Forces of random wave groups on vertical cylinders

The paper analyses the diffraction problem of two bottom mounted vertical circular cylinders. The randomness and directional spreading of sea waves are taken into account and a new procedure is proposed to estimate the largest forces on the bodies when extreme waves occur. Firstly extreme forces on the array of cylinders are obtained in two cases: - when a large crest occurs at a given point in the undisturbed wave field (which is the incident wave field in diffraction conditions); - when a large crest-to-trough wave height occurs in the e undisturbed wave field. Finally, it is investigated where extreme crests or crest-totrough heights should occur in order to produce the maximum value of the force on a cylinder. It is shown that, because the second condition is always the most conservative, it is the most suitable to predict design conditions.