On the Suppression of Coupled Liquid/Pipe Vibrations

The vibration of liquid-filled pipe systems can be caused by internal (pressure surges) or external (rotating machinery) sources, or a combination of both. Liquid pulsations can be diminished by devices like an air chamber, whereas pipe vibrations can be reduced by suitable supports. The performance of vibration suppression devices in the system under consideration can be investigated by numerical simulation. This is usually done with conventional waterhammer or pipe-stress computer codes. Present-day software also permits fully-coupled liquid-pipe analyses. The analysis of suppression devices and their interaction with the entire system is an important tool in design and trouble shooting.The dynamic behaviour of a simple system consisting of one pipe, one liquid column and one suppression device is studied herein by numerical simulation and physical experiment. Liquid-pipe interaction mechanisms are taken into account. A closed water-filled steel pipe is excited by external impact. The suppression device is a short piece of plastic pipe. The closed system prevents rigid-column behaviour of the liquid relative to the pipe, so that the local device does not decrease amplitudes of vibration. It does, however, shift the natural frequencies of the system, which is an important means of vibration control. This simple and cheap device may find its application in reducing fatigue problems and in noise reduction.