Responses of an articulated tower in waves and currents
Academic Article
Overview
Additional Document Info
View All
Overview
abstract
The responses of an articulated loading platform (ALP) in random waves and currents are investigated both in frequency and time domain. The first- and second-order wave diffraction-radiation is solved by the ring source boundary integral equation method, and the viscous drag forces are computed from the modified Morison equation using relative velocity squared. In the frequency-domain analysis, the nonlinear drag is stochastically linearized and the resulting equation is solved iteratively. In the time-domain analysis, the nonlinear equation - including the quadratic drag term and a convolution integral - is directly integrated using a Newmark-beta method. From our numerical examples, it is shown that the slowly varying resonant responses in random waves are significant compared to wave-frequency responses when there is no current or when the current is normal to the wave direction, while they are greatly reduced when there exists strong in-line (coplanar or adverse) current. However, the presence of strong in-line current significantly increases the mean pitch angle.