Sunday, 3 October 2010

Modeling Tools

Introduction

This tutorial was completed using ANSYS 7.1 The purpose of the tutorial is to show several modeling tools available in ANSYS.
Three methods will be shown to create the meshed plate shown below.

Using Cutlines in ANSYS

  1. Give example a TitleUtility Menu > File > Change Title ...
    /title, meshing a plate using cutlines
  2. Open preprocessor menuANSYS Main Menu > Preprocessor
    /PREP7
  3. Create a block at origin (0,0) with a width and height of 1Preprocessor > Modeling > Create > Areas > Rectangle > By 2 Corners...
    blc4,0,0,1,1
  4. Divide the area into 4 parts using 2 diagonal lines
    • Create a line Preprocessor > Modeling > Create > Lines > Lines > Straight Line
    • Select the top left keypoint and draw the line to the bottom right keypoint by clicking on that keypoint
    • Now divide the area into 2 areas using the line by selecting Preprocessor > Modeling > Operate > Booleans > Divide > Area by Line
    • Select the area and click OK in the 'Divide Area by Line' window
    • Now select the line and click OK in the 'Divide Area by Line' windowThe area is now divided into 2 as shown in the figure below. A warning may appear with the statement "Line 5 is attached to 2 area(s) and cannot be deleted. This is expected because the command which divides the area deletes the line used to create the area. However, in this case, the line is required to define the new areas. Click OK and ignore the warning.

    • Now we need to further divide the 2 areas to make 4 areas. Using the same method, create a line from the top right keypoint to the bottom left. Be sure to select both areas to divide, otherwise, you will have to create the line again to divide the second area.

  5. Define the Type of Element
    6. Preprocessor > Element Type > Add/Edit/Delete... > Add... > Structural Mass, Solid > Quad 4node 42For this problem we will use the PLANE42 (2D plane stress or plane strain) element. This element has 4 nodes each with 2 degrees of freedom(translation along the X and Y axes).
  6. Select Plane Stress with Thickness
    7. In the Element Types window, select Options... and in Element behavior select Plane strs w/thk
  7. Define Real Constants
    8. Preprocessor > Real Constants > Add/Edit/Delete > Add... > OKIn the 'Real Constants for PLANE42' window, enter the thickness: 0.1
  8. Define Element Material PropertiesPreprocessor > Material Props > Material Models > Structural > Linear > Elastic > IsotropicIn the window that appears, enter the following geometric properties for steel:
    1. Young's modulus EX: 200000
    2. Poisson's Ratio PRXY: 0.3

  9. Define Mesh SizePreprocessor > Meshing > Size Cntrls > ManualSize > Lines > All Lines...To obtain the desired mesh we need to set NDIV to 2
  10. Create a hardpointPreprocessor > Modeling > Create > Keypoints > Hard PT on line > Hard PT by ratioFor demonstration purposes only, we are going to create a hardpoint on one of the diagonal lines. Select the bottom right diagonal line and enter a ratio of 0.41 This will ensure the creation of a node at a location 41% down the line
  11. Mesh the framePreprocessor > Meshing > Mesh > Areas > click 'Pick All'
    amesh,all    The mesh should then appear as shown below. Note that the node is not at the midway point on the bottom right diagonal line due to the hardpoint.

Merging Objects in ANSYS

  1. Clear the memory and start a new modelUtility Menu > File > Clear & Start New ...
    /clear
  2. Give example a TitleUtility Menu > File > Change Title ...
    /title, meshing a plate by copying elements
  3. Open preprocessor menuANSYS Main Menu > Preprocessor
    /PREP7
  4. Define KeypointsPreprocessor > Modeling > Create > Keypoints > In Active CS...
    K,#,x,y,zWe are going to define 3 keypoints as given in the following table:

    KeypointCoordinates (x,y)
    1(0,0)
    2(1,0)
    3(0.5,0.5)

  5. Create AreaPreprocessor > Modeling > Create > Areas > Arbitrary > Through KPs
    a,k1,k2,k3...We are going to define an area through keypoints 1,2,3. Select keypoints 1,2 and 3 and then select 'OK'.
  6. Define the Type of Element
    7. Preprocessor > Element Type > Add/Edit/Delete... > Add... > Structural Mass, Solid > Quad 4node 42As in the previous mesh, we will use the PLANE42 (2D plane stress or plane strain) element. This element has 4 nodes each with 2 degrees of freedom(translation along the X and Y axes).
  7. Select Plane Stress with Thickness
    8. In the Element Types window, select Options... and in Element behavior select Plane strs w/thk
  8. Define Real Constants
    9. Preprocessor > Real Constants > Add/Edit/Delete > Add... > OKIn the 'Real Constants for PLANE42' window, enter the thickness: 0.1
  9. Define Element Material PropertiesPreprocessor > Material Props > Material Models > Structural > Linear > Elastic > IsotropicIn the window that appears, enter the following geometric properties for steel:
    1. Young's modulus EX: 200000
    2. Poisson's Ratio PRXY: 0.3

  10. Define Mesh SizePreprocessor > Meshing > Size Cntrls > ManualSize > Lines > All Lines...To obtain the desired mesh we need to set NDIV to 2
  11. Mesh the areaPreprocessor > Meshing > Mesh > Areas > click 'Pick All'
    amesh,all

  12. Mirror the geometry
    • Create local coord system to mirror geom.
      Select: Utility Menu > WorkPlane > Local Coordinate Systems > Create Local CS > At specified Loc
    • We are first going to mirror the geometry about the diagonal from node 1 to 4. Click on the lower left node (bottom corner) and select 'OK'
    • As shown below, create a coordinate system rotated 45 degrees about Z
    • Next, mirror the geometry
      Select: Preprocessor > Modeling > Reflect > Areas Click 'Pick All'
    • In the window that appears select X-Z plane Y and click 'OK'. This will mirror the geometry about the X-Z plane
    • Use the same technique to obtain the full geometry

  13. Re-activate the global coordinate systemUtility Menu > WorkPlane > Change Active CS to > Global Cartesian
    csys,0
  14. Plot ElementsUtility Menu > Plot > ElementsYour mesh should now appear as follows:

    However, you are not done! If you plot the node numbers you will note that some duplicate nodes exist (created in mirroring).

  15. Merge duplicate nodes/elementsPreprocessor > Numbering Ctrls > Merge Items > All
    nummrg,all

Gluing Areas in ANSYS

  1. Clear the memory and start a new modelUtility Menu > File > Clear & Start New ...
    /clear
  2. Give example a TitleUtility Menu > File > Change Title ...
    /title, meshing a plate by copying areas
  3. Open preprocessor menuANSYS Main Menu > Preprocessor
    /PREP7
  4. Define KeypointsPreprocessor > Modeling > Create > Keypoints > In Active CS...
    K,#,x,y,zWe are going to define 7 keypoints as given in the following table:

    KeypointCoordinates (x,y)
    1(0,0)
    2(0.5,0)
    3(1,0)
    4(0.75,0.25)
    5(0.5,0.5)
    6(0.25,0.25)
    7(0.5,0.166667)

  5. Create AreaPreprocessor > Modeling > Create > Areas > Arbitrary > Through KPs
    a,k1,k2,k3...Now we are going to define 3 areas; (1,2,7,6), (2,3,4,7), (4,5,6,7)
  6. Mirror the geometry
    • As shown in the previous section, create a local coordinate system and mirror the geometry
      Utility Menu > WorkPlane > Local Coordinate Systems > Create Local CS > At specified Loc
    • Then, mirror the geometry, select: Preprocessor > Modeling > Reflect > Areas
    • Do this twice to obtain the full geometry

  7. Re-activate the global coordinate systemUtility Menu > WorkPlane > Change Active CS to > Global Cartesian
    csys,0
  8. Glue the areas togetherPreprocessor > Modeling > Operate > Booleans > Glue > Areas
    aglue,allWe need to glue the areas together so that the areas are attached but that the subdivided areas remain to give us the elements we want
  9. Define the Type of Element
    10. Preprocessor > Element Type > Add/Edit/Delete... > Add... > Structural Mass, Solid > Quad 4node 42As in the previous mesh, we will use the PLANE42 (2D plane stress or plane strain) element. This element has 4 nodes each with 2 degrees of freedom(translation along the X and Y axes).
  10. Select Plane Stress with Thickness
    11. In the Element Types window, select Options... and in Element behavior select Plane strs w/thk
  11. Define Real Constants
    12. Preprocessor > Real Constants > Add/Edit/Delete > Add... > OKIn the 'Real Constants for PLANE42' window, enter the thickness: 0.1
  12. Define Element Material PropertiesPreprocessor > Material Props > Material Models > Structural > Linear > Elastic > IsotropicIn the window that appears, enter the following geometric properties for steel:
    1. Young's modulus EX: 200000
    2. Poisson's Ratio PRXY: 0.3

  13. Define Mesh SizePreprocessor > Meshing > Size Cntrls > ManualSize > Areas > All Areas...To obtain the desired mesh we need to set SIZE to 1
  14. Mesh the areaPreprocessor > Meshing > Mesh > Areas > click 'Pick All'
    amesh,all    And again we obtain the desired mesh:
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