Learning Forum

[Eddie2324]

Hello,

I am trying to do a modal analysis for a welded structruce by using shell elements. I have a lot of assembled bodies in my model and I defined bonded contacts for the welded sections because I will only do modal analysis. I defined each contact myself by manully, I choosed MPC method, I had zero freq problem If I choose this settings as program controlled. I let the program define pinball radius.

After first solve I saw some absurt contacts in the modal shape animation and defined the pinball radius by myself for these parts. It seems ok when I checked the information. Also I dont see any penetration in my contact tool. 

After some fix in contacts the deformation mode animation seems ok, and I get 30 hz for the first mode which seems a bit low but not sounds weird. I want to define point masses in my model to make a simulation similar to real life condition of the part.However, after I added point masses my first node freq had a huge drop. It dropped to 6 hz from 30 hz which seems not logical to me.

I know natural freq formula is in root square k/m, so according to that my point mass changed the ''m'' and did not changed the stifness. I have two questions here ;

1-) Since all of my contacts defined as bonded, if I merge all of this parts to one body and use shared topology, will it act same as bonded contact? Because defining all of these contacts one by one takes too much time. If one merged part will act same as bonded contact I would rather to merge the parts but I could not be sure about it.

2-) How can I get reasoneble freq with using point mass? 

3-)I get this warning in solution procces ;
'' One or more MPC contact regions or remote boundary conditions may have conflicts with other applied boundary conditions or other contact or symmetry regions. This may reduce solution accuracy. Tip: You may graphically display FE Connections from the Solution Information Object for non-cyclic analysis. Refer to Troubleshooting in the Help System for more details.''

I guess this warning is about rigid body motion, but I did not see any in animation.

 

Thanks for help

[ErKo]

 

 

 

 

Hi

 

1) I prefer to use shared topology and a compatible mesh instead of contacts

2) It should drop when we add mass – point mass can be ok to represent say only the mass of a bulky/stiff component (rigid option on remote point mass), but we cannot say that this will always represent reality in a good way – perhaps one needs to model these components – also one can do a modal test (measurements) and compare that with the FE results, say with the new Addon NVH toolkit that can copmare the MAC for measured/test and numerical FE results (modal analysis)

3) that says that some contacts (MPC) or remote boundary conditions or mass might have some conflicts with displacement say type of boundary conditions, etc. If you search in the forum and on the internet for this warning you will get perhaps some more info – in general it says that it can impact the solution accuracy –