Today, it seems there are endless options for optimizing part geometry. Here at CATI we offer no less than 3 solutions that can accomplish just that; Topology study in SOLIDWORKS Simulation Professional, Tosca from SIMULIA, and Altair Inspire. All three of these are great tools, and each has their own merits. However, one of the main downsides to topology studies is that parts come out as a tessellated mess, like the one below:
Uniquely, Altair Inspire not only performs topology analysis, but also includes a great PolyNURBS tool that excels at making the organic geometry we so desire.
The part pictured above is a bracket for a mountain bike rear suspension, an ideal candidate for topology studies. It’s my first real experience with Altir Inspire, so the goal of this blog is to show a few features of the PolyNURBS tool as we work our way through.
I imported this part from SOLIDWORKS, but the same process stands for native Altair parts or otherwise.
It’s best to start by cleaning up sharp edges. Use the PolyNURBS selection at the top of the screen to open the toolbar and Select smooth. From there select the mesh from the graphics window and enter the parameters for the smoothing algorithm.
From here we can begin “wrapping” the mesh with PolyNURBS by selecting the Wrap tool. Since our part is symmetric about the center, we will start there. Hover the mouse over the area, and a red preview of the initial cross section and a black box indicating the cage of the PolyNURBS shows up.
Each click generates a PolyNURBS cage. We will work our way to the left side of the part. Note that we have made a protrusion into the cylindrical hole of the part. This is intentional.
Each face of a cage can be used for starting a new wrap feature. To begin making the right side of the part, I select the long face of the second cage to start wrapping that direction.
Creating the desirable wrap cage takes some manipulation of the viewport but is as easy as just continuing to click. Again, I have extruded the shape into the area that I want the cylindrical hole.
Sometimes faces of the cage are too large for the next section of wrapping you wish to begin. You can fit the faces to more manageable sizes using the split tool. There’s an option to split the whole cage or just a face. In this case, we Split the face. Select a location on the edge of the cage face you want to split and a location on the opposite edge. The face of the cage will then be split.
We continue creating wrap sections from the cage faces until we have an acceptable shape.
Sometimes faces of a PolyNURBS cage are not facing the direction you want them to. To change this, simply de-select whichever tool we are in (the wrap tool in our case) and select the face. Moving the mouse around the face will give you in-context options to move and rotate the face of that cage to orient it.
As you can see from the screenshot above, I need to connect those two members of the part. I can simply go back into the wrap tool and select the cage faces that are now more directly facing each other.
Next, we’ll begin the process for our cylindrical holes. We select the circle tool from the top menu, then we are prompted to create a new plane. Select in the graphics window to set the plane going normal to the axis of our cylinders.
Then, Altair Inspire will bring up a grid for sketching on. Adding sketch entities will bring up an in-context menu to size them properly.
Once the lines are sketched, we click Transfer Sketch to create the circles as a new part in the model.
After renaming the part “Circles,” it shows up in the Model Browser and the associated circular surfaces now show up in the graphics area.
Now, we use the Push/Pull tool to extrude the faces of those circles. We will extend them further than needed. These cylinders represent the holes for our bracket and will be removed via Boolean operations later.
We need another set of cylinders to represent the material that will surround the holes, so repeating the same process as above, we can create those.
Before we begin Boolean operations, we convert the PolyNURBS body to a part. So, we will go through and finalize the PolyNURBS shape. You will find this easy and intuitive. Simply click and drag vertices, edges, and faces of cages and watch how the shape changes. When doing this, watch out for areas of red appearing in the model. This indicates self-intersecting geometry and will not be a valid PolyNURBS surface.
A simple Ctrl+Z will undo these errors.
To convert this finalized shape to a part, right click its name in the Model Browser and select Convert Bodies to Parts.
Finally, we can begin Boolean Operations. We want to subtract the first set of cylinders from the rest of the parts in the model. So, we select Boolean, Subtract, define the targets (the bodies to remove material from), and select the tools (the parts we will be using to remove the material), then click Subtract.
Next, we will combine the PolyNURBS surface with the second set of cylinders we created. So, we will select those bodies and click combine.
Finally, we can perform the final mirror to obtain the whole part. Select Mirror, then the part to be mirrored, then the plane to mirror it about.
At last, we are left with the finalized part. Looks a lot better than the original if you ask me.
This was my first attempt at a PolyNURBS part outside of the tutorials in Altair Inspire, but I found the process to be quick, intuitive, and easy. It is a big step towards the organic, optimized geometries of the future.
For more information about optimization tools, or freeform modeling tools like this one, call us today at 888-308-2284, or find a local office near you.
Matthew Sherak, CSWE-Simulation
Simulation Product Specialist, Application Engineer
Computer Aided Technology, Inc.