Thesis
Novel representations for modelling free-form objects under constraints : a parametric modelling tool for computer-aided ship design
- Creator
- Rights statement
- Awarding institution
- University of Strathclyde
- Date of award
- 2021
- Thesis identifier
- T15893
- Person Identifier (Local)
- 201860169
- Qualification Level
- Qualification Name
- Department, School or Faculty
- Abstract
- Digital design of engineering systems, using Computer-Aided Design (CAD) tools for developing and optimising products, has been used in the manufacturing process since 1957, when Patrick Hanratty built the first commercial numerical-control programming system known as PRONTO, while he was working for General Electric. One year later, the French physicist and mathematician Paul de Casteljau invented a system based on the use of Bernstein polynomials, during his employment with the French automobile manufacturer Citro¨en. In 1968, another French engineer named Pierre B´ezier, launched on behalf of the automobile manufacturer Renault the CAD/CAM UNISURF system for surface design, which was fully in use by 1975. The stepping stone of Computer-Aided Ship Design (CASD) was set in 1963, when the Norwegian CAD/CAM software Autokon was first used, developed by Trygve Reenskaug. It was 14 years later when parametric modelling in ship design introduced by Prof. H. Nowacki who pioneered in CASD via coupling form parameters with the then novel technology of B-splines. Since then, Parametric Modellers (PM) play a crucial role in the development and -most importantly- shape optimisation of free-form objects with increased complexity such as ship-hulls, for they have to represent robustly and efficiently every solid object. The purpose of the current work is three-fold: Firstly, it is meant to develop and present the corresponding methodology of two tools: a) an innovative, robust, and cost-efficient parametric modelling tool for container and tanker ship-hulls, which are hull forms of increased complexity. The tool is named TshipPM and is an extension of the work presented in, b) a ship-hull shape optimisation tool based on geometric criteria, namely volume moments up to 2nd order. Secondly, to evaluate the performance of TshipPM by comparing it with a wellestablished, commercial parametric modelling tool, CAESES®1 , opting for its NURBS functionality. Finally, was to provide an easy to follow ”handbook” for developers and users on the development of parametric modelling tools, illustrating as well how a PM can be utilised for the construction of a given ship-hull. The key findings of the current work which also coincide with the main objectives, are: A method of constructing a T-splines-based parametric modelling tool (TshipPM) for complex ship-hull design, the development of which is taking into consideration the detailed characteristics of two different ship-hull types, i.e., tankers and containers. A set of geometric and design constraints imposed to TshipPM to tackle the intricate and complex issue of Geometric Validity, ascertaining the production of valid models for the whole design space the modeller covers. A step-by-step method to remodel (using TshipPM) a great variety of complex hulls with complexity not-higher than that of tankers and containers. The exceptional performance of TshipPM. A comparative study is conducted to evaluate the performance of TshipPM against CAESES, a well-established commercial parametric modeller for ship design. This work is published in the Ocean Engineering2 international journal, titled ”A T-splines-based parametric modeller for computer-aided ship design”. A method for ship-hull shape optimisation with respect to geometric criteria and especially volume moments up to 2nd order, utilising TshipPM and a multiobjective Teaching-Learning-based optimisation tool. This part of the work also stresses the insufficiency of 2nd order moments to perform as complex-shape optimisers. TshipPM is a parametric modelling tool for ship-hull design under geometric and design constraints. It uses as a mathematical representation of surfaces -and to some extend solids- the fairly new technology of T-splines, introduced by Sederberg et al. in 2003, which constitutes a generalisation of NURBS, exhibiting several advantages over the latter. T-splines technology aids towards the development of modellers for complex ship forms, by providing geometrically valid objects with smooth surfaces and increased fairness throughout the model’s surface, and much lower complexity in comparison with PMs employing the standard NURBS technology. TshipPM uses 27 external (or input) parameters to produce the control cage of the ship-hull, 3 of which are global and dimensional, while 24 are non-dimensional and of local nature. It employs Autodesk® T-splines plug-in® v.4.0 for Rhino5® 3D to create the final, smooth T-splines surfaces using as input the control cage created by TshipPM. The PhD thesis consists of 6 Chapters, structured in the following way: The Novelties of the current work and its contribution to the field of parametric modelling in CASD. Chapter 1, after a brief discussion on the historical background of splines, it delivers a comparison between T-splines, the representation underlying TshipPM, and NURBS, the industrial standard in CAD, which is also used in the context of CAESES (§1.1). In addition, it introduces the reader to parametric modelling, reviewing in brief the main advancements in the field (§1.2). Chapter 2, after the necessary introduction to TshipPM’s features and characteristics (§2.1), analyses the structure of TshipPM regarding the parameters involved (§2.2), making the distinction into internal and external, dimensional (or physical) and nondimensional. §2.3 demonstrates the process of creating a ship-hull model, starting from building the control cage along with its link to external parameters, which are used as input for TshipPM, up to its conversion into the resulting ship-hull surface with the aid of T-splines plug-in. Chapter 3, after a brief introduction on the importance of robust PMs (§3.1), defines the constraints encountered in ship-hull design and introduces the reader to the concept of geometric validity, illustrating examples of invalid ship-hull models (§3.2). §3.3 presents the geometric and design constraints imposed to TshipPM to ascertain its robustness as far as the production of geometrically valid models is concerned. In §3.4 we provide an experimental indication of the robustness of TshipPM in its response to strong parameter values variation. Finally, in the last section (§3.5), we present the output of a Monte Carlo sampling of 200,000 ship-hull instances produced by TshipPM for both containers and tankers, and we analyse its output information to determine the design space of the PM, by measuring TshipPM’s flexibility with regards to geometric characteristics, namely volume centroid and moments of inertia. Chapter 4 begins by stressing the need of remodelling a given ship-hull with PMs to use it as basis for optimisation (§4.1), while §4.2 refers to the remodelling evaluation criteria. The remodelling process is thoroughly described in §4.3 using as a case study the MOERI KCS container ship-hull, and aims to the reconstruction of a parent ship-hull CAD model; we use TshipPM for the construction of model’s control cage and we feed it into Rhino5 to create the corresponding surfaces with the aid of the T-splines plug-in. Finally, in §4.4 the evaluation of the remodelled MOERI KVLCC tanker [10] ship-hull is conducted, under a predefined set of criteria, providing feedback to users and developers for any adjustments and their specific locations. The evaluation of MOERI KCS container hull is conducted in Chapter 5. In Chapter 5, TshipPM is compared against CAESES with regards to their outputs against a parent hull, the KCS container ship-hull, which has been extensively used by the research community for CAD and Computational Fluid Dynamics (CFD) benchmarking purposes. The comparison criteria are described in §5.1. §5.2 presents the basic characteristics of the CAESES parametric modelling tool, as well as a description of the physical (or dimensional) parameters CAESES uses to remodel KCS ship-hull and the corresponding external non-dimensional parameters, while §5.3 refers to the common external parameters both PMs use. Finally, in §§5.4 - 5.8 the comparison of both PMs is conducted. Lastly, Chapter 6 presents an in-house, C#-built, shape-optimisation tool using TshipPM and an adjusted to the needs of the current work Multi-objective TeachingLearning-based Optimisation (MO-TLBO) method. TshipPM MO-TLBO is optimising the shape of a given hull (MOERI KCS) against a set of ship-design criteria, and especially volume moments up to 2nd order. After the required introduction to the chapter (§6.1), a brief presentation of the TLBO method is conducted (§6.2). The set of the objective functions against which the optimisation is conducted is provided in §6.3, while in §6.4 the method of building TshipPM MO-TLBO, its features and functionality are presented in detail. The chapter concludes with §6.5, illustrating the resulted KCS-ship-hull instances produced by TshipPM MO-TLBO. The thesis concludes with the Discussion and Summary of the current work, highlighting its key points, stressing the delivered novelties and main contributions to the field of parametric modelling in CASD.
- Advisor / supervisor
- Kaklis, Panagiotis
- Resource Type
- Note
- Previously held under moratorium from 23rd June 2021 until 3rd July 2023.
- DOI
- Date Created
- 2021
- Former identifier
- 9912989592402996
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