# Multidisciplinary Design Optimization of Life Cycle Benefit of Trimarans Using Monte Carlo Method

9-2018

Dissertation

## Degree Name

Doctor of Philosophy (PhD)

## Department

Mechanical and Civil Engineering

Hamid Hefazi

Prasanta. K. Sahoo

Ju Zhang

Munevver Subasi

## Abstract

This thesis presents a methodology for multidisciplinary design and optimization (MDO) of the life cycle benefit (LCB) of trimarans. Unlike naval vessels which have a robust fire power and other capabilities which are very difficult to be quantified, the essence of a commercial ship’s construction and operation is an investment. The ship owners must consider the benefits accruing from lifelong development/deployment of a commercial vessel, taking in to account the construction time, interest rate, cost of operation, maintenance, drydocking, annual revenue, etc. Whether or not a ship design has outstanding economic potential, depends on only one standard value in the opinion of the shipowner which is the life cycle benefit (LCB). It is envisaged that an optimal design, must lead to substantial benefits accruing over the life-span of a vessel. In this thesis, the LCB of a notional trimaran is considered as the system level objective function for multidisciplinary design optimization. There are two major subsystems to calculate the trimarans’s performances in the MDO program. One of them is the resistance estimation subsystem. This subsystem considering the total resistance of high-speed trimarans equals to the combination of the viscous and wave-making resistance. The viscous resistance of trimaran equals to the product of the form factor (1+k) and the frictional resistance coefficient calculated by the ITTC 1957 friction correlation line. The wave-making resistance is based on the Michill’s equation modified by Yeung in 2004. He comsidered the trimarans’wave-making resistance equals to the summation of the individual hull form’s wave-making resistance and the interferences wave-making resistance. The structural weight estimation subsystem is based on the Lloyd’s Register classification rules. The total weight equals to the combination of mainhull, sidehulls and the cross decks’ weight. The value of weight provided by this subsystem is absolutely obey the regulation. The structural strength is completely satisfied. In the end, the optimization algorithm applies the Monte Carlo Method (MCM) to achieve an optimal design. This dissertation attempts to only investigate the application of the method in the concept design stage. Results indicate that the design variable considered have a dramatic influence on the life cycle benefit, rendering some designs highly profitable and some unprofitable over the entire service life of the trimaran.

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