Abstract
Response-conditioning wave techniques are a rational way to link wave excitation environments with return-period extreme loading responses. By retaining the wave excitation which leads to a design response, these techniques can also define extreme combined loading scenarios. For complex or novel hull forms, combined loading may be relevant for evaluating structural reliability or adequacy. But using combined loading scenarios as inputs to high-fidelity structural or dynamic modeling tools implies that such load scenarios are realistic for the defined return-period. This paper investigates three response-conditioning wave techniques: a modified Equivalent Design Wave method, a modified Conditioned Random Response Wave method, and the Design Loads Generator, to evaluate how well they reproduce combined loading statistics for a 1000-hr return-period as compared to stochastic brute-force simulations. The investigation is carried out for extreme combined loading scenarios on a 110 m trimaran hull. The Design Loads Generator produces the most realistic extreme combined loading statistics as compared to the brute-force approach with a significant reduction in computation time based on combined load conditional probability density functions, cumulative density functions, and individual stochastic load vectors.
Highlights
To ensure adequate lifetime structural performance, many classification societies suggest using combined loading scenarios as possible loading conditions to test a vessel’s structural compliance, see, e.g. Lloyd’s Register (2017), Bureau Veritas (2018a), DNV-GL (2018), Bureau Veritas (2017, 2018b), American Bureau of Shipping (2016, 2005), IACS (2018), Horn et al (2013), ClassNK (2013) and Lloyd’s Register (2014)
Based on this ensemble of extreme load values which follow the Gaussian extreme value distribution (EVD), an ensemble of Equivalent Design Waves and Conditioned Random Response Waves can be constructed which excite these load values. This approach distinguishes the modified-EDW (m-EDW) and modified-CRRW (m-CRRW) approaches used in this investigation. This modification allows a direct comparison between the m-EDW, m-CRRW, Design Loads Generator (DLG), and Monte Carlo Simulations (MCS) approaches for the different combined loading scenarios considered, as all Response-Conditioning Wave Techniques (RCWTs) construct ensembles of waves leading to distributions of extreme load responses
This paper investigated 1000-h extreme combined loading statistics on a trimaran generated by three response-conditioning wave techniques: a modified Equivalent Design Wave (m-EDW) approach, modified Conditioned Random Response Wave (m-CRRW) approach, and the Design Loads Generator (DLG), and compared the results with load statistics from brute-force Monte Carlo Simulations (MCS)
Summary
To ensure adequate lifetime structural performance, many classification societies suggest using combined loading scenarios as possible loading conditions to test a vessel’s structural compliance, see, e.g. Lloyd’s Register (2017), Bureau Veritas (2018a), DNV-GL (2018), Bureau Veritas (2017, 2018b), American Bureau of Shipping (2016, 2005), IACS (2018), Horn et al (2013), ClassNK (2013) and Lloyd’s Register (2014). Multiple Response-Conditioning Wave Techniques (RCWTs), such as the Equivalent Design Wave (EDW), Conditioned Random Response Wave (CRRW), and the Design Loads Generator (DLG), have been developed to construct wave profiles expected to excite specific loading scenarios These methods are significantly more computationally efficient than MCS because they do not simulate the entire return-period to construct waves that excite return-period extreme load responses. Such efficiency and simplicity have made these methods popular because they can be implemented by engineers to define lifetime combined loading scenarios. Though, that the processes employed in this investigation and conclusions would be similar for nonlinear, non-Gaussian models
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