Study on the interaction between water waves and structures

Abstract

This dissertation presents numerical models for investigating the evolution of free surface waves and the viscous flow fields near various coastal structures and a model for forecasting the wave run-up height on a seawall To provide early warning of possible coastal flooding a wave run-up monitoring system and a model for forecasting the wave run-up height on real seawall were developed in present study The Princeton Ocean Model and WAVEWATCH III were used to predict the water levels and ocean waves respectively The empirical formulas recommended in the Coastal Engineering Manual (2011) and EurOtop (2018) were adopted to estimate the run-up height The wave run-up monitoring system was set up at three seawalls along the southwestern coast of Taiwan from 2013 to 2016 Consistency between the forecasted and measured wave run-up heights during typhoon periods demonstrated the feasibility of using the proposed method for monitoring and forecasting wave run-up heights Furthermore the multi-model ensemble approach was adopted to improve the unsatisfactory run-up forecasting performance during typhoon periods and the forecasted run-up heights were eventually presented as a band with upper and lower limits as opposed to single values The forecast results can be used to provide advance warning of possible wave overtopping and associated coastal flooding during typhoon periods In addition to using available empirical formulas to forecast wave run-up on a real seawall a two-dimensional numerical wave tank was developed to simulate the wave and flow fields near a real seawall Permeable structures on the real seawalls such as rubble-mounds revetment and armor blocks were considered A two-dimensional Volume-Averaged Reynolds Averaged Navier-Stokes equation (VARANS) and turbulence model were solved for simulating the flow characteristics inside and outside the porous media Particle level set method was used to capture the evolution of the complex free surface An innovative solid-fluid coupling method (Huang et al 2015) was employed to mimic the solid-fluid interaction on fixed Cartesian grids The accuracy of this numerical model was verified by comparing the numerical results with the experimental data (Losada et al 1997) After having verified the accuracy of the numerical model the model was applied to simulate the flow field and wave run-up on Tsen-Wen seawall in the southwestern Taiwan during typhoons Kalmaegi and Fung-Wong The numerical results for maximum wave run-up height on the seawall were compared with the data obtained by in-situ measurements The comparisons revealed that the present numerical results were consistent with the observed values Finally a three-dimensional numerical wave model based on a multi-block Cartesian grid system (English et al 2013) was developed to investigate the interaction between water waves and offshore structures The model solves three-dimensional spatially averaged Navier-Stokes equations The Large-Eddy Simulation (LES) was applied to reveal the behavior of the associated turbulent flows In order to reduce the computational time the proposed 3-D numerical model was established in a GPU-based parallel computing environment The proposed numerical model was applied to simulate the 3-D lid-driven cavity flow and the wave fields induced by a solitary wave past a vertical circular cylinder The good agreement of the numerical results with available numerical results and experimental data verifies the accuracy of the proposed 3-D numerical model The 3-D numerical model was then applied to simulate the wave propagation over an offshore mono-pile structure

Date of Award	2020
Original language	English
Supervisor	Ching-Jer Huang (Supervisor)