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Binu K. Mukherjee, Royal Military College of Canada (Canada)
S. Sherrit, Royal Military College of Canada (Canada)
Piezoelectric transducers are frequently used as acoustic sensors and projectors as well as in active methods of vibration control. Their proper utilisation requires a good understanding of their non- linear properties and of the dielectric, mechanical and piezoelectric losses in the material. Besides, new computer codes are being developed for the modelling of piezoelectric materials and transducers and these are precise enough to require accurate material constants. The complex impedance of piezoelectric resonators of different geometries can be analysed around their resonances to determine the dielectric, elastic and piezoelectric coefficients as complex constants to take account of all the losses in these materials. The impedance curves may be measured as a function of applied dc voltage in order to determine the field dependence of the material constants. By analysing the fundamental and higher resonances, the dispersion in the material constants can be studied and the real and imaginary parts of the constants may be described by frequency dependent polynomials. A new equivalent circuit for the material takes account of all the losses. We gratefully acknowledge funding support from the Defence Research Establishment Atlantic, Canada, and the Office of Naval Research, USA through the Naval Undersea Warfare Centre, Newport, USA.
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Binu K. Mukherjee, Royal Military College of Canada (Canada)
S. Sherrit, Royal Military College of Canada (Canada)
Piezoelectric transducers are frequently used as acoustic sensors and projectors as well as in active methods of vibration control. Their proper utilisation requires a good understanding of the non- linear properties of the material. Quasistatic experiments have been developed to determine the dependence of the more important material constants on the temperature and on the levels of voltage and stress applied singly or simultaneously to the material. The response time of the piezoelectric effect has been studied and it has been found that the observations can be understood by assuming that the domain wall movements in the material are governed by a distribution of activation energies. More recently, high strain electrostrictive materials have been developed and these are inherently non-linear. Many of the above experiments can be used to characterise these materials as well. We gratefully acknowledge funding support from the Defence Research Establishment Atlantic, Canada, and the Office of Naval Research, USA through the Naval Undersea Warfare Centre, Newport, USA.
sv970518.pdf (Scanned) TOPYitshak M. Ram, University of Adelaide (Australia)
Recent results associated with simultaneous assignment of poles and zeros by state feedback control will be presented. It will be shown that the poles and some zeros of a vibratory system maybe assigned by choosing the position vector and the control force. This objective can be achieved with partial knowledge of the system, where the high frequency modal date and the damping matrix may be considered unknown. An example demonstrating the results will be given.
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Nobuo Tanaka, Mechanical Engineering Laboratory (Japan)
Yoshihiro Kikushima, Mechanical Engineering Laboratory (Japan)
This paper deals with distributed parameter sensors designed with a view to extracting a vibration mode. Compared to conventional point-type sensors such as acceleration pickups, displacement sensors etc., the distributed parameter sensors have many benefits provided that they are properly designed. First, this paper overviews a conventional modal filter designed by use of point sensors, and enumerates the problems it involves. To overcome the drawbacks of the point sensor based modal filtering, a novel modal filtering technique based upon a PVDF film sensor, a distributed parameter sensor, is proposed. Two-dimensional modal filters are discussed, and then, by taking into consideration a practicability of the sensors, a design procedure of one-dimensional modal filters is presented; the number, location and shaping of the one dimensional sensors are clarified. Finally, an experiment is conducted, showing the capability of the distributed parameter modal filtering.
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Carl Q. Howard, University of Adelaide (Australia)
Colin H. Hansen, The University of Adelaide (Australia)
Finite element analysis was used to predict the power transmission from an actively isolated vibrating rigid mass to a simply supported beam. Vibrational power transmission was used as the cost function to be minimised. The work demonstrated that neglect of power transmission due to moments in experimental work is the reason why negative power transmission in the vertical direction at some frequencies has been reported in the literature. Simulations show that under active control when power transmission in the vertical direction is used as a cost function to be minimised, the overall vibration isolation performance of the active isolator can be worse than without control.
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Thanh Lan Vu, University of Western Australia (Australia)
Jie Pan, The University of Western Australia (Australia)
The aim of this paper is firstly to address the consequences of the nonlinear interactions between higher order modes and the first order mode of a flexible cantilever beam. The tested cantilever beam exhibited numerous nonlinear phenomena that are commonly observed in many flexible structures. The experimental results have shown that active control of the nonlinear vibration in a flexible structure is effective. Secondly, the paper describes how the nonlinear vibration in the cantilever beam was cancelled using a digital feedback controller implemented in a dSpace TM Digital Signal Processing board. It has been demonstrated experimentally that the on-line feedback controller was capable of cancelling the low frequency vibration generated in the flexible cantilever beam due to nonlinear interaction between the modes of the beam. This control scheme has considerable potential for cancelling of nonlinear vibration in large structures such as aircraft, ships, etc. in order to reduce stress and fatigue of these structures.
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C. Mei, The University of Auckland (New Zealand)
Brian R. Mace, The University of Auckland (New Zealand)
R.W. Jones, The University of Auckland (New Zealand)
Modal approaches to active vibration control, such as independent modal state control (lMSC), suffer difficulties especially at higher frequencies. These arise due to robustness considerations in the presence of unmodelled and uncontrolled (since the modal properties a structure at higher frequencies are normally not known accurately) and from increasing controller complexity (due to the large number of of modes which need to be controlled at higher frequencies). Wave-based methods offer advantages at these higher frequencies. This paper describes a hybrid approach with specific application to the control of flexural vibrations of a beam. Velocity feedback control is applied to the system to add damping. This is designed using a wave-based approach to optimise energy absorption at a particular frequency. The modes of the controlled structure are now different to those of the uncontrolled structure and from these IMSC is designed to provide low frequency modal control. Numerical results are presented. The effects of controller location and digital implementation issues are discussed.
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N.R. Harland, The University of Auckland (New Zealand)
Brian R. Mace, The University of Auckland (New Zealand)
R.W. Jones, The University of Auckland (New Zealand)
The shear modulus and damping loss factor of electro-rheological (ER) fluids vary when the fluid is exposed to an electric field. This behaviour can be exploited to engineer smart structures with controllable dynamic properties. This paper describes one example of such a system. The intention is to control the transmission of structure-borne sound through a structural member such as a beam. This is achieved by inserting a length of a composite ER beam, comprising two elastic outer Iayers between which is sandwiched a layer of ER fluid, into the otherwise uniform beam. A voltage is applied across the outer layers of the ER beam, hence enabling the stiffness and loss factor of the composite beam to be altered. This in turn alters the wavenumbers and wave transmission characteristics of the structure. In broad terms, waves propagate along the waveguide and suffer reflections at the junctions between the beam and the ER fluid beam. Expressions for the power transmitted through the beam/ER beam/beam combination are given and numerical results are presented. In general the power is minimum at certain frequencies which depend primarily on the wavenumbers of the ER beam. In the presence of narrow-band structure-borne noise therefore the structure can be tuned by controlling the applied voltage in such a way as to minimise the transmitted power.
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M.A. Hossain, University of Dhaka
Osman Tokhi, The University of Sheffield
This paper presents an investigation into practical real-time realisation issues of active vibration control (AVC) systems. An adaptive active control system is considered. The control strategy is realised for a cantilever beam system in transverse vibration. The unwanted vibrations in the structure are assumed to be due to a single point disturbance of broadband nature. An AVC system is designed on the basis of optimum cancellation of broadband vibration at an observation point along the beam. Practical issues related to the design and implementation of the system are high-lighted and discussed. An adaptive algorithm consisting of a simulation, control and identification processes is developed. This is implemented on a number of computing domains involving high-performance reduced instruction set computer (RISC) processors and digital signal processing (DSP) devices. A comparison of the results of the implementations, on the basis of real-time computation performance, is made to establish merits of development of fast processing methods in real-time active control applications.
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M.A. Hossain, University of Dhaka
Osman Tokhi, The University of Sheffield
This paper presents an investigation into the development of an active vibration control (AVC) system using genetic algorithms (GAs). During the last two decades, a substantial amount of research work has been carried out using GAs in various disciplines. Although GAs have gained popularity as parallel, global search techniques, their use in the area of active control is limited. This investigation attempts to develop evolutionary techniques utilising GAs for AVC applications. A flexible beam system in transverse vibration is considered in this investigation. The unwanted vibrations in the structure are assumed to be due to a single point disturbance of broadband nature. A multi-source adaptive AVC strategy is adopted for optimum cancellation of broadband vibration along the beam. This incorporates an on-line controller design and implementation strategy. Genetic algorithms are used for estimation of the adaptive controller characteristics. The AVC algorithm thus developed is implemented and simulation results verifying its performance in the suppression of broadband vibration along the beam presented and discussed.
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Koichi Matsuda, Kyushu University (Japan)
Yoichi Kanemitsu, Kyushu University (Japan)
Shinya Kijimoto, Kyushu University (Japan)
Owing to the nonholonomic structure, a free-flying space robot can reorient its attitude only by actuating the manipulators. We formulate the approach to plan the optimal path of the manipulator movement to achieve such reorientation. This formulation has been done as an optimal control problem in a more general way than that of the problem to have been solved so far. That is, the approach can afford to solve the case where the initial and final posture of the manipulators are different and where the optimal solution is not a smooth and continuous function of time. The optimal control problem is converted via discretization with high-order integration methods into a finite dimensional problem and solved by the periodically preconditioned conjugate gradient-restoration algorithm.
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Thomas Lago, University of Karlskrona/Ronneby (Sweden)
Mathias Winberg, University of Karlskrona/Ronneby (Sweden)
Sven Johansson, University of Karlskrona/Ronneby (Sweden)
Engine induced sound and vibration levels in boats for professional and leisure use is in many cases unacceptably high in term of comfort and the environment. Classical methods for passive treatment are normally less effective due to the low frequency content and often leads to an increase in weight. This contradicts the requirements for lower weight for increased speed. More efficient vibration damping methods must therefore be found. With active engine mounts, it is possible to achieve a decrease in the vibrations even when the hull is not very stiff. This is especially important in marine applications since the engines are mounted on weak and light structures. The AVIIS project aims at investigating the effects of a combined passive/active engine mount for use in boats. A Storebro 36 Royal Cruiser with two Volvo Penta engines has been used in the project. Four different approaches have been appraised, the results of which are presented here: 1. passive engine mounts, with and without thrust bearings, 2. optimized passive engine mounts, 3. passive engine mounts, rigidly mounted, 4. A combined active/passive engine mount. This paper reports the key data from the measurements and how the different primary sources have been estimated from the analysis. This analysis has then been used to select the ANVC approach.
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P.K. Boominathan, Indian Institute of Technology (India)
Y.G. Srinivasa, Indian Institute of Technology (India)
M. Singaperumal, Indian Institute of Technology (India)
Active vibration control using shape memory actuator is utilised to make a two degree of freedom dynamic absorber and demonstrate its effectiveness in vibration suppression. A two degree of freedom spring-mass system interconnected by shape memory wires
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Osman Tokhi, The University of Sheffield
R. Wood, The University of Sheffield
This paper presents an investigation into the development of an intelligent neuro-active noise control strategy which accounts for both linear and nonlinear dynamics of the system. Multi-layered perceptron neural networks with a backpropagation learning algorithm and radial basis function neural networks with an orthogonal forward regression algorithm are considered in both the modelling and control contexts. A feedforward active noise control (ANC) structure is considered for optimum cancellation of broadband noise in a three-dimensional propagation medium. An on-line adaptation and training mechanism allowing a neural network architecture to characterise the optimal linear controller and nonlinear system dynamics within the ANC system is developed. The neuro-adaptive ANC algorithm thus developed is implemented within a free-field environment and simulation results verifying its performance in the cancellation of broadband noise are presented and discussed.
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Ingvar Claesson, University of Karlskrona/Ronneby (Sweden)
L. Hakansson, Lund University (Sweden)
In the turning operation the relative dynamic motion between cutting tool and workpiece, or vibration is a frequent problem, which affects the result of the machining, in particular the surface finish. The tool life is also influenced by the vibrations. When the working environment is considered, noise is frequently introduced by dynamic motion between the cutting tool and the workpiece. By proper machine design, e.g. improved stiffness of the machine structure, the problem of relative dynamic motion between cutting tool and workpiece may be partially solved. However, by active control of machine-tool vibration, a further reduction of the dynamic motion between cutting tool and workpiece can be achieved. It was found that adaptive feedback control based on the filtered-x LMS-algorithm enables a reduction of the vibration with up to 40 dB at 1.5 kHz and simultaneously with approximately 40 dB at 3 kHz. A significant improvement of the workpiece surface was observed and a substantial improvement of the acoustic noise level was obtained with adaptive control.
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