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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