• 한국해양공학회지
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• 제28권3호
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• pp.185-192
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• 2014

The riser systems for floating offshore structures are known to experience tri-modal dynamic responses. These are owing to the combined loadings from the low-frequency response due to riser tension behavior, middle-range frequency response coming from winds and waves, and high-frequency response due to vortex induced-vibration. In this study, fatigue damage models were applied to predict the fatigue damages in a well-separated tri-modal spectrum, and the resultant fatigue damages of each model were compared with the most reasonable fatigue damage calculated by the inverse Fourier transform of the spectrum, rain-flow counting method, and Palmgren-Miner rule as a reference. The results show that the fatigue damage models developed for a wide-band spectrum are applicable to the tri-modal spectrum, and both the Benasciutti-Tovo and JB models could most accurately predict the fatigue damages of the tri-modal spectrum responses.

• 대한조선학회논문집
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• 제53권6호
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• pp.514-520
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• 2016

Oil and gas production riser systems need to be designed considering a wide band quarter-modal analysis which contains low-, wave-, VIV(Vortex induced vibration) frequencies. The VIV can be separated into cross-flow(CF) and in-line(IL) components. In this study, the various idealized tri- and quarter-modal spectra are suggested to analyze fatigue damage on the production riser system. In order to evaluate the fatigue damage increment caused by the IL's motion, tri- and quarter-modal spectral fatigue damages are calculated in time domain. And the fatigue damage calculated from two different modal spectra are compared quantitatively. Then the suitability of existent wide band fatigue damage models for quarter modal spectrum was evaluated by comparison of frequency domain calculation and time domain calculation. The result show that although spectral density of IL motion is not remarkable in quantity, the effect on the fatigue damage is significant and existent fatigue damage models are not adequately estimating damage by quarter-modal spectra.

• 한국전산구조공학회논문집
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• 제29권6호
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• pp.539-545
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• 2016

천연가스 생산기지 내의 UPS시스템은 지진 시에도 기능성을 유지해야 하는 주요 설비 중 하나이다. 이 연구에서는 IEEE Std 693-2005 기준을 토대로 대형 진동대를 이용한 UPS시스템의 동특성 탐색시험을 수행하고 기기의 고유진동수와 모드감쇠, 모드형상 등을 도출하였다. 또한, 3축 시간이력시험을 통해 지진 시 기기의 거동 및 부재의 발생응력을 확인하였다. 유한요소모델을 생성하여 고유치해석을 수행하고 이를 동특성 탐색시험의 시험값과 비교, 분석하여 해석모델을 개선하고 자중해석과 응답스펙트럼 해석을 수행하여 조합응력을 3축 시간이력시험의 시험값과 비교하였다. 개선된 유한요소 해석모델의 동특성과 조합응력이 시험 결과와 유사함을 입증하여 개선된 UPS시스템 해석모델의 적합성을 제시하였다.