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This paper investigates the rocking behavior of rigid bodies seismically protected by means of lead rubber bearings and high damping rubber bearings, which are the most popular kinds of elastomeric isolators in the market. The complex nonlinear force–displacement relationship displayed by such devices is predicted by a phenomenological model based on a small set of parameters having a clear mechanical meaning. The algebraic nature of the proposed hysteretic model makes it suitable for a design procedure, using an energy‐based approach, that allows one to obtain the hysteretic model parameters on the basis of the mass and the isolation period. Overturning spectra are evaluated and discussed to illustrate the effect of the isolation devices on the rigid bodies' rocking behavior. Furthermore, nonlinear time history analyses associated with six real earthquakes are carried out on six of Michelangelo's sculptures, located in the Galleria dei Prigioni at the Accademia Gallery of Florence, in order to examine their actual behavior under real strong ground motions. [ABSTRACT FROM AUTHOR]

Researchers have been able to develop a computation method for one-dimensional piezoelectric transducers, resonators or interferometers which have a random number of layers and piezoelectric elements electrically in parallel. The resulting one-dimensional model of thickness-vibrating piezoelectric elements can give clear and relatively simple expressions for the acoustic velocities on its faces and for its electric impedance. Linking this model with systematic application of the transmission line analogy gives simple computation of ultrasonic transducers, spectrometers and resonators made up of any number of piezoelectric elements electrically in parallel.

Transmission line theory uses the superposition theorem to develop a new multilayered piezoelectric transducer model of the thickness or the shear vibrating type. Acoustic perturbations are assumed to originate from electrode piezoelectric surfaces since surface stresses are applied on the two ends of an acoustic transmission line. The model derives equations for electrical impedance, acoustic stresses and velocities. Results agree well with results obtained by the classic rigorous method.

In many engineering applications, the vibration analysis of a structure requires the set up of a large number of sensors. These studies are mostly performed in post processing and based on linear modal analysis. However, many studied devices highlight that modal parameters depend on the vibration level non linearities and are performed with sensors as accelerometers that modify the dynamics of the device. This work proposes a significant evolution of modal testing based on the real time identification of non linear parameters (natural frequencies and damping) tracked with a linear modal basis. This method, called Kinematic-SAMI (for multiSensors Assimilation Modal Identification) is assessed firstly on a numerical case with known non linearities and secondly in the framework of a classical cantilever beam with contactless measurement technique (high speed and high resolution cameras). Finally, the efficiency and the limits of the method are discussed. [ABSTRACT FROM AUTHOR]

The prediction of damping remains an important research challenge in structural dynamics. This paper deals with the energy losses caused by friction in assembled structures. From previous analytical works and experimental studies of the bending vibrations of a clamped-clamped beam with original positions of the interfaces, the objective of this work is to compute the damping of the structure taking into account the local properties of the joints. The purpose is to understand and analyze the contribution of the surface defects on the damping due to the joints based on multi-spherical contacts governed by Hertz' and Mindlin's theories. A design of experiments based on the model parameters is proposed and the final results are compared to the experimental's ones. [ABSTRACT FROM AUTHOR]

This paper deals with the use of piezoelectric patches for nonlinear dynamic identification. The patches are glued on the structure to identify amplitude-dependent damping and natural frequency; their positions are defined in order to perform the excitation concentrated on the first bending mode. Their locations on the structure allow to perform “stop sines” tests, as, unlike electrodynamic shakers, piezos are embedded on structures and do not modify the studied structure after the excitation signal is switched off. Although, despite the piezo and the stop-sine , the signal is still modulated by other frequency components or polluted by random signals, a post processing with the extended Kalman Filter allows a very good determination of the modal damping and the natural frequency, especially when they depends on the free vibration amplitude. [ABSTRACT FROM AUTHOR]

Abstract: This work describes an automatic method for removing modulated sinusoidal components in signals. The method consists in using the Optimized Spectral Kurtosis for initializing Series of Extended Kalman Filters. The first section is an introduction to vibration applications with Kalman Filters and modulated sinusoids. The detection process with OSK is described in the second section. The third section concerns the tracking algorithm with SEKF for amplitude and frequency modulated sinusoidal components. The last section deals with the complete process illustrated with an experimental application on a rotating machine. [Copyright &y& Elsevier]

Abstract: This paper deals with the damping caused by friction in joints. A new test bench is presented and justified by comparisons made with devices described in the literature. The purpose of this academic bench is to measure the damping induced by partial slip and friction in a planar joint. Moreover, allows uncoupling normal static and dynamic tangential forces. A new method for so-called stopped-sine excitation was developed. It allows more precise monitoring of the evolution of the vibration frequency and damping of non-linear modes. This method is associated with piezoelectric exciters for greater efficiency when stopping excitation. A large number of experimental results are presented and discussed. They are used to characterize the damping induced by micro-sliding in the bonds. [Copyright &y& Elsevier]

Abstract: This paper focuses on the generalized Maxwell model (GMM) identification. The formulation of the transfer function of the GMM is defined, as well as its asymptotes. To compare identification methods of the parameters of the GMM, a test transfer function and two quality indicators are defined. Then, three graphical methods are described, the enclosing curve method, the CRONE method and an original one. But the results of graphical methods are not good enough. Thus, two optimization recursive processes are described to improve the results of graphical methods. The first one is based on an unconstrained non-linear optimization algorithm and the second one is original and allows constraining identified parameters. This new process uses the asymptotes of the modulus and the phase of the transfer function of the GMM. The result of the graphical method optimized with the new process is very accurate and fast. [Copyright &y& Elsevier]

The behaviour of dynamical systems is modified by the use of viscoelastic materials. In order to lead realistic complex eigenvalues analysis on dynamical systems, one need to model the behaviour of viscoelastic materials. The experiments show that the stiffness and the damping of such materials are frequency dependent. A large number of models often used are not able to describe this dependence; this is why the generalised Maxwell's model has been chosen. This paper describes a method based on modulus and angle curves to identify the parameters of this model. Between all the different formulations of generalized Maxwell, the pole-zero formulation is the most suited to lead the identification. However, some formulas allow to find the parameters of others formulations like the Prony one. The identification method presented here is based on the asymptotic curves of generalised Maxwell's model. This identification is led in two step, first parameters are initialised and second they are optimised. This method is confronted to others ones. If several viscoelastic materials have to be modelled in the same dynamical system, the size of the finite element model grows as quick as the number of poles. A way to reduce this size consists in constraining the poles to be equal for all materials. The method presented in this paper allows to perform the identification by taking this new constraint into account. [ABSTRACT FROM AUTHOR]

Abstract: This paper develops an experimental and numerical study of dynamic phenomena involving gear impacts with one loose gear (non-engaged gear pair) inside an automotive gearbox. A dedicated test bench was designed for this study. Signal processing tools, based on the Order Tracking Method, were specially developed in order to clarify the underlying phenomena. A particular attention was paid to the relationship between the drive shaft excitation and the energy and nature of impacts. A topological model of contact is being proposed, based on a geometric description of solids in contact. The contact between gear meshes is defined using a Single Degree of Freedom, non-linear, elastic and dissipative model. The chosen parameters of the model are not updated from measurements, but from the knowledge of the gear topology and tolerance class. Simulations, compared with experimental results, confirm the accuracy of the model proposed. Both model and experiments show, for particular excitation conditions, the emergence of repeated impacts on one side of the gear mesh. [Copyright &y& Elsevier]

Abstract: A new sonoreactor technology is presented here which should give a decisive impulse to sonochemistry in various areas of chemical processing. These exclusive systems use high power converging acoustic waves in a tube to produce a relatively large volume confined acoustic cavitation zone in flowing liquid reagents under pressure. It is well known that numerous chemical reactions are strongly accelerated when they take place inside such a zone. The new cylindrical sonoreactors do not contaminate the processed liquids with erosion products as most other devices do since the cavitation zone is maintained away from the wall of the tube. The processing conditions can be widely varied with pressure, power, temperature, and flow rate. The processing capacity of the largest models may be up to several tons per hour, depending on the required cavitation energy per unit volume to produce the desired process enhancement, using an electric power input of about 50kW. [Copyright &y& Elsevier]

The article presents questions and answers related to dentistry including issues that dental professional must be concerned with in doping control and prohibited substances, role of the dental team in elite and amateur sports, and recommendation for a kind of mouthguard that young athletes can use comfortably during the game.

Presents a study which examined the configuration of class D amplifiers or inverters with field effect transistors for piezoelectric transducers. Operating principles of the inverters; Results; Conclusion.

Abstract: The operating deflection shape of a pad during squeal noise is measured on a real brake system with three-axis accelerometers. A time-frequency analysis is performed that highlights the dependency of squeal on the hydraulic pressure of the system and shows that squeal occurs simultaneously with harmonic components. The operating deflection shape of this pad before and during squeal is then visualized using interpolation, showing the predominance of bending motion. Finally, the pad motions observed are compared to the real modal basis of a detailed Finite Element model. [Copyright &y& Elsevier]

Herein we develop a creep test method for characterizing nonlinear viscoelastic behaviour of an elastomer through weak deformation. This approach is based on an expanded Schapery model. Short term creep tests at various stress levels were performed upon specimens composed of a synthetic elastomer. A method to predict the long term creep behaviour using short term creep tests is presented. Experimental results and theoretical predictions are compared. [ABSTRACT FROM AUTHOR]

Friction modeling is essential in a vast amount of engineering applications. In this paper Mindlin contact friction model, a Masing rule compliant model, is manipulated in order to find a correlation with Dahl dynamic friction model, a Masing rule not compliant model. The resulting equations are then numerically compared and the correlation demonstrated with several loading functions. The result is a modified Dahl model that captures the partial slip behavior following the contact theory. The Dahl model, classically used in control engineering as an empirical model due to its implementation facility, finds in this new formulation a physical meaning to its parameters and finally identified physical parameters (according from Mindlin model) for the Dahl model. [ABSTRACT FROM AUTHOR]

This paper describes a method for the identification and the tracking of poles of a weakly nonlinear structure from its free responses. This method is based on a model of multichannel damped sines whose parameters evolve over time. Their variations are approximated in discrete time by a nonlinear state space model. States are estimated by an iterative process which couples a two-pass Bayesian smoother with an Expectation-Maximization (EM) algorithm. The method is applied on numerical and experimental cases. As a result, accurate frequency and damping estimates are obtained as a function of amplitude. [ABSTRACT FROM AUTHOR]

In the context of brake system simulation, the highlight of phenomenon like squeal needs specific methods. We will focus on stability analysis by complex modal analysis. The use of damping system called shims for squeal noise reduction implies that simulations take into account the damping of materials. To do this, we use parametric viscoelastic models and particularly the generalised Maxwell model. Work consisted in tools choice and validation (viscoelastic models, finite elements formulations, ...) and in simulation method implementation. It was divided in several steps. In a first step, we have selected, among several mathematical models able to describe viscoelasticity, the best for damping modelisation in brake systems. We studied the complex modulus model, the Kelvin-Voigt model and the generalised Maxwell model. In a second step, we sought a formulation of the finite element problem adapted to the modal analysis. We then used a state space model formulation. A capital hypothesis on the equality of the pole of the generalised Maxwell model permits to reduce the size of the model and in the same time to simplify its formulation. Finally, the developed methods have been applied to simulate a pad and a full brake system. The influence of the number of modes used in model reduction and the order of the Maxwell model has been quantified in parametric studies. In the pad case, we performed a complex modal analysis with friction material considered as viscoelastic. The objective was to update the pad frequencies and damping according to FRF measures. In the brake case, we performed a complex modal analysis with the two friction materials and one shim considered as viscoelastic. This model has also been used to exhibit the link between the strain energy distribution in the brake and the damping level obtained by complex modal analysis. To conclude, we developed a simulation method using Abaqus® and Matlab® for the complex modal analysis with viscoelasticity effects and Python to make data exchange between Abaqus® and Matlab® possible. This method permits to perform stability analysis with several viscoelastic materials, on large models, without degradation of computation time. [ABSTRACT FROM AUTHOR]