272 research outputs found

    A model for soap film dynamics with evolving thickness

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    Previous research on animations of soap bubbles, films, and foams largely focuses on the motion and geometric shape of the bubble surface. These works neglect the evolution of the bubble’s thickness, which is normally responsible for visual phenomena like surface vortices, Newton’s interference patterns, capillary waves, and deformation-dependent rupturing of films in a foam. In this paper, we model these natural phenomena by introducing the film thickness as a reduced degree of freedom in the Navier-Stokes equations and deriving their equations of motion. We discretize the equations on a nonmanifold triangle mesh surface and couple it to an existing bubble solver. In doing so, we also introduce an incompressible fluid solver for 2.5D films and a novel advection algorithm for convecting fields across non-manifold surface junctions. Our simulations enhance state-of-the-art bubble solvers with additional effects caused by convection, rippling, draining, and evaporation of the thin film

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

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    In this paper, we present a novel pairwise-force smoothed particle hydrodynamics (PF-SPH) model to allow modeling 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 kinds 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

    A Survey of Ocean Simulation and Rendering Techniques in Computer Graphics

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    This paper presents a survey of ocean simulation and rendering methods in computer graphics. To model and animate the ocean's surface, these methods mainly rely on two main approaches: on the one hand, those which approximate ocean dynamics with parametric, spectral or hybrid models and use empirical laws from oceanographic research. We will see that this type of methods essentially allows the simulation of ocean scenes in the deep water domain, without breaking waves. On the other hand, physically-based methods use Navier-Stokes Equations (NSE) to represent breaking waves and more generally ocean surface near the shore. We also describe ocean rendering methods in computer graphics, with a special interest in the simulation of phenomena such as foam and spray, and light's interaction with the ocean surface

    A particle-based dissolution model using chemical collision energy

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    We propose a new energy-based method for real-time dissolution simulation. A unified particle representation is used for both fluid solvent and solid solute. We derive a novel dissolution model from the collision theory in chemical reactions: physical laws govern the local excitation of solid particles based on the relative motion of the fluid and solid. When the local excitation energy exceeds a user specified threshold (activation energy), the particle will be dislodged from the solid. Unlike previous methods, our model ensures that the dissolution result is independent of solute sampling resolution. We also establish a mathematical relationship between the activation energy, the inter-facial surface area, and the total dissolution time - allowing for accurate artistic control over the global dissolution rate while maintaining the physical plausibility of the simulation. We demonstrate applications of our method using a number of practical examples, including antacid pills dissolving in water and hydraulic erosion of non-homogeneous terrains. Our method is straightforward to incorporate with existing particle-based fluid simulations

    Versatile interactions at interfaces for SPH-based simulations

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    The realistic capture of various interactions at interfaces is a challenging problem for SPH-based simulation. Previous works have mainly considered a single type of interaction, while real-world phenomena typically exhibit multiple interactions at different interfaces. For instance, when cracking an egg, there are simultaneous interactions between air, egg white, egg yolk, and the shell. To conveniently handle all interactions simultaneously in a single simulation, a versatile approach is critical. In this paper, we present a new approach to the surface tension model based on pairwise interaction forces; its basis is to use a larger number of neighboring particles. Our model is stable, conserves momentum, and furthermore, prevents the particle clustering problem which commonly occurs at the free surface. It can be applied to simultaneous interactions at multiple interfaces (e.g. fluid-solid and fluid-fluid). Our method is versatile, physically plausible and easy-to-implement. We also consider the close connection between droplets and bubbles, and show how to animate bubbles in air as droplets, with the help of a new surface particle detection method. Examples are provided to demonstrate the capabilities and effectiveness of our approach

    Double Bubbles Sans Toil and Trouble: Discrete Circulation-Preserving Vortex Sheets for Soap Films and Foams

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    © ACM, 2015. This is the author's version of the work. It is posted here by permission of ACM for your personal use. Not for redistribution. The definitive version was published in Da, F., Batty, C., Wojtan, C., & Grinspun, E. (2015). Double Bubbles Sans Toil and Trouble: Discrete Circulation-Preserving Vortex Sheets for Soap Films and Foams. Acm Transactions on Graphics, 34(4), 149. https://doi.org/10.1145/2767003Simulating the delightful dynamics of soap films, bubbles, and foams has traditionally required the use of a fully three-dimensional many-phase Navier-Stokes solver, even though their visual appearance is completely dominated by the thin liquid surface. We depart from earlier work on soap bubbles and foams by noting that their dynamics are naturally described by a Lagrangian vortex sheet model in which circulation is the primary variable. This leads us to derive a novel circulation-preserving surface-only discretization of foam dynamics driven by surface tension on a non-manifold triangle mesh. We represent the surface using a mesh-based multimaterial surface tracker which supports complex bubble topology changes, and evolve the surface according to the ambient air flow induced by a scalar circulation field stored on the mesh. Surface tension forces give rise to a simple update rule for circulation, even at non-manifold Plateau borders, based on a discrete measure of signed scalar mean curvature. We further incorporate vertex constraints to enable the interaction of soap films with wires. The result is a method that is at once simple, robust, and efficient, yet able to capture an array of soap films behaviors including foam rearrangement, catenoid collapse, blowing bubbles, and double bubbles being pulled apart.This work was supported in part by the NSF (Grant IIS-1319483),ERC (Grant ERC-2014-StG-638176), NSERC (Grant RGPIN-04360-2014), Adobe, and Intel

    Physically-Based Droplet Interaction

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    In this paper we present a physically-based model for simulating realistic interactions between liquid droplets in an efficient manner. Our particle-based system recreates the coalescence, separation and fragmentation interactions that occur between colliding liquid droplets and allows systems of droplets to be meaningfully repre- sented by an equivalent number of simulated particles. By consid- ering the interactions specific to liquid droplet phenomena directly, we display novel levels of detail that cannot be captured using other interaction models at a similar scale. Our work combines experi- mentally validated components, originating in engineering, with a collection of novel modifications to create a particle-based interac- tion model for use in the development of mid-to-large scale droplet- based liquid spray effects. We demonstrate this model, alongside a size-dependent drag force, as an extension to a commonly-used ballistic particle system and show how the introduction of these interactions improves the quality and variety of results possible in recreating liquid droplets and sprays, even using these otherwise simple systems

    Continuum Foam: A Material Point Method for Shear-Dependent Flows

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    © ACM, 2015. This is the author's version of the work. It is posted here by permission of ACM for your personal use. Not for redistribution. The definitive version was published in Yue, Y., Smith, B., Batty, C., Zheng, C., & Grinspun, E. (2015). Continuum Foam: A Material Point Method for Shear-Dependent Flows. Acm Transactions on Graphics, 34(5), 160. https://doi.org/10.1145/2751541We consider the simulation of dense foams composed of microscopic bubbles, such as shaving cream and whipped cream. We represent foam not as a collection of discrete bubbles, but instead as a continuum. We employ the material point method (MPM) to discretize a hyperelastic constitutive relation augmented with the Herschel-Bulkleymodel of non-Newtonian viscoplastic flow, which is known to closely approximate foam behavior. Since large shearing flows in foam can produce poor distributions of material points, a typical MPM implementation can produce non-physical internal holes in the continuum. To address these artifacts, we introduce a particle resampling method for MPM. In addition, we introduce an explicit tearing model to prevent regions from shearing into artificially thin, honey-like threads. We evaluate our method's efficacy by simulating a number of dense foams, and we validate our method by comparing to real-world footage of foam.This work was supported in part by the JSPS Postdoctoral Fellowshipsfor Research Abroad, NSF (Grants IIS-13-19483, CMMI-11-29917, CAREER-1453101), NSERC (Grant RGPIN-04360-2014), Intel, The Walt Disney Company, Autodesk, Side Effects, NVIDIA,Adobe, and The Foundry
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