• Title, Summary, Keyword: Mooring loads

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Mooring loads analysis of submersible aquaculture cage system using finite element method

  • Kim, Tae-Ho
    • Journal of the Korean Society of Fisheries and Ocean Technology
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    • v.42 no.1
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    • pp.44-53
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    • 2006
  • The expansion of near shore aquaculture is feasibility of moving aquaculture facilities into the open ocean. Numerical modeling technique using finite element method was used to enable the optimum design and evaluation of submersible aquaculture cage system. The characteristics of mooring loads response in mooring lines under waves and current and their response amplitude operators were calculated for single and three point mooring configuration at the surface condition and submerged one. The static mooring loads without wave and current loading were similar for both the surface and submerged configuration. It was calculated that three point mooring was more adequate than single point mooring for the mooring configuration of submersible aquaculture cage system. The wave induced response amplitude operators for the single point mooring configuration with the influence of currents were identical to those without the influence of currents.

A Study on Effect of Aerodynamic Loads on Mooring Line Responses of a Floating Offshore Wind Turbine (공기 동역학 하중이 부유식 해상 풍력 발전기의 계류선 응답에 미치는 영향에 관한 연구)

  • Kim, Hyungjun;Han, Seungoh;Choung, Joonmo
    • Journal of the Society of Naval Architects of Korea
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    • v.52 no.1
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    • pp.43-51
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    • 2015
  • This paper presents effect of aerodynamic loads on mooring line responses of a floating offshore wind turbine. A Matlab code based on blade element momentum (BEM) theory is developed to consider aerodynamic loads acting on NREL 5MW wind turbine. The aerodynamic loads are coupled with time-domain hydrodynamic analyses using one-way interaction scheme of the wave and wind loads. A semi-submersible floating platform which is from Offshore Code Comparison Collaborative Continuation(OC4) DeepCWind platform is used with catenary mooring lines simply composed of studless chain links. Average values of mooring peak tensions obtained from aerodynamic load consideration are significantly increased compared to those from simple wind drag force consideration. Consideration of aerodynamic loads also yield larger tension ranges which can be important factor to reduce fatigue life of the mooring lines.

Study on the Mooring Stability of Floating Dock with Ultra Large Offshore Structure (초대형 부유식 해양구조물 탑재 플로팅 도크 계류안전성 연구)

  • Yang, Seungho;Cho, Jinwoog;Kim, Hyunjoe;Kim, Booki
    • Journal of the Society of Naval Architects of Korea
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    • v.52 no.6
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    • pp.509-519
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    • 2015
  • Mooring stability of floating dock for construction of Ichthys CPF (central processing facilities), an ultra large offshore structure, was studied. Normal and typhoon conditions were considered for mooring analysis. There have been changes in construction stages of the CPF as project progresses. These changes were reflected on the mooring stability analysis for both conditions. In order to secure the mooring stability of the floating dock for Ichthys CPF under typhoon, maximum loads of mooring chains and maximum offset of the floating dock with Ichthys CPF were examined. Also the shapes of the catenary mooring were investigated to check interferences among mooring chains. As it was confirmed that the mooring loads were within SWL (safe working load) of mooring chains and underwater sinkers, the mooring stability of the floating dock for construction of Ichthys CPF was secured. By achieving security of mooring stability of the floating dock, it is assured that Ichthys project is on its way to success.

A Study on the Hydrostatic Mooring Stability of Submerged Floating Ellipsoidal Habitats

  • Pak, Sang-Wook;Lee, Han-Seok;Park, Jin
    • Journal of Navigation and Port Research
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    • v.43 no.5
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    • pp.328-334
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    • 2019
  • Underwater architecture in providing a comfortable living space underwater is mandated to survive prevailing environmental loads, especially hydrostatic ambient water pressure exerted on the structure of individual habitat hulls at depth and hydrodynamic fluctuation of external forces that perturb the postural equilibrium and mooring stability of the underwater housing system, for which the design including the hull shape and mooring system constraint the responses. In this study, the postural stability of a proposed underwater floating housing system with three vertically connected ellipsoidal-shape habitat hulls of different sizes are theorized and calculated for hydrostatic stability, using MATLAB in the volumetric integration of a hull and the weight of operational loads under assumed scenarios. The assumptions made in the numerical method to estimate the stability of the habitat system include the fixed weight of the hulls, and their adjustable loads within operational limits for the set meteorological oceanic conditions. The purpose of this study was to numerically manipulate a) The buoyancy and b) The adjusted center of mass of the system within the range of designed external and internal load changes, by which the effective mooring system capability and postural equilibrium requirements were argued with the quantitative analysis.

Estimation of Dynamic Motions and Mooring Forces for Floating Type Offshore Platform Based on Hydrodynamic Analysis (동수력학 해석 기반 부유식 해양 플랫폼의 동적 운동 및 계류력 산정)

  • Cha, Ju-Hwan;Moon, Chang-Il;Song, Chang-Yong
    • Journal of Ocean Engineering and Technology
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    • v.26 no.2
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    • pp.48-57
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    • 2012
  • This paper deals with numerical analyses in the context of estimations of hydrodynamic motions and dynamic loads for a floating type offshore platform using some exclusive simulation code such as code for the simulation of a floating type of offshore crane based on multi-body dynamics, along with the commercial code AQWA. Verifications of numerical models are carried out by comparing the RAO results from the simulation code. In the verification analyses, hydrodynamic motions are examined in the frequency domain for the floating type offshore platform according to the mooring lines. Both the hydrodynamic motions and dynamic loads are estimated for floating type offshore platforms equipped with the catenary type and taut mooring lines. A review and comparison are carried out for the numerically estimated results. The structural safety of the connection parts in an offshore structure such as a floating type offshore platform is one of the most important design criteria in view of fatigue life. The dynamic loads in the connecting area between a floating type offshore platform and its mooring lines are estimated in detail according to variations in the mechanical properties of the mooring lines. The dynamic tension load on the mooring lines is also estimated.

A Study on the Analysis of Multi-let Spread Mooring Systems (다점지지 계류시스템의 정적해석에 대한 연구)

  • Sin, Hyeon-Gyeong;Kim, Deok-Su
    • Journal of Ocean Engineering and Technology
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    • v.9 no.2
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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.

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Wind tunnel test of wind loads and current loads acting on FLBT and LNG bunkering shuttles in side-by-side configuration and comparison with empirical formula (병렬 배치된 FLBT 및 LNG-BS에 작용하는 풍하중 및 조류하중에 대한 풍동 시험 및 경험식 비교 연구)

  • Park, Byeongwon;Jung, Jae-Hwan;Hwang, Sung-Chul;Cho, Seok-Kyu;Jung, Dongho;Sung, Hong Gun
    • Journal of Ocean Engineering and Technology
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    • v.31 no.4
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    • pp.266-273
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    • 2017
  • In recent years, LNG bunkering terminals are needed to supply LNG as fuel to meet the emission requirements of the International Maritime Organization (IMO). A floating LNG bunkering terminal (FLBT) is one of the most cost-effective and environmentally friendly LNG bunkering systems for storing LNG and transferring it directly to an LNG fuel vessel. The FLBT maintains its position using mooring systems such as spread mooring and turret mooring. The loads on the vessel and mooring lines must be carefully determined to maintain their positions within the operable area. In this study, the wind loads acting in several side-by-side arrangements on the FLBT and LNG-BS were estimated using wind tunnel tests in the Force Technology, and the shielding effect due to the presence of ships upstream was evaluated. In addition, the empirical formulations proposed by Fujiwara et al. (2012) were used to estimate the wind force coefficients acting on the FLBT and those results were compared with experimental results.

Fatigue analysis on the mooring chain of a spread moored FPSO considering the OPB and IPB

  • Kim, Yooil;Kim, Min-Suk;Park, Myong-Jin
    • International Journal of Naval Architecture and Ocean Engineering
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    • v.11 no.1
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    • pp.178-201
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    • 2019
  • The appropriate design of a mooring system to maintain the position of an offshore structure in deep sea under various environmental loads is important. Fatigue design of the mooring line considering OPB/IPB(out-of-plane bending/in-plane bending) became an essential factor after the incident of premature fatigue failure of the mooring chain due to OPB/IPB in the Girassol region in West Africa. In this study, mooring line fatigue analysis was performed considering the OPB/IPB of a spread moored FPSO in deep sea. The tension of the mooring line was derived by hydrodynamic analysis using the de-coupled analysis method. The floater motion time histories were calculated under the assumption that the mooring line behaves in quasi-static manner. Additional time domain analysis was carried out by prescribing the obtained motions on top of the selected critical mooring line, which was determined based on spectral fatigue analysis. In addition, nonlinear finite element analysis was performed considering the material nonlinearities, and both the interlink stiffness and stress concentration factors were derived. The fatigue damage to the chain surface was estimated by combining both the hydrodynamic and stress analysis results.

Dynamic responses of an FPSO moored on sloped seabed under the action of environmental loads

  • Roy, Shovan;Banik, Atul K.
    • Ocean Systems Engineering
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    • v.8 no.3
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    • pp.329-343
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    • 2018
  • The inclination of seabed profile (sloped seabed) is one of the known topographic features which can be observed at different seabed level in the large offshore basin. A mooring system connected between the platform and global seabed is an integral part of the floating structure which tries to keep the floating platform settled in its own position against hostile sea environment. This paper deals with an investigation of the motion responses of an FPSO platform moored on the sloped seabed under the combined action of wave, wind and current loads. A three-dimensional panel discretization method has been used to model the floating body. To introduce the connection of multi-segmented non-linear elastic catenary mooring cables with the sloped seabed, a quasi-static composite catenary model is employed. The model and analysis have been completed by using hydrodynamic diffraction code AQWA. Validation of the numerical model has been successfully carried out with an experimental work published in the latest literature. The analysis procedure in this study has been followed time domain analysis. The study involves an objective oriented investigation on platform motions, in order to identify the effects of the slopped seabed, the action of the wave, wind and current loads and the presence of riser system. In the end, an effective analysis has been performed to identify a stable mooring model in demand of reducing structural responses of the FPSO.

Dynamic response analysis of floating offshore wind turbine with different types of heave plates and mooring systems by using a fully nonlinear model

  • Waris, Muhammad Bilal;Ishihara, Takeshi
    • Coupled systems mechanics
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    • v.1 no.3
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    • pp.247-268
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    • 2012
  • A finite element model is developed for dynamic response prediction of floating offshore wind turbine systems considering coupling of wind turbine, floater and mooring system. The model employs Morison's equation with Srinivasan's model for hydrodynamic force and a non-hydrostatic model for restoring force. It is observed that for estimation of restoring force of a small floater, simple hydrostatic model underestimates the heave response after the resonance peak, while non-hydrostatic model shows good agreement with experiment. The developed model is used to discuss influence of heave plates and modeling of mooring system on floater response. Heave plates are found to influence heave response by shifting the resonance peak to longer period, while response after resonance is unaffected. The applicability of simplified linear modeling of mooring system is investigated using nonlinear model for Catenary and Tension Legged mooring. The linear model is found to provide good agreement with nonlinear model for Tension Leg mooring while it overestimates the surge response for Catenary mooring system. Floater response characteristics under different wave directions for the two types of mooring system are similar in all six modes but heave, pitch and roll amplitudes is negligible in tension leg due to high restraint. The reduced amplitude shall lead to reduction in wind turbine loads.