Part 15 - Identifying Structural Stiffness and Damping

[@RotorDynamics]

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[@cck1496]

As usual excellent work.... Keep it up...

[@RotorDynamics]

Thank you immensely! If you enjoy the videos, I'd greatly appreciate it if you could share them with your colleagues and engineering acquaintances.

[@teb7002]

Thank you so much. Very clear explanation.

[@RotorDynamics]

Thank you for your kind words! I'm glad the explanation was clear for you. If you have any more questions or if there's anything else you'd like to know, feel free to ask. I'm here to help! If you like the videos, I would also be grateful if you could share this video with your colleagues and fellow engineers. :)

[@akmax8647]

Hi, great video (as always). I have a question regarding the way you are suggesting to evaluate stiffness and damping. Regarding stiffness - if I know the natural frequency (and mass of the system), I can get the stiffness from - ω_n=sqrt(k/m), no? For damping - from the time domain plot (possibly should be displacement Vs time) , I can extract two consecutive peaks, get δ=ln⁡(x_1/x_3 ), the zeta: ζ=δ/√(δ^2+〖(2π)〗^2 ) and then ζ=c/(2mω_n ). Does this makes sense?

[@RotorDynamics]

There all many ways estimate stiffness and damping. I am just showing one example. Yes, using peaks from time domain to estimate damping is very well known method.

[@rishijawahir1422]

How do you calculate the Stiffness and Damping from the Impact test? Can you use the FRF of the Displacement and Velocity against the applied Force?

[@RotorDynamics]

Thanks for reaching out with your question! Calculating stiffness and damping from an impact test involves some key steps, and using the Frequency Response Functions (FRF). Here's a general outline of the process: Modeling: You can model the system using appropriate equations, such as those from the single-degree-of-freedom (SDOF) model. FRF Calculation: Calculate the Frequency Response Functions (FRF) by taking the ratio of the output (displacement or velocity) to the input (applied force) in the frequency domain. This will give you a representation of the system's dynamic behavior. Stiffness and Damping Calculation: Stiffness (K) and damping (C) can be extracted from the FRF. The resonant frequency corresponds to the natural frequency of the system, and the width of the peak in the FRF curve provides information about damping. I'll be delving deeper into this subject in future videos, so be sure to stay tuned for a more detailed exploration.