle Technology Symposium Kaiserslautern (2018).
Authors: Martin Servin, Michael Brandl
Date: 2018-03-12

Abstract

The scientific foundation for constructing virtual environments (VE) that support the development of earthmoving and mining machinery with autonomous capabilities is summarized. It is explained how the physics simulation engine AGX Dynamics supports this. Finally, a methodology for computational design exploration of an autonomous load-haul-dump machine in a physics-based VE is described.

Read full paper: pdf

Hybrid, multi-resolution wires with massless frictional contacts

Published in: Visualization and Computer Graphics, IEEE Transactions on (Volume:17 , Issue: 7)
Authors: Claude Lacoursière, Martin Servin, Fredrik Nordfeldth, Kenneth Bodin
Date: 2010-10-14
ISSN: 1077-2626

Abstract

We describe a method for the visual interactive simulation of wires contacting with rigid multibodies. The physical model used is a hybrid combining lumped elements and massless quasistatic representations. The latter is based on a kinematic constraint preserving the total length of the wire along a segmented path which can involve multiple bodies simultaneously and dry frictional contact nodes used for roping, lassoing, and fastening. These nodes provide stick and slide friction along the edges of the contacting geometries. The lumped element resolution is adapted dynamically based on local stability criteria, becoming coarser as the tension increases, and up to the purely kinematic representation. Kinematic segments and contact nodes are added, deleted, and propagated based on contact geometries and dry friction configurations. The method gives a dramatic increase in both performance and robustness because it quickly decimates superfluous nodes without loosing stability, yet adapts to complex configurations with many contacts and high curvature, keeping a fixed, large integration time step. Numerical results demonstrating the performance and stability of the adaptive multiresolution scheme are presented along with an array of representative simulation examples illustrating the versatility of the frictional contact model.

Read full paper: IEEE Xplore

Accelerated granular matter simulation

Published in: PhD thesis. Department of Physics, Umeå University, Sweden, SE-901 87, Umeå, Sweden.
Authors: D. Wang
Date: Nov 2015

Summary

Modeling and simulation of granular matter has important applications in both natural science and industry. One widely used method is the discrete element method (DEM). It can be used for simulating granular matter in the gaseous, liquid as well as solid regime whereas alternative methods are in general applicable to only one. Discrete element analysis of large systems is, however, limited by long computational time. A number of solutions to radically improve the computational efficiency of DEM simulations are developed and analysed. These include treating the material as a nonsmooth dynamical system and methods for reducing the computational effort for solving the complementarity problem that arise from implicit treatment of the contact laws. This allow for large time-step integration and ultimately more and faster simulation studies or analysis of more complex systems. Acceleration methods that can reduce the computational complexity and degrees of freedom have been invented. These solutions are investigated in numerical experiments, validated using experimental data and applied for design exploration of iron ore pelletising systems.

Read full thesis: pdf

Adaptive model reduction for nonsmooth discrete element simulation

Published in: Computational Particle Mechanics, 3(1):107–121 (2016).
Authors: M. Servin and D. Wang.
Date: 2016

Summary

A method for adaptive model order reduction for nonsmooth discrete element simulation is developed and analysed in numerical experiments. Regions of the granular media that collectively move as rigid bodies are substituted with rigid bodies of the corresponding shape and mass distribution. The method also support particles merging with articulated multibody systems. A model approximation error is defined and used to derive conditions for when and where to apply reduction and refinement back into particles and smaller rigid bodies. Three methods for refinement are proposed and tested: prediction from contact events, trial solutions computed in the background and using split sensors. The computational performance can be increased by 5–50 times for model reduction level between 70–95 %.

Read full paper: pdf

Warm starting the projected Gauss-Seidel algorithm for granular matter simulation

Published in: Computational Particle Mechanics, 3(1):43-52 (2016).
Authors: D. Wang, M. Servin, and T. Berglund.
Date: 2016

Summary

The effect on the convergence of warm starting the projected Gauss–Seidel solver for nonsmooth discrete element simulation of granular matter are investigated. It is found that the computational performance can be increased by a factor 2–5.

Read full paper: pdf

Parametrization and validation of a nonsmooth discrete element method for simulating flows of iron ore green pellets

Published in: Powder Technology, Powder Technology, Vol. 283, 475-487 (2015).
Authors: D. Wang, M. Servin, T. Berglund, K-O. Mickelsson, and S. Rönnbäck.
Date: 2015

Summary

The nonsmooth discrete element method (NDEM) have the potential of high computational efficiency for rapid exploration of large design space of systems for processing and transportation of mineral ore. We present parametrization, verification and validation of a simulation model based on NDEM for iron ore green pellet flow in balling circuits. Simulations are compared with camera based measurements of individual pellet motion as well as bulk behaviour of pellets on conveyors and in rotating balling drum. It is shown that the NDEM simulation model is applicable for the purpose of analysis, design and control of iron ore pelletizing systems. The sensitivity to model and simulation parameters is investigated. It is found that: the errors associated with large time-step integration do not cause statistically significant errors to the bulk behaviour;
rolling resistance is a necessary model component; and the outlet flow from the drum is sensitive to fine material adhering to the outlet creating a thick coating that narrows the outlet gaps.

Read full paper: pdf

Examining the smooth and nonsmooth discrete element approaches to granular matter

Published in: Visualization and Computer Graphics, IEEE Transactions on (Volume:17 , Issue: 7 )
Authors: M. Servin, D. Wang, C. Lacoursière and K. Bodin
Date: 2014-01-16

Summary

The smooth and nonsmooth approaches to the discrete element method (DEM) are examined from a computational perspective. The main difference can be understood as using explicit versus implicit time integration. A formula is obtained for estimating the computational effort depending on error tolerance, system geometric shape and size, and on the dynamic state. For the nonsmooth DEM (NDEM), a regularized version mapping to the Hertz contact law is presented. This method has the conventional nonsmooth and smooth DEM as special cases depending on size of time step and value of regularization. The use of the projected Gauss-Seidel solver for NDEM simulation is studied on a range of test systems. The following characteristics are found. First, the smooth DEM is computationally more efficient for soft materials, wide and tall systems, and with increasing flow rate. Secondly, the NDEM is more beneficial for stiff materials, shallow systems, static or slow flow, and with increasing error tolerance. Furthermore, it is found that just as pressure saturates with depth in a granular column, due to force arching, also the required number of iterations saturates and become independent of system size. This effect make the projected Gauss-Seidel solver scale much better than previously thought. Copyright © 2014 John Wiley & Sons, Ltd.

Read full paper: Wiley Online Library

Outlet design optimization based on large-scale nonsmooth DEM simulation

Authors: Wang, Da (Umeå University, Faculty of Science and Technology, Department of Physics)
Servin, Martin (Umeå University, Faculty of Science and Technology, Department of Physics)
Mickelsson, Kjell-Ove (LKAB)
Date: 2014
ISI: 000332430600056

Abstract

We consider the application of a nonsmooth discrete element method to geometric design optimization of a balling drum outlet used in production of iron ore balls. The geometric design optimization problem is based on the need for homogeneous flow of balls from the balling drum onto a wide belt conveyor feeding a roller screen (sieve). An outlet with two design variables is investigated and the optimal shape for the given system and production flow is found by exploring the design space with 2000 simulations.

Read full paper: Umeå University

Constraint based particle fluids on GPGPU

Authors: Bodin, Kenneth (Umeå University, Faculty of Science and Technology, High Performance Computing Center North (HPC2N)) Lacoursière, Claude (Umeå University, Faculty of Science and Technology, High Performance Computing Center North (HPC2N)) Nilsson, Martin and Servin, Martin (Umeå University, Faculty of Science and Technology, Department of Physics)
Date: 2011
ISI: 000332430600056

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.

Read full paper: Umeå University

Regularized multibody dynamics with dry frictional contact

Authors: Lacoursière, Claude (Umeå University, Faculty of Science and Technology, High Performance Computing Center North (HPC2N)) Servin, Martin (Umeå University, Faculty of Science and Technology, Department of Physics)
Date: 2011

Read full paper: download article

Constraint Fluids

Authors: Kenneth Bodin, Claude Lacoursière, Martin Servin
Date: 2009

Abstract

Read full paper: Umeå University

Ghosts and machines

Author: Lacoursière, Claude
Date: 2007

Title

Ghosts and machines: Regularized variational methods for interactive simulations of multibodies with dry frictional contacts.

Read full thesis: UMU DIVA

Interactive Simulation of Elastic Deformable Materials

Abstract

A novel, fast, stable, physics-based numerical method for interac- tive simulation of elastically deformable objects is presented. Start- ing from elasticity theory, the deformation energy is modeled in terms of the positions of point masses using the linear shape func- tions of finite element analysis, providing for an exact correspon- dence between the known physical properties of deformable bodies such as Young’s modulus, and the simulation parameter. By treating the infinitely stiff case as a kinematic constraint on a system of point particles and using a regularization technique, a stable first order stepping algorithm is constructed which allows the simulation of materials over the entire range of stiffness values, including incom- pressibility. The main cost of this method is the solution of a linear system of equations which is large but sparse. Commonly available sparse matrix packages can process this problem with linear com- plexity in the number of elements for many cases. This method is contrasted with other well-known point mass models of deformable solids which rely on penalty forces constructed from simple local geometric quantities, e.g., spring-and-damper models. For these, the mapping between the simulation parameters and the physical observables is not well defined and they are either strongly limited to the low stiffness case when using explicit integration methods, or produce grossly inaccurate results when using simple linearly im- plicit method. Validation and timing tests on the new method show that it produces very good physical behavior at a moderate compu- tational cost, and it is usable in the context of real-time interactive simulations.

Authors: Martin Servin – Department of Physics, Umeå University, Claude Lacoursi`ere – HPC2N/VRlab and Computing Science Department, Umeå University, Niklas Melin – Department of Physics, Umeå University
Date: 2014

Read full paper: Researchgate

A regularized time stepper for multibody system

Author: Claude Lacoursière
Date: 2006
ISSN: 0348-0542

Read full paper: Computer Science Umeå University

Regularized, stabilized, variational methods for multibodies

Authors: Lacoursière, Claude (Umeå University, Faculty of Science and Technology, High Performance Computing Center North (HPC2N)) (Umeå University, Faculty of Science and Technology, Department of Computing Science) (UMIT)
Date: 2007

Abstract

A time-discrete formulation of the variational principle of mechanics is used to construct a novel first order, fixed time step integration method for multibody systems subject to mixed constraints. The new stepper, coined Spook, includes physics motivated constraint regularization and stabilization terms. The stepper is proved to be stable for the case of linear constraints, for non-zero regularization and stabilization parameters. For fixed stabilization value, the regularization can be made arbitrarily small, corresponding to arbitrarily stiff penalty forces. The “relaxed” constraint formulation permits a separation of time scales so that stiff forces are treated as relaxed constraints. Constraint stabilization makes the stiff forces modeled this way strictly dissipative, and thus, the stepper essentially filters out the high oscillations, but is rigorously symplectic for the rest of the motion. Spook solves a single linear system per time step and is insensitive to constraint degeneracies for non-zero regularization. In addition, it keeps the constraint violations within bounds of O(h2), where h is the time step. Because it is derived from the discrete variational principle, the stepping scheme globally preserves the symmetries of the physical system. The combination of these features make Spook a very good choice for interactive simulations. Numerical experiments on simple multibody systems are presented to demonstrate the performance and stability properties.

Read full paper: DIVA Umeå University

A parallel block iterative method for interactive contacting rigid multibody simulations on multicore PCs

Author: Claude Lacoursière
Date: 2006

Abstract

A hybrid, asynchronous, block parallel method to approxi- mately solve complementarity problems (CPs) in real-time on multicore CPUs is described. These problems arise from interactive real-time sim- ulations of systems of constrained, contacting rigid bodies, which are useful in virtual operator training systems for instance. A graph analy- sis 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 sep- arate 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.

Read full paper: Umeå University

Colosseum3D – Authoring framework for Virtual Environments

Author: Anders Backman, VRlab/HPC2N, Umeå University, Sweden
Date: 2005

Abstract

This paper describes an authoring environment for real time 3D environments, Colosseum3D. The framework makes it possible to easily create rich virtual environments with rigid-body dynamics, 3D rendering using OpenGL Shaders, 3D sound and human avatars. The creative process of building com- plex simulators is supported by allowing several authoring paths such as a low level C++ API, an ex- pressive high level file format and a scripting layer. To exemplify the use of the framework, an immersive wheelchair simulator application is presented. A natural and intuitive interaction method is implemented using dynamic simulation.

Read full paper:Computer Science Umeå University

Massless cable for Real-time Simulation

Authors: M. Servin and C. Lacoursière
Date: 2007

Abstract

A technique for real-time simulation of hoisting cable systems based on a multibody nonideal constraint is presented. The hoisting cable constraint is derived from the cable internal energies for stretching and twisting. Each hoisting cable introduces two constraint equations, one for stretching and one for torsion, which include all the rigid bodies attached by the same cable. The computation produces the global tension and torsion in the cable as well as the resulting forces and torques on each attached body. The complexity of the computation grows linearly with the number of bodies attached to a given cable and is weakly coupled to the rest of the simulation. The nonideal constraint formulation allows stable simulations of cables over wide ranges of linear and torsional stiffness, including the rigid limit. This contrasts with lumped element formulations including the cable internal degrees of freedom in which computational complexity grows at least linearly with the number of cable elements – usually proportional to cable length – and where numerical stability is sensitive to the mass ratio between the load and the lumped elements.

Read full paper: Wiley Online Library

Rigid Body Cable for Virtual Environments

Authors: Martin Servin, and Claude Lacoursière
Date: 2008

Abstract

The present paper addresses real-time simulation of cables for virtual environments. A faithful physical model based on constrained rigid bodies is introduced and discretized. The performance and stability of the numerical method are analyzed in detail and found to meet the requirements of interactive heavy hoisting simulations. The physical model is well behaved in the limit of infinite stiffness as well as in the elastic regime, and the tuning parameters correspond directly to conventional material constants. The integration scheme mixes the well known Sto ̈ rmer-Verlet method for the dynamics equations with the linearly implicit Euler method for the constraint equations and enables physical constraint relaxation and stabilization terms. The technique is shown to have superior numerical stability properties in comparison with either chain link systems, or spring and damper models. Experimental results are presented to show that the method results in stable, real-time simulations. Stability persists for moderately large fixed integration step of ∆t = 1/60 s, with hoisting loads of up to 105 times heavier than the elements of the cable. Further numerical experiments validating the physical model are also presented.

Read full paper: Umeå University

Master Theses

Collision detection for trimming curves and BREPs

Author: Alexander Östman
Date: April 19, 2014
Master’s Thesis in Engineering Physics, 30 credits
Umeå University, Department of Physics

Abstract

This report treats the implementation of collision detection algorithms for Boundary representations (BREPs) consisting of connected trimmed surfaces, mainly Non Uniform Rational Basis Spline (NURBS) surfaces. Using the OpenNurbs software package, complicated geometries created in CAD program Space Claim were imported to the physics engine AgX, where dynamic simulations were carried out. Collision detection algorithms for the geometry pairs BREP-line, BREP-plane and BREP-sphere have been developed and investigated. In the case of BREP-sphere collision detection, experiments have been carried out which show that BREP-shape representation exceeds trimesh-shape representation both in computational performance and in collision accuracy. The conclusion is that BREP representation has the potential to replace trimesh representation for some complex geometries with higher computational performance and more accurate simulations as a result.

Read full report: university page

Application programming Interface for Native Web Applications

Author: Tobias Widlund
Date: 2012-06-21
Bachelor’s Thesis in Engineering Science, 15 credits
Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering

Abstract

This report describes a project about designing and implementing a usable application programming interface [API] for an existing application that was being ported to a web platform.
Today we experience a shift in how we humans work with computers in the sense that everything becomes more and more web oriented. To stay usable, software has to adapt to this and this project is an example on how such adaption may be performed.
The application, called Algodoo is an interactive 2D physics simulator written in C++ and as this was ported to the web using Native Client [NaCl] , it required new functionality to allow web page elements to interact with it. In other words, an API. It is the design and implementation of this API that is the focus of this report, but within it, the background for the project, will also be explained.

Read full report:university page

Ice fracture model for real-time ship simulator

Author: Tomas Berglund
Date: 2012-11-29
Master’s Thesis in Technical Physics, 30 credits
Umeå University, Department of Physics

Abstract

Navigating in the arctic has become more common, but it is dificult and dangerous due to the presence of ice. Any training under safer circumstances is therefore very valuable, enter the need for ship simulators. Ship simulators today incorporate many features, such as cranes, anchors, wires, and state of the art physics. However, the inclusion of ice is very rare due to the complexity of simulating the feedback from the ice breaking progress.The purpose of this project is to build a model and numerical methods to simulate icefracture in real-time, which is to be used in ship simulators. The model presented inthis project is implemented with the use of the physics engine AgX Dynamics made by Algoryx Simulation AB. The method represents the ice sheet as a non-homogeneous mesh. A collision with thehull of the ship injects deformation energy into the ice. The energy from the inelasticimpact is distributed on the ice sheet according to a quasi-static crack propagationmodel that is dened on a static mesh. The cracks are guided using stress elds thatapproximate the strain in each vertex. The distribution of the strain is done by a simple model which allows for breaking ice in non-uniform fragments. This is more realistic than fracture in predened shapes which is the main contribution of this project. The fragments become unbreakable rigid body ice oes that interact with the ship’s hull by collision and friction. The implementation of the ice model is tested by using a trimesh model of the TorViking II icebreaker using approximated buoyancy calculations, damping equations, and engine forces. Real-time performance is not achieved yet in the general case, but this is due to the choice of collision geometry and the oe creation. Unstable force spikes from the contacts between the ship and the ice is detected, but the overall global ice resistance shows few abnormalities. Replacing the collision geometry and the rigid body oes isnecessary for the implementation to be able to run in real-time. Further experiments to compare with real model data is needed to be able to validate the model.

Read full report: University page

Applications of advanced physics in visual effects

Author: Tor Sterner
Date: 2011-09-11
Master’s Thesis in Computing Science, 30 credits
Umeå University, Department of Computing Science

Abstract

AgX Multiphysics is a toolkit for performing physics-based simulations, developed by Algoryx Simulations AB. AgX provides stable physics simulations and is used for industrial and engineering simulations around the world.This thesis examines the possibilities for AgX to be used in the visual effects market for films and commercials. The thesis includes a survey of opinions of professionals from the visual effects company Digital Domain. The three most wanted capabilities from AgX was according to the survey; stiff constraints, fluid-rigid body interaction and hair simulation. Furthermore, all new tools must improve or be equal on all aspects compared to the old tools, and have good scalability.Several simulations were run to compare the stiff constraints and scalability of AgX with the currently used tools. The results show that AgX handles stiff constraints a lot better than the old tool and is also highly scalable.In summary, for saving time from doing tedius tasks and for using physics to an extent earlier not possible, AgX would be a good addition to the current use of physics in visual effects.

Read full report: university page

Electricity in a 2D mechanics simulator for education

Author: Emanuel Dahlberg
Date: January 31, 2011f
Master’s Thesis in Computing Science, 30 credits
Umeå University, Department of Computing Science

Abstract

Electricity can be a difficult topic to grasp since it is abstract, it is e.g. not possible to see the current and the voltage in a circuit. If electricity can be simulated and visualized, it can become less abstract and easier to understand. This thesis covers the process of simulating electricity in real-time together with a mechanics simulator, called Algodoo.
The process of analyzing electric circuits from a computers point of view is covered as well as different ways of simulating electric motors, generators and lasers. A large part of the thesis covers how to integrate the electricity and the mechanics simulators in a stable and accurate way. Furthermore, making the objects of the mechanics simulator able to conduct electricity is also covered.
The thesis shows that it is possible to simulate electricity in real-time, and that physically correct conducting objects requires a lot of processing power, but can be simplified without losing too much correctness. The thesis also shows that the electrical and mechanics simulators preferably should be solved together to get a stable simulation.
Simulating electricity opens up an endless number of interactive scenarios, e.g. mechanical switches, potentiometers, relays and even logic gates. It can be a helpful aid as an introduction to electronics and since the simulators are integrated, it can also provide an introduction to mechanical work. The amount of energy required to perform different tasks can be compared and analyzed.

Read full report: university page

Collision detection of triangle meshes using GPU

Author: Nils Bäckman
Date: March 13, 2011
Master’s Thesis in Computing Science, 30 credits
Umeå University, Department of Computing Science

Abstract

Collision detection in physics engines often use primitives such as spheres and boxes since collisions between these objects are straightforward to compute. More complicated objects can then be modeled using compounds of these simpler primitives.
However, in the pursuit of making it easier to construct and simulate complicated objects, triangle meshes are a good alternative since it is usually the format used by modeling tools.
This thesis demonstrates how triangle meshes can be used directly as collision objects within a physics engine. The collision detection is done using triangle mesh models with tests accelerated using a tree-based bounding volume hierarchy structure.
OpenCL is a new open industry framework for writing programs on heterogeneous platforms, including highly parallel platforms such as Graphics Processing Units(GPUs).
Through the use of OpenCL, parallelization of triangle mesh collision detection is implemented for the GPU, then evaluated and compared to the CPU implementation.

Read full report: university page

Robot design optimization by means of a genetic algorithm and physics simulation

Author: Morgan Gunnarsson
Date: December 2, 2010
Master’s Thesis in Computing Science, 30 ECTS credits
Umeå University, Department of Computing Science

Abstract

This thesis presents a new robot design paradigm that utilizes evolutionary optimization techniques and advanced physics simulations. This technology makes it possible to design and test robots in virtual environments before the physical robots are built, which enables robot manufacturers to improve the performance of their products and decrease the time and cost for development. In this project, a 3D robot model was defined in geometric, kinematic and dynamic terms. Also, a piece of software was developed in C++ to optimize the robot design, and to simulate and visualize the robot model with the aid of a physics engine. A genetic algorithm was developed for the optimization and used to minimize the average positional error and the total torque magnitude under constraints on speed, and the design variables were the PID controller parameters and the torque actuator limits. Only predefined robots can be programmed and simulated with current software packages for offline-programming and robot simulation. It was concluded that such software packages can be improved by robot design optimization using the software developed in this project, by means of a genetic algorithm and simulations using a physics engine.

Read full report: university page

Distance fields accelerated with OpenCL

Author: Erik Sundholm
Date: June 8, 2010
Master’s Thesis in Computing Science, 30 credits
Umeå University, Department of Computing Science

Abstract

An important task in any graphical simulation is the collision detection between the objects in the simulation. It is desirable to have a good general method for collision detection with high performance. This thesis describes an implementation of a collision detection method that uses distance fields to detect collisions. This method is quite robust and able to detect collisions between most possible shapes. It is also capable of computing contact data for collisions. A problem with distance fields is that the performance cost for making a distance field is quite extensive. It is therefore customary to have some way of accelerating the computation of the distance field (usually by only computing select parts of the field). The application implemented in this thesis solves this performance problem by using the parallel framework OpenCL for accelerating the construction of the field.OpenCL enables programmers to execute code on the GPU. The GPU is highly data parallel and a huge increase in performance can be obtained by letting the GPU handle the computations associated with the initiation of the field.

Read full report; university page

Constraint fluids on GPU

Author: Martin Nilsson
Date: September 7, 2009
Master’s Thesis in Computing Science, 30 ECTS credits
Umeå University, Department of Computing Science

Abstract

The processing power of graphics hardware has increased tremendously in the last several years and they are therefore used more and more outside of their intended domain of graphics rendering. This thesis describes the implementation and results of a fluid simulator, using the constraint fluid method, which harnesses the processing power of modern GPUs, in particular NVIDIA’s CUDA platform. As demonstrated in this thesis, particle systems with hundreds of thousands of particles can be simulated and visualized at interactive rates and systems containing up to a million particles can be run at a few frames per second. The biggest performance bottleneck is currently in the solver, in particular the lack of a working preconditioned Conjugate Gradient implementation.

Read full report: Thesis report