Yazar "Meran, Ahmad Partovi" seçeneğine göre listele

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    Design and analysis of a hydraulic-elastic railcar buffer
    (Sage Publications Ltd, 2018) Meran, Ahmad Partovi; Mugan, Ata
    This paper presents a study on the development of a side buffer to absorb the impact energy of colliding railcars. Buffers are essential elements for improving the traveling comfort of passengers and extending the service life of a wagon chassis. In designing the buffer's energy absorption characteristics, a combination of a hydraulic damper and a stack of disc springs (Belleville springs) were utilized. Disc springs have nonlinear load-deflection characteristics; by stacking them in series and parallel arrangements, the desired load-deflection characteristics can be achieved. The finite element method was employed to evaluate the performance of the designed buffer in terms of force-stroke and kinetic, strain, and viscous energies for 5, 7, and 9 km/h impact velocities. Simulation results proved that the designed buffer ensures the requirements of EN 15551 easily for various collision speeds. Low level of acceleration values and small peak collision forces proved that the proposed buffer has superior performance in comparison with the existing buffers in service by improving the shock absorption and crashworthiness features of railcars.
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    Numerical analysis of elastomer buffer embedded in the suspension of automobile for vibration damping improvement
    (2018) Meran, Ahmad Partovi
    Elastomers, due to their excellent damping and energy absorption characteristics and low cost are used extensively in automobile industry to isolate the structures from vibration and shock loads. In this study, it was aimed to analyze the damping performance of an elastomer buffer embedded in the suspension of an automobile. To reach to this aim, vibration simulation of an automobile suspension model was conducted by using a nonlinear explicit finite element code, Abaqus. In order to simulate the damping behavior of elastomer buffer, the hyperelastic and linear viscoelastic material models were used together. The numerical model was validated with results of exact solution method in terms of transmissibility ratio and phase shift in a wide range of input excitation frequencies. Good agreement was observed between the exact solution and finite element results, which indicate that finite element model is sufficiently accurate. To examine the damping performance of the buffer, the displacement time history curves were extracted for suspension with and without buffer under the sinusoidal base excitation. The vibrating motions of suspension for both conditions were compared. The comparison results proved that the elastomer buffer was effective in improvement of damping performance of suspension. It reduced the amplitude of vibration and oscillation time of sprung mass remarkable in excitation frequencies around and over the natural frequency of the system.
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    Solidity effect on crashworthiness characteristics of thin-walled tubes having various cross-sectional shapes
    (Taylor & Francis Ltd, 2016) Meran, Ahmad Partovi
    In this paper, effects of solidity and cross-sectional shape on crashworthiness characteristics of thin-walled tubes under dynamic axial impact load are examined. For this purpose, explicit finite element analyses are conducted for tubes having triangular, square, circular, hexagonal, octagonal and multi-cell cross-sectional shapes. The FE model is validated with analytical and experimental results that were reported in literature. It is found that FE solutions agree well with analytical and experimental results presented in the literature. To compare the tubes having different geometric dimensions and shapes on the same ground, the tubes are selected such that they have the same mass and length, and the striker mass and velocity are identical for all tubes as well. By changing solidity of tubes between 0.05 and 0.25, the cross-sectional dimensions of tubes are specified. The crushing force efficiency, crushing strain, total efficiency, structural efficiency and dynamic energy absorbing effectiveness parameters are calculated for various tubes as a function of the solidity parameter. It is concluded that crashworthiness performance of thin-walled tubes is significantly influenced by the solidity and cross-sectional shape. Results about the most effective solidity values and cross-sectional shapes are presented.