Troubleshooting Cantilever Beam Simulation in COMSOL

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Discussion Overview

The discussion revolves around troubleshooting issues encountered while simulating a cantilever beam using COMSOL, specifically focusing on calculating eigenfrequencies and frequency response. Participants explore various aspects of the simulation setup, including boundary conditions, material properties, and solver settings.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant reports obtaining a resonant frequency of 49 kHz but an implausibly large z displacement of 3.33 m, questioning whether this is due to the absence of air damping.
  • Another participant suggests that the amplitude of mode shapes in vibration analysis can be arbitrary and discusses normalization options that may affect displacement values.
  • Concerns are raised about potentially specifying frequency in incorrect units, with a recommendation to check whether the input should be in rad/sec or Hz.
  • One participant notes that the resonance at 0 Hz in frequency analysis may indicate a lack of constraints applied to the model.
  • Another participant provides ratios of vibration frequencies for clamped and free cantilevers, comparing them to the reported frequencies and suggesting checking constraints.
  • Several participants share results from modal analyses conducted in ANSYS, showing calculated modes that are similar but not identical to those obtained in COMSOL, raising questions about discrepancies between software outputs.
  • One participant expresses uncertainty about whether the applied constraints are sufficient for a clamped beam and considers the need for a mass-on-spring model for validation.
  • Another participant offers to perform a confirmation analysis in ANSYS if the beam's properties are provided.

Areas of Agreement / Disagreement

Participants express various viewpoints on the issues faced, with no consensus reached on the causes of the discrepancies in results. Multiple competing explanations and hypotheses are presented, indicating that the discussion remains unresolved.

Contextual Notes

Participants mention specific material properties and boundary conditions, but there are unresolved questions regarding the adequacy of constraints and the influence of normalization on displacement values. The discussion also highlights potential differences in results between COMSOL and ANSYS simulations.

Who May Find This Useful

This discussion may be useful for individuals working with COMSOL for structural simulations, particularly those interested in eigenfrequency analysis and frequency response of cantilever beams.

  • #31
I was wondering how would you solve this problem (Eigenfrequency Analysis) if you were to include ''air damping'' any user of COMSOL has any idea? because i kinda have the same problem. i want to include air damping in my eigenfrequency analysis...
 
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  • #32
Lucas84 said:
First of all thank you very much for your help alephzero.

I've look at COMSOL help, and the input is in Hz as well as the results. However, I did a simulation on a wide range of frequency and here's what I got :

I have a question concerning performing the simulation over a wide range of frequency in comsol. You mentioned you could do it in the comsol, can you tell me how? When I did the eigenfrequency analysis, it shows me a set of frequencies from which I have to select but not the frequencies of my choice. Thanks for your response!
 

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