Simulation of Pollutant Transport in Rivers Using Particle Methods

• Main Authors: Yan-Ting Lin, 林彥廷
• Other Authors: An-Pei Wang
• Format: Others
• Language: zh-TW
• Published: 2014
• Online Access: http://ndltd.ncl.edu.tw/handle/22356345132915851299

碩士 === 中原大學 === 土木工程研究所 === 102 === This study develops a numerical model to simulate two-dimensional mixing in rivers and estuaries using a Lagrangian particle method. In this model, concentration is discretized by a series of particles. Using a Lagrangian frame, the positions of particles shift along the fluid flow, and their strength updates due to diffusion and dispersion. The major advantage of this model is the essentially grid-nature of the particle method, which may reduce the numerical dissipation in solving the mass transport equation, and also concentrate the computational resources on the simulation of concentration field which is predominantly confined in a compact region. To accomplish the simulation of mass transport in Lagrangian frame, the rate of change of particle strength is calculated using a Particle Strength Exchange (PSE) scheme. At each time step the redistribution of particles is performed to interpolate the concentration onto a mesh to maintain the overlapping of particles for the stability criterion of PSE. To reduce the difficulty of compution, in all simulations the dispersion coefficient is set to be a constant. Severl benchmark problems of two-dimensional advection-diffusion equation were simulated using this mode fo validation, such as the impulsive injection of point source in the uniform flow in an infinite-wide channel and a channel with boundaries, and the spread of a plume from a point source. The comparisons between numerical and analytical results show good agreements. To test the capability of the model, the mixing of contaminant in a rectangular estuary with simplified geometry caused by a monotonic tidal wave was simulated, and the longitudinal dispersion in the estuary due to the shear flow caused by the variation of bed geometry was investigated.