Dynamic Modeling and Experimental Validation of Eddy Current Dampers and Couplers

2008 ◽  
Vol 130 (2) ◽  
Author(s):  
Andrea Tonoli ◽  
Nicola Amati
Keyword(s):  
Eddy Current ◽  
Mechanical Impedance ◽  
Experimental Tests ◽  
Analytical Models ◽  
Basic Principles ◽  
Practical Applications ◽  
Eddy Current Damper ◽  
Band Limited ◽  
Definition Of ◽  
Damping Torque

The interest in eddy current dampers is increasing especially in aeronautic and automotive industry. Such devices seem to be a valid alternative to conventional fluid film and viscoelastc dampers. Even if several papers have been published on this topic, an electromechanical model taking into account both the resistance and the inductance of the conductor is still lacking. The aim of the present paper is to model the electromagnetic interaction of an eddy current device operating as a damper or as a coupler and to validate it by means of experimental tests performed at steady state and vibrating about a fixed position. The study is based on the computation of the damping torque starting from the basic principles. The analytical models are developed using the bond graph formalism that allows to obtain purely mechanical analogs of the electromechanical system. The main results are the identification of eddy current damper dynamic model and the definition of a set of “conversion rules” allowing to readily obtain the mechanical impedance from the torque to slip speed characteristic and vice versa. The experimental results confirm the band limited effect of the damping, which cannot be neglected for practical applications. The effect can be exploited in eddy current couplers to filter higher order disturbances.

Analysis and Experimental Evaluation of Inherent Instability in Electromagnetic Eddy-Current Dampers Intended for Reducing Lateral Vibration of Rotating Machinery

1995 ◽  
Author(s):  
Yuri Kligerman ◽  
Asif Grushkevich ◽  
Mark S. Darlow ◽  
Adrian Zuckerberger
Keyword(s):  
Magnetic Field ◽  
Eddy Current ◽  
High Speed ◽  
Experimental Tests ◽  
Rotating Machinery ◽  
Lateral Vibration ◽  
Negative Effect ◽  
Eddy Current Damper ◽  
Analytical Approaches ◽  
The Magnetic Field

Abstract There have been a number of papers published that concern the design and operation of electromagnetic, eddy-current dampers for controlling lateral vibration of rotating machinery. Many of these papers have included analysis approaches and all have been generally effective for low-speed operations. There have been a few reports concerning high-speed (supercritical) operations and many of these have indicated instability problems, but none of these have provided a valid analysis to account for instability. That is, all of the analytical approaches have ignored the disk rotation, relative to the magnetic field, and no obvious sources of instability have been found. In this paper, we will present our work in which we have rederived the analyses of this system in which we have not made the common assumption of no rotation between the disk and the magnetic field. In this case, the potential of instability for supercritical speed operation is clear and, in fact, the equivalent negative damping contribution of the eddy-current damper, under these conditions, has a negative effect on the system even if not fully unstable. We have carefully performed a series of experimental tests which corroborate this analytical approach. Finally, we briefly discuss alternative eddy-current damper design approaches that could be considered to provide effective damping at all speeds and avoid these instability problems.

Analytical and Experimental Evaluation of Instability in Rotordynamic System With Electromagnetic Eddy-Current Damper

1998 ◽  
Vol 120 (1) ◽  
pp. 272-278 ◽  
Author(s):  
Y. Kligerman ◽  
A. Grushkevich ◽  
M. S. Darlow
Keyword(s):  
Magnetic Field ◽  
Eddy Current ◽  
High Speed ◽  
Experimental Tests ◽  
Disk Rotation ◽  
Negative Effect ◽  
Eddy Current Damper ◽  
All Speeds ◽  
Analytical Approaches ◽  
The Magnetic Field

There have been a number of papers published that concern the design and operation of electromagnetic, eddy-current dampers for controlling lateral vibration of rotating machinery. Many of these papers have included analysis approaches and all have been generally effective for low-speed operations. There have been a few reports concerning high-speed (supercritical) operations and many of these have indicated instability problems, but none of these have provided a valid analysis to account for instability. That is, all of the analytical approaches have ignored the disk rotation, relative to the magnetic field, and no obvious sources of instability have been found. In this paper, we will present our work in which we have rederived the analyses of this system in which we have not made the common assumption of no rotation between the disk and the magnetic field. In this case, the potential of instability for supercritical speed operation is clear and, in fact, the equivalent negative damping contribution of the eddy-current damper, under these conditions, has a negative effect on the system even if not fully unstable. We have carefully performed a series of experimental tests which corroborate this analytical approach. Finally, we briefly discuss alternative eddy-current damper design approaches that could be considered to provide effective damping at all speeds and avoid these instability problems.

Theoretical investigations on the linear and nonlinear damping force for an eddy current damper combining with rack and gear

2021 ◽  
pp. 107754632098778
Author(s):  
Shouying Li ◽  
Yafeng Li ◽  
Jianzhong Wang ◽  
Zhengqing Chen
Keyword(s):  
Relative Error ◽  
Eddy Current ◽  
Permanent Magnets ◽  
Air Gap ◽  
Numerical Results ◽  
Comsol Multiphysics ◽  
Theoretical Formula ◽  
Iron Plate ◽  
Eddy Current Damper ◽  
Damping Torque

To study the damping characteristics of a new type of eddy current damper with rack and gear recently proposed by the authors, the damping torque for the eddy current damper with rack and gear was theoretically investigated based on some fundamental assumptions, including evenly distributed magnetic field on a conductor plate and no magnetic leakage. A linear relationship between damping torque and velocity was obtained. Numerical simulations by using COMSOL Multiphysics were conducted to evaluate the accuracy of the linear theoretical formula. When angular velocity is less than 30 rad/s, it seems that the linear theoretical results agree well with the numerical results, and maximum relative error between them is about 6.58%. Then, by using COMSOL Multiphysics, a series of parametric studies on damping torque, including the effects of the air gap, the thickness of a back iron plate, the location and number of permanent magnets, and the thickness of a conductor plate, were carried out to further examine the linear theoretical formula. The results show the effects of the air gap and back iron plate on the relative error between linear theoretical and numerical results can be ignored, whereas the location and number of permanent magnets and the thickness of the conductor plate have significant influences on the relative error. Finally, a nonlinear theoretical formula was obtained by introducing three modified coefficients into the linear theoretical formula, and its accuracy was verified in some typical cases. It is proved that there is sufficient accuracy to adopt the nonlinear theoretical formula in preliminary design of the eddy current damper with rack and gear to determine the main structural parameters.

scholarly journals Experimental analysis and mechanical modeling of T-stubs with four bolts per row

2021 ◽  
Author(s):  
Massimo Latour ◽  
Gianvittorio Rizzano
Keyword(s):  
Steel Structures ◽  
Experimental Tests ◽  
Analytical Models ◽  
Fe Model ◽  
Yield Line ◽  
Collapse Mechanisms ◽  
Steel Members ◽  
Eurocode 3 ◽  
Set Up ◽  
Definition Of

The behavior of steel structures is significantly affected by the connections between the steel members. For this reason, special attention to the prediction of the joint rotational behavior is devoted by Eurocode 3 which provides the well-known component method. In EC3, starting from the results of several researches, the formulations for the characterization of the behavior of T-stubs with two bolts per row are given, but with reference to T-stubs with four bolts per row, even though they are present in many actual structural situations, the limited number of experimental tests and analytical models has not led yet to the codification of this component in the code. In this work, starting from the results of three experimental tests on T-stub with four bolts per row, carried out at the laboratory on materials and structures of the University of Coimbra, a FE model in ABAQUS has been set up in order to analyze the yield line patterns corresponding to the different collapse mechanisms. Subsequently, with reference to the yield line shape different from that of T-stub with two bolts per row, the effective lengths have been revaluated applying an energy approach. The definition of the effective width for all the possible collapse mechanisms allowed to set up a proposal for determining the resistance of T-stubs with 4 bolts per row consistent with the approach provided by Eurocode 3. The model accuracy has been verified by means of a comparison with the results provided by a numerical analysis.

Resolution and measurement in the scanning electron microscope

1987 ◽  
Vol 45 ◽  
pp. 534-537 ◽  
Author(s):  
Michael T. Postek
Keyword(s):  
Electron Microscope ◽  
Scanning Electron Microscope ◽  
Engineering Design ◽  
Resolving Power ◽  
Practical Applications ◽  
Instrument Resolution ◽  
Accurate Definition ◽  
Definition Of ◽  
Scanning Electron ◽  
Better Than

The term ultimate resolution or resolving power is the very best performance that can be obtained from a scanning electron microscope (SEM) given the optimum instrumental conditions and sample. However, as it relates to SEM users, the conventional definitions of this figure are ambiguous. The numbers quoted for the resolution of an instrument are not only theoretically derived, but are also verified through the direct measurement of images on micrographs. However, the samples commonly used for this purpose are specifically optimized for the measurement of instrument resolution and are most often not typical of the sample used in practical applications.SEM RESOLUTION. Some instruments resolve better than others either due to engineering design or other reasons. There is no definitively accurate definition of how to quantify instrument resolution and its measurement in the SEM.

Toxicology

2017 ◽  
Author(s):  
Robert Laumbach ◽  
Michael Gochfeld
Keyword(s):  
Molecular Mechanisms ◽  
Molecular Targets ◽  
Toxicity Testing ◽  
The Body ◽  
Toxic Substances ◽  
Basic Principles ◽  
Practical Applications ◽  
Mechanisms Of Toxicity ◽  
Body Distribution ◽  
Threshold Doses

This chapter describes the basic principles of toxicology and their application to occupational and environmental health. Topics covered include pathways that toxic substances may take from sources in the environment to molecular targets in the cells of the body where toxic effects occur. These pathways include routes of exposure, absorption into the body, distribution to organs and tissues, metabolism, storage, and excretion. The various types of toxicological endpoints are discussed, along with the concepts of dose-response relationships, threshold doses, and the basis of interindividual differences and interspecies differences in response to exposure to toxic substances. The diversity of cellular and molecular mechanisms of toxicity, including enzyme induction and inhibition, oxidative stress, mutagenesis, carcinogenesis, and teratogenesis, are discussed and the chapter concludes with examples of practical applications in clinical evaluation and in toxicity testing.

Impedance Reduction Controller Design for Mechanical Systems

2013 ◽  
Author(s):  
Hanseung Woo ◽  
Kyoungchul Kong
Keyword(s):  
Case Studies ◽  
Closed Loop ◽  
Controller Design ◽  
Mechanical Impedance ◽  
Open Loop ◽  
Mechatronic Systems ◽  
Closed Loop Systems ◽  
Guaranteed Stability ◽  
Reaction Forces ◽  
Definition Of

Safety is one of important factors in control of mechatronic systems interacting with humans. In order to evaluate the safety of such systems, mechanical impedance is often utilized as it indicates the magnitude of reaction forces when the systems are subjected to motions. Namely, the mechatronic systems should have low mechanical impedance for improved safety. In this paper, a methodology to design controllers for reduction of mechanical impedance is proposed. For the proposed controller design, the mathematical definition of the mechanical impedance for open-loop and closed-loop systems is introduced. Then the controllers are designed for stable and unstable systems such that they effectively lower the magnitude of mechanical impedance with guaranteed stability. The proposed method is verified through case studies including simulations.

scholarly journals International law protecting the environment during armed conflict: gaps and opportunities

2010 ◽  
Vol 92 (879) ◽  
pp. 569-592 ◽  
Author(s):  
Michael Bothe ◽  
Carl Bruch ◽  
Jordan Diamond ◽  
David Jensen
Keyword(s):  
International Law ◽  
Armed Conflict ◽  
Environmental Law ◽  
International Humanitarian Law ◽  
Environmental Damage ◽  
Humanitarian Law ◽  
International Environmental Law ◽  
Basic Principles ◽  
Principle Of Proportionality ◽  
Definition Of

AbstractThere are three key deficiencies in the existing body of international humanitarian law (IHL) relating to protection of the environment during armed conflict. First, the definition of impermissible environmental damage is both too restrictive and unclear; second, there are legal uncertainties regarding the protection of elements of the environment as civilian objects; and third, the application of the principle of proportionality where harm to the environment constitutes ‘collateral damage’ is also problematic. These gaps present specific opportunities for clarifying and developing the existing framework. One approach to addressing some of the inadequacies of IHL could be application of international environmental law during armed conflict. The detailed norms, standards, approaches, and mechanisms found in international environmental law might also help to clarify and extend basic principles of IHL to prevent, address, or assess liability for environmental damage incurred during armed conflict.

SEA model for structural acoustic coupling by means of periodic finite element models of the structural subsystems

2021 ◽  
Vol 263 (1) ◽  
pp. 5301-5309
Author(s):  
Luca Alimonti ◽  
Abderrazak Mejdi ◽  
Andrea Parrinello
Keyword(s):  
Finite Element ◽  
Numerical Approach ◽  
Unit Cell ◽  
Analytical Models ◽  
Finite Element Models ◽  
Fe Model ◽  
Acoustic Coupling ◽  
Representative Unit Cell ◽  
Definition Of ◽  
Acoustic Treatment

Statistical Energy Analysis (SEA) often relies on simplified analytical models to compute the parameters required to build the power balance equations of a coupled vibro-acoustic system. However, the vibro-acoustic of modern structural components, such as thick sandwich composites, ribbed panels, isogrids and metamaterials, is often too complex to be amenable to analytical developments without introducing further approximations. To overcome this limitation, a more general numerical approach is considered. It was shown in previous publications that, under the assumption that the structure is made of repetitions of a representative unit cell, a detailed Finite Element (FE) model of the unit cell can be used within a general and accurate numerical SEA framework. In this work, such framework is extended to account for structural-acoustic coupling. Resonant as well as non-resonant acoustic and structural paths are formulated. The effect of any acoustic treatment applied to coupling areas is considered by means of a Generalized Transfer Matrix (TM) approach. Moreover, the formulation employs a definition of pressure loads based on the wavenumber-frequency spectrum, hence allowing for general sources to be fully represented without simplifications. Validations cases are presented to show the effectiveness and generality of the approach.

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