1,720,976 research outputs found
Stability and convergence analysis for different harmonic control algorithm implementations
Full text linkIn many engineering systems there is a common requirement to isolate the supporting foundation from low frequency periodic machinery vibration sources. In such cases the vibration is mainly transmitted at the fundamental excitation frequency and its multiple harmonics. It is well known that passive approaches have poor performance at low frequencies and for this reason a number of active control technologies have been developed. For discrete frequencies disturbance rejection Harmonic Control (HC) techniques provide excellent performance. In the general case of variable speed engines or motors, the disturbance frequency changes with time, following the rotational speed of the engine or motor. For such applications, an important requirement for the control system is to converge to the optimal solution as rapidly as possible for all variations without altering the system's stability. For a variety of applications this may be difficult to achieve, especially when the disturbance frequency is close to a resonance peak and a small value of convergence gain is usually preferred to ensure closed-loop stability. This can lead to poor vibration isolation performance and long convergence times. In this paper, the performance of two recently developed HC algorithms are compared (in terms of both closed-loop stability and speed of convergence) in a vibration control application and for the case when the disturbance frequency is close to a resonant frequency. In earlier work it has been shown that both frequency domain HC algorithms can be represented by Linear Time Invariant (LTI) feedback compensators each designed to operate at the disturbance frequency. As a result, the convergence and stability analysis can be performed using the LTI representations with any suitable method from the LTI framework. For the example mentioned above, the speed of convergence provided by each algorithm is compared by determining the locations of the dominant closed-loop poles and stability analysis is performed using the open-loop frequency responses and the Nyquist criterion. The theoretical findings are validated through simulations and experimental analysi
Active structural acoustic control of a flat plate using an experimentally identified radiation resistance matrix
No full textActive Structural Acoustic Control (ASAC) is a widely used active noise control technique, which provides global control of structurally radiated noise by controlling structural vibrations. Many current ASAC systems rely upon the availability of an accurate, real-time measure of the radiated sound field. This often requires positioning of acoustic error sensors in the radiated sound field, which for many practical setups may not always be possible. Previous research has investigated the implementation of ASAC using structural measurements that can be related to the radiated noise. One such method employs the use of the radiation resistance matrix to estimate the radiated sound power from structural measurements. However, estimation of the radiation resistance matrix has generally relied upon precise modelling of the radiating structure which, for practical structures, can lead to limitations in the accuracy of the estimate. To overcome this problem, this paper presents an ASAC system that utilises an experimentally identified radiation resistance matrix. It is shown via real-time implementation of the proposed strategy for a flat plate, that the proposed ASAC system is effective at controlling structurally radiated noise and out performs an Active Vibration Control (AVC) system using identical hardware. At the first three radiating modes, the proposed method achieves 9, 9 and 23 dB more attenuation in the radiated sound power than AVC
Controller architectures for optimum performance in practical active acoustic metamaterials
No full textOver the last decade there has been significant interest in the design and production of acoustic metamaterials with physical qualities not seen in naturally occurring media. Progress in this area has been stimulated by the desire to create materials that exhibit novel behaviour when subject to acoustic waves,such as negative refraction or the appearance of band gaps in the frequency response of the material. Proposed designs range from locally resonant phononic crystals to arrays of Helmholtz resonators within ducts and past research has investigated both passive and active materials. Much of the research into active acoustic metamaterials remains theoretical, therefore to determine whether such materials are physically realisable and of potentially practical use it is important to understand the physical constraints that may arise in a produced active metamaterial. In this paper a 1-dimensional active acoustic metamaterial derived from a passive, Helmholtz resonator based design is considered where the applied control forces produce controllable double negative behaviour. The physical dimensions and active forces required to achieve the desired novel behaviour are explored for different architectures and any trade-offs that might have to be considered when producing a practically useful active metamaterial are identifie
Mathematical modelling and dynamical analysis of a magnetorheological elastomer tuneable absorber
No full textMagnetorheological elastomers (MREs) are a smart material whose mechanical properties can be adjusted through an external magnetic field. Because their field dependent properties can be selectively tuned, MREs are highly suitable for vibration control system. In this study, the dynamical properties of MREs are investigated experimentally in shear mode under different driving frequency and strain amplitude. The results show that both of the storage modulus and loss modulus decrease slightly with the strain amplitude; whereas the driving frequencies lead to increasing storage modulus and a maximum in loss modulus. Based on experimental results, a mathematical model is proposed to predict the frequency- and amplitude-dependent properties of MREs and a dynamical system with an adaptive tuned vibration absorber is build up to estimate the control efficiency of MRE absorber. Compared to conventional absorber, the performance of vibration control is improved obviously with MRE absorbers
A robust optimised multi-material 3D inkjet printed elastic metamaterial
No full textThis paper presents and validates a novel elastic metamaterial design, that is optimised for broadband robust vibration control of a structure in the presence of uncertainties, and realised using multi-material additive manufacturing. A novel concept resonator design that allows the resonance frequency to be flexibly tuned via both geometrical and material property modifications is presented and characterised. A unit cell consisting of 12 of these resonators is then proposed. The resonance frequencies and damping ratios of this elastic metamaterial unit cell when attached to a parametrically uncertain example structure are then optimised using a Particle Swarm Optimisation to maximise the mean attenuation in kinetic energy of a structure with parametric uncertainties, based on an analytical model of the system. The performance of the optimised metamaterial is then validated experimentally, and it is shown that the realised metamaterial design is able to achieve a mean of 3.5 dB of broadband attenuation in the presence of uncertainties in the structure. In addition, in the presence of structural uncertainties the robustly optimised design achieves 0.5 dB greater mean attenuation than a design optimised on the nominal structural response alone, and reduced variation in attenuation for different levels of uncertainty
Active control of a frequency varying tonal disturbance by a nonlinear optimal controller with frequency tracking
No full textActive structural acoustic control using an experimentally identified radiation resistance matrix
No full textActive structural acoustic control (ASAC) is a widely used active noise control technique that provides control of structurally radiated noise through actuation of the radiating structure. Typically, ASAC drives structural actuators to minimise a real-time measurement of the radiated sound field. However, it is often not practical to position error microphones in the radiated sound field. To overcome this limitation, a number of methods have previously been proposed. One such method utilises the radiation resistance matrix to map structural response measurements to the acoustic response and, thus, enable an estimate of the structurally radiated sound power from structural measurements alone. This has previously relied upon precise modelling of the radiating structure which, for practical structures, can lead to limitations in the accuracy of the estimate. In this paper, an ASAC strategy that utilises an experimentally identified radiation resistance matrix is presented. The robustness of both the sound power estimation and the ASAC controller to system uncertainties is investigated, and it has been shown that the proposed ASAC strategy is able to achieve effective control of the radiated sound power.</p
Recent advances in micro-vibration isolation
No full textMicro-vibration caused by disturbance sources on-board spacecraft can severely degrade the working environment of sensitive payloads. Some notable vibration control methods have been developed particularly for the suppression or isolation of micro-vibration over recent decades. Usually, passive isolation techniques are deployed in aerospace engineering. Active isolators, however, are often proposed to deal with the low frequency vibration that is common in spacecraft. Active/passive hybrid isolation has also been effectively used in some spacecraft structures for a number of years. In semi-active isolation systems, the inherent structural performance can be adjusted to deal with variation in the aerospace environment. This latter approach is potentially one of the most practical isolation techniques for micro-vibration isolation tasks. Some emerging advanced vibration isolation methods that exploit the benefits of nonlinearity have also been reported in the literature. This represents an interesting and highly promising approach for solving some challenging problems in the area. This paper serves as a state-of-the-art review of the vibration isolation theory and/or methods which were developed, mainly over the last decade, specifically for or potentially could be used for, micro-vibration control
Fault Diagnosis of a Simulated Model of an Industrial Gas Turbine Prototype Using Identification Techniques
No full textIn this paper a model-based procedure exploiting analytical
redundancy for the detection and isolation of faults of a gas
turbine system is presented. The diagnosis scheme is based on the
generation of so--called ``residuals'' that are errors between
estimated and measured variables of the process. The work is
completed under both noise-free (deterministic) and noisy
(stochastic) conditions. Residual analysis and statistical tests
are used for fault detection and isolation, respectively. The final
section shows how the actual size of each fault can be estimated
using a multi-layer perceptron neural network used as a non-linear
function approximator. The proposed fault detection and isolation
tool has been tested on a single-shaft industrial gas turbine model
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