topic Re: Confusing regarding number of modes and modal mass in Robot in Robot Structural Analysis Forum

Confusing regarding number of modes and modal mass in Robot

Anonymous — Thu, 12 Dec 2019 09:33:54 GMT

Hi,

I am currently testing out robot but have some years of experience with modal analysis in other softwares. I have to issues:

1) In my simpel beam model I want to include 10 modes in the results, but I dont know how to tell robot that I want this. It only gives me 1 or up to 4 modes. (maybe due to a too few numbers of nodes?)

2) The modal mass is equal to the total mass. This shouldn't be the case. The modal mass is ½ of the total mass for the 1. mode of a simple supported beam and even lower for a clamped-clamped as in my example.

I cannot attached the rtd file

(error: "The attachment's 1beam.rtd content type (application/octet-stream) does not match its file extension and has been removed"

Re: Confusing regarding number of modes and modal mass in Robot

Simau — Thu, 12 Dec 2019 11:02:12 GMT

Hi @Anonymous

You may tell Robot the number of desired mode here

If you want to upload your model, zip it before

Attached example file

Re: Confusing regarding number of modes and modal mass in Robot

Anonymous — Thu, 12 Dec 2019 11:10:11 GMT

Hi Simau,

Thanks. Im am writing 10, but the it says it can only find 1 (or 4).

The model zipped is attached.

Re: Confusing regarding number of modes and modal mass in Robot

Simau — Thu, 12 Dec 2019 12:05:03 GMT

You must create intermedite nodes. The more the number of nodes, the more modes.

Create nodes with: edit>divide then

Re: Confusing regarding number of modes and modal mass in Robot

Anonymous — Fri, 13 Dec 2019 10:06:11 GMT

That solves both issues - thanks !