Smoothed Particle Hydrodynamics Simulations Research Articles

SPH simulation and experimental validation of the dynamic response of floating offshore wind turbines in waves

The SPH (smoothed particle hydrodynamics) method coupled with a mooring analysis program is adopted to investigate the accuracy of the SPH method in simulating the hydrodynamics of FOWTs (floating offshore wind turbines). Both experimental and numerical studies were conducted for a floating box and a scaled FOWT model interacting with multiple wave conditions. The SPH method is proven to be accurate in solving the motion of the floaters under multiple wave conditions, showing good consistency with the experimental data. In addition, the snapshots of the wave profile and the motions of the box and FOWT model are compared between SPH results and experiments. Finally, the application of the SPH method is extended to real-scale FOWT simulations. The motion response and mooring line force in the simulations are analyzed and show that the SPH method has the potential to be applied to real-scale FOWT hydrodynamics problems.

A pressure-dependent adaptive resolution scheme for smoothed particle hydrodynamics simulation of underwater explosion

For promoting numerical efficiency in smoothed particle hydrodynamics (SPH) simulation of underwater explosion, a pressure-dependent adaptive resolution scheme (PARS) is proposed. The approach involves dividing computation domain into several regions of different resolution and automatic splitting or merging particles in these regions. Methods are established for identifying resolution regions and for adapting particle resolutions, so that the wave front and the zone with sharp pressure variation is dynamically covered in the region of the highest resolution. Numerical examples are present to demonstrate that the proposed technique can reduce significantly the number of particles and computing time to produce solutions of adequate accuracy. The main features of shockwave propagation can be well captured using much less particles. For large scale or 3D problems, the technique can be decisive for completing a numerical simulation. Numerical examples also testified that the proposed PARS is robust and effective in capturing the complicated phenomena of wave interferences and interaction between shock wave and solid barrier.

Black hole binaries with natal kicks

AbstractWe study the viability of obtaining large natal kicks during the formation of massive black holes (BHs) by studying the asymmetric mild explosion of 21 M⊙ pre‐supernova stellar models, by means of 3D Smooth Particle Hydrodynamics (SPH) simulations. Our preliminary results show either smaller or higher values for the final velocity of the BH than the reduced velocity expected from BH mass accretion, depending on the energy of the explosion.

CosmoDRAGoN simulations—I. Dynamics and observable signatures of radio jets in cosmological environments

Abstract We present the Cosmological Double Radio Active Galactic Nuclei (CosmoDRAGoN) project: a large suite of simulated AGN jets in cosmological environments. These environments sample the intra-cluster media of galaxy clusters that form in cosmological smooth particle hydrodynamics (SPH) simulations, which we then use as inputs for grid-based hydrodynamic simulations of radio jets. Initially conical jets are injected with a range of jet powers, speeds (both relativistic and non-relativistic), and opening angles; we follow their collimation and propagation on scales of tens to hundreds of kiloparsecs, and calculate spatially resolved synthetic radio spectra in post-processing. In this paper, we present a technical overview of the project, and key early science results from six representative simulations which produce radio sources with both core- (Fanaroff-Riley Type I) and edge-brightened (Fanaroff-Riley Type II) radio morphologies. Our simulations highlight the importance of accurate representation of both jets and environments for radio morphology, radio spectra, and feedback the jets provide to their surroundings.

Simulating AGN feedback and its evolution in galaxy mergers: case study for NGC 5252

We are investigating the evolution of merging galaxies using numerical simulations. This research focuses on the AGN-driven feedback mechanism that can be responsible for the outflow gas found on kiloparsecs scales in Seyfert galaxies. The initial conditions of the galaxy were designed to replicate the observable characteristics of NGC 5252. NGC 5252 is an off-nucleus ultraluminous X-ray (ULX) source and has extended [OIII] emission up to 10 kpc scales. The optical spectrum properties of CXO J133815.6+043255 are comparable to those of Low-Luminosity AGNs (LLAGNs). Observations of high angular resolution very long baseline interferometry (VLBI) also showed that it is a suitable option for a dual radio-emitting AGN system. Moreover, the NGC 5252 off-nucleus component is thought to be a stripped leftover of a merging dwarf galaxy. The supermassive black hole (SMBH) physics module is used in smoothed-particle hydrodynamics (SPH) simulations of merging galaxies using the GIZMO code to investigate the evolutionary changes of such a system. Our major-merger test run could not produce the observed morphology contrary to a report that one would be able to produce a spiral galaxy. The minor-merger test run up to around 0.2-0.3 Gyr shows a promising early result of the final system however further works will be conducted to investigate the properties of the resulting double AGN system and its evolution.

Experiment and smooth particle hydrodynamic modeling of single-grain diamond scribing of silicon carbide fiber reinforced silicon carbide (SiCf/SiC)

The smoothed particle hydrodynamics (SPH) is applied to model the single-grain diamond scribing of the silicon carbide fiber reinforced silicon carbide (SiCf/SiC). Experiments of diamond scribing on SiCf/SiC were performed with three parameters: fiber orientation, depth of cut, and speed of cut. The scribing force and 3D shape diamond tip was measured. The SPH simulation based on JH-2 material model of the SiCf and SiC matrix as well as the experimental modeling is performed. Comparison of SPH-predicted and experimentally measured force identifies parameters for the JH-2 work-material and SPH modeling of SiCf/SiC for accurate prediction of diamond scribing force.

Tidal capture of stars by supermassive black holes: implications for periodic nuclear transients and quasi-periodic eruptions

ABSTRACT Stars that plunge into the centre of a galaxy are tidally perturbed by a supermassive black hole (SMBH), with closer encounters resulting in larger perturbations. Exciting these tides comes at the expense of the star’s orbital energy, which leads to the naive conclusion that a smaller pericentre (i.e. a closer encounter between the star and SMBH) always yields a more tightly bound star to the SMBH. However, once the pericentre distance is small enough that the star is partially disrupted, morphological asymmetries in the mass lost by the star can yield an increase in the orbital energy of the surviving core, resulting in its ejection – not capture – by the SMBH. Using smoothed particle hydrodynamics simulations, we show that the combination of these two effects – tidal excitation and asymmetric mass-loss – results in a maximum amount of energy lost through tides of $\sim 2.5{{\ \rm per\ cent}}$ of the binding energy of the star, which is significantly smaller than the theoretical maximum of the total stellar binding energy. This result implies that stars that are repeatedly partially disrupted by SMBHs many (≳10) times on short-period orbits (≲few years), as has been invoked to explain the periodic nuclear transient ASASSN-14ko and quasi-periodic eruptions, must be bound to the SMBH through a mechanism other than tidal capture, such as a dynamical exchange (i.e. Hills capture).

SPH simulations of the induced gravitational collapse

In the induced gravitational collapse (IGC) paradigm, a carbon–oxygen (CO) star collapses and explodes in a supernova (SN) in the presence of a binary companion, a neutron star (NS). The material ejected in the explosion is gravitationally attracted by the NS, triggering a hypercritical accretion process onto it. For compact systems, the accretion rate could be high enough for the NS to reach its critical mass, collapse in a black hole (BH) and emit an energetic (energy release $\gtrsim 10^{52}$ erg) gamma-ray burst (GRB). With the aim to identify the separatrix of systems in which a BH is formed and characterize the observational signatures of the above process, we have performed three-dimensional (3D) smoothed-particle-hydrodynamics (SPH) numerical simulations of the SN expansion in the presence of the NS companion and the evolution of the NS during the accretion process. We here summarize the results of the above simulations for a wide range of the initial conditions of the parameter space.

Pharmaceutical hot melt extrusion process development using QbD and digital twins

Pharmaceutical product development guided by Quality by Design (QbD) is based on a complete understanding of the critical process parameters (CPPs) that are important for achieving the desired product critical quality attributes (CQAs). The effect of process settings, such as the screw speed, the throughput, the barrel temperature, and the screw configuration, is a well-known factor in the setup of pharmaceutical hot melt extrusion (HME) processes. A CPP that has not yet been extensively researched is the type of cross-section geometry of the screw elements. Typically, pharmaceutical extruders have double-flighted screw cross-sections, with some elements having a single- or triple-flighted element section. The exception is a NANO16 extruder from Leistritz, with all screw elements having a triple-flighted screw geometry. We investigated the process setup and scale-up to a double-flighted extruder experimentally and in silico via a digital twin. Two formulations were processed on a NANO16 extruder and virtually transferred to a ZSE18 double-flighted co-rotating twin-screw extruder. Detailed smoothed particle hydrodynamics simulations of all screw elements available from both extruders were performed, and their efficiency in conveying, pressure build-up, and power consumption were studied. Reduced-order 1D HME simulations, which were carried out to investigate the process space and scalability of both extruders, were experimentally validated.

Super-critical accretion of medium-weight seed black holes in gaseous proto-galactic nuclei

ABSTRACT Accretion at sustained or episodic super-Eddington (SE) rates has been proposed as a pathway to grow efficiently light seeds produced by Pop-III stars. We investigate if SE accretion can be sustained onto a black hole (BH) with MBH ∼ 103 M⊙ in the centre of a gas-rich proto-galaxy at z = 15. We perform high-resolution smoothed-particle hydrodynamical simulations, including two different sub-grid models for SE accretion, one based on the slim disc paradigm, and one inspired by recent radiation-magnetohydrodynamical simulations by Jiang and collaborators. Radiative feedback has the form of a thermal dump to surrounding gas particles, with the radiative efficiency being set according to the different SE accretion models. We find that, in all simulations, star formation, BH feedback, and interactions between clumps and the BH rapidly quench accretion after ∼1 Myr, irrespective of the sub-grid model used for accretion. Quenching is stronger in the model based on the simulations of Jiang and collaborators relative to the slim disc model because of its higher radiative efficiency. The SE growth phase is always very brief, lasting a few 0.1 Myr. In the most optimistic case, the BH reaches a mass of ∼104 M⊙. We extrapolate the final BH masses from z = 15 to z ∼ 6, assuming subsequent galaxy mergers will replenish the gas reservoir and trigger new cycles of SE accretion. We find that at most BH seeds would grow to ∼106 M⊙, comparable to the mass of massive BHs in spiral galaxies such as the Milky Way, but falling short of the mass of the high-redshift quasars.

Numerical Calculation of Slosh Dissipation

As part of the Sloshing Wing Dynamics H2020 EU project, an experimental campaign was conducted to study slosh-induced damping in a vertically excited tank filled with liquid water or oil and air. In this work, we simulate these experiments using two numerical approaches. First, a single-phase, weakly compressible liquid model is used, and the gas flow (air) is not modeled. For this approach, a proven Smoothed Particle Hydrodynamics (SPH) model is used. In the second approach, both phases are simulated with an incompressible liquid and weakly compressible gas model via a Finite Volume Method (FVM) using Volume-of-Fluid (VOF) to track the liquid phase. In both approaches, the energy distribution of the flow is calculated over time in two- and three-dimensional simulations. It is found that there is reasonable agreement on the energy dissipation evolution between the methods. Both approaches show converging results in 2D simulations, although the SPH simulations seem to have a faster convergence rate. In general, the SPH results tend to overpredict the total dissipation compared to the experiment, while the finite volume 2D results underpredict it. Time histories of the center of mass positions are also compared. The SPH results show a much larger vertical center of mass motion compared to the FVM results, which is more pronounced for the high Reynolds number (water) case, probably linked to the absence of the air phase. On the other hand, the limited center of mass motion of the FVM could be linked to the need for higher spatial resolutions in order to resolve the complex gas–liquid interactions, particularly in 3D.

Surface derusting of rust-covered metallic surface via shot blasting: A smoothed particle hydrodynamics simulation

In the shot blasting process, the micromechanical behaviors of the targeted structure induced by particle impact may cause considerable local deformation of the surface or even chip separation, making it difficult to quantitatively analyze via traditional methods. In this study, the smoothed particle hydrodynamics (SPH) method is used to simulate the impact process of hard particles on a metallic substrate covered by a rust layer, and the surface derusting mechanism owing to impact is investigated. First, a metallic target model with a rust layer impacted by particles of different shapes is established using the SPH method. The SPH discrete equation of the metal and rust layer materials is given, and elasto-plastic constitutive and failure models are formulated for the two materials. Next, the accuracy of the model in simulating impact-induced plastic craters and material removal is validated by a particle impact experiment. Further, the impact and erosion behaviors of particles with different shapes on the deformation and damage of the rust layer and metal are investigated under various initial orientations and impact angles. The results show that the model can effectively simulate the large local deformation and material removal of the rust layer caused by the impact of small particles.

OSSOS. XXVI. On the Lack of Catastrophic Collisions in the Present Kuiper Belt

We investigate different conditions, including the orbital and size–frequency distribution (SFD) of the early Kuiper Belt, that can trigger catastrophic planetesimal destruction. The goal of this study is to test if there is evidence for collisional grinding in the Kuiper Belt that has occurred since its formation. This analysis has important implications for whether the present-day SFD of the cold classical trans-Neptunian objects (TNOs) is a result of collisional equilibrium or if it reflects the primordial stage of planetesimal accretion. As an input to our modeling, we use the most up-to-date debiased OSSOS++ ensemble sample of the TNO population and orbital model based on the present-day architecture of the Kuiper Belt. We calculate the specific impact energies between impactor–target pairs from different TNO groups and compare our computed energies to catastrophic disruption results from smoothed particle hydrodynamics simulations. We explore different scenarios by considering different total primordial Kuiper Belt masses and power slopes of the SFD and allowing collisions to take place over different timescales. The collisional evolution of the Kuiper Belt is a strong function of the unknown initial mass in the trans-Neptunian region, where collisional grinding of planetesimals requires a total primordial Kuiper Belt mass of M > 5 M ⊕, collision speeds as high as 3 km s−1, and collisions over at least 0.5 Gyr. We conclude that presently, most of the collisions in the trans-Neptunian region are in the cratering rather than disruption regime. Given the low collision rates among the cold classical Kuiper Belt objects, their SFD most likely represents the primordial planetesimal accretion.

Material removal mechanism of non-resonant vibration-assisted magnetorheological finishing of silicon carbide ceramics

In this study, the material removal mechanism of non-resonant vibration-assisted magnetorheological finishing (NVMRF) of SiC ceramics was researched for improving their surface quality and finishing efficiency. A theoretical model of the polishing forces considering the vibration was proposed to explain the effects of the vibration on the polishing forces. A theoretical model of material removal rate (MRR) based on the Preston equation was proposed for quantitative analysis by considering the synergistic effects of the normal force and total shear force. Moreover, a theoretical model and the smoothed-particle hydrodynamics (SPH) simulation of a single diamond abrasive for material removal were proposed to explain the reasons for the increase in the MRR. Combined designed processing experiment, introducing the vibration can enhance the normal force and total shear force, which make improvement of the MRR, surface quality and subsurface damage (SSD). Moreover, both the enhanced normal force and total shear force contribute to the MRR, and the normal force contributes more to the MRR than the total shear force. Thus, understanding the material removal mechanism of proposed NVMRF plays indispensable role to extend its application into more wider areas.

Research Progress of SPH Simulations for Complex Multiphase Flows in Ocean Engineering

Complex multiphase flow problems in ocean engineering have long been challenging topics. Problems such as large deformations at interfaces, multi-media interfaces, and multiple physical processes are difficult to simulate. Mesh-based algorithms could have limitations in dealing with multiphase interface capture and large interface deformations. On the contrary, the Smoothed Particle Hydrodynamics (SPH) method, as a Lagrangian meshless particle method, has some merit and flexibility in capturing multiphase interfaces and dealing with large boundary deformations. In recent years, with the improvement of SPH theory and numerical models, the SPH method has made significant advances and breakthroughs in terms of theoretical completeness and computational stability, which starts to be widely used in ocean engineering problems, including multiphase flows under atmospheric pressure, high-pressure multiphase flows, phase-change multiphase flows, granular multiphase flows and so on. In this paper, we review the progress of SPH theory and models in multiphase flow simulations, discussing the problems and challenges faced by the method, prospecting to future research works, and aiming to provide a reference for subsequent research.

Experimental study and smoothed particle hydrodynamics simulation of synthetic diamond grit scratching on steel

Superabrasives like synthetic diamonds are indispensable in today’s construction industry, particularly for core drilling applications in reinforced concrete. The increase of the cutting efficiency of such core bits strongly depends on the material removal behavior of single diamond grains placed in a diamond segment acting as cutting elements. Therefore, this paper presents a newly developed experimental setup for a 3-mm single diamond grain scratch test, as well as the application of a Smoothed Particle Hydrodynamics (SPH) method to model single diamond grains scratching a rebar base material at operational parameters. Diamonds in two main different crystallographic and geometric orientations are tested and investigated with respect to their forces and temperatures at the cutting edge. Furthermore, the chip formation and different material removal mechanisms are analyzed for each orientation and compared with the model output. Validation tests and sensitivity analyses are performed in 3D and high resolution, thanks to the runtime acceleration of SPH through parallel computing on the graphics card. The results indicate: 1) A significantly different material removal behavior as a result of changing the diamond orientation; 2) The capability and high efficiency of SPH for modeling single grain scratch tests.

A minimalistic approach to physics-informed machine learning using neighbour lists as physics-optimized convolutions for inverse problems involving particle systems

This study proposes a hybrid approach for combining mechanistic (first principle) and Machine Learning models. This approach applies to discrete (particle-based) systems and continuous systems that can be recast as a particle problem by a framework like Smoothed Particle Hydrodynamics. The governing equations are written as a set of equations describing the motion of the particle system. Artificial Neural Networks are used to derive from data the forces acting on the particles, while the system's path in the state-space is calculated with the equation of motion. This ensures that fundamental physical principles such as Newton's laws of motion are always satisfied in a strong sense. Neighbour lists automatically introduce dimensionality reduction into the system by functioning as physics-optimized convolutions. Therefore, the network can be smaller, simpler, and more easily trainable than other physics-informed machine learning models. The proposed technique is applied to three inverse modelling problems. The method is designed to learn the pairwise forces acting between particles without knowing these forces from the training data. In fact, the training data contains the total force acting on each particle, not the pairwise forces between pairs of particles. Data for Molecular Dynamics, Smoothed Particle Hydrodynamics and Discrete Element Method simulations are fed into the model that ‘extracts’ their physics and reproduces the simulations with a high degree of accuracy. The model's capability for generalization is noteworthy. As long as the underlying physics remains the same, the model can predict the dynamics of systems with geometries and boundary conditions very different from those of the training dataset. As a remarkable example, a model trained surface-flow data also correctly replicates channel flow.

Enhanced resolution of the continuity equation in explicit weakly compressible SPH simulations of incompressible free‐surface fluid flows

This paper is dedicated to improved resolution of the continuity equation and thus more precise satisfaction of incompressibility conditions in explicit weakly compressible SPH (Smoothed Particle Hydrodynamics) simulations of incompressible free-surface fluid flows. In the explicit weakly compressible SPH methods, including δ-SPH with a widely adopted particle shifting scheme (or the so-called δ-plus-SPH), two incompressibility conditions corresponding to the invariant density condition and divergence-free velocity condition are not well resolved. To achieve enhanced resolution of the continuity equation as well as satisfaction of both incompressibility conditions, this paper presents two novel schemes, namely, Velocity-divergence Error Mitigating (VEM) and Volume Conservation Shifting (VCS) schemes. The VEM scheme corresponds to an additional term in the momentum equation that mitigates the velocity divergence error at every computational time step. The VEM term is derived by linking the instantaneous velocity divergence error to the undesired density time variations and accordingly to an error mitigating pressure pVEM obtained through an Equation of State (EOS). The corresponding pressure gradient term or acceleration leads to attenuation of numerical noise in the velocity divergence field. The VCS acts as a distinct particle shifting scheme to enforce local and thus global volume conservation. This distinct shifting is obtained through calculation of the gradient of a corresponding pressure, namely, pVCS, obtained through efficient solution of a Poisson Pressure Equation (PPE) derived from the concept of projection-based particle methods. By adopting both proposed schemes, the explicit SPH method is shown to provide enhanced satisfaction of both incompressibility conditions, i.e., divergence-free velocity and invariant density conditions, in simulation of incompressible free-surface fluid flows.

Smoothed particle hydrodynamics physically reconsidered: The relation to explicit large eddy simulation and the issue of particle duality

In this work, we will identify a novel relation between Smoothed Particle Hydrodynamics (SPH) and explicit large eddy simulation using a coarse-graining method from non-equilibrium molecular dynamics. While the current literature points at the conclusion that characteristic SPH issues become restrictive for subsonic turbulent flows, we see the potential to mitigate these SPH issues by explicit subfilter stress modeling. We verify our theory by various simulations of homogeneous, isotropic turbulence at Re=104 and compare the results to a direct numerical simulation [T. Dairay et al., “Numerical dissipation vs subgrid-scale modelling for large eddy simulation,” J. Comput. Phys. 337, 252–274 (2017)]. Although the simulations substantiate our theory, we see another issue arising, which is conceptually rooted in the particle itself, termed as particle duality. Finally, we conclude our work by acknowledging SPH as a coarse-graining method for turbulent flows, highlighting its capabilities and limitations.

SPH simulations of transient non-isothermal viscoelastic flows with free surfaces

• Transient non-isothermal viscoelastic free surface flows are simulated by SPH. • SPH discretization of the temperature equation is derived. • The impacting droplet and the filling process of circular disc with core are studied. • Both Oldroyd-B and UCM fluid models are considered. • The work provides references to handle non-isothermal viscoelastic flows in an entirely meshfree framework. This study presents a smoothed particle hydrodynamics (SPH) method for simulating transient non-isothermal viscoelastic flows with free surfaces. The basic equations governing the non-isothermal free surface flow of an Oldroyd-B fluid are considered and approximated by SPH. To model non-isothermal fluid flows, a working SPH discretization of the temperature equation is derived, and the temperature-dependent viscosity and relaxation time are represented by the time–temperature superposition principle. The proposed SPH method is first validated by solving the viscoelastic Poiseuille flow problem under isothermal and non-isothermal conditions and comparing the SPH solutions with the analytical solutions or those obtained by other methods. Then, the SPH method is extended to deal with the impact of a non-isothermal viscoelastic droplet with a cold wall and the non-isothermal filling process of a circular disc with a core. The convergence of the method is verified by four particle spacings of different levels of refinement. The effects of some important parameters, including the temperature dependency coefficient, reference temperature of the fluid, and Péclet number, on the flow behavior are analyzed in detail. All the results demonstrate that the proposed SPH method is capable of accurately and stably simulating transient non-isothermal viscoelastic free surface flows in an entirely meshfree framework.