Tobias Preclik

Simulation of a hard-spherocylinder liquid crystal with the pe

Abstract The pe physics engine is validated through the simulation of a liquid crystal model system consisting of hard spherocylinders. For this purpose we evaluate several characteristic parameters of this system, namely the nematic order parameter, the pressure, and the Frank elastic constants. We compare these to the values reported in literature and find a very good agreement, which demonstrates that the pe physics engine can accurately treat such densely packed particle systems. Simultaneously we are able to examine the influence of finite size effects, especially on the evaluation of the Frank elastic constants, as we are far less restricted in system size than earlier simulations.

Regularized solution of LCP problems with application to rigid body dynamics

For Linear Complementarity Problems (LCP) with a positive semidefinite matrix M, iterative solvers can be derived by a process of regularization. In [3] the initial LCP is replaced by a sequence of positive definite ones, with the matrices M + αI. Here we analyse a generalization of this method where the identity I is replaced by a positive definite diagonal matrix D. We prove that the sequence of approximations so defined converges to the minimal D-norm solution of the initial LCP. This extension opens the possibility for interesting applications in the field of rigid multibody dynamics.

Fully Resolved Simulations of Dune Formation in Riverbeds

The formation and dynamics of dunes is an important phenomenon that occurs in many environmental systems, such as riverbeds. The physical interactions are complex and thus evaluating and quantifying the factors of influence is challenging. Simulation models can be used to conduct large scale parameter studies and allow a more detailed analysis of the system than laboratory experiments. Here, we present new coupled numerical models for sediment transport that are based on first principles. The lattice Boltzmann method is used in combination with a non-smooth granular dynamics model to simulate the fluid flow and the sediment particles. Numerical predictions of dune formation require a fully resolved modeling of the particulate flow which is only achieved by massively parallel simulations. For that purpose, the method employs advanced parallel grid refinement techniques and carefully designed compute kernels. The weak- and strong-scaling behavior is evaluated in detail and shows overall excellent parallel performance and efficiency.

Interactive particle dynamics using OpenCL and Kinect

In this paper, we describe an interactive real-time simulation of granular, spherical particles which is able to run on a single workstation. The simulation is based on a discrete element method approach and fully implemented using Open Computing Language, enabling execution on CPUs and GPUs alike. The simulation results are visualised using DirectX 10 and instancing. Furthermore, we enable the user to control the visualisation and the simulation in a very intuitive way by supporting user tracking and speech recognition, both using the Microsoft Kinect sensor. We also compare the performance of different implementation strategies on both CPUs and GPUs, and, as a sample application, we simulate the Brazil nut effect.

The maximum dissipation principle in rigid-body dynamics with inelastic impacts

Formulating a consistent theory for rigid-body dynamics with impacts is an intricate problem. Twenty years ago Stewart published the first consistent theory with purely inelastic impacts and an impulsive friction model analogous to Coulomb friction. In this paper we demonstrate that the consistent impact model can exhibit multiple solutions with a varying degree of dissipation even in the single-contact case. Replacing the impulsive friction model based on Coulomb friction by a model based on the maximum dissipation principle resolves the non-uniqueness in the single-contact impact problem. The paper constructs the alternative impact model and presents integral equations describing rigid-body dynamics with a non-impulsive and non-compliant contact model and an associated purely inelastic impact model maximizing dissipation. An analytic solution is derived for the single-contact impact problem. The models are then embedded into a time-stepping scheme. The macroscopic behaviour is compared to Coulomb friction in a large-scale granular flow problem.