Logarithmic sine sweep: how to compute cycles?

[Rhei]

Hi,

I am running a transient simulation in Nastran. The structure undergoes a sine-sweep base acceleration and I need to compute the number of cycles the structure will se during the whole simulation.
How do I do that knowing the sweep rate (R [oct/min]), the total duraton (T ) and the frequency range (Df [Hz])?

Thank you
Regards

 

[GregLocock]

And what have you found so far? I'll assume you mean that num_cycles=(zero_crossings/2)-1

In my opinion the first thing to do is use Df and the number of octaves (T/60*R) to find a start frequency. The simplest approach from then is to model the waveform and count zero crossings, but a calculus based approach is more elegant.

Cheers

Greg Locock


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[Rhei]

This equation
num_cycles=(zero_crossings/2)-1
is what I was missing. Since I generated the sweep using Matlab, I could just make it count the number of zero-crossing points and use it in the previous equation.
Until now I was trying to follow the procedure explained in the book written by Wijker, but I was not sure about the result I got (nearly 1500 cycles). I will cross check the result.

Thank you!