Drawing Planes


Drawing planes are used to add geometry to the model. Instead of the freedom of adding the geometry in 3-D space, the geometry is always snapped into the plane. In addition to the obvious advantage of being able to draw flat geometry, regions created with construction objects drawn in a plane can be meshed with the "2-D mesher". See the page "Meshing Overview: Meshing Hand-built Models: 2-D Mesh Generation" for details.

 

When using a drawing plane, the FEA Editor environment is in "sketch" mode. Hence, the terminology "sketch" and "drawing plane" will be used interchangeably.

Creating a New Plane:

The three global planes XY-Top, YZ-Right, and XZ-Front exist by default for all new models. Additional planes can be created by using the "Geometry: New Plane..." pull-down menu, or by right-clicking on the "Planes" branch of the tree view and choosing "New Plane...".

 

You can select between the three planes parallel to the global axes ("XY", "YZ" or "XZ"). You can also select the "Advanced..." option or the "3 points..." option to define an off-axis plane. Activating the "Use Offset" checkbox will allow you to offset one of the global planes from the origin. A positive offset places the plane in the positive direction. For example if you want to draw in the X=10 plane, select the "YZ" option, activate the "Use Offset" checkbox and type "10" in the adjacent field.

 

Entering, Using, and Exiting "Sketch" Mode:

To enter sketch mode to draw on a plane, right-click on the desired drawing plane in the tree view and choose "Sketch". When in sketch mode, a grid will appear in the display area and the drawing plane is shown in bold in the tree view. All sketching will be done in this plane. The grid can be turned off by right clicking on the plane in the tree view and selecting the "Hide" command. The spacing of the grid can be customized in the "Sketching" tab of the "Tools: Options..." screen.

 

Geometry is added to the sketch just like any other geometry: use the "Geometry: Add" pull-down menu. All properties such as part, surface, and layer number, and any object specific input, are used in the sketch mode just like it is in the 3-D mode. (See the page "Adding Geometry" for details.) The only real difference between adding these objects in 3-D mode versus adding them in sketch mode is whether the entered points snap to the drawing plane or not.

 

When drawing sketch entities, if the cursor is close to a grid point, a lock icon will appear on the cursor. If you click, the item you are drawing will be snapped to that grid point. Likewise, you can snap the new geometry to existing geometry. The points will be projected into the drawing plane.

 

When an item is added to a sketch, a branch is created under the appropriate part that lists the drawing plane, and this branch includes an entry for each item drawn in that sketch. Click on the drawing plane entry under the part to highlight the corresponding items.

 

To exit sketch mode, right-click on the drawing plane and deactivate "Sketch". Also, activating the sketch mode for another plane will deactivate the sketch mode for the current plane.

Copying Between Sketches:

Here are the ways to copy items or sketches to other sketches:

Note

If a construction object in a sketch is selected and changed with the "Geometry: Tools: Move or Copy" command, then the object is no longer associated with a sketch. It becomes a 3-D Object and is listed in a separate branch under the part.

Converting from 3-D Objects to a "Sketch":

There are situations in which a construction object is not in a drawing plane, so the tree view lists the item as a 3-D object. Some commands are not available on 3-D construction objects, such as 2D meshing. These 3-D objects can be copied to a sketch as follows:

  1. Select the 3-D construction objects. ("Selection: Select: Construction Objects")

  2. Copy or cut the objects to the clipboard. (Right-click and choose either "Cut" or "Copy".)

  3. Activate the drawing plane into which the objects should go. (Right-click on the appropriate plane under the "Planes" branch of the tree view and choose "Sketch".)

  4. Paste the 3-D objects into the part. (Right-click on the part name in the tree view and choose "Paste".) Note that the object must be pasted into a sketch on a different part than the original objects.

Note that the original 3-D construction object is not projected into the drawing plane. Therefore, the object should lie in the plane into which it is being pasted.

Calculating the Properties of a Sketched Region:

The cross sectional properties of a sketch can be calculated. The guidelines for the sketch or sketches are as follows:

  1. Draw the region to be calculated using construction objects.

  2. Draw the objects while in sketch mode. (See "Entering, Using, and Exiting "Sketch" Mode:" above.)

  3. The objects can be in different parts but need to be in the same drawing plane. The combination of all parts on all selected sketches will define the region or regions.

  4. Any drawing plane can be used. The results will be in the local coordinates of the plane.

  5. The sketch must enclose an area or multiple areas.

  6. Holes within the area are permitted.

  7. Regions can overlap, in which case the overlap region is calculated as if it were a hole, but separate regions should not touch. See Figure 1.

(a) Two overlapping regions (above) are supported by the 2D Moment of Inertia. The overlapping region between the square and the circle becomes a hole in the cross section. The calculations are based on shaded the regions (below).

(b) Two regions that do not overlap (above) are not supported by the 2D Moment of Inertia. The problem areas are identified with the inverted triangles (below) when the command is executed. In order to calculate this area, remove the line in common between the square and the semi-circle. (Alternatively, a duplicate line – one for the square and one for the semi-circle – could be used. For example, the duplicate would be required if the square and semi-circle were on separate parts and the two regions were going to be meshed with the 2D mesh engine.)

Figure 1: Proper and Improper Regions for 2D Moment of Inertia

 

Once the sketches are made, either select the plane in the "Planes" branch of the tree view or select the plane entries in the tree view under the part, then right-click, and choose "2D Moment of Inertia". Selecting the "Planes" branch is equivalent to selecting each of the individual planes appearing under each part. The calculator will split the combined sketches into a series of horizontal rectangular strips and perform a numerical integration based on these strips. The results are given in the "2-D Moment of Inertia Results" dialog and consist of the following:

A construction vertex is also added to the model at the location of the center of gravity.

 

Tip

The accuracy of the calculation depends on the number of divisions used to split the sketch into rectangular strips. The height of the sketch (in the v direction) is divided into the number of divisions specified under the "Tools: Options..." dialog on the "Sketching" tab.

 

The "Save Results" dialog will appear when the "Save" button is clicked. Choose the file name and location of the area calculation results. Activate the "Append" checkbox on the "Save Results" dialog before clicking the "Save" button to append the current results to an existing file. Otherwise, the existing file will be overwritten with the current results.

 

Similar calculations can be performed on fully meshed models by using the "Tools: Weight and Center-of-Gravity..." menu. See the page "General Options: Weight and Center of Gravity Calculator".