Focusing waves of different parameters are generated in the experimental flume using JONSWAP spectrum in this paper. Interactions including the dynamic wave pressure and the inline wave force between the focusing waves and a vertical cylinder are studied simultaneously. The experimental transfer functions about dynamic wave pressure and inline wave force are calculated and then compared with the theoretical solutions based on the linear diffraction theory and Morrison equation separately. Investigations on the characteristics of the frequency response caused by focusing waves will provide practical references in ocean engineering.
Studies of the interactions between ocean waves and offshore structures are a fundamental consideration in ocean engineering design. Real ocean waves are normally irregular and nonlinear. Regular waves or random waves of long time will not describe the real wave situation accurately. With the development of technology, more types of waves similar to true ocean waves such as focusing waves, freak waves and broken waves and so on are broadly used in experimental and numerical simulation. Focusing waves generated by the superposition of component waves with different frequency at a fixed place and time can well simulate the largest transient wave in a short time. For example, Baldock and Swan (1996a, 1996b) produced a large transient wave group using constant wave amplitude as the input spectrum and analyzed the wave transformation in different water depth. Smith and Swan (2002) compared the experimental focusing waves with several existing design solutions especially in the simulations of underlying water particle kinematics. Hong et al. (2004) and Liu et al. (2005) studied the directional wave focusing and breaking waves experimentally. All these researches proved that it is practical and convenient using focusing waves to study the interaction between nonlinear extreme waves and structures.
