On the treatment of solid boundary in smoothed particle hydrodynamics

As a popular meshfree particle method, the smoothed particle hydrodynamics (SPH) has suffered from not being able to directly implement the solid boundary conditions. This influences the SPH approximation accuracy and hinders its further development and application to engineering and scientific problems. In this paper, a coupled dynamic solid boundary treatment (SBT) algorithm has been proposed, after investigating the features of existing SPH SBT algorithms. The novelty of the coupled dynamic SBT algorithm includes a new repulsive force between approaching fluid and solid particles, and a new numerical approximation scheme for estimating field functions of virtual solid particles. The new SBT algorithm has been examined with three numerical examples including a typical dam-break flow, a dam-break flow with a sharp-edged obstacle, and a water entry problem. It is demonstrated that SPH with this coupled dynamic boundary algorithm can lead to accurate results with smooth pressure field, and that the new SBT algorithm is also suitable for complex and even moving solid boundaries.</div

DPD simulation of multiphase flow at small scales

Small scale multiphase fluid motion is fundamentally important for applications in environmental, biological and chemical engineering as well as many other areas. Due to the existence of complex geometries, arbitrarily moving interfaces, and large density and viscosity contrast, simulation of small scale multiphase flows has been a formidable task for traditional grid-based numerical methods. This paper presents the application of a meso-scale, Lagrangian particle method, dissipative particle dynamics (DPD), for simulating multiphase fluid flows. For multiple component multiphase flows, with properly selected coefficients, the conventional DPD model can be directly used. For single component multiphase flows, the conservative weight function describing DPD particle-particle interactions has to be modified to model the existing liquid-gas phases. The effectiveness of the DPD model in simulating multiphase flows has been demonstrated by two numerical examples of twocomponent two phase flow, and one-component two phase flow. ©2010 IEEE

Bending modes and transition criteria for a flexible fiber in viscous flows

The present paper follows our previous work in which a coupling approach of smoothed particle hydrodynamics (SPH) and element bending group (EBG) was developed for modeling the interaction of viscous incompressible flows with flexible fibers. It was also shown that a flexible object may experience drag reduction because of its reconfiguration due to fluid force on it. However, the reconfiguration of deformable bodies does not always result in drag reduction as different deformation patterns can result in different drag scales. In the present work, we studied the bending modes of a flexible fiber in viscous flows using the presented SPH and EBG coupling approach. The flexible fiber is immersed in a fluid and is tethered at its center point, while the two ends of the fiber are free to move. We showed that the fiber undergoes four different bending modes: stable U-shape, slight swing, violent flapping, and stable closure modes. We found there is a transition criterion for the flexible fiber from slight swing, suddenly to violent flapping. We defined a bending number to characterize the bending dynamics of the interaction of flexible fiber with viscous fluid and revealed that this bending number is relevant to the non-dimensional fiber length. We also identified the critical bending number from slight swing mode to violent flapping mode

MODELING OF CONTACT ANGLES AND WETTING EFFECTS WITH PARTICLE METHODS

The physics of fluid-fluid-solid contact line dynamics and wetting behaviors are closely related to the inter-particle and intra-molecular hydrodynamic interactions of the concerned multiple phase system. Investigation of surface tension, contact angle, and wetting behavior using molecular dynamics (MD) is practical only on extremely small time scales (nanoseconds) and length scales (nanometers) even if the most advanced high-performance computers are used. In this article we introduce two particle methods, which are smoothed particle hydrodynamics (SPH) and dissipative particle dynamics (DPD), for multiphase fluid motion on continuum scale and meso-scale (between the molecular and continuum scales). In both methods, the interaction of fluid particles and solid particles can be used to study fluid-fluid-solid contact line dynamics with different wetting behaviors. The interaction strengths between fluid particles and between fluid and wall particles are closely related to the wetting behavior and the contact angles. The effectiveness of SPH and DPD in modeling contact line dynamics and wetting behavior has been demonstrated by a number of numerical examples that show the complexity of different multiphase flow behaviors

MODELING OF CONTACT ANGLES AND WETTING EFFECTS WITH PARTICLE METHODS

The physics of fluid-fluid-solid contact line dynamics and wetting behaviors are closely related to the inter-particle and intra-molecular hydrodynamic interactions of the concerned multiple phase system. Investigation of surface tension, contact angle, and wetting behavior using molecular dynamics (MD) is practical only on extremely small time scales (nanoseconds) and length scales (nanometers) even if the most advanced high-performance computers are used. In this article we introduce two particle methods, which are smoothed particle hydrodynamics (SPH) and dissipative particle dynamics (DPD), for multiphase fluid motion on continuum scale and meso-scale (between the molecular and continuum scales). In both methods, the interaction of fluid particles and solid particles can be used to study fluid-fluid-solid contact line dynamics with different wetting behaviors. The interaction strengths between fluid particles and between fluid and wall particles are closely related to the wetting behavior and the contact angles. The effectiveness of SPH and DPD in modeling contact line dynamics and wetting behavior has been demonstrated by a number of numerical examples that show the complexity of different multiphase flow behaviors

SPH simulation of free surface flows with moving objects

Free surface flows with moving objects are very difficult to simulate for conventional numerical methods as the flows involve rapid movement of solid objects,changing and breakup of free surfaces,strong turbulence and vortex,and violent fluid-solid interaction. Smoothed particle hydrodynamics(SPH..

爆炸焊接过程的光滑粒子动力学模拟

应用改进的SPH方法分别对理想和非理想炸药爆炸驱动的焊接过程进行了模拟。提出了SPH方法求解连续方程过程中重要的密度无量纲数,进而提出了一种适用于爆炸驱动金属运动问题的自适应SPH连续性方程求解方法。本文的模拟结果成功地展现了爆炸焊接过程炸药和金属板的典型力学行为特征。分别从爆炸波、射流、焊接

Movement and evolution of macromolecules in a grooved micro-channel

This paper presented an investigation of macromolecular suspension in a grooved channel by using the dissipative particle dynamics (DPD) with finitely extensible non-linear elastic (FENE) bead spring chains model. Before studying the movement and evolution of macromolecules, the DPD method was first validated by modeling the simple fluid flow in the grooved channel. For both simple fluid flow and macromolecular suspension, the flow fields were analyzed in detail. It is found that the structure of the grooved channel with sudden contraction and expansion strongly affects the velocity distribution. As the width of the channel reduces, the horizontal velocity increases simultaneously. Vortices can also be found at the top and bottom corners behind the contraction section. For macromolecular suspension, the macromolecular chains influence velocity and density distribution rather than the temperature and pressure. Macromolecules tend to drag simple fluid particles, reducing the velocity with density and velocity fluctuations. Particle trajectories and evolution of macromolecular conformation were investigated. The structure of the grooved channel with sudden contraction and expansion significantly influence the evolution of macromolecular conformation, while macromolecules display adaptivity to adjust their own conformation and angle to suit the structure so as to pass the channel smoothly

SPH modeling of multiphase drop dynamics

This paper presents an SPH (smoothed particle hydrodynamics) model for numerical simulation of multiphase drop dynamics including liquid drop formation and deformation, coalescence and separation, liquid drop impacting, spreading and splashing. SPH is a Lagrangian, meshfree particle method. It has special advantages in modeling multiphase drop dynamics. Surface tension effects are modeled using a particle-particle interaction force, which avoids the calculation of surface and interface curvature. Solid boundaries are modeled using a coupled dynamic boundary treatment algorithm, which ensures the accuracy and flexibility of the SPH method. Numerical investigations of a liquid drop oscillation and a single liquid drop impacting onto a liquid film are conducted. The inherent physics of multiphase drop dynamics are well described