Incoherent mesh on edges and distorted elements

[Anonymous]

Dear Sir,

I have been working on the attached model for more than two days trying to solve the problem I’m facing because of the “incoherent mesh on edges” message and “distorted element”. The attached model basically contains two parts. The first part (the one at the higher level), I have completed it first after spending some time on fixing the model because of the same message, however, finally it works after considering removing the meshes locally for many panels and generating them again. Second part including the tunnel, I have added it recently but I couldn’t solve the problem of getting the message “incoherent mesh on edges” and “distorted element”. I have read the other posts related to the same subject but without getting better result. I tried using iterative adjustment of FE mesh and kinematic constrains in incoherent points options, removing meshes locally and generating them again and sometimes I have removed some of the panels completely and drawn them again without luck of getting the problem solved. Please advise on the possible ways to solve this as I’m not able to continue with the work I’m doing.

Thanks and regards

Ahmed

[Rafacascudo]

Did you try watching the Robot official webinars (1 and 2) on 

Build your Robot Structural Analysis IQ - YouTube

All the problems you encountered in your model are very well explained there by Artur and Rafal ,on how to avoid them.

[Anonymous]

Dear Rafael,

Thanks for your response. I have seen part of the webinars, and I understand that the main reason behind getting such problem is the inaccuracy in drawing and assigning the panels, which I always consider when I do such modelling, e.g. when I draw a contour to which I will assign a plate element, I used to select the exact nodes which will be used as a geometry boundaries and I view them separately in different view and I make sure that the contour is exactly drawn using these nodes (no possible mistake to happen as the required nodes are the only ones in the view). However, following completing the model and meshing the panels I noticed that the software develops at some locations additional nodes which are very close to those defining contour boundaries. If I check the difference in length or in the coordinates, I always find them exactly the same (please refer to the image below). Following running the model, I get the errors I have mentioned. Generally, I’m aware of the requirement of accurately assigning the panels and this is what I always do.

Robot generates additional nodes other than those used for drawing the model. Those nodes are having the same coordinates.

In addition to the above, when getting the error of “distorted element” the software doesn’t tell which element in order to check it. Please refer to the image below.

Please advise on how I can solve this.

Regards

Ahmed

[Artur.Kosakowski]

Robot generates additional nodes other than those used for drawing the model. Those nodes are having the same coordinates.

This is the result of inaccurate definition of the panels which don't have 'exactly' the same common edges. 

In addition to the above, when getting the error of “distorted element” the software doesn’t tell which element in order to check it. Please refer to the image below.

The number displayed in the warning (15696) is the number of surface element with wrong geometry.

I'm attaching the model with corrected meshing but have a closer look at it as I might have overlooked some issues.

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.

[Rafacascudo · Accepted solution]

1 - Distorted element - select the error message and distorted element will be selected. It´s very small and hard to see. Then on display mark to show finite element number and to show atributes only to selected elements.

For a clearer view ,select the panel based on the finite element already selected and then open in another window

2- Node coordinates - increase the decimals and you will see ,they are not the same

3- Defining the contour snapping to created nodes is a good practice. I always do it myself. But if the panel is totally plane , you got to make sure that these created nodes lie on the exact same plane.

And this is what is happenning on your troubled panels and causing so many mesh problems.

Robot will try to mesh any panel . So if it is not a perfect plane ,it will create a slight curvature to make the best match it can imagine. Below ,the panel that contains nodes 8274 and 8019 , almost with same coordinates . One of them it´s your original node and the other the node created by robot trying to make the panel coherent.

You can see by its coordinates that the 4 panels charateristics points do not form a perfect plane.

Figure shows discrepances on the X coordinates , but also , Y and Z coordinates also have to equal in pairs.

Try to check the other troubled panels and you will surely notice the same problem occurs on them.

[Anonymous]

Dear Artur,

Thanks for your support. However, when I tried to run the file using “iterative adjustment of the FE mesh” I get a message saying “9727 – distorted element” and when I try to locate that element, I don’t get any member highlighted. When I try to use “kinematic constrains in incoherent points” I get a message saying “model error..”. And even when I don’t choose any of them, I get the same error message “9727 – distorted element”. I’m wondering if you have tried to run the model after verifying the meshes. Please note that I’m using Robot2014.

Regards

Ahmed

[Artur.Kosakowski · Accepted solution]

Solved by merging nodes. You can easily see what the issue is following Rafael's tip on the surface element selection. You may also consider blocking UX and UY in the supports (see the last Robot webinar ).

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.

[Anonymous]

Thank you very much for your support!

[Anonymous]

Thank you very much for your support!