Structural Stress Monitoring and FEM Analysis of the Cutting Operation of the Main Bracket of A Semi-Submersible Platform

• Published in: China ocean engineering Vol. 33; no. 6; pp. 649 - 659
• Main Authors: Kou, Yu-feng, Yang, Jian-min, Xu, Sheng-wen, Peng, Tao, Liu, Jun, Wu, Zhuo-wei
• Format: Journal Article
• Language: English
• Published: Nanjing Chinese Ocean Engineering Society 01.12.2019; Springer Nature B.V
• Subjects: Brackets; Calibration; Coastal Sciences; Columns (structural); Condition monitoring; Cutting; Cuttings; Engineering; Finite element method; Fluid- and Aerodynamics; Initial stresses; Marine & Freshwater Sciences; Mathematical analysis; Mathematical models; Monitoring; Numerical and Computational Physics; Oceanography; Offshore Engineering; Pontoons; Semisubmersible platforms; Simulation; Spots; Stress; Submersible platforms; Submersibles; cutting operation; main bracket; field stress monitoring; FEM analysis; semi-submersible platform
• ISSN: 0890-5487; 2191-8945
• DOI: 10.1007/s13344-019-0062-0

For a semi-submersible platform in repair, the eight old main brackets which connect columns with pontoons need to be replaced by new ones. In order to ensure the safety of the cutting operation of the old main bracket and calculate the initial stress condition of new main bracket, the structural stress monitoring of eight key spots is carried out, and then the calibrated finite element model is established according to the field monitoring results. Before cutting the main bracket and all associated structures, eight rectangular rosettes were installed, and a tailored cutting scheme was proposed to release the initial stress, in which the main bracket and associated column and pontoon plates were partly cut. During the cutting procedure, the strains of the monitoring spots were measured, and then the structural stress of the monitored spots were obtained. The stress variation characteristics at different spots during the initial cutting operation were shown and the initial stress condition of the monitored spots was figured out. The loading and support conditions of the semi-submersible platform were calibrated based on the measured initial stress condition, which made the finite element model more credible. The stress condition with the main bracket and associated structures being entirely cut out is analyzed by the Finite Element Method (FEM), which demonstrates the cutting operation to be safe and feasible. In addition, the calibrated finite element model can be used to calculate the initial stress condition of the new main bracket, which will be very helpful for the long-term stress monitoring on the main bracket.