• Title, Summary, Keyword: 현수선 방정식

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Slow Drift Motion Analyses for a FPSO with Spread Mooring Systems (다점 계류된 원유 저장선에 대한 저주파수 운동 해석)

  • 이호영;박종환;곽영기
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.13 no.3
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    • pp.195-201
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    • 2001
  • The time simulation of slow drift motions of moored FPSO in waves is presented. The equation of motion based on Cummin's theory of impulse responses are employed, and are consisted of horizontal plane motions such as surge, sway and yaw. The added mass, wave damping coefficients, first order wave exciting forces and the second order wave drift forces involved in the equations are obtained from three-dimensional panel method in the frequency domain. The mooring lines are modeled as quasi-static catenary cable. As a numerical example, time domain analyses are carried out for a box-type FPSO in long crest irregular wave condition.

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Dynamic Analysis of Elastic Catenary Cable Subjected to Current (조류 하중을 받는 탄성 현수선 케이블의 동적 해석)

  • 백인열;장승필;윤종윤
    • Journal of the Earthquake Engineering Society of Korea
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    • v.2 no.2
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    • pp.95-104
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    • 1998
  • The dynamic behavior of the marine cable is essentially nonlinear and dominated by geometric nonlinearity. Furthermore, fluid drag force makes the problem more complex and difficult. Therefore, it has certain limitations to obtain the dynamic behavior of the marine cable by analytical method. The purpose of this paper is to apply the elastic catenary cable element to the problem of under water cable including the hydrodynamic effects of fluids. The static and dynamic formulations for the three-dimensional elastic catenary coble under water effects are derived and the finite element analysis procedures are presented. In the analysis, the hydrodynamic forces are modeled by modified Morison equation. A comparison of the results obtained using present method with previously published results showed the validity of present method. The dynamic behavior of the marine cable subjected to current is investigated using present method and it can be illustrated that the dynamic behavior of the marine cable subjected to current varies with the incident angle of the current and inclined angle of the cable.

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Design of Mooring Lines of a Floating Offshore Wind Turbine in South Offshore Area of Jeju (제주 해양환경에 적합한 부유식 해상풍력발전기 계류선 설계)

  • Choung, Joonmo;Kim, Hyungjun;Jeon, Gi-Young
    • Journal of the Society of Naval Architects of Korea
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    • v.51 no.4
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    • pp.300-310
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    • 2014
  • This paper presents a mooring design procedure of a floating offshore wind turbine. The environment data of south offshore area of Jeju collected from Korea Hydrographic and Oceanographic Administration(KHOA) are used for hydrodynamic analyses as environmental conditions. We considered a semi-submersible type floating wind turbine based on Offshore Code Comparison Collaborative Continuation(OC4) DeepCWind platform and National Renewable Energy Laboratory(NREL) 5 MW class wind turbine. Catenary mooring with studless chain is chosen as the mooring system. Important design decisions such as how large the nomial sizes are, how long the mooring lines are, how far the anchor points are located, are demonstrated in detail. Considering ultimate limit state and fatigue limit state based on 100-year return period and 50-year design life, respectively, longterm predictions of breaking strength and fatigue are proposed.

Development of quasi-static analysis program for catenary mooring system using OpenFOAM (OpenFOAM을 이용한 catenary 계류시스템의 준정적 해석 프로그램 개발)

  • Choi, Jun Hyeok;Lee, Seung Jae
    • Journal of Ocean Engineering and Technology
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    • v.31 no.4
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    • pp.274-280
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    • 2017
  • Generally, global performance analysis in offshore platforms is performed using potential-based numerical tools, which neglect hydrodynamic viscous effects. In comparison with the potential theory, computational fluid dynamics (CFD) methods can take into account the viscous effects by solving the Navier-Stokes equation using the finite-volume method. The open-source field operation and manipulation (OpenFOAM) C++ libraries are employed for a finite volume method (FVM) numerical analysis. In this study, in order to apply CFD to the global performance analysis of a hull-mooring coupled system, we developed a numerical wave basin to analyze the global performance problem of a floating body with a catenary mooring system under regular wave conditions. The mooring system was modeled using a catenary equation and solved in a quasi-static condition, which excluded the dynamics of the mooring lines such as the inertia and drag effects. To demonstrate the capability of the numerical basin, the global performance of a barge with four mooring lines was simulated under regular wave conditions. The simulation results were compared to the analysis results from a commercial mooring analysis program, Orcaflex. The comparison included the motion of the barge, catenary shape, and tension in the mooring lines. The study found good agreement between the results from the developed CFD-based numerical calculation and commercial software.

Study on Optimum Design of FPSO Spread Mooring System (FPSO 다점 계류 시스템의 최적 설계 연구)

  • Lim, Yu-Chang;Kim, Kyung-Su;Choung, Joon-Mo;Kim, Jae-Woo;Kim, Jin-Tae;Yeo, Seung-Hoon
    • Journal of Ocean Engineering and Technology
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    • v.23 no.6
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    • pp.61-66
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    • 2009
  • For a spread-moored FPSO (Floating Production, Storage, & Off-loading) subjected to environmental excitation from waves, current, and wind, a procedure to determine optimum length and stiffness of mooring lines is suggested using quasi-static frequency domain response analyses. Coupled relations between design parameters are closely examined. In consideration of this, optimized design parameters are proposed based on minimum weight condition. The initial design parameters for numerical analyses are calculated using the static catenary equation of mooring lines. It is demonstrated the line tension and vessel's offset are influenced by the mooring line length and stiffness. Accordingly it is suggested the optimum vessel's offset range should be determined considering line fatigue damage. The availability and limitation of the application of quasi-static analysis method for spread mooring system are explained by comparing the result of time domain analysis with one of frequency domain analysis.

Closing Analysis of Symmetric Steel Cable-stayed Bridges and Estimation of Construction Error (대칭형 강 사장교의 폐합해석과 시공오차의 예측)

  • Lee, Min Kwon;Lee, Hae Sung
    • Journal of The Korean Society of Civil Engineers
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    • v.26 no.1A
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    • pp.55-65
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    • 2006
  • This paper presents the closing analysis of a symmetric steel cable-stayed bridge erected by a free cantilever method. Two independent structural systems are formed before the closing procedure of a bridge is performed, and thus the compatibility conditions for vertical displacement and rotational angle are not satisfied at the closing section without the application of proper sectional forces. Since, however, it is usually impossible to apply sectional forces at the closing section, the compatibility conditions should be satisfied by proper external forces that can be actually applicable to a bridge. Unstrained lengths of selected cables and the pull-up force of a derrick crane are adjusted to satisfy nonlinear compatibility conditions, which are solved iteratively by the Newton-Raphson method. Cable members are modeled by the elastic catenary cable elements, and towers and main girders are discretized by linear 3-D frame elements. The sensitivities of displacement with respect to the unstrained lengths of selected cables and the pull-up force of the derrick crane are evaluated by the direct differentiation of the equilibrium equation. A Monte-Carlo simulation approach is proposed to estimate expected construction errors for a given confidence level. The proposed method is applied to the second Jindo Grand Bridge to demonstrate its validity and effectiveness.

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Shear Force Variation of Stiffening Girder caused by Vibration of Stay Cable (사장 케이블 진동에 의한 보강형의 전단력 변화)

  • Kim, Hyeon Kyeom;Hwang, Jae Woong;Lee, Myeong Jae
    • Journal of The Korean Society of Civil Engineers
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    • v.29 no.1A
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    • pp.1-8
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    • 2009
  • Stay cable is easily exposed to vibration induced rainy wind effects. There are some problems for not only unexpected vibration but also well-known vibration. An outbreak of displacement by the said effects brings damages such as over-tension of cables and barriers, fatigue of anchorages and dampers, and additional shear force variation of stiffening girders. This study suggests analytic methodology for dynamic tension variation of cables and shear force variation of stiffening girders. Additionally this study announces with dynamic problems for cable stayed bridge briefly. To realize this subject, we divide restoring force into chord component and normal component and then make up the differential equations which can satisfy physical phenomenon for each component. Finally we apply adequate functions such as sinusoidal and parabola in order to reduce these differential equations. Therefore we can meet with good results through a series of above process. As a remarkable result, CIP recommendations (2002) give inadequate solution with over 10% error. However it gives very good solution if parts of our study are reflected at the said recommendations. The fact means that CIP recommendations (2002) well-known as international standard of stay cables are not even concern about this subject yet. For verification of this study, F.E. analysis using E.C.C. with external forces was fulfilled, and the accuracy and conciseness of this study were shown.

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