Dynamic Response of an Experimental Model for Offshore Platforms with Periodic Legs

Abstract. A new class of offshore platforms with periodic legs ispresented. The dynamic response of this class of platforms to waveexcitation is determined theoretically and experimentally. Theemphasis is placed here on studying the behavior of legs withgeometric and material periodicity.A theoretical model is developed to model the dynamics ofperiodic legs using the Transfer Matrix method. The predictions of themodel are validated experimentally using a scaled experimental modelof an offshore platform. The experimental model is tested inside awater basin which is provided with a water wave generatormechanism capable of generating periodic as well as random waves.The dynamic response of the platform with periodic legs is determinedfor different submergence levels. The obtained results are comparedwith the response when the platform is provided with plain legs. It isfound that the periodic legs are capable of attenuating considerably thevibration transmitted from the water to the platform both in the axialand lateral directions over a broad frequency band. Comparisonsbetween the experimental results and the theoretical predictions arefound to be in close agreement. The developed theoretical andexperimental techniques provide invaluable tools for the design of thisnew class of offshore platforms with periodic legs.