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(2006)ThesisThis thesis reports on research into the causes of local optima when optimization algorithms are applied to aerospace structural design. A thorough understanding of local optima will enable the engineers to select the algorithm for optimization or to guide the optimization to ensure either global optima or near optimal solutions are achieved. Therefore, a comprehensive literature review has been conducted and several illustrative examples have been identified to help fully understand the cause and importance of local optima. The first application involved the design of the internal structure of a simplified wing spoiler. MSC.NASTRAN was used to optimize each discretized location of an additional rib with the aid of a Patran Command Language (PCL) algorithm. The objective function of minimum weight was approximated as a multimodal function in a 2D smooth curve where the local and global optima were identified. The theory of continuous rectangular plates was used to explain the phenomena. The second problem considered buckling of a wing rib. A PCL code was written to obtain the rib buckling factors as the position of the center of a square cutout was varied within a constrained area. The rib linear buckling factor versus the centre position O(X, Y) of the square cutout was plotted in a 3D surface contour plot. Load path theory and relevant plate buckling theories were used to explain the local and global maxima identified. The final example considered the maximization of the buckling load of a simply supported composite laminated plate under in-plane loading. A conventional Genetic Algorithm was used to examine the local and global optima of the critical buckling load factor. Many local and global optima were identified and explained and many near-optimal solutions were found in a single run. A significant understanding of local optima in aerospace structural design with the optimal utilization of available software and the appropriate selection of optimization algorithms has been achieved. Further work could either include implementing the proposed global optimization strategies or include implementing rapid methods for identifying multiple local optima.
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(2006)ThesisReuse of components as opposed to material recovery, recycling or disposal has been identified as one of the most efficient EOL strategies for products. The concept behind reuse is that some components and subassemblies have a design life that exceeds the life of the product itself. In order for reuse to be successfully implemented as an EOL strategy, a designer needs to incorporate into a product a philosophy of Design for Reuse (DfRe) at the early design stage. Reliable methods to assess the remaining life of used components based on a products usage life are also required. Furthermore, current industry practices and literature advocate that there is no methodology to decide which parameters need to be redesigned so as to change the life of a selected component to a desired level. The objective of this research is to develop a methodology to assess the reuse potential of product groups based on component failure mechanisms and their associated critical lifetime prediction design parameters. Utilising these clustered groups mathematical models were then developed to establish the useful life of the components for each clustered group. Finally, a means of equating useful life to design life was established and the relationship between, the failure mechanisms, critical lifetime prediction design parameters and design life were represented in graphical format. In order to achieve the proposed objective, Cluster analysis, in particular Group Technology (GT) and Hierarchical clustering were employed to group components with similar failure mechanisms. Following this, multiple linear regression was used to establish mathematical models based on condition monitoring data for each of the clustered groups and their related critical lifetime prediction design parameters. A sensitivity analysis was conducted using the mathematical models, in order to produce graphical relations between the useful life and design parameters of a product. The validity of the suggested methodology was tested on electric motors and a gearbox as both these components have demonstrated great reuse potential. The results demonstrate that the methodology can assist designers in estimating the design life and associated design parameters with great accuracy, and subsequently aiding in a stratagem for reuse.
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(2006)ThesisIt is widely believed that with the transition from the industrial to information-based economics, organizational knowledge has emerged as the single most critical resource at both macro and micro levels, which promotes the creation, sharing, and leveraging of the organization’s knowledge in current Customer Order Driven Engineering (CODE) environment. Insufficient knowledge management, hence lack of a structured Enterprise Knowledge Base (EKB) in a CODE environment, whilst involved in New Product Development (NPD) process may result in several problems resulting in creating less successful products. This research establishes an “Enterprise Knowledge Base (EKB) framework” with focus on the Product, Process and Organizational issues related to the NPD process. The framework has three major stages, namely “Knowledge Acquisition”, “Knowledge Organizing” and “Knowledge Validating”. Various frameworks/methods/models are developed as steps for each of these stages. The framework may increase the effectiveness of product and process development as well as enterprise competitiveness through developing a system architecture to understand, analyse and map organisational, operational activities and business objectives; and increasing the ability of an organisation to establish an integrated partnerships to share efforts on the design, manufacture and delivery of products. In knowledge acquisition stage, a “Knowledge Capture framework” and the “Relationship matrices” are developed to analyse and link the generic knowledge items of a NPD process in concurrent engineering environment. Among the relationship matrices, Task versus Task (Design Structure Matrix - DSM) matrix is comprehensively explored and decomposed to structure and link several processes at different levels for effective representation of the overall enterprise representation. In knowledge organizing stage, the acquired knowledge (important relations identified in the Task versus Task matrices) is represented in the form of “Questionnaires”. Best practices gathered from several manufacturing firms in NPD in CODE have also been used as knowledge resource base for the Questionnaires. For grouping and validation of these Questionnaires, an “Assessment Model” is developed, which consists of five performance indicators of the organization namely ‘Marketing’, ‘Technical’, ‘Financial’, ‘Resource Management’, and ‘Project Management’. Industry applications are carried out in two Australian Manufacturing Companies for the validation of the acquired knowledge. Two tests are carried out; in order to assess the sensitivity of question categories followed by another test to observe whether the model can accurately display the overall performance of the company in the five categories of NPD phases. These two tests have identified possible improvement areas in the NPD process of manufacturing organizations involved in the validation phase. Up to 80% of the findings of the EKB framework and assessment model were found to reflect the actual practices of the organizations.
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(2006)ThesisAs a result of rapid product development, the product life cycle has become shorter, and thus the amount of waste from discarded industrial products has risen dramatically. An awareness of the world s environmental problems has stimulated researchers to explore the opportunities to reuse, recycle and remanufacture end-of-life products. Disassembly is a systematic approach to separating products into components or subassemblies in order to facilitate recovery of components or materials. However, the full disassembly of a product tends to be unproductive due to technical and cost constraints and product conditions after usage. Therefore, selective disassembly has been introduced as a more practical approach, where only a limited number of disassembly paths that lead to selected parts with recovering potential are considered. This research focuses on the development of a selective disassembly methodology by reversing an assembly sequencing approach. The methodology uses a step-by-step approach to generate a disassembly sequence diagram. This involves listing all the parts within the product, generating a liaison diagram to illustrate part relationships and then establishing precedence rules describing prerequisite actions for each liaison. This is followed by segregating disassembly paths that lead to the removal of selected parts or subassemblies. Then a winnowing process is applied to these paths to eliminate invalid disassembly states and transitions. The last step is to select the optimal disassembly path by using the time requirement as the main selection criterion. In order to shorten the time for carrying out the sequencing process, a javabased program that is capable of performing the first three steps has been created. The program requires three basic inputs in forms of precedence rules, and user-required part (s) and disassembly rules, prescribing which liaison (s) should be done subsequent to a particular liaison. The viability of the methodology and the program is proved through seven case studies conducted on a fishing reel, a single-hole punch, a kettle, an entire washing machine and three washing machine subassemblies. The application of the program allows the users to determine an optimal disassembly sequence in a very short time and with only basic product information as the input.