Analysis of harbor oscillation with a boussinesq model

Abstract

Seiches or long-wave oscillations in harbors are normally the result of nonlinear interactions within groups of narrow-banded wind waves and swell. These oscillations may cause excessive vessel motions and disrupt loading and unloading operations at port facilities. Accurate prediction of harbor oscillation patterns is therefore an important aspect in harbor design. Most previous studies have used linear models to predict these nonlinear oscillation behaviors. This study uses an extended Boussinesq model that is applicable from deep to shallow water and takes into account the generation mechanism of these oscillations along with their interaction with the wind waves or swell. The finite difference model utilizes a predictor-corrector scheme to march the solution forward in time. It has a moving boundary algorithm to account for wave swashing, thereby allowing the correct boundary condition to be imposed at shorelines. The model is applied to examine the natural oscillation modes at Barbers Point Harbor and Kahului Harbor located on the West and North shores of Oʻahu and Maui respectively. The computed responses at each harbor are compared with previous linear model results and data gathered from pressure sensors. The analysis shows that harbor oscillation is primarily excited by infragravity waves, which can be simulated by a Boussinesq model.