International Journal of Engineering Research in Africa Vol. 43

Abstract: In the process of forming solid materials, the plastic instability phenomena often control the appearance and performance of the finished product. The study of these phenomena is therefore of great scientific and technological importance. Polymers materials, for example, polyvinyl chloride (PVC) are frequently used in the plastic pipes in pressure vessels and pipelines, which require details that are more serious, it is therefore essential to understand the mechanisms of plastic instability in polymers in order to know how to control them. In order to determine the plastic behaviour of PVC, the true stress-strain response under large plastic deformation was investigated in different stress triaxiality frameworks. A particular attention was given on the volumetric strain evolution and the damage. The effect of stress triaxiality on the fracture strain was also examined. In the second part of this paper, an elasto-viscoplastic behaviour model is presented, with non associated plasticity, damage and coalescence, which represents the observed behaviours of a PVC material under different triaxialities and for three initial void shapes

Abstract: The possibility of obtaining the vermiculite fire treatment at low temperature (burnt vermiculite) is considered in the article. The vermiculite structure features are investigated to reduce the subsequent burn temperature. By X-ray diffraction analysis it is established that the pre-treatment by a salt solution causes a change in the elementary cell of the vermiculite crystalline grid. It allows to receive the extended vermiculite under the lower burn temperature than in case of the ordinary non-treated vermiculite. To show the creation possibility of the building materials with burnt vermiculite the concrete unit weight and strength with gypsum and cement binder are studied. It is determined that the mentioned concrete strength is higher compared to concrete with ordinary vermiculite at the same density of these concretes. The thermal insulation properties are also significantly higher. The light concrete with vermiculite aggregate is used as the thermal-shield enclosing structures in building and structure constructions. The decrease of the vermiculite burn temperature will contribute to reducing the energy intensity of construction as a whole.

Abstract: Climatic and traffic effects are the causes of aging of the surface layer of asphalt, which leads to the necessary renovation of the latter. The use of waste from the tread layer provides a viable and beneficial solution for the environment and the economy. However, this solution must meet the requirement of sustainable development, which necessitates that a road has a very long lifespan. In this study we investigated the performance of recycled asphalt in terms of fatigue (as an element of life-cycle control). All the formulas were tested by the fatigue test in order to define the influence of the proportions of the asphalt aggregates, penetrability of the new binder used, and the manufacturing temperature. The results obtained showed the relationship between the contribution binder (reproduced between the new binder and the old binder) and the fatigue resistance under the influence of the parameters that we have mentioned above. At the end an optimization study has been carried out in order to determine exactly the doses required to formulate recycled asphalt resisted to fatigue The optimization seeks to maximize the asphalt aggregates and minimize the temperature of manufacture with a class of the binder compatible.

Abstract: Alum is a useful product in both leather tanning and water treatment purposes where it serves as a coagulant and disinfectant. High quality alum has recently been produced from some Nigerian kaolinite (Bauchi and Kankara) via the energy-saving process. This process utilizes the heat generated when sulfuric acid is mixed with water to dealuminate the metakaolin, instead of the usual application of external heat source. This study focuses on testing their effectiveness in actual water treatment process in comparison with a commercial alum. Several parameters of the raw water and 50 to 300 ppm of alum-raw water solution were measured to determine the effects of the alum addition. The influence of both alums was found to be strikingly similar. While the total dissolved solids (TDS) and conductivity increased with alum concentration, the biological oxygen demand (BOD), chemical oxygen demand (COD), and alkalinity of the water showed reduction. The coagulating effectiveness of both alums was demonstrated by over 95% reduction in the turbidity of the raw water sample. The results also revealed that the alum from Nigerian kaolinites showed remarkable and desirable water treatment qualities and compares well with the commercial alum for all the tested parameters. The development of alum production plant using Nigerian kaolinite is therefore recommended as it can serve as alternative to the present commercial alum that is majorly imported.

Abstract: Due to the awareness of adverse effects of conventional fuels to environment and the frequent rise in crude oil price, the need for sustainable and environmentally friendly alternative source of energy has gained importance in recent years. This alternative has been identified to be biofuel, one of which is biodiesel. As such, this work was carried out to contribute to the development of biodiesel. The aim was accomplished by employing Design Expert, based on the chosen operating factors (reaction temperature and methanol-to-oil ratio), to design experiments carried out for the production of biodiesel using used cooking oil and methanol in the presence of alkaline catalyst. After carrying out the experiments using the design parameters generated, the results were analysed, and a model equation was developed for the system. Furthermore, the model equation was used to optimize the process using Excel Solver to obtain a temperature, a methanol-to-oil ratio and a yield of 63.45 °C, 3 and 59.32 as the optimum values, respectively. The optimum parameters estimated were validated experimentally and with the Aspen HYSYS model of the process that was also developed. The results obtained using the design factors showed that the factors considered were having effects on the yield of biodiesel. Also, the results of the experimental validation carried out with the optimum parameters obtained with the aid of Excel Solver were found to compare very well with those obtained from the simulation of the developed Aspen HYSYS model of the biodiesel production because the errors were estimated to be less than 5%. Therefore, the developed Aspen HYSYS model of biodiesel production of this work was able to represent the process very well and can be used for further studies on the process.

Abstract: The relationship of oscillations amplitude of the granular medium-elastic screw system whilst passing over resonance at different values of the bulk mass per unit length at different motion velocity has been studied. The relation of resonance oscillations of the granular medium-elastic screw system described by ratio α(t) and ν(t) has been shown. Based on these ratios, we plotted time variations of amplitude against quick passing over resonance.

Abstract: The Modelling and control design of Two Wheel Vehicle represents an open and a challenging problem in terms of the complexity in these kind of vehicles. This article aims to represent a comparative analysis of two strategies of control which are modern controller LQR and Conventional Controller PID for the two wheeled vehicle. The main goal is to compare their performances in terms of the time specification and to determine the best control strategy. We begin our development with the implementation of the dynamic model of the two wheeled vehicle using Lagrange modeling with holonomic constraints. Further, the article deals with analyzing the eigenvalues of the linearized dynamic system at which the two wheeled vehicle lean and steer are stable. This research targets the development of the two controllers: PID and LQR. Those controllers are used to control both steer angle, and lean rate angle of two wheeled vehicle. The study includes as well a comparative assessment of those control strategies in terms of performance.

Abstract: Images are susceptible to degradation by noise from different sources as they undergo various processes. The effect of noise degradation affects the visual information fidelity, structural content and the decryption performance of an image encryption algorithm. In this paper, the effects of noise attacks on the performance of a hyperchaos-based digital image encryption algorithm is evaluated. In hyperchaos-based encryption algorithm, chaotic dynamics are used to encrypt the pixels of images. Two noise models, namely Gaussian noise and salt and pepper noise were added to test images, prior to encryption operations, in order to test for the robustness of the algorithm to noise attacks. The mean square error, peak signal – to – noise ratio, structural content and normalized correlation coefficient of the plain and decrypted images were evaluated. The results obtained indicated that noise has insignificant effect on the decryption performance of the algorithm, as the noise-degraded images and their decrypted counterparts were very identical. Thus, the image encryption algorithm is tolerant of noise and can therefore be used in noisy channels.

Abstract: The growing demand for bandwidth and spectrum has inspired the ongoing efforts to establish the future 5G network supporting vertical sectors such as cyber-physical systems (CPS). Cooperative communication is one of the requisite techniques to improve coverage, network capacity and reduce power consumption in the network. In this paper, a symbiotic two-phase intelligent transmission is considered. The first phase occurs between the source and the candidate relays, and involves the selection of a set of “reliable relays”. The second phase occurs between the reliable relays and the destination, and involves the selection of the “best relay” for transmission. Dynamic relay selection using k-means clustering is used to detect the most significant correlation between all the channel state information (CSI) attributes in the system. The work identified the reliable relays while reducing the number of relay nodes for the second transmission phase. Contextual scenarios are created with typical network configuration using three geographical locations Coventry, Birmingham and London. An experimental validation is done with Omnet++ environment for the scenarios of three geographical locations. A natural grouping of mobile users is carried out leveraging the relay capabilities. The results are validated using support vector machine (SVM) classification algorithm. Considering urban environment deployment of relay nodes, metrics such as signal-to-noise-plus-interference ratio (SINR), attenuation, signal to noise ratio (SNR), link quality, k-means clustering, accuracy, and root mean square error (RMSE) are investigated for the Direct-2-Direct (D2D) capable relays. It was observed that the proposed technique both outperforms the other fixed-parameter relay selection techniques and improves with larger datasets unlike the other techniques.

Abstract: Most African remote telecoms base stations are powered from diesel generators, however, these generators are losing attractiveness due to their less reliability in addition to high operational and maintenance costs. Over 65% of the loss of telecom services observed in remote areas are caused by outages resulting from diverse types of failures that these generators can suffer, on top of their impacts on the environment. As alternative, off-grid renewable energy systems are often employed in place of diesel generators due to their capability to provide reliable electricity at an acceptable cost. This study proposes an off-grid system based on PV generators and backup energy storage consisting of lithium-ion batteries as an extended solution for powering remote telecom base stations in Africa. Modelling and simulation is performed using Matlab/Simulink environment. The findings showed better characteristics of lithium-ion battery bank as compared to lead-acid unit; lithium-ion battery bank displayed higher initial current and voltage over lead-acid battery bank. Moreover, when, both battery banks reached 50 % of their state of charge, lithium-ion bank current was still higher than that of lead-acid bank. In the same vein, lithium-ion battery bank presented a slower discharge time than lead-acid battery bank on top higher values at 50 % and 70% state of charges. Lastly, the state of charge of the lead-acid battery at the end of the simulation was 50 %, while that of the lithium-ion battery bank was around 60 %.