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Closely spaced cylinder arrays are widely used in offshore platform designs. When subject to random waves and currents, their interactive response behavior is very complicated and perhaps beyond the ability of direct analytical formulations to model their motions. In this study extremal statistics methods were utilized to analyze model basin data that investigated the response behavior of in-line paired and triple deep-water cylinder arrays. The cylinder models used in the model basin experiments were constructed with an ABS outer plastic shell that surrounded an inner steel wire core that could be pretensioned. The cylinder model diameter ratio of the outer shell to steel wire was 4.25 with a slenderness ratio of approximately 1300. The cylinder arrays were pretensioned on the top side and were tested varying pitch to diameter ratios of 3.0, 4.4, and 8.75. The random sea states were simulated using a JONSWAP spectrum. The response time series were investigated using generalized extreme value (GEV) distributions that were fitted to the block maxima that represented the maximum in-line relative displacement between two adjacent tendons. The most appropriate models were selected by comparing their goodness of fit via the Anderson-Darling (AD) test criterion with special attentions paid to their performance in fitting the upper tail of the distribution. The selected models were then used to predict threshold-crossing probabilities of the cylinder array relative response behavior. Both tabular and graphical interpretations of the findings are presented and discussed.

A general approach that utilizes both spectral and extremal statistical methods are utilized to investigate the time series of flow-induced response behavior of a flexible horizontal cylinder subject to both random waves and constant current conditions. The cylinder model was 29 m long and had a slenderness ratio of approximately 760. The random waves were generated using a JONSWAP wave amplitude spectrum. In addition, for some tests, the cylinder was towed at two different speeds to simulate the combined loading of random waves and constant current conditions. The data were initially analyzed using standard spectral analyses to interpret the cylinder's flow-induced response behavior and relate the findings to traditional deterministic parameters. Further analyses were performed using a generalized extreme value (GEV) distribution procedure that involved dividing the time series into blocks and fitting the block maxima of the extreme values in the measured response time series data. The Anderson-Darling (AD) test criterion and quantile plots were then used to assess whether the GEV distribution provides a satisfactory fit to the data capturing the statistical characteristics in the flexible cylinder's flow-induced response behavior, which was stochastic in nature. For the data set analyzed, the extremal GEV methodology presented was observed to provide excellent results for the random wave cases and moderately good-to-good results for the combined random wave and constant current cases.

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