Adaptive Smoothed Particle Hydrodynamics Research Articles

Study on Water Entry of a 3D Torpedo Based on the Improved Smoothed Particle Hydrodynamics Method

The water entry of a torpedo is a complex nonlinear problem, involving transient impact, free surface deformation, droplet splashing, and fluid–structure coupling, which poses severe challenges to traditional mesh methods. The meshless smoothed particle hydrodynamics (SPH) method shows unique advantages in capturing the complex features of the water entry of the torpedo at different entry angles. However, it still suffers from some inherent shortcomings, such as low surface discretization accuracy, poor discretization flexibility, and low calculation efficiency. In this study, an improved adaptive SPH algorithm is proposed to investigate the water entry of the torpedo accurately and efficiently. This method integrates meshless point generation and adaptive techniques simultaneously. The numerical results demonstrate that when the torpedo vertically enters the water at different velocities, the induced impact loads acting on the head of the torpedo fluctuate significantly with two peak values in the initial stage and thereafter stabilize in a later stage. The impact load acting on the torpedo, the entry depth of the torpedo, the splash height of the droplets, and the size of the cavity generated around the torpedo increase with the increment in the entry velocity. When the torpedo enters the water at different entry angles under the same initial entry velocity, both the vertical and the horizontal movements of the torpedo are observed, which results in more complex variations in parameters along the x- and y-axes. The findings and the corresponding numerical method in this study can provide a certain basis for the future designs of the entry trajectory and the structural bearing capacity of torpedoes.

Research on space-based kinetic impactor disrupting small-sized asteroids under short warning time conditions

Near Earth asteroids with diameters less than 50 m possess distinct characteristics including a large population, a high likelihood of Earth impact, and limited warning time. While small asteroid impacts may not induce global disasters, they can still result in localized hazard. This study focuses on investigating the feasibility and strategies for disrupting small-sized asteroid structures through kinetic impact under short-term warning scenarios. Initially, a dataset comprising ten asteroids ranging from 20 m to 50 m in diameter is compiled by correcting their orbital parameters to simulate potential impacts on Earth. Subsequently, a space-based interception constellation is designed and deployed at the L3, L4, and L5 points of the Cislunar space. The study further examines the trajectory design methodology for achieving rapid interception of asteroids, enabling timely response within a warning period of 7 to 14 days. Additionally, the paper discusses the feasibility of impactors in disrupting asteroids through analytical models and Adaptive Smoothed Particle Hydrodynamics (ASPH) numerical simulation method. Lastly, the defense capability of the space-based interception constellation against Earth-impacting asteroids approaching from various directions is assessed. The simulations show that C and S-type asteroids below 40 m can be effectively fragmented using an impactor with an initial mass of 2 tons within the specified 7 to 14-day warning time. Furthermore, the deployment of impactors at L3, L4, and L5 allows for comprehensive coverage of asteroids approaching from diverse directions.

An adaptive multi-resolution SPH approach for three-dimensional free-surface flow with fluid impacting

This paper presents a new adaptive multi-resolution smoothed particle hydrodynamics (SPH) approach for simulating three-dimensional free surface flows with fluid impacting. The governing equations for multi-resolution SPH are derived based on the finite particle method (FPM) particle interpolation, which is an alternative SPH formulation for improving interpolation accuracy in the non-uniform particle distribution. A variable kernel length related to the volume of neighbor particles is proposed to control the numerical instability due to the multi-resolution scheme. In adaptive particle refinement (APR), a concept named as continuously-variable characteristic length (CCL) for each particle is defined to determine the splitting or merging scheme and then build a smoothing non-uniform particle distribution. Three-dimensional examples are conducted to validate the presented new APR approach, and the capability and numerical efficiency of the proposed numerical model are verified through solving free-surface flow problems with middle and low Weber numbers. After validation, a refined simulation of droplet impacting is conducted using the proposed adaptive multi-resolution SPH approach. The results show that the proposed SPH could well adapt to the large deformation of three-dimensional free-surface flow, and only provide a refinement near the free-surface domain.

An adaptive smoothed particle hydrodynamics (SPH) scheme for efficient melt pool simulations in additive manufacturing

An adaptive smoothed particle hydrodynamics (SPH) scheme for efficient melt pool simulations in additive manufacturing

Simulating hypervelocity impacts into rubble pile structures for planetary defense

Kinetic impactors are one of the most mature technologies for planetary defense and this technique was tested for the first time by NASA's Double Asteroid Redirection Test (DART) mission. The material and physical properties of the asteroid are very important in understanding the efficacy of a kinetic impactor. To constrain how the local topography of an impactor alters the response to the hypervelocity impact of a kinetic impactor, we used the adaptive smoothed particle hydrodynamics code, Spheral++, to impact plates into a rubble pile asteroid. By varying both the impact location and the strength between the boulders and regolith of the formed asteroid, we find that variations in the rubble pile contributes approximately 10% uncertainty to the resulting momentum enhancement in regolith dominated impacts. We further demonstrate that the craters produced from the impacts into the rubble pile are wide, shallow, and show deviations from symmetry due to the presence of boulders on the surface near the impact site. These simulations help us constrain the potential outcomes that may occur from a hypervelocity kinetic impact in a planetary defense scenario.

Simulation of van der Waals liquid droplets within a hot air atmosphere using the smoothed particle hydrodynamics method

The mass and heat transfer of van der Waals liquid droplets within a hot air atmosphere in microgravity have been studied using adaptive Smoothed Particle Hydrodynamics by assuming that the gas atmosphere is in contact with a thermal reservoir for a single-component two-dimensional system. A better definition of the diffuse interface between the phases was obtained through the introduction of a Korteweg tensor. As in previous works, the best initial particle distribution was obtained using the process of spinodal decomposition. The temperature obtained from the van der Waals cycle was compared with the temperature that arises from the integration of the conservation laws that contain the heat-flux vector. The calculated temperature profiles are the same for both the liquid and gas phases. The interface satisfies the condition of coexistence between the phases. In addition, the mass and heat transfer rates as well as the decrease of the drop radius were obtained for the three temperatures studied, finding that these are enhanced as the temperature of the reservoir is increased. Finally, it was possible to observe a damped oscillatory behavior of the temperature between the liquid phase and the interface for the first instants of time. We conclude that this is the mechanism by which the areas with lower temperature within the drop are heated before starting the mass transfer between the liquid and the gas phase.

Development of time-space adaptive SPH for large deformation and impact

<p indent="0mm">A spatially adaptive smoothed particle hydrodynamics (ASPH) method, where the particles can split and merge according to the adaptive criteria, was developed to improve the computational efficiency of the classical smoothed particle hydrodynamics (SPH) method. Recently, the ASPH algorithm has been widely applied to solve complex problems in mechanics. However, the splitting pattern in the current ASPH algorithm may lead to particle disorder when simulating large deformation and impact problems, and a smaller time step should be performed after particle splitting. An adaptive splitting pattern that is based on a relative position vector and velocity interpolation is introduced in this study. Subsequently, this numerical method is combined with the Runge-Kutta Chebyshev method to achieve adaptive time integration. Thus, the time-space adaptive smoothed particle hydrodynamics method (T-S ASPH) is proposed in this study. This algorithm can increase the computational accuracy by eliminating the particle disorder when simulating the large deformation and impact problems while improving the computational efficiency and time integration accuracy. Typical examples are simulated by the classical SPH, current ASPH and developed T-S ASPH methods. The results indicate that, compared with the other two methods, the proposed T-S ASPH method exhibits higher accuracy, efficiency, stability, and order of convergence for the large deformation and impact problems.

Loki

We introduce Loki, a new framework for robust simulation of fluid, rigid, and deformable objects with non-compromising fidelity on any single element, and capabilities for coupling and representation transitions across multiple elements. Loki adapts multiple best-in-class solvers into a unified framework driven by a declarative state machine where users declare 'what' is simulated but not 'when,' so an automatic scheduling system takes care of mixing any combination of objects. This leads to intuitive setups for coupled simulations such as hair in the wind or objects transitioning from one representation to another, for example bulk water FLIP particles to SPH spray particles to volumetric mist. We also provide a consistent treatment for components used in several domains, such as unified collision and attachment constraints across 1D, 2D, 3D deforming and rigid objects. Distribution over MPI, custom linear equation solvers, and aggressive application of sparse techniques keep performance within production requirements. We demonstrate a variety of solvers within the framework and their interactions, including FLIPstyle liquids, spatially adaptive volumetric fluids, SPH, MPM, and mesh-based solids, including but not limited to discrete elastic rods, elastons, and FEM with state-of-the-art constitutive models. Our framework has proven powerful and intuitive enough for voluntary artist adoption and has delivered creature and FX simulations for multiple major movie productions in the preceding four years.

Parallel adaptive weakly-compressible SPH for complex moving geometries

The use of adaptive spatial resolution to simulate flows of practical interest using Smoothed Particle Hydrodynamics (SPH) is of considerable importance. Recently, Muta and Ramachandran [1] have proposed an efficient adaptive SPH method which is capable of handling large changes in particle resolution. This allows the authors to simulate problems with much fewer particles than was possible earlier. The method was not demonstrated or tested with moving bodies or multiple bodies. In addition, the original method employed a large number of background particles to determine the spatial resolution of the fluid particles. In the present work we establish the formulation's effectiveness for simulating flow around stationary and moving geometries. We eliminate the need for the background particles in order to specify the geometry-based or solution-based adaptivity and we discuss the algorithms employed in detail. We consider a variety of benchmark problems, including the flow past two stationary cylinders, flow past different NACA airfoils at a range of Reynolds numbers, a moving square at various Reynolds numbers, and the flow past an oscillating cylinder. We also demonstrate different types of motions using single and multiple bodies. The source code is made available under an open source license, and our results are reproducible. Program summaryProgram Title: Parallel adaptive EDAC-SPHCPC Library link to program files:https://doi.org/10.17632/62rhbb9p4t.1Developer's repository link:https://gitlab.com/pypr/asph_motion.Code Ocean capsule:https://codeocean.com/capsule/4785489Licensing provisions: BSD 3-clauseProgramming language: PythonExternal routines/libraries:: PySPH (https://github.com/pypr/pysph), matplotlib (https://pypi.org/project/matplotlib/), NumPy (https://pypi.org/project/numpy/), automan (https://pypi.org/project/automan/), compyle (https://pypi.org/project/compyle/).Nature of problem: Simulating fluid flow around multiple moving bodies requires the local resolution to be automatically adapted in order to capture all the necessary flow features. If a single resolution is used throughout the domain, the number of particles would be excessively large.Solution method: We validate and demonstrate the accuracy of the adaptive particle refinement algorithm in simulating flow past moving multiple geometries. Our algorithm is fully parallel, and we provide an open-source implementation.

Adaptive smoothing length method based on weighted average of neighboring particle density for SPH fluid simulation

BackgroundIn the smoothed particle hydrodynamics (SPH) fluid simulation method, thesmoothing length affects not only the process of neighbor search but also the calculation accuracy of the pressure solver. Therefore, it plays a crucial role in ensuring the accuracy and stability of SPH. MethodsIn this study, an adaptive SPH fluid simulation method with a variable smoothing length is designed. In this method, the smoothing length is adaptively adjusted according to the ratio of the particle density to the weighted average of the density of the neighboring particles. Additionally, a neighbor search scheme and kernel function scheme are designed to solve the asymmetry problems caused by the variable smoothing length. ResultsThe simulation efficiency of the proposed algorithm is comparable to that of some classical methods, and the variance of the number of neighboring particles is reduced. Thus, the visual effect is more similar to the corresponding physical reality. ConclusionsThe precision of the interpolation calculation performed in the SPH algorithm is improved using the adaptive-smoothing length scheme; thus, the stability of the algorithm is enhanced, and a larger timestep is possible.

Development of time-space adaptive smoothed particle hydrodynamics method with Runge-Kutta Chebyshev scheme

Smoothed particle hydrodynamics (SPH) method is a Lagrangian particle method that has been widely used for solving complex mechanics problems. To reduce the SPH computational cost, the adaptive SPH (ASPH) with time-varying particle distribution has been proposed using the particle splitting and merging techniques. However, the particle splitting in the adaptive SPH results in a decreased time step due to the reduced particle spacing and thus requires an increased amount of computing time. In the present work, an explicit Runge-Kutta Chebyshev time stepping scheme is implemented within the adaptive SPH, by including the stabilizing substeps into the Runge-Kutta integration method with the use of the Chebyshev polynomials. The number of stabilizing substeps in a single SPH time step can be adaptive after particle splitting while the Runge-Kutta integration time step remains the same. Therefore, the proposed SPH algorithm is adaptive in both time and space domains. Representative example problems are simulated using the developed time-space adaptive SPH method. It is demonstrated that, as compared to the standard SPH and the conventional adaptive SPH with varying particle distribution only, the presented time-space ASPH method exhibits much higher efficiency without compromising accuracy and the superiority in terms of stability.

Optimized Refinement for Spatially Adaptive SPH

In this article, we propose an improved refinement process for the simulation of incompressible low-viscosity turbulent flows using Smoothed Particle Hydrodynamics, under adaptive volume ratios of up to 1 : 1, 000, 000. We derive a discretized objective function, which allows us to generate ideal refinement patterns for any kernel function and any number of particles a priori without requiring intuitive initial user-input. We also demonstrate how this objective function can be optimized online to further improve the refinement process during simulations by utilizing a gradient descent and a modified evolutionary optimization. Our investigation reveals an inherent residual refinement error term, which we smooth out using improved and novel methods. Our improved adaptive method is able to simulate adaptive volume ratios of 1 : 1, 000, 000 and higher, even under highly turbulent flows, only being limited by memory consumption. In general, we achieve more than an order of magnitude greater adaptive volume ratios than prior work.

Adaptive Smoothed Particle Hydrodynamics for Study of Friction of Silica at Micronscale

Adaptive Smoothed Particle Hydrodynamics for Study of Friction of Silica at Micronscale

Numerical Simulations of Laboratory‐Scale, Hypervelocity‐Impact Experiments for Asteroid‐Deflection Code Validation

AbstractAsteroids and comets have the potential to impact Earth and cause damage at the local to global scale. Deflection or disruption of a potentially hazardous object could prevent future Earth impacts, but due to our limited ability to perform experiments directly on asteroids, our understanding of the process relies upon large‐scale hydrodynamic simulations. Related simulations must be vetted through code validation by benchmarking against relevant laboratory‐scale, hypervelocity‐impact experiments. To this end, we compare simulation results from Spheral, an adaptive smoothed particle hydrodynamics code, to the fragment‐mass and velocity data from the 1991 two‐stage light gas‐gun impact experiment on a basalt sphere target, conducted at Kyoto University by Nakamura and Fujiwara. We find that the simulations are sensitive to the selected strain models, strength models, and material parameters. We find that, by using appropriate choices for these models in conjunction with well‐constrained material parameters, the simulations closely resemble with the experimental results. Numerical codes implementing these model and parameter selections may provide new insight into the formation of asteroid families (Michel et al., 2015, https://doi.org/10.2458/azu_uapress_9780816532131‐ch018) and predictions of deflection for the Double Asteroid Redirection mission (Stickle et al., 2017, https://doi.org/10.1016/j.proeng.2017.09.763).

Numerical Methods for Simulating Star Formation

We review the numerical techniques for ideal and non-ideal magneto-hydrodynamics (MHD) used in the context of star formation simulations. We outline the specific challenges offered by modelling star forming environments, which are dominated by supersonic turbulence in a radiative, self-gravitating fluid. These conditions are rather unique in physics and engineering and pose particularly severe restrictions on the robustness and accuracy of numerical codes. One striking aspect is the formation of collapsing fluid elements leading to the formation of singularities that represent point-like objects, namely the proto-stars. Although a few studies have attempted to resolve the formation of the first and second Larson's cores, resolution limitations force us to use sink particle techniques, with sub-grid models to compute the accretion rates of mass, momentum and energy, as well as their ejection rate due to radiation and jets from the proto-stars. We discuss the most popular discretisation techniques used in the community, namely smoothed particle hydrodynamics, finite difference and finite volume methods, stressing the importance to maintain a divergence free magnetic field. We discuss how to estimate the truncation error of a given numerical scheme, and its importance in setting the magnitude of the numerical diffusion. This can have a strong impact on the outcome of these simulations, where viscosity and resistivity are implemented at the grid scale. We then present various numerical techniques to model non-ideal MHD effects (Ohmic and ambipolar diffusion, and Hall effect). These physical ingredients are posing strong challenges in term of resolution and time stepping. For the latter, several strategies are discussed to overcome the limitations due to ridiculously small time steps. An important aspect of star formation simulations is the radiation field. We discuss the current state-of-the-art, with a variety of techniques offering pros and cons in different conditions. Finally, we present more advanced strategies to mitigate the adverse effect of finite numerical resolution, which are very popular in the context of supersonic, self-gravitating fluids, namely adaptive mesh refinement, moving meshes, SPH and high-order methods. Advances in these directions are likely to trigger immense progresses in the future of our field.

Numerical studies on explosive welding with ANFO by 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. The EXW has not been well modeled before since in most numerical simulations the EXW is simply treated as the impact of two plates at high velocities. Recently, the authors developed a density adaptive smoothed particle hydrodynamics (SPH) method to successfully model the whole EXW process considering the high explosive explosion and its driving effects on flyer plate [ 1 ]. Later, this model is applied to investigate the mechanisms in EXW such as the wave formation mechanism and weldability windows [ 2 ]. The explosive TNT used in the previous model can be regarded as an ideal explosive while the complex and non-ideal explosive ANFO is more frequently used in practical welding operations. In this paper, the JWL++ model is incorporated into the density adaptive SPH to simulate the detonation of ANFO. The slab detonation and the explosive welding with TNT or ANFO explosive are simulated using the developed models. Good agreement can be observed between computational results and analytical solutions or experimental observations. Some typical characteristics in TNT and ANFO EXW including the detonation of explosive, wavy interface, jet formation, weldability windows are comparatively studied.

A consistent spatially adaptive smoothed particle hydrodynamics method for fluid–structure interactions

A new consistent, spatially adaptive, smoothed particle hydrodynamics (SPH) method for fluid–structureinteractions (FSI) is presented. The method combines several attributes that have not been simultaneously satisfied by other SPH methods. Specifically, it employs the second-order consistent discretization for differential operators; it allows for resolutions spatially adapted with moving (translating and rotating) boundaries of arbitrary geometries; and, it accelerates the FSI solution as the adaptive approach leads to fewer degrees of freedom without sacrificing accuracy. The key ingredients in the method are a posteriori error estimator/distance-based criterion of adaptivity and a particle-shifting technique. The method is applied in simulating six different flows or FSI problems in two dimensions. The new method’s convergence, accuracy, and efficiency attributes are assessed by comparing the results it produces with analytical, finite element, and consistent SPH uniform high-resolution solutions as well as experimental data.

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.