International Journal of Engineering Research in Africa Vol. 33
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International Journal of Engineering Research in Africa Vol. 29
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International Journal of Engineering Research in Africa Vol. 26
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摘要: This study investigated bending stress distribution on involute spur gear tooth profiles with pressure angle of 20 ̊ but different modules 2.5, 4.0 and 6.0 mm, using a finite-element-based simulation package - AutoFEA JL Analyzer. The drafting of the geometry for the three gear tooth profiles were implemented on the platform of VB-AutoCAD customized environment, before importing to the package. These were separately subjected to analysis for bending stresses for a point at the tooth fillet region with appropriate settings of material property, load and boundary conditions. With the same settings, the bending stresses were computed analytically using American Gear Manufacturers Association (AGMA) established equation. The results of the two approaches were in good agreement, with maximum relative deviation of 4.38%. This informed the confidence in the implementation of the package to investigate the variation of bending stress within the gear tooth profile. The simulation revealed decrease in the bending stresses at the investigated regions with increase in the module of the involute spur-gear. The study confirms that Finite element simulation of stresses on gear tooth can be obtained accurately and quickly with the AutoFEA JL Analyzer.
摘要: A nonlinear 3-D finite element analysis was conducted to analyze the crack front behavior of a center cracked aluminum plate, asymmetrically repaired with composite patch. According to experimental observations, the crack front was modeled as an inclined shape from the initial state where the crack front is straight and parallel to the thickness direction from the patched side toward the un-patched side. The skew degree is found to strongly influence the stress intensity factor (SIF) distribution along the crack front. In effect, the obtained trends of the SIF’s distribution are different and changes during crack growth stages. The main finding is that regardless the crack front shape (inclination), the average stress intensity factor through the crack front remains constant and consequently, it means to be an effective parameter to estimate the fatigue life and crack growth of the asymmetrically patched structures. The performed models gave good results compared to the literature and the different findings correlate well with the experimental observations and make sense with a realistic crack development.
摘要: Beam-like members such as shafts, levers, frame components, beam structures, etc. are regularly designed and constructed in the field of mechanical and civil engineering. It is pertinent to know the structural integrity of the design before construction or fabrication. Beam deflection and stress calculations can be cumbersome and results from commercial simulation packages are not devoid of truncation and/or round-off errors because they are based on numerical schemes. To reduce or eliminate these issues, a computational tool, CABDA, has been designed and developed on matlab. The algorithm is based on analytic equations of beam deflection and bending stress theories; a design flow chart and graphic user interface were done to implement the algorithm. Experiments and simulations have been carried out for steel and brass rectangular beams which were compared with results obtained from CABDA for the same beam model. Average deflection errors recorded for steel beam are-0.4 and-0.015; for brass beam are-0.69 and-0.1 for experiment and simulation respectively. Average bending stress error recorded is-0.19 for simulation. It is observable that simulation results compare closely but CABDA gives exact results and therefore is very appropriate for simple beam problems.
摘要: In this paper, a new hybrid method of optimization by the heuristics algorithms to evaluate the reliability of the electronic card by simulating its thermo-mechanical behavior is presented. A model of simulation by finite element is developed to consider the maximal deformations due to temperature; a mechanico- computing coupling is used to find the optimal structure. Embedded electronic systems are playing a very important role in several areas, such as in automotive, aerospace, telecommunications and medical sectors. To properly perform their functions, electronic systems must be reliable .This powerful and robust algorithm which is based on hybridization of Differential Evolutionary algorithm with Particle Swarm Optimization (PSO) gives performance results .
摘要: The aim of this study is to model the distribution patterns of the different mechanical properties of a submerged arc welded pipeline steel API X70 and to investigate the relationship between Vickers hardness and other mechanical properties of API X70. In this study, serial mechanical properties of 70 pipes, formed by spiral submerged arc welding of high strength low alloy steel (HSLA) API X70, were measured in base metal and weldments. Four main statistical distributions: Normal, Log-normal, Weibull and smallest extreme value distributions were chosen to test the goodness of fit to the experimental data. As a result, normal and lognormal distributions can equally model the distribution patterns of the whole experimental data of studied mechanical properties except for the hardness and toughness of the base metal that can be approximated by Weibull and smallest extreme value distributions, respectively. Using the current data, a weak but statistically significant correlation is obtained only between the toughness of the fusion zone and the hardness of both the base metal and the heat affected zone. Consequently, the calculated regression models were unable to estimate impact toughness values based on future measures of Vickers hardness components.
摘要: In this research, the effect of nanosized air bubbles embedded within carbon nanotubes (CNTs) coated by various thicknesses of alumina (Al2O3) reinforced epoxy resin based composite on the natural frequencies of a multi-cracked bar is investigated in details. The impact of cracks’ locations and depths within the hybrid composite structure on the natural frequency profiles is investigated. The volume fraction of CNTs is fixed to 0.5 wt. % due to the significant improvements reported in the literature when the composite is reinforced with this volume fraction of CNTs. The results of the multi-scale finite element analysis are verified by comparing with previous studies and a good agreement is shown relating to the longitudinal natural frequencies. The results of the research show that the dynamic response of cracked bar is highly sensitive to the volume fractions of nanosized air bubbles located within the composite. The results of the study supported the hypothesis that the nanosized air bubbles can be used to reduce the weight of heavy composite structures along with using of suitable coatings to improve the mechanical properties of the hybrid composite. Furthermore. The results of the study can be employed to detect multiple cracks located within similar structures like wind turbine blade (WTB) fabricated from a hybrid composite structure composed of carbon fiber reinforced modified epoxy resin which contains nanosized air bubbles and CNTs nanofillers coated by Al2O3 at different thicknesses.
摘要: In an attempt to reuse and convert agro wastes into useful materials for the construction industry, this research considered the application of corn stalk ash (CSA) as partial replacement for ordinary Portland cement (OPC) in the production of interlocking paving stones. The study investigated the oxide composition of CSA to ascertain its suitability as a pozzolanic material. Some properties of paving stones with CSA as a replacement for OPC were examined. The results showed that CSA is a good pozzolana having satisfied the required standards. The compressive strength of the specimens with replacement levels ranging from 5 to 25% cured for periods of 3–56 days was lower at early curing time but improved significantly at later age. 10% replacement level showed increased strength compared to 0% CSA at 28 days curing period. Density decreased with increasing ash content, water absorption rate increased with increased CSA contents, while abrasion resistance increased with increasing amount of CSA substitutions. The test results revealed that CSA paving stones can attain higher strength than the conventional ones at longer curing periods, due to its pozzolanic reactions.
摘要: Modeling and simulation of mechanical structures in development phase are fundamental to optimize and improve the stability and reliability of the final product as well as to reduce the cost of prototyping and testing. Wind turbines are subject to critical loading to the centrifugal force due to wind speed and gravitational force. The present study discusses three-dimensional numerical simulations of combined Darrieus-Savonius wind turbine D-SWT for applications in urban and isolated areas for lighting, pumping water, etc. The Darrieus turbine is used to produce wind power and the Savonius rotor to start the system. Finite Element Analysis (FEA) using SolidWorks 2015 is employed to generate the geometry of the structure and SolidWorks Simulation to investigate the stability and reliability static on the structure of the D-WST built by two types of material of the blade Galvanized Steel (GS) and Aluminum alloys 1060-H18 (ALU). Mechanical parameter of the structure are calculated for critical loading conditions, including the gravity and wind pressure loading due to the wind speed of 23m/s. Simulations results indicate no structural failure is predicted for all components of the D-SWT for both materials used according to Von Mises criterion stresses and the factors of safety of the most fragile material are greater than (the unity) 1. The maximum displacements found (3.84 & 6.81mm), occurred at the tip blades (free ends levels). These displacements are accepted relatively to the structure size.
摘要: This paper presents a study of proposed approach founded on series active power filter based on photovoltaic array (PV-SAPF) which is controlled by classical PI using pulse width modulation inverter (PWM). The proposed system is connected to grid system to feed linear and nonlinear loads to handle deep sags, swells voltage, voltage distortion and power factor crushing caused by any electrical perturbation. In the other hand, the excess of the energy is injected into the mains when the network is not affected and after compensation. To prove the effectiveness of the planned system, the PV-SAPF is carried out using MATLAB / Simulink environment. The results Simulations results proved the ability and the efficiency of the proposed system in mitigation the harmonic voltage distortion, correction the voltage sag and swell, power factor improvment and power quality enhancement.
摘要: Micro-algae are a large and diverse group of simple typically autotrophic organisms which have the potential to produce greater amounts of non-polar lipids and biomass than most terrestrial biodiesel feedstocks. Having emerged as one of the most promising sources for biodiesel production, they are gaining research interests in the current energy scenario due to their phenomenal growth potential (< 21 days log phase) in addition to relatively high lipids production which are also excellent source of biodiesel. In this study, engine performance and emission profile was performed using biodiesel fuels and blends from micro-algal technology in a compression ignition engine. The technology of micro-algae involved open pond cultivation and the use of photo-bioreactor model BF-115 Bioflo/celli Gen made in the US of 14 litre capacity (200 Lux light intensity) and flowrate of 2.5L/min. The micro-algal species used were Chlorella vulgaris and Scenedesmus spp. The biodiesel produced were blended with conventional diesel (AGO) at different proportions. The performance parameters evaluated include: engine power, torque, brake specific fuel consumption (BSFC), smoke opacity, thermal gravimetry, thermal efficiency, exhaust gas temperatures and lubricity while the varying effects of emission pollutants during combustion were also studied. Results showed that viscosity, density and lubricity have significant effects on engine output power and torque than when throttled with AGO which was used as control. Combustion efficiency and emission profile were better than the AGO due to the oxygenated nature of the micro-algal biodiesel which brought about complete combustion. A striking deduction arrived is that oxygen content of the algal biodiesel had direct influence on smoke opacity and emissions in the engine and also thermo-gravimetrically stable for other thermal applications. The engine tests (BSFC, BTE, ThE, MechE, EGT) and overall emissions (CO2, CO, VOCs, HC, SOx, NOx) were within acceptable limits and comparable with AGO. The implication of the study is that Micro-algal technology is feasible and can revolutionise development in biodiesel industry.