1985 Fiscal Year Final Research Report Summary
ZONE PROTECTION SYSTEM FOR REDUCTION OF WAVE OVER TOPPING
| Project/Area Number |
59850090
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| Research Category |
Grant-in-Aid for Developmental Scientific Research
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| Allocation Type | Single-year Grants |
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| Research Field |
Hydraulic engineering
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| Research Institution | Osaka University |
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Principal Investigator |
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| Project Period (FY) |
1984 – 1985
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| Keywords | artificially nourished beach / wave over-topping / submerged breakwater / 潜堤 |
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| Research Abstract |
A zone protection system, which is different from a line protection system with the use of offshore breakwater so far in use, usually consists of a submerged offshore breakwater and an artificially nourished beach behined it. This protection system enables us to improve a view from shoreline and to create a pro-water wave front. However, a variety of problems remain unsolved for the adoption of this system. The aims of this study are to investigate versatile functions of zone protection system. Main results obtained in this study are summarized as follows:
1. Iwata investigated transformation characteristics of wave height and period of irregular waves on an artificially nourished beach and proposed the expression for the potential and kinematic energies in a swash zone. He also discussed the effect of air-entrainment on wave decay after breaking.
2. Nochino investigated firstly, the effect of height and width of artificially nourished beach on wave over-topping and found that they are c
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losely related to the wave deformation on the artificially nourished beach. Then, he proposed a modified wave breaking criteria on the submerged breakwater in front of the artificially nourished beach.
3. Matsumi and Aoki studied the effect of submerged breakwater in multi-rows,which are also used as fishhouses, on the decrease of incident wave heights and obtained the following results: i) the maximum wave attenuation is expected when the distance of the rows is ((2i-1)/4+1/8) where i is an integer and L is the wave length, ii) the transmitted waves contain harmonics of high frequencies and these harmonics bring spatial variations of transmitted wave heights.
4. Deguchi investigated the stability of replenished sand on the artificially nourished beach experimentally and found the following results:
i) the volume of reprenished sand which flow out offshore over the submerged breakwater becomes less when the location of submerged breakwater is in the outside of wave breaking point and forced wave breaking takes place on the submerged breakwater,
ii) severe erosion takes place on the artificially nourished beach in the region where u*/wo 0.6 where u* is the frictional velocity and wo is the settling velocity of the replenished sand.
5 Sawaragi studied the effect of zone protection systems on the reduction of wave over-topping and found that there exists a region on the artificially nourished beach where the turbulence generated by the forced wave breaking on the submerged breakwater almost decreases and that for the estimation of the volume of wave over-topping in these region, the formula proposed for the estimation of the volume of wave overtopping in non-breaking, standing wave region can apply. Less
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