Robot Structural Analysis Forum
Welcome to Autodesk’s Robot Structural Analysis Forums. Share your knowledge, ask questions, and explore popular Robot Structural Analysis topics.
cancel
Showing results for 
Show  only  | Search instead for 
Did you mean: 

instability type 3 RX direction

18 REPLIES 18
SOLVED
Reply
Message 1 of 19
Jorgew09
7501 Views, 18 Replies

instability type 3 RX direction

When I calculate my modell i get the following error: instability of type 3 in RX direction

I have looked at the node but everything seems to be correct. I the releases box I have tried to tick off RX, but that did not help.

18 REPLIES 18
Message 2 of 19
Rafal.Gaweda
in reply to: Jorgew09

Open calculatin Report , find there Max min values on stiffeness matrix diagonal and write here these two values.



Rafal Gaweda
Message 3 of 19
Jorgew09
in reply to: Rafal.Gaweda

Min/Max after decomposition:    7,463808e+006         6,847539e+019

precision: 1 

Message 4 of 19
Rafal.Gaweda
in reply to: Jorgew09

if the difference between these values is greater than 1e11 \ 1e12 program reports instability number 3.

It is related to big differences in stiffenes of elements for example very short elements exist in model = some inaccuracies.

You can check it this way: on dummy model select everything, make intersection, then open Bars table on View tab. Find shortests bars. Then locate nodes \ places on original model and correct location of nodes.

If it is not the case. Send me model. You already know how.



Rafal Gaweda
Message 5 of 19
Jorgew09
in reply to: Rafal.Gaweda

I don't understand how to do what you told me to do

Message 6 of 19
Jorgew09
in reply to: Jorgew09

I'm sending the file:)

Message 7 of 19
Rafal.Gaweda
in reply to: Jorgew09

Example below

 

leng.jpg

 

 

If not - send me the file. 



Rafal Gaweda
Message 8 of 19
Rafal.Gaweda
in reply to: Rafal.Gaweda

Inacurracies in your model:

 

4243.jpg



Rafal Gaweda
Message 9 of 19
TraitCarré
in reply to: Rafal.Gaweda

Hi,

please find attached 2 files.

https://dl.dropboxusercontent.com/u/79282449/AUVENT_V2.zip

the first, AUVENT_V2, is calculated without sismic load and is free of instability.

the second, AUVENT_V2_SISMIQUE, contains sismic loads and shows instability.

Calculation report :

Elém. diagon. de la matrice de rigidité  
                Min/Max après décomposition:    4.067231e+002     2.066486e+015
     Précision:    2
Shortest calculaltion element : 0.16 m -> I think it's not too short

 

- Why?

- How be sure than we can ignore this instability (after checking node displacements, shorts elements)?

- Is it possible to highlight calculation node?

 

thanks

 

benoît

Message 10 of 19
Rafal.Gaweda
in reply to: TraitCarré

the first, AUVENT_V2, is calculated without sismic load and is free of instability.

 

I do not think so :
i3.jpg

 



Rafal Gaweda
Message 11 of 19
Rafal.Gaweda
in reply to: Rafal.Gaweda

Ignore it. Related to solver tolerances.

To check - use Skyline solver -> no instability.



Rafal Gaweda
Message 12 of 19
TraitCarré
in reply to: Rafal.Gaweda

For me, "AUVENT_V2" has no instability (with automatic solver). I can't make a snapshot since there's no message 😉

For "AUVENT_V2_SISMIQUE", only multithread method gives no instability.

 

-> How is it possible to justify that the instability can be ignored?

 

-> How is it possible to highlight the calculation node wich is going wrong?

 

thanks

 

benoît

Message 13 of 19
Rafal.Gaweda
in reply to: TraitCarré

 

-> How is it possible to justify that the instability can be ignored?

 

In this case - change solver onto Skyline ; 

Create new case apply nodal load on direction given in warning message, after caclulations check displacement and rotations in this node

 

-> How is it possible to highlight the calculation node wich is going wrong?

 

In general this way starting from v 2014:

(In your model there is nothing wrong in this node - see above)

 

in3.jpg

 

 



Rafal Gaweda
Message 14 of 19
TraitCarré
in reply to: Rafal.Gaweda

 Create new case apply nodal load on direction given in warning message, after caclulations check displacement and rotations in this node

 

-> what must be the result? no displacement or rotation?

 

Benoît

Message 15 of 19
Rafal.Gaweda
in reply to: TraitCarré

Huge displacement or rotation => problem in this node


Rafal Gaweda
Message 16 of 19
Jade_Cereno
in reply to: Rafal.Gaweda

Had the Same Error, But on verification it doesn't appear.Smiley Indifferent

 

See attached Screenies

 

MIT-BsCE
Message 17 of 19
Rafal.Gaweda
in reply to: Jade_Cereno

File please


Rafal Gaweda
Message 18 of 19
EY23
in reply to: Rafal.Gaweda

Dear Rafal,

I have the same issue here. can you check my model please?

Message 19 of 19
Rafal.Gaweda
in reply to: EY23

Move node 88 onto 89

 

8889.jpg



Rafal Gaweda

Can't find what you're looking for? Ask the community or share your knowledge.

Post to forums  

Autodesk Design & Make Report