Browsing by Author "Silcox, Richard J."
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- Acoustics 1991: Active structural acoustic controlFuller, Chris R.; Silcox, Richard J. (Acoustical Society of America, 1992-01-01)In summary, the ASAC technique has demonstrated much potential in aerospace and marine applications. Future work will center on extending these techniques to broadband disturbances, more complex structures and improved modeling. It is known that optimizing transducer positions is as important as increasing the number of control channels. A multidisciplinary approach is required to synthesize a design procedure that integrates the elements of structural acoustics, transducer, and control technology. The pay off will be in significant cost and weight savings, and in performance improvements for other industrial applications.
- Adaptive Predictive Feedback Techniques for Vibration ControlEure, Kenneth W. II (Virginia Tech, 1998-02-03)In this dissertation, adaptive predictive feedback control is used to suppress plate vibrations. The adaptive predictive controller consists of an on-line identification technique coupled with a control scheme. Various system identification techniques are investigated and implemented including batch least squares, projection algorithm, and recursive least squares. The control algorithms used include Generalized Predictive Control and Deadbeat Predictive Control. This dissertation combines system identification and control to regulate broadband disturbances in modally-dense structures. As it is assumed that the system to be regulated is unknown or time varying, the control schemes presented in this work have the ability to identify and regulate a plant with only an initial estimate of the system order. In addition, theoretical development and experimental results presented in this work confirm the fact that an adaptive controller operating in the presence of disturbances will automatically incorporate an internal noise model of the disturbance perturbing the plant if the system model order is chosen sufficiently large. It is also shown that the adaptive controller has the ability to track changes in the disturbance spectrum as well as track a time varying plant under certain conditions. This work presents a broadband multi-input multi-output control scheme which utilizes both the DSP processor and the PC processor in order to handle the computational demand of broadband regulation of a modally-dense plant. Also, the system identification technique and the control algorithm may be combined to produce a direct adaptive control scheme which estimates the control parameters directly from input and output data. Experimental results for various control techniques are presented using an acoustic plant, a rectangular plate with clamped boundary conditions, and a time varying plate.
- Optimum Actuator Grouping in Feedforward Active Control ApplicationsSmith, G. Clark II (Virginia Tech, 1994-10-06)Previous work has demonstrated the benefit of grouping actuators to increase the controllability of an active control system, without increasing the number of control channels. By driving two or more secondary sources with the same control input, one is also able to reduce the hardware cost and complexity. In this work, a time domain cost function is developed for on-line actuator grouping and active structural acoustic control (ASAC) of a simply-supported beam excited with a broadband disturbance. Three PZT actuators are mounted on the beam structure to control the wavenumber components corresponding to five radiation angles. The propagation angles are selected to represent the total radiated sound power. The point force disturbance is bandlimited random noise which encompasses the first three modes of beam vibration. Actuators are considered grouped when their compensators are equal. Therefore, the cost function presented here incorporates an additional non-quadratic term which penalizes the controller for differences between the feedforward compensator coefficients. The backpropagation neural network algorithm provides the proper procedure to determine the minimum of this cost function. The main disadvantage of using a stochastic gradient technique, while searching the prescribed control surface, is convergence to local minima. In this thesis, a resolution to this problem is suggested which incorporates using a variety of initial conditions. Two initialization conditions are considered: grouping actuators based upon weights determined by converging the filtered-x LMS algorithm and simultaneously grouping and controlling with the compensator weights initialized to small arbitrary numbers. Test cases of heavy and light grouping parameters were evaluated from both initial conditions. The computer simulations demonstrate the ability of this new form of the cost function to group actuators and control the error response with either initial condition. The heavy grouping cases achieved the same one channel control system from both initial conditions. The performance of the one channel solution was 1.5 dB lower than the performance of the ungrouped filtered-x LMS solution. The ability to select the different levels of grouping was demonstrated when the algorithm was initialized with the filtered-x LMS weights and run with light grouping parameters. For this case, the on-line algorithm grouped two actuators, but allowed the third actuator to exist independently. The performance of the two channel control system was only 0.6 dB less than the performance of the filtered-x LMS solution. In all grouping cases investigated, the convergence times of the grouping algorithm were within the same order as for the filtered-x LMS algorithm. The effect of uncorrelated error sensor noise on the actuator groupings is also briefly discussed.
- A Principal Component Algorithm for Feedforward Active Noise and Vibration ControlCabell, Randolph H. III (Virginia Tech, 1998-04-17)A principal component least mean square (PC-LMS) adaptive algorithm is described that has considerable benefits for large control systems used to implement feedforward control of single frequency disturbances. The algorithm is a transform domain version of the multichannel filtered-x LMS algorithm. The transformation corresponds to the principal components of the transfer function matrix between the sensors and actuators in a control system at a single frequency. The method is similar to other transform domain LMS algorithms because the transformation can be used to accelerate convergence when the control system is ill-conditioned. This ill-conditioning is due to actuator and sensor placement on a continuous structure. The principal component transformation rotates the control filter coefficient axes to a more convenient coordinate system where (1) independent convergence factors can be used on each coordinate to accelerate convergence, (2) insignificant control coordinates can be eliminated from the controller, and (3) coordinates that require excessive control effort can be eliminated from the controller. The resulting transform domain algorithm has lower computational requirements than the filtered-x LMS algorithm. The formulation of the algorithm given here applies only to single frequency control problems, and computation of the decoupling transforms requires an estimate of the transfer function matrix between control actuators and error sensors at the frequency of interest. The feasibility of the method was demonstrated in real-time noise control experiments involving 48 microphones and 12 control actuators mounted on a closed cylindrical shell. Convergence of the PC-LMS algorithm was more stable than the filtered-x LMS algorithm. In addition, the PC-LMS controller produced more noise reduction with less control effort than the filtered-x LMS controller in several tests.
- Simultaneous active control of flexural and extension power flow in thin beamsGibbs, Gary P. (Virginia Tech, 1993-04-05)The primary goal of this dissertation consisted of two related parts. The first was to develop an analytical basis for predicting the active control of flexural and extensional power flow in thin semi-infinite and finite beams using piezoelectric actuators and sensors. The second part was to experimentally demonstrate these techniques applied to actual beam systems. In order to maintain total control authority over the system, the control actuators must be able to adequately excite both flexural and extensional motion in the beam. Accurate sensing or estimation of the actual power flow (or variables that can be related to the power flow) in the finite beam in real time is also a requirement. This dictated the development of advanced, new sensing techniques. In order that these overall goals were achieved several tasks were carried out as discussed below. A theoretical model for the excitation of a thin beam by a single piezoelectric actuator mounted on the surface was developed. The model predicts the simultaneous excitation of flexural and extensional motion by a single actuator whose relative amplitudes are functions of beam and actuator parameters. Further, a single pair of axially co-located, symmetrically bonded, and independently driven piezoelectric actuators can excite flexural and extensional motion of variable complex amplitudes. A method for the real time filtering of net positive and negative traveling flexural and extensional waves was developed. The theoretical actuator and sensor models were used to study the control of flexural and extensional power.flow in both finite and semi-infinite beams subjected to point force excitation at the free end. These actuator and sensing techniques when combined with an multiple input/output adaptive controller can simultaneously control flexural and extensional power flow in regions of a beam system over a band of frequencies. The control of flexural and extensional power flow in thin beams was also experimentally investigated for both finite and semi-infinite beams. Power flow attenuations of 30 dB or more downstream of the control actuator location were demonstrated using a single pair of piezoelectric actuators for both resonant and damped beam systems. The experimental and theoretical results demonstrate the effectiveness of piezoelectric actuators and piezoelectric wave vector filters in the control of flexural and extensional power flow in thin beams.