A 2D hybrid method for interfacial transport of passive scalars

A hybrid Eulerian-Lagrangian method is proposed to simulate passive scalar transport on arbitrary shape interface. In this method, interface deformation is tracked by an Eulerian method while the transport of the passive scalar on the material interface is solved by a single-layer Lagrangian particle method. To avoid particle clustering, a novel remeshing approach is proposed. This remeshing method can resample particles, adjust the position of particles by a relaxation process, and transfer mass from pre-existing particles to resampled particles via a redistribution process, which preserves mass both globally and locally. Computational costs are controlled by an adaptive remeshing strategy. Accuracy is assessed by a series of test cases.Comment: 32 pages 1nd 14 figure

Modeling the shock-induced multiple reactions in a random bed of metallic granules in an energetic material

An investigation of shock–particle interactions in reactive flows is performed using an Eulerian hydrodynamic method with a hybrid particle level-set algorithm to handle the material interface dynamics. The analysis is focused on the meso- to macro-scale numerical modeling of a granular metalized explosive containing randomly distributed metal particles intended to enhance its blast effect. The reactive flow model is used for the cyclotrimethylene-trinitramine (RDX) component, while thermally induced deflagration kinetics describes the aerobic reaction of the metal particles. The complex interfacial algorithm, which uses aligned level sets to track deforming surface between multi materials and to generate the random shape of granule elements, is described for aluminized and copperized RDX. Then, the shock-induced collapse of metal particles embedded in the condensed phase domain of a high explosive is simulated. Both aluminized and copperized RDX are shown to detonate with a shock wave followed by the burning of the metal particles. The energy release and the afterburning behavior behind the detonating shock wave successfully identified the precursor that gave rise to the development of deflagration of the metal particles

Doctor of Philosophy

dissertationPhysical simulation has become an essential tool in computer animation. As the use of visual effects increases, the need for simulating real-world materials increases. In this dissertation, we consider three problems in physics-based animation: large-scale splashing liquids, elastoplastic material simulation, and dimensionality reduction techniques for fluid simulation. Fluid simulation has been one of the greatest successes of physics-based animation, generating hundreds of research papers and a great many special effects over the last fifteen years. However, the animation of large-scale, splashing liquids remains challenging. We show that a novel combination of unilateral incompressibility, mass-full FLIP, and blurred boundaries is extremely well-suited to the animation of large-scale, violent, splashing liquids. Materials that incorporate both plastic and elastic deformations, also referred to as elastioplastic materials, are frequently encountered in everyday life. Methods for animating such common real-world materials are useful for effects practitioners and have been successfully employed in films. We describe a point-based method for animating elastoplastic materials. Our primary contribution is a simple method for computing the deformation gradient for each particle in the simulation. Given the deformation gradient, we can apply arbitrary constitutive models and compute the resulting elastic forces. Our method has two primary advantages: we do not store or compare to an initial rest configuration and we work directly with the deformation gradient. The first advantage avoids poor numerical conditioning and the second naturally leads to a multiplicative model of deformation appropriate for finite deformations. One of the most significant drawbacks of physics-based animation is that ever-higher fidelity leads to an explosion in the number of degrees of freedom

Finite-Volume Filtering in Large-Eddy Simulations Using a Minimum-Dissipation Model

Large-eddy simulation (LES) seeks to predict the dynamics of the larger eddies in turbulent flow by applying a spatial filter to the Navier-Stokes equations and by modeling the unclosed terms resulting from the convective non-linearity. Thus the (explicit) calculation of all small-scale turbulence can be avoided. This paper is about LES-models that truncate the small scales of motion for which numerical resolution is not available by making sure that they do not get energy from the larger, resolved, eddies. To identify the resolved eddies, we apply Schumann’s filter to the (incompressible) Navier-Stokes equations, that is the turbulent velocity field is filtered as in a finite-volume method. The spatial discretization effectively act as a filter; hence we define the resolved eddies for a finite-volume discretization. The interpolation rule for approximating the convective flux through the faces of the finite volumes determines the smallest resolved length scale δ. The resolved length δ is twice as large as the grid spacing h for an usual interpolation rule. Thus, the resolved scales are defined with the help of box filter having diameter δ= 2 h. The closure model is to be chosen such that the solution of the resulting LES-equations is confined to length scales that have at least the size δ. This condition is worked out with the help of Poincarés inequality to determine the amount of dissipation that is to be generated by the closure model in order to counterbalance the nonlinear production of too small, unresolved scales. The procedure is applied to an eddy-viscosity model using a uniform mesh

Preserving Geometry and Topology for Fluid Flows with Thin Obstacles and Narrow Gaps

© ACM, 2016. 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 Azevedo, V. C., Batty, C., & Oliveira, M. M. (2016). Preserving Geometry and Topology for Fluid Flows with Thin Obstacles and Narrow Gaps. Acm Transactions on Graphics, 35(4), 97. https://doi.org/10.1145/2897824.292591Fluid animation methods based on Eulerian grids have long struggled to resolve flows involving narrow gaps and thin solid features. Past approaches have artificially inflated or voxelized boundaries, although this sacrifices the correct geometry and topology of the fluid domain and prevents flow through narrow regions. We present a boundary-respecting fluid simulator that overcomes these challenges. Our solution is to intersect the solid boundary geometry with the cells of a background regular grid to generate a topologically correct, boundary-conforming cut-cell mesh. We extend both pressure projection and velocity advection to support this enhanced grid structure. For pressure projection, we introduce a general graph-based scheme that properly preserves discrete incompressibility even in thin and topologically complex flow regions, while nevertheless yielding symmetric positive definite linear systems. For advection, we exploit polyhedral interpolation to improve the degree to which the flow conforms to irregular and possibly non-convex cell boundaries, and propose a modified PIC/FLIP advection scheme to eliminate the need to inaccurately reinitialize invalid cells that are swept over by moving boundaries. The method naturally extends the standard Eulerian fluid simulation framework, and while we focus on thin boundaries, our contributions are beneficial for volumetric solids as well. Our results demonstrate successful one-way fluid-solid coupling in the presence of thin objects and narrow flow regions even on very coarse grids.Conselho Nacional de Desenvolvimento Científico e Tecnológico, Natural Sciences and Engineering Research Council of Canad

Tools for fluid simulation control in computer graphics

L’animation basée sur la physique peut générer des systèmes aux comportements complexes et réalistes. Malheureusement, contrôler de tels systèmes est une tâche ardue. Dans le cas de la simulation de fluide, le processus de contrôle est particulièrement complexe. Bien que de nombreuses méthodes et outils ont été mis au point pour simuler et faire le rendu de fluides, trop peu de méthodes offrent un contrôle efficace et intuitif sur une simulation de fluide. Étant donné que le coût associé au contrôle vient souvent s’additionner au coût de la simulation, appliquer un contrôle sur une simulation à plus haute résolution rallonge chaque itération du processus de création. Afin d’accélérer ce processus, l’édition peut se faire sur une simulation basse résolution moins coûteuse. Nous pouvons donc considérer que la création d’un fluide contrôlé peut se diviser en deux phases: une phase de contrôle durant laquelle un artiste modifie le comportement d’une simulation basse résolution, et une phase d’augmentation de détail durant laquelle une version haute résolution de cette simulation est générée. Cette thèse présente deux projets, chacun contribuant à l’état de l’art relié à chacune de ces deux phases. Dans un premier temps, on introduit un nouveau système de contrôle de liquide représenté par un modèle particulaire. À l’aide de ce système, un artiste peut sélectionner dans une base de données une parcelle de liquide animé précalculée. Cette parcelle peut ensuite être placée dans une simulation afin d’en modifier son comportement. À chaque pas de simulation, notre système utilise la liste de parcelles actives afin de reproduire localement la vision de l’artiste. Une interface graphique intuitive a été développée, inspirée par les logiciels de montage vidéo, et permettant à un utilisateur non expert de simplement éditer une simulation de liquide. Dans un second temps, une méthode d’augmentation de détail est décrite. Nous proposons d’ajouter une étape supplémentaire de suivi après l’étape de projection du champ de vitesse d’une simulation de fumée eulérienne classique. Durant cette étape, un champ de perturbations de vitesse non-divergent est calculé, résultant en une meilleure correspondance des densités à haute et à basse résolution. L’animation de fumée résultante reproduit fidèlement l’aspect grossier de la simulation d’entrée, tout en étant augmentée à l’aide de détails simulés.Physics-based animation can generate dynamic systems of very complex and realistic behaviors. Unfortunately, controlling them is a daunting task. In particular, fluid simulation brings up particularly difficult problems to the control process. Although many methods and tools have been developed to convincingly simulate and render fluids, too few methods provide efficient and intuitive control over a simulation. Since control often comes with extra computations on top of the simulation cost, art-directing a high-resolution simulation leads to long iterations of the creative process. In order to shorten this process, editing could be performed on a faster, low-resolution model. Therefore, we can consider that the process of generating an art-directed fluid could be split into two stages: a control stage during which an artist modifies the behavior of a low-resolution simulation, and an upresolution stage during which a final high-resolution version of this simulation is driven. This thesis presents two projects, each one improving on the state of the art related to each of these two stages. First, we introduce a new particle-based liquid control system. Using this system, an artist selects patches of precomputed liquid animations from a database, and places them in a simulation to modify its behavior. At each simulation time step, our system uses these entities to control the simulation in order to reproduce the artist’s vision. An intuitive graphical user interface inspired by video editing tools has been developed, allowing a nontechnical user to simply edit a liquid animation. Second, a tracking solution for smoke upresolution is described. We propose to add an extra tracking step after the projection of a classical Eulerian smoke simulation. During this step, we solve for a divergence-free velocity perturbation field resulting in a better matching of the low-frequency density distribution between the low-resolution guide and the high-resolution simulation. The resulting smoke animation faithfully reproduces the coarse aspect of the low-resolution input, while being enhanced with simulated small-scale details

A Study on Combustion/Explosion of Heterogeneous Energetic Materials Using Multiscale and Multi-Material Analysis Method

학위논문 (석사) -- 서울대학교 대학원 : 공과대학 기계항공공학부, 2020. 8. 여재익.반응 유동에서의 충격파-입자 상호작용에 대한 연구는 물질 경계면 처리를 위해 하이브리드 입자 레벨 셋 알고리즘과 함께 오일러리안 유체 역학 방법을 사용하여 수행되었다. 본 연구에서는 열압 효과를 향상시키기 위해 무작위로 분포된 반응성 금속 입자를 포함하는 고에너지 물질의 메조-메크로 스케일 수치 모델링을 다루고 있다. 반응성 유동 모델에서 압력기반 폭굉 해석을 위해 고폭화약으로 RDX, HMX 들을 사용하였으며 온도기반 폭연 모델링을 위해 알루미늄이나 구리 반응성 입자를 사용하였다. 고폭발성 응축된 상태의 고에너지물질에서 충격파로 인한 입자들의 붕괴를 시뮬레이션 하였으며 금속입자가 다량 함유된 RDX는 충격파와 함께 폭발하며 폭발 충격파 뒤의 에너지 방출 및 알루미늄의 후 연소 반응을 수치적으로 모사하였다. 또한, 동일한 조성에서 연속체 모델과 이종모델을 가지고 충격파 전달 폭굉과정에 대해 비교 분석을 진행하였다. 다 물질 및 3차원 시뮬레이션으로의 확장은 복합화약의 반응성 유동에서 입자 열/구조적 거동의 정확한 계산을 가능하게 하였다.An investigation of shock–particle interactions in reactive flows is performed using Eulerian hydrodynamic method with a hybrid particle level-set algorithm to handle the material interface dynamics. The analysis is focused on the meso- to macro-scale numerical modeling of a granular metalized explosive containing randomly distributed metal particles intended to enhance its blast effect. The reactive flow model is used for the cyclotrimethylene-trinitramine (RDX) and 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX) component, while thermally induced deflagration kinetics describes the aerobic reaction of the metal particles. Then, the shock-induced collapse of metal particles embedded in the condensed phase domain of a high explosive is simulated. Both aluminized and copperized RDX are shown to detonate with a shock wave followed by the burning of the metal particles. The energy release and the afterburning behavior behind the detonating shock wave successfully identified the precursor that gave rise to the development of deflagration of the metal particles. In addition, the homogeneous model and the heterogeneous model were compared and analyzed on the mesoscale for the detonation phenomenon with the same composition. The expansion to multi-material and three-dimensional simulation allowed accurate calculation of the thermal/structural behavior of grains in the reactive flow of heterogeneous explosive.제 1 장 서 론 1 제 2 장 하이드로다이나믹 해석 6 2.1 지배 방정식 6 2.2 상태 방정식 10 2.3 연소 반응 모델 13 2.3.1 압력기반 폭굉(Detonation) 화학반응 13 2.3.2 온도기반 폭연(Deflagration) 화학반응 14 2.4 멀티스케일/다물질해석 16 2.4.1 레벨셋(Level set) 기반 다물질 경게면 처리 기법 16 2.4.2 메조스케일(Mesoscale) 시뮬레이션을 위한 초기 조건 17 2.5 하이드로다이나믹 코드 검증 22 2.5.1 Rayleigh bubble collapse 22 2.5.2 충격파 전달 bubble collapse 23 제 3 장 열압탄 메조스케일 반응해석 27 3.1 고에너지물질 내부에서의 알루미늄 입자 연소 27 3.2 무한대 반지름을 가지는 반응막대의 연소해석 29 3.3 유한한 반지름을 가지는 반응막대의 연소해석 33 제 4 장 다물질 고폭화약 수치해석 40 4.1 고폭화약의 연속체 해석과 메조스케일 해석 40 4.1.1 반응막대 시뮬레이션 결과 40 4.1.2 통계적 열/연소 분석 47 4.2 3물질 복합화약 반응막대 해석 52 제 5 장 입자기반 3차원 복합화약의 충격파 전달 폭굉 수치해석 58 5.1 3차원 2물질 복합화약의 충격파 전달 폭굉 시뮬레이션 58 5.2 3차원 3물질 복합화약의 충격파 전달 폭굉 시뮬레이션 60 제 6 장 결 론 63 참고문헌 64 Abstract 68Maste

Numerical simulation of subcontinent lithosphere dynamics: craton stability, evolution and formation

Through geodynamical modelling, two hypotheses about the craton stability and evolution were revisited and an important process of cratonization is investigated. Unlike most previous, related numerical studies, non-Newtonian rheology with composition dependence was used in these studies, and the rheological parameters are thus directly comparable with laboratory experiment of mantle. The first hypothesis, that the cratonic lithosphere is “isopycnic”, is found to be not strictly necessary for craton stability and longevity. The high viscosity of the cratonic litho- sphere due to compositional effects on the mantle rheology is found to be essential to maintain a thickness difference between cratonic and non-cratonic lithosphere for over billions of years and it allows a modest negative buoyancy of the cratonic root, depending on the strengthening factor due to the compositional effects. The second hypothesis to be tested is that mantle plume im- pingements cause rapid, significant removal of subcontinental lithosphere. The results presented in this thesis show that the erosion caused by a plume impact on a continent that is strong enough to have survived billions of years of Earth’s history is rather limited. A special weaken- ing mechanism of such highly viscous and buoyant roots is required to reactivate this cratonic lithosphere and thus cause significant thinning within 10s of Myrs. The fluid/melt-rock interac- tion during mantle metasomatism is probably the most likely mechanism to modify and weaken depleted cratonic lithosphere. Therefore, metasomatic weakening is essential for the significant thinning of subcontinental lithosphere observed, e.g.at North China Craton and Namibia, south- ern African, no matter whether caused by a plume impact or another tectonic event. Using the reasonable compositional effects on the buoyancy and rheology of mantle rocks from the above studies, numerical experiments are performed to study the formation of thick cratonic lithosphere from a layered, depleted mantle material. In this scenario, substantial tec- tonic shortening and thickening of previously depleted material seems to be an essential ingre- dient to initiate the cratonization process. Afterwards, gravitational self-thickening will cause further thickening. Compositional buoyancy resists Rayleigh-Taylor instability collapse and stabilizes the thick cratonic root, while the secular cooling also has a stabilizing effect on the cratonic root by reducing the thermal buoyancy contrast between lithosphere and asthenosphere and increasing mantle viscosity. The presented numerical results are consistent with the vertical movement of cratonic peridotite as suggested on petrological grounds

Interactive Three-Dimensional Simulation and Visualisation of Real Time Blood Flow in Vascular Networks

One of the challenges in cardiovascular disease management is the clinical decision-making process. When a clinician is dealing with complex and uncertain situations, the decision on whether or how to intervene is made based upon distinct information from diverse sources. There are several variables that can affect how the vascular system responds to treatment. These include: the extent of the damage and scarring, the efficiency of blood flow remodelling, and any associated pathology. Moreover, the effect of an intervention may lead to further unforeseen complications (e.g. another stenosis may be “hidden” further along the vessel). Currently, there is no tool for predicting or exploring such scenarios. This thesis explores the development of a highly adaptive real-time simulation of blood flow that considers patient specific data and clinician interaction. The simulation should model blood realistically, accurately, and through complex vascular networks in real-time. Developing robust flow scenarios that can be incorporated into the decision and planning medical tool set. The focus will be on specific regions of the anatomy, where accuracy is of the utmost importance and the flow can develop into specific patterns, with the aim of better understanding their condition and predicting factors of their future evolution. Results from the validation of the simulation showed promising comparisons with the literature and demonstrated a viability for clinical use