Analysis of the Dynamic Behavior of the Ventilation Duct, for a Varied Range of Air Flow and Wall Thicknesses for the Long Circular Duct
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Abstract
The present paper approaches the analysis of the dynamic behavior induced by different values of air flow, which correspond with specific speeds of air, for the circular ventilation ducts, for a varied range of air flow rates and of wall thicknesses of the air passage channels. The study focuses on airflow-induced vibrations and the possibility of resonance in certain sections of the ventilation system [2], as well as the causes and effects of turbulent airflow in ventilation systems, which can negatively impact pipes and their supports. Using the Bentley AutoPIPE CONNECT Advanced Edition software for the ventilation air ducts, we perform a modal analysis and simulate the displacements on the three axes, the forces and moments additionally induced on the piping system, factors that contribute significantly to the weight of the system of air ducts, with another amplificant factors depending on pressure and temperature. Based on seven different air flow values and corresponding specific air speed values in the duct system, the specific turbulent regimes were calculated, and the different excitation frequencies were obtained. That excitation frequency is compared with the frequency corresponding to the maximum mass influence, obtained on the modal analysis, with the final scope being to completely evaluate these effects of the Vortex-Induced Vibration (VIV) mechanism [3] associated with the periodic appearance of vortices in areas with geometric discontinuities, respectively, in the vicinity of bends. The characterization of the phenomenon was achieved using the Reynolds and Strouhal numbers, which describe the oscillatory nature of the airflow and allow the estimation of the vortex shedding frequency.
The final scope is as follows: in the first part, determining the value of the most unfavorable frequency obtained through modal analysis with the Bentley AutoPIPE CONNECT Advanced Edition software; and in the second part, calculating the excitation frequency from air turbulence. Thus, obtaining the most unfavorable value of the frequency, a technical parameter that leads to the destruction of the air ducts, results in the loss of airtightness as well as the destruction of the air transport installation.
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