O.N. Baumann

Centralized and decentralized control of structural vibration and sound radiation

This paper examines the performance of centralized and decentralized feedback controllers on a plate with multiple colocated velocity sensors and force actuators. The performance is measured by the reduction in either kinetic energy or sound radiation, when the plate is excited with a randomly distributed, white pressure field or colored noise. The trade-off between performance and control effort is examined for each case. The controllers examined are decentralized absolute velocity feedback, centralized absolute velocity feedback control and linear quadratic Gaussian (LQG) control. It is seen that, despite the fact that LQG control is a centralized, dynamic controller, there is little overall performance improvement in comparison to decentralized direct velocity feedback control if both are limited to the same control effort.

The stability of decentralized multichannel velocity feedback controllers using inertial actuators

The application of direct velocity feedback control on vibrating structures is well known to provide additional damping and reduce vibration levels. A number of previously studied control systems use multiple feedback loops with ideal velocity sensors and force actuators. While accelerometer signals may be utilized to accurately estimate velocity, there is rarely a structure off which one may react an ideal force. This paper concentrates on the use of multiple electrodynamic inertial actuators as a means of applying a force. A time domain model of a plate structure with multiple velocity sensors and collocated inertial actuators is derived. This model is then used to optimize the decentralized controller in order to minimize the total kinetic energy of the plate. These results are compared with those obtained with a decentralized controller in which each local loop has the same gain. It is demonstrated that for low control efforts, and hence control gains, both controllers perform almost identically, howe...

Destabilization of velocity feedback controllers with stroke limited inertial actuators

It has been observed when using inertial actuators for the active reduction of structural vibration, that velocity feedback controllers are liable to become unstable if the actuator is subject to stroke saturation. This article presents a simple nonlinear, time domain model of an inertial actuator mounted on a single degree of freedom system. At low amplitudes the actuator, when used in a velocity feedback control loop, increases the effective damping of the structure. At higher amplitudes the system is shown to become unstable, however, and generates limit cycle oscillations having a predictable frequency.

A comparison of decentralized, distributed, and centralized vibro-acoustic control

Direct velocity feedback control of structures is well known to increase structural damping and thus reduce vibration. In multi-channel systems the way in which the velocity signals are used to inform the actuators ranges from decentralized control, through distributed or clustered control to fully centralized control. The objective of distributed controllers is to exploit the anticipated performance advantage of the centralized control while maintaining the scalability, ease of implementation, and robustness of decentralized control. However, and in seeming contradiction, some investigations have concluded that decentralized control performs as well as distributed and centralized control, while other results have indicated that distributed control has significant performance advantages over decentralized control. The purpose of this work is to explain this seeming contradiction in results, to explore the effectiveness of decentralized, distributed, and centralized vibro-acoustic control, and to expand the concept of distributed control to include the distribution of the optimization process and the cost function employed.

Global optimization of distributed output feedback controllers

When the frequency range over which a reduction in vibration is desired is limited to a particular structural mode of vibration, for example, it is shown that a centralized velocity feedback controller can perform better than a decentralized controller for a given level of control effort. The decentralized controller, however, has the desirable properties of scalability and ease of implementation. A number of strategies for clustering the control locations have been proposed to exploit both the performance of the centralized controller and the scalability of decentralized controllers but these have previously been only locally optimal. This paper describes methods by which these distributed controllers may be designed to be globally optimal and gives examples of simulated results of these optimal distributed controllers.

The performance trade off of decentralised, distributed and centralised controllers

Direct velocity feedback control of structures is well known to increase structural damping and thus reduce vibration. In multichannel systems the way in which the velocity signals are used to inform the actuators ranges from decentralised controller through distributed or clustered controllers to the fully centralised controller. The objective of distributed controllers is to exploit the anticipated performance advantage of the centralised controller whilst maintaining the ease of implementation and robustness of the decentralised controller. It has been observed, however, that in many vibration control systems the centralised controller struggles to perform significantly better than a decentralised controller. This paper compares a number of distributed controllers and optimisation techniques for the reduction of kinetic energy and radiated sound power and identifies the conditions under which the centralised and distributed controllers offer a significant performance advantage.

Recent developments in the use of structural actuators for decentralized active control

With an array of ideal, dual, collocated actuators and sensors, decentralized feedback controllers can not only be unconditionally stable, but their performance in reducing vibration and, hence, radiated sound, can approach that of a centralized LQG controller [W. P. Engles et al., JASA 119, 1487–1495 (2005)]. They also have a modular architecture that scales well, even for very large structures. This paper discusses some of the problems that arise in practice when proof‐mass or piezoelectric transducers are used instead of ideal force or moment‐pair actuators in such decentralized controllers. Proof‐mass actuators are attractive when generating significant forces, but their natural frequency must be well below the first structural resonance frequency for stable operation. Even when this is achieved, impulsive forces due to the actuators hitting their end‐stops have recently been shown to potentially be an additional source of instability. Piezoceramic actuators can give significant control in thinner str...