When the very large offshore structures are constructed at sea, the site has a various wave in which the physical phenomena are very complicated. But most research on the wave force of the very large offshore structures are carried out on linear wave force. Because of the complexity of analysis and difficulties of measurement. To get more realistic estimations of force on offshore structures in real sea, it is necessary to consider the effects of nonlinear water waves. Some research has been carried out analysis of transient waves to consider breaking waves. However, almost all of the simulations to transient waves are very complicated and difficult because of taking measurements.
This paper first presents easier simulation to transient wave. Second, It compares wave force based on the 3-D source distribution method and measured in breaking waves. A numerical procedure is described for predicting the wave force of cylinders by the 3-D source distribution method. As well as, to analysis of irregular wave, carried out a convolution integral with a response impulse function which is to take inverse FFT the wave exciting force in frequency domain. And transient wave is solved from linear Airy wave theory and based on combining an energy transmission velocity and a wave phase velocity. This formula applies to any water depth, because this formula includes linear dispersion relationship.
When the 3-D source distribution method is used to calculate the wave force and generated by breaking wave meets the very large floating body, the resulting figures are smaller than the real wave force.