SPH Technique Research Articles

Development and Validation of a Finite Element Model for Bird Strike Test

A bird strike describes a collision between an aircraft and a bird or a group of birds. A bird strike refers to any collision between a moving vehicle and a fly creatures. Bird strike are studied through experiments or simulations. The testing method produces reliable results, close to reali-ty. However, these practical experiments are expensive and time-consuming. This study performs numerical simulation of bird strike phenomenon using SPH technique. This article presents how to build a bird strike model on LS-DYNA software. The results of the simulation were compared with experiments, demonstrating that the numerical method is a reasonable approach to examine bird strike problems.

SPH Technique to Study the Sloshing in Concrete Liquid Tanks

SPH Technique to Study the Sloshing in Concrete Liquid Tanks

The two roles of the SPH Kernel and dissipation on accretion disc modelling in semi-detached Low-Mass Close Binaries

This study addresses two aspects of the SPH technique. The first aspect regards the 3D (2D) numerical integration. The second aspect deals with the necessary damping for handling inviscid flow discontinuities. Accretion discs in Low-Mass Close Binaries (LMCBs) are a context pushing the limit of SPH codes since turbulence, shocks, and shear flows coexist. Thus, an LMCB with high mass-transfer from the inner Lagrangian point is considered. This choice is made for an in-depth understanding of the numerical and physical aspects related to pressure forces computed through SPH Kernel spatial gradients in high-speed collisional flows. In this regard, gas compressibility also plays a role. Firstly, we pay attention to the algebraic term 4πr2 coming from the cubic differential d3r and affecting any 3D SPH integration. This is made through a comparison of physically inviscid SPH structures referring to the same LMCB and mass-transfer conditions. Then, a reformulation of the non-viscous damping is also considered by adopting a Lagrangian-free physical formulation. Inviscid accretion discs should develop a steady toroidal structure because radial transport mechanisms should be excluded by missing any radial shear flow damping. Therefore, thinner discs, also including a steady toroidal ring, identify that SPH inviscid modelling free of any incorrect pressure gradient excess among thick disc structures. This task is simplified since initial conditions deliberately favour thick discs. The physically viscous hydrodynamics of the disc is also addressed by adopting a Prandtl-like turbulent kinematic viscosity coefficient in the Navier–Stokes equations, distinguishing the roles of the bulk and shear viscosities.

A Review of SPH Techniques for Hydrodynamic Simulations of Ocean Energy Devices

This article is dedicated to providing a detailed review concerning the SPH-based hydrodynamic simulations for ocean energy devices (OEDs). Attention is particularly focused on three topics that are tightly related to the concerning field, covering (1) SPH-based numerical fluid tanks, (2) multi-physics SPH techniques towards simulating OEDs, and finally (3) computational efficiency and capacity. In addition, the striking challenges of the SPH method with respect to simulating OEDs are elaborated, and the future prospects of the SPH method for the concerning topics are also provided.

SPH modeling of wave interaction with reshaped and non-reshaped berm breakwaters with permeable layers

A berm breakwater may reshape during storms while its hydraulic performance depends on its reshaping status. Some experimental studies have been done to evaluate berm recession and to suggest the final reshaped breakwater section. Some numerical models have also been developed in the recent years especially by taking into account the permeability of breakwater layers and these powerful models cab be utilized efficiently to simulate wave interaction with permeable reshaping breakwaters. In this study, a numerical model based on SPH technique is developed to compare the hydraulic performance of a non-reshaped with a reshaped breakwater. To validate this model, wave transmissions from a permeable submerged breakwater as well as wave penetration through a reshaping breakwater are modeled and the calculated wave profile as well as wave pressure inside the porous breakwater are compared with the recorded data in available experimental studies. Then, by modeling both reshaped and non-reshaped breakwaters with different porosities, different hydraulic responses such as wave reflection, dissipation, transmission and run-up are calculated for these cases. It has been shown that the hydraulic performance of a berm breakwater depends on both its reshaping status and permeability of armor layer. In addition, either modeling the reshaped geometry or neglecting the permeability of armor layer results in overestimated responses such as overestimated wave run-up and overtopping. Therefore, it is necessary to model a reshaping section with actual permeability to evaluate hydraulic performance of a berm breakwater accurately. However, for initial design purposes, a reshaped impermeable breakwater can be applied conservatively.

Dynamic particle partitioning SPH model for high-speed fluids simulation

The popular SPH method still remains as one of the most widely-used methods in fluid simulation, exhibiting its longevity with new and diverse variants in recent decades. New progress in the SPH simulation in most recent years are still hampered by such challenge when simulating high-speed fluids. In this paper, our research efforts are devoted to the efficiency issue of the SPH simulation when the ratio of velocities among fluid particles is large. Specifically, we introduce a k-means clustering method into the SPH framework to dynamically partition fluid particles into two disjoint groups based on their velocities. Then, we use a two-scale time-step scheme for these two types of particles. The smaller time steps are for particles with higher speed in order to preserve temporal details and guarantee stability. In contrast, the larger time steps are used for particles with smaller speed to reduce the computational expense, and both types of particles are tightly coupled in the simulation. We conduct various experiments and compare our method with some of the most relevant works, which have manifested the advantages of our methods over the conventional SPH technique and its new variants in terms of efficiency and stability.

Cornering characteristics of a truck tire on wet surface using finite element analysis and smoothed-particle hydrodynamics

This paper presents the cornering characteristics of a wide base truck tire 445/50R22.5 over dry and wet surfaces in a virtual software package Pam-Crash. The wide base truck tire is modeled and validated using finite element analysis, while the water is modeled using smoothed-particle hydrodynamics technique. The tire–terrain interaction algorithm captures the node-symmetric node-to-segment contact with edge treatment. The simulation is repeated for several inflation pressure, applied vertical loading, cornering angles and water depth to evaluate the influence of these parameters on the tire operational performance. The simulation results obtained are validated against experimental data published in literature. The cornering characteristics investigated includes the lateral force, rolling resistance, cornering stiffness and self-aligning moment. Finally, the optimal operating conditions of the wide base tire are presented. To the author’s knowledge, no previous attempt to compute cornering characteristics of a truck tire on a wet surface using SPH technique has been made. This work will be further used for tire performance prediction research.

Validation of the DYN3D-Serpent code system for SFR cores using selected BFS experiments. Part II: DYN3D calculations

The capability of the DYN3D-Serpent codes system to simulate highly heterogeneous sodium-cooled fast reactor cores has been studied. The BFS-73-1 and the BFS-62-3A critical assemblies were chosen for the investigation. The study was performed in two parts. In the first part of the study, a 3D full model of each of the assemblies was simulated using the Serpent Monte-Carlo (MC) code, and the basic neutronic characteristics were evaluated and compared against experimental values. In the second part of the study, which is the subject of this paper, the assemblies were modeled using the DYN3D nodal diffusion code. The few-group cross-sections for the DYN3D analysis were generated using the Serpent MC code. The generation of effective few-group cross-sections of such assemblies is quite a challenge due to the substantial heterogeneity of the assemblies configuration. Therefore, the use of homogenization techniques was considered and evaluated. Initially, the GET and SPH techniques were applied for the analysis of the BFS-73-1 assembly core fuel rods, and of selected fuel rods from the BFS-62-3A assembly. Then, the SPH method was implemented and demonstrated for a pin-by-pin calculation of the BFS-73-1 assembly. It was shown that the GET and the SPH method noticeably improve the prediction accuracy of the DYN3D code. The results of the DYN3D pin-by-pin calculation with the SPH correction agree very well with that of the full assembly Serpent results, which in turn agree very well with the experimental data.

A new open-source pin power reconstruction capability in DRAGON5 and DONJON5 neutronic codes

In order to better optimize the fuel energy efficiency in PWRs, the burnup distribution has to be known as accurately as possible, ideally in each pin. However, this level of detail is lost when core calculations are performed with homogenized cross-sections. The pin power reconstruction (PPR) method can be used to get back those levels of details as accurately as possible in a small additional computing time frame compared to classical core calculations. Such a de-homogenization technique for core calculations using arbitrarily homogenized fuel assembly geometries was presented originally by Fliscounakis et al. In our work, the same methodology was implemented in the open-source neutronic codes DRAGON5 and DONJON5. The new type of Selengut homogenization, called macro-calculation water gap, also proposed by Fliscounakis et al. was implemented. Some important details on the methodology were emphasized in order to get precise results.Validation tests were performed on 12 configurations of 3×3 clusters where simulations in transport theory and in diffusion theory followed by pin-power reconstruction were compared. The results shows that the pin power reconstruction and the Selengut macro-calculation water gap methods were correctly implemented. The accuracy of the simulations depends on the SPH method and on the homogenization geometry choices. Results show that the heterogeneous homogenization is highly recommended. SPH techniques were investigated with flux-volume and Selengut normalization, but the former leads to inaccurate results. Even though the new Selengut macro-calculation water gap method gives promising results regarding flux continuity at assembly interfaces, the classical Selengut approach is more reliable in terms of maximum and average errors in the whole range of configurations.

Boosting the accuracy of SPH techniques: Newtonian and special-relativistic tests

We study the impact of different discretization choices on the accuracy of SPH and we explore them in a large number of Newtonian and special-relativistic benchmark tests. As a first improvement, we explore a gradient prescription that requires the (analytical) inversion of a small matrix. For a regular particle distribution this improves gradient accuracies by approximately ten orders of magnitude and the SPH formulations with this gradient outperform the standard approach in all benchmark tests. Second, we demonstrate that a simple change of the kernel function can substantially increase the accuracy of an SPH scheme. While the "standard" cubic spline kernel generally performs poorly, the best overall performance is found for a high-order Wendland kernel which allows for only very little velocity noise and enforces a very regular particle distribution, even in highly dynamical tests. Third, we explore new SPH volume elements that enhance the treatment of fluid instabilities and, last, but not least, we design new dissipation triggers. They switch on near shocks and in regions where the flow --without dissipation-- starts to become noisy. The resulting new SPH formulation yields excellent results even in challenging tests where standard techniques fail completely.

TIDAL DISRUPTIONS IN CIRCUMBINARY DISKS. I. STAR FORMATION, DYNAMICS, AND BINARY EVOLUTION

In our current interpretation of the hierarchical structure of the universe it is well established that galaxies collide and merge with each other during their lifetime. If massive black holes (MBHs) reside in galactic centres, we expect them to form binaries in galactic nuclei surrounded by a circumbinary disc. If cooling is efficient enough, the gas in the disc will clump and trigger stellar formation in situ. In this first paper we address the evolution of the binary under the influence of the newly formed stars, which form individually and also clustered. We use SPH techniques to evolve the gas in the circumbinary disc and to study the phase of star formation. When the amount of gas in the disc is negligible, we further evolve the system with a high-accurate direct-summation $N-$body code to follow the evolution of the stars, the innermost binary and tidal disruption events (TDEs). For this, we modify the direct N-body code to (i) include treatment of TDEs and to (ii) include "gas cloud particles" that mimic the gas, so that the stellar clusters do not disolve when we follow their infall on to the MBHs. We find that the amount of stars disrupted by either infalling stellar clusters or individual stars is as large as 10^{-4}/yr per binary, higher than expected for typical galaxies.

Testing the concept of integral approach to derivatives within the smoothed particle hydrodynamics technique in astrophysical scenarios

The behavior of IAD_0 scheme, a fully conservative SPH scheme based on a tensor formulation, is analyzed in connection with several astrophysical scenarios, and compared to the same simulations carried out with the standard SPH technique. The proposed hydrodynamic scheme is validated using a variety of numerical tests that cover important topics in astrophysics, such as the evolution of supernova remnants, the stability of self-gravitating bodies and the coalescence of compact objects. The results suggest that the SPH scheme built with the integral approach to the derivatives premise improves the results of the standard SPH technique. In particular, it is observed a better development of hydrodynamic instabilities, an improved description of self-gravitant structures in equilibrium and a reasonable description of the process of coalescence of two white dwarfs. A good energy, and linear and angular momentum conservation, generally better than that of standard SPH, was also obtained. In addition the new scheme is less susceptible to suffer pairing instability.

SPHysics – development of a free-surface fluid solver – Part 2: Efficiency and test cases

This paper, the second of a two-part series, analyses the efficiency of SPHysics and illustrates its capabilities by means of several test cases. Some intrinsic features of the SPH technique such as the use of link lists and the check for the limits are analysed here in detail. Numerical results are compared to experimental data for several cases studies: (i) Creation of waves by landslides, (ii) Dam-break propagation over wet beds and (iii) Wave-structure interaction. In addition, the capabilities of SPHysics to deal with realistic cases are depicted using the GPU version for several visual examples.

Incompressible smoothed particle hydrodynamics simulation of multifluid flows

SUMMARYThis paper presents an incompressible SPH (ISPH) technique to simulate multifluid flows. The SPH method is a mesh‐free particle modeling approach that can treat free surfaces and multi‐interfaces in a simple and efficient manner. The ISPH method employs an incompressible hydrodynamic formulation to solve the fluid pressure that ensures a stable pressure field. Two multifluid ISPH models are proposed following different interface treatments: the coupled ISPH model does not distinguish the different fluid phases and applies the standard ISPH technique across the interface, whereas the decoupled ISPH model first treats each fluid phase separately and then couples the different phases by applying pressure and shear stress continuities across the interface. The two proposed models were used to investigate a gravity underflow with a low density ratio in a Generalized Reservoir Hydrodynamics (GRH) flume and a horizontal lock exchange flow with a high density ratio. Comparisons with data and relevant numerical error analysis indicated that the decoupled model performed well in cases of both low and high density ratios because of the accurate treatment of interface boundaries. Copyright © 2011 John Wiley & Sons, Ltd.

SPH modelling of fluid at the grain level in a porous medium

Computational modelling of the flow of fluids in porous media has traditionally been at a macroscopic level where the medium’s permeability and porosity are an input (from experiments for example). In many cases this is difficult, especially if the porous medium changes its solid structure as a function of time. This situation occurs in reactive systems such as “heap-leaching”, where biological and/or chemical solutions are introduced into the heap to dissolve or react with valuable materials. In this case, modelling fluid flow at the grain level is paramount and we show how this can be done with the SPH technique. We present three-dimensional SPH simulations of fluid flow in an idealised porous medium and show that the technique yields flows which are physically realistic. The permeability of the medium is then predicted.

Magnetic fields and Turbulence in Star Formation using Smoothed Particle Hydrodynamics

AbstractFirstly, we give a historical overview of attempts to incorporate magnetic fields into the Smoothed Particle Hydrodynamics method by solving the equations of Magnetohydrodynamics (MHD), leading an honest assessment of the current state-of-the-art in terms of the limitations to performing realistic calculations of the star formation process. Secondly, we discuss the results of a recent comparison we have performed on simulations of driven, supersonic turbulence with SPH and Eulerian techniques. Finally we present some new results on the relationship between the density variance and the Mach number in supersonic turbulent flows, finding σ2ln ρ = ln(1 + b22 with b = 0.33 up to Mach 20, consistent with other numerical results at lower Mach number (Lemaster & Stone 2008) but inconsistent with observational constraints on σρ and in Taurus and IC5146.

E pur si muove:Galilean-invariant cosmological hydrodynamical simulations on a moving mesh

Hydrodynamic cosmological simulations at present usually employ either the Lagrangian SPH technique, or Eulerian hydrodynamics on a Cartesian mesh with adaptive mesh refinement. Both of these methods have disadvantages that negatively impact their accuracy in certain situations. We here propose a novel scheme which largely eliminates these weaknesses. It is based on a moving unstructured mesh defined by the Voronoi tessellation of a set of discrete points. The mesh is used to solve the hyperbolic conservation laws of ideal hydrodynamics with a finite volume approach, based on a second-order unsplit Godunov scheme with an exact Riemann solver. The mesh-generating points can in principle be moved arbitrarily. If they are chosen to be stationary, the scheme is equivalent to an ordinary Eulerian method with second order accuracy. If they instead move with the velocity of the local flow, one obtains a Lagrangian formulation of hydrodynamics that does not suffer from the mesh distortion limitations inherent in other mesh-based Lagrangian schemes. In this mode, our new method is fully Galilean-invariant, unlike ordinary Eulerian codes, a property that is of significant importance for cosmological simulations. In addition, the new scheme can adjust its spatial resolution automatically and continuously, and hence inherits the principal advantage of SPH for simulations of cosmological structure growth. The high accuracy of Eulerian methods in the treatment of shocks is retained, while the treatment of contact discontinuities improves. We discuss how this approach is implemented in our new parallel code AREPO, both in 2D and 3D. We use a suite of test problems to examine the performance of the new code and argue that it provides an attractive and competitive alternative to current SPH and Eulerian techniques. (abridged)

An SPH Technique for Evaluating the Behaviour of Ships in Extreme Ocean Waves

An SPH Technique for Evaluating the Behaviour of Ships in Extreme Ocean Waves

Modeling Dam Break Behavior over a Wet Bed by a SPH Technique

Dam break evolution over dry and wet beds is analyzed with a smoothed particle hydrodynamics model. The model is shown to accurately fit both experimental dam break profiles and the measured velocities. In addition, the model allows one to study different propagation regimes during the dam break evolution. In particular, different dissipation mechanisms were identified: bottom friction and wave breaking. Although breaking dominates over wet beds at the beginning of the movement, bottom friction becomes the main dissipation mechanism in the long run.

Numerical modelling of the hydrodynamic ram phenomenon

Hydrodynamic ram (HRAM) is a phenomenon that occurs when a high-kinetic energy object penetrates a fluid-filled container. The projectile transfers its momentum and kinetic energy through the fluid to the surrounding structure, increasing the risk of catastrophic failure and excessive structural damage. This is of particular concern in the design of wing fuel tanks for aircraft since it has been identified as one of the important factors in aircraft vulnerability. In the present paper, the commercial finite-element code LS-DYNA has been used to simulate an HRAM event created by a steel spherical projectile impacting a water-filled aluminium square tube. Two different formulations (ALE and SPH) are employed to reproduce the event. Experimental tests which indicate the pressure at different points of the fluid, displacement of the walls and cavity evolution for different impact velocities are compared with the numerical results in order to assess the validity and accuracy of both ALE and SPH techniques in reproducing such a complex phenomenon.