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

Abstract

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•10 4. 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.

Damage Detection of the Rod in the Crossflow Using Surrogate-Based Modelling

“…The full model uses the configuration of the rod bundle described in Upnere et al [9], in which laboratory experiments were carried out to examine the vibrations of single flexible-mounted rod caused by the crossflow in the rigid rod array. The configuration has a triangular array with pitchto-diameter ratio, P/d = 1.1.…”

“…Based on the results of the laboratory experiments described in Upnere et al [9], the frequency ratio between the natural frequency of the rod in the flow f n and the flow-induced frequency f t is selected as a response for the surrogate modelling.…”

“…2) is orthogonal, Legendre polynomials can be used as an approximation. The transformation from physical units to the unit cube [-1; 1] 2 is as (9) where m = [0.2765, 0.3253] and k = [15725, Analysis significance of polynomial based on Euclid norm in Eq. ( 6) shows that the coefficient per term does not depend on the number of terms used for approximation.…”