A monitoring method of hull structural bending and torsional moment

Abstract

The online identification of wave bending and torsional moment can be used for hull structural safety monitoring, that is, identifying the wave bending and torsional moment of the key cross section of the hull structure, comparing it to the threshold of the bending and torsional moment of the cross section, and finally evaluating the safety of the hull structure online. Therefore, the premise of the aforementioned structural safety monitoring is to accurately identify wave bending and torsional moments. For hull structures without large openings, a stable and high-precision method for identifying the wave bending moment is proposed, in which the position where the long baseline strain gauge (LBSG) installed is optimised using C-optimal and D-optimal design methods, and the mathematical model of the proposed method is established using a full-ship finite element simulation. The accuracy of the method for identifying the wave bending moment was verified using several numerical examples and the on-site monitoring of a large semi-submersible vessel. The results of the numerical simulations and onsite monitoring showed that the method for identifying the bending moment has high accuracy. For hull structures with large openings, a joint dual-section monitoring method (JDSMM) is proposed, in which two adjacent cross sections of the hull structure are monitored simultaneously; the vertical and horizontal bending moments, free torsional moment, and bimoment of the two cross sections being monitored are first identified, and then the bending and torsional moments of the middle section are obtained. The accuracy of the JDSMM was verified using several time-domain numerical examples. The results of the numerical simulations indicated that the JDSMM can accurately identify wave bending and torsional moment.