Nonlinear time-domain simulation of pneumatic floating breakwater

Abstract

The performance of pneumatic-type floating breakwaters was studied using a Numerical Wave Tank (NWT) in time domain. The 2D fully nonlinear NWT was developed based on potential theory, Boundary Element Method (BEM)/Constant Panel Method (CPM), MEL-nonlinear free surface treatment, and Runge-Kutta 4 th-order (RK4) time-marching scheme. The inner chamber of the pneumatic breakwater was modeled by the volume-dependent pressurized air and its flow through a nozzle outlet causing pneumatic damping. The damping effect of pneumatic floating breakwaters on wave-blocking performance is assessed for two different (linear and quadratic) damping models and various damping coefficients. The transmission coefficients are evaluated for fixed and floating conditions and various wave lengths and heights. It is seen that a significant damping effect can be achieved if the breakwater is stationary. When the breakwater is floating against incident waves, the maximum transmission- coefficient-reduction ratio becomes much smaller since the floating body tends to follow the vertical motion of incident waves and the resulting volume-change effect is small. The fully nonlinear simulations with different wave heights are compared with linear ones. Copyright ？ 2005 by The International Society of Offshore and Polar Engineers.