• International Journal of Naval Architecture and Ocean Engineering
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• 제7권3호
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• pp.559-579
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• 2015

An experimental study of the effect of mooring systems on the dynamics of a SPAR buoy-type floating offshore wind turbine is presented. The effects of the Center of Gravity (COG), mooring line spring constant, and fairlead location on the turbine's motion in response to regular waves are investigated. Experimental results show that for a typical mooring system of a SPAR buoy-type Floating Offshore Wind Turbine (FOWT), the effect of mooring systems on the dynamics of the turbine can be considered negligible. However, the pitch decreases notably as the COG increases. The COG and spring constant of the mooring line have a negligible effect on the fairlead displacement. Numerical simulation and sensitivity analysis show that the wind turbine motion and its sensitivity to changes in the mooring system and COG are very large near resonant frequencies. The test results can be used to validate numerical simulation tools for FOWTs.

• 수산해양기술연구
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• 제44권1호
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• pp.46-56
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• 2008

A numerical model analysis was performed to analyze the motion and mooring tension response of submersible fish cage systems in irregular waves and currents. Two systems were examined: a submersible cage mooring with a single, high tension mooring and the same system, but with an additional three point mooring. Using a Morison equation type model, simulations of the systems were conducted with the cage at the surface and submerged. Irregular waves(JONSWAP spectrum) with and without a co-linear current with a magnitude of 0.5m/s were simulated into the model as input parameters. Surge, heave and pitch dynamic calculations were made, along with tension responses in the mooring lines. Results were analyzed in both the time and frequency domains and linear transfer functions were calculated.

• 대한토목학회논문집
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• 제9권1호
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• pp.11-23
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• 1989

본 논문에서는 guyed tower의 mooring system에 관한 수치해석결과를 제시하였다. 가상일의 원리와 유한요소법을 사용하여 기본식을 유도하였으며 케이블의 기하학적 비선형성을 고려하였다. 유체의 항력과 관성력은 Morrison식을 사용하여 고려하였으며 비선형 운동방정식의 해는 Newton-Raphson방법과 Newmark-${\beta}$ 방법을 사용하여 구하였다. Tower와 mooring line의 부착점에서의 초기경사각, 인장력, clump weight를 집중하중으로 이상화 시키는 종래의 해석방법의 문제점도 아울러 고찰하였다. 수치해석 예를 통하여 본 논문에서의 해석방법의 정당성을 입증하였다.

• 해양환경안전학회지
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• 제29권2호
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• pp.248-253
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• 2023

대다수의 부유식 해양플랜트는 위치 유지의 방법으로서 체인 계류 시스템을 사용하나, 그 설계 변경 과정은 논문으로 찾아보기 힘들다. 본 연구는 FLBT를 대상 해양플랜트로 선정하여 계류 초기설계안과 모형시험을 수치해석으로 분석하고, 변경된 설계조건에 따라 새로운 계류 설계안을 제시하였다. 주된 환경 방향에 따라 계류선 묶음(bundle)의 주 방향을 조절하는 것이 계류 설계하중 감소에 크게 유효했다. 터렛 계류된 해양플랜트라도 횡파에 노출되며, 횡파 중 운동 때문에 높은 계류 인장력이 발생했다. 일치된 환경 방향 조건은 설계조건이 될 수 없으며, 바람, 파도, 조류의 각 환경 방향이 복잡한 조건에서 설계 계류 하중이 발생했다. 횡요 운동이 계류 인장력에 미치는 영향이 큼으로 적절한 횡요 감쇠 계수를 계류해석에 적용하는 것이 중요하다.

• 한국해양공학회지
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• 제9권2호
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• pp.53-60
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• 1995

A multi-leg spread mooring system for floating offshore structures is important, but the multi-leg static analysis is complicated due to the nonlinear behavior of each line and the effect of current which affects each line differently. The pretensioned position of the multi-leg mooring system obtained from the static equilibrium condition changes into a different position due to external loads and current. In this paper, the new position and the static tension at each line are caculated. The relation between the initial static equilibrium position and the new position due to the external loads is expressed in terms of the Taylor's series expansion. The Runge-Kutta $4^{th}$ method is employed in analyzing the 3-dimensional static cable nonlinear equations.

• 해양환경안전학회지
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• 제22권1호
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• pp.67-73
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• 2016

항만물동량이 증가하고 선박의 대형화가 급격하게 이루어짐에 따라 부두의 설계 접안능력보다 큰 선박이 부두를 이용하는 사례가 빈번하게 발생하고 있다. 본 연구에서는 우리나라 주요 위험물 취급항만인 울산항을 대상으로 접안능력을 초과하여 위험물 부두를 이용한 선박 실태를 조사하였고 기존 부두 접안능력의 최대 3배가 넘는 선박이 이용하는 것으로 분석하였다. 그에 따라, 50,000 DWT급 부두를 모델링하여 50,000 DWT급, 70,000 DWT급, 100,000 DWT급 선박을 대상으로 계류 프로그램을 통해 선박 규모의 변화에 따른 계류 안전성 평가를 수행하였다. 평가는 OCIMF에서 제시하고 있는 표준환경기준에 따라 수행되었으며 50,000 DWT급 선박은 대체로 허용기준을 만족하는 것으로 평가되었으나, 70,000 DWT급 선박의 경우 풍속 60 kts, 파고 1.5 m 이상의 기상조건에서 100,000 DWT급 선박은 풍속 60 kts 조건 등에서 허용한계를 초과하는 것으로 분석되었다. 도출된 결과를 바탕으로 평가 대상부두에 대한 안전 계류 가이드라인 사례를 제시하였고 향후 다양한 사례에 대한 평가를 수행하여 해당항만에 일반적으로 적용 가능한 가이드라인을 수립하도록 제언하였다.

• 대한조선학회논문집
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• 제49권2호
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• pp.132-145
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• 2012

Mooring fittings mean various devices and fittings to safely fasten vessels to quays, jetties and sea-floating buoys, etc. They include mooing winches, capstans, chocks, fairleads, guide rollers, bollards, and bitts. Not only the seats and reinforced parts for the installation of fittings but also ropes and chains for mooring and chain stoppers can be also considered. Because of damages to mooring fittings during mooring directly related to large-scale accidents such as the drifting of vessels, mooring fittings with strength appropriate for the physical features of the vessels must be installed. The reinforcement of the vessels on which the mooring fittings are installed must be designed to withstand the loads transferred from the fittings as well. Also mooring fittings with efficient strength should be required because damaged ships lead to sea pollution such as oil or fuel oil spillage. This study has been performed by the Finite Element Method for two aspects of closed chocks which are divided into structure-supporting shapes and working load. In the case of structure-supporting shapes, they have been performed in the field of sheet and bulwark. As for working load, it has been analyzed according to working load direction such as chock's side and below. At first, strength analysis for unique closed chocks has been carried out by using the Finite Element Method, they are applied for the situation when vessels pass by the panama canal. And then the experiment has been done to verify the analyzed date obtained by FEM. The experimental results were found to be similar to the numerical results with up to 16% difference. On the basis of the results obtained, standardization has been carried out by the Finite Element Method for various sizes of closed chocks.

• Ocean Systems Engineering
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• 제3권4호
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• pp.295-307
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• 2013

More FOWTs (floating offshore wind turbines) will be installed as relevant regulations and technological hurdles are removed in the coming years. In the present study, a numerical prediction tool has been developed for the fully coupled dynamic analysis of FOWTs in time domain including aero-loading, tower elasticity, blade-rotor dynamics and control, mooring dynamics, and platform motions so that the influence of rotor-control dynamics on the hull-mooring performance and vice versa can be assessed. The developed coupled analysis program is applied to Hywind spar design with 5 MW turbine. In case of spar-type floaters, the control strategy significantly influences the hull and mooring dynamics. If one of the control systems fails, the entire dynamic responses of FOWT can be significantly different. Therefore, it is important to maintain various control systems in a good operational condition. In this regard, the effects of failed blade pitch control system on FOWT performance including structural and dynamic responses of blades, tower, and floater are systematically investigated. Through this study, it is seen that the failure of one of the blade pitch control system can induce significant dynamic loadings on the other blades and the entire FOWT system. The developed technology and numerical tool are readily applicable to any types of floating wind farms in any combinations of irregular waves, dynamic winds, and steady currents.

• 한국해양공학회지
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• 제12권3호통권29호
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• pp.19-30
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• 1998

In this paper, the dynamic analysis of a dolphin system for mooring a floating structure such as barge mounted plant is studied. The characteristics of the soil-pile system are simplified by a set of equivalent spring elements at the mudline. To evaluate the equivalent spring constants, the finite difference method is used. Since the characteristics of the soil-pile system are nonlinear in case of soft foundation, the nonlinear dynamic analysis technique is needed. The Newmark $beta$ method incorporating the modified Newton-Raphson method(initial stiffness method) is used. A numerical analysis is performed on two mooring dolphin systems on soft foundation and rock foundation. In case of the rock foundation, the characteristics are found to be nearly linear, so the linear dynamic analysis may be sufficient to consider the foundation effect. But in case of soft foundation, the non-linearity of the foundation appears to be very signigicant, so the nonlinear dynamic analysis si needed.

• Journal of Ship and Ocean Technology
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• 제9권1호
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• pp.11-26
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• 2005

In this study, the program to investigate the multiple body interaction effects between a floating platform and a shuttle tanker considering the coupled effect of hull (FPSO) with mooring lines and risers was developed. The coupled analysis program, which is called WINPOST-MULT using the hydrodynamic analysis results by WAMIT, was made. For the verification of WINPOST-MULT by means of numerical experiments, two multiple-body models of an FPSO-FPSO and an FPSO-shuttle tanker system are adopted. With the FPSO-FPSO model and a two-mass-spring system to idealize two identical bodies for the 100-year storm wave condition in GOM, the numerical simulations were performed to investigate the interaction effects between two identical bodies. For the more reality, the coupled analysis for the FPSO-shuttle tanker model in the tandem arrangement was carried out in the consideration of the environmental condition of the West Africa Sea as a rather mild condition. Through the case studies with interaction effect and without interaction effect by the iteration method and the combined method, it is verified that the program is a very useful tool for the analysis of the interaction problem of multiple-body system and the coupled problem of the hull/mooring/riser.