Department of Mechanical and Industrial Engineering

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    Ethanol - Activated Carbon Solar Refrigeration
    (University of Reading, 1986-08) Kimambo, C. Z. M.
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    System Identification of Linear Vibrating Structures
    (1991) Nalitolela, Noel Gerald
    Methods of dynamic modelling and analysis of structures, for example the finite element method, are well developed. However, it is generally agreed that accurate modelling of complex structures is difficult and for critical applications it is necessary to validate or update the theoretical models using data measured from actual structures. The techniques of identifying the parameters of linear dynamic models using Vibration test data have attracted considerable interest recently. However, no method has received a general acceptance due to a number of difficulties. These difficulties are mainly due to (i) Incomplete number of Vibration modes that can be excited and measured, (ii) Incomplete number of coordinates that can be measured, (iii) Inaccuracy in the experimental data (iv) Inaccuracy in the model structure. This thesis reports on a new approach to update the parameters of a finite element model as well as a lumped parameter model with a diagonal mass matrix. The structure and its theoretical model are equally perturbed by adding mass or stiffness and the incomplete number of eigen-data is measured. The parameters are then identified by an iterative updating of the initial estimates, by sensitivity analysis, using eigenvalues or both eigenvalues and eigenvectors of the structure before and after perturbation. It is shown that with a suitable choice of the perturbing coordinates exact parameters can be identified if the data and the model structure are exact. The theoretical basis of the technique is presented. To cope with measurement errors and possible inaccuracies in the model structure, a well known Bayesian approach is used to minimize the least squares difference between the updated and the initial parameters. The eigen-data of the structure with added mass or stiffness is also determined using the frequency response data of the unmodified structure by a structural modification technique. Thus, mass or stiffness do not have to be added physically. The mass-stiffness addition technique is demonstrated by simulation examples and Laboratory experiments on beams and an H-frame.
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    The Running and Gating of Light Alloys
    (1992) Runyoro, Joseph J.; Campbell, J.
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    A New Approach to Update Model Parameters Using the Frequency Response Data
    (SEM SOCIETY FOR EXPERIMENTAL MECHANICS INC, 1992) Nalitolela, Noel Gerald
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    Development of a Compact Solar Water Heater for Africa
    (1992-06-04) Siddiqui, K. M.; Kimambo, C. Z. M.
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    A Mass or Stiffness Addition Technique for Structural Parameter Updating
    (International Journal of Analytical and Experimental Modal Analysis, 1992-07) Nalitolela, Noel Gerald; Penny, J. E. T.; Friswell, I. M.
    Most methods used to update dynamic structural models use either frequency response data or both eigenvalues and mode shape data. This paper presents a technique to adjust the parameters using eigenvalues alone. Eigenvalues may be measured very accurately whereas mode shapes often contain substantial errors. The structure and its theoretical model are perturbed by adding mass of stiffness. The measured eigenvalues before and after each mass or stiffness addition are used to update the parameters by sensitivity analysis. It is shown that with error-free data and a proper choice of the perturbing coordinates, exact parameters can be identified from eigenvalues alone using unconstrained optimization. Due to measurement errors and possible inaccuracies in the structure of the model matrices, the parameters of a real structure are adjusted by incorporating a constraint of minimum changes from the initial estimates using a Bayesian estimator.
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    A frequency Domain Technique for Structural Parameter Updating
    (SEM SOCIETY FOR EXPERIMENTAL MECHANICS INC, 1993) Nalitolela, Noel Gerald
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    Updating Structural Parameters of a Finite Element Model by Adding Mass or Stiffness to the System
    (1993) Nalitolela, Noel Gerald; Penny, J. E. T.; Friswell, I. M.
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    A Model of Organizational Commitment and a Comparative Study of Parastatal and Private Organizations in Tanzania.
    (1993) Kundi, Beatus A. T.; Saleh, Shoukry D.
    Organizational commitment is defined as the tendency, based on cognitive, affective, and normative forces on the individual, to behave in ways which place primacy on the promotion and protection of the interests of the organization rather than the immediate and/or direct personal or sub-group interests. This definition goes beyond instrumental and intrinsic motivation through its encouragement of employees to sacrifice their interests for the sake of those of the organization. The model based on this definition is made up of four extraindividual factors: job integration, employee investments, organizational support and role-model leadership. These factors are posited as influencing commitment through the intraindividual processes of responsibility to the organization, reciprocation, and organizational identification. Organizational values for performance and collectivism are shown in the model as important facilitators of the effects of the commitment factors. On the other hand, organizational conflicts and the complexity of organizational goals are posited as attenuators of the positive effects of the commitment factors. The model considered simultaneously task-oriented outcomes (e. g., productivity, product/service quality, innovation, and adaptability) and employee-related outcomes (e. g., work satisfaction). These outcomes are posited as positively feeding back to the antecedents, thus further increasing the influence of the commitment factors.
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    Updating Model Parameters by Adding an Imagined Stiffness to the Structure
    (Academic Press, 1993-03-03) Nalitolela, Noel Gerald; Penny, J. E. T.; Friswell, I. M.
    A mass addition technique for structural parameters updating has recently been described by the authors. It uses eigenvalues of the structure, before and after it is perturbed by adding mass, to adjust selected parameters by sensitivity analysis. The technique avoids the use of noisy mode shape data and overcomes the problem of a non-unique set of parameters when eigenvalues alone are used. However, it is not suitable for a large structure because of the difficulty of adding the necessarily large perturbing mass to the existing structure. This paper presents an alternative technique. An "imagined" stiffness is added to the structure and the FRF of this perturbed structure is obtained from the measured FRF of the original structure by a simple structural modification technique. The eigenvalues of the original and perturbed structures are obtained from the measured and constructed FRFs respectively. These eigenvalues, together with the eigenvalues predicted from an analytical model of the structure, are used to adjust the structural parameters by sensitivity analysis. The technique is demonstrated by a simulated example and by an experiment on an H-frame.
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    Design, Manufacture and Testing of Oil Press Systems: Issues and Concerns
    (1994) Kaunde, O. K.; Chungu, A. S.; Towo, Arnold. N.
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    Development of a compact integral solar water heater for Africa
    (Elsevier B.V., 1994-06) Siddiqui, K. M.; Kimambo, C. Z. M.
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    Influence of Gas Type and Injection System on Simultanous Reduction of Soot and NOx in IDI Diesel Engine.
    (1995-09) Mkilaha, Iddi; Kawai, Daizaburo; Inoue, Mitsunori; Naruse, Ichiro; Ohtake, Kazutomo
    Modification has been made to one of the prechambers of a 4-cylinder. IDI diesel engine used to study the combustion process, for the purpose of reducing emissions. With the provisions for optical assessment o the combustion process in the prechamber, the effect of high-pressure gas injection into the prechamber during injection has been carried out. Results of this work indicate that high-pressure gas injection during combustion can affect simultaneous soot and NOx reduction with a reasonably low amount of emission of other diesel engine pollutants. An optimum chamber type is suggested based on analysis of the effect of air, argon and nitrogen injection.
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    Computer Modelling of Transients in Ruptured High Pressure Natural Gas Pipelines: A Review of Experimental and Numerical Studies
    (Institution of Mechanical Engineers, UK, 1995-10) Kimambo, C. Z. M.; Thorley, A. R. D.
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    Optimisation of Machining Parameters with Consideration of Tool Adjustment in Turning Operations
    (University of Ottawa, 1996) Mgwatu, Mussa I.
    This thesis presents six optimization models which are developed and solved in two stages in order to integrate tolerancing and machining parameters decisions. One model is developed in the first stage. The first-stage model is related to a design problem and provides better part tolerance to be used in the second stage to incorporate tool adjustment decisions into the optimization of machining parameters. Five models are developed in the second stage and are divided into single-machine and multi-machine turning operation problems. For single-machine turning operations, three models are formulated. The first is a single-product multi-pass model considering pass selection for determining optimum cutting speed, feed rate, depth of cut, dimension deviation and number of passes. The second is a single-product multi-pass model considering inventory and setup costs to find optimum cutting speed, feed rate, depth of cut, dimension deviation and batch size. The third is a multi-product multi-pass model considering inventory and setup costs for selection of optimum cutting speed, feed rate, depth of cut, dimension deviations and production cycle time. For multi-machine turning operations, two models are formulated. One is a multi-feature multi-pass model with the objective of minimizing total cost for determining optimum workload assignment, cutting speed, feed rate, depth of cut, and feature dimension deviations of machine-pass-feature combinations. The second is a multi-feature multi-pass model with the objective of minimizing cycle time which, once solved, will give optimum workload assignment, cutting speed, feed rate, depth of cut, and feature dimension deviations of machine-pass-feature combinations. A solution method and illustrative examples are given to test the feasibility of the developed optimization models.
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    Energy efficiency in current tobacco-curing practice in Tanzania and its consequences
    (Elsevier, 1996-02) Siddiqui, K.M.; Rajabu, Hassan
    The energy efficiency of tobacco-curing practice in Tanzania is investigated. A one-quarter size laboratory model of a traditional, fuelwood-fired, rural barn is used. The energy consumed in the tobacco-curing process is monitored together with emissions of CO and CO2. An average of 14 kg of fuelwood is consumed to obtain 1 kg of cured tobacco. The emission of CO is 0.6% of total volume. It is estimated that 0.6 hectare of woodland have to be cleared to cure 1 hectare of tobacco, leading to a deforestation rate of 13,000 hectares per annum. Alternative sources of energy to fuelwood should be developed.
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    Modelling of Linebreak in High-Pressure Gas Pipes
    (http://openaccess.city.ac.uk/7934/1/Modelling_of_linebreak_in_high-pressure_gas_pipes.pdf, 1996-07) Kimambo, C. Z. M.
    Although there are many computer codes available for analysis of fluid transients, only. a few are known to be applicable to linebreak situations and their scope is limited. There is, therefore, still a big potential for development work in the subject. Discrepancies between different models which have been developed have mainly centred on the assumptions used in developing the basic partial differential equations of flow, and subsequent simplifications; the thermophysical model used; representation of various terms in the equations such as the friction term; and the numerical method of solution of the basic partial differential equations. A previous model developed by Tiley (1989), overestimated the actual wave speeds and had problems of instability of the solution. A new approach, in which the three basic partial differential equation of flow are derived, based on the assumption of an unsteady quasi-one-dimensional flow of a real gas through a rigid constant cross-section area pipe,and using the Gamma Delta method is used. No further simplification is made on the basic equations. Significant improvements have been made on the type of equation of state, thermodynamic model, heat transfer approximation and friction factor representation. The QUANT software for thermodynamic and transport properties of real gases is used. A flow dependent explicit equation of Chen (1979) is used to calculate the frictional force and heat transfer is calculated using the concept of recovery factor and adiabatic wall temperature. Numerical solution of the basic equations is performed using the third-order WarmingKutler-Lomax method, the second-order MacCormack method and the method of characteristics. A pc based computer coding with the C language is used. The QUANT software has successfully been incorporated with the programme. The full benefits of the software could not be realised with linebreak problems due to limitation of the range within which it gives output at present, but satisfactory results have nevertheless been attained. An improved and more accurate way of calculating the break boundary condition has been used. A non-uniform grid spacing has been used, which allow fine grid spacing in the vicinity of the break in order to enable accurate modelling of the rapid transients occurring in that part. Two different models for calculating the heat transfer i. e. one for the case of pipes exposed to the atmosphere and buried pipes have been incorporated with the model. Experimental data from full-scale pipeline tests is used to validate the computer models. Results from the computer model simulations show good agreement with the experimental data. The MacCormack method has been found to be unsuitable for modelling transient flow following linebreak in high-pressure gas pipelines. The method of characteristics has proved to be the method of solution for such applications. A better understanding of the flow following a break in high-pressure gas pipes is achieved, especially the decompression behaviour at the break boundary. Data gathered from feasibility studies conducted in the late 1980's for a pipeline in Tanzania is used to validate the steady state analysis model and to simulate a linebreak in the pipeline. Results of the computer simulation are discussed and recommendations made on the suitability the pipeline design. Additional work is recommended on refining andfurther testing of the computer programmes and using the Gamdeleps method which covers all the three phases region i. e. gas, liquid and gas/liquid.
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    Critical Gate Velocity for Film-Forming Casting Alloys; A Basis for Process Specifications
    (1997) Runyoro, Joseph J.; Boutorabi, S. M. A.; Campbell, J.