topic Re: wrong load on panel in Robot Structural Analysis Forum

wrong load on panel

RobertoPalladino — Mon, 13 Jun 2011 08:49:51 GMT

Hello,

I have a problem applying hydrostatic load on two manual meshed panels.....it is not the first time I have this problem.

Local axis for panel and f.e. are the same, not the load??!!!

Any advice??.....perhaps a bug to be solved for 2012 release??

Bye

Roberto

Re: wrong load on panel

Artur.Kosakowski — Mon, 13 Jun 2011 08:53:42 GMT

Roberto send me this model please.

Re: wrong load on panel

Artur.Kosakowski — Mon, 13 Jun 2011 09:52:52 GMT

Roberto,

I have used the Local (panel) system orientation dialog to set the right orientation of both local X (0,0,1) and Z axis for the vertical 'wall' of the structure to make sure the load is correctly applied.

Regards,

Re: wrong load on panel

RobertoPalladino — Mon, 13 Jun 2011 11:59:46 GMT

Artur,

many thanks for your reply.

You have to consider that me too have used the dialog set to orient the panel in direction 0,0,1 but sometimes, apparently without any reason, axis exchange their local direction with strange behaviour on hydro load (sometimes different behaviour before and after calculation)

The two added images are taken from your correct model......I think you can agree with me that it is a little strange.

Take in mind that with other more complex models (generated with copy and paste option from more Robot session at the same time) I had to fight a lot to have exactly the correct axis and load direction, and you well known the amount of hours I spent with Robot..... I'm sure you can understand that in my honest opinion this is a problem that need to be solved in the next version.

Bye

Roberto

Re: wrong load on panel

Artur.Kosakowski — Mon, 13 Jun 2011 12:12:44 GMT

Roberto,

There is nothing wrong with both displays you shown. You simply compare two set of information. If you display local axis of surface elements without displaying local axis of panels you see the directions of surface elements as generated during meshing (in such case the direction of the local X axes of a particular surface element is governed by order in which its nodes have been created). If you display both elements and panels local axis, the prior are shown in the way they are set for model calculations (direction of the local X axes of a panel is used to set the directions of each of element of the mesh generated for this panel). In fact display of local axis of surface elements only is of limited use for Robot users and they should display both attributes at the same time.

I hope this clarifies this issue.

Regards,

Re: wrong load on panel

RobertoPalladino — Mon, 13 Jun 2011 12:39:26 GMT

Artur,

ok for the clarification, but consider that even if I use the dialog set to re-orient the vertical part of the model according to 0,0,1 vector (for x axes, because z is ok) I have not the correct load direction for those two panel.....what exactly have you done (step by step) please??

Many thanks

Roberto

Re: wrong load on panel

Artur.Kosakowski — Mon, 13 Jun 2011 13:12:40 GMT

Roberto,

1. Select panels 1 and 2 (the ones with the opposite load directions)

2. Set their local X axis directions as 0,0,1

3. Select panels 1 and 2 again and run local mesh generation for these panels

4. Change load case selection from case 2 to case 1 and to case 2 again to refresh the display

In case you need further help with your case create a service request using the subscription site.

Regards,

Re: wrong load on panel

RobertoPalladino — Mon, 13 Jun 2011 13:50:54 GMT

Ok Artur,

many thanks

Bye

Roberto

Re: wrong load on panel

mgaafar — Thu, 31 May 2012 20:09:05 GMT

Hi I am having a very strange problem with load direction on panels using hydrostatic load(in MATERIAL UPSET load case, LC 9). the load is applied properly and is properly shown. after running it switched the direction if i press on the "show load value description". also I do not know why the local axis of the generated finite element is different than that of the panel, I think they should be the same.

attached are the files showing my problem..please help!!

Re: wrong load on panel

Pawel.Pulak — Fri, 01 Jun 2012 16:27:40 GMT

The reason of strange effects you observed was opposite local Z direction for panel 594 than for finite elements contained in it - see the screen capture below:

The source of it was in panel slightly non-planar (twisted). After correcting it and remeshing the panels local Z directions are coherent. The effect you observed concerning the display and application of hydrostatic loads is not observed too. Attached corrected model.

Regards,

Re: wrong load on panel

mgaafar — Fri, 01 Jun 2012 17:10:27 GMT

Thanks for the clarification Pawel, but should the load be reversed when the Z-axis of the panel is reversed? even if it is not planer? or the program does not understand that?

Also how to make sure that the panel is planer or how to fix that or check that?

Thanks

Re: wrong load on panel

Pawel.Pulak — Mon, 04 Jun 2012 08:33:18 GMT

After changing local Z of the panel the load will be reversed but for your original file the effect of opposite load direction with/without description will still be observed - because of no planarity of panel resulting in opposite Z for finite elements than for panel.

The sensitivity to such small planarity inaccuracies was reported to developement team to be analyzed and eliminated.

Planarity can be corrected:

1/ or correcting to plane from Edit>Detailed correct

2/ or extending the number of decimals and correcting coordinates of some points of contour

Regards,

Re: wrong load on panel

mgaafar — Mon, 04 Jun 2012 17:47:43 GMT

Thanks for the clarification Pawel!!

Re: wrong load on panel

Anonymous — Tue, 05 Jun 2012 01:55:24 GMT

or use Rafals' add in.....................

http://forums.autodesk.com/t5/Autodesk-Robot-Structural/Rounding-up-coordinates-API/m-p/3430533#M4399

Re: wrong load on panel

Pawel.Pulak — Tue, 05 Jun 2012 08:15:21 GMT

Tony,

kudos for adding this info 🙂

Using "rounding add-in" of Rafal results in bigger "curving" of panel instead of "flattening" it but it helps too.

The effect noticed by mgaafar can be observed for some range of panel unplanarity.

Regards,

Re: wrong load on panel

mgaafar — Tue, 05 Jun 2012 15:00:14 GMT

Since almost no one works with warped panels, I think there should be an option that checks all panels if they are planer or not and then fix the warped ones automatically instead of checking and fixing panel by panel.

Re: wrong load on panel

RobertoPalladino — Tue, 05 Jun 2012 19:04:01 GMT

Hi Pawel,

consider that I had this problem (you can see the first post) more than one time and apparently in a random manner applying hydrostatic load on curved shell.......sometimes is not possible to flatten a cylindrical tank!!!!

Bye

Roberto

Re: wrong load on panel

Pawel.Pulak — Wed, 06 Jun 2012 08:45:23 GMT

Hi Roberto,

I agree that it should not be necessary to eliminate any planarity inaccuracies - especially that sometimes (slightly twisted roofs, intersections of cylinders, etc) they cannot be avoided.

As I have mentioned in my previous answer:

"The sensitivity to such small planarity inaccuracies was reported to developement team to be analyzed and eliminated."

Regards,

Re: wrong load on panel

RobertoPalladino — Wed, 06 Jun 2012 12:03:58 GMT

Ok Pawel, many thanks.......we will wait for this correction

Bye

Roberto