• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 153
  • 139
  • 1
  • Tagged with
  • 299
  • 299
  • 299
  • 199
  • 47
  • 35
  • 33
  • 31
  • 30
  • 29
  • 27
  • 26
  • 25
  • 25
  • 25
  • 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.

The development of instrumentation for the direct measurement of heat loss from man in a normal working mode.

Hodgson, T. January 1974 (has links)
Based on a theoretical analysis of the heat transfer process between the human body and its environment, graphs are presented for determining the theoretical skin surface temperatures and sweat rates as a function of the physiological conductance, under certain assumed environmental conditions with regard to air temperature, relative humidity and wind speed. In addition, the development of unique measuring techniques for the direct measurement of the evaporative and radiative heat transfer rates between a human body in a natural working position and its environment as well as the development of a low-cos~ radiometer for the measurement of the emissivity and temperature of human skin are described. The heat loss measuring equipment was installed in the horizontal test section of the climatic chamber of the Human Sciences Laboratory of the Chamber of Mines. Basically the evaporative heat loss measuring system consists of two air-sampling probes, for sampling the air on the upstream and downstream sides of the body , a double circuit heat exchanger, for equalising the dry- bulb temperatures of the two air samples and a differential humidity- measuring system incorporating electrical resistance hygrometero, for measuring the difference in specific humidity between the two air samples. In addition, a steam generator is provided for introducing a known amount of steam at a predetermined rate into the wake of the body. Since the output of the humidity-measuring system is linearly related to the evaporative heat loss rate, the unknown rate of evaporation of moisture from the human body can be determined relatively easily from a knowledge of the respective outputs of the humidity-measuring system due to the moisture evaporation rate of the human body and the known vapour production rate by the steam generator. The direct- measuring instrument for determining the radiation energy exchange rate of a working subject is in the form of a rotating hoop. The inside and outside surfaces of the hoop are lined with thermal radiation-sensing elements, so connected as to measure the net radiation energy exchange between the subject and the surroundings. The hoop integrates over the circular strip formed by the elements and upon rotation, integrates the radiation over the total 4n surface enveloping the subject . While the interposition of a surface between the body and its surroundings must of necessity influence the radiation exchange, the method introduces a small surface only . The significance of the evaporative and radiative heat loss measuring techniques which were successfully used in animate studies, is reflected in the, hitherto unknown, accuracy regarding partial calorimetric studies . The low- cost radiometer for measuring the skin temperature and emissivity is equipped with two non-selective thermal radiation detectors in the form of semi-conductor thermocouples. The one radiation-sensing element faces a built-in reference black body. The other detector, which can be temperature controlled, is used to detect the incoming radiation from the target. The output of the radiation-sensing elements which is sufficiently high to be measured on a recorder without the use of a chopper-amplifier system, can either be measured differentially or the output of the radiation-sensing element facing the target can be measured separately; for the purpose of temperature and emissivity measurements, respectively. The unique facility of being able to vary the temperature of the radiation detector enabled a new method of determining the emissivity of a surface to be developed. As a result, accurate measurements of the emissivities of samples of excised skin could be carried out. An improvement in the response of the radiometer would, however, be necessary for the rapid determination of the emissivity of . living skin by this means. The accuracy with which surface temperatures could be determined by means of the radiometer compared favourably with more sophisticated radiometers. / Thesis (Ph.D.)-University of Natal, Durban, 1974.

Non-stationary responses on hoisting cables with slowly varying length.

Kaczmarczyk, Stefan. January 1999 (has links)
Cables in hoisting installations, due to their flexibility, are susceptible to vibrations. A common arrangement in industrial hoisting systems comprises a driving winder drum, a steel wire cable, a sheave mounted in headgear, a vertical shaft and a conveyance. This system can be treated as an assemblage of two connected interactive, continuous substructures, namely of the catenary and of the vertical rope, with the sheave acting as a coupling member, and with the winder drum regarded as an ideal energy source. The length of the vertical rope is varying during the wind so that the mean catenary tension is continuously varying. Therefore, the natural frequencies of both subsystems are time-dependent and the entire structure represents a non-stationary dynamic system. The main dynamic response, namely lateral vibrations of the catenary and longitudinal vibrations of the vertical rope, are caused by various sources of excitation present in the system. The most significant sources are loads due to the winding cycle acceleration/deceleration profile and a mechanism applied on the winder drum surface in order to achieve a uniform coiling pattern. The classical moving frame approach is used to derive a mathematical model describing the non-stationary response of the system. First the longitudinal response and passage through primary resonance is examined. The response is analyzed using a combined perturbation and numerical technique. The method of multiple scales is used to formulate a uniformly valid perturbation expansion for the response near the resonance, and a system of first order ordinary differential equations for the slowly varying amplitude and phase of the response results. This system is integrated numerically on a slow time scale. A model example is discussed, and the behaviour of the essential dynamic properties of the system during the transition through resonance is examined. Interactions between various types of vibration within the system exist. The sheave inertial coupling between the catenary and the vertical rope subsystems facilitates extensive interactions between the catenary and the vertical rope motions. The nature of these interactions is strongly non-linear. The lateral vibration of the catenary induces the longitudinal oscillations in the vertical system and vice-versa. In order to analyze dynamic phenomena arising due these interactions the nonlinear partial-differential equations of motion are discretised by writing the deflections in terms of the linear, free-vibration modes of the system, which result in a non-linear set of coupled, second order ordinary differential equations with slowly varying coefficients. Using this formulation, the dynamic response of an existing hoisting installation, where problematic dynamic behaviour was observed, is simulated numerically. The simulation predicts strong modal interactions during passage through external, parametric and internal resonances, confirming the autoparametric and non-stationary nature of the system recorded during its operation. The results of this research demonstrate the non-stationary and non-linear behaviour of hoisting cables with slowly varying length. It is shown that during passage through resonance a large response may lead to high oscillations in the cables' tensions, which in turn contribute directly to fatigue damage effects. The results obtained show also that the non-linear coupling in the system promotes significant modal interactions during the passage through the instability regions. The analysis techniques presented in the study form a useful tool that can be employed in determining the design parameters of hoisting systems, as well as in developing a careful winding strategy, to ensure that the regions of excessive dynamic response are avoided during the normal operating regimes. / Thesis (Ph.D.)-University of Natal, Durban, 1999.

The effect of tip clearance and tip gap geometry on the performance of a one and a half stage axial gas turbine.

Kaiser, Ivan. January 1996 (has links)
In a previous work of a similar nature, the performance of a low speed axial turbine with a second stage nozzle was examined with respect to the effect of the variation of tip clearance for various tip shapes. Present findings suggest some interesting phenomena, including the effect of tip clearance on the flow within the rotor and show that poor resolution from a transducer and insufficient data points in the critical tip region, where a high velocity peak was found, were responsible for a number of incorrect conclusions in the original study. In terms of blade tip geometry, a standard flat tip shape was found to deliver only a marginally better performance when compared to a double squealer tip and the two streamlined shapes previously investigated. Although contemporary opinion suggests that a streamlined tip should increase the leakage flow and hence cause greater mixing losses, the machine efficiency was not significantly reduced. This is an exciting result since it suggests that a streamlined tip shape can be used to alleviate the problem of blade tip burnout without significantly reducing machine efficiency. When the single stage performance in the absence of a second nozzle was examined, slightly different trends were obtained. The low entropy tips produced slightly lower mixing loss, suggesting that the internal gap loss is an important parameter in determining the rate at which the leakage jet mixes downstream of the rotor. The flow behind the rotor (ie time averaged) was found to be in remarkable agreement with linear cascade data when time averaged even though the latter did not include any effects of relative motion. An increase in clearance was seen to reduce the Euler work and also to cause a deficit of mass flow across the remainder of the blade right down to the hub. The leakage flow was also seen to induce a flow blockage which resulted in a higher driving pressure across the rotor for the same mass flow rate. As in the previous study, the second stage nozzle efficiency was seen to be independent of tip clearance or tip shape and was moderately better than that of the first nozzle. However, the improvement was not found to be as large, due to a previously undetected very thin ring of high energy leakage fluid. When this is taken into account, the efficiency of the second stage nozzle is comparable to the first. The second nozzle was seen to have a flow straightening effect on the poorly deflected, high energy leakage flow, causing a rapid mixing process within these downstream blade passages. The growth of secondary flow was reduced at both the hub and the tip and this is believed to result in a slight decrease in loss. The outlet flow was closer to design conditions than that of the first stage nozzle. / Thesis (Ph.D.)-University of Natal, Durban, 1996.

The use of discrete event simulation techniques to optimize a proposed factory layout.

Gokal, Manooj. 28 November 2013 (has links)
This project has proved conclusively that discrete event simulation techniques can be used to simulate, on computer, a complex stochastic materials handling system. The packing, automatic palletising and warehousing departments of a large powders manufacturing factory was used as an example to investigate the capabilities of computer simulation. The company intends to increase the number of packing machines from seven to eleven, and has embarked on productivity improvement projects that aims to increase the average packing efficiency from the current 50%, to 60% with a long term goal of 70%. Due to the stochastic nature of the run and stop durations of the packing machines, it was impossible to predict the effect of the increased throughput on the palletising system by conventional means. The system was modelled on computer using the SIMAN simulation language. Extensive research was initially carried out in order to determine the operating parameters of the system. The generation of cases from the packing machines in the program was verified against actual production runs. Various alternatives were analyzed to assist in decision making on the expansion of the palletising system in order to accommodate the increased throughput expected from the packing floor. The simulation was therefore used to increase the capacity of the automatic palletising system at minimal cost while meeting demands from the packing floor. It was established that the only capital expenditure required would be about R500 000 to increase the capacity of a palletiser and to provide a pallet conveyor to transport 40% of the pallets to direct despatch. / Thesis (M.Eng.)-University of Durban-Westville, 1989.

Investigation and development of structural composite materials for use as electromagnetic shielding agents in the current aerospace industry.

20 October 2010 (has links)
Due to the nature of today's competitive electronics market, the development of new electronic / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, 2007.

Experimental and numerical study of heat transfer on turbine blades.

20 January 2011 (has links)
An experimental and numerical study of he aerodynamics and the associated heat transfer on turbine blades, has been carried out as part of the ongoing Armscor Denel aircraft engine maintenance program. The experimental tests were performed using an existing continuous flow cascade test facility at the University of KwaZulu-Natal, Durban. These experimental results were used to validate the two-dimensional numerical results, generated usmg a commercially available Computational Fluid Dynamics (CFD) package, FLUENT. The existing experimental turbine test facility utilises a continuous flow cascade technique where a cooled, instrumented blade is rapidly introduced to the hot-air stream exposing it to the cascade flow. This creates the heat transient required for measurement of the isothermal heat transfer coefficients, using thin-film heat flux gauges. A static pressure test blade is used in conjunction with a scanivalve system, to determine the blade mid-span pressure distribution. This latest research effort requires validation of de Villiers' [2002] results, whilst improving the error discrepancies between the experimental and numerical analyses. Maintenance on the test rig has been performed, including the addition of a new pressure control system to ensure the correct cascade flow conditions and boundary conditions are obtained. Experimental pressure distribution measurements were performed, to validate previous work by de Villiers [2002] and to ensure the correct operation of the test rig. Experimental error was identified in de Villiers' [2002] suction surface pressure distribution, and new experimental pressure results were acquired. Following the essential overhaul of critical rig components, experimental heat transfer tests were performed. The newly restored equipment produced new isothermal heat transfer coefficient results that validated the results of de Villiers' [2002]. Numerous CFD meshing techniques were investigated and implemented in FLUENT, to produce the numerical solution. The pressure correlation proved to be excellent with an average error of 3%. The varying cascade inlet turbulence intensity was identified as a major source of heat transfer error. Implementing this variance into FLUENT, a significant reduction in error was seen. The resulting average heat transfer error measured 12%, a major improvement from 29% error in 2002. / Thesis (M.Sc.Eng.)-University of Kwazulu-Natal, 2007.

The formulation of process variables for the elimination of defects in a semi-solid high pressure die cast component.

Reinhardt, Carl Jurgen. January 2006 (has links)
Semi-Solid Metal (SSM) forming has distinct advantages: strength, near net shape, thick and thin sections and a large scope of materials able to be cast. The aim of this project is to produce a near net shape component using SSM casting with A356 primary Semi Solid Aluminum feed stock from SAG. The selected Short Arm Component was identified as a suitable component for SSM forming, it is used as part of an insulated securing mechanism in overhead pylons, demands high strength and has relatively thick sections. A combination of full and short shot castings from the component and modular die were produced, on the real time shot controlled 62.5 ton high pressure die casting machine, at varying casting parameters of die temperature between 140-250°C, gate velocities of between 1.01-2.87ms_1 and a billet temperature of between 578-582°C. To understand fluid flow and locate possible defects, X-ray radiography and naked eye surface observations of the castings were used to locate possible defects and irregularities, which were cross sectioned and analysed using a Scanning Electron Microscope with an Energy Dispersion Spectroscopy module. It was apparent from the current project, as well as from literature, that increases in the die cross-sectional area reduce the shear surface area and increase the viscosity causing undesirable mould filling behaviour. / Thesis (M.Sc.)-University of KwaZulu-Natal, Durban, 2006.

Heat transfer enhancement in nano-fluids suspensions : thermal wave effects and hyperbolic heat conduction.

Vadasz, Johnathan J. January 2005 (has links)
The spectacular heat transfer enhancement revealed experimentally in nanofluids suspensions is being investigated theoretically at the macro-scale level aiming at explaining the possible mechanisms that lead to such impressive experimental results. In particular, the possibility that thermal wave effects via hyperbolic heat conduction could have been the source of the excessively improved effective thermal conductivity of the suspension is shown to provide a viable explanation although the investigation of alternative possibilities is needed prior to reaching an ultimate conclusion. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2005.

Thermal shock and thermal stress prediction on a highly loaded turbine nozzle guide vane based on an aerodynamic and thermal analysis.

Kulik, Krzysztof. January 2005 (has links)
A 2-D plain strain CFD/FEM model to simulate thermal shocks and stresses in a turbine blade has been set up using the commercially available software FLUENT and NASTRAN. The model was validated against the experimental data of Bohn et. al. and used to simulate real test cases. The steady state numerical model was set up for a single Mark II nozzle guide vane using the correct boundary conditions to resolve the flow field. A combined laminar and turbulent model was developed in FLUENT that was used to highly accurately predict the pressure, temperature and heat transfer coefficient distribution on the blade surface as well as the temperature distribution on the cooling holes inside the blade. The resulting temperature profiles on the blade and cooling holes were used as boundary conditions for the FEM analysis to resolve the internal temperature and stress profiles. The pressure, temperature and heat transfer distribution on the blade, from FLUENT, were compared to those from Bohn et. al. The predicted pressure distribution was exact with the experimental results and the predicted temperature distribution had an average overprediction of 1.4 % on both the pressure and suction side. The internal temperature profile predicted by NASTRAN was correctly predicted with an average over-prediction of 2 %. The stress contours were accurately predicted with the stress magnitude varying by 17 % to that of Bohn et. al. The reason for the difference between the MSC.NASTRAN and Bohn et. al. stress results is believed to be purely solver related. Bohn et al. used a FEM package called MSC.MARClMentat. With the steady state model validated, transient test cases were simulated that represent typical operational data. The mission profile was obtained for the T-56 engine found on the C130 cargo plane. The model was used to simulate the test case where the turbine inlet temperature (TIT) varied with time. The simulation results showed that stress was proportional to TIT, where changes in the TIT were seen later in the stress curve, due to conduction in the blade. Steep TIT changes, such as shock loads affected stress later than gentler TIT changes. Thus, the FLUENT / NASTRAN model was successfully validated, and used to simulate a flight mission profile. The goal to calculate quality unsteady stress profiles was achieved and forms the boundary conditions for thermal fatigue calculations. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, 2005.

Bio-mechatronic implementation of a portable upper limb rehabilitative exoskeleton.

Naidu, Dasheek. January 2011 (has links)
The rationale behind this research originates from the lack of public health care in South Africa. There is an escalation in the number of stroke victims which is a consequence of the increase in hypertension in this urbanising society. This increase results in a growing need for physiotherapists and occupational therapists in this country which is further hindered by the division between urban and rural areas. The exoskeleton device has been formulated to encapsulate methodologies that enable the anthropomorphic integration between a biological and mechatronic limb. The physiotherapeutic mechanism was designed to be portable and adjustable, without limiting the spherical motion and workspace of the human arm. The exoskeleton was portable in the sense that it could be transported geographically and is a complete device allowing for motion in the shoulder, elbow, wrist and hand joints. The avoidance of singularities in the workspace required the implementation of non-orthogonal joints which produces extensive forward kinematics. Traditional geometric or analytical derivations of the inverse kinematics are complicated by the nonorthogonal layout. This hindrance was resolved iteratively via the Damped Least Squares method. The electronic and computer system allowed for professional personnel, such as an occupational therapist or a physiotherapist, to either change an individual joint or a combination of joints angles. A ramp PI controller was established to provide a smooth response in order to simulate the passive therapy motion. / Thesis (M.Sc.Eng)-University of KwaZulu-Natal, Durban, 2011.

Page generated in 0.1068 seconds