Comparing 2D and 3D Structural Analysis

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Comparing 2D and 3D Structural Analysis

• Workshop 4.2

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Workshop 4.2 - Goals

• Workshop 4.1 consists of a 2 part assembly
  representing a pressure cap and retaining flange
  (full model shown below).
• We will solve the model in 2 ways, as a 90 degree
  symmetry sector and as a 2D axisymmetric model
  (shown on next page).
• Our goal is to compare the 2 methods both for
  consistency and for economy.

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Workshop 4.2 - Geometry

• Shown here are the 3D sector model and the 2D
  axisymmetry model.

Pressure Cap
Retaining Ring
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Workshop 4.2 - Assumptions

• Assumptions
• The retaining ring is fixed at its mounting
  holes.
• The contact region between the parts is
  frictionless.
• The base of the pressure cap is constrained using
  a compression only support.
• Note due to the presence of the bolt holes the
  structure is not truly axisymmetric. Part of our
  goal is to determine the validity of the
  axisymmetric assumption in this case.

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Workshop 4.2 - Start Page

• From the launcher start Simulation.
• When DS starts, close the Template menu by
  clicking the X in the corner of the window.

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Workshop 4.2 Geometry Setup

• Before importing the geometry highlight the
  Geometry branch and change the Analysis Type
  preference to 2D in the details.
• Choose Geometry gt From File . . . and browse
  to the file Axisym_pressure_2D.x_t.

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Workshop 4.2 Preprocessing

• Set the working unit system to the metric mm
  system.
• Units gt Metric (mm, Kg, MPa, C, s).
• Highlight Parts 1 and 2 in the tree and rename
  Retaining Ring and Pressure Cap.
• In the details for each part, change their
  Behavior to Axisymmetric.

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Workshop 4.2 Preprocessing

• From details for the Pressure Cap and import
  the material Stainless Steel.

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Workshop 4.2 Contact

• Highlight the Contact Region and notice the
  target contains a single edge. We will add a
  second edge to insure all possible contact is
  detected.

Additional target edge to be added (shown dashed)
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Workshop 4.2 Contact

1. Click in the Target field then select the 2
   edges of the pressure cap shown here.
2. Apply the new selection.

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Select Edges
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Note if you have difficulty selecting the edges
of the Pressure Cap, use the hide feature to
hide the retaining ring during selection.
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Workshop 4.2 Contact

1. In the Contact Region detail change the Type to
   Frictionless.
2. Highlight the Mesh branch, RMB and Preview
   Mesh (note the speed with which the 2D mesh is
   generated as well as the density).

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Workshop 4.2 Environment

1. Highlight the Environment branch.
2. Select the 3 inside edges of the Pressure Cap.
3. RMB gt Insert gt Structural gt Pressure.
4. Set the pressure magnitude 0.1 MPa.

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Workshop 4.2 Environment

1. Highlight the bottom edge of the pressure cap.
2. RMB gt Insert gt Compression Only Support.

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Workshop 4.2 Environment

1. Select the middle line on the top of the
   retaining ring.
2. RMB gt Insert gt Fixed Support.

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Remember, the axisymmetric assumption here is
that the retaining ring is a continuous solid.
Actually there are bolt holes around its
circumference. For this reason, when the model
was created in DesignModeler this separate line
was intentionally created to provide a location
to add our support.
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Workshop 4.2 Solution

• Highlight the Solution branch, RMB and insert
• Stress gt Equivalent (von-Mises)
• Deformation gt Total
• Switch to body select mode, select the pressure
  cap and repeat steps 16 and 17.
• Solve

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Note, the last two results are now scoped to the
pressure cap. This will allow us to isolate its
response.
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Workshop 4.2 Solution

• OK the weak spring message.
• Note due to the fact that the pressure cap is
  constrained using frictionless contact and a
  compression only support, weak springs are added
  to prevent rigid body motion.

• Notes on axisymmetry
• Notice that the model lies completely in X space
  with the Y axis as the axis of revolution. This
  is required for axisymmetry.
• Axisymmetry assumes that the model is a complete
  360 degree model. For this reason no constraints
  in the X direction are required. The portion of
  the pressure load acting in the X direction is
  assumed to be offset by an equal portion in the
  X direction.

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Workshop 4.2 Postprocessing

• Highlight each of the result objects to inspect
  the response.
• Note due to meshing and machine variations,
  results may not match exactly those shown here.
• For future reference, highlight the Equivalent
  Stress 2 result (scoped) and note the maximum
  value here________________

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Workshop 4.2 Postprocessing

• Highlight the Solution branch, RMB gt Insert gt
  Solution Information gt Solution Information.

The graphics window will change to the Worksheet
view. Scroll to the bottom of the solution
information and note the Elapsed Time (this will
vary by machine). Elapsed Time
___________________________ Note, CP time
represents the sum for all processors used. In
multiprocessor machines it will generally exceed
elapsed time.
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Workshop 4.2 3D Symmetry Model

• Close the current project (you may save the
  current 2D Simulation if desired).
• Well now set up and solve the 3D symmetry model
  using the same boundary conditions.

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Workshop 4.2 - Start Page

• From the launcher start Simulation.
• When DS starts, close the Template menu by
  clicking the X in the corner of the window.

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Workshop 4.2 Geometry Setup

• Choose Geometry gt From File . . . and browse
  to the file Axisym_pressure_3D.x_t.

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Workshop 4.2 Preprocessing

• The working unit system should still be set to
  the metric mm system.
• Units gt Metric (mm, Kg, MPa, C, s).

• Note, once again rename the 2 parts in the model
  Retaining Ring and Pressure Cap

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Workshop 4.2 Preprocessing

• From details for the Pressure Cap and import
  the material Stainless Steel.

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Workshop 4.2 Contact

• Highlight the Contact Region branch and change
  the Type to Frictionless.
• Highlight the Mesh branch, RMB and Preview
  Mesh.
• Refer to p. 4.1-11 to compare the 2D mesh.

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Workshop 4.2 Environment

1. From the Environment branch highlight the 6 faces
   representing the planes of symmetry (cut planes).
2. RMB gt Insert gt Frictionless Support.

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Note there are six (6) faces to select.
Note, frictionless supports provide constraints
in the normal direction. This is used to model
the symmetry condition.
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Workshop 4.2 Environment

1. Highlight the bottom face of the pressure cap,
   RMB gt Insert gt Compression Only Support.

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Workshop 4.2 Environment

1. Highlight the 3 inside faces on the pressure cap,
   RMB gt Insert gt Pressure.

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1. Change the Magnitude to 0.1 in the detail
   window.

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Workshop 4.2 Environment

1. Highlight the 3 cylindrical faces of the bolt
   holes, RMB gt Insert gt Fixed Support.

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Workshop 4.2 Solution

• Highlight the Solution branch, RMB and insert
• Stress gt Equivalent (von-Mises)
• Deformation gt Total
• Switch to body select mode, select the pressure
  cap and repeat steps 16 and 17.
• Solve

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As before, the last two results are scoped to the
pressure cap.
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Workshop 4.2 Postprocessing

• As before highlight each of the result objects
  and inspect the response.
• For reference, highlight the Equivalent Stress
  2 result (scoped) and note the maximum value
  here________________

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Workshop 4.2 Postprocessing

• Highlight the Solution branch, RMB gt Insert gt
  Solution Information gt Solution Information.

The graphics window will change to the Worksheet
view. Scroll to the bottom of the solution
information and note the Elapsed Time (this will
vary by machine). Elapsed Time
___________________________
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Workshop 4.2 Comparison

• Using the example shown in the exercise we now
  compare analyses (note, your actual results may
  vary from those shown here. Also, your solution
  times will almost certainly differ from those
  shown here.
• Maximum von-Mises Stress Results
• Axisymmetric 0.840 MPa
• 3D Symmetry 0.735 MPa
• Note, meshing differences account for the results
  difference (see next page). Recall that the 2D
  model resulted in a more refined mesh than the
  3D. The next page shows the results from a more
  refined 3D model.
• Elapsed Time
• Axisymmetric 7.0 seconds
• 3D Symmetry 46.0 seconds

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Workshop 4.2 Comparison

• Maximum von-Mises Stress Results
• 3D Symmetry (refined) 0.852 MPa
• Elapsed Time
• 3D Symmetry (refined) 578.0 seconds

Results using a more refined mesh with the 3D
symmetry model
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