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A vibration isolator is designed to reduce the vibration and structure borne noise transmitted from a vibratory source, such as machinery and equipment, to the supporting structure. The vibration and structure borne noise transmitted depends upon the dynamic properties of the foundation, the source mounting point and the vibration isolator. Therefore knowledge of the frequency dependent dynamic properties of vibration isolators is a necessary part of the acoustic prediction and control/reduction process. Vibration isolators may be characterised by measuring their four-pole parameters. A measurement procedure is proposed that employs the floating mass method, measures the direct forces and corrects for the errors introduced by the direct force measurement. Compared to the basic method, it extends the frequency limits of measurement in both directions. The development of a novel vibration isolator test facility that implements the proposed measurement procedure is described, and its satisfactory operation is experimentally demonstrated. The vibration isolator test facility is capable of characterizing vibration isolators commonly used in industrial and maritime applications, under service conditions. A method is proposed for measuring the four-pole parameters of a uni-directional asymmetrical vibration isolator under static load. The method is called the two masses method, and is suitable for determining the four???pole parameters of active vibration isolators with feedback control. The method is also applicable to uni-directional symmetrical and bi-directional symmetrical and bi-directional asymmetrical vibration isolators. It may be regarded as a universal method for characterising vibration isolators. Experimental data is presented and the method is validated. Modelling of vibration isolators is complicated by the highly non-linear nature of their rubber elements. The notion of an effective rubber cylinder is proposed to account for the barrelling of rubber elements under static load. Consequently, a general static compression model is proposed that applies to vibration isolators having unfilled and filled rubber elements of regular prismatic shapes. The model predicts the dependence of the four-pole parameters on the compression ratio of the rubber element. The predictions derived from the effective rubber cylinder and general static compression model agree excellently with experimental work of this study and other researchers.

Thesis (M.A.)--University of South Florida, 2007. / Title from PDF of title page. Document formatted into pages; contains 55 pages. Includes bibliographical references.

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Digitized by Kansas Correctional Industries

L'industrie du vélo utilise à profusion le terme confort sans savoir parfaitement ce que cela représente. Aucun outil scientifique n'existe afin d'identifier le confort et ainsi la conception d'un simulateur de vibration de la route est envisagée. Le principal objectif de ce projet de maîtrise est de concevoir un simulateur permettant de reproduire le profil de la route afin de retrouver les mêmes niveaux de vibration que lorsque le vélo roule sur la route. Ainsi, la conception du simulateur se divise en deux parties : la conception mécanique du banc de test qui sert de pièce maîtresse du simulateur ainsi que le calcul des profils numériques des routes. Le premier volet présente la conception mécanique du banc de test. Le banc de test est la pièce maîtresse qui supporte le vélo et qui transmet le mouvement provenant des actionneurs à l'aide d'un bras d'amplification mécanique des mouvements. Le mouvement est créé par des actionneurs de la compagnie D-Box qui présentent plusieurs limitations et contraintes influençant directement la conception du banc de test et le calcul des profils de route. La démarche afin de calculer des profils numériques des routes est présentée dans le deuxième volet. Les profils de route sont la représentation numérique de la route réelle. Ces derniers servent de signal alimentant les actionneurs du banc de test. Afin de calculer les profils, il est nécessaire de faire des mesures d'accélération sur la route et, à l'aide de la technique du problème inverse, les profils de route sont calculés. La démarche de conception se termine avec une validation du simulateur. Ce chapitre dédié à la validation démontre que l'utilisation d'une amplification mécanique à l'aide d'un bras de levier n'influence pas les mesures. La précision de la reproduction de la route est également étudiée alors qu'un écart de 6% à 9% est remarqué entre les mesures d'accélération sur la route et celles sur le banc de test. Le dernier volet du mémoire présente un exemple d'utilisation possible du banc de test. Une étude comparative identifie qu'il n'est pas suggéré d'utiliser des masses inertes afin de remplacer un cycliste. Ces résultats sont basés sur des études dynamiques d'un cadre de vélo.

Poro-viscoelastic materials are well modelled with Biot-Allard equations. This model needs a number of geometrical parameters in order to describe the macroscopic geometry of the material and elastic parameters in order to describe the elastic properties of the material skeleton. Several characterisation methods of viscoelastic parameters of porous materials are studied in this thesis. Firstly, quasistatic and resonant characterization methods are described and analyzed. Secondly, a new inverse dynamic characterization of the same modulus is developed. The latter involves a two layers metal-porous beam, which is excited at the center. The input mobility is measured. The set-up is simplified compared to previous methods. The parameters are obtained via an inversion procedure based on the minimisation of the cost function comparing the measured and calculated frequency response functions (FRF). The calculation is done with a general laminate model. A parametric study identifies the optimal beam dimensions for maximum sensitivity of the inversion model. The advantage of using a code which is not taking into account fluid-structure interactions is the low computation time. For most materials, the effect of this interaction on the elastic properties is negligible. Several materials are tested to demonstrate the performance of the method compared to the classical quasi-static approaches, and set its limitations and range of validity. Finally, conclusions about their utilisation are given.

International Telemetering Conference Proceedings / October 26-29, 1998 / Town & Country Resort Hotel and Convention Center, San Diego, California / Acquiring shock and vibration data from flight vehicles through rf telemetry links has numerous associated challenges. Yet, these measurements are important to establish environmental specifications to provide a basis for system or component design and testing. The principal limitation in acquiring these measurements is the frequency bandwidth available for data transmission. This limited bandwidth is often responsible for invalid data being accepted as valid. This work provides a brief review of time and frequency division multiplexing to identify the potential error contributors to shock and vibration measurements. Its focus is on the design of acceleration measurement systems to eliminate these errors and optimize individual measurement channel performance.

This work is centered on low-frequency and high-frequency multiphysics problems of piezoelectric structures submerged in a quiescent fluid domain for the applications of vibration energy harvesting, biomimetic actuation, and contactless acoustic energy transfer. In the first part of this research, Macro-Fiber Composite (MFC)-based piezoelectric structures are employed for underwater mechanical base excitation and electrical biomimetic actuation in bending mode at low frequencies (the fundamental underwater bending resonance being in the infrasonic frequency range). The MFC technology (fiber-based piezoelectric composites with interdigitated electrodes) exploits the effective 33-mode of piezoelectricity, and strikes a balance between structural deformation and force levels for actuation to use in underwater locomotion, in addition to offering high power density for energy harvesting to enable battery-less aquatic sensors. Following in-air electroelastic composite model development, the fundamental research problem is to establish semi-analytical models that can predict the underwater dynamics of thin MFC cantilevers for different length-to-width aspect ratios. In-air analytical electroelastic dynamics of MFCs is therefore coupled with added mass and nonlinear hydrodynamic damping effects of fluid to describe the underwater electrohydroelastic dynamics in harvesting and actuation. To this end, passive plates of different aspect ratios are tested to extract and explore the repeatability of the inertia and drag coefficients in Morison’s equation. The focus is placed on the first two bending modes in this semi-empirical approach. In particular, electrode segmentation is studied for performance enhancement in the second bending mode. Additionally, nonlinear dependence of the output power density to aspect ratio is characterized theoretically and experimentally in the underwater base excitation problem. In the second part of this work, Ultrasonic Acoustic Energy Transfer via piezoelectric transduction is investigated theoretically and experimentally. Contactless energy transfer using acoustic excitation offers larger distances of power transmission as compared to well-studied inductive method. Various transmitter configurations (e.g. spherical, cylindrical, and focused) are explored for energy transfer to a piezoelectric receiver bar (operating in the longitudinal/thickness mode) that is shunted to a generalized resistive-reactive circuit. Fixed-free and free-free mechanical boundary conditions of the receiver are explored in detail. The resulting multiphysics analytical model framework is compared with finite-element simulations and experiments conducted in fluid (water and oil). Optimal piezoelectric receiver material and electrical loading conditions are sought for performance and bandwidth enhancement.