Download - Vibration 2003
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Vibration
Presented by
Anubhab Pal 11AG61R09
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Physics behind vibration
Vibration occurs when a body oscillates
repeatedly around an equilibrium position
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On crossing the neutral point w > Fs deceleration starts
When velocity = 0, w > Fs Accelerates
Reaches equilibrium position, but due to velocity,
crosses the equilibrium position and moves downwards
Process continues until external force acts to change its
motion
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The quantityxm, calledthe amplitude of themotion
The cosine functionvaries between 1
The time-varyingquantity (t+ ) iscalled the phase of themotion
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The constant is called the phase angle
The value of depends on the displacement and
velocity of the particle at time t = 0.
The constant , called the angular frequency of the
motion
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Damped vibration External forces that oppose the motion of the vibrating
body
Damping reduces the amplitude of the vibration
As the vane moves up and
down, the liquid exerts an force
on it.
With time, the mechanical
energy of the blockspring
system decreases.
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C
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Measurement of vibration
Measurement of displacement or velocity or
acceleration can be done
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Ergonomical aspect
Types of vibration
Whole body vibration
Hand arm vibration
Standards
Whole bodyISO 2631:1997
Hand armISO 5349:2001
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Whole body vibration (WBV)
Enters the body via a number of routes and canaffect organs which are not adjacent to the point of
entry to the body.
Entry points
The feet
The buttocks
The back
The back of the head
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ISO guidelines relating magnitude to comfort
for passengers on public transport
< 0.315 m/s2 not uncomfortable
0.315-0.63 m/s2 a little uncomfortable
0.5-1 m/s2 fairly uncomfortable
0.8-1.6 m/s2 uncomfortable
1.25-2.5 m/s2 very uncomfortable
>2 m/s2 extremely uncomfortable
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Health effects
Whole body vibration has been linked with the
following effects on human beings
Discomfort
Interference with vision
Interference with fine motor tasks Spinal injuries
Damage to the digestive system
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ISO 2631:1997
Part 1Deals with direct health effects Part 2Deals with vibration transmitted through
buildings and is more concerned with nuisance
vibrations
Part 4Deals with the effects of vibration on trainpassengers and crews
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Standards for appropriate exposure to WBV
Reduced comfort boundary
Limit beyond which the operator feels uncomfortable
Fatigue-decreased proficiency boundary (FDPB)
Reduction of proficiency of work due to fatigue
Exposure limit Limit beyond which the health and safety of the
operator gets affected
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Fatigue-decreased proficiency boundary (FDPB)
For Z axis
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Fatigue-decreased proficiency boundary (FDPB)
For X and Y axis
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Axis system
Three axes are measured, based on the orientation
of the human body
The x-axis is in the
back-to-front direction
The y-axis is from side-to-side
The z-axis is from feet
to head
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Frequency weighing
Six frequency weighing to be used in different
circumstances
Wc, Wd, We, Wf, Wj, Wk
Two are mostly used (WdX and Y axis, WkZ axis)
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Measurement of WBV
Equipment
Tri-axial seat accelerometer
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Hand Arm Vibration(HAV)
Hand-arm vibration is the transfer of vibrationfrom a tool or work place to a workers hands and
arms
Hand-arm vibration may lead to circulatory
disturbances, sensory and motor disturbances and
musculoskeletal disturbances (Hand Arm Vibration
Syndrome or HAVS)
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ISO 5349:2001
Part 1Deals with general requirements formeasurement of hand arm vibration
Part 2Deals with guidance for measurement at
the workplace
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Axis system
The origin of the coordinate system is the head of
the third metacarpal
TheZh-axis is defined as the longitudinal axis of
the third metacarpal bone and is oriented positively
towards the distal end of the finger. TheXh-axis passes through the origin, is
perpendicular to theZh-axis, and is positive in the
forward direction when the palm is facing forward.
The Yh-axis is perpendicular to the other two axes
and is positive in the direction towards the thumb.
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For hand-grip position
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For flat palm condition
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Frequency weighing
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Methods for reducing vibration
Reduction of the the transmission of vibration to
the worker by,
Improving vehicle suspension
Altering the position of the seat within the vehicle
Mounting equipment on springs or compression pads Use materials that generate less vibration
Decreasing the amount of vibration to which the
worker is exposed by,
Reducing the speed of travel
Minimizing the exposure period by alternating
Increasing rest/recovery time between exposures
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Where feasible, reducing or isolating workers from
the vibration source by,
Providing a spring or cushion as a vibration isolator inseated tasks.
Providing a rubber or vinyl floor mat for workers doing
standing tasks.
Minimizing the undulations of the surface over whichthe vehicle must travel.
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References
Managing Noise and Vibration at Work Apractical guide to assessment, measurement and
controlTim South, 1st Edition, Elsevier, 2004
Fitting The Task to the Man A Textbook of
occupational ErgonomicsEtienne Grandjean, 4thEdition, Taylor & Francis, 1988
Human Factors in Engineering and Design
Mark S. Sanders, Ernest J. McCormick, 6th Edition,
McGraw-Hill International, 1987
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Off-road Vehicle Engineering Principles
Carroll E. Goering, Marvin L. Stone, David W.
Smith, Paul K. Turnquist, 1st Edition, ASAE, 2003
Halliday & Resnick Fundamentals of Physics
Jearl Walker, 9th Edition, John Willey & Sons,
2011 Measurement and Instrumentation Principles
Alan S. Morris, 1st Edition, Butterworth-
Heinemann, 2001
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Thank You