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An interim model to predict maximum wave heights of low speed displacement mono-hull ships Sireli, Eyup Mete

Abstract

Hull shapes of ships are highly complex. A formula giving ship-generated maximum wave heights should contain all the main characteristics of ship hulls. Nevertheless, having a universal formula for all ship types is practically not possible, therefore different maximum wave height formulas for particular ships or ship families have been derived by previous researchers. This requires tedious work for each ship family, and the result is usually a complex regression formula whose parameters can only be understood by a naval architect. To avoid these problems, an interim model is proposed in this thesis, whose results are to be corrected by a simple correction formula for a particular ship family. By this way, the number of parameters in the formula is reduced significantly, which also reduces the time and money to derive the formula and makes it understandable for users lacking naval architectural background. The interim model is based on the results of experiments of three barge-like models of 1 m in length, which are constructed in three different beam sizes and three different draft levels, which increases the number of models virtually to nine. The experiments were conducted at BC Research Ocean Engineering Centre's towing tank facility. The models were towed at three different ship length Froude numbers. Measurements from three wave probes positioned at different proximities were used to investigate the effect of distance from sailing line (towline). The effects of distance, speed and shape on wave height are defined in separate functions, which are then combined in the maximum wave height formula. To derive the functions, regression analysis is used. The results of the interim model are compared to the experimental data of three ferries in Nece et al.'s study (1986) with the formulas of Sorensen and Weggel (1984) and the Ship Wave Committee (1976). The interim model gives closer results to the measured data than the two formulas. Still, correction formulas are provided for three ferries. Then, the interim model is compared to the experimental data of a ship model of 1.146 m in length towed at BC Research Ocean Engineering Centre. Interestingly, the interim model did not require a correction formula for the ship model. In addition to the wave height analysis, the adequacy of the theoretical maximum wave period formula is also investigated as a secondary objective. It was observed that the theoretical wave period formula provides good results and requires no correction in practical applications.

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