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 1.64·104. 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.
Highlights
Vibration analysis is commonly used for structural health monitoring
Vibrations induced by the crossflow are responsible for the vast majority of failures in the multi-tube systems [1], see Fig. 1
The responses of the test rod (TR) using data from accelerometers are reconstructed by employing the fast Fourier transform (FFT) and the inverse Fourier transform
Summary
Vibration analysis is commonly used for structural health monitoring. Vibrations induced by the crossflow (flow is perpendicular to the rod axis) are responsible for the vast majority of failures in the multi-tube systems [1], see Fig. 1. Already in the early researches were founded three leading causes of vibration of the structural element in a liquid flow: vortex shedding, turbulent buffeting and fluidelastic excitation. An instrumented test bundle was constructed to measure fluid excitation forces (from vortex shedding and turbulence) acting on cylinders in the normal triangular tube array (P⁄d = 1.28) with water cross-flow. Rigid-body like motion with two degrees-of-freedom is achieved using two elastic beams at both ends of the test rod, similar to in [16, 17] Such a system is chosen as a model system for vibration analysis of an individual beam in SINQ target. The inverse model was build using flow rate Q and frequency ratio f ⁄f , as inputs and the stiffness coefficient k as a response
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