Nastran 2020 Editor showing inconsistent post processing data

[Anonymous]

Hello,

I built a Nastran model, where I applied a force on a external Node, which is connected to the structure by a stiff connector.

For postprocessing I need to know the displacement of the external node.

With the Inventor Add-In I can't probe the external node directly.

In Addition the connectors don't get distorted in distorted display.

Hence, I'm viewing the results in the Autodesk Nastran Editor.

When probing the external node two different values are shown (see attached screenshot).

What's the difference between the two values?

And which one is correct if I need to know the total vectorial displacement?

Thanks for your help.

Greetings

Sven

[Roelof.Feijen]

Hello @Anonymous ,

The first total translation is related to the node. The sum of T1, T2 and T3.

The second total translation is related to the complete model (see the yellow arrow)

[Anonymous]

Thanks for your reply.

Can you explain in detail, what's the different beween the two values?

When I use another postprocessor (HyperView) the total displacement of the external node is 0.2599 (like the second value).

Thus, I think the second value is the correct value I was looking for.

You wrote:

'The first total translation is related to the node. The sum of T1, T2 and T3.'

But what values are T1, T2, T3?

If I compare T1, T2 and T3 with the values of the x-, y- and z-Translation, those are not equal.

To which Node do T1, T2 and T3 relate?

[Roelof.Feijen]

I haven't got much experience with the Nastran Editor, but I would expect T1, T2 and T3 would be x,y and z.

Can you share your .nas file? 

[Anonymous]

Sorry but I'm not allowed to share the model.

In my opinion it's a little bit confusing to show values with the same name on a single probe.

I took a look in the Editor user manuel and found nothing.

Furthermore, I run an example model coming with Autodesk Nastran (tank.nas).

When I probe the results, the first and second value for total displacement are the same (see attached screenshot).

Maybe it's a bug in the Nastran Editor, which appears when using connectors for offset loads and boundaries?

[delaroca]

That is weird...

By the first image I would assume the first "TOTAL TRANSLATION" (TT) would be the probed translation (with TT=sqrt(T1²+T2²+T3²) and I assume 1, 2 and 3 represent the X, Y and Z directions unless maybe you are using another type of coord. system - spherical or cylindrical?) and the second TT indicating the maximum value of the model.

But in the second image both TTs indicate the probed value, ignoring the max value displayed at the bottom left.

Well, in any case I would trust the first TT value as being the probed value, ignoring the second one.

[John_Holtz]

This is strange.

The last line in the probe is always the result for the contour type selected, such as this:

Deformed shape is off

When the deformed shape is shown, then the probe includes the displacements too. So in my case, it adds the displacements (total, T1, T2, T3) and the selected contour (X -rotation), and there is no duplication. In your case, you happen to be showing the same result as added when showing the deformed shape, so it looks odd.

Deformed shape is on

I agree that the 0.25 total displacement is correct for that node in your model. What I cannot explain is why the displacements shown when the deformed shape is on are wrong in your model!

1. What is the input for your rigid connector?
2. What other input do you have that might be different from any other model? (Parameters? Loads?)
3. Did you change any settings in the Editor that might be scaling the deformed displacement results?

[John_Holtz]

I wanted to follow-up with some background information for other readers who may be interested in getting the displacement and/or rotation results at the "center point" of a rigid body.

• If using Nastran In-CAD or Inventor Nastran, you can create an XY Plot and graph the results at the center point of a rigid connector! (I just thought of this and confirmed that it is possible.)
• If you want to use the Nastran Editor and the probe, here are the basic steps.
  • Start the Nastran Editor Utility.
  • Open the .nas file.
  • Click the "Model/Results" tab.
  • Right-click in the graphics window and choose "Load Results".
  • Then using this image,

1.  Select the result that you want to view in the model tree, right-click, and choose "Contour".
2. To probe the results, click in the graphics and then click the "Toggle query display" button in the toolbar.
3. To probe on nodes, select Nodes from the list. 
4. When you place the mouse over a node,
5. the result is shown in a tooltip.