• Title/Summary/Keyword: perforated wall caisson

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Comparative Study of Design Methods for Sliding of Perforated-wall Caisson Breakwater (유공케이슨 방파제의 활동에 대한 설계법 비교 연구)

  • Kim, Nam-Hoon;Suh, Kyung-Duck
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.26 no.5
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    • pp.267-277
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    • 2014
  • The conventional performance-based design method for the solid-wall caisson breakwater has been extended and applied to the perforated-wall caisson. The mathematical model to calculate the sliding distance of a perforated-wall caisson is verified against hydraulic experimental data. The developed performance-based design method is then compared with the conventional deterministic method in different water depths. Both the expected sliding distance and the exceedance percentage of total sliding distance during the structure lifetime decrease with decreasing water depth outside the surf zone, but they increase with decreasing water depth inside the surf zone. The performance-based design method is either more economical or less economical than the deterministic method depending on which design criterion is used. If the criterion for the ultimate limit state is used, the former method is less economical than the latter outside the surf zone, whereas the two methods are equally economical inside the surf zone. However, if the breakwater is designed to satisfy the criterion for the repairable limit state, the former method is more economical than the latter in all water depths.

Three-dimensional Simulation of Wave Reflection and Pressure Acting on Circular Perforated Caisson Breakwater by OLAFOAM (OLAFOAM에 기초한 원형유공케이슨 방파제의 반사율 및 작용파압에 관한 3차원시뮬레이션)

  • Lee, Kwang-Ho;Bae, Ju-Hyun;Kim, Sang-Gi;Kim, Do-Sam
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.29 no.6
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    • pp.286-304
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    • 2017
  • In this study, we proposed a new-type of circular perforated caisson breakwater consisting of a bundle of latticed blocks that can be applied to a small port such as a fishing port, and numerically investigated the hydraulic characteristics of the breakwater. The numerical method used in this study is OLAFOAM which newly added wave generation module, porous media analysis module and reflected wave control module based on OpenFOAM that is open source CFD software published under the GPL license. To investigate the applicability of OLAFOAM, the variations of wave pressure acting on the three-dimensional slit caisson were compared to the previous experimental results under the regular wave conditions, and then the performance for irregular waves was examined from the reproducibility of the target irregular waves and frequency spectrum analysis. As a result, a series of numerical simulations for the new-type of circular perforated caisson breakwaters, which is similar to slit caisson breakwater, was carried out under the irregular wave actions. The hydraulic characteristics of the breakwater such as wave overtopping, reflection, and wave pressure distribution were carefully investigated respect to the significant wave height and period, the wave chamber width, and the interconnectivity between them. The numerical results revealed that the wave pressure acting on the new-type of circular perforated caisson breakwaters was considerably smaller than the result of the impermeable vertical wall computed by the Goda equation. Also, the reflection of the new-type caisson breakwater was similar to the variation range of the reflection coefficient of the existing slit caisson breakwater.

On the Calculation of Irregular Wave Reflection from Perforated-Wall Caisson Breakwaters Using a Regular Wave Model (규칙파 모델을 이용한 유공케이슨 방파제로부터의 불규칙파 반사율 산정에 대하여)

  • 서경덕;손상영
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.15 no.1
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    • pp.11-20
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    • 2003
  • In this paper we examine several methods tor calculating the reflection of irregular waves from a perforated-wall caisson breakwater using a regular wave model. The first method is to approximate the irregular waves as a regular wave whose height and period are the same as the root-mean-squared wave height and significant wave period, respectively, of the irregular waves. The second is to use the regular wave model, repeatedly, for each frequency component of the irregular wave spectrum. The wave period is determined according to the frequency of the component wave, and the root-mean-squared wave height is used for all the frequencies. The third method is the same as the second one except that the wave height corresponding to the energy of each component wave is used. Comparison with experimental data from previous authors shows the second method is the most adequate, giving reasonable agreement in both frequency-averaged reflection coefficients and reflected wave spectra.

Experimental Investigation for Evaluating Wave Forces on Perforated Caisson with Two Wave Chambers (유수실이 2개인 유공케이슨의 파력 산정에 관한 실험적 연구)

  • Oh, Sang-Ho;Ji, Chang-Hwan;Lee, Dal Soo
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.27 no.6
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    • pp.443-451
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    • 2015
  • Design formula for estimating the wave loading on the perforated caisson having two wave chambers is yet available. In this study, the analysis results are presented with the experimental data for the wave force acting on such a breakwater model. Based on the experimental results, it was able to clarify the variation of wave action according to five different wave phases that are associated with peak wave loading at the three vertical walls. Then the force adjustment factor for double-chamber caisson was estimated, similarly as Takahashi and Shimosako (1994), which needs to be further validated with subsequent experiments and practical application in the field.

Calculation of Expected Sliding Distance of Wave Dissipating Caisson Breakwater (소파케이슨 방파제의 기대활동량 산정)

  • Kim, Dong-Hyawn
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.17 no.4
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    • pp.213-220
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    • 2005
  • An approach to calculate expected sliding distance of wave dissipating caisson breakwater is proposed. Time history of dynamic wave pressure for the calculation of sliding distance is made by extending conventional static wave pressure developed for the wave dissipating caisson breakwater. Construction of impact wave and standing wave was done by using duration time and maximum wave pressures of themselves. In the numerical analysis, the sliding distance for an attack of single wave and expected sliding distance for 50 years of wave dissipating breakwater by proposed method were compared with those by conventional method for uplift caisson breakwater. It was found that the sliding distance of wave dissipating breakwater by the proposed method is smaller than by conventional method.

Comparison of Wave Pressure Acting on the Front Wall According to the Porosity of Caisson Breakwater Having the Cap of Wave Chamber (유수실 상부 덮개가 있는 케이슨 방파제의 유공률에 따른 전면벽 작용 파압 비교)

  • Oh, Sang-Ho;Ji, Chang-Hwan;Oh, Young Min;Jang, Se-Chul
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.33 no.2
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    • pp.573-584
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    • 2013
  • This study experimentally investigated the change in distribution of wave pressure on the front wall according to the variation of the front wall porosity of the caisson breakwater having the cap of wave chamber. First, the wave pressure for the non-porous caissson corresponding to zero porosity was measured and compared with the pressure formula suggested by Goda(1974). The analysis showed that the measured pressure distribution fairly well agreed with the Goda formula, which confirmed the accurate measurement of wave pressure in the present experiment. In case of the porous caisson, meanwhile, the experiment was performed by varying the front wall porosity as 0.2, 0.25, and 0.3. The wave pressure distribution at the front wall showed little difference according to the porosity for most of the test wave conditions, whereas the pressure slightly increased with the porosity for some test waves whose wave heights and periods were relatively large. However, the difference according to the porsosity was insignificant for the wave force at the front wall.

Reflection Characteristics of Vortical Slit Caisson Breakwater (종 SLIT형 케이슨 방파제의 반사특성)

  • 이종인;조지훈
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.13 no.4
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    • pp.263-272
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    • 2001
  • Recently, some attempts to construct slit caisson-type breakwaters are made in Korea. Since slit caisson-type breakwaters are suitable for relatively deep sea areas, a lot of theoretical and experimental researches have been performed. In this study, the reflection characteristics of vertical slit caisson breakwaters are investigated based on the measured data in two-dimensional hydraulic model tests with irregular waves. The experiments were conducted for various cases; variation of porosity of perforated-wall, width of wave chamber, number of slits for single-and double-chamber, respectively. It is found that in the case when the wave steepness (H/L$_{s}$ ) is small, the reflection coefficients are large. The existing researches have shown that the wave reflection is minimized when the nondimensional width of wave chamber B/L is about 0.2~0.25 for the regular waves. However, for the irregular waves the reflection is lowest when $B/L_2$, is 0.13~0.15. For a same porosity condition, the wave dissipation is stronger as the width of s1it is larger. The double-chamber caisson is superior to single- chamber caisson in the wave dissipating effects.

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Wave Reflection of Perforated-Wall Caisson Breakwaters with Curtain-Wall (직립 유공케이슨 방파제의 현수판 사용에 따른 반사특성)

  • Lee, Seung Hyeob;Hwang, Jong Kil;Cho, Yong-Sik
    • Proceedings of the Korea Water Resources Association Conference
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    • 2004.05b
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    • pp.1454-1458
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    • 2004
  • 본 인구에서는 직립 유공 케이슨에 현수판을 설치함으로서 입사파의 반사율을 저감시키고자 하였다. 먼저 케이슨 단면의 적정 유공율을 선정하기 위해 횡 SLIT 케이슨식 2개안 및 종 SLIT 1개안 단면에 대한 단면 실험을 실시하였다. 선행된 실험에서 가장 반사율이 낮은 SLIT 케이슨을 선택하여 유수실에 현수판을 설치 하였으며 현수판의 설치유무 및 현수판의 길이에 따른 반사계수를 검토하였다. 설치된 현수판은 장주기파에 대해서 반사율 저감효과를 얻을 수 없었지만 단주기 파에서는 반사율이 줄어드는 효과를 얻을 수 있었다. 해역에따라 단주기가 주류를 이루는 해역에서 현수판을 설치하면 파랑내습시 소파효과가 증대될 것으로 기대된다.

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Two and Three Dimensional Analysis about the Reflection Coefficient by the Slit Caisson and Resulting Wave Pressure Acting on the Structure (슬리트케이슨제에 의한 반사율과 구조물에 작용하는 파압에 관한 2차원 및 3차원해석)

  • Lee, Kwang-Ho;Choi, Hyun-Seok;Baek, Dong-Jin;Kim, Do-Sam
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.22 no.6
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    • pp.374-386
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    • 2010
  • Recently, the theoretical and experimental research is being made actively in control character of waves of perforated-wall caisson breakwater like the slit caisson. This study showed that the character of reflection coefficient and the wave pressure acting on the front and inner of slit caisson were estimated in two and three dimensional numerical wave flume and compared each other. The numerical experiment was set and conducted by various cases as to a variety of wave steepness under 7 sec, 9 sec, 11sec and 13 sec period condition. In this study using a 2 and 3 dimensional numerical wave flume, it applied the Model for the immiscible two-phase flow based on the Naveir-Stokes Equations. This technique can easily reproduce a complicated physical phenomenon more than others and organize the program simply. According to the results of the experiment, the reflection coefficient was estimated high in short-period waves. However, 2-dimensional numerical experiment and 3-dimensional numerical experiment were the same in case of the long-period waves and high wave steepness. And to conclude in case of short-period waves the pressures were a relatively small difference between the two, but there was a big gap in longperiod waves and high wave steepness.