Month: September 2010

Some recent theses

Catching up on some recent theses:

If there are other recent ones I’ve missed, post them in the comments and I’ll add them to the list!

Free-Flowing Granular Material with Two-Way Solid Coupling

We present a novel continuum-based model that enables efficient simulation of granular materials. Our approach fully solves the internal pressure and frictional stresses in a granular material, thereby allows visually noticeable behaviors of granular materials to be reproduced, including freely dispersing splashes without cohesion, and a global coupling between friction and pressure. The full treatment of internal forces in the material also enables two-way interaction with solid bodies. Our method achieves these results at only a very small fraction of computational costs of the comparable particle-based models for granular flows.

Free-Flowing Granular Material with Two-Way Solid Coupling

Boundary handling and adaptive time-stepping for PCISPH

We present a novel boundary handling scheme for incompressible fluids based on Smoothed Particle Hydro-dynamics (SPH). In combination with the predictive-corrective incompressible SPH (PCISPH) method, the boundary handling scheme allows for larger time steps compared to existing solutions. Furthermore, an adaptive time-stepping approach is proposed. The approach automatically estimates appropriate time steps independent of the scenario. Due to its adaptivity, the overall computation time of dynamic scenarios is significantly reduced compared to simulations with constant time steps.

Boundary handling and adaptive time-stepping for PCISPH

A Parallel SPH Implementation on Multi-core CPUs

This paper presents a parallel framework for simulating fluids with the Smoothed Particle Hydrodynamics (SPH) method. For low computational costs per simulation step, efficient parallel neighborhood queries are proposed and compared. To further minimize the computing time for entire simulation sequences, strategies for maximizing the time step and the respective consequences for parallel implementations are investigated. The presented experiments illustrate that the parallel framework can efficiently compute large numbers of time steps for large scenarios. In the context of neighborhood queries, the paper presents optimizations for two efficient instances of uniform grids, i. e. spatial hashing and index sort. For implementations on parallel architectures with shared memory, the paper discusses techniques with improved cache-hit rate and reduced memory transfer. The performance of the parallel implementations of both optimized data structures is compared. The proposed solutions focus on systems with multiple CPUs. Benefits and challenges of potential GPU implementations are only briefly discussed.

A Parallel SPH Implementation on Multi-core CPUs

Scalable Fluid Simulation using Anisotropic Turbulence Particles

It is usually difficult to resolve the fine details of turbulent flows, especially when targeting real-time applications. We present a novel, scalable turbulence method that uses a realistic energy model and an efficient particle representation that allows for the accurate and robust simulation of small-scale detail. We compute transport of turbulent energy using a complete two-equation k–e model with accurate production terms that allows us to capture anisotropic turbulence effects, which integrate smoothly into the base flow. We only require a very low grid resolution to resolve the underlying base flow. As we offload complexity from the fluid solver to the particle system, we can control the detail of the simulation easily by adjusting the number of particles, without changing the large scale behavior. In addition, no computations are wasted on areas that are not visible. We demonstrate that due to the design of our algorithm it is highly suitable for massively parallel architectures, and is able to generate detailed turbulent simulations with millions of particles at high framerates.

Scalable Fluid Simulation using Anisotropic Turbulence Particles

Animation Wrinkling: Augmenting Coarse Cloth Simulations with Realistic-Looking Wrinkles

Moving garments and other cloth objects exhibit dynamic, complex wrinkles. Generating such wrinkles in a virtual environment currently requires either a time-consuming manual design process, or a computationally expensive simulation, often combined with accurate parameter-tuning requiring specialized animator skills. Our work presents an alternative approach for wrinkle generation which combines coarse cloth animation with a post-processing step for efficient generation of realistic-looking fine dynamic wrinkles. Our method uses the stretch tensor of the coarse animation output as a guide for wrinkle placement. To ensure temporal coherence, the placement mechanism uses a space-time approach allowing not only for smooth wrinkle appearance and disappearance, but also for wrinkle motion, splitting, and merging over time. Our method generates believable wrinkle geometry using specialized curve-based implicit deformers. The method is fully automatic and has a single user control parameter that enables the user to mimic different fabrics.

Animation Wrinkling: Augmenting Coarse Cloth Simulations with Realistic-Looking Wrinkles

Real-Time Collision Culling of a Million Bodies on Graphics Processing Units

We cull collisions between very large numbers of moving bodies using graphics processing units (GPUs). To perform massively parallel sweep-and-prune (SaP), we mitigate the great density of intervals along the axis of sweep by using principal component analysis to choose the best sweep direction, together with spatial subdivisions to further reduce the number of false positive overlaps. Our algorithm implemented entirely on GPUs using the CUDA framework can handle a million moving objects at interactive rates. As application of our algorithm, we demonstrate the real-time simulation of very large numbers of particles and rigid-body dynamics.

Real-Time Collision Culling of a Million Bodies on Graphics Processing Units

Stable Inverse Dynamic Curves

2d animation is a traditional but fascinating domain that has recently regained popularity both in animated movies and video games. This paper introduces a method for automatically converting a smooth sketched curve into a 2d dynamic curve at stable equilibrium under gravity. The curve can then be physically animated to produce secondary motions in 2d animations or simple video games. Our approach proceeds in two steps. We first present a new technique to fit a smooth piecewise circular arcs curve to a sketched curve. Then we show how to compute the physical parameters of a dynamic rod model (super-circle) so that its stable rest shape under gravity exactly matches the fitted circular arcs curve. We demonstrate the interactivity and controllability of our approach on various examples where a user can intuitively setup efficient and precise 2d animations by specifying the input geometry.

Stable Inverse Dynamic Curves

Multi-Phase Fluid Simulation Using Regional Level Sets

We address the problem of Multi-Phase (or Many-Phase) Fluid simulations. We propose to use the regional level set (RLS) that can handle a large number of regions and materials, and hence, is appropriate for simulations of many immiscible materials. Towards this goal, we improve the interpolation of the RLS, and develop the regional level set graph (RLSG), which registers connected components and their contacts, and tracks their properties such as region volumes, film life times, and film material types, as regions evolve, merge, split, or are squeezed into films. Using RLSG’s tracking feature, we generate particles from tiny regions or rupturing films.

Multi-Phase Fluid Simulation Using Regional Level Sets

Creating and Preserving Vortical Details in SPH Fluid

We present a new method to create and preserve the turbulent details generated around moving objects in SPH fluid. In our approach, a high-resolution overlapping grid is bounded to each object and translates with the object. The turbulence formation is modeled by resolving the local flow around objects using a hybrid SPH-FLIP method. Then these vortical details are carried on SPH particles flowing through the local region and preserved in the global field in a synthetic way. Our method provides a physically plausible way to model the turbulent details around both rigid and deformable objects in SPH fluid, and can efficiently produce animations of complex gaseous phenomena with rich visual details.

Creating and Preserving Vortical Details in SPH Fluid