Vortex Induced Vibrations

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Vortex Induced Vibrations
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Contents

• Vortices and Induced Vibrations.
• Phenomena and Reduction of Vortex Induced
  Vibrations.
• Latest Research Papers.
• Summary.

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Vortices

• A vortex is defined as the motion of
• multitude of fluid particles around a
• common center.
• Types of vortices
• - Forced Vortex
• - Free Vortex

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Vortices in the Real World

• Vortices in the real world like Tornados,
  Whirlpool in rivers are often a combination of
  free and forced vortices.
• Forced vortex flow occurs at and near the center
  of the vortex while free vortex conditions are
  approximated outside this region.

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Fig.(1) Velocity Distribution
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Flow-Induced Vibration

• The vibration caused by a fluid flowing around a
  body is known as flow-induced vibration.
• In the following examples, the vibration of the
  system continuously extracts energy from the
  source, leading to larger and larger amplitudes
  of vibration.

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Phenomena of Induced Vibration

• Tall chimneys, Submarine periscopes,
• Electric transmission lines and Nuclear fuel
  rods are found to vibrate violently under certain
  conditions of fluid flow around them.
• Similarly, water and oil pipe lines and tubes in
  air compressors undergo sever vibrations under
  certain conditions of fluid flow through them.

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• In ice-covered electric transmission lines and
  the unstable vibration, known as flutter, of air
  foil sections.
• High frequency vibration known as singing of
  transmission lines occurs due to the phenomena of
  vortex shedding.

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Why Vortex Shedding Phenomena

• Vortex shedding was the primary cause of failure
  of the Tacoma Narrows suspension bridge in the
  state of Washington in 1940.
• If the frequency of the vortex shedding is in
  resonance with the natural frequency of the
  member that produces it, large amplitudes of
  vibrations with resulting large stresses can
  develop.

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• Experimental data show that regular vortex
  shedding occurs strongly in the range of Reynolds
  number (Re) from about 60 to 5000.
• Experiments shows also that the frequency of
  shedding is given in terms of Strouhal number
  (St), and this in turn is a function of the
  Reynolds number.
• Other cylindrical and two dimensional bodies can
  also shed vortices.

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Reduction of Flow-Induced Vibration
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