Closed-Form Expressions Of Wave Induced Forces On Members Of Offshore Structures In Deep Water

Abstract

The paper deals with the estimation of equivalent nodal forces and moments which can be useful in the analysis of beam element based Finite Element (FE) models of offshore structures. Ocean wave forces do not follow any standard pattern, thus, if the global X-Y reference plane is horizontal, the X and Y co-ordinates will not vary along the length of a vertical beam element. Taking advantage of such a situation, a number of closed form expressions for equivalent nodal loads can be derived. The analytical diffraction force from the MacCamy and Fuchs' theory as well as the Morison equation based inertia and drag forces are considered here as wave loading. A step-by-step calculation procedure is also proposed which transfers complex member loads to the nodes of a FE model with beam elements, arbitrarily oriented in space.