• Journal of Ocean Engineering and Technology
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• v.32 no.1
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• pp.21-27
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• 2018

The design and analysis of a quayside mooring system for safe mooring of Prelude FLNG under extreme environmental conditions were carried out. The design of the mooring system considered the yard operation conditions and maximum wind speed during a typhoon. In order to secure the mooring safety of Prelude FLNG under an extreme environment, a special steel structure was designed between the quay and Prelude FLNG to maintain the distance from the quay to a certain extent to avoid a collision with the inclined base. The mooring safety was also ensured by installing additional new parts on the quay. A mooring analysis and mooring safety review were performed with more rigorous modeling considering the nonlinearity of the mooring rope and fender. In order to secure additional safety of the mooring system under extreme environmental conditions, a safety assessment was conducted on the failures of the mooring components proposed in the marine mooring guidelines. Based on the results of the mooring analysis, it was confirmed that the Prelude FLNG can be safely moored even under the extreme conditions of typhoons, and a worst case scenario analysis verified that the mooring system design was robust enough. The proposed mooring analysis and design method will provide a basis for the safe mooring of ultra-large floating offshore structures of similar size in the future.

• Journal of Ocean Engineering and Technology
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• v.23 no.1
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• pp.1-6
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• 2009

The paper describes results of a sensitivity study on an optimum mooring cost as a function of safety factor and allowable maximum offset of the offshore floating structure by finding the anchor leg component size and the declination angle. A harmony search (HS) based mooring optimization program was developed to conduct the study. This mooring optimization model was integrated with a frequency-domain global motion analysis program to assess both cost and design constraints of the mooring system. To find a trend of anchor leg system cost for the proposed sensitivity study, optimum costs after a certain number of improvisation were found and compared. For a case study a turret-moored FPSO with 3 ${\times}$ 3 anchor leg system was considered. To better guide search for the optimum cost, three different penalty functions were applied. The results show that the presented HS-based cost-optimum offshore mooring design tool can be used to find optimum mooring design values such as declination angle and horizontal end point separation as well as a cost-optimum mooring system in case either the allowable maximum offset or factor of safety varies.

• Journal of the Society of Naval Architects of Korea
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• v.45 no.4
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• pp.462-467
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• 2008

In this paper, we investigated the design method of mooring system in ultra deep sea and carried out the conceptual design for offshore West Africa oil field in ultra deep sea of 3000 meters. Recently, it was feasible to design and install the offshore floating structures in deep sea of up to 2000 meters. Due to the simplicity, two-point mooring design is fully utilized. Force-excursion curves are throughly examined to find out the feasibility of various combinations of mooring lines. Free length and pretension effects are discussed. It is found that composite materials including synthetic fiber rope may be good solution for ultra deep sea mooring design.

• Journal of Ocean Engineering and Technology
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• v.26 no.4
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• pp.77-85
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• 2012

A study was performed on the design of a mooring line to maintain the position of a floating WEC (wave energy conversion) system. The procedure to design a mooring line is set up and the safety of the designed mooring system is evaluated using commercial software, Orcaflex. The characteristics curve for one line is analyzed to determine the properties and pretension of a mooring line. While considering the ocean environmental condition and importance of a floating WEC system, a multi-line layout is determined. A 4-point mooring system with 4 lines shows the instability in the yaw motion of the floating WEC system under a designed ocean environmental condition. The redesigned 4-point mooring system with 8 lines is found to be safe on the condition of a harsh ocean environment. The floating WEC system with the redesigned mooring system also shows stable motion in surge and pitch under operating conditions. From a parametric study on the mooring line length, the extreme value of the mooring line tension is found to be very sensitive to the pretension and length of mooring line. The results of this study can contribute to the establishment of a design procedure for mooring lines.

• Special Issue of the Society of Naval Architects of Korea
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• 2011.09a
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• pp.70-74
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• 2011

This paper describes the quay mooring analysis to verify the safety of a moored drillship in typhoon conditions. Mooring system consists of mooring equipments(deck bollards, shore bitts, mooring lines, fenders) to resist the extreme environmental condition. Wind force acting on the drillship is obtained from the wind tunnel test results. The strength of quay mooring system has been checked. The static mooring analysis shows that the designed mooring system satisfies the mooring design criteria. Vertical displacements of the drillship have been calculated considering the dynamic wave motions and static heelings due to the wind force acting on the ship. With the vertical displacements and the hull draft of drillship, the required water depth for quay mooring has been derived.

• Journal of Ocean Engineering and Technology
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• v.27 no.6
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• pp.22-26
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• 2013

The purpose of this study was to improve the design of a mooring line by attaching a lumped mass to it on the seabed. A numerical analysis of the redesigned mooring system is performed to analyze the effect of the weight of the attached lumped mass using the commercial software Orcaflex. The ultimate tension of the mooring system with the lumped mass is compared with that of a bare mooring line in the original design. An appropriately designed weight for the lumped mass is found to induce a critical lifted point in the mooring line by floater motion in the ultimate condition to move toward the floater position from the anchor point, while maintaining a similar safety factor for the mooring line. On the other hand, it is shown that excess weight for the lumped mass induces snapping in a mooring line, resulting in low safety factor for the mooring system. The distance between lumped weights is shown to be a minor parameter affecting the safety of a mooring line, although a shorter line has an advantage from an economic point of view. Using the optimal weight for the lumped mass attached to the mooring line on a seabed reduces the mooring line length and installation area occupied by a mooring system under real sea conditions.

• The Journal of Korea Robotics Society
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• v.17 no.4
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• pp.493-499
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• 2022

This paper presents the design for the kinematic structure of a system for an automatically moored 6000 ton autonomous ship in a port, and the process and results of optimal design for the link cross-sectional shape. We propose an automatic mooring system with a PPP type serial manipulator structure capable of linear motion in the XYZ axis. The mooring force applied by the mooring system was derived with dynamics simulation tool "ADAMS". The design goal is the minimization of the cross-sectional area of the link. Constrains include compressive stress and shear stress. The optimization problems were solved by using the sequential quadratic programing method implemented in the fmincon package. The shape of the cross section was assumed to be rectangle. Through future research, we plan to manufacture automatic mooring system for 6000ton class autonomous ship.

• Journal of Ocean Engineering and Technology
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• v.13 no.3 s.33
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• pp.3-11
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• 1999

Optimum design of mooring dolphin is numerically investigated. Design optimization problem of moring dolphin is first formulated. Geometry and cross sections of piles are used as design variables. Design objective is the total weight of steel piles of mooring dolphin, and the constraints of stress, penetration depth, lower and upper bounds on design variables are imposed. Based on the design variable linking and fixing, several class of design variations are sought. For the numerical optimization, both PLBA(Pshenichny - Lim - Belegundu - Arora) program and DNCONF subroutine code in IMSL library are used. For a dolphin structure with 20 steel piles, vertical and inclined, optimum designs for different cases are successfully obtained, which can be applied for the mooring of a very large floating structure.

• Proceedings of the Korea Concrete Institute Conference
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• 2000.10a
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• pp.253-258
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• 2000

Recently, the area of design optimization, especially structural optimization, has been and to be a continuous active area of research. And the design optimizations of port facilities have been achieved by many other civil engineers. But the design optimization of port facilities were limited to the design optimization of the breasting dolphin. This paper invested the design optimization of mooring pier and the foundations of mooring pier was suggested considering the convenience of repair and reinforcement work. The mooring pier devised with prestressed precast concrete panel and rigid frame welded wide flange beam to steel pipe pile. To accomplish the design optimization of mooring pier, the Augmented Lagrangian Multiplier Method(ALM) of ADS(Garret N. Vanderplaats) optimization routine, BFGS method as optimizer and Golden Section Method as one dimensional search were utilized. As a result, thirty percent of material cost for construction was reduced by design optimization. The tensile stress of concrete panel and bottom flage was critical constraints under service load. So, using high strength concrete and steel will be economical. And lots of initial values must be invested to accomplish the design optimization in design procedures.

• International Journal of Ocean System Engineering
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• v.3 no.4
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• pp.209-217
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• 2013

This paper presents a mooring design procedure for a floating offshore wind turbine. Offshore environmental data for Jeju are taken from KHOA (Korea Hydrographic and Oceanographic Administration) and used for the environmental conditions in numerical analyses. A semi-submersible-type floating wind system with a 5-MW-class wind turbine studied by the DeepCwind Consortium is applied. Catenary mooring with a studless chain is chosen as the mooring system. Design deliverables such as the nominal sizes of chain and length of the mooring line are decided by considering the long-term prediction of the breaking strength of the mooring lines where a 100-year return period is used. The designed mooring system is verified using a fatigue calculation based on rain-flow cycle counting, an S-N curve, and a Miner's damage summation of rule. The mooring tension process is obtained from time-domain motion analyses using ANSYS/AQWA.