SPH Simulations Research Articles

Study on hydrodynamics of fish school based on SPH simulation

Abstract In this paper, the effect of spatial configurations on the hydrodynamic characteristics of fish is investigated numerically using the δ+-SPH model. The spatial configurations include side-by-side and triangular. The fluid field, including the pressure field and velocity field, are obtained by SPH simulation. The results show that the SPH method can well simulate the self-propelled movement of fish. Under the viscous flow waters, the side-by-side fish will be close to each other due to the Bernoulli effect. For triangular configurations, fish will tend to form inverted triangular configurations due to passage effects, which accompany the changes in the cost of transportation.

Modeling and mitigation of vortex formation in ejector deep hole drilling with smoothed particle hydrodynamics

Ejector deep hole drilling achieves high-quality boreholes in production processes. High feed rates are applied to ensure a high productivity level, requiring reliable chip removal from the cutting zone for a stable process. Therefore, a constant metalworking fluid flow under high volume flow rates or high pressure is required. Experimental results show a vortex formation at the outer cutting edge. This vortex can lead to delayed chip removal from the cutting zone, and ultimately, it can lead to chip clogging and result in drill breakage due to increased torque. This paper investigates modified drill head designs using the smoothed particle hydrodynamics method. The investigated modifications include various designs of the chip mouth covering. Besides graphical analysis based on flow visualizations, flow meters are placed at the tool’s head to evaluate the impact of the modifications on the flow rate and possible increased resistance and relocation of the fluid flow from the outer cutting edge to other parts of the tool. The simulation results for the reference design show the experimentally observed vortex formation, validating the simulation model. By adding the tool’s rotation in the SPH simulation, which is not included in the experiments for observation reasons, the vortex formation is positively influenced. In addition, some designs show promising results to further mitigate the vortex formation while maintaining a sufficient fluid flow around the cutting edges.

Examination of Variable Tilting Speed on Flow Behavior During Ladle Pouring in Die Casting Using SPH Simulation

Examination of Variable Tilting Speed on Flow Behavior During Ladle Pouring in Die Casting Using SPH Simulation

SPH Simulation of Cnoidal Wave Generation by Cylinder-Shaped Plunger

SPH Simulation of Cnoidal Wave Generation by Cylinder-Shaped Plunger

Advancing blast fragmentation simulation of RC slabs: A graph neural network approach

Accurate prediction of blast-induced fragmentation in reinforced concrete (RC) structures is pivotal for structural debris hazard assessment in an explosion event. This assessment is essential for designing effective measures for protection of people and structure in the vicinity. While conventional computational techniques are proficient, they are computationally very demanding and may not be readily adaptable in practical applications. This study proposes a novel approach, the Fragment Graph Network (FGN), a specialized variant of graph neural networks (GNNs), to simulate complex interactions between macro-level particles of RC structures subjected to close-in blast loads. The RC structure is discretised into particles, with the model predicting structural responses and fragmentation based on states of these particles. Utilizing an autoregressive prediction mechanism, our model can accurately simulate spatiotemporal responses of RC slabs against blast loads. The efficacy of the model was tested on a dataset consisting of 149 simulated cases, encompassing around 180,000 states each, covering a wide range of blasting scenarios and structural design parameters including TNT charge weight, standoff distance, slab dimension, concrete strength, and reinforcement ratio and layout. Notably, the proposed model delivered accurate predictions, achieving relative errors under 10% and R2 values exceeding 0.93 for both standard and extrapolated test scenarios as compared to the SPH simulations. Remarkably, our model dramatically outpaced traditional numerical approaches, reducing simulation times from hours to minutes on CPUs and seconds on GPUs. This pioneering effort paves the way for efficient and accurate simulations of RC blast fragmentations, offering a rapid alternative to standard numerical approaches.

A modified lognormal approximation of the Lyman-α forest: comparison with full hydrodynamic simulations at 2 ≤ z ≤ 2.7

Observations of the Lyman-α forest in distant quasar spectra with upcoming surveys are expected to provide significantly larger and higher-quality datasets. To interpret these datasets, it is imperative to develop efficient simulations. One such approach is based on the assumption that baryonic densities in the intergalactic medium (IGM) follow a lognormal distribution. We extend our earlier work to assess the robustness of the lognormal model of the Lyman-α forest in recovering the parameters characterizing IGM state, namely, the mean-density IGM temperature (T 0), the slope of the temperature-density relation (γ), and the hydrogen photoionization rate (Γ12), by comparing with high-resolution Sherwood SPH simulations across the redshift range 2 ≤ z ≤ 2.7. These parameters are estimated through a Markov Chain Monte Carlo (MCMC) technique, using the mean and power spectrum of the transmitted flux. We find that the usual lognormal distribution of IGM densities cannot recover the parameters of the SPH simulations. This limitation arises from the fact that the SPH baryonic density distribution cannot be described by a simple lognormal form. To address this, we extend the model by scaling the linear density contrast by a parameter ν. While the resulting baryonic density is still lognormal, the additional parameter gives us extra freedom in setting the variance of density fluctuations. With this extension, values of T 0 and γ implied in the SPH simulations are recovered at ∼ 1 - σ (≲ 10%) of the median (best-fit) values for most redshifts bins. However, this extended lognormal model cannot recover Γ12 reliably, with the best-fit value discrepant by ≳ 3 - σ for z > 2.2. Despite this limitation in the recovery of Γ12, whose origins we explain, we argue that the model remains useful for constraining cosmological parameters.

Particle initialization effects on Lyman-α forest statistics in cosmological SPH simulations

ABSTRACT Confronting measurements of the Lyman-α forest with cosmological hydrodynamical simulations has produced stringent constraints on models of particle dark matter and the thermal and ionization state of the intergalactic medium. We investigate the robustness of such models of the Lyman-α forest, focusing on the effect of particle initial conditions on the Lyman-α forest statistics in cosmological SPH simulations. We study multiple particle initialization algorithms in simulations that are designed to be identical in other respects. In agreement with the literature, we find that the correct linear theory evolution is obtained when a glass-like configuration is used for initial unperturbed gas particle positions alongside a regular grid configuration for dark matter particles and the use of non-identical initial density perturbations for gas and dark matter. However, we report that this introduces a large scale-dependent distortion in the 1D Lyman-α transmission power spectrum at small scales (k > 0.05 s km−1). The effect is close to 50 per cent at k ∼ 0.1 s km−1, and persists at higher resolution. This can severely bias inferences in parameters such as the dark matter particle mass. By considering multiple initial conditions codes and their variations, we also study the impact of a variety of other assumptions and algorithmic choices, such as adaptive softening, background radiation density, particle staggering, and perturbation theory accuracy, on the matter power spectrum, the Lyman-α flux power spectrum, and the Lyman-α flux PDF. This work reveals possible pathways towards more accurate theoretical models of the Lyman-α forest to match the quality of upcoming measurements.

Reliability analysis using Limit equilibrium and Smoothed Particle Hydrodynamics-based method for homogeneous soil slopes.

This paper develops a combined method to predict the volume of sliding mass for homogeneous slopes in an efficient manner. Firstly, the failure surface with minimum factor of safety (FS) in Limit Equilibrium Method is equated to that one determined by Smoothed Particle Hydrodynamics algorithm to obtain the threshold displacement value for unstable and stable particles. Secondly, the threshold displacement value is used to identify the volume of sliding mass using SPH. Finally, a regression model is developed based on a finite number of SPH simulations for homogeneous soil slopes. The proposed LEM-SPH based method is illustrated through a cohesive soil slope. It is concluded that the use of failure surface with minimum FS in LEM tends to underestimate the volume of sliding mass and to give an unconservative risk value. The Coefficient of Variation (Cov) of volume of sliding mass are 0.14, 0.28, 0.4, 0.48, 0.53 for Cov of soil properties = 0.2, 0.3, 0.4, 0.5, and 0.6, respectively. The uncertainty of soil properties has a significant effect on the mean value of volume of sliding mass and therefore the landslide risk value. The proposed method is necessitated for cases where large uncertainties in soil properties exist.

Protoplanet collisions: New scaling laws from smooth particle hydrodynamics simulations

One common approach for solving collisions between protoplanets in simulations of planet formation is to employ analytical scaling laws. The most widely used one was developed by Leinhardt2012 from a catalog of sim 180 N-body simulations of rubble--pile collisions. In this work, we use a new catalogue of more than 20,000 SPH simulations to test the validity and the prediction capability of Leinhardt2012 scaling laws. We find that these laws overestimate the fragmentation efficiency in the merging regime and they are not able to properly reproduce the collision outcomes in the super--catastrophic regime. In the merging regime, we also notice a significant dependence between the collision outcome, in terms of the largest remnant mass, and the relative mass of the colliding protoplanets. Here, we present a new set of scaling laws that are able to better predict the collision outcome in all regimes and it is also able to reproduce the observed dependence on the mass ratio. We compare our new scaling laws against a machine learning approach and obtain similar prediction efficiency.

Adaptive moving window technique for SPH simulation of stationary shock waves

A novel adaptive moving window (AMW) technique is developed for simulating stationary shock waves in a moving coordinate system associated with a simulation box. The velocity of this system is adjusted by an iterative feedback algorithm with the purpose of establishing a desirable position of shock front. Galilean transformations are iteratively used to maintain the shape of the flow profile. The moving coordinate system has advantages in simulation over a conventional coordinate system associated with the intact material at rest. In particular, a truly steady flow regime can be established in this moving window (MW). Comparative simulation using the smoothed particle hydrodynamics method to study shock propagation in copper confirms that the AMW converges to a steady state faster than a MW technique with a fixed velocity. We demonstrate that AMW can be applied for very weak shocks. Advantage of AMW is revealed in SPH simulation of the front structure for weak shocks in porous copper that result in a partial pore compaction. Specifically, we clarify the mechanism of the partial pore collapse for shock velocities below a knee on a calculated shock Hugoniot, where this knee corresponds to the complete collapse of pores.

WInDI: a Warp-Induced Dust Instability in protoplanetary discs

ABSTRACT We identify a new dust instability that occurs in warped discs. The instability is caused by the oscillatory gas motions induced by the warp in the bending wave regime. We first demonstrate the instability using a local 1D (vertical) toy model based on the warped shearing box coordinates and investigate the effects of the warp magnitude and dust Stokes number on the growth of the instability. We then run 3D smoothed particle hydrodynamics (SPH) simulations and show that the instability is manifested globally by producing unique dust structures that do not correspond to gas pressure maxima. The 1D and SPH analysis suggest that the instability grows on dynamical time-scales and hence is potentially significant for planet formation.

SPH Simulation of Pin Shape Influence on Material Flow in Friction Stir Welding (FSW)

SPH Simulation of Pin Shape Influence on Material Flow in Friction Stir Welding (FSW)

Interaction between regular waves and floating breakwater with protruding plates: Laboratory experiments and SPH simulations

Overseas construction often adopts floating breakwaters as working platforms or wave attenuation. Laboratory and numerical investigations of the hydrodynamics during the interaction between regular waves and floating breakwater with protruding plates were conducted. By coupling DualSPHysics and MoorDyn, the motion of the floating structure under the mooring system is realized. The accuracy of the coupling model is verified by comparing the free surface elevation and floating motion. The effects of protruding types and plate length on the performance of the floating breakwater are analyzed. The results show that the reflection and dissipation coefficients increase with the increase of plate length. Under medium-long period waves, the wave attenuation of floating breakwater with protruding plates is weak. Horizontal protruding plates are more capable of restraining sway than vertical plates. Under the large draft, the horizontal protruding plates are more effective in suppressing the roll.

Numerical simulation of “sand-like” polymer flow during rotational moulding using smoothed particle hydrodynamics method

Rotational moulding is a versatile polymer shaping process used to create enclosed parts from powdered precursors using heat and multi-axis rotation. Controlling the heating process and mould motion is critical to producing high-quality parts, and failures due to incorrect mould coverage or variable wall thickness are common. To date, limited simulation tools exist to predict the motion of the powder within the mould, and operators rely on unreliable prior experience to avoid defects. This paper presents an SPH simulation framework to predict particle flow patterns and powder contact time within a rotating mould. The powder-to-wall contact time was derived from the transient rigid body force (RBF) of different sensors on the mould. The method was compared with the results of DEM simulation and validated by the particle flow pattern of two experimental results. Results showed that the SPH method was capable of simulating particle flow macroscopic properties. The great computing efficiency of SPH compared to DEM simulation was also demonstrated.

2021 occultations and transits of Linus orbiting (22) Kalliope

Aims.The satellite Linus orbiting the main-belt asteroid (22) Kalliope exhibited mutual occultation and transit events in late 2021. A photometric campaign was organised and observations were undertaken by the TRAPPIST-South, SPECULOOS-Artemis, OWL-Net, and BOAO telescopes, with the goal to further constrain dynamical and photometric models of this sizeable asteroid-satellite system.Methods.Our dynamical model is sufficiently complex, featuring multipoles (up to the order ofℓ= 2), internal tides, and external tides. The model was constrained by astrometry (spanning 2001–2021), occultations, adaptive-optics imaging, and calibrated photometry, as well as relative photometry. Our photometric model was substantially improved. A new precise (<0.1 mmag) light curve algorithm was implemented, based on polygon intersections, which are computed exactly by including partial eclipses and partial visibility of polygons. Moreover, we implemented a ‘cliptracing’ algorithm, again based on polygon intersections, in which partial contributions to individual pixels are computed exactly. Both synthetic light curves and synthetic images then become very smooth.Results.Based on our combined solution, we confirmed the size of Linus, namely, (28 ± 1)km. However, this solution exhibits some tension among the light curves and the PISCO speckle-interferometry dataset, acquired simultaneously with the 2021 events. This indicates that improvements of the shape are still possible. In most solutions, Linus is darker than Kalliope, with the single-scattering albedosAw= 0.40 vs. 0.44. This is confirmed on deconvolved images. A detailed revision of astrometric data has allowed us to revise also theJ2≡ −C20value of Kalliope. Most importantly, a homogeneous body is excluded. For a differentiated body, two solutions exist: low-oblateness (C20≃ −0.12), with a spherical iron core, and, alternatively, high-oblateness (C20≃ −0.22) with an elongated iron core. These values correspond, respectively, to the low- and high-energy collisions we studied via SPH simulations in our previous work.

Three-dimensional SPH Simulations of FU Orionis Star Flares in the Clumpy Accretion Model

One of the early hypotheses about the origin of FU Orionis star (FUORs) outbursts explains them based on the fall of gas clumps from the remnants of protostellar clouds onto protoplanetary disks surrounding young stars. To calculate the consequences of such an event, we make 3D hydrodynamic simulations using the smoothed particle hydrodynamics method. It is shown that the fall of the clump on the disk in the vicinity of the star actually causes a burst of the star’s accretion activity, resembling in its characteristics the flares of known FUORs. In the region of incidence, an inhomogeneous gas ring is formed, which is inclined relative to the outer disk. During several revolutions around the star, this ring combines with the inner disk and forms a tilted disk. In the process of evolution, the inner disk expands, and its inclination relative to the outer disk decreases. After 100 revolutions, the angle of inclination is a few degrees. This result is of interest in connection with the discovery in recent years of protoplanetary disks, the inner region of which is inclined relative to the outer one. Such structures are usually associated with the existence in the vicinity of a star of a massive body (planet or brown dwarf), whose orbit is inclined relative to the plane of the disk. The results of our modeling indicate the possibility of an alternative explanation for this phenomenon.

Interfacial investigations on the microstructure evolution and thermomechanical behavior of explosive welded CLAM/316L composite

In this paper, a comprehensive study combined multiple characterizations and SPH numerical simulation was conducted to investigate the microstructure evolution, extreme thermomechanical behavior and consequences of the explosive welded CLAM/316L interface. The interfaces of the two welding materials underwent remarkable temperature rise and rapid cooling under high-speed collision conditions, forming a tight bond that presents a wavy structure with vortices. The SPH simulation adequately reproduced the heating and cooling process of the interface during explosive welding, revealing the high heterogeneity of the thermodynamic behavior during the impact process. Furthermore, the EBSD analyses showed the perplexing evolution of crystal structure at the bonding interface with vortex, including ultra-fine grains, columnar grains, equiaxed grains, deformed grains and serious lattice distortion. By correlating the temperature histories and grain characteristics at different positions of the interface, the formation mechanism of diverse grains was revealed, referring to crystallization from liquid, recrystallization from the solid and plastic deformation. The recrystallization at the interface was closely related to the material properties, and the significant variations in dislocation density and plastic strain values at the interface, as well as the thermal softening of the material, could be explained by different degrees of dynamic recovery and recrystallization.

On the impact off(Q) gravity on the large scale structure

ABSTRACTWe investigate the exponential f(Q) symmetric teleparallel gravitation, namely $f(Q)=Q+\alpha Q_0(1-e^{-\beta \sqrt{Q/Q_0}})$ using ME-GADGET code to probe the structure formation with box sizes LBox = 10/100 Mpc h–1 and middle resolution $N_p^{1/3}=512$. To reproduce viable cosmology within the aforementioned modified gravity theory, we first perform Markov Chain Monte Carlo (MCMC) sampling on OHD/BAO/Pantheon data sets and constrain a parameter space. Furthermore, we also derive theoretical values for deceleration parameter q(z), statefinder pair {r, s} and effective gravitational constant Geff, perform Om(z) diagnostics. While carrying out N-body+SPH simulations, we derive CDM+baryons over density/temperature/mean molecular weight fields, matter power spectrum (both 2/3D, with/without redshift space distortions), bispectrum, two-point correlation function and halo mass function. Results for small and big simulation box sizes are therefore properly compared, halo mass function is related to the Seth–Tormen theoretical prediction and matter power spectrum to the standard CAMB output.

Design of fluid flow optimized ejector drill heads for efficient metalworking fluid supply to the cutting zone

Ejector deep hole drilling is used for demanding drilling applications with high quality requirements, performed on conventional machining centers and lathes. The characteristically distributed metal working fluid flow based on the ejector effect is responsible for a stable and efficient process. The metal working fluid supply of the cutting edges as well as of the guide pads and the maintaining of a stable process are a major challenge for the optimization of ejector tools. To achieve an enhanced understanding of the fluid flow at the ejector drill head, a Smoothed Particle Hydrodynamics based simulation model was developed, which allows to simulate the challenging effects and conditions of the process. Different variants of optimized drill head concepts in favor of fluid flow are designed in this scientific paper, which lead to an enhanced metal working fluid supply to the cutting edges and guide pads at the drill head. The analysis of the fluid flow at the drill head is carried out with the results of the SPH simulation.

Interaction between medium-long period waves and smoothed mound breakwater: Physical model tests and SPH simulations

Medium-long period waves have attracted increasing attention. Laboratory and numerical investigations on the interaction between medium-long period waves and a smoothed mound breakwater were conducted. A two-dimensional numerical wave flume based on smoothed particle hydrodynamics was established. A good agreement between experimental and numerical results was observed.Wave force on the slope is positively correlated with the wave period. It is found that Neelamani's method is slightly overestimated wave force on the slope. By comparing with other overtopping methods, a new formula considering the wave period was proposed to predict the overtopping of the smoothed mound breakwater. The energy transmission coefficient was used to evaluate the protective effect of the breakwater. The results show that the smooth mound breakwater provides significant protection against longer-period waves. As the wave period increases, the number of peaks (Np) in the wave spectrum behind the breakwater increases. A formula was presented to describe the relationship between Np and wave period.