Moubin Liu

Constructing smoothing functions in smoothed particle hydrodynamics with applications

This paper presents a general approach to construct analytical smoothing functions for the meshfree, Lagrangian and particle method of smoothed particle hydrodynamics. The approach uses integral form of function representation and applies Taylor series expansion to the SPH function and derivative approximations. The constructing conditions are derived systematically, which not only interpret the consistency condition of the method, but also describe the compact supportness requirement of the smoothing function. Examples of SPH smoothing function are constructed including some existing ones. With this approach, a new quartic smoothing function with some advantages is constructed, and is applied to the one dimensional shock problem and a one dimensional TNT detonation problem. The good agreement between the SPH results and those from other sources shows the effectiveness of the approach and the newly constructed smoothing function in numerical simulations.

Computer simulation of high explosive explosion using smoothed particle hydrodynamics methodology

Abstract In this paper, the smoothed particle hydrodynamics (SPH) is applied to simulate the high explosive (HE) explosion which consists of detonation and dispersion process. The combination of meshless and Lagrangian nature inherent in the SPH methodology avoids the disadvantages of traditional numerical methods in treating large deformations, large inhomogeneities and tracing free surfaces in the extremely transient explosion process. Four numerical examples are presented with comparisons from different sources. The presented numerical examples involve in various HE explosion scenarios of arbitrary charge shape and different detonation orientations. The simulation results show that the presented SPH methodology can give good prediction for both the magnitude and form of the detonation wave as well as the pressure transient in the explosion process. Major physics of the HE explosion can be well captured in the simulation.

AN OVERVIEW ON SMOOTHED PARTICLE HYDRODYNAMICS

This paper presents an overview on smoothed particle hydrodynamics (SPH), which is a meshfree, particle method of Lagrangian nature. In theory, the interpolation and approximations of the SPH method and the corresponding numerical errors are analyzed. The inherent particle inconsistency has been discussed in detail. It has been demonstrated that the particle inconsistency originates from the discrete particle approximation process and is the fundamental cause for poor approximation accuracy. Some particle consistency restoring approaches have been reviewed. In application, SPH modeling of general fluid dynamics and hyperdynamics with material strength have been reviewed with emphases on (1) microfluidics and microdrop dynamics, (2) coast hydrodynamics and offshore engineering, (3) environmental and geophysical flows, (4) high-explosive detonation and explosions, (5) underwater explosions, and (6) hydrodynamics with material strength including hypervelocity impact and penetration.

Dissipative particle dynamics with attractive and repulsive particle-particle interactions

In molecular dynamics simulations, a combination of short-range repulsive and long-range attractive interactions allows the behavior of gases, liquids, solids, and multiphase systems to be simulated. We demonstrate that dissipative particle dynamics (DPD) simulations with similar pairwise particle-particle interactions can also be used to simulate the dynamics of multiphase fluids. In these simulations, the positive, short-range, repulsive part of the interaction potentials were represented by polynomial spline functions such as those used as smoothing functions in smoothed particle hydrodynamics, and the negative long-range part of the interaction has the same form but a different range and amplitude. If a single spline function corresponding to a purely repulsive interaction is used, the DPD fluid is a gas, and we show that the Poiseuille flow of this gas can be described accurately by the Navier-Stokes equation at low Reynolds numbers. In a two-component system in which the purely repulsive interaction...

Computer simulation of two‐phase immiscible fluid motion in unsaturated complex fractures using a volume of fluid method

[1]xa0Complex fluid behavior in unsaturated fracture and fracture networks, such as film flow, the migration, fragmentation, and coalescence of droplets, and rivulet flow with or without meandering or pulsation, has been widely observed in laboratory experiments. In this study, a modified two-dimensional volume of fluid (VOF) method was used to simulate liquid motion in partially saturated fracture apertures under a variety of flow conditions. This modeling approach systematically incorporates the effects of inertial forces, viscosity, gravity acting on the fluid densities, fracture wall wetting, and the pressure drop across curved fluid-fluid interfaces due to surface tension. This allows us to obtain a better understanding of the fundamental physics governing unsaturated fluid flow in fracture apertures. The VOF method is able to handle the complex dynamics of fluid-fluid interfaces and free surfaces in unsaturated fractures by using a fixed Eulerian grid. Fragmentation and coalescence of the fluids are automatically handled without resorting to complex adaptive mesh refinement or interface repairing algorithms. The wetting of fracture walls was modeled by imposing contact angles near the contact lines (contact points in two-dimensional simulations), and different contact angles were automatically chosen depending on whether the liquid interface is advancing, receding, or essentially stationary. The qualitative agreements between the numerical simulations and complex multiphase fluid dynamics reported in laboratory experiments clearly demonstrate the potential value of the VOF method for the mechanistically based modeling of immiscible liquid motion in unsaturated fracture networks.

An SPH model for multiphase flows with complex interfaces and large density differences

In this paper, an improved SPH model for multiphase flows with complex interfaces and large density differences is developed. The multiphase SPH model is based on the assumption of pressure continuity over the interfaces and avoids directly using the information of neighboring particles densities or masses in solving governing equations. In order to improve computational accuracy and to obtain smooth pressure fields, a corrected density re-initialization is applied. A coupled dynamic solid boundary treatment (SBT) is implemented both to reduce numerical oscillations and to prevent unphysical particle penetration in the boundary area. The density correction and coupled dynamics SBT algorithms are modified to adapt to the density discontinuity on fluid interfaces in multiphase simulation. A cut-off value of the particle density is set to avoid negative pressure, which can lead to severe numerical difficulties and may even terminate the simulations. Three representative numerical examples, including a Rayleigh-Taylor instability test, a non-Boussinesq problem and a dam breaking simulation, are presented and compared with analytical results or experimental data. It is demonstrated that the present SPH model is capable of modeling complex multiphase flows with large interfacial deformations and density ratios.

Dissipative particle dynamics simulation of multiphase fluid flow in microchannels and microchannel networks

Multiphase fluid motion in microchannels and microchannel networks involves complicated fluid dynamics and is fundamentally important to diverse practical engineering applications such as ink-jet printing, DNA and protein micro-/nano-arraying, and fabrication of particles and capsules for controlled release of medicines. This paper presented the simulations of multiphase fluid motion in microchannels and microchannel networks using a modified dissipative particle dynamics method that employs a new conservative particle-particle interaction combining short-range repulsive and long-range attractive interactions to simulate multiphase systems. This new conservative particle-particle interaction allows the behavior of multiphase systems consisting of gases, liquids, and solids to be simulated. Three numerical examples that are closely related to engineering applications were simulated. These examples involve multiple fluid motions in (i) a simple microchannel within two parallel plates; (ii) an inverted Y-sha...

Dissipative particle dynamics simulation of fluid motion through an unsaturated fracture and fracture junction

Multiphase fluid motion in unsaturated fractures and fracture networks involves complicated fluid dynamics, which is difficult to model using grid-based continuum methods. In this paper, the application of dissipative particle dynamics (DPD), a relatively new mesoscale method to simulate fluid motion in unsaturated fractures is described. Unlike the conventional DPD method that employs a purely repulsive conservative (non-dissipative) particle-particle interaction to simulate the behavior of gases, we used conservative particle-particle interactions that combine short-range repulsive and long-range attractive interactions. This new conservative particle-particle interaction allows the behavior of multiphase systems consisting of gases, liquids and solids to be simulated. Our simulation results demonstrate that, for a fracture with flat parallel walls, the DPD method with the new interaction potential function is able to reproduce the hydrodynamic behavior of fully saturated flow, and various unsaturated flow modes including thin film flow, wetting and non-wetting flow. During simulations of flow through a fracture junction, the fracture junction can be fully or partially saturated depending on the wetting property of the fluid, the injection rate and the geometry of the fracture junction. Flow mode switching from a fully saturated flow to a thin film flow can also be observed in the fracture junction.

On the modeling of viscous incompressible flows with smoothed particle hydro-dynamics

Smoothed particle hydrodynamics (SPH) is a Lagrangian, meshfree particle method and has been widely applied to different areas in engineering and science. Since its original extension to modeling free surface flows by Monaghan in 1994, SPH has been gradually developed into an attractive approach for modeling viscous incompressible fluid flows. This paper presents an overview on the recent progresses of SPH in modeling viscous incompressible flows in four major aspects which are closely related to the computational accuracy of SPH simulations. The advantages and disadvantages of different SPH particle approximation schemes, pressure field solution approaches, solid boundary treatment algorithms and particle adapting algorithms are described and analyzed. Some new perspectives and future trends in SPH modeling of viscous incompressible flows are discussed.

Dissipative particle dynamics simulation of pore‐scale multiphase fluid flow

Multiphase fluid flow through porous media involves complex fluid dynamics, and it is difficult to model such complex behavior, on the pore scale, using grid-based continuum models. In this paper, the application of dissipative particle dynamics (DPD), a relatively new mesoscale method, to the simulation of pore-scale multiphase fluid flows under a variety of flow conditions is described. We demonstrate that the conventional DPD method using purely repulsive conservative (nondissipative) particle-particle interactions is capable of modeling single-phase flow fields in saturated porous media. In order to simulate unsaturated multiphase flow through porous media, we applied a modified model for the conservative particle-particle interactions that combines short-range repulsive and long-range attractive interactions. This form for the conservative particle-particle interactions allows the behavior of multiphase systems consisting of gases, liquids, and solids to be simulated. We also demonstrated that the flow of both wetting and nonwetting fluids through porous media can be simulated by controlling the ratios between the fluid-fluid and fluid-solid (fluid-wall) interparticle interaction strengths.