Author(s): Didia Covas; Helena Ramos; Antonio Betamio De Almeida
Linked Author(s): Dídia Isabel Cameira Covas
Keywords: Frequency domain; Impulse response; Transients; Viscoelastic; Fourier analysis
Abstract: The current paper focuses on the application of the Impulse Response Method (IRM) for solving hydraulic transients in pressurised viscoelastic pipes. Basic fluid equations are described in the frequency domain by transfer functions, as for steady oscillatory flows, and are used for the evaluation of response functions by the inverse Fast Fourier Transform (invFFT) technique. Non-periodic pressure perturbations are obtained by the direct convolution of the response function with the discharge change (or pressure pulse). This method is a particularly useful procedure to take into account frequency-dependent factors, such as unsteady skin friction and pipe-wall viscoelasticity, which considerably influence the dynamic behaviour of the fluid system in transient or steady oscillatory conditions. These two phenomena were incorporated into the transfer functions by using a complex-valued wave speed and propagation operators. Transient data collected from a 270 m polyethylene (PE) pipeline, with 50 mm diameter, at Imperial College (London, UK) are used for validating the developed method. Numerical results obtained are compared with experimental data. An excellent agreement is observed. The use of this method (i. e. IRM) is much faster than the typical method of characteristics and can straightforwardly include frequency-dependent factors; however, it has the disadvantage of the loss of accuracy due to the linearization of the friction term and the valve equation, and the complex application to multi-pipe systems.
Year: 2005