2008
|
 | Hansson, Anders; Servin, Martin: Semi-autonomous Shared Control for Redundant Forwarder Cranes. Umeå Universitet 2008. @techreport{semiauto_servin2008,
title = {Semi-autonomous Shared Control for Redundant Forwarder Cranes},
author = {Anders Hansson and Martin Servin},
url = {http://umit.cs.umu.se/modsimcomplmech/docs/papers/Hansson_Servin_Semi-autonomous%20Shared%20Control%20for%20Redundant%20Forwarder%20Cranes.pdf
http://umit.cs.umu.se/wiki/Semi-Autonomous_Crane
https://www.youtube.com/watch?v=OHj97eEGfxs&ab_channel=UMITResearchLab},
year = {2008},
date = {2008-06-01},
institution = {Umeå Universitet},
abstract = {Semi-autonomous operation with shared control between the human operator and an autonomous control system has been developed and examined for a forwarder crane. Shared control gives the operator and the autonomous control system simultaneous control over the same task. It also enables smooth transitions between manual and autonomous operation. Operators with professional experience of forwarder crane control as well as inexperienced operators have been engaged in experiments where performance was measured. The experiments were conducted on a forwarder crane of reduced size at Smart Crane Lab, Umeå University. Three levels of automation were evaluated: pure manual operation, semi{autonomous operation with traded control and semi{autonomous operation with shared control. The semi-autonomous operation were examined along with two methods for manual operation: conventional joint control and boom-tip control.
The time-efficiency of log loading as well as smoothness of transitions between autonomous and manual operation were examined. The experiments show that with the aid of shared control the performance of the inexperienced operators increases with a factor two as compared to manual joint control. The performance of the professional operators decreases somewhat with shared control as compared to manual joint control. With shared control both professional and inexperienced operators experience a reduction in workload. Smoothness of transitions were found satisfactory.},
keywords = {Algoryx},
pubstate = {published},
tppubtype = {techreport}
}
Semi-autonomous operation with shared control between the human operator and an autonomous control system has been developed and examined for a forwarder crane. Shared control gives the operator and the autonomous control system simultaneous control over the same task. It also enables smooth transitions between manual and autonomous operation. Operators with professional experience of forwarder crane control as well as inexperienced operators have been engaged in experiments where performance was measured. The experiments were conducted on a forwarder crane of reduced size at Smart Crane Lab, Umeå University. Three levels of automation were evaluated: pure manual operation, semi{autonomous operation with traded control and semi{autonomous operation with shared control. The semi-autonomous operation were examined along with two methods for manual operation: conventional joint control and boom-tip control.
The time-efficiency of log loading as well as smoothness of transitions between autonomous and manual operation were examined. The experiments show that with the aid of shared control the performance of the inexperienced operators increases with a factor two as compared to manual joint control. The performance of the professional operators decreases somewhat with shared control as compared to manual joint control. With shared control both professional and inexperienced operators experience a reduction in workload. Smoothness of transitions were found satisfactory. |
 | Servin, Martin; Backman, Anders; Bodin, Kenneth; Bergsten, Urban; Bergström, Dan; Löfgren, Björn; Nordfjell, Tomas; Wästerlund, Iwan: Visual simulation of machine concepts for forest biomass harvesting. In: 10th Virtual Reality International Conference (VRIC '08 Laval Virtual), Laval, France (2008), 2008. @inproceedings{servin2008visual,
title = {Visual simulation of machine concepts for forest biomass harvesting},
author = {Martin Servin and Anders Backman and Kenneth Bodin and Urban Bergsten and Dan Bergström and Björn Löfgren and Tomas Nordfjell and Iwan Wästerlund},
url = {http://umit.cs.umu.se/modsimcomplmech/docs/papers/Servin_et_al_2008_VRIC_2008.pdf},
year = {2008},
date = {2008-01-01},
booktitle = {10th Virtual Reality International Conference (VRIC '08 Laval Virtual), Laval, France (2008)},
abstract = {We present work-in-progress of applying simulator technology for developing, demonstrating and evaluating new machine concepts and work methods in off-road environments. In particular we consider a new concept machine for making efficient biomass harvesting in the process of thinning in dense forest stands and we describe how this machine concept is realized in a virtual environment and plan for simulator experiments. },
keywords = {Algoryx},
pubstate = {published},
tppubtype = {inproceedings}
}
We present work-in-progress of applying simulator technology for developing, demonstrating and evaluating new machine concepts and work methods in off-road environments. In particular we consider a new concept machine for making efficient biomass harvesting in the process of thinning in dense forest stands and we describe how this machine concept is realized in a virtual environment and plan for simulator experiments. |
 | Servin, Martin; Lacoursière, Claude: Rigid body cable for virtual environments. In: IEEE Transactions on Visualization and Computer Graphics, vol. 14, no. 4, pp. 783–796, 2008. @article{servin2008rigid,
title = {Rigid body cable for virtual environments},
author = {Martin Servin and Claude Lacoursière},
url = {http://umit.cs.umu.se/modsimcomplmech/docs/papers/rbcve_ieee_final.pdf},
doi = {10.1109/TVCG.2007.70629},
year = {2008},
date = {2008-01-01},
journal = {IEEE Transactions on Visualization and Computer Graphics},
volume = {14},
number = {4},
pages = {783--796},
publisher = {IEEE},
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.},
keywords = {Algoryx},
pubstate = {published},
tppubtype = {article}
}
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. |
 | Servin, Martin; Lacoursière, Claude; Nordfelth, Fredrik: Adaptive resolution in physics based virtual environments. In: SIGRAD 2008. The Annual SIGRAD Conference Special Theme: Interaction; November 27-28; 2008 Stockholm; Sweden, pp. 47–52, Linköping University Electronic Press 2008. @inproceedings{servin2008adaptive,
title = {Adaptive resolution in physics based virtual environments},
author = {Martin Servin and Claude Lacoursière and Fredrik Nordfelth},
url = {http://www.ep.liu.se/ecp/034/012/ecp083412.pdf
https://ep.liu.se/konferensartikel.aspx?series=ecp&issue=34&Article_No=12},
year = {2008},
date = {2008-01-01},
booktitle = {SIGRAD 2008. The Annual SIGRAD Conference Special Theme: Interaction; November 27-28; 2008 Stockholm; Sweden},
number = {034},
pages = {47--52},
organization = {Linköping University Electronic Press},
abstract = {We propose a systematic approach to adaptive resolution in physics based virtual environments (VEs) that combines the conventional requirements of realtime performance; visual appearance with important requirements on the physical simulation; such as accuracy and numerical robustness. In particular; we argue that adaptive resolution is a key element to achieve robustness in fixed time-step VEs. The idea is to adaptively substitute unstable subsystems with more simplified and robust models. The method is demonstrated on systems including stiff wires. The algorithm brings stability; realtime performance and preservation of the important physical invariants to the system. The application to general systems is discussed.},
keywords = {Algoryx},
pubstate = {published},
tppubtype = {inproceedings}
}
We propose a systematic approach to adaptive resolution in physics based virtual environments (VEs) that combines the conventional requirements of realtime performance; visual appearance with important requirements on the physical simulation; such as accuracy and numerical robustness. In particular; we argue that adaptive resolution is a key element to achieve robustness in fixed time-step VEs. The idea is to adaptively substitute unstable subsystems with more simplified and robust models. The method is demonstrated on systems including stiff wires. The algorithm brings stability; realtime performance and preservation of the important physical invariants to the system. The application to general systems is discussed. |
2007
|
 | Lacoursière, Claude: Regularized, stabilized, variational methods for multibodies. In: Dag Fritzson Peter Bunus, Claus Führer (Ed.): The 48th Scandinavian Conference on Simulation and Modeling (SIMS 2007), 30-31 October, 2007, Göteborg (Särö), pp. 40–48, Linköping University Electronic Press, 2007, ISSN: 1650-3740. @inproceedings{lacoursiere2007regularized,
title = {Regularized, stabilized, variational methods for multibodies},
author = {Claude Lacoursière},
editor = {Peter Bunus, Dag Fritzson, Claus Führer},
url = {http://www.ep.liu.se/ecp/027/005/ecp072705.pdf
https://ep.liu.se/en/conference-article.aspx?series=ecp&issue=27&Article_No=5},
issn = {1650-3740},
year = {2007},
date = {2007-10-21},
booktitle = {The 48th Scandinavian Conference on Simulation and Modeling (SIMS 2007), 30-31 October, 2007, Göteborg (Särö)},
pages = {40--48},
publisher = {Linköping University Electronic Press},
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(h 2), 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.},
keywords = {Algoryx},
pubstate = {published},
tppubtype = {inproceedings}
}
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(h 2), 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. |
 | Servin, Martin; Lacoursière, Claude: Massless Cable for Real-time Simulation. In: Computer Graphics Forum, pp. 172–184, Blackwell Publishing Ltd Oxford, UK 2007. @inproceedings{servin2007massless,
title = {Massless Cable for Real-time Simulation},
author = {Martin Servin and Claude Lacoursière},
url = {http://umit.cs.umu.se/modsimcomplmech/docs/papers/Massless.pdf
https://www.youtube.com/watch?v=H8Xbtl7jX-k},
doi = {10.1111/j.1467-8659.2007.01014.x},
year = {2007},
date = {2007-01-01},
booktitle = {Computer Graphics Forum},
volume = {26},
number = {2},
pages = {172--184},
organization = {Blackwell Publishing Ltd Oxford, UK},
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.},
keywords = {Algoryx},
pubstate = {published},
tppubtype = {inproceedings}
}
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. |
 | Lacoursière, Claude: Ghosts and machines: regularized variational methods for interactive simulations of multibodies with dry frictional contacts. Department of Computing Science, Umeå University, Sweden, 2007. @phdthesis{lacoursiere2007ghosts,
title = {Ghosts and machines: regularized variational methods for interactive simulations of multibodies with dry frictional contacts},
author = {Claude Lacoursière},
url = {http://umu.diva-portal.org/smash/get/diva2:140361/FULLTEXT01
http://urn.kb.se/resolve?urn=urn%3Anbn%3Ase%3Aumu%3Adiva-1143},
year = {2007},
date = {2007-01-01},
school = {Department of Computing Science, Umeå University, Sweden},
abstract = {A time-discrete formulation of the variational principle of mechanics is used to provide a consistent theoretical framework for the construction and analysis of low order integration methods. These are applied to mechanical systems subject to mixed constraints and dry frictional contacts and impacts|machines. The framework includes physics motivated constraint regularization and stabilization schemes. This is done by adding potential energy and Rayleigh dissipation terms in the Lagrangian formulation used throughout. These terms explicitly depend on the value of the Lagrange multipliers enforcing constraints. Having finite energy, the multipliers are thus massless ghost particles. The main numerical stepping method produced with the framework is called SPOOK.
Variational integrators preserve physical invariants globally, exactly in some cases, approximately but withinfixed global bounds for others. This allows to product realistic physical trajectories even with the low order methods. These are needed in the solution of nonsmooth problems such as dry frictional contacts and in addition, they are computationally inexpensive. The combination of strong stability, low order, and the global preservation of invariants allows for large integration time steps, but without loosing accuracy on the important and visible physical quantities. SPOOK is thus well-suited for interactive simulations, such as those commonly used in virtual environment applications, because it is fast, stable, and faithful to the physics.
New results include a stable discretization of highly oscillatory terms of constraint regularization; a linearly stable constraint stabilization scheme based on ghost potential and Rayleigh dissipation terms; a single-step, strictly dissipative, approximate impact model; a quasi-linear complementarity formulation of dry friction that is isotropic and solvable for any nonnegative value of friction coefficients; an analysis of a splitting scheme to solve frictional contact complementarity problems; a stable, quaternion-based rigid body stepping scheme and a stable linear approximation thereof. SPOOK includes all these elements. It is linearly implicit and linearly stable, it requires the solution of either one linear system of equations of one mixed linear complementarity problem per regular time step, and two of the same when an impact condition is detected. The changes in energy caused by constraints, impacts, and dry friction, are all shown to be strictly dissipative in comparison with the free system. Since all regularization and stabilization parameters are introduced in the physics, they map directly onto physical properties and thus allow modeling of a variety of phenomena, such as constraint compliance, for instance.
Tutorial material is included for continuous and discrete-time analytic mechanics, quaternion algebra, complementarity problems, rigid body dynamics, constraint kinematics, and special topics in numerical linear algebra needed in the solution of the stepping equations of SPOOK.
The qualitative and quantitative aspects of SPOOK are demonstrated by comparison with a variety of standard techniques on well known test cases which are analyzed in details. SPOOK compares favorably for all these examples. In particular, it handles ill-posed and degenerate problems seamlessly and systematically. An implementation suitable for large scale performance and accuracy testing is left for future work.},
keywords = {Algoryx},
pubstate = {published},
tppubtype = {phdthesis}
}
A time-discrete formulation of the variational principle of mechanics is used to provide a consistent theoretical framework for the construction and analysis of low order integration methods. These are applied to mechanical systems subject to mixed constraints and dry frictional contacts and impacts|machines. The framework includes physics motivated constraint regularization and stabilization schemes. This is done by adding potential energy and Rayleigh dissipation terms in the Lagrangian formulation used throughout. These terms explicitly depend on the value of the Lagrange multipliers enforcing constraints. Having finite energy, the multipliers are thus massless ghost particles. The main numerical stepping method produced with the framework is called SPOOK.
Variational integrators preserve physical invariants globally, exactly in some cases, approximately but withinfixed global bounds for others. This allows to product realistic physical trajectories even with the low order methods. These are needed in the solution of nonsmooth problems such as dry frictional contacts and in addition, they are computationally inexpensive. The combination of strong stability, low order, and the global preservation of invariants allows for large integration time steps, but without loosing accuracy on the important and visible physical quantities. SPOOK is thus well-suited for interactive simulations, such as those commonly used in virtual environment applications, because it is fast, stable, and faithful to the physics.
New results include a stable discretization of highly oscillatory terms of constraint regularization; a linearly stable constraint stabilization scheme based on ghost potential and Rayleigh dissipation terms; a single-step, strictly dissipative, approximate impact model; a quasi-linear complementarity formulation of dry friction that is isotropic and solvable for any nonnegative value of friction coefficients; an analysis of a splitting scheme to solve frictional contact complementarity problems; a stable, quaternion-based rigid body stepping scheme and a stable linear approximation thereof. SPOOK includes all these elements. It is linearly implicit and linearly stable, it requires the solution of either one linear system of equations of one mixed linear complementarity problem per regular time step, and two of the same when an impact condition is detected. The changes in energy caused by constraints, impacts, and dry friction, are all shown to be strictly dissipative in comparison with the free system. Since all regularization and stabilization parameters are introduced in the physics, they map directly onto physical properties and thus allow modeling of a variety of phenomena, such as constraint compliance, for instance.
Tutorial material is included for continuous and discrete-time analytic mechanics, quaternion algebra, complementarity problems, rigid body dynamics, constraint kinematics, and special topics in numerical linear algebra needed in the solution of the stepping equations of SPOOK.
The qualitative and quantitative aspects of SPOOK are demonstrated by comparison with a variety of standard techniques on well known test cases which are analyzed in details. SPOOK compares favorably for all these examples. In particular, it handles ill-posed and degenerate problems seamlessly and systematically. An implementation suitable for large scale performance and accuracy testing is left for future work. |
 | Lacoursière, Claude: A Parallel Block Iterative Method for Interactive Contacting Rigid Multibody Simulations on Multicore PCs. In: Kågström, Bo; Elmroth, Erik; Dongarra, Jack; Wasniewski, Jerzy (Ed.): Applied Parallel Computing. State of the Art in Scientific Computing, PARA 2006. Lecture Notes in Computer Science, pp. 956–965, Springer Berlin Heidelberg, Berlin, Heidelberg, 2007, ISBN: 978-3-540-75755-9. @inproceedings{parallell_block_lacoursiere2007,
title = {A Parallel Block Iterative Method for Interactive Contacting Rigid Multibody Simulations on Multicore PCs},
author = {Claude Lacoursière},
editor = {Bo Kågström and Erik Elmroth and Jack Dongarra and Jerzy Wasniewski},
url = {http://umu.diva-portal.org/smash/record.jsf?language=sv&pid=diva2%3A916717&dswid=-5162
http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.98.366&rep=rep1&type=pdf
},
doi = {10.1007/978-3-540-75755-9_113},
isbn = {978-3-540-75755-9},
year = {2007},
date = {2007-01-01},
booktitle = {Applied Parallel Computing. State of the Art in Scientific Computing, PARA 2006. Lecture Notes in Computer Science},
volume = {4699},
pages = {956--965},
publisher = {Springer Berlin Heidelberg},
address = {Berlin, Heidelberg},
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.},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
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. |
2006
|
| Lacoursière, Claude: A regularized time stepper for multibody systems. Department of Computing Science, Umeå University, 2006. @book{lacoursiere2006regularized,
title = {A regularized time stepper for multibody systems},
author = {Claude Lacoursière},
year = {2006},
date = {2006-01-01},
publisher = {Department of Computing Science, Umeå University},
keywords = {Algoryx},
pubstate = {published},
tppubtype = {book}
}
|
 | Servin, Martin; Lacoursière, Claude; Melin, Niklas: Interactive simulation of elastic deformable materials. In: SIGRAD 2006. The Annual SIGRAD Conference; Special Theme: Computer Games, Linköping University Electronic Press 2006. @inproceedings{servin2006interactive,
title = {Interactive simulation of elastic deformable materials},
author = {Martin Servin and Claude Lacoursière and Niklas Melin},
url = {https://ep.liu.se/ecp/019/005/ecp01905.pdf
https://ep.liu.se/konferensartikel.aspx?series=ecp&issue=19&Article_No=5},
year = {2006},
date = {2006-01-01},
booktitle = {SIGRAD 2006. The Annual SIGRAD Conference; Special Theme: Computer Games},
number = {019},
organization = {Linköping University Electronic Press},
abstract = {A novel; fast; stable; physics-based numerical method for interactive simulation of elastically deformable objects is presented. Starting from elasticity theory; the deformation energy is modeled in terms of the positions of point masses using the linear shape functions of finite element analysis; providing for an exact correspondence 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 incompressibility. 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 complexity 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 implicit method. Validation and timing tests on the new method show that it produces very good physical behavior at a moderate computational cost; and it is usable in the context of real-time interactive simulations.},
keywords = {Algoryx},
pubstate = {published},
tppubtype = {inproceedings}
}
A novel; fast; stable; physics-based numerical method for interactive simulation of elastically deformable objects is presented. Starting from elasticity theory; the deformation energy is modeled in terms of the positions of point masses using the linear shape functions of finite element analysis; providing for an exact correspondence 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 incompressibility. 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 complexity 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 implicit method. Validation and timing tests on the new method show that it produces very good physical behavior at a moderate computational cost; and it is usable in the context of real-time interactive simulations. |
2005
|
 | Backman, Anders: Colosseum3D-Authoring framework for Virtual Environments.. In: IPT/EGVE, pp. 225–226, Citeseer 2005. @inproceedings{backman2005colosseum3d,
title = {Colosseum3D-Authoring framework for Virtual Environments.},
author = {Anders Backman},
url = {http://www8.cs.umu.se/research/ifor/dl/SEQUENCE%20LEARINIG/colosseum3d_egve05.pdf},
year = {2005},
date = {2005-01-01},
booktitle = {IPT/EGVE},
pages = {225--226},
organization = {Citeseer},
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.},
keywords = {Algoryx},
pubstate = {published},
tppubtype = {inproceedings}
}
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. |
2003
|
 | Lacoursière, Claude: Splitting methods for dry frictional contact problems in rigid multibody systems: Preliminary performance results. In: The Annual SIGRAD Conference. Special Theme-Real-Time Simulations. Conference Proceedings from SIGRAD2003, pp. 11–16, Linköping University Electronic Press 2003. @inproceedings{lacoursiere2003splitting,
title = {Splitting methods for dry frictional contact problems in rigid multibody systems: Preliminary performance results},
author = {Claude Lacoursière},
url = {http://www.ep.liu.se/ecp/010/004/ecp01004.pdf
https://ep.liu.se/en/conference-article.aspx?series=ecp&issue=10&Article_No=4},
year = {2003},
date = {2003-01-01},
booktitle = {The Annual SIGRAD Conference. Special Theme-Real-Time Simulations. Conference Proceedings from SIGRAD2003},
number = {010},
pages = {11--16},
organization = {Linköping University Electronic Press},
abstract = {A splitting method for solving LCP based models of dry frictional contact problems in rigid multibody systems based on box MLCP solver is presented. Since such methods rely on fast and robust box MLCP solvers; several methods are reviewed and their performance is compared both on random problems and on simulation data. We provide data illustrating the convergence rate of the splitting method which demonstrates that they present a viable alternative to currently available methods.},
keywords = {Algoryx},
pubstate = {published},
tppubtype = {inproceedings}
}
A splitting method for solving LCP based models of dry frictional contact problems in rigid multibody systems based on box MLCP solver is presented. Since such methods rely on fast and robust box MLCP solvers; several methods are reviewed and their performance is compared both on random problems and on simulation data. We provide data illustrating the convergence rate of the splitting method which demonstrates that they present a viable alternative to currently available methods. |
