This paper examines the performance of 6 stiffened ship panel designs in different operational profiles. The main question of interest is: which sea states will lead to the worst panel performances in terms of reliability? As stiffened panel collapse is governed by combined lateral and in-plane loading effects (non-linear functions of the wave environment) this is not a simple problem and does not easily fit into the confines of traditional analyses. Interesting sea states for stiffened panel collapse are identified by a low-order design contour method which uses order statistics and extreme value theory. The resulting multimodal design contours pinpoint areas of interest and the panel performances are confirmed using a higher-order reliability analysis: the non-linear Design Loads Generator process. Such results have impact for creating and interpreting environmental and design contours, as well as assumptions about which operational profiles will lead to the worst system responses.

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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.

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With harshening ocean environments and the push to extend the service life of vessels and platforms, lifetime structural design performance is an increasingly important factor to differentiate between design options. But despite many advancements in structural modeling, reliability analysis may still be too time consuming and computationally expensive to be employed for local design choices. Reliability analysis for stiffened ship panels is additionally complicated as the collapse mechanism is due to combined stochastic lateral and in-plane loading effects [1]. This paper employs the non-linear Design Loads Generator (NL-DLG) process [2] to efficiently estimate the probability of stiffened ship panel collapse while retaining the wave profiles which lead to lifetime responses. This information allows a direct comparison between panel options and highlights critical panel parameters which are strongly related to design robustness. The resulting ensemble of short NL-DLG wave profiles lead to similar statistical characteristics of the panel designs as do brute-force Monte Carlo Simulations, but reduce the required simulation time by a factor of nearly 87,000 for the same number of simulations. These directed wave profiles offer naval architects the opportunity to efficiently examine rare complex structural responses by linking high-fidelity structural and hydrodynamic models. The potential of the NL-DLG process is that relevant information about complex marine structures, even those with limit surfaces excited by combined non-Gaussian loading, can be obtained efficiently and in earlier stages of the design process via low-order surrogate models.@en