Screening for extreme wave events


Extreme waves can have significant consequences for ships and offshore structures at sea. When hit by a wave local damage may occur, personnel may be endangered or even the total integrity of a ship or platform may be at risk.


Figure 1: Validation of CFD for green water loading on a container vessel at forward speed, by using deterministic reproduction of an extreme wave basin event


H


Tim Bunnik, Sanne van Essen & Jule Scharnke t.bunnik@marin.nl


10 report


owever, it is difficult to judge whether or not this risk is at an acceptably low level. A wave-


impact risk assessment requires a selection of dangerous sea states and load levels (such as slamming pressures or forces on deck structures) in random realisations of these sea states. This is a stochastic process, which means that a large number of wave sequences have to be analysed to derive converged statistical values of the maximum load to occur in a 3-hour sea state. This involves many model tests or complex (CFD) simulations. The purpose of ‘screening’ is to determine


which sea states and which events in a random wave sequence are critical for impacts, by using simpler calculation methods. The highest wave is not always associated with the largest impact load. Therefore an impact indicator is required, which has a sufficiently good correlation with the critical load and can be calculated using a faster method than CFD. Complex calculations or tests can be focused on these critical events [1]


, resulting in more reliable


impact statistics. At MARIN several wave impact indicators have been studied [2] [3]


,


for instance for loads due to green water on deck or slamming impacts.


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20