ABSTRACT

The kinematics and dynamics of oscillatory flow around a pervious detached breakwater are experimentally studied for an idealized offshore permeable structure with rectangular cross-section. Laboratory measurements including wave-induced Lagrangian and Eulerian flows, and wave height distribution around structure were conducted bo visualize the wave-induced flow field and its interaction with porous structure. For parametric study of the wave-induced flow, experiments were conducted with different conditions of regular water waves, ponous media characteristics, and structure length. It is confirmed that there is a flow inside the pervious structure, which is expected to play an important role for natural water purification caused by the microorganisms living on the bio-film coat the surface of materials filled in structures. Also wave nonlinearity effect on the flow field was investigated to discuss the generation mechanism of the wave-induced flows.

INTRODUCTION

The flow induced by waves around and inside rubble mound breakwaters and their mutual interaction has been pointed out to be an important aspect in beach morphodynamics and rubble mound stability and functionality. Accurate prediction and estimation of the wave deformation around permeable structure are important for calmness condition in ports and coastal areas to reach to safety condition for berthing of the vessels commuting there and cargo handling. Regarding the interaction between porous media and water waves several analytical/numerical solutions have been developed yet (Sollitt and Cross, 1972; Madsen, 1974; McCorquodale et al, 1987; Sakakiyama and Kajima, 1992; Van Gent et al, 1994; Mizutani et al, 1996; Losada et al, 1998; Hm, 2000). Also, Losada et al (1995) experimentally studied wave induced flow inside a porous structure in the wave flume. Furthermore, it is understood that the microorganisms, living on the surface of rubbles of rubble mound breakwater, form biotilm that gives contribution to natural water purification by biological processes.

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