Browsing by Author "Behailu Mamo (Mr.)"

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    Numerical Analysis of the Effect of Surface Finish and Material Properties on the Carburized Moly Based Low Alloy Material Subjected to A Contact Load
    (Addis Ababa University, 2022-10) Yibeltal Ali; Behailu Mamo (Mr.)
    Contact between rough surfaces between surfaces affects a variety of phenomena including friction, wear, thermal contact resistance, and electrical contact resistance. Different studies done on the mechanics of contacting bodies using analytical and experimental methods. Even though the experimental method to determine the surface treatment parameters is convenient and effective, the method is very expensive, consume more time to complete and it needs advanced tools. Furthermore, the analytical methods in analyzing real surface topography is a simplifying approach, which has low accuracy. Therefore, numerical modeling of the contact between rough surfaces is the alternative method. the aim of the study was to model the contact pressure contacting bodies to determine the effect of material density variation and surface finish method (machined and powder metallurgy surface) using finite element analysis utilizing ABAQUS software. The plastic contact of a rough surface and smooth flat surface is analyzed by modeling the rough surface as an isotopic, Gaussian, and random process. For running FE analysis an interface MATLAB code and Solid work software were used to create a 3D model from the measurement data. To achieve the objectives of the study particular material were selected and data were collected and rough surface modeling using computational model were performed. Result of the study in terms of contact load, real area of contact, and contact pressure are extracted from each contact analysis depicted that, the lowdensity PM rough surface leads to minimum area of contact but attains the maximum value of contact pressure maxP and cross hardness limit earlier when compared with the low-density machined and highdensity PM rough surface. In the PM surface model, the max PY ratio to cross the hardness limit of 2.22 at n n P A E of 0.0042 and in the machined surface model the max PY ratio to cross the hardness limit of 2.22 at n n P A E of 0.0057. The area of contact decrease whereas the mean P and maxP increases with a decrease in density value. In the machined surfaces, the contact load is shared by most of the contacting asperities and the asperity interactions restrain the asperities to remain in elastic state mostly even at high loads relative to PM surfaces. The real contact area is low and the von mises stresses and contact pressure are high for the low-density surface as compared to high-density surface, for the surface with ρ = 7.35g/cm3, real contact area occurs at 0.6377mm2 or 10.2% of nominal contact area, for the surface with ρ = 7.35g/cm3, real contact area occurs at 1.14115 mm2 or 18.25% of nominal contact area.
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    Simulation of the Effect of Aerodynamics on Quadcopter UAV for Precision Agricultural Sowing
    (Addis Ababa University, 2023-10) Anania Mulugeta; Behailu Mamo (Mr.)
    Nowadays, agricultural aerial vehicles are being broadly applied at the focal point of the farming development. Where crop damage rate raised by 1 % without mechanization at sown area, wind was one of the negative factors to utilization of UAVs for this purpose. This research was directed with the objective of characterizing three quadcopter UAV models and numerical CFD analysis of the models to study the aerodynamic behavior and stability analysis for precise agricultural sowing application. Implementing the finite volumetric analysis using Rynolds Average Navier Stock method, Ansys was used to simulate the fluid flow simulation along the identified horizontal and downwash wind fields for wind speed ranges of 0.3 m/s, 0.6 m/s, 0.9 m/s, and 1.2 m/s, 2.5 m/s considered in case of altitude increase. The objective parameters were velocity magnitude, pressure distribution, drag force, drag coefficient and moment coefficients. Findings of drag coefficients of rectangular solid, crossed helical, mobius ring all with elliptical hopper were 0.274, 1.29, 2.5 respectively, for downwash flow and 1.5, 2.6, 3.7 respectively, for horizontal flow during 2.5 m/s wind flow. Instability in terms of impulse response were more pronounced on mobius ring with elliptical hopper at 2.5 m/s wind gust while rectangular solid with elliptical hopper had revealed a desirable minimum drag coefficient and stability condition on moment coefficients for both flow cases as compared to the other models. In conclusion, shape effects had been observed on the variation of drag and stability values particularly on mobius ring with elliptical hopper