An alternative Stochastic Rapresentation of Drag Forces on Offshore Structures for Dynamic Analyses

A new method for stochastic representation of the hydrodynamic drag forces on offshore structures subjected to irregular waves is described. For the case of zero current, it is shown that it is possible to construct a genuinly quadratic representation of the drag force that reproduces the statistical properties of the standard formulation of the drag force closely, and which has a spectral density that approximates the desired force spectrum reasonably well. The distinct advantage of this representation is that it bring dynamic analysis back into the frequency domain, in a similar manner as achieved for a linearized force representation.