Learning Forum

[KDH]

First, obtain the FRF by nodal force in the harmonic.

When I get the FRF in the transient under the same conditions, I want to make sure it is the same as the result in the harmonic.

But I'm confused about giving the same condition.

If a nodal force of 10 N is applied in the Y direction in the harmonic, how should it be applied in the transient?

Finally, how can I compare the two results?

[peteroznewman]

I don't understand what you mean in your first two sentences.
A 10 N force applied in a harmonic response means that a force with an amplitude of 10 N and a sinusoidal waveform was applied to the structure at a range of frequencies. Let's say you specified a lower frequency of 20 Hz and an upper frequency of 200 Hz with a 20 Hz increment. That means the results of the harmonic response was evaluated at 20, 40 60, ... 160, 180 and 200 Hz. That is 10 points on a graph or 10 contour plots.
To do that in a Transient solution, you need to have 10 transient models. Each one will have a unique input waveform. The first waveform will have a 10 N amplitude with a 20 Hz frequency. The last waveform will have a 10 N amplitude with a 200 Hz frequency.
You need to simulate each Transient for a long enough time for the transient portion of the solution to decay away leaving only the steady-state solution.
In the steady-state portion of the solution, you need to find the time when the maximum response is seen since the response will oscillate over time from a maximum value, through zero to a minimum value. It is the maximum response that is captured in the harmonic response analysis.
I suggest you browse the free courses in the structures category. There are courses on dynamics, modal, harmonic response and transient analysis.