1,720,964 research outputs found
Feedforward adaptive control of flexural vibration using wave amplitudes
No full textThis paper concerns the real-time estimation of wave amplitudes and their subsequent use as a cost function in adaptive active control of bending vibrations in a beam. The amplitude of the wave propagating downstream from the control location is estimated by filtering the outputs of an array of sensors. Minimizing this wave amplitude has significant advantages over the more conventional approach in which velocity at some point is minimized. Expressions for the ideal frequency responses of the wave filters are found for the case of an array comprising two sensors in the far field. These filters are non-causal. FIR implementations designed using direct and time-delay methods are described, the latter offering some substantial advantages. Practical performance considerations are discussed, including filter length, frequency range, effects of near fields, group delays, accuracy and cross-sensitivity. Simulations and experimental measurements are performed and compared
Real-time estimation of flexural wave amplitude in a beam in the presence of a nearfield
No full text
Time domain estimation of response and intensity in beams using wave decomposition and reconstruction
No full textA method is described by which instantaneous values of the response, the internal forces and the intensity in beams can be estimated as functions of time. The individual components of intensity which propagate in each direction and the components due to shear and moment can also be estimated. The estimates are provided in real time by digitally filtering the outputs of an array of sensors. The digital filters are designed in the frequency domain using a wave decomposition approach and reconstructed in the time domain as FIR filters in this paper. The design and implementation process is described, numerical simulations of measurements in the farfield performed and an experimental implementation presented. The method is relatively insensitive to sensor miscalibration and measurement noise compared to other approaches, and yields instantaneous estimates as well as time averages
Adaptive active control of flexural waves in a beam in the presence of a nearfield
No full textThis paper describes a wave-based, adaptive, feedforward system for the control of flexural waves in a beam when a significant nearfield wave is present. Many potential applications for active vibration control require a physically compact control system, in which the error sensors are located close to the control actuator. Because of the small physical size of the control system, there can be a significant nearfield wave as well as propagating waves in the vicinity of the error sensors, and the presence of this nearfield must be taken into account. An estimate of the downstream propagating wave amplitude is obtained by digitally filtering and combining the outputs of an array of three sensors, and is used as a cost function in a conventional filtered X-LMS adaptive algorithm. This has significant advantages over the more conventional approach in which the response at a single point is used as a cost function. Numerical simulations and experimental implementation of the control achieved with the wave-based and conventional systems are presented. It is seen that the wave-based system can offer significantly better broadband attenuation than the conventional approach in which response at a point is minimised
Real-time measurement of wave components and intensity in a beam in the presence of a near field
No full textA method is described by which the individual flexural wave components in a beam can be measured in real time. Attention is focussed on the case in which two propagating waves and a single near-field wave exist, although the case of two near fields is also considered. Because the presence of the near field is included, the measurements can be taken close to the force, boundary or discontinuity from which the near field arises. Potential applications include intensity measurement, active control and adaptive-passive vibration control.The wave components are measured by digitally filtering and combining the outputs of an array of sensors, with an array of three, equally spaced sensors being considered in detail. The filters are designed in the frequency domain using a wave decomposition approach, and implemented in the time domain as FIR filters. Design, implementation and performance issues are discussed and an experimental implementation described. It is seen that accurate estimates of the amplitudes of the wave components can be obtained using FIR filters of moderate order, and that the method is relatively insensitive to sensor miscalibration and measurement noise
Low-frequency measurements and predictions of the structural-acoustic properties of the INCE standard T-beam structure
No full textSound transmission through concrete floors and suspended ceiling system : a vibroacoustic analysis : a Thesis submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy of Mechanical Engineering
No full textFull text is available to authenticated members of The University of Auckland only.The understanding of the sound transmission mechanisms through suspended ceilings beneath concrete floors is today essentially of empirical nature, or originating from prediction models the level of simplificatlon of which is a significant obstacle to their widespread application. The prediction and control of sound transmission through suspended ceilings beneath concrete floors requires the knowledge of the forces, moments and sound pressures present within and acting on the structure. The interactions between the different components of such a floor are yet to be understood, particularly at low frequencies where the modal effects associated with the finite size of the structure need to be considered. By proposing a theoretical model describing these mechanisms, this thesis aims at providing a deeper appreciation of these components' contribution to the sound transmission. The finite dimensions of the structure a.re taken into consideration by adopting a modal approach whereby the displacements and pressure fields are expanded into infinite series of admissible functions. By expressing these quantities as functions of the displacement fields of the concrete floor and ceiling panel, coupling terms describing the interactions between the different components are obtained and from which a substantial amount of information is extracted. The coupled equations governing the motions and sound pressures within the structure are then written as a set of matrix equations, the only unknowns of which are the expansion coefficients for the displacements of the concrete floor and ceiling panel. Finally, the solutions are calculated numerically. It is shown that the solution is applicable to non-periodic geometries and thus opens the door to a new range of investigations on the dynamics of non periodic finite double plate structures. Once the model is experimentally validated, a parametric analysis is conducted on the effects of the material properties, the geometry and the design characteristics of the structure. The parameters that affect the most the sound insulation of the system are identified and their effects are quantified
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