Browsing by Author "Bekele, Desta"

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    Effect of Railway Vehicle Parameters Variation on Derailment Running on Curved Track
    (AAU, 2015-03) Bekele, Desta; Tollossa, Deberie (Mr.)
    Railroad systems are the most widely used methods of transporting passengers in the world, so the system must be safe and comfortable. Safety is one of and critical railway system running behaivior. In this paper effect of railway vehicle parameters varation on derailment running on curved track at curved critical speed was studed. The parameters are carbody parameters(mass,rolling mass moment of inertia Ixx, pitch mass moment of inertia Iyy, yaw mass moment of inertia Izz and vertical mass center ), secondary suspenssion parameters, wheelbase distance and wheel radius. Each parameters in the study had to varying 25% upper and lower of original designed value. The study has been peformed by developing 41 DOFs, 4 axles and two bogie railway vehicle with SIMPACK software. First it was determined the curved track critical speed of the model vehicle on curved track scenario, when increasing speed above this maximum speed derailment occurs on the railway vehicle. After determination of the curved critical speed or maximum safe speed parameteric varation was analaysed. In general terms, it was concluded that carbody mass, carbody yaw mass moment of inertia(Izz), carbody height of center of mass, secondary spring longitudinal shear stiffness, wheel base and wheel radius are more sensitive to derailment, thus parameters have a roll to improve curved track critical speed and safety design of railway vehicle. Increasing or decreasing of rolling mass moment of inertia(Ixx) of carbody, pitch mass moment of inertia(Iyy) of carbody, secondary vertical damper damping and secondary lateral damper damping, decreasing secondary spring lateral shear stiveness and secondary spring vertical shear stiffness have no effect to derailment of railway vehicle running on curved track at curved critical speed. This research analyzes only the safety running behaivor of of the railway vehicle running on curved track, this means in the study was not included other running behaivior such as ride confort and wear. These parametric variation may have negative effect on other running behaivior. There fore decreasing yaw mass moment of inertia(Izz) of carbody, vertical mass center of carbody, secondary spring longitudinal shear stiveness, bogie wheelbase, wheel radius below the original value have safe to risk of derailment and improve curved track critical speed, but to take the parameters variation as positive the effect of those vriation will investigate to other running behaivior, must be improved or with in the permissible limit.
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    An Investigation of History Teaching Learning Process: A Survey Study of The Current Status In Secondary Schools of Hadiya Zone- Snnprs
    (Addis Ababauniversity, 2006-06) Bekele, Desta; Fanta, Tilahun (Professor)
    Different researchers in their studies identified several areas of concern for history educators regarding inadequate and unsatisfactory educational provisions that tend to inhibit instruction and learning history in secondary schools. In view of this, such kind of study with regard to the problems of history teaching and learning in our secondary schools is highly needed. The study was conducted to investigate the teaching and learning of history with respect to the effects of some of the teacher and school related variables. Attempts were also made to examine classroom-teaching competences. To this end, a descriptive survey research technique was employed. The descriptive survey research attempted to describe the present status of history teaching and learning, with particular reference to the secondary schools of Hadiya zone- SNNPRS. The findings of this descriptive study are reflective of the situation in these schools . The survey derived data from all the six secondary schools of the study area. Within these schools, all history teachers (34 in number) and thirty-six students were selected as sources of information using available and purposive sampling techniques respectively. Questionnaires, classroom observation, interviews, and documents were the instruments of data collection. The data gathered through these instruments were analyzed USIng percentages, mean scores and descriptive statements. The present study has found out a number of interrelated factors, which hinder the teaching, and learning of history. Some among these are; the insufficient training and orientation of teachers in higher learning institutions; the incompatibility between the volume of the book and the period allowed; the insufficient provision of instructional resources that c(fuld' be used for history instruction; and history teaching is highly textbook oriented. The results of the study also show a large-group instruction with lecture teaching strategy predominates the history classroom and the low level of English language ability of students in understanding and following Up of the subject matter of history. The findings further indicated that the overall level of history teacher classroom performance was found to be low in view of questioning skills, content knowledge, and general teaching characteristics. Based on these findings and the conclusions drawn, related recommendations regarding the improvement of teacher training and the provision of the necessary instructional resources were forwarded