半潜式平台大肘板局部切割作业的结构应力监测与分析

某半潜式平台立柱与浮箱间的8个大肘板需要在坞修中拆除并更换新的大肘板,通过结构有限元方法可以分析大肘板拆除过程的安全性,但在坞修中平台外部载荷和支撑条件的不确定性为建立精确的有限元模型带来困难。文章针对一处大肘板,提出了一种应力释放局部切割流程和应力监测方案,采用光纤光栅传感器对应力释放过程中大肘板及附近8个关键位置的应变情况进行了实时监测。采用Mises屈服准则计算得到局部切割过程中各测点的相当应力,分析了局部切割过程中不同位置的应力变化特点。分析得到切割前8个关键位置的初始应力状态,为有限元模型提供校核依据,最终获得了经过验证的有限元模型,为进一步研究切割方案安全性和分析新大肘板初始应力状态奠定基础。

Monitor and analysis of structural stress in partial cutting of bracket of a semi-submersible platform

The eight old main brackets in a semi-submersible platform which connect columns with pontoons need be removed and replaced by new ones. It could be determined by Finite Element Analysis (FEA) that whether the operation of removing the old main brackets is safe or not, however, it is difficult to establish an accurate Finite Element Model (FEM) because of the uncertainty of external loading and supporting conditions for the semi-submersible platform in dry dock. A tailored cutting scheme is proposed to release the initial stress of an old main bracket, in which the main bracket and associated column and pontoon plates were partially cut. During the cutting procedure, the strains of 8 monitoring spots are measured by optic fiber grating sensors. The equivalent stress of 8 gauging points is calculated based on the Von Mises yield criterion, and the characteristics of stress variation in different locations is analyzed. The initial structural stress of all gauging points before cutting is obtained to improve the FEM with the calibrated loading and supporting conditions, which will be helpful to evaluate the feasibility of removing all old main brackets and provide the initial stress condition of the new main brackets for long-term stress monitoring.