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Thermal Stress

Experimenter
Experimenter

Hi, I am a new femap user and passed several examples from the tutorial but still have some questions:

 

 - how can I hide some elements? For example I have a fem model of a valve, the results are loaded but I want to do a cross-section to see what is inside.... is there at all a possibility to hide particular elements?

 

- what do I wrong in this model setup?

I wanted to analyze a cylinder with inner and outer radius and lenght. At the outer surface there is 500 deg F, inner surface 300F, both roll stands are fixed. I perform the thermal analysis and obtain quite nice temperature field, then I map the temperature as nodal load for static analysis and during the calculation the model failes.... I have absolutely no idea what's wrong

 

thank you!

3 REPLIES

Re: Thermal Stress

Solution Partner Valued Contributor Solution Partner Valued Contributor
Solution Partner Valued Contributor

To look at cross section results, use F5 (View | Select) -> Section Cut.  Also use Deformed and Contour Data button on that dialog to define the cutting plane.  Other means of hiding / showing specific elements / parts / subassemblies is via Groups and / or layers.  But to look at cross section thermal results, then Section Cut is the best method.  For your thermal static stress problem, what is the FATAL errror message reported in the f06?  My guess is you have not got constraints selected, or they are insufficient (these would give FATAL 9137), or you do not have a reference temp defined on the material, or an expansion coefficient - these being needed to calculate the thermal strains.

Re: Thermal Stress

Experimenter
Experimenter

Thanks for answer.

 

What I do in my thermal stress is:

 

1) temperature loads in the pipe and outside the pipe + reference temp for the body

2) temperature field calculated properly

3) I give constraints: symmetry at the cut walls (I have modeled only the hald of pipe) + I take the axis translation to the side walls of pipe) and take thermal load from output

4) Static analysis shows error: 9137.

 

the same analysis in ansys is ok...

 

 

Another question: How can I applay a convection BC (with temperature) for an area of elements that are under one layer of elements (in the half of the pipe thickness). How can I hide external elements?

Re: Thermal Stress

Solution Partner Valued Contributor Solution Partner Valued Contributor
Solution Partner Valued Contributor

OK, so as a reseller of Femap with NX Nastran, I should say that your best option would be to get some training from someone experienced in Femap, because whatever you spend will be saved about 10 times over in time and money in not having to figure out stuff by yourself.

 

User Fatal 9137 definitely means you have insufficient constraints, or something is not connected.  Because the shape is so simple, then insuffcient global constraints is most likely.  Your image is too crowded to see what you have missed, but the most likely one is... what stops the entire thing floating in X?  If Ansys solved it, then either the model has different constraints in Ansys, or some fudged "bailout" or maybe even "inertia relief" option has been checked.  Either way, if the static constraints are insufficent then a fudge MUST have been applied (no exceptions, no matter what FEA) and you would want to understand what that fudge is.  Even if the model has no net forces in the X direction, some X constraint is compulsory in order to have a reference zero for the X displacements.  No X constraint, then the position from which X deformations are calculated is "guessed".

 

Anyway, I suggest if you want to understand more about the User Fatal 9137, we have authored a tech tip here:  

http://www.cadimageplm.com/learn/tech-tips

It's the one on Overcoming Model Singularities, and covers Fatal 9137.

 

If you want to peel off layers of elements, you need to use Groups or Layers.  A Group is simply a collection of rules that defines the Group, and can be as simple as a list of entities.  It could include, for example, a list of all elements, but excluding all elements connected to the outside surface (assuming you have geometry).  Or it can be a list of elements selected using Coordinate Picking (via your chosen cylindrical coord system) on the Entity Selection dialog.  Then via the Model Info Tree pane -> Groups, you can choose how you want to visualise the Group(s).