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Alice

ERRORS ON RIGID BODY FORMULATION

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Hy all, 

 

I am trying to make my own study on a cantilever beam (implicit option) in order to master the basics of Radioss, and I take as an example the example 37_cantilever_beam. 

 

Though, I get 2 errors in the starter coming from the rigid body:

 

-------------------------------------------------------------------------

in the rigid body definition

ERROR ID :           55
** ERROR IN INPUT FORMAT
DESCRIPTION :  
   -- OPTION : RBODY
   -- BLOCK : /RBODY/301
   -- LINE : /BEGIN

------------------------------------------------------------------------

in the rigid body initialization

ERROR ID :          274
** ERROR IN RIGID BODY DEFINITION (INERTIA)
DESCRIPTION :  
   -- RIGID BODY ID : 301
   -- RIGID BODY TITLE : FREE_EDGE
   RIGID BODY HAS A NULL OR NEGATIVE INERTIA

----------------------------------------------------------------------

 

I don't understand the first error at all, having compared my starter with the example.

Concerning the second error, I indeed input "0" for each inertia parameter, but this is also the case in the example.

 

What do I do wrong ? Find attached my starter file.

 

Thanks in advance,

 

Alice

pression_statique_02_0000.rad

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Hi George,

 

Thanks for your help. Can you explain me what the problem was and what you changed in the file ? 

 

The starter works, printing 2 warnings : they concern the master node, which is also a slave node. Does this lead to computation errors ? 

 

Indeed I have an error during computation :  ** ERROR : RADIOSS IMPLICIT STOPPED DUE TO LOADING DATA **

What does this mean ? 

 

Thanks in advance,

Alice

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Hi Alice,

 

Below are the suggested workarounds for the error:

1.Check loading in the model.

2.Increase the initial time step.

3.Creating a slight contact penetration in cases where loading is due to contact.

The standard formulation for rigid bodies will not work if a master node of a rigid body appears as a slave node of another rigid body. It can provide bad energy balance during the run.

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So how do I to apply a concentrated load on the end of a beam, which meshing is as in the attached file ? I want all the 25 nodes to be part of the rigid body. Of course the node 1044 in the center is the center of mass and is the master node of the rigid body. Am I right ? 

 

 

2017-01-09_14h39_48.png

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Hi again,

 

So I changed the grnod for the rigid body, removing the 1044 master node. 

And what you changed in my file and what makes it work is the option #Ioptoff. I would have appreciated to know this immediately to save some time. Anyway, thank you for the working file, and thanks for your explanation on rigid bodies. 

 

I am now struggling with a new problem : 

I first applied a concentrated load of 50N/25nodes on each node of the free edge. I then wanted to find the exact same results by applying 50 N with the corresponding rigid body. 

However, I do not obtain the same results as you can see in the attached screenshots (scaled a lot as to see the bending). Do you understand how this can happen ? 

 

Thank you in advance,

Alice

dispY_CLOAD_on_RB.png

dispY_CLOAD_on_nodes.png

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Hi Alice,

When you apply /CLOAD to the nodal group the force is applied to each node individually, so:total force = F(t) * number of nodes. So, when you apply to the master node of the rigid body, apply the total force to the master node. (Suppose, 100N to 25 nodes, then apply 2500N to the master node of the rigid body which has 25 dependent slave nodes)

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