In-line response of a horizontal cylinder in regular and random waves

The in-line response of a horizontal flexibly mounted cylinder in regular and random waves are reported in this paper. Both theoretical analyses and experimental measurements have been carried out. The theoretical predictions are based on the Morison equation which is solved by the incremental harmonic balance method. The relationship between the response of the cylinder and the ratio of natural frequency of the cylinder to the wave frequency is first determined. Experiments are then performed in a wave flume to determine the accuracy of the Morison equation in predicting the in-line response of the cylinder in regular and in random waves. It has been verified that the Morison equation is valid under regular waves. For random waves, it is found that the in-line response can be predicted accurately by a superposition of the response to wave components of different frequencies using the Morison equation, only when the ratio of wave height to cylinder diameter is small. (C) 1997 Academic Press Limited.