Adaptive Smoothed Particle Hydrodynamics Research Articles

Investigation of explosive welding through whole process modeling using a density adaptive SPH method

Explosive welding (EXW) involves processes like the detonation of explosive charge, impact of metal structures and strong fluid-structure interaction with complex features such as interfacial waves and jet generation. The whole EXW process has not been well modeled before due to the large deformation and moving interfaces while the associated mechanisms inherent in EXW are also not well understood. In this paper, the whole EXW process is simulated using a density adaptive smoothed particle hydrodynamics (SPH) model, in which a density adaptive algorithm is used to treat variable large density ratio in EXW and the kernel gradient correction (KGC) is used to improve computational accuracy of SPH. The mechanisms in EXW are investigated, and typical phenomena including the wavy interface, jet formation, interfacial temperature and pressure distribution as well as melting voids are examined. The mechanisms of wave formation are studied while two existing mechanisms, namely, the Jet Indentation Mechanism and the Vortex Shedding Mechanism are revealed with the present SPH simulations. It is demonstrated that with proper amount of explosive charge and initial welding angle, the present SPH method can well reproduce the morphology evolution of the welding interface from straight to wavy and further to wavy with vortex shedding. Furthermore, based on comprehensive numerical data from SPH simulations, two types of numerical weldability windows for EXW are presented together with discussions about different welding limits and effective explosive charge.

Visualization of fluid simulation: An SPH‐based multi‐resolution method

SummaryFluid simulation is an important research topic since it is widely used in virtual training, education, computer games, and digital entertainment. Generating fluid simulation results with high degree of visual realism is challenging in these applications. We present a visualization approach for fluid simulation in this paper. Our method allows students to understand the complex natural phenomena so as to solve the fluid engineering problems intuitively. In this study, an SPH (Smoothed Particle Hydrodynamics)‐based multi‐resolution method is proposed for fluid simulation. The method can keep the accuracy while improve the efficiency significantly. We construct a multi‐resolution fluid model from bottom to top by combining fluid computation and surface reconstruction. We first compute multi‐resolution particles with a novel adaptive SPH model in the bottom layer. Next, surface particles are extracted and pre‐processed to provide samples for surface extraction. Then, the multi‐resolution surface reconstruction model is built in the top layer. Meshes from different reconstruction resolutions are merged to obtain the final fluid surface. Experimental results show that our approach can effectively represent multi‐scale fluid details and efficiently produce visual‐pleasing fluid simulation results.

Pore-scale flow simulation in anisotropic porous material via fluid-structure coupling

This paper describes a novel hybrid method for fluid simulation of saturating anisotropic porous material via fluid-structure coupling. Our framework employs particle finite element method (PFEM) that not only adopts Lagrangian scheme to model the motion of freely-moving particles, but also produces the extended Delaunay Tessellation to furnish the governing equations with FEM discretization. We first employ adaptive smoothed particle hydrodynamics (SPH) to simulate porous flow respecting the anisotropic permeability with little cost. Second, the extended Delaunay Tessellation is obtained to solve differential equations for skeletal deformation. Third, a hybrid particle system is adopted to track the surface and topological changes. At the physical level, we introduce dynamic permeability considering skeletal deformation via fluid-structure coupling. At the geometric level, PFEM reduces the computational cost and effectively tracks topological changes. Moreover, our implementation on CUDA improves the performance in high-quality physics-based graphics applications. Consequently, the proposed method realistically reproduces interactions between pore-scale flow and anisotropic porous material.

Infinite continuous adaptivity for incompressible SPH

In this paper we introduce a novel method to adaptive incompressible SPH simulations. Instead of using a scheme with a number of fixed particle sizes or levels, our approach allows continuous particle sizes. This enables us to define optimal particle masses with respect to, e.g., the distance to the fluid's surface. A required change in mass due to the dynamics of the fluid is properly and stably handled by our scheme of mass redistribution. This includes temporally smooth changes in particle masses as well as sudden mass variations in regions of high flow dynamics. Our approach guarantees low spatial variations in particle size, which is a core property in order to achieve large adaptivity ratios for incompressible fluid simulations. Conceptually, our approach allows for infinite continuous adaptivity, practically we achieved adaptivity ratios up to 5 orders of magnitude, while still being mass preserving and numerically stable, yielding unprecedented vivid surface detail at comparably low computational cost and moderate particle counts.

Modelling and Simulation of Cratering and Ejecta Production During High Velocity Impacts

During an impact event from a high velocity particle (moving at speeds of around 100 m/s or greater) a significant amount of ejecta can be formed and thrown away from the impact point at velocities on the same order as the original impactor. The amount, size distribution, and speed distribution of this ejecta vary with the impact conditions. Predicting this cratering and ejecta phenomena has applications to many areas, including solar system formation, asteroid defense considerations, and micrometeorite impacts on satellites. This paper will look at the physics and modeling of these impacts and the subsequent ejecta formation from these hypervelocity particles. Impacts are modeled using adaptive smooth particle hydrodynamics, and crater volume and ejecta characteristics are quantified and presented. Good agreement with two experimental test cases is obtained.

A Numerical Study on the Pull-Out Strengths of Anchor Bolts Embedded in Concrete Using the Smoothed Particle Hydrodynamics Method

The strength of an anchor bolt in concrete structure under pull-out load is usually designed by three possible failure modes such as fracture of anchor bolt, cone failure of concrete and bond failure between anchor bolt and concrete. In general, the design load is considered the smallest load corresponding to the aforementioned failure mechanisms. However, unexpected failure often occurs in the anchorage zone due to the complex failure or the change of failure condition. Therefore, it is important to develop the accurate analysis method of ultimate load bearing capacity of the anchor bolt. In this study, we conducted an analytical study using Adaptive Smoothed Particle Hydrodynamics (ASPH) in order to simulate the failure process of anchorage zone and discussed the effect of embedment depth of anchor bolts on their ultimate strength.

Deflection by kinetic impact: Sensitivity to asteroid properties

Impacting an asteroid with a spacecraft traveling at high speed delivers an impulsive change in velocity to the body. In certain circumstances, this strategy could be used to deflect a hazardous asteroid, moving its orbital path off of an Earth-impacting course. However, the efficacy of momentum delivery to asteroids by hypervelocity impact is sensitive to both the impact conditions (particularly velocity) and specific characteristics of the target asteroid. Here we numerically model asteroid response to kinetic impactors under a wide range of initial conditions, using an Adaptive Smoothed Particle Hydrodynamics code. Impact velocities spanning 1–30 km/s were investigated, yielding, for a particular set of assumptions about the modeled target material, a power-law dependence consistent with a velocity-scaling exponent of μ = 0.44. Target characteristics including equation of state, strength model, porosity, rotational state, and shape were varied, and corresponding changes in asteroid response were documented. The kinetic-impact momentum-multiplication factor, β, decreases with increasing asteroid cohesion and increasing porosity. Although increased porosity lowers β, larger porosities result in greater deflection velocities, as a consequence of reduced target masses for asteroids of fixed size. Porosity also lowers disruption risk for kinetic impacts near the threshold of disruption. Including fast (P = 2.5 h) and very fast (P = 100 s) rotation did not significantly alter β but did affect the risk of disruption by the impact event. Asteroid shape is found to influence the efficiency of momentum delivery, as local slope conditions can change the orientation of the crater ejecta momentum vector. These results emphasize the need for asteroid characterization studies to bracket the range of target conditions expected at near-Earth asteroids while also highlighting some of the principal uncertainties associated with the kinetic-impact deflection strategy.

Novel adaptive SPH with geometric subdivision for brittle fracture animation of anisotropic materials

In this paper, we articulate a novel particle-centric method to simulate the dynamics of brittle fracture for anisotropic materials. The key motivation of this paper is to develop a new hybrid, particle-based simulation that inherits advantages from both powerful finite element methods and popular mesh-free methods, while overcoming certain disadvantages of both types of methods. Our method stems from two novel aspects: (1) a physical model built upon an improved mechanical framework and the adaptive smoothed particle hydrodynamics (SPH), an improved variant of traditional SPH, which can handle complicated anisotropic elastic behaviors with little extra cost; and (2) a hybrid, adaptive particle system that serves for more accurate fracture modeling with richer details. At the physical level, in order to facilitate better control during the formation of fracture and improve its time performance, we develop a physical framework based on contact mechanics and adopt the stress and energy analysis on the anisotropic SPH numerical integration to pinpoint fracture generation and propagation. At the geometric level, in order to reduce time consumption and enhance accuracy in rigid dynamics and fracture generation, we employ hybrid, fully adaptive particles in the vicinity of fracture regions via geometric subdivision. Our novel approach can facilitate the user to control the generation of cracks with low computational cost and retain high-fidelity crack details during animation. Our comprehensive experiments demonstrate the controllability, effectiveness, and accuracy of our method when simulating various brittle fracture patterns for anisotropic materials.

Asteroid Diversion Considerations and Comparisons of Diversion Techniques

The threat of asteroid impacts on Earth poses a low-probability but high consequence risk, with possible outcomes ranging from regional to global catastrophe. However, unique amongst such global threats we have the capability of averting such disasters. Diversion approaches by either kinetic impactor or nuclear energy deposition are the two most practical technologies for mitigating hazardous near Earth asteroids. One of the greatest challenges in understanding our options is the uncertain response of asteroids to such impulsive techniques, due both to our lack of knowledge of the composition and structure of these objects as well as their highly varied nature. Predicting whether we will simply divert or break up a given object is a crucial: the weak self-gravity and inferred weak structure of typical asteroids present the strong possibility the body will fragment for modest impulses. Predictive modeling of failure and fragmentation is one important tool for such studies. In this paper we apply advances in modeling failure and fracture using Adaptive Smoothed Particle Hydrodynamics (ASPH) to understand mega-cratering on asteroids as a validation exercise, and show examples of diverting the near Earth asteroid Bennu using both a kinetic impactor and ablative blow-off due to nuclear energy deposition.

The effect of recombination radiation on the temperature and ionization state of partially ionized gas

A substantial fraction of all ionizing photons originate from radiative recombinations. However, in radiative transfer calculations this recombination radiation is often assumed to be absorbed ‘on-the-spot’ because for most methods the computational cost associated with the inclusion of gas elements as sources is prohibitive. We present a new, CPU and memory efficient implementation for the transport of ionizing recombination radiation in the traphic radiative transfer scheme. traphic solves the radiative transfer equation by tracing photon packets at the speed of light and in a photon-conserving manner in spatially adaptive smoothed particle hydrodynamics simulations. Our new implementation uses existing features of the traphic scheme to add recombination radiation at no additional cost in the limit in which the fraction of the simulation box filled with radiation approaches 1. We test the implementation by simulating an H ii region in photoionization equilibrium and comparing to reference solutions presented in the literature, finding excellent agreement. We apply our implementation to discuss the evolution of the H ii region to equilibrium. We show that the widely used case A and B approximations yield accurate ionization profiles only near the source and near the ionization front, respectively. We also discuss the impact of recombination radiation on the geometry of shadows behind optically thick absorbers. We demonstrate that the shadow region may be completely ionized by the diffuse recombination radiation field and discuss the important role of heating by recombination radiation in the shadow region.

Temporal Blending for Adaptive SPH

AbstractIn this paper, we introduce a fast and consistent smoothed particle hydrodynamics (SPH) technique which is suitable for convection–diffusion simulations of incompressible fluids. We apply our temporal blending technique to reduce the number of particles in the simulation while smoothly changing quantity fields. Our approach greatly reduces the error introduced in the pressure term when changing particle configurations. Compared to other methods, this enables larger integration time‐steps in the transition phase. Our implementation is fully GPU‐based to take advantage of the parallel nature of particle simulations.

An approach to solving the boundary free edge difficulties in SPH modelling: application to a viscous accretion disc in close binaries

In this work, we propose a SPH interpolating Kernel reformulation suitable also to treat free edge boundaries in the computational domain. Application to both inviscid and viscous stationary low compressibility accretion disc models in Close Binaries (CB) are shown. The investigation carried out in this paper is a consequence of the fact that a low compressibility modelling is crucial to check numerical reliability. Results show that physical viscosity supports a well-bound accretion disc formation, despite the low gas compressibility, when a Gaussian-derived Kernel (from the Error Function) is assumed, in extended particle range - whose Half Width at Half Maximum (HWHM) is fixed to a constant $h$ value - without any spatial restrictions on its radial interaction (hereinafter GASPHER). At the same time, GASPHER ensures adequate particle interpolations at the boundary free edges. Both SPH and adaptive SPH (hereinafter ASPH) methods lack accuracy if there are not constraints on the boundary conditions, in particular at the edge of the particle envelope: Free Edge (FE) conditions. In SPH, an inefficient particle interpolation involves a few neighbour particles; instead, in the second case, non-physical effects involve both the boundary layer particles themselves and the radial transport. Either in a regime where FE conditions involve the computational domain, or in a viscous fluid dynamics, or both, a GASPHER scheme can be rightly adopted in such troublesome physical regimes. Despite the applied low compressibiity condition, viscous GASPHER model shows clear spiral pattern profiles demonstrating the better quality of results compared to SPH viscous ones. Moreover a successful comparison of results concerning GASPHER 1D inviscid shock tube with analytical solution is also reported.

Convergence of SPH and AMR simulations

AbstractWe present the first results of a large suite of convergence tests between Adaptive Mesh Refinement (AMR) Finite Difference Hydrodynamics and Smoothed Particle Hydrodynamics (SPH) simulations of the non-linear thin shell instability and the Kelvin-Helmholtz instability. We find that the two methods converge in the limit of high resolution and accuracy. AMR and SPH simulations of the non-linear thin shell instability converge with each other with standard algorithms and parameters. The Kelvin-Helmholtz instability in SPH requires both an artificial conductivity term and a kernel with larger compact support and more neighbours (e.g. the quintic kernel) in order converge with AMR. For purely hydrodynamical problems, SPH simulations take an order of magnitude longer than the grid code when converged.

Real-time adaptive fluid simulation with complex boundaries

In this paper, we present a new adaptive model for real-time fluid simulation with complex boundaries based on Smoothed Particle Hydrodynamics (SPH) framework. Firstly, we introduce an adaptive SPH framework that is based on our character field function composed of four factors: geometrical complexity, boundary condition, physical complexity, and complementary condition in terms of the neighboring particle number. Meanwhile, the rule for particle adaptation is presented. We also present a two-step method to fast detect collision with complex boundary. The first step is voxelization on the complex scene. In the second step, based on the result of voxelization, we propose a three-phase method to fast detect collisions between complex boundaries and particles. By using this method, we avoid most of the useless intersection detection computation and greatly enhance the computation efficiency. In addition, a subdivision of boundary is precomputed before the collision interaction method so that fluid in a scene with complex boundary can still be simulated at relatively high speed and system stability risk is reduced greatly. To further accelerate the simulation, a highly parallel fluid algorithm is presented and implemented using GPU so that we can simulate dynamic fluid with mutual interaction between fluid and complex boundary at a considerably fast speed without compromising realism.

An adaptive SPH method for strong shocks

We propose an alternative SPH scheme to usual SPH Godunov-type methods for simulating supersonic compressible flows with sharp discontinuities. The method relies on an adaptive density kernel estimation (ADKE) algorithm, which allows the width of the kernel interpolant to vary locally in space and time so that the minimum necessary smoothing is applied in regions of low density. We have performed a von Neumann stability analysis of the SPH equations for an ideal gas and derived the corresponding dispersion relation in terms of the local width of the kernel. Solution of the dispersion relation in the short wavelength limit shows that stability is achieved for a wide range of the ADKE parameters. Application of the method to high Mach number shocks confirms the predictions of the linear analysis. Examples of the resolving power of the method are given for a set of difficult problems, involving the collision of two strong shocks, the strong shock-tube test, and the interaction of two blast waves.

Real‐time fluid simulation with adaptive SPH

AbstractWe present a new adaptive model for real‐time fluid simulation based on Smoothed Particle Hydrodynamics (SPH) framework. Unlike traditional time‐consuming SPH methods, our model can simulate fluid at a considerably faster speed without losing realism. In our model, we first introduce the non‐uniform particle system and propose a generalized distance field function which considers not only geometrical complexity but also physical complexity of fluid body. And the new sampling rules for splitting and merging of particles are also presented. This can greatly reduce the computation time of the dynamic fluid simulation. Then, a new pressure state equation and an adaptive surface tension model are proposed to enhance the stability of the system and to make the free surface more realistic. To further accelerate the computation, a special fluid solver is designed and implemented using GPU. Various fluid phenomena like breaking wave and flood are simulated at real‐time. Experiments demonstrate that our new adaptive model can greatly enhance the computation efficiency of fluid simulation compared with previous adaptive methods. Copyright © 2009 John Wiley & Sons, Ltd.

Adaptive smoothed particle hydrodynamics for high strain hydrodynamics with material strength

This paper presents the implementation of an adaptive smoothed particle hydrodynamics (ASPH) method for high strain Lagrangian hydrodynamics with material strength. In ASPH, the isotropic kernel in the standard SPH is replaced with an anisotropic kernel whose axes evolve automatically to follow the mean particle spacing as it varies in time, space, and direction around each particle. Except for the features inherited from the standard SPH, ASPH can capture dimension-dependent features such as anisotropic deformations with a more generalized elliptical or ellipsoidal influence domain. Two numerical examples, the impact of a plate against a rigid surface and the penetration of a cylinder through a plate, are investigated using both SPH and ASPH. The comparative studies show that ASPH has better accuracy than the standard SPH when being used for high strain hydrodynamic problems with inherent anisotropic deformations.

Meshfree particle simulation of micro channel flows with surface tension

This paper presents a study of micro channel flows using a meshfree particle approach. The approach is based on smoothed particle hydrodynamics (SPH) and its variant, adaptive smoothed particle hydrodynamics (ASPH). The incompressible flow in the micro channels is modeled as an artificially compressible flow. The surface tension is incorporated into the equations of motion. The classic Poiseuille flow and a practical micro channel flow problem of flip-chip underfill encapsulation process are investigated. It is found that the adaptive kernel can well match the computational geometry with long channels and can greatly save computational time. The simulation results are in close agreement with the analytical solutions.

Cosmological Simulations with Adaptive Smoothed Particle Hydrodynamics

We summarize the ideas that led to the Adaptive Smoothed Particle Hydrodynamics (ASPH) algorithm, with anisotropic smoothing and shock-tracking. We then identify a serious new problem for SPH simulations with shocks and radiative cooling — false cooling — and discuss a possible solution based on the shock-tracking ability of ASPH.

Adaptive Smoothed Particle Hydrodynamics, with Application to Cosmology: Methodology

Adaptive Smoothed Particle Hydrodynamics, with Application to Cosmology: Methodology