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Edges along z are of two different lengths, as should be apparent from the geometry display. For instance, the edge between keypoints #5 and #9 is smaller than that between keypoints #3 and #5. By setting the element size rather than the number of divisions, we can use the same parameter for both edge lengths.
Bring up the MeshTool: Main Menu > Preprocessor > MeshTool
We are going to continually use the MeshTool to generate the mesh. So resize and rearrange the windows slightly so that you can access the MeshTool, ANSYS GUI, and tutorial simultaneously.
If you have trouble selecting the correct line below, hold down the left mouse button until the line is selected and then release the left button. If you want to deselect a line, right-click to go into deselect mode, left-click on the line to be deselected and right-click again to go back into select mode. |
Under Size Controls and Lines, click Set. Pick all four lines in the x-_direction. and click OK in the pick menu. Enter NDIV_X for No. of element divisions and click Apply.
Next, pick all three lines in the y-direction and click OK in the pick menu. Enter NDIV_Y for No. of element divisions and click Apply.
Last, pick all five lines in the z-direction and click OK in the pick menu. Enter SIZE_Z for Element edge length. Make sure No. of element divisions is blank. Click OK.
Plot lines to see the element divisions along edges and check that they have been set correctly: Utility Menu > Plot > Lines. If you made an error, repeat the above steps before saving.
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We'll first mesh the plate using real constant set #1. Under Element Attributes in MeshTool, click on Set. You will see that the element type and material number are already set and the default real constant set is #1. These are the options we need for the plate; so these don't need to be changed. Click Cancel.
Plot areas: Utility Menu > Plot > Areas
Click on Mesh in MeshTool. Pick area A1 and click OK. The resulting mesh for the plate is displayed.
Generate Mesh for Vertical Stiffener
Under Element Attributes in MeshTool, click on Set. Set Real constant set number to 2 and click OK.
Plot areas: Utility Menu > Plot > Areas
Click on Mesh in MeshTool. Pick area A2 and click OK. The resulting mesh for the plate is displayed.
Generate Mesh for Horizontal Stiffener
Under Element Attributes, click on Set. Set Real constant set number to 3 and click OK.
Plot areas: Utility Menu > Plot > Areas
Click on Mesh in MeshTool. Pick areas A3 and A4 and click OK.
Let's change the graphical display so that the geometry is displayed as a solid model with the shell thicknesses shown. At the command prompt, type /eshape, 1 and then select Utility Menu > Plot > Replot. When the /ESHAPE command in issued, ANSYS uses the real constants associated with each element to determine its shape. (Note that commands are not case-senstive.)
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You can access different model views such as front, right, isometric etc. using the buttons to the right of the graphics window. At the bottom of this row of icons is the Dynamic Model Mode |
Save: Toolbar > SAVE_DB
Copy Mesh in x-Direction
Turn off the element shapes to make the display less cluttered by entering the following commands:
/eshape,0
/replot
Plot areas: Utility Menu > Plot > Areas
Copy areas: Main Menu > Preprocessor > Modeling > Copy > Areas
Pick A1, A3, and A4 and click OK. (Hold down the left mouse button until the correct area is selected.)
Copy Areas menu: We want two copies including the original, so leave Number of copies as 2. For X-offset, enter W1/ (2*NSX), leave Y- and Z-offsets blank and click OK.
Since the associated keypoints are also copied over, you'll notice that there is a collection of two coincident but separate keypoints along shared boundaries where the original and copied entities overlap. It's key that we [merge these coincident keypoints|SIMULATION:Semi-monocoque shell page 5]; we'll undertake this after we are finished with the copy step.
Have the elements associated with the areas also been copied? Check this: Utility Menu > Plot > Elements
Save: Toolbar > SAVE_DB
As with keypoints (and lines too), there is a collection of two coincident but separate nodes along the shared boundaries. Let's convince ourselves of this truism:
- Turn on node numbers (in addition to keypoint and area numbers) using Utility Menu > PlotCtrls > Numbering
- Display elements and nodes together: Utility Menu > PlotCtrls > Multi-Plot Ctrls > OK. Leave only Nodes and Elements turned on and click OK. Select Utility Menu > Plot > Multi-Plots.
- Zoom into the bottom-center of the model as in the snaphsot below. At the bottom of the symmetry plane, you should notice that there are actually two nodes, 2 and 172. Node 2 is associated with the original area and node 172 with the copy. We'll merge coincident nodes a little later. (Note that your node numbers may be different from mine since numbering can vary on different computer systems.)
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Copy Mesh in y-Direction
Plot areas: Utility Menu > Plot > Areas
Click on the Fit View and Isometric View icons in the rightmost part of the GUI.
Copy areas: Main Menu > Preprocessor > Modeling > Copy > Areas
Pick A1, A2, and A5 and click OK.
Copy Areas menu: Leave Number of copies as 2. For Y-offset, enter L1/ (2*NSY); delete X-offset; leave Z-offset blank and click OK.
Check the resulting mesh for sub-section ABCD: Utility Menu > Plot > Elements
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Copy areas: Main Menu > Preprocessor > Modeling > Copy > Areas > Pick All
Copy Areas menu: Number of copies = NSX; X-offset = W1/NSX; Y- and Z-offsets should be blank or zero. Click Apply.
Repeat copy in y-direction: Select Pick All again in the pick menu.
Copy Areas menu: Number of copies = NSY; Y-offset = L1/NSY; X- and Z-offsets should be blank or zero. Click OK.
Check the resulting mesh: Utility Menu > Plot > Elements
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Select Main Menu> Preprocessor> Numbering Ctrls> Merge Items
For Type of item to be merged, select All and click OK. This will merge all coincident entities.
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Compress numbering for all items (nodes, elements, etc.): Main Menu> Preprocessor> Numbering Ctrls> Compress Numbers
For Item to be compressed , select All and click OK.
Re-check the range of node numbers after compressing. You should find that the range of node numbers is reduced since there are now no gaps in the numbering.
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