Interactive Wood Combustion for Botanical Tree Models

Sören Pirk, Michał Jarząbek, Torsten Hädrich, Dominik L. Michels, Wojciech Palubicki

We present a novel method for the combustion of botanical tree models. Tree models are represented as connected particles for the branching structure and a polygonal surface mesh for the combustion. Each particle stores biological and physical attributes that drive the kinetic behavior of a plant and the exothermic reaction of the combustion. Coupled with realistic physics for rods, the particles enable dynamic branch motions. We model material properties, such as moisture and charring behavior, and associate them with individual particles. The combustion is efficiently processed in the surface domain of the tree model on a polygonal mesh. A user can dynamically interact with the model by initiating fires and by inducing stress on branches. The flames realistically propagate through the tree model by consuming the available resources. Our method runs at interactive rates and supports multiple tree instances in parallel. We demonstrate the effectiveness of our approach through numerous examples and evaluate its plausibility against the combustion of real wood samples.

Interactive Wood Combustion for Botanical Tree Models

Posted by christopherbatty on September 10th, 2017 | Comments Off on Interactive Wood Combustion for Botanical Tree Models Posted in Deformables, Fire, Fluids

Conformation Constraints for Efficient Viscoelastic Fluid Simulation

Hector Barreiro, Ignacio Garcia-Fernandez, Ivan Alduan, Miguel A. Otaduy

The simulation of high viscoelasticity poses important computational challenges. One is the difficulty to robustly measure strain and its derivatives in a medium without permanent structure. Another is the high stiffness of the governing differential equations. Solutions that tackle these challenges exist, but they are computationally slow. We propose a constraint-based model of viscoelasticity that enables efficient simulation of highly viscous and viscoelastic phenomena. Our model reformulates, in a constraint-based fashion, a constitutive model of viscoelasticity for polymeric fluids, which defi€nes simple governing equations for a conformation tensor. The model can represent a diverse palette of materials, spanning elastoplastic, highly viscous, and inviscid liquid behaviors. In addition, we have designed a constrained dynamics solver that extends the position-based dynamics method to handle efficiently both position-based and velocity-based constraints. We show results that range from interactive simulation of viscoelastic effects to large-scale simulation of high viscosity with competitive performance

Conformation Constraints for Efficient Viscoelastic Fluid Simulation

Posted by christopherbatty on September 6th, 2017 | Comments Off on Conformation Constraints for Efficient Viscoelastic Fluid Simulation Posted in Deformables, Fluids

SIGGRAPH Asia 2017

Posted by christopherbatty on September 6th, 2017 | Comments Off on SIGGRAPH Asia 2017 Posted in Uncategorized

Pairwise Force SPH Model for Real-Time Multi-Interaction Applications

Tao Yang, Ralph R. Martin, Ming C. Lin, Jian Chang, and Shi-Min Hu

In this paper, we present a novel pairwise-force smoothed particle hydrodynamics (PF-SPH) model to enable simulation of various interactions at interfaces in real time. Realistic capture of interactions at interfaces is a challenging problem for SPH-based simulations, especially for scenarios involving multiple interactions at different interfaces. Our PF-SPH model can readily handle multiple types of interactions simultaneously in a single simulation; its basis is to use a larger support radius than that used in standard SPH. We adopt a novel anisotropic filtering term to further improve the performance of interaction forces. The proposed model is stable; furthermore, it avoids the particle clustering problem which commonly occurs at the free surface. We show how our model can be used to capture various interactions. We also consider the close connection between droplets and bubbles, and show how to animate bubbles rising in liquid as well as bubbles in air. Our method is versatile, physically plausible and easy-to-implement. Examples are provided to demonstrate the capabilities and effectiveness of our approach.

Pairwise Force SPH Model for Real-Time Multi-Interaction Applications

 

 

Posted by christopherbatty on August 31st, 2017 | Comments Off on Pairwise Force SPH Model for Real-Time Multi-Interaction Applications Posted in Fluids

Modeling and Data-Driven Parameter Estimation for Woven Fabrics

David Clyde, Joseph Teran, Rasmus Tamstorf

Accurate estimation of mechanical parameters for simulation of woven fabrics is essential in many fields. To facilitate this we first present a new orthotropic hyperelastic constitutive model for woven fabrics. Next, we design an experimental protocol for characterizing real fabrics based on commercially available tests. Finally, we create a method for accurately fitting the material parameters to the experimental data. The last step is accomplished by solving inverse problems based on a Catmull-Clark subdivision finite element discretization of the Kirchhoff-Love equations for thin shells. Using this approach we are able to reproduce the fully nonlinear behavior corresponding to the captured data with a small number of parameters while maintaining all fundamental invariants from continuum mechanics. The resulting constitutive model can be used with any discretization (e.g., simple triangle meshes) and not just subdivision finite elements. We illustrate the entire process with results for five types of fabric and compare photo reference of the real fabrics to the simulated equivalents.

Modeling and Data-Driven Parameter Estimation for Woven Fabrics

Posted by christopherbatty on August 22nd, 2017 | Comments Off on Modeling and Data-Driven Parameter Estimation for Woven Fabrics Posted in Cloth

Inequality Cloth

Ning Jin, Wenlong Lu, Zhenglin Geng, Ronald Fedkiw

As has been noted and discussed by various authors, numerical simulations of deformable bodies often adversely suffer from so-called “locking” artifacts. We illustrate that the “locking” of out-of-plane bending motion that results from even an edge-spring-only cloth simulation can be quite severe, noting that the typical remedy of softening the elastic model leads to an unwanted rubbery look. We demonstrate that this “locking” is due to the well-accepted notion that edge springs in the cloth mesh should preserve their lengths, and instead propose an inequality constraint that stops edges from stretching while allowing for edge compression as a surrogate for bending. Notably, this also allows for the capturing of bending modes at scales smaller than those which could typically be represented by the mesh. Various authors have recently begun to explore optimization frameworks for deformable body simulation, which is particularly germane to our inequality cloth framework. After exploring such approaches, we choose a particular approach and illustrate its feasibility in a number of scenarios including contact, collision, and self-collision. Our results demonstrate the efficacy of the inequality approach when it comes to folding, bending, and wrinkling, especially on coarser meshes, thus opening up a plethora of interesting possibilities.

Inequality Cloth

Posted by christopherbatty on August 22nd, 2017 | Comments Off on Inequality Cloth Posted in Cloth, Shells

Hierarchical Vorticity Skeletons

Sebastian Eberhardt, Steffen Weissmann, Ulrich Pinkall, Nils Thuerey

We propose a novel method to extract hierarchies of vortex filaments from given three-dimensional flow velocity fields. We call these collections of filaments Hierarchical Vorticity Skeletons (HVS). They extract multi-scale information from the input velocity field, which is not possible with any previous filament extraction approach. Once computed, these HVSs provide a powerful mechanism for data compression and a very natural way for modifying flows. The data compression rates for all presented examples are above 99%. Employing our skeletons for flow modification has several advantages over traditional approaches. Most importantly, they reduce the complexity of three-dimensional fields to one-dimensional lines and, make complex fluid data more accessible for changing defining features of a flow. The strongly reduced HVS dataset still carries the main characteristics of the flow. Through the hierarchy we can capture the main features of different scales in the flow and by that provide a level of detail control. In contrast to previous work, we present a fully automated pipeline to robustly decompose dense velocities into filaments.

Hierarchical Vorticity Skeletons

Posted by christopherbatty on August 4th, 2017 | Comments Off on Hierarchical Vorticity Skeletons Posted in Fluids

Designing Cable-Driven Actuation Networks for Kinematic Chains and Trees

Vittorio Megaro, Espen Knoop, Andrew Spielberg, David I.W. Levin, Wojciech Matusik,Markus Gross, Bernhard Thomaszewski, Moritz Bächer

In this paper, we present an optimization-based approach for the design of cable-driven kinematic chains and trees. Our system takes as input a hierarchical assembly consisting of rigid links jointed together with hinges. The user also specifies a set of target poses or keyframes using inverse kinematics. Our approach places torsional springs at the joints and computes a cable network that allows us to reproduce the specified target poses. We start with a large set of cables that have randomly chosen routing points and we gradually remove the redundancy. Then we refine the routing points taking into account the path between poses or keyframes in order to further reduce the number of cables and minimize required control forces. We propose a reduced coordinate formulation that links control forces to joint angles and routing points, enabling the co-optimization of a cable network together with the required actuation forces. We demonstrate the efficacy of our technique by designing and fabricating a cable-driven, animated character, an animatronic hand, and a specialized gripper.

Designing Cable-Driven Actuation Networks for Kinematic Chains and Trees

Posted by christopherbatty on July 29th, 2017 | Comments Off on Designing Cable-Driven Actuation Networks for Kinematic Chains and Trees Posted in Uncategorized

Rigid Body Contact Problems using Proximal Operators

Kenny Erleben

Iterative methods are popular for solving contact force problems in rigid body dynamics. They are loved for their robustness and surrounded by mystery as to whether they converge or not. We provide a mathematical foundation for iterative (PROX) schemes based on proximal operators. This is a class of iterative Jacobi and blocked Gauss–Seidel variants that theoretically proven always converge and provides a flexible plug and play framework for exploring different friction laws. We provide a portfolio of experience for choosing r-Factor strategies for such schemes and we analyze the distribution of convergence behaviors. Our results indicate the Gauss-Seidel variant is superior in terms of delivering predictable convergence behaviour and hence should be preferred over Jacobi variants. Our results also suggest that Global r -Factor strategies are better for structured stacking scenarios and can achieve absolute convergence in more cases.

Rigid Body Contact Problems using Proximal Operators

Posted by christopherbatty on July 29th, 2017 | Comments Off on Rigid Body Contact Problems using Proximal Operators Posted in Collisions, Rigid bodies

Improving the GJK algorithm for faster and more reliable distance queries between convex objects

Mattia Montanari, Nik Petrinic, and Ettore Barbieri

This article presents a new version of the Gilbert-Johnson-Keerthi (GJK) algorithm that circumvents the shortcomings introduced by degenerate geometries. The original Johnson algorithm and Backup procedure are replaced by a distance subalgorithm that is faster and accurate to machine precision, thus guiding the GJK algorithm toward a shorter search path in less computing time. Numerical tests demonstrate that this effectively is a more robust procedure. In particular, when the objects are found in contact, the newly proposed subalgorithm runs from 15% to 30% times faster than the original one. The improved performance has a significant impact on various applications, such as real-time simulations and collision avoidance systems. Altogether, the main contributions made to the GJK algorithm are faster convergence rate and reduced computational time. These improvements may be easily added into existing implementations; furthermore, engineering applications that require solutions of distance queries to machine precision can now be tackled using the GJK algorithm.

Improving the GJK algorithm for faster and more reliable distance queries between convex objects

Posted by christopherbatty on July 28th, 2017 | Comments Off on Improving the GJK algorithm for faster and more reliable distance queries between convex objects Posted in Collisions, Rigid bodies
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