An Experimental Study on the Dynamic Response of a Vertical Cantilever Pipe Conveying Fluid

Abstract

Transverse vibrations of elastic pipes conveying a fluid have been observed in pipelines and heat exchangers. These fluid-induced vibrations can be a serious problem and in some incidents have caused structural failure resulting in environmental damage and economic loss. For offshore applications such as marine risers, the Ocean Thermal Energy Conversion Plant and deep ocean mining vacuums, the problem is compounded by the existence of vortex shedding, wave excitations, currents, and platform motions. An experimental study was conducted to investigate the effects of internal flow rate and the depth of immersion on the dynamic response of a vertical cantilever pipe discharging a fluid. It was found that the internal flow rate and the surrounding fluid have a significant effect on the natural frequencies of the system. Specifically it was found, that depending on the relative value of the forcing frequency, in comparison to the system natural frequencies, an increase in flow rate may not necessarily result in a larger system response. Conversely, an increase in the length of pipe immersion does not necessarily decrease the response of the system. It is also observed that with increasing flow rate, an auspicious increase in the response of the higher harmonics is noted, indicating an increase fluid coupling of the system. System natural frequencies were observed to decrease with increasing flow rate.