Experimental Study on Dynamic Responses of Truss Spar Platform Subjected To Long-Crested Waves and Short-Crested Waves with Current

The environmental conditions e.g. wave and current are the important aspects that shall be considered in the design of offshore structures. Research have been highlighted on the long-crested waves or unidirectional wave. However, the occurrence of such waves are seldom found in the real sea condition [1]. Studies also stated that wave force by long-crested waves would be overestimated or overdesigned [2]. On the other hand, short-crested wave would be better representing the real sea condition. By considering short-crested waves, an optimum design of the offshore structure with cost and time effectiveness could be achieved [2]. Yet, there no experimental studies has been reported comparing the dynamic responses of truss spar platform subjected to long-crested and short-crested wave with current in six degree of freedom. Thus, an experimental study by wave tank test has been performed in order to quantify the effectiveness of the dynamic responses of the truss spar platform subjected to short-crested waves by comparing to the long-crested waves with current. A model of truss spar platform which is fabricated by steel plate with 1:100 ratio scale from the prototype was used in the study of dynamic responses. In wave tank test, long-crested waves with current and short-crested waves with current was generated by wave and current generator. Spreading function, cosine squared (cos2) was implemented and incorporated with JONSWAP spectrum to produce short-crested wave. Current as well has been considered in this study. Wave probe was adopted to record the wave profile while the Qualisys Track Manager (QTM) was used to record the dynamic motion responses in six degree of freedom. The dynamic motion responses of truss spar platform model were compared among the long and short-crested waves with current. As results, the responses of truss spar considering short-crested waves with current were found to smaller compare to long-crested wave with current. This indicated that offshore structure design considering short-crested waves with current could the optimized and provide an economical design.