Download - Ex 7 Tetra vs Hexa Meshing
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2-1
Exercise 7 Tetra versus Hexahedral Meshing
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UGS Corp. 2006. All rights reserved.Femap with NX Nastran 1-2
Exercise 7 Tet vs. Hex Meshing
In this example we will explore two mesh representations
of the same model
First build by tetrahedral and second by of hexahedral solid elements
We start with loads and constraints and solution of the tetrahedral model
Next we will delete the Tetrahedral mesh and mesh the part with
Hexahedral elements. Again we will solve the model in Nastran
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UGS Corp. 2006. All rights reserved.Femap with NX Nastran 1-3
Exercise 7 Tet vs. Hex Meshing
1. Import the Geometry
a) Select File, Import, Geometry and choose
the file Ch16hexmesh.x_t from Femap
training folder.
b) Accept or enter values in Solid Model Read
Options dialog box by clicking OK.
2. Rotate the view
a) Rotate the model into the position shown
here by clicking the left mouse button, and
holding it while dragging the mouse.
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UGS Corp. 2006. All rights reserved.Femap with NX Nastran 1-4
Exercise 7 Tet vs. Hex Meshing
3. Apply the Geometric Load
Select Model, Load, On Surface
Type in title for Load Set, e.g. Vertical load on boss and click OK
Preview Selection icon if needed to display the selected surface before OK
From list select Force and enter value 200 in FZ direction, then OK
Click Cancel to exit
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UGS Corp. 2006. All rights reserved.Femap with NX Nastran 1-5
Exercise 7 Tet vs. Hex Meshing
4. Create geometric constraints on
the inside of the bracket
a) Select the Model, Constraint, On
Surface
b) Enter a title for the Constraint Set,
press OK
c) Select three inside surfaces of the
bracket and confirm clicking OK.
d) Select Fixed constraint on the
geometry and press OK to create
the constraint.
e) Click Cancel to exit the command
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UGS Corp. 2006. All rights reserved.Femap with NX Nastran 1-6
Exercise 7 Tet vs. Hex Meshing
5. Create the Material
a) Select Model, Material
b) In the Define Material
press Load for the list of
materials in the material
library and elect 2024-
T351 Al Plate .25-.5
and press OK.
c) Femap displays values
of aluminum material
filled in. Press OK then
Cancel
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UGS Corp. 2006. All rights reserved.Femap with NX Nastran 1-7
Exercise 7 Tet vs. Hex Meshing
6. Create the Solid Property
a) Select Model, Property
and click on
Elem/Property Type then
select Solid. Press OK.
b) Property dialog box is
changed to Define
Property - Solid Element
Type.
c) Enter the title as Solid
Aluminum 2024-T351.
Set the material to 2024-
T351 Al Plate .25-.5.
d) Press OK and Cancel to
exit
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UGS Corp. 2006. All rights reserved.Femap with NX Nastran 1-8
Exercise 7 Tet vs. Hex Meshing
The meshing process generally consists of 2 steps
Establishing mesh sizing and control on the part, and
Meshing the part
7. Mesh the part with tetrahedral
elements
a) Select the Mesh, Mesh Control,
Size on Solid command
b) In Automatic Mesh Sizing box,
change Element Size to 2,
Minimum Elements on Edge to 2,
and Max Angle Tolerance to 15.
c) Uncheck Max Element on Small
Feature option.
d) Press OK to set mesh size.
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UGS Corp. 2006. All rights reserved.Femap with NX Nastran 1-9
Exercise 7 Tet vs. Hex Meshing
8. Mesh the part
a) Select the Mesh, Geometry,
Solids
b) In the Automesh Solids box,
set Tet Growth Ratio to 1.
This is recommended when
meshing thin-section parts
with solid elements.
c) Leave the option to create
Midside Nodes enabled (or
checked on).
d) Click OK to mesh the part.
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UGS Corp. 2006. All rights reserved.Femap with NX Nastran 1-10
Exercise 7 Tet vs. Hex Meshing
9. Use Analysis Set Manager
to generate an analysis
solution
a) Select Model, Analysis
b) Click on New to create
analysis set.
c) Enter Title, select
31..NEiNastran for the
solver, and 1..Static for
analysis type.
d) Click OK to create the
Analysis Set.
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UGS Corp. 2006. All rights reserved.Femap with NX Nastran 1-11
Exercise 7 Tet vs. Hex Meshing
10.Run Analysis
a) Click Analyze button, save Nastran file and press F5 in NEiNastran Editor
11.Close Editor when NEiNastran has finished
12.Display the Von Mises stress contour on the deformed shape
a) Select View, Select (F5)
b) Select Deform for Deformed Style and
Contour for Contoured Style and click
on Deformed and Contour Options.
c) Select Total Translation for deformation
and Solid Von Mises vector for contour
d) Save the model as tetmesh.mod, for
later comparison
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UGS Corp. 2006. All rights reserved.Femap with NX Nastran 1-12
Exercise 7 Tet vs. Hex Meshing
13.Prepare the model for remeshing with hex elements
a) Save the model file as hexmesh.mod.
b) Turn off the contour and deformed displays using the Post toolbar
c) Delete the mesh using Delete, Model, Mesh, select All, then press OK
d) Choose NO so that created properties and materials remain in the model
14. Rebuild and compact the model which will also reset the entity counters
a) Select the File, Rebuild command.
b) Select Yes to compact the Femap database.
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UGS Corp. 2006. All rights reserved.Femap with NX Nastran 1-13
Exercise 7 Tet vs. Hex Meshing
15.Subdivide the solid into ten
independent solids to aid in meshing
a) Run Geometry, Solid, Embed Face
b) Pick surface A and select Automatic
as the embed option, and press OK.
c) Repeat this for surfaces B and C.
d) For B, select the All Curves button.
A
B
C
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UGS Corp. 2006. All rights reserved.Femap with NX Nastran 1-14
Exercise 7 Tet vs. Hex Meshing
16.Continue to subdivide the solid
a) Select the Geometry, Solid, Slice
b) Select solids 5 and 6, then OK
c) Use right-mouse click and select Snap to Point, select Points A, B, and C to define the cutting plane and OK to slice the parts
d) Repeat Geometry, Solid, Slice and select both halves of solids 5 and 7
e) In Plane Locate Specify Plane for click on Methods, and select Global Plane as the cutting method, the YZ plane as the cutting plane, and point B as the base for the plane.
f) Press OK to slice the solid.
ABC
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UGS Corp. 2006. All rights reserved.Femap with NX Nastran 1-15
Exercise 7 Tet vs. Hex Meshing
17.Check to see that you sliced your part into the proper sub-solids
In Model Info use the command Transparent Highlight to display and
explore each solid which will highlight to see the separate solids
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UGS Corp. 2006. All rights reserved.Femap with NX Nastran 1-16
Exercise 7 Tet vs. Hex Meshing
18. Hex mesh the model
a) Select the menu command
Mesh, Mesh Control, Size on
Solid. Select All solids and
press OK.
b) In the Automatic Mesh Sizing
box select Hex Meshing, set
Min Elements on Edge to 2.
c) Deselect both Max Angle
Tolerance and Max Elem on
Small Feature options.
d) Press OK to set the mesh size
on the parts.
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UGS Corp. 2006. All rights reserved.Femap with NX Nastran 1-17
Exercise 7 Tet vs. Hex Meshing
19.The model is ready to mesh
a) Select the command Mesh, Geometry, Hex Mesh Solids.
b) Select All, and press OK.
c) We will use the default hex meshing options, so press OK to hex mesh
the part.
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UGS Corp. 2006. All rights reserved.Femap with NX Nastran 1-18
Exercise 7 Tet vs. Hex Meshing
20.Two of sub-solids need to be
mapped meshed
The default free mesher will always use a
combination of triangles and quads on any
surface that is not a simple 4-sided region.
To force Femap to map mesh surfaces that
are not 4-sided, you will use the Mesh,
Mesh Control, Approach on Surface
command.
a) Delete the previous hex mesh using
Delete, Model, Mesh
b) Select All elements
c) Press No when prompted to delete
unused properties and materials.
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UGS Corp. 2006. All rights reserved.Femap with NX Nastran 1-19
Exercise 7 Tet vs. Hex Meshing
21. Specify the Mesh Approach
a) Select Mesh, Mesh Control,
Approach on Surface command
b) Pick surface A then, select for
Mesher Mapped, Four Corner
option
c) Since the surface has more than
four corners, Femap will
automatically detect corners to map
between. Press OK.
d) The command will automatically
repeat. Perform the same
procedure for surface B
A
B
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UGS Corp. 2006. All rights reserved.Femap with NX Nastran 1-20
Exercise 7 Tet vs. Hex Meshing
22. Continue to specify the Mesh Approach
e) Mesh Approach command continues to automatically repeat
f) Perform the same process for both surfaces C and D
C
D
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UGS Corp. 2006. All rights reserved.Femap with NX Nastran 1-21
23. Hex Mesh the Solid
a) Set the mesh size with the Mesh, Mesh Control, Size on Solid command.
Select All of the solids. Set the Size for to Hex Meshing, Element Size to 3,
Min Elements on Edge to 3 and Max Angle Tolerance to 15. Deselect the
Max Elem on Small Feature option.
b) Select the Mesh, Geometry, Hexmesh Solids command, Select All of the
solids, and mesh with the default options.
Exercise 7 Tet vs. Hex Meshing
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UGS Corp. 2006. All rights reserved.Femap with NX Nastran 1-22
24. Solve the model and compare Solid Von Mises Stress contour
for hex meshed model with that obtained from the tet meshed
model you analyzed earlier
25. Perform the following below before analyzing the model
a) Because slicing of the solids for hex meshing caused the geometry
ID numbers to change, you cannot use the old load and constraint
sets for this model.
b) Delete the old load and constraint sets
c) Re-create them with the same load values and constraint
configurations
Exercise 7 Tet vs. Hex Meshing
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UGS Corp. 2006. All rights reserved.Femap with NX Nastran 1-23
Comparison of the Solid Von Mises
stresses for hex meshed model with
that obtained from the tet meshed
model you analyzed earlier in the
exercise
Hex meshed model statistics
Nodes: 5568
Hex Solid Elements: 3942
Tet meshed model statistics
Nodes: 34307
Tet Solid Elements: 19756
Exercise 7 Tet vs. Hex Meshing