Development of a full particle PIC method for simulating nonlinear wave-structure interaction

During the past few decades, Computational Fluid Dynamics (CFD) modelling hasbecome very popular in the coastal and offshore engineering community. Both Eulerianand Lagrangian methods have achieved great successes; typical examples are thegrid-based OpenFOAM® model and the meshless Smoothed Particle Hydrodynamics(SPH) method based model (e.g. SPHysics). While the former tends to be moreefficient and has advantages in enforcing incompressibility and boundary conditionsvia use of a grid, the latter is more suitable for handling large free-surface deformationsusing particles. In an attempt to combine the advantages of both methods, theParticle-In-Cell (PIC) method was devised through a combined use of particles andgrid. However, so far this hybrid method has not been very well exploited for use inthe coastal and offshore engineering field, where modelling complex wave-structureinteraction with computational efficiency still remains an important challenge. This thesis develops a novel "full particle" PIC based numerical model that solves theincompressible Newtonian Navier-Stokes equations for single-phase free-surface flowswith an emphasis on fluid-structure interaction. The use of the phrase "full particle"here indicates that all of the fluid properties, such as the mass and momentum,are assigned only to the particles, rather than being split between the particles andgrid as is the case in "classical" PIC. The novelty of the model lies in the fact thatthe particles are employed to solve the nonlinear advection term and track the fluidconguration (including the free surface), while the underlying grid is solely usedfor computational convenience for solving the non-advection terms. In addition, atailored Distributed Lagrange Multiplier method and a Cartesian cut cell based two-waystrong coupling algorithm are incorporated for fluid-structure interaction. Themodel is developed in both two and three spatial dimensions, and the 3D modelis parallelised using the Message Passing Interface (MPI) approach. The model isvalidated using benchmark tests in the coastal and offshore engineering field withsimulating nonlinear wave-structure interaction being the principal interest. It isshown that the present "full particle" PIC model is flexible, efficient (in terms ofCPU cost) and accurate when modelling complex free-surface flows and the violentinteraction of such flows with (surface-piercing) structures of arbitrary shape anddegree of freedom. With new innovations, the model has great potential to become ahigh quality numerical tool for use in coastal and offshore engineering applications.