ex 8 midsurface modelling

2-1

Exercise 8 – Midsurface Modelling

© UGS Corp. 2006. All rights reserved.Femap with NX Nastran 2-2


Exercise Description and Objectives:

Extract mids-urfaces from a solid model of a machined bracket

The solid model has multiple wall thicknesses

Use Geometry, Mid-surface commands to edit and assign properties to

the mid-surface model.

Mesh and analyze the mid-surface model.



Import the parasolid geometry of the multi-thickness solid model.

Start new Femap model selecting File, Import, Geometry command.

Choose Parasolid file Femap_Training\bracket.x_t.

Press OK to accept the defaults in the Solid Model Read Options

Change the view orientation to the Isometric view

Press the F8 key (or use the View, Rotate, Model command)

Select the Trimetric button.

Press OK or use the Esc key to close the dialog box.



1. Save the model

a) Save the model in your Femap_Training folder as “Ex 7 Midsurface”



2. Extract the midsurfaces from the solid.

a) Select Geometry, Midsurface, Automatic

b) Press Select All button to select all the

surfaces on the solid. OK.

c) In the Mid-Surface Tolerance box, click

„Measure Distance” icon (or Ctrl+D) to

enable measuring distance

d) When the Locate – Define Location to

Measure From box is displayed choose

Method to On Point, select one of the

points on the thickest edge of the sold,

than press OK to confirm the selection of

the first point.



e) Now select another point on the other end of the edge and press OK to

confirm the selection.

f) Press OK to accept the calculated distance,

in the Mid-Surface Tolerance dialog box.

Femap will now extract the mid-surfaces.



3. Display the automatically generated

Mid-surfaces group

a) In the Model Info window, first confirm

that Highlighting is enabled.

b) Select the Group object 1..Midsurfaces

in the Model Info window. This will

highlight the newly created group.

4. Since we are only working with a single part, you

can delete the group and the original solid.

a) Right-click the Group object 1..Midsurfaces and

select Delete from the context-sensitive menu.

b) Expand the Geometry object tree, select the first

solid, 1..Bracket, and using the context-sensitive

menu, Delete the part.

c) Expand the view if needed with the Ctrl+A


5. Trim the mid-surface of the rib to remove the tab where the rib

intersects the back of the side wall.

a) Select the Geometry, Midsurface, Trim with Curve command.

b) Select the surface representing the rib as the Surface/Solid to Trim.

c) Select the small edge on the tab on the top of the rib and the short edge

at the end of the rib as the lines to trim with. Press OK to complete the

trimming operation.

The rib will be split into three (3) separate surfaces.


Note: A better method to trim the rib would

be to select the edge on the top of the

rib instead of the edge on the small

tab closest to the end of the bracket.

Selecting the top edge would have

eliminated the need to use the Extend

Surface command in Step 8.



6. Delete the two (2) rectangular surfaces created by the trimming

7. Clean up the mid-surfaces.

a) With Highlighting still enabled in the Model Info window, select all the

sheet solids. Note the curves at the intersection of the mid-surfaces.

b) Select the Geometry, Solid, Cleanup then Select All the solids and OK.

c) In the Solid Cleanup dialog box, check the Remove Redundant

Geometry option on. Press OK to complete the removal of intersecting

curves on the three sheet solids. Note how the intersecting curves have

been removed.



8. Extend the edge of the rib to re-intersect

the side wall

a) Select the Geometry, Midsurface, Extend.

b) Select the edge of the rib closest to the side

wall as the curve to extend and press OK.

c) In the Surface Extend Options dialog box,

set theExtend Shape option to Linear, set

the Extend to option to Solid and select the

surface of the side wall closet to the rib.

Then press OK to complete operation.

9. Re-intersect the mid-surfaces

a) Select the command, Geometry, Midsurface, Intersect.

b) Select the five (5) sheet solids representing the mid-surfaces. Note how

the intersect operation command you just ran created the intersections

between the trimmed mid-surfaces.



10. Assign the mesh attributes (property) to the midsurfaces

a) Select the Geometry, Midsurface, Assign Mesh Attributes and Select

All the surfaces and press OK.

b) Assign the material to the surfaces when the Define Material –

ISOTROPIC dialog box is opened. Press the Load button to open up

the default material library.

c) Select one of the Aluminum materials and press OK, OK in the Material

dialog box and press NO for Consolidate by Thickness

d) In Property object tree in the Model Info window there are now six (6)

properties that reflect the six surfaces that make up the mid-surface

model.

e) Review the properties in the Entity Editor window. You can always

reassign the properties to different surfaces



11.Set the mesh size for the

mid-surfaces

a) Using the Select Toolbar,

set the Selector Entity to

Surface and Selector Mode

to Select Multiple.

b) Select all the surfaces.

c) In the Model Info window,

right-click the Surfaces (6)

object and select Mesh Size

from the context-sensitive

menu.



11.Set the mesh size for the mid-surfaces.

d) In the Automatic Mesh Sizing dialog box enter

Element Size to 0.1,

Max Angle Tolerance to 15,

Max Elem on Small Feature to 6,

Max Size of Small Feature to 0.1 and press OK



12.Mesh the model.

a) Select the Mesh, Geometry, Surfaces command.

b) Select All surfaces, and press OK to mesh the model

c) Clear present surface selection using Selector Toolbar, Clear All



13. Create the constraints on

the base of the part.

a) Using Selector, choose two

surfaces on the right-side

end plate of the part.

b) Right-click the Surfaces(s)

selection and run Constraint

and Create Constraint Set

c) In the Create Constraints

on Geometry dialog box set

the constraint to Surface

and check the Sliding along

Surface (Symmetry) check

box.

d) Press OK to create the

constraint.



13.Create the constraints on the base

of the part.

a) Clear the selection list using the Select

toolbar, set the Selector Entity type to

Curves and select the eight (8) arcs

representing the holes in the right-side

end plate.

b) Again, using the context-sensitive

menu for Curves (8) object in the

Model Info window, create a Fixed

constraint on the two curves.

c) Toggle off the Selector Entity icon and

clear selection list using the Selector

Clear All icon on View toolbar.



14.Create the loads on the holes on

the left end of the bracket. Use an API script to create a “spider”

or RBE2 element on each of the two

holes.

a) If Custom Tools is not open, open it

with the Tools, Toolbars, Custom

Tools command



14.Create the loads on the holes on the left end of the bracket

a) Using Custom Tools access and run Meshing, Spider API script



d) When prompted to select the

nodes for the Rigid Spider,

change the Methods to on

Curve and select the two curves

on one of the two holes.

e) Repeat those steps for the

second hole.

14.Create the loads on the holes on the left end of the bracket using

API script



15.Create the loads on the holes on the left end of the bracket

a) Zoom in on the end of the bracket rigid “spiders”.

b) Use the command Model, Load, Nodal.

c) Create a Load Set if prompted.

d) Select the two nodes at the center of the two spiders elements.

e) Select the load type as Force, and set the Load magnitude to FZ = -50.



16.Display the element thickness

a) Press View Style icon and select Thickness/Cross Section command



17.Create an Analysis Set and run the analysis

a) Create an Analysis Set for a Linear Statics analysis and run the analysis.

b) Display the results of the analysis.

c) Optionally, change the element thickness of the rib and rerun/review the

analysis. You can do this Modify, Update Elements, Property ID command.

ex 8 midsurface modelling

Documents