The research focused on two aspects of the behaviour of long waves forced by shortwave groups. The first part of the research consisted of the analysis of data obtained in the Research Flume at the Technical University Delft. The long wave system was separated using a newly developed iterative procedure into an incoming long wave which propagates with a speed which is just slower than the group speed towards the beach, and an outgoing long wave which propagates with the shallow water speed in the offshore direction.
Physical and numerical modelling results were used to analyse the shoaling behaviour of the incoming long wave. It was verified that the shoaling rate is indeed a function of bed slope and group frequency. It was found that shoreline reflection is a function of the same parameter as well because in the direct vicinity of the shoreline, the long waves steepen up and break. This has ramifications for the reflection of long waves which until now has been assumed to be full from the shoreline. The results of the research provide better insight into the behaviour of long waves and will contribute to a reduction of the uncertainties in the wave-induced timevarying set-up which are to this date accounted for with extra allowances on the dike levels. In future, these allowances can be better substantiated and possibly reduced, saving money in construction and maintenance. The other area of study is the response of harbour basins to long waves which are generated in the nearshore region. Model-data comparisons were made using data from two actual ports: Tomakomai Harbor in Japan and Barber's Point Harbor in Hawaii USA. In the first case, wave data as well as ship motions were measured during a Typhoon event. The combination of the Surfbeat model with the ship motion model BAS could successfully hindcast long wave motions and ship motions as well as the effect of increasing pretension in mooring lines and a line-breaking event during the storm. The wave motion inside and outside the second harbour has been monitored thoroughly and the data is used to show the effect of approximations in the frequency and directional spreading in the wind wave spectrum which are used as boundary conditions for the long wave model. With the results of this research, harbour authorities and consultants will have a tool with which long wave penetration, amplification and mooring problems can be better understood and mitigating measures can be evaluated. |
