Random Response Analysis of Off-Shore Structures

Abstract

In this chapter the dynamic response of off-shore structures in deep water under random waves forces will be analysed. The structures will be considered to be such that they do not substantially change the motion of the waves, and that this motion can be represented by linear gravity theory. In this theory horizontal velocities and accelerations are linearly related to the wave heights, which are represented by a spectrum and assumed to be a zero-mean Gaussian process. Once the velocities and accelerations are known we can compute the forces on the structure. During this process drag forces coefficients are linearized in the form described in chapter 13. To obtain a better estimate of the drag, the designer could correct the linearized values during a second cycle and run the problem again. This is not important however in many practical cases where the inertia forces tend to be very much larger than the drag components.