In this paper results will be discussed of model experiments andcomputations of the wavecurrent interaction effects on the motions of a tensionleg platform in deep water with waves and current coming in from ahead.
The model experiments were performed in the deep water testing facility, recently installed in the Yave and Current Basin of the Maritime ResearchInstitute Netherlands (MARIN).
It is shown that the neglect of wave-current interaction in bothcomputations as well as in model test experiments will lead to substantiallyhigher motion amplitudes.
The first tension leg platform (TLP) was installed in 1984 at the Huttonfield in the North Sea in 150 metres water depth. At present the use of the TLPconcept is being considered for a number of locations in the US gulf area, North Sea and Mediterranean, all having water depths over 500 metres.
For the evaluation of design alternatives accurate prediction methods aswell as well conducted model experiments are indispensable. The character ofthe TLP concept requires that such tools include non-linearities.
One of the aspects that has not yet been fully understood is the combinedeffect of waves and current. A lot of attention has been devoted to theseparate action of waves and current.
The influence of current is described through Morison's equation, whereasthe first order motions are modelled e.g. using slenderness assumptions withrespect to the wave length, see Hooft . As such the mean and slowly varyingwave drift forces are calculated using results of three dimensional diffractionprograms or using results of algebraic methods, see Yue .
Due to the natural periods of the heave and pitch motions of the TLP alsodouble frequency or sum frequency wave excitation is addressed, see Pinkster etal.  and Huijsmans .