Ethiopian Journals Online (EJOL)
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Detention tanks as a means of urban storm water management
No full textUrban storm sewers, be itfor separate or combined systems, are designed (dimensioned) for a specific rainfall intensity, duration and frequency. But, during the life of these sewers, rainfall of different intensities, duration and frequency can occur. Besides new settlements may develop. All these result in exceeding the design discharges of the sewers causingj/ooding. Thus, in this paper, some means of reducing -such risks are indicated. In particular, the application and design principles of storm water detention tanks is presented. The general principles of dimensioning sewers is also described. In order to elaborate and for better understanding, a simplified illustrative example of dimensioning a storm water detention tank is worked out
Digital computer control of servomotor angular position
No full textThe paper discussess the design and simulation methodology of digital control systems for the benefit of the interested practicing engineer. A lead-type digital controller for a 2nd order system and a leadlag type digital controller for a 3rd order system are designed. The simulations show that the design methods are acceptable
A monte carlo comparison of parametric and nonparametric estimation of low flow frequencies
No full textLow streamflow, which u one aspect of drought, constitutes one of the extremes of.the hydrological regime. Among the low flow characteristics of rivers, lowflow frequency analysis, that isfundamental to a wide range of design and operational problems in area of both water quality and quantity, is the one. Thu paper deals with the introduction of the nonpaiame~c methods in the low flow frequency analysis and then make comparative evaluation on the magnitude of low flow quantile corresponding to a ghien return period with the parametric statistics. A currently used approach to low flow frequency analysu is based on the assumption made that the distribution function describing the anntlal minimum lowflow data is known, which is never known exactly. Recently, nonparametric method of estimating probability distribution functions have been developed, which doesn't require a distributional assumption. This involves the use of a suitable smoothing function known as a kernel. The fIXed kernel nonparametric method is proposed and developed for estimating low flow quantiles. Based on annual minimum low flow data and Monte Carlo SimulaJion Experiments, the proposed model is compared with Weibull models both for its descriptive and predicthie ability. Computed reSftlts showed that the fIXed kernel estimator has small bias and root mean square error in low '.flow quantile estimates. Applicalion of the model to data from the Blue Nile at E/deim (Sudan) and Komati (South Africa) rivers have shown that the nonparametric approach is viable alternathie to the Weibul/ modeu. It is, therefore, concluded that the nonparametric method u accurate, uniform, and particularly suitable for the muJtimodal data
A FEM analysis of a flexible manipulator(ARM)
No full textThis paper present dynamic behaviour analysis and time history of responses of a flexible arm. Lagrange equation are employed to develop the governing equations of motion which are discretized by using the finite element method. An illustrative example of a pin-pin beam-like flexible arm is treated and results obtained are presented
MULTI-OBJECTIVE OPTIMIZATION OF TRAIN SPEED PROFILES ON THE AYAT-MEGENAGNA LINE
No full textIn this paper, a new approach has been developedfor train speed profile optimization, discrete spacebased modeling followed by the determination of anoptimal set of riding modes using multi-objectiveoptimization techniques. The optimization problemis formulated by making energy and time as thecomponents of the two element objective vectorfunction. A point mass model of the operation oftrains is developed by considering all the importantforce components acting on the train. The distanceto travel between stations is discretized into 20equal length elements where a two stage solutionprocedure has been applied to get to the final results.The first stage of the solution procedure is theapplication of a Non dominated Sorting Genetic AlgorithmII (NSGA II) based optimization techniquetaking vector of riding modes as the decision variable.Using the developed algorithms for the calculationof cost functions, a Pareto-optimal set of ridingmodes are determined. The second stage of the solutionprocess smoothes out the results found in theprevious stage without bringing about considerablechange in the values of the cost functions. Variousspeed profiles are generated as optimal for the caseof Ayat to Megenagna line of Addis Ababa LightRail Transit (AALRT). The speed profiles that aregenerated as the fastest can bring about up to 30%reduction in headway over the plan. Furthermore,by choosing the slowest trajectories over the fastestones, it is possible to save up to 38.18% of energy,while 23.98% of reduction in riding time can beachieved by preferring the fastest profiles over theslowest ones
WAVELET BASED MULTICARRlER CODE DIVISION MUL TTPLE ACCESS COMMUNICATION FOR WIRELESS ENVIRONMENT
No full textThIS paper presents the study on Wavelet transform based Mull/carrier Code D,VISIOn Multiple Access (MC-CDMA) system Jor a downlmk wlre/ess channel The performance of the .lystem IS slI/died for Additive While Gaussian Noise Channel (.4 WGN) and slowly varymg mulripafh channels. The bll error rale (BER) versus Signal to NOise ratIo (SNR) is Ilsed as a performance measure usmg Simulation done on compuler Comparison of the simulated results wilh the Iheoret/cal limit of a BPSK modulaled signal shows thai fhis system perJormsnear Ihe theoretical limit Jar both A WGN and slowly vQO'ing Flal fading channel. Also, a compal'lson with the Discrete Fourier Transform (DFJ) based system was made for A WGN channel and the result shows thai even In the absence of a guard Interval, the wavelet based system performs equally With(he DF
Engineered practices of adobe masonry production in Ziway, Ethiopia
No full textA non-engineered production practice of adobe-blocks prevails in southern Ethiopia around Ziway, which are used for rural housing. These blocks have a compressive strength of less than 1 MPa and exhibit deformed shape due to excess water and non-uniform distribution of teff straw during mixing. The objective of this research was to advocate a better practice to enhance the strength of adobe masonry unit. Tests were conducted on the soil samples for its suitability to produce adobe masonry units. Pumice aggregate and teff straw were used as additives. Compressive and flexural strength values observed for brick size specimens with 9% of pumice aggregate and 0.4% of teff straw content were 2.6MPa and 0.36MPa respectively. These values have passed the minimum requirement of California Building Code which is considered as standard for the present research. Whereas block size specimens showed compressive strength values less than the minimum requirement. Hence brick size was recommended to use in practice, over block size. Unit cost was considered affordable as the cost of pumice and teff straw used per unit was extremely low in value. Also around 60% cost reduction was observed when adobe units were used instead of Hollow Concrete Blocks for masonry construction
Method of amended soils for compressed block and mortar in earthen construction
No full textThe paper presents the results of a research conducted aiming at developing a method of producing building block and mortar from locally available natural soils and earth minerals. The main focus of the effort is to establish or advance wall making building blocks and jointing/binding mortars from amended soils with cementitious raw lime/nonfactory manufactured and pozzolanic minerals. The targeted beneficiaries of the success are the over eighty million disadvantaged Ethiopians residing in the rural and semi-rural areas of the country. They deserve a decent, sustainable, ecofriendly and a popular technology based habitat. The long journey towards achieving the noble goal was initiated by investigating the suitability of soils and earth minerals, preparation and testing of informative specimens and the production of mortar cubes and proto-type building blocks in their actual size to simulate field application conditions. The specifics of this particular move is thoroughly focusing on the two prime parameters of compressive strength and durability (water resistance) which are the determinant factors for the viable application of earth based wall making in puts. The attained results of the effort indicated that the designed mix proportioning of the ingredients confirmed that the products are acceptable both in compressive strength and durability terms for the intended purpose. To this effect, the blocks produced using the proposed method, are named as amended compressed earth blocks (ACEBs)
Fat or elastic: an inquiry into classification of black clay soils of Addis Ababa around Tulu Dimtu area
No full textAddis Ababa Black clays are one of two dominant clay found in the city and known for its expansive nature. Using the unified soil classification system, such soil, traditionally, is classified by the group name fat clay and group symbol of CH. But some investigations on local soil have resulted in classifying the soil as elastic silt, MH. In this research laboratory investigation is conducted to determine if in fact Addis Ababa black clays may end up being classed as elastic silts and if so, what may be the parameters that play a role in such a classification. For the study three samples were collected from Tulu-Dimtu, where previous investigations have resulted in the discrepancy. Simple classification tests were conducted on the samples. In addition, the effect of sample preparation, utilization of tap water, experience level of operator and variations among laboratories investigated. It was found that Addis Ababa black clay soils mayend up being classified as elastic silts but in general remain within the boundary region of the A-line on both sides. The experience level of the operator was found to have the most profound effect on index tests and classification