A fast framework construction and visualization method for particle-based fluid

© 2017, The Author(s). Fast and vivid fluid simulation and visualization is a challenge topic of study in recent years. Particle-based simulation method has been widely used in the art animation modeling and multimedia field. However, the requirements of huge numerical calculation and high quality of visualization usually result in a poor computing efficiency. In this work, in order to improve those issues, we present a fast framework for 3D fluid fast constructing and visualization which parallelizes the fluid algorithm based on the GPU computing framework and designs a direct surface visualization method for particle-based fluid data such as WCSPH, IISPH, and PCISPH. Considering on conventional polygonization or adaptive mesh methods may incur high computing costs and detail losses, an improved particle-based method is provided for real-time fluid surface rendering with the screen-space technology and the utilities of the modern graphics hardware to achieve the high performance rendering; meanwhile, it effectively protects fluid details. Furthermore, to realize the fast construction of scenes, an optimized design of parallel framework and interface is also discussed in our paper. Our method is convenient to enforce, and the results demonstrate a significant improvement in the performance and efficiency by being compared with several examples

Embedded Implicit Stand-ins for Animated Meshes: a Case of Hybrid Modelling

In this paper we address shape modelling problems, encountered in computer animation and computer games development that are difficult to solve just using polygonal meshes. Our approach is based on a hybrid modelling concept that combines polygonal meshes with implicit surfaces. A hybrid model consists of an animated polygonal mesh and an approximation of this mesh by a convolution surface stand-in that is embedded within it or is attached to it. The motions of both objects are synchronised using a rigging skeleton. This approach is used to model the interaction between an animated mesh object and a viscoelastic substance, normally modelled in implicit form. The adhesive behaviour of the viscous object is modelled using geometric blending operations on the corresponding implicit surfaces. Another application of this approach is the creation of metamorphosing implicit surface parts that are attached to an animated mesh. A prototype implementation of the proposed approach and several examples of modelling and animation with near real-time preview times are presented

A Survey of Ocean Simulation and Rendering Techniques in Computer Graphics

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

Numerical hydrodynamics in general relativity

The current status of numerical solutions for the equations of ideal general relativistic hydrodynamics is reviewed. With respect to an earlier version of the article the present update provides additional information on numerical schemes and extends the discussion of astrophysical simulations in general relativistic hydrodynamics. Different formulations of the equations are presented, with special mention of conservative and hyperbolic formulations well-adapted to advanced numerical methods. A large sample of available numerical schemes is discussed, paying particular attention to solution procedures based on schemes exploiting the characteristic structure of the equations through linearized Riemann solvers. A comprehensive summary of astrophysical simulations in strong gravitational fields is presented. These include gravitational collapse, accretion onto black holes and hydrodynamical evolutions of neutron stars. The material contained in these sections highlights the numerical challenges of various representative simulations. It also follows, to some extent, the chronological development of the field, concerning advances on the formulation of the gravitational field and hydrodynamic equations and the numerical methodology designed to solve them.Comment: 105 pages, 12 figures. The full online-readable version of this article, including several animations, will be published in Living Reviews in Relativity at http://www.livingreviews.or

Fast SPH simulation for gaseous fluids

This paper presents a fast smoothed particle hydro-dynamics (SPH) simulation approach for gaseous fluids. Unlike previous SPH gas simulators, which solve the transparent air flow in a fixed simulation domain, the proposed approach directly solves the visible gas without involving the transparent air. By compensating the density and force calculation for the visible gas particles, we completely avoid the need of computational cost on ambient air particles in previous approaches. This allows the computational resources to be exclusively focused on the visible gas, leading to significant performance improvement of SPH gas simulation. The proposed approach is at least ten times faster than the standard SPH gas simulation strategy and is able to reduce the total particle number by 25–400 times in large open scenes. The proposed approach also enables fast SPH simulation of complex scenes involving liquid–gas transition, such as boiling and evaporation. A particle splitting and merging scheme is proposed to handle the degraded resolution in liquid–gas phase transition. Various examples are provided to demonstrate the effectiveness and efficiency of the proposed approach

Towards practice real-time water simulations : multiphase smoothed particle hydrodynamics (M-SPH)

Ankara : The Department of Computer Engineering and the Institute of Engineering and Science of Bilkent Univ., 2008.Thesis (Master's) -- Bilkent University, 2008.Includes bibliographical references leaves 53-54.Simulation of water and other fluid phenomena have always been a popular topic in the computer graphics research area and many solutions provided in this topic covers many fluid simulation aspects. However, with the complex nature of physics of fluid dynamics, usually these solutions are not applicable to the real-time domain, especially interactive applications like computer games. The solutions that both target a realistic behavior and real-time CPU boundaries tend to solve the problem by utilizing Smoothed Particle Hydrodynamics (SPH) technique in the solution of Navier-Stokes equations. In this study, we introduce a novel approach for modeling of the water dynamics with multiple layers of SPH. This approach increases the level of detail in the constructed water surfaces while decreasing the required overall computation time. To achieve this, an extra SPH layer is introduced to use larger particles to fill most of the fluid volume which helps to simulate general fluid behavior in less numbers while utilizing other extra SPH layers with small particles to fill up in-betweens for finer detail in water surfaces. The performance gain can be up to several magnitudes with the increase of the water size while maintaining visually similar or more appealing results.Gökdoğan, Göktuğ FM.S

Animated surfaces in physically-based simulation

Physics-based animation has become a ubiquitous element in all application areas of computer animation, especially in the entertainment sector. Animation and feature films, video games, and advertisement contain visual effects using physically-based simulation that blend in seamlessly with animated or live-action productions. When simulating deformable materials and fluids, especially liquids, objects are usually represented by animated surfaces. The visual quality of these surfaces not only depends on the actual properties of the surface itself but also on its generation and relation to the underlying simulation. This thesis focuses on surfaces of cloth simulations and fluid simulations based on Smoothed Particle Hydrodynamics (SPH), and contributes to improving the creation of animations by specifying surface shapes, modeling contact of surfaces, and evaluating surface effects of fluids. In many applications, there is a reference given for a surface animation in terms of its shape. Matching a given reference with a simulation is a challenging task and similarity is often determined by visual inspection. The first part of this thesis presents a signature for cloth animations that captures characteristic shapes and their temporal evolution. It combines geometric features with physical properties to represent accurately the typical deformation behavior. The signature enables calculating similarities between animations and is applied to retrieve cloth animations from collections by example. Interactions between particle-based fluids and deformable objects are usually modeled by sampling the deformable objects with particles. When interacting with cloth, however, this would require resampling the surface at large planar deformations and the thickness of cloth would be bound to the particle size. This problem is addressed in this thesis by presenting a two-way coupling technique for cloth and fluids based on the simulation mesh of the textile. It allows robust contact handling and intuitive control of boundary conditions. Further, a solution for intersection-free fluid surface reconstruction at contact with thin flexible objects is presented. The visual quality of particle-based fluid animation highly depends on the properties of the reconstructed surface. An important aspect of the reconstruction method is that it accurately represents the underlying simulation. This thesis presents an evaluation of surfaces at interfaces of SPH simulations incorporating the connection to the simulation model. A typical approach in computer graphics is compared to surface reconstruction used in material sciences. The behavior of free surfaces in fluid animations is highly influenced by surface tension. This thesis presents an evaluation of three types of surface tension models in combination with different pressure force models for SPH to identify the individual characteristics of these models. Systematic tests using a set of benchmark scenes are performed to reveal strengths and weaknesses, and possible areas of applications.Physikalisch basierte Animationen sind ein allgegenwärtiger Teil in jeglichen Anwendungsbereichen der Computeranimation, insbesondere dem Unterhaltungssektor. Animations- und Spielfilme, Videospiele und Werbung enthalten visuelle Effekte unter Verwendung von physikalisch basierter Simulation, die sich nahtlos in Animations- oder Realfilme einfügen. Bei der Simulation von deformierbaren Materialien und Fluiden, insbesondere Flüssigkeiten, werden die Objekte gewöhnlich durch animierte Oberflächen dargestellt. Die visuelle Qualität dieser Oberflächen hängt nicht nur von den Eigenschaften der Fläche selbst ab, sondern auch von deren Erstellung und der Verbindung zu der zugrundeliegenden Simulation. Diese Dissertation widmet sich Oberflächen von Textil- und Fluidsimulationen mit der Methode der Smoothed Particle Hydrodynamics (SPH) und leistet einen Beitrag zur Verbesserung der Erstellung von Animationen durch die Beschreibung von Oberflächenformen, der Modellierung von Kontakt von Oberflächen und der Evaluierung von Oberflächeneffekten von Fluiden. In vielen Anwendungen gibt es eine Referenz für eine Oberflächenanimation, die ihre Form beschreibt. Das Abgleichen einer Referenz mit einer Simulation ist eine große Herausforderung und die Ähnlichkeit wird häufig visuell überprüft. Im ersten Teil der Dissertation wird eine Signatur für Textilanimationen vorgestellt, die charakteristische Formen und ihre zeitliche Veränderung erfasst. Sie ist eine Kombination aus geometrischen Merkmalen und physikalischen Eigenschaften, um das typische Deformationsverhalten genau zu repräsentieren. Die Signatur erlaubt es, Ähnlichkeiten zwischen Animationen zu berechnen, und wird angewendet, um Textilanimationen aus Kollektionen anhand eines Beispiels aufzufinden. Interaktionen zwischen partikelbasierten Fluiden und deformierbaren Objekten werden gewöhnlich durch das Abtasten des deformierbaren Objekts mit Partikeln modelliert. Bei der Interaktion mit Textilien würde dies jedoch ein neues Abtasten bei großen planaren Deformation erfordern und die Stärke des Textils wäre an die Partikelgröße gebunden. Mit diesem Problem befasst sich diese Dissertation und stellt eine Technik für die wechselseitige Kopplung zwischen Textilien und Fluiden vor, die auf dem Simulationsnetz des Textils beruht. Diese erlaubt eine robuste Kontaktbehandlung und intuitive Kontrolle von Randbedingungen. Des Weiteren wird ein Lösungsansatz für eine durchdringungsfreie Oberflächenrekonstruktion beim Kontakt mit dünnen flexiblen Objekten präsentiert. Die visuelle Qualität von partikelbasierten Fluidanimationen hängt stark von den Eigenschaften der rekonstruierten Oberfläche ab. Wichtig bei Rekonstruktionsmethoden ist, dass sie die zugrundeliegende Simulation genau repräsentieren. Die Dissertation präsentiert eine Evaluierung von Oberflächen an Grenzflächen, die den Zusammenhang zum Simulationsmodell miteinbezieht. Ein typischer Ansatz aus der Computergrafik wird mit der Oberflächenrekonstruktion in der Werkstoffkunde verglichen. Das Verhalten von freien Oberflächen in Fluidanimationen wird stark von der Oberflächenspannung beeinflusst. In dieser Dissertation wird eine Evaluierung von drei Oberflächenspannungsmodellen in Kombination mit verschiedenen Druckmodellen für SPH präsentiert, um die Charakteristika der jeweiligen Modelle zu identifizieren. Es werden systematische Tests mit Hilfe von Benchmark-Tests durchgeführt, um Stärken, Schwächen und mögliche Anwendungsbereiche deutlich zu machen

Example Based Caricature Synthesis

The likeness of a caricature to the original face image is an essential and often overlooked part of caricature production. In this paper we present an example based caricature synthesis technique, consisting of shape exaggeration, relationship exaggeration, and optimization for likeness. Rather than relying on a large training set of caricature face pairs, our shape exaggeration step is based on only one or a small number of examples of facial features. The relationship exaggeration step introduces two definitions which facilitate global facial feature synthesis. The first is the T-Shape rule, which describes the relative relationship between the facial elements in an intuitive manner. The second is the so called proportions, which characterizes the facial features in a proportion form. Finally we introduce a similarity metric as the likeness metric based on the Modified Hausdorff Distance (MHD) which allows us to optimize the configuration of facial elements, maximizing likeness while satisfying a number of constraints. The effectiveness of our algorithm is demonstrated with experimental results

Smoothed Particle Hydrodynamics for Computational Fluid Dynamics

Smoothed particle hydrodynamics (SPH) is a simple and effective numerical method that can be used to solve a variety of challenging problems in computational mechanics. It is a Lagrangian mesh-free method ideal for solving deformation problems. In the SPH method, the state of a system is represented by a set of particles, which possesses individual material properties and interact with each other within a specific range defined as a support domain by a weight function or smoothing function. SPH features flexibility in handling complex flow fields and in including physical effects. In theory, the basic concept of the SPH method is introduced in this paper. Some detailed numerical aspects are discussed including the kernel approximation in continuous form and particle approximation in discrete form, the properties for the smoothing functions and some of the most frequently used ones in the SPH literature, the concept of support and interface domain, SPH formulations for Navier-Stokes equation, time integration, boundary treatment, particle interaction, artificial viscosity, laminar viscosity, shifting algorithm, and so on. In applications, this paper presents an improved SPH method for modeling the diffusion process of a microneedle and using smoothed particle hydrodynamics (SPH) method to simulate the 25% cross-section stenosis blood vessel model and the 75% crosssection stenosis blood vessel model. The obtained numerical results are in close agreement with available theoretical and experimental results in the literature. As an emerging transdermal drug delivery device, microneedles demonstrate some superior potential and advantages over traditional metallic needles-on-syringes in skin injection and vaccine [1]. However, very few research papers are available. This project uses a high order continuous method, the spectral element method (SEM), and a low order discrete method, the Smoothed Particle Hydrodynamics (SPH), to investigate this new drug delivery system. The incompressible Navier-Stokes equations were solved with SEM under appropriate initial and slip boundary conditions for the transport of medicine inside microneedles of rectangular and circular cross-sections. In addition, Darcy-Brinkman equations and a concentration equation were solved with SEM under appropriate initial and boundary conditions for the infiltration of medicine solution through porous media of the dermis tissue once a microneedle enters the skin. Meanwhile, the Lagrangian form of the Navier-Stokes equations were solved with the weighted interpolation approach via numerical integrations without inverting any matrices. Results from the mesh-based SEM and the mesh-free SPH simulations revealed technical details about the processes of delivery of medicine particles through microneedles and diffusion in the skin tissue, and the medicine concentration changes with space and time. The overall effect of medicine delivery under initial concentration and conditions were simulated and the effect of drug delivery were assessed. The formation of thrombus is a complicated process. The existing literature rarely has a model for high-fidelity simulation of the effects and hazards of blood clots on blood flow. In this model, high-fidelity simulations are performed for complex human internal environments. The result of this simulation indicates high pressure area in blood vessel wall which matches the real condition of the vessel experiment

Improved Interpolation in SPH in Cases of Less Smooth Flow

We introduced a method presented in Information Field Theory (IFT) [Abramovich et al., 2007] to improve interpolation in Smoothed Particle Hydrodynamics (SPH) in cases of less smooth flow. The method makes use of wavelet theory combined with B-splines for interpolation. The idea is to identify any jumps a function may have and then reconstruct the smoother segments between the jumps. The results of our work demonstrated superior capability when compared to a particular challenging SPH application, to better conserve jumps and more accurately interpolate the smoother segments of the function. The results of our work also demonstrated increased computational efficiency with limited loss in accuracy as number of multiplications and execution time were reduced. Similar benefits were observed for functions with spikes analyzed by the same method. Lesser, but similar effects were also demonstrated for real life data sets of less smooth nature. SPH is widely used in modeling and simulation of flow of matters. SPH presents advantages compared to grid based methods both in terms of computational efficiency and accuracy, in particular when dealing with less smooth flow. The results we achieved through our research is an improvement to the model in cases of less smooth flow, in particular flow with jumps and spikes. Up until now such improvements have been sought through modifications to the models\u27 physical equations and/or kernel functions and have only partially been able to address the issue. This research, as it introduced wavelet theory and IFT to a field of science that, to our knowledge, not currently are utilizing these methods, did lay the groundwork for future research ideas to benefit SPH. Among those ideas are further development of criteria for wavelet selection, use of smoothing splines for SPH interpolation and incorporation of Bayesian field theory. Improving the method\u27s accuracy, stability and efficiency under more challenging conditions such as flow with jumps and spikes, will benefit applications in a wide area of science. Just in medicine alone, such improvements will further increase real time diagnostics, treatments and training opportunities because jumps and spikes are often the characteristics of significant physiological and anatomic conditions such as pulsatile blood flow, peristaltic intestine contractions and organs\u27 edges appearance in imaging