Step 1. Create a New Database
Create a new database called
mesh_on_mesh.db and set the new model preferences.
a. Click on the File New icon.
b. Enter mesh_on_mesh for the file name and click OK.
c. Select the Based on Model toggle under Tolerance.
d. Make sure that the Analysis Code and Analysis Type are set to MSC.Nastran and Structural, respectively.
e. Click OK.
b
c
d
e
Step 2. Import MSC.Patran neutral file
Import the MSC.Patran neutral file called non_cong_surfs.out.
a. File/Import
b. Change Source: to
Neutral and select the file, non_cong_surfs.out.
c. Click Apply.
d. Click Yes for both messages that appear.
e. Click the Front view icon.
Step 2. Import MSC.Patran neutral file (Cont.)
Shown below is the model geometry
Step 3. Create 2D Tri Element Meshes
A single 2D congruent mesh that is coincident the surfaces is needed. First, IsoMesh all the surfaces using tri3 elements.
a. Elements : Create / Mesh / Surface.
b. Set Elem. Shape,
Mesher, and Topology to Tria, IsoMesh, and Tria3, respectively.
c. Under Surface List
select the entire model by dragging a box around it.
d. Remove check from Automatic Calculation, and enter 5.0 for
Global Edge Length.
e. Click Apply.
Step 4. Sew the Elements
Equivalence and create tri elements by sewing the mesh.
a. Elements : Modify / Mesh / Sew.
b. Enter 5.0 for the Target Element Edge Length.
c. Under Tria Element List select the entire model by dragging a box around it, and click Apply.
a
b
c
Step 4. Sew the Elements (Cont.)
Check the free edges of the model to see if the sewing technique worked.
a. Elements : Verify / Element / Boundaries.
b. Set the Display Type to Free Edges.
c. Click Apply.
d. Click the Reset Graphics button.
a
b
c
d
Step 5. Re-sew the Elements
Undo and repeat the sew command, using a different Target Element Edge Length.
a. Click on the Undo icon.
b. Elements : Modify / Mesh Sew.
c. Enter 20.0 for the Target Element Edge Length.
d. Under Tria Element List select the entire model.
e. Click Apply.
b c d
e
Step 5. Re-sew the Elements (Cont.)
Check the free edges of the model to see if the sewing technique worked.
a. Elements : Verify / Element / Boundaries.
b. Set the Display Type to Free Edges.
c. Click Apply.
d. Click on the Reset Graphics button.
There are no element free edges internal to the mesh.
This tri mesh is not
acceptable for performing a finite element analysis.
However, it is acceptable for using the MSC.Patran Mesh/On Mesh capability to create a mesh that can be used to perform an
analysis.
a
b
c
d
Step 6. Create a Mesh Using the Mesh/On Mesh Tool
Use the Mesh/On Mesh tool to create a mesh that can be used for an
analysis.
a. Elements: Create/Mesh/
On Mesh.
b. Select the checkbox for Delete Elements.
c. Under 2D Elem List select the entire model.
d. Enter 5 for Global Edge Length.
e. Click Apply.
f. Click on the Plot/Erase icon.
g. Click on Erase under Geometry.
h. Click on the Smooth Shaded icon.
a
d
g
c
This mesh is too coarse.
Therefore, it will be necessary to undo the previous step, and run the Mesh/On Mesh application again, this time with a smaller element size.
Step 6. Create a Mesh Using the Mesh/On Mesh Tool (Cont.)
Step 7. Create Another Mesh With the Mesh/On Mesh Tool
Undo the previous Mesh/On Mesh creation, and create a new one with a smaller element size.
a. Click on the Undo icon.
b. Elements: Create/Mesh/
On Mesh
c. Make sure the Delete Elements toggle is on.
d. Under 2D Elem List select the entire model.
d. Enter 2.5 under Global Edge Length.
f. Click Apply.
Although this mesh is much finer it still does not follow the original model geometry closely enough. It will be necessary to do another Mesh/On Mesh operation, with a slightly smaller element size and with control using 1D elements on some of the surface edges.
The control on the edges is achieved by using 1D Bar2
elements shown in the following step.
Step 7. Create Another Mesh With the Mesh/On Mesh Tool (Cont.)
Step 8. Mesh Surface Edges With Bar2 Elements
Undo the mesh created by the Mesh/
On Mesh application, and re-mesh using select edges with Bar2 elements.
a. Click on the Undo icon.
b. Click on the Plot/Erase icon.
c. Click on Erase under FEM.
d. Click on OK.
e. Elements: Create/Mesh/
Curve.
f. Change the Topology to Bar2.
g. Under Curve List select the indicated curves(shown on next page)
g. Remove the check for Automatic Calculation and enter 2.0 for Global Edge Length.
i. Click Apply.
Illustrated here are the surface edges that are to be meshed with Bar2
elements. There are 26 edges. On the left the red arrows point to 8 of the edges. Below 18 of the edges are highlighted in orange.
Step 8. Mesh Surface Edges With Bar2 Elements (Cont.)
The Bar2 elements are shown in yellow
Step 8. Mesh Surface Edges With Bar2 Elements (Cont.)
Step 9. Create the Final Mesh
Use the Mesh/On Mesh application to create a final mesh that should
follow the geometry.
a. Elements: Create/Mesh/On Mesh.
b. Make sure the Delete Elements toggle is on.
c. Click Feature Selection
d. Under Soft Bars select all the 1D bar elements.
e. OK
f. Under 2D Elem List select the entire model.
g. Enter 2.0 for Global Edge Length.
h. Click on Apply.
i. Click on the Plot/Erase icon.
j. Click on Erase under Geometry.
k. Click on the Smooth Shaded icon.
Step 9. Create the Final Mesh (Cont.)
Illustrated here is the final mesh created by the Mesh/On Mesh application.
Observe how the mesh follows the model geometry far better than for the previous meshes.