• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2002.10a
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• pp.155-160
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• 2002

In this paper, a compliant buoy mooring system of a floating cylindrical structure in shallow water depth is studied experimentally. The compliant buoy mooring system consists of four buoys, vertical mooring legs and horizontal mooring lines. A series of model test were carried out at KRISO ocean engineering basin for various mooring parameters; line length, pretension of mooring leg and mooring layouts and environmental conditions; regular and irregular waves combined with current and wind. The mooring line tensions and 6-DOF motions of the floating structure were measured using water-proof load cells and 3 CCD camera system. The results of a series of model tests were discussed on nonlinear motion behaviors of the floating structure and characterisitics of cumulative distributions of mooring line peak tensions.

• 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.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.23 no.5
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• pp.407-413
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• 2013

This paper deals with the analysis of dynamic characteristics of mooring system of floating-type offshore wind turbine. A spar-type floating structure which consists of a nacelle, a tower and the platform excepting blades, is used to model the floating wind turbine and connect three catenary cables to substructure. The motion of floating structure is simulated when the mooring system is attached using irregular wave Pierson-Moskowitz model. The mooring system is analyzed by changing cable position of floating structure. The dynamic behavior characteristics of mooring system are investigated comparing with cable tension and 6-dof motion of floating structure. These characteristics are much useful to initial design of floating-type structure. From the simulation results, the optimized design parameter that is cable position of connect point of mooring cable can be obtained.

• Journal of the Society of Naval Architects of Korea
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• v.47 no.6
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• pp.813-820
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• 2010

The spread mooring system for FPSO is developed to explore deep sea area, in which swell is dominant. It is known that the tension response of mooring lines in this sea area shows bimodal spectrum. Assuming normal distribution of tension profile and Rayleigh distribution of tension amplitude, the power spectral density function (PSD) of the mooring tension under the bimodal stationary random process is applied for the calculation of spectrum fatigue. Three popular methods, which are simple summation method, combined spectrum method and Jioa-Moan method, are used to combine fatigue damages from bimodal spectrum characteristics. Each damage value is compared with damage using Rainflow Cycle Counting (RCC) method which is believed to be close to exact solution. Vanmarcke' parameter and RMS(Root Mean Square) ratio are employed to assess relative damage variations between from RCC method and from three combination methods. Finally the most reliable fatigue damage combining method for spread mooring system is suggested.

• Ocean Systems Engineering
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• v.11 no.4
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• pp.313-330
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• 2021

In this study, the dynamic interaction between an Arctic Spar and drifting level ice is examined in time domain using the newly developed ice-hull-mooring coupled dynamics program. The in-house program, CHARM3D, which is the hull-riser-mooring coupled dynamic simulator is extended by coupling with the open-source discrete element method (DEM) simulator, LIGGGHTS. In the LIGGGHTS module, the parallel-bonding method is implemented to model the level ice using an assembly of multiple bonded spherical particles. As a case study, a spread-moored Artic Spar platform, whose hull surface near waterline is the inverted conical shape, is chosen. To determine the breaking-related DEM parameter (the critical bonding strength), the four-point numerical bending test is used. A series of numerical simulations is systematically performed under the various ice conditions including ice drift velocity, flexural strength, and thickness. Then, the effects of these parameters on the ice force, platform motions, and mooring tensions are discussed. The simulations reveal various features of dynamic interactions between the drifting ice and moored platform for various ice conditions including the novel synchronous resonance at low ice speed. The newly developed simulator is promising and can repeatedly be used for the future design and analysis including ice-floater-mooring coupled dynamics.

• Journal of the Korean Society of Marine Environment & Safety
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• v.24 no.2
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• pp.140-145
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• 2018

This paper deals with the dynamical analysis of a two-point mooring vessel under surge excitations. The characteristics of nonlinear behaviors are investigated completely including bifurcation and limit cycle according to particular input parameter changes. The strong nonlinearity of the mooring system is mainly caused by linear and cubic terms of restoring force. The numerical simulation is performed based on the fourth order Runge-Kutta algorithm. The bifurcation diagram and several instability phenomena are observed clearly by varying amplitudes as well as frequencies of surge excitations. Stable periodic solutions, called the periodic windows, can be obtained in succession between chaotic clouds of dots in case of frequency ${\omega}=0.4rad/s$. In addition, the chaotic region is unexpectedly increased when external forcing amplitude exceeds 1.0 with the angular frequency of ${\omega}=0.7rad/s$. Compared to the cases for ${\omega}=0.4$, 0.7rad/s, the region of chaotic behavior becomes more fragile than in the case of ${\omega}=1.0rad/s$. Finally, various types of steady states including sub-harmonic motion, limit cycle, and symmetry breaking phenomenon are observed in the two-point mooring system at each parameter value.

• Journal of the Korean Society of Marine Environment & Safety
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• v.24 no.7
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• pp.953-959
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• 2018

This paper deals with controlling surge oscillations of a mooring vessel system under large external disturbances such as wind, waves and currents. A control synthesis based on Sliding Mode Control (SMC) with a Super-Twisting Algorithm (STA) has been applied to suppress nonlinear surge oscillations of a two-point mooring system. Despite the advantages of robustness against parameter uncertainties and disturbances for SMC, chattering is the main drawback for implementing sliding mode controllers. First-order SMC shows convergence within the desired level of accuracy, in which chattering is the main obstacle related to the destructive phenomenon. Alternatively, STA completely eliminates chattering phenomenon with high accuracy even for large disturbances. SMC based on STA is an effective tool for the motion control of a nonlinear mooring system because it avoids the chattering problems of a first-order sliding mode controller. In addition, the error trajectories of controlled mooring systems implemented by means of STA form in the bounded region. Finally, the control gain effect of STA can be observed in sliding surface and position trajectory errors.

• Journal of Navigation and Port Research
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• v.38 no.6
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• pp.673-681
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• 2014

Due to the increased demand for safety and security requirements on the port infrastructure, the harbor tranquility is one of the important parameter in the mooring basin of harbor. It relates keenly to berthing/unberthing and cargo handling works but also it is an important indicator to get the minimum water area as the safe refuge. Hupo harbor is a national coastal harbor located in east coast of Korea and a development plan for a new marina near the entrance is being carried out including berth layouts, breakwater extensions, 300m marina berths, dredging and land reclamation works. The new plan will impact on calmness of the existing port. Therefore, it is necessary to analyze in complex the variation of wave height and direction caused by wave refraction, diffraction, shoaling and reflection from the incident waves from outside the harbor. In order to check the calmness inside a harbor, the numerical models are being used currently need fundamental reviews according to the difference of results which depend on their respective features. In this study, hence, it was introduced the validity of numerical models by comparing the computational results with the hydraulic model experiment. The current investigations contribute to the existing development recommendations and provide further solutions for port planning.

• 제어로봇시스템학회:학술대회논문집
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• 2004.08a
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• pp.699-703
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• 2004

The autopilot system targets decreasing labor, working environment, service safety security and elevation of service efficiency. Ultimate purpose is minimizing number of crew for guarantee economical efficiency of shipping service. Recently, being achieving research about Course Keeping Control, Track Keeping Control, Roll-Rudder Stabilization, Dynamic ship Positioning and Automatic Mooring Control etc. which compensate nonlinear characteristic using optimizing control technique. And application research is progressing using real ship on actual field. Relation of Rudder angle which adjusted by Steering Machine and ship-heading angle are non-linear. And, Load Condition of ship acts as non-linear element that influence to Parameter of ship. Also, because the speed of a current and direction of waves, velocity and quantity of wind etc. that id disturbance act in non-linear form, become factor who make service of shipping painfully. Therefore, service system of shipping requires robust control algorithm that can overcome nonlinearity. In this paper, Using GA algorithm,design autopilot system of ship that could overcome the non-linear factor of ship and disturbance and examined result through simulation.

• Journal of Advanced Research in Ocean Engineering
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• v.3 no.3
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• pp.102-111
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• 2017

This study considered the effects on the seabed of a harbor and quay wall from ship maneuvers in relation to the thruster jet flow and initial velocity. This study also included the engine capacity, RPM, and diameter and pitch of a ship's thruster for a required speed. The impact of a scour hole on the environment of a quay wall was investigated. Based on these results, a risk based analysis was conducted to evaluate different strategies and their consequences. There has been an increase in the loads on the bottom of a harbor during ship maneuvering. This increase is caused by the propeller loads of mooring and unmooring vessels. This indicates a greater number of arrivals and departures of vessels with larger drafts, larger thruster diameters, and larger available thruster power capacities. Another important cause could be an increase in the maneuverability of vessels from the use of bow thrusters. The increasing loads, which cause a higher jet flow above the bottom, can lead to undesirable scour holes.