Journal of the Society of Naval Architects of Korea (대한조선학회논문집)

The Society of Naval Architects of Korea (대한조선학회)
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Fatigue Damage Combination for Spread Mooring System under Stationary Random Process with Bimodal Spectrum Characteristics

바이모달 스펙트럼 특성을 가지는 정상확률과정에 대한 다점계류라인의 피로손상도 조합기법 연구

  • Lim, Yu-Chang (Dept., of Naval Architecture & Ocean Engineering, Inha University) ;
  • Kim, Kyung-Su (Dept., of Naval Architecture & Ocean Engineering, Inha University) ;
  • Choung, Joon-Mo (Dept., of Naval Architecture & Ocean Engineering, Inha University)
  • 임유창 (인하대학교 조선해양공학과) ;
  • 김경수 (인하대학교 조선해양공학과) ;
  • 정준모 (인하대학교 조선해양공학과)
  • Received : 2009.12.11
  • Accepted : 2010.10.18
  • Published : 2010.12.20
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Abstract

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.

Keywords

References

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