Research Areas

This page presents some examples of our current research projects. If you are interested in one of the topics please contact us by email for further detailed information and check out our publications page where you can find papers, software, and additional download material.

Cutting and Fracture

In our natural environment objects fracture or tear when heavy mechanical stresses are applied or when they are subject to collisions with other objects. Similarly materials can be dissected in a controlled way using knifes or scissors. While this behavior seems natural and obvious in the context of our everyday experience, it describes complex physical phenomena. Simulating these phenomena is therefore non-trivial but essential to enrich the realism in virtual reality applications, animations for special effects in feature films and computer games. Moreover, such simulations are at the core of virtual surgery simulators. Traditionally, deformable objects are simulated by discretizing the geometry and underlying equations into meshes or particles. In this research area, we develop new methods to extend rigid and deformable object simulators by cutting and fracture.

See also our papers:

Physically-based animation of deformable solids using Eulerian approaches in computer graphics

Supported by the German Research Foundation (DFG)

The goal of our project is the physically-based animation of elastic and elasto-plastic bodies with applications in computer graphics, e.g., virtual reality applications, digital games, and special effects. In many of these applications large deformations and complex collisions are crucial for practical applications, such as medical training simulators. Almost exclusively, Lagrangian simulation approaches are used in such settings today. Here, the bodies are represented as collections of mass points, which move with the body and which contain the degrees of freedom, in combination with a set of connectivity information (the mesh). Large deformations (e.g., resulting from strong collisions) cause problems as they lead to strong deformations of the simulation mesh. Single elements can quickly become degenerate or even inverted. As a consequence, the material models that are typically used become invalid. Approaches to circumvent these problems usually require complex and expensive re-meshing operations, and smaller time-steps, which lead to drastic increases in computation time. Nonetheless, these techniques cannot guarantee an inversion-free state. Other approaches resolve degenerate or inverted elements with unphysical modifications of the material model. This effectively reduces the accuracy of the simulation. Additionally, these approaches lead to discontinuities which, e.g., prevent the use of higher-order time integration schemes.

To solve the aforementioned problems we plan to develop simulation approaches based on Eulerian representations, which use a spatially fixed simulation grid for discretization. Such approaches have been prominent in the area of fluid simulation, while first attempts to use them for simulations of deformable bodies were only made very recently. These attempts indicate the potential of Eulerian methods, but the lack of research in the area leaves many problems unsolved. With our project we will address the most important problems. We will develop efficient and accurate simulators based on higher-order integrators, adaptive discretizations and methods for continuous collision detection and resolution. In addition, we will develop hybrid methods to combine advantages of Lagrangian and Eulerian representations, and investigate the simulation of progressive cuts and fracture. Finally, we want to develop algorithms for efficiently visualizing the results with the help of procedural synthesis to achieve highly detailed animations.

Robust Methods for the Physically-Based Animation of Large Deformations in Computer Graphics

Supported by the German Research Foundation (DFG)

The research topic of this project is the robust physically-based animation of deformable bodies in computer graphics. Physically-based animation has many application areas in computer graphics, e.g. virtual reality, computer games and special effects in movies and commercials.

In this project we focus on the animation of deformable volumetric bodies using continuum mechanical approaches. These approaches are widely-used in computer graphics since they allow a high degree of realism. The simulation is usually performed using finite element methods. For these methods a volumetric body must be discretized, e.g. using tetrahedral or hexahedral meshes. However, these meshes cause problems when simulating large deformations, which are essential in many computer graphics applications. Large deformations can occur locally, e.g. when two bodies collide. Such a deformation can lead to degenerate or inverted elements in the discretization mesh. These elements can cause unrealistic material behavior, numerical problems and even an abort of the simulation since different constitutive laws are not defined for inverted elements. A mesh with degenerate and inverted elements represents an invalid state in the simulation since such deformations are not possible in the real world.

In the application areas of mechanics and engineering sciences degenerate and inverted elements must be avoided in order to guarantee accurate simulation results. This is achieved e.g. by a restart of the simulation with an adapted discretization. In computer graphics and especially in interactive applications the performance and robustness of the simulation is the main goal, while accuracy is often of secondary importance. Since degenerate and inverted elements cannot be prevented reliably in dynamic simulations and a restart is not possible in interactive applications, different methods have been developed in computer graphics to allow a stable simulation even if ill-shaped elements occur. These methods modify the constitutive laws which yields a local error. However, this error is tolerated since visual plausible results can be achieved. Existing methods use heuristic approaches to resolve ill-shaped elements. But this resolution is often inconsistent and therefore causes artifacts, numerical problems and discontinuous elastic forces.

The goal of this project is the development of a novel numerical method to resolve degenerate and inverted elements consistently. This method should solve the above mentioned problems. The resulting continuous elastic forces allow to apply implicit integration methods of higher order which were neglected in computer graphics so far.

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