Development of Safety Criteria as to Installation and Retrieval Operations of Self-Elevating Platform

Research Project

Project/Area Number	61850078
Research Category	Grant-in-Aid for Developmental Scientific Research
Allocation Type	Single-year Grants
Research Field	船舶構造・建造
Research Institution	HIROSHIMA UNIVERSITY
Principal Investigator	TAMEHIRO Masayuki Hiroshima University, Faculty of Engineering, Professor, 工学部, 教授 (70155274)
Co-Investigator(Kenkyū-buntansha)	KATAYAMA Susumu Japan Drilling Co.,Ltd., Project Team of Planning and Construction of New Drilli, 企画開発部, 副部長片山正敏三菱重工業(株), 広島研究所・海洋土木研究室, 主査 YOSHIDA Koichiro Tokyo University, Faculty of Engineering, Porfessor, 工学部, 教授 (90010694) FUJIKUBO Masahiko Hiroshima University, Faculty of Engineering, Research assistant, 工学部, 助手 (30156848) NOBUKAWA Hisashi Hiroshima University, Faculty of Engineering, Assistant Professor, 工学部, 助教授 (60034344) KATAYAMA Masatoshi Mitubishi Heavy Industries, Ltd., Hiroshima Laboratory, Assistant chief research 肥後靖広島大学, 工学部, 助手 (20156582)
Project Period (FY)	1986 – 1987
Project Status	Completed (Fiscal Year 1987)
Budget Amount *help	¥5,000,000 (Direct Cost: ¥5,000,000) Fiscal Year 1987: ¥1,100,000 (Direct Cost: ¥1,100,000) Fiscal Year 1986: ¥3,900,000 (Direct Cost: ¥3,900,000)
Keywords	Self-elecvating platform / Jack-up rig / Impact load / Stiffness of sea bottom / Impact bending moment / Safety criteria / モード解析法 / 着離底作業 / 安全性評価基準 / 衝撃力 / 摩擦力
Research Abstract	In this project, experiments on a model platform subjected to impact loads from bottom were carried out in regular waves. Theoretical analyses in time domain were also performed using newly developed analytical model where a main structure is treated as a rigid body and legs as elastic ones. From the both results on model platform, the good applicability of the anlytical model was made clear. simultaneously, the following basic characteristics of the behavior of plat- form, vertical impact forces on leg-end and bending moments on leg-top at colli- sion were obtained; (1) vertical impact loads on weather side are much larger than those on lee side. (2) The legs on weather side are first subjected to vertical impact loads, and secondary to bending moments resulting from pitching rotation and acceleration of platform to lee side due to vertical impact loads. (3) Vertical impact loads are approximately proportional to the square root of bottom stiffness. Bending moment on leg-top are not much influenced by bottom stiffness. (4) Vertical impact loads can be accurately estimated by simplified calculation based on energy concept, which means the decrease of kinematic and potential energy of platfgorm before collision are absorbed by soil. (5) Vertical impact loads become maximum near the resonance wave period of roll/pitch motion of platform. The response of the proto-type platform at collision are also analyzed, and it becomes clear that vertical impact loads have more effects for the structural safety of jacking unit comparing with bending moment on leg-top. Finally, the safgety criteria for installation and retrieval operation of platform based on an allowable strength of jacking pinion is presented in the form of critical wave height.