• International Journal of Ocean System Engineering
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• 제1권2호
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• pp.76-88
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• 2011

The present study deals with the hydroelastic vibration analysis of structures in contact with fluid via coupled fluid-structure interaction (FSI) embedded with a finite element method (FEM) such that a structure displacement formulation is coupled with a fluid pressure-displacement formulation. For the preliminary study and validation of FEM based coupled FSI analysis, hydroelastic vibration characteristics of a rectangular plate in contact with fluid are first compared with the elastic vibration in terms of boundary condition and mode frequency. Numerical results from coupled FSI analysis have been shown to be rational and accurate, compared to energy method based theoretical solutions and experimental results. The effect of free surface on the vibration mode is numerically studied by changing the submerged depth of a rectangular plate. As a practical application, the hull structural vibration of 4,000 twenty-foot equivalent units (TEU) container ship is considered. Hydroelastic results of the ship hull structure are compared with those obtained from the elastic condition.

• 한국소음진동공학회논문집
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• 제21권10호
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• pp.905-915
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• 2011

The free flexural vibration of a hanged clamped-free cylindrical shell partially submerged in water with gap from bottom is investigated. The fluid is assumed to be inviscid and irrotational. The cylindrical shell is modeled by using the Rayleigh-Ritz method based on the Sanders shell theory. The kinetic energy of the fluid is derived by solving the boundary-value problem related to the fluid motion. The natural vibration characteristics of the partially submerged cylindrical shell are discussed with respect to the added virtual mass approach. In this study, experiments were carried out to confirm theoretical results. It was found that theoretical prediction is in good agreement with experimental results.

• 한국해양공학회지
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• 제15권2호
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• pp.22-32
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• 2001

The numerical investigation of obliquely incident wave interactions with fully submerged dual buoy/porous-membrane floating breakwaters placed in parallel with spacing is studied based on linear potential theory and Darcy's law. The numerical solutions are obtained by using a discrete-membrane dynamic model and second-kind modified Bessel function distribution over the entire boundaries of fluid regions. First, numerical solutions for an idealized dual submerged system without buoys are obtained. Second, a more practical dual submerged system with membrane tension provided by buoys at its tops is investigated by the multi-domain boundary element method particularly devised for dual buoy/porous-membrane problems with gaps. The velocity potentials of wave motion are coupled with porous-membrane deformation, and solved simultaneously since the boundary condition on porous-membrane is not known in advance. The effects of varying permeability on membranes and wave characteristics are discussed for the optimum design parameters of systems previously studied. The inclusion of permeability on membrane eliminates the resonances that aggravate the breakwater performance. The system is highly efficient when waves generated by the buoys and membranes were mutually canceled and its energy at resonance frequency dissipates through fine pores on membranes.

• 한국해양공학회지
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• 제15권2호
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• pp.11-21
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• 2001

The focus of this paper is on the numerical investigation of obliquely incident wav interactions with a system composed of fully submerged and floating dual buoy/vertical-flexible-membrane breakwaters placed in parallel with spacing between two systems. The fully submerged two systems allow surface and bottom gaps to enable wave transmission over and under the system. The problem is formulated based on the two-dimensional multi-domain hydro-elastic linear wave-body interaction theory. The hydrodynamic interaction of oblique incident waves with the combination of the rigid and flexible bodies was solved by the distribution of the simple sources (modified Bessel function of the second kind) that satisfy the Helmholz governing equation in fluid domains. A boundary element program for three fluid domains based on a discrete membrane dynamic model and simple source distribution method is developed. Using this developed computer program, the performance of various dual systems varying buoy radiuses and drafts, membrane lengths, gaps, spacing, mooring-lines stiffness, mooring types, water depth, and wave characteristics is thoroughly examined. It is found that the fully submerged and floating dual buoy/membrane breakwaters can, if it is properly tuned to the coming waves, have good performances in reflecting the obliquely incident waves over a wide range of wave frequency and headings.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2022년도 학술발표회
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• pp.155-155
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• 2022

Low head, ogee spillways is popularly used to defense against floods as well as to provide water for irrigation. Spillway is also used to assess compliance with water quality regulations by controlling amount of discharge to the downstream of a channel. For the purpose of water resource management and/or environmental aspects as explained above, the flow discharge through spillways need to be correctly rated as a function of geometry and hydraulic variables. Typically, four flow conditions are encountered during the operation of spillway: (a) uncontrolled free flow (UF); (b) uncontrolled submerged flow (US); controlled free flow (CF); and controlled submerged flow (CS), and each condition has a unique rating equation. However, one of the tricky part of the spillway operation is finding correct flow type over the spillway because structures can operate under both submerged and free flow conditions, and the types are continuously changing over time depending on the amount of discharge, head water and tail water elevation. Quite obviously, if the wrong rating curve relationship is applied because of misjudgment of the flow type due to a transition, a serious error can occur. Thus, an hydraulic model study of one of spillway structure located in South Florida was conducted for the purpose of developing transition relationships. In this presentation, US to UF transition is highlighted.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2014년도 추계학술대회 논문집
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• pp.236-239
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• 2014

Most naval underwater weapon system can be simplified to a circular cylindrical structure which has vibrating machineries inside. In order to predict efficiently the total acoustic radiation power of cylindrical structure, surface velocity is measured and radiation efficiency of surface element is calculated. Then, they are substituted to the surface pressure in the simplified Helmholtz integral equation which assumes acoustic far-field and plane-wave approximation at the surface. Surface velocity and total acoustic radiation power for a submerged cylinder are measured in water-tank. In this example, it is found that total acoustic power output obtained from the prediction is in good agreement with that of measurement in mid-high frequency range.

• 한국해양공학회지
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• 제19권6호통권67호
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• pp.35-43
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• 2005

Recently, various-shaped coastal structures have been studied and developed. Among them, the submerged breakwater became generally known as a more effective structure than other structures, bemuse it not only serves its original function, but also has the ability to preserve the coastal environment. Most previous investigations have been focused on the wave deformation and energy dissipation due to submerged breakwater, but less interest was given to their internal properties and dynamic behavior of the seabed foundation under wave loadings. In this study, a direct numerical simulation (DNS) is newly proposed to study the dynamic interaction between a permeable submerged breakwater aver a sand seabed and nonlinear waves, including wave breaking. The accuracy of the model is checked by comparing the numerical solution with the existing experimental data related to wave $\cdot$ permeable submerged breakwater $\cdot$ seabed interaction, and showed fairly nice agreement between them. From the numerical results, based on the newly proposed numerical model, the properties of the wave-induced pore water pressure and the flow in the seabed foundation are studied. In relation to their internal properties, the stability oj the permeable submerged breakwater is discussed.

• 한국해양공학회지
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• 제24권2호
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• pp.18-24
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• 2010

Submerged rubble structures include artificial reef and the mound part of the rubble mound breakwater. Artificial reef is a type of the submerged wave absorbing structure installed in a coastal zone to prevent beach erosion and designed to initially reduce the energy of incoming waves so that its run-up height and overtopping quantity can be decreased. In order to ascertain the stability of such submerged rubble structures, minimum weight of the rubble has to be calculated first from the incoming wave height using Hudson's formula or Brebner-Donnelly formula. Based on the calculated minimum weight, a model is built for use in a hydraulic model test carried out to check its stability. The foregoing two formulas used to calculate the minimum weight are empirically derived formulas based on the result of the tests on the rubble mound breakwater and it is, therefore, difficult for us to apply them directly in the calculation of the minimum weight of the submerged structures. Accordingly, this study comes up with a numerical simulation method capable of deformation analysis for rubble structures. This study also tries to identify the deformation mechanism of the submerged rubble structures using the numerical simulation. The method researched through this study will be sufficient for use for usual preparations of the design guidelines for submerged rubble structures.

• 대한토목학회논문집
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• 제28권4B호
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• pp.429-439
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• 2008

본 연구에서는 잠제의 제원(천단수심, 천단폭, 사면경사, 제장)에 따라 해빈상을 전파하는 풍파의 처오름 높이 변화특성을 논의하기 위하여, 기존의 수리모형 실험치와 계산치를 비교 검토를 통해 타당성과 유효성이 검증된 수치모델로서, 파 투과성구조물 해빈의 상호간섭을 직접 해석할 수 있는 3D-수치모델(LES-WASS-3D; 허와 이, 2007)을 이용하여 잠제 2기의 제원에 따른 수치시뮬레이션을 실시하였다. 그 결과 천단수심, 천단폭, 사면경사, 제장의 변화가 연안에서의 처오름 높이에 미치는 영향에 관하여 검토하였으며, 아울러, 잠제 주변의 파고분포 및 상층흐름특성과의 관계에 대해서도 논의하였다.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2003년도 학술발표회논문집(1)
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• pp.293-296
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• 2003