• KSCE Journal of Civil and Environmental Engineering Research
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• v.5 no.2
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• pp.1-9
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• 1985

Two methods for the dynamic analysis of fixed offshore structures subjected to random waves are studied. They are the frequency domain method using the equivalent linearization of the nonlinear drag force, and the time domain method utilizing the Monte Carlo simulation technique for time series of random wave particle velocities and accelerations. Example analyses are carried out for two structures with different structural characteristics and for various wave conditions. A comparison has been made between the results obtained by two methods.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.9 no.4
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• pp.51-61
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• 1989

The classical spectral analysis of random vibration is not applicable to the random vibration of nonlinear structures or the dynamic response of active mechanical systems whose governing equations contain random parametric and inhomogeneous excitations. If the random load is simulated, dynamic responses can be obtained with the application of numerical integration schemes to the governing equations of above problems. Thus, in this paper, efficient and practical methods of simulating nonstationary random seismic ground accelerations are presented by using the fast Fourier transform technique. Typical applications of the simulated ground accelerations are the simulations of the dynamic response of rotor-bearing systems under earthquake excitations. The study of accuracy is presented to determine the applicability and practicality of methods of simulation.

• Journal of the Earthquake Engineering Society of Korea
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• v.11 no.2 s.54
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• pp.81-94
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• 2007

In most experimental researches on the liquefaction phenomenon, an earthquake as a random vibration has been regraded as a sinusoidal wave or a triangular wave with an equivalent amplitude. Together with the development in the part of signal control and data acquisition, dynamic experimental equipments in the soil dynamics have also developed rapidly and further more, several real earthquakes have been simulated in the large model test such as shaking table tests and centrifuge tests. In Korea, several elementary laboratory tests to simulate the real earthquake load were performed. From these test results, it was reported that the sinusoidal wave cannot reliably reflect the soil dynamic behavior under the real earthquake motion. In this study, 4 types of dynamic motions such as the sinusoidal wave, the triangular wave, the incremental triangular wave and several real earthquake motions which were classified with shock-type and vibration-type were loaded to find something new to explain the change of the excess pore water pressure under the real earthquake load. Through the detailed investigation and comparison on all test results, it is found that the dynamic flow is generated by the soil plastic deformation and the velocity head of dynamic flow is changed the pressure head in the un-drained condition. It can be concluded that the change of the excess pore water pressure is related to the pressure head of dynamic flow. Lastly, a new hypothesis to explain such a liquefaction initiation phenomenon under the real earthquake load is also proposed and verified.

• Journal of the KSME
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• v.36 no.9
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• pp.855-866
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• 1996

승요차 앞자축에 장착되어 회전하면서 동력을 전달하는 드라이브축은 운행중에 주로 비틀림하중을 받는다. 따라서 동 부품의 피로해석 및 설계를 위해서는 실제 운행중에 받는 서비스토크의 크기, 주파수 등에 관한 데이터가 필요하다. 차량에 탑재된 엔진의 토크와 회전수 등의 규격으로부터 드라이브축에 부가되는 최대 토크 값을 예측할 수 있으나, 자동차 운행주에는 승차인원, 도로조건, 운전자의 운전습관 등 여러가지 외적인 영향으로 인하여 서비스토크가 불규칙하게 변할 것으로 예상되므로 서비스토크를 정확히 예측하기는 어려운 실정이다. 또한, 최근의 자동차 구조부품에 대한 설계개념이 무한수명 설계에서 경량화 설계로 변화되고 있으며, 따라서 자동차 드라이브축도 실제 운용하중을 바탕으로 한 정확한 수명예측 및 강도설계가 요구되고 있다. 본 연구에서는 4륜구동형 승용차용 드라이브축에 대해 실제 운용하중에서의 피로수명을 예측하기 위해 1)텔리메트리를 이용하여 토크를 측정하고, 2) 일정진촉하중하에서의 드라이브축의 비틀림 피로시험을 수행하고, 3) 일정진폭하중하에서의 드라이브축의 비틀림 피로시험을 수행하고, 4) 축류 소재의 피로특성 데이터를 구성하여 5) 자체 개발한 프로그램으로 피로수명을 예측하고자 한다.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.22 no.1
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• pp.45-52
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• 2009

In this paper, a guideline for designing breakwater in wave loads and in seismic loads is proposed. A simple model structure in breaking wave zone is examined using Morison equation in consideration with the effect of an impact load, for evaluation of the wave loads. As the impact load effect is not significant, pressure distributions according to Goda are applied for evaluation of wave loads on breakwater. Structural behavior of breakwater in wave loads can be obtained using the Goda method, as well. For seismic analysis, Ofunato and Hachinohe models, as well as an artificial seismic acceleration loads model, are adopted. Soil-structure interaction analysis is carried out to find the seismic load effect. It is found that, in certain cases, structural deformation in wave loads is in the same level as deformation that in seismic loads. Thus, it is our recommendation that these two loads are considered at the same level in breakwater design.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1993.04b
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• pp.365-369
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• 1993

The reliability assessment of a simple porbabilistic fatigue analysis under random loading is proposed. Using the crack closure concept, the crack opening stress is assumed to be constant during random loading. The available loading history and test data are used for the comparison with the results of the reliability assessment of probabilistic fatigue analysis.

• Transactions of the Korean Society of Automotive Engineers
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• v.20 no.4
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• pp.133-141
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• 2012

This study investigates structural and fatigue analyses of bike brake. Maximum equivalent stress of the model of mountain bike is 4 times as much as the model of general bike at static analysis. In cases of mountain and general bikes, maximum damage frequency at load of 'SAE bracket history' with the severest change of load becomes as much as 16 times than the most stable load of 'Sample history' among the nonuniform fatigue loads. In case of mountain bike, the possibility of maximum damage becomes 3% at the load of 'Sample history' with the average stress of 0 to $-3{\times}10^4$MPa and the amplitude stress of 0 to $10^4$MPa. In case of general bike, the possibility of maximum damage becomes 3% at the load of 'Sample history' with the average stress of 0 to $-0.8{\times}10^4$MPa and the amplitude stress of 0 to $0.2{\times}10^4$MPa. This stress state can be shown as 5 to 6 times more than the damage possibility of 'SAE bracket history' or 'SAE transmission'. The analysis result of this study can be effectively utilized for the safe design of bike brake.

• 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.

• Journal of Korean Society of Steel Construction
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• v.29 no.1
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• pp.49-60
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• 2017

As well as the strength check, fatigue life check is also mainly required for designing mooring lines of the floating structures. In general, forces which induce dynamic structural response significantly affect to fatigue design of the mooring lines. So, waves are mainly considered as the governing loading for fatigue design of the mooring lines. In this study, characteristics of the fatigue damage of the mooring lines for submerged floating tunnels (SFT) under irregular waves are investigated. For this study time domain hydrodynamic analysis is used to obtain motion of the tunnel and tension and stresses of the mooring lines under the specific environmental conditions. Also, the Rainflow-counting method, the Palmgren-Miner's rule, and S-N curves for floating offshore structures presented by DNV recommendation is applied to calculate the fatigue damage due to the fluctuating stresses. Referring to the design plactice of the tendon pipes for TLP (tension-leg platform), which is very similar structural system to SFT, it is assumed that a 100 year return period wave attacks the SFT systems during 48 hours and the fatigue damages due to the environmental loading are calculated. Following the analysis sequence, the effects of the tunnel draft, spacing and initial inclination angle of the mooring lines on the fatigue damage under the specific environmental loadings are investigated.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.5 no.4
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• pp.286-291
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• 2004

There are fatigue fractures at the practical area. The fatigue load happens non- constantly. As it is impossible to be predicted, it can not be known when the fracture happens. Non -constant fatigue load is simulated in this study. The stability and the life of the material are analyzed theoretically by the program of Ansys workbench. These results are greatly applied as the practical structures to predict the prevention of failure and the endurance.