Modal Analysis Behavior

michael.loreantz — Tue, 17 Jan 2023 19:26:18 GMT

Hi everyone, I was scrolling through the forum and found out that modal analysis can be done multiple time in one model, and it will be used for the following case ID.

I want to know how the modal analysis behaves in Robot though, does it also contributes to the arrangement of mass matrix?

Let's say I have:

Modal Case 1 without any eccentricity, followed by a response spectrum case

and

Modal Case 2 with eccentricity, followed by a direct integration time history case

The direct integration case supposedly does not use modal information, as the calculation is not done by modal superposition right? Does the Modal Case 2 with eccentricity still affects the mass matrix calculation in the direct integration case, even though the modal information are not used? In that case the mass matrix following case 1 and case 2 will be different?

Apologies if this may be trivial to you, as I just get into Robot and could not find mass source option in Robot. Thank you.

Re: Modal Analysis Behavior

GGB.BHB — Fri, 20 Jan 2023 15:01:40 GMT

@michael.loreantz just to be safe I always only do one modal analysis using the same 'load to mass conversion' as any other dynamic analysis I am running on the model. I am never totally sure which analysis types run their own modal analysis (I think footfall does) and which rely on a modal analysis case already having been done higher up the analysis cases. If I want to check out different loading etc., I set up parallel models.

topic Re: Modal Analysis Behavior in Robot Structural Analysis Forum

Modal Analysis Behavior

Re: Modal Analysis Behavior