1992 Fiscal Year Final Research Report Summary
A method of spatial arrangement of offshore breakwaters for effective wave attenuation and changing currents
| Project/Area Number |
02650362
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
Hydraulic engineering
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| Research Institution | Ehime University |
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Principal Investigator |
NAKAMURA Takayuki Ehime University, Faculty of Engineering, Associate Professor, 工学部, 助教授 (60108404)
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| Project Period (FY) |
1990 – 1992
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| Keywords | Offshore breakwater system / Effective spatial array / Wave directional change / Wave height attenuation / Wave-induced current / Wave energy dissipation / Green's function method |
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| Research Abstract |
In order to effectively attenuate incoming waves and control wave-induced currents, the spatial arrangement and allocation of offshore breakwaters is examined extensively. The following 3 topics have been especially dealt with in this study. (1)Wave dissipation mechanism and the resultant mean current features based on the vertical 2-D model of the breakwaters: Various types of breakwater, e.g. a concrete block breakwater, caisson breakwater, curtain-walled breakwater, floating breakwater and submerged breakwater, are used in order to clarify the wave dissipation mechanism of each type of breakwater. Characteristics of the mean current caused by the wave dissipation around the breakwater have been also studied. As a result, if is confirmed that the wave energy dissipation by the concrete block breakwater is mainly caused by the wave slamming inside the breakwater, wave breaking for the rubble mound breakwater, vortex formation around the angular or sharp corners for the curtain-walled
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breakwater and floating breakwater. It is also shown that the mean current around the breakwater has a close relation with the wave dissipation mechanism.
(2)Effective arrangement and allocation of offshore breakwaters for reducing incoming waves: For all types of the breakwater used in this study, it is recommended that the pitch length between neighboring breakwaters should be less than the incident wave length because the generation of obliquely transmitted waves through the breakwater array is restrained. Furthermore, in the case of a floating breakwater array, the staggered array is very effective for reducing incoming waves if the projected gap length of the neighboring breakwaters on the array axis is equal to 0.
(3)Effective arrangement and allocation of offshore breakwaters for changing the wave propagation direction: When the rectangular caisson is placed in such a way that the inclination angle from the array axis is in the range of 8 to 20 degrees, it is clarified that the obliquely propagating wave component becomes predominant in the lee side of the breakwater array. As a result, it is possible to control the intensity and direction of the wave induced current in the near shore region. Less
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