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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

A state dependent heuristic method of job shop scheduling

El-Kilani, Mohamad Abdullah January 1992 (has links)
The main object of this work is to develop a 'Fair Delivery and Shop State Dependent Scheduling dispatching rule' (FDSSD) in a job shop environment. The fairness principle could be defined by saying that the customers who came first be given a higher priority than those who came afterwards. The basic principle behind the FDSSD rule is fairness towards customers. This is to some extent taken into account by the First Received First Served and Earliest Due Date scheduling rules. The FDSSD rule, however, takes into account both the order in which orders have been received and related delivery dates. Techniques which do not consider both of these criteria can produce unnecessary anomalies. These anomalies can often be overcome by human judgement in a relatively simple situation where results produced by logical scheduling may be immediately seen as unfair. The FDSSD rule introduces this moral element into logical scheduling. Because of this, many more anomalies which could adversely affect customers can be thrown out. The unecessary unfairness within the schedule may not be apparent to management until too much work has been done to change things. Owing to the moral principles introduced within the FDSSD rule, a direct comparison (one to one) with other scheduling rules does not exhibit the complete performance of the FDSSD rule. However, some comparisons based on tardiness criteria are made. Towards this end, a computer simulation model has been developed. The computer model is named herein as 'Job Shop Scheduling Simulation Model' (JSSM). The model has been used in improving the procedure of In-Process scheduling of the FDSSD rule. In contrast to the currently available scheduling rules which tend to be used, the FDSSD rule achieves a balance between the three main objectives of a production system. The objectives are: (i) to meet delivery dates,: (ii) to decrease Work-In-Process (WIP), and (iii) to increase machine utilisation. This balance compromises the Fairness Principle. The FDSSD rule uses First Received First Served rule (FRFS), delivery date consideration and state in the shop. The FDSSD rule offers a very close result if not better than some other known rules such as FRFS, FCFS and EDD rules.
2

Shape and topology optimisation for manufactured products

Mill, Frank January 2003 (has links)
The work described represents the candidate’s research in the area of engineering component representation, particularly in the context of constrained optimisation. Early papers describe a general approach to detail design that has since become commonplace, however, the advances that were hoped for in some downstream applications are proving more elusive. Whilst the early work describes constraint generation later work looks at different approaches to the shape and topology optimisation problems. The latest papers also include part of the candidate’s work in considering specific applications of parameterised manufacturing features.
3

Kinematics, motion analysis and path planning for four kinds of wheeled mobile robots

Wang, Yongji January 1995 (has links)
This dissertation presents a comprehensive and systematic investigation of some fundamental issues relating to creating an autonomous wheeled mobile robot (WMR). The forms of WMRs with various structures developed in the past are first classified into four groups according to the method of steering and powering. The four groups are: a. ordinary car-like robots (including passenger cars, single trucks, single unit buses and articulated trucks); b. dual drive robots (dual drive motors with various casters); c. synchro drive and steering robots; and d. omnidirectional robots. The concepts of inverse and direct kinematics widely used in non-mobile manipulators are, for the first time, introduced to WMRs, and a unified treatment of the kinematics for the four kinds of WMRs is presented. A motion feasibility and smoothness analysis for each of them is carried out, revealing the motion characteristics resulting from each of the different mechanical structures. This provides a better understanding of their motion characteristics and forms the basis for discussing the path planning problem. The concept of deviation angle interval is defined and used to explain the strange phenomenon of a pirouette. The conditions and formula for pure translation, pure rotation, straight line motion and circular motion are developed. In order to verify the correctness and to illustrate the advantages of the developed kinematic model, the simulation results from the present model are compared with the existing standards from other kinematic models. Path planning is essential for creating an autonomous robot. Various methods for dealing with the find-path problem have been developed in the past. Based on the motion analysis of the four kinds of WMRs, a critical review of the presently available algorithms for moving a WMR among known static obstacles from a given start location to a given goal location is presented, and the suitability of the existing algorithms to each of the four kinds of WMRs is examined.
4

Conceptual programming : a new approach for the optimisation, analysis and novel development of simple and complex separation systems

Shah, Piyush B. January 1999 (has links)
Despite recognised potential of complex distillation schemes in energy savings, their industrial applications are rather slow due to the difficulties on the design and synthesis fronts. These difficulties can be attributed to the large number of design options and the complicated trade-offs associated with them. The mathematical programming approaches embrace to highly interconnected superstructures and disregard available conceptual information in developing the general purpose formulations. That has overloaded the synthesis efforts and restricted their applications to simple and academic problems. In practice, engineers study some basic parameters and apply engineering knowledge to arrive at good designs. So, the challenge is to develop efficient synthesis representation and absorb the process knowledge to screen and target complex design options. This work first presents a new synthesis framework based on tasks and hybrids to effectively represent and address complex distillation systems. It conceptualises each complex design option as an aggregate of simple tasks by defining hybrids and introduces transformations to account for different complex column configurations. It postulates the supertask representation that can develop different non-conventional and novel designs featuring fully integrated columns, parallel sequences and multiple-effect columns. Due to discrete representation of options, the supertask offers distinctive advantage on the modelling and optimisation fronts. The conceptual model for the analysis of complex separation systems that exploits thermodynamics insights and engineering knowledge of the distributed sequence and the primary separation is developed. The design drives of competing options are systematically assessed with the prepositions of general terms "conceptual losses" that enable trade-offs to become clear in the optimal solution. This conceptual information is embedded in the mathematical model to allow efficient screening. In all cases, the approach guarantees simple model that upon formulation results in the mixed integer linear programming (MILP) problem and ensures the global optimum. Furthermore, the approach provides venues to interpret the results and explain the layouts selected by the optimisation. The approach is used to solve several examples of non-azeotropic separation systems that involve complications of industrial problems. The results of these examples show that the approach outperforms conventional techniques in time and effort and allow the optimisation to launch ahead and independent of simulation experiments. The distinguishing aspect of the new approach is that it can systematically translate optimisation solutions and muster support for the favourite designs by reviewing the values of conceptual terms. This provides a confidence in the quality of the solution and reveals dominant trade-offs. Also, due to the speed and the efficiency of the approach, it is used to analyse the effect of process parameters on the structure and performance targets of the designs.
5

Retrofit design for debottlenecking distillation process

Liu, Zhi-Yong January 2000 (has links)
Distillation is one of the most important separation processes in the chemical industry. Retrofit design of distillation processes receives much attention from chemical engineers. Retrofit design for debottlenecking distillation processes is one of the most important objectives in the retrofit of distillation processes. The existing approaches for retrofit design for debottlenecking distillation processes can be classified into: (a) replacing the existing internals with high capacity and/or high efficiency internals; (b) improving the performance of the existing equipment by making some necessary modifications, such as adjusting the operating conditions, adding some extra equipment, etc. The retrofit cost of class (b) is often lower than class (a). However, there is little work that provides both qualitative and quantitative tools for the methods of this second approach to retrofit design. In this thesis, new methods are proposed to solve the problems of debottlenecking distillation columns, by carrying out minor modifications to the columns. Both qualitative and quantitative guidelines and methods are developed. To analyse the hydraulic performance of distillation columns, we propose a new graphical tool to identify the bottlenecks of a distillation column when the throughput of the column is to be increased. This tool can also be used to evaluate, in both qualitative and quantitative ways, the potential modifications that can be applied to increase the throughput of the column. Several guidelines, based on the performance of a distillation column and the characteristics of the mixture being separated, are proposed to evaluate potential modifications. The potential modifications discussed in this thesis include: adjusting the operating conditions, such as, the thermal condition of the feed, operating pressure, etc.; adding extra equipment, such as side heat exchangers, heat pumps, etc.; increasing the number of theoretical stages, using high efficiency and/or high performance internals, for example. The influence of the operating pressure on the throughput of distillation columns-is investigated. This work reveals that at low pressures, increasing the operating pressure can increase the throughput of a distillation column. At high pressures, decreasing the operating pressure can increase the throughput of a distillation column; and at moderate pressures, pressure has little influence on the throughput of a distillation column. This thesis provides a clear and complete picture of the influence of the operating pressure on the throughput of distillation columns. Downcomer flooding, which is another limitation of the capacity of a frayed distillation column at high pressure or high liquid flow rate, is also addressed. Some minor modifications are suggested, which can be used to increase the capacity of the downcomer. The selection of suitable column internals is also addressed in this thesis. A two-stage procedure is proposed to select new internals. In retrofit design, the existing internals should be re-used if possible to reduce costs. The operating conditions can be adjusted to increase the capacity of the internals. Several examples are studied to illustrate the proposed methods. The results show that the proposed methods can solve the problem of debottlenecking distillation processes successfully, effectively and relatively easily.
6

Studies in dynamic programming

White, Douglas John January 1962 (has links)
No description available.
7

Understanding the cultural constraints of TQM implementation in Qatar industries

Al-Khalifa, K. N. January 2000 (has links)
No description available.
8

Evaluation of operating policies for automated distribution warehouses

Boey, Peter January 1994 (has links)
No description available.
9

The next generation planning board : a visible solution for effective manufacturing planning and control for a process manufacturing environment

Ford, Derek William January 2001 (has links)
No description available.
10

Defect recognition in automated surface inspection

Hill, W. J. January 1977 (has links)
No description available.

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