Browsing by Author "Meron, Alebachew"

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    Application of a Generalized Subgrade Model in the Analysis of Circular Plates on Elastic Foundations
    (AAU, 2018-06) Meron, Alebachew; Asrat, Worku (Asst Prof.)
    The solution to the problem of beams and plates on an elastic foundation has been attempted in the past using various subgrade models developed by many researchers, one of the pioneers being Winkler. Most recently, a new calibrated and more advanced multifaceted continuum foundation model has been presented by Worku without neglecting any stress, strain, or deformation component in the continuum unlike previously proposed models. The study of interaction between a plate and an elastic medium has useful applications in geotechnical engineering. This research investigates the use of a generalized continuum subgrade model of Worku for analyzing circular plates resting on an elastic foundation. The approach employed is both analytical and numerical. In the analytical work, the governing differential equations of an axisymmetric circular plate on a homogeneous elastic foundation has been formulated that incorporates Winkler and Pasternak-type subgrade models. Closed form particular solutions have been presented for different loading conditions of small and large circular plates after obtaining a general solution of the differential equations. A math solving software (i.e. Mathematica) is used to compute the deflections and internal actions in a spreadsheet program due to the complexity of the functions. In the numerical study a FEM based software (i.e. PLAXIS 2D) is used to calibrate the analyzed circular plate using the presented models by seeking adequate agreements with the FE outputs. At last, numerical examples are solved using these models and compared with PLAXIS 2D for small and large radii circular plates of some loading conditions. From the plots of the outputs, it is observed that the generalized models of Worku are suitable and more appropriate than classical models to analyze circular plates on elastic foundations.
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    Assessment and Improvement of Reliability of Electrical Power Distribution System Case Study: - Sheno 15 Kv Distribution Feeder, Debre Berhan
    (Addis Ababa University, 2019-10) Meron, Alebachew; Singh, N.P. (Prof.)
    Distribution feeders are to deliver energy consistently to customers as electric power distribution systems reliability is a foremost concern to any electric power utility company. Power utility companies are working to provide reliable power through many systems. This thesis assesses the reliability of an electric power distribution feeder named Sheno 15 kV distribution feeder among the feeders that supplies an electric power to Debre Berhan city, an old city in Ethiopia. Power interruption data on daily basis for a period of two years on the feeder was collected and analyzed for the main causes of interruptions along with other two feeders namely Enewary and Aliyu Amba. Based on the data collected, system reliability indices (SAIFI, SAIDI, CAIDI, ASAI, EENS and ECOST) of the feeder were calculated using both mathematical and simulation methods andthe obtained results are 103.1271 f/customer.yr, 289.7872 hr/ customer.yr, 2.81 hr/customer interruption, 0.9669 Pu, 1361.01 MWhr/yr and 5,820,054 $/yr respectively. These values indicate poor reliability of the feeder when the results obtained are compared with averages of some countries. Currently, power utilities are trying to provide reliable electric power to their customers through many possible ways. Studying these methods; the method of adding a distributed wind power seems better option for our case study. Predictive reliability assessment of the feeder under study with the added distributed wind power along with possible locations of connection is performed and the results showed much improvement in system reliability indices of the feeder at bas bar 34(B34). These are 36.9719 f/customer.yr, 107.6154 hr/ customer.yr, 2.911 hr/ customer interruption ,0.9877 Pu , 579.565 MWhr/yr and 2,758,927 $/yr. Afterwards, the cost of realizing this method of reliability improvement for the distribution feeder has been performed. The cost analysis showed that reliability improvement with the help of distributed wind power can be realized economically.