Learning Forum

[GeorgeAerospace]

Dear Folks

In NX Nastran, I can calculate the FRF using either "Sol 108 (Direct Frequency Response Function)" or "Sol 111 (Modal Frequency Response Function)". Both these analyses are different from "Sol 103 (Response Dynamics)" which can calculate both "sine-sweep harmonic response" and "Random Response".

I know that Ansys provides "Harmonic Response" and "Random Vibration" analyses. I understand that both these analyses are equivalent to Nastran's Sol 103

My questions are:

1) Is my understanding correct, that is, are Ansys' "Harmonic Response" and "Random Vibration" analyses equivalent to Nastran's Sol 103?

2) What are Ansys analyses equivalent to Nastran's Sol 108 and Sol 111?

 

Thanks

[peteroznewman]

To answer your questions, refer to the following Workbench figure.

Your understanding is wrong. Nastran SOL103 is what Ansys calls Modal and is also called Normal Modes or Eigenvalue analysis.

Nastran SOL111 can do Random Vibration and Harmonic Response. One of the cards used is EIGRL which requests the Modal analysis.

In ANSYS, you put a Modal analysis upstream and link the Solution cell of Modal to either a Harmonic Response or a Random Vibration analysis Setup cell.

[ahmed.desoki]

Dear Peteronz

Thank you for your information.

Ansys "Harmonic Response" takes the base sine-sweep spectrum as input, and calculate the  response. This should simulate the sine-sweep test, right?

Similarly, the "Random vibration" takes the base PSD as input, and calculated the PSD of the response. This should simulate the random vibration test, right?

Could you inform me which Ansys analysis type can calculate the FRF? The FRF does not need input sine-sweep spectrum. It only needs one/several points as input and one/several points as output.

Thanks and regards

[peteroznewman]

Dear Ahmed,

Ansys Harmonic Response can output FRF. Since the FRF is a plot on the frequency axis, you do need the sine-frequencies at the input points to get the FRF at the output points.