Learning Forum

[thornyak]

 

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Hi! I have a crane structure in AIM 2020 R1. The structure itself weights cca 650kg and other suppressed parts added as Point Mass cca 1200 kg, so the sum mass of the model is cca 1800-1900kg. Amplified Earth Gravity (Inertial Load) is 15.2 m/s2 so the full downward acting force in the system equals 15.2*1900kg = 29 kN. Nonetheless, the Reaction Force is only 8kN as you can see on the attached picture. Can you explain this difference please? WBPZ file attached. Regards, Tamas

[Subashni Ravichandran]

Hello Tamas

Let me look into the file shared and get back to you.

[thornyak]

Subashni thank you.

In the meantime I tried Force instead of Point Mass, but I got the same result. It would be very important to know the correct Force- and Moment Reaction. There is an upper part of the crane which I would like to check (in a separate model) based on the reaction forces coming from the lower part. And the client is waiting for the results.

[thornyak]

Dear Subashni

Can you give an update please? Thanks.

[Subashni Ravichandran]

Hello Tamas

Have you checked the Moment Reaction as well? 

When I run your simulation, I'm getting Moment Reactions of the order 10^7 Nmm + Reaction Force of ~8000N as you have mentioned. 
This should be balanced with the total Force + Moment on the system. 

Calculating just the reaction Force would not be the correct comparison.

[thornyak]

Hello Subashni This is a cantilever-like structure with only one support so the forces (weights) acting on the system should equal with the reaction force at the support position (regardless of moment). Additionally Moment Reaction arises at the support as well in function with the lever arm of the sum weight (distance between support and COG of crane). I checked the reactions by hand calculations and Force Reaction should equal 28-29 kN, and the Moment Reaction 53 kNm. In the meantime I build the model with solid elements (instead of shells), and I get the correct reactions, see attached pictures. So there is the problem with the shell representation. I think AIM can't handle correctly the shell finite elements in general. Can you investigate the shell model please? Regards, Tamas