Numerical simulation of long-period waves and ship motions in Tomakomai port, Japan

Long waves can penetrate easily into ocean facing ports or even be amplified if the wave frequency is close to one of the natural frequencies of the harbor. Moreover, the moored ship can have its natural frequency close a natural frequency of the basin, so that large ship motions can occur at relatively low offshore wave heights. Correct prediction (using e.g. numerical models) of long wave penetration and amplification is important in the design of new ports or port expansions. In this work, numerical simulations are presented using a wave model that accounts for the generation and propagation of bound and free long waves. The forces on the moored ship are calculated using the time-series of wave elevations and fluid motions at the location of the ship applying a strip theory approach. The ship motions are simulated using the calculated exciting wave forces, considering the non-linear characteristics of fenders and mooring lines. The numerical results are compared with prototype measurements carried out during a typhoon event in the port of Tomakomai in Japan and show good agreement.