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Two major, largely unknown, areas of process synthesis are explored in this dissertation, and procedures are proposed for the solving of problems within them. In each area, case studies are reported. The work on the first area results in the development of a general procedure for the efficient screening of alternative process routes. The procedure is applied to two examples of commodity chemicals: methyl methacrylate (MMA) and vinyl chloride monomer (VCM). By using suitable knowledge of organic chemistry, thermodynamics, kinetics, and costing, gradual screening of the process alternatives can be achieved from the earliest stages of conceptual design, with minimum calculation effort. The MMA example is concentrated on the selection of raw materials and of chemical routes; by following a number of heuristic and of rigorous rules, a list of prototype raw materials is rapidly developed. From this list it proves possible to create a reaction network connecting the selected raw materials with the target molecule, and 54 routes to MMA (including the two current commercial routes) were found to be of potential interest. Compared with the MMA case study, the VCM example moves further through the procedure to include pre-design capital costing; 14 reactions, resulting in 63 routes to VCM, are rapidly selected, and equilibrium and kinetics calculations reduce the number of promising VCM processes to 24. The operating conditions of the process reactors are also specified, and only three processes are eventually admitted to the final costing stage. 'Elementary plant sections', effecting only one reaction each, are costed separately for the three remaining processes, and it is shown that the three most promising processes can be analysed by joining together the 'sections' relevant to each process. The costing estimates are found to agree well with current practice. Furthermore, a graphical approach is devised to give quick estimates of product selling prices for a wide range of plant capacities and raw materials costs. The second major area of process synthesis considered is the synthesis of reactor networks integrated with the rest of the flowsheet. The complex reaction scheme by Van de Vusse (1964) was employed as an example in a pioneering study. A new procedural approach, which uses a hierarchy of three heuristics, is implemented. In this approach, the designer first devises a simple base case, and then methodically increases its complexity. A powerful analytical tool used is to target for maximum reactor system selectivity, in contrast with the target of maximum reactor yield proposed by previous workers. The dissertation ends with an example illustrating the scope for heat and power integration techniques in the later stages of the design of a flowsheet. A computerised model of a pressurised sulphuric acid plant is developed, and a number of suggestions are made for the improvement of a commercial process, leading to an increase of 15% in steam production.

This thesis investigates methods of modelling problems containing uncertainty, paying particular attention to situations where there is hole empirical data and the modeller chooses to employ subjective expert assessments. In chapter 1 we examine the historical and philosophical underpinnings of subjective probability, discuss how it can be used in practical situations and investigate some of the typical errors associated with eliciting expert assessments. We describe an experiment in which experts assess multi-outcome events with which they are familiar and examine whether they suffer from the same types of assessment errors as naive subjects tend to exhibit As a foundation for our further experiments we discuss the methods and procedures which other practitioners have adopted for eliciting expert judgements and examine how conflicting assessments might be resolved into a coherent position. Chapter 2 investigates ways in which univariatc uncertainty can be quantified and modelled. We conduct an experiment on the elicitation of means and variances for a variety of real distributions and procedures suggested in previous studies. The standard methods of representing random variables with differential equations, series expansions, transformations and inverse functions are discussed and we develop a new functional form for simulation studies. This NB function is both more flexible and computationally faster than the standard alternatives. We have also developed interactive software for the elicitation and quantification of a variable in this NB functional form and describe an experiment to verify this approach. Chapter 3 develops the univariate approaches of chapter 2 for applications involving dependent variables. We first discuss the standard methods of representing multivariate distributions and highlight their limitations. Having examined the requirements of a multivariate representation suitable for simulation and expert elicitation, we develop two approaches based upon the NB functions already described and dependence measures. These are compared with various standard forms, fitting them to both theoretical and real distributions, with some very promising results. Finally we describe an experiment in which we subjectively elicit measures of dependence for a number of real distributions, comparing the accuracy and acceptability of the various techniques.

This thesis uses numerical simulations to assess the most suitable model type for simulating dispersive and non dispersive tsunami wave propagation over a range of bathymetries. These simulations are presented in two parts. The first part highlights differences between results as predicted by a fully nonlinear Boussinesq model (with its ability to predict dispersion) and a non dispersive, linear or weakly nonlinear model, for simulations of a dispersive wave incident at various idealized bathymetric features. The second part determines the efficacy in a real world application of the Boussinesq model as opposed to a nonlinear shallow water model. In addition, a discussion on the geophysical parameters which influence the choice of numerical model for simulating tsunami propagation in a particular bathymetric region is provided.

No description available.

Current trends in sprinkler irrigation to improve application uniformity and reduce energy requirements haste led to problems of water application and potential surface runoff, which in turn have highlighted the importance of the soil and cultivation practice in making best use of irrigation water. The objective of this study was to begin the development of a mathematical model, which will simulate the operation of current sprinkler-soil-crop system, in order to provide a means of predicting surface runoff and so provide a more effective approach to system design. A model has now been developed which will predict runoff from a small simple agricultural catchment in the form of a ridge and furrow cultivation system. The model is based on the kinematic wave theory involving the continuity equation and the simplified momentum equation. A four-point implicit finite difference scheme is used to solve numerically the kinematic wave equations. The model (SROFF) may be used to predict the runoff at various times from a simple catchment with different slopes, water application rates and soil infiltration rate. A further development of the model was made by the introduction of the interception loss model (INCEPT) to predict the amount of water intercepted by the crop canopy during irrigation. The validity of the model was tested and supported by the results of laboratory experiments conducted on two soil samples with different infiltration rates, using three different application rates. The performance of the model was also evaluated by statistical test. There was good agreement between experiment and model results. The results indicated that this model can provide valuable information for the effective design of sprinkler systems, particularly where runoff may be a potential problem. This is particularly the case with current low pressure irrigation systems but equally the problem is common with high pressure systems when applied to soils with low infiltration rates.

This thesis is divided into six chapters. The first chapter provides a brief introduction concerning the behaviour of brittle materials. It also contains the justification for the undertaking of the study as well as a brief description of the method of approach adopted, and thesis layout. Chapter two provides a critical review of the current literature available at present in the failure prediction brittle materials. Both theoretical and experimental studies are discussed and the relevance to the present work is justified. Chapter three deals with the numerical analyses adopted within the thesis. Five different failure criteria were utilized in the initial analysis of the results presented. Among them, the empirical model using the Principle of Independent Action satisfactorily represents the biaxial fracture behaviour of brittle materials in both tension-tension and tension-compression quadrants. Its validity has never been tested before. Various statistical fracture models were used to analyze the failure of brittle materials under multiaxial states of stress, the experimental failure data for simple tension being a starting point for their calculation. It was shown that the Energy Density theory led to a better agreement with the experiments than any other well-known fracture criterion. The study investigates methods of evaluating the Weibull parameters which were crucial in the failure prediction of brittle materials. Monte Carlo simulation techniques are also presented as a method of evaluating the data ranking for the failure probability of brittle materials. Chapter four is devoted to the description of experimental techniques adopted in the study, using specially designed rigs. Six different tests were conducted to evaluate the performance of brittle materials in static loading and also to enable comparisons with the theoretical predictions. Attention was given to specimen casting, loading frames, alignment, measurement techniques and other relevant parameters. The use of the linear elastic fracture mechanics method to predict the behaviour of cracks in bodies, which are subjected to steady stresses, is discussed. The compliance function for the three-point notch bend specimen is presented in addition to the determination of the fracture toughness of Herculite LX plaster. The work was also supplemented by the use of scanning electron microscopy (SEM) to failure analysis of plaster material. This is an extremely important tool in the study of brittle materials since the dimensions of small defects and fracture features on individual grains are often pertinent information to the failure analysis. Chapter five details the analysis of the theoretical results as well as the experimental findings. Based upon the previously mentioned approaches, a comparison was made between theoretically predicted and experimentally observed data. The comparison indicates that discrepancies exist between the observed and predicted results, the reasons for the discrepancies have been justified in this work. Chapter six provides a brief summary of conclusions derived from the complete study, together with recommendations for future work.