Effects of variable parameters on the behaviour of the single flexibly-mounted rod in a closely-packed array

• Main Authors: Sabine Upnere, Normunds Jekabsons, Sergejs Dementjevs, Michael Wohlmuther
• Format: Article
• Language: English
• Published: JVE International 2020-05-01
• Series: Journal of Vibroengineering
• Subjects: crossflow; dominant frequencies; increasing and decreasing flow; metamodeling; rods bundle; vibrations
• Online Access: https://www.jvejournals.com/article/20596

Experiments of flow-induced vibrations using a closely-packed triangular rods array with a pitch-to-diameter ratio of 1.1 in water cross-flow were carried out to analyse the detected effects of system parameters in the frequency domain and vibration amplitudes. Single flexibly mounted rod with two degrees of freedom at each end of it was located in the second or the fourth row in the bundle with 21 row. Influence of increasing/decreasing flow, the test rod mass and support stiffness changes were analysed. Reynolds number based on the freestream velocity and a rod diameter was up to 1.64·104. Accelerometers and laser sensors were used to measure the time-varying response of the test rod. FFT approach was adopted to reconstruct the displacements from accelerometer measurements. Experimental results show that the behaviour of the flexibly-mounted rod is dependent on the flow time-history. Dominant flow-dependent and flow-independent frequencies were observed in the frequency domain. Changes in the frequency spectrum introduced by the test rod mass and support stiffness were identified. Oscillation regime of the test rod when the state equilibrium position becomes unstable with the limited oscillations was detected. Metamodeling approach was applied to develop mathematical approximation using three parameters: flow rate, stiffness coefficient and frequency ratio. Good accordance has been found between the inverse model and laboratory experiments.