A dissipative particle dynamics method for arbitrarily complex geometries

Abstract

Dissipative particle dynamics (DPD) is an effective Lagrangian method for modeling complex fluids in the mesoscale regime but so far it has been limited to relatively simple geometries. Here, we formulate a local detection method for DPD involving arbitrarily shaped geometric threedimensional domains. By introducing an indicator variable of boundary volume fraction (BVF) for each fluid particle, the boundary of arbitrary-shape objects is detected on-the-fly for the moving fluid particles using only the local particle configuration. Therefore, this approach eliminates the need of an analytical description of the boundary and geometry of objects in DPD simulations and makes it possible to load the geometry of a system directly from experimental images or computer-aided designs/drawings. More specifically, the BVF of a fluid particle is defined by the weighted summation over its neighboring particles within a cutoff distance. Wall penetration is inferred from the value of the BVF and prevented by a predictor-corrector algorithm. The noslip boundary condition is achieved by employing effective dissipative coefficients for liquid-solid interactions. Quantitative evaluations of the new method are performed for the plane Poiseuille flow, the plane Couette flow and the Wannier flow in a cylindrical domain and compared with their corresponding analytical solutions and (high-order) spectral element solution of the Navier-Stokes equations. We verify that the proposed method yields correct no-slip boundary conditions for velocity and generates negligible fluctuations of density and temperature in the vicinity of the wall surface. Moreover, we construct a very complex 3D geometry -the "Brown Pacman" microfluidic device -to explicitly demonstrate how to construct a DPD system with complex geometry directly from loading a graphical image. Subsequently, we simulate the flow of a surfactant solution through this complex microfluidic device using the new method. Its effectiveness is demonstrated by examining the rich dynamics of surfactant micelles, which are flowing around multiple small cylinders and stenotic regions in the microfluidic device without wall penetration. In addition to stationary arbitrary-shape objects, the new method is particularly useful for problems involving moving and deformable boundaries, because it only uses local information of neighboring particles and satisfies the desired boundary conditions on-the-fly. *

A GPU-accelerated package for simulation of flow in nanoporous source rocks with many-body dissipative particle dynamics

“…To construct bounding walls in DPD based fluid flow simulations, most researchers (e.g. Chen et al [8], Li et al [33], Meakin et al [39]) have followed a particle packing approach proposed in Liu et al [36]. Using this packing approach, the whole simulation system will be first filled with DPD particles at a particle number density (e.g.…”

“…In this work, a generalized GPU-accelerated implementation of the mDPD based multiphase pore flow model with a solid wall boundary model for arbitrary pore geometries is developed to simulate flow dynamics in realistic source shale pores. The software features a tight integration of our earlier works including a mDPD pore flow model [58], an arbitrary-geometry wall boundary model [33] and a GPU-accelerated DPD simulator [5,50], and delivers an efficient rock analysis throughput from digital rock imaging to pore flow simulations, as shown in Figure 2. With the new ability to model multiphase flow in arbitrary-shaped, nano-to micro-scale channels, the code package can be used to investigate the critical material properties of shale such as permeability and relative permeability with unprecedented time and length scales.…”

A new wall model for slip boundary conditions in dissipative particle dynamics

“…Thus, it is not trivial to impose a correct boundary condition, and a great deal of effort has been committed to search for the most effective boundary modeling approaches in the past two decades. 32,48 In recent years, researchers have developed DPD wall models without using frozen wall particles, [47][48][49] instead, the no-slip boundary condition was set by increasing the friction coefficient of the dissipative force. [35][36][37][38][39][40] Note that only using the frozen particles cannot reach the no-slip boundary condition, and extra efforts should be committed.…”

“…Thus, it is not trivial to impose a correct boundary condition, and a great deal of effort has been committed to search for the most effective boundary modeling approaches in the past two decades. 32,[35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][51] Among these works, the most widely used wall models utilized several layers of frozen particles to form the wall and implemented a reflection scheme, such as bouncing-back, specular, or Maxwellian reflection, to prevent fluid-particle penetration. [35][36][37][38][39][40] Note that only using the frozen particles cannot reach the no-slip boundary condition, and extra efforts should be committed.…”

“…Such effects are mainly due to the unbalanced forces acting on the near-wall fluid particles. 32,48 In recent years, researchers have developed DPD wall models without using frozen wall particles, [47][48][49] instead, the no-slip boundary condition was set by increasing the friction coefficient of the dissipative force. It should be noted that, in the simulation, the DPD system becomes unstable with the increase in friction coefficient.…”