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A Study on Load-carrying Capacity Design Criteria of Jack-up Rigs under Environmental Loading Conditions

환경하중을 고려한 Jack-up rig의 내하력 설계 기준에 대한 연구

  • Park, Joo Shin (Ship and Offshore Research Institute, Samsung Heavy Industry Co. Ltd.) ;
  • Ha, Yeon Chul (The Korea Ship and Offshore Research Institute, Pusan National University) ;
  • Seo, Jung Kwan (The Korea Ship and Offshore Research Institute, Pusan National University)
  • 박주신 (삼성중공업 조선해양연구소) ;
  • 하연철 (부산대학교 선박해양플랜트기술연구원) ;
  • 서정관 (부산대학교 선박해양플랜트기술연구원)
  • Received : 2019.12.18
  • Accepted : 2020.02.25
  • Published : 2020.02.28

Abstract

Jack-up drilling rigs are widely used in the offshore oil and gas exploration industry. Although originally designed for use in shallow waters, trends in the energy industry have led to a growing demand for their use in deep sea and harsh environmental conditions. To extend the operating range of jack-up units, their design must be based on reliable analysis while eliminating excessive conservatism. In current industrial practice, jack-up drilling rigs are designed using the working(or allowable) stress design (WSD) method. Recently, classifications have been developed for specific regulations based on the load and resistance factor design (LRFD) method, which emphasises the reliability of the methods. This statistical method utilises the concept of limit state design and uses factored loads and resistance factors to account for uncertainly in the loads and computed strength of the leg components in a jack-up drilling rig. The key differences between the LRFD method and the WSD method must be identified to enable appropriate use of the LRFD method for designing jack-up rigs. Therefore, the aim of this study is to compare and quantitatively investigate the differences between actual jack-up lattice leg structures, which are designed by the WSD and LRFD methods, and subject to different environmental load-to-dead-load ratios, thereby delineating the load-to-capacity ratios of rigs designed using theses methods under these different enviromental conditions. The comparative results are significantly advantageous in the leg design of jack-up rigs, and determine that the jack-up rigs designed using the WSD and LRFD methods with UC values differ by approximately 31 % with respect to the API-RP code basis. It can be observed that the LRFD design method is more advantageous to structure optimization compared to the WSD method.

잭업 드릴링 리그 (Jack-up drilling rigs)는 해양자원개발 분야 중 석유 및 가스 탐사 산업에서 널리 사용되는 대표적인 해양구조물이다. 이러한 잭업 구조물은 대체로 얕은 수심에서 사용하도록 설계되었지만 에너지 산업의 추세로 대수심 및 가혹한 환경 조건에서도 사용이 가능한 설계가 요구되고 있다. 이러한 잭업구조물의 운영환경 확장에 따라서 과도한 설계를 최소화하고 신뢰성 반영된 설계법이 요구되었다. 기존의 해양구조물 산업에서 잭업 구조물의 설계법은 사용(혹은 허용)응력 설계 (WSD: Working (or Allowable) Stress Design) 방법을 사용하여 설계가 되고 있었다. 이러한 설치환경변화에 따라서 충분한 신뢰성을 확보가 가능한 하중 및 저항계수 (LRFD: Load and Resistance Factored Design) 방법을 최근 개발되었고 규정화가 되었다. LRFD 방법은 통계적 기반으로 한 한계상태설계 개념으로 잭업구조물의 구성구조부재의 하중과 전산수치해석을 이용한 강도의 불확성을 하중 및 저항 계수로 표현하는 설계법이다. 개발된 LRFD 방법은 실제 잭업구조물 설계의 적합성 판단을 위하여 기존의 WSD 방법과의 정량적인 비교 분석이 반드시 필요하다. 따라서 본 연구는 기존의 WSD와 LRFD 방법으로 이용하여 실 잭업 구조물의 레그 구조를 대상으로 상용유한요소해석코드를 이용하여 정량적인 UC (Unity Check)값을 기반으로 비교 분석하였다. 분석된 결과로 다양한 환경하중조건 하에서 LRFD 방법을 사용하여 잭업구조물의 레그(Leg) 설계에서 상당히 합리적인 UC 값을 가지고 기존 대표적인 WSD기법 중에 하나인 API-RP 코드 대비 약 31 % 차이가 분석되었다. 따라서 LRFD 설계 방법이 WSD 방법에 비해 구조 최적화 및 합리적인 설계에 더 유리하다는 것을 확인할 수 있었다.

Keywords

References

  1. American Concrete Institute (ACI) (1995), Building code requirements for reinforced concrete.
  2. American Institute of Steel Construction (AISC) (1989), Specification for structural steel buildings, Allowable stress design and plastic design.
  3. American Petroleum Institute (API) (1993), Recommended practice for planning, designing and constructing fixed offshore platforms-Load and Resistance Factor Design.
  4. ASME(2017), International code, Boiler and Pressure Vessel, Sec. Powered Boilers and Sec. Pressure Vessels.
  5. DNV-RP-C104(2011), Self Elevating Units, Recommended Practice, Det Norske Veritas, Oslo.
  6. ISO(2016), Petroleum and natural gas industries, Site specific assessment of mobile offshore units, Part 1, Jack-ups (2nd edition).
  7. Lewis, D. R. and J. Brekke(2006), Site assessment for jack-ups in Gulf of Mexico, 2006 Offshore Technology Conference, Houston, Texas, USA.
  8. Ma, K. Y., J. H. Kim, J. S. Park, J. M. Lee, and J. K. Seo(2019), A study on collision strength assessment of a jack-up rig with attendant vessel, International Journal of Naval Architecture and Ocean Engineering (doi.org/10.1016/j.ijnaoe.2019.10.002).
  9. Morandi, A. C., P. A. Frieze, M. Birkinshaw, D. Smith, and A. Dixon(1999), Jack-up and jacket platforms: a comparison of system strength and reliability, Marine Structures, Vol. 12, pp. 311-325. https://doi.org/10.1016/S0951-8339(99)00019-2
  10. Paik, J. K. and A. K. Thayamballi(2007), Ship-Shaped Installations: design, building, and operation, Cambrige Univesity Press, UK.
  11. SACS user's manual(2016), Introduction of linear and nonlinear analysis and it's application of shell modeling Vol. 2, pp. 50-65.
  12. SNAME RP 5A-5(2002), Guidelines for Site Specific Assessment of Mobile Jack-Up Units, Technical & Research Bulletin 5-5A, The Society of Naval Architects and Marine Engineers, Offshore Committee.
  13. Tan, X. M. and J. Lu(2003), Structural behavior prediction for jack-up units during jacking operations, Computer and Structures, Vol. 81, pp. 2409-2416. https://doi.org/10.1016/S0045-7949(03)00299-2
  14. Williams, M. S., R. S. G. Thompson, G. T. Houlsby(1999), A parametric study of the non-linear dynamic behavior of an offshore jack-up unit, Engineering Structures, Vol. 21, pp. 383-394. https://doi.org/10.1016/S0141-0296(97)00222-8