Stress field reconstruction method for cargo hold structures of large ore carriers under combined global−local loads

The discontinuities in the large opening design and the non-uniform distribution of high-density cargo in the cargo hold section of large ore carriers pose significant challenges to hull structural safety. Therefore, it is essential to enhance the structural health monitoring system's ability to perceive and adapt to the structural safety status of ore carriers.

A real-time reconstruction method for the hull stress field under the combined action of global and local loads was proposed. A refined finite element model of the cargo hold section of a large ore carrier was selected as the research object, ensuring that the structural characteristics of the hull were represented comprehensively. The combined action of global-local and time-varying-static loads was comprehensively considered, and complex load conditions that closely mimicked the actual ship navigation environment were constructed. Based on the load forms and hull structural response characteristics, a monitoring point layout scheme and a unit load basis with various forms were designed. Monitoring points were positioned on the side shell plates, main decks, bottom girders and longitudinal bulkheads. Using the multi-source load superposition principle and limited measurement data, the real-time reconstruction of the structural stress field in the cargo hold section of the large ore carrier was achieved. Furthermore, the influence of dynamic load amplitude and periodic characteristics on the accuracy of stress reconstruction was analyzed.

The results showed that the method exhibited good prediction accuracy under typical wave conditions, with the prediction results accurately reflecting the spatiotemporal inhomogeneity of the hull's structural response. Over 97% of the reconstructed data points had a relative error rate within 5%, and the maximum relative error rate was approximately 10%. The reconstruction error increased with the load amplitude but remained highly accurate within the standard design value range, with the error always less than 1.0 MPa. The variation in load period had a more significant impact on the reconstruction results: the reconstruction error increased as the load period decreased. Within the common wave period range, the maximum absolute error of this method did not exceed 6 MPa, which could meet the practical engineering requirements to a certain extent.

The proposed methodology demonstrates strong engineering applicability for the structural stress field reconstruction of large ore carriers. It can effectively support hull structural health monitoring and residual life assessment.