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The purpose of my talk today is To equip you with background knowledge and expertise needed to conduct a successful vib

Fundamentals of VibrationsPlanning and Conducting a Vibration TestInterpreting the Vibration Test Results. FUNDAMENTALS OF VIBRATION. Harmonic waveSingle Degree of Freedom SystemDamped System. ?t. VibrationOscillatory motion of a mechanical component due to interplay of kinetic and potential energies. Harmonic Wavex(t) = X sin (?t).

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The purpose of my talk today is To equip you with background knowledge and expertise needed to conduct a successful vib

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    3. FUNDAMENTALS OF VIBRATION

    4. Vibration Oscillatory motion of a mechanical component due to interplay of kinetic and potential energies. Harmonic Wave x(t) = X sin (?t)

    5. Harmonic wave x = X sin ? t xo = ? X cos ? t xoo = - ? 2 X sin ? t Condition for Harmonic Motion xoo = - ? 2 x

    6.

    8. Tacoma Narrows Bridge

    9. Response to a Harmonic Excitation

    10. Damper

    11. Damping Ratio

    13. Response of damped system to a Harmonic Excitation

    14. Response to a Harmonic Excitation

    16. Damped Natural Frequency

    18.

    19. Equation of Motion for a Multi-Degree of Freedom System

    20. Solution Methods for continuous systems

    24. Vibration Measurement Unit of Vibration Displacement (amplitude=X) mm Mostly peak-peak Velocity V = 2*?*f*X Amplitude (V) mm/sec or m/s Acceleration A = 4* ?2*f2*X Measured as peak value m/s2 or ‘g’ (=9.81m/s2)

    25. Vibration Sensors Accelerometer Velocity Probe Laser Doppler Vibrometer Other Transducers such as Strain Guage, LVDT etc.

    27. Velocity Probes Comparatively Heavy Good Velocity Response in Medium frequency range (20-100 Hz) Common in Power Plant monitoring Relatively Cheaper electronics and hence lower overall cost

    29. Laser Doppler Vibrometer Non-contact Measurement Very Good Frequency response up-to 100 MHz (only limited by electronics ) Costly Currently becoming popular for Automated Measurements and Scanning

    31. Vibration Exciter- Various Types Mechanical Exciter Electro-dynamic Electro-Hydraulic Non-Contact Type (Electro-Magnetic) Electrodynamic exciter is the most popular and versatile

    34. Electrodynamic Exciter- Important Specifications Frequency Range Dynamic Force Rating Maximum Pay load Natural Frequency Moving Mass

    43. Tacoma Narrows Bridge

    46. Free Vibration Decay

    48. Identifying Multiple Vibration Sources

    49. Frequency Response Function FRF is a transfer function between the response of structure measured at some point I and force applied at some point J ?ij= FFT of (x(t) at point I) / FFT of f(t) at point J FRF gives accurate picture of resonances of the structure

    51. Frequency Response Function Frequency response function when found at different point can be combined to get the different mode shapes of the structure and their corresponding modal properties This very important procedure in vibration testing is called MODAL TESTING

    52. Use Modal Exciter Cross stiffness to be very low for determining the FRF Moving mass should be minimum fs=fe - M xoo Use a stringer. Thin rod which is much less stiff in cross direction

    53. Some Test Cases

    58. Virtual Instrumentation and Vibration Measurement The goal of this lecture is to introduce virtual instrumentation and expose you to the power and flexibility of using it in Vibration Measurement

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