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A Hybrid LagrangianEulerian Formulation for Bubble Generation and Dynamics
"... Figure 1: (Left) a faucet generating bubbles through air entrainment, (Center) a source seeding tiny bubbles which merge and grow as they rise, as well as interact with a moving armadillo illustrating complex object interaction, (Right) a cavitating propeller generates the characteristic helical pat ..."
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Figure 1: (Left) a faucet generating bubbles through air entrainment, (Center) a source seeding tiny bubbles which merge and grow as they rise, as well as interact with a moving armadillo illustrating complex object interaction, (Right) a cavitating propeller generates the characteristic helical pattern in its wake. We present a hybrid LagrangianEulerian framework for simulating both small and large scale bubble dynamics, where the bubbles can grow or shrink in volume as dictated by pressure forces in the surrounding fluid. Small underresolved bubbles are evolved using Lagrangian particles that are monolithically twoway coupled to the surrounding flow in a manner that closely approximates the analytic bubble oscillation frequency while converging to the analytic volume as predicted by the wellknown RayleighPlesset equation. We present a novel scheme for interconverting between these underresolved Lagrangian bubbles and larger wellresolved bubbles that are modeled with a traditional Eulerian level set approach. We also present a novel seeding mechanism to realistically generate bubbles when simulating fluid structure interaction with complex objects such as ship propellers. Moreover, our framework for bubble generation is general enough to be incorporated into all gridbased as well as particlebased fluid simulation methods.
The Affine ParticleInCell Method
"... Figure 1: APIC/PIC blends yield more energetic and more stable behavior than FLIP/PIC blends in a wine pour example. APIC/PIC blends are achieved analogously to FLIP/PIC in that it is a scaling of the particle affine matrices. c©Disney. Hybrid Lagrangian/Eulerian simulation is commonplace in comput ..."
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Figure 1: APIC/PIC blends yield more energetic and more stable behavior than FLIP/PIC blends in a wine pour example. APIC/PIC blends are achieved analogously to FLIP/PIC in that it is a scaling of the particle affine matrices. c©Disney. Hybrid Lagrangian/Eulerian simulation is commonplace in computer graphics for fluids and other materials undergoing large deformation. In these methods, particles are used to resolve transport and topological change, while a background Eulerian grid is used for computing mechanical forces and collision responses. ParticleinCell (PIC) techniques, particularly the Fluid Implicit Particle (FLIP) variants have become the norm in computer graphics calculations. While these approaches have proven very powerful, they do suffer from some well known limitations. The original PIC is stable, but highly dissipative, while FLIP, designed to remove this dissipation, is more noisy and at times, unstable. We present a novel technique designed to retain the stability of the original PIC, without suffering from the noise and instability of FLIP. Our primary observation is that the dissipation in the original PIC results from a loss of information when transferring between grid and particle representations. We prevent this loss of information by augmenting each particle with a locally affine, rather than locally constant, description of the velocity. We show that this not only stably removes the dissipation of PIC, but that it also allows for exact conservation of angular momentum across the transfers between particles and grid.
Swansea University
"... This paper presents a versatile and robust SPH simulation approach for multiplefluid flows. The spatial distribution of different phases or components is modeled using the volume fraction representation, the dynamics of multiplefluid flows is captured by using an improved mixture model, and a s ..."
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This paper presents a versatile and robust SPH simulation approach for multiplefluid flows. The spatial distribution of different phases or components is modeled using the volume fraction representation, the dynamics of multiplefluid flows is captured by using an improved mixture model, and a stable and accurate SPH formulation is rigorously derived to resolve the complex transport and transformation processes encountered in multiplefluid flows. The new approach can capture a wide range of realworld multiplefluid phenomena, including mixing/unmixing of miscible and immiscible fluids, diffusion effect and chemical reaction etc. Moreover,
Highly Adaptive Liquid Simulations on Tetrahedral Meshes Ryoichi
"... Figure 1: Our adaptive simulation framework allows us to efficiently simulate highly detailed splashes on large open surfaces. In this case, maximum BCC mesh resolutions from 8 to 1024 cells were used, leading to strong horizontal grading along the surface. We introduce a new method for efficiently ..."
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Figure 1: Our adaptive simulation framework allows us to efficiently simulate highly detailed splashes on large open surfaces. In this case, maximum BCC mesh resolutions from 8 to 1024 cells were used, leading to strong horizontal grading along the surface. We introduce a new method for efficiently simulating liquid with extreme amounts of spatial adaptivity. Our method combines several key components to drastically speed up the simulation of largescale fluid phenomena: We leverage an alternative Eulerian tetrahedral mesh discretization to significantly reduce the complexity of the pressure solve while increasing the robustness with respect to element quality and removing the possibility of locking. Next, we enable subtle freesurface phenomena by deriving novel secondorder boundary conditions consistent with our discretization. We couple this discretization with a spatially adaptive FluidImplicit Particle (FLIP) method, enabling efficient, robust, minimallydissipative simulations that can undergo sharp changes in spatial resolution while minimizing artifacts. Along the way, we provide a new method for generating a smooth and detailed surface from a set of particles with variable sizes. Finally, we explore several new sizing functions for determining spatially adaptive simulation resolutions, and we show how to couple them to our simulator. We combine each of these elements to produce a simulation algorithm that is capable of creating animations at high maximum resolutions while avoiding common pitfalls like inaccurate boundary conditions and inefficient computation.
Enhancing Particle Methods for Fluid Simulation in Computer Graphics
, 2013
"... We introduce novel methods for enriched Lagrangian fluid simulation in three distinct areas: smoke animation, liquid animation, and surfacing of simulation particle data. The techniques share a common goal, to efficiently enhance realism of naturalphenomena animations in particle simulation framewo ..."
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We introduce novel methods for enriched Lagrangian fluid simulation in three distinct areas: smoke animation, liquid animation, and surfacing of simulation particle data. The techniques share a common goal, to efficiently enhance realism of naturalphenomena animations in particle simulation framework. SubGrid Turbulence adds synthesized small scale detail to large scale smoke simulation. The transport, diffusion and spectral cascade of turbulent energy are captured, whereas they are left unresolved on a typical simulation grid. GhostSPH handling of freesurface and solidboundary conditions in Smoothed Particle Hydrodynamics liquid simulation captures realistic cohesion for the first time and avoids the spurious numerical errors of previous approaches. Ghost particles are carefully seeded in the air and solid regions near the fluid and are assigned with extrapolated fluid quantities to reach correct boundary conditions. The Beta Mesh is a new method for reconstructing mostly temporally coherent surface meshes from particles representing the volume of a liquid. While current particle surfacing techniques address the geometrical characteristics of the surface, the focus in Beta Mesh is producing a surface which varies smoothly in time, outside of topological changes, while preserving essential geometrical properties. ii Preface All work in this thesis was done under the supervision of Dr. Robert Bridson without other collaborators besides Dr. Bridson.
Author’s version IISPHFLIP for incompressible fluids
"... Figure 1: Scene with 160 million FLIP particles. Particles are color coded with respect to velocity. We propose to use Implicit Incompressible Smoothed Particle Hydrodynamics (IISPH) for pressure projection and boundary handling in FluidImplicitParticle (FLIP) solvers for the simulation of incompr ..."
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Figure 1: Scene with 160 million FLIP particles. Particles are color coded with respect to velocity. We propose to use Implicit Incompressible Smoothed Particle Hydrodynamics (IISPH) for pressure projection and boundary handling in FluidImplicitParticle (FLIP) solvers for the simulation of incompressible fluids. This novel combination addresses two issues of existing SPH and FLIP solvers, namely mass preservation in FLIP and efficiency and memory consumption in SPH. First, the SPH component enables the simulation of incompressible fluids with perfect mass preservation. Second, the FLIP component efficiently enriches the SPH component with detail that is comparable to a standard SPH simulation with the same number of particles, while improving the performance by a factor of 7 and significantly reducing the memory consumption. We demonstrate that the proposed IISPHFLIP solver can simulate incompressible fluids with a quantifiable, imperceptible density deviation below 0.1%. We show largescale scenarios with up to 160 million particles that have been processed on a single desktop PC using only 15GB of memory. One and twoway coupled solids are illustrated.
Fast Multiplefluid Simulation Using Helmholtz Free Energy
"... Figure 1: Egg Mixture. In simulating the stirring of 3 eggs by a blender, the resulting simulation presents visually plausible mixing results. This mixing effect is achieved using our novel “extended mobility ” formulation of the NavierStokesCahnHilliard Model. Multiplefluid interaction is an in ..."
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Figure 1: Egg Mixture. In simulating the stirring of 3 eggs by a blender, the resulting simulation presents visually plausible mixing results. This mixing effect is achieved using our novel “extended mobility ” formulation of the NavierStokesCahnHilliard Model. Multiplefluid interaction is an interesting and common visual phenomenon we often observe. In this paper, we present an energybased Lagrangian method that expands the capability of existing multiplefluid methods to handle various phenomena, such as extraction, partial dissolution, etc. Based on our useradjusted Helmholtz free energy functions, the simulated fluid evolves from highenergy states to lowenergy states, allowing flexible capture of various mixing and unmixing processes. We also extend the original CahnHilliard equation to be better able to simulate complex fluidfluid interaction and rich visual phenomena such as motionrelated mixing and position based pattern. Our approach is easily integrated with existing stateoftheart smooth particle hydrodynamic (SPH) solvers and can be further implemented on top of the position based dynamics (PBD) method, improving the stability and incompressibility of the fluid during Lagrangian simulation under large time steps. Performance analysis shows that our method is at least 4 times faster than the stateoftheart multiplefluid method. Examples are provided to demonstrate the new capability and effectiveness of our approach.