Bernhard Thomaszewski [b.thomaszewski (at) gmail (dot) com]  
   

 

 

 

Publications

Anisotropic Friction for Deformable Surfaces and Solids (Video)
S. Pabst, B. Thomaszewski and W. Strasser
Accepted at Symposium on Computer Animation (SCA), 2009
Abstract: This paper presents a method for simulating anisotropic friction for deforming surfaces and solids. Frictional contact is a complex phenomenon that fuels research in mechanical engineering, computational contact mechanics, composite material design and rigid body dynamics, to name just a few. Many real-world materials have anisotropic surface properties. As an example, most textile materials exhibit direction-dependent frictional behavior, but despite its tremendous impact on visual appearance, only simple isotropic models have been considered for cloth and solid simulation so far. In this work, we propose a simple, application-oriented but physically sound model that extends existing methods to account for anisotropic friction. The sliding properties of surfaces are encoded in friction tensors, which allows us to model frictional resistance freely along arbitrary directions. We also consider heterogeneous and asymmetric surface roughness and demonstrate the increased simulation quality on a number of two- and three-dimensional examples. Our method is computationally efficient and can easily be integrated into existing systems.

   

Continuum-based Strain Limiting (Video)
B. Thomaszewski, S. Pabst and W. Strasser
Computer Graphics Forum
, Proceedings of Eurographics 2009
Abstract: We present Continuum-based Strain Limiting (CSL) – a new method for limiting deformations in physically-based cloth simulations. Despite recent developments for nearly inextensible materials, the efficient simulation of general biphasic textiles and their anisotropic behavior remains challenging. Many approaches use soft materials and enforce limits on edge elongations, leading to discretization-dependent behavior. Moreover, they offer no explicit control over shearing and stretching unless specifically aligned meshes are used. Based on a continuum deformation measure, our method allows accurate control over all strain components using individual thresholds. We impose deformation limits element-wise and cast the problem as a 6×6 system of linear equations. CSL can be combined with any cloth simulator and, as a velocity filter, integrates seamlessly into standard collision handling.

 

   

Magnets in Motion
B. Thomaszewski, A. Gumann, S. Pabst and W. Strasser
ACM Transactions on Graphics, Proceedings of SIGGRAPH Asia 2008
Abstract: We introduce magnetic interaction for rigid body simulation. Our approach is based on an equivalent dipole method and as such it is discrete from the ground up. Our approach is symmetric as we base both field and force computations on dipole interactions. Apart from enriching rigid body simulation with magnetic effects, our method also allows the accurate computation of magnetic fields for arbitrarily shaped objects. This is especially interesting for pedagogy as it allows the user to visually discover properties of magnetism which would otherwise be difficult to grasp. We demonstrate our method on a variety of problems and our results reflect intuitive as well as surprising effects. Our method is fast and can be coupled with any rigid body solver to simulate dozens of magnetic objects at interactive rates.

 

 

 

Seams and Bending in Cloth Simulation (Video)
S. Pabst, S. Krzywinski, A. Schenk and B. Thomaszewski
Accepted at EG Workshop on Virtual Reality Interaction and Physical Simulation (VRIPHYS), 2008
Abstract: Accurate modeling of bending behavior is one of the most important tasks in the field of cloth simulation. Bending stiffness is probably the most significant material parameter describing a given textile. Much work has been done in recent years to allow a fast and authentic reproduction of the effect of bending in cloth simulation systems. However, these approaches usually treat the textiles as consisting of a single, homogeneous material. The effects of seams, interlining and multilayer materials have not been considered so far. Recent work showed that the bending stiffness of a textile is greatly influenced by the presence of seams and that a good cloth simulation system needs to consider these effects. In this work we show how accurate modeling of bending and seams can be achieved in a state-of-the-art cloth simulation system. Our system can make use of measured bending stiffness data, but also allows intuitive user control, if desired. We verify our approach using virtual draping tests and garments in the simulation and comparing the results to their real-world counterparts. Furthermore, we provide heuristics derived from measurements that can be used to approximate the influence of several common types of seams.

 

 

Asynchronous Cloth Simulation (Video)
B. Thomaszewski, S. Pabst and W. Strasser
Computer Graphics International (CGI) 2008
Abstract:This paper presents a new method for cloth simulation, which uses asynchronous variants of both time integration and collision handling. Implicit integration methods like backward Euler and BDF-2 are very popular in computer graphics, since they allow for fast and stable animations. However, when combined with large time steps, their inherent numerical dissipation results in over-damped simulations, which lack high frequency details such as small folds and wrinkles.  In this paper, we present a computationally efficient method which does not suffer from these restrictions. The time integration component uses an asynchronous variational integrator (AVI), which allows dedicated time steps for every element. Thanks to its energy preserving nature, low-damped cloth materials can be simulated without compromising dynamic motion or suppressing important details.
Our collision handling scheme combines both synchronous and asynchronous strategies and, in this way, allows focusing computation power on the important regions where collisions actually occur. We provide timings for several integration methods and show that our AVI-based scheme consistently outperforms synchronous explicit variants. Compared to implicit schemes, superior quality is obtained while remaining comparable in terms of computation times. Finally, we demonstrate the robustness of our method on a series of challenging animations.

 

 

Interactive Physically-Based Shape Editing (Video)
J. Mezger, B. Thomaszewski, S. Pabst and W. Strasser
ACM Solid and Physical Modeling Conference (SPM) 2008
Abstract:We present an alternative approach to standard geometric shape editing using physically-based simulation. With our technique, the user can deform complex objects in real-time. The basis of our method is formed by a fast and accurate finite element implementation of an elasto-plastic material model, specifically designed for interactive shape manipulation. Using quadratic shape functions, we reduce approximation errors inherent to methods based on linear finite elements. The physical simulation uses a volume mesh comprised of quadratic tetrahedra, which are constructed from a coarser approximation of the detailed surface. In order to guarantee stability and real-time frame rates during the simulation, we cast the elasto-plastic problem into a linear formulation. For this purpose, we present a corotational formulation for quadratic finite elements. We demonstrate the versatility of our approach in interactive manipulation sessions and show that our animation system can be coupled with further physics-based animations like, e.g. fluids and cloth, in a bi-directional way.

 

 

Parallel Techniques for Physically-Based Simulation on Multi-Core Processor Architectures (Video)
B. Thomaszewski, S. Pabst and W. Blochinger
Computers & Graphics, 31(1):25-40, 2008
Abstract: As multi-core processor systems become more and more widespread, the demand for efficient parallel algorithms also propagates into the field of computer graphics. This is especially true for physically-based simulation, which is notorious for expensive numerical methods. In this work, we explore possibilities for accelerating physically-based simulation algorithms on multi-core architectures. Two components of physically-based simulation represent a great potential for bottlenecks in parallelisation: implicit time integration and collision handling.
From the parallelisation point of view these two components are substantially different. Implicit time integration can be treated efficiently using static problem decomposition. The linear system arising in this context is solved using a data-parallel preconditioned conjugate gradient algorithm. The collision handling stage, however, requires a different approach, due to its dynamic structure. This stage is handled using multi-threaded programming with fully dynamic task decomposition. In particular, we propose a new task splitting approach based on a reasonable estimation of work, which analyses previous simulation steps. Altogether, the combination of different parallelisation techniques leads to a concise and yet versatile framework for highly efficient physical simulation.

 

 

Exploiting Parallelism in Physically-Based Simulations on Multi-Core Processor Architectures (Video)
B. Thomaszewski, S. Pabst and W. Blochinger
EG Symposium on Parallel Graphics and Visualization (EGPGV 07)
Abstract: Physically based simulation of cloth in virtual environments is a computationally demanding problem. It involves modeling the internal material properties of the textile (physical modeling) and also treating interactions with the surrounding scene (collision handling). In this paper, we present an approach to parallel cloth simulation designed for distributed memory parallel architectures, particularly clusters built of commodity components. We discuss parallel techniques for the physical modeling phase as well as for the collision handling phase which can significantly reduce the respective computation times. To deal with the very fine granularity of the physical modeling phase we apply a static data decomposition approach based on graph partitioning. In order to cope with the high irregularity of the collision handling phase we employ task-parallel techniques based on fully dynamic problem decomposition. We show how both techniques can be integrated into a robust parallel cloth simulation method which can deal with considerably complex scenes. 

 

 

 

 

Physically Based Simulation of Cloth on Distributed Memory Architectures
B. Thomaszewski and W. Blochinger
Parallel Computing, 33(6):377-390, 2007.
Abstract: Physically based simulation of cloth in virtual environments is a computationally demanding problem. It involves modeling the internal material properties of the textile (physical modeling) and also treating interactions with the surrounding scene (collision handling). In this paper, we present an approach to parallel cloth simulation designed for distributed memory parallel architectures, particularly clusters built of commodity components. We discuss parallel techniques for the physical modeling phase as well as for the collision handling phase which can significantly reduce the respective computation times. To deal with the very fine granularity of the physical modeling phase we apply a static data decomposition approach based on graph partitioning. In order to cope with the high irregularity of the collision handling phase we employ task-parallel techniques based on fully dynamic problem decomposition. We show how both techniques can be integrated into a robust parallel cloth simulation method which can deal with considerably complex scenes. 

 

 

 

 

 

A Consistent Bending Model for Cloth Simulation with Corotational Subdivision Finite Elements (Video)
B. Thomaszewski, M. Wacker and W. Straßer
ACM/EG Symposium on Computer Animation (SCA 06)
Abstract: Wrinkles and folds play an important role in the appearance of real textiles. The way in which they form depends mainly on the bending properties of the specific material type. Existing approaches fail to reliably reproduce characteristic behaviour like folding and buckling for different material types or resolutions. It is therefore crucial for the realistic simulation of cloth to model bending energy in a physically accurate and consistent way.
In this paper we present a new method based on a corotational formulation of subdivision finite elements. Due to the non-local nature of the employed subdivision basis functions a C1-continuous displacement field can be defined. In this way, it is possible to use the governing equations of thin shell analysis leading to physically accurate bending behaviour. Using a corotated strain tensor allows the large displacement analysis of cloth while retaining a linear system of equations. Hence, known convergence properties and computational efficiency are preserved while convincing and detailed folding behaviour is obtained in the simualtion.

 

 

 

 

Parallel Simulation of Cloth on Distributed Memory Architectures
B. Thomaszewski and W. Blochinger
EG Symposium on Parallel Graphics and Visualization (EGPGV 06)
Abstract: The physically based simulation of clothes in virtual environments is a highly demanding problem. It involves both modeling the internal material properties of the textile and the interaction with the surrounding scene. We present a parallel cloth simulation approach designed for distributed memory parallel architectures, in particular clusters built of commodity components. In this paper, we focus on the parallelization of the collision handling phase. In order to cope with the high irregularity of this problem we employ a task parallel approach with fully dynamic problem decomposition. This leads to a robust algorithm, regardless of the complexity of the scene. We report on initial performance measurements indicating the usefulness of our approach.

 

 

 

Tutorials

Advanced Topics in Virtual Garment Simulation, Part 1
B. Thomaszewski, M. Wacker, W. Straßer
Eurographics 2007, Tutorial 10
Abstract
: For more than two decades, cloth simulation has been an active research area in computer graphics. In order to create efficient, high-quality animations, techniques from many research fields have to be thoroughly combined. The ongoing interest in this field is also due to the multidisciplinary nature of cloth simulation which spurs development and progess in collision detection, numerical time integration, constrained dynamics or motion control, to name just a few areas. Beyond the very basic approaches, the complexity of the material can be daunting if no guidance is given. It is therefore the goal of this tutorial to provide the reader with an introduction and a guideline to the relevant matter. In order to provide a concise review, we will focus on advanced topics in cloth simulation, shedding light on both theoretical and practical aspects. We cover challenging research fields like the correct and efficient modelling of textile bending behaviour, parallel implementation of cloth simulation modules, multilayer garments. Moreover, an integrated framework for virtual try-on applications including body modelling and animation combined with real time cloth simulation is discussed. This will pave the ground for those willing to implement a contemporaneous cloth simulation system as well as for researchers who consider to start working in this area.

 

 

 

 

High Performance Virtual Garment Simulation
M. Wacker, W. Straßer, B. Thomaszewski, N. Magnenat-Thalmann and P. Volino
Eurographics 2006, Tutorial 6
For virtual characters the simulation of garments is a vital component towards realistic and believable scenarios that range from interactive virtual reality (virtual tailoring and cultural heritage) to realistic synthetic animation (CAD modeling and film production). This course addresses the key techniques involved in the latest state-of-theart in physically based cloth simulation.

 

 

 

 

 

Key Techniques for Interactive Virtual Garment Simulation
N. Magnenat-Thalmann, P. Volino, M. Wacker, B. Thomaszewski and M. Keckeisen

Eurographics 2005, Tutorial 4
Simulating dressed virtual characters is required in an increasingly large number of applications that range from interactive virtual reality to realistic synthetic animation and from gaming to CAD modeling. This course details the techniques involved in the latest state-of-the- art in real-time cloth simulation.

 

 

 


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