People talk about automation, mostly with respecte to manufacturing, like it is something that is comming. But “Automation is here and we need to pay attention.” If you don’t understand how computer software, robotics, and sensors are changing every aspect of our lives, odds are you will miss how it will change your business.
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.
Why should I spend time making a good mesh?
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.
When is it going to matter?
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.
What should I do when I need to create a good mesh?
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).
Step 1) Know your tools
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.
Step 2) Know your physics
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.
Step 3) Know your mesh quality statistics
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.
Step 4) Know your uncertainty
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:
- Choose your turbulence model wisely and make sure your mesh meets the quality metrics for that model.
- Make sure you don’t have boundary conditions near an area of flow recirculation. If you are getting reverse flows at the boundary then you need to move your boundary conditions further away from the feature that’s causing the flow to swirl in and out of the boundary.
Download all 5 parts of this series as a single PDF here.
What are the safety risks in laser powder bed fusion metal 3D printing?
This is the first half of the 3rd post in a series of 5 on things we learned installing a metal 3D printer (laser powder bed fusion). Links to previous posts are below:
- Part 1: Equipment needed (beyond the 3D printer)
- Part 2: Facilities requirements (electricity, water, ESD mats etc.)
The most important discussions around installing and operating a metal 3D printer involve safety. The requirements can be difficult to pin down since they depend on several things: whether you are using reactive or non-reactive alloys (read a previous post on this subject here), the risk perception of your local building safety director and fire marshal, local regulations (and exceptions) and the volume of material you are dealing with. As with all things safety and more so because of how nascent metal 3D printing technology is, I list a few disclaimers at the bottom of this page.
There is so much to say about safety in this process that half-way through writing this post, it became clear it would not fit in one post. Therefore, I have split the content into two: in this post (3A) I talk about the risks: where they come from and why they matter. In the next post (3B), I will discuss how these risks can be mitigated.
1. Sources of Risk
Broadly speaking, I like to think of two sources of risk in this process since as an operator of these machines you have to think differently about how you interact with these sources.
1.1 Metal Powder
Metal 3D printing involves fusing together powder in a bed. Typical metal powders used for laser based 3D printing are spherical in shape and range from 10-70 microns in diameter, as shown in Figure 1. At this size, a metal can be prone to fire and explosion (under the right circumstances) and there is also the physiological concern of long-term inhalation of, and contact with, these powders. The powder also has a long life cycle and requires human interaction at many steps – from arriving in a container (as shown in Figure 2), through multiple recycling steps through final disposal. These risks come into play just when handling the powder (independent of its use in the process) – an additional risk comes from the melting process itself.
1.2 The Laser Fusion Process
The powder in the bed described before is fused together into a solid using a laser that locally melts the powder one layer at a time. This is conducted in an inert atmosphere (Argon or Nitrogen) and is the second source of risk since these gases can displace Oxygen from a closed environment. Additionally, the process of laser melting of metals creates vaporized soot (see video below), some of which deposits on the process chamber and in the extraction module and filter. The smoke particles can be even finer than the powder itself, and need to be cleaned out with care on a regular basis.
There are 4 main risks arising from the laser powder bed fusion process: fire and explosion, powder inhalation and contact, inert gas asphyxiation and the environmental impact of the wastes generated.
2.1 Fire and Explosion
In May 2014, OSHA cited a 3D printing company for 10 violations deriving from the workplace safety standards surrounding the operation of a metal 3D printer (including not having the proper Class D fire extinguisher). The disregard of multiple safety measures during a routine build setup procedure resulted in a fire which caused life-threatening burns to the operator of the printer. While this incident was the result of gross negligence, it is nonetheless a cautionary tale that should drive us to understand the fundamental reasons why a metal 3D printer can cause fires and to appreciate the underlying reasons for why suppliers recommend the safety measures they do.
Fire and explosion require a combination of conditions as shown in the commonly cited image below used by OSHA and other agencies to communicate risks of powder handling.
As shown in Fig. 3, when handling powder in ambient atmospheres (with oxygen), all that is needed is a suitable ignition source to initiate a fire. Further, if this occurs in the presence of a dust cloud with many particles dispersed in a contained area (such as a small room or an air duct), this could lead to a more damaging explosion.
- Fire: When handling metal powder, the user needs to be aware that she/he already has 2 of the 3 requirements of a fire met and the main aim must be to ensure protection against any ignition source. There are several sources that could cause an ignition, the most likely one for a user of a metal 3D printer is static electricity. Additionally, it is possible that a fire can be initiated by hot surfaces, flames, hot gases and particles, mechanically generated sparks and strayelectrical currents.
- Explosion: With regard to explosions, in addition to the 3 requirements above, dust clouds in contained areas can exacerbate any ignition to a much larger impact within milliseconds. Therefore, the prevention of the formation of metal dust clouds (as unlikely as that may seem), is of paramount importance.
In addition to the requirements above, there are levels associated with each requirement that need to be met together for an actual fire or explosion to occur. The risk of ignition increases with reducing particle diameter and given a certain particle size, the most significant factor governing risk is the nature of the metal. Reactive metals (Aluminum alloys, Titanium and its alloys, as well as smoke particles from both reactives and non-reactives) pose much higher risk than non-reactive metals (steels, Inconels, bronze, Cobalt Chrome alloys) – this is a subject I wrote about in more detail in a previous post.
2.2 Powder Inhalation & Contact
As discussed before, most metal 3D powder particles range in size from 10-70um. This is at the very edge of what is considered respirable and damaging to our lungs. While contact physically is to be avoided since it may initiate irritation and potential dermatitis, there is greater concern about the long-term inhalation exposure risks of these powders. Particles of the size range in this process can get deposited in the tracheo-bronchial region per Jenson  and Goldich . Ultimately, these particles are discharged from the body or swallowed, but effects of long term exposure for the wide range of metals and alloys is not fully studied – which is why suppliers insist on respirators (more on that in the next post). It is worth pointing out though, from the work published by Jenson and Goldich, that it appears that while metal 3D printing powders are small enough to travel past the nasal cavity if inhaled, their sizes are large enough that respiratory damage in the lungs is highly unlikely – only particles under 2 microns are at risk of making it all the way to the alveoli and causing lung disease .
2.3 Inert Gas Asphyxiation
Inert gases are used in laser metal 3D printers to reduce the reactivity of the metal for processing purposes. Most metal 3D printers either use Nitrogen or Argon. Inert gas asphyxiation is the main risk due to oxygen being displaced by either of these gases that have leaked for some reason. Since both gases are not detectable by humans, victims do not realize that they are inhaling air depleted of oxygen and as a result this can have a serious impact. The human body is used to atmospheric percentages of oxygen (21%) and values below 19.5% can be harmful and are defined as oxygen-deficient per OSHA . Thus, any user of nitrogen or argon gas (and this applies not just to any process using inert gases), especially in small spaces such as a closed room, needs to be aware of this risk and protect against it.
2.4 Environmental Impact
A key challenge with powder based processes lies in collecting and disposing the stray or “fugitive” powder from different locations such as the tool, PPE, containers and vacuum systems into temporary storage, during which the above risks of fire/explosion and inhalation remain. Additionally, the storage typically results in loose powder and solid waste as well as water with powder particles, both of which need to be disposed into the outside world and could pose an environmental hazard. I will discuss this further in a future post, when I attempt to look at some of the environmental aspects around this technology.
- This is intended to supplement the supplier training you must receive before using the equipment and not meant to replace it – in case of conflicting information, your supplier’s training and equipment requirements override any discussion here. PADT assumes no legal responsibilities for any decisions or actions taken by the readers of this document.
- My personal experience derives specifically from the use of Laser-based metal 3D printing tools, specifically Concept Laser’s MLab Cusing R equipment. I expect majority of this information to be of use to users of other laser based powder bed fusion metal systems and to a lesser extent to Electron Beam systems, but have no personal experience to vouch for this.
- Local, state and federal regulations vary, and are important – partner with your local fire marshal (or equivalent authority) as a starting point and take them along with you every step of the way. If in the US, familiarize yourself in particular with OSHA’s guidance on dust explosions  and NFPA 484 , the National Fire Protection Association’s standard for combustible metals (links below).
- J.M. Benson, “Safety considerations when handling metal powders,” Southern African Institute of Mining and Metallurgy, 2012
- R. G. Goldich, “Fundamentals of Particle Technology,” Chapter 15, Midland IT and Publishing, UK, 2002
- OSHA on Oxygen Deficiency
- OSHA’s Guidance on Dust Explosions
- National Fire Protection Association’s standard for combustible metals, NFPA 484
- D. Bhate, “Reactive and Non-Reactive Metal Alloys in Laser-based Powder Bed Fusion,” PADT Blog Post, 2016
Continue to Part 3B here, where I address mitigation strategies to address the risks described in this post. In the meantime, please read my prior posts below if you haven’t already, or send your inputs to me via message on LinkedIn. Thank you!
Introducing New PolyJet Material: Agilus30
PADT is excited to introduce the newest polyjet material available from Stratasys, Agilus30! Agilus30 is a superior Rubber-like PolyJet photopolymer family ideal for advanced design verification and rapid prototyping.
Get more durable, tear-resistant prototypes that can stand up to repeated flexing and bending. With a Shore A value of 30 in clear or black, Agilus30 accurately simulates the look, feel and function of Rubber-like products. 3D print rubber surrounds, overmolds, soft-touch coatings, living hinges, jigs and fixtures, wearables, grips and seals with improved surface texture.
Agilus30 has applications in a number of areas, including:
Tooling needing rubber-like characteristics
Overmolding & many more!
Want to know more about PolyJet’s toughest flexible material to date?
Join PADT’s 3D Printing Application Engineer James Barker along with Stratasys Materials Business Manager Ken Burns for a presentation on the various benefits and attributes that Agilus30 has to offer, which machines are compatible with it, and how companies are making use of it’s unique capabilities.
Like so much else these days, the way that we deliver training to employees has changed over time to take advantage of new technologies. This is especially true for technical training on how to use hardware and software. The traditional classroom approach has been replaced with online and on-demand training. In “Technical training for employees is changing, is that a good thing?” I put on my curmudgeon hat and talk about why the traditional way has advantages that outway the negatives.
If you have ever implemented a Database appcliation at your business you know it can be a pain. In “5 things to think about when implementing a database product at your business” I go over some lessons that we have learned over time to make the whole process and outcome better.
The project to keep a 1944 P-51 Mustang flying was covered again, this time in 3D Metal Printing Magazine (Pg 23-33). Concept Laser worked with PADT to reverse engineer and print the exhaust manifold from a P-51 to keep it flying. Unlike the other article and video on the project, this reporter used this example as a great way to look at the readiness of military aircraft, and not just antique planes.
As PADT’s Rey Chu says ““This was a great exercise that’s suitable for numerous military applications and very relevant to the future use of 3D metal printing to maintain fleets in the field,” Chu says. “Maintaining spare-parts inventory has become a significant challenge, for example, to the Air Force. Additive manufacturing could be the solution.”
The Speed of Simulation – with Velox Motorsports
With thoroughly engineered components including the use of Finite Element Analysis (FEA), thermodynamics, heat transfer, and Computational Fluid Dynamics (CFD), PADT Startup Spotlight Velox Motorsports strives to produce aftermarket parts that can effectively outperform the factory components.
Join Velox Co-Owners Eric Hazen and Paul Lucas for a discussion on what they use ANSYS simulation software for and how they have benefited from it’s introduction into their manufacturing process.
This webinar will focus on two projects within which the engineers at Velox have see the impact of ANSYS, including:
Using Finite Element Analysis (FEA) to reverse engineer a Subaru fork, find the cause of failure and develop an improved replacement part.
Using Computational Fluid Dynamics (CFD) to rub a shape sensitivity study on Nissan GT R strakes, and develop a replacement that increases down-force without significantly increasing drag.
In its latest release, ANSYS SpaceClaim further integrates its ease of use and rapid geometry manipulation capabilities into common simulation workflows. From large changes to behind the scenes enhancements, you’ll notice efficiency improvements across the board. You’ll save time automating geometry tasks with the expanded recording and replay capabilities of SpaceClaim’s enhanced scripting environment.
Join PADT’s Application Engineer Tyler Smith for this webinar and learn about several improvements that are guaranteed to save time, enhance your designs and improve overall usability. We’ll cover:
Continued development of SpaceClaim’s scripting environment. With expanded recording capabilities and replayability of scripts on model versions, you’ll save time in the steps needed to automate geometry tasks.
Faceted data optimization and smoothing enhancements. You can greatly simplify and smooth topology optimized STL data for downstream printing, while preserving the integrity of localized regions.
Lattice Infilling for additive manufacturing. The Infilling functionality has greatly expanded to include several lattice infill types, all with custom options to ensure your 3-D printed component has an ideal strength-to-weight relationship.
Exploration of inner details of a model with the new fly-through capability. Without hiding components or using cross sections, this capability provides graphical feedback at your fingertips while making it even more enjoyable to work in a 3-D environment.
Mostly we make boxes. Pretty boxes but the bulk of what we 3D Print is some sort of plastic box that people stuff electronics in to. Most of the time we also don’t really know what customers do with the objects we make for them. But every once in a while you get involved in a project that really makes a difference. That could not be more true than two recent medical applications for 3D Printing that we worked on with Intermountain Healthcare (IHC) in Salt Lake City, Utah.
KSL, a local TV station, did a story on our IHC was deploying 3D Printing to produce better outcomes for their patients. You can view the story here.
PADT was fortunate enough to be part of two of the cases mentioned in the story. The first was a St George man who was feeling some pain in his back. He had a scan and they found 12 kidney stones. On top of that, his kidney was not in the right place and was distorted. PADT helped print a model of the scan so that the doctors could just get a real feel for what they were dealing with, and then plan the surgery.
The second situation really pulled at our heart strings. A 10 year old boy needs heart surgery and its a complicated problem. They need a model fast so we worked with Stratasy to quickly print an accurate model so tha the surgeons could come up with a plan. We still have not heard how it went, they are scheduling things, but the feedback from the team was that the 3D model was extremely helpful. We are talking life saving.
Both of these recent situations build on years of examples where we have worked the doctors and their technical assistance to convert scans of patients into usable 3D Models. If you are in the surgery or surgery planning space and want to learn more about how accurate 3D models printed directly from scan data can be used to improve patient outcome, contact PADT at firstname.lastname@example.org and we will connect you with our 3D Printing team.
Sometimes you want to take two parts and and prepare them for meshing so that they either share a surface between them, or have identical but distinct surfaces on each part where they touch. In this simple How-To, we share the steps for creating both of these situations so you can get a continuous mesh or create a matching contact surface in ANSYS Mechanical.PADT-Presentations-Grey_White-Wide
By using the power of ANSYS SpaceClaim to quickly modify geometry, you can set up your surface models in ANSYS Mechanical to easily be connected. Take a look in this How-To slide deck to see how easy it is to extend geometry and intersect surfaces.PADT-ANSYS-Connecting-Shells-SpaceClaim-Mechanical
For those that don’t know, Flownex is a thermal-fluid system modeling tool that is great for modeling heat, flow, pressure, etc… in systems. At PADT we often connect it to ANSYS Mechanical to do more detailed component level simulation when needed.
Why the need for the link in the fist place?
- It is an automated workflow to couple Flownex and ANSYS through direct mapping of Flownex results (HTC and bulk temperatures) as boundary condition to an ANSYS thermal analysis.
- Represents a conjugate heat transfer model with fluid calculations handled in Flownex
- Allows one to easily/quickly investigate fluid flow and heat transfer properties under a wide range operating conditions.
First we will discuss the steady state thermal ANSYS Mechanical model that will be linked to Flownex.
We have a pipe Pipe with arbritraty geometry and material properties. Convection boundary conditions have been applied to both the internal and external pipe walls. The inernal Bulk Temperature will be supplied by Flownex.
- External BC
- HTC 100 w/m2K
- Bulk Temperature 22C
- Internal BC
- HTC 1500 w/m2K
- Bulk Temperature will be supplied by Flownex
In order to achieve a bidirectional coupling, Flownex will execute the Mechanical APDL batch file. We can generate the Mechanical APDL batch file (ds.dat), from within Mechanical.
The soluiton procedure is as follows
- Flownex modifies the ds.dat file
- Flownex executes the modified ds.dat file
- The modified ds.dat file generates the d_result.txt file
- Flownex reads the d_result.txt file
- Flownex executes an iteration, using value from d_result.txt
- Repeat untill solutions are converged.
The next step after creating the ds.dat file is to set up your Flownex model.
The Flownex model comprises of a pipe component with arbritrary geomery, filled with air with an inlet temperature and pressure of 500˚C and 120 kPa respectilvy and a flow rate of approximatly 1kg/s.
We have connected the pipe component to the Mechanical Generic Interface using data transfer links.
The data transfer links pass the bulk fluid temperature form the pipe to the Mechanical Generic Interface component, and return the heat flow value calculated using ANSYS to the pipe.
Next we need place the ds.dat file in the AnsysMechanical_Files folder which is located in the Flownex project folder. It is necessary to create a copy of the ds.dat called ModifiedData.dat in the same location.
C:\Program Files\ANSYS Inc\v180\ansys\bin\winx64\Ansys180.exe
This is the path to ANSYS executable. Pay particular attention to the version number (eg 180, 172), as this will be different depending on the version of ANSYS you have installed.
2) Command line parameters
-b -i ModifiedData.dat -o results
Flownex will launch ANSYS, and execute the ModifiedData.dat Mechanical APDL batch file from the command line, using the above command a detailed description of command line options can be found in another blog post here.
3) Project files folder, Data file name and Modified data file name
Here we specify location of the Mechanical APDL batch files
Here we will define where in ModifiedData.dat the value from Flownex, fluid temperature in this case, will be placed. This is done by determining what the boundary condition variable and ID is, and finding the prefix before the boundary condition value in the ds.dat file. Typically the variable for temperature is _loadvari and for HTC it is _convari.
It is possible to know the boundary condition ID by activating the appearance of Beta options in WB.
Here we will specify the location of the d_result.txt that ANSYS generates. It should appear in the same folder as the Mechanical APDL batch files after successful execution.
Flownex and ANSYS will pass data back and forth every time step of a transient Flownex run.
The simulation should continue to run up to, and beyond the point where the Flownex and ANSYS simulation have converged. If we plot out the heat input or temperature value vs time we should be able to visualize convergence, akin to residual plots when running a CFD simulation, and then manually stop the simulation after values have stabilized.
Below we increase the fluid inlet temperature form 500˚C to 1000˚C after 10 iterations, and observed a increase in heat flow from ~1.4kW to ~2.8kW.
Everywhere you drive in Phoenix you see autonomous cars being tested. These are cool and all, but they also are a sign of a whole new boom in technological change. In “Self-driving cars are driving big changes in tech” I go over some of the key disruptive innovations that will be driven by these new vehicles.
When Cox Communications asked us to be part of its local Smart Home Tour I said yes for one simple reason: I wanted to see a truly connected home. in “3 keys to success for smart home devices” I discuss some of the lessons I learned about IoT devices that actually work in the home.