Perforated Caisson Breakwater Research Articles

Interaction between oblique waves and perforated caisson breakwaters with perforated partition walls

This study gives an analytical solution for oblique wave interaction with perforated caisson breakwaters having perforated partition walls. The periodic boundary conditions of the velocity potential and its derivative in the caisson length direction are incorporated into the solution. A velocity potential decomposition method is used to obtain velocity potentials inside caisson chambers. The newly developed analytical solution is confirmed by the solutions for several special cases of the present breakwater and an independently developed multi-domain boundary element method solution for the present problem. The analytical solution is also validated by experimental data. The reflection coefficients, the wave forces and the surface amplitudes near the breakwater are examined, and some useful results are presented. This study may give a better understanding of the effect of perforated partition walls on the hydrodynamic performance of perforated caisson breakwaters.

유공케이슨 방파제에 작용하는 파력 공식의 비교

In this study, two-dimensional physical experiment was carried out to examine the applicability of the three formulas(Takahashi and Shimosako, 1994; Tabet-Aoul and Lambert, 2003; Li, 2007), which were proposed to calculate the wave forces acting on perforated caisson breakwaters. In order to quantitatively compare the measured with the estimated values based on the wave formulas, the refined index of agreement and the coefficient of determination were calculated, by which the degree of agreement was evaluated. Among the three wave formulas, DUT formula (Li, 2007) showed the smallest deviation from the measured forces, whereas Takahashi formula (Takahashi and Shimosako, 1994) showed the largest deviation. Meanwhile, comparison of the magnitude of the measured wave forces with those from the three formulas revealed that DUT formula slightly underestimate, while the others overestimate the measured forces.

단일 및 이중유수실 유공케이슨 방파제에 작용하는 최대 수평파력 비교

Physical experiments were carried out to measure the wave force on the vertical walls of perforated breakwater considering several phases of a wave acting on the breakwater. The maximum horizontal wave force acting on each vertical wall was compared between single and double chamber caisson breakwater. The experimental data in this study showed that the total horizontal wave force for double chamber caisson was 9.6% smaller on average than that for single chamber caisson when the total chamber width was the same for both caissons. Such reduction of the wave force is due to the dissipation of wave energy at the porous middle wall, which is located between the porous front wall and non-porous rear wall. 핵심용어: Perforated caisson breakwater, Double chamber, Middle wall, Wave force, Physical experiment, 케이슨 ë°©íŒŒì œ, ì´ì¤‘ìœ ìˆ˜ì‹¤, 중간벽, íŒŒë ¥, 수리모형실험

EXPERIMENTAL INVESTIGATION OF HORIZONTAL WAVE FORCES ON THE PERFORATED CAISSON WITH SINGLE AND DOUBLE WAVE CHAMBERS

The horizontal wave force acting on vertical walls of perforated caisson breakwater was experimentally investigated in this study. The maximum horizontal wave force acting on single and double chamber caisson was measured respectively and compared each other. By analyzing the obtained experimental data, it was clarified that the total horizontal wave force for double chamber caisson was 9% smaller on average than that for single chamber caisson when the total chamber width was the same for both caissons. The reason for such reduction of horizontal wave force on the double chamber caisson is found from additional dissipation of wave energy at the porous middle wall of the structure, by which rather impulsive wave force on the rear wall could be slightly diminished compared to the single chamber caisson.

Influence of Wave Chamber Slab on Wave Pressure on First and Second Wall of Perforated Caisson Breakwater

이 연구에서는 수리모형실험을 통해 유수실 상부 덮개가 유공 케이슨 방파제 전면벽 및 후면벽에서의 파압에 미치는 영향을 고찰하였다. 수리모형실험은 유공 케이슨의 유수실 상부 덮개가 있는 경우 및 없는 경우에 대해서 전면벽 유공률을 변화시키면서 이루어졌다. 유수실 상부가 덮개로 막혀 있을 때에는 모든 실험 조건에서 유의미하게 더 큰 파압이 취득되었으며 따라서 유수실 상부 덮개 존재에 따른 두 벽에서의 계측 파압 차이는 매우 뚜렷하게 나타났다. 그 결과 계측 파압을 적분하여 계산된 전파력의 크기 역시 상부 덮개가 있는 케이슨 방파제의 경우가 더 컸으며, 이 경우 잘 알려진 Takahashi의 파압식에 근거한 파력값을 상회하였다. 한편, 전면벽 유공률에 따라서는 방파제 전면벽 및 후면벽에서 모두 유공률이 클수록 더 큰 파압이 계측되었다. In this study, the effect of wave chamber slab on wave pressure along the first and second wall of the perforated caisson breakwater was investigated by performing physical experiment. The experiment was performed without and with the wave chamber slab of the perforated caisson by varying the front wall porosity. The discrepancy in magnitudes of the measured wave pressure along the both walls of the perforated caisson was apparent according to the existence of the wave chamber slab as significantly greater pressures were acquired for all the test cases when the wave chamber was closed upward by the slab. As a result, the magnitudes of the total wave force calculated by integration of the measured wave pressure also were much larger for the caisson breakwater having the wave chamber slab, exceeding the value based on the well known Takahashi's formula (Takahashi and Shimosako, 1994). With respect to the porosity of the front wall, meanwhile, higher pressures were obtained with a larger porosity, at both the first and second wall of the breakwater.

Reduction of non-breaking wave loads on caisson type breakwaters using a modified perforated configuration

In this study a new type of partially perforated caisson breakwater is introduced with two shallow chambers split horizontally by an impermeable plate at the mean sea level. A plexiglass laboratory model of the structure was manufactured with different frontface perforation ratios and adjustable chamber breadths, then tested under 2D non-breaking regular and irregular waves. The horizontal wave force and wave moment are evaluated as dimensionless parameters from measured pressure–time series. A control group of tests was also conducted with plain vertical face under identical waves, also the wave loads on a vertical face for the same wave properties were computed using Goda (1985) formulation. Results show that the dimensionless wave forces and dimensionless wave moments can be reduced by a ratio up to 35%–40% under regular and irregular waves and structure performance increases with decreasing wave length. The obtained results are also compared with reference to a fully perforated (Jarlan) caisson using the method given by Tabet-Aoul and Lambert (2003) and a general harmony was seen both for the magnitudes and variation of wave loads with dimensionless chamber breadth ( B/ L).

Total horizontal and vertical forces of irregular waves on partially perforated caisson breakwaters

In this study, the total horizontal and vertical forces as well as the phase differences of irregular waves on a partially perforated caisson breakwater are investigated. The partially perforated caisson is located on a rubble fill foundation and filled with rock. Based on linear potential theory, a simple semi-analytical solution of the present problem is developed by means of the matched eigenfunction method and the finite element method. Experimental tests are also conducted to validate the theoretical model and examine the wave forces acting on the perforated caisson. The effects of some of the main factors on the total wave forces and the phase difference are examined. Theoretical and experimental studies show that when the total horizontal force reaches its peak, the simultaneous total vertical (upward) force is rather small or even becomes downwards. This is due to the existence of an obvious phase difference between the time histories of the total horizontal and vertical forces, which is an important advantage of perforated caissons over traditional structures.

Tentative New Formula for Maximum Horizontal Wave Forces Acting on Perforated Caisson

This paper summarizes a part of the work carried out in the framework of the European research program MAST III-PROVERBS. It deals with the evaluation of pressure distribution and forces acting on the different faces of a perforated caisson breakwater. Various 2D model tests were performed at LeHavre and Caen Universities, and field measurements were made on the Dieppe breakwater. The aim of the study was to improve common knowledge and design of this type of dissipative monolithic breakwater. A new method for the calculation of maximum horizontal wave forces is proposed. The method is tested for more than 120 force estimates derived from various experimental sources, and it proves to be fairly good and reliable for engineering applications.

Design Wave Force on Perforated Caisson Breakwaters with Wave Dissipating Blocks

A perforated caisson breakwater with wave-dissipating blocks, which has passage holes in the caissons, was developed for the purpose of maintaining a superior water quality environment in the landward area of a port. This structure allows permeability of tides and permanent currents, and uses wave energy to introduce seaward water into the landward water area of the port.In order to examine the wave force characteristics on perforated caisson breakwaters with wavedissipating blocks, a, two-dimensional hydraulic model experiment was conducted. Based on the results, a method of structurally resistive design against wave action was proposed. This method is an expansion the general design method for breakwaters covered with wave?dissipating blocks, upon which the Goda's method had been applied. It is believed that general horizontal wave forces and uplift pressure, which were obtained by introducing the wave pressure reduction coefficient to the Goda's method, are applied to the front and bottom surfaces of the caisson. The horizontal wave force, however, was not applied because there were no pressure receiving surfaces at the openings of the passage holes, but inner-hole uplift pressure was applied onto the upper surface in the passage holes. Appropriateness of this method was confirmed in sliding tests.