Browsing by Author "Samuel, Tilahun"

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    Design Module for Self-Supporting Steel Latticed Communication Towers
    (Addis Ababa University, 2018-10) Samuel, Tilahun; Shifferaw, Taye (PhD)
    Self-supporting towers are one of the most essential and common steel structures which are being constructed quite frequently to provide a better facility in communication network to the people. Hence, the failure of such a structure is a major concern. Therefore, utmost priority must be given in considering all possible extreme conditions for designing communication towers, by evaluating and studying their wind and seismic behaviors properly. In this study, concepts behind codes specifications in relation with, equal angle steel section used as structural members in communication towers and communication tower itself, have been investigated thoroughly, so that they can be referred as a principles for analysis and design. In this research, wind and seismic behavior of self-supporting steel latticed communication towers have been studied for 35 m/s, 40 m/s, 45 m/s, and 50 m/s wind speed, in five different seismic zones, by analyzing different height of bare towers with XX bracing system. Moreover, charts for specified wind speeds and seismic zones which can be used as preliminary design for communication towers has been developed. These charts shows the responses of towers with different heights, wind speeds and seismic loads in different loading directions. In addition to that, step by step design procedure and design of articulated modular self supporting steel latticed tower is presented with the help of algorithm and flowchart by using recommended allowable strength design codes specifications, in relation with analyzing and designing of steel communication tower. Finally, the design module is prepared in a way that it can be used as a Guide line in designing and analyzing the effect of wind load and seismic load on the steel latticed communication towers.
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    A DFT study of 2D Van der Waals Heterostructures of Janus Transition Metal Dichalcogenides with WSe2 Monolayer for Energy Applications
    (Addis Ababa University, 2021-09) Samuel, Tilahun; Georgies, Alene (PhD)
    Atomically thin two-dimensional layered semiconductor materials such as Transition Metal Dichalcogenides (TMDs) have a great potential for solar cells applications due to their favorable photon absorption and electronic transport properties. The combination of 2D materials in the form of van der Waals heterostructures has been proved to be an effective approach for improving the electronic properties of the material. In this work, the electronic properties, such as band structure, bandgap, and band alignment of MoSSe/WSe2, WSSe/WSe2, and WSeTe/WSe2 vdW heterostructures were obtained from Density Functional Theory (DFT). The potential of the exchange and correlation was calculated using the Generalized Gradient-Perdew Berk Ernzed (GGA-PBE) approximation. MoSSe/WSe2, WSeTe/WSe2, and WSSe/WSe2 heterostructures have type-II band alignments, which is advantageous for electron-hole pair separation. Photons can be absorbed directly in MoSSe/WSe2 and WSeTe/WSe2 semiconductors because they have direct bandgaps. WSSe/WSe2 semiconductor has an indirect bandgap, which means that a phonon must also be absorbed or emitted for a photon to be absorbed. The most stable stacking order in heterostructures comprising Janus monolayers of TMDs and WSe2 has been ascertained based on interlayer binding energies. The binding energies in MoSSe/WSe2, WSSe/WSe2, and WSeTe/WSe2 heterostructures were found to be -18216.75 eV, -38995.69 eV, and -0.3296 eV at an equilibrium interlayer space of 5.75 Å, 4.02 Å, and 4.72 Å respectively, which are more stable than the other tested configurations. The solar cell and photocatalytic applications of the heterostructures were investigated. The structures were not promising for photocatalytic applications because the band levels of semiconductors were insufficient to support full water splitting. When MoSSe/WSe2, WSSe/WSe2, and WSeTe/WSe2 were used as PV materials, the Power Conversion Efficiency (PCE) was found to be 20.16%, 20.48%, and 19.05%, respectively. The results show that it can serve as a suitable photovoltaic material with high efficiency and opening possibilities to develop solar cells based on 2D TMDs materials.