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Results
Submerged Porous Plate Wave Absorber
Park, W.T. (Civil Engrg Dept. Seoul National University of Technology) | Lee, S.H. (Civil Engrg Dept. Seoul National University of Technology) | Kee, S.T. (Civil Engrg Dept. Seoul National University of Technology) | Park, J.K. (Civil Engrg Dept. Seoul National University of Technology)
ABSTRACT In the present paper, the wave absorbing performance of the fully submerged horizontal porous plates has been investigated numerically and experimentally. The hydrodynamic interaction of incident waves with the rigid porous multi-layered plates was formulated in the context of linear wave-body interaction theory and Darcy's law. The accuracy and convergence of the developed numerical codes were cross-checked based on the energy-conservation formula for a limiting case, and the comparison with the experiment in a two-dimensional wave tank. It is found that triple horizontal porous plates with slight inclination can, if it is properly tuned for wave energy dissipating against the standing waves in front the vertical wall, have high performances in reducing the reflected wave amplitudes against the incident waves over a wide range of wave frequency. INTRODUCTION The wave absorbing breakwater inside of the sheltered region is one of the current engineering advancements in port design, in order to provide a further calm basin to insure safer and more efficient port operation, ship berthing and navigation inside of inner harbors (Yip & Chwang, 2000). In view of this, many researchers have been particularly interested in the interaction between the water waves and porous structures. Based on the linear water wave theory, a series of study can be traced back to the analysis of wave motion over a submerged porous plate by using boundary element method (Yu and Chwang, 1994) and found that a plate with proper porosity can suppress significantly the wave reflection. The water wave reflection by a vertical wall with a horizontal submerged porous plate was investigated by Wu et al. (1998) using the eigenfunction expansion method, and found that the larger plate with proper porosity behaves similarly to a wave absorber which can suppress the wave amplitude on the vertical wall surface and reflected waves.
ABSTRACT In the present paper, the hydrodynamic properties of a Rahmen type flexible porous breakwater with dual fixed—pontoon system interacting with obliquely or normally incident small amplitude waves are numerically investigated. This system is composed of dual vertical porous membranes hinged at the side edges of dual fixed pontoons, and a submerged horizontal membrane that both ends are hinged at the steel frames mounted pontoons. The dual vertical membranes are extended downward and hinged at bottom steal frame fixed into seabed. The wave blocking and dissipation mechanism and its effects of permeability, Rahmen type membrane and pontoon geometry, pretensions on membranes, relative dimensionless wave number, and incident wave headings are thoroughly examined. INTRODUCTION During the past decades, there has been a gradual increase of interest in the use of the flexible plate or membranes as the desirable characteristics of being transportable, relatively inexpensive, rapidly deployable, easily detachable, and even sacrificial. Thus, it may be an ideal candidate as a portable and temporal breakwater for the protection of various coastal/offshore structures and sea operations requiring relatively calm sea states. In this regard, the performance of a vertical screen membrane breakwater was investigated by Thomson et al. (1992), Aoki et al. (1994), Kim and Kee (1996), Williams (1996), Kee and Kim (1997), and Cho et al. (1997, 1998). The interaction of monochromatic incident wave with dual pre-tensioned, inextensible, vertical nonporous membrane wave barrier extending the entire water depth has been investigated by Edmond Y.M. (1998) using eigenfunction expansions for the velocity potential and linear membrane theory. Cho et al. (1998) developed an analytic solution for dual solid membrane system and a boundary integral method solution for more practical dual buoy/membrane wave barriers with either surface piercing or fully submerged system in oblique seas.