Guixun Zhu

Abstract

The Oscillating water column (OWC) device is a type of wave energy converter (WEC) that has received wide investigation. Integrating OWC with breakwaters can reduce construction and maintenance costs. However, there is a risk of damage to these OWC devices under extreme sea conditions. This thesis focuses on the study of OWC devices based on the Smoothed Particle Hydrodynamics (SPH) model. The SPH method, a fully Lagrangian approach that simulates fluid problems using a set of moving particles carrying physical properties, is particularly well-suited to simulating flows with large deformation. The SPH model can therefore handle the strong non-linear situations resulting from wave slamming against OWC devices. Nevertheless, high computational cost of SPH model limits the large-scale investigation of SPH applications for OWC installations. The main work of this thesis can be therefore divided into two main parts: improving efficiency of SPH model and applying SPH model to the design of OWC devices. First, to simulate OWC devices with power take-off (PTO) systems, a single-phase SPH model with a pneumatic model was developed. Based on the correlation between air pressure and airflow rate over the orifice, the air pressure inside the chamber is determined. In this way, only the water phase, which takes into account the effect of air inside the chamber, is simulated. To model the thin front wall of OWC devices, a regional ghost particle approach is introduced. As a result, particle resolution for the thin wall can be independent of wall thickness. Then a new massively parallel SPH framework with a dynamic load balance strategy is presented for free-surface flow. The development of the parallel SPH model has improved computational speed and allows the model to run on High Performance Computing (HPC) systems. A two-way coupled model to hybridize the SPH model with OceanWave3D is proposed. The nonlinear region is simulated using the SPH model, while the other regions are modelled using OceanWave3D, which is based on fully less nonlinear potential flow theory and has less computational expense. Finally, the present model is applied to study wave loads of a U-shaped OWC device for the purpose of reliable design. It is found that the maximum wave force can be decreased by more than 20% by carefully optimising the width and height of the U-OWC vertical duct.

Keywords

Wave Energy Converter, Smoothed Particle Hydrodynamics, Oscillating Water Column

Document Type

Thesis

Publication Date

2023

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