Modified dynamic boundary conditions (mDBC) for general-purpose smoothed particle hydrodynamics (SPH): application to tank sloshing, dam break and fish pass problems

Abstract

Dynamic boundary conditions (DBC) for solid surfaces are standard in the weakly compressible smoothed particle hydrodynamics (SPH) code DualSPHysics. A stationary solid is simply represented by fixed particles with pressure from the equation of state. Boundaries are easy to set up and computations are relatively stable and efficient, providing robust numerical simulation for complex geometries. However, a small unphysical gap between the fluid and solid boundaries can form, decreasing the accuracy of pressures measured on the boundary. A method is presented where the density of solid particles is obtained from ghost positions within the fluid domain by linear extrapolation. With this approach, the gap between fluid and boundary is reduced and pressures in still water converge to hydrostatic, including the case of a bed with a sharp corner. The violent free-surface cases of a sloshing tank and dam break impact on an obstacle show pressures measured directly on solid surfaces in close agreement with experiments. The complex 3-D flow in a fish pass, with baffles to divert the flow, is simulated showing close agreement with measured water levels with weirs open and gates closed, but less close with gates open and weirs closed. This indicates the method is suitable for rapidly varying free-surface flows, but development for complex turbulent flows is necessary. The code with the modified dynamic boundary condition (mDBC) is available in DualSPHysics to run on CPUs or GPUs.

A Review of SPH Techniques for Hydrodynamic Simulations of Ocean Energy Devices

“…One way is to distribute particles on wall surfaces to complete the kernel support near the boundary, which is the most popular method in the present SPH community. For example, the technique named Fixed Ghost Particle proposed by Adami et al [121] was adopted in SPHinXsys or Dynamic Boundary Condition by Crespo et al [122,123] in DualSPHysics. Another method is based on the normal-flux method that discretizes physical walls into several segments, i.e., line elements in 2D and triangle elements in 3D; this method was adopted by several commercial SPH packages, such as Nextflow Software [115] and Dive Solution [124].…”

A Numerical Validation of 3D Experimental Dam-Break Wave Interaction with a Sharp Obstacle Using DualSPHysics

“…To enhance this formulation, a new boundary method has been developed: the modified dynamic boundary conditions (mDBC) [53]. In this method, the density of solid particles, arranged in the same way as in the original DBC, is obtained from ghost positions within the fluid domain by linear extrapolation.…”

3-D Numerical Study of a Bottom Ramp Fish Passage Using Smoothed Particle Hydrodynamics

“…When using DBC, an unphysical gap between the fluid and the solid boundaries appears, lowering the accuracy of the pressure prediction at the boundaries. To alleviate this, a second approach called modified dynamic boundary conditions (mDBC) has recently been added [30], with the density of boundary particles obtained from "ghost nodes" cleverly positioned within the fluid domain.…”

“…The initial focus for applications with DualSPHysics has been on wave generation [24,25] and its interaction with coastal structures with good results [26,27]. However, this code has then been applied successfully to hydraulic problems such as runoff on sloping terrain [28], dam safety [29], fish passage constructions [14,30], added mass and damping coefficient [31], and drag coefficient analysis in channels [32].…”