Sensitivity Study of Semisubmersible Motions to Hull Form Parameters and Their Optimisation

Abstract: An optimisation routine is developed to find the optimal size of a semisubmersible regarding the seven geometrical variables, column radius, column draught, pontoon height, pontoon beam, horizontal column distance and total underwater beam. Depending on the user’s input, the objective function consists of both heave, roll and pitch motions in several different wave directions. The aim is to minimise the motions of a semisubmersible to increase its workability in a specific sea state. Overall, it is proven that the optimal design of a semisubmersible depends on the objective function. Hence, depending if the user wants to decrease the heave, roll or pitch motions, different designs will be obtained. Furthermore, it is shown that a single goal objective function works better than a multiple goal objective function for the optimiser. A multiple goal function should preferably be rewritten as a single goal function with several constraints.