Damping

4 Key excerpts on "Damping"

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  eBook - PDF

  Vibration

  Fundamentals and Practice, Second Edition

  • Clarence W. de Silva(Author)
  • 2006(Publication Date)
  • CRC Press

    (Publisher)

  7 Vibration Damping 7.1 Introduction Damping is the phenomenon by which mechanical energy is dissipated (usually con-verted into internal thermal energy) in dynamic systems. Some knowledge of the level of Damping in a dynamic system is important in the utilization, analysis, and testing of a system. For example, a device having natural frequencies within the seismic range (i.e., less than 33 Hz) and having relatively low Damping could produce damaging motions under resonance conditions when subjected to a seismic disturbance. Also, the device motions could be further magnified by low-frequency support structures and panels having low Damping. This illustrates that knowledge of Damping in constituent devices, components, and support structure is particularly useful in the design and operation of a complex mechanical system. The nature and the level of component Damping should be known in order to develop a dynamic model of the system and its peripherals. Know-ledge of Damping in a system is also important in imposing dynamic environmental limitations on the system (i.e., the maximum dynamic excitation the system could with-stand) under in-service conditions. Furthermore, some knowledge of its Damping could be useful in order to make design modifications in a system that has failed the accept-ance test. However, the significance of knowledge of Damping level in a test object, for the development of test excitation (input), is often overemphasized. Specifically, if the response-spectrum method is used to represent the required excitation in a vibration test, it is not necessary that the Damping value used in the development of the required response spectrum specification be equal to the actual Damping in the test object. It is only necessary that the Damping used in the specified response spectrum be equal to that used in the test-response spectrum.

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  eBook - ePub

  Mechanical Vibration

  Analysis, Uncertainties, and Control, Fourth Edition

  • Haym Benaroya, Mark Nagurka, Seon Han(Authors)
  • 2017(Publication Date)
  • CRC Press

    (Publisher)

  Figure 3.3 Large damper installed at the Los Angeles Regional Transportation Management Center. (Courtesy of Douglas P. Taylor of Taylor Devices, Inc.)

  In 1999 a new Airport Rail Transit and Bay Area Rapid Transit structure (Figure 3.4 ) was constructed at the San Francisco International Airport. Ten fluid dampers were installed for earthquake energy dissipation. Two different types were employed, all with a ±508 mm stroke, some capable of resisting a 3115 kN load and others a 4225 kN load.

  Figure 3.4 Dampers installed at the San Francisco International Airport. (Courtesy of Douglas P. Taylor of Taylor Devices, Inc.)

  The Poplar Street Bridge (Figure 3.5 ), a large highway bridge over the Mississippi River in Wt. Louis, uses 64 fluid dampers to control longitudinal earthquake movement while allowing for free thermal movement. Two different types of dampers ware very, some with a ± 183 mm stroke and capable of resisting a 1334 kN load and others with a ± 229 mm stroke and capable of resisting a 2224

  kN

  load.

  Figure 3.5 Vibration dampers are used under the Poplar Street bridge near the Riverfront in St. Louis. (Courtesy of Douglas P. Taylor of Taylor Devices, Inc.)

  3.2 lntroduction to Damping

  Damping refers to the removal of energy from vibratory motion wed is primarily associated with the irreversible transformation of mechanical energy into thermal energy. Damping is the energy dissipation property of material and structures undergoing time‐dependent deformation and/or displacements.

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  A deformation occurs when a body’s shape changes as a result of forces acting on it, whereas a displacement is a change in location of a point or points on a body. In most instances, both occur. Lumped‐parameter models idealize this situation by concentrating their mass, Damping, and stiffness properties at discrete locations.

  Depending on the mechanism of energy dissipation, Damping can be classified according to the following overlapping characteristics:

  • Viscous Damping

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  eBook - ePub

  Structural Vibration

  Analysis and Damping

  • C. Beards(Author)
  • 1996(Publication Date)
  • Butterworth-Heinemann

    (Publisher)

  Damping Applications for Vibration Control edited by P J Torvik (ASME Publication AMD, vol. 38, 1974).

  More recently, the Damping that can be achieved in structures has been comprehensively studied and researched, particularly with regard to industrial, military and aerospace applications, and improving analytical techniques. The results of some of this work have been published in conference proceedings and relevant learned journals such as The Journal of Sound and Vibration, The Proceedings of the ASME and The Shock and Vibration Digest .

  5.7.2.5 Vibration dampers and absorbers

  A wide range of Damping devices is commercially available; these may rely on viscous, dry friction or hysteretic effects. In most cases some degree of adjustment is provided, although the effect of the damper can usually be fairly well predicted by using the above theory. The viscous type damper is usually a cylinder with a closely fitting piston and filled with a fluid. Suitable valves and porting give the required resistance to motion of the piston in the cylinder. Dry friction dampers rely on the friction force generated between two or more surfaces pressed together under a controlled force. Hysteretic type dampers are usually made from an elastic material with high internal Damping, such as natural rubber. Occasionally dampers relying on other effects such as eddy currents are used.

  However, these added dampers only act to reduce the vibration of a structure. If a particularly troublesome resonance exists it may be preferable to add a vibration absorber

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  eBook - PDF

  Handbook of Structural Engineering

  • W.F. Chen, E.M. Lui, W.F. Chen, E.M. Lui(Authors)
  • 2005(Publication Date)
  • CRC Press

    (Publisher)

  35 Passive Energy Dissipation and Active Control 35.1 Introduction In recent years, innovative means of enhancing structural functionality and safety against natural and man-made hazards have been in various stages of research and development. By and large, these approaches can be grouped into three broad areas as shown in Table 35.1: (1) base isolation; (2) passive energy dissipation; and (3) active control. Of the three, base isolation can be considered a more mature technology (e.g., ATC 1993; Skinner et al. 1993) with wider applications as compared with the other two. Passive energy dissipation systems encompass a range of materials and devices for enhancing Damping, stiffness, and strength, and can be used both for natural hazard mitigation and for rehabilitation of aging or deficient structures (e.g., Soong and Dargush 1997; Constantinou et al. 1998; Hanson and Soong 2001). In recent years, serious efforts have been undertaken to develop the concept of energy dissipation, or supplemental Damping, into a workable technology, and a number of these devices have been installed in structures throughout the world. In general, such systems are characterized by a capability to enhance energy dissipation in the structural systems in which they are installed. This effect may be achieved either by conversion of kinetic energy to heat or by transferring of energy among vibrating modes. The first method includes devices that operate on principles such as yielding of metals, phase transformation in metals, frictional sliding, deformation of viscoelastic solids or fluids, and fluid orificing. The latter method includes supplemental oscillators that act as dynamic absorbers. A list of such devices, which have found applications, is given in Table 35.1. T. T. Soong Department of Civil Engineering, State University of New York, Buffalo, NY G.

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