Ethiopian Journal of Engineering and Technology

A Study of Aerodynamic Pressure Drag and Skin Friction Resistance Comparison on ICE 3 Train under Different Yaw-angles

Kibret Molla — 2024-03-25

The chief purpose of this research was to compare the aerodynamic pressure drag and train body skin friction resistance contribution on ICE 3 HST vehicles, which run at 320km/h speed. It has also determined the flow character of each car on the train according to its position. The two main factors of external HST body resistance have been studied in different yaw-angle conditions of open embankment infrastructure. The full-scale test is conducted to verify the computer, mesh, and a serious numerical simulation to the performed investigation of aerodynamic loads for comparison pressure drag and frictional resistances. Has used PHOENICS VR CFD numerical test approach, and validated by EN14067-6:2010 standard report and experimental test values in Table 9. For applying in the LES turbulence model, a blockage ratio of 3.015% and at Reynold’s maximum number of 1.120E+08.
From the detailed flow analysis, the research found out that pressure drag is the dominant air resistance compared to train body skin friction. Especially, it showed that the frictional resistance became much less when the wind attack angles were different from zero. Particularly, are from drag components, the maximum pressure drag in the x-axis recorded when a wind yaw-zero, and which is decreased as the wind yaw-angle attack increases. That is illustrated in Table 8 from the range of 22.45% for a minimum of 10.53%. But, the side force is increased by 66.36% to a maximum of 97.38%. The lift force was recorded higher at yaw-zero and dropped in a very noticeable effect from case-1 to case-2 tests by 98.48%. On the other hand, it started to increase gradually while the wind yaw-angle increased, which was in the range of 21.64% to a maximum of 69.15%. Hence, the study predicted that the running stability of the ICE3 train worsen when the wind attack yaw-angle increased. This is owing to lift and side force coefficients drastically raised. The study clearly has provided that the aerodynamics pressure drag is dominant over friction resistance when an HST runs under an incompressible medium.

Cause of Failure Investigation of Masonry Retaining Walls at Logita Bridge Site, Sidama Southern Ethiopia

Bereket Bezabih — 2024-03-25

A masonry retaining wall supporting the approach embankment of Logita Bridge suffered significant distresses, which led to a dispute between the client, the consultant, and the contractor. As a result, the construction work has been interrupted for a prolonged time causing frustration on all stakeholders. This paper presents the investigation work undertaken to establish the causes of the observed distresses. Based on preliminary investigations, a hypothesis was developed that the observed distresses were due to the choice of ambiguous structural system, use of materials with widely varying stiffness and the sole use of standard stability checks, which failed to verify the complex design. A numerical simulation was undertaken using FLAC 8.1 by assuming elastic behavior for the reinforced concrete and stone masonry parts of the wall and Mohr-Coulomb model for the various backfill materials and foundation. The values of parameters were either adopted directly from code provisions or were estimated using methods specified in relevant codes. The modeling was undertaken for the current construction state as well as the final designed state. The numerical analysis conclusively proves that the distress observed in Logita Bridge retaining wall is caused by development of tensile internal stresses at the face of the wall. If the final wall is constructed, the numerical simulation indicates that structure will collapse, not necessarily from stability of the wall but through deep-seated stability failure through the backfill and foundation.

IT Adoption Model Development for Improving Supply Chain Performance of Enterprises in Developing Countries: A Case of Ethiopian Manufacturing

Fentahun Moges — 2024-03-25

Information technology (IT) is one of the biggest enablers in the contemporary SCM. However, the roles of IT adoption models on the supply chain performance of manufacturing enterprises in developing countries were not adequately investigated in the past. This study investigates the effects of IT models on supply chain (SC) performance in manufacturing enterprises of developing counties. It starts by measuring the level of understanding about the roles of IT adoption models on SC performance from survey enterprises. Further, depending upon identified critical success factors and barriers to IT adoption from the literature and empirical survey, a new IT adoption model is proposed. A cross-sectional survey was conducted by taking 438 samples from a population of 2,758 Ethiopian medium and large-scale manufacturing firms. The findings from the survey generally indicated significant positive relationships between IT practice levels and SC performances, although they faced different challenges to implement IT adoption models.

Development of a decision support system for cutting tools planning using fuzzy case-based reasoning

Fentahun Moges — 2024-03-25

Cutting tools management is one of the main issues in metal cutting operations. This important problem has not been adequately studied in the past. Most of the problems in cutting tool management were addressed using optimization techniques alone. This study proposed a decision support system (DSS) to articulate this problem by combining artificial intelligence (AI) and optimization techniques. The proposed DSS retrieves the most similar historical cases to adapt their cutting tool requirements to the current part orders. The DSS integrates case-based reasoning (CBR), rule-based reasoning, and fuzzy set theory (FST) in AI. It uses the analytic hierarchy process (AHP) and distance from target methods of multiple-attribute decision-making (MADM) in decision analysis. Cases were represented using an Object-Oriented (OO) approach to characterize cases for their toolset requirements. A numerical example was illustrated to show the soundness of the proposed methodological approach.

The Effects of Deficit Irrigation and Irrigation Interval on Yield and above ground Biomass of Haricot Bean (Phaseolus vulgaris L.) at Adami Tullu, Oromia, Ethiopia.

Tewodros Assefa Nigussie — 2024-03-25

This study assessed the response of haricot bean to deficit irrigation and irrigation intervals (II) at Adami Tullu, Oromia, Ethiopia using a factorial experiment. The treatments were comprised of factorial combinations of two factors: four levels of water application (100%ETc, 85%ETc, 70%ETc, and 50%ETc) and three IIs (3 days, 5 days and 7 days). The experiment was replicated three times and the treatments were placed in each block in a randomized manner. Analyses of Variance (ANOVA) was used to analyze the results of the study and it showed highly significant (P < 0.05) differences among values of yield, above ground biomass and wateruse efficiency (WUE) under the considered treatments. The highest yield was obtained under 100%ETc with 3 days II; the lowest yield was obtained under 50%ETc with 7 days II. In terms of crop and field wateruse efficiencies (CWUE and FWUE, respectively), 50%ETc with 3 days II gave the highest CWUE and FWUE values (0.54kg/m³ and 0.38kg/m³, respectively). The lowest values of CWUE and FWUE were obtained under100%ETc with 7 days II (0.32kg/m³ and 0.26kg/m³, respectively). In general, 85%ETc with 5 days II could be recommended in the study area for optimum production under water scarce condition.

SWAT-WEAP Model-based Water Supply-Demand Analyses and Identification of Critical Areas under Different Scenarios in Bilate River Watershed, Ethiopia

Tewodros Assefa — 2024-03-25

Water scarcity has increased the interest in improving water use efficiency and productivity in various parts of the world. As a solution to the problems associated to water scarcity, it is very useful to conduct water demand-supply and water allocation analyses (under current and future condition), even after water shortage has manifested itself, as it would lead to seeking a win-win situation among different water users (demand sites) in the watershed. Accordingly, this study focused on water allocation for existing and future demands in Bilate River Watershed using the WEAP model as by generating stream flow data using the SWAT model. For this purpose, observed meteorological and hydrological data for the period of 2010–2019 were employed. The model outputs were further analyzed to determine long-term mean flow values. Under the Current Scenario, the irrigation, domestic and livestock water demands were found to be 49.05 MMC, 21.41MMC and 8.58 MMC, respectively, with a total of 79.04 MMC. Under this scenario, the available water was not found to meet the demands in the months from October to February, particularly at Badessa and Chorake sub-watersheds. Under the reference scenario, the annual unmet water demand in the watershed as a whole changes from 1.21 MMC in 2021 (current scenario) to 1.78 MMC in 2030, which is expected to increase to 5.78 MMC in 2030 under the Increased water demand scenario with irrigation expansion, population growth, and environmental flow consideration. Thus, to address the current and eve future supply-demand gap, a storage structure needs to be constructed at appropriate place.

Internal Factors Affecting Contractors’ Performance and the Improvement Mechanisms

Desalegn Girma — 2024-03-25

The purpose of this study is to assess the internal factors affecting contractors’ performance in construction projects and indicate the potential improvement mechanisms in the context of the Ethiopian construction industry. Quantitative data was collected through a structured questionnaire. While the internal factors were evaluated and prioritized using the analytical hierarchy process (AHP), the improvement mechanisms were evaluated using the technique for order of preference by similarity to the ideal solution (TOPSIS). The findings indicated that the internal factors affecting contractors’ performance are cash flow problem, payment delay to subcontractors, poor leadership, understaffing, poor equipment condition, lack of coordination, lack of training, improper planning and scheduling, ineffective communication, and lack of motivation. The identified improvement mechanisms are adopting dynamic management approach, hiring the right people, efficient organization structures, effective incentive mechanism, on time payment, well-established communication system, training, and continuous learning, developing knowledge sharing culture, standardization of working procedures and promoting group work. Identifying and evaluating the internal factors would help to take effective management measures by the top management. Contractors’ capacity development is among the agenda of construction industry development in different countries. Hence, identification of the internal factors is important to governments to frame effective intervention strategies.

Sewing Line Efficiency Improvement Using Line Balancing Methods for Case of JP Garment

Fentahun Moges Kasie — 2024-03-25

Abstract: Line balancing in the garment industry is one of the responsibilities of industrial engineers to improve the efficiency of sewing lines by leveling the output of every operation. In JP Garment Plc, the line efficiency of the long shirt sewing line is below the planned. One of the reasons was unbalanced workload distribution. This study focused on balancing the sewing line through different line-balancing techniques. To perform line balancing analysis primarily the researcher collects the operation breakdown and standard time of shirt production in JP garment. Next, a flow process chart and a precedence diagram were developed. The cycle time, which depends on the available time and the production target, is one of the key parameters in line balancing analysis and this time found as 33 seconds. Based on this cycle time, ranked positional weight and the largest candidate rule method of line balancing were used to improve the efficiency of the sewing line. The existing system has forty-one workstations with an efficiency of 67.6 %. By applying the ranked positional method, the number of workstations becomes thirty-four with 85.9% line efficiency and production enhanced to 902 shirts. Alternatively, the largest candidate rule method was applied and resulted in thirty-one workstations with an efficiency of 94.2%. Lastly, Kilbridge and Wester’s method was applied and resulted in 97.35% efficiency and the number of workstations became thirty.

Assessment of Radiation Shielding Property of Heavyweight Concrete Incorporating Hematite Iron Ore

Samson Tesfaye — 2024-03-25

The aim of this research was to produce and assess the property of heavyweight concrete which could be used to shield photon radiation. The shielding capacity is achieved by incorporating a denser aggregate into the concrete mixture. The concrete is prepared by partially substituting basalt aggregate with hematite ore. Five concrete mixtures with varying content of hematite aggregate per total volume of coarse aggregate (0%, 25%, 50%, 75% and 100%) are produced in the laboratory. Three concrete slabs with a dimension of 200*200 mm sides and 100 mm thickness are prepared as a representative for each concrete mixture. The photon radiation shielding property of the concrete samples is evaluated using two separate experiments. In the first experiment Cesium-137 is used as a gamma radiation source and radiation survey meter was used to measure the intensity of radiation passing through the shield. In the second experiment Cobalt-60 is used as a radiation source and a combination of ionization chamber and an electrometer is used to measure the dose. The result of the experiments showed that radiation shielding property of the concrete increase with an increase in hematite content. For a Cesium-137 source with a radiation intensity of 0.64 µSv/hr. at 1 m in straight line, the linear attenuation coefficient of the samples increased from 0.023 for normal concrete with no hematite to 0.127 for concrete with 100% hematite coarse aggregate. For Cobalt-60 with energy 1.25 MeV, the linear attenuation coefficient of the samples increased from 0.135 for normal concrete with no hematite to 0.196 for a concrete with 100% hematite coarse aggregate. Generally, heavyweight concrete which is made of hematite is found to be good for gamma radiation shielding purpose.

Challenges of Construction Scheduling Practice in Ethiopian Construction Industry

Desalegn Girma — 2024-04-25

Practice of construction scheduling includes tasks of developing, controlling, and communicating the schedule to the concerned parties. This study focuses on identifying the major challenges of construction scheduling practice in Ethiopia. Questionnaire survey was used to collected data from selected construction professionals and one hundred fifty-five valid responses were collected. The data was checked for construct validity and internal reliability. Exploratory factor analysis was conducted to identify challenges of construction scheduling practice. The factor analysis has resulted in four challenge affecting construction scheduling practice: (1) lack of top management commitment, (2) lack of scheduling knowledge and nature of construction projects, (3) lack of scheduling standards and (4) reliable resource scheduling in a resource constrained environment. One sample T-test was conducted to evaluate relative significance of the challenges, and reliable resource scheduling in a resource constrained environment was found to be the most challenging factor of construction scheduling practice. Developing countries’ construction industry faces major uncertainties in the resource availability and quality aspect than developed countries. Hence, it is important to understand the operating environment and consider the situation to improve the construction scheduling practice.