Browsing by Author "Daniel Tilahun (PhD)"

Now showing 1 - 2 of 2
  • No Thumbnail Available
    Item
    Investigating the Influence of Wheel Wear on Vehicle Dynamic Behavior by Introducing Yaw and Track Irregularity
    (Addis Ababa University, 2023-02) Biruk Yifru; Daniel Tilahun (PhD); Awel Mohammed (Mr.) Co-Advisor
    This research intends to indicate the influence of wheel wear due to yaw and track irregularity on vehicle dynamic behavior demonstrated in terms of waer depth, derailment coefficient and ride index. Software simulation-based and wear data validation was used. A Hertzian contact model was used for the wheel-rail contact while SIMPACK and in house made MATLAB code of Archard wear model were used for multibody modeling and analysis of wear depth of each wheel. Main influencing factors involved in the analysis were curvature radius, speed, yaw, and track irregularities variations which were demonstrated in terms of wear depth and vehicle dynamic behavior expressed in derailment coefficient and ride index. A 1 km track long specified curve radius, speed, and yaw damper values were devised for the analysis process with a wear factor of 10,000 applied for the wear depth calculation. Based on the analysis, re-profiling analysis was performed till 60,000km with 10,000km interval data extraction and wear depth was found to match close to the values from wear data collected from AALRT. Further case studies also confirmed that 50m radius of curvature resulted the highest wear depth (6.18mm) and higher derailment coefficient (1.01) and unconfortable despite the existence of yaw damper or track irregularity. Yaw at lower running speeds on the other hand didn’t affect much the ride index while it improved the derailment coefficient. But when speed becomes higher and its value increased, wear depth reduced and both ride index and derailment coefficient deteriorated. Finally, track irregularity alone brought only slight disturbance to the derailment coefficient and ride index. But it has significant increase to both values when combined with factors like yaw. As a result, measures shall be taken to minimize the combined effect of yaw and track irregularity.
  • No Thumbnail Available
    Item
    Stress And Deflection Analysis of Cracked Composite Pressure Vessel by Finite Element Method
    (Addis Ababa University, 2015-10) Tekeliye Tasachew; Daniel Tilahun (PhD)
    The aim of this thesis is to develop crack and investigate techniques and parameters that could be used to identify crack if it exist in a composite pressure vessel. Many researchers discovered formation or propagation of a crack in a composite pressure vessel will cause a catastrophic failure. Thus, health monitoring for a pressure vessel due to crack using crack detection techniques will minimize or reduce the failure that probably to occur. This research first focused on mathematical and numerical relation which, represent the governing equation of composite material winding on in a pressure vessel. For modeling different crack size in the composite overwrapped pressure vessel fracture stress theories applied. Different surface Crack size are considering according to the literature standard values. Model actual size of composite pressure vessel with varied crack size “a” develops on the surface of composite pressure vessel. This research thoroughly analysis the effect of crack on the surface of composite pressure vessel. Those parameters are considered to see the variation of result due to presence of crack. The main parameters are considering stress, principal stress, von mises stress, deflection and fracture stress. According to the parameters it shows that as crack size increase, the average stress will be increase with the given pressure in composite pressure vessel. In contradict; the fracture stress will be decrease as the crack size increase. In this study, optimal angle-ply orientations of symmetric [550, -550] shells designed for maximum burst pressure with allowable crack size were investigated. It is shown that all the strength characteristics of carbon fiber relevant to structural engineering can be explained by the cracks present in the carbon fiber and can be analyzed using fracture mechanics. The stress and deformation are affected due to the presence of crack in composite pressure vessel. These parameter are takes a design crack as the basis for design. Rather than an allowable stress as in current approaches, with which it is compared cracked composite pressure vessel. A full size cylindrical shell of composite pressure vessels is conducted. A mathematical method, A finite element method and compare experimental test are studied to verify a maximum allowable crack size in composite overwrapped pressure vessel with a given optimum winding angles. The roll of crack size design within the wider philosophy of limit state design is discussed.