SPH Simulations Research Articles

Incompressible SPH simulation of solitary wave propagation on permeable beaches

Wave propagation on uniformly sloped beaches is a canonical coastal engineering topic that has been studied extensively in the past few decades. However, most of these studies treat beaches as solid boundaries even though they are often made of porous materials, such as sediment and vegetation. Permeable beaches struck by tsunami-like waves have not been adequately investigated. It is expected that the degree of permeability plays a crucial role in mitigating the impact of the wave. This study examines solitary wave run-ups on sandy beaches using an incompressible smoothed particle hydrodynamics (ISPH) model. The permeability of the beach is considered to be directly related to the diameter of its constituent sand particles. To obtain a satisfactory pressure field, which cannot be achieved using the original ISPH algorithm, the source term of the pressure Poisson equation has been modified based on a higher-order source-term expression. Flows within the porous medium are computed in the same framework as those outside the porous medium. In the current model, no transition zone is needed at the boundary of the porous structure. The wave-attenuation effect of the porous medium is discussed, with a particular focus on the relationship between the run-up height and grainsize.

Properties of the post in-spiral common envelope ejecta II: dust formation

ABSTRACT We study the formation of dust in the expanding gas ejected as a result of a common envelope binary interaction. In our novel approach, we apply the dust formation model of Nozawa et al. to the outputs of the 3D hydrodynamic SPH simulation performed by Iaconi et al. that involves a giant of 0.88 M⊙ and 83 R⊙, with a companion of 0.6 M⊙ placed on the surface of the giant in circular orbit. After simulating the dynamic in-spiral phase, we follow the expansion of the ejecta for $\simeq 18\, 000$ d. During this period, the gas is able to cool down enough to reach dust formation temperatures. Our results show that dust forms efficiently in the window between ≃ 300 d (the end of the dynamic in-spiral) and ≃ 5000 d. The dust forms in two separate populations; an outer one in the material ejected during the first few orbits of the companion inside the primary’s envelope and an inner one in the rest of the ejected material. We are able to fit the grain-size distribution at the end of the simulation with a double power law. The slope of the power law for smaller grains is flatter than that for larger grains, creating a knee-shaped distribution. The power-law indexes are, however, different from the classical values determined for the interstellar medium. We also estimate that the contribution to cosmic dust by common envelope events is not negligible and comparable to that of novae and supernovae.

Atmosphere loss in planet–planet collisions

ABSTRACT Many of the planets discovered by the Kepler satellite are close orbiting super-Earths or mini-Neptunes. Such objects exhibit a wide spread of densities for similar masses. One possible explanation for this density spread is giant collisions stripping planets of their atmospheres. In this paper, we present the results from a series of smoothed particle hydrodynamics (sph) simulations of head-on collisions of planets with significant atmospheres and bare projectiles without atmospheres. Collisions between planets can have sufficient energy to remove substantial fractions of the mass from the target planet. We find the fraction of mass lost splits into two regimes – at low impact energies only the outer layers are ejected corresponding to atmosphere dominated loss, at higher energies material deeper in the potential is excavated resulting in significant core and mantle loss. Mass removal is less efficient in the atmosphere loss dominated regime compared to the core and mantle loss regime, due to the higher compressibility of atmosphere relative to core and mantle. We find roughly 20 per cent atmosphere remains at the transition between the two regimes. We find that the specific energy of this transition scales linearly with the ratio of projectile to target mass for all projectile-target mass ratios measured. The fraction of atmosphere lost is well approximated by a quadratic in terms of the ratio of specific energy and transition energy. We provide algorithms for the incorporation of our scaling law into future numerical studies.

An axisymmetric multiphase SPH model for the simulation of rising bubble

3-D SPH simulations are often time-consuming due to the massive particle numbers. For the problem which has axisymmetric characteristics, the solving of the entire three-dimensional domain can be simplified which saves computational cost dramatically. In this paper, a novel derivation for the SPH formulation in cylindrical coordinate is presented, which is straightforward and physically meaningful. A multiphase numerical model is developed based on the derived formulation including the discretization formulas of surface tension force, viscous force, interface sharpness force and the treatment of high density ratio near the multiphase interface, as well as an improved anti-penetration treatment close to the axis. The effectiveness and robustness of the proposed multiphase SPH model are demonstrated via the classical surface-tension test and bubble rising problems at different conditions. The results are compared with analytical solutions, the experimental data and other numerical results. The promising results of the novel axisymmetric SPH model demonstrate a great potential for an efficient SPH modeling of complex axisymmetric multiphase flows. Dramatic efficiency boost is achieved by comparing the axisymmetric simulation with 3-D simulation in terms of CPU time.

Nonlinear waves in a floating thin elastic plate, predicted by a coupled SPH and FEM simulation and by an analytical solution

This paper highlights linear and nonlinear waves under the influence of surficial structural stiffness and inertia. The main focus is on the waves in a thin elastic plate floating on the water surface. A numerical simulation method, combining smoothed-particle hydrodynamics and the finite element method, is developed to predict the waves propagating in the thin elastic plate. For validation, the simulation results are compared to those obtained through a numerical method, based on the linear potential theory for linear regular wave cases. When the incident wave amplitude was increased, the waves' nonlinearity was observed in the simulation results. The nonlinear waves' characteristics are elucidated through a mathematical solution derived in a similar manner to Stokes wave theory. A significant difference is confirmed through comparisons with the conventional, nonlinear, free-surface wave. The positive peak was higher than the negative peak due to nonlinearity in one frequency range, while it was the opposite in the other frequency range. The nonlinear wave's amplitude increased divergently at the frequency between the two frequency ranges. Overall, it is shown that the mathematical solution effectively explains the characteristics of the nonlinear waves in the elastic plate observed in the numerical simulations.

Incompressible SPH simulation and experimental validation of Buoy-Wave interaction

Incompressible SPH simulation and experimental validation of Buoy-Wave interaction

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.

Tidal disruption of planetary bodies by white dwarfs I: a hybrid sph-analytical approach

ABSTRACT We introduce a new hybrid method to perform high-resolution tidal disruption simulations, at arbitrary orbits. An sph code is used to simulate tidal disruptions only in the immediate spatial domain of the star, namely, where the tidal forces dominate over gravity, and then during the fragmentation phase in which the emerging tidal stream may collapse under its own gravity to form fragments. Following each hydrodynamical simulation, an analytical treatment is then applied to instantaneously transfer each fragment back to the tidal sphere for its subsequent disruption, in an iterative process. We validate the hybrid model by comparing it to both an analytical impulse approximation model of single tidal disruptions, as well as full-scale sph simulations spanning the entire disc formation. The hybrid simulations are essentially indistinguishable from the full-scale sph simulations, while computationally outperforming their counterparts by orders of magnitude. Thereby our new hybrid approach uniquely enables us to follow the long-term formation and continuous tidal disruption of the planet/planetesimal debris, without the resolution and orbital configuration limitation of previous studies. In addition, we describe a variety of future directions and applications for our hybrid model, which is in principle applicable to any star, not merely white dwarfs.

Efficient dust ring formation in misaligned circumbinary discs

ABSTRACT Binary systems exert a gravitational torque on misaligned discs orbiting them, causing differential precession which may produce disc warping and tearing. While this is well understood for gas-only discs, misaligned cirumbinary discs of gas and dust have not been thoroughly investigated. We perform SPH simulations of misaligned gas and dust discs around binaries to investigate the different evolution of these two components. We choose two different disc aspect ratios: A thin case for which the gas disc always breaks, and a thick one where a smooth warp develops throughout the disc. For each case, we run simulations of five different dust species with different degrees of coupling with the gas component, varying in Stokes number from 0.002 (strongly coupled dust) to 1000 (effectively decoupled dust). We report two new phenomena: First, large dust grains in thick discs pile up at the warp location, forming narrow dust rings, due to a difference in precession between the gas and dust components. These pile ups do not form at gas pressure maxima, and hence are different from conventional dust traps. This effect is most evident for St ∼ 10–100. Secondly, thin discs tear and break only in the gas, while dust particles with St ≥ 10 form a dense dust trap due to the steep pressure gradient caused by the break in the gas. We find that dust with St ≤ 0.02 closely follow the gas particles, for both thin and thick discs, with radial drift becoming noticeable only for the largest grains in this range.

Stationary shock waves in porous copper by SPH simulation

Stationary shock waves in porous copper by SPH simulation

SPH simulation of droplet bouncing on a vibrating liquid surface

SPH simulation of droplet bouncing on a vibrating liquid surface

Angular Momentum Distribution in Galaxies and Inner Haloes Profile

In this paper, we extend the Romanowsky and Fall (2012) results concerning the stellar angular momentum to the mass range 103 ≲ M*/M⊙ ≲ 1012, and using this result, we calculate the inner slope, α of haloes density profiles in terms of Vrot, by using a previous model of Del Popolo, taking into account the interactions between dark matter and baryons through dynamical friction. Using the McConnachie sample, and that of Romanowsky and Fall, based only on observations, we show that in the quoted sample the rotationally supported galaxies, and the pressure supported ones are divided by a break atM* ≃ 107.8M⊙. Then we show that the slope α flattens monotonically, from α ≃ − 1 to α ≃ 0. The flattening is due to the increase of specific angular momentum moving fromMilkyWay-type galaxies to disk dwarf galaxies. Since at M* < 107.8M⊙, non-rotational supported galaxies start to dominate, the inner slope steepens again. The paper also extends the main result of Del Popolo (2016) to morphologies different from spheroids, and disks, taking into account the different morphologies delimited by the quoted ones. We finally compared our results with Di Cintio SPH simulations. The two models differ mainly at stellar masses smaller than M* ≲ 107.8M⊙. In our model the inner slope is flatter than in simulations. This imply that even finding a cored, α ≃ 0.4, profile in dSphs with masses slightly smaller than ≃106M⊙ will not imply necessarily a problem for the ΛCDM mode, as predicted by some simulations. To check which one of the two model was better describing data in this region, we used the LITTLE THINGS data, and compared the two models through a χ2, finding that our model gives a better description of the data.

Bifurcation in the history of Uranus and Neptune: the role of giant impacts

ABSTRACT Despite many similarities, there are significant observed differences between Uranus and Neptune: While Uranus is tilted and has a regular set of satellites, suggesting their accretion from a disc, Neptune’s moons are irregular and are captured objects. In addition, Neptune seems to have an internal heat source, while Uranus is in equilibrium with solar insulation. Finally, structure models based on gravity data suggest that Uranus is more centrally condensed than Neptune. We perform a large suite of high-resolution SPH simulations to investigate whether these differences can be explained by giant impacts. For Uranus, we find that an oblique impact can tilt its spin axis and eject enough material to create a disc where the regular satellites are formed. Some of the discs are massive and extended enough, and consist of enough rocky material to explain the formation of Uranus’ regular satellites. For Neptune, we investigate whether a head-on collision could mix the interior, and lead to an adiabatic temperature profile, which may explain its larger flux and higher moment of inertia value. We find that massive and dense projectiles can penetrate towards the centre and deposit mass and energy in the deep interior, leading to a less centrally concentrated interior for Neptune. We conclude that the dichotomy between the ice giants can be explained by violent impacts after their formation.

Study on influence of grinding depth and grain shape on grinding damage of K9 glass by SPH simulation

This work use the SPH method to study the relationship between grinding depth and grinding force of K9 glass in ultra-precision grinding, and the effect of grain shape on material removal. The relationship between the force and the depth in the stable scratching stage is FR = 0.55078ap1.15356, which provides a basis for controlling the grinding depth by force. The material removal modes at different grinding depths were obtained, that is, plastic removal occurs below 0.2 μm, brittle transition occurs between 0.2 and 0.4 μm, and brittle removal occurs at more than 0.5 μm. It is found that the cutting resultant force of sharp grains is smaller and the normal force is smaller than the tangential force. By analyzing the plastic deformation depth and residual stress depth, it is found that the material removal mode with small deformation and little removal has the lowest cutting force fluctuation and the highest grinding quality. It provides a reference for the choosing of grain shape in rough grinding and ultra-precision grinding. The correctness and reliability of the simulation results were verified by the comparison of the simulation findings with the results obtained from varied-depth scratching experiments and the multi-shape indenter scratch experiments.

Particle coalescing with angular momentum conservation in SPH simulations

The present work introduces a simple, yet effective particle coalescing procedure for two-dimensional SPH simulations with spatially varying resolution. In addition to the regular conservation properties of former algorithms concerning the mass and linear momentum, the current model provides the exact conservation of the angular momentum as well. The detailed discussion of the coalescing method is followed by its verification through a frozen Taylor-Green vortex example with gradually derefined particle configuration. As a demonstration of the applicability of the proposed technique, a typical weakly compressible dam break simulation and an evolution of a two-dimensional Taylor-Green vortex pattern with local refinement are presented and comparisons are made with analytical and experimental data.

Investigating Early-type Galaxy Evolution with a Multiwavelength Approach. III. Insights from SPH Simulations with Chemophotometric Implementation

We are exploring galaxy evolution in low density environments exploiting smooth particle hydrodynamic simulations including chemo-photometric implementation. From a large grid of simulations of galaxy encounters and mergers starting from triaxial halos of gas e dark matter, we single out the simulations matching the global properties of our targets. These simulations are used to give insights into their evolution. We focus on 11 early-type galaxies selected because of their nearly passive stage of evolution in the nuclear region. However, a variety of UV features are detected in more than half of these galaxies. We find no significant differences in the formation mechanisms between galaxies with or without UV features. Major and minor mergers are able to reproduce their peculiar UV morphologies, galaxy encounters are more suitable for 'normal' early-type galaxies. Their star formation rate self-quenches several Gyr later the merger/encounter occurred, via gas exhaustion and stellar feedback, moving the galaxy from blue to red colors, driving the galaxy transformation. The length of the quenching is mass dependent and lasts from 1 to 5 Gyr or more in the less massive systems. All our targets are gas rich at redshift 1. Three of them assembled at most 40% of their current stellar mass at z>1, and seven assembled more than 50% between redshift 0.5 and 1. Their stellar mass grows with 4% by crossing the Green Valley before reaching their current position on the NUV-r vs. Mr diagram.

A study on the oil transport in piston skirt-cylinder liner under fully flooded conditions using improved SPH simulations

In the present work, we studied the mechanical friction losses of the piston assembly-cylinder system that can be reduced by the fully flooded hydrodynamics lubrication during the oil film developed between the piston skirt and the cylinder liner. The lubricating oil transport process was described with Navier-Stokes equations in the clearance of piston skirt and liner with the piston reciprocating motion based on fully flooded hydrodynamics lubrication. The improved SPH method was then used to study such oil transport process with the piston reciprocating motion for the first time. The effects of the viscosity of lubricating oil, inertia force of oil film, the velocity of piston reciprocating motion, oil film thickness on oil transport were studied systematically. It was found that the inertia force of oil film plays a very important role in oil transport process under the condition of large clearances between the piston skirt and cylinder liner, small kinematic viscosities (i.e. large Reynolds numbers), and/or large frequencies of velocity evolution (i.e. large velocity gradient of piston reciprocating motion). Specifically, the results demonstrate that the internal friction effect of the fluid becomes prominent on maintaining the stability of lubricating oil transport process. It is also found that influence of the velocity of piston reciprocating motion on oil flow stable is not obvious. We expect that the study presented here can provide a useful guidance for the design of low-mechanical friction losses internal combustion engines.

Size and density sorting of dust grains in SPH simulations of protoplanetary discs – II. Fragmentation

ABSTRACTGrain growth and fragmentation are important processes in building up large dust aggregates in protoplanetary discs. Using a 3D two-phase (gas–dust) sph code, we investigate the combined effects of growth and fragmentation of a multiphase dust with different fragmentation thresholds in a time-evolving disc. We find that our fiducial disc, initially in a fragmentation regime, moves towards a pure-growth regime in a few thousands years. Time-scales change as a function of the disc and dust properties. When fragmentation is efficient, it produces, in different zones of the disc, Fe/Si and rock/ice ratios different from those predicted when only pure growth is considered. Chemical fractionation and the depletion/enrichment in iron observed in some chondrites can be linked to the size–density sorting and fragmentation properties of precursor dusty grains. We suggest that aggregation of chondritic components could have occurred where/when fragmentation was not efficient if their aerodynamical sorting has to be preserved. Chondritic components would allow aerodynamical sorting in a fragmentation regime only if they have similar fragmentation properties. We find that, in the inner disc, and for the same interval of time, fragmenting dust can grow larger when compared to the size of grains predicted by pure growth. This counter-intuitive behaviour is due to the large amount of dust that piles up in a fragmenting zone followed by the rapid growth that occurs when this zone transitions to a pure growth regime. As an important consequence, dust can overcome the radial-drift barrier within a few thousands years.

Characteristics structure analysis on debris cloud in the hypervelocity impact of disk projectile on thin plate

In this paper, the gauge points setting is introduced in the SPH simulation to analyze the debris cloud structure generated by the hypervelocity impact of disk projectile on thin plate. Compared with the experiments, more detailed information of the debris cloud structure can be classified from the numerical simulation. However, due to the solitary dispersion and overlap display of the particles in the SPH simulation, accurate comparison between numerical and experimental results is difficult to be performed. To track the velocity and spatial distribution of the particles in the debris cloud induced from disk and plate, gauge points are locally set in the single-layer profile in the SPH model. By analyzing the gauge points’ spatial coordinate and velocity, the location and velocity of characteristic points in the debris cloud are determined. The boundary of debris cloud is achieved, as well as the fragments distribution outside the main structure of debris cloud.

SPH simulation of floating structures with moorings

The open-source code DualSPHysics is applied to simulate the interaction of sea waves with floating offshore structures, which are typically moored to the seabed, such as vessels, boats, floating breakwaters and wave energy converters (WECs). The goal is to develop a numerical tool that allows the study of the survivability of floating moored devices under highly energetic sea states, obtaining the optimum mooring layout to increase lifetime. The moorings are modelled by coupling DualSPHysics with MoorDyn, a lumped-mass mooring dynamics model. MoorDyn represents mooring line behaviour subject to axial elasticity, hydrodynamic forces in quiescent water, and vertical contact forces with the seabed. Calculated mooring tensions at the fairlead are added as external forces in order to compute the resulting response and motions of the floating structures in DualSPHysics. The coupled model has been validated against data from scale model tests generated during the experimental campaigns for the European MaRINET2 EsflOWC project. In order to evaluate the accuracy of the coupling implementation with the lumped-mass mooring model, free-surface elevation, motions of the floater and mooring tensions are numerically computed and compared to experimental data. Overall, the results demonstrate the accuracy of the coupling between DualSPHysics and MoorDyn to simulate the motion of a moored floating structure under the action of regular waves. Going forward, this modelling approach can be employed to simulate more complex floating structures such as floating wind turbines, buoys, WECs, offshore platforms, etc.