Showing papers in "The Shock and Vibration Digest in 2004"

A Review of Power Harvesting from Vibration using Piezoelectric Materials

Abstract: The process of acquiring the energy surrounding a system and converting it into usable electrical energy is termed power harvesting. In the last few years, there has been a surge of research in the area of power harvesting. This increase in research has been brought on by the modern advances in wireless technology and low-power electronics such as microelectromechanical systems. The advances have allowed numerous doors to open for power harvesting systems in practical real-world applications. The use of piezoelectric materials to capitalize on the ambient vibrations surrounding a system is one method that has seen a dramatic rise in use for power harvesting. Piezoelectric materials have a crystalline structure that provides them with the ability to transform mechanical strain energy into electrical charge and, vice versa, to convert an applied electrical potential into mechanical strain. This property provides these materials with the ability to absorb mechanical energy from their surroundings, usually ambient vibration, and transform it into electrical energy that can be used to power other devices. While piezoelectric materials are the major method of harvesting energy, other methods do exist; for example, one of the conventional methods is the use of electromagnetic devices. In this paper we discuss the research that has been performed in the area of power harvesting, and the future goals that must be achieved for power harvesting systems to find their way into everyday use.

Cracked shaft detection and diagnostics: A literature review

Abstract: Cracks in shafts have long been identified as factors limiting the safe and reliable operation of turbomachines. They can sometimes result in catastrophic failure of equipment (rotor bursts) and, more often, in costly process upsets, repairs and premature scrapping and replacement of equipment. Cracked shafts still pose a significant and real threat to equipment in spite of the great advances made in the areas of metallurgy, manufacturing and design. In the past two decades, much research and many resources have gone into developing various on-line and off-line diagnostic techniques to effectively detect cracks before they cause serious damage. Because of the enormous amount of ongoing research in this area (more than 500 technical papers have been published in English alone in the past 30 years), there is a real need to periodically condense and summarize the information. This paper reviews literature on cracked shaft detection and diagnostics published after 1990.

Identification of Dynamic Bearing Parameters: A Review

Abstract: In this paper, we present a review of the experimental identification of dynamic parameters of bearings in a rotating machine. Major emphasis is given to vibration-based identification methods and the review encompasses descriptions of experimental measurement techniques, mathematical modeling, parameter extraction algorithms and uncertainty in the estimates applied to a variety of bearings. The parameter extraction algorithms include the descriptions of governing equations of the rotor-bearing system and identification methods in both time and frequency domains. The identification techniques have been classified based on methods used to excite the system. The review includes a variety of bearings and similar components, which play an active link between the rotating and stationary parts of a machine. Based on the state of the art in bearing identification, conclusions are made and future directions are suggested.

Eddy Current Damping in Structures

Abstract: When a conductive material is subjected to a time-varying magnetic flux, eddy currents are generated in the conductor. These eddy currents circulate inside the con- ductor generating a magnetic field of opposite polarity as the applied magnetic field. The interaction of the two magnetic fields causes a force that resists the change in magnetic flux. However, due to the internal resistance of the conductive material, the eddy currents will be dissipated into heat and the force will die out. As the eddy currents are dissipated, energy is removed from the system, thus producing a damp- ing effect. There are several different methods of inducing a time-varying magnetic field, and from each method arises the potential for a different type of damping system. There- fore, the research into eddy current and magnetic damping mechanisms has led to a diverse range of dampers, many of which are detailed in this paper. The majority of the research in eddy current damping has taken place in the area of mag- netic braking. A second topic that has received significant interest is the use of eddy current dampers for the suppres- sion of structural vibrations. However, much of this research is not concentrated in one area, but has been applied to a variety of different structural systems in a number of distinct ways. In this paper, we review the research into various types of eddy current damping mechanisms and we discuss the future of eddy currents with some potential uses that have not yet been studied.

Analysis of the viscoelastic rod dynamics via models involving fractional derivatives or operators of two different orders

Abstract: We present an overview of articles devoted to the analysis of dynamic behavior of viscoelastic rods, whose features are described by rheological models involving fractional derivatives or operators of two different orders. We investigate ten rheological models: the generalized viscoelastic Kelvin-Voigt, Maxwell, Zener models and other models containing fractional derivatives or fractional operators of two different fractional orders. For each of the above-mentioned rheological models, we carry out a comparative analysis between the behavior of its rheological and dynamic characteristics. Vector diagrams are used as the rheological characteristics, but the roots of the characteristic equations in the problems of longitudinal vibrations of rods, the velocities and coefficients of attenuation in the problems of propagation of harmonic waves, and the stress function in the problems of transient wave propagation are considered as the dynamic characteristics. The analysis of the rheological and dynamic characteristics shows that, depending on the relative magnitudes of the orders of the fractional derivatives and fractional operators entering into the rheological model, some of the models considered may describe both the wave and diffusion processes occurring in mechanical systems, but others describe only wave or only diffusion phenomena. The parallels between the behavior of the vector diagrams, the roots of the characteristic equations, the velocities and coefficients of attenuation, and the stress functions are revealed. We also show the analogy in the behavior of viscoelastic rods, whose rheological features are described by the models with fractional time derivatives and ordinary time derivatives.

A Review of the Vibrations of Plates and Shells

Abstract: In this paper, we present an updated review of papers, conference papers, dissertations, and books dealing with the vibrations of plates and shells. The paper includes 236 citations, and it also includes a section on reduced-order models in cables, beams, plates, and shells. The references are categorized by shell type and assumptions. This review will provide a very useful list of references for research.

A review of recent ship vibration papers

Abstract: The vibration analysis of large and complex structures such as ships is difficult, because a vibrating ship hull (or its components) exhibits quite different vibration characteristics. Technological developments offer new concepts, definitions and comprehensive studies in the ship vibration field. The aim of this paper (bibliography) is to list references to papers, conferences, and proceedings dealing with ship vibrations that were published between January 2000 and April 2003. It contains 64 bibliographic references. The following types of ship vibrations are included: sea conditions, structural analysis, machine components, ship propulsive system, ship machines and special studies. Moreover, basic and brief information (reference, publication type, simulation models, utilizing methods and/or models, examined subject and/or problem about grouped references has been given in the tables. So, this review paper not only lists references to papers at the millennium, but also helps researchers in their studies on ship vibration to find the necessary references quickly and practically.