International Journal of Engineering Research in Africa Vol. 12

Abstract: This paper examines further a novel series-parallel system reliability optimisation model and methodology earlier developed by the authors. The aim was to investigate how the model constructed for hypothetical series-parallel systems, reacted to slight variations to its parameters, which are the weights for the subsystem reliabilities, the feasibility factors which quantify the level of difficulty of improving a component’s reliability, and the subsystem reliability lower bounds. The optimisation algorithm based on a convex combination of the subsystem reliabilities was run using various combinations of the values of these parameters. The results show that the model was stable under the weighting scheme used and the most sensitive parameters were the feasibility factors and the subsystem reliability lower bounds.

Abstract: In recent years, to a large extent the emergence and development of micro businesses has shown the gaps of comparative advantages between large and medium sized enterprises and small enterprises. Owing to its economics of scope in production, micro businesses contribute to the development and prosperity of the overall market. For the multinational micro business, it is exposed to associated micro political risks in a foreign market in different developing stages (i.e. startup, developing, and mature periods). However, literature review indicates that little work has been done to assess and manage the political risks of multinational micro businesses, let alone provide the multi-stage analysis. To address this problem, this paper develops a multi-stage data envelopment analysis (MSDEA) model to investigate the influence of micro political risks on the efficiency of multinational micro businesses. The main influence factors of the micro political risks in the host country in different stages of startup, developing, and mature periods have been modeled by the MSDEA, to provide new perspectives on the influence mechanism of micro political risk on the multinational micro business. Then the decision makers can assess their companies’ micro political risks in different stages and hence develop target-oriented risk prevention policies. Empirical analysis has been implemented in this paper, along with discussion of potential strategies on assessment and management of the micro political risks for multinational micro businesses. The analysis results demonstrate that the factor of labor conditions was the critical one in the development of the multinational micro business in the startup stage. Good labor conditions may be more likely to avoid micro political risk. The factor of the congruence with national economic interests and goals also impacted the development of the multinational micro business in the startup stage. Hence, the findings of this work could provide valuable reference for multinational micro businesses in restraining the micro political risk.

Abstract: The tensile and fracture strength of a medium carbon steel containing 0.2wt%C were determined after austenitisation at 1100^oC for 1 h and subsequent isothermal transformation at 700^oC for 0.5, 2, 6 and 8 h. Only the specimens transformed for 0.5 and 2 h contained martensite and these were l5.67 and 7.20%, respectively. The maximum measured tensile and fracture strength were 91l and 852 MPa, respectively and these were obtained in the specimens with the most martensite (0.5 h). Although after austenitisation and subsequent isothermal transformation there was a loss in ductility, this was accompanied by a very significant improvement in tensile and fracture strength.

Abstract: Corrosion is a major problem all over the world. A lot of researches on corrosion are ongoing all over the world and will continue to go on. This paper investigates the effect of corrosion on the tensile properties of AISI 1040 steel in seawater. The samples were austenised at 830⁰C, 930⁰C, and 1030⁰C, while some were not. The austenised samples were quenched in water and tempered at 500⁰C. The samples were further machined into tensile test specimens and then exposed to stagnant aerated seawater. Two samples each from each austenised temperature were tested using a tensile test machine at every 15-days interval, for a duration of 90 days. Some of the fracture surfaces were examined using scanning electron microscope. The results shows a 25% decrease in tensile strength for as received sample, 20.1% decrease for samples austenised at 830⁰C, 20.9% decrease for samples austenised at 930⁰C and 22.4% decrease for samples austenised at 1030⁰C at the end of the 90^th day.

Abstract: Passive millimeter wave detection offers great advantages of covertness and anti-interference in surveillance and concealed weapon detection but suffers from disabilities of distance measurement. Based on the conically scanned single pixel millimeter wave radiometer, this paper presents a ranging method via dual-measurement utilizing the relation between the solid angle of the object and its distance from antenna. Both one-dimensional and two-dimensional detections are considered. For one-dimensional detection, the relation between the solid angle of the object and the range is reflected by the pulse width of the radiometer output, and the pulse widths of the radiometer output in two measurements could be extracted by derivative or threshold method. Then the range is calculated since it is inversely proportional to the pulse width, which is demonstrated in simulation. For two-dimensional imaging, a scale extracting algorithm is developed to search the scale between the object sizes of bi-measured images. Experiments are performed using a 94.5GHz total-power radiometer mounted on conically scanning platform. The obtained radiometric images are processed by the developed algorithm and the results indicated that both the scale extracting algorithm and the ranging method are effective and practical.

Abstract: This work develops a 2KVA inverter with timing capability for load supply.The development of timing-capable inverter draws from a DC input which could be a solar/deep cycle battery source. Public power supply could be used to charge the battery. The inverter used the pulse width modulation (PWM) approach and used the SG3524N IC as the Pulse Width Modulator (PWM).Dual channel MOSFETs are supplied current of 10ms duration every 20ms and are used to alternately supply the primary windings of a step up transformer thereby producing an AC in the secondary of the transformer. A step-down transformer, bridge rectifier, and the pulse width modulator were used to provide voltage regulation of the output supply to the load. A keypad, a GDM1602A LCD screen and a PIC16F84A microcontroller were employed in the timing control of the voltage from the output of the inverter. Relays were employed in switching the voltage to the output based on the timing algorithm from the microcontroller. A prototype 2kVA inverter with timing was designed and implemented with a satisfactory output and suitable timing control.

Abstract: Extreme learning machine (ELM), as an emergent technique for training feed-forward neural networks, has shown good performance on various learning domains. This work evaluates the effectiveness of a new Gaussian kernel function-based extreme learning machine (KELM) algorithm for the deformation prediction of mine slope surface utilizing various kinds of meteorological influence factor data including the temperature, atmospheric pressure, cumulative rainfall, relative humidity and refractive index of the mining slope. The KELM model was applied to the deformation of Anjialing diggings, which is an open-pit mine of the China Coal PingShuo Group Co., Ltd. in China. The prediction performance on real data suggests that the proposed KELM model can effectively express the non-linear relationship between the mine open-pit slope surface deformation and various kinds of meteorological influence factors. The prediction results are compared with the most widely used algorithms – Support vector machine (SVM) and back-propagation neural networks (BP NN) in terms of the ease of use ( for example, the number of user-defined parameters), regression accuracy and computation cost. The comparison shows that the new algorithm is similar to SVM and BP NN but more accurate, and has notable lower computational cost and stronger generalization ability.

Abstract: Energy and exergy analyses were carried out on an active 42MW open cycle gas turbine power plant. Data from the power plant record book were employed in the investigation. The First and Second Laws of Thermodynamics were applied to each component of the gas power plant at ambient air temperature range of 21 - 33⁰C. Results obtained from the analyses show that the energy and exergy efficiencies decrease with increase in ambient air temperature entering the compressor. It was also shown that 66.98% of fuel input and 54.53% of chemical exergy are both lost to the environment as heat from the combustion chamber in the energy and exergy analysis respectively. The energy analysis quantified the efficiency of the plant arising from energy losses , while exergy analysis revealed the magnitude of losses in various components of the plant. Therefore a complete thermodynamic evaluation of gas turbine power plants requires the use of both analytical methods.

Abstract: A study was carried to develop model equations for selecting optimum storage parameters for stored cabbages in passive evaporative cooling structures.Three sets of four different types of passive evaporative cooling structures made of two different materials; clay and aluminium were designed and constructed as part of the study. One set consists of four separate cooling chambers. Two cooling chambers were made with aluminium container (cylindrical and square shapes) and the other two were made of clay container (cylindrical and square). These four containers were separately inserted inside a bigger clay pot inter-spaced with clay soil of 5 cm (to form tin-in-pot, pot-in-pot, tin-in-wall and wall-in wall) with the outside structure wrapped with jute sack. The other two sets followed the same pattern with interspacing of 7 cm and 10 cm, respectively. The set with 7 cm clearance served as the control in which the interspace soil and the jute sacks were constantly wetted at intervals of between 2 to 4 hours depending on the rate of evaporation with water at room temperature. The other two sets (5 cm and 10 cm interspaced soil) were constantly wetted with salt solution (sodium chloride) at the same interval to keep the soil in moist condition. Freshly harvested matured cabbages were used for the experiments and the temperature and relative humidity were monitored daily. The vitamin A, vitamin E, bacterial and fungal counts of this produce were determined at intervals of three days for a period of 21 days. Mathematical models (using essential regression software package) were developed to predict the vitamin A and vitamin E contents of the stored produce at various conditions considered in the study. Further analysis by optimization process revealed optimum storage conditions for the stored produce using essential regression software package. Optimum values of 8.86IU and 4.03 mg/ml in storage were obtained for vitamin A and vitamin E contents, respectively for stored cabbages at various conditions.