Learning Forum

[Ethan Perez]

I am running into an issue meshing a line using LMESH with TARGE170 elements.

The line is imported from a Parasolid file and happens to be a circular arc in three dimensional space. Upon running LMESH with this line selected, the application displays an error message which reads "The definition implied by the TSHAP command is improper for element 1. Please check the TSHAP command." It seems this occurs because LMESH automatically sets TSHAP and TARGE170 elements do not have ARC or CARC as an option. LMESH does successfully complete with TARGE169 elements but this causes the elements to be generated on the X-Y plane, which is unacceptable. I have also tried splitting the line with LDIV but it seems each individual segment is also an arc and fails with LMESH. My desired result would be for LMESH to generate LINE or PARA shaped TARGE170 elements with the ability to use LESIZE to split the line into N segments. Is this possible? Are there any APDL commands which approximate the arc as a bspline?

[Rahul Kumbhar]

Hi Ethan,

 

Can you give more clarification or APDL commands which you used? Why do you need TARGET170 element on the line? is it in contact with other 1d elements? Normally first you should generate mesh on line (probably beams?) and then define contacts.

[Ethan Perez]

Hi Rahul,

Thank you for your response. I am working on a model with rigid bodies and encountered this error as I was developing an early demo version using simplified geometry. My intent was to create a rigid body with MASS21 and TARGE170 elements. The TARGE170 elements were intended to form the outline of the rigid body mainly for visual purposes but could also be used for applying load conditions (in addition to a TARGE170 element for the pilot node). I am open to other suggestions but I have gotten something similar to work with straight lines and splines. It was also unexpected that LMESH can only produce a single TARGE169 element with TSHAP,ARC and could not automatically discretize the arc into smaller pieces using LINE or PARA shaped TARGE170 elements.

Below is a minimum working example which reproduces the issue. Here though I am creating a line using LARC instead of importing from Parasolid. The example can be run without an error message if the element is changed to TARGE169 but then the element is projected to the X-Y plane.

FINISH
/CLEAR

/PREP7

K,1,-0.5,0.5,0.1
K,2,0.5,0.5,0.1
K,3,0,0,0
LARC,1,2,3,1

ET,1,TARGE170
ALLSEL
LATT,,,1
LMESH,ALL

[Rahul Kumbhar]

Hi Ethan,

This doesn't seem right appraoch. But if you still want to use, you can try generating mesh200 elements first and then convert them into Target170.

[Ethan Perez]

Hi Rahul,

Thank you very much for your suggestion. I was unaware of MESH200 elements and had not considered changing element types. I was able to get the arc meshed with LMESH by converting MESH200 elements with keyopt(1)=2 into TARGE170 elements with shape LINE. Unexpectedly, the elements were converted into TARGE170 elements with shape TRIA when using MESH200 with keyopt(1)=3. I had expected this would result in TARGE170 elements with shape PARA. I am using EMODIF to convert the element type and it appears to control the shape automatically and ignores TSHAP. Thus, this method seems solve the issue for obtaining LINE shaped elements but not PARA.

I am interested in your view on the approach. Can you share any other ideas you may have for a different approach?