Introduction

This book provides the reader with the basic procedures for performing a dynamic analysis of marine structures subjected to environmental stochastic load processes such as wind and ocean waves. The dynamics of rigid bodies and flexible structures are considered. As opposed to the static analysis of structures, the dynamic analysis of a structure concerns itself with time-variant external forces, inertia, damping, reaction forces, and the corresponding responses. Dynamic behavior differs from static behavior. Consider, for instance, the cantilevered tower shown in Fig. 1.1a.

Figures 1.1(b) and 1.1(d) display the bending moment in the tower with a deck (i.e., mass) on the top when the hydrodynamic forces from a long wave are considered as static and dynamic, respectively. Obviously, the dynamic case is relevant for a certain time variation and an instant in time. The difference is due to the inertia forces (on the deck Qi and along the tower qi).

Clearly, dynamic behavior is more complex than static, and its calculation is also more demanding. This becomes even more clear by considering a buoyant, rigid, articulated tower such as the one shown in Fig. 1.2. The static response is such that the tower rotates in such a way that the net effect of buoyancy and gravity balances the external forces (expressed by zero total moment with respect to the pin joint). If the external forces are considered as time variant, the external force at any time instant is balanced by the mentioned reaction forces as well as by inertia and damping forces.