Determine the natural frequencies experimentally

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SUMMARY

The discussion focuses on determining natural frequencies and damping ratios experimentally through forced vibration techniques. Key methods include measuring the phase angle using a Bode plot, where the frequency corresponding to a 90-degree phase shift indicates the natural frequency. Additionally, a practical approach involves exciting the system with a known forced displacement and analyzing the ring down to calculate the fundamental frequency and damping ratio in the time domain. The conversation also highlights the importance of clarifying the system type, whether it is a mass-spring-damper system or a motorized system.

PREREQUISITES
  • Understanding of forced vibration techniques
  • Familiarity with Bode plots and phase angle measurement
  • Knowledge of time-domain analysis for frequency and damping calculations
  • Experience with displacement sensors and shaker tables
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  • Research methods for measuring phase angles in vibration analysis
  • Learn about time-domain analysis techniques for calculating natural frequencies
  • Explore the use of shaker tables for forced vibration experiments
  • Investigate the characteristics of mass-spring-damper systems
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Engineers, researchers, and students involved in mechanical systems analysis, particularly those focused on vibration testing and system dynamics.

Mohamed_Wael
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How can we determine the system properties (natural frequencies & damping ratio ) practically using forced vibration?
One way is to measure the phase angle, using the bode plot, the exciting frequency corresponding to 90 (deg) phase shift should be the natural frequency, are there any other approaches using forced vibration as well?
 
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Do you have a forcing mechanism with displacement sensor for the output? (e.g. shaker table?)

If not, a quick and dirty method is to excite the system with a known/repeatable forced displacement, then watch the ring down to calculate the fundamental frequency (counting peaks and calculating period) and damping ratio in the time domain.

Maybe I have interpreted your system wrongly, is this a mass spring damper system, or a motorized system? Maybe describe what it is.
 

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