Some question about Modal Analysis

[Adil Memet]

Hello every one!
I made a simulation for Modal analysis of given geometry in Abaqus, as I simulate the first 10 Modal value is almost acceptable, shown as below :

but when I want to run simulation of Modal value let's say from 489Hz , the Modal value is looks bit strange, as it is differ only very small digit between the two adjacent value. Modal value is shown in the picture below.

has anyone out there encountered the same problem during Modal analysis `

Best regards
Adil

 

[FEA way]

Did you check the corresponding mode shapes ? Do they make sense ? What kind of structure is that and how is it modeled ?

 

[Adil Memet]

Thanks for your reply and yes, I checked the Mode shapes, it looks normal at the range of first 15 or till 50 Mode, after that, the result is bit strange, the geometry is simple plate or shell element.

 

[FEA way]

What is strange about that result ? Can you share some screenshots ?

Do you mean single finite element ? What are the boundary conditions ?

 

[Adil Memet]

I found the solution for, the problem was the geometry dimension was not correctly defined for material parameter input, units are not fit (S.I unit system mixed up with S.I(mm)for material parameters input) . after correcting , it shows the correct result. Thanks

Best regards
Adil

 

[Adil Memet]

Dear all,
I have a new question about results from Modal analysis, after performing Modal analysis , I've done Frequency Regponse Analysis of the geometry and there is some thing still not clear for me. after FRF , there is graphics (Displacement vs Frequency.
I was wondering what is the units in this case, my geometry is millimeter scale(S.I (mm scale))and load is KPa. there are displacement in my graphics about 350 (???) vs 300 Hz. just wondering if it is not practical or sth else ?

Bet regards
Adil

 

[FEA way]

If your geometry is in mm but load is in kPa then you’re using inconsistent units. Check the unit tables for Abaqus in the internet. When the dimensions are in mm, pressure must be in MPa.

 

[Adil Memet]

Thank you very much for your quick reply. yes, your are right, I took Mpa as give in the Table below. what is the units I got for Amplitute in this case ? micrometer or millimeter ? Thank in advance

 

[FEA way]

When using the SI(mm) system consistently, all inputs and outputs with length units are in mm.

 

[Adil Memet]

Thanks

 

[oldNail]

mm-tonne-sec is a very common unit system but many others are also possible as long as you are consistent. This tool can be very helpful to get the correct units defined: [URL unfurl="true"]https://msgfile.info/fea-units.html[/url]