Editing Fluid Animation Using Flow Interpolation

Syuhei Sato, Yoshinori Dobashi, Tomoyuki Nishita

The computational cost for creating realistic fluid animations by numerical simulation is generally expensive. In digital production environments, existing precomputed fluid animations are often reused for different scenes in order to reduce the cost of creating scenes containing fluids. However, applying the same animation to different scenes often produces unacceptable results, so the animation needs to be edited. In order to help animators with the editing process, we develop a novel method for synthesizing the desired fluid animations by combining existing flow data. Our system allows the user to place flows at desired positions, and combine them. We do this by interpolating velocities at the boundaries between the flows. The interpolation is formulated as a minimization problem of an energy function, which is designed to take into account the inviscid, incompressible Navier-Stokes equations. Our method focuses on smoke simulations defined on a uniform grid. We demonstrate the potential of our method by showing a set of examples, including a large-scale sandstorm created from a few flow data simulated in a small-scale space.

Editing Fluid Animation Using Flow Interpolation

Posted by christopherbatty on September 20th, 2018 | Comments Off on Editing Fluid Animation Using Flow Interpolation Posted in Fluids

Hybrid Grains: Adaptive Coupling of Discrete and Continuum Simulations of Granular Media

Yonghao Yue*, Breannan Smith*, Peter Yichen Chen*, Maytee Chantharayukhonthorn*, Ken Kamrin, Eitan Grinspun

We propose a technique to simulate granular materials that exploits the dual strengths of discrete and continuum treatments. Discrete element simulations provide unmatched levels of detail and generality, but prove excessively costly when applied to large scale systems. Continuum approaches are computationally tractable, but limited in applicability due to built-in modeling assumptions; e.g., models suitable for granular flows typically fail to capture clogging, bouncing and ballistic motion. In our hybrid approach, an oracle dynamically partitions the domain into continuum regions where safe, and discrete regions where necessary. The domains overlap along transition zones, where a Lagrangian dynamics mass-splitting coupling principle enforces agreement between the two simulation states. Enrichment and homogenization operations allow the partitions to evolve over time. This approach accurately and efficiently simulates scenarios that previously required an entirely discrete treatment.

Hybrid Grains: Adaptive Coupling of Discrete and Continuum Simulations of Granular Media

Posted by christopherbatty on September 19th, 2018 | Comments Off on Hybrid Grains: Adaptive Coupling of Discrete and Continuum Simulations of Granular Media Posted in Deformables, Fluids, Rigid bodies

GPU Optimization of Material Point Methods

Ming Gao*, Xinlei Wang*, Kui Wu*, Andre Pradhana, Eftychios Sifakis, Cem Yuksel, Chenfanfu Jiang

The Material Point Method (MPM) has been shown to facilitate effective simulations of physically complex and topologically challenging materials, with a wealth of emerging applications in computational engineering and visual computing. Borne out of the extreme importance of regularity, MPM is given attractive parallelization opportunities on high-performance modern multiprocessors. Parallelization of MPM that fully leverages computing resources presents challenges that require exploring an extensive design-space for favorable data structures and algorithms. Unlike the conceptually simple CPU parallelization, where the coarse partition of tasks can be easily applied, it takes greater effort to reach the GPU hardware saturation due to its many-core SIMT architecture. In this paper we introduce methods for addressing the computational challenges of MPM and extending the capabilities of general simulation systems based on MPM, particularly concentrating on GPU optimization. In addition to our open-source high-performance framework, we also conduct performance analyses and benchmark experiments to compare against alternative design choices which may superficially appear to be reasonable, but can suffer from suboptimal performance in practice. Our explicit and fully implicit GPU MPM solvers are further equipped with a Moving Least Squares MPM heat solver and a novel sand constitutive model to enable fast simulations of a wide range of materials. We demonstrate that more than an order of magnitude performance improvement can be achieved with our GPU solvers. Practical high-resolution examples with up to ten million particles run in less than one minute per frame.

GPU Optimization of Material Point Methods

Posted by christopherbatty on September 19th, 2018 | Comments Off on GPU Optimization of Material Point Methods Posted in Deformables, Fluids

Physical Simulation of Environmentally Induced Thin Shell Deformation

Hsiao-yu Chen, Arnav Sastry, Wim M. van Rees, Etienne Vouga

We present a physically accurate low-order elastic shell model that incorporates active material response to dynamically changing stimuli such as heat, moisture, and growth. Our continuous formulation of the geometrically non-linear elastic energy derives from the principles of differential geometry, and as such naturally incorporates shell thickness, non-zero rest curvature, and physical material properties. By modeling the environmental stimulus as local, dynamic changes in the rest metric of the material, we are able to solve for the corresponding shape changes by integrating the equations of motions given this non-Euclidean rest state. We present models for differential growth and shrinking due to moisture and temperature gradients along and across the surface, and incorporate anisotropic growth by defining an intrinsic machine direction within the material. Comparisons with experiments and volumetric finite elements show that our simulations achieve excellent qualitative and quantitative agreement. By combining the reduced-order shell theory with appropriate physical models, our approach accurately captures all the physical phenomena while avoiding expensive volumetric discretization of the shell volume.

Physical Simulation of Environmentally Induced Thin Shell Deformation

Posted by christopherbatty on August 17th, 2018 | Comments Off on Physical Simulation of Environmentally Induced Thin Shell Deformation Posted in Shells

Mechanical Characterization of Structured Sheet Materials

Christian Schumacher, Steve Marschner, Markus Gross, Bernhard Thomaszewski

We propose a comprehensive approach to characterizing the mechanical properties of structured sheet materials, i.e., planar rod networks whose mechanics and aesthetics are inextricably linked. We establish a connection between the complex mesoscopic deformation behavior of such structures and their macroscopic elastic properties through numerical homogenization. Our approach leverages 3D Kirchhoff rod simulation in order to capture nonlinear effects for both in-plane and bending deformations. We apply our method to different families of structures based on isohedral tilings— a simple yet extensive and aesthetically interesting group of space-filling patterns. We show that these tilings admit a wide range of material properties, and our homogenization approach allows us to create concise and intuitive descriptions of a material’s direction-dependent macromechanical behavior that are easy to communicate even to non-experts. We perform this characterization for an extensive set of structures and organize these data in a material browser to enable efficient forward exploration of the aesthetic-mechanical space of structured sheet materials. We also propose an inverse design method to automatically find structure parameters that best approximate a user-specified target behavior.

Mechanical Characterization of Structured Sheet Materials

Posted by christopherbatty on August 9th, 2018 | Comments Off on Mechanical Characterization of Structured Sheet Materials Posted in Uncategorized

Methodology for Assessing Mesh-Based Contact Point Methods

Kenny Erleben

Computation of contact points is a critical sub-component of physics-based animation. The success and correctness of simulation results are very sensitive to the quality of the contact points. Hence, quality plays a critical role when comparing methods, and this is highly relevant for simulating objects with sharp edges. The importance of contact point quality is largely overlooked and lacks rigor and as such may become a bottleneck in moving the research field forward. We establish a taxonomy of contact point generation methods and lay down an analysis of what normal contact quality implies. The analysis enables us to establish a novel methodology for assessing and studying quality for mesh-based shapes. The core idea is based on a test suite of three complex cases and a small portfolio of simple cases. We apply our methodology to eight local contact point generation methods and conclude that the selected local methods are unable to provide correct information in all cases. The immediate benefit of the proposed methodology is a foundation for others to evaluate and select the best local method for their specific application. In the longer perspective, the presented work suggests future research focusing on semi-local methods.

Methodology for Assesing Mesh-Based Contact Point Methods

Posted by christopherbatty on August 9th, 2018 | Comments Off on Methodology for Assessing Mesh-Based Contact Point Methods Posted in Collisions, Deformables, Rigid bodies

The Human Touch: Measuring Contact with Real Human Soft Tissues

D. K. Pai, A. Rothwell, P. Wyder-Hodge, A. Wick, Y. Fan, E. Larionov, D. Harrison, D. R. Neog, and C. Shing

Simulating how the human body deforms in contact with clothing, wearables, and other objects is of central importance to many fields. However, the tissue material properties needed to accurately simulate real human bodies had been sorely lacking. We showed that these mechanical properties can be directly measured using a novel hand-held device. We have developed a complete pipeline for measurement, modelling, parameter estimation, and simulation using the finite element method. Our unique data may be used to create personalized models of an individual human or of a population. Consequently, our methods may have many potential applications in apparel design, e-commerce, computer animation, and medicine.

The Human Touch: Measuring Contact with Real Human Soft Tissues

Posted by christopherbatty on August 9th, 2018 | Comments Off on The Human Touch: Measuring Contact with Real Human Soft Tissues Posted in Deformables

Cable Joints

Matthias Müller, Nuttapong Chentanez, Stefan Jeschke, Miles Macklin

Robustly and efficiently simulating cables and ropes that are part of a larger system such as cable driven machines, cable cars or tendons in a human or robot is a challenging task. To be able to adapt to the environment, cables are typically modeled as a large number of small segments that are connected via joints. The two main difficulties with this approach are to satisfy the inextensibility constraint and to handle the typically large mass ratio between the small segments and the larger objects they connect. In this paper we present a new approach which solves these problems in a simple and effective way. Our method is based on the idea to simulate the effect of the cables instead of the cables themselves. To this end we propose a new special type of distance constraint we call cable joint that changes both its attachment points and its rest length dynamically. A cable connecting a series of objects is then modeled as a sequence of cable joints which reduces the complexity of the simulation from the order of the number of segments to just the number of connected objects. This makes simulations both faster and more robust as we will demonstrate on a variety of examples.

Cable Joints

Posted by christopherbatty on July 20th, 2018 | Comments Off on Cable Joints Posted in Hair/Rods/Rope, Rigid bodies, Rods

Distributing and Load Balancing Sparse Fluid Simulations

Chinmayee Shah, David Hyde, Hang Qu, and Philip Levis

This paper describes a general algorithm and a system for load balancing sparse fluid simulations. Automatically distributing sparse fluid simulations efficiently is challenging because the computational load varies across the simulation domain and time. A key challenge with load balancing is that optimal decision making requires knowing the fluid distribution across partitions for future time steps, but computing this state for an arbitrary simulation requires running the simulation itself. The key insight of this paper is that it is possible to predict future load by running a low resolution simulation in parallel. This paper describes a system design and techniques to automatically distribute and load balance sparse fluid simulations, and presents speculative load balancing, a general technique to effectively balance future load using information about future load distribution obtained via a low resolution simulation. We mathematically formulate the problem of load balancing over multiple time-steps and present a polynomial time algorithm to compute an approximate solution to it. Our experimental results show that distributing and speculatively load balancing sparse FLIP simulations over 8 nodes speeds them up by 5.5x to 7.2x, and that speculative load balancing generates assignments that perform within 20% of optimal.

Distributing and Load Balancing Sparse Fluid Simulations

Posted by christopherbatty on July 20th, 2018 | Comments Off on Distributing and Load Balancing Sparse Fluid Simulations Posted in Fluids

Fast Corotated FEM using Operator Splitting

Tassilo Kugelstadt, Dan Koschier, Jan Bender

In this paper we present a novel operator splitting approach for corotated FEM simulations. The deformation energy of the corotated linear material model consists of two additive terms. The first term models stretching in the individual spatial directions and the second term describes resistance to volume changes. By formulating the backward Euler time integration scheme as an optimization problem, we show that the first term is invariant to rotations. This allows us to use an operator splitting approach and to solve both terms individually with different numerical methods. The stretching part is solved accurately with an optimization integrator, which can be done very efficiently because the system matrix is constant over time such that its Cholesky factorization can be precomputed. The volume term is solved approximately by using the compliant constraints method and Gauss-Seidel iterations. Further, we introduce the analytic polar decomposition which allows us to speed up the extraction of the rotational part of the deformation gradient and to recover inverted elements. Finally, this results in an extremely fast and robust simulation method with high visual quality that outperforms standard corotated FEMs by more than two orders of magnitude and even the fast but inaccurate PBD and shape matching methods by more than one order of magnitude without having their typical drawbacks. This enables a very efficient simulation of complex scenes containing more than a million elements.

Fast Corotated FEM using Operator Splitting

Posted by christopherbatty on July 16th, 2018 | Comments Off on Fast Corotated FEM using Operator Splitting Posted in Deformables
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