• Title/Summary/Keyword: Perforated breakwater

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Experiments on Tension Characteristics of Perforated-type Floating Breakwaters (유공형 부방파제의 장력특성에 관한 실험)

  • Yoon, Jae Seon;Ha, Taemin
    • Proceedings of the Korea Water Resources Association Conference
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    • 2017.05a
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    • pp.514-514
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    • 2017
  • Floating breakwaters were treated as solid bodies without any perforation in previous studies. In this study, however, a floating breakwater is perforated to allow the partial absorption of the energy produced by incident waves and an air chamber is placed in the upper part to control the breakwater draft. A series of laboratory experiments for a floating breakwater installed with a mooring system are carried out. In general, a mooring system can be classified by the number of mooring points, the shape of the mooring lines, and the degree of line tension. In this study, a four-point mooring is employed since it is relatively easier to analyze the measured results. Furthermore, both the tension-leg and the catenary mooring systems have been adopted to compare the performance of the system. In laboratory experiments, the hydraulic characteristics of a floating breakwater were obtained and analyzed in detail. Also, a hydraulic model test was carried out on variable changes by changing the mooring angle and thickness of perforated wall. A hydraulic model was designed to produce wave energy by generating a vortex with the existing reflection method. Analysis on wave changes was conducted and the flow field around the floating breakwater and draft area, which have elastic behavior, was collected using the PIV system. From the test results the strong vortex was identified in the draft area of the perforated both-sides-type floating breakwater. Also, the wave control performance of the floating breakwater was improved due to the vortex produced as the tension in the mooring line decreased.

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Wave Reflection from Partially Perforated Wall Caisson Breakwater

  • K. D. Suh;Park, W. S.;Lee, D. S.
    • Proceedings of the Korean Society of Coastal and Ocean Engineers Conference
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    • 1996.10a
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    • pp.176-183
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    • 1996
  • In order to reduce wave reflection from a breakwater, a perforated wall caisson is often used. A conventional perforated wall caisson breakwater for which the water depth inside the wave chamber is the same as that on the rubble mound berm has less weight than a vertical solid caisson with the same width and moreover the weight is concentrated on the rear side of the caisson. (omitted)

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Wave Reflections from Breakwaters Having Resonance Channels with Perforated Plates (유공판을 갖는 공진수로 내장형 방파제의 반사특성)

  • Kim, Jeongseok;Seo, Jihye;Lee, Younghoon;Lee, Joongwoo;Park, Woosun
    • Proceedings of the Korean Institute of Navigation and Port Research Conference
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    • 2013.10a
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    • pp.149-150
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    • 2013
  • Recently, various types of perforated breakwaters are being constructed for protecting offshore storm waves. In general, perforated breakwaters have wave chambers with perforated walls at seaside. Purposes of the wave chambers are to reduce wave reflections and maximum wave forces acting on the breakwater. Impact wave forces due to wave breaking can attack to the perforated wall directly, so the effects have to be considered in the design of the perforated wall carefully. Using resonance channels for wave energy dissipation, a new concept perforated breakwater is proposed, which is free from impact loads. Numerical simulation was made for wave reflection characteristics of the breakwater with respect to major design parameters. Numerical analysis was carried out using the Galerkin's FE model based on the linear potential theory considering energy dissipation on the perforated plate. Variations of wave reflection was investigated according to perforated ratios of perforated plate.

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Experimental Study of Flow Fields around a Perforated Breakwater

  • Ariyarathne, H.A. Kusalika S.;Chang, Kuang-An;Lee, Jong-In;Ryu, Yong-Uk
    • International Journal of Ocean System Engineering
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    • v.2 no.1
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    • pp.50-56
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    • 2012
  • This study investigates flow fields and energy dissipation due to regular wave interaction with a perforated vertical breakwater, through velocity data measurement in a two-dimensional wave tank. As the waves propagate through the perforated breakwater, the incoming wave energy is reflected back to the ocean, dissipated due to very turbulent flows near the perforations and inside the chamber, and transmitted through the perforations of the breakwater. This transmitted energy is further reduced due to the presence of the perforated back wall. Hence most of the energy is either reflected or dissipated in the vicinity of the structure, and only a small amount of the incoming wave energy is transmitted through the structure. In this study, particle image velocimetry (PIV) technique was employed to measure two-dimensional instantaneous velocity fields in the vicinity of the structure. Measured velocity data was treated statistically, and used to calculate mean flow fields, turbulence intensity and turbulent kinetic energy. For investigation of the flow pattern, time-averaged mean velocity fields were examined, and discussed using the cross-sections through slot and wall for comparison. Flow fields were obtained and compared for various cases with different regular wave conditions. In addition, turbulent kinetic energy was estimated as an approach to understand energy dissipation near the perforated breakwater. The turbulent kinetic energy was distributed against wave height and wave period to see the dependence on wave conditions.

Numerical Analysis of Reflection Characteristics of Perforated Breakwater with a Resonant Channel (공진수로 내장형 유공방파제의 반사특성에 관한 수치해석 연구)

  • Kim, Jeong-Seok;Seo, Ji-Hye;Lee, Joong-Woo;Park, Woo-Sun
    • Journal of Navigation and Port Research
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    • v.38 no.5
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    • pp.503-509
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    • 2014
  • In this study, a new concept perforated breakwater is proposed, which is having resonant channels. In the channel, perforated plate is installed for dissipating wave energy induced by flow separations. The breakwater has two advantages compared with conventional perforated breakwater having wave chamber with slotted walls. One is easy to control the target wave condition for dissipating wave energy, and the other is having the high structural safety because the structural members are not exposed to impact waves, directly. To evaluate wave reflection characteristics of the proposed breakwater, numerical experiment was carried out by using Galerkin's finite element model based on the linear potential theory. The results indicated that considerable energy dissipation occurs near the resonant period of channel, and wave reflection characteristics are affected by channel shape, location and opening ratio.

Experimental Study on Hydraulic Performance of Perforated Caisson Breakwater with Turning Wave Blocks (회파블록케이슨 방파제의 수리학적 성능에 관한 실험적 연구)

  • Kim, In-Chul;Park, Ki-Chul
    • Journal of Ocean Engineering and Technology
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    • v.33 no.1
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    • pp.61-67
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    • 2019
  • Recently, a perforated caisson breakwater with turning wave blocks was developed to improve the water affinity and public safety of a rubble mound armored by TTP. In this study, hydraulic model tests were performed to examine the hydraulic performance of a non-porous caisson and new caisson breakwater with perforated blocks for attacking waves in a small fishery harbor near Busan. The model test results showed that the new caisson was more effective in dissipating the wave energy under normal wave conditions and in reducing the wave overtopping rates under design wave conditions than the non-porous caisson. It was found that the horizontal wave forces acting on the perforated caisson were slightly larger than those on the non-porous caisson because of the impulsive forces on the caisson with the turning wave blocks.

Influence of Wave Chamber Slab on Wave Pressure on First and Second Wall of Perforated Caisson Breakwater (유수실 상부 덮개가 유공 케이슨 방파제의 전면벽 및 후면벽 파압에 미치는 영향)

  • 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.6
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    • pp.2317-2328
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    • 2013
  • 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.

Design of Vertical Slit type perforated Breakwater at Busan New Marine Town (부산 해상신도시에 있어서의 종 Slit형 유공방파제 설계)

  • 김재경;주희찬;안익성
    • Proceedings of the Korean Society of Coastal and Ocean Engineers Conference
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    • 1992.08a
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    • pp.58-63
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    • 1992
  • In addition to the traditional breakwater faculty, multipurpose breakwater of vertical slit type perforated breakwater was planed and designed using the idea of waterfront and wave dissipation of breakwater. As a result of experimental test, the good hydraulic characteristics was confirmed by comparison of traditional structure, and in order to the field application the section was improved on the test of result.

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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.

Load & Resistance Factors Calibration for Sliding and Overturning Limit State Design of Perforated Caisson Breakwater (유공케이슨 방파제 활동 및 전도 한계상태설계를 위한 하중저항계수 보정)

  • Kim, Dong Hyawn
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.32 no.6
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    • pp.458-464
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    • 2020
  • Calibration of load-resistance factors for the limit state design of perforated caisson breakwaters are presented. Reliability analysis of 12 breakwaters in nationwide ports was conducted. Then, partial safety factors and load-resistance factors were sequentially calculated according to target reliability index. Load resistance factors were optimized to give one set of factor for limit state design of breakwater. The breakwaters were redesigned by using the optimal load resistance factor and verified whether reliability indices larger than the target value. Finally, some load-resistance factors were proposed by changing target reliability index.