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From Ideation to Operation: The ANSYS Discovery Product Family in R19 – Webinar

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Coupling ANSYS Mechanical and Flownex

The below example demontrates how to couple Flownex and ANSYS mechanical using the Mechanical Generic Interface component.

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

A command snippet, which will calculate the total heat flow through the inner wall surface and write the value out into a text file called d_result, has been inlcuded in the ANSYS Mechanical model.

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

  1. Flownex modifies the ds.dat file
  2. Flownex executes the modified ds.dat file
  3. The modified ds.dat file generates the d_result.txt file
  4. Flownex reads the d_result.txt file
  5. Flownex executes an iteration, using value from d_result.txt
  6. 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.

Let’s go over the inputs to the Mechanical Generic Interface component in Flownex:

1) Executable 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

4) Inputs

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.

5) Outputs

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.

7 Reasons why ANSYS AIM Will Change the Way Simulation is Done

ANSYS-AIM-Icon1When ANSYS, Inc. released their ANSYS AIM product they didn’t just introduce a better way to do simulation, they introduced a tool that will change the way we all do simulation.  A bold statement, but after PADT has used the tool here, and worked with customers who are using it, we feel confident that this is a software package will drive that level of change.   It enables the type of change that will drive down schedule time and cost for product development, and allow companies to use simulation more effectively to drive their product development towards better performance and robustness.

It’s Time for a Productivity Increase

AIM-7-old-modelIf you have been doing simulation as long as I have (29 years for me) you have heard it before. And sometimes it was true.  GUI’s on solvers was the first big change I saw. Then came robust 3D tetrahedral meshing, which we coasted on for a while until fully associative and parametric CAD connections made another giant step forward in productivity and simulation accuracy. Then more recently, robust CFD meshing of dirty geometry. And of course HPC improvements on the solver side.

That was then.  Right now everyone is happily working away in their tool of choice, simulating their physics of choice.  ANSYS Mechanical for structural, ANSYS Fluent for fluids, and maybe ANSYS HFSS for electromagnetics. Insert your tool of choice, it doesn’t really matter. They are all best-in-breed advanced tools for doing a certain type of physical simulation.  Most users are actually pretty happy. But if you talk to their managers or methods engineers, you find less happiness. Why? They want more engineers to have access to these great tools and they also want people to be working together more with less specialization.

Putting it all Together in One Place

AIM-7-valve2-multiphysicsANSYS AIM is, among many other things, an answer to this need.  Instead of one new way of doing something or a new breakthrough feature, it is more of a product that puts everything together to deliver a step change in productivity. It is built on top of these same world class best-in-bread solvers. But from the ground up it is an environment that enables productivity, processes, ease-of-use, collaboration, and automation. All in one tool, with one interface.

Changing the Way Simulation is Done

Before we list where we see things changing, let’s repeat that list of what AIM brings to the table, because those key deliverables in the software are what are driving the change:

  • IAIM-7-pipe-setupmproved Productivity
  • Standardized Processes
  • True Ease-of-Use
  • Inherent Collaboration
  • Intuitive Automation
  • Single Interface

Each of these on their own would be good, but together, they allow a fundamental shift in how a simulation tool can be used. And here are the seven way we predict you will be doing things differently.

1) Standardized processes across an organization

The workflow in ANSYS AIM is process oriented from the beginning, which is a key step in standardizing processes.  This is amplified by tools that allow users, not just programmers, to create templates, capturing the preferred steps for a given type of simulation.  Others have tried this in the past, but the workflows were either too rigid or not able to capture complex simulations.  This experience was used to make sure the same thing does not happen in ANSYS AIM.

2) No more “good enough” simulation done by Design Engineers

Ease of use and training issue has kept robust simulation tools out of the hands of design engineers.  Programs for that group of users have usually been so watered down or lack so much functionality, that they simply deliver a quick answer. The math is the same, but it is not as detailed or accurate.  ANSYS AIM solves this by give the design engineer a tool they can pick up and use, but that also gives them access to the most capable solvers on the market.

3) Multiphysics by one user

Multiphysics simulation often involves the use of multiple simulation tools.  Say a CFD Solver and a Thermal Solver. The problem is that very few users have the time to learn two or more tools, and to learn how to hook them together. So some Multiphysics is done with several experts working together, some in tools that do multiple physics, but none well, or by a rare expert that has multi-tool expertise.  Because ANSYS AIM is a Multiphysics tool from the ground up, built on high-power physics solvers, the limitations go away and almost any engineer can now do Multiphysics simulation.

AIM-7-study4) True collaboration

The issues discussed above about Multiphysics requiring multiple users in most tools, also inhibit true collaboration. Using one user’s model in one tool is difficult when another user has another tool. Collaboration is difficult when so much is different in processes as well.  The workflow-driven approach in ANSYS AIM lends itself to collaboration, and the consistent look-and-feel makes it happen.

5) Enables use when you need it

This is a huge one.  Many engineers do not use simulation tools because they are occasional users.  They feel that the time required to re-familiarize themselves with their tools is longer than it takes to do the simulation. The combination of features unique to ANSYS AIM deal with this in an effective manner, making accurate simulation something a user can pick up when they need it, use it to drive their design, and move on to the next task.

6) Stepping away from CAD embedded Simulation

The growth of CAD embedded simulation tools, programs that are built into a CAD product, has been driven by the need to tightly integrate with geometry and provide ease of use for the users who only occasionally need to do simulation. Although the geometry integration was solved years ago, the ease-of-use and process control needed is only now becoming available in a dedicated simulation tool with ANSYS AIM.

7) A Return to home-grown automation for simulation

AIM-7-scriptIf you have been doing simulation since the 80’s like I have, you probably remember a day when every company had scripts and tools they used to automate their simulation process. They were extremely powerful and delivered huge productivity gains. But as tools got more powerful and user interfaces became more mature, the ability to create your own automation tools faded.  You needed to be a programmer. ANSYS AIM brings this back with recording and scripting for every feature in the tool, with a common and easy to use language, Python.

How does this Impact Me and or my Company?

It is kind of fun to play prognosticator and try and figure out how a revolutionary advance in our industry is going to impact that industry. But in the end it really does not matter unless the changes improve the product development process. We feel pretty strongly that it does.  Because of the changes in how simulation is done, brought about by ANSYS AIM, we feel that more companies will use simulation to drive their product development, more users within a company will have access to those tools, and the impact of simulation will be greater.

AIM-f1_car_pressure_ui

To fully grasp the impact you need to step back and ponder why you do simulation.  The fast cars and crazy parties are just gravy. The core reason is to quickly and effectively test your designs.  By using virtual testing, you can explore how your product behaves early in the design process and answer those questions that always come up.  The sooner, faster, and more accurately you answer those questions, the lower the cost of your product development and the better your final product.

Along comes a product like ANSYS AIM.  It is designed by the largest simulation software company in the world to give the users of today and tomorrow access to the power they need. It enables that “sooner, faster, and more accurately” by allowing us to change, for the better, the way we do virtual testing.

The best way to see this for yourself is to explore ANSYS AIM.  Sign up for our AIM Resource Kit here or contact us and we will be more than happy to show it to you.

AIM_City_CFD

Free ANSYS AIM Resource Kit — Expert Advice, Insights and Best Practices for Multiphysics Simulation

ANSYS-AIM-Icon1We have been talking a lot about ANSYS AIM lately.  Mostly because we really like ANSYS AIM and we think a large number of engineers out there need to know more about it and understand it’s advantages.  And the way we do that is through blog posts, emails, seminars, and training sessions.  A new tool that we have started using are “Resource and Productivity Kits,” collections of information that users can download.

Earlier in the year we introduced several kits, including ANSYS Structural, ANSYS Fluids, and ANSYS ElectroMechanical.  Now we are pleased to offer up a collection of useful information on ANSYS AIM.  This kit includes:

  • “Getting to know ANSYS AIM,” a video by PADT application engineer Manoj Mahendran
  • “What I like about ANSYS AIM,” a video featuring insights on the tool
  • Six ANSYS AIM demonstration videos, including simulations and a custom template demonstration
  • Five slide decks that provide an overview of ANSYS AIM and describe its new features
  • An exclusive whitepaper on effectively training product development engineers in simulation.

You can download the kit here.

If you need more info, view the ANSYS AIM Overview video or read about it on our ANSYS AIM page.

Watch this blog for more useful content on AIM in the future.


AIM_City_CFD

Direct Coupled-Field Elements in Mechanical APDL

We received one of those tech support calls last week that you hate getting.  It was something like “I need to transfer my ANSYS model to this other FEA package, how do I do that?”  We of course asked “Why do you need to go to this other package?” The answer was “Because they have elements that solve for stress and thermal degrees of freedom in the same element.”  Well, so does ANSYS Mechanical APDL, and it has for years.  But as a Workbench user they had only been exposed to Multiphysics that uses Load transfer as the mechanism to solve different domains in the same run

Therefore, a The Focus posting is born.

In this posting we will go over the basics of direct coupled-field elements and simulation to make everyone aware of what is available.

Direct Coupled-Field vs. Load Transfer

When most people talk about Multiphysics they are talking about Fluid-Structural Interaction (FSI) or some other interaction between two different models where the program solves each physics by itself and transfers the resulting values from one physics as a load on the next physics.  This is called load transfer Multiphysics and it is very useful and powerful.  But it requires a solve for each physics for each step in your solving process, and often more because you have to iterate back and forth between physics till things converge before you can move to the next substep.

There is a whole other way to do Multiphysics if you have the same mesh for each physics: you can modify your finite element equations to cover all the different physics in one set of equations, therefore in one matrix, and therefore in one pass through the solver for each solve.  This capability has been in the ANSYS Mechanical APDL solver for a very long time and has been expanded over time to cover some surprising combinations of physics.

So when should you use one over the other? That depends. Here are some thoughts:

  • Load Transfer Approach:
    • Your meshes need to be or are different
    • Fluid flow with something other then heat-transfer
  • Direct Approach:
    • The interaction between two physics is strongly coupled
    • The interaction is non-linear
    • Acoustics is involved
    • Piezoelectric is involved
    • Porous fluid flow is involved
    • Diffusion is involved

In general, if you can use Direct Coupling and you know MAPDL well, it is the preferred way to go, it is just a lot easier to do. But if you are not familiar with MAPDL for running and post processing, you may be better off with the Load Transfer approach.

The Coupled-Field Elements

You access the coupled-field capabilities in the solver through the use of the coupled-field elements.  Although there are some legacy elements that can be used as well, we will focus on the three standard coupled-field elements. They all have the same capability, and just vary in topology:

  • PLANE223: 2D 8 Node Quad
  • SOLID226: 3D 20 Node Hex
  • SOLID227: 3D 10 Node Tet

All of these support the following physics, DOF’s, forces and reaction loads:

Field DOF Label Force Label Reaction Solution
Structural UX, UY, UZ FX, FY, FZ Force
Thermal TEMP HEAT Heat Flow
Electric Conduction VOLT AMPS Electric Current
Electrostatic/Piezo VOLT CHRG Electric Charge
Diffusion CONC RATE Diffusion Flow Rate

You use a combination of KEYOPTS and material properties to enable the various types of coupling.  Take a look at the element documentation to see how it all works.

In addition to these, there are some specialty elements worth discussion. The first are FLUID29/FLUID30. These are the Acoustic field elements. These solve for displacement and pressure. They also can share the displacement DOF’s with structural elements where they touch.

Unfortunately the electromagnetic coupled field elements have been put on legacy status, as ANSYS Maxwell is where the development effort is going in this area. But you can still use them for coupled-field simulation that involves the MAG degree of freedom.  The elements are: PLANE13, SOLID5, SOLID98. ANSYS MAPDL still has actively supported electromagnetic elements, but they are electromagnetic only and do no support displacement or thermal degrees of freedom.

Flow in a fully saturated porous media can be modeled with the Coupled Pore-Pressure elements. These elements: CPT212/213/215/216/217, solve for pressure and deflection and are used for things like modeling nuclear waste issues, soil subsidence, oil well stability, and bone deformation and healing.

We should also mention that ANSYS supports circuit simulation using the CIRCU124 element.  This element can be coupled to other elements that have VOLT, CURR, or EMF capability.

image

Running Direct Coupled-Field Multiphysics in ANSYS Mechanical APDL

When I wrote this section heading it seemed like a good idea. But this is supposed to be a short blog entry and not a full one day training class. So I will wimp out and share where you can find more information in the help:

There is a whole manual dedicated to coupled-field analysis: Mechanical APDL // Coupled Field Analysis Guide. Within that guide is the Direct Coupled-Field Analysis section, Chapter 2.  In it you will not only find discussions about how to do what you need to do, but also a whole bunch of simple examples that are very helpful.

In general, you run like any other simulation.  There is really nothing special or unique and you do not have to deal with managing the load transfer like you do with load transfer coupled field simulations.

Running Direct Coupled-Field Multiphysics in ANSYS Mechanical

This is a question that comes up a lot. Unfortunately only one type of direct coupling is supported, Thermal-Electric.  What we recommend people do is they build their models in ANSYS mechanical for one of the physics, then use code snippets to change the elements to the proper direct coupled-field type and to also do any post processing. It will run when you solve, but it will come back with an error, and you need to post processes via APDL code or you need to post process in MAPDL interactively.

NEW INFO:  Edward points out in the comment below that you can get this to work.  I’ll repeat it here:

“We’ve had some success post-processing U-TEMP-VOLT analyses in Mechanical. Mechanical seems to accept a model as solved, so long as it sees a result file of the correct type in the Solver Files directory. The coupled field analysis in this case output a .rst file, so we used a Static Structural object as the base model. 
We could access the structural results directly and used User-defined results to access most of the thermal and electric results.
I seem to recall that we also had success using a Thermal analysis as a base and then changing the result file extension from .rst to .rth, but I can’t find my test model to confirm this.”

I can verify that both of these approaches work. I added a /sys, copy file.rst to file.rth to a code segment for the thermal base.  But it was simpler to just use the structural as the base.  If you do this you can do your post processing for the most part in ANSYS Mechanical. [E. Miller 3/28/2013)

Thoughts

So this was, as promised, a very high level overview. The fact of the matter is that there are a significant number of users, especially in the MEMS industry, that use these direct coupled-field elements all the time.  They are powerful and robust with as many uses as you can dream up, truly expanding the reach of what you can model and the accuracy of those models.

Over the years we have found some good tricks for using these elements effectively:

  1. Pick one of the physics and get a static run of that physics by itself running first. Debugging your model this way is usually faster and clears out any issues before you deal with the direct coupling issues. If you have more than two physics, add them in one at a time.
  2. Pay attention to units. When you start mixing voltage and distance or what not, it is easy to get confused. If you are doing MEMS devices, you need to make sure you are using the MEMS units and that you are consistent.  Unlike ANSYS Mechanical, ANSYS Mechanical APLD is unitless and requires the user to make sure the are consistent across physics.
  3. Try not to use the legacy elements if you don’t have to. They may not be around in the future.
  4. If you are doing EMAG, you may want to look at using load coupling with Maxwell or MAPDL instead of using the legacy direct coupled elements.  Maxwell and the newer elements in MAPDL have more capabilities and are more efficient.
  5. Make sure you really understand how your physics interact. Go through the thought experiment of predicting the interaction on as simple of a problem as you can, while keeping it relevant. Think about what loads interact with what structures and what that interaction implies.