Influence of the wave-current interaction on drift loads in FPSO

Some procedures for mooring system design have been developed in last years. The most important point of these procedures is the correct determination of the environmental loads that the mooring system should withstand. It is known that most of these procedures do not consider the effect of the wave-current interaction. In the present paper the authors show that the wave-current interaction produces an increase on the drift load which cannot be ignored in the design of mooring systems. In order to introduce the wave-current interaction on the environmental loads, this work takes profit of recently developed expressions for the second-order horizontal steady loads on a floating body with small forward speed. Two units operated by PETROBRAS are used to illustrate the mentioned effect, one of them a VLCC operating in deep water. Besides the significative change of the drift loads composition, the wave-current interaction causes the modification of the equilibrium position of the unit. The same VLCC in a turret configuration is used to illustrate this effect, showing the change of the equilibrium position when the wave-current interaction is considered.