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Example: Predicting the tone of a tuning fork

So this is my tuning fork bought for around 5 dollars from ebay. What I wanted to do was to see if I could use LUCID to predict the tone which the fork would make.

Now, I could calculate this mode by hand using a method such as that on Wikipedia.

I'll add the hand calculation later. If you needed to do this in a job you would be wasting your time making a FEM - use the equation from a good text book.

Anyway, the measurements of the fork are as follows:

The fork is between 4.6 to 4.7mm thick over the entire length of the fork (measured using a micrometer).

Converting these measurements into a finite element model gives this (the node numbers are plotted to give an indication of the mesh density).

Note: This example highlights a couple of issues with LUCID:

(i) the CBAR orientation is not working correctly (it is currently arbitrary) In this case the fork prongs cross-section is approximately square;

(ii) the normal modes method in LUCID expects to see a LOAD statement in the case control section (although it is not actually used).

Once these are corrected in LUCID I will upload the FEM data file.

Anyway, using the current implementation LUCID predicts a frequency of 290.0Hz. You can download a clip of what this tone sounds like here (Ogg Vorbis format).

Using Audacity I recorded the tuning fork here (Ogg Vorbis format) and plotted the content in the frequency domain as shown below:

In addition I created the pure tone using Audacity here (Ogg Vorbis format).

Please leave any comments below - I intend to add the FEM, a link to material properties and a hand calculation soon.

Subpages (1): mysounds