RESEARCHES ON DOUBLE CURTAIN WALL BREAKWATER

Shigeru Tanaka

Abstract


It has been clarified by some researchers(R. L. Wiegel1 , F. Ursell", R. Morihira & S. Anezaki3), etc.) that the single curtain wall breakwater has no good wave-dissipating effect at the usual coastal area where the ratio of water-depth to wave-length is considerably small. The author has made researches concerning "Multiple Curtain Wall Breakwater", anticipating the supposition that it may be very effective for the dissipation of wave energy even at a shallow coastal zone, because of its peculiar effectiveness upon wave dissipation. Double curtain wall breakwater is composed of two parallel rows of curtain walls attached to the supporting props installed at an adequate interval. The interval of the said two rows is very important, and the determination of a proper interval, relating to a high wind wave having a definite length and a definite wave height, is one of the main objects of this research. These researches were mainly made experimentally. At first the author assumed that the design wave had the period of 5-6 sec, the length of 50 - 60 m and the height of 1.5 m. The results of the model experiment show that the double curtain wall breakwater, installed at the depth ranging 3 - 10 m, has remarkable effect on wave dissipation.Secondly the author selected a particular location on the north coast of Osaka Bay where the design wave has the period of 7 - 9 sec, the wave length of 65 - 70 m and the wave height of 3.8 - 4.0 m at offshore. At the expected site of thebreakwater, the sea bottom is flat and nearly horizontal, and the water depth under the condition of the extraordinary high tide is 10.5 m above the sea bottom, and an experiment was carried out by the model for this location. One kind of model was constructed in a shallow basin of 0.5 m x 25 m x 30 m, in the scale of 1 to 40 and of 1 to 70, in order to determine its transmission coefficient of wave height. Another kind of model was made in a glazed steel frame tank of 1.6 mx 1.8 m x 28 m, equipped with a piston type wave generator operated by 5 HP motor. The scale of this model is 1 to 10, and its purpose is to secure the surface disturbance and to trace the trajectories of small suspended particles by a 16 mm cine camera and a high speed motion camera.

Keywords


breakwater design; double curtain wall breakwater

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