Active Vibration Control for the Measurement of Fluidelastic Effects

Abstract

A new method based on active vibration control is proposed to investigate fluidelastic coupling effects beyond fluidelastic instability. This active control method allows to extend the range of flow velocity explored for single input-single output control systems. The method is applied on a flexible tube inserted in a rigid bundle in water and air-water cross-flows. This structure becomes unstable for high flow velocities, fluidelastic forces then causing the damping of the fluid-structure system to fall towards zero. The active control method allows to carry out tests beyond the fluidelastic instability. The flow velocity range explored is doubled in two-phase flow.

Vibro-Impact Experiments and Computations of a Gap-Supported Tube Subjected to Single-Phase Fluid-Elastic Coupling Forces

“…2 and 3. It is, essentially, the one used in [12][13][14] in their tests, however a new instrumented tube with quite different modal frequency was used in the present experiments. Furthermore, the present experiments were designed for flow-excited vibro-impacting on an instrumented loose support.…”

“…, the added mass m C being assumed independent of the flow velocity. In order to explore the full range of experimental reduced velocity -well beyond the fluid-elastic stability boundary of the "normal" system -the analog feedback stabilization technique [12][13][14] has been adopted. It is, essentially, the one used earlier by Antunes et al [9] in their feedback controlled instability tests, but with reversed polarity.…”

“…Therefore, based on the active vibration control method proposed by Caillaud et al [12][13][14], new experiments have recently been performed at CEA-Saclay on the same experimental rig, consisting on a flexible tube (vibrating along the lift direction) inserted in a rigid square bundle. First, the linearized fluid-elastic coupling coefficients, as well as the turbulence excitation, were identified for a significant range of reduced velocity, in water cross-flow.…”

“…Therefore, in the specific case of our experiments, the dominant response frequency is mostly the same irrespectively of the tube coordinateused for the nonlinear computations. Numerical integration of the nonlinear formulation (3)-(14)…”

Fluid-Elastic Coefficients in Single Phase Cross Flow: Dimensional Analysis, Direct and Indirect Experimental Methods

“…This instability can be described as a self-excited feedback mechanism between the motion of the structure and the fluid forces. Since the pioneering work of Tanaka and Takahara [1], several authors [2][3][4][5][6][7][8][9][10] measured the fluid-elastic force to feed the stability criterion models developed by Connors [11], Blevins [12], Chen [2,3], Lever and Weaver [13][14][15], Price and Païdoussis [16][17][18], Granger et al [19,20] and Tanaka et al [21].…”