333 research outputs found
Divergence-Free and Boundary-Respecting Velocity Interpolation Using Stream Functions
No full textIn grid-based fluid simulation, discrete incompressibility of each cell is enforced by the pressure projection. However, pointwise velocities constructed by interpolating the discrete velocity samples from the staggered grid are not truly divergence-free, resulting in unphysical local volume changes that manifests as particle spreading and clustering.We present a new velocity interpolation method that produces analytically divergence-free velocity fields in 2D using a stream function. The resulting fields are guaranteed to be divergence-free by a simple calculus identity: the curl of any vector field yields a divergence-free vector field. Furthermore, our method works on cut cell grids to produce fields that strictly obey solid boundary conditions. Therefore, no artificial gaps are created between fluid particles and solids, and fluid particles do not trespass into solid regions.Eurographics/ ACM SIGGRAPH Symposium on Computer AnimationPoster
Batty Stories: Ramblings with Gramdad
No full textBatty Stories is a biography of the author\u27s grandfather, Merle Batty. Found in this version are chapters on Merle\u27s time in the army and on his time teaching, plus miscellaneous stories from other parts of his life
A collection of hymns for the use of those that seek, [electronic resource] : and those that have redemption In the Blood of Christ.
No full textPreface signed: I.A., C.B., &c. (i.e. James Allen, Christopher Batty, etc.).The two leaves following the titlepage form the preface, and are numbered 2 and 4 on the rectos and 3 on the first verso.Electronic reproduction.English Short Title Catalog,Reproduction of original from British Library
Accurate viscous free surfaces for buckling, coiling, and rotating liquids
No full text© Christopher Batty & Robert Bridson | ACM 2008. This is the author's version of the work. It is posted here for your personal use. Not for redistribution. The definitive Version of Record was published in SCA '08: Proceedings of the 2008 ACM SIGGRAPH/Eurographics Symposium on Computer Animation, https://dl.acm.org/doi/10.5555/1632592.1632624?cid=81320487818.We present a fully implicit Eulerian technique for simulating free surface viscous liquids which eliminates artifacts in previous approaches, efficiently supports variable viscosity, and allows the simulation of more compelling viscous behaviour than previously achieved in graphics. Our method exploits a variational principle which automatically enforces the complex boundary condition on the shear stress at the free surface, while giving rise to a simple discretization with a symmetric positive definite linear system. We demonstrate examples of our technique capturing realistic buckling, folding and coiling behavior. In addition, we explain how to handle domains whose boundary comprises both ghost fluid Dirichlet and variational Neumann parts, allowing correct behaviour at free surfaces and solid walls for both our viscous solve and the variational pressure projection of Batty et al. [BBB07].This work was supported in part by a grant from the Natural Sciences and Engineering Research Council of Canada
A simple finite volume method for adaptive viscous liquids
No full text© Christopher Batty & Ben Houston | ACM 2011. This is the author's version of the work. It is posted here for your personal use. Not for redistribution. The definitive Version of Record was published in SCA '11: Proceedings of the 2011 ACM SIGGRAPH/Eurographics Symposium on Computer Animation, http://dx.doi.org/10.1145/2019406.2019421We present the first spatially adaptive Eulerian fluid animation method to support challenging viscous liquid effects such as folding, coiling, and variable viscosity. We propose a tetrahedral node-based embedded finite volume method for fluid viscosity, adapted from popular techniques for Lagrangian deformable objects. Applied in an Eulerian fashion with implicit integration, this scheme stably and efficiently supports high viscosity fluids while yielding symmetric positive definite linear systems. To integrate this scheme into standard tetrahedral mesh-based fluid simulators, which store normal velocities on faces rather than velocity vectors at nodes, we offer two methods to reconcile these representations. The first incorporates a mapping between different degrees of freedom into the viscosity solve itself. The second uses a FLIP-like approach to transfer velocity data between nodes and faces before and after the linear solve. The former offers tighter coupling by enabling the linear solver to act directly on the face velocities of the staggered mesh, while the latter provides a sparser linear system and a simpler implementation. We demonstrate the effectiveness of our approach with animations of spatially varying viscosity, realistic rotational motion, and viscous liquid buckling and coiling
Differentiable Curl-Noise
No full text© Xinwen Ding and Christopher Batty | ACM (2023). This is the author's version of the work. It is posted here for your personal use. Not for redistribution. The definitive Version of Record was published in Proceedings of the ACM on Computer Graphics and Interactive Techniques, http://dx.doi.org/10.1145/3585511.We present Differentiable Curl-Noise, a C1 procedural method to animate strictly incompressible fluid flows in two dimensions. While both the original Curl-Noise method of Bridson et al. [2007] and a recent modification by Chang et al. [2022] have been used to design incompressible flow fields, they often suffer from non-smoothness in their handling of obstacles, owing in part to properties of the underlying Euclidean distance function or closest point function. We therefore propose a differentiable scheme that modulates the background potential in a manner that respects arbitrary solid simple polygonal objects placed at any location, without introducing discontinuities. We demonstrate that our new method yields improved flow fields in a set of two dimensional examples, including when obstacles are in close proximity or possess concavities.NSERC, Discovery Grant RGPIN-2021-02524
Viscous Liquid Animation with Spatially Adaptive Grids
No full textViscous fluid behaviors are among the most complex yet familiar physical phenomena we encounter in everyday life. Much attention and investigation has been paid to the creation of visually realistic results, especially some unique effects such as folding and buckling, in computer graphics. However, simulation of viscous fluids requires more computational resources than its inviscid counterpart, since the viscous solve typically has lower sparsity and more degrees of freedom than the Poisson problem used to compute pressure forces. One interesting feature of viscous fluids is that the most important visual details happen at free surfaces of the fluid, while the interior flow remains relatively smooth. Therefore, a spatially adaptive grid with higher density of cells for fluid surfaces and lower density for the interior can be very useful in reducing computational resources and maintaining high-fidelity imagery at the same time.
The focus of this thesis is to provide a method for simulating a highly viscous liquid on an adaptive quadtree grid, and generating visually plausible results. Aside from reviewing the techniques for viscous fluid simulation in computer graphics, we propose a new finite difference scheme to accurately compute the results at junctions where different levels of the quadtree are adjacent to each other. In addition, we apply the variational approach originally proposed by Batty and Bridson [2008] to this scheme, and generate a symmetric positive definite system on which a preconditioned
conjugate gradient solver works very well. Thanks to the variational formulation, our method enforces the boundary condition at viscous free surfaces without the need of extra efforts. Lastly, this thesis presents a new scheme transferring velocities between an adaptive grid and a regular grid, which makes it easy to embed our viscosity solver into any grid-based inviscid fluid solver. We experimentally demonstrate that our method is first order accurate and achieves visual results that are qualitatively consistent with those of dense uniform grids, while reducing the number of degrees of freedom by a factor between 2 and 6, depending on the scenario
Efficient Liquid Animation: New Discretizations for Spatially Adaptive Liquid Viscosity and Reduced-Model Two-Phase Bubbles and Inviscid Liquids
No full textThe work presented in this thesis focuses on improving the computational efficiency when simulating viscous liquids and air bubbles immersed in liquids by designing new discretizations to focus computational effort in regions that meaningfully contribute to creating realistic motion. For example, when simulating air bubbles rising through a liquid, the entire bubble volume is traditionally simulated despite the bubble’s interior being visually unimportant. We propose our constraint bubbles model to avoid simulating the interior of the bubble volume by reformulating the usual incompressibility constraint throughout a bubble volume as a constraint over only the bubble’s surface. Our constraint method achieves qualitatively similar results compared to a two-phase simulation ground-truth for bubbles with low densities (e.g., air bubbles in water). For bubbles with higher densities,
we propose our novel affine regions to model the bubble’s entire velocity field with a single affine vector field. We demonstrate that affine regions can correctly achieve hydrostatic equilibrium for bubble densities that match the surrounding liquid and correctly sink for higher densities. Finally, we introduce a tiled approach to subdivide large-scale affine regions into smaller subregions. Using this strategy, we are able to accelerate single-phase free surface flow simulations, offering a novel approach to adaptively enforce incompressibility in free surface liquids without complex data structures.
While pressure forces are often the bottleneck for inviscid fluid simulations, viscosity can impose orders of magnitude greater computational costs. We observed that viscous liquids require high simulation resolution at the surface to capture detailed viscous buckling and rotational motion but, because viscosity dampens relative motion, do not require the same resolution in the liquid’s interior. We therefore propose a novel adaptive method to solve free surface viscosity equations by discretizing the variational finite difference approach of Batty and Bridson (2008) on an octree grid. Our key insight is that the variational method
guarantees a symmetric positive definite linear system by construction, allowing the use of fast numerical solvers like the Conjugate Gradients method. By coarsening simulation grid cells inside the liquid volume, we rapidly reduce the degrees-of-freedom in the viscosity linear system up to a factor of 7.7x and achieve performance improvements for the linear solve between 3.8x and 9.4x compared to a regular grid equivalent. The results of our adaptive method closely match an equivalent regular grid for common scenarios such as: rotation and bending, buckling and folding, and solid-liquid interactions
Memory Walking with Urban Bush Women's <i>Batty Moves</i>
No full text Like the childhood songs and butt-shaking contests of Ghana, Batty Moves by the Brooklyn-based dance company Urban Bush Women celebrates the African American female form. The choreographer and the dancers share their memories of butt-tucking ballet classes, and the author shares her memory walk from Ghana to black America. </jats:p
Discrete viscous sheets
No full text© Christopher Batty, Andres Uribe, Basile Audoly, Eitan Grinspun | ACM 2012. This is the author's version of the work. It is posted here for your personal use. Not for redistribution. The definitive Version of Record was published in ACM Transactions on Graphics, http://dx.doi.org/10.1145/2185520.2185609.We present the first reduced-dimensional technique to simulate the dynamics of thin sheets of viscous incompressible liquid in three dimensions. Beginning from a discrete Lagrangian model for elastic thin shells, we apply the Stokes-Rayleigh analogy to derive a simple yet consistent model for viscous forces. We incorporate nonlinear surface tension forces with a formulation based on minimizing discrete surface area, and preserve the quality of triangular mesh elements through local remeshing operations. Simultaneously, we track and evolve the thickness of each triangle to exactly conserve liquid volume. This approach enables the simulation of extremely thin sheets of viscous liquids, which are difficult to animate with existing volumetric approaches. We demonstrate our method with examples of several characteristic viscous sheet behaviors, including stretching, buckling, sagging, and wrinkling.This research is supported in part by the Sloan Foundation, the NSF (grants CMMI-11-29917, IIS-11-17257, IIS-10-48948, IIS- 09-16129, CCF-06-43268), and generous gifts from Adobe, Au- todesk, Intel, mental images, NVIDIA, Side Effects Software, and The Walt Disney Company. The first author is supported by a Bant- ing Postdoctoral Fellowship
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