topic Re: instability type 3 RX direction in Robot Structural Analysis Forum

instability type 3 RX direction

Anonymous — Fri, 09 Mar 2012 13:23:50 GMT

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.

Re: instability type 3 RX direction

Rafal.Gaweda — Fri, 09 Mar 2012 14:05:28 GMT

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

Re: instability type 3 RX direction

Anonymous — Fri, 09 Mar 2012 14:31:11 GMT

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

precision: 1

Re: instability type 3 RX direction

Rafal.Gaweda — Fri, 09 Mar 2012 15:04:58 GMT

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.

Re: instability type 3 RX direction

Anonymous — Fri, 09 Mar 2012 15:15:14 GMT

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

Re: instability type 3 RX direction

Anonymous — Fri, 09 Mar 2012 15:28:26 GMT

I'm sending the file:)

Re: instability type 3 RX direction

Rafal.Gaweda — Fri, 09 Mar 2012 15:33:49 GMT

Example below

If not - send me the file.

Re: instability type 3 RX direction

Rafal.Gaweda — Fri, 09 Mar 2012 15:54:48 GMT

Inacurracies in your model:

Re: instability type 3 RX direction

Anonymous — Wed, 06 Nov 2013 11:24:19 GMT

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

Re: instability type 3 RX direction

Rafal.Gaweda — Wed, 06 Nov 2013 14:16:23 GMT

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

I do not think so :

Re: instability type 3 RX direction

Rafal.Gaweda — Wed, 06 Nov 2013 14:22:42 GMT

Ignore it. Related to solver tolerances.

To check - use Skyline solver -> no instability.

Re: instability type 3 RX direction

Anonymous — Thu, 07 Nov 2013 03:19:44 GMT

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

Re: instability type 3 RX direction

Rafal.Gaweda — Thu, 07 Nov 2013 07:55:00 GMT

-> 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)

Re: instability type 3 RX direction

Anonymous — Tue, 12 Nov 2013 14:10:23 GMT

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

Re: instability type 3 RX direction

Rafal.Gaweda — Tue, 12 Nov 2013 14:58:53 GMT

Huge displacement or rotation => problem in this node

Re: instability type 3 RX direction

Anonymous — Fri, 15 Nov 2013 02:21:38 GMT

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

See attached Screenies

Re: instability type 3 RX direction

Rafal.Gaweda — Fri, 15 Nov 2013 07:20:10 GMT

File please

Re: instability type 3 RX direction

EY23 — Wed, 12 Nov 2014 07:21:20 GMT

Dear Rafal,

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

Re: instability type 3 RX direction

Rafal.Gaweda — Wed, 12 Nov 2014 09:44:59 GMT

Move node 88 onto 89