Element type & attributes

[neema1984]

Hey,

I am making some surfaces from points > curves and then surface by taking {edge curve}. Whenever I try to assign any property it goes to solid element. I am creating surfaces and I do not know why it is going in solids. Any recommendation or suggessions ? ....

Thanks

 

[rb1957]

if you've got 2D surfaces ... you should get 2D elements (as you're expecting)

maybe look into the mesh menu, maybe your default is 3D elements ??

 

[trainguy]

Make sure you have a shell type property generated and have it be the active property before assigning mesh attributes to the created surfaces.

tg

 

[neema1984]

Thanks trainguy,

I created a shell type property by MODEL > PROPERTY > ELEM/PRPT >> PLATE/AXISYMMETRIC SHELL < and chose a thickness for the shell. then activated the property and getting same problem while assigning attributes by clicking

GEOMETRY < right click > > ATTRIBUTES > .. PLATE/SHELL

any further comments ? ... though I can do it from mesh menu correctly by assigning mesh attributes on the surface.

 

[BlasMolero]

Dear neema1984,
Please explain why you select "axisymmetric shell" option, choosing this option means you will mesh a line with 1-D elements representing an axisymmetric conical shell of revolution, then this is why FEMAP ask you for the thickness of the conical shell. This meshing approach is valid for conical shells with small thickness, and also the problem will need to be fully axisymmetric geometry, loads & BCs.

If you want to mesh with 2D elements an axisymmetric thick 3D solid of revolution problem meshing in detail the 2D thickness of the model wall, then in fact, you can create the surface in the plane Z-X and mesh with 2D Shell elements. In this case, you will have to select "Model > Property > Elem/Prop Type > Volume Elements > Axisymmetric".
In fact, in FEMAP & NX NASTRAN you have axisymmetric 2D solid of revolution elements CTRAX3, CQUADX4, CTRAX6, CQUADX8, CTRIAX6, CTRIAX, and CQUADX to define a solid ring by sweeping a surface defined on a plane through a circular arc. Loads are constant with azimuth for these elements; that is, only the zeroth harmonic is considered. There may be innovative modeling techniques that allow coupling this class of axisymmetric element with other elements, but there are no features to provide correct automatic coupling.

Please note that these axisymmetric elements are defined in the X-Z basic coordinate system, and are supported in solutions 101, 103, 105, 106 (hyperelastic), 107, 108, 109, 110, 111, 112, 153, 159 and 601.

Assumptions:
===========
• The Z axis of the basic coordinate system is the axis of symmetry.
• The X axis of the basic coordinate system is the radial direction.
• All grids must lie in the X-Z plane of the basic coordinate system.
• All loads must be in the X-Z plane.
• XY and YZ shear stresses and strains are zero.
• Gravity vectors must be parallel to the axis of symmetry.
• All angular velocity vectors must lie on the axis of symmetry.
• Grid points G1 through G8 must be numbered as shown below (midside grids on the CTRAX6 and CQUADX8 cannot be eliminated).

Loads
======
• A concentrated load (e.g., FORCE entry) at Gi is divided by the radius to Gi and then applied as a force per unit circumferential length.
• Pressures can be applied using the PLOADX1 bulk data entry.
• Gravity vectors must be parallel to the axis of symmetry.

Grid Point DOF
===============
• Three translational degrees of freedom are assigned to each grid. Translations are in the directions of the nodal displacement coordinate system X and Z axes and have the dimensions of length. The Y direction DOF must be restraint by specifying an SPC, or PARAM,AUTOSPC,YES.

Output
=======
• Displacements
• Stress
• Strain
• Reaction Forces
• Elastic Strain Energy (per radian)

I hope the above serves to understand the 2D Axisymmetric elements of FEMAP & NX Nastran. In fact, I agree the clasification in FEMAP is not very affortunate including a 2D axisymmetric element under Volume clasification, is correct in the sense that we are representing a full 3D problem meshing with 2D elements, but the topology of the elements are surface elements, is simply a question of terminology, I will move "Axisymmetric Shell" to 1-D elements and "Axisymmetric solid of revolution" to 2-D elements, is simply a question to understand the meaning of each element.
Best regards,
Blas.