Trimaran Structural Weight Optimization Based on Classification Rules

Abstract

Structural optimization is one of the important aspects of the overall ship design process. A number of advanced optimization tools are available. As these tools require large computational resources, they are not suitable for use in the preliminary design stages, when many important aspects of the design, such as overall dimensions and hull configurations, are determined. This article describes the development of an efficient structural weight optimization method for a trimaran hull form within the governing rules and regulations of the classification society. The method is particularly useful in the early design stage because of its simplicity. Two trimaran hull forms (HSTT-180 and TriFerry) are selected and optimized using the multi-island genetic algorithm optimization process. The weight optimization process achieved a weight reduction for HSTT-180 and TriFerry of about 32.85% and 8.95%, respectively. Furthermore, in both cases, optimum structural weights were obtained with smaller values of main-hull and side-hull stiffener spacing but higher values of main-hull frame spacing. Results obtained indicate that the structural weight of trimaran designs, such as those referenced here, can be substantially reduced by advanced optimization methods. 1. Introduction High-speed ships are of increasing interest for diverse applications, including military and commercial purposes. Hydrodynamic requirements for many high-speed concepts can only realistically be addressed by multihull designs since multihull ships provide better performance than monohull ships at high speeds. Trimaran hull form vessels, in particular, can offer several favorable characteristics over comparable monohulls, including fuel efficiency and the possibility of superior seakeeping characteristics (Fuentes et al. 2015). Trimarans are designed as Ro-Ro and passenger ships, ferries, containers, and military vessels. Multidisciplinary design and optimization (MDO) of trimarans, particularly at the synthesis design level, is an active area of research (Hefazi et al. 2010, 2011). A major element of the MDO process is the development of a structural optimization subsystem to investigate the impact of variations in vessel configurations on structural design and weight. A number of advanced analysis tools for calculation of structural weight are available. However, these tools require large computational resources and time and as such are not suitable to use in the preliminary design stages. Ironically, that is when many important aspects of the design, such as overall dimensions and hull configurations, are often determined. Therefore, an efficient method for calculation of structural weight, and its integration in an automated optimization process, is highly desirable and is the focus of this article. This approach allows structural weight optimization to be included in determining important principal characteristics of the ship at the early stage of the design.