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HELP - Nodes not connected to the main structure

Experimenter
Experimenter

Hi. I'm wiriting to you because i have a big problem with a model i'm making for a university project. The aim of this project is to analize aspecific aeroplane, simulating its most crucial maneuvers in its life time and to make a detailed structural project of one of its part.

I've already complete the model of my aircraft and i was simulatung its maneuvers when i noticed that my model has a problem with some nodes which reamins blocked during the analysis. I noticed that the "blocked" nodes are the ones i inserted in a second time, after the stick model of the aircraft was already done, in order to add some concentrated mass into my model. I don't know if i missed something generating them, but it seems like those nodes are indipendent from the elements of my model, and so they don't move during the analysis. 
Can you suggest me a way to correctly connect those nodes to my structure? 

thank you all in advance for your help!

5 REPLIES 5

Re: HELP - Nodes not connected to the main structure

Gears Phenom Gears Phenom
Gears Phenom

Delete this nodes and place masses to existing structure.

Re: HELP - Nodes not connected to the main structure

Experimenter
Experimenter
The problem is that those masses must be located in a specific position, often bit corresponding to structural nodes; as example: I have to model the masses of pilot and co-pilot which are located in the middle of an element; their seats don't belong to the axe of the fuselage and so I placed a node in the middle of the element, two more nodes alligned to the last one, connected to it through 2 RBE2 elements perpendicular to the axe of fuselage. In the analysis the "fuselage" node remain fixed and doesn't move according to the fuselage movements.

Re: HELP - Nodes not connected to the main structure

Gears Phenom Gears Phenom
Gears Phenom

In this case, for modeling nonstructural masses, good choice is to use RBE2 or RBE3 element. RBE3 will work better, but you have to read some tutorials to understand features of RBE3 element.

https://iberisa.wordpress.com/tag/rbe3/

https://www.youtube.com/watch?v=xwNiuOJGaPQ

https://www.youtube.com/watch?v=A2-OlkB9sdI

http://www.predictiveengineering.com/sites/default/files/predictive_engineering_white_paper_on_small...

https://www.predictiveengineering.com/system/files_force/making_efficient_connections_with_rbe2_rbe3...

Read your message again - maybe you mess with some options or constrain this node. It is difficult to tell something without a model. Can you post here a whole model, or small part with problematic node?

Re: HELP - Nodes not connected to the main structure

Experimenter
Experimenter

Ok, i'll check if i can use RBE2 to insert those masses; the doubt comes because the masses distribution in the fuselage is crucial for the correct location of the center of gravity and i have to verify if this approximation is acceptable.

 

Regarding the unlinked node, to be honest i haven't constrained it... the professor teach us only how to globally constain something through SPC or SUPPORT and not how to constrain some nodes to elements or something else. Stupidly, when i modelled the aircraft i thought that inserting some nodes automatically they should belong to the element. 

 

Anyway, attached you can find my entire structural model; i'm sorry, i would have preferred to send you a smaller model, but my skills with femap aren't so good and i'm worried to delete something important and so generating some errors. 

There are about 20 nodes blocked in my model, but i think that the cause is always the same; please, focus only to the front parte of the fuselage; the nodes i mentioned before (the ones for the crew masses) are the number 9005 and 9006, rigid connected through RBE2 to the node 9004 (node belonging to the fuselage but not structural). I would like that this node remain attached to the fuselage during the analysis but it doesn't and remains fixed to the "ground" blocking also the crew masses.

 

PS: thank you very much for your help!!! i'm really appreciating it!!!

Re: HELP - Nodes not connected to the main structure

Gears Phenom Gears Phenom
Gears Phenom

The problem is that element 17 (beam fuselage) is not conected to RBE2 element. Split it onto two parts by Mesh -> Refine and move new node to indepentent RBE2 element and merge it. Run normal modes and check other not conected parts.