• Journal of the Society of Naval Architects of Korea
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• v.48 no.3
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• pp.260-266
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• 2011

For long slender offshore structures, such as cables and pipe lines, their interaction with surrounding fluid flow becomes an important issue for global design of ocean systems. We employ a long circular cylinder as a representative case of slender offshore structure. A flexibly mounted cylinder in cross-flow generates complex vortex shedding and results in oscillation of the structure. In this paper, flow behind a circular cylinder at Re=100 is simulated. The vortex shedding pattern and flow induced motion are examined in the cross flow configuration as well as with various yaw-angled configurations. The "Lock-in" phenomenon is also observed when reduced velocity is approximately 4.0. The MAC Grid system, which is the typical grid system for Cartesian mesh and pressure correction methods, are used for solving the incompressible Navier-Stokes equations. Predictor/Corrector method is applied for obtaining a non-linear response of structure at the flexibly mounted. The existance and motion of the body is represented by the immersed boundary technique.

• Journal of Navigation and Port Research
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• v.44 no.3
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• pp.264-274
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• 2020

The Ro-Ro ferry ship capsized and sank to the bottom of the sea because of the rapid turning for several reasons, such as lack of stability due to the center of gravity rise from the extension and rebuilding of the stern cabin, excessive cargo loading, and shortage ballast, poor lashing, etc. The purpose of this study was to investigate and analyze the cause of the ship's rapid flooding, capsizing, and sinking accident according to rapid turning scientifically and accurately using the Fluid-Structure Interaction( FSI) analysis technique. Several tests were conducted for this cause investigation of the flooding and sinking accident correctly and objectively, such as the realization of the accurate ship posture tracks according to the accident time using several accident movies and photos, the validation of cargo moving track, and sea water inflow amount through the exterior openings and interior paths compared with the ship's posture according to the accident time using the floating simulation and hydrostatic characteristics program calculation, and the performance of a full-scale ship flooding·sinking simulation.

• Journal of computational fluids engineering
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• v.18 no.1
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• pp.49-57
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• 2013

Analysis of fluid-structure interaction for two nearby underwater vehicles immersed in the sea is quite challenging because simulation of flow around them is very difficult due to the complexity of underwater vehicle shapes. The conventional approach using body-fitted or unstructured grids demands much time in dynamic grid generation, and yields slow convergence of solution. Since an analysis of fluid-structure interaction must be based on accurate simulation results, a more efficient way of simulating flow around underwater vehicles, without sacrificing accuracy, is desirable. An immersed boundary method facilitates implementation of complicated underwater-vehicle shapes on a Cartesian grid system. An LES modeling is also incorporated to resolve turbulent eddies. In this paper, we will demonstrate the effectiveness of the immersed boundary method we adopted, by presenting the simulation results on the flow around a modeled high-speed underwater vehicle interacting with a modeled low-speed one.

• The KSFM Journal of Fluid Machinery
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• v.8 no.6 s.33
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• pp.40-46
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• 2005

Because of design and manufacturing costs, it is important to predict an expected life of bellows with component stresses of bellows as its design factors and material characteristics. In this study, numerical analyses are carried out to elucidate the thermal and flow characteristics of the bellows-seal gate and globe valves for high temperature (max. $600^{\circ}C$) and for high pressure (max. $104 kgf/cm^2$) conditions. Using commercial codes, FLUENT, which uses FVM and SIMPLE algorithm, and ANSYS, which uses FEM, the pressure and temperature fields are graphically depicted. In addition, when bellows have an axial displacement, thermal stress affecting bellows life is studied. The pressure and temperature values obtained from the flow analyses are adopted as the boundary conditions for thermal stress analyses. As the result of this study, we got the reasonable coefficients for valve and thermal stress for bellows, compared with existing coefficients and calculated values.

• Journal of the Korean Institute of Gas
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• v.17 no.2
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• pp.85-89
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• 2013

The purpose of the development of KC-1 LNG cargo containment system is reduction in royalty and increase in competitiveness of shipbuilding industry. An assessment of structure safety for LNG cargo containment system under sloshing load due to ship motion has become an important design element. The ideal way is to implement fully interaction of the fluid domain and the cargo containment system. However the irregular sloshing pressure were idealized in the form of a triangular wave for safety assessment because the fluid- structure interaction analysis is taken the extensive computation time and difficult to ensure the accuracy of the results. In this study, the sloshing load was assumed to be a triangular wave with a maximum pressure of 10 bar during 15/1000 seconds. In the analytic results, the basic insulation panel of KC-1 LNG cargo containment system was assessed to be structurally safe for sloshing load.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.13 no.10
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• pp.791-797
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• 2003

A liquid storage rectangular tank structures are used In many fields of civil, mechanical and marine engineering. Especially, Ship structures have many tanks In contact with Inner or outer fluid, like ballast, fuel and cargo tanks. Fatigue damages are sometimes observed in these tanks which seem to be caused by resonance with exciting force of engine and propeller. Vibration characteristics of these thin walled tanks in contact with fluid near engine or propeller are strongly affected by added mass of containing fluid. Therefore it is essentially important to estimate the added mass effect to predict vibration of the tank structures. In the previous report, we have developed numerical tool of vibration analysis of 3-dimensional tank structure using finite elements for plates and boundary elements for fluid region. In the present report, using the numerical analysis, vibrations characteristics In deep water tank are investigated and discussed.

• Journal of Power System Engineering
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• v.5 no.4
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• pp.38-43
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• 2001

This paper describes the effect of dynamic characteristics in tube line by external vibration conveying fluid with the power steering system. By the experimental analysis we found out that the factor of system vibration is the fluid-structure interaction of tube line. In fluid-filled tube system we study on the influence that the natural frequency of system and the frequency of wave motion produce upon through experiment. Experiments are modal test, frequency response function in continuous system, and vibrating tests when the system is driving with bolted clamping joint condition. From the results of the experimental studies, we obtained that the natural frequencies of system are very important than the wave induced vibrations. And we found that the tendency of system vibration level was decreased by bolting force, bolting condition and clamping distance.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.05a
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• pp.1079-1084
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• 2003

A liquid storage rectangular tank structures are used in many fields of civil, mechanical and marine engineering. Especially, Ship structures have many tanks in contact with inner or outer fluid, like ballast, fuel and cargo tanks. Fatigue damages are sometimes observed in these tanks which seem to be caused by resonance with exciting force of engine and propeller. Vibration characteristics of these thin walled tanks ill contact with fluid near engine or propeller are strongly affected by added mass of containing fluid. Therefore it is essentially important to estimate the added mass effect to predict vibration of the tank structures. In the previous report, we have developed numerical tool of vibration analysis of 3-dimensional tank structure using finite elements for plates and boundary elements for fluid region. In the present report, using the numerical analysis, vibrations characteristics in deep water tank are investigated and discussed.

• 한국신재생에너지학회:학술대회논문집
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• 2011.05a
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• pp.57.1-57.1
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• 2011

본 논문에서는 소음을 저감하고 구조적 안전도를 향상시키기 위하여 10kW급 소형 복합재 풍력터빈 블레이드를 해석, 설계하였다. 풍력터빈 블레이드 설계의 기본 사항에 맞추어 블레이드의 스팬 길이는 약 4m, 중량은 30kg 내외가 되도록 설정하였다. 풍력발전기용 블레이드는 경량화가 중요하므로 유리섬유복합재 (glass fiber reinforce pastics), 탄소섬유복합재 (carbon fiber reinforced plastics)가 사용되었다. 본 설계에서는 Carbon prepreg (WSN3KY), Carbon UD(UIN150c), E-glass 등을 사용하였다. 상용 유한요소 프로그램인 NASTRAN을 이용해 Carbon prepreg (WSN3KY), Carbon UD (UIN150c)의 탄소섬유복합재만으로 구성된 블레이드 구조해석을 수행한 결과 중량 조건 및 강도의 안전도는 충족되었으나, 높은 가격을 감안하여 E-glass와 조합하여 블레이드를 재설계할 예정이다. 이번 설계는 소형 풍력발전용 블레이드 설계이므로 좌굴은 고려하지 않았으며, 향후 필요에 따라서 좌굴 및 피로해석도 수행하여 검증할 예정이다. 그리고 블레이드가 복합재로 구성되면 감쇠력이 감소할 가능성이 있다. 탄소섬유복합재로만 구성된 블레이드 구조해석에서도 최대 40cm의 변형이 예측되었으며, 감쇠값 저하 문제도 고려하여야 될 것 같아 BEMT (Blade Element Momentum Theory) 공력모델을 이용해 구조-유체 연성 결합 해석을 수행할 계획이다.

• The Journal of the Acoustical Society of Korea
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• v.20 no.1
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• pp.68-76
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• 2001

Sonar is the system that detects objects and finds their location in water by using the echo ranging technique. In order to have excellent performance in variable environment, acoustic characteristics of this system must be analyzed accurately. In this paper, based on the finite element analysis, modeling and analysis of acoustic characteristics of underwater acoustic sensors are preformed. Couplings between piezoelectric and elastic materials, and fluid and structure systems associated with the modeling of piezoelectric underwater acoustic sensors are formulated. In the finite element modeling of unbounded acoustic fluid, IWEE (Infinite Eave Envelop Element) is adopted to take into account the infinite domain. When an incidence wave excites the surface of Tonpilz underwater acoustic sensor, the scattered wave on the sensor is founded by satisfying the radiation condition at the artificial boundary approximately. Based on this scattering analysis, the electrical response of the underwater acoustic sensor under incidence, so called RVS (Receiving Voltage Signal) is founded accurately. This will devote to design Sonar systems accurately.