Identification of the strength of junction coupling effects in water hammer

• Published in: Journal of fluids and structures Vol. 68; pp. 224 - 244
• Main Authors: Riedelmeier, S., Becker, S., Schlücker, E.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01-01-2017
• Subjects: FSI; Junction coupling; Oscillation; Two-mass oscillator; Water hammer; Water hammer; FSI; Junction coupling; Oscillation; Two-mass oscillator
• ISSN: 0889-9746; 1095-8622
• DOI: 10.1016/j.jfluidstructs.2016.09.006

In order to analyse the effects of junction coupling during water hammer in piping systems, a test facility has been designed and constructed. The main objective is to identify the dependence on the bend geometry and the strength of two-way coupling, and to derive a critical, geometric parameter, by means of which it is easily evaluated whether significant two-way effects occur or not. Oscillation experiments on movable U-shaped bends with various geometries were carried out. The excitation was realised by water hammer. The bend configurations differed in distance between the parallel levers, which results in different excitation forces, masses and stiffnesses. Inter alia the vertical displacement of the bend and the pressure inside the pipe were measured for various free oscillating lengths while the rest of the piping system was restrained. The results are displayed in curves of the maximum displacement and frequency spectra of the pressure and the displacement for the different bend configurations. Additional experiments with variable excitation at the coincidence frequency for two bend configurations were performed. Only for the medium and long bend configurations, two-way junction coupling effects were resolved. The strength of the coupling was found to be independent of the excitation, which just scaled the amplitudes. A quantification of the strength of the two-way coupling effects was performed by an analogy with the two-mass oscillator. This method was verified using coupled simulations. Owing to the good agreement between the results of the experiments and the simulations, additional bend configurations were calculated. Using this data, it is possible to evaluate the strength of the coupling on the basis of the geometry and mass of the bend.