파랑하중에 의한 Steel Catenary Riser 피로손상 평가 방법의 비교검토

• Published in: 大韓造船學會 論文集 Vol. 52; no. 3; pp. 222 - 235
• Main Authors: 이정대(Jeong-Dae Lee), 이성제(Sung-Je Lee), 장창환(Chang-Hwan Jang), 전석희(Seock-Hee Jun), 오영태(Yeong-Tae Oh)
• Format: Journal Article
• Language: Korean
• Published: 대한조선학회 2015
• Subjects: 조선공학; SCR(스틸 카테너리 라이저); Rain-flow counting(레인플로우 카운팅); Spectral response analysis(스팩트럴 응답해석); Regular wave scatter diagram(규칙파 산포도)
• ISSN: 1225-1143

The purpose of this study is to suggest guidelines for riser fatigue analysis in terms of selection of reasonable analysis method. Three analysis methods (spectral, regular wave, rain-flow counting) are introduced and compared. As the riser systems give non-linear response, the time-domain analysis method is more preferred than frequency-domain analysis method. The spectral fatigue analysis method, however, is still useful for identifying fatigue prone areas. Once stress RAO is established, fatigue damage can be calculated very quickly. The regular wave method and the rain-flow counting method are more time consuming but give more exact results compare to spectral method. In case of regular wave method, a set of regular waves which represent random sea states is considered for dynamic analysis. The rain-flow counting method is the most intuitive and exact method because it refers time history stresses containing most of non-linear effects of the riser system. However, it is not common for early design stage to use rain-flow counting method because of its high cost. In this study, it was confirmed that the regular wave method is the most cost effective way in specific cases. However, if the system is highly non-linear, it seems that the regular wave method gives less accurate results than rain-flow counting method. Therefore, it is imperative that the engineers select appropriate analysis method based on design stage and given engineering period. This paper also discusses the theoretical background of each calculation method and hydrodynamic aspects of marine riser systems. A steel catenary riser (SCR) line on FPSO was considered and marine dynamic program (OrcaFlex) was used for static and dynamic analysis.