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BASIC COASTAL ENGINEERING Part 4

Tham khảo tài liệu 'basic coastal engineering part 4', kỹ thuật - công nghệ, kiến trúc - xây dựng phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Wave Refraction Diffraction and Reflection 93 on the cross-section geometry and composition of the barrier. The portion of the wave passing the end of the barrier will have a lateral transfer of wave energy along the wave crest into the lee of the barrier. The diffracted wave crests in the lee of the barrier will form approximately concentric circular arcs with the wave height decreasing exponentially along the crests. The shadow region out to the dashed line will have a wave height that is less than the incident wave height at the end of the barrier. Note that the water depth in Figure 4.8 is constant otherwise the wave crest pattern and wave heights would also be affected by refraction. If Hi is the incident wave height at the end of the barrier and Hd is the diffracted wave height at a point of interest in the lee of the barrier we can define a diffraction coefficient Kd Hd Hi. The value of Kd depends on the location behind the barrier deWned by r and b and the incident wave direction deWned by 0 or in dimensionless form Kd f 0 b r L where L is the wave length in the lee of the barrier. Since the wave length is a function of the wave period and water depth the resulting diffraction coefficient for each component of the wave spectrum would depend on the incident direction and period of that component. Water wave diffraction is analogous to the diffraction of light. The two most common diffraction problems encountered in coastal engineering design are diffraction past the end of a semi-inWnite barrier as depicted in Figure 4.8 and diffraction through a relatively small gap in a barrier. Penny and Price 1952 showed that the mathematical solution for the diffraction of light can be used to predict the wave crest pattern and height variation for these two wave diffraction problems. Semi-infinite Barrier A summary of the diffraction solution for a semi-inWnite barrier is presented by Wiegel 1964 and by Putnam and Arthur 1948 who also conducted some wave tank .