DSpace Collection:
http://hdl.handle.net/10261/29554
2024-03-29T15:18:04Z
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Generating "idealised" impulse response functions to improve or repair single degree of freedom system measurements
http://hdl.handle.net/10261/351012
Título: Generating "idealised" impulse response functions to improve or repair single degree of freedom system measurements
Autor: Anthony, David K.; Simón, Francisco
Resumen: A single degree of freedom (SDOF) system can be characterised using transient or continuous time signals and both should lead to the same frequency response function. As commonly defined, the equation of the displacement response of a SDOF system to impulse excitation alone is ambiguous leading to two possible interpretations: the impulse response (IR) and one corresponding to solely the free oscillation of the system (FR). These are analysed in detail for idealised and practical cases and it is found that the IR and FR yield two distinct acceleration spectra, and that only the phase distinguishes the normalised FR between displacement, velocity and acceleration alleviating the need to perform differentiation and integration to generate the response in other parameters. An unambiguous mathematical definition of the IR is suggested for the velocity response. Finally, it is shown that an idealised version of the IR can be artificially generated from the FR. This can be used to repair acceleration signals that have a truncated or distorted impulsive part, alleviate spectral windowing effects and generally allow cleaner response spectra. This is demonstrated experimentally. © 2008 Elsevier Ltd. All rights reserved.
Descripción: 9 páginas, 9 figuras
2024-03-19T13:20:14Z
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Determining material damping type by comparing modal frequency estimators
http://hdl.handle.net/10261/351004
Título: Determining material damping type by comparing modal frequency estimators
Autor: Anthony, David K.; Simón, Francisco; Juan, Jesús
Resumen: The accuracy of modal frequency and damping estimators for non-lightly damped single degree of freedom systems depend on the response parameter used as well as the damping mechanism. Therefore, in order to make accurate modal parameter measurements, the damping mechanism at play must be known to be either viscous or hysteretic a priori. Here, comparisons between the evaluated frequency values are used to glean this information. The damping mechanism of an experimental system (consisting of resilient layer and mass plate) is then determined using two simple modal parameter estimators and applying statistical methods. © 2009 Acoustical Society of America.
Descripción: 8 páginas, 4 figuras, 1 tabla
2024-03-19T13:00:38Z
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Accuracy and robustness of four basic single degree of freedom methods for determining the modal parameters of non-lightly damped systems
http://hdl.handle.net/10261/348989
Título: Accuracy and robustness of four basic single degree of freedom methods for determining the modal parameters of non-lightly damped systems
Autor: Anthony, David K.; Simón, Francisco
Resumen: An adequate measurement strategy (the combination of measurement method, response parameter, and where applicable, damping estimator) should be used for accurate determination of the natural frequency and damping of non-lightly damped single degree of freedom (SDOF) systems, otherwise, significant measurement bias errors can exist. The accuracy of four commonly used methods is studied and the measurement strategies that are exact are identified. This can depend on the damping mechanism, which if not known can be gleaned from patterns of bias errors between frequency estimations from different strategies. Since in practice a SDOF system rarely exists, or as SDOF techniques are knowingly applied to multiple degree of freedom (MDOF) systems, the robustness of the strategies in the presence of a secondary mode is studied, and the more robust (and therefore preferable) strategies are identified. The measurement method based on the real spectral part is advantageous as it evaluates the damping exactly and is independent of the damping mechanism, in addition the natural frequency obtained is independent of the response parameter. However, this method is not a relatively robust one, and is also sensitive to phase changes accrued during measurements. © 2012 Elsevier Ltd. All rights reserved.
Descripción: 18 páginas, 10 figuras, 4 tablas
2024-03-01T13:00:21Z
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Monochromatic Transfer Matrix method for acoustic field simulation through media boundaries
http://hdl.handle.net/10261/72406
Título: Monochromatic Transfer Matrix method for acoustic field simulation through media boundaries
Autor: Ibáñez Rodríguez, Alberto; Fritsch Yusta, Carlos; Parrilla Romero, Montserrat; Villazón, J.
Resumen: In ultrasonic NDE applications, situations involving propagation of acoustic waves through interfaces are usual. Effects of reflection, refraction, diffraction, and mode changes at interfaces must be considered both to plan and to explain inspections. Ray-tracing based simulation methods, commonly used, have a limited or null consideration of much of involved physic phenomena. In the other hand, numeric methods for acoustic field simulation are usually computationally expensive and non suitable for interactive applications. In this work we present a full matrix formulated method for continuous wave field simulation in which each process: propagation in homogeneous media, refraction at interfaces, etc., are described by matrices that can be composed to model a complex problem with a single Monochromatic Transfer Matrix that can be used to interactively compute fields produced by different excitation patterns of the used transducers. Keywords: Acoustic field simulation; Interfaces; Monochromatic transfer matrix
2013-03-19T14:57:57Z