Naoki Tsuruta

Space potential particles to enhance the stability of projection-based particle methods

Particle methods have been seldom verified by a Karman vortex simulation, which is commonly performed as a typical benchmark in computational fluid dynamics. This is mainly due to a difficulty in suppression of occurrence of unphysical voids manifested usually in a strong vortex on account of definition of free surface by the Lagrangian tracking framework with inconsistency in volume conservation. This paper presents a simple and effective scheme as a free-surface boundary condition of projection-based particle methods, namely the MPS (moving particle semi-implicit) and Incompressible SPH (ISPH) methods to handle the free surface with consistency in volume conservation. The new scheme is introduced into the Poisson pressure equation (PPE) with consideration of a potential in void space as space potential particle (SPP), to reproduce physical motions of particles around free surface through a particle–void interaction. The enhancing effect of the newly proposed SPP scheme is shown by simulating a few numerical tests, including a whirling water flow, a two-phase surfacing flow, and a set of Karman vortex simulations.

Two-phase flow LES of the sedimentation process of a particle cloud

To predict the sedimentation process practically with high resolution, a large eddy simulation (LES) is performed. A solid/liquid two-phase flow model based on the Euler–Lagrange coupling is developed. Then the discrete element method is applied to calculate inter-particle forces during individual particle motion. The computational grid scale of the Eulerian fluid method is less than the particle diameter to simulate a wake induced by settling particles. Comparison of the simulated and experimental results for the particle sedimentation process verified the performance of the developed numerical model. Finally, the mechanism of the inner structure of the settling particles is investigated from a computational point of view. Consequently, the positive relationship between the turbulence-energy production rate and the inter-particle collisions would be shown.

Vertical sorting process under oscillatory sheet flow condition by resolved discrete particle model

ABSTRACT To computationally investigate the vertical sorting mechanism under an oscillatory sheet flow condition with graded particles, a resolved discrete particle model is employed in conjunction with a large eddy simulation (LES) of a solid–liquid two-phase flow. In the proposed approach, the resolvable scale in the Eulerian flow field is smaller than the diameter of the particle and the Lagrangian motion of each particle is simulated using the discrete element method. The numerical model is verified using previously obtained experimental data. The simulations reveal that most active vertical sorting occurs in the acceleration phase, with interparticle forces acting on each particle being dominant over the hydrodynamic forces. Regarding interparticle forces in the sheet flow layer, the profile of the particle ‘temperature’ supports the suggestion that the collision force dominates over the contact force.

NUMERICAL SIMULATION FOR SEDIMENTATION PROCESS OF BLOCKS ON A SEA BED BY HIGH-RESOLUTION MULTIPHASE MODEL

For land creation regarding coastal structures, large mounds of soil, sand, and blocks are emplaced for mound formation, while accurate prediction of sedimentation deposition steps is necessary for cost reduction of construction work. In this study, high-resolution calculations using computational grids as fine as one to several tens with regard to typical block size are performed to ascertain details of flow fields around the blocks. The Smagorinsky model is introduced to investigate a turbulence field under high particle Reynolds number conditions. The deposition steps of block groups thrown into the water and the flow fields surrounding blocks that are difficult for measurements are presented in detail. Complex turbulent flow is formed in the sedimentation process and the influence of turbulence is not negligible.