Application of the shock response spectrum method to severity assessment of water hammer loads

Abstract

Water hammer (WH) is a transient phenomenon which happens to appear in pipe flow systems as an effect of a sudden change in pipe flow conditions. Various origins can be the primary source of WH. They usually come from the liquid (e.g. operation of valves), but when the pipeline system is significantly elastic, WH can be produced by an external impact or transient vibration due to fluid structure interaction (FSI) effect. Hydraulic transients are usually undesired effects as large amplitudes of pressure waves, pipe stresses or vibration accompanying this phenomenon can be the source of pipeline system malfunction. Therefore, many efforts are taken by scientists and engineers to avoid unexpected WH events or to reduce their harmfulness. Systematic protection of pipeline systems requires a reliable method of severity estimation of WH loads. Various ways can be used for evaluation of WH strength. In general, severity of a transient depends on its amplitude, i.e. the maximum value of the liquid pressure. Another important factor is time dependence of the load signal however, a simple observation of its shape in time domain is usually not an effective technique. Instead, frequency domain analysis can be exploited. A specific kind of spectral analysis used in structural mechanics for assessment of shock loads and transients is the shock response spectrum (SRS) method. An original concept of application of this technique to WH events is proposed in this study. The method is shortly presented and its numerical approach developed by the author and applicable to WH loads are described. As an example of use the SRS computations and analysis of own WH experimental results measured at a laboratory pipeline are performed and concluded. Specific preprocessing of WH signal was applied and explained. It is evidenced in the paper that the applied SRS method gives a valuable and effective tool for determination of WH load severity. Therefore, it can also be used for comparison between alternative designs of pipeline system applied for protection from undesired WH events.