A new interpretation for the non-stationary behavior of offshore floating structures under complex environmental conditions

With the increasing operational water depth, the non-stationary behavior of offshore floating structures has attracted significant attention. However, current detection methods for this behavior rely heavily on subjective judgment, limiting the understanding of motion mechanisms under non-stationary conditions due to the complexity of the operating environment. This paper proposes an algorithm for detecting the non-stationary behavior, emphasizing its impact on the behavior of offshore floating structures. The main contributions of this paper include (1) the development of an algorithm for detecting non-stationary behavior by constructing pseudo-distributions of motion responses using adaptive bootstrapping technology, thereby linking these pseudo-distributions to engineering intuition, and (2) the analysis of factors influencing non-stationary behavior using dimensionless analysis, as well as the exploration of the effects of marine environments and ancillary structures on structural non-stationary behavior. To demonstrate the correctness of the proposed algorithm, harmonic signals were first used to investigate the influencing factors, with the results compared to traditional methods. The numerical results demonstrate that the proposed algorithm effectively detects non-stationary behavior while being less impacted by timescale, sampling frequency, and environmental noise. Furthermore, the effects of marine environments, second-order wave forces, and ancillary structural failures on the non-stationary behavior were examined through both numerical and physical model experiments using a semi-submersible platform. The findings indicate that the proposed algorithm successfully detects non-stationary behavior and offers valuable insights for engineering applications, including assessing changes in marine environments and the integrity of mooring systems.