Feedforward active control of free field structural radiation using vibration control sources and piezo-electric polymer fdm error sensors is considered. The problem of what should be measured by the sensors is first examined, where it is shown that orthonormal decomposition of the equation governing the acoustic power output of the structure will define the optimal quantities, which are described using the in vacuo structural modes as a basis function. Computer simulations show that by using only a few of these quantities as error signals, practically the maximum levels of acoustic power attenuation can be obtained at low frequencies. Tonal and broadband experimental results are presented using the shaped piezo-electric polymer film sensors which demonstrate the effectiveness of the described approach.
This article examines the characteristics of real vibrational power flow in a simply supported rectangular panel under the action of feedforward vibration control, induced by a control source input which is slightly suboptimal such that the primary source is producing a slight amount of real vibrational power, and the control source is absorbing the same amount. It is found that the path of the power flow is a combination of translations and rotations, the rotations induced by the interference of two modes which produces a "vortex generating block." A qualitative formula for predicting the number of power flow vortices, as well as the discussion of the vortex period, is put forward. A novel method to induce a vortex at an arbitrary location of the plate is also shown, which may have practical applications in controlling the path of vibrational power flow in systems of large extent. Moreover, the influence of the induced vortex power flow on the plate onto the acoustic intensity distribution is investigated, showing that the rotational direction of the vortex on the plate is not always the same with that of the acoustic intensity in the near field.
This paper discusses the optimal vibration feedback control of an Euler-Bernoulli beam from a viewpoint of active wave control making all structural modes inactive (more than suppressed). Using a transfer matrix method, the paper derives two kinds of optimal control laws termed “active sink” which inactivates all structural modes; one obtained by eliminating reflected waves and the other by transmitted waves at a control point. Moreover, the characteristic equation of the active sink system is derived, the fundamental properties being investigated. Towards the goal of implementing the optimal control law that is likely to be non-causal, a “classical” velocity feedback control law (Balas, 1979) widely used in a vibration control engineering is applied, revealing a substantial shortcoming. Introduction of a “classical” displacement feedback to the velocity is found to realize the optimal control law in a restricted frequency range. Finally, two kinds of stability verification for closed feedback control systems are presented for distributed parameter structures.
Feedback control of free field structural radiation is considered. State equations are formulated with a transformation which decouples the acoustic power error criterion. Using the resultant equations, expressed in terms of ' 'transformed mode'' states, the order of the state equations can be significantly reduced at low frequencies. Two experimental implementations of feedback control strategies using shaped piezoelectric polymer film sensors to measure the transformed system states are described. The first of these is a simple analog implementation. The second implementation is in discrete time, where an adaptive algorithm for optimizing the weights of IIR filters for practical use is described. It is shown that by using the outlined control approach significant levels of low frequency acoustic power attenuation can be obtained with no control spillover and subsequent increase in higher frequency acoustic power output.
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