A Dynamic Simulation of Wave Impact Loads on Offshore Floating Platforms

Some of the most critical loads to consider in developing design criteria for offshore platforms are those caused by wave hydrodynamic impact. The effect of these loads can be of a local nature in the form of plating damage as a result of impulsive loading, or it can be felt on the overall structure in the form of induced vibration, and increased bending moments and shears. Traditionally, the prediction of these loads has been highly empirical and designers have had to rely heavily on conservative factors of safety in order to account for the lack of confidence in these predictions. The current degree of sophistication of advanced techniques of structural analysis such as the finite element method has not been matched by equally sophisticated loads prediction methods. Consequently, the advantages offered by the computerized structural analysis schemes are considerably reduced due to the unacceptable load inputs. This paper fills part of this void by presenting an analytical model for predicting wave impact loads for the design of offshore platforms. The method is based on the Payne Impact Program which has been used before for predicting impact pressures and loads acting on high speed marine vehicles. The model simulates six-degrees-of-freedom and allows impacts at any wave heading. As inputs it requires geometric information, sea state definition, and a description of the relative motion of platform and wave. It is particularly suited to allow analysis of the results in probabilistic form, so that the severity and frequency of occurrence of impacts can be predicted.