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We propose to couple a state-resolved rovibrational coarse-grain model to a stochastic particle method for simulating internal energy excitation and dissociation of a molecular gas. A coarse-grained model for a rovibrational reaction mechanism of an ab initio database developed at the NASA Ames Research Center for the N2–N system is modified based on variably spaced energy bins. The thermodynamic properties of the modified coarse-grained model allow us to closely match those obtained with the full set of rovibrational levels over a wide temperature range, while using a number of bins significantly smaller than the complete mechanism. The chemical-kinetic behavior of equally and variably spaced bin formulations is compared by simulating internal energy excitation and dissociation of nitrogen in an adiabatic, isochoric reactor. We find that the variably spaced formulation is better suited for reproducing the dynamics of the full database at conditions of interest in the Earth atmospheric entry. Also in this paper, we discuss the details of our particle method implementation for the uniform rovibrational collisional bin model and describe changes to the Direct Simulation Monte Carlo (DSMC) collision algorithm, which become necessary to accommodate our state-resolved reaction mechanism for excitation and dissociation reactions. The DSMC code is then verified against equivalent master equation calculations. In these simulations, state-resolved cross sections are used in analytical form. These cross sections verify micro-reversibility relations for the rovibrational bins and allow for fast execution of the DSMC code. In our verification calculations, we obtain very close agreement for the concentrations profiles of N and N2, as well as the translational and rovibrational mode temperatures obtained independently through both methods. In addition to macroscopic moments, we compare discrete internal energy populations predicted at selected time steps via DSMC and the master equations. We observe good agreement between the two sets of results within the limits imposed by statistical scatter, which is inherent to particle-based DSMC solutions. As future work, the rovibrational coarse-grain model coupled to the particle method will allow us to study 3D reentry flow configurations. [ABSTRACT FROM AUTHOR]

Self Consistent Field (SCF) theory serves as an efficient tool for studying mesoscale structure and thermodynamics of polymeric liquid crystals (LC). We investigate how some of the intrinsic approximations of SCF affect the description of the thermodynamics of polymeric LC, using a coarse-grained model. Polymer nematics are represented as discrete worm-like chains (WLC) where non-bonded interactions are defined combining an isotropic repulsive and an anisotropic attractive Maier-Saupe (MS) potential. The range of the potentials, σ, controls the strength of correlations due to non-bonded interactions. Increasing σ (which can be seen as an increase of coarse-graining) while preserving the integrated strength of the potentials reduces correlations. The model is studied with particle-based Monte Carlo (MC) simulations and SCF theory which uses partial enumeration to describe discrete WLC. In MC simulations the Helmholtz free energy is calculated as a function of strength of MS interactions to obtain reference thermodynamic data. To calculate the free energy of the nematic branch with respect to the disordered melt, we employ a special thermodynamic integration (TI) scheme invoking an external field to bypass the first-order isotropic-nematic transition. Methodological aspects which have not been discussed in earlier implementations of the TI to LC are considered. Special attention is given to the rotational Goldstone mode. The free-energy landscape in MC and SCF is directly compared. For moderate σ the differences highlight the importance of local non-bonded orientation correlations between segments, which SCF neglects. Simple renormalization of parameters in SCF cannot compensate the missing correlations. Increasing σ reduces correlations and SCF reproduces well the free energy in MC simulations. [ABSTRACT FROM AUTHOR]

We report a methodology to optimize vertically grown carbon nanotube (CNT) ultracapacitor (CNU) geometrical features such as CNT length, electrode-to-electrode separation, and CNT packing density. The electric field and electrolyte ionic motion within the CNU are critical in determining the device performance. Using a particle-based model (PBM) based on the molecular dynamics techniques we developed and reported previously, we compute the electric field in the device, keep track of the electrolyte ionic motion in the device volume, and evaluate the CNU electrical performance as a function of the aforementioned geometrical features. We show that the PBM predicts an optimal CNT density. Electrolyte ionic trapping occurs in the high CNT density regime, which limits the electrolyte ions from forming a double layer capacitance. In this regime, the CNU capacitance does not increase with the CNT packing density as expected, but dramatically decreases. Our results compare well with existing experimental data and the PBM methodology can be applied to an ultracapacitor built from any metallic electrode materials, as well as the vertical CNTs studied here. [ABSTRACT FROM AUTHOR]

In this work the first 3D Smoothed Particle Hydrodynamics model of a Rayleigh collapse for an empty cavity is proposed with the aim of improving the hydrodynamic analysis of a non-symmetrical collapse. The hydrodynamics of the model is validated against the solution of the Rayleigh-Plesset equation for a symmetrical collapse. The model is then used to simulate a non-symmetrical collapse of an empty cavity attached to a solid surface with induced by an external pressure of 50 [MPa]. The results shows that is possible to identify three regions where the hydrodynamics of the collapsing cavity shows different features. For all the stages of the collapse the simulation shows smooth pressure and velocity fields in the liquid and in the solid phase with the formation of a vortex ring in the final phase of the collapse. Finally, the model is compared to a previous 2D model to highlight strong, weak points and the key differences of both approaches in final phase of the collapse. [ABSTRACT FROM AUTHOR]

The present study investigates nonlinear buckling and post-buckling behaviors of composite plates with the circular/elliptical cut-out using Particle Semi-Energy (PSE) method. The semi-energy is based on the solution of the compatibility equation obtained from an Airy force and out-of-plane displacement functions. The unknown parameters of these functions were determined by minimizing the potential energy. The integrals of the potential energy were then replaced by the summations at the perforated plate particle (node). The cut-out was easily modeled using these nodes. This method enjoys some advantages, namely easy cut-out modeling by nodes and proposing just one of the displacement fields (i.e., out-of-plane). According to the results, there was good agreement (1.25%) between the post-buckling loads derived from PSE in this paper and the experimental test of the literature. According to the experimental test results, the accuracy of Finite Element Method (FEM) was 7.5%. This study also evaluated the effects of rotating the elliptical cut-out and replacing it with two other circular cut-outs in the same areas on the post-buckling load. [ABSTRACT FROM AUTHOR]

LAMMPS is a powerful simulator originally developed for molecular dynamics that, today, also accounts for other particle-based algorithms such as DEM, SPH, or Peridynamics. The versatility of this software is further enhanced by the fact that it is open-source and modifiable by users. This property suits particularly well Discrete Multiphysics and hybrid models that combine multiple particle methods in the same simulation. Modifying LAMMPS can be challenging for researchers with little coding experience. The available material explaining how to modify LAMMPS is either too basic or too advanced for the average researcher. In this work, we provide several examples, with increasing level of complexity, suitable for researchers and practitioners in physics and engineering, who are familiar with coding without been experts. For each feature, step by step instructions for implementing them in LAMMPS are shown to allow researchers to easily follow the procedure and compile a new version of the code. The aim is to fill a gap in the literature with particular reference to the scientific community that uses particle methods for (discrete) multiphysics. [ABSTRACT FROM AUTHOR]

We tested the isotropic periodic sum (IPS) method for computing Madelung energies of ionic crystals. The performance of the method, both in its nonpolar (IPSn) and polar (IPSp) forms, was compared with that of the zero-charge and Wolf potentials [D. Wolf, P. Keblinski, S. R. Phillpot, and J. Eggebrecht, J. Chem. Phys. 110, 8254 (1999)]. The results show that the IPSn and IPSp methods converge the Madelung energy to its reference value with an average deviation of ~10-4 and ~10-7 energy units, respectively, for a cutoff range of 18-24a (a/2 being the nearest-neighbor ion separation). However, minor oscillations were detected for the IPS methods when deviations of the computed Madelung energies were plotted on a logarithmic scale as a function of the cutoff distance. To remove such oscillations, we introduced a modified IPSn potential in which both the localregion and long-range electrostatic terms are damped, in analogy to the Wolf potential. With the damped-IPSn potential, a smoother convergence was achieved. In addition, we observed a better agreement between the damped-IPSn and IPSp methods, which suggests that damping the IPSn potential is in effect similar to adding a screening potential in IPSp. [ABSTRACT FROM AUTHOR]

The interlaced and non-interlaced versions of the dipolar particle-particle particle-mesh (P3M) method implemented using the analytic differentiation scheme (AD-P3M) are presented together with their respective error estimates for the calculation of the forces, torques, and energies. Expressions for the optimized lattice Green functions, and for the Madelung self-forces, self-torques and self-energies are given. The applicability of the theoretical error estimates are thoroughly tested and confirmed in several numerical examples. Our results show that the accuracy of the calculations can be improved substantially when the approximate (mesh computed) Madelung self-interactions are subtracted. Furthermore, we show that the interlaced dipolar AD-P3M method delivers a significantly higher accuracy (which corresponds approximately to using a twice finer mesh) than the conventional method, allowing thereby to reduce the mesh size with respect to the non-interlaced version for a given accuracy. In addition, we present similar expressions for the dipolar ik-differentiation interlaced scheme, and we perform a comparison with the AD interlaced scheme. Rough tests for the relative speed of the dipolar P3M method using ik-differentiation and the interlaced/non-interlaced AD schemes show that when FFT computing time is the bottleneck, usually when working at high precisions, the interlaced AD-scheme can be several times faster than the other two schemes. For calculations with a low accuracy requirement, the interlaced version can perform worse than the ik and the non-interlaced AD schemes. [ABSTRACT FROM AUTHOR]

The salting out of methane by adding NaCl to water at 25 °C and 1 atm is investigated by calculating the work of cavity creation by means of scaled particle theory and the methane-solvent energy of attraction. The latter quantity changes to little extent on passing from pure water to an aqueous 4M NaCl solution, whereas the magnitude of the work of cavity creation increases significantly, accounting for the salting out effect. There is quantitative agreement between the experimental values of the hydration Gibbs energy and the calculated ones. The behavior of the work of cavity creation is due to the increase in the volume packing density of NaCl solutions, since the average effective molecular diameter does not change, being always 2.80 Å. The same approach allows the rationalization of the difference in methane salting out along the alkali chloride series. These results indicate that, fixed the aqueous solution density, the solubility of nonpolar species is mainly determined by the effective diameter of solvent molecules and the corresponding volume packing density. There is no need to take into account the H-bond rearrangement because it is characterized by an almost complete enthalpy-entropy compensation. [ABSTRACT FROM AUTHOR]

Spatially distributed problems are often approximately modeled in terms of partial differential equations (PDEs) for appropriate coarse-grained quantities (e.g., concentrations). The derivation of accurate such PDEs starting from finer scale, atomistic models, and using suitable averaging is often a challenging task; approximate PDEs are typically obtained through mathematical closure procedures (e.g., mean field approximations). In this paper, we show how such approximate macroscopic PDEs can be exploited in constructing preconditioners to accelerate stochastic computations for spatially distributed particle-based process models. We illustrate how such preconditioning can improve the convergence of equation-free coarse-grained methods based on coarse timesteppers. Our model problem is a stochastic reaction-diffusion model capable of exhibiting Turing instabilities. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Simulation of convection-reaction-diffusion for heterogenous catalytic reactors. • Numerical computation of bulk mutual diffusivity using SRD. • Incorporation of complex reaction systems while maintaining the interfacial physics. • Dimensionless analysis to convey physical information between reactive systems. • Different modeling examples show from linear systems to nonlinear reaction systems. Abstract Particle based approaches are one of the recent modeling techniques to overcome the computational limitation in multiscale modeling of complex processes, for example a heterogeneous catalytic reactor. We propose an efficient model for a chemical reactor where hydrodynamics of the solvent is determined by Stochastic Rotation Dynamics and a reaction occurs over a catalytic surface where the reaction kinetics follows the mean-field assumption. We highlight the modeling techniques required to simulate such a system and then validate the model for its separate and combined components of convection, diffusion and reaction(s). A dimensionless analysis helps compare processes occurring at different scales. We determine the Reynolds number, Re , and the Damkohler numbers, Da and Da L in terms of key quantities. The approach is then used to analyse a reaction (a) following the Langmuir-Hinshelwood kinetics, (b) generating product particles with different self-diffusivity values as compared to the reactant particles. The model developed can further incorporate reactions occurring inside complex geometries (pore diffusion) and also be used to study complex reaction systems for which the mean-field assumption is no longer valid. [ABSTRACT FROM AUTHOR]

This paper aims to discuss the boundary conditions techniques employed in the solution of physical and engineering problems using the Lagrangian particle approach in continuum mechanics. Simulations using different boundary treatment techniques have been performed, and in addition, a review of the literature on the techniques commonly employed in SPH simulations was also performed. The fictitious (virtual/ghost), the dynamic particles and the artificial repulsive forces are widely employed in problem-solving, mixing concepts of molecular and continuum scales, being inadequate for the use in continuum scale (considering the disrespect of the classical physics laws). On the other hand, the reflective boundary conditions, based on fundamentals of Physics (Newton's restitution law) and analytic geometry, are in accordance with the continuum hypothesis and their use is recommended in continuum mechanics problems, out of the molecular scale. In many boundary conditions employed in particle methods, models of repulsive molecular forces in conjunction with virtual particles are being used without theoretical foundation in continuum mechanics and classical Physics. Purely computational solutions employing fictitious particles and artificial molecular forces should be avoided, and methods that respect the continuum theory, such as the reflective boundary conditions, should be employed on the macroscopic scale. Both hydrostatic and hydrodynamics analysis have been performed. An excellent agreement with the analytical solution or experimental results have been achieved. From the results found, the applicability of the reflexive boundary technique in the continuum domain, discretized by particles, was verified. [ABSTRACT FROM AUTHOR]

Highlights • Accurate upscaling of reactive transport Poiseuille flow with Reactive Particle Tracking (RPT) model. • RPT model separately simulates mixing with local molecular diffusion and spreading by Taylor macro-dispersion. • Comparison to two semi-analytic upscaling techniques: Volume-averaging and Ensemble Streamtube. • Separate treatment of mixing and spreading makes Lagrangian RPT model more representative than Eulerian advection-dispersion-reaction equation. Abstract The Eulerian advection-dispersion-reaction equation (ADRE) suffers the well-known scale-effect of reduced apparent reaction rates between chemically dissimilar fluids at larger scales (or dimensional averaging). The dispersion tensor in the ADRE must equally and simultaneously account for both solute mixing and spreading. Recent reactive-particle-tracking (RPT) algorithms can, by separate mechanisms, simulate 1) smaller-scale mixing by inter-particle mass transfer, and 2) mass spreading by traditional random walks. To test the supposition that the RPT can accurately track these separate mechanisms, we upscale reactive transport in Hagen-Poiseuille flow between two plates. The simple upscaled 1-D RPT model with one velocity value, an upscaled Taylor macro-dispersivity, and the local molecular diffusion coefficient matches the results obtained from a detailed 2-D model with fully described velocity and diffusion. Both models use the same thermodynamic reaction rate, because the rate is not forced to absorb the loss of information upon upscaling. Analytic and semi-analytic upscaling is also performed using volume averaging and ensemble streamtube techniques. Volume averaging does not perform as well as the RPT, while the streamtube approach (using an effective dispersion coefficient along with macro-dispersion) performs almost exactly the same as RPT. [ABSTRACT FROM AUTHOR]

Abstract: Spatially and temporally adaptive algorithms can substantially improve the computational efficiency of many numerical schemes in computational mechanics and physics‐based animation. Recently, a crucial need for temporal adaptivity in the Material Point Method (MPM) is emerging due to the potentially substantial variation of material stiffness and velocities in multi‐material scenes. In this work, we propose a novel temporally adaptive symplectic Euler scheme for MPM with regional time stepping (RTS), where different time steps are used in different regions. We design a time stepping scheduler operating at the granularity of small blocks to maintain a natural consistency with the hybrid particle/grid nature of MPM. Our method utilizes the Sparse Paged Grid (SPGrid) data structure and simultaneously offers high efficiency and notable ease of implementation with a practical multi‐threaded particle‐grid transfer strategy. We demonstrate the efficacy of our asynchronous MPM method on various examples including elastic objects, granular media, and fluids. [ABSTRACT FROM AUTHOR]

Abstract The paper presents a numerical wave flume with porous media of variable porosity. A fully-Lagrangian computational method is developed for simulation of fluid flow interactions with porous media based on a projection-based (or Incompressible) SPH (Smoothed Particle Hydrodynamics) method. The continuity and Navier-Stokes equations are reformulated with incorporation of volume fraction, based on two-phase mixture theory. The proposed method benefits from a set of enhanced schemes and is therefore referred to as Enhanced Incompressible SPH (ISPH). The effect of porous media is represented by considering linear and nonlinear resistance force terms as well as incorporation of a newly-derived source term of PPE (Poisson Pressure Equation). The results are characterized by smooth and continuous pressure fields, as well as regular particle distributions at the fluid-porous media interface in absence of any artificial smoothing schemes. Since the local volume fraction of fluid phase particles is consistently calculated based on the volume fraction of surrounding porous phase particles, the method is capable of accurately reproducing fluid flow interactions with spatially varying porous media. Validations are made through a set of benchmark tests including fluid flow in a U-tube with uniform and multi-layered porous media, rapid seepage flows in rockfill dam, solitary wave attenuation over a porous bed, solitary wave interaction with a submerged porous structure and wave propagation over a submerged triangular permeable bar. Graphical abstract Image 1 Highlights • A novel fully-Lagrangian grid-less method is proposed for numerical wave flume with porous media of variable porosity. • The proposed method corresponds to a projection-based SPH on the basis of two-phase liquid-solid mixture theory. • Resistance force terms and a newly-derived source term of Poisson Pressure Equation represent the effect of porous media. • Results are characterized by continuity of pressure/velocity and regularity of particle distributions at the interface. • Validations are made by consideration of a set of benchmark tests through analytical/experimental comparisons. [ABSTRACT FROM AUTHOR]

Abstract We propose extending Bohmian mechanics (BM) with the moving particle semi-implicit method, a particle method for uncompressed fluids. The application of this method prevents the node of the Bohm quantum potential from breaking numerical calculations while maintaining a low calculation cost. We validated our extended method by comparing our results with those from the conventional method for a one-dimensional harmonic oscillator, Gaussian barrier and rectangular barrier. The proposed method was found to simulate the temporal changes in the probability density for a rectangular barrier. In addition, the relational equation obtained by this method reveals an interesting correspondence between the pressure of a classical fluid and the Bohm quantum potential. Highlights • Bohmian mechanics is extended using moving particle semi-implicit method. • The interesting relation between the pressure of a classical fluid and the Bohm quantum potential is obtained. • The calculation cost is reduced more than the conventional method. • The temporal changes in the probability density for a rectangular barrier is simulated using the proposed method. [ABSTRACT FROM AUTHOR]

A meshfree approach to the simulation of the large deformation of a curved shell by the reproducing kernel particle method (RKPM) is presented. Since the kinematic description is based on the Mindlin-Reissner shell theory, only one layer of particles is needed to model the shell and the time increment is not limited by the shell thickness. The reproducing interpolation function is adopted to discretize the kinematic quantities of the shell; thus, the spatial discretization is independent of the finite element mesh, so it can address large deformations without mesh distortion. The governing equation of an arbitrary curved shell is derived in detail based on the principle of virtual power, for which reasonable simplifications have been taken. The Lagrangian kernel and stress points are adopted in the calculation, which are sufficient to eliminate instability. Several numerical examples are performed, verifying the reliability and numerical accuracy of the RKPM shell model. No locking is observed in the numerical solutions. [ABSTRACT FROM AUTHOR]

The material point method (MPM), which is a combination of the finite element and meshfree methods, suffers from significant computational workload due to the fine mesh required in spite of its advantages in simulating large deformations. This paper presents a parallel computing strategy for the MPM with multiple Graphics Processing Units (GPUs) to boost the method’s computational efficiency in large scale problems. Domain decomposition method is used to split the workload over subdomains onto a number of GPUs. Communication between the subdomains is implemented by the data transfer between GPUs and random access memory. On each GPU the MPM algorithm is parallelised over nodes or particles. Benchmark problems of slurry runout and surface pipe penetration are analysed to quantify the speedup of the multiple-GPU parallel simulations over the sequential counterparts on the central processing unit. The maximum speedup with 1 GPU is 84 and increases to ∼1280 using 16 GPUs. [ABSTRACT FROM AUTHOR]

An advanced moving particle semi-implicit (MPS) method for the simulation of incompressible flows that provides enhanced accuracy and stability is proposed. Up to now, existing high-order accurate MPS pressure gradient schemes suffer from instability produced by attractive pressure gradient while some stabilized pressure gradient schemes have the shortcomings of large discretization error. We propose a high-order stabilized gradient model in which first-order Taylor-series consistency is ensured and stability is guaranteed by purely repulsive pressure gradient. Laplacian model and divergence model are modified and enable accurate and stable solution for the pressure Poisson equation (PPE). The proposed MPS scheme provides a more accurate and stable simulation of incompressible flows. Several two-dimensional numerical simulations are presented to demonstrate the enhanced performance of the proposed MPS method. [ABSTRACT FROM AUTHOR]

A fully-Lagrangian particle-based computational method is developed for simulation of incompressible Fluid, non-linear Structure Interaction (FSI) with incorporation of stress point integration (Randles and Libersky, 2005) to resolve instabilities related to zero-energy modes. Structural dynamics is founded on discretization of the divergence of stress according to Moving Least Squares (MLS) method. The stress point integration is incorporated in calculation of structural dynamics, resulting in a Dual Particle Dynamics (DPD) structure model (Randles and Libersky, 2005). A structure model based on nodal integration is also considered for comparison and simply referred to as MLS. The DPD and MLS structure models are coupled with an enhanced projection-based Moving Particle Semi-implicit (MPS) method as the fluid model, resulting in DPD–MPS and MLS–MPS FSI solvers, respectively. The enhanced performance of DPD with respect to MLS is first shown through a set of tests for structure model. Then the superior performance of DPD–MPS FSI solver with respect to MLS–MPS one is demonstrated through a set of FSI benchmark tests. The present study also presents a new algorithm for fluid–structure coupling via components of stress tensors in surface boundary stress points. [ABSTRACT FROM AUTHOR]

In this work, a modified Particle Method in fluid mechanics involving irregular distribution and discontinuity issues is proposed. Due to the approximation accuracy, momentum conservation and governing equation feasibility, traditional Particle Method, Moving Particle Semi-implicit (MPS) method in this paper, cannot guarantee the accuracy and stability of computation, and the divergence calculation in Navier–Stokes equation may cause numerical error in computation domain with discontinuity. To enhance the computation accuracy of Particle Method, we modify the gradient operator with a corrected tensor emanating from minimizing the local error of the first-order Taylor Expansion approximation. Besides, inspired by Peridynamic which is mostly used in solid mechanics, a new governing equation in an integral form which maintains the momentum conservation is obtained. Combining the modified gradient and new governing equation, we obtain a new particle-based method. The numerical results verify its feasibility and illustrate a good computational performance of proposed Method in the fluid dynamics involving non-uniform particle distribution. [ABSTRACT FROM AUTHOR]

Coarse grained particle methods significantly reduce the computation cost of large‐scale fluidized bed simulation by lumping many real particles into a computation parcel. This research provides a method to estimate the errors associated with parcel size in large‐scale fluidized bed simulations. This uncertainty is first quantified in small scale domains by comparing results of discrete particle method with that employing coarse parcels of different sizes. Then, this uncertainty is correlated with parcel size and simulation domains consisting of a simple homogeneous cooling system and more complex bubbling and circulating fluidized beds. These correlations allow us to accurately estimate the uncertainty in large‐scale fluidized beds based solely on data obtained in smaller systems. The ability to estimate model‐related uncertainty in larger systems makes this method relevant for industrial applications. © 2018 American Institute of Chemical Engineers AIChE J, 64: 2340–2350, 2018 [ABSTRACT FROM AUTHOR]

The "pseudo-wedge" failure is a name for a complex instability occurring at the Sarcheshmeh open-pit mine (Iran). The pseudo-wedge failure contains both the rock bridge failure and sliding along pre-existing discontinuities. In this paper, a cross section of the failure area was first modeled using a bonded-particle method. The results indicated development of tensile cracks at the slope toe which explains the freedom of pseudo-wedge blocks to slide. Then, a three-dimensional discrete element method was used to perform a block analysis of the instability. The technique of shear strength reduction was used to calculate the factor of safety. Finally, the influence of geometrical characteristics of the mine wall on the pseudo-wedge failure was investigated. The safety factor significantly increases as the dip and dip direction of the wall decrease, and reaches an acceptable value with a 10-degree decrease of them. [ABSTRACT FROM AUTHOR]

Abstract: The Fluid Implicit Particle method (FLIP) reduces numerical dissipation by combining particles with grids. To improve performance, the subsequent narrow band FLIP method (NB‐FLIP) uses a FLIP‐based fluid simulation only near the liquid surface and a traditional grid‐based fluid simulation away from the surface. This spatially‐limited FLIP simulation significantly reduces the number of particles and alleviates a computational bottleneck. In this paper, we extend the NB‐FLIP idea even further, by allowing a simulation to transition between a FLIP‐like fluid simulation and a grid‐based simulation in arbitrary locations, not just near the surface. This approach leads to even more savings in memory and computation, because we can concentrate the particles only in areas where they are needed. More importantly, this new method allows us to seamlessly transition to smooth implicit surface geometry wherever the particle‐based simulation is unnecessary. Consequently, our method leads to a practical algorithm for avoiding the noisy surface artifacts associated with particle‐based liquid simulations, while simultaneously maintaining the benefits of a FLIP simulation in regions of dynamic motion. [ABSTRACT FROM AUTHOR]

ABSTRACT Wang, L.; Jiang, Q.; Nie, S.; Zhang, J., and Iddy, I., 2018. Improvement on MPS method for simulation of dynamic pressure in dam break flows. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 971–975. Coconut Creek (Florida), ISSN 0749-0208. The obvious unphysical pressure fluctuation is a serious issue when the original MPS method is used for the simulation of a violent flow problem, such as dam break flow. In this study, some modifications on the original MPS method are proposed to decrease the unreasonable pressure biases, in which a simple and effective auxiliary criterion for free surface particles is proposed to increase the accuracy of surface representation, and a new form of source term is implemented in the pressure Poison equation. The improved MPS model is applied to simulate the dam break flows so as to examine the effectiveness of the proposed methods on the improvement of dynamic pressure calculation. Comparisons with the experimental results for the dam break flow verified that the new free surface detection method is effective to avoid the misrecognition of free surface particles. Meanwhile, through examining the calculated pressure histories at a fixed point with different forms of source term, the importance of the source term of pressure Poison equation in the calculation of the dynamic pressure is demonstrated. [ABSTRACT FROM AUTHOR]

The multi-environment probability density function approach has been applied to numerically investigate the Moderate or Intense Low-Oxygen (MILD) oxy-combustion processes encountered in the non-catalytic partial oxidation (POX) gasifier. The multi-environment PDF approach has the form of a conventional Eulerian scheme and retains the desirable property of a particle-based method. Micro-mixing is represented via the IEM model, and the detailed chemistry is based on GRI 3.0 mechanism without NO x chemistry. In terms of the mean temperature, the present multi-environment PDF approach yields the overall agreement with the measurements in the highly fuel-rich MILD oxy-combustion situation with the strong flue gas recirculation even if there exist the certain discrepancies in the upstream region. Special emphasis is given to the effects of the fuel/oxygen injection velocity and O 2 /CH 4 ratio on the characteristics of the strongly recirculated MILD oxy-combustion processes. Depending on injection velocity or O 2 /CH 4 ratio, the present MEPDF approach well reproduces the qualitative flame transition characteristics from MILD combustion to conventional combustion. The higher fuel/oxygen injection velocity leads to the much longer jet penetration and the much higher SDR level which makes the ignition to occur at further downstream region. The relatively lower O 2 /CH 4 ratios maintain the basic characteristics of the MILD combustion while the highest O 2 /CH 4 ratio locally creates the oxy-flame like structure rather than the non-visible flame field. Based on numerical results, the detailed discussions are made for flame stabilization, auto-ignition process and precise flame structure in terms of recirculation rate, distribution of turbulent Damköhler number, scalar dissipation rate, mean temperature and mole fraction of CH 2 O and OH. [ABSTRACT FROM AUTHOR]

The article aims at providing an up-to-date review on several latest advancements related to particle methods with applications in coastal and ocean engineering. The latest advancements corresponding to accuracy, stability, conservation properties, multiphase multi-physics multi-scale simulations, fluid-structure interactions, exclusive coastal/ocean engineering applications and computational efficiency are reviewed. The future perspectives for further enhancement of applicability and reliability of particle methods for coastal/ocean engineering applications are also highlighted. [ABSTRACT FROM AUTHOR]

This paper presents a methodology to simulate penetration of a foundation element in Tresca soil using the generalized interpolation material point method (GIMP). The methodology relies on block-structured rectilinear background grids with hanging nodes to improve computational efficiency. For both efficiency and accuracy, material points are split into smaller material points as they enter grid elements that are not sufficiently large in comparison. Moving and compressible background grids are used to handle velocity boundary conditions. Comparison of simulations of foundation response during vertical, quasi-static motion with previous solutions illustrate the effectiveness and efficiency of the proposed schemes. [ABSTRACT FROM AUTHOR]

In order to study the separation mechanism of CO 2 droplets and natural gas in a supersonic separator, different structure of cyclones were designed and the flow characteristics of natural gas in the supersonic separator were numerically calculated. The mathematical model of the continuous phase (methane gas) and the dispersed phase (CO 2 droplets) was established, the distribution of the gas flow field and the droplets paths in the supersonic separator were obtained using Discrete Particle Method, the droplet separation efficiency was defined, and the effect of the droplet sizes and speed on the separation efficiency were analyzed. The results show that there is an obvious restriction relation between the pressure and tangential velocity distribution caused by the swirl blade, a balanced point (optimized structure) is necessary to achieve the purpose of condensation and separation of CO 2 droplets. And the separation efficiency increases with the increase of droplet size and the CO 2 droplets can be separated completely when the droplet size is greater than 1.5 μm. The initial axial velocity has no obvious effect on the separation efficiency of the supersonic separator. [ABSTRACT FROM AUTHOR]

A finite volume particle (FVP) method for simulation of incompressible flows that provides enhanced accuracy is proposed. In this enhanced FVP method, a dummy neighbor particle is introduced for each particle in the calculation and used for the discretization of the gradient model and Laplacian model. The error-compensating term produced by introducing the dummy neighbor particle enables higher order terms to be calculated. The proposed gradient model and Laplacian model are applied in both pressure and pressure gradient calculations. This enhanced FVP scheme provides more accurate simulations of incompressible flows. Several 2-dimensional numerical simulations are given to confirm its enhanced performance. [ABSTRACT FROM AUTHOR]

We use a particle method to study a Vlasov-type equation with local alignment, which was proposed by Sebastien Motsch and Eitan Tadmor [ J. Statist. Phys., 141(2011), pp. 923-947]. For N-particle system, we study the unconditional flocking behavior for a weighted Motsch-Tadmor model and a model with a 'tail'. When N goes to infinity, global existence and stability (hence uniqueness) of measure valued solutions to the kinetic equation of this model are obtained. We also prove that measure valued solutions converge to a flock. The main tool we use in this paper is Monge-Kantorovich-Rubinstein distance. [ABSTRACT FROM AUTHOR]

Shot peening is a cold working process used mainly to improve the fatigue life of metallic components. The complexity of the process makes it difficult and costly to evaluate the mechanism through experiment. Therefore, the purpose of this study is to provide an numerical model for simulating this process. Smoothed particle hydrodynamics (SPH), which is a meshfree particle method, is employed. SPH formulations are presented for conducting dynamic elastic-plastic analysis. The target material is discretized into a set of SPH particles, and the shot is modeled as a rigid body. Contact algorithm is used to calculate the contact force between target and shots. In order to simulate a large number of shots, a particle-based periodic cell model is proposed. Then, the model is applied to simulate shot peening process for both single impact and multiple impacts. Coverage percentage is estimated by evaluating the plastic deformation of target material. Comparisons of results with theoretical model for coverage assessment show that the proposed SPH model can help predicting the shot peening process. The present work extends the application of SPH method in modeling the shot peening, which may be helpful in optimization of the treatment. [ABSTRACT FROM AUTHOR]

Compared with the traditional Smoothed Particle Hydrodynamics (SPH), Finite Particle Method (FPM) has higher accuracy for boundary region. However, there are still two inherent defects which are the time consuming and the numerical instability in FPM. In this paper, a high-order algorithm based on the Taylor series expansion and the matrix theory is proposed and the corresponding particles selected mode is discussed. It is validated that the algorithm has higher-order accuracy than the previous low-order improvement algorithm for FPM. Further, transient heat conduction examples have been discussed to verify the feasibility and effectiveness of the new algorithm. [ABSTRACT FROM AUTHOR]

We present a multiscale mathematical model for the regulation of the cell cycle by the circadian clock. Biologically, the model describes the proliferation of a population of heterogeneous cells connected to each other. The model consists of a high dimensional transport equation structured by molecular contents of the cell cycle-circadian clock coupled oscillator. We propose a computational method for resolution adapted from the concept of particle methods. We study the impact of molecular dynamics on cell proliferation and show an example where discordance of division rhythms between population and single cell levels is observed. This highlights the importance of multiscale modeling where such results cannot be inferred from considering solely one biological level. [ABSTRACT FROM AUTHOR]

The heat transfer in a gas-solids fluidized bed is simulated with computational fluid dynamic-discrete element method (CFD-DEM) and coarse grained particle method (CGPM). In CGPM fewer numerical particles and their collisions are tracked by lumping several real particles into a computational parcel. The assumption is that the real particles inside a coarse grained particle (CGP) are made from same species and share identical physical properties including density, diameter and temperature. The parcel-fluid convection term in CGPM is calculated using the same method as in DEM. For all other heat transfer mechanisms, we derive in this study mathematical expressions that relate the new heat transfer terms for CGPM to those traditionally derived in DEM. This newly derived CGPM model is verified and validated by comparing the results with CFD-DEM simulation results and experiment data. The numerical results compare well with experimental data for both hydrodynamics and temperature profiles. The proposed CGPM model can be used for fast and accurate simulations of heat transfer in large scale gas-solids fluidized beds. [ABSTRACT FROM AUTHOR]

In the present work we use molecular dynamics simulations and graph-theory based cluster analysis to compare self-assembly in systems of magnetic spheres, and cubes where the dipole moment is oriented along the side of the cube in the [001] crystallographic direction. We show that under the same conditions cubes aggregate far less than their spherical counterparts. This difference can be explained in terms of the volume of phase space in which the formation of the bond is thermodynamically advantageous. It follows that this volume is much larger for a dipolar sphere than for a dipolar cube. [ABSTRACT FROM AUTHOR]

This paper examines the laws of stable ignition of organic coal-water slurry containing petrochemicals (CWSP). The CWSP is based on the filter cake of coal and scavenge oil. The experiments are performed for individual CWSP particles soaring in a special set-up. The temperature and velocity of an oxidizer flow are varied between 500-1200 K, and 0.5-3 m/s. The dimensions (longitudinal and transverse) of particles range are from 0.5 mm to 5 mm. The study indicates how the shape of a fuel particle (sphere, ellipsoid, and polyhedron) influences its ignition characteristics (delay time, minimum temperature, modes, stages). Based on the experimental results, the paper explains why the surface configuration of particles influences the conditions of heat transfer with an oxidizer. The results obtained for soaring particles are compared with the results for fixed CWSP particles having different surface configurations (sphere, ellipsoid, and polyhedron). In general, the study may contribute to the expansion of the fuel resource base. The experimental data may be used for the development of the technologies of burning CWSP prepared by recycling traditional fuels. As a result of this study, several recommendations for the practical application of research results are made. [ABSTRACT FROM AUTHOR]

Current material point method (MPM) particle updates use a PIC approach, a FLIP approach, or a linear combination of PIC and FLIP. A PIC update filters velocity in each time step, which causes unwanted numerical diffusion, while FLIP eliminates that diffusion, but may retain too much noise. This paper develops a new particle update termed XPIC( m ) (for eXtended PIC of order m ) because it generalizes PIC updates. XPIC(1) is identical to current PIC methods, but higher orders of XPIC( m ) address the over filtering and numerical diffusion of PIC, while still filtering out noise caused by the nontrivial null space of the extrapolation matrix used in MPM. As m → ∞ , XPIC( m ) converges to a modified FLIP update with orthogonal removal of null space noise. The frequency response and filtering properties of XPIC( m ) are investigated and several numerical examples demonstrate its advantages over other update methods. [ABSTRACT FROM AUTHOR]

Currently, the spotlight for new type production method is on 3D printers instead of conventional production such as injection and extrusion molding. One of the widespread 3D printing method is the deposition modeling method. In the deposition method, the melted material is injected from the nozzle and deposited on the substrate. The final shape of the produced objects depends on viscosity, surface tension of materials, migration speed of nozzle and injection speed. In this study, we develop and simulate the deposition modeling using one of the particle methods, Smoothed Particle Hydrodynamics Method. The height and width of the produced products are examined in various viscosities and injection speeds. The results show that high viscosity and slow injection speed are favorable to produce the objects. [ABSTRACT FROM AUTHOR]