• 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 the Computational Structural Engineering Institute of Korea
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• v.32 no.2
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• pp.125-132
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• 2019

This paper presents a seismic reliability analysis method for an offshore wind turbine with a twisted tripod support structure under earthquake loading. A three dimensional dynamic finite element model is proposed to consider the nonlinearity of the ground-pile interactions and the geometrical characteristics of the twisted tripod support structure where out-of-plane displacement occurs even under in-plane lateral loadings. For the evaluation of seismic reliability, the failure probability was calculated for the maximum horizontal displacement of the pile head, which is calculated from time history analysis using artificial earthquakes for the design return periods. The application of the subset simulation method using the Markov Chain Monte Carlo(MCMC) sampling is proposed for efficient reliability analysis considering the limit state equation evaluation by the nonlinear time history analysis. The proposed method can be applied to the reliability evaluation and design criteria development of the offshore wind turbine with twisted tripod support structure in which two dimensional models and static analysis can not produce accurate results.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.12
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• pp.301-306
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• 2016

In bridge performance assessments, a new load carrying capacity evaluation model of simple bridges was proposed, which is based on the developed simple support impact factor spectrum. In this paper, a conservative assumption that the inner span with the both ends fixed boundary condition is ideal for applying the impact factor response spectrum for continuous bridges. The impact factor response spectrum has been proposed based on this assumption. The response spectrum by comparing the numerical analysis result and actual measurement data verified the applicability. The analysis was loading the moving load of DB-24 in a six-span continuous bridge, which was the same as the actual measurement data, the dynamic response was measured in the fourth span. The frequency of the bridge was obtained by FFT on the acceleration response and the span-frequency of sample bridge was calculated by the frequency. The impact factor of the sample bridge was determined by applying the span-frequency of the bridge to the proposed response spectrum; it was similar to the result of comparing the actual measured impact factor. Therefore, the method using the impact factor response spectrum based on the frequency response of both ends-fixed beam was found to be applicable to an actual continuous bridge.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.19 no.2 s.72
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• pp.195-202
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• 2006

Thin-walled structures are efficiently utilized an automobiles, aircraft, satellite and ship as well as needed light weight simultaneously. This paper presents new shape of automobile hood reinforcement that rotating parts as engine, transmission are protected by thin-walled structures. The automobile hood is concerned about the resonance occurs due to the frequency of the rotating parts. The hood must be designed by supporting the stiffness of design loads and considering the natural frequencies. Hence, it is sustained the stiffness and considered the vibration by resonance. It is deep related to ride. Therefore, the topology, shape and size optimization methods are used to design the automobile hood. Topology technique is applied to determine the layout of a structural component optimum size with maximized natural frequency by volume reduction. In this research, The optimal structure layout of an inner reinforcement of an automobile hood for the natural frequency of a designated mode is obtained by using topology optimization method. The optimum size and the optimum shape are determined by PLBA(Pshenichny-Lim-Belegundu-Arora) algorithm.

• Journal of Korean Society of Steel Construction
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• v.16 no.6 s.73
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• pp.793-805
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• 2004

The main objective of this paper is to evaluate the ductility and strength factors that are key components of the response modification factor for special steel moment-resistant frames. The ductility factors for special steel moment-resistant frames were calculated by multiplying the ductility factor for SDOF systems and the MDOF modification factors. Ductility factors were computed for elastic and perfectly plastic SDOF systems undergoing different levels of inelastic deformation and periods when subjected to a large number of recorded earthquake ground motions. Based on the results of the regression analysis, simplified expressions were proposed to compute the ductility factors. Based on previous studies, the MDOF modification factors were also proposed to account for the MDOF systems. Strength factors for special steel moment resisting frames were estimated from the results of the nonlinear static analysis. A total of 36 sample steel frames were designed to investigate the ductility and strength factors considering design parameters such as number of stories (4, 8, and 16 stories), seismic zone factors (Z = 0.075, 0.2, and 0.4), framing system (Perimeter Frames, PF and Distributed Frames, DF), and failure mechanism (Strong-Column Weak Beam, SCWB, and Weak-Column Strong-Beam, WCSB). The effects of these design parameters on the ductility and strength factors for special steel moment-resisting frames were investigated.

• Journal of the Korean Society of Marine Environment & Safety
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• v.28 no.4
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• pp.601-609
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• 2022

Jack-up drilling rigs are mobile offshore platforms widely used in the offshore oil and gas exploration industry. These are independent, three-legged, self-elevating units with a cantilevered drilling facility for drilling and production. A typical jack-up rig includes a triangular hull, a tower derrick, a cantilever, a jackcase, living quarters and legs which comprise three-chord, open-truss, X-braced structure with a spudcan. Generally, jack-up rigs can only operate in water depths ranging from 130m to 170m. Recently, there has been an increasing demand for jack-up rigs for operating at deeper water levels and harsher environmental conditions such as waves, currents and wind loads. All static and dynamic loads are supported through legs in the jack-up mode. The most important issue by society is to secure the safety of the leg structure against collision that causes large instantaneous impact energy. In this study, nonlinear FE -analysis and verification of the requirement against collision for 35MJ recommended by DNV was performed using LS-Dyna software. The colliding ship used a 7,500ton of shore supply vessel, and five scenarios of collisions were selected. From the results, all conditions do not satisfy the class requirement of 35MJ. The loading conditions associated with chord collision are reasonable collision energy of 15M and brace collisions are 6MJ. Therefore, it can be confirmed that the identical collision criteria by DNV need to be modified based on collision scenarios and colliding members.

• Journal of the Korea institute for structural maintenance and inspection
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• v.27 no.4
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• pp.33-44
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• 2023

Wind power is one of the most efficient and reliable energy sources in the transition to a low-carbon society. In particular, offshore wind power provides a high-quality and stable wind resource compared to onshore wind power while both present a higher installed capacity than other renewables. In this paper, we present our new program, the X-WIND program well suitable for the assessment of the substructure of offshore wind turbines. We have developed this program to increase the usability of analysis programs for offshore wind energy substructures by addressing the shortcomings of existing programs. Unlike the existing programs which cannot solely perform the substructure analyses or lack pre-post processors, our X-WIND program can complete the assessment analysis for the offshore wind turbines alone. The X-WIND program is embedded in AutoCAD so that both design and analysis are performed on a single platform. This also performs static and dynamic analysis for wind, wave, and current loads, essential for offshore wind power structures, and includes pre/post processors for designs, mesh developments, graph plotting, and code checking. With this expertise, our program enhances the usability of analysis programs for offshore wind energy substructures, promoting convenience and efficiency.