|Published on:||June 8th, 2018|
|Description:||The All Things ANSYS Podcast will be back in full swing in the near future, however we wanted to give you a quick heads up on where we’ve been, and how we plan on reformatting and presenting the show going forward. We love putting these together and sharing them with you all, so we will be regrouping and exploring some new options to ensure we can continue to share the high quality news, content, and discussion that you’ve come to expect from this show as we move forward.
For the time being, check out this update on the new release of ANSYS Mechanical 19.0 and 19.1, and stay tuned for more content, hopefully coming soon.
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Below you can find some of the most frequently asked questions from this webinar, along with our answers.
Q: What computer and license type are you actually using for running the simulation? Ram, cores, CPU, etc.
A: 16 GB RAM Intel i7, NVIDIA Quadro K1100M
Q: Is the solver running a transient solution in the background while you are post processing and haven’t paused it, or is it marching towards better convergence of a steady state solution?
A: The solver is running a transient solution the entire time. The only time it is not doing this is if I pause the simulation.
Q: Does this require 3D models to be built within Discovery Live, or it can import outside 3D models (Solidworks etc) and still allows the user to add/modify geometry objects on the fly within Discovery Live?
A: Yes, you can import any CAD native format or neutral format in Discovery Live. You can also create Geometry from scratch in Discovery Live using the SpaceClaim tools.
Q: It looks like when you change the “speed – fidelity” setting, the solver resets; while when you change other settings (like domain geometry), the solution continues from last step. What’s being changed when you change the “speed-fidelity” setting?
A: When you change the Speed-Fidelity setting, the computational grid of the domain is coarsened or refined. It is also re-partitioned/parallelized on the GPU cores.
Q: Are there predictive features of simulation, obtaining design suggestions from the end results? Are there inputs for end results to accomplish reverse engineering?
A: Yes, in a sense. Because Discovery Live provides literally “real-time” feedback on design changes, you have design suggestions based on the end results. For reverse engineering in Discovery Live: there are not inputs for end results, but the part you’d like to reverse engineer can be imported (or created) in Discovery Live, and then analyzed in the range of operating conditions to understand it’s performance.
Q: Do you have any control of the mesh? How boundary/layer effects can be checked?
A: Control of the mesh available via the Speed-Fidelity slider bar. Boundary layer effects could be checked using surface integrals of force, but again recall that if you’re trying to finely resolve details such as boundary layer physics, you may need to consider the next level of accuracy which would be Discovery AIM or Fluent.
|Published on:||February 12, 2018|
|With:||Joe Woodword, Tom Chadwick, Ted Harris, Eric Miller|
|Description:||In this episode your host and Co-Founder of PADT, Eric Miller is joined by PADT’s Joe Woodword, Tom Chadwick, and Ted Harris, for a discussion on what they learned about the world of simulation by attending this year’s Pacific Design & Manufacturing show, North America’s largest Advanced Design and Manufacturing event. This talk includes tips for a variety of ANSYS tools, along with some general “how-to” points regarding overall process that will help to ensure your simulation runs smoothly.|
The ANSYS App Store contains all sorts of free and paid apps developed by ANSYS as well as trusted partners. These apps improve workflows and allow users to build in best practices. An app that has been of particular interest to me is Workbench Poly Meshing for Fluent.
This app enables the power and capacity of Fluent Meshing, most notably the polyhedral meshing feature, with the ease of use of the ANSYS Workbench Meshing environment. In order to show the functionality of this app, I will demonstrate with the generation of a polyhedral mesh on a sample geometry from the Fluent Meshing tutorials.
To start out, I have imported a .igs file of an exhaust manifold into ANSYS SpaceClaim Direct Modeler, which has powerful repair and prepare tools that will come in handy. I notice that the geometry is comprised of 250 surfaces, which I need to fix in order to create a solid body. By navigating into the ‘Repair’ tab and selecting the ‘Stitch’ operation, SpaceClaim notes there are two stitchable edges in my geometry. I select the green check mark to perform this operation and am greeted with a solid geometry. I complete my tasks in SpaceClaim by extracting the fluid volume using the ‘Volume Extract’ tool in the ‘Prepare’ tab.
I setup my workflow in ANSYS workbench with my added ‘Fluent Meshing’ ACT module between the ‘Mesh’ module and ‘Fluent’ module. I can then proceed to create my desired surface mesh in ANSYS meshing and setup a few required inputs for Fluent Meshing.
Once this process has been completed, I can update my ‘Fluent Meshing’ cell and open the ‘Fluent’ setup cell to display my polyhedral mesh!
IMPORTANT NOTE: all named selections must be lowercase with no spaces, and the file path(s) cannot contain any spaces.
If you do CFD simulations then you know the struggle that is involved in meshing. It is a fine balance of accuracy, speed, and ease of set up. If you have complex geometry, large assemblies, or any difficulty meshing then this blog article is for you.
The mesh is arguably one of the most important parts of any simulation set up. A good mesh can solve significantly faster and provide more accurate results. Conversely, a poor mesh can make the simulation have inaccurate results and be slow to converge or not converge at all. If you have done any simulation then you know that hitting the solve button can feel like rolling the dice if you don’t have a robust meshing tool.
A good mesh is going to matter on a Friday afternoon when you need to get the simulation started before you leave for the weekend because it takes two days to run and you need to deliver results on Monday but you are up against the clock because you have to get to your kid’s soccer game by 5pm and the mesh keeps crashing.
A poor mesh can do more than just reorganizing you’re social agenda. A poor mesh can drastically change results like pressure drop in an internal flow passage or drag over a body. If you go into that meeting on Monday and tell your boss that the new design is going to perform 10% better than the previous design – you need to be confident that the design is 10% better not 10% worse.
If you’re the poor soul reading this on a Friday afternoon because you are trying to frantically fix you’re mesh so you can get your simulation running before the weekend – I pity you. Continue reading for my proprietary step by step approach titled “How to get you’re CFD mesh back on track!” (Patent pending).
ANSYS has been developing its meshing technology since the beginning of time (not really but almost) – it’s no surprise that its meshing algorithms are the best in the business. In ANSYS you have a large number of tools at your disposal, know how to use them.
The first tool in your toolbox is the ANSYS automatic meshing technology. It is able to predictively apply settings for your part to get the most accurate automatic mesh possible. It has gotten so good that the automatic mesh is a great place to start for any preliminary simulations. If you want to get into the details, ANSYS meshing has two main groups of mesh settings – Global Meshing Parameters and Local Meshing Parameters. Global mesh parameters are great for getting a good mesh on the entire model without going into detailed mesh settings for each part.
But when you do have to add detailed meshing settings on a part by part basis then local mesh settings won’t let you down.
What is your primary result of interest? Drag? Pressure drop? Max velocity? Stagnation? If you can quantify what you are most interested in then you can work to refine the mesh in that region so as to capture the physics accurately. ANSYS allows you set local sizing parameters on bodies, faces, lines, and regions which allow you to get the most accurate mesh possible but without having to use a fine mesh on the entire part.
Mesh quality statistics can be a good way to gauge the health of your mesh. They are not a foolproof method for creating a mesh that will be accurate but you will be able to get an idea of how well it will converge. In ANSYS meshing there is a number of mesh quality statistics at your fingertips. A quick and easy way to check your mesh is to look at the Minimum Orthogonal Quality statistic and make sure it is greater than 0.1 and Maximum Skewness is less than 0.95.
Every test, simulation, design, process etc… has uncertainty. The goal of engineering is to reduce that uncertainty. In simulation meshing is always a source of uncertainty but it can be minimized by creating high quality meshes that accurately model the actual physical process. To reduce the uncertainty in meshing we can perform what is called a mesh refinement study. Using the concept of limits we can say that in the limit of the mesh elements getting infinitely small than the results will asymptotically approach the exact solution. In the graph below it can be seen that as the number of elements in the model are increased from 500 – 1.5million the result of interest approached the dotted line which we can assume is close to the exact solution.
By completing a mesh refinement study as shown above you can be confident that the mesh you have created is accurately capturing the physics you are modeling because you can quantify the uncertainty.
If you currently just skip over the meshing part of your CFD analysis thinking that it’s good enough or if your current meshing tool doesn’t give you any more details than just a green check mark or a red X then it’s time dig into the details of meshing and start creating high quality meshes that you can count on.
For more info about advanced meshing techniques in ANSYS – see this PDF presentation that is a compilation of ANSYS training material on the meshing subject.Advanced Techniques in ANSYS Meshing_Blog
If you still haven’t figured out how to get your mesh to solve and its 5pm on Friday see below*
*Common pitfalls and mistakes for CFD meshing: