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BASIC COASTAL ENGINEERING Part 8

Tham khảo tài liệu 'basic coastal engineering part 8', kỹ thuật - công nghệ, kiến trúc - xây dựng phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 230 Basic Coastal Engineering Example 7.6-1 The breakwater for a small marina is constructed of vertical concrete panels supported by piles. The water depth at the structure is 4 m and the panels have an opening of 0.5 m at the bottom to enhance water circulation in the marina. The panels extend 1.5 m above the still water level i.e. panel lengths are 5 m . For an incident wave height of 1 m and a period of 4 s determine the maximum wave-induced force and moment on the breakwater per unit length. Assume still water on the lee side. Solution Since the bottom opening will diminish reflection to a small extent we will assume Cr 0.9. Then Eq. 7.18 yields H 1 20 9 1 0.95 m From Eq. 2.14 with d 4m and T 4s L 20.86m and k 0.3013. Then Eq. 7.17 yields p 0.95 2 . . Dz coth 0.3013 4 0.15 m and Eq. 7.16 yields a maximum bottom dynamic pressure of Pd 9810 0.95 cosh 0.3013 4 5125 N m2 Then the pressure on the structure will vary as follows z 0.95 0.15 1.10m p 0 z -4.0 m p 9810 4 5125 44 365 N m2 z 3.5 m p 44 365 3.5 0.95 0.15 4 0.95 0.15 40 040N m2 Thus the total force per unit length is 402040 3.5 0.95 0.15 1 92 092N m This force acts at a distance of 3 _ . 3.5 0.95 .015 0.5 2.03 m Coastal Structures 231 above the sea floor so the moment per unit length around the sea floor is 92 092 2.03 187 254 N m m Breaking-Wave Forces When a wave breaks directly on the face of a vertical structure there is a dynamic impact force on the structure that acts around the still water line. This is superimposed on the normal hydrostatic force. On rare occasions the breaking wave will have a vertical face that slams against the structure and causes an extremely high intensity short duration less than 0.01 s typically pressure on the structure. Although a high instantaneous force can develop this force is of very short duration so the effect may not be great particularly for massive structures that require a sustained force to dislocate them. The force may cause localized damage on a