Second-order mean wave forces and moments on ISSC TLP in uni- and multi-directional random seas

A higher-order boundary element method (HOBEM) is used for the computation of the second-order mean wave forces and moments on the ISSC TLP for three different (stationary, freely, floating, and tendon-attached) conditions. The direct pressure integration method, which has not been widely used due to the slow convergence and uncertainty associated with the velocity computation on the body surface, is used, and it is shown that reliable results can be obtained even with 152 total higher-order boundary elements. While vertical-plane motions are almost negligible in the actual TLP condition, the mean force results are close to those of the freely-floating condition due to the weak resistance of the tendons against the horizontal-plane responses. It is also shown that the first order motion effects are important particularly in the mean yaw moment calculation, hence, in general, need to be included. In all cases, the mean forces and moments are sensitive to the wave incident angles and can be greatly reduced or amplified depending on wave headings, which underscores the importance of wave directionality. To illustrate this, the surge and sway first-order forces and responses, and second-order mean forces are computed for typical uni- and multi-directional storm seas and the corresponding reduction factors are obtained.

Second-order mean wave forces and moments on ISSC TLP in uni- and multi-directional random seas Conference Paper