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Damping Rate of Transient Oscillations in Pressurized Closed Conduits

Author(s): Sahad Khilqa, Mohamed Elkholy, Mohamed H. Al-Tofan, Juan M. Caicedo, M. Hanif Chaudhry

Linked Author(s): M.Hanif Chaudhry

Keywords: Damping ratio, piping system, transient, unsteady friction

Abstract: Although the modeling of transient conditions in closed conduit has advanced significantly during the last four decades, the dissipation of transient oscillations with time is not completely understood at present, and usually, dissipation in computed results is slower than that in the actual systems. Since the first transient state peak pressure that is not affected by the dissipation of pressure oscillations is utilized for design, the dissipation is not considered important in typical situations. However, for multiple operations in a system, dissipation is important for determining the time for the second operation to reduce the severity of the subsequent transient conditions. If not done properly, the resulting transient conditions may be worse than those in a single operation. Two-dimensional models, convolution-integral and instantaneous-acceleration based methods have been used for including unsteady friction in simulations. The first two models are computationally intensive while the selection of coefficients for the latter has been challenging in addition to the requirement of the simulation for the entire system. Consequently, these methods have not been utilized for general real-life applications. In this paper, a method is presented following the methodology for the computation of the dissipation of structural oscillations initiated by impulse loading, e. g. earthquake. This method does not require simulation of the entire system, is not computationally intensive and yields reasonable results for practical applications. An empirical equation is developed for the damping ratio by using the dimensional analysis and nonlinear regression. Comparisons of the computed results for a pipeline with a constant-level upstream reservoir and a downstream control valve with the experimental measurements during 18 transient experiments show good agreement


Year: 2017

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