How to Sketch and Mesh 2-D Models

Superdraw sketching and meshing capabilities can be used to build 2-D models directly within the FEA Editor environment of FEMPRO. These integrated Superdraw modeling tools complement ALGOR's full suite of modeling capabilities including InCAD technology and CAD support and make it easy to perform first-pass or proof-of-concept analyses. For example, you can quickly create and analyze a 2-D static model to gain an understanding of its loading and behavior within the linear range as preparation and justification for a subsequent 3-D nonlinear analysis or Mechanical Event Simulation (MES).

The general process for building 2-D models in the FEA Editor environment consists of three steps:

1. Create a sketch of the wireframe of each part.
2. Specify contact, edge divisions and refinement points.
3. Generate the 2-D mesh.

Sketching Parts

Before beginning a sketch, plan ahead to determine the parts of your model and how they fit together. Keep the following requirements in mind:

• Each part must be drawn in its own sketch.
• Each part must consist of a single enclosed area and must be a uniform material.
• Line elements can be added to 2-D models but must be drawn in the YZ plane at X=0.
• Sketch parts cannot be added to models with solid element parts.
• The lines where two parts meet must be identical in both parts.

The sketching capabilities are accessed through the GEOMETRY pull-down menu or the "Sketch Entities" and "Sketch Tools" toolbars. To begin a sketch, use the "Geometry:Sketch:New Sketch" command sequence (see Figure 1) or click on the "New Sketch" icon in the "Sketch Entities" toolbar. (The "New Sketch" command will only be available when you open a new model or a model that exists entirely in the YZ plane.)

Figure 1: The "New Sketch" command is used to create a new sketch in a new part.

In the tree view, a new part number will be added with the sketch number nested beneath it. In the display area, a grid drawn in the YZ plane will appear. Right click in the display area and a pop-up menu of options for the sketch will appear including the "Show Grid" command, which will toggle off the grid display. (You can modify grid settings by using the "Sketching" tab of the "Options" dialog, which can be accessed with the "Tools:Options..." command sequence.)

Use the "Geometry:Sketch Entities" command sequence to access a menu of sketch entities that can be added including a point, a line, tangent lines, a rectangle, an arc, a circle and a spline. Additionally, selected entities can be defined as construction entities (which are used for sketching operations such as trimming or mirroring but are not considered during meshing) or as regular entities (see Figure 2).

Figure 2: Adding a rectangle sketch entity.

Use the "Geometry:Tools" command sequence to access a menu of tools for performing operations on sketch entities including point move, split, intersect, fillet, trim, extend, rotate, scale, move, mirror and parallel offset (see Figure 3).

Figure 3: Moving a selected sketch entity.

Specifying Contact, Edge Divisions and Refinement Points

Once all of the sketches are complete, specify options for the 2-D meshing operation. To do so, select the "Sketch" heading(s) in the tree view (add to the selection set by holding down the Ctrl key) and then right click and choose the "Generate 2-D Mesh..." command (see Figure 4) to access the "2-D Mesh Generation" dialog.

Figure 4: With the sketch headings selected in the tree view, right clicking accesses a pop-up menu of options including the "Generate 2-D Mesh..." command.

Before performing the meshing operation, you can perform the following meshing-related operations:

• Contact – You can specify contact between any two coincident edges in an assembly. Select the edge and right click and then choose "Contact" and choose from three contact options: bonded, free/no contact or surface contact (see Figure 5).

Figure 5: Specifying surface contact between coincident edges.

• Divisions... – Control how many elements are created along a particular edge by selecting the edge and right clicking and then choosing the "Divisions..." command. The "Sketch Entity Mesh Divisions" dialog will appear. Specify the number of divisions to be made along the selected edge (see Figure 6).

Figure 6: Specifying edge divisions to control how many elements are created along a particular edge.

• Add Refinement Point... – Add a refinement point to the sketch by right clicking at the location where you want to define the refinement point and choosing the "Add Refinement Point..." command. The "2D Mesh Refinement" dialog will appear (see Figure 7). Specify parameters for the refinement point including choosing between three types of refinement: divide, radius divide and mesh size.

Figure 7: Specifying refinement point parameters.

Generating the 2-D Mesh

After using the "Generate 2-D Mesh..." command to access the "2-D Mesh Generation" dialog, you can specify the element shape and the mesh density or mesh size (see Figure 8). The default mesh density should be a good first approximation for most models. Afterward, you can add refinement points as needed to selectively refine regions. The "Advanced" section provides additional meshing parameters (including Angle, Geometric Ratio, Close Factor, Refinement Factor and Tolerance), but, for most cases, the default values will suffice. Click on the "Preview" button to display a preview of the meshed model. After meshing, this button will change to "Sketch", which you can use to return to the sketch. Thus, you can easily toggle between the preview mesh and the sketch to go back and modify the sketch. When you are satisfied with the mesh, click on the "OK" button to accept the mesh.

Figure 8: Using the "Two-Dimensional Mesh Generation" dialog to perform the meshing operation.

With the mesh defined, you can specify data needed for analysis including the element definition, loads, constraints and analysis parameters and then analyze the model.

Thus, the ability to sketch and mesh multiple parts in the FEA Editor environment provides flexibility and convenience for 2-D modeling. For a step-by-step demonstration of these sketching and meshing capabilities, see the Modeling with 2-D Elements Tutorial. For more information about Superdraw 2-D sketching and meshing tools in the FEA Editor environment, see the ALGOR User's Guide.