Real-time lattice boltzmann shallow waters method for breaking wave simulations

We present a new approach for the simulation of surfacebased fluids based in a hybrid formulation of Lattice Boltzmann Method for Shallow Waters and particle systems. The modified LBM can handle arbitrary underlying terrain conditions and arbitrary fluid depth. It also introduces a novel method for tracking dry-wet regions and moving boundaries. Dynamic rigid bodies are also included in our simulations using a two-way coupling. Certain features of the simulation that the LBM can not handle because of its heightfield nature, as breaking waves, are detected and automatically turned into splash particles. Here we use a ballistic particle system, but our hybrid method can handle more complex systems as SPH. Both the LBM and particle systems are implemented in CUDA, although dynamic rigid bodies are simulated in CPU. We show the effectiveness of our method with various examples which achieve real-time on consumer-level hardware.Peer ReviewedPostprint (author's final draft

Efficient algorithms for the realistic simulation of fluids

Nowadays there is great demand for realistic simulations in the computer graphics field. Physically-based animations are commonly used, and one of the more complex problems in this field is fluid simulation, more so if real-time applications are the goal. Videogames, in particular, resort to different techniques that, in order to represent fluids, just simulate the consequence and not the cause, using procedural or parametric methods and often discriminating the physical solution. This need motivates the present thesis, the interactive simulation of free-surface flows, usually liquids, which are the feature of interest in most common applications. Due to the complexity of fluid simulation, in order to achieve real-time framerates, we have resorted to use the high parallelism provided by actual consumer-level GPUs. The simulation algorithm, the Lattice Boltzmann Method, has been chosen accordingly due to its efficiency and the direct mapping to the hardware architecture because of its local operations. We have created two free-surface simulations in the GPU: one fully in 3D and another restricted only to the upper surface of a big bulk of fluid, limiting the simulation domain to 2D. We have extended the latter to track dry regions and is also coupled with obstacles in a geometry-independent fashion. As it is restricted to 2D, the simulation loses some features due to the impossibility of simulating vertical separation of the fluid. To account for this we have coupled the surface simulation to a generic particle system with breaking wave conditions; the simulations are totally independent and only the coupling binds the LBM with the chosen particle system. Furthermore, the visualization of both systems is also done in a realistic way within the interactive framerates; raycasting techniques are used to provide the expected light-related effects as refractions, reflections and caustics. Other techniques that improve the overall detail are also applied as low-level detail ripples and surface foam

Water wave packets

This paper presents a method for simulating water surface waves as a displacement field on a 2D domain. Our method relies on Lagrangian particles that carry packets of water wave energy; each packet carries information about an entire group of wave trains, as opposed to only a single wave crest. Our approach is unconditionally stable and can simulate high resolution geometric details. This approach also presents a straightforward interface for artistic control, because it is essentially a particle system with intuitive parameters like wavelength and amplitude. Our implementation parallelizes well and runs in real time for moderately challenging scenarios

Wave curves: Simulating Lagrangian water waves on dynamically deforming surfaces

We propose a method to enhance the visual detail of a water surface simulation. Our method works as a post-processing step which takes a simulation as input and increases its apparent resolution by simulating many detailed Lagrangian water waves on top of it. We extend linear water wave theory to work in non-planar domains which deform over time, and we discretize the theory using Lagrangian wave packets attached to spline curves. The method is numerically stable and trivially parallelizable, and it produces high frequency ripples with dispersive wave-like behaviors customized to the underlying fluid simulation

Modelling of tsunami-like wave run-up, breaking and impact on a vertical wall by SPH method

Natural Hazards and Earth System Sciences13123457-346

Real-time Water Waves with Wave Particles

This dissertation describes the wave particles technique for simulating water surface waves and two way fluid-object interactions for real-time applications, such as video games. Water exists in various different forms in our environment and it is important to develop necessary technologies to be able to incorporate all these forms in real-time virtual environments. Handling the behavior of large bodies of water, such as an ocean, lake, or pool, has been computationally expensive with traditional techniques even for offline graphics applications, because of the high resolution requirements of these simulations. A significant portion of water behavior for large bodies of water is the surface wave phenomenon. This dissertation discusses how water surface waves can be simulated efficiently and effectively at real-time frame rates using a simple particle system that we call "wave particles." This approach offers a simple, fast, and unconditionally stable solution to wave simulation. Unlike traditional techniques that try to simulate the water body (or its surface) as a whole with numerical techniques, wave particles merely track the deviations of the surface due to waves forming an analytical solution. This allows simulation of seemingly infinite water surfaces, like an open ocean. Both the theory and implementation of wave particles are discussed in great detail. Two-way interactions of floating objects with water is explained, including generation of waves due to object interaction and proper simulation of the effect of water on the object motion. Timing studies show that the method is scalable, allowing simulation of wave interaction with several hundreds of objects at real-time rates

The explosion mechanism of core-collapse supernovae: progress in supernova theory and experiments

The explosion of core-collapse supernova depends on a sequence of events taking place in less than a second in a region of a few hundred kilometers at the center of a supergiant star, after the stellar core approaches the Chandrasekhar mass and collapses into a proto-neutron star, and before a shock wave is launched across the stellar envelope. Theoretical efforts to understand stellar death focus on the mechanism which transforms the collapse into an explosion. Progress in understanding this mechanism is reviewed with particular attention to its asymmetric character. We highlight a series of successful studies connecting observations of supernova remnants and pulsars properties to the theory of core-collapse using numerical simulations. The encouraging results from first principles models in axisymmetric simulations is tempered by new puzzles in 3D. The diversity of explosion paths and the dependence on the pre-collapse stellar structure is stressed, as well as the need to gain a better understanding of hydrodynamical and MHD instabilities such as SASI and neutrino-driven convection. The shallow water analogy of shock dynamics is presented as a comparative system where buoyancy effects are absent. This dynamical system can be studied numerically and also experimentally with a water fountain. The potential of this complementary research tool for supernova theory is analyzed. We also review its potential for public outreach in science museums.Comment: 19 pages, 6 figures, invited review accepted for publication in PAS

SIGGRAPH

The current state of the art in real-time two-dimensional water wave simulation requires developers to choose between efficient Fourier-based methods, which lack interactions with moving obstacles, and finite-difference or finite element methods, which handle environmental interactions but are significantly more expensive. This paper attempts to bridge this long-standing gap between complexity and performance, by proposing a new wave simulation method that can faithfully simulate wave interactions with moving obstacles in real time while simultaneously preserving minute details and accommodating very large simulation domains. Previous methods for simulating 2D water waves directly compute the change in height of the water surface, a strategy which imposes limitations based on the CFL condition (fast moving waves require small time steps) and Nyquist's limit (small wave details require closely-spaced simulation variables). This paper proposes a novel wavelet transformation that discretizes the liquid motion in terms of amplitude-like functions that vary over space, frequency, and direction, effectively generalizing Fourier-based methods to handle local interactions. Because these new variables change much more slowly over space than the original water height function, our change of variables drastically reduces the limitations of the CFL condition and Nyquist limit, allowing us to simulate highly detailed water waves at very large visual resolutions. Our discretization is amenable to fast summation and easy to parallelize. We also present basic extensions like pre-computed wave paths and two-way solid fluid coupling. Finally, we argue that our discretization provides a convenient set of variables for artistic manipulation, which we illustrate with a novel wave-painting interface

Shallow waters simulation

Dissertação de mestrado integrado em Informatics EngineeringRealistic simulation and rendering of water in real-time is a challenge within the field of computer graphics, as it is very computationally demanding. A common simulation approach is to reduce the problem from 3D to 2D by treating the water surface as a 2D heightfield. When simulating 2D fluids, the Shallow Water Equations (SWE) are often employed, which work under the assumption that the water’s horizontal scale is much greater than it’s vertical scale. There are several methods that have been developed or adapted to model the SWE, each with its own advantages and disadvantages. A common solution is to use grid-based methods where there is the classic approach of solving the equations in a grid, but also the Lattice-Boltzmann Method (LBM) which originated from the field of statistical physics. Particle based methods have also been used for modeling the SWE, namely as a variation of the popular Smoothed-Particle Hydrodynamics (SPH) method. This thesis presents an implementation for real-time simulation and rendering of a heightfield surface water volume. The water’s behavior is modeled by a grid-based SWE scheme with an efficient single kernel compute shader implementation. When it comes to visualizing the water volume created by the simulation, there are a variety of effects that can contribute to its realism and provide visual cues for its motion. In particular, When considering shallow water, there are certain features that can be highlighted, such as the refraction of the ground below and corresponding light attenuation, and the caustics patterns projected on it. Using the state produced by the simulation, a water surface mesh is rendered, where set of visual effects are explored. First, the water’s color is defined as a combination of reflected and transmitted light, while using a Cook- Torrance Bidirectional Reflectance Distribution Function (BRDF) to describe the Sun’s reflection. These results are then enhanced by data from a separate pass which provides caustics patterns and improved attenuation computations. Lastly, small-scale details are added to the surface by applying a normal map generated using noise. As part of the work, a thorough evaluation of the developed application is performed, providing a showcase of the results, insight into some of the parameters and options, and performance benchmarks.Simulação e renderização realista de água em tempo real é um desafio dentro do campo de computação gráfica, visto que é muito computacionalmente exigente. Uma abordagem comum de simulação é de reduzir o problema de 3D para 2D ao tratar a superfície da água como um campo de alturas 2D. Ao simular fluidos em 2D, é frequente usar as equações de águas rasas, que funcionam sobre o pressuposto de que a escala horizontal da água é muito maior que a sua escala vertical. Há vários métodos que foram desenvolvidos ou adaptados para modelar as equações de águas rasas, cada uma com as suas vantagens e desvantagens. Uma solução comum é utilizar métodos baseados em grelhas onde existe a abordagem clássica de resolver as equações numa grelha, mas também existe o método de Lattice Boltzmann que originou do campo de física estatística. Métodos baseados em partículas também já foram usados para modelar as equações de águas rasas, nomeadamente como uma variação do popular método de SPH. Esta tese apresenta uma implementação para simulação e renderização em tempo real de um volume de água com uma superfície de campo de alturas. O comportamento da água é modelado por um esquema de equações de águas rasas baseado na grelha com uma implementação eficiente de um único kernel de compute shader. No que toca a visualizar o volume de água criado pela simulação, existe uma variedade de efeitos que podem contribuir para o seu realismo e fornecer dicas visuais sobre o seu movimento. Ao considerar águas rasas, existem certas características que podem ser destacadas, como a refração do terreno por baixo e correspondente atenuação da luz, e padrões de cáusticas projetados nele. Usando o estado produzido pela simulação, uma malha da superfície da água é renderizada, onde um conjunto de efeitos visuais são explorados. Em primeiro lugar, a cor da água é definida como uma combinação de luz refletida e transmitida, sendo que uma BRDF de Cook-Torrance é usada para descrever a reflexão do Sol. Estes resultados são depois complementados com dados gerados num passo separado que fornece padrões de cáusticas e melhora as computações de atenuação. Por fim, detalhes de pequena escala são adicionados à superfície ao aplicar um mapa de normais gerado com ruído. Como parte do trabalho desenvolvido, é feita uma avaliação detalhada da aplicação desenvolvida, onde é apresentada uma demonstração dos resultados, comentários sobre alguns dos parâmetros e opções, e referências de desempenho

Large-Scale Water Simulation in Games

Water is an important element in the nature. It is also often encountered in digital games and other virtual environments, but unfortunately interaction with it is typically very limited. The main reason for this is probably the immense computational cost of simulating water behavior. Simulating water and other fluids by numerically solving emph{Navier-Stokes equations} is commonplace for offline engineering applications such as bridge building, weather prediction, or aeronautics. Since the 1990s, these methods have also been applied to computer graphics, but the focus has been in offline applications such as movie special effects. Recent advances in programmable graphics hardware have facilitated real-time fluid simulation in a large enough scale to be applicable in games. This far these methods have been mostly used in games only for visual purposes. This thesis is motivated by the wish to see more games where also the gameplay is affected by water simulation.The first part of this thesis studies the roles of interactive water in different kinds of games. Requirements for water simulation methods are formulated by examining those roles. The thesis then introduces some background theory and various methods for water simulation. The focus is in heightfield-based methods, which simplify the problem by assuming that the water surface can be represented as a vertical displacement from a neutral level. This assumption allows very large amounts of water to be simulated with the very limited resources available for this purpose in a typical game. Most of these methods work on a heightfield terrain and can be enriched with fully 3D effects such as splashes and waterfalls by adding a particle simulation system.An important problem is coupling the water simulation with existing rigid body simulations that are largely used for the dynamics of game objects. The coupling includes effects such as floating, objects moving with the flow, and building dams out of bodies. The thesis introduces a new heightfield-based coupling method, which allows the building of dams from rigid bodies in the heightfield context, unlike the previous approaches. The proposed methods, including the underlying water simulation method and visualization, were implemented in parallel using graphics processing units. The methods were found to be fast enough to be applicable in games.Finally, the most promising current simulation methods are compared from a games point-of-view using the criteria set in the beginning: performance, simplicity, visual quality, richness of behavior, and rigid body coupling. Since quality of experience is a subjective matter, user tests are recommended for comparison. Included in the thesis is one of the first such studies, which found out that leaving out the velocity self-advection step of a shallow water equation solver had no statistically significant effect on any of the measured psychological impacts. Based on the analysis, recommendations for the choice of simulation methods are given for different kinds of games