• Structural Engineering and Mechanics
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• 제89권4호
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• pp.421-436
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• 2024

This research addresses experimentally the relationship between the excitation frequency and both hoop and axial wall stresses in a water storage tank. A low-density polyethylene tank with six different aspect ratios (water level to tank radius) was tested using a shake table. A laminar box with sand represents a soil site to simulate Soil-Structure Interaction (SSI). Sine excitations with eight frequencies that cover the first free vibration frequency of the tank-water system were applied. Additionally, Ricker wavelet excitations of two different dominant frequencies were considered. The maximum stresses are compared with those using a nonlinear elastic spring-mass model. The results reveal that the coincidence between the excitation frequency and the free-vibration frequency of the soil-tank-water system increases the sloshing intensity and the rigid-like body motion of the system, amplifying the stress development considerably. The relationship between the excitation frequency and wall stresses is nonlinear and depends simultaneously on both sloshing and uplift. In most cases, the maximum stresses using the nonlinear elastic spring-mass model agree with those from the experiments.

• 대한토목학회논문집
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• 제7권4호
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• pp.21-29
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• 1987

직립원통형 액체저장탱크가 지진하중을 받을 때, 벽면 유연성이 벽면에 작용하는 유동압력에 미치는 영향에 대해 연구하였다. 탱크 구조물은 환(ring)형 유한요소를 사용하여 이상화하였으며, 유동에 대한 해는 Laplace 방정식을 이용하여 구하였다. 쉘-유체계의 운동방정식은 자유표면거동과 벽면유연성의 상관효과까지 포함하여 구성하였으며, 이에 따른 쉘 거동과 자유표면거동에 대한 자유진동모우드를 해석하는 방법이 개발되었다. 예제해석으로는, 구조적 특성이 다른 몇개의 저장탱크에 대해, 응답스펙트럼 해석법과 시간영역 해석법을 사용하여 동적응답을 구하였고, 그 결과들을 비교 분석하였다.

• 대한조선학회논문집
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• 제45권2호
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• pp.132-143
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• 2008

The sloshing phenomena in a two-dimensional rectangular tank are investigated using a level set method based on finite volume method. The code validations are performed by comparing between the present results and previous numerical results, which gives a good agreement. We present the streamlines pattern, free surface shape, maximum free surface elevation and pressure fluctuation patterns in the tank under the pitch and surge motions with various frequencies. These two different motions cause the different flow structures in the tank. The time variations of surface elevation and pressure at the different locations in the tank strongly depend on the exciting frequency of tank moving.

• 대한조선학회논문집
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• 제50권2호
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• pp.120-128
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• 2013

This paper presents the results of sloshing experiments having different fluids in model tanks with various density ratios. The experimental model consisting water and air at ambient, which has been commonly used, is not consistent in density ratio with that of an actual LNG cargo tank. Therefore, an advanced experimental scheme is developed to consider the same density ratio of LNG and NG by using a mixed gas of sulfur hexafluoride ($SF_6$) and nitrogen ($N_2$). For experimental observation, a two-dimensional model tank of 1/40 scale and a three-dimensional model tank of 1/50 scale have been manufactured and tested at various conditions. Two different fillings with various excitation frequencies under regular motions have been considered for the two-dimensional model tank, and three different filling levels under irregular motions have been imposed for the three-dimensional model tank. The density ratio between gas and liquid varies from the ratio of the ambient air and water to that of the actual LNG cargo container, and the different composition of gas is used for this variation. Based on the present experimental results, it is found that the decrease of sloshing pressure is predicted when the density ratio increases.

• 한국전산구조공학회논문집
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• 제15권4호
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• pp.619-628
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• 2002

본 논문은 배플을 설치한 수평으로 놓인 원통형 탱크내 슬로싱 고유진동에 대한 유한요소 해석을 다룬다. 지배방정식으로 포텐셜 이론을 기반으로 한 라플라스 방정식을 적용한다. 이 문제를 선형의 등매개 요소를 적용한 유한요소법을 이용해 해석한다. 탱크와 배플은 강체로 가정하였으며, 배플의 효과 구현은 배플의 설치 위치에 절점을 두 개로 분리함으로써 얻을 수 있다. 고유주파수와 고유모드의 추출을 위하여 Lanczos 변환법 및 Jacobi 반복법을 도입하였다. 종진동과 횡진동 모드에 대한 수치 해석결과가 참고 문헌과 비교해 볼 때 잘 일치함을 알 수 있었다. 또한 유체 높이, 배플 개수, 내공 크기, 배플 위치 등의 파라메트릭 해석을 통하여 슬로싱 특성 및 링형 배플의 영향을 고찰하였다.

• 대한조선학회논문집
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• 제35권4호
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• pp.27-37
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• 1998

선박이 대형화되고, LNG선의 건조가 활발해지면서 액체화물탱크의 내부유동을 뜻하는 슬로싱에 대한 연구가 중요해지고 있다. 슬로싱에 의한 충격압력의 크기와 특성을 파악하기 위하여 직사각형 모델에 대한 체계적인 실험을 수행하여 회전각, 동요주파수, 적재수심에 따른 내부유동의 특성을 분석하였고, 충격압력이 가해지는 탱크벽면의 구조응답을 계측하여 유탄성효과를 고찰하였다. 탱크의 내부유동은 고차경계요소법을 이용하여 해석하였고, 평판의 진동에 의해 유기되는 유체력은 고유함수 전개법을 이용하여 부가질량과 감쇠력으로 표현하였다. 충격하중이 작용하는 경우 유탄성 효과를 고려한 탱크 벽면은 부가질량의 영향으로 그 때의 수심에 해당하는 접수진동수로 진동하였고, 벽면에서 압력은 유탄성효과를 고려하지 않은 경우에 비해 두 배 이상 크게 나타났다. 이를 실험과 계산에서 모두 확인하였고, 충격하중에 의한 평판의 거동에서 유탄성효과를 규명하였다

• Earthquakes and Structures
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• 제17권2호
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• pp.175-189
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• 2019

The aim of the study is to show the results of complex shaking table experimental investigation focused on the response of two models of cylindrical steel tanks under mining tremors and moderate earthquakes, including the aspects of diagnosis of structural damage. Firstly, the impact and the sweep-sine tests have been carried out, so as to determine the dynamic properties of models filled with different levels of liquid. Then, the models have been subjected to seismic and paraseismic excitations. Finally, one fully filled structure has been tested after introducing two different types of damages, so as to verify the method of damage diagnosis. The results of the impact and the sweep-sine tests show that filling the models with liquid leads to substantial reduction in natural frequencies, due to gradually increasing overall mass. Moreover, the results of sweep-sine tests clearly indicate that the increase in the liquid level results in significant increase in the damping structural ratio, which is the effect of damping properties of liquid due to its sloshing. The results of seismic and paraseismic tests indicate that filling the tank with liquid leads initially to considerable reduction in values of acceleration (damping effect of liquid sloshing); however, beyond a certain level of water filling, this regularity is inverted and acceleration values increase (effect of increasing total mass of the structure). Moreover, comparison of the responses under mining tremors and moderate earthquakes indicate that the power amplification factor of the mining tremors may be larger than the seismic power amplification factor. Finally, the results of damage diagnosis of fully filled steel tank model indicate that the forms of the Fourier spectra, together with the frequency and power spectral density values, can be directly related to the specific type of structural damage. They show a decrease in the natural frequencies for the model with unscrewed support bolts (global type of damage), while cutting the welds (local type of damage) has resulted in significant increase in values of the power spectral density for higher vibration modes.

• 한국해양공학회지
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• 제27권3호
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• pp.53-60
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• 2013

A drillship is a representative floating offshore installation. The boom in oil and gas field development has dramatically increased the demands for drillships. Drillships have a moonpool in the center area of the ship for the purpose of drilling. This moonpool has an effect on the seakeeping performance of a drillship in the vicinity of the resonance frequency. Because of the moonpool, drillships act in different resonance modes, called the sloshing mode and piston mode. The objective of this study was to find the moonpool effect on the motion of a drillship through the motion analysis of a currently operating modern compact drillship. The predicted resonance frequencies based on Molin's theoretical formula, Fukuda's empirical formula, and BEM-based numerical analysis are compared. The accuracy of the predictions using the theoretical and empirical formulas is compared with the numerical analysis and evaluated. In the case of the piston mode, the difference between the resonance frequency from theoretical formula and the resonance frequency from the numerical analysis is analyzed. The resonance frequency formula for more a complex moonpool geometry such as a moonpool with a cofferdam is necessarily emphasized.

• Smart Structures and Systems
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• 제24권3호
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• pp.391-401
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• 2019

Control of vibrations against extraordinary excitations such as wind and earthquake is very important to the protection of life and financial concerns. One of the methods of structural control is to use Tuned Liquid Damper (TLD), however due to the nature of TLD only one sloshing frequency can be created when the water is sloshing. Among various ideas proposed to compensate this problem, by changing the angle of some rotatable baffles embedded inside a TLD, a frequency range is created such that these baffles are tuned manually at different frequencies. In this study, the effect of cross sectional shape of container with rotating baffles on seismic behavior of TLD is experimentally studied. For this purpose, rectangular and cylindrical containers are designed and used to suppress the vibrations of a Single Degree-Of-Freedom (SDOF) structure under harmonic and earthquake excitations considering three baffle angles. The results show that the rectangular-shaped damper reduces the structural response in all load cases more than the damper with a cylindrical shape, such that maximum differences of two dampers to reduce the structural displacement and structural acceleration are 5.5% and 3% respectively, when compared to the cases where no baffles are employed.

• 한국항공우주학회지
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• 제37권7호
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• pp.661-668
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• 2009

본 논문에서는 시간영역에서 최소자승법을 이용하여 실린더 용기의 슬로시 주파수와 댐핑 계수와 함께 슬로시 모드 질량 및 슬로시 힘 작용점 높이를 시험을 통해 추정하였다. 추정한 결과가 해석 결과와 비교적 잘 일치함을 확인 할 수 있었으며 추정기법의 정확성을 파악할 수 있었다. 향후 이 기법을 이용해 액체 연료 용기의 슬로시 모델 파라미터를 추정하는데 적용할 예정이다.