Active Control Applications Research Articles

Control of Sound Radiating from an Orthotropic Plate

This paper is concerned with the problem of actively suppressing the acoustic radiation pressure generated by an orthotropic plate vibrating in air. The approach is to control the vibration of the modes of the plate most responsible for acoustic radiation pressure. This is accomplished by relating the far-field radiation pressure to the state of the plate. The control of the far-field radiation pressure is carried out by means of actuators placed on the elastic plate. A numerical example demonstrates the application of active control to suppress the far-field sound radiating from a simply-supported rectangular thin orthotropic plate subjected to a harmonic disturbance. The influence on the control effectiveness of various design parameters, such as the number of controlled modes, the choice of controlled modes, and the number of actuators, is investigated.

Combustion instabilities coupled by pressure waves and their active control

This article contains a review of combustion instabilities coupled by pressure waves and of the related pulse combustor and active control principles and applications. The basic mechanisms leading to combustion oscillations are first identified from experimental evidence gathered in recent years. It is shown that in the presence of pressure waves, the flow features large scale motions which drive the instability. The dynamics of the flame is then dominated by processes of hydrodynamic instability, vortex roll-up, vortex interactions, front and reacting stream pulsations, periodic extinctions and reignitions, self acceleration. Knowledge accumulated on these various aspects has provided guidelines in combustor design. Progress accomplished in the special domain of pulse combustors is surveyed. These devices which operate under sustained pressure oscillations have been the subject of intensive research with as objective the understanding of the dynamics of the flow in various geometrical situations in order to improve the heat transfer efficiency and diminish the level of pollutant formation. While pulse combustors use pressure oscillations in normal operation, in most circumstances the presence of pressure waves causes problems of vibration, enhanced heat fluxes to the walls, cyclic fatigue, and in some cases important damage to the combustor. One generally wishes to eliminate or attenuate these waves. This is usually achieved by changes in the geometrical design and in the operation of the system. New possibilities based on active control have been investigated in recent years. The basic principles and the initial demonstrations of active instability control are first reviewed. It is then shown that such methods constitute a promising technology and that they are also a unique tool in the experimental investigation of combustion instability and pressure related phenomena.

Application of Active Control to Axial Flow Fans

Application of Active Control to Axial Flow Fans

Spatial simulation of instability control by periodic suction blowing

The applicability of active control by periodic suction blowing in spatially evolving plane Poiseuille flow is investigated by the direct simulation of the three-dimensional, incompressible Navier–Stokes equations. The results reveal that significant reductions in perturbation amplitudes can be obtained by a proper choice of the control wave amplitude and phase. The upstream influence of the control wave is shown to be confined to a region in the vicinity of the control slot with no apparent effect on the flow development.

One-Dimensional Thermomechanical Constitutive Relations for Shape Memory Materials

The use of the thermoelastic martensitic transformation and its reverse transformation has recently been proposed and demonstrated for several active control ap plications. However, the present constitutive models have lacked several important funda mental concepts that are essential for many of the proposed intelligent material system ap plications such as shape memory hybrid composites. A complete, unified, one-dimensional constitutive model of shape memory materials is developed and presented in this paper. The thermomechanical model formulation herein will investigate important material characteristics involved with the internal phase transformation of shape memory alloys. These characteristics include energy dissipation in the material that governs the damping behavior, stress-strain-temperature relations for pseudoelasticity, and the shape memory effect. Some numerical examples using the model are also presented.

The active control of sound

Active control of sound results from destructive interference between the sound field of an original acoustic source and that from a controllable array of ‘secondary’ acoustic sources. For this destructive interference to occur over an appreciable region of space the sound field of the secondary sources must match that from the primary source in both time and space. The spatial matching requirement leads to an upper frequency of applicability of active control. Active control complements conventional passive methods of sound control, which do not work well at low frequencies. Practical feedforward controllers, using a multichannel generalisation of the well known LMS adaptive algorithm, have been developed, using as many as 16 loudspeakers and 32 microphones, and applied with considerable success in the control of low-frequency propeller noise inside aircraft and low-frequency engine noise inside cars.

Active position control of stepping motors with flexible transmission shaft

In this paper the authors present an active control algorithm for position control of stepping servomotors with flexible transmission shaft. A non-linear mathematical model is derived to describe the dynamic behaviour of the system. To implement the full state-variable active-control technique, the non-linear model is first linearised. It is shown that the full state variables could be used in a closed-loop controller to introduce damping in the eigenvalues of the system. For realistic application of active control, a state estimator (observer) is used to construct the full state variables from a single measured signal. The estimated state variables are fed in the controller to generate the control signal. It is shown that this method facilitates the introduction of damping in all eigenvalues of the system and so eliminates the undesirable oscillation due to the flexibility of the transmission shaft. Furthermore the effectiveness of linear control algorithm on the non-linear system is studied.

Application of localized active control to reduce propeller noise transmitted through fuselage surface

An innovative concept of “localized active noise control” is experimentally demonstrated in achieving a satisfactory cabin noise reduction for propeller aircraft. The principle of localized active noise control is to reduce the propeller noise (primary source) only locally in the vicinity of an antiphase sound source (secondary source) which is mounted on the wall of an aircraft cabin. Then, several such sound sources mounted on the cabin wall can reduce the propeller noise over a large area on the cabin surface and behind it. This has been demonstrated by conducting a laboratory experiment in which an acoustic driver generating discrete frequency sound behind a thin metallic surface was used as the primary source. Four other acoustic drivers mounted on the surface were used to generate the antiphase sound on the other side of the surface. The measured noise field behind the metallic surface indicates satisfactory noise reduction. The present experimental arrangement works particularly well at low frequencies, but more secondary sources will be required for high-frequency noise. Another potential application of this technique, demonstrated in this paper, is to reduce noise levels in selected areas on the exterior of the aircraft where sonic fatigue may be critical.

Block-Krylov component synthesis method for structural model reduction

A new analytical method is presented for generating component shape vectors, or Ritz vectors, for use in component synthesis. Based on the concept of a block-Krylov subspace, easily derived recurrence relations generate blocks of Ritz vectors for each component. The subspace spanned by the Ritz vectors is called a block-Krylov subspace. The synthesis uses the new Ritz vectors rather than component normal modes to reduce the order of large, finite-element component models. An advantage of the Ritz vectors is that they involve significantly less computation than component normal modes. Both 'free-interface' and 'fixed-interface' component models are derived. They yield block-Krylov formulations paralleling the concepts of free-interface and fixed-interface component modal synthesis. Additionally, block-Krylov reduced-order component models are shown to have special disturbability/observability properties. Consequently, the method is attractive in active structural control applications, such as large space structures. The new fixed-interface methodology is demonstrated by a numerical example. The accuracy is found to be comparable to that of fixed-interface component modal synthesis.

Experiments on Active Control of Seismic Structures

This paper presents the first phase of a comprehensive experimental study concerning the possible application of active control to structures under seismic excitations. In the laboratory, a single‐degree‐of‐freedom model structure was used which was controlled using prestressing tendons connected to a servohydraulic actuator. An optimal closed‐loop control scheme using a quadratic performance index was employed to reduce the response of structure under base motion generated by a large‐scale seismic simulator. The time delay between the observed motion and the implemented control forces, an important factor in control implementation, was integrated in the control algorithm. Using a carefully designed, fabricated, and calibrated experimental setup, the correlation between the analytical and experimental results was studied. Based on similitude relations, the experimental results obtained for the model structure were extrapolated to the full‐scale structures and are analyzed.

The active minimization of harmonic enclosed sound fields, part II: A computer simulation

This paper is Part II in a series of three papers on the active minimization of harmonic enclosed sound fields. In Part I it was shown that in order to achieve appreciable reductions in the total time averaged acoustic potential energy, E p , in an enclosed sound field of high modal density then the primary and secondary sources must be separated by less than one half wavelength, even when a relatively large number of secondary sources are used. In this report the same theoretical basis is used to investigate the application of active control to sound fields of low modal density. By the use of a computer model of a shallow rectangular enclosure it is demonstrated that whilst the reductions in E p which can be achieved are still critically dependent on the source locations, the criteria governing the levels of reduction are somewhat different. In particular it is shown that for a lightly damped sound field of low modal density substantial reductions in E p can be achieved by using a single secondary source placed greater than half a wavelength from the primary source, provided that the source is placed at a maximum of the primary sound field. The problems of applying this idealized form of active noise control are then discussed, and a more practical method is presented. This involves the sampling of the sound field at a number of discrete sensor locations, and then minimizing the sum of the squared pressures at these locations. Again by use of the computer model of a shallow rectangular enclosure, the effects of the number of sensors and of the locations of these sensors are investigated. It is demonstrated that when a single mode dominates the response near optimal reductions in E p can be achieved by minimizing the pressure at a single sensor, provided the sensor is at a maximum of the primary sound field. When two or three modes dominate the response it is found that if only a limited number of sensors are available then minimizing the sum of the squared pressures in the corners of the enclosure gives the best reductions in E p . The reasons for this behaviour are discussed.

Numerical study of transition control by periodic suction blowing

The applicability of active control of transition by periodic suction-blowing is investigated via direct numerical simulations of the Navier-Stokes equations. The time-evolution of finite-amplitude disturbances in plane channel flow is compared in detail with and without control. The analysis indicates that, for relatively small three dimensional amplitudes, a two dimensional control effectively reduces disturbance growth rates even for linearly unstable Reynolds numbers. After the flow goes through secondary instability, three dimensional control seems necessary to stabilize the flow. An investigation of the temperature field suggests that passive temperature contamination is operative to reflect the flow dynamics during transition.

The Active Control of Noise and Vibration and Some Applications in Industry

During the last decade, advances in signal processing and microelectronics have brought to reality the development of active devices for suppressing noise and vibration. These have now been successfully demonstrated both in laboratory experiments, and under more rigorous conditions of large-scale industrial application. It is shown that close parallels exist between these novel active techniques and certain well-proven mechanical methods of reducing vibration. Examples of the latter are given which date back to the last century, and highlight the extent to which the basic principles of dynamic vibration cancellation have been applied with confidence by mechanical engineers. Now, in common with many other applications of control technology, the process of replacing simple mechanical linkages with more precise and responsive electronically activated servomechanisms has led to considerably improved flexibility and adaptability. In this respect the application of active control to vibration attenuation represents a natural and timely step in engineering development. A more recent advance, however, has been the application of these techniques to the direct control of airborne sound, which represents a greater departure from conventional engineering practice. A number of successful examples of such methods have now been demonstrated. It is proposed that more sophisticated devices, which will take even greater advantage of the power of modern signal processing, will be developed for the future. These devices promise to enhance considerably the overall scope of the technology.

An assessment of the application of active control to reduce the seismic response of nuclear power plants

Active control techniques offer the possibility of achieving a single plant design suitable for all seismic regions. Based on the information determined by sensors on the actual state of the dynamic system control forces are fed back acting, e.g. on reactor plant subelements. Limitations of passive systems are examined. The basic concepts of active control are illustrated. The potential for active control of a reactor pressure vessel is demonstrated. A quite simple equivalent dynamic model is shown to be adequate to design the feedback law of the structure which is actually of very high dynamic order. By judicious placement of structural motion sensors and by limitation of the bandwidth of force actuators, destabilizing effects of the higher order structural dynamics (unmodelled for the purpose of control design) are easily controlled in this application. The choice of various controllers for design on the basis of the performance (acceleration of the vessel) versus the control energy are discussed. The controllers designed on the basis of correlated white noise input, which require the feedback of the earthquake acceleration from a sensor dedicated to this task, perform better than those based on a pure white noise input.

Wing/store flutter: An active adaptive control application

Wing/store flutter: An active adaptive control application

Active Control Transport Design Criteria

Active Control Transport Design Criteria

The Application of Active Control to Improve Boring Bar Performance

A previously established theoretical basis for controlling both the static stiffness as well as dynamic vibrations and regenerative chatter in particular was implemented in the work described by this paper. It was found that the experimental boring bar setup did exhibit two principal modes but that the controller could be synthesized largely independent of these modes. Cutting tests were performed using Delrin acetal plastic on a lathe equipped with a pivoted boring bar which was controlled by an electro-hydraulic servo system. It was found that the theory established earlier did in fact predict qualitatively the new stability borderline. Width of cut was improved by a factor of twelve and equivalent static stiffness was increased without bound.

A Theoretical Basis for the Active Control of a Boring Bar Operation

The properties of low stiffness and low structural damping in boring bars are widely known to be factors resulting in chatter and inaccurate machining. The application of active control offers a new alternative to improving the performance of a boring bar. This paper presents the theoretical basis for such an active control system. The analysis includes the practical consideration of principal modes in the boring bar model and discusses this influence on controller design. Simulation results using data from an experimental system illustrate some important factors of system design.

An Analytical Study of Controlled Buoyancy in Laying Deep-Sea Pipelines

The application of active and passive buoyance control as an aid to deep marine pipelines has been quantitatively investigated. The use of buoys yields a substantial reduction of barge thrust and pipe tension. A systematic method is used to calculate buoy forces from a desired stress distribution. An efficient numerical solution procedure has been developed for predicting static marine pipeline geometries during laying operations. The iterative procedure is well suited for solving the two-point boundary value problem over a wide range of ocean depths.

Some Applications of Optimization Techniques to Water Quality Modeling and Control

Dynamic water quality modeling methodology is presented along with a number of applications of optimization theory to deterministic water quality modeling and control. Two of the applications are basically parameter estimation problems. The first involves the generation of a dynamic model for the behavior of coliform bacteria in Grand Traverse Bay, while the second is concerned with the estimation of parameters in an existing model for the growth of bacteria in organic carbon limited media. The third application utilizes the proposition that the laws of nature are in some sense optimal to aid in the characterization of an algae inhibition function. The basic problem involves the development of a model of phytoplankton succession in lakes involving two species of algae and two nutrients. An unknown algal inhibition function is treated as an unknown control that is to be determined to minimize the loss of nutrients from the system, which is considered as an approximate optimality principle for the system. The resultant solution possesses an optimal singular subarc that has an interesting ecological interpretation. An active control application utilizing the same model is also presented.