Predicting Motions of Fast Ships in Following Seas using a Time
Domain Potential Flow Simulation
Erik Verboom
October 13, 2014
Submitted to the Department of Maritime Engineering on October 13, 2014 in partial fulfillment of the
requirements for the degree of Master of Science.
Abstract
One aspect that significantly influences the operational safety of a fast sailing vessel is its behaviour in steep stern quartering waves. Especially course stability plays a great roll when it comes to prevent-ing uncontrollable and potentially dangerous situations in these sea states. Durprevent-ing the design process of such a vessel, it is of interest predict its behaviour mentioned conditions, give an idea about which conditions are still save for operation and in a next step, try to maximise the set of those conditions. Due to the computational power of modern desktop computers, one way for obtaining such a prediction within a limited time frame are time domain potential flow simulations. Through reproduction of series of model tests, captive and free sailing, with and without waves, this report gives a thorough validation of such a potential flow code for following sea states up to conditions that possibly lead to a capsize of the vessel. The main conclusion is that the motions of a vessel in the tested conditions are predicted well by the simulation in all tested sea states. The risk of exceeding certain motion amplitudes is very similar in simulations and model tests. Nevertheless, there exist a couple of findings in the simulation results that are worth mentioning. The prediction of dynamic trim and sinkage is a weak point for the tested potential flow code. Vessels in the simulation consistently show larger dynamic rise and less bow up trim. The exact reason of this inaccuracy remains unknown. Further more, the results of free sailing conditions including irregular waves showed an extreme sensitivity for small variations in the simula-tion input. Especially since in without excepsimula-tion the input that matched the the model test the closest also lead to the best fit in the simulation results, further investigation would be interesting into whether this sensitivity actually exists in model tests or whether it is only a result of the chosen simulation method.
Thesis Supervisors: Prof. dr. ir. Rene Huijsmans Dr. ir. Frans van Walree Dr. ir. Pepijn de Jong
