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VisualAnalysis Tutorials: Complex Mesh Generation

Introduction

We want to create a rectangular mat footing that has a complex loading of circular tanks sitting on top. In this project we are not going to model the tanks, we just want the loads from them to be applied easily to the mat. In order to accomplish this, we will create a complex plate mesh on the mat that includes a ring of nodes for each tank.

Version Note: This tutorial was created using a prior version of VisualAnalysis. Minor changes to the software may have occurred including new features and graphics updates. The appearance of dialog boxes and the Project Manager may be altered slightly. () or the User's Guide () if steps do not appear correct.

Step1 : Define our "Area"

Specifically our mat will be 60 ft by 40 ft. We will set up a "Space Frame" project so that loads can be applied "out of plane". Set up a Grid (in Project Manager) in the ZX direction to be the size of our mat, with big dots.

First we will create an area the size of our footing. Go to Model | Drawing Mode | Areas and starting the top left corner at (0 ft, 0 ft, 0 ft) drag the mouse between the nodes like you were drawing a plate element. You complete the node chain by clicking on the original starting node. This area will define the external boundary of the surface to be meshed.

Step 2 : Create Hole Areas for Each Tank

We will now create the circular rings of nodes on the mat that can be easily loaded later representing tank weight. To accomplish this we will draw areas within our defined surface. First, set up a polar grid originating at (15 ft, 0 ft, 20 ft) with a radius of 10ft and nodes at 22.5 degrees apart (Set the # of Sectors to 16). Orient the grid 900 to the X & Y axes.

Now draw an area within the polar grid to create a space for the first tank. (You may have to hide areas using the Filter | Show or Hide in order to draw the new areas.) Once you've clicked on the starting node a dialog box will appear. Select "Make it a Hole."

In a similar process, create an equivalent hole originating from point (45 ft, 0 ft, 20 ft). With both holes in place your model should appear like the one shown.

Step 3 : Mesh the Surface

To create a mesh over the rectangle, including the holes, we simply go to the Project Manager and check Yes for Auto-Meshing. Finally, we can also specify the material thickness and type here. For now, let's use 12" thick, 4 ksi concrete.

Note: The mesh count can be changed in the "Modify" tab of the Project Manager when nothing is selected. (The default of 300 was used here.)



Step 4 : Generate the circular meshes under the tanks

Our final step is to fill-in the missing mesh areas of the mat footing. We will use the Generate Standard features located in the Create tab of the Project Manager. Locate the Circular Disk Mesh option under Plates. For the first tank, specify the origin at (15 ft, 0 ft, 20 ft) and click Next.

In the next dialog box specify the rotation to be about the Y-Axis direction. Click Next. For the Starting Rotation Axis, choose the Z-axis and click Next. In the last dialog box input values of 0 ft for the Inner radius, 10 ft for the outer radius, 360 degrees for the Interior angle, 3 radial elements (M), and 16 circumferential elements (N). Keep in mind that the number of circumferential elements should be compatible with our previously drawn shape to ensure nodes will line up. If you end up with fewer or more nodes here than were created in the surface mesh, you will have connectivity problems (gaps or overlaps).Select Finish. You will be prompted for plate thickness and material. As before, choose 12" thick 4 ksi concrete. Select OK.

You should now see the hole filled and the elements lining up nicely around the circular boundary. Repeat this step for the remaining hole in the mesh, changing the origin of the circular disk to (45 ft, 0 ft, 20 ft). The final mesh is shown above with rings of circular elements selected to emphasize their locations.

Step 6: Completing the Project

At this point, the complex mesh is complete. To complete the project you would want to create compression-only spring supports to model the soil (i.e., using the Model | Soil Spring Generator), and apply loads in various places, such on the nodes defining the rings of the tanks.

Further Tips: You will want to create a couple of rigid supports in the X and Z directions to ensure the overall model is stable. Also, you may find that renaming certain nodes and/or plates will help you filter views to make selection of these items easier for loading or reporting.