DLF

Hello Fellow Stressers,

Does the Pulse Table/DLF Spectrum Generator which performs the automatic
integration of Duhamels integral is also same as Fast Fourier Transform (FFT). Converting the time domain to frequency domain. I also observe that when I increase the natural frequency in the frequency cutoff say from default of 100Hz to 150Hz & maximum points on each DLF curve say from default of 20 to 30, the results has significant difference. How to determine which result is reliable to use and is it the same as in FEA where by increasing the mesh density will give reliable result (except at singularity). Or the default is good enough for use in dynamic analysis.

Your opinion is greatly appreciated.

Thanks,

The number of points (20 vs 30) just smooths out the curve. You can test this out by generating multiple DLFs, and only changing the number of points. A smooth curve enables better interpolation between the system's natural frequencies when determining the effects of the applied load. I've always suggested 25 to 30 points, more than 50 is over-kill.

As to extending the frequency cut-off, yes this will change the resulting DLF. There is a good explanation in our newsletter article in the "November 1994" issue of M.E.N. If you don't have this, I'll request a link from Tech Support.

Thanks Richard for that information.

I have a copy of Nov. 94 M.E.N.

Instead, Do you have a copy of data files and charts for "A Survey of Impact Load Analysis in CAESAR II" featured in "Coade Mechanical Engineering News" of December 1998. This example is a relief valve assessed using 1) static equivalent 2) response spectrum and 3) time history, I think by Dave.

Thanks,

Unfortunately I do not. Let me ask Dave and get back to you here.

Thanks Richard for your time.

Warm Regards,

See attached Dec 98 and Nov 94 bulletins.

Thanks Mariog for sharing. If anyone has the sample CII file for this article kindly share.

Cheers!!!

Here are the files supporting the referenced M.E.N. article.

Wow. Thanks Richard. This is a goldmine.

More Power & Warm Regards,