Ching-Yun Yueh

Dual boundary element analysis of oblique incident wave passing a thin submerged breakwater

In this paper, the dual integral formulation for the modified Helmholtz equation in solving the propagation of oblique incident wave passing a thin barrier (a degenerate boundary) is derived. All the improper integrals for the kernel functions in the dual integral equations are reformulated into regular integrals by integrating by parts and are calculated by means of the Gaussian quadrature rule. The jump properties for the single layer potential, double layer potential and their directional derivatives are examined and the potential distributions are shown. To demonstrate the validity of the present formulation, the transmission and reflection coefficients of oblique incident wave passing a thin rigid barrier are determined by the developed dual boundary element method program. Also, the results are obtained for the cases of wave scattering by a rigid barrier with a finite or zero thickness in a constant water depth and compared with those of experiment and analytical solution using eigenfunction expansion method. Good agreement is observed.

A Piston-Type Porous Wave Energy Converter Theory

This study investigates the performance of a piston-type porous wave energy converter (PTPWEC), which consists of a solid wall, a vertical porous plate, a transmission bar, a rigid block constrained by rollers, a spring, and a damper. The PTPWEC is subjected to dynamic external loading by wave actions. To simulate this dynamic system, a mathematical model is used with a single-degree-of-freedom (SDOF) system. Linear wave theory governs the entire fluid domain, which is divided into two regions by the vertical porous plate. Darcys law is applied to flow through the porous plate. Finally, this investigation employs an eigenfunction expansion to yield a solution. A series of numerical experiments are conducted to determine the hydrodynamic added mass, radiation damping, converter response, and instantaneous mechanical power obtained from the wave.

The study of wave pressure and uplift force on a submerged plate

Abstract Boundary element method (BEM) is used to study wave pressure acting on a vertical quay, as well as the uplift forces on a submerged plate. The plate, placed in front of the quay, is bored with holes. The results are then compared with the case of a plate without any perforation. The results showed that: for q/h = 0.45, where q is the depth of submergence of the plate and h is water depth, wave pressure acting on the vertical quay is very similar for plates with or without borings. However, with q/h = 0.20, wave pressure on the quay is changed according to wave periods, widths of the plate, the distance of the plate away from the quay, as well as the ratio of the holes to the plates. Uplift forces exerted on the plate are indeed smaller for plates with borings than without, and decrease with increasing porous ratio. Furthermore, the uplift forces will be the same for the same porous ratios, regardless of these ratios being caused by a single or a double perforation.

The nonlinear wave effects by a submerged horizontal plate to the vertical wall

Wave pressure reduction due to a submerged horizontal plate placed before a vertical wall was investigated both numerically as well as experimentally. Pressure-reduction due to the submerged plate for short period waves was clearly evident. For all the case studies, the optimal submergence depth was found to be equal to d = 0.20h rather than 0.45h, where h is the total water depth. However, at this depth, d = 0.20/;, the pressurereduction effect will vary according to wave conditions, the width of the plate, (l), and the distance of the plate away from the vertical wall (w). Furthermore, it was found that the wider the plates, the longer the waves that will be affected. Calculated reflection coefficients were found to be in satisfactory agreements with experiments for nonbreaking waves.

The Hydrodynamic Characteristics of an Inclined Submerged Porous Plate with Rock Filled Structure

In this paper, we investigate the hydrodynamic efficiency of normal incident waves interacting with an absorbing system. The wave absorbing system consists of a submerged permeable structure filled with rock, a solid back wall, and a submerged horizontal or slightly inclined porous plate. Using a linear wave theory assumption, a multi-domain BEM (MBEM) model was created to calculate and discuss the reflection coefficients, free surface wave profiles, total wave force on the solid wall, and the horizontal and uplift forces acting on the porous plate of the water waves from several properties of the breakwater. The numerical model was calibrated using previous numerical studies to act as limiting cases for a partially submerged impermeable structure and a horizontal porous plate with a solid back wall. The accuracy of the solution is demonstrated by comparing the numerical values with those obtained from other analytical solutions. From the numerical results, the wave dissipation effect from the permeable rock-filled structure was found to perform better than expected when compared to an impermeable structure. In the case of a horizontal porous plate, the smaller submergence depth of the plate results in a smaller reflection coefficient. The larger the porous effect parameter, the smaller the value of the reflection coefficient and the larger the porous effect parameter, the greater the ability of the porous plate to reduce the uplift forces.

ANALYSIS OF WAVE INTERACTION WITH DOUBLE VERTICAL SLOTTED WALLS USING MBEM

In this paper, a multi-domain boundary element method (MBEM) is formulated and applied to study wave interaction with double vertical slotted walls, which are modeled as thin or non-thickness structures. Two-dimensional motion with wave crests parallel to the vertical slotted walls and linearized irrotational flow are assumed. The accuracy of the solution obtained using the numerical technique is demonstrated by comparing the numerical values with those obtained from experiments and from other analytical solutions. A comparison of the hydrodynamic performance of the breakwater with identical or different double vertical slotted walls is conducted. In addition, the numerical results of the wave reflection, transmission and energy dissipation for different relative permeable depths, chamber widths, and porosities are presented and discussed. Double vertical slotted walls with a longer rear wall are recommended because they more effectively suppressed wave energy at deeper submergence. The double vertical slotted walls also very effectively dissipate the incident wave energy. Our numerical results indicate that when the permeable middle part of the seaward (first) wall (dm_1/h = 0.6) and the permeable middle part of the leeward (second) wall (dm_2/h = 0.2) have different porosities of e_1 = 0.5 and e_2 = 0.3, respectively, the breakwater has a high reflection coefficient, a low transmission coefficient and the maximum energy dissipation coefficient. The maximum energy dissipation coefficient of 0.963 occurs at kh = 1.635.