3-DIMENSIONAL STOCHASTIC RESPONSE OF OFFSHORE TOWERS TO RANDOM SEA WAVES

In this paper, a three-dimensional model for dynamic response analysis of jacket-type offshore platforms under random sea waves is established. The sea waves are considered to be zero mean, stationary and ergodic Gaussian random processes specified by the P-M wave height spectrum. Linear wave theory and the generalized Morrison equation are used to calculate the wave forces on the structure. The fluid-structure interaction and the couplings of the motion in different directions at each node are considered. The fluid drag forces are linearized by stochastic linearization techniques. The mean-square responses are obtained by Gauss-Legendre numerical integration. Numerical results for a platform with a height of 65 m to symmetrical and unsymmetrical loads are presented and contrast with the corresponding results of one- and two-dimensional models. Some more detail and practical description, such as the response in the vertical direction and the unsymmetrically loaded behaviour, are given.