Study on hydro-kinematic characteristics of green water over different fixed decks using immersed boundary method

Abstract

An immersed boundary method is applied to simulate the green water over a fixed deck by combining a level set method for the free water surface capturing. An efficient Navier-Stokes equation solver of second-order accuracy adopting the fractional step method at a staggered Cartesian grid system is used to solve the incompressible fluid motion. The numerical model is validated by comparing extensively the wave elevation and pressure with the experimental data for two types of fixed decks, which suggests that the developed immersed boundary method coupled with the level set method is very promising to predict green water problems due to its accuracy and efficiency. Furthermore, the cross-sectional velocity distribution over the deck, which is an important parameter in the industrial application, is computed and compared to the analytical Ritter's solution. It is found that Ritter's solution is much more conservative than the numerical simulations, which confirms the safe application of the simplified analytical solution in the current design practise. Volume of green water over the deck that affects the stability of deck is also tracked. The numerical results reveal that the amount of green water over both the two types of fixed decks shows a linear relationship with the relative wave height. This important finding may be very helpful for the prediction of deck elevation under a certain wave condition to reduce the occurrence of green water event.