Myxobacteria are social bacteria, that can glide in two dimensions and form counterpropagating, interacting waves. Here, we present a novel age-structured, continuous macroscopic model for the movement of myxobacteria. The derivation is based on microscopic interaction rules that can be formulated as a particle-based model and set within the Self-Organized Hydrodynamics (SOH) framework. The strength of this combined approach is that microscopic knowledge or data can be incorporated easily into the particle model, whilst the continuous model allows for easy numerical analysis of the diﬀerent eﬀects. However, we found that the derived macroscopic model lacks a diﬀusion term in the density equations, which is necessary to control the number of waves, indicating that a higher order approximation during the derivation is crucial. Upon ad hoc addition of the diﬀusion term, we found very good agreement between the age-structured model and the biology. In particular, we analyzed the inﬂuence of a refractory (insensitivity) period following a reversal of movement. Our analysis reveals that the refractory period is not necessary for wave formation, but essential to wave synchronization, indicating separate molecular mechanisms.
We introduce a unified particle framework which integrates the phase-field method with multi-material simulation to allow modeling of both liquids and solids, as well as phase transitions between them. A simple elastoplastic model is used to capture the behavior of various kinds of solids, including deformable bodies, granular materials, and cohesive soils. States of
matter or phases, particularly liquids and solids, are modeled using the non-conservative Allen-Cahn equation. In contrast, materials—made of different substances—are advected by the conservative Cahn-Hilliard equation. The distributions of phases and materials are represented by a phase variable and a concentration variable, respectively, allowing us to represent commonly observed fluid-solid interactions. Our multi-phase, multi-material system is governed by a unified Helmholtz free energy density. This framework provides the first method in computer graphics capable of modeling a continuous interface between phases. It is versatile and can be readily used in many scenarios that are challenging to simulate. Examples are provided to demonstrate the capabilities and effectiveness of this approach.
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.
Surface flow phenomena, such as rain water flowing down a tree trunk and progressive water front in a shower room, are common in real life. However, compared with the 3D spatial fluid flow, these surface flow problems have been much less studied in the graphics community. To tackle this research gap, we present an efficient, robust and high-fidelity simulation approach based on the shallow-water equations. Specifically, the standard shallow-water flow model is extended to general triangle meshes with a feature-based bottom friction model, and a series of coherent mathematical formulations are derived to represent the full range of physical effects that are important for real-world surface flow phenomena. In addition, by achieving compatibility with existing 3D fluid simulators and by supporting physically realistic interactions with multiple fluids and solid surfaces, the new model is flexible and readily extensible for coupled phenomena. A wide range of simulation examples are presented to demonstrate the performance of the new approach.
Markus Ihmsen · Jens Cornelis · Barbara Solenthaler · Christopher J Horvath · Matthias Teschner. Implicit Incompressible SPH. 2014.
Lentine M, Zheng W, Fedkiw R, et al. A novel algorithm for incompressible flow using only a coarse grid projection[J]. international conference on computer graphics and interactive techniques, 2010, 29(4).
Zhu B, Yang X, Fan Y, et al. Creating and Preserving Vortical Details in SPH Fluid[J]. Computer Graphics Forum, 2010, 29(7): 2207-2214.
Chenfanfu Jiang · Craig Schroeder · Andrew Selle · Joseph Teran · Alexey Stomakhin. The affine particle-in-cell method. 2015.
Chang Y, Bao K, Zhu J, et al. A particle-based method for granular flow simulation[J]. Science in China Series F: Information Sciences, 2012, 55(5): 1062-1072.
Cornelis J, Ihmsen M, Peer A, et al. IISPH-FLIP for incompressible fluids[J]. Computer Graphics Forum, 2014, 33(2): 255-262.
Yusuke Tsuda · Yonghao Yue · Yoshinori Dobashi · Tomoyuki Nishita. Visual simulation of mixed-motion avalanches with interactions between snow layers. 2010.
Ren B, Yan X, Yang T, et al. Fast SPH simulation for gaseous fluids[J]. The Visual Computer, 2016, 32(4): 523-534.
Suntae Kim · Jeongmo Hong. Visual simulation of turbulent fluids using MLS interpolation profiles. 2013.
Shiguang Liu · Yixin Xu · Junyong Noh · Yiying Tong. Visual fluid animation via lifting wavelet transform: Fluid animation via lifting wavelet transform. 2014.
Gaseous fluids may move slowly, as smoke does, or at high speed, such as occurs with explosions. High-speed gas flow is always accompanied by low-speed gas flow, which produces rich visual details in the fluid motion. Realistic visualization involves a complex dynamic flow field with both low and high speed fluid behavior. In computer graphics, algorithms to simulate gaseous fluids address either the low speed case or the high speed case, but no algorithm handles both efficiently. With the aim of providing visually pleasing results, we present a hybrid algorithm that efficiently captures the essential physics of both low- and high-speed gaseous fluids. We model the low speed gaseous fluids by a grid approach and use a particle approach for the high speed gaseous fluids. In addition, we propose a physically sound method to connect the particle model to the grid model. By exploiting complementary strengths and avoiding weaknesses of the grid and particle approaches, we produce some animation examples and analyze their computational performance to demonstrate the effectiveness of the new hybrid method.