부산대학교 도서관

Tension leg platform (TLP) is one of promising production systems for deep offshore oil fields. TLP has three major components consisting of upper construction installing production equipments, foundations on the seabed and tethers connecting the former two components. Therefore, the tether, installed in seawater, must have high tensile and fatigue strength. For a steel pipe tether with threaded connection, heat treatment for high tensile strength and upset at pipe end for high fatigue life of connection are required. When a pipe with upset is heated by induction heating, it is not so easy to get uniform heating temperature, since induction heating has electro-magnetic edge effect at discontinuous shape, and the effect causes distributed Joule heat generation. For uniform heating of tether pipe with upset, optimal control procedures, composing of forward analysis using finite element method and regression analysis and of inverse analysis using nonlinear programming, are presented. It is found that the control procedures are effective to get optimal heating conditions, since preheating temperature distribution and heating current pattern can be almost systematically obtained for much complicated shape of pipe with upset.