Extracting Mass and Stiffness Values from Compliance Plots for Vibration Mode Validation

Question:

Have you successfully used the modal skeleton concept to extract mass and stiffness values from compliance plots and validate modes of vibration? While this method works well for simple single degree systems, it can become more complex when other modes influence the response. Our rotor kit provides accurate values with a clear separation between the 1st and 2nd critical modes. The compliance plot is shown in a log-log scale. Recently, I utilized this approach to confirm a resonance in a vertical pump, determining that the entire pump was part of the mode rather than just the upper section. By adjusting FEA base stiffness values to match impact tests, we achieved a precise match with various modes, taking into account the distribution of upper and lower masses.

Top Replies

Dan Ambre and Tony DeMatteo have both showcased their expertise in the field. For a copy of the application used in Tony's class, reach out to him via email. Additionally, Dan's thorough diagnosis of a vertical pump problem was featured in Uptime Magazine's November/December 2008 issue. You can find more information about Dan's work by following the provided link.

Your experience with the modal skeleton concept sounds fascinating, especially its application in resolving the vibration issue in the vertical pump! Your method of adjusting the FEA base stiffness values to match impact tests appears to be a viable solution for modeling complex multi-degree systems. This resonates with my own experience in rotor dynamics where we often struggle with overlapping modes. It would be interesting to discuss this further, perhaps you might have more insights into how we can better distinguish separate modes in complex systems?

That's really interesting to hear about your experience with the modal skeleton concept, especially with a complex system such as a vertical pump. Your approach to adjusting FEA base stiffness values to match the impact tests actually reminds me a lot of my own experiences working with multi-modal vibration systems. Always more of a puzzle to align theory and reality when there are mutual influences between different modes!

Your success in using the modal skeleton concept, particularly in such a complex system as a vertical pump, is impressive - it epitomizes the value of this method in fine-tuning FEA models. The clear distinction between the 1st and 2nd critical modes indeed confirms the accuracy of the rotor kit, and the way you adjusted the base stiffness to match the impact tests demonstrates a thorough understanding of how to extract real-world value from compliance plots. I'm curious if you encountered any challenges in interpreting the influence of other modes on the response, as that has been a hurdle in my own work.

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Frequently Asked Questions (FAQ)

FAQ: 1. What is the modal skeleton concept for extracting mass and stiffness values from compliance plots for vibration mode validation?

Answer: - The modal skeleton concept is a method used to extract mass and stiffness values from compliance plots to validate modes of vibration. It works well for simple single degree systems but can become more complex when other modes influence the response.

FAQ: 2. How can the rotor kit be helpful in providing accurate values for mass and stiffness with clear separation between critical modes?

Answer: - The rotor kit provides accurate values for mass and stiffness with a clear separation between the 1st and 2nd critical modes, making it easier to analyze and validate vibration modes.

FAQ: 3. How can adjusting FEA base stiffness values help achieve a precise match with various modes in vibration analysis?

Answer: - By adjusting Finite Element Analysis (FEA) base stiffness values to match impact tests, a precise match with various modes can be achieved. This accounts for the distribution of upper and lower masses in the system.

FAQ: 4. Can the modal skeleton concept be applied to complex systems where multiple modes influence the response?

Answer: - While the modal skeleton concept works well for simple single degree systems, it can become more complex in systems where multiple modes influence the response. Additional considerations and adjustments may be needed in such cases.

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