International Journal of Engineering Research in Africa Vol. 51

Abstract: The adaptive control of metal cutting processes is a logical extension of the CNC systems. In CNC systems of metal-cutting processes the machining variables (e.g., the cutting speed and feedrate) are prescribed by the part programmer. The determination of these variables depends on experience and knowledge regarding the workpiece and tool materials, coolant conditions, and other factors.The determination of these operating parameters depends on experience and knowledgeregarding the workpiece and tool materials, coolant conditions, and other factors. By contrast,the main idea in adaptive control is the improvement of the production rate, or the reductionof machining costs, by calculation and setting of the optimal operating parameters duringmachining itself. This calculation is based upon measurements of process variables in real time and is followed by a subsequent on-line adjustment of the machining variables subject to constraints with the objective to optimize the performance of the overall system.The adaptive control is basically a feedback system, in which the operatingparameters automatically adapt themselves to actual condition of the process. AC system formachine tools can be classified into two categories:1.Adaptive control with optimization(ACO);2.Adaptive control with constraints(ACC);ACO refers to systems in which a given performance index (usually an economicfunction) is extremized subject to process and system constraints. With ACC, the machiningparameters are maximized within a prescribed region bounded by process and systemconstraints, such as maximum torque or power. ACC systems, however, do not use aperformance index. In both systems an adaptation strategy is used to vary the operatingparameters in real time cutting progresses. Although there has been considerable research onthe development of ACO systems, few, if any, of these systems are used in practice. The major problems with such systems have been difficulties in defining realistic indexes of performance and the lack of suitable sensors which can reliably measure on-line thenecessary parameters in a production environment. The objective of most AC systems isimprovement in productivity, which is achieved by increasing the metal removal rate (MRR)during rough cutting operations. The increases in productivity range from approximately 20 to 80 percent and clearly depend on the material being machined and the complexity of the part tobe produced.

Abstract: One of the most important steps during manufacturing of solar modules is lamination. This paper focuses on monitoring of behavior of used encapsulant Ethylene/Vinyl-Acetate (EVA) and impact on overall quality of module during lamination. Monitoring is performed by employing external thermocouple sensor inside the lamination chamber as well as by. Real-time analysis of the results helps to predict the quality of final product in terms of ensuring lamination quality in real time and provides possibility to tune the process during manufacturing cycle to achieve the best result of encapsulant cross-linking.

Abstract: This research work mainly focuses on the flexibility and productivity improvement through the execution of different lean techniques in the valve assembly of medium scale manufacturing unit. The different types of wastes percentage are determined to find out the waste which mainly affects the productivity. The major wastes of motion waste by about 30% and unwanted distance of 250 square foot were reduced by implementation of kaizen in the valve assembly area. Value stream mapping was used to identify the bottleneck process and by eliminating the bottleneck process results in the reduction of excess motion and non-value added activity by 45%. Work-in-process aging and work-in-process inventory cost was calculated and the production level was estimated by using 95th Percentile calculation. The total lead time was reduced about 54minutes with reduction of transportation time 2.7minutes after the implementation of lean techniques and the productivity of the valve assembly was also increased to about 6% after reducing the non-value added activities.

Abstract: In this paper, the sine and cosine algorithm is enhanced (ESCA) by selecting the best elements of the group in the next iterations to reduce active power loss. The sine and cosine algorithm (SCA) converges to an optimal solution through the sinus and cosine-based mathematical relations and the destination or the best global element in each iteration. Also, it uses the current elements for generating new elements without keeping the elements that have a better solution in the next generations. In ESCA this problem is avoided by applying the selection operator for keeping the best elements to the next generation. This method improves the optimal solution and is obtained in most implementations of the algorithm, which reduces the disturbances in obtaining the optimal solution. Also, one of the parameters of the standard method is fixed to the normal one value for the performance improvement of the algorithm. This method has been applied to a typical power network such as IEEE 30-bus and IEEE 118-bus in order to reduce the active power loss, reduce the power loss with the voltage deviation and with the stability of the voltage. Finally, this method proved effective than the standard method and with the previously applied metaheuristic methods.

Abstract: One major feature of a granary is the uneven distribution of temperature and airflow. Due to the large variability in the parameters to be considered in characterizing the feature, a pilot test serves as the better way to performing the experiment, which subsequently affects the airflow velocity distribution, and is very difficult to determine by natural experiment. This paper develops a model for uneven airflow and temperature distribution through the layers of stored grains, relative to the indicated parameters. The study aims at predicting the various thermo-physical properties of maize grains using the developed model with the incorporated several expressions obtained, and compare with the measured values through the deployed pilot mini silo. To validate the model, the bin was aerated with forced air at constant humidity and temperature. A mini cylindrical silo was also developed and deployed with bulk grains for a pilot test. The predicted results were compared with the measured values of the temperatures obtained in the various locations of the pilot silo. The two results were closely related, thereby establishing the validity of our model. The model provides information on the direction of flow and velocity in each location within the stored volume of grains, and data for grain cooling, airing and drying in the bin. The developed model is useful for predicting the temperature distribution, airflow and the cooling time for bulk grains under varying aeration conditions, and suitable for optimizing the design and operation of granary systems.

Abstract: Locally produced crucibles in Ghana experience dimensional failures during fire assaying of ores, therefore, even with a higher cost, imported crucibles are still the most preferred choice by laboratories in Ghana because of the stable performance of up to three cycles. Assay crucibles of locally manufactured, imported and theoretically composed were sampled and analysed via reverse engineering to identify factors that are attributed to the failure during use. Field investigation and compositional, physical and structural investigations were carried out using XRD, water boiling and SEM-EDS analyses, respectively. The results indicated that failure of the local crucible can be attributed to low mullite phase in both content and planes, which could ease the crack development and enhance the thermal stability of the crucible; non converted quartz into cristobalite, which stabilises the volume expansion coefficient during the fire assaying cycles; excess quartz content and absence of alumina content weakened the corrosion resistance against attack from the basic flux of litharge; and high porosity, allowed penetration of molten charge into the structure of crucible, leading to the dissolution of free silica content into the charge and causing structural failure. To overcome such deficiencies, higher firing temperature (~1240 °C), extra soaking time, and blending of high alumina contained clay/minerals were suggested.

Abstract: The historical building which can reflect the local history and culture of a city is the wealth of all mankind, but after the baptism of time, the historical building has been damaged by nature or man. In order to preserve the historical buildings and the culture contained therein, the damaged historical buildings need to be reinforced and restored. In this study, ABAQUS finite element software was used to simulate and analyze the reinforcement and repair effects of four kinds of damage states (mild damage, moderate damage, severe damage, and nearly collapse) of historical building walls caused by reinforced mesh cement. The results showed that in the case of mild damage, moderate damage and severe damage, the ultimate load displacement of the wall was raised in different degrees (the ultimate load and displacement were 200 kN and 4 mm respectively in case of mild damage and were 400 kN and 8 mm respectively after reinforcement; the ultimate load and displacement were 210 kN and 4 mm respectively in case of moderate damage and were 400 kN and 6 mm respectively after reinforcement; the ultimate load and displacement were 150 kN and 4 mm respectively in case of severe damage and were 375 kN and 7 mm respectively after reinforcement) and restored or even exceeded the performance of the wall without damage by using the reinforced mesh cement layer. In the nearly collapse wall, the ultimate load and displacement of the wall could be improved, but the performance of the wall could not be recovered as it was before being damaged (40 kN and 3 mm before reinforcement, and 165 kN and 6 mm after reinforcement). Reinforced reticulated concrete can be used to reinforce and repair historic buildings with mild, moderate and severe wall cracking, but it is not suitable for the reinforcement and restoration of cracked historical buildings which are nearly collapsing.

Abstract: The Port of Durban (PoD) is currently upgrading its existing power supply to a supply voltage of 132 kV. The existing 33 kV supply cables are old and have exceeded their designed life resulting in unplanned power outages. The existing 33 kV switchgear is old and obsolete as a result it is difficult to maintain. The existing maximum demand capacity will not be able to cater for the additional loads required for the planned expansion developments.The electrical load flow is a very important and fundamental tool for the analysis of any power systems and in the operations as well as planning stages. The electrical load flow study was conducted using PowaMaster software to analyse the behaviour of PoD’s electrical network post implementation of the new substation onto the currently existing network. In performing the electrical load flow study, load diversification is one of the critical input parameters that was considered because it is a true representation of the network behavior. The load forecasting was based on the planned developments commissioned between 2017 and 2027. The electrical load flow study was also to validate if all the new selected reticulation cables and transformers as part of the design have been correctly sized and will be able to operate reliably without compromising security of firm supply with the implementation of all the planned future loads. This report entails the results of the electrical load flow study that was conducted to analyse the voltage stability and system reliability of the PoD’s electrical network in conjunction with new 132/33 kV Langeberg Substation.

Abstract: In this work, the Yb:YAG laser beam welding of the magnesium alloy AM60 was studied. A laser power of 2 kW and a welding speed of 3.5 m / min give a different welding quality than that obtained by CO2 laser with the same parameters. The metallurgical characterization, by optical microscopy, showed the formation of four distinct zones : base metal (BM), heat affected zone (HAZ), the partially fusion zone (PFZ) and the fusion zone (FZ), due to the thermal effect produced by the laser welding thermal cycle. Their dimensions are quantified. The microstructural examination using scanning electron microscopy showed the presence of fine dendritic structure in the FZ although the use of electron dispersive spectroscopy analysis confirm that an eutectic Mg₁₇Al₁₂ phase are surrounded by α-Mg solid solution in the HAZ. Electron backscattered diffraction technique revealed an important grain refinement in FZ and considerable twining phenomena in HAZ, but no texture. X-ray diffraction technique has been used, full width at half maximum of diffraction peaks is measured; it also confirmed the grain refinement in FZ in comparison to BM and HAZ. Both microhardness and tensile proprieties of the complete weld joint are similar to those of the BM.

Abstract: Frequency control is becoming increasingly critical today due to the growing size and changing structure of complex interconnected power networks. Scaling up economic pressures for efficiency and reliability of the power system has necessitated a requirement for maintaining system frequency, and tie-line power flows as close as possible to scheduled values. High-frequency deviations may degrade load performance, damage equipment, resulting in overloading of transmission lines, which may interfere with system protection schemes, and, finally, may also result in an unstable condition of the power system. More so, Load Frequency Control ( LFC) plays a vital role in the modern power system as an auxiliary service to support power exchanges and, at the same time, to provide better conditions for the trading of electricity. Therefore, the tuning of the dynamic controller (i.e., net frequency and net power interchange errors) is a significant factor in achieving optimum LFC performance. Appropriate tuning of the controller parameters is required in order to achieve excellent control action. In view of this, this paper introduces the dynamic tuning of controller parameters in a two-area multi-source power system with an AC-DC parallel tie line for optimum load-frequency control performance. Matlab/Simulink software is used to realize the system simulation. System dynamic performance is observed for conventional PID tuning by the Ziegler Nichols method and the Kitamori method, fuzzy logic controllers, fuzzy-logic PID controllers, fuzzy PID controllers, and polar-Fuzzy controllers. Furthermore, the frequency and tie-line power response of the interconnected areas were compared based on the setting-time, peak-overshoot, and peak-undershoot. The simulation results show that the responses of the fuzzy-based controllers are faster than those of the classical controllers, resulting in minimized frequency and tie-line power deviations.