Mechanical Design

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Abrasive Wear Behavior of Bamboo Reinforced Polymer Composite with PTFE
(Addis Ababa University, 2020-06) Sentayehu, Worku; Eyasu, Woldesenbet (Prof.)
The aim of the present work is to study the abrasive wear behavior of composites made by reinforcing bamboo fibers with the addition of PTFE and thermoset resin matrix. The fibers are extracted by hand and manual process and the composite samples were prepared to a maximum of 30% volume of fiber. Wear tests were carried out in dry conditions on a pin-ondisc which is modified by me and the machine at a constant sliding distance of 1000 m with sliding velocities of 2m/s and 4m/s and normal loads of 15N and 30N. The effect of PTFE content on abrasive wear properties of composites were investigated and compared with pure BPC composites made under the similar testing conditions. It is observed that the wear loss of composites increase with increase of normal load whereas the specific wear rate decreases. The optimum weight loss and specific wear rate for bamboo fiber reinforced composites were obtained at 30% volume of pure composite.
Analysis Effect of Surface Roughness, Material Removal Rate and Tool Life in Turning of Mild Steel Material
(Addis Ababa University, 2017-05) Muluken, Tesfaye; Daniel, Tilahun (PhD)
This Experimental work presents a technique to determine the better productive quality by Analysis of Effect Surface Roughness, Material Removal Rate and Tool Life in Turning of Mild Steel by controlling cutting experiment. Turning Experiments on Laze Machine were conducted with Spindle Speeds: 530, 700, 860 rev/min, Feeds: 0.5, 0.6, 0.7 mm/rev and Depth of cuts: 0.5, 1.0, 1.5 mm. Thus the three input process parameters such as Spindle Speed, Depth of Cut and Feed Rate have been selected to minimize the Surface Roughness, maximize Material Removal Rate and Tool life simultaneously The present work focused by using L9 Orthogonal Array (OA) on the processing steps to get the optimal values with the help of Minitab software using main effects graph, and Analysis of variance (ANOVA) was employed to investigate the characteristics and experimental results are provided the effectiveness of this approach. This technology has met the current needs of Industry owing to its shorter design cycles and improved the design of quality using Taguchi Method. The results revealed that the feed rate (68.7%) is only significant to minimize surface roughness and optimum values are (530rpm, 0.5mm/rev, 0.5mm) secondly spindle speed (48.7%) the major significant parameter for Maximize Material Removal Rate and the Optimum values are (860rpm, 0.7mm/rev, 1.5mm) lastly spindle speed (75.3%) is Highly significant parameter for maximize Tool life and the optimum values are (530rpm, 1mm/rev, 0.5mm), Finally, the relationship between cutting parameters and the performance measures ( Surface Roughness, Material Removal Rate and Tool life) were developed by using multiple regression analysis.
Analysis of Fatigue Crack Propagation and Life Estimation of Pelton Turbine Bucket by Finite Element Method
(Addis Ababa University, 2020-11) Tadele, Libay; Mulugeta, Habtemariam (PhD)
The Pelton turbine bucket is subjected to different loads under the turbine operating conditions of high rotational speed. One of the most catastrophic failures that could occur in a Pelton turbine is the fracture of the bucket, where the hydraulic jet force is at its maximum and applied for various cycles. The continual application of this cyclic load will result in nucleation and then fatigue crack propagation. This failure of Pelton turbine bucket has a great influence on durability of the turbine. The aim of this thesis is to analyze fatigue crack propagation and estimating the life of Pelton turbine bucket. To do this, a governing equation for crack propagation and life estimation was derived and a Pelton turbine bucket was designed. The three-dimensional model of Pelton turbine bucket was modeled by commercial software SOLIDWORKS. The modeled bucket was then imported to ANSYS 19 workbench. Finite Element analysis was done after meshing, boundary conditions and applying load. Then, static stress analysis and fatigue crack propagation of the turbine bucket was investigated using stress intensity factors. The stress-intensity factor was evaluated for each increment of crack depth and it was related with fatigue crack growth rate. The fatigue crack life was then calculated for each crack increment. As the result obtained, analysis of fatigue crack propagation and life estimation of the bucket are discussed. And few recommendations are made for the future study.
Analysis of Mechanical Properties of Automotive Disc Brake by Finite Element of Method (FEM)
(Addis Ababa University, 2018-06) Oliyadi, Dereje; Daniel, Tilahun (PhD); Muluken, Maseresha (Mr.) Co-Adviser
Excellent control of braking system in automobile is the essential for safety of braking performance. The brake disc is affected by type of friction material of brake pad. The determination of mechanical interaction that happen between brake disc of automobile and brake pads are very important in design consideration of braking system of automobiles. For this investigation, the TOYOTA HIACE minibus taxi of 12 seats that used in Ethiopia City is taken as a sample. While, the problem occurred in this automobile is most of time failure of brake pads when braking is applied, and wear and fade of brake disc is occurred. Due to this kind of problem some time accident is happen; so the cause of this kind of problem happens in brake disc and brake pad of automobiles of TOYOTA HIACE minibus taxi that used in Ethiopian City is the idealization of selection of good performance friction material of brake pad with corresponding brake disc. Further, due to lack of consideration for selecting best friction material of brake pad with environmental friendliness, in the case of TOYOTA HIACE automobiles dust is produced from friction material of brake pad during braking time affect the aquatic life. Thus, the study of mechanical properties of brake disc with interface of brake pad by finite element method with the help of ANSYS software and experimental investigation of friction materials of brake disc used in local City taxi is very important regarding to best braking performance of automobiles and environmental protection. Hence, as result obtain from analysis of finite element method with the help of software and experimental result of laboratory test; for safe environmental protection, reducing (or) free of Copper in brake pad of automobile especially in brake pad of TOYOTA-HIACE minibus 5L. And the use of Al-MMC brake disc with Ceramic brake pad is best for braking performance of automobiles rather than other interface.
Analysis of Stresses in Helical Gears by Finite Element Method
(Addis Ababa University, 2007-10) Alemu, Negash; Tesfaye, Tamrat (phD)
Gears are one of the most critical components in mechanical power transmission systems. The bending and surface strength of the gear tooth are considered to be one of the main contributors for the failure of the gear in a gear set. Thus, analysis of stresses has become popular as an area of research on gears to minimize or to reduce the failures and for optimal design of gears. This thesis investigates the characteristics of an involute helical gear system mainly focused on bending and contact stresses using analytical and finite element analysis. To estimate the bending stress, three-dimensional solid models for different number of teeth are generated by Pro/Engineer that is a powerful and modern solid modeling software and the numerical solution is done by ANSYS, which is a finite element analysis package. The analytical investigation is based on Lewis stress formula. This thesis also considers the study of contact stresses induced between two gears. Present method of calculating gear contact stress uses Hertz's equation. To determine the contact stresses between two mating gears the analysis is carried out on the equivalent contacting cylinders. The results obtained from ANSYS are presented and compared with theoretical values. Face width and helix angle are important geometrical parameters in determining the state of stresses during the design of gears. Thus, in this work a parametric study is conducted by varying the face width and helix angle to study their effect on the bending stress of helical gear.
Analysis of Traffic Accident In Addis Ababa: Traffic Simulation
(Addis Ababa University, 2006-06) Samson, Fanueal; CHANDRA (PhD)
This paper discusses the growing problem of road traffic crashes, particularly in Addis Ababa with particular reference to the magnitude, risk factors, interventions and research priorities. The 2004 World Health Report shows that of the 1.2 million people killed in road crash worldwide, 85% are in developing countries. The traffic police reports human error, road environment and vehicle factors as the main causes of road crashes. However, little documentation is available on the broader underlying factors such as deficiencies in the breviaries changes, ineffective road safety legislation and enforcement, systems for data collection and management, and inadequate medical infrastructure for post-injury management. Although a variety of road safety interventions have been successfully applied, little attempt has been made to promote and implement them. Every year, around 300 people are killed on Addis Ababa's roads and 1500 are light and seriously injured [Federal Police Central Bureau]. The governments have launched several campaigns, such as “Think!” and Road Safety Campaign (RSC), to help people become aware of road safety issues and try to reduce road accident. This study tries to analyze the traffic accidents, and develop a computer-based traffic simulation for the route selection. This thesis has two main functions. Firstly, the aim is to provide users with an understanding of the major causes of traffic accidents and present using several Statistical tools. At the second function, it will apply an innovative, hybrid statistical model for route selection based on accident prediction to traffic police office data. The system, if developed to include the whole network in Addis Ababa, will support several target groups, viz. all road users, Traffic Police and the Emergency and Fire Service through to insurance companies, and local government. The ideal system will Analysis of road traffic accidents in Addis Ababa: Traffic simulation iii give people useful suggestions about how to improve road planning and traffic management. In this paper, a survey is done on current prediction models and visualization techniques. A prototype system is developed using these theories. The functions in the prototype system are limited. More data is required to actualize the system on real terms. The study consists of two major parts: the first part gives detail about the road traffic accident, and Ant Based Control Algorithm implemented for road traffic management. The second part, customization of research empirical equations and experiences to our local conditions and simulate/ forecast the future trend and also with the help of software developed, route selection at the pick hours is managed for the specific path in Addis Ababa. In conclusion, the paper highlights the background of the growing problem of road traffic injuries in the city and provides some basis for optimism in tackling it.
Analysis of Wear Resistance of Wheel-Rail Contact Surface Materials: In the Case of Addis Ababa Light Rail Transit
(Addis Ababa University, 2020-01) Teshome, Meku; Daniel, Tilahun (PhD); Muluken, Masresha (Mr.) Co-Advisor
The purpose of this thesis is to study wear resistance of wheel-rail contact materials of Manganese steel and Pearlite steel. The wheel-rail contact is a critical interface in the railway technology and study of failures in most railways may cause due to wear of wheel-rail contact surfaces. Application of this thesis is on railway technology in the specific area of Addis Ababa Light Rail Transit. It is a new railway technology in Ethiopia. So researches on this area are needed to identify the existing problems and to avoid such problems from the start. The method of this thesis is numerical and analytical analysis of wear resistance of Manganese and Pearlite steels. Based on this method wear and wear resistance of wheel-rail contact materials are evaluated. Using the results of wear and wear resistance of Manganese Steel (current material of Addis Ababa Light Rail Transit) is compared with Pearlite Steel (new material). Since, wear volume of Manganese steel and Pearlite is 0.00169 m 3 3 and 0.00141m respectively at maximum load and maximum distance traveled and wear rate value of Manganese steel is 0.00000335 m 3 /m and Pearlite steel is 0.00000205m 3 /m. On the other hand wear resistance value of Manganese steel and Pearlite steel is 3.98e 5 5 3 and 4.88e m/m respectively. And also wear index value of Manganese steel is 1846.43 and 1599.97 for Pearlite steel. Results of this wear analysis shows that there is less amount of wear volume, wear rate and wear index in Pearlite steel than Manganese steel. On the other hand wear resistance of Pearlite steel has higher than Manganese steel. Finally, this thesis verified that Pearlite steel is better in hardness than Manganese steel.
Analysis of Wheel/Rail Contact Geometry and Applied Load Conditions on the Rail Head Surface
(Addis Ababa University, 2012-10) Addisu, Negash; Daniel, Tilahun (PhD)
Now a day the railway transport infrastructure in Ethiopia is the major issues in relation to the development of the country. To strengthen this infrastructure, related researches must be conducted at the beginning of the construction of the sector. This paper which mainly concerned about the analysis of wheel/rail contact is done to predict and minimize failures caused by improper wheel/rail contact. The objective of this research is to determine the optimum wheel/rail contact and to identify the position of contact, which is basic to justify the way of load distribution on the contacting interface. In this paper the analysis of wheel/rail contact is based on the X, Y, and Z coordinate systems. With the help of these coordinates the type and place of contact on the wheel/rail interface and the way of stress distribution on the rail head surface is identified. Throughout the whole wheel/rail contact analysis, the Hertz contact theory assumptions are basically considered. Therefore based on Hertz contact theory and analytical results (mathematical models developed), the type of contact between wheel and rail is identified as point contact. The positions of the contact point is on the center of rail head where the rail lateral surface parameter ��2��=0 and varies across the wheel lateral surface depending on the position and arrangement of the wheelset. During the analysis of wheel/rail contact the parameters considered are axle load, wheel and rail profiles. By using these parameters the maximum pressure applied throughout the contact point is calculated to be 794.9 MPa. From MATLAB (7.6) and ANSYS (13) simulation results the main failure causes due to maximum pressure applied are principal and shear stresses having their own direction of application on the rail head surface under axle load applied. The shape of the contact patch on the rail head surface is elliptical. The shape identified is practically matched with the assumptions taken from Hertz contact theory. However the size of elliptical patch depends on the size of load applied. The stress distribution throughout the area of contact patch and the neighboring surfaces depends also on the size and direction of applied load.
Analytical and Finite Element Analysis of Surface Wear on Disc Brake Rotor
(Addis Ababa University, 2015-04) Shegaw, Hailemariam; Tilahun, Daniel (PhD))
A particular type of dry contact condition, known as disc and pad brake in contact, in which exposed to wear. In this thesis the wear analysis of disc brake is analyzed by using analytical and finite element method during short brake condition. One particular existing disc brake design for a SUV car of model DD6470C is selected for the study. The dimensions, material property and maximum allowable speed and variable applied brake pressure of this car are used as an input both for analytical and finite element method. Analytical analysis of distribution of contact temperature along in radial direction of disc brake caused by applied heat flux is solved by using separation of variable method. Finite element model of disc and pad brake assembly is done using the CATIA software. Finite element simulation for contact pressure and von misses stress using ANSYS workbench for the case of the structural analysis of disc brake is done by applying only brake pressure and angular velocity. But, in the case of thermal-structural analysis the maximum contact temperature value of disc and pad is considered in addition to applied brake pressure. The contact pressure and von misses stress are calculated analytically and ANSYS workbench results are presented in contour plot and numerically. Contact pressure, von misses stress and wear depth are increasing as increasing of both brake pressure and contact temperature of disc in case of thermal-structural analysis. The structural analysis is less effect than that of thermal-structural analysis in all contact pressure, von misses stress and wear. Based upon the analytical and ANSYS workbench analysis, an analytical model of dry sliding wear was developed. A multi-aspect comparison between analytical and ANSYS workbench results were made. A good agreement between analytical and ANSYS workbench results shows that model provided a reliable prediction of the tribological systems of disc-pad contact. The critical point of contact for disc in contact with pad in the case of structural analysis is near to inner and outer radius of disc brake while thermal-structural is at 95.859mm along radial direction from its center. Thus, this study provides effective reference for design and engineering application of brake disc and brake pad. Key words: Analytical analysis, finite element method, contact pressure, wear
Analytical and Numerical Analysis of Adhesive Joints for Vehicle Application
(Addis Ababa University, 2018-12) Sura, Keneni; Ermias, G. Koricho (Assis Prof.); Araya, Abera (Mr.)
Adhesively joining technique becomes very important due to capability like joining dissimilar material, lighter vehicle design, and composite material assembly than mechanical fastening. During combining dissimilar or similar materials together there must be adequate understanding of the behavior of multi-material adhesively bonded joints to ensure efficiency, safety and reliability of such joints. This may include adhesive thickness, bond length, amount of load to be applied, type material to be joined, type adhesive to be used and other factors used in analysis parameters. Using Elastomeric adhesives such as polyurethanes Sikaflex 265 as adhesive and steel, aluminum, glass and composite as adherend, analytical and numerical analysis has been done on single lap joint for elastic limit. In analytical, derivation of analytical equation that describe peel and shear stress profiles along adhesive length which is to be validated by comparing to numerical analysis done by Finite Element commercial package ABAQUS for metals. By varying the parameters used in stress equation derivation the effect they have on strength of joint also shown on failure load determination for steel, glass and aluminum. For all metals the analysis done is valid for elastic Range only. Effect of fiber orientation of glass fiber reinforced polymer (GFRP) composite on the joint also analyzed. Selecting suitable failure criteria then failure load for each combination of joint parameters are done.
Analytical Selection of Material for Lifan 520 model vehicle Brake Disc
(AAU, 2018-06) Hailemariam, Getachew; Daniel, Tilahun (PhD)
In automotive engineering sector, the safety aspect is a major consideration in development of a new vehicle. Each single system has been studied and developed in order to meet safety requirements. Widely Disc Type Brake used for this safety requirements and manufactured for first time in 1902 G.C in United Kingdom. In Braking time, the Kinetic energy of a Vehicle changed to heat energy. This high temperature leads to reduce the rotors performance and failures will occur. The existing material of Brake Disc has suitable properties to facilitate this reduction in performance of Brake Disc. The objective of this research is analytically, Selecting alternative material for Lifan 520 model vehicle Disc Brake Rotor. the weighting of material is done among Cast Iron, Stainless Steel, carbon-ceramic, Aluminum Metal Matrix composite and Titanium alloys. From those Candidate Materials, Digital Logic Methods (DLM) is a method used to Select suitable material for Brake Rotor. Density, wear rate, coefficient of friction, compressive strength, Specific heat and Cost are a property of Candidate materials that considered in selection of suitable material for brake disc by Digital Logic method. The result of this analysis shows that, Aluminum Metal Matrix composite (AMMC) is the material that higher value of figure of merit (FOM) from all above five Candidate materials. Therefore, this material is best material for Disc Brake than Gray Cast Iron (GCI). Lifan 520 model vehicle is selected for this purpose. Some variables such as: Deceleration of a vehicle, Stopping Distance, mass of Disc, deformation and Von-misses Stress on Brake Disc is calculated in order to see the visible differences between Disc Brake made from new(AMMC) and old(GCI) materials. A 3D Modeling of Disc Brake is done by SOLIDWORK 2018® modeling software and FEA ANSYS 18.2® is used to calculate mass of Disc, deformation and Von-misses Stress. Result obtained from Numerical and FEA showed that; Disc Brake made from AMMC reduce the mass by 62.4 %, increase Deceleration by 33.16%, Reduce Stopping Distance by 31.7%. Generally, it increases over all performance of Brake Disc by 8.7%. Therefore, based on Shown result, it can be concluding that Aluminum Metal Matrix composite (AMMC) material is the Suitable material for Lifan 520 brake disc.
Aspects of Lean and Agile Manufacturing Systems and Their Appropriatness in Ethiopia
(Addis Ababa University, 2004-10) Zehrudin, Idris; Roy, R.N. (PhD)
The thesis deals with the principles of Lean and Agile Manufacturing Systems and their appropriateness in Ethiopian context. Inflexible mass-production methods that produce voluminous of standardized products were inadequate for demands of increased variety. In pursuit of greater flexibility and elimination of manufacturing wastes, Lean Production System has been developed. More recently, demand for further responsiveness to the everchanging customer demand and turbulent business environment, led to a formulation of Agile Manufacturing concept with the intention of greater adaptability. Thus, it is necessary to study their vital principles and adopt the appropriate system to improve the competitive capability of industries. Using available literatures, Internet, industry survey and analyzing the gathered pertinent information, the thesis reviewed the main principles of lean production system. Taking authentic pilot cases, enhanced value stream map is generated and lean Manufacturing Cell for cutlery production is designed. The fundamental principles of agile manufacturing system and then, the comparison of the two systems are also discussed. Finally the suitability of these systems in Ethiopia context is analyzed. It is found that Lean Manufacturing is a collection of technical and operational systems focused on productivity improvements with limited resources (44). LPS focuses on minimizing manufacturing wastes, continuously improving methods, utilizing flexible production system to produce variety of defect-free goods. Agile manufacturing (AM), on iii the other hand, is a comprehensive manufacturing system focused on thriving in unpredictable business environment. AM focuses on enriching customers, reorganizing production system for greater flexibility, cooperation to enhance market responsiveness and increased use of Information technology. The comparison between these systems shows a difference in viewpoint and perhaps strategy with regard to change, but not in method or approach. Cases on the implementation of Lean techniques indicate that industries can enhance competitiveness by adapting Lean. The survey revealed that Industries are experiencing forces that lead to more responsiveness. More over, it is found that most industries believe that the Lean Production is more appealing in current Ethiopian Industries Situation.
Assembly Line Modeling and Simulation of Footwear Manufacturing (a Case Study on Ramsey Shoe Factory
(Addis Ababa University, 2011-09) Mulugeta, Nahom; Kitaw, Daniel (PhD))
In today’s competitive global market, companies are mostly striving to strengthen themselves as much as possible in all competiveness dimensions of business. This demands for optimal production system which increases the overall productivity of the company. Survival of any business in today’s competitive market place depends mainly on response time, production cost, market price and flexibility of manufacturing. These things motivated continuous research in modeling and performance evaluation of manufacturing systems. In parallel to this, different simulation software play a great role in designing a model of a real system and conducting experiments with this model for the purpose of understanding the behavior of the system and evaluating various strategies and scenarios for the operating or manufacturing system. Since the majority of consumable and non consumable goods are manufactured on assembly line system; assembly line balancing problem is getting importance now a day. Footwear is one of the goods which are manufactured on assembly line system. Hence, this thesis is concerned with the modeling and simulation of assembly line balancing of footwear manufacturing in Ramsey Shoe Factory. Within the production department this thesis is mainly concerned with the modeling and simulation of the two assembly lines: Stitching and Lasting assembly line. To do so, Arena simulation software is employed to model and measure performance of existing manufacturing systems of both assembly lines. Based on the simulation model result of the existing system, different scenarios are proposed to solve observed problems of the existing manufacturing system. Problems that are identified in simulation model analysis were: Line balance efficiency for both assembly lines is low, Relatively high level of WIP is observed in some work station of stitching assembly line, low production output with respect to the installed capacity, and the output of stitching assembly line is significantly higher than that of the lasting assembly line which causes WIP of different model shoes to be piled up in between the two assembly lines. To solve these problems, five possible scenarios are developed. These are: Avoiding unnecessary Assembly line modeling and simulation of footwear manufacturing 2011 A case study on Ramsey shoe factory, AAiT (By Nahom M.) Page vi duplication resource from station with low capacity utilization, merging similar operations with low resource utilization together and assign to one worker, increasing level of resource at stations with high WIP, changing working method, and combination of all the above alternatives. Among the five developed scenarios, the last one, ‘Combination of all the above alternatives’ gives better performance of footwear manufacturing for the selected model shoe.
Assessment of Energy recovery options and its Economic evaluation from Municipal solid wastes in Addis Ababa (Arada subcity)
(Addis Ababa University, 2011-10) Amanuel, Tarikayehu; Dama, Tesfaye (PhD)
This thesis is intended to assess the energy recovery options from Municipal solid wastes that are collected from Arada Subcity. In the analysis, two particular schemes are analyzed and evaluated for their economic viability. They are Energy recovery through incineration and Landfilling. A detail analysis of each of these options is done to determine how much energy can be recovered by implementing them. Also the detail economic evaluation is conducted to decide on the more viable scheme. The analysis shows that the implementation of the Landfill gas-to-Energy scheme incurs the total estimated capital cost of around 37 million birr. The electricity generation potential of this scheme is around 23MW, which will make a financial value of around 160,000birr.While the capital cost required to implement incineration with energy recovery is estimated around 120 million birr. By implementing this option, around 2600MW of electricity can be produced, which makes a saving of 18,049,681birr, where the current electricity selling price is 0.29 birr/kWh. The analysis is done for the waste capacity of 25,000t per year.
Automobile Bumper Beam Analysis to Improve Energy Absorption
(AAU, 2017-10) Habtamu, Molla; Daniel, Tilahun (PhD)
Automotive Bumper is one of the main parts which is used as protection for passengers from front and rear collision. Bumpers beam play an important role in preventing the impact load from being transferred to the automobile and passengers. So it becomes an important part of a vehicle as a safety and performance point of view. The basic use of bumper is to absorb energy in case of a collision. The main purpose of this paper is to design a bumper beam which is to improve crashworthiness of the bumper and analyzes the impact behavior of a composite car bumper beam made from s-glass fiber reinforced epoxy composite materials with a volume fraction 60% fiber and 40% matrix. Crashworthiness is the ability of the bumper beam to prevent occupant injuries in the event of an accident and this is achieved by minimizing the impact force during the collision. The existing lifan 520 model bumper beam is replaced with composite bumper. The internal energy which is absorbed by steel material is 1200.9 J where the composite material is 1960 J which is 38.7 % higher than that of steel. The study is performed using ANSYS software for the design of the new car bumper made from s-glass fiber reinforced epoxy composite materials and the internal energy absorbed by the materials, total deformation as well are evaluated by use of finite element method.
Bending-Torsion Decoupling in Eigen Mode of Subsonic and Supersonic Composite Monocoque Aircraft Wing
(Addis Ababa University, 2007-11) Masresha, Muluken; Ramman, A.(PhD)
The thesis deals with bending-torsion decoupling in eigen modes of monocoque laminated composite aircraft (subsonic and supersonic) wing using commercial software ANSYS. Theoretical background, mathematical formulation and finite element solution for a laminated composite shell structure are presented in this study. A monocoque aircraft wing is made of laminated composite with fiber angles in each ply aligned in different direction. Various airfoil thickness and ply angles were considered to study the effect of bending-torsion decoupling. Results obtained are presented and parametric studies are made to show the effect of airfoil thickness variation and ply orientation. The effect of location of shear center relative to the center of gravity is also studied and the results are presented.
Biodiesel Production Optimization and Quality Assessment Using Jatropha Curcas Oil And Ethanol Alcohol
(Addis Ababa University, 2001) Demissie, Biniyam; Alemu, Demiss (PhD)
Concern over high transportation fuel costs, trade deficits, depleting resources, energy security, and mounting evidence of global climate change has led to re-investigation of fossil fuel alternatives. For this reason Ethiopian Ministry of Water and Energy has started promoting bio-energy as a means to transform the nation’s abundant renewable biomass resources into cost competitive, high power biofuels and products. Biodiesel offers one renewable fuel option that can be produced from non edible vegetable oil sources. Fortunately Ethiopia has many opportunities for biodiesel production. The country´s favorable climatic condition for the cultivation of non edible vegetable oil bearing plants and the abundance of ethanol alcohol produced from the byproduct of local sugar factories gave the country a great advantage in producing biodiesel and get a little relief from petroleum related problems. However, the effort made to introduce the technology and take the most out of it is so low to force policy makers and encourage local and foreign businessmen towards the production of biodiesel using local resources. Therefore this research tries to fill this gap. The main purpose of this research is therefore to develop a biodiesel production technique from Jatropha oil (Jatropha curcas Linnaeus) and a locally produced ethanol alcohol. Special attention was paid to the optimization of base-catalyzed transesterification for converting fatty acid ethyl ester (FAEE). The crude Jatropha oil used in the transesterification contained 5.01 mg KOH/g of acid and after neutralization it was possible to bring down the acid value to 1.35 mg KOH/g. Inorder to determine the optimum condition for tranestefication of Jatopha oil using ethanol and caustic soda as input, 16 experiments varyings ethanol-to-oil molar ratio (6:-9:1) and reaction temperature (55, 65, 70, and 78 oC). Reaction time, mixing intensity, and catalyst concentration was fixed to 3 hrs, 600 rpm, and 1.5 % by weight of the oil respectively. The optimum conditions found for transesterification were an ethanol-to-oil molar ratio of 9:1 and a reaction temperature of 70 0C. At the optimum condition obtained a FAEE conversion of 80 % v/v was achieved. The resulting Jatropha biodiesel has, a density of 0.86 g/ml, viscosity of 4.13 mm2/s, acid value of 0.71 mg KOH/g, and flash point of 173 0C satisfing ASTM D6751-02 and EN 14214 biodiesel standards. The production proces developed in this work will be used in production of a small scale plant withh capcity of 300 liter per day.
Biogas Production System Design for Condominium and its Feasibility
(Addis Ababa University, 2011-11) Gaddisa, Bekele; Alemu, Demiss (PhD)
The research is concerned with designing of Biogas Production System for Condominium and studying its Feasibility by crosschecking field survey and information from literatures. The field survey data support the opinion about the importance of constructing biogas plant for Condominium where the average family members’ number is five with average monthly energy cost for cooking is Birr 385 per family. The study indicates that at optimum condition 43.2 m3 day of biogas is obtained from the substrate collected from 10 blocks of Condominium. Based on present energy consumption, 43.2 m3 day biogas fulfills the cooking energy requirement for 43 households. If households use biogas instead of kerosene only, it can serve the cooking energy need for 115 households. Compressing biogas reduces storage requirements, concentrates energy content and increases pressure to the level needed to overcome resistance to gas flow. As the result of installing compressor for this system, 43.2m3 of biogas volume is stored in 7m3 of pressure vessel and the pressure increased to 11bar from 1.106bar. In this study, it was possible to see that the Biogas System Design for Condominium is financially as well as economically feasible as the NPV is positive and benefit cost ratio is greater than one. As financial analysis shows the 40 households will save annually Birr 121,175 or Birr 3,029 per family as a result of using biogas instead of other cooking energy sources & using biogas only instead of kerosene, the 115 households save Birr 1,067 per family per annual. This result is obtained if households construct a 96 m3 biogas plant with daily loading 1.5m3 of night soil in to digester
Characterizing Tensile and Flexural Properties of Synthetic Fibers-Reinforced Epoxy Composite for Foot Prosthetic Application
(Addis Ababa University, 2021-09) Galana, Abay; Samuel, Tesfaye (PhD)
Materials has direct and critical impact on the performance of prosthetic foot. The aim of this thesis is to characterize the tensile and flexural properties of the four stacking sequences of E-glass and hybrid (E-glass/carbon) epoxy composite for prosthetic foot using powerful FEA software (ANSYS 19.2) for selecting stacking sequence that yields high strength without experimental cost. Additionally, to compare the design and strength performance of prosthetic foot model for two materials (Homo-polymer-polypropylene and selected composite) by numerical simulation. This starts from determining the elastic property of lamina to modeling of testing samples according to their standards for each stacking configuration using ANSYS workbench and verifying the numerical result with analytical MATLAB solution. The result shows that the ROM and Halpin-Tsai predicts longitudinal and transversal properties of the lamina with an acceptable range of errors from (1.66%-3.04%) and (0.5%-3.02%) respectively compared to experimental result of [34]. In pure E-glass/epoxy and hybrid/epoxy laminate the ultimate tensile strength is increased from 777.44MPa to1475.5MPa and 1865MPa to 1935MPa respectively. Similarly, in flexural testing the ultimate flexural strength of hybrid composite is increased from 1299.2Mpa -1934.3MPa due effect of stacking sequence. Among the all stacking configuration the SS-3 ( ��) results higher tensile and flexural strength and selected for prosthetic foot. The failure loads of laminate in each stacking sequence verified the numerical results with an error less than 2% and 3% for tensile and flexural loading respectively. The composite prosthetic model has higher performance than Homo-polymer-polypropylene model. The model of prosthetic foot from Homo-polymer-polypropylene is not operating under the material stress limits. The deformation resistance, energy storage capacity, safety factor and stiffness of composite foot is increased by 18.9%, 53.2%, 56.2% and 18.8% respectively compared to HPP prosthetic foot. Its weight and is reduced by 30.62%. Finally, this composite is suggested for prosthetic producers (Prosthetic and orthotic center).
Computer Modeling and Simulation of Coal fired Cogeneration Power Plant
(Addis Ababa University, 2004-07) Tamirat, Yohannes; Alemu, Demiss (PhD)
This thesis describes a power plant simulator which has been developed using MATLAB code. The basis of the power plant modeled here is the design data of Coal-Phosphate Fertilizer Complex Project (COFCOP), and the type of boiler and turbine are taken as selected by the project. Therefore, the boiler modeled here is a circulating fluidized bed coal combustor type, and the turbine is an extraction condensing type at heat to power ratio. Conservation equations and characteristic curves are used to model each component of the power plant. From these mathematical model equations, the component modules are developed using MATLAB code. Output parameters are obtained from input data to the component modules. Simulation of systems, subsystems and components are accomplished using the Newton-Raphson technique. The total system of the power plant is simulated by a program called powerplant_main. In this program there are four basic solvers. These are: the turbine solver, the boiler solver, the water flow solver and the steam flow solver. Each solver has its own residue generator function and Jacobean generator function. The Gaussian elimination function is called by any solver during simulation. The power plant in COFCOP is still in design stage, and it cannot be used for program verification in this paper. Hence, a hypothetical power plant data is taken and the output of the simulation closely approximates the real case.

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