preloading stress in a Harmonic Analysis

[proEdj]

Hello,

It seems that when I run a harmonic analysis the magnitude all of my applied forces including gravity are based on a sin function. I am fine with this for gravity, because I am essentially performing a vibrational analysis at a set frequency using gravity as my vib load. My applied (nodal)force, on the other hand, actually simulates preloading of the part which should be constant through out the analysis. Is anyone familiar with how to select some forces to be static and some foces to be harmonic in a harmonic analysis. I guess that I could do a dynamic analysis, write a constant function for my preloading force, and write a sinusoidal function for the gravity load, however this would only allow me to view results at a given frequency. An entire defined frequency spectrum of results would be obtainable through an harmonic analysis.

Thanks,

proEdj

sorry for being wordy

 

[Drej]

EVERYTHING in an harmonic analysis (every applied load that is) is applied as a harmonic function i.e. is applied as a sinusoidal function: gravity, temperature, pressure, force, displacement... everything. You cannot apply a "constant" force in an harmonic analysis (since by its nature harmonic analysis means harmonic analysis). If you have one force which is static (constant) and another which is a function of frequency then you need to consider some form of dynamic transient approach (ANTYP,TRANS). Remember, this is carried out in the TIME domain, and hence all results would be a function of TIME and not frequency.


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[GregLocock]

And of course in a linear model you can just use superposition to add the results of the different loadcases.

Cheers

Greg Locock

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