Can I parameterize ANSYS Mechanical material assignments?

So we have known for a long time that we can parameterize material properties in the Engineering Data screen. That works great if we want to adjust the modulus of a material to account for material irregularities. But what if you want to change the entire material of a part from steel to aluminum? Or if you have 5 different types of aluminum to choose, on several different parts, and you want to run a Design Study to see what combination of materials is the best? Well, then you do this. The process includes some extra bodies, some Named Selections, and a single command snippet.
The first thing to do is to add a small body to your model for each different material that you want to swap in and out, and assign your needed material to them. You’ll have to add the materials to your Engineering Data prior to this. For my example I added three cubes and just put Frictionless supports on three sides of each cube. This assures that they are constrained but not going to cause any stresses from thermal loads if you forget and import a thermal profile for “All Bodies”.

ansys-material-parameters-01

Next, you make a Named Selection for each cube, named Holder1, Holder2, etc. This allows us to later grab the correct material based on the number of the Holder.

ansys-material-parameters-02

You also make a Named selection for each group of bodies for which you want to swap the materials. Name these selections as MatSwap1, MatSwap2, etc.

ansys-material-parameters-03

The command snippet goes in the Environment Branch. (ex. Static Structural, Steady-State Thermal, etc.)

ansys-material-parameters-04

!###############################################################################################################################
! MATSWAP.MAC
! Created by Joe Woodward at PADT,Inc.
! Created on 2/12/2016
!
! Usage: Create Named Selections, Holder1, Holder2, etc.,for BODIES using the materials that you want to use.
! Create Named Selections called MatSwap1, MatSwap2, etc. for the groups of BODIES for which you want to swap materials.
! Set ARG1 equal to the Holder number that has the material to give to MatSwap1.
! Set ARG2 equal to the Holder number that has the material to give to MatSwap2.
! And so on....
! A value of 0 will not swap materials for that given group.
!
! Use as is. No Modification to this command snippet is necessary.
!###############################################################################################################################
/prep7
*CREATE,MATSWAP,MAC
*if,arg1,NE,0,then
 *get,isthere,COMP,holder%arg1%,TYPE
 *get,swapgood,COMP,matswap%ARG2%,TYPE
 *if,isthere,eq,2,then
 esel,s,,,holder%arg1%
 *get,newmat,elem,ELNEXT(0),ATTR,MAT
 !swap material for Body 1
 *if,swapgood,eq,2,then
 esel,s,,,matswap%ARG2%
 emodif,all,mat,newmat
 *else
 /COM,The Named Selection - MatSwap%ARG2% is not set to one or more bodies
 *endif
 *else
 /COM,The Named Selection Holder%ARG1% is not set to one or more bodies
*endif
*endif
*END
MATSWAP,ARG1,1 !Use material from Holder1 for Swap1
MATSWAP,ARG2,2 !Use material from Holder1 for Swap2
MATSWAP,ARG3,3 !Use material from Holder1 for Swap3
MATSWAP,ARG4,4 !Use material from Holder1 for Swap4
MATSWAP,ARG5,5 !Use material from Holder1 for Swap5
MATSWAP,ARG6,6 !Use material from Holder1 for Swap6
MATSWAP,ARG7,7 !Use material from Holder1 for Swap7
MATSWAP,ARG8,8 !Use material from Holder1 for Swap8
MATSWAP,ARG9,9 !Use material from Holder1 for Swap9

alls
/solu

Now, each of the Arguments in the Command Snippet Details corresponds to the ‘MatSwap’ Name Selection of the same number. ARG1 controls the material assignment for all the bodies in the MatSwap1 name selection. The value of the argument is the number of the ‘Holder’ body with the material that you want to use. A value of zero leaves the material assignment alone and does not change the original material assignment for the bodies of that particular ‘MatSwap’ Named Selection. There is no limit on the number of ‘Holder’ bodies and materials that you can use, but there is a limit of nine ‘MatSwap’ groups that you can modify, because there are only nine ARG variables that you can parameterize in the Command Snippet details.

ansys-material-parameters-05

You can see how the deflection changes for the different material combinations. These three steps, holder bodies, Named Selections, and the command snippet above, will give you design study options that were not available before. Hopefully I’ll have an even simpler way in the future. Stay tuned.

10x with ANSYS 17.0 – Get an Order of Magnitude Impact

The ANSYS 17.0 release improves the impact of driving design with simulation by a factor of 10.  This 10x  jump is across physics and delivers real step-change enhancements in how simulation is done or the improvements that can be realized in products.

ANSYS-R17-Banner
Unless you were disconnected from the simulation world last week you should be aware of the fact that ANSYS, Inc released their latest version of the entire product suite.  We wanted to let the initial announcement get out there and spread the word, then come back and talk a little about the details.  This blog post is the start of a what should be a long line of discussions on how you can realize 10x impact from your investment in ANSYS tools.

As you may have noticed, the theme for this release is 10x. A 10x improvement in speed, efficiency, capability, and impact.  Watch this short video to get an idea of what we are talking about.

Where is the Meat?

We are already seeing this type of improvement here at PADT and with our customers. There is some great stuff in this release that delivers some real game-changing efficiency and/or capability.  That is fine and dandy, but how is this 10x achieved.  There are a lot of little changes and enhancements, but they can mostly be summed up with the following four things:

temperature-on-a-cpu-cooler-bgTighter Integration of Multiphysics

Having the best in breed simulation tools is worth a lot, and the ANSYS suite leads in almost every physics.  But real power comes when these products can easily work together.  At ANSYS 17.0 almost all of the various tools that ANSYS, Inc. has written or acquired can be used together. Multiphysics simulation allows you to remove assumption and approximations and get a more accurate simulation of your products.

And Multiphysics is about more than doing bi-directional simulation, which ANSYS is very good at. It is about being able to transfer loads, properties, and even geometry between different software tools. It is about being able to look at your full design space across multiple physics and getting more accurate answers in less time.  You can take heat loads generated in ANSYS HFSS and use them in ANSYS Mechanical or ANSYS FLUENT.  You can take the temperatures from ANSYS FLUENT and use them with ANSYS SiWave.  And you can run a full bidirectional fluid-solid model with all the bells and whistles and without the hassles of hooking together other packages.

simplorer-17-1500-modelica-components-smTo top it all off, the system level modeler ANSYS Simplorer has been improved and integrated further, allowing for true system level Multiphysics virtual prototyping of your entire system.  One of the changes we are most excited about is full support for Modelica models – allowing you to stay in Simplorer to model your entire system.

Improved Usability

Speed is always good, and we have come to expect 10%-30% increases in productivity at almost every release. A new feature here, a new module there. This time the developers went a lot further and across the product lines.

clip-regions-with-named-selections-bgThe closer integration of ANSYS SpaceClaim really delivers on a 10x or better speedup for geometry creation and cleanup when compared to other methods. We love SpaceClaim here at PADT and have been using it for some time.  Version 17 is not only integrated tighter, it also introduces scripting that allows users to take processes they have automated in older and clunker interfaces into this new more powerful tool.

One of our other favorites is the new interface in ANSYS Fluent, just making things faster and easier. More capability in the ANSYS Customization Toolkit (ACT) also allows users to get 10x or better improvements in productivity.  And for those who work with electronics, a host of ECAD geometry import tools are making that whole process an order of magnitude faster.

import-ecad-layout-geometry-bgIndustry Specific Workflows

Many of the past releases have been focused on establishing underlying technology, integration, and adding features. This has all paid off and at 17.0 we are starting to see some industry specific workflows that get models done faster and produce more accurate results.

The workflow for semiconductor packaging, the Chip Package System or CPS, is the best example of this. Here is a video showing how power integrity, signal integrity, thermal modeling, and integration across tools:

A similar effort was released in Turbomachinary with improvements to advanced blade row simulation, meshing, and HPC performance.

ansys-fluent-hpc-max-coresOverall Capability Enhancements

A large portion of the improvements at 17.0 are made up of relatively small enhancements that add up to so big benefits.  The largest development team in simulation has not been sitting around for a year, they have been hard at work adding and improving functionality.  We will cover a lot of these in coming posts, but some of our favorites are:

  1. Improvements to distributed solving in ANSYS Mechanical that show good scaling on dozens of cores
  2. Enhancements to ACT allowing for greater automation in ANSYS Mechanical
  3. ACT is now available to automate your CFD processes
  4. Significant improvements in meshing robustness, accuracy and speed (If you are using that other CFD package because of meshing, its time to look at ANSYS Fluent again)
  5. Fracture mechanics
  6. ECAD import in electromagnetic, fluids, and mechanical products.
  7. A new solver in ANSYS Maxwell that solves more than 10x faster for transient runs
  8. ANSYS AIM just keeps getting more functions and easier to use
  9. A pile of SpaceClaim new and improved features that greatly speed up geometry repair and modification
  10. Improved rigid body dynamics in ANSYS Mechanical

ansys-17-ribbons-UIMore to Come

And a ton more. It may take us all of the time we have before ANSYS 18.0 comes out before we have a chance to go over in The Focus all of the great new stuff.  But we will be giving a try in the coming weeks and months. ANSYS, Inc. will be hosting some great webinars as well.

If you see something that interests you or something you would like to see that was not there, shoot us an email at support@padtinc.com or call 480.813.4884.

Constitutive Modeling of 3D Printed FDM Parts: Part 2 (Approaches)

In part 1 of this two-part post, I reviewed the challenges in the constitutive modeling of 3D printed parts using the Fused Deposition Modeling (FDM) process. In this second part, I discuss some of the approaches that may be used to enable analyses of FDM parts even in presence of these challenges. I present them below in increasing order of the detail captured by the model.

  • Conservative Value: The simplest method is to represent the material with an isotropic material model using the most conservative value of the 3 directions specified in the material datasheet, such as the one from Stratasys shown below for ULTEM-9085 showing the lower of the two modulii selected. The conservative value can be selected based on the desired risk assessment (e.g. lower modulus if maximum deflection is the key concern). This simplification brings with it a few problems:
    • The material property reported is only good for the specific build parameters, stacking and layer thickness used in the creation of the samples used to collect the data
    • This gives no insight into build orientation or processing conditions that can be improved and as such has limited value to an anlayst seeking to use simulation to improve part design and performance
    • Finally, in terms of failure prediction, the conservative value approach disregards inter-layer effects and defects described in the previous blog post and is not recommended to be used for this reason
ULTEM-9085 datasheet from Stratasys - selecting the conservative value is the easiest way to enable preliminary analysis
ULTEM-9085 datasheet from Stratasys – selecting the conservative value is the easiest way to enable preliminary analysis
  • Orthotropic Properties: A significant improvement from an isotropic assumption is to develop a constitutive model with orthotropic properties, which has properties defined in all three directions. Solid mechanicians will recognize the equation below as the compliance matrix representation of the Hooke’s Law for an orthortropic material, with the strain matrix on the left equal to the compliance matrix by the stress matrix on the right. The large compliance matrix in the middle is composed of three elastic modulii (E), Poisson’s ratios (v) and shear modulii (G) that need to be determined experimentally.
Hooke's Law for Orthotropic Materials (Compliance Form)
Hooke’s Law for Orthotropic Materials (Compliance Form)

Good agreement between numerical and experimental results can be achieved using orthotropic properties when the structures being modeled are simple rectangular structures with uniaxial loading states. In addition to require extensive testing to collect this data set (as shown in this 2007 Master’s thesis), this approach does have a few limitations. Like the isotropic assumption, it is only valid for the specific set of build parameters that were used to manufacture the test samples from which the data was initially obtained. Additionally, since the model has no explicit sense of layers and inter-layer effects, it is unlikely to perform well at stresses leading up to failure, especially for complex loading conditions.  This was shown in a 2010 paper that demonstrated these limitations  in the analysis of a bracket that itself was built in three different orientations. The authors concluded however that there was good agreement at low loads and deflections for all build directions, and that the margin of error as load increased varied across the three build orientations.

An FDM bracket modeled with Orthotropic properties compared to experimentally observed results
An FDM bracket modeled with Orthotropic properties compared to experimentally observed results
  • Laminar Composite Theory: The FDM process results in structures that are very similar to laminar composites, with a stack of plies consisting of individual fibers/filaments laid down next to each other. The only difference is the absence of a matrix binder – in the FDM process, the filaments fuse with neighboring filaments to form a meso-structure. As shown in this 2014 project report, a laminar approach allows one to model different ply raster angles that are not possible with the orthotropic approach. This is exciting because it could expand insight into optimizing raster angles for optimum performance of a part, and in theory reduce the experimental datasets needed to develop models. At this time however, there is very limited data validating predicted values against experiments. ANSYS and other software that have been designed for composite modeling (see image below from ANSYS Composite PrepPost) can be used as starting points to explore this space.
Schematic of a laminate build-up as analyzed in ANSYS Composite PrepPost
Schematic of a laminate build-up as analyzed in ANSYS Composite PrepPost
  • Hybrid Tool-path Composite Representation: One of the limitations of the above approach is that it does not model any of the details within the layer. As we saw in part 1 of this post, each layer is composed of tool-paths that leave behind voids and curvature errors that could be significant in simulation, particularly in failure modeling. Perhaps the most promising approach to modeling FDM parts is to explicitly link tool-path information in the build software to the analysis software. Coupling this with existing composite simulation is another potential idea that would help reduce computational expense. This is an idea I have captured below in the schematic that shows one possible way this could be done, using ANSYS Composite PrepPost as an example platform.
Potential approach to blending toolpath information with composite analysis software
Potential approach to blending toolpath information with composite analysis software

Discussion: At the present moment, the orthotropic approach is perhaps the most appropriate method for modeling parts since it is allows some level of build orientation optimization, as well as for meaningful design comparisons and comparison to bulk properties one may expect from alternative technologies such as injection molding. However, as the application of FDM in end-use parts increases, the demands on simulation are also likely to increase, one of which will involve representing these materials more accurately than continuum solids.

Activating Hyperdrive in ANSYS Simulations

punch-it-chewie-ansysWith PADT and the rest of the world getting ready to pile into dark rooms to watch a saga that we’ve been waiting for 10 years to see, I figured I’d take this opportunity to address a common, yet simple, question that we get:

“How do I turn on HPC to use multiple cores when running an analysis?”

For those that don’t know, ANSYS spends a significant amount of resources into making the various solvers it has utilize multiple CPU processors more efficiently than before.  By default, depending on the solver, you are able to use between 1-2 cores without needing HPC licenses.

With the utilization of HPC licenses, users can unlock hyperdrive in ANSYS.  If you are equipped with HPC licenses it’s just a matter of where to look for each of the ANSYS products to activate it.

ANSYS Mechanical

Whether or not you are performing a structural, thermal or explicit simulation the process to activate multiple cores is identical.

  1. Go to Tools > Solve Process Settings
  2. The Solve Process Settings Window will pop up
  3. Click on Advanced to open up the Advanced Settings window
  4. You will see an option for Max number of utilized cores
  5. Simply change the value to your desired core count
  6. You will see below an option to allow for GPU acceleration (if your computer is equipped with the appropriate hardware)
  7. Select the GPU type from the dropdown and choose how many GPUs you want to utilize
  8. Click Ok and close
hyperdrive-ansys-f01
Go the proper settings dialog
hyperdrive-ansys-f02
Choose Advanced…
hyperdrive-ansys-f03
Specify the number of cores to use

Distributed Solve in ANSYS Mechanical

One other thing you’ll notice in the Advanced Settings Window is the option to turn “Distributed” On or Off using the checkbox.

In many cases Distributing a solution can be significantly faster than the opposite (Shared Memory Parallel).  It requires that MPI be configured properly (PADT can help guide you through those steps).  Please see this article by Eric Miller that references GPU usage and Distributed solve in ANSYS Mechanical

hyperdrive-ansys-f04
Turn on Distributed Solve if MPI is Configured

ANSYS Fluent

Whether launching Fluent through Workbench or standalone you will first see the Fluent Launcher window.  It has several options regarding the project.

  1. Under the Processing Options you will see 2 options: Serial and Parallel
  2. Simply select Parallel and you will see 2 new dropdowns
  3. The first dropdown lets you select the number of processes (equal to the number of cores) to use in not only during Fluent’s calculations but also during pre-processing as well
Default Settings in Fluent Launch Window
Default Settings in Fluent Launch Window
Options When Parallel is Picked
Options When Parallel is Picked

ANSYS CFX

For CFX simulations through Workbench, the option to activate HPC exists in the Solution Manager

  1. Open the CFX Solver Manager
  2. You will see a dropdown for Run Mode
  3. Rather than the default “Serial” option choose from one of the available “Parallel” options.
  4. For example, if running on the same machine select Platform MPI Local Parallel
  5. Once selected in the section below you will see the name of the computer and a column called Partitions
  6. Simply type the desired number of cores under the Partitions column and then either click “Save Settings” or “Start Run”
Change the Run Mode
Change the Run Mode
Specify number of cores for each machine
Specify number of cores for each machine

ANSYS Electronics Desktop/HFSS/Maxwell

Regardless of which electromagnetic solver you are using: HFSS or Maxwell you can access the ability to change the number of cores by going to the HPC and Analysis Options.

  1. Go to Tools > Options > HPC and Analysis Options.
  2. In the window that pops up you will see a summary of the HPC configuration
  3. Click on Edit and you will see a column for Tasks and a column for Cores.
  4. Tasks relate to job distribution utilizing Optimetrics and DSO licenses
  5. To simply increase the number of cores you want to run the simulation on, change the cores column to your desired value
  6. Click OK on all windows
hyperdrive-ansys-f09
Select the proper settings dialog
hyperdrive-ansys-f10
Select Edit to change the configuration
Specify Tasks and Cores
Specify Tasks and Cores

There you have it.  That’s how easy it is to turn on Hyperdrive in the flagship ANSYS products to advance your simulations and get to your endpoint faster than before.

If you have any questions or would like to discuss the possibility of upgrading your ship with Hyperdrive (HPC capabilities) please feel free to call us at 1-800-293-PADT or email us at support@padtinc.com.

PID Thermostat Boundary Condition ACT Extension for ANSYS Mechanical

ANSYS-ACT-PID-ThermostatPADT is pleased to announce that we have uploaded a new ACT Extension to the ANSYS ACT App Store.  This new extension implements a PID based thermostat boundary condition that can be used within a transient thermal simulation.  This boundary condition is quite general purpose in nature.  For example, it can be setup to use any combination of (P)roportional (I)ntegral or (D)erivate control.   It supports locally monitoring the instantaneous temperature of any piece of geometry within the model.  For a piece of geometry that is associated with more than one node, such as an edge or a face, it uses a novel averaging scheme implemented using constraint equations so that the control law references a single temperature value regardless of the reference geometry.

ANSYS-ACT-PID-Thermostat-img1

The set-point value for the controller can be specified in one of two ways.  First, it can be specified as a simple table that is a function of time.  In this scenario, the PID ACT Extension will attempt to inject or remove energy from some location on the model such that a potentially different location of the model tracks the tabular values.   Alternatively, the PID thermostat boundary condition can be set up to “follow” the temperature value of a portion of the model.  This location again can be a vertex, edge or face and the ACT extension uses the same averaging scheme mentioned above for situations in which more than one node is associated with the reference geometry.  Finally, an offset value can be specified so that the set point temperature tracks a given location in the model with some nonzero offset.

ANSYS-ACT-PID-Thermostat-img2

For thermal models that require some notion of control the PID thermostat element can be used effectively.  Please do note, however, that the extension works best with the SI units system (m-kg-s).

A Guide to Crawling, Walking, and Running with ANSYS Structural Analysis

crawl-walk-runAt PADT, we apply a Crawl, Walk, Run philosophy to just about everything we do. Start with the basics, build knowledge and capability on that, and then continue to develop your skills throughout your career. Unfortunately, all too often I run across some poor new grad, two weeks out of school, contending with a problem that’s more befitting someone with about a decade of experience under his or her belt.

Now, the point of this article isn’t to call anyone out. Rather, I sincerely hope that managers and supervisors see this and use it as a guideline in assigning tasks to their direct reports. Note that the recommendations are relative and general. Some people may be quite competent in the “run” categories after just a few months of usage and study while others may have been using the software for a decade and still have trouble figuring out how to even start it. It’s also possible that, for certain projects, the “crawl” categories may actually end up being more difficult to contend with than the “run” categories.

With those caveats in mind, here is our list of recommendations for Crawling, Walking, and Running with ANSYS. Note that these apply to structural analysis. I fully plan to hit up my colleagues for similar blog posts about heat transfer, CFD, and electrical simulation.

Crawlsimple-stress1

  • Linear static
  • Basic modal
  • Eigenvalue (linear) buckling, but don’t forget to apply a knock-down factor

Walkstruct-techtip6-contacts-between-bolts

  • Nonlinearities
    • Large Deflection
    • Rate-independent plasticity
    • Nonlinear contact (frictionless and frictional)
  • Dynamics
    • Modal with linear perturbation
    • Spectrum analyses (running the analysis is easy; understanding what you’re doing and interpreting results correctly is hard)
      • Shock/Single point response
      • Random Vibration (PSD)
    • Harmonic analysis
  • Fatigue

Runvibration-pumping platforms

  • Nonlinearities
    • Advanced element options
    • Hyperelasticity
    • Rate-dependent phenomena
      • Creep
      • Viscoelasticity
      • Viscoplasticity
    • Other advanced material models such as shape memory alloy and gaskets
    • Element birth and death
  • Dynamics
    • Transient dynamics (implicit)
    • Explicit dynamics (e.g. LS-Dyna and Autodyn)
    • Rotordynamics
  • Fracture and crack growth

So what’s the best, quickest way to move from crawling to walking or walking to running? Invest in general or consultative (or even better, both) ANSYS training with PADT. We’ll help you get to where you need to be.

Be a Pinball Wizard with Contact Regions in ANSYS Mechanical

pinball-wizard-pinball-machine-ANSYS-3
A pinball machine based on The Who’s Tommy

I had a very cool music teacher back in 6th or 7th grade in the 1970’s in upstate New York.  Today we’d probably say she was eclectic.  In that class we listened to and discussed fairly recent songs in addition to general music studies.  Two songs I remember in particular are ‘Hurdy Gurdy Man’ by Donovan and ‘Pinball Wizard’ by The Who.  If you’re not familiar with Pinball Wizard, it’s from The Who’s rock opera Tommy, and is about a deaf, mute, blind young man who happens to be adept at the game of pinball.  Yes, he is a Pinball Wizard.  This sing popped into my head recently when we had some customer questions here at PADT regarding the pinball region concept as it pertains to ANSYS contact regions.

I’m not sure if the developers at ANSYS, Inc. had this song in mind when they came up with the nomenclature for the 17X (latest and greatest) series of contact elements in ANSYS, but regardless, you too can be a pinball wizard when it comes to understanding contact elements in ANSYS Mechanical and MAPDL.

Fans of this blog may remember one of my prior posts on contact regions in ANSYS that also had a musical theme (bringing to mind Peter Gabriel’s song “I Have the Touch”):

In this current entry we will go more in depth on the pinball region, also known as the pinball radius.  The pinball region is involved with the distance from contact element to target element in a given contact region.  Outside the pinball region, ANSYS doesn’t bother to check to see if the elements on opposite sides of the contact region are touching or not.  The program assumes they are far away from each other and doesn’t worry about any additional calculations for the most part.

Here is an illustration.  The gray elements on the left represent the contact body and the red elements on the right represent the target body (assuming asymmetric contact).  Target elements outside the pinball radius will not be checked for contact.  The contact and target elements actually ‘coat’ the underlying solid elements so they are shown as dashed lines slightly offset from the solid elements for the sake of visibility.  Here the pinball radius is displayed as a dashed blue circle, centered on the contact elements, with a radius of 2X the depth of the underlying solid elements.

pinball_radius_contact_illustration

So, outside the pinball region, we know ANSYS doesn’t check to see if the contact and target are actually in contact.  It just assumes they are far away and not in contact.  What about what happens if the contact and target are inside the pinball region?  The answer to that question depends on which contact type we have selected.

For frictionless contact (aka standard contact in MAPDL) and frictional contact, the program will then check to see if the contact and target are truly touching.  If they are touching, the program will check to see if they are sliding or possibly separating.  If they are touching and penetrating, the program will check to see if the penetration exceeds the allowable amount and will make adjustments, etc.  In other words, for frictionless and frictional contact, if the contact and target elements are close enough to be inside the pinball region, the program will make all sorts of checks and adjustments to make sure the contact behavior is adequately captured.

The other scenario is for bonded and no separation contact.  With these contact types, the program’s behavior when the contact and target elements are within the pinball region is different.  For these types, as long as the contact and target are close enough to be within the pinball region, the program considers the contact region to be closed.  So, for bonded and no separation, your contact and target elements do not need to be line on line touching in order for contact to be recognized.  The contact and target pairs just need to be inside the pinball region.  This can be good, in that it allows for some ‘slop’ in the geometry to be automatically ignored, but it also can have a downside if we have a curved surface touching a flat surface for example.  In that case, more of the curved surface may be considered in contact than would be the case if the pinball region was smaller.  This effect is shown in the image below.  Reducing the pinball radius to an appropriate smaller amount would be the fix for eliminating this ‘overconstraint’ if desired.

pinball_radius_bonded_noseparation

There is a default value for the pinball region/radius.  It can be changed if needed.  We’ll add more details in a moment.  First, why is it called the “pinball” region?  I like to think it’s because when it’s visualized in the Mechanical window, it looks like a blue pinball from an actual pinball arcade game, but I’ll admit that the ANSYS terminology may predate the Mechanical interface.  The image below shows what I mean.  The blue balls are the different pinball radii for different contact regions.

pinball_radius_visualization

 

Note that you don’t see the pinball region displayed as shown in the above image unless you have manually changed the pinball size in Mechanical.  The pinball region can be changed in the Mechanical window in the details view for each contact region by changing Pinball Region from Program Controlled to Radius, like this:

pinball_radius_change

In MAPDL, the pinball radius value can be changed by defining or editing the real constant labeled PINB.

By now you’re probably wondering what is the default value for the pinball radius?  The good news is that it is intelligently decided by the program for each contact region.  The default is always a scale factor on the depth of the underlying elements of each contact region.  In the first pinball region image shown near the beginning of this article, the example plot shows the pinball region/radius as two times the depth of the underlying elements.

The table below summarizes the default pinball radius values for most circumstances for 2D and 3D solid element models.  More detailed information is available in the ANSYS Help.

Default Pinball Radius ValuesLarge Deflection Off
Flexible-Flexible
Large Deflection On
Flexible-Flexible
Frictionless and Frictional1* Underlying Element Depth2*Underlying Element Depth
Bonded and No Seperation0.25*Underlying Element Depth0.5*Underlying Element Depth
Rigid-Flexible Contact: Typically the Default Values are Doubled

Summing it all up:  we have seen how the default values are calculated and also how to change them.  We have seen what they look like as blue balls in a plot of contact regions in Mechanical if the pinball radius has been explicitly defined.  We also discussed what the pinball radius does and how it’s different for frictionless/frictional contact and bonded/no separation contact.

You should be well on your way to becoming a pinball wizard at this point.

Does performing simulation in ANSYS make you think of certain songs, or are there songs you like to listen to while working away on your simulations an addition to The Who’s “Pinball Wizard” and Peter Gabriel’s “I Have the Touch”?  If so, we’d love to hear about your song preferences in the comments below.

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

To Use Large Deflection or Not, That Is the Question

Hamlet-Large-DeflectionIt seems like I’ve been explaining large deflection effects a lot recently. Between co-teaching an engineering class at nearby Arizona State University and also having a couple of customer issues regarding the concept, large deflection in structural analyses has been on my mind.

Before I explain any further, the thing you should note if you are an ANSYS Mechanical simulation user is this: If you don’t know if you need large deflection or not, you should turn it on. There is really no way to know for certain if it’s needed or not unless you perform a comparison study with and without it.

So, what are large deflection effects? In simple terms the inclusion of large deflection means that ANSYS accounts for changes in stiffness due to changes in shape of the parts you are simulating. The classic case to consider is the loaded fishing rod.

In its undeflected state, the fishing rod is very flexible at the tip. With a heavy fish on the end of the line, the rod deflects downward and it is then easy to observe that the stiffness of the rod has increased. In other words, when the rod is lightly loaded, a small amount of force will cause a certain downward deflection at the top. When the rod is heavily loaded however, a much larger amount of force will be needed to cause the tip to deflect downward by the same amount.

This change in the force amount required to achieve the same change in displacement implies that we do not have a linear relationship between force and displacement.
Consider Hooke’s law, also known as the spring equation:

F = Kx

Where F is the force applied, K is the stiffness of the structure, and x is the deflection. In a linear system, doubling the force results in double the displacement. In our fishing rod case, though, we have a nonlinear system. We might need to triple the force to double the displacement, depending on how much the rod is loaded relative to its size and other properties, and then to double the displacement again we might need to apply four times that force, just using numbers out of my head as examples.

Ted-rod-fishing1

So, in the case of the fishing rod, Hooke’s law in a linear form does not apply. In order to capture the nonlinear effect we need a way for the stiffness to change as the shape of the rod changes. In our finite element solution in ANSYS, it means that we want to recalculate the stiffness as the structure deflects.

This recalculation of the stiffness as the structure deflects is activated by turning on large deflection effects. Without large deflection turned on, we are constrained to using the linear equation, and no matter how much the structure deflects we are still using the original stiffness.

So, why not just have large deflection on by default and use it all the time? My understanding is that since large deflection adds computation expense to have it on, it’s off by default. It’s the same as for a lot of advanced usage, such as frictionless or frictional contact vs. the default bonded (simpler) behavior. In other words, turning on large deflection will trigger a nonlinear solution, meaning multiple passes through the solver using the Newton Raphson method instead of the single pass needed for a linear problem.

Here is an example of a simplified fishing rod. The image shows the undeflected rod (top), which is held fixed on the left side and has a downward force load applied on the right end. The bottom image shows the final deflected shape, with large deflection effects included. The deflection at the tip in this case is 34 inches.

Undeformed_deformed_rod

In comparison running the same load with large deflection turned off resulted in a tip deflection of 40 inches. Thus, the calculated tip deflection is 15% less with large deflection turned on, since we are now accounting for change in stiffness with change in shape as the rod deflects.

Below we have a force (horizontal axis) vs. deflection (vertical axis) plot for a nonlinear simulation of a fishing rod with large deflection turned on. The fact that the curve is not a straight line confirms that this is a nonlinear problem, with the stiffness (slope of the curve) not constant. We can also see that as the force gets higher, the slope of the curve is more horizontal, meaning that more force is needed for each incremental amount of displacement. This matches our observations of the fishing rod behavior.

Force_vs_Deflection

So, getting back to our original point, it’s often the case that we don’t know if we need to include large deflection effects or not. When in doubt, run cases with and without. If you don’t see a change in your key results, you can probably do without large deflection.

Here is an example using an idealized compressor vane. In this case, the deflections and stresses with and without large deflection effects are nearly the same (the stress difference is about 0.2%).

Large Deflection On:blade_large_defl

Small Deflection:blade_small_defl

Bottom line: when in doubt, try it out, with and without large deflection. In ANSYS Mechanical, Large Deflection effects are turned on or off in the details of the Analysis Settings branch.

It’s worth noting that turning on large deflection in ANSYS actually activates four different behaviors, known as large deflection which include large rotation, large strain, stress stiffening, and spin softening. All of these involve change in stiffness due to deformation in one way or another.

If you like this kind of info, or find it useful, we cover topics like this in our training classes. For more info, check out our training pages at http://www.padtinc.com/support/software/training.html.

Donny Don’t – Thin Sweep Meshing

It’s not a series of articles until there’s at least 3, so here’s the second article in my series of ‘what not to do’ in ANSYS…

Just in case you’re not familiar with thin sweep meshing, here’s an older article that goes over the basics.  Long story short, the thing sweep mesher allows you to use multiple source faces to generate a hex mesh.  It does this by essentially ‘destroying’ the backside topology.  Here’s a dummy board with imprints on the top and bottom surface:

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If I use the automatic thin sweep mesher, I let the mesher pick which topology to use as the source mesh, and which topology to ‘destroy’.  A picture might make this easier to understand…

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As you can see, the bottom (right picture) topology now lines up with the mesh, but when I look at the top (left picture) the topology does not line up with the mesh.  If I want to apply boundary conditions to the top of the board (left picture), I will get some very odd behavior:

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I’ve fixed three sides of the board (why 3?  because I meant to do 4 but missed one and was too lazy to go back and re-run the analysis to explain for some of future deflection plots…sorry, that’s what you get in a free publication) and then applied a pressure to all of those faces.  When I look at the results:

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Only one spot on the surface has been loaded.  If you go back to the mesh-with-lines picture, you’ll see that there is only a single element face fully contained in the outline of the red lines.  That is the face that gets loaded.  Looking at the input deck, we can see that the only surface effect element (how pressure loads are applied to the underlying solid) is on the one fully-contained element face:

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If I go back and change my thin sweep to use the top surface topology, things make sense:

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The top left image shows the thin sweep source definition.  Top right shows the new mesh where the top topology is kept.  Bottom left shows the same boundary conditions.  Bottom right shows the deformation contour.

The same problem occurs if you have contact between the top and bottom of a thin-meshed part.  I’ll switch the model above to a modal analysis and include parts on the top and bottom, with contact regions already imprinted.

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I’ll leave the thin sweeping meshing control in place and fix three sides of the board (see previous laziness disclosure).  I hit solve and nothing happens:

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Ah, the dreaded empty contact message.  I’ll set the variable to run just to see what’s going on.  Pro Tip:  If you don’t want to use that variable then you would have to write out the input deck, it will stop writing once it gets to the empty contact set.  Then go back and correlate the contact pair ID with the naming convection in the Connections branch.

The model solves and I get a bunch of 0-Hz (or near-0) modes, indicating rigid body motion:

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Looking at some of those modes, I can see that the components on one side of my board are not connected:

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The missing contacts are on the bottom of the board, where there are three surface mounted components (makes sense…I get 18 rigid body modes, or 6 modes per body).  The first ‘correct’ mode is in the bottom right image above, where it’s a flapping motion of a top-mounted component.

So…why don’t we get any contact defined on the bottom surface?  It’s because of the thin meshing.  The faces that were used to define the contact pair were ‘destroyed’ by the meshing:

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Great…so what’s the take-away from this?  Thin sweep meshing is great, but if  you need to apply loads, constraints, define contact…basically interact with ANYTHING on both sides of the part, you may want to use a different meshing technique.  You’ve got several different options…

  1. Use the tet mesher.  Hey, 2001 called and wants its model size limits back.  The HPC capabilities of ANSYS make it pretty painless to create larger models and use additional cores and GPUs (if you have a solve-capable GPU).  I used to be worried if my model size was above 200k nodes when I first started using ANSYS…now I don’t flinch until it’s over 1.5M
    image
    Look ma, no 0-Hz modes!
  2. Use the multi-zone mesher.  With each release the mutli-zone mesher has gotten better, but for most practical applications you need to manually specify the source faces and possibly define a smaller mesh size in order to handle all the surface blocking features.
    image
    Look pa, no 0-Hz modes!Full disclosure…the multi-zone mesher did an adequate job but didn’t exactly capture all of the details of my contact patches.  It did well enough with a body sizing and manual source definition in order to ‘mostly’ bond each component to the board.
  3. Use the hex-dominant mesher.  Wow, that was hard for me to say.  I’m a bit of a meshing snob, and the hex dominant mesher was immature when it was released way back when.  There were a few instances when it was good, but for the most part, it typically created a good surface mesh and a nightmare volume mesh.  People have been telling me to give it another shot, and for the most part…they’re right.  It’s much, much better.  However, for this model, it has a hard time because of the aspect ratio.  I get the following message when I apply a hex dominant control:

    image
  4. The warning is right…the mesh looks decent on the surface but upon further investigation I get some skewed tets/pyramids.  If I reduce the element size I can significantly reduce the amount of poorly formed elements:image
  5. That’s going on the refrigerator door tonight!
    image
    And…no 0-Hz modes!
  • Lastly…go back to DesignModeler or SpaceClaim and slice/dice the model and use a multi-body part.image
    3 operations, ~2 minutes of work (I was eating at the same time)

    image
    Modify the connection group to search/sort across parts

    image

    That’s a purdy mesh!  (Note:  most of the lower-quality elements, .5 and under, are because there are 2-elements through thickness, reducing the element size or using a single element thru-thickness would fix that right up)

    image
    And…no 0-Hz modes.

Phew…this was a long one.  Sorry about that.  Get me talking about meshing and look what happens.  Again, the take-away from all of this should be that the thin sweeper is a great tool.  Just be aware of its limitations and you’ll be able to avoid some of these ‘odd’ behaviors (it’s not all that odd when you understand what happens behind the scenes).

Peeling Away the *VMASK

vmask-icon2One way to really unleash the power of APDL is to become familiar, and ultimately fluent, with array parameters. The APDL student will quickly learn that array manipulation involves heavy use of the *V commands, which are used to operate on vectors (single columns of an array). These commands can be used to add two vectors together, find the standard deviation of a column of data, and so on. *V commands consist of what I like to refer to as “action” commands and “setting” commands. The action commands, such as *VOPER, *VFILL, and *VFUN * have their own default behaviors, but these defaults may be overridden by a preceding setting command, such as *VABS, *VLEN, or *VMASK.

*VMASK is one of the most useful, but one of the most difficult to understand, *V command. At its essence it is a setting command that directs the following action command to a “masking” array of true/false values. Only cells corresponding to “true” values in the masking array are considered for the array being operated on in the subsequent action command.

For example, a frequently used application of *VMASK is in the compression of an array—for instance to only include data for selected entities. The array to be compressed would consist of data for all entities, such as element numbers, x-locations for all nodes, etc. The masking array would consist of values indicating the select status for the entities of interest: 1 for selected, –1 for unselected, and 0 for not even in the model to begin with. Only array cells corresponding to a masking array value of 1 would be included in the compression operation, with those corresponding to a value or 0 or –1 being thrown out. Here is a slide from our APDL training class that I hope illustrates things a little better.

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Take the class or buy the manual (and review it at Amazon, please!)

What we’ve learned so far is that the masking array contains a list of true/false (or not true) values to refer to when performing its vector operation. But actually, it’s much more general than 1, 0, and –1. What *VMASK does is include cells corresponding to all positive numbers in the masking array (not just +1) and exclude cells corresponding to all values less than or equal to zero in the masking array (not just 0 and            -1), which broadens the possibilities for how *VMASK can be handy.

Everything I’ve used *VMASK for up to this point in my career has involved array compression, and I figured I’d be put out on a sweep meshed ice floe into a sea of CFD velocity streamlines (that’s what happens to old CAE engineers; you didn’t know that?) before I came up with anything else. However, I recently ran into a situation where I needed to add up just the positive numbers in an array. I was about to construct an algorithm that would test each individual number in the array to see if it was positive and, if so, add it to the total. It would’ve been cumbersome. Then I came up with a much less cumbersome approach: use the array as it’s own masking array and then perform the addition operation. Let’s look at an example.

Take the following array:

image

The sum of all values in the array is 1.5 whereas the sum of just the positive values is 11.5. What’s the most efficient way to have APDL calculate each?

In the case of summing all values in the array, it’s easy, just simply execute

*VSCFUN,sum_total,SUM,sum_exmpl(1)

which gives you

image

But what about summing just the positive values? That’s easy, just use SUM_EXMPL as its own masking array so that only the positive values are included in the operation.

*VMASK,sum_exmpl(1)

*VSCFUN,sum_pos,SUM,sum_exmpl(1)

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Boo yeah

Now why was I doing this? I had to create a macro to calculate total nodal loads for an unconstrained component in just the positive direction (to ignore the loads counteracting in the negative direction), and this was my approach. Feel free to download the macro: facelds.mac and try it out yourself.

Vibro-Acoustics Analysis in ANSYS Mechanical as Told by a Structures Guy

Vibro-Acoustics-ANSYS-iconWith the introduction of ACT, the ANSYS Workbench editors have gained capabilities and shortcuts at much faster rate than what can be introduced in a development cycle. One of first and most far-reaching extensions is the acoustics. Inevitably I was called on by one of our customers to show them how to do a vibro-acoustics analysis (harmonic with acoustic excitation), which I did. Since the need for this type of analysis is quite broad, I’ll share it here too.

There was an extra level of excitement with this, in that I’m a structures specialist with no prior acoustics experience. So, I did my own self-training on this topic. I have to give tons of credit to Sheldon Imaoka of ANSYS Inc., who took the time to thoroughly answer the questions I had. That being said, this article will be from the standpoint of a structures engineer who’s just recently learned acoustics.

The first thing you’ll need to do is download the Acoustics extension from the Downloads section at the ANSYS Customer Portal and install it in Workbench.

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It’s at the very top, under ‘A’ for “Acoustics”

One thing you’ll notice when you unzip the Acoustics Extension package is that it contains and entire Acoustics training course. Take advantage of this freebie when learning acoustics analysis. I’ll note that, most of the process outlined in this article comes from the Submarine workshop in the acoustics training course.

Once you’ve installed and turned on the Acoustics extension, insert a Harmonic Analysis system into the project schematic, link to the solid geometry file, and specify the material properties for the solid. You’ll specify the properties for the acoustic region in Mechanical under the appropriate Acoustics extension objects.

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Rename as you see fit

Assuming you just have the geometry for the solid and not the acoustics domain, create two acoustics regions around the solid. The first region, surrounding the solid, will function as the fluid region itself, through which the acoustic waves travel and interact with the structure. The second region, surrounding the first acoustics region, will function as the Perfectly Matched Layer (PML). The PML essentially acts as the infinite boundary of the system. (If you’re an electromagnetics expert, you already know this and I’m boring you.) You can easily create these domains using the enclosure tool in DesignModeler.

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Acoustics Regions

Now we’re ready for the analysis. Open up Mechanical. Look at all those buttons on the Acoustics toolbar! Yikes! Fortunately we just need a few of them.

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Here they are

Insert an Acoustic Body and scope it to the acoustic region surrounding the structural solid. In the Details, enter the density and speed of sound for the fluid. Also set the Acoustic-Structural Coupled Body Options to Coupled With Symmetric Algorithm.

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Pay attention to the menu picks, Details, and geometry scoping here and in the rest of the image captures

“Coupled” refers to coupled-field behavior, i.e. the mutual interaction between the structure and the fluid. You’re probably familiar with this. You need that, otherwise the acoustic waves are just bouncing off the structure and the structure isn’t doing anything. Regarding the Symmetric Algorithm: The degrees of freedom for the acoustic system consists of both structural displacements and fluid pressures, giving you an asymmetric stiffness matrix. However, ANSYS has incorporated a symmetrization algorithm to convert the asymmetric stiffness matrix to a symmetric matrix, resulting in half as many equations that need to be solved and thus a faster solution time yadda yadda yadda, so go with that.

Now insert another Acoustic Body, this time scoped to the outer acoustic region (body). This is your Perfectly Matched Layer. Specify fluid density and speed of sound as before. This time, leave the Coupled Body Option as Uncoupled. But, set Perfectly Matched Layers to On.

 imageimage

Apply an Acoustic Pressure of zero to the outer faces of the PML body (Boundary Conditions > Acoustic Pressure). As you may have guessed from the menu pick, this is your acoustics boundary condition.

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Now we’ll apply some acoustic wave excitation to this thing. From the Excitation menu, select Wave Sources (Harmonic). In the Details, set the Excitation Type to either Pressure or Velocity, set the Source Location and specify the excitation pressure or velocity value. In this example, I went with Pressure since that’s what MIL-STD-810 specifies, but this option will be based on your customer requirements. I also assumed an external acoustic source (hence, Outside the Model), but again, that will be based on your particular project. You also need to specify the vector of the wave source, via rotations about the Z and Y axes (f and q). In this case I chose 30 and 60 degrees, respectfully, to make it interesting. Once again, enter the density and speed of sound for the fluid.

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Insert Scattering Controls under the Analysis Settings menu and specify whether the Field Output should be Total or Scattered. Total gives you constant pressure waves that interact with the solid but not each other. Scattered gives you wave that interact and interfere with each other as well as the solid.

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Set up the Fluid-Structural Interaction boundary condition where the structural faces are “wetted” by the acoustic domain. The FSI Interface is found under the Boundary Conditions menu.

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Apply structural constraints and specify harmonic analysis settings just like you would with a standard harmonic analysis. Make sure you request Stresses under the Output Controls. Solve the model.

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Plot your structural results as you would for a typical harmonic analysis. Acoustic Pressure wave results may be found under the Results menu in the Acoustics toolbar. If you used Total field output for the scattering option, you can verify your wave source direction by looking at the Acoustic Pressure Contours. Keep in mind that the contours will be orthogonal to the axis of the sine wave; you may need to put some extra spatial thought into it to fully understand what’s going on.

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Acoustic Pressures: Field Output = Total

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Acoustic Pressures: Field Output = Scattered

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Von-Mises Stresses, Max Over Phase: Field Output = Scattered

As you’ll note in the training course, there are a number of design questions that can be answered with acoustics analysis. In this article, I’ve addressed what I thought would be one of the more popular applications of acoustics simulation. If the demand is there, I’ll research and compose more articles on various acoustics applications in the future. For instance, another area I’ve examined is natural frequencies of a structure that’s submerged in a fluid. If there’s another acoustics topic you’d like us to write about, please let us know in the comments.

Taking NASTRAN Input Files Into ANSYS Mechanical via External Model in ANSYS 16.0

nastran-ansys-external-model-tnI found another very nice enhancement to version 16.0 of the ANSYS Workbench/ANSYS Mechanical toolset.  If you happen to have a NASTRAN input file (.dat, .nas, and .bdf) that you need to get into ANSYS Mechanical, no longer do you have to use FE Modeler in ANSYS Workbench to perform the translation.  In fact, not only can you move the NASTRAN model into ANSYS Mechanical, but you get the existing mesh as well as newly-created geometry that can be used for boundary condition application, etc.  As with most translations from one FE tool to another, you can’t expect everything will be translated.  However, this new technique can be an incredible time saver in addition to giving us capabilities to continue and augment simulations that were previously performed in NASTRAN, now in ANSYS.

Here is an example of this new procedure.  (Note that we don’t have NASTRAN here at PADT, so I couldn’t create a generic sample of a NASTRAN model in NASTRAN.  Instead, I created a model in ANSYS, then converted it into NASTRAN using ANSYS FE Modeler to get a NASTRAN input file for the purpose of this exercise.)

Once I have the NASTRAN input file that I need to convert into ANSYS Mechanical, I launch ANSYS Workbench 16.0 and insert an External Model branch.  I then click the … button to browse to the NASTRAN input file.  In this case, the file is NASTRAN.nas.

nastran-ansys-external-model-f1

Next, I drag and drop a new analysis type block into the Project Schematic.  In this case, it was a modal analysis.  Note that you can’t drop this onto the Setup cell in the External Model block as you might expect.  You set it up as a separate block and establish the link in the next step.

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Next, we drag and drop the Setup cell from the External Model block onto the Model cell of the Modal analysis block.  This establishes the link from the NASTRAN model to the new Modal analysis.

nastran-ansys-external-model-f3

We also need to right click on the Setup cell in the External Model block and select Update to get a green checkmark in that cell:

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Notice that there is no Geometry cell in the resulting Modal analysis block.  If all goes well, there will be geometry within the Mechanical model that can be used for selection purposes (in addition to the mesh that comes in from NASTRAN). 

Next we open the Mechanical editor by double clicking on one of the cells in the Modal analysis blocks (other than the Engineering Data cell).  It may take several minutes to bring in the NASTRAN model depending on the size of the NASTRAN model.  The Mechanical window doesn’t really let you know that it’s working, but if it’s sitting there with nothing being displayed, it’s probably churning away at bringing in the NASTRAN mesh and creating surface geometry on it.

Here is what the Mechanical window looks like after the mesh is read in and geometry is automatically created.  This is the mesh from the NASTRAN file, but in this case both solid and surface geometry is also present.  It’s not guaranteed that everything will come across.  I’ve seen contact elements come through for certain types of contact but not for other types of contact for example.

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The next image shows that geometry was created that can be used for the purposes of inserting fixed supports, just as if the geometry had come in from a CAD system.  Note that the NASTRAN input file had NO geometry, just finite element entities.  ANSYS is creating the geometry for use in Mechanical from the information in the NASTRAN input file.

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Finally, after manually creating a needed contact region, I was able to solve the modal analysis, demonstrating that further simulation can be performed in ANSYS Mechanical from this model which originally came from NASTRAN.

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So, the main take away here is that with version 16.0 of ANSYS, we can take a NASTRAN input file and through the use of the External Model block, go directly into ANSYS Mechanical.  Not only do we get the nodes and elements as well as other finite element entities from the NASTRAN model, but if all goes well we get geometry that facilitates further processing within ANSYS Mechanical.

We certainly hope this new capability makes it easier for you to perform additional simulations in ANSYS when the starting point is a NASTRAN model.  The other formats documented for version 16.0 are ABAQUS, Fluent input files, and ICEM CFD input files.

Tech Tips and Videos for ANSYS Mechanical and CFD

ansys_free_techtipsA few weeks ago we added some great free resources to our website for existing and potential users of ANSYS Structural and CFD tools.  It includes some great videos from ANSYS, Inc. on a variety of topics as well as productivity kits. It dawned on us that many of you are faithful readers of The Focus but don’t often check out our ANSYS product web pages. So, we are including the material here for your viewing pleasure.

(7/9/2015: We just added the Electromechanical kit here.)

For structural users, we have a link to “The Structural Simulation Productivity Kit ” here. The kit includes:

  • Analyzing Vibration with Acoustic–Structural Coupling Article
  • Contact Enhancements in ANSYS Mechanical and MAPDL 15.0 Webinar
  • ANSYS Helps KTM Develop a 21st Century Super Sports Car Case Study
  • A Practical Discussion on Fatigue White Paper
  • Designing Solid Composites Article

We also have a collection of videos from ANSYS, Inc that we found useful:

For CFD users, we have a link to “The CFD Simulation Productivity Kit ” here. The kit includes:

  • Simulating Erosion Using ANSYS Computational Fluid Dynamics Presentation,
  • Cutting Design Costs: How Industry leaders benefit from Fast and Reliable CFD  White Paper,
  • Introduction to Multiphase Models in ANSYS CFD Three Part Webinar,
  • Advances in Core CFD Technology: Meeting Your Evolving Product Development Needs White Paper,
  • Turbulence Modeling for Engineering Flows Application Brief.

We also have a collection of videos from ANSYS, Inc that we found useful:

Interested in learning more, contact us or simply request a quote.

Press Release: Structural Optimization from VR&D Added to PADT Portfolio

varand-gtam-w-logosWe 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.  

Press Release:

PADT is now a reseller of the GTAM and GENESIS optimization tools from Vanderplaats R&D, offering leading structural geometry and topological optimization tools to enable simulation for components made with 3D Printing

Tempe, AZ – March 24, 2015 – Phoenix Analysis & Design Technologies, Inc. (PADT, Inc.), the Southwest’s largest provider of simulation, product development, and 3D Printing services and products, is pleased to announce that an agreement has been reached with Vanderplaats Research & Development, Inc. (VR&D) for PADT to become a distributor of VR&D’s industry leading structural optimization tools in the Southwestern United States. These powerful tools will be offered alongside ANSYS Mechanical as a way for PADT’s customers to use topological optimization and shape optimization to determine the best geometry for their products.

The GENESIS program is a Finite Element solver written by leaders in the optimization space. It offers sizing, shape, topography, topometry, freeform, and topology optimization algorithms.  No other tool delivers so many methods for users to determine the ideal configuration for their mechanical components. These methods can be used in conjunction with static, modal, random vibration, heat transfer, and buckling simulations.  More information on GENESIS can be found at http://www.vrand.com/Genesis.html

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PADT recommends that ANSYS Mechanical users who require topological optimization access GENESIS through the GENESIS Topology for ANSYS Mechanical tool, or GTAM. This extension runs inside ANSYS Mechanical, allowing users the ability to use their ANSYS models and the ANSYS user interface while still accessing the power of GENESIS.  The extension allows the user to setup the topology optimization problem, optimize, post-processing, export optimized geometry all within ANSYS Mechanical user interface.

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“We had a customer ask us to find a topological optimization solution for optimizing the shape of a part they were manufacturing with 3D Printing. We tried GTAM and immediately found it to be the type of technically superior tool we like to represent” commented Ward Rand, a co-owner of PADT.  “It didn’t take our engineers long to learn it and after receiving great support from VR&D, we knew this was a tool we should add to our portfolio.”

Besides reselling the tool, PADT is adopting both GENESIS and GTAM as their internal tools for shape optimization in support of their growing consulting in the area of design and simulation for Additive Manufacturing, popularly known as 3D Printing. PADT combines these with ANSYS SpaceClaim and Geomagic Studio to design and optimize components that will be created using 3D Printing.

“We are thrilled to partner with PADT because of their deep knowledge in simulation, additive manufacturing, and 3D printing and for their extraordinary ability to help their clients”, stated Juan Pablo Leiva, President and COO of VR&D, “We feel that their unique talents are crucial in supporting clients in today’s demanding and changing market.”

To learn more about the GENESIS and GTAM products, visit http://www.padtinc.com/vrand or contact our technical sales team at 480.813.4884 or sales@padtinc.com.

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About Phoenix Analysis and Design Technologies
Phoenix Analysis and Design Technologies, Inc. (PADT) is an engineering service company that focuses on helping customers who develop physical products by providing Numerical Simulation, Product Development, and Rapid Prototyping products and services. PADT’s worldwide reputation for technical excellence and an experienced staff is based on its proven record of building long term win-win partnerships with vendors and customers. Since its establishment in 1994, companies have relied on PADT because “We Make Innovation Work.“  With over 75 employees, PADT services customers from its headquarters at the Arizona State University Research Park in Tempe, Arizona, its Littleton, Colorado office, Albuquerque, New Mexico office, and Murray, Utah office, as well as through staff members located around the country. More information on PADT can be found at www.PADTINC.com.

About Vanderplaats Research & Development
Since its founding in 1984, Vanderplaats Research & Development, Inc. (VR&D) has advocated for the advancement of numerical optimization in industry. The company is a premier software company, developing and marketing a number of design optimization tools, providing professional services and training, and engaging in ongoing advanced research. VR&D products include GENESIS, GTAM, VisualDOC, Design Studio, SMS, DOT, and BIGDOT. For more information on VR&D, please visit:  www.vrand.com.