Design of eco blocks for protection of submerged pipeline
In order to protect coastal facilities mainly from wave and current actions, the self-locking eco blocks constituting elements of protecting shore structures against scouring were designed. These blocks are adapted to the sloping bottom, coastal dunes, and submerged coastal pipelines, counteracting the destructive and erosive impulse action. A series of laboratory experiments has been conducted to investigate the reflection of water waves over and against a train of protruded or submerged shore structures and compare the reflecting capabilities of incident waves including wave forces. In this study the hydraulic model experiment was conducted to identify the performance of newly designed water affinity eco blocks to keep the coast slope and bottom mound from scouring by reduction of the wave reflection and to convince stability of the block placement. Revised design of each block element was also tested for field conditions. From the result of experiments, the field applicability of the developed blocks and placement was discussed afterward.
CONTROL OF CROSS-SHORE SEDIMENT TRANSPORT BY A DISTORTED RIPPLE MAT
A method to control cross-shore sediment transport by a distorted ripple mat which is the artificial ripples of distorted cross section has been studied through hydraulic experiments and numerical simulation. First of all,the relative importance of factors affecting cross-shore sediment transport on fixed bed ripples and the condition on which sediment is definitely transported onshoreward are obtained. Based on this condition,experiments with movable bed are carried out to see how efficiently the distorted ripple mat can be utilized in stabilizing natural/artificial beaches. Furthermore,a. numerical model of beach profile change in which effects of ripple distortion are considered has been developed and beach stabilizing effects of the mat are also reproduced numerically.
ORIGIN, EFFECT AND SUPPRESSION OF SECONDARY WAVES
Beach profile formation may be severely affected by secondary waves which, together with the basic wave, always originate from a sinusoidally.moving wave board The ascertainment of this experimental fact is followed by an investigation of the behaviour of the generated waves and their interactions It appears that the many characteristic features, among which the spatial beat phenomenon and the secondary crest formation, are generally in good accordance with the theories of Fontanet [I4j, and Kravtchenko and Santon I 20J It is concluded that an "outer" analysis, eg by plotting the x-tlines of visible peaks, is only of limited use to describe the "inner" character of the complex phenomenon. The subsequent study of the effect of secondary waves on a horizontal sand bed reveals that not only the wave form, but also the sand transport varies spatially, resulting in the formation of bars and troughs This typical behaviour of the onshore-offshore transport is provisionally investigated in a small pulsating water block. Finally, a method is described which suppresses the secondary waves, by using a low rectangular sill on the otherwise horizontal bottom.