• Journal of Ocean Engineering and Technology
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• v.27 no.1
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• pp.93-101
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• 2013

The incident bore impact loads acting on a tall structure is simulated using the refined Moving Particle Simulation (MPS) method. The particle method is more feasible and effective than conventional grid-based methods for the violent free-surface problems. In the present study, the simulation results for the temporal change of the hydrodynamic force on the structure and longitudinal velocity component around the structure are compared with the experiments (Radd and Bidoae, 2005). And the mitigation effects by installation of various obstacles in front of the main structure are investigated and discussed form the simulation results.

• Journal of the Society of Naval Architects of Korea
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• v.30 no.4
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• pp.93-101
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• 1993

This paper deals tilth an efficient algorithm in spectral fatigue analysis of ship structures. The concept of stress influence coefficients is suggested in order to obtain stress transfer functions efficiently which are the structural responses for unit load components. Strip method is applied to obtain the motion response and pressure distributions exerted on the hull. Since a number of the structural analysis should be performed for the various wave frequencies and heading angles in the spectral analysis, the algorithm developed in this study improves the efficiency of the analysis. Finally, the calculation example with application to this concept is shown in this paper.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.2 no.3
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• pp.152-161
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• 1990

In this paper, a hybrid element method(HEM) for the evaluation of the hydrodynamic responses of arbitrary-shaped offshore structures is studied. The hydrodynamic pressure forces are assumed to be inertially dominated, and viscous effects are neglected. The mathematical formulation procedure of the hybrid element method with the analytical eigenseries solution is established systematically. The computer program based on the HEM has been developed, and applied to solving the wave diffraction and radiation problems for arbitrary shaped structures. From comparisons of the results obtained by using the other avaliable solution methods, the method for the evaluation of the hydrodynamic forces using the HEM and the computer program developed here have been proved to be valid.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.6 no.2
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• pp.85-91
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• 1986

Fatigue life is an important consideration for the design of offshore structures in deep sea and in hostile environments. In this paper, the effect of the bandwidth of random stresses on the fatigue life estimation of fixed offshore structures is investigated. The dynamic analysis is carried out in the frequency domain by using the equivalent linearization technique. Fatigue damages are calculated by two stress cycle counting methods; i.e., the narrow band method and the wide band method using rainflow counting technique. Example studies are carried out for two different structures. Numerical results indicate that the wide band approach, which is more complex but theoretically more appropriate pridicts smaller values of fatigue damages compared with those by the narrow band approach for all seastate conditions. Such trend becomes more apparent for the cases of severe seastates where the bandwidth of random stresses becomes large.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.26 no.1
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• pp.25-32
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• 2014

Offshore wind power structures are subject to coastal hydrodynamic loading such as wind and wave loads. A considerable number of turbines have been installed in Europe, but so far none in Korea. Interest in offshore wind energy is growing in Korea, and it is expected that projects will reach the design stage in the near future. This paper discusses the level of structural reliability implied by the design rules of ABS(2010, 2013) and IEC(2009). Metocean conditions in 4 Korean seas(Gunsan, HeMOSU 1, Mokpo, Jeju) were used in the calibrations to calculate the aerodynamic and hydrodynamic loads as well as the structural responses of the typical designs of offshore wind turbines. Due to the higher variability of the wind and wave climate in hurricane-prone areas, applying IEC strength design criteria in combination with Korea west sea conditions could result in a design with much lower reliability index than what is anticipated from a design in European waters. To achieve the same level of safety as those in European waters, application of ABS 100 year design standards are recommended. Level-1 reliability-based design suitable for the Korean sea state conditions should be introduced because the IEC standards does not consider the typhoon effects in depth and the ABS standards is a WSD design method. In addition, the design equation should be established based on the statistical characteristics of the wind and wave loads of the Korean sea areas.

• Computational Structural Engineering
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• v.4 no.3
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• pp.117-127
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• 1991

For the reliability analysis of offshore guyed towers for large storm events, failure of an anchor pile of the guyline system is investigated. Two failure modes of the anchor pile due to the extreme and the cyclic wave loadings are considered. The probability of failure due to the extreme anchor load is evaluated based on the first excursion probability analysis. Degradation of the pile capacity due to cyclic loadings is evaluated by using empirical fatigue curves for a driven pile in clay. The numerical results indicate that the failure probability due to the cyclic loadings can be as large as the risk due to extreme loading, particularly for the cases with the low design safety level of the pile strength and the large uncertainty of the pile resistance.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.8 no.1
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• pp.87-95
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• 1988

In the arctic offshore regions, massive offshore gravity platforms are recommended to be construced because of severe environments. In such structures which is so large that its characteristic length is of the order of the wave length, wave-structure interaction problem has been solved using linear diffraction theory. Structural analysis of the large scale offshore structures requires wave force distribution along depth and wave pressure distribution on the body surface. In this study, existing computer program which calculates the total wave force acting on axisymmetric bodies has been modified to calculate wave force distribution along depth and wave pressure distribution on the body surface. Numerical results of pressure distribution for a fixed vertical cylinder obtained from this analysis has been compared with the results of an analytic solution of MacCamy-Fuchs, and good agreements has been obtained. It is desirable to use 6 in the case of analytic solution, and 5 in the case of numerical solution as the Fourier Mode of Green function. The results in this study are expected to be utilized for structural analysis such as pseudo-static analysis, dynamic analysis and fatigue analysis.

• Journal of Navigation and Port Research
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• v.34 no.10
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• pp.741-746
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• 2010

It is necessary to estimate more accurately the resistance of barge in still water and waves to compute the break load of towline and towing power for safety towing performance. The method proposed by government has calculated the total resistance of barge which is composed of frictional resistance, wave making resistance and air resistance considering the shape of hull and towing speed. However, the added resistance is equally applied with the significant wave height regardless of the type of vessels. In this study, we have carried out the numerical calculation to estimate the added resistance of wigley model in waves and compared with the experiment data to confirm the accuracy of the method. Then the computation was executed for the barge varying shape of the bow. As a result, added resistance of barge was differently occurred i.e. 0.3∼1.1 ton according to encounter angle, 0.4∼1.2 ton according to towing speed and 0.5∼1.1 ton according to shape of bow.

• Journal of Ocean Engineering and Technology
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• v.24 no.6
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• pp.16-22
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• 2010

In this paper, the diffraction problems for fixed offshore structures are solved using a hybrid scheme. In this hybrid scheme, potential-based solutions and the Navier-Stokes-based finite volume method (FVM) with a volume-of-fluid (VOF) method are combined. We introduce a buffer zone for efficient wave-making and damping. In this buffer zone, the near field solution from FVM-VOF is gradually changed to Stokes' 2nd order wave solutions. Three different models, including the truncated cylinder, sphere, and wigleyIII model, are numerically investigated in regular waves with a wave steepness of 1/30. The efficiency and accuracy of the hybrid scheme are numerically validated from results using different domain sizes and buffer zones. The wave exciting forces from the FVM-VOF simulations are compared with experiments and potential-based solutions from the higher-order boundary element method (HOBEM). This comparison shows good agreement between the hybrid scheme and potential-based solutions.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.5 no.4
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• pp.87-94
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• 1985

Dynamic analysis of guyed tower is presented in this paper. The scope of the study is twofold. The one is to determine an efficient analysis method to include the nonlinearity of the mooring system and the nonlinear hydrodynamic wave forces. The other is to investigate the sensitivity of two major design parameters, that is the stiffness of mooring system and the fixity condition of the tower at mud line. Time history analysis method utilizing mode superposition is mainly considered. However several other methods are also used for the purpose of comparison. Analyses are carried out using the Lena Guyed Tower, which is the first structure of this kind, as a standard structure.