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Geometry
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The Geometry of the Tertiary Truss is the most complicated part of the design process. Many hours were spent creating the Solidworks geometry for the truss. This requires much time and practice in Engineering Design. However, this tutorial focuses on properly analyzing the structure, not creating it from scratch, so we will provide the created geometry. ANSYS is able to import Solidworks files directly, however, it also requires the Solidworks program to be installed on the same machine, so we provide the file in .STEP format, the "neutral" format for computer modelling.
Click here to download the geometry file.
Unzip the folder, and open up ANSYS. Use the import button to open up the file. (Remember to select "geometry file" from the drop down menu, so you can see .STEP files.)
After opening and generating the import, you should see the entire geometry has been detailed in the window. You should take this time to familiarize yourself with the structure.
For users of ANSYS 15.0, please check this link for procedures for turning on the Auto Constraint feature before creating sketches in DesignModeler. |
Line Body Truss
1. Parts
Part groupings are ways for ANSYS to automatically group pieces together and create automatic connections. We should create 2 part groups: the Truss K-1, and the Tertiary Subframe Surface.
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The shell models of the entire Subframe Part all need a thickness of 2.75 mm, (2.75e-3 m).
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2. Coordinate Files
If we were to directly evaluate the imported geometry, ANSYS would consider the Truss as solid body objects, and generate a highly complex mesh on each of the Truss members by creating a mesh around each circular and rectangular tube. This is wasted computational time. Each of the Truss members is a simple beam, and can be evaluated using beam theory. In order to tell ANSYS to compute it as such, we need to convert these members into line bodies and assign them a cross section.
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You will need to change the Definition to "From Coordinates File", as well as the Operation to "Add Frozen," and then select your file and generate. Adding Frozen means that the bodies created will not merge with existing bodies.
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Remember to select all the created line bodies and create a new Part out of them. I recommend naming it "Truss Assembly."
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Once the line bodies have been created, we need to assign cross-sections to them. There are two types: the Cylinder Tube and Rectangular Tube.
Circular Tube
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Rectangular Tube
Apply the Circular Tube cross sections to the outside and conical line bodies, and the Rectangular Tube cross section to the horizontal line bodies.
Rectangular Offset
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As you can imagine, there are times and geometries that this simple result will not happen. Always check the individual coordinate systems of the line bodies.
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5. Geometry Connections
In the Setup portion, we will need to define the connections between the geometry pieces, specifically the line bodies we have defined as the truss supports. The surface areas of the flexure mounts provide a good surface to define a connection between the line body and mounts. However, we need to define the area where the line body connects to the circular mount pad: equivalent to the diameter of the truss' cross-section.
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Select "New Plane", then select "From Face" in the type detail. Then select the circular base support plane, and apply.
Now that the plane has been created, we will create a sketch for the circular connections. Click the "New Sketch" button with the created plane selected. Once created, click on the "Sketching tab" to start sketching.
Create a circle of .03m diameter centered around the construction points. There are a total of six circles on this sketch.
Return to the modelling tab. Now that the sketch has been created, we actually have to apply it to the geometry. Otherwise, it is just an unattached sketch. Since we are just making a surface area to attach a connection to, all we need to do is project some lines into the surface. This requires two steps: 1. Create a Concept > Lines from Sketchs. Select the sketch you created, and Add Frozen.
Generate. Now that the lines are created, we need to "etch" them into the base surface. Create a Tools>Projection. Use Edges onto Face. Select the created lines as the edges, and the surface face for the face. Make sure "Imprint" is selected to "Yes."
Generate the Projection. This now has created lines on the Circular Mount Pad. We can now use the created surface area as a connection surface for the Setup step.
Lastly, remember to show all the hidden parts. Remember to keep the imported Truss (as machined) parts suppressed. Suppress the Line bodies created by the above step.
