Category: Collisions

VolCCD: Fast Continuous Collision Culling Between Deforming Volume Meshes

Min Tang, Dinesh Manocha, Sung-Eui Yoon, Peng Du, Jae-Pil Heo, Ruofeng Tong

We present a novel culling algorithm to perform fast and robust continuous collision detection between deforming volume meshes. This includes a continuous separating axis test that can conservatively check whether two volume meshes overlap during a given time interval. Moreover, we present efficient methods to eliminate redundant elementary tests between the features (e.g., vertices, edges, and faces) of volume elements (e.g., tetrahedra). Our approach is applicable to various deforming meshes, including those with changing topologies, and efficiently computes the first time of contact. We are able to perform inter-object and intra-object collision queries in models represented with tens of thousands of volume elements at interactive rates on a single CPU core. Moreover, we observe more than an order of magnitude performance improvement over prior methods.

VolCCD: Fast Continuous Collision Culling Between Deforming Volume Meshes

Asynchronous Integration with Phantom Meshes

David Harmon, Qingnan Zhou, Denis Zorin

Asynchronous variational integration of layered contact models provides a framework for robust collision handling, correct physical behavior, and guaranteed eventual resolution of even the most difficult contact problems. Yet, even for low-contact scenarios, this approach is significantly slower compared to its less robust alternatives — often due to handling of stiff elastic forces in an explicit framework. We propose a method that retains the guarantees, but allows for variational implicit integration of some of the forces, while maintaining asynchronous integration needed for contact handling. Our method uses phantom meshes for calculations with stiff forces, which are then coupled to the original mesh through constraints. We use the augmented discrete Lagrangian of the constrained system to derive a variational integrator with the desired conservation properties.

Asynchronous Integration with Phantom Meshes

Eulerian Solid Simulation with Contact

David I. W. Levin, Joshua Litven, Garrett L. Jones, Shinjiro Sueda, Dinesh K. Pai

Simulating viscoelastic solids undergoing large, nonlinear deformations in close contact is challenging. In addition to inter-object contact, methods relying on Lagrangian discretizations must handle degenerate cases by explicitly remeshing or resampling the object. Eulerian methods, which discretize space itself, provide an interesting alternative due to the fixed nature of the discretization. In this paper we present a new Eulerian method for viscoelastic materials that features a collision detection and resolution scheme which does not require explicit surface tracking to achieve accurate collision response. Time-stepping with contact is performed by the efficient solution of large sparse quadratic programs; this avoids constraint sticking and other difficulties. Simulation and collision processing can share the same uniform grid, making the algorithm easy to parallelize. We demonstrate an implementation of all the steps of the algorithm on the GPU. The method is effective for simulation of complicated contact scenarios involving multiple highly deformable objects, and can directly simulate volumetric models obtained from medical imaging techniques such as CT and MRI.

Eulerian Solid Simulation with Contact

SPH Granular Flow with Friction and Cohesion

Ivan Alduan, Miguel Otaduy

Combining mechanical properties of solids and fluids, granular materials pose important challenges for the design of algorithms for realistic animation. In this paper, we present a simulation algorithm based on smoothed particle hydrodynamics (SPH) that succeeds in modeling important features of the behavior of granular materials. These features are unilateral incompressibility, friction and cohesion. We extend an existing unilateral incompressibility formulation to be added at almost no effort to an existing SPH-based algorithm for fluids. The main advantages of this extension are the ease of implementation, the lack of grid artifacts, and the simple two-way coupling with other objects. Our friction and cohesion models can also be incorporated in a seamless manner in the overall SPH simulation algorithm.

SPH Granular Flow with Friction and Cohesion

Robust Real-Time Deformation of Incompressible Surface Meshes

Raphael Diziol, Jan Bender, Daniel Bayer

We introduce an efficient technique for robustly simulating incompressible objects with thousands of elements in real-time. Instead of considering a tetrahedral model, commonly used to simulate volumetric bodies, we simply use their surfaces. Not requiring hundreds or even thousands of elements in the interior of the object enables us to simulate more elements on the surface, resulting in high quality deformations at low computation costs. The elasticity of the objects is robustly simulated with a geometrically motivated shape matching approach which is extended by a fast summation technique for arbitrary triangle meshes suitable for an efficient parallel computation on the GPU. Moreover, we present an oscillation-free and collision-aware volume constraint, purely based on the surface of the incompressible body. The novel heuristic we propose in our approach enables us to conserve the volume, both globally and locally. Our volume constraint is not limited to the shape matching method and can be used with any method simulating the elasticity of an object. We present several examples which demonstrate high quality volume conserving deformations and compare the run-times of our CPU implementation, as well as our GPU implementation with similar methods.

Robust Real-Time Deformation of Incompressible Surface Meshes

Efficient Elasticity for Character Skinning with Contact and Collisions

We present a new algorithm for near-interactive simulation of skeleton driven, high resolution elasticity models. Our methodology is used for soft tissue deformation in character animation. The algorithm is based on a novel discretization of corotational elasticity over a hexahedral lattice. Within this framework we enforce positive definiteness of the stiffness matrix to allow efficient quasistatics and dynamics. In addition, we present a multigrid method that converges with very high efficiency. Our design targets performance through parallelism using a fully vectorized and branch-free SVD algorithm as well as a stable one-point quadrature scheme. Since body collisions, self collisions and soft-constraints are necessary for real-world examples, we present a simple framework for enforcing them. The whole approach is demonstrated in an end-to-end production-level character skinning system.

Efficient Elasticity for Character Skinning with Contact and Collisions

Fast and Scalable CPU/GPU Collision Detection for Rigid and Deformable Surfaces

We present a new hybrid CPU/GPU collision detection technique for rigid and deformable objects based on spatial subdivision. Our approach efficiently exploits the massive computational capabilities of modern CPUs and GPUs commonly found in off-the-shelf computer systems. The algorithm is specifically tailored to be highly scalable on both the CPU and the GPU sides. We can compute discrete and continuous external and self-collisions of non-penetrating rigid and deformable objects consisting of many tens of thousands of triangles in few milliseconds on a modern PC. Our approach is orders of magnitude faster than earlier CPU-based approaches and up to twice as fast as the most recent GPU-based techniques.

Fast and Scalable CPU/GPU Collision Detection for Rigid and Deformable Surfaces

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

FASTCD: Fracturing-Aware Stable Collision Detection

We present a collision detection (CD) method for complex and large-scale fracturing models that have geometric and topological changes. We first propose a novel dual-cone culling method to improve the performance of CD, especially self-collision detection among fracturing models. Our dual-cone culling method has a small computational overhead and a conservative algorithm. Combined with bounding volume hierarchies (BVHs), our dual-cone culling method becomes approximate. However, we found that our method does not miss any collisions in the tested benchmarks. We also propose a novel, selective restructuring method that improves the overall performance of CD and reduces performance degradations at fracturing events. Our restructuring method is based on a culling efficiency metric that measures the expected number of overlap tests of a BVH. To further reduce the performance degradations at fracturing events, we also propose a novel, fast BVH construction method that builds multiple levels of the hierarchy in one iteration using a grid and hashing. We test our method with four different large-scale deforming benchmarks. Compared to the state-of-the-art methods, our method shows a more stable performance for CD by improving the performance by a factor of up to two orders of magnitude at frames when deforming models change their mesh topologies.

FASTCD: Fracturing-Aware Stable Collision Detection

Constraint Based Simulation of Adhesive Contact

Dynamics with contact are often formulated as a constrained optimization problem. This approach allows handling in an integrated manner both non-penetration and frictional constraints. Following developments in the computational mechanics field, we have designed an algorithm for adding the simulation of adhesive contact constraints in the context of state-of-the-art constraint-based contact solvers. We show that implicit adhesion constraints can be handled with minor changes to existing solvers, and we demonstrate our algorithm on a diverse range of objects, including mass-spring cloth, volumetric finite-element models, and rigid bodies.

Constraint Based Simulation of Adhesive Contact