31 research outputs found
Scalable partitioning for parallel position based dynamics
We introduce a practical partitioning technique designed for parallelizing Position Based Dynamics, and exploiting
the ubiquitous multi-core processors present in current commodity GPUs. The input is a set of particles whose
dynamics is influenced by spatial constraints. In the initialization phase, we build a graph in which each node
corresponds to a constraint and two constraints are connected by an edge if they influence at least one common
particle. We introduce a novel greedy algorithm for inserting additional constraints (phantoms) in the graph
such that the resulting topology is q-colourable, where ˆ qˆ ≥ 2 is an arbitrary number. We color the graph, and
the constraints with the same color are assigned to the same partition. Then, the set of constraints belonging to
each partition is solved in parallel during the animation phase. We demonstrate this by using our partitioning
technique; the performance hit caused by the GPU kernel calls is significantly decreased, leaving unaffected the
visual quality, robustness and speed of serial position based dynamics
Parallelized Incomplete Poisson Preconditioner in Cloth Simulation
Efficient cloth simulation is an important problem for interactive applications that involve virtual humans, such as computer games. A common aspect of many methods that have been developed to simulate cloth is a linear system of equations, which is commonly solved using conjugate gradient or multi-grid approaches. In this paper, we introduce to the computer gaming community a recently proposed preconditioner, the incomplete Poisson preconditioner, for conjugate gradient solvers. We show that the parallelized incomplete Poisson preconditioner (PIPP) performs as well as the current state-of-the-art preconditioners, while being much more amenable to standard thread-level parallelism. We demonstrate our results on an 8-core Apple* Mac* Pro and a 32-core code name Emerald Ridge system
Cute Balloons with Thickness
Based on the fnite element method, we present a simple volume-preserved thin shell deformation algorithm to simulate the process of inflating a balloon. Diff erent from other thin shells, the material of balloons has special features: large stretch, small bend and shear, and incompressibility. Previous deformation methods often focus on typical three-dimensional models or thin plate models such as cloth model. The rest thin shell methods are complex or ignore the special features of thin shells especially balloons. We modify the triangle element to simple three-prism element, ignore bending and shearing deformation, and use volume preservation algorithm to match the incompressibility of balloons. Simple gas model is used, which interacts with shells to make the balloons inflated. Di different balloon examples have been tested in our experiments and the results are compared with those of other methods. The experiments show that our algorithm is simple and effective
Interactive Thin Elastic Materials
Despite great strides in past years are being made to generate motions of elastic 1 materials such as cloth and biological skin in virtual world, unfortunately, the computational cost of realistic high-resolution simulations currently precludes their use in interactive applications. Thin elastic materials such as cloth and biological skin often exhibit complex nonlinear elastic behaviors. However, modeling elastic nonlinearity can be computationally expensive and numerically unstable, imposing significant challenges for their use in interactive applications. This paper presents a novel simulation framework for simulating realistic material behaviours with interactive frame rate. Central to the framework is the use of a constraint-based multi-resolution solver for efficient and robust modelling of the material nonlinearity. We extend a strain limiting method to work on deformation gradients of triangulated surface models in three dimensional space with a novel data structure. The simulation framework utilises an iterative nonlinear Gauss-Seidel procedure and a multilevel hierarchy structure to achieve computational speed ups. As material non-linearity are generated by enforcing strain limiting constraints at a multilevel hierarchy, our simulation system can rapidly accelerate the convergence of the large constraint system with simultaneous enforcement of boundary conditions. The simplicity and efficiency of the framework makes simulations of highly realistic thin elastic materials substantially fast and is applicable of simulations for interactive applications
Constrained Soft Tissue Simulation for Virtual Surgical Simulation
yesMost of surgical simulators employ a linear elastic
model to simulate soft tissue material properties due to its computational
efficiency and the simplicity. However, soft tissues often
have elaborate nonlinearmaterial characteristics. Most prominently,
soft tissues are soft and compliant to small strains, but after
initial deformations they are very resistant to further deformations
even under large forces. Such material characteristic is referred as
the nonlinear material incompliant which is computationally expensive
and numerically difficult to simulate. This paper presents a
constraint-based finite-element algorithm to simulate the nonlinear
incompliant tissue materials efficiently for interactive simulation
applications such as virtual surgery. Firstly, the proposed algorithm
models the material stiffness behavior of soft tissues with a
set of 3-D strain limit constraints on deformation strain tensors.
By enforcing a large number of geometric constraints to achieve
the material stiffness, the algorithm reduces the task of solving
stiff equations of motion with a general numerical solver to iteratively
resolving a set of constraints with a nonlinear Gauss–Seidel
iterative process. Secondly, as a Gauss–Seidel method processes
constraints individually, in order to speed up the global convergence
of the large constrained system, a multiresolution hierarchy
structure is also used to accelerate the computation significantly,
making interactive simulations possible at a high level of details .
Finally, this paper also presents a simple-to-build data acquisition
system to validate simulation results with ex vivo tissue measurements.
An interactive virtual reality-based simulation system is
also demonstrated
Multi-resolution isotropic strain limiting
In this paper we describe a fast strain-limiting method that allows stiff, incompliant materials to be simulated efficiently. Unlike prior approaches, which act on springs or individual strain components, this method acts on the strain tensors in a coordinate-invariant fashion allowing isotropic behavior. Our method applies to both two-and three-dimensional strains, and only requires computing the singular value decomposition of the deformation gradient, either a small 2x2 or 3x3 matrix, for each element. We demonstrate its use with triangular and tetrahedral linear-basis elements. For triangulated surfaces in three-dimensional space, we also describe a complementary edge-angle-limiting method to limit out-of-plane bending. All of the limits are enforced through an iterative, non-linear, Gauss-Seidel-like constraint procedure. To accelerate convergence, we propose a novel multi-resolution algorithm that enforces fitted limits at each level of a non-conforming hierarchy. Compared with other constraint-based techniques, our isotropic multi-resolution strain-limiting method is straightforward to implement, efficient to use, and applicable to a wide range of shell and solid materials. © 2010 ACM
ClothCombo: Modeling Inter-Cloth Interaction for Draping Multi-Layered Clothes
We present ClothCombo, a pipeline to drape arbitrary combinations of clothes
on 3D human models with varying body shapes and poses. While existing
learning-based approaches for draping clothes have shown promising results,
multi-layered clothing remains challenging as it is non-trivial to model
inter-cloth interaction. To this end, our method utilizes a GNN-based network
to efficiently model the interaction between clothes in different layers, thus
enabling multi-layered clothing. Specifically, we first create feature
embedding for each cloth using a topology-agnostic network. Then, the draping
network deforms all clothes to fit the target body shape and pose without
considering inter-cloth interaction. Lastly, the untangling network predicts
the per-vertex displacements in a way that resolves interpenetration between
clothes. In experiments, the proposed model demonstrates strong performance in
complex multi-layered scenarios. Being agnostic to cloth topology, our method
can be readily used for layered virtual try-on of real clothes in diverse poses
and combinations of clothes
Fast GPU-Based Two-Way Continuous Collision Handling
Step-and-project is a popular way to simulate non-penetrated deformable
bodies in physically-based animation. First integrating the system in time
regardless of contacts and post resolving potential intersections practically
strike a good balance between plausibility and efficiency. However, existing
methods could be defective and unsafe when the time step is large, taking risks
of failures or demands of repetitive collision testing and resolving that
severely degrade performance. In this paper, we propose a novel two-way method
for fast and reliable continuous collision handling. Our method launches the
optimization at both ends of the intermediate time-integrated state and the
previous intersection-free state, progressively generating a piecewise-linear
path and finally reaching a feasible solution for the next time step.
Technically, our method interleaves between a forward step and a backward step
at a low cost, until the result is conditionally converged. Due to a set of
unified volume-based contact constraints, our method can flexibly and reliably
handle a variety of codimensional deformable bodies, including volumetric
bodies, cloth, hair and sand. The experiments show that our method is safe,
robust, physically faithful and numerically efficient, especially suitable for
large deformations or large time steps