Ethiopian Journals Online (EJOL)
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Computer simulation of gear cutting and strength analysis with special regard to extremely low teeth numbers
No full textThe involute gear system is widely used by gear manufacturers for spur and -helical gear in mechanical power transmissions. This is because of its advantages in standardization, machining, high efficiency and adaptability to load and center distance. For mechanical power transmission, involving high speed a maximum, gear ratio in one step and pinions with minimum possible teeth number are recommended Usually, extremely low teeth numbers, particularly for rack and pinion, are not treated in detail in the literature. These are of interest for cases of slow moving machines or manually operated mechanisms where lifetime and uniformity of motion is not crucial, but a bigger gearing ratio of single gear set for achieving cheap and small transmissions is important. For such gears with small number of teeth, modifications of parameters like teeth number, profile co"ection, undercut, head shortening, rack pressure angle and their interactions are investigated An instructive computer-based modeling of involute gear cutting using the gear generation method is given preference over purely theoretical investigations. A number of gear dimensions are taken from the modeled gears and conclusions are drawn from them. Except mentioning some important features, there is no intention to represent in this article the internationally acknowledged involute gear system and its definitions in detail which can be studied separately
Conceptual cost estimation of road projects in Ethiopia using neural networks
No full textThe rapid technological changes and advances in all business sectors strongly impose construction managers to facilitate their work through advanced software applications available to simplify different tasks. A research has shown that inaccurate cost estimation method is among the cause of cost overrun in the Ethiopian construction industry. This article presents conceptual cost estimation model developed using neural networks for federal road projects of Ethiopia. The conceptual cost estimation model developed has a mean absolute percentage error of 32.58% trained with only 48 exemplars. If the model is developed with the provision of enough data set to represent the road project with all-state of affairs, it is forecasted to improve the estimating capability of financers, employers and consultants. In addition, a friendly user interface is built to enable the utilization of the model developed easily and this article presents this interface with an example of actual road project in Ethiopia. The findings of this study indicate the prospect of application of neural network for cost estimation during early phase of the project development for Ethiopian road projects
INVESTIGATING PERFORMANCE OF VERTICAL CARBONIZING KILN FOR BRIQUETTE PRODUCTION
No full textCarbonization experiments of rice husk were carried in pilot cylindrical fluidized bed carbonizing kiln using nitrogen gas as fluidization medium.Husk was collected from rice miller, Amhara Region Wereta Town, Ethiopia and screened by standard sieves. To initate and supply the necessary heat, controlled amount of air is supplied from compressor.Gate valve and air flow meter was installed for regulating and measuring the amount of air.K-type thermocouples and pyrometer were used to monitor progress of bed and external drum temperature distribution. Kiln performance was investigated via studying the effects of air flow rate, air contact time and particle size.The phycochemical properties of raw material and its char were determined by proximate analysis. The results obtained demonistrate that air flow rate, air contact time and particle size have significant effect not on conversion efficiency of kiln and char composition but it affects both carbonization time and temperature distribution of kiln.Generally, char yield varies from 24.87 to 32.49%. Furthermore, lower air flow rate, shorter air contact time and higher particle size is suitable to achiev maximum char yield with 48.63% fixed carbon. Besides, char yield were improved from 18 to 27% to the range of 24.87 to 32.49%
Parametric investigation and survey of spintronic sensors v-s electronic sensors (case study: current sensors)
No full textConventional electronic devices depend on the transport of electrical charge carriers–electrons in a semiconductor such as silicon [1]. Now, however, physicists are trying to exploit the 'spin' of the electron rather than its charge to create a remarkable new generation of spintronic devices which are smaller, more versatile and more robust than those currently making up silicon chips and circuit elements. Compared with other solid-state sensors, spintronic sensors offer more sensitivity and precision and are not damaged by large magnetic fields. This paper presents the investigation results of the comparison of the conventional electronics current sensors and spintronics current sensors relying on the sensitivity of the two. To extract our conclusion survey of the researches on spintronics sensors and conventional electronic sensors are done separately
OPTIMAL DESIGN AND ANALYSIS OF PRE-STRESSED CONCRETE SLEEPERS
No full textThe track system consists of structural componentslike a sleeper that has to be designed to accommodatethe maximum tonnage. The main function of a sleeperis to transfer the load from the rail to the ballast viathe rail pad and to the under laid formation. Theanalysis and design of concrete sleepers requires theassessment of load on the sleepers, ballast pressuredistribution, selection of the dimensions of the sleeperand moment calculations at critical sections. In thispaper a pre-stressed pre-tensioned concrete sleeperhaving an optimal shape, strength and tendon typeand profile with reference to the existing sleeper typethat is used by the Ethiopian Railways Corporation(ERC), which is the new type II Chinese sleeper, wasanalyzed and designed. Moreover, FEM modeling ofpre-stressed concrete sleepers was conducted. Theoptimal design output of this research shows that increasingthe concrete grade results an increase insleeper capacity but has no more effect on momentcapacity which is largely dependent on the sectiondimension of the sleeper, tendon strength and eccentricity.The final optimized design outputs and analysisresult of the existing sleepers are compared withrespect to raw material consumption for productionand its capacit
MORPIIOLOGICAL COMPOSITION OF WEB-BREAK INDUCING SHIVES IN COMMERICAL NEWSPRINT PULP
No full textWeb-bnab dUring poper production causl? a so-iow incOtJWnience in produCtion pnxus and ;"awI? COlt of production.' Earlier studiesindicate that web breakJ occur at tensions far belOw the ultimate 'tensile strength mlues determined by tensile tuting in the laboratory. It~ abo reported that most of the web-breaks were ~ ca~,d by sbw .. (JmndJe of unsepararedjiberJ). In this paper the re$1.llt of an investigation an lhe morphological composition of shives in commerd~lnewJprini pulp at dwhole and those cawing wehbnakJ is preJenred. It waJ found that 93% of the shives -re earlywood and only 7% late"l\!ood. II was also deurmined that latewood shives are the null" ,causes of web-break More than 90% of the' web-break indUCing shives were found to be fatewood "hives
EXTENT OF ADHESION LOSSES IN THE WHEEL-RAIL CONTACT UNDER CONTAMINATED CONDITIONS
No full textRailway vehicles require a certain level of adhesionbetween wheel and rail to operate efficiently, reliably,and economically. Different levels of adhesionare needed depending on the vehicle running conditions.In the wheel tread-railhead contact, the dominantproblem is low adhesion, as low adhesion onthe railhead negatively affects railway operation. Onone hand, the vehicle will lose traction resulting indelay when driving on low-adhesion tracks and onthe other, low adhesion during deceleration will extendthe braking distance, which is a safety issue.This research work examines the influence of thecontaminants, i.e., water, mud, leaves, oil andgrease, with a twin disc machine which is designedand constructed as part of this study to simulatewheel tread-railhead contact. Thus, the researchmethodology is a laboratory test without and withthe different contaminants aimed at studying the extentof adhesion coefficients of each contaminantover the range of slip values 0 to 10% and comparingwhich of them are the worst to cause loss of adhesion.As the lab results revealed, oil, grease andwater have been found to cause less adhesions thanleaves. Unlike the research made justifying leaves,they were found the worst in causing adhesion losses
ALKALI AGGREGATE REACTIONS IN CONCRETE: A REVIEW OF THE ETHIOPIAN SITUATION
No full textThe reaction of aggregates with alkalu If! the «men' /0 produce alkali .filleo reaction and alkali carbonate reacliOl1 is reVIewed. The ejJecu of Ihe two reactIOns 011 the ~rabdity of COIItTetl! slrllcmru are highlighted. 8y laking samples of aggregaU$ and cernenf leJ/ ruul/s, the potential of a/1fIl11 .fll,ea reactlOll 111 Ethiopia IJ preliminarily(useJsed. Finally a Jel of 'conclwions and ru:ommendatioru are jorwtJrded
CREEP ANALYSIS OF BOILER TUBES BY FEM
No full textIn this paper an andlyslY i.r developed for fhe determination of creep deformation o[ an axisymmetric boiler Illbu SlIbjeCled (0 axiJymmetnc loods. The stresseJ and Ihl' permanent sCrams 01 a particular time and o.t the steady state cond'lion, resultmgfrom loading of the tube under constant inlernal pressure and elevlI/ed temperatUre are evaluated laking Into account the secondary creep charac/erislics of a gIvenmatenol. Finae element solution 1.1 pruented and discussed/or 1I class of problems Ifl which no prior analytical solution may exiSI. The method of lohman developed is an extension of Ihe direct Jfiffneu me/hod. The body IS replaced by a .!'yJtem of dllcrete triangular cross-section ring elements interconnected along circurl1Jerential nodal eircles.TIle equations of equilibrium Jar the element are derl"ved from the 'princIple oj mimmum potential. energy. The creep behaVior, of the body is formulated m terms of creep laws in current lue. Starting wah the elaslic so/ulion oj the problem, creep strains are treated as initial strains to de termme the new strell d'stribld/(Jf'lS at the end ofthe pre-set time interval. The procedure is repeated until the final time is reached and/or until the stress distribl4lion reaches a steady stated condition. Numerical results obtained for a tube maten'alJ 2CrMoV are presented at the end
Ancient Ethiopic manuscripts character recognition using Deep Belief Networks
No full textVery large proportion of Ethiopian literature is found in ancient ge’ez manuscripts in the form of old scriptures with papers from animal hides and skins (Branas) on which the ancient Ethiopic knowledge and civilization is recorded. This knowledge can be extracted and made usable by applying optical character recognition (OCR) systems on document images. Little efforts have been done for OCR of Ethiopic ancient manuscripts. Handwritten OCR process is considered as one of the most challenging problems in the area of image processing . The unique morphology of ge’ez hand-writing system (known as “Kum Tsihfet”), the degraded quality of the documents, and non-uniform background of the Branas poses additional challenges. Because of this, the OCR technique employed can’t be addressed directly by using OCR systems designed for modern printed and handwritten documents. Machine learning techniques like deep belief networks (DBNs) are becoming powerful set techniques that attempt to model complicated morphological features of handwritten texts. In this research we developed an OCR system using DBNs. The system was trained and tested using our own segmented datasets of ancient ge’ez characters containing 24 base characters only. The test result shows that a recognition accuracy of 93.75% was obtained, which is a promising result