International Journal of Engineering Research in Africa Vol. 11

Abstract: In the Sahel, a vertical wind shear appears in the dry and in the wet seasons. In Niamey, Niger, during the dry season, the period of strong shears is clearly linked to the Nocturnal Low Level Jet (LLJ) since it occurs in a narrow time period around 06H00 UTC at 60% of the cases reach shears which require an alert to the pilots (higher than 4 ms^-1 per 100 m). The majority of cases occur during the night with a wind shear direction between 90 and 150° per 100 m, which is shown that it is dangerous for aircraft. In Bamako, Mali, high wind shears represent (higher than 4 ms^-1 per 100 m) only 16-22% of the cases and can occur at any time of the day. There are, however, 8% of the cases, the whole day long, when the wind shear can reach more than 6 ms^-1 per 100 m. Most of the wind shear directions are also between 0 and 90° per 100 m during the night. This is why the Agency for the safety of aircraft navigation in Africa and Madagascar (ASECNA) has put in 2004 at Bamako airport an UHF wind profiler radar for monitoring nocturnal strong Low Level Jet wind shear which occur regularly in this airport.

Abstract: The tensile strength, specific tensile strength, breaking force, tenacity and percent elongation of some fibres extracted from eight fibrous plants found in Northern Nigeria were determined with a view to ascertaining their suitability for the replacement of glass fibre in plastic composites. Also the crimp properties and work of rupture with the specific work of rupture for all the plant fibres were analysed. The fibrous plants were Sisal (Agave Sisalana) (ASA), Lalloh (Corchorus Triden L.) (CCR), Dargaza (Grewia Mollis Juss) (GRW), Kenaf (Hibiscus Cannabinus L.) (HCB), Goruba (Hyphaene Thebaica)(HYP), Sukuwa (Sida Acuta) (SDA), Karlgo (Piliostigma Thoningii) (PTA) and Shikuri Tuggah (Urena Lobata) (ULB). Their properties were compared with E-Glass. The results show that whereas the highest tensile strength of the plant fibre (ASB) was about one-third that of the glass fibre, the highest specific tensile strength of the plant fibre (HCB) was about 5 times that of the glass fibre. The percent elongation of the plant fibres except HYB and SDA were at least 5.6 times that of the glass fibre. The specific work of rupture for the plant fibre were also found to be upto 31% higher compared with that of glass. Three of the plant fibres, (HCB, ASA and ULB) were observed to be possible replacements for the classic glass fibre.

Abstract: Investigations were carried out to evaluate the performance of a low heat rejection (LHR) diesel engine consisting of air gap insulated piston with 3-mm air gap, with superni (an alloy of nickel) crown, air gap insulated liner with superni insert and ceramic coated cylinder head with different operating conditions of crude jatropha oil (CJO) with varied injection timing and injector opening pressure . Performance parameters [brake thermal efficiency, exhaust gas temperature, coolant load and volumetric efficienc and exhaust emissions [smoke and oxides of nitroge were determined at various values of brake mean effective pressure (BMEP). Combustion characteristics [ peak pressure, time of occurrence of peak pressure and maximum rate of pressure ris of the engine were at peak load operation of the engine. Conventional engine (CE) showed deteriorated performance, while LHR engine showed improved performance with vegetable operation at recommended injection timing and pressure. The performance of both versions of the engine improved with advanced injection timing and higher injector opening pressure when compared with CE with pure diesel operation. Relatively, peak brake thermal efficiency increased by 14%, smoke levels decreased by 27% and NOx levels increased by 49% with vegetable oil operation on LHR engine at its optimum injection timing, when compared with pure diesel operation on CE at manufacturers recommended injection timing.

Abstract: Impact coal cutting is a new kind of coal cutting method, totally different from conventional coal cutting in mechanism. To increase the blocky coal in long-wall coal face with low energy consumption, impact coal cutting is a good way to go. In this paper, an analysis of energy dissipation in impact coal cutting using stress wave is carried out. Firstly, the production, transmission and dissipation of energy are analyzed during the process of coal impact cutting, and the energy distribution area is also obtained. Secondly, the transmission rule of stress and energy are studied by the method of stress wave; through measuring the amplitude attenuation quantity of the first and any other cycle in oscillograph, the attenuation radio can be worked out. Lastly, the propagation process of energy was analyzed based on the impacting rule and propagation rule of energy; the relation between impacting consumption of energy and minimal irreversibly lost energy is expounded. It is pointed out that if the coal block is destroyed, the impacting consumption of energy must be more than the minimal irreversibly lost energy.

Abstract: Water production in an oil well is undesirable both economically and environmentally. Therefore water arrival pattern into a well has to be understood clearly where a reservoir is surrounded by an aquifer. However, predicting the breakthrough time of water in a producing well has been a controversial issue and a major challenge to petroleum engineers. This paper investigates water arrival pattern into a vertical well completed in reservoir with double-edge water external lateral boundaries to be able to understand important factors affecting water breakthrough. Water breakthrough time is the time it takes for the first droplet of water cut to reach the wellbore under the prevailing production rate regime. This marks the end of the production of clean oil from the well. Once the breakthrough time is approached, depending on the strength of the external boundary (supplying aquifer) the pressure responses in the reservoir first attain a steady state condition. Further production then leads to steady rise in produced water-oil ratio. Real time dimensionless pressure distribution, using appropriate source functions for a vertical well in a reservoir with double-edge water as its lateral external boundaries was utilized for the study. Well responses were computed for a wide range of reservoir, wellbore and fluid properties. Results show that water breakthrough time is strongly affected by the lateral distance of the external edge water from the perforations according to the relation t_D x²_eD/π²(k_h/ k_v). Not too far edge water would yield earlier breakthrough than far away edge water for a well completed in an isotropic reservoir. In a largely horizontally anisotropic reservoir therefore, water breakthrough may be delayed if the water from the edges respond unequally to a production transient in the well. For a reservoir with reasonable horizontal isotropy, only central well location may delay water breakthrough. If this does not yield the desired delay, then the perforation should be located farther vertically above the points opposite to the pay zone.

Abstract: In this paper a new kind of splines, called cubic trigonometric polynomial B-spline (cubic TP B-spline) curves with a shape parameter, are constructed over the space spanned by As each piece of the curve is generated by three consecutive control points, they posses many properties of the quadratic B-spline curves. These trigonometric curves with a non-uniform knot vector are C1 and G2 continuous. They are C2 continuous when choosing special shape parameter for non-uniform knot vector. These curves are closer to the control polygon than the quadratic B-spline curves when choosing special shape parameters. With the increase of the shape parameter, the trigonometric spline curves approximate to the control polygon. The given curves posses many properties of the quadratic B-spline curves. The generation of tensor product surfaces by these new splines is straightforward.

Abstract: Two coarse-grained granitic rocks - charnockite and biotite granite were studied with the aim of estimating their unconfined compressive strength from simpler non-destructive test values. The simpler tests were the ultrasonic pulse velocity, the Schmidt hammer rebound, and the specific gravity. Another test carried out was the moisture absorption. The rocks had compressive strength in the range 115-250 MPa, Schmidt hammer rebound number or index of 35-55, and pulse velocity of 3.4-5.5 km/s. The correlation coefficients between the uniaxial compressive strength and the rebound number were 0.86 and 0.81 for the biotite granite and the charnockite, respectively. Products of the rebound index and the pulse velocity and the specific gravity improved the correlation coefficients to 0.94 and 0.91 respectively. The high correlation factors implied that the compressive strength can be estimated using the simpler tests parameters. These simpler parameters also relate indirectly to geomechanical properties of the rocks such as drillability, boreability and machine tool wear. The moisture absorption alone and its combination with the rebound number correlated inversely and poorly with the compressive strength. The correlation coefficient ranged between 0.45 to 0.67. The moisture absorption therefore proved to be a poor predictor of the uniaxial compressive strength of the rocks.