Advanced MSC.patran Exercises

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Advanced MSC.Patran

PAT302 Workbook

June 2003

MSC.Software Corporation

United States MSC.Patran Support Tel: 1-800-732-7284 Fax: 714-979-2990 Tokyo, Japan Tel: 81-3-3505-0266 Fax: 81-3-3505-0914 Munich, Germany Tel: (+49)-89-43 19 87 0 Fax: (+49)-89-43 61 716 2 MacArthur Place Santa Ana, CA 92707, USA

Tel: (714) 540-8900 Fax: (714) 784-4056 Web: http://www.mscsoftware.com

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DISCLAIMER

MSC.Software Corporation reserves the right to make changes in specifications and other information contained in this document without prior notice.

The concepts, methods, and examples presented in this text are for illustrative and educational purposes only, and are not intended to be exhaustive or to apply to any particular engineering problem or design. MSC.Software Corporation assumes no liability or responsibility to any person or company for direct or indirect damages resulting from the use of any

information contained herein.

This notice shall be marked on any reproduction of this documentation, in whole or in part. Any reproduction or distribution of this document, in whole or in part, without the prior written consent of MSC.Software Corporation is prohibited.

MSC and MSC. are registered trademarks and service marks of MSC.Software Corporation. NASTRAN is a registered trademark of the National Aeronautics and Space Administration. MSC.Nastran is an enhanced proprietary version developed and maintained by MSC.Software Corporation. MSC.Patran is a trademark of MSC.Software Corporation. All other trademarks are the property of their respective owners.

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WORKSHOP 1

SURFACE EDIT, THEN MESH

COMPUTER PANEL

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SURFACE MODELING OF

COMPUTER PANEL

Problem Description

An instrument panel design was modified in a Case Study shown in

Section 3. For this workshop add fillets to the corners of a surface for a

computer panel, remove the small tooling holes, and reduce the

size of the two openings on the right side of the panel for the

speaker plugs.

Create nodes and elements by meshing.

The geometry of the computer panel is shown on the following

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260 mm

50 m

m

outer corners

tooling holes

(eight total)

replace

outer corners

SURFACE MODELING OF

COMPUTER PANEL

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General outline of the steps to be performed

Import the STEP AP203 file computer_panel.step containing the

surface to be modified

Follow the steps outlined in the case study Instrument Panel to

create the fillets at the four outer corners of the panel, using fillet

radius 4 mm

Remove the small tooling holes that are in the middle of the panel

(8 holes)

Remove the two circular openings on the right side of the panel and

add new ones with a radius of 2 mm

Mesh the part with the Paver mesher using Quad4 elements and an

appropriate global edge length

Evaluate the quality of the mesh

SURFACE MODELING OF

COMPUTER PANEL

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After importing the solid, create the corner fillets

Geometry: Edit/Surface/Add Fillet

Enter 4.0 as the radius

Select the vertex, then the surface

Repeat the steps until all four fillets are created

SURFACE MODELING OF

COMPUTER PANEL

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Remove the desired holes and create 2 holes for the

speaker plugs

Geometry: Edit/Surface/Remove Hole

Under Inner Loop List select all of the desired holes, the eight

tooling holes and the two holes for the speaker plugs

Select the trimmed surface

Illustrated above is the computer panel surface after all the tooling holes and speaker plug holes have been removed.

SURFACE MODELING OF

COMPUTER PANEL

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Create the speaker plug holes using a smaller radius

Geometry: Edit/Surface/Add Hole

Set the Option to Center Point

Set Hole Radius to 2.0

Use the following center points

z

[239 25 0]

z

[251 25 0]

Use Surface 1 for the Surface, and click on Apply

SURFACE MODELING OF

COMPUTER PANEL

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Mesh the model

Elements: Create/Mesh/Surface

Set the Elem Shape, Mesher, and Topology to Quad, Paver, and

Quad4, respectively

Enter an appropriate GEL for the model(around 2.5 or so)

Determine the quality of the elements

z

Finite Elements: Verify/Quad/All

SURFACE MODELING OF

COMPUTER PANEL

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WORKSHOP 2

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Problem Description

In this exercise a CAD(IGES) file for a plate structure is imported into

a database. However, the translation leads to gaps and

discontinuities in the geometric model. In order to create a suitable

mesh for analysis the geometry needs to be “cleaned up”. This is

where the concept of composite surfaces is introduced.

Combine the disjoint(non-congruent) surfaces, which represent the

plate structure, to create a set of composite surfaces. Mesh seeds

will be created on the edges of the composite surfaces. Finally, the

surfaces will be meshed.

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Suggested Exercise Steps

1.

Create a new database called composite_surfaces.db.

2.

Import the surface geometry from an IGES file.

3.

Check the model for geometric incongruencies.

4.

Formulate the procedure for creating the composite surfaces for the model.

5.

Change the picking preferences.

6.

Create the composite surface for the first quarter of the model.

7.

Create the second composite surface.

8.

Create a third composite surface.

9.

Change the picking preferences back to the original settings.

10.

Create the final composite surface.

11.

Determine where the internal surface free edges are.

12.

Create the mesh seeds.

13.

Mesh the composite surfaces.

14.

Connect elements by equivalencing.

15.

Change the lighting and display options.

16.

Display only the composite surfaces.

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Step 1. Create a New Database

Create a new database called

composite_surfaces.db and set the

new model preferences.

a. Click on the File New icon. b. Enter composite_surfaces

for the file name and click OK. c. Select the Based on Model

toggle under Tolerance.

d. Set the Approximate Maximum

Model Dimension to 10.0.

e. Make sure that the Analysis

Code and Analysis Type are

set to MSC.Nastran and

Structural, respectively. f. Click OK.

b

c

d

e

f

a

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Step 2. Import the Surface Geometry

Import the IGES file called

non_cong_surfs.igs and change

the display and view to get a better representation of the model.

a. File : Import…

b. Select non_cong_surfs.igs. c. Click on Apply.

d. Click OK when IGES Report Summary Appears.

e. Click on the Iso 1 View icon. f. Click on the Smooth Shaded

icon.

g. Click on the Fit View icon.

a

b

c

d

e

f

g

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Step 2. Import the Surface Geometry

Illustrated here is the imported surface geometry.

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Step 3. Check the Model for Geometric Incongruencies

Check the model for geometric incongruencies by verifying the surface boundaries.

a. Click on the Wireframe view icon.

b. Geometry : Verify / Surface / Boundary.

c. Make sure that the

Topology toggle is set

under Verification Criteria. d. Under Surface List, select

the entire model. e. Click Apply.

A warning message will appear in the history window stating that free edges and/or

non-a

b

c

d

e

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Step 4. Formulate Procedure for Creating Composite Surfaces

Observations

From the markers displayed on the interior of the model it can be

seen that there exists a non-congruency problem which will affect the

congruency of the meshes. That is, the meshes will not be

compatible at adjacent boundary interfaces of the non-congruent

surfaces.

This problem can be dealt with by using composite surfaces in

MSC.Patran. To do this a set of several surfaces is combined into a

new simple or trimmed surface whose perimeter is identical to the

original set of surfaces. A plan has to be developed to use

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Step 4. Formulate Procedure for Creating Composite Surfaces (Cont.)

Composite Surface Outline

The model is to be divided into four quarters(labeled below). The

surfaces in each of the quarters are to be used to construct a single

composite surface for each quarter of the model. The four composite

surfaces are then to be meshed, and the elements connected by

equivalencing, creating a single congruent mesh that can be used for

performing an analysis.

Also, because there are no surfaces edges interior to a composite

surface when the composite surface is meshed the created nodes do

not have to follow interior edges or vertices.

1

2

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Step 5. Change the Picking Preferences

Change the Picking Preferences. a. Preferences : Picking

b. Under Single Picking, make sure that Entity is selected. c. Under Rectangle/Polygon

Picking, select Enclose entire

entity.

d. Select Cycle picking form and Horizontal select menus. e. Under Preselection Settings,

select Entity Highlighting. f. Click on Close.

g. Click on the Front View icon.

a

b

c

d

e

f

g

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Step 6. Create the first Composite Surface

Create the first composite surface. a. Geometry : Create /

Surface / Composite.

b. Select the toggle for Delete

Constituent Surfaces.

c. Under Surface List, select the upper right quarter of the model (i.e section 1). d. Under Vertex List, select

points (indicated by the black squares) to define the outside corners of the composite surface.

a

b

c

d

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Step 6. Create the first Composite Surface (Cont.)

View the current perimeter of the set of surfaces, as seen by the composite surface application.

a. Click on the Preview Boundary button.

b. Click No when the Question from application SGM appears.

c. An informational message will appear in the history window describing the following colors

White free edges within the current surface selection

Dark blue two coincident surface edges

Light blue more than two coincident surface edges

Red surface edges that are not part of the boundary due to a gap

a

b

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Step 6. Create the first Composite Surface (Cont.)

In this illustration, and throughout the remainder of the exercise, the white dots and white lines are represented in black. The boundary definition

(represented by black and dark blue lines with solid dots) needs to be modified so it will include only the desired surface edges. For this problem, only the surface edges on the outside(outer perimeter) of the set of surfaces in the Surface List are to be used. The surface edges colored white with white dots that are interior to the surfaces must be removed from the boundary definition.

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Step 6. Create the first Composite Surface (Cont.)

Remove the four interior edges from the desired composite surface perimeter.

a. Geometry : Create / Surface / Composite.

b. Click on the Remove toggle. c. Hold down shift and select the

four interior edges. d. Click on Apply.

e. A message will appear indicating that the boundary loop is not

closed at the red square(there is a gap). Click OK.

a

b

c

d

e

c

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Step 6. Create the first Composite Surface (Cont.)

The red square indicates the area where the boundary loop is not closed. To close the loop, a curve needs to be created.

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Step 6. Create the first Composite Surface (Cont.)

Zoom in on the red square and create a curve that closes the gap.

a. Click on the View corners icon. b. Zoom in on the corner with the red

square. (zooming may need to be done a few times in order to get a good view)

c. Click on the Label Control icon and show click on Point.

d. Geometry : Create / Surface / Composite.

e. Change the Modify Boundary toggle to Add.

f. Click on the Two Points icon. g. Under Edge List, select point 58

and 75.

h. Click on the Fit view icon. i. Turn of the Label Control.

a

b

d

e

g

i c

f

h

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Step 6. Create the first Composite Surface (Cont.)

The composite surface is now ready to be submitted. a. Geometry : Create / Surface / Composite. b. Click on Apply.

c. Click Yes to message asking to change the view.

d. Click on OK to message asking to increase the gap tolerance to 0.386.

a

b

c

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Step 6. Create the first Composite Surface (Cont.)

Modify the Cleanup Tolerance and create the composite surface.

a. Click on the Options… button. b. Enter 0.4 for both the Cleanup Tol.

and Gap Distance. c. Click on OK. d. Click on Apply.

e. Click Yes when asked to delete the original surfaces.

f. Click on the Refresh graphics icon.

a

b

c

d

e

f

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Step 6. Create the first Composite Surface (Cont.)

Magenta lines indicate that the surface has more than four edges

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Step 7. Create the Next Composite Surface

Select the boundary for the second composite surface.

a. Geometry : Create / Surface / Composite. b. Under Surface List, select upper left

quarter (i.e section 2).

c. Under Vertex List, select the 5 points (indicated by the black squares).

a

b

c

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Step 7. Create the Next Composite Surface (Cont.)

Set the Composite Options back to the default setting. a. Click on Options…

b. Click on the Defaults button and both the Cleanup

Tol. and the Gap Distance should change back to

0.005.

c. Click OK.

d. Click on Preview Boundary.

e. Click Yes when asked to change the tolerance. f. Click on Apply.

a

b

c

d

e

f

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Step 7. Create the Next Composite Surface (Cont.)

Finish creating the second composite surface.

a. Click Yes when asked to change to optimal view. b. Click on Yes when asked to

delete the original surfaces. c. Click on the Refresh graphics

icon.

a

c

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Step 8. Create another Composite Surface

Create the composite surface for the lower right quarter of the model.

a. Geometry : Create / Surface / Composite. b. Under Surface List, select the lower-right

quarter of the model (i.e, section 3). c. Under Vertex List, select the four points

(indicated by the black squares).

a

b

c

b

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Step 8. Create another Composite Surface (Cont.)

Set the Composite Options back to the default setting. a. Click on Options…

b. Click on the Defaults button and both the Cleanup

Tol. and the Gap Distance should change back to

0.005.

c. Click OK.

e. Click Yes when asked to change the tolerance. f. Click on the View corners icon and zoom in

on the lower-right quarter of the model.

a

b

c

d

e

f

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Step 8. Create another Composite Surface (Cont.)

Change the picking preferences and remove the edges internal to the desired composite surface.

a. Preferences : Picking

b. Change Rectangle/Polygon Picking toggle to Enclose any

portion of entity.

c. Click on Close.

d. Click on Remove under Modify Boundary. e. Under Edge List, hold

down shift and select the two internal

surfaces (as indicated) by dragging a box around the circle. f. Click on Apply.

a

b

c

d

f

e

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Step 8. Create another Composite Surface (Cont.)

Finish creating the composite surface.

a. Click on Yes when asked to change to a better view. b. Click on Yes when asked to delete the original surfaces. c. Click on the Refresh graphics icon.

d. Click on the Fit View icon.

a

b

d

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Step 8. Create another Composite Surface (Cont.)

Shown here is the model with three completed composite surfaces.

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Step 9. Change the Picking Preferences

Change the Picking Preferences back to the previous setting.

a. Preferences : Picking

b. Under Single Picking, make sure that Entity is selected. c. Under Rectangle/Polygon

Picking, select Enclose entire

entity.

d. Select Cycle picking form and Horizontal select

menus.

e. Under Preselection Settings, select Entity Highlighting. f. Click on Close.

a

b

c

d

e

f

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Step 10. Create the Final Composite Surface

Select the surface boundary for the fourth composite surface.

a. Geometry : Create / Surface / Composite.

b. Under Surface List, select the lower-left section (i.e section4) by dragging a box around it.

c. Under Vertex List, select the four points (indicated by the black squares).

a

b

c

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Step 10. Create the Final Composite Surface (Cont.)

Set the Composite Options to the default. a. Click on the Options… button. b. Click on the Defaults button and

both the Cleanup Tol and Gap

Distance should change to 0.005.

c. Click on OK.

e. Click on Yes when asked to change tolerance. f. Click on Apply.

a

b

c

d

e

f

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Step 10. Create the Final Composite Surface (Cont.)

Finish creating the composite surface.

a. Click on Yes when asked to delete original surfaces.

b. Click on the Refresh graphics icon.

c. Change the view by clicking on

Iso 2 view icon.

d. Click on the Fit view icon.

a

c

d

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Step 11. Check the Model

Check the model once again to verify that there are no geometric incongruencies.

a. Geometry : Verify / Surface / Boundary.

b. Select Topology under

Verification Criteria.

c. Under Surface List, select the entire model.

d. Click Apply.

e. Click on the Update

Graphics button.

f. Click on the Erase Markers button.

g. Click on OK.

h. Click on the Front view icon.

a

b

c

d

e

f

g

h

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Step 12. Create Mesh Seeds

Create mesh seeds for the model. a. Elements : Create / Mesh

Seed / Uniform. b. Select the toggle for

Number of Elements.

c. Enter 10 under Number. d. Under Curve List,Shift-select

the 7 curves (indicated by the red arrows). e. Click Apply.

a

b

c

d

e

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Step 12. Create Mesh Seeds (Cont.)

Continue to create mesh seeds for the rest of the model.

a. Elements : Create / Mesh Seed / Uniform.

b. Select the toggle for

Number of Elements.

c. Enter 4 under Number. d. Shift-select the 3 curves

(indicated by the red arrows). e. Click Apply.

a

b

c

d

e

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Step 13. Create a Surface Mesh

Create the mesh for the model. a. Elements : Create /

Mesh / Surface. b. Select Quad, Paver,

and Quad4 for the

Elem. Shape, Mesher,

and Topology. c. Under Surface List,

select the top two surfaces (i.e sections 1 and 2).

d. Remove the check for

Automatic Calculation and enter 5.0 for the Global Edge

Length.

e. Click on the Paver Parameters… button. f. Select Used Desired Edge Lengths toggle.

g. Enter 4.8 and 5.2 for the Min Edge and Max Edge Length, respectively. h. Click OK. i. Click on Apply.

a

b

c

d

e

f

g

h

_i

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Step 13. Create a Surface Mesh (Cont.)

Mesh the remaining composite Surfaces, this time using the Isomesher.

a. Elements : Create / Mesh / Surface.

b. Select Quad, IsoMesh, and

Quad4 for the Elem. Shape,

Mesher, and Topology.

c. Under Surface List, select the bottom two surfaces (i.e sections 3 and 4).

d. Remove the check for

Automatic Calculation and

enter 5.0 for the Global Edge

Length. e. Click on Apply.

a

b

c

d

e

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Step 13. Create a Surface Mesh (Cont.)

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Step 14. Equivalence the Mesh

Equivalence the model.

a. Elements : Equivalence / All / Tolerance Cube.

b. Change the Equivalencing

Tolerance to 0.05.

c. Click Apply.

a

b

c

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Step 15. Change the Display and Lighting for the Model

Modify certain display parameters to get a better view of the model.

a. Click on the Smooth shaded icon.

b. Click on the Plot/Erase icon. c. Click on Erase under

Geometry.

d. Click on OK. e. Viewing : Angles…

f. Enter -10 -30 -20 for the angles.

g. Click on the Fit view icon. h. Click on Apply, then Cancel.

c

d

e

f

h

b

a

g

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Step 15. Change the Display and Lighting for the Model (Cont.)

Modify the lighting sources. a. Display : Light Sources…

b. Under Post/Unpost Sources, select

ambient, directional_1, directional_2,

and directional_3. c. Click on Apply. d. Click on Cancel.

a

b

c

d

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Step 16. Display the Composite Surfaces.

Plot only the composite surfaces. a. Click on the Plot/Erase icon. b. Under FEM, click Erase. c. Under Geometry, click Plot. d. Click on OK.

e. Close the database and quit MSC.Patran after finishing the exercise.

b

c

d

a

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WORKSHOP 3

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Problem Description

A continuous 2D quadrilateral element mesh needs to be created

for a set of surfaces. The problem is that the surfaces in the set are

not congruent because of the presence of gaps, non-coincident

adjacent vertices, and overlapping surface edges. Also, even if the

surfaces were all congruent some of the edges internal to the outer

perimeter are too close to each other for the creation of a large

element mesh.

The approach to be used for this workshop is to

Mesh the entire set of surfaces

Connect elements and fill gaps with elements

Create a single surface from the connected 2D element mesh

IsoMesh the created single surface

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Suggested Exercise Steps

1.

Create a new database.

2.

Import the surface geometry.

3.

Determine where the surface free edges are.

4.

Create tri3 meshes using the IsoMesher.

5.

Sew the elements together.

6.

Observe where the free edges of the elements are.

7.

Create a group for the surface to be created from the tri3 elements.

8.

Create a surface from the 2D tri3 mesh.

9.

Display only the group with the new surface.

10.

Mesh the new surface using IsoMesh.

11.

Smooth the new surface mesh.

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Step 1. Create a New Database

Create a new database. a. File / New.

b. Enter tessellated for File

Name.

c. Click OK.

d. Under New Model

Preferences, select Based

on Model Tolerance.

e. Select MSC.Nastran for

Analysis Code.

f. Select Structural for

Analysis Type. g. Click on OK.

f

e

d

c

b

a

g

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Step 2. Import the Surface Geometry

Import the model geometry. a. File / Import.

b. Change the Object and

Source to Model and Neutral,

respectively.

c. Select non_cong_surfs.out. d. Click on Apply.

e. Click Yes for the import summary.

d

c

b

a

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Step 3. Determine Where the Surface Free Edges Are

Determine where the surface free edges are.

a. Geometry : Verify / Surface / Boundary.

b. Under Surface List select the entire model.

c. Click on Apply.

d. Click on OK to the Update

Graphics dialogue box.

c

b

a

Note that there are numerous locations where there are surfaces free edges(indicated by magenta circles).

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Create tri3 mesh using the IsoMesh-er.

a. Finite Elements : Create / Mesh / Surface.

b. Select Tria for Elem

Shape, IsoMesh for Mesher, and Tria3 for Topology.

c. Select all the surfaces in the display for Surface

List.

d. Deselect Automatic

Calculation.

e. Enter 2.0 for Global Edge

Length.

f. Click on Apply.

Step 4. Create Tri3 meshes using IsoMesh

e

d

c

b

a

f

Note that IsoMesh can be used because all of the surfaces are parametric.

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Sew the elements together. a. Finite Elements : Modify /

Mesh / Sew.

b. Enter 2.0 for Target Element

Edge Length.

c. Select all the tri elements under Tria Element List. d. Click on Apply.

Step 5. Sew the Elements Together

d

c

b

a

What does the Sew command do?

The Sewing command will equivalence finite element nodes and create tri elements to fill any gaps. The quality of the tri elements may not be very good, but that is acceptable because a surface is to be created from them and the original tri elements will be deleted after the surface has been created.

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Now, check for element free edges. a. Finite Elements : Verify /

Element / Boundaries. b. Select Free Edges for

Display Type.

Step 6. Look at the Element Free Edges

Hole in Tri3 Mesh

c

b

a

Is it ok the have a hole in the mesh ?

Yes. When the surface is created the inner loop can be excluded. However, it is important to realize that the presence of inner loops, even if they are excluded in creating a surface, may result in inaccurate geometry at the location of the inner loops.

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Step 7. Create a Group

Create a group for the surface to be created from the tri3 elements. Make the group “current”so when the

surface is created it will be placed in it. a. Group : Create / Select Entity. b. Enter tess_surf for New Group

Name.

c. Check the Make Current toggle. d. Click on Apply.

d

c

b

a

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Create a surface from the 2D tri3 mesh.

a. Geometry : Create / Surface / Mesh.

b. Select the tri3 elements for

Element List.

c. Select the four corner nodes for Outer Corner Nodes. No additional nodes are to be selected, under Additional

Vertex Nodes, so that a

parametric surface will be created.

d. Select None for Inner Loop

Options.

e. Click on Apply.

Step 8. Create a Surface From the 2D tri3 Mesh

e

d

c

b

a

c

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Display only the group with the new surface, tess_surf.

a. Group / Post…

b. Select tess_surf for Select

Groups to Post.

d. Turn on the display lines.

Step 9. Display Only the Group With the New Surface

d

c

b

a

This is a parametric surface. The display lines are obviously not smooth. The elements created by IsoMesh-ing this surface will have problems.

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Check various views of the model either by rotating it or using the view icons

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Mesh the new surface using IsoMesh (Use Larger Element Size).

a. Finite Elements : Create / Mesh / Surface.

b. Select Quad for Elem Size, IsoMesh for Mesher, and Quad4 for Topology. c. Select Surface 602 (the new surface)

for Surface List.

d. Deselect Automatic Calculation and enter 6.0 for Global Edge Length. e. Click on Apply.

Step 10. Mesh the New Surface using IsoMesh

e

d

c

b

a

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Step 11. Smooth the New Surface Mesh

Smooth the new 2D surface mesh using an application in Finite Elements.

a. Finite Elements : Modify / Mesh / Surface.

b. Select the newly created tessellated surface, Surface 602, for Surface

List.

c

b

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Erase the Geometry so that the mesh can be seen better.

a. Display / Plot/Erase. b. Under Geometry click on

Erase.

c. Click OK.

Step 11. Smooth the New Surface Mesh (Cont.)

c

b

a

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Step 11. Smooth the New Surface Mesh (Cont.)

Before Smoothing

After Smoothing

The quality of the quad elements can be checked for the two meshes using Finite Elements: Verify / Quad / All.

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Quite MSC.PATRAN. a. File / Close.

This ends this exercise.

Step 12. Quit MSC.Patran

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WORKSHOP 4

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Problem Description

This exercise introduces another method of creating a 2D mesh for

a set of non-congruent surfaces. So far non-congruent surfaces

have been dealt with using several methods. They are composite

surface, trimmed composite surface, and tessellated surface. This

method involves the use of the Mesh/On Mesh tool. This involves

creating a high quality continuous 2D mesh from poor quality 2D

continuous mesh. The poor quality mesh can be created by

meshing a set of non-congruent surfaces, then sew-ing; this is what

is to be done for this workshop.

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Suggested Exercise Steps

1.

Create a new database.

2.

Import a MSC.Patran neutral file.

3.

Create a Tri3 Element mesh for each surface.

4.

Connect the triangular elements by sew-ing. This includes equivalencing and

element creation.

5.

Repeat Step 4 using a different target element edge length.

6.

Using the Mesh/On Mesh tool create a mesh for the model that can be used

for analysis.

7.

Because the initial mesh is too course repeat Step 6 using a smaller element

size.

8.

In order to create a mesh that follows the model geometry more closely mesh

select surface edges with Bar2 Elements for use with the Mesh/On Mesh

application.

9.

Create the final mesh, that will follow the model geometry, using the Mesh/

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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

(82)

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.

(83)

Step 2. Import MSC.Patran neutral file (Cont.)

(84)

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.

a

b

d

c

e

(85)

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

(86)

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

(87)

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

(88)

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

(89)

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

(90)

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.

(91)

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.

(92)

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.

(93)

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.

(94)

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.

(95)

The Bar2 elements are shown in yellow

(96)

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.

(97)

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.

(98)

(99)

WORKSHOP 5

MID-SURFACE CREATION

SIMPLE BRACKET

(100)

(101)

Problem Description

Produce a mid-surface model from an imported simple bracket.

First use the manual mid-surface option.

Second use the automatic mid-surface option.

Workshop Objectives

See the difference between manual and automatic mid-surface

generation for the same part.

Determine how and where additional surface editing is needed

when using the manual mid-surface.

MID-SURFACE

SIMPLE BRACKET

(102)

General outline for manual mid-surface creation

Import the Parasolid file MS_bracket.xmt_txt.

Geometry: Create/Surface/Midsurface

z

Using the Manual mode create a mid-surface for the solid bracket

z

Three separate midsurfaces must be created, one corresponding to

each plate of the bracket

MID-SURFACE

SIMPLE BRACKET

(103)

Overlap of mid-surfaces

Extra surfaces from Break

Final mid-surfaces

General outline for manual mid-surface creation (continued)

Geometry: Edit/Surface/Break

z

Use the Surface option to break the mid-surfaces where they intersect.

Geometry: Delete/Surface

z

Delete the unneeded mid-surface fragments(sliver surfaces).

MID-SURFACE

SIMPLE BRACKET

(104)

General outline for automatic mid-surface creation

Close the current database and create a new one

Import the Parasolid file MS_bracket.xmt_txt.

Using the automatic mode create a mid-surface for the solid

bracket.

z

Note: The bracket walls are 0.1 inch thick. A workable range for the

Max. Thickness is 0.1 to 1.0 inch.

MID-SURFACE

SIMPLE BRACKET

(105)

WORKSHOP 6

MID-SURFACE EXTRACTION

WING SECTION

(106)

(107)

Problem Description

The design department has produced a solid model of an

aircraft wing section.

The task is to extract mid-surfaces from the solid model,

preparing for shell meshing.

MID-SURFACE

WING SECTION

(108)

The solid model consists of five individual solids as

shown in the exploded view.

MID-SURFACE

WING SECTION

(109)

The model of the wing section is shown without the

upper wing skin.

Rib (3)

Rib stiffener (9)

Lower wing skin

Rib cap (6)

MID-SURFACE

WING SECTION

(110)

Idealization

Replace the solid geometry with surface geometry. Mesh the surfaces

to create plate elements. Mesh the edges of surfaces to create bar

elements.

Wing skins and ribs

are modeled using

plate elements

Rib stiffeners and

rib caps are

modeled using

bar elements

MID-SURFACE

WING SECTION

(111)

General outline of workshop steps

Import the Parasolid model file wing_section.xmt_txt

MID-SURFACE

WING SECTION

(112)

Rib Solids, Solid 1:3

General outline of workshop steps (continued)

Five parasolid solids

MID-SURFACE

WING SECTION

(113)

Rib

3 2 1 Solid 3.7 Solid 2.7 Solid 1.7 Offset Solid Face List Solid 3.5 Solid 2.5 Solid 1.5 Solid Face List

General outline of workshop steps (continued)

Create rib surfaces

They will be the length(X-direction) of the ribs

MID-SURFACE

WING SECTION

(114)

General outline of workshop steps (continued)

Create rib stiffener surfaces

They will be the width(Z-direction) of the ribs

Solid 3.41 Solid 3.37 Solid 3.33 Solid 2.41 Solid 2.37 Solid 2.33 Solid 1.41 Solid 1.37 Solid 1.33 Offset Solid Face Solid 3.40 Solid 3.36 Solid 3.32 Solid 2.40 Solid 2.36 Solid 2.32 Solid 1.40 Solid 1.36 Solid 1.32 Solid Face List 9 8 7 6 5 4 3 2 1

MID-SURFACE

WING SECTION

(115)

General outline of workshop steps (continued)

Created rib and rib stiffener surfaces

MID-SURFACE

WING SECTION

(116)

General outline of workshop steps (continued)

Use the manual or automatic mode to extract mid-surfaces from the

wing skin solids.

Solid Face List: Solid 4.6 5.6

Offset Solid Face List: Solid 4.1 5.1

MID-SURFACE

WING SECTION

(117)

General outline of workshop steps (continued)

There is a gap between the top or bottom of the rib/rib stiffener surfaces

and the wing skin surfaces. It is 0.050 inch which is half of the wing skin

thickness.

Wing skin surface

Rib surface

Rib stiffener

surface

Gap

MID-SURFACE

WING SECTION

(118)

General outline of workshop steps (continued)

Only simple (green) surfaces can be extended. MSC.Patran will

automatically attempt to convert complex (magenta) surfaces into

green surfaces before performing the surface extend operation.

In cases where the automatic conversion fails, a manual surface refit

may be required using Geometry: Edit/Surface/Refit.

MID-SURFACE

WING SECTION

(119)

General outline of workshop steps (continued)

Extend the rib stiffener surfaces to the wing skin surfaces to eliminate

those gaps. Do not break the wing skin surfaces during the extend

operation.

Extend rib stiffener

surface at both ends

MID-SURFACE

WING SECTION

(120)

General outline of workshop steps (continued)

Extend the rib surfaces to the wing skin surfaces to eliminate those

gaps. Do not break the wing skin surfaces during the extend operation.

Extend rib surface at

both top and bottom

MID-SURFACE

WING SECTION

(121)

General outline of workshop steps (continued)

Use the rib stiffener surfaces to break the rib surfaces. The rib surface

edges resulting from this operation can be meshed with bar elements to

represent the stiffeners.

Delete the rib stiffener surfaces.

MID-SURFACE

WING SECTION

(122)

General outline of workshop steps (continued)

Extend the wing skin surfaces 4.5 inches in the span direction.

Notice that MSC.Patran automatically refits the magenta surfaces to green

surfaces.

Note that the surface extension retains the contour of the surface.

MID-SURFACE

WING SECTION

(123)

General outline of workshop steps (continued)

For a further demonstration of the Surface Extend tool, use the extend

by percentage to lengthen the cord of the wing skin by 10% in

anticipation of front and rear spars.

MID-SURFACE

WING SECTION

(124)

General outline of workshop steps (continued)

Finally associate the upper and lower rib surface edges with the wing

skin surfaces. This will enforce congruent meshes between the ribs and

wing skins.

MID-SURFACE

WING SECTION

(125)

MID-SURFACE

WING SECTION

(126)

(127)

WORKSHOP 7

(128)

(129)

MID-PLANE MESHER

Problem Description

Create a 2D mesh inside the sheet metal clip solid using Midplane

Mesh.

Create a 2D mesh using a midsurface extracted from the sheet

metal clip solid .

(130)

Create a 2D mesh using Midplane Mesh

Import the Parasolid solid model clip.xmt

Determine the solid dimensions so can estimate the value of the

global edge length. Use Geometry: Show/Point/Distance.

Use the mid-plane mesher to create a 2D mesh in the solid.

z

Tools/Pre Release/Midplane Mesh

z

Input List: Solid 1

z

Use GEL of 2.50 inches

(131)

(132)

Create a 2D mesh using extracted mid-surfaces

Geometry: Transform/Solid/Translate, Translation Vector: <0 75 0> to

make a copy of the original solid.

Create a group called mid_surface, and make it current

Geometry: Create/Surface/Midsurface

z

Select Automatic option and enter 3.0 for Max. Thickness

Post the group mid_surface

(133)

Create a 2D mesh using extracted mid-surfaces

(continued)

Elements: Create/Mesh/Surface

z

Mesher: Paver

z

Surface List: select all surfaces in group mid_surface

z

GEL: 2.50

(134)

Compare the two 2D meshes

Post both groups default_group and mid_surface

Erase the geometry, displaying only the FEM

Look at each meshed model carefully and note the differences

Meshed extracted mid-surfaces

Midplane mesh

(135)

Midplane mesh Meshed extracted

Compare the two 2D meshes (continued)

Elements: Verify/Quad/Skew

(136)

(137)

WORKSHOP 8

(138)

(139)

MESH ON MESH

2D TO 3D

Problem Description

The lifting rig model has several

areas where elements are not

connected where they should be

connected.

Repair the model by moving/

aligning several nodes and using

Finite Elements: Create/Mesh/

On Mesh.

(140)

General outline of analysis steps

Import the MSC.Nastran model file lifting_rig.bdf

Display element free edges

Region 3

Region 2

Region 1

Shown here is a plot of the element free edges. Note three areas where there are unwanted free edges. They are labeled as Region 1, 2, and 3.

MESH ON MESH

2D TO 3D

(141)

Region 1

Region 2

_{Region 3}

Again, note three areas where the elements are not connected where they need to be. As before they are labeled as Region 1, 2, and 3. Each of these regions are to be repaired one at a time.

MESH ON MESH

2D TO 3D

(142)

General outline of analysis steps (continued)

For Region 1 align the nodes of the 2D mesh to the nodes of the 3D mesh

z

Finite Elements: Modify/Node/Move.

Align as many of the nodes between the two meshes as possible

Equivalence the model.

Before

After

Note that the nodes here are now aligned.

Region 1

MESH ON MESH

2D TO 3D

(143)

General outline of analysis steps

(continued)

Next use Finite Elements: Create/Mesh/On Mesh

to finish fixing the mesh.

z

Finite Elements: Create/Mesh/On Mesh

z

Click on the Delete Elements toggle

z

Change Seed Option to Existing Boundary

z

Click on Feature Selection

Select Boundary Seeds, then unmatched nodes as

indicated on next page.

z

Under 2D Elem List select several rows of

elements as indicated on next page.

z

Specify the GEL as 0.2

z

Click on Apply

MESH ON MESH

2D TO 3D

(144)

Select unmatched

nodes as Boundary

Seeds

Using polygon pick

to select these 2D

elements. Use

enclose any portion

of entity.

Region 1

MESH ON MESH

2D TO 3D

(145)

Region 1

General outline of analysis steps (continued)

Region 1 repaired

MESH ON MESH

2D TO 3D

(146)

General outline of analysis steps (continued)

Repair Regions 2 and 3 using the same technique

that was used for Region 1

MESH ON MESH

2D TO 3D

(147)

General outline of analysis steps (continued)

Region 2 repaired

Region 2

MESH ON MESH

2D TO 3D

(148)

Region 3

General outline of analysis steps (continued)

Region 3 repaired

MESH ON MESH

2D TO 3D

(149)

General outline of analysis steps (continued)

Free edge plot

The free edge plot indicates that the cracks have now been eliminated.

MESH ON MESH

2D TO 3D

(150)

(151)

WORKSHOP 9

(152)

(153)

Problem Description

This exercise involves importing curve geometry from an IGES file. The

curves are used to create other curves. From the curves trimmed surfaces

are created

The trimmed surfaces are Paver meshed. For the meshing, lists(e.g. `lista`)

are used for the list of surfaces. An IsoMesh is created using two parallel

opposing curves. Prior to meshing select surface edges and curves are

mesh seeded to force the desired mesh size in select regions.

Finally, the 2D quadralateral elements are swept to create 3D hexahedral

elements. Some 2D elements are extruded using a constant sweep vector,

e.g. <x y z>. Other elements are swept using a previously created vector

field.

(154)

Suggested Exercise Steps

1.

Create a new database.

2.

Import the IGES file with curves.

3.

Create a curve to intersect two curves.

4.

Break two vertical curves for side of model.

5.

Break the breaking curve.

6.

Change the geometric shrink.

7.

Create a group for a quarter of the model.

8.

Break a fillet curve.

9.

Display trimmed surface label for subsequent trimmed surface creation.

10.

Create curves for trimmed surface creation.

11.

Create trimmed surfaces.

12.

Create mesh seeds on select surface edges.

13.

Create the meshes for the surfaces.

14.

Create lists for sweeping to create solid elements.

15.

Create solid element meshes by sweeping.

16.

Create a spatial vector field.

17.

Create the remainder of the solid elements by sweeping using a vector field.

18.

Display of all the solid elements.

19.

Look for element free edges

20.

Advanced MSC.patran Exercises