How to analyse a hyperbolic paraboloid panel in Robot?

[xu.marc7]

Hello,

I want to analyse a hyperbolic paraboloid panel in Robot, I've created it in Rhino and imported in Robot to a panel element, but I can't successfully caculate it, two main problems:

1 I can't give a surface load on the panel.

2 I can't well mesh it cause there's always some parts that couldn't be meshed

When I assign a surface load to the panel or do the caculation, there's always an error saying "twisty element!"

Could anyone please help with that, thanks!

[Rafal.Gaweda]

Try this addin:
http://forums.autodesk.com/t5/Robot-Structural-Analysis/API-objects-geometry-to-triangles-converter/...

[xu.marc7]

Hi,

Thank you so much for your answer, I've tried your addin but it seems not very adaptive to my problem, the converter changed my HP surface (see original panel) into two groups of perpendicular triangles (see converted panel) which is a little far from what I want. By the way when I mesh these triangles there's problems at the boundry of panels for which I don't know why, how do you choose mesh method for this kind of configuration?

However, I seem to be able to caculate directly with HP panel, in fact what I want to do is to add a HP panel into a spatial truss formed by bars to optimise its rigidity, I've made a test with the file attached, but I just added 9 bars to form a truss with the 3 perpendicular sides of th HP panel, warning for caculation is instablity type 3 for element 11(HP panel), and the results seem to be unreliable. So question is: how they're connected with each others, the panel and the bars, are they working together or not? And how to get rid of the warning?

Thanks a lot!

[Rafal.Gaweda · Accepted solution]

PLease check model size \ units - 2mm edge cube?

Meshing option for your model

[xu.marc7]

Hi Rafal Thank you so much for your answer. Now I got the result, question is, I know that in the Detail tab of result for Maps(panel), the Sxx, Syy Sxy are stresses in local coordinate system, but does my HP panel have only one local coordinate system (what I can make visible/invisible in the view) or each segment of the mesh has one local coordinate system, how can I know the direction of X and Y axes at any point of the panel, please? While in Principal tab, the S11 S22 S12 are stresses in main coordinate system, does this mean the global coordinate system? If so, this tab is not useful at all for a curved surface panel, no? Thanks!

[Rafal.Gaweda]

Hi Rafal Thank you so much for your answer. Now I got the result, question is, I know that in the Detail tab of result for Maps(panel), the Sxx, Syy Sxy are stresses in local coordinate system, but does my HP panel have only one local coordinate system (what I can make visible/invisible in the view) or each segment of the mesh has one local coordinate system, how can I know the direction of X and Y axes at any point of the panel, please?

Results of each FE are projected to direction set on Detailed tab. In case of Automatic direction - projected to LCS os panel. If you have angle between Fe direction X and DIrection set for results display  = 90deg you will get result =0 on display.

While in Principal tab, the S11 S22 S12 are stresses in main coordinate system, does this mean the global coordinate system? If so, this tab is not useful at all for a curved surface panel, no? Thanks!

---

http://docs.autodesk.com/RSAPRO/2014/ENU/filesROBOT/GUID-BD23B817-BEE0-4DB2-97AF-2571B877F803.htm

Principal stresses do not depend on direction settings. Only angle is caculated with relation to Direction set on Detailed tab. 

[xu.marc7]

Hi Rafal, 

Is that possbile to import in Robot the bars and the panels at the same time? To creat my structure, I know to import a surface by .sat, but then I need to draw the lines to make bars myself?

I'm going to do a calculation of a configuration with dozens of identical blocks which we have been talking about, if I can't import the model directly, I can only do copy, repeat mirror etc. from one block in Robot, but these operations always creat  unnecessary nodes at the same point which are almost unavoidables. I think this cause problems in the results, like the image attached, I got two displacement at the same points, is this normal?

Furhter more, are the panels and the bars hinged or fixed as default? How can I change this boundry condition?  

Thank you very much!

[Rafal.Gaweda]

Is that possbile to import in Robot the bars and the panels at the same time? To creat my structure, I know to import a surface by .sat, but then I need to draw the lines to make bars myself?

I think so.

I'm going to do a calculation of a configuration with dozens of identical blocks which we have been talking about, if I can't import the model directly, I can only do copy, repeat mirror etc. from one block in Robot, but these operations always creat  unnecessary nodes at the same point which are almost unavoidables. I think this cause problems in the results, like the image attached, I got two displacement at the same points, is this normal?

File please.

Furhter more, are the panels and the bars hinged or fixed as default?

Fixed.

How can I change this boundry condition?  

Apply releases.

[xu.marc7]

Hi, Here attached the files, the original block and the configuration with 36 blocks in which it appears the unnecessary nodes at the same point, the image show the two values of displacement at one point. Thanks a lot!

[Rafal.Gaweda]

No files.

[Artur.Kosakowski]

Make sure you created the correct model.

If you find your post answered press the Accept as Solution button please. This will help other users to find solutions much faster. Thank you.

[xu.marc7]

What do you mean by creating the correct model?

[Artur.Kosakowski]

With nodes of the meshes being at the locations of the bars.

[xu.marc7]

Hi!

Thank you so much for the model!

In the conception, we are to restrain the shell by the bars all along, is the shell fixed along the bar or is it just connected at the two ends of the bar by default?

Do the nodes created by the mesh as you mentioned cut the bars? What's the result of it, and how could I avoid to do so while meshing the shells, please?

[Artur.Kosakowski]

In the conception, we are to restrain the shell by the bars all along, is the shell fixed along the bar or is it just connected at the two ends of the bar by default?

By default a node generated on a bar is a common node for both a bar and a panel (this is the connection).

Do the nodes created by the mesh as you mentioned cut the bars?

Yes, they divide bars into calculation elements

What's the result of it, and how could I avoid to do so while meshing the shells, please?

 I'm not sure what is the situation you want to avoid - having the panel connected to the bar along its entire edge?

[xu.marc7]

In fact I want to have the panel connected to the bar along its entire edge, and to be fixed on it, not articulated. Is this feasible?

[Artur.Kosakowski]

This is the default behavior. You can use the 'corrected' model as it is.

[xu.marc7]

Hello!

Always the same subject, in the calculation of my model, there is alwyas at certains nodes the type 1 instability of RZ, and to see from the displacement diagram, it seems that the truss is not well restained and I don't know why.

Could you please check this? Attached the model.

Thank you!