We’ve discussed topological optimization in this space before, notably here:
If you’re not familiar with topological or topology optimization, a simple description is that we are using the physics of the problem combined with the finite element computational method to decide what the optimal shape is for a given design space and set of loads and constraints. Typically our goal is to maximize stiffness while reducing weight. We may also be trying to keep maximum stress below a certain value. Frequencies can come into play as well by linking a modal analysis to a topology optimization.
Why is topology optimization important? First, it produces shapes which may be more optimal than we could determine by engineering intuition coupled with trial and error. Second, with the rise of additive manufacturing, it is now much easier and more practical to produce the often complex and organic looking shapes which come out of a topological optimization.
ANSYS, Inc. has really upped the game when it comes to utilizing topology optimization. Starting with version 18.0, topo opt is built in functionality within ANSYS. If you already know ANSYS Mechanical, you already know the tool that’s used. The ANSYS capability uses the proven ANSYS solvers, including HPC capability for efficient solves. Another huge plus is the fact that SpaceClaim is linked right in to the process, allowing us to much more easily make the optimized mesh shape produced by a topological optimization into a more CAD representation set for use in validation simulations, 3D printing, or traditional manufacturing.
The intent of this blog is to show the current process in ANSYS version 18.1 using a simple example of an idealized motorcycle front fork bracket optimization. We don’t claim to be experts on motorcycle design, but we do want to showcase what the technology can do with a simple example. We start with a ‘blob’ or envelope for the geometry of our design space, then perform an optimization based on an assumed set of loads the system will experience. Next we convert the optimized mesh information into solid geometry using ANSYS SpaceClaim, and then perform a validation study on the optimized geometry.
Here we show our starting point – an idealized motorcycle fork with a fairly large blob of geometry. The intent is to let ANSYS come up with an optimal shape for the bracket connecting the two sides of the fork.
The first step of the simulation in this case is a traditional Static Structural simulation within ANSYS Workbench. The starting point for the geometry was ANSYS SpaceClaim, but the initial geometry could have come from any geometry source that ANSYS can read in, meaning most CAD systems as well as Parasolid, SAT, and STEP neutral file formats.
A single set of loads can be used, or multiple load cases can be defined. That’s what we did here, to simulate various sets of loads that the fork assembly might experience during optimization. All or a portion of the load cases can be utilized in the topological optimization, and weighting factors can be used on each set of loads if needed.
Here we see the workflow in the ANSYS Workbench Project Schematic:
Block A is the standard static structural analysis on the original, starting geometry. This includes all load cases needed to describe the operating environment. Block B is the actual topological optimization. Block C is a validation study, performed on the optimized geometry. This step is needed to ensure that the optimized shape still meets our design intent.
Within the topology optimization, we set our objective. He we choose minimizing compliance, which is a standard terminology in topology optimization and we can think of it as the inverse which is maximizing stiffness.
In the static structural analysis, 7 load cases were used to describe different loading situations on the motorcycle fork, and here all have been used in the optimization.
Further, we defined a response constraint, which in this example is to reduce mass (actually retain 15% of the mass):
Another quantity that’s often useful to specify is a minimum member constraint. That will keep the topology optimization from making regions that are too small to 3D print or otherwise manufacture. Here we have specified a minimum member size of 0.3 inches:
Since the topological optimization solution uses the same ANSYS solvers for the finite element solution as a normal solution, we can leverage high performance computing (distributed solvers, typically) to speed up the solution process. Multiple iterations are needed to converge on the topology optimization, so realize that the topo opt process is going to be more computationally expensive than a normal solution.
Once the optimization is complete, we can view the shape the topo opt method has obtained:
Notice that only a portion of the original model has been affected. ANSYS allows us to specify which regions of the model are to be considered for optimization, and which are to be excluded.
Now that we have a shape that looks promising, we still need to perform a validation step, in which we rerun our static simulation with the loads and constraints we expect the fork assembly to experience. To do that, we really want a ‘CAD’ model of the optimized shape. The images shown above show the mesh information that results from the topo opt solution. What we need to do next is leverage the ANSYS SpaceClaim geometry tool to create a solid model from the optimized shape.
A simple beauty in the ANSYS process is that with just a couple of clicks we proceed from Block B to Block C in the Workbench project schematic, and can then work with the optimized shape in SpaceClaim.
As you can see in the above image, SpaceClaim automatically has the original geometry as well as the new, optimized shape. We can do as much or as little to the optimized shape as we need, from smoothing and simplification to adding manufacturing features such as holes, bosses, etc. In this case we simply shrink wrapped it as-is.
Continuing with the validation step, the geometry from SpaceClaim automatically opens in the Mechanical window and we can then re-apply the needed loads and constraints and then solve to determine if the optimized shape truly meets our design objectives. If not, we can make some tweaks and run again.
The above image shows a result plot from the validation step. The geometry efficiently comes through SpaceClaim from the optimization step to the validation step. The needed tools are all nicely contained within ANSYS.
Hopefully this has given you an idea of what can be done with topology optimization in ANSYS as well as how it’s done. Again, if you already know ANSYS Mechanical, you already know the bulk of how to do this. If not, then perhaps what you have seen here will spark a craving to learn. We can’t wait to see what you create.
What is Topological Optimization? If you’re not familiar with the concept, in finite element terms it means performing a shape optimization utilizing mesh information to achieve a goal such as minimizing volume subject to certain loads and constraints. Unlike parameter optimization such as with ANSYS DesignXplorer, we are not varying geometry parameters. Rather, we’re letting the program decide on an optimal shape based on the removal of material, accomplished by deactivating mesh elements. If the mesh is fine enough, we are left with an ‘organic’ sculpted shape elements. Ideally we can then create CAD geometry from this organic looking mesh shape. ANSYS SpaceClaim has tools available to facilitate doing this.
Topological optimization has seen a return to prominence in the last couple of years due to advances in additive manufacturing. With additive manufacturing, it has become much easier to make parts with the organic shapes resulting from topological optimization. ANSYS has had topological optimization capability both in Mechanical APDL and Workbench in the past, but the capabilities as well as the applications at the time were limited, so those tools eventually died off. New to the fold are ANSYS ACT Extensions for Topological Optimization in ANSYS Mechanical for versions 17.0, 17.1, and 17.2. These are free to customers with current maintenance and are available on the ANSYS Customer Portal.
In deciding to write this piece, I decided an interesting example would be the brace that is part of all curved saxophones. This brace connects the bell to the rest of the saxophone body, and provides stiffness and strength to the instrument. Various designs of this brace have been used by different manufacturers over the years. Since saxophone manufacturers like those in other industries are often looking for product differentiation, the use of an optimized organic shape in this structural component could be a nice marketing advantage.
This article is not intended to be a technical discourse on the principles behind topological optimization, nor is it intended to show expertise in saxophone design. Rather, the intent is to show an example of the kind of work that can be done using topological optimization and will hopefully get the creative juices flowing for lots of ANSYS users who now have access to this capability.
That being said, here are some images of example bell to body braces in vintage and modern saxophones. Like anything collectible, saxophones have fans of various manufacturers over the years, and horns going back to production as early as the 1920’s are still being used by some players. The older designs tend to have a simple thin brace connecting two pads soldered to the bell and body on each end. Newer designs can include rings with pivot connections between the brace and soldered pads.
Hopefully those examples show there can be variation in the design of this brace, while not largely tampering with the musical performance of the saxophone in general. The intent was to pick a saxophone part that could undergo topological optimization which would not significantly alter the musical characteristics of the instrument.
The first step was to obtain a CAD model of a saxophone body. Since I was not able to easily find one freely available on the internet that looked accurate enough to be useful, I created my own in ANSYS SpaceClaim using some basic measurements of an example instrument. I then modeled a ‘blob’ of material at the brace location. The idea is that the topological optimization process will remove non-needed material from this blob, leaving an optimized shape after a certain level of volume reduction.
In ANSYS Mechanical, the applied boundary conditions consisted of frictionless support constraints at the thumb rest locations and a vertical displacement constraint at the attachment point for the neck strap. Acceleration due to gravity was applied as well. Other loads, such as sideways inertial acceleration, could have been considered as well but were ignored for the sake of simplicity for this article. The material property used was brass, with values taken from Shigley and Mitchell’s Mechanical Engineering Design text, 1983 edition.
This plot shows the resulting displacement distribution due to the gravity load:
Now that things are looking as I expect, the next step is performing the topological optimization.
Once the topological optimization ACT Extension has been downloaded from the ANSYS Customer Portal and installed, ANSYS Mechanical will automatically include a Topological Optimization menu:
I set the Design Region to be the blog of material that I want to end up as the optimized brace. I did a few trials with varying mesh refinement. Obviously, the finer the mesh, the smoother the surface of the optimized shape as elements that are determined to be unnecessary are removed from consideration. The optimization Objective was set to minimize compliance (maximize stiffness). The optimization Constraint was set to volume at 30%, meaning reduce the volume to 30% of the current value of the ‘blob’.
After running the solution and plotting Averaged Node Values, we can see the ANSYS-determined optimized shape:
What is apparent when looking at these shapes is that the ‘solder patch’ where the brace attaches to the bell on one end and the body on the other end was allowed to be reduced. For example, in the left image we can see that a hole has been ‘drilled’ through the patch that would connect the brace to the body. On the other end, the patch has been split through the middle, making it look something like an alligator clip.
Another optimization run was performed in which the solder pads were held as surfaces that were not to be changed by the optimization. The resulting optimized shape is shown here:
Noticing that my optimized shape seemed on the thick side when compared to production braces, I then changed the ‘blob’ in ANSYS SpaceClaim so that it was thinner to start with. With ANSYS it’s very easy to propagate geometry changes as all of the simulation and topological optimizations settings stay tied to the geometry as long as the topology of those items stays the same.
Here is the thinner chunk after making a simple change in ANSYS SpacClaim:
And here is the result of the topological optimization using the thinner blob as the starting point:
Using the ANSYS SpaceClaim Direct Modeler, the faceted STL file that results from the ANSYS topological optimization can be converted into a geometry file. This can be done in a variety of ways, including a ‘shrink wrap’ onto the faceted geometry as well as surfaces fit onto the facets. Another option is to fit geometry in a more general way in an around the faceted result. These methods can also be combined. SpaceClaim is really a great tool for this. Using SpaceClaim and the topological optimization (faceted) result, I came up with three different ‘looks’ of the optimized part.
Using ANSYS Workbench, it’s very easy to plug the new geometry component into the simulation model that I already had setup and run in ANSYS Mechanical using the ‘blob’ as the brace in the original model. I then checked the displacement and stress results to see how they compared.
First, we have an organic looking shape that is mostly faithful to the results from the topological optimization run. This image is from ANSYS SpaceClaim, after a few minutes of ‘digital filing and sanding’ work on the STL faceted geometry output from ANSYS Mechanical.
This shows the resulting deflection from this first, ‘organic’ candidate:
The next candidate is one where more traditional looking solid geometry was created in SpaceClaim, using the topological optimization result as a guide. This is what it looks like:
This is the same configuration, but showing it in place within the saxophone bell and body model in ANSYS SpaceClaim:
Next, here is the deformation result for our simple loading condition using this second geometry configuration:
The third and final design candidate uses the second set of geometry as a starting point, and then adds a bit of style while still maintaining the topological optimization shape as an overall guide. Here is this third candidate in ANSYS SpaceClaim:
Here are is the resulting displacement distribution using this design:
This shows the maximum principal stress distribution within the brace for this candidate:
Again, I want to emphasize that this was a simple example and there are other considerations that could have been included, such as loading conditions other than acceleration due to gravity. Also, while it’s simple to include modal analysis results, in the interest of brevity I have not included them here. The main point is that topological optimization is a tool available within ANSYS Mechanical using the ACT extension that’s available for download on the customer portal. This is yet another tool available to us within our ANSYS simulation suite. It is my hope that you will also explore what can be done with this tool.
Regarding this effort, clearly a next step would be to 3D print one or more of these designs and test it out for real. Time permitting, we’ll give that a try at some point in the future.
Joining Two of PADT’s Favorite Things: Simulation and 3D Printing
Recent advances in Additive Manufacturing (3D Printing) have removed barriers to manufacturing certain geometry because of constraints in traditional manufacturing methods. Although you can make almost any shape, how do you figure out what shape to make. Using ANSYS products you can apply topological optimization to come up with a free-form shape that best meets your needs, and that can be made with Additive Manufacturing.
A few months ago we presented some background information on how to drive the design of this type of part using ANSYS tools to a few of our customers. It was a well received so we cleaned it up a bit (no guarantee there all the typos are gone) and recorded the presentation. Here it is on YouTube
Let us know what you think and if you have any questions or comments, please contact us.
When Desktop Engineering needed a subject matter expert on Topological Optimization and its use to drive product development, they called on PADT’s Manoj Mahendran. The article “Your Optimization Software Respectfully Suggests a Revision” gives a great overview of how designs can be driven by the use of Topological Optimization. They also mention a few of the more common tools, and with Manoj’s help, discuss the importance of 3D Printing to the process. An important take away is how these tools can be used to suggest design changes to the designer.
This video will show you how you can optimize a part using Topology Optimization with GENESIS through ANSYS Mechanical with support from ANSYS SpaceClaim
We are very pleased to announce that we have added another great partner to our product portfolio: Vanderplaats Research Development. VR&D is a leading provider of structural optimization tools for simulation, and a strong partner with ANSYS. We came across their Genesis and GTAM products when we were looking for a good topological optimization tool for one of our ANSYS customers. We quickly found it to be a great compliment, especially for the growing need to support optimization for parts made with 3D Printing.
Please find the official press release below or as a PDF file. You can also learn more about the products on our website here. We hope to schedule some webinars on this tool, and publish some blog articles, in the coming months.
As always, feel free to contact us for more information.