• 해양환경안전학회지
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• 제1권2호
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• pp.61-67
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• 1995

This study examines experimentally and theoretically, the wave deformation by two large cylindrical structure in relation to the case of one structure. The wave height around the structures varies, according to the changes of the incident wave angles, the number of the structure, and the distances between the two structures. The wave deformation around the large cylindrical structures is shown to be well predicted theoretically by the diffraction theory based on the singular point distribution method using a vertical line wave source Green's function.

• Ocean Systems Engineering
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• 제1권4호
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• pp.337-353
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• 2011

In the present study, an offshore platform having large partial porous cylindrical members, which are composed of permeable and impermeable cylinders, is suggested. In order to calculate the wave force on large partial porous cylindrical members, the fluid domain is divided into three regions: a single exterior region, N inner regions and N beneath regions, and the scattering wave in each fluid region is expressed by an Eigen-function expansion method. Applying Darcy's law to the porous boundary condition, the effect of porosity is simplified. Wave excitation forces and wave run up on the structures are presented for various wave conditions. For the idealized three-dimensional platform having large partial porous cylindrical members, the dynamic response evaluations of the platform due to wave forces are carried out through the modal analysis. In order to examine the effects of soil-structure interaction, the substructure method is also applied. The displacement and bending stress at the selective nodal points of the structure are computed using various input parameters, such as the shear-wave velocity of soil, the wave height and the wave period. Applying the Monte Carlo Simulation (MCS) method, the reliability evaluations at critical structure members, which contained uncertainties caused by dynamic forces and structural properties, are examined by the reliability index with the results obtained from MCS.

• 대한조선학회논문집
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• 제56권5호
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• pp.389-395
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• 2019

Turret mooring type Floating Production Storage and Offloading (FPSO) is designed to rotate the hull around a turret system. The system is mounted inside a cylindrical moon-pool structure of the ship hull structure. The upper part of the moon-pool structure called Bogie Support Structure (BSS) is supported on ring type rail structure (bogie), so high roundness is required at the top of the structure. In this study, the deformation measured during BSS installation was compared with the predicted values through the thermal elasto-plastic analysis, and the causes of deformation were analyzed. Deformation behavior of cylindrical structure with a very large diameter compared to the thickness was investigated. In addition, a proper welding sequence and correction method for the deformed structure were proposed. This study can be an example of the solution to the tolerance problem of large cylindrical structures.

• 한국해양공학회지
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• 제29권1호
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• pp.9-15
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• 2015

We investigated the Reynolds number effects on the flow over a twisted offshore structure in the range of 3×10³≤ Re ≤ 1 × 10⁴. To analyze the effect of the twisted surface treatment, a large eddy simulation (LES) with a dynamic subgrid model was employed. A simulation of the cylindrical structure was also carried out to compare the results with those of the twisted offshore structure. As Re increased, the mean drag and lift coefficient of the twisted offshore structure increased with the same tendency as those of the cylindrical structure. However, the increases in the mean drag and lift coefficient of the twisted offshore structure were much smaller than those of the cylindrical structure. Furthermore, elongated shear layer and suppressed vortex shedding from the twisted offshore structure occurred compared to those of the cylindrical cylinder, resulting in a drag reduction and suppression of the vortex-induced vibration (VIV). In particular, the twisted offshore structure achieved a significant reduction of over 96% in VIV compared with that of the cylindrical structure, regardless of increasing Re. As a result, we concluded that the twisted offshore structure effectively controlled the flow structures with reductions in the drag and VIV compared with the cylindrical structure, irrespective of increasing Re.

• 국제강구조저널
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• 제18권4호
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• pp.1167-1176
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• 2018

Steel cylindrical tanks are widely used for the storage of hazardous substances of which leakage must be prevented under any circumstances. However, the dynamic response of the steel cylindrical liquid storage tank depends sensitively on the fluid-structure interaction and the vibration of the tank structure and necessitates clarification for the safety of the tank structure. This paper presents the results of shaking table tests performed to examine the dynamic behavior of a scaled cylindrical steel tank model considering the presence or not of fixed roof and added mass at the top of the tank for various fluid levels. The test results confirm the occurrence of both beam-type and oval-type vibration modes and show that the larger content of liquid inside the container amplified the acceleration along the height of the cylindrical tank. The oval-type vibration modes are seen to be more dominant in case of large water-to-structure mass ratio.

• Journal of Advanced Marine Engineering and Technology
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• 제33권1호
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• pp.175-182
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• 2009

This paper summarizes a solution procedure for a large cylindrical structure mounted underneath a ship as a sonar. Vibration analysis of the water loaded structure is required to enhance the structural reliability as well as acoustic performance of the sonar. It is, however, often very difficult to solve such structures since they have many DOFs, considering the frequency of interest and the water-loading. The mode mapping method is proposed and verified to take into account the water-loading with the minimum DOF for the analysis. The cyclic symmetric method is then reviewed to show how the eigen properties of the full model can be obtained from the representative segment model. The solution procedure is finally proposed and applied successfully for a simplified water-loaded cylindrical array structure.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2007년도 추계학술대회논문집
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• pp.1054-1059
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• 2007

This paper summarized a solution procedure for a large cylindrical structure mounted underneath a ship as a sonar. Vibration analysis of the water loaded structure is required to enhance the structural reliability as well as acoustic performance of the sonar. It is, however, often very difficult to solve such structures since they have many DOFs, considering the frequency of interest and the waterloading. The cyclic symmetric method is firstly reviewed to show how the eigen properties of the full model can be obtained from the representative segment model. The mode mapping method is then proposed and verified to take into account the waterloading with the minimum DOF for the analysis. The solution procedure is finally proposed and applied for a waterloaded cylindrical array structure.

• 한국해안·해양공학회논문집
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• 제20권4호
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• pp.401-412
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• 2008

본 연구에서는 3차원수치파동수로내에 쇄파후의 파랑이 대형연직원주구조물에 작용할 때 작용파력과 구조물에 의한 파랑변형을 수치적으로 해석한다. 수치해석법으로 파랑과 구조물과의 비선형상호간섭에 따른 쇄파현상을 포함하는 복잡한 자유수면의 거동특성을 고정도로 해석할 수 있는 3차원Navier-Stokes운동방정식과 자유수면추적에 3차원VOF(Volume Of Fluid)법을 결합한 강비선형해석법을 적용한다. 3차원파동장내에서 해저는 쇄파를 상대적으로 쉽게 발생시킬 수 있는 경사스텝의 해저(변수심의 경사수역과 일정수심역으로 구성)로 이루어진 경우를 고려하며, 파고의 변화에 따라 쇄파가 경사수역 또는 일정수심역에서 발생하여 일정수심역의 대형연직원주구조물에는 쇄파후의 파랑만이 작용하는 경우로 한정한다. 구조물의 위치 및 입사파랑의 파고변화가 구조물에 작용하는 파력 및 파랑변형에 미치는 특성을 쇄파전후의 파랑을 중심으로 검토하고, 쇄파후 파랑의 전파에 따른 파랑에너지의 변화와 구조물에 작용하는 파력특성과를 연관시켜 논의하여 3차원파동장에서 파랑과 구조물과의 강비선형간섭현상의 특성을 규명한다.

• 대한기계학회논문집A
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• 제29권1호
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• pp.132-138
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• 2005

In heavy industrial fields such as power plant and chemical plant, it is often necessary to restore damaged part of large machinery and structure which is installed in the hazard working place. In this paper, to estimate stress distribution which occurs during damage and restoration of cylindrical beam structure, the finite element technique has been used. A finite element model was verified by experiment for non deformed cylindrical beam structure. The displacements and elastic recovery have an excellent agreement between experiment and finite element analysis. The variations of stress distribution on deformation and restoration procedure for surfaces have been examined. The maximum von Mises stress appears in the surface for deformation and restoration procedure. In deformation procedure, the maximum stress occurs in the vicinity of support body. In restoration procedure, the maximum stress occurs in the vicinity of the fixing body. The fixing body allows avoiding stress concentration in adjacent support structure boundary.

• 한국해양공학회지
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• 제35권3호
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• pp.191-202
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• 2021

Studies on very large offshore structures are increasing owing to the development of deep sea, large-scale energy generation using ocean resources, and so on. The enlargement of offshore structures makes the hydroelastic effect and low natural frequency related responses important. Numerical analyses and model tests for hydroelastic and higher-order springing responses of fixed cylindrical structures are conducted in this study. The panel methods with and without the hydroelastic effect with shell elements, and the Morison analysis method with beam elements are applied. To observe the hydroelastic effect for structural strength, two structures are considered: bottom-fixed cylindrical structures with high and low bending stiffnesses, respectively. The surge motions at the top of the structure and bending stresses on the structure are observed under regular and irregular wave conditions. The regular wave conditions are generated considering the ratios of the cylindrical outer diameter to the wave lengths, and keeping the wave steepness constant. The model tests are performed in the three-dimensional ocean engineering basin in the KRISO (Korea Research Institute of Ships and Ocean Engineering). From the numerical and experimental results, in which the hydroelastic responses are only observed in the case of the structure with a low bending stiffness, it is confirmed that the hydroelastic responses are highly dependent on the structural stiffness. Additionally, the higher-order phenomenon on the specified wave condition is analyzed by observing the higher-order springing responses when the incident wave frequency or its multiples with the high wave height coincides with the natural frequency of the structure.