Description
ABSTRACT
A method for optimizing of hull forms with respect to their hydrodynamic performance in calm and rough water is presented. The method is based on an initial optimization of a parent hull form for tugboat and the improvement of the resulting optimum hull form for calm water resistance. In the first part of the method, variant hull forms differing from a parent in the main dimensions and/or in one or more hull form parameters such as CWP, LCF, CB, LCB, KB, CP are automatically generated and their tugboat qualities evaluated. When appropriate ranges for the principal characteristics and parameters of the hull form under investigation are prescribed, a formal optimization procedure is used to obtain the variant with the best tugboat behaviour. The weighted sum of the resonant values of selected tugboat operating in Onne port Harcourt responses for a number of tugboat speeds and headings in regular waves forms the objective function. Hooke & Jeeves Algorithm is used to accomplish the optimization. The procedure results in a set of trends regarding the proposed variations of the selected hull form parameters, within the specified constraints. These trends are then applied on the parent hull to derive an optimized hull form with fair lines. Subsequently this hull form can be locally modified to improve its calm water resistance or, as it should be done, its propulsion characteristics.
The applicability of the method is demonstrated in two cases: a conventional reefer tugboat and a naval destroyer. Scaled models of the parent and the optimized hull forms have been tested for calm water resistance and tugboat. In both cases the validity of the methodology is demonstrated.
TABLE OF CONTENTS
COVER PAGE
TITLE PAGE
APPROVAL PAGE
DEDICATION
ACKNOWLEDGEMENT
ABSTRACT
CHAPTER ONE
1.0 INTRODUCTION
1.1 BACKGROUND OF THE PROJECT
- AIM OF THE PROJECT
- SIGNIFICANCE OF THE PROJECT
- SCOPE OF THE PROJECT
CHAPTER TWO
LITERATURE REVIEW
- REVIEW OF RELATED STUDIES
- HYDRODYNAMIC OPTIMIZATION IN TUGBOAT DESIGN
CHAPTER THREE
- METHODOLOGY
3.1 DESCRIPTION OF THE METHOD
3.2 HULL FORM DESCRIPTION
3.3 HULL FORM VARIANTS
3.4 ANALYTICAL TOOLS FOR SEAKEEPING AND RESISTANCE CALCULATIONS
3.5 THE FIGURE OF MERIT
3.6 THE OPTIMIZATION PROBLEM
3.7 APPLICATION OF THE METHOD
CHAPTER FOUR
4.1 THE REEFER TUGBOAT CASE
4.2 THE DESTROYER CASE
CHAPTER FIVE
5.1 DISCUSSION AND CONCLUSIONS
REFERENCES
CHAPTER ONE
1.0 INTRODUCTION
1.1 BACKGROUND OF THE STUDY
In general, tugboats are used to convey many kinds of surface vessels, including unactuated vessels, such as barge ships and offshore structures. This requires an adequate model for tugboat operation to precisely take into account surge, sway, and yaw motions. We present an optimization method of tugboat operation. Fifty years after the development of the first practical strip theory by Korvin- Kroukovsky (1955), analytical seakeeping prediction methods are widely used for the evaluation of the seakeeping qualities of tugboats. Twenty-five years ago, Bales (1980) published a paper treating the optimization of the seakeeping performance of Destroyer-type hull forms, based on the analytical predictions. By that time the analytical tools available to the profession were considered reliable enough to be used for optimization purposes, in contrast to seakeeping experiments which cannot be practically used for the same purpose, due to excessive time and cost involved. Bales used analytical results to derive a regression formula correlating the performance of this type of ships in head seas and at various speeds to certain empirically selected hull form parameters.
Grigoropoulos and Loukakis (1988) presented a new method for developing hull forms with superior seakeeping qualities. The new method, described in Grigoropoulos (1989), was used for the analytical development of an optimized hull form for a tugboat. Models of both the parent and the optimum hull forms were tested and the analytical optimization procedure was experimentally verified.
1.2 AIM AND OBJECTIVES OF THE STUDY
The main aim of this study is to carry out the optimization of hull forms with respect to their hydrodynamic performance of a tugboat operating in Onne Portharcourt in calm and rough water.
1.3 SCOPE OF THE STUDY
In this paper, the aforementioned method is further extended and improved to take advantage of modern computer-aided design (CAD) and Computational Fluid Dynamics (CFD) tools, currently available to the profession. Utilizing these tools, the hull form of a modern destroyer was optimized with respect to both its performance in calm water and in waves. Model tests with the parent and the optimized hull forms verified the efficiency of the optimization methodology. Furthermore, additional calculations for the reefer vessel have been carried out, extending the optimization gains.
1.4 SIGNIFICANCE OF THE STUDY
This study will serve as a means of improving tugboat calm water resistance thereby improving the operation of the tugboat.
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