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Can I Split Frequency Ranges in Harmonic Analysis for Separate Simulations?

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hawkish_man

Mechanical
Sep 23, 2024
6
Hey everyone,

I’m working on a harmonic analysis simulation and have a question about splitting the frequency range.

Let’s say the frequency range I’m analyzing is from 10 Hz to 100 Hz. Instead of running the harmonic simulation for the entire range in one go, is it feasible to split the range into smaller intervals, for example:

One simulation for 10-50 Hz, and

Another for 50-100 Hz?

I’m trying to understand if this approach would still provide accurate results or if there are any drawbacks, particularly at the boundaries where the ranges are split. Has anyone used this method in their analysis, and if so, were there any issues with accuracy or continuity?

From my understanding, harmonic analysis calculates the steady-state response at a specific frequency. For example, consider the system at 10 Hz, assuming no damping. We know the equation is:

M(x′′)+k(x)=Fsin⁡(ωt)M(x'') + k(x) = F \sin(\omega t)M(x′′)+k(x)=Fsin(ωt)

Since 10 Hz is the starting frequency, the initial displacement at all nodes would be zero, x(t)=0x(t) = 0x(t)=0. By solving this, we get the response for this frequency.

Now, when the solver moves to 11 Hz, will it assume the initial displacement is zero again, or will it consider the solution from the previous frequency?

I’d appreciate any insights or suggestions regarding the feasibility of splitting the frequency range and how solvers handle initial conditions between different frequencies.
 
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I'm guessing you are doing linear FEA?

"Since 10 Hz is the starting frequency, the initial displacement at all nodes would be zero, x(t)=0x(t) = 0x(t)=0. By solving this, we get the response for this frequency.
Now, when the solver moves to 11 Hz, will it assume the initial displacement is zero again, or will it consider the solution from the previous frequency?"

That's not a how a a linear FEA solver works.



Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376
 
Hi,

Thanks, Greg. You're right—I misunderstood how the linear FEA solver works.

That said, my main question is about splitting the frequency range. If I were to run separate simulations for smaller intervals, like 10-50 Hz and 50-100 Hz, would that still give accurate results? I'm particularly curious if there are any concerns about accuracy or continuity at the boundary between these intervals (e.g., around 50 Hz).

I appreciate any thoughts you or others might have on this.

Thanks and regards.
 
I can't see any advantage in doing that in linear FEA, but I can't see it is a problem either. I'm used to people extracting the first x hundred modes, or all modes up to 3 times the frequency range of interest.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376
 
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