## Default Contact Stiffness Behavior for Bonded Contact

It recently came to my attention that the default contact stiffness factor for bonded contact can change based on other contact regions in a model. This applies both to Mechanical as well as Mechanical APDL. If all contacts are bonded, the default contact stiffness factor is 10.0. This means that in our bonded region, the stiffness tending to hold the two sides of contact together is 10 times the underlying stiffness of the underlying solid or shell elements.

However, if there is at least one other contact region that has a type set to anything other than bonded, then the default contact stiffness for ALL contact pairs becomes 1.0. This is the default behavior as documented in the ANSYS Mechanical APDL Help, in section 3.9 of the Contact Technology Guide in the notes for Table 3.1:

“FKN = 10 for bonded. For all other, FKN = 1.0, but if bonded and other contact behavior exists, FKN = 1 for all.”

So, why should we care about this? It’s possible that if you are relying on bonded contact to simulate a connection between one part and another, the resulting stress in those parts could be different in a run with all bonded contact vs. a run with all bonded and one or more contact pairs set to a type other than bonded. The default contact stiffness is now less than it would be if all the contact regions were set to bonded.

This can occur even if the non-bonded contact is in a region of the model that is in no way connected to the bonded region of interest. Simply the presence of any non-bonded contact region results in the contact stiffness factor for all contact pairs to have a default value of 1.0 rather than the 10.0 value you might expect.

Here is an example, consisting of a simple static structural model. In this model, we have an inner column with a disk on top. There are also two blocks supporting a ring. The inner column and disk are completely separate from the blocks and ring, sharing no load path or other interaction. Initially all contact pairs are set to bonded for the contact type. All default settings are used for contact.

Loading consists of a uniform temperature differential as well as a bearing load on the disk at the top. Both blocks as well as the column have their bases constrained in all degrees of freedom.

After solving, this is the calculated maximum principal stress distribution in the ring. The max value is 41,382.

Next, to demonstrate the behavior described above, we changed the contact type for the connection between the column and the disk from bonded to rough, all else remaining the same.

After solving, we check the stresses in the ring again. The max stress in the ring has dropped from 41,283 to 15,277 as you can see in the figure below. Again, the only change that was made was in a part of the model that was in no way connected to the ring for which we are checking stresses. The change in stress is due solely to a change in contact type setting in a different part of the model. The reason the stress has decreased is that the stiffness of the bonded connection is less by a factor of 10, so the bonded region is a softer connection than it was in the original run.

So, what do we as analysts need to do in light of this information? A good practice would be to manually specify the contact stiffness factor for all contact pairs. This behavior only crops up when the default values for contact stiffness factor are utilized. We can define these stiffness factors easily in ANSYS Mechanical in the details view for each contact region. Further, we need to always remember that ANSYS as well as other analytical tools are just that – tools. It’s up to us to ensure that the results of interest we are getting are not sensitive to factors we can adjust, such as mesh density, contact stiffness, weak spring stiffness, stabilization factors, etc.

## Learn Linux on edX

The balance of Linux vs. Windows for simulation users is always in flux. For some time it was predicted that Windows would win the battle but in recent years Linux has made a resurgence, especially on clusters and in the cloud.  We strongly recommend that ANSYS users who want to be power users gain a good understanding of Linux from a user and sysadmin perspective. Especially CFD users since they are most likely to be solving on a Linux devices.  Too many of the people we interface with are left at the mercy of an IT support team that doesn’t know, or even fears Linux.

The best way to solve this problem is to learn Linux yourself. To help people get there, recommended a few books and “learn by doing.” Now we have a better option.

edX offers an Introduction to Linux class that looks outstanding, and you can audit it for free or take the course for real for a \$250 minimum contribution.  The quality of these courses is fantastic. The material is thorough and practical.

If you do take the class, give us some feedback when you finish in the comments below.

Here is the video describing the course.

## Using Probes to Obtain Contact Forces in ANSYS Mechanical

Recently we have had a few questions on obtaining contact results in ANSYS Mechanical. A lot of contact results can be accessed using the Contact Tool, but to obtain contact forces we use Probes. Since not everyone is familiar with how it’s done, we’ll explain the basics here.

Below is a screen shot of a Mechanical model involving two parts. One part has a load that causes it to be deflected into the other part.

We are interested in obtaining the total force that is being transmitted across the contact elements as the analysis progresses. Fortunately this is easy to do using Probes in Mechanical.

The first thing we do is click on the Solution branch in the tree so we can see the Probes button in the context toolbar. We then click on the Probe drop down button and select Force Reaction, as shown here:

Next, we click on the resulting Force Reaction result item under the Solution branch to continue with the configuration. We first change the Location Method from Boundary Condition to Contact Region:

We then specify the desired contact region for the force calculation from the Contact Region dropdown:

Note that the coordinate system for force calculation can either be Cartesian or Cylindrical. You can setup a coordinate system wherever you need it, selectable via the Orientation dropdown.

There is also an Extraction dropdown with various options for using the contact elements themselves, the elements underlying the contact elements, or the elements underlying the target elements (target elements themselves have no reaction forces or other results calculated). Care must be taken when using underlying elements to make sure we’re not also calculating forces from other contact regions that are part of the same elements, or from applied loads or constraints. In most cases you will want to use either Contact (Underlying Element) or Target (Underlying Element). If contact is non-symmetric, only one of these will have non zero values.

In this case, the setting Contact (Contact Element) was a choice that gave us appropriate results, based on our contact behavior method of Asymmetric:

Here are the details including the contact force results:

This is a close up of the force vs. ‘time’ graphs and table (this was a static structural analysis with a varying pressure load):

***** SUMMATION OF TOTAL FORCES AND MOMENTS IN THE GLOBAL COORDINATE SYSTEM *****

FX = -0.4640219E-04
FY = -251.1265
FZ = -0.1995618E-06
MX = 62.78195
MY = -0.1096794E-04
MZ = -688.9742
SUMMATION POINT= 0.0000 0.0000 0.0000

We hope this information is useful to you in being able to quickly and easily obtain your contact forces.

## Video Tips: Using ACT to change Default Settings in ANSYS Mechanical

A short video showing how ACT (ANSYS Customization Toolkit) can be used to change Default Settings for analyses done in ANSYS Mechanical.  This is a very small subset of the capabilities that ACT can provide.  Stay tuned for other videos showing further customization examples.

The example .xml and python file is located below.  Please bear in mind that to use these “scripted” ACT extension files you will need to have an ACT license.  Compiled versions of extensions don’t require any licenses to use.  Please send me an email (manoj@padtinc.com) if you are wondering how to translate this example into your own needs.

NLdefaults

A group of enthusiastic students at the University of Houston are doing their part at solving that age old academia problem: not enough hand’s on experience.  They are designing and building a working steam turbine for the schools Thermodynamics lab so students can experiment with a Rankin cycle, learn how to take meaningful measurements, and study how to control a real thermodynamic system.

After meeting a team member at the 2014 Houston ANSYS User conference, PADT saw a great opportunity to help the team by providing them with access to a full seat of Flownex SE so that they can create a virtual prototype of their steam turbine and the control system they are developing.

The four team members have the following goals for their project:

1. Create a fully automated system control
2. Create system with rolling frame for ease of transport
3. Create system with dimensions of 4x2x3.5 ft
5.  Produce an aesthetically pleasing product

Flownex should be a great tool for them, allowing the team to simulate the thermodynamics and flow in the system as well as the system controls before committing to hardware.

We hope to share their models and what they have learned when their project is complete. If you are interested in using Flownex for your work or school project, contact PADT.

## A 3D Mouse Testimonial

The following is from an email that I received from Johnathon Wright.  I think he likes his brand new 3DConnexion Space Pilot Pro.
-David Mastel
IT Manager

——————-

Recently PADT became a certified reseller for 3Dconnexion. Shortly following the agreement a sleek and elegant SpacePilot PRO landed on my desk. Immediately the ergonomic design, LCD display, and blue LED under the space ball appealed to the techie inside of me. As a new 3D mouse user I was a little skeptical about the effectiveness of this little machine, yet it quickly has gained my trust as an invaluable tool to any Designer or Engineer. On a daily basis it allows me to seamlessly transition from CAD to 3D printing software and then to Geomagic Scanning software, allowing dynamic control of my models, screen views, hotkeys and shortcuts.

Outside of its consistency as an exceptional 3D modeling aid, the SpacePilot PRO also has a configurable home screen that allows quick navigation of email, calendar or tasks. This ensures that I can keep in touch with my team without having to ever leave my engineering programs, which is invaluable to my production on a daily basis. Whether you are a first time user who is looking to tryout a 3D Mouse for the first time or an experienced 3D mouse user who is looking to upgrade, you need to check out the SpacePilot Pro. I can’t imagine returning to producing CAD models or manipulating scan data without one. Combine the SpacePilot PRO cross-compatibility with its programmability and ease of use and you have a quality computer tool that applies to a wide range of users who are looking at new ways to increase productivity.

Link to You Tube video – watch it do its thing along with a look at my 3D scanning workstation, the GEOCUBE: http://youtu.be/fsfkLPaZJe4

Johnathon Wright
Applications Engineer,
Hardware Solutions

———————————————————————————————-
Editors Note:

Not familiar with what a 3D Mouse is?  It is a device that lets a use control 3D objects on their computer in an intuitive manner. Just as you move a 2D mouse on the plane of your desk, you spin a 3D Mouse in all three dimensions.  Learn more here

## Integrating ANSYS Fluent and Mechanical with Flownex

Component boundaries generated in Flownex are useful in CFD simulation (inlet velocities, pressures, temperatures, mass flow). Generation of fluid and surface temperature distribution results from Flownex can also be useful in many FEA simulations. For this reason the latest release of Flownex SE was enhance to include several levels of integration with ANSYS.

## ANF Import

By simply clicking on an Import ANF icon on the Flownex Ribbon bar users can select the file that they want to import. The user will be requested to select whether the file must be imported as 3D Geometry which conserves the coordinates system or as an isometric drawing.

The user can also select the type of component which should be imported in the Flownex library. Since the import only supports lines and line related items this will typically be a pipe component.

Following a similar procedure, a DXF importer allows users to import files from AutoCAD.

This rapid model construction gives Flownex users the ability to create and simulate networks quicker. With faster model construction, users can easily get to results and spend less time constructing models.

## ANSYS Flow Solver Coupling and Generic Interface

The Flownex library was extended to include components for co-simulation with ANSYS Fluent and ANSYS Mechanical.

These include a flow solver coupling checks, combined convergence and exchanges data on each iteration, and a generic coupling that can be used for cases when convergence between the two software programs is not necessary.

The general procedure for both the Fluent and Mechanical co-simulation is the same:

1. By identifying specified named selections, Flownex will replace values in a Fluent journal file or ds.dat file in the case of Mechanical.
2. From Flownex, Fluent/Mechanical will then be run in batch mode
3. The ANSYS results are then written into text files that are used inputs into Flownex.
4. When applicable, specified convergence criteria will be checked and the procedure repeated if necessary.

## FDA Opening to Simulation Supported Verification and Validation for Medical Devices

Bringing new medical device products to market requires verification and validation (V&V) of the product’s safety and efficacy. V&V is required by the FDA as part of their submission/approval process. The overall product development process is illustrated in the chart below and phases 4 and 5 show where verification is used to prove the device meets the design inputs (requirements) and where validation is used to prove the device’s efficacy. Historically, the V&V processes have required extensive and expensive testing. However, recently, the FDA’s Center for Devices and Radiological Health (CDRH) has issued a guidance document that helps companies uses computational modeling (e.g FEA and CFD) to support the medical device submission/approval process.

The document called, “Reporting of Computational Modeling Studies in Medical Device Submissions”, is a draft guidance document that was issued on January 17th, 2014. The guidance document specifically addresses the use of computation in the following areas for verification and/or validation:

1. Computational Fluid Dynamics and Mass Transport
2. Computation Solid Mechanics
3. Computational Electromagnetics and Optics
4. Computational Ultrasound
5. Computational Heat Transfer

The guidance specifically outlines what form reports need to take if a device developer is going to use simulation for V&V.  By following the guidance, a device sponsor can be assured that all the information required by the FDA is included. The FDA can also work with a consistent set of input from various applicants.

Computational Modeling & Simulation, or what we usually call simulation, has always been an ideal tool for reducing the cost of V&V by allowing virtual testing on the computer before physical testing. This reduces the number of iterations on physical testing and avoids the discovery of design problems during testing, which is usually late in the development process and when making changes is the most expensive. But in the past, you had to still conduct the physical testing. With these new guidelines, you may now be able to submit simulation results to reduce the amount of required testing.

Validation and verification using simulation has been part of the product development process in the aerospace industry for decades and has been very successful in increasing product performance and safety while reducing development costs.  It has proven to be a very effective tool, when applied properly.  Just as with physical testing, it is important that the virtual test be designed to verify and validate specific items in the design, and that the simulation makes the right assumptions and that the results are meaningful and accurate.

PADT is somewhat unique because we have broad experience with product development, various types of computational modeling and simulation, and the process of submission/approval with the FDA. In addition, we are ISO 13485 certified. We can provide the testing that is needed for the V&V process and employ simulation to accelerate and support that testing to help our medical device customers get their products to market faster and with less testing cost.  We can also work with customers to help them understand the proper application of simulation in their product development process while operating within their quality system.

## Flownex 2014 Released and Webinars Announced

The June release of Flownex SE software includes numerous updates for companies that model thermal fluid systems; videos and webinars are available to showcase the impact of these enhancements.

Flownex SE has increased the ability of engineers to accurately model their fluid-thermal with the release of version of Flownex 2014 on June 19th, 2014. The program is known for its in ease of use, breadth of capability, and depth of functionality.  With enhancements in turbomachinery modeling, support for 3D networks, GIS data import, heat transfer and a myriad of additional new features impacting efficiency, integration, and automation, this release expands the industries that can take advantage of it, and will help current users model their systems more accurately with greater ease.

To help the user community understand the impact of these significant enhancements, PADT is offering two webinars. Both webinars will include a brief introduction to the tool, so if you are new to Flownex SE you will have a good foundation to get started.

Webinar Sign-Up:

Overview webinar: July 24, 2014, 1:00-2:00 PM MST

This webinar will focus all of the new features in Flownex SE 8.3.6.
Register here

Turbomachinery webinar: August 7, 2014, 1:00-2:00 PM MST

This webinar will be a deep dive into the extensive turbomachinery capabilities added in this release, and will be of interest to anyone simulating turbine engines, pumps, blowers, or other rotating machinery that involves fluids.
Register here

All registrants will be sent links to recordings so they can view the presentation even if they cannot attend them live.

Video Resources:

A video is also available that hits the important new capabilities:

Key Features:

The key features introduced in Flownex 2014 (Flownex SE 8.3.6) are:

1. Rotating components, Swirl Boundary, and General Turbine and Compressor Models
2. Importing and Geometries
3. GIS File Support
4. Connections to ANSYS Products
6. Graphical Script Generation Tool
7. New Designer Tools to Quickly Model Common Systems.
10. Additional Enhancements ranging from 3D Graphs to Support for Miter Bends in Piping

Visit here to see a detailed list of these key features, or download the complete release notes here.

These additional features reflect the growing diversity of industries that are using Flownex SE to model their systems.  Users in oil and gas, mining, chemical processing, and turbomachinery will all see additional accuracy, functionality, and efficiency from this release. Built on an existing strong foundation that offers un-paralleled capability with  intuitive ease of use, a short look at Flownex SE will show you why so many users around the world are choosing it as their thermo-fluid modeling tool.

PADT is the distributor of Flownex SE in the United States.  Our experienced staff is eager to discuss your system modeling needs and is ready to show you how Flownex SE can start delivering value almost immediately. Contact us today to meet with our experts.

## Video Tips: Workflow for Designing Electric Motors in ANSYS

A quick video showing you a great workflow for designing electric motors. It shows going from a quick template based design tool to a full 3D analysis tool

## Top 10 New Thermal Fluid Modeling Capabilities in Flownex 2014

We are pleased to announce the release of Flownex SE 2014.  This is a very exciting release for all of us involved in Flownex because it introduces a mix of advanced features and usability enhancements – we love better and easier.  We will be publishing more information about this release, as well as videos and webinars. While we set all of that up, we wanted to whet everyone’s appetite and give you a list of what we feel are the 10 most important enhancements.

1. Rotating components, Swirl Boundary, and General Turbine and Compressor Models
A new library has been added which models rotating flow on a system level. Focusing on secondary flow and heat transfer in turbine engines, it includes all the components needed including compressors, turbines, seals, gaps, nozzles, and cavities. A complete library for Steam Turbine modeling was also added.
2. Importing and Geometries
Users can read in 2D and 3D layout files in common formats and directly create Flownex models from the geometry. The model and results can then be visualized with the 3D geometry.
3. GIS File Support
When modeling systems that cover a large area, such as water or gas pipelines, the geographical data can be imported for display and to automatically include altitude into the model.
4. Connections to ANSYS Products
Users can import 3D Pipe geometry as an ANF file, and connect to ANSYS Mechanical and ANSYS Fluent for co-simulation.
Users can transfer parametric data to and from Mathcad worksheets
6. Graphical Script Generation Tool
Users can use Quick Script to create complex scripts to customize their processes or models without having to learn the full scripting language
7. New Designer Tools to Quickly Model Common Systems.
Designer tools atomically iterate on a user’s model to calculate unknown values for them. This release includes tools for calculating mass flow when only pressure is known at a boundary, automatically calculating steady state conditions in a two-phase tank, and a component designer that calculates input parameters for common components so that those components deliver the users requested mass flow.
Based on user input, five new models were added to the Dittus-Boelter correlation for calculating heat transfer coefficients: tube, shell-side single phase, shell-side horizontal tube condensation, ribbed wall channel, and channel with pedestals.
New model in subsonic and supersonic flow at the outlet of a flow network with gasses and superheated fluids
Support for miter bends in piping
3D graphs
The range of methane two phase fluid was increased
Support for 64 bit
Several more values can be changed during a transient solution

There is also some more detailed material here:

## Recommended Free Utilities for the ANSYS User’s Toolbox

What do you have in your toolbox? The ANSYS suite of tools is pretty comprehensive.  But an efficient user always has a collection of utilities that they use with ANSYS products to automate processes, convert data, and scrub results.  In 2008 we published a list of free and commercial tools that we were using at PADT, and web results show that it is one of our more popular posts. So we thought it was a good time to revisit and update those lists.

We will start with the free tools, well because everyone loves something for free. This is by no means a comprehensive list, these are simply the tools we currently use here at PADT. If you have alternative suggestions, please leave them in a comment.  I tried to put them in some logical grouping, but failed.  So here they are, in no particular order:

 pythonScripting Languagewww.python.org Every good simulation user needs scripting.  We spend a lot of time dealing with large amounts of data and setting up all sorts of complicated processes.  Scripting can be used to create, modify, sift through, or translate text versions of our models, loads, and results.  Some users like to stick with APDL and never leave ANSYS, some know Matlab very well.  Others may use newer languages like Lua or older ones like perl. Here at PADT we have found that python is the best tool for scripting outside of ANSYS MAPDL (we use APDL if we are in the program).  Not only is it easy to learn and use, it has hundreds of free libraries that do almost anything you want. Lots of people know it, and you are not dependent on some other piece of software. Python also works on Linux and Windows. In addition, most CAE tools these days support python scripting.  This is certainly true of the Workbench project page and ANSYS ACT for ANSYS Mechanical.  Alternatives: perl, Lua, linux shell scripts.
 VTKVisualization Librarywww.vtk.org Did you ever wish there was a toolkit out there that you could use to quickly build a visualization tool?  I know I spent days of my early career writing simple tools from scratch, and spending most of my time on graphics stuff.  Well, VTK is that toolkit.  It consists of C++ class libraries, and includes interpreters for Tcl/Tk, Java, and python.  With python, you can create little applications very quickly without having to know a full object oriented programming language.  The resulting graphics are fast and attractive. If you are going to be writting your own vertical application that works with your FEA or CFD tool, use VTK for the graphics.
 ParaViewVisualization Toolwww.paraview.org The first time you use ParaView, your response will most likely be OMG. It is a visualization tool written in VTK.  It reads most FEA and CFD formats, along with pretty much any faceted geometry data format.  [Unfortunately it is not reading the current ANSYS ds.dat file that ANSYS mechanical writes (or a cdb file)  I’ll try and submit a bug report. ]  But it does read a CGNS file, which you can export to from Workbench.  But we don’t use it for working with ANSYS files so much, we have tools for that. We use it to deal with other file formats like STL, NASTRAN, CGNS, ExodusII, etc…  Very handy and intuitive to use. It is also an example of how powerful VTK is. Alternatives: OpenCascade
 Notepad++Source Code Editornotepad-plus-plus.org This is a great text editor.  Newer than most, it builds on the dozens of previous text editors out there.  It does syntax highlighting and auto completion for many languages. For ANSYS users, it has a powerful column editing mode, very sophisticated search and replace, and macro recording and playback.  I’m not aware of an APDL syntax highlighter, but you have PeDAL for that. There are a lot of text editors out there, and this one has bubbled to the top as the most popular at PADT. Alternatives: Notepad, PSPad, TextPad, UltraEdit, and dozens more
 Vim/GVimVI Text Editorwww.vim.org Some people love VI, the old Unix text editor.  I’m one of those people. I’ve been using VI for over 30 years.  So I have to have a VI editor on my machine and I use it instead of Notepad++ or other text editors. Because I don’t want to touch a mouse, I want to [Esc] jjjj llll .  instead.  Vim is really the only good VI tool out there anymore, and it comes standard on most Linux installs instead of the old Vi.  The windows version works great. Alternatives: Elvis, Vile, Lemmy
 OpenOfficeWord Processor, Spreadsheet, Slide Shows, Databasewww.openoffice.org Let’s be honest, MS Office dominates this type of tool. It works, everyone has it, and everyone knows it.  But sometime you don’t want to fork over cash to those guys in Seattle. Or maybe you spend your day on Linux.  OpenOffice is about 90% of what MS Office does, and it is free. It kind of died at Sun when they got bought by Oracle.. Since Apache has taken up the market, it has seen a lot of enhancements. Many people just think about the word processor, but remember it has a simple drawing tool, an equation editor, a a very good database program. Alternatives: GoogleDocs, LibreOffice
 LaTeXDocument Perpetration Systemwww.latex-project.org How do you tell an engineer with an advanced degree from one who just has a BS?  The one with the MS or PhD like LaTeX. Traditionally the tool of thesis writers, LaTeX has significant utility for the ANSYS user.  It allows you to create nice looking documents by imbedding tags in the document.  A pain when we have WYSIWYG editors, but very useful if you want to use scripting to create a document.  It is also a great way to create very good looking equations and tables.  Think of it as HTML for nice looking documents. Alternatives: Word Processors
 CutePDFPDF Creator/Writerwww.cutepdf.com This tool is not as important as it once was, since many programs write to PDF for you. But every once in a while you run across one that does not.  It installs like a printer, so anything program with a print command allows you to save as PDF.  Alternatives: Adobe Online PDF Creator, PDF reDirect, PDFCreator, and a ton more.
 Adobe ReaderPDF Viewerget.adobe.com/reader I almost left this off the list, but to be fair I included this. If you don’t have Acrobat Reader, you must live in a cave.  It is pretty much required to do business in this day and age.
 GhostscriptGhostviewGSViewPostScript Toolspages.cs.wissc.edu/~ghost Ghostscript is an old Gnu project that contains tools for working with PostScript.  Ghostview is the viewing tool on Linux, although it has been replaced by GV.  GSView is a viewer for Windows.  Look at the website to learn about which tool you should be using. If you just look at PDF’s, then Adobe Reader is all you need. But if you have an older program that output PostScript directly, or you want to write a tool that create PostScript, then this toolset is for you.
 Windows Snipping ToolScreen Capture Toolen.wikipedia.org/wiki/Snipping_Tool This comes with all modern Window’s operating systems.  And, to be honest, this is the one free utility most of us use more than any other.  Who saves images to files any more, we just snip them!  If you don’t have it in your task bar, put it there and get used to using it.  Your Linux Desktop Environment will have a similar tool: KSnapshot or GNOME Screenshot
 CamStudioScreen Capture Toolcamstudio.org CamStudio is an open source tool for capturing video and audio off your screen.  Now one may want this to create screen grabs of “Lost in Space” reruns… but what does an ANSYS user need this for.  We use it to make tutorials for other users.  It is a great way to capture what you are doing on your screen for training or to share with co-workers. Alternatives:  We mostly use commercial tools for this… see the next article.
 GIMPImage Editing Toolswww.gimp.org I hate the name of this product. The politically-correct-Berkley-grad in me finds it very distasteful. But it stands for Gnu Image Manipulation Program.  It is not Adobe PhotoShop, but every release it gets closer. And in some areas it is better. It runs on Linux and Windows, always a plus.  We use it on our Unix machines to crop and clean up images. It can also be used to combine a series of images into an Animated GIF.  It is not bad at deleting backgrounds to make images with transparency for presentations as well.  It also has a fairly good vector creation layer. We used to recommend a mixture of free tools to deal with image manipulation and editing, but now we feel that GIMP does it all. Alternatives; ImageMagick, MS Paint
 Movie to GIF MovieToAniGifMake Animated GIF’s from AVI’swww.evanolds.com/movtogifsimple.html Everyone uses Microsoft PowerPoint to do presentations, and for most things it works great. But one thing is really sucks at is animations: you have to keep the movie files you are showing in the same directory because you can not embed them.  The simplest solution to this problem is to convert your animations into animated GIF files. Then insert those in your presentation. It also solves the problem of putting animations on your website without using YouTube or Flash. The tool we use mostly is Move to Animated GIF Converter.  It is old, the last version came out in 2010, but it still works just fine.  Not much to it, point it at an AVI file and then save it as an animated GIF. Alternatives: There are a bunch of tools out there, we have not used any so can’t really recommend an alternative.
 EngaugeConverts Images of Graphs into Datadigitizer.sourceforge.net Have you ever asked someone for material properties and you get a scan of a phototcopy of a book page back?  It happens less these days than it used to but you still sometimes get an image of a graph rather than a spreadsheet file.  Have no fear, Engauge is here!  It takes your image and allows you to identify the axis and the scale, then the data.  With a few clicks you have a table of useful data.  Alternatives: A ruler.
 Gnuplot GnuplotPlotting Toolwww.gnuplot.info Most FEA tools have their own 2D and 3D Graphing options, and of course Excel does a pretty good job. But sometimes you need more, or you want a plotting tool you can script. Gnuplot is that tool. It has been around forever and has about every type of graph imaginable. As a command line based program with its own scripting language, it can be generated by your programs to get the exact plot that you want. Alternatives: Python’s matplotlib or PyQtGraph, Scilab
 ScilabNumerical Computation Toolwww.scilab.org We don’t us a lot of Matlab here at PADT, we try and beat it out of new grads when we hire them… no not really.  It is a tool that our younger engineers are used to using.  The problem is it is kind of expensive when you use it every once in a while. Scilab is a nice open source alternative.  It works well and runs on Linux and Windows.  Alternatives: Julia, Sage.
 Windows Remote DesktopRemote Desktop ToolBuilt in to Windows Operating Systems This is another “free” utility that comes with the windows operating system. Strictly speaking, it is not free because you paid for Windows, but it is so important, I thought it it was worth mentioning.  Accessing your a windows computer remotely was something we can now do all the time, even from a mobile device. And internet connections are fast enough to where you can do real work from a coffee shop, home, or even from an airplane with WiFi.  More importantly, in March of 2014, Microsoft released apps for iOS, Android, and Mac that work really, really well. We had been using 3rd party apps that were OK, but the new MS apps are great and I log on to my desktop all the time from my iPad and work fairly productively.
 VNCRemote Desktop Toolwww.tightvnc.comwww.realvnc.com Remote Desktop works great for Windows boxes.  But if you want to do a remote desktop thing with Linux, or cross platform, we recommend VNC.  There are a ton of VNC tools out there, we seem to use tightVNC, and realVNC.  You need a server on the remote machine, and a viewer on the machine you are using. The viewers are free, not all servers are free.  There are also apps for iOS and Android for VNC viewers. We recommend using VNC only if you are connecting to a Linux machine from a Windows machine and you don’t want to mess with an X11 server on your Windows Machine (See below for X11 servers for Windows).  VNC does a pixel copy across the network, which is not as fast as X11 or Remote Desktop that send primitives back and forth. We have not had time to investigate VNC tools like TurboVNC that use VirtualGL and other tools to speed up the sending of the graphics window back and forth. NX (see below) uses VirtualGL Alternatives: Tons, just google.
 NX NXRemote X11 Desktop Client and Serverwww.nomachine.com Above we talk about Remote Desktop and VNC as ways to see remote machines.  If you want to see a Linux machine the best free way we have found is to use NX. This is one of those open source tools that is free and not free, and can get confusing.  It works like VNC in that you need a server on your remote machine, and a client on your machine. The client from www.nomachine.com is free.  The server is something you need to load on the remote machine, and probably comes in your Linux distribution. FreeNX seems to be the most popular. You should get very nice performance for 3D graphics on your internal internet, and not bad over the internet either.  We recomend NX over Cygwin if you don’t need a full unix clone on your windows machine, if you are just logging in to a LInux box, use NX. (and yes, we hate that the name is the same as the CAD/PLM tool… causes great confusion) Alternatives: Cygwin, VNC
 cygwinLinux on Windowswww.cygwin.com If you need more than visualization on a remote Linux machine from your Windows box, you actually want to run Linux on top of Windows without rebooting or using a virtual machine, then you need cygwin.  It is a fairly full linux distribution that runs on Windows, including full X11 capability.  We don’t recommend it for people who are not Linux savvy, but if you are and you want to work in that environment, then it works very well.
 puttyssh Toolwww.putty.org The best, and most secure, way to connect to a Linux machine is through SSH. If you have NX or cygwin you just open up a terminal and connect. But what if you just want a text connection. Putty is a simple tool that will store your connections and let you log right in and provide you with that terminal.  Better yet, it has an SCP tool (ssh copy) that is very handy for transferring files between machines.
 dropboxFile sharing Toolwww.dropbox.com There are a ton of “cloud” tools out there that let you load a file up on a server in the sky, backing it up or sharing it with others.  We use Dropbox at PADT for a couple of reasons.  The first is that it is more than a cloud solution, the files you put on Dropbox get copied to all of the computers you have that are connected to your Dropbox.  I keep all the essential files I need every day, and for whatever project I’m working on in a Dropbox folder and I have access to it at home, on my laptop, even on my iPad.  I also use it to transfer files to other people who don’t know what FTP is. Alternatives: Box, Copy, GoogleDrive (with Sync)
 filezillaFTP Toolwww.filezilla-project.org Real simulation users FTP from the command line… and waste time doing so.  FileZilla is a great tool that uses a GUI to connect to FTP servers and transfer files by dragging and dropping.  It makes finding files, transferring multiple files, and monitoring those big transfers a breeze. Alternatives: ftp command line, cURL,lftp
 7-ZipFile Compression Toolwww.7-zip.org This is the most capable windows based compression tool we have found.  For many people the built in compression in Windows is fine, but if you want other options, and the ability to work with formats besides .ZIP ( including TAR, GZIP, RAR, LZH) this is the preferred tool. Alternatives: windows compression, we have not used any other free tools for this
 Encryption I was going to recommend two tools for encryption: TrueCrypt and PGP.  But it looks like both tools are in flux right now.  TrueCrypt makes virtual drives as files. When you decrypt them they show up as a drive on your machine. Very handy for achieving any special security concerns you may have.  But in march it was mysteriously shut down. They recommend that you use BitLocker which comes free with Windows.  We have not tried it so we can’t recommend it. Too bad, it was a great tool.  An alternative is PGPDisk, but that costs money or you have to compile it yourself. PGP encrypts files and had great email plug-ins. It was a nice tools for sending customer data back and forth in a secure way.  It was purchased by a series of companies and ended up sort of becoming static. You can read about it on Wikipedia. The good news is that there is an open source version called PGP, available on www.pgpi.org.  You want the GnuPG version which is free.  There are links here to PGPDisk source code as well. Bottom line, if you need to encrypt, you might as well pay for a commercial version that is supported.

So, that is all of the tools we could think of, a very diverse list.  Remember, put any other suggestions you have in the comments below.

## Slide Rules, Logarithms, and Compute Servers

If any of you have been to PADT’s headquarters in Tempe, Arizona, you probably noticed the giant slide rule in the middle of our building.  You can see a portion of it in the picture below, at the top of our Training, Mentoring, and Support group picture.

This thing is huge, over 6 feet (2 m) from side to side, in its un-extended position hanging on the wall.

In theory a gigantic slide rule could provide more accuracy, but our trophy, a Kueffel & Esser model 68 1929 copyrighted 1947 and 1961, was intended for teaching purposes in classrooms.  Most engineers had essentially pocket size or belt holder sized slide rules, also known as slip sticks.

For the real thing, here is a picture of a slide rule used by Eric Miller’s father Col. BT Miller while at West Point from 1955 to 1958 as well as during his Master’s program in 1964.

Why do we care about the slide rule today?  Have you ever seen World War II aircraft, submarines, or aircraft carriers?  These were designed using slide rules and/or logarithms.  The early space program?  Slide rules were used then too.  Some phenomenal engineering was accomplished by our predecessors using these devices.  Back then the numerical operations were just a tool to utilize their engineering knowledge.  Now I think we have a tendency to focus on the numerical due to its ease of use and impressive presentation, while perhaps forgetting or at least de-emphasizing the underlying engineering.  That’s not to say that we don’t have great engineers out there; rather it’s a call to energize you all to remember, consider, and utilize your engineering knowledge as you use your simulation tools.

By contrast, here is a picture of PADT’s brand new server room, with cluster machines being put together in the big cabinets.  Hundreds of cores.

What about the giant slide rule?

My father found a thick book at an estate sale a few months ago.  There are a lot of retirees living in Arizona, so estate sales are quite common and popular.  They occur at a life stage when due to death or the need for assisted living, folks are no longer able to live in their home so the contents are sold, clearing out the home and generating some cash for the family.  This particular estate sale was for a retired engineer.  The book caught my father’s eye, first because it was quite thick and second because the title was, Mechanical Engineers’ Handbook.  Figuring it was a bargain for the amazing price of \$1.00, he bought it for me.  This book is better known as Marks’ Handbook.  It’s apparently still in publication, at least as late as the 11th Edition in 2006, but the particular edition my father bought for me is the Fifth Edition from 1951.

Although the slide rule is mostly a curiosity to us today, in 1951 it was state of the art for numerical computation.  While Marks’ has a couple of paragraphs on “Computing Machines”, described as “electrically driven mechanical desk calculators such as the Marchant, Monroe, or Friden”, the slide rule was what I will call the calculator of choice by mechanical engineers at the beginning of the 2nd half of the 20th century.

As an aside, these mechanical calculators performed multiplication and division, using what I will describe as incredibly complex mechanisms.  Here is a link to a Wikipedia article on the Marchant Calculator:  http://en.wikipedia.org/wiki/Marchant_Calculator

Marks’ Handbook devotes about 3 pages to the operation of the slide rule, starting with simple multiplication and division and then discussing various methods of utilization and various types of slide rules.  It starts off by stating, “The slide rule is an indispensable aid in all problems in multiplication, division, proportion, squares, square roots, etc., in which a limited degree of accuracy is sufficient.”

The slide rule operates using logarithms.  If you’re not familiar with using logarithms then you are probably younger than me, since I recall learning them in math class in probably junior high in the late 1970’s.  The slide rule uses common logarithms, meaning the log of a number is the exponent needed to raise a base of 10 to get that number.  For example, the common log of 100 is 2.  The common log table in the 1951 edition of Marks shows us that the common log of 4.44 is 0.6474.  For the sake of completeness, the ‘other’ logarithm is the natural log, meaning the base is the irrational number e, approximated as 2.718.

Getting back to common (base of 10) logs, the math magic is that logarithms allow for shortcuts in fairly complex computations.  For example, log (ab) = log a + log b.  That means if we want to multiple two fairly complicated numbers, we can simply look up the common log of each and add them together.  Similarly, log (a/b) = log a – log b.

Here is an example, which I will keep simple.  Let’s say we want to multiple 0.0512 by 0.624.  On a calculator this is simple, but what if you are stranded on a remote island and all you have is a log table?  Knowing the equations above, you can look up the log of 0.0512 which is 0.7093-2 and the log of 0.624 which is 0.7952-1.  We now add:

Writing that sum as a positive decimal minus an integer is important to being able to look up the antilogarithm or number whose log is 0.5045 – 2.

Looking up the number whose log is 0.5045 we get 3.195, using a little bit of linear interpolation.  The “-2” tells us to shift the decimal point to the left twice, meaning our answer is 0.003195.  Thus, using a little addition, some table lookup, a bit of in the head interpolation, and some knowledge on how to shift decimal points, we fairly easily arrive at the product of two three digit fractional numbers.  Now you are free to look for more coconuts on the island.  Or maybe get back to a hatch in the ground where you need to type in the numbers 4, 8, 14, 16, 23, and 42 every 108 minutes.  Oops, I’m really becoming Lost here…

Getting back to the slide rule, one way to think of it is a graphical representation of the log tables.  In its most basic form, the slide rule consists of two logarithmic scales.  By lining up the scales, the log values can be added or subtracted.  For example, if we want to multiply something simple, like 4 x 6, we simply look from left to right on the scale on the ‘fixed’ portion of the slide rule to get to 4, then slide the moving portion of the slide so that its 1 lines up with the 4 found above on the fixed portion.  We then move left to right on the movable scale to find the 6.  Where the 6 on the movable slide lines up with on the fixed portion is our solution, 24.  What we’ve really done is add the log of 4 to the log of 6 and then find the antilog of that result, which is 24.  Now that we’ve found 24, we’re not Lost

We don’t intend to give detailed instructions on all phases of performing calculations using slide rules here, but hopefully you get the basics of how it is done.  There are plenty of online resources as well as slide rule apps that provide all sorts of details.  Besides multiplication and division, slide rules can be used for squares and square roots.  There are (were) specialty slide rules for other purposes.  Note that with additional knowledge and skill in visually interpolating on a log scale, up to 3 or even 4 significant digits can be determined depending on the size of the slide rule.

The author, attempting to prove that 4 x 6 is indeed 24

After having studied the Marks’ section on slide rules, experimenting with a slide rule app on an iPad as well as the PADT behemoth on the wall, I conclude that it was a very elegant method for calculating numbers much more quickly than could be done by traditional pencil and paper.  It’s must faster to add and subtract vs. complicated multiplication and long division.  My high school physics teacher actually spent a day or two teaching us how to use slide rules back in the early 1980’s.  By then they had been made functionally obsolete by scientific calculators, so looking back it was perhaps more about nostalgia than the math needed.  It does help me to appreciate the accomplishments made in science and engineering before the advent of numerical computing.

The preparation of this article has made me wonder what the guys and gals who used these tools proficiently back in the 1930’s, 40’s, and 50’s would think if they had access to the kind of compute power we have available today.  It also makes me wonder what people will think of our current tools 50 or 60 years from now.  When I first started in simulation over 25 years ago, it would have seemed quite a stretch to be able to solve simultaneously on hundreds if not thousands of compute cores as can be done today.  Back then we were happy to get time on the one number cruncher we had that was dedicated to ANSYS simulation.

Incidentally, this article was inspired by my colleague David Mastel’s recent blog entry on numerical simulation and how PADT is helping our customers take compute servers and work stations to the next level:

If you are ever in our PADT headquarters building in Tempe, don’t forget to look for the giant slide rule.  Now you will know its original purpose.

## IGES Can’t Stand IGES Anymore!

Users:

I got some errors when I imported my geometry.
I have some holes and stray surfaces in my geometry.
The edges are twisting around on my geometry import.
ANSYS blows up when I’m trying to mesh my imported geometry.

Me:

What geometry format are you using?

Users:

IGES.

IGEEEEEEESSSSSS!!!

The vast majority of the time, geometry import errors are attributable to the choice of geometry format. And that choice is IGES. To understand the problems with IGES, it helps to know a little bit of IGES history.

IGES, which stands for Initial Graphics Exchange Specification, was released in 1980 as a neutral format for sharing data between CAD systems. The most recent version, 5.3 came out in 1996.

IGES: The “Izzy” of geometry formats

Besides being old, there are a few other problems with this format:

• IGES only contains surface information. When the IGES file is read in, ANSYS has to take the additional step of creating a volume from the region enclosed by the surfaces. The IGES file contains no additional information about how the surfaces should be stitched together, so ANSYS has to figure it out, leading to possible errors, particularly with assemblies.
• Each CAD application has its own tolerances when exporting to IGES, and loose tolerances are more likely to lead to errors in the ANSYS import.
• Somewhat related to the previous bullet point, IGES is a middleman between the CAD system and ANSYS, creating two paths for error propagation: Exporting from CAD to the IGES file and importing the IGES file into ANSYS.

Generally speaking, IGES is typically the worst geometry format to import into ANSYS.

Now that I’ve trashed IGES, here is what I recommend:

## Native Geometry

ANSYS offers several native geometry readers, such as Connections for Pro/E, NX, Solidworks, SolidEdge, etc. that bring in geometry directly from the CAD modeler. There are two advantages here:

1. Geometry comes over directly from the CAD tool, therefore no tolerance errors propagating through a neutral geometry format “middleman.”
2. CAD readers allow for bi-direction associativity between the CAD tool and Workbench, so a Workbench model can be refreshed to reflect updated geometry which still retaining mesh settings, loads, etc. Also, the CAD model can be refreshed based on updated geometry in Workbench.

The only catch when it comes to native geometry readers is that they require a separate license. However, about 90% of the tech support calls I’ve received about IGES import errors are from people who have licenses for native geometry readers and just aren’t using them.

Even if you have a native geometry reader license, you’ll need to be sure to check the box to install the reader during ANSYS installation. You may also need to use the CAD Configuration Manager (found in the Utilities folder in the ANSYS start menu) to configure the CAD reader if you didn’t do so during installation.

The one unfortunate exception to this is CATIA. The CATIA kernel is a bit more guarded than the other CAD kernels, and this is frequently noted in CATIA geometry import errors. Also, you can only import CATIA geometry, not associate to it as with other CAD tools.

## Neutral Files That Aren’t IGES

Your ANSYS installation comes with the capabilities to import both IGES and STEP files without having to purchase an additional geometry connection license. Of the two, STEP is typically the better option. There are two reasons for this:

1. STEP (which stands for “Standard for the Exchange of Product model data,” because these people do not bow down to society’s piddly  rules of acronym construction) contains true 3D volume definitions, instead of having to construct volumes between enclosed surface regions post-import, so the solid model definition ends up being more robust.
2. STEP was first developed in 1984 and continues to be developed, even as recently as 2011, so export/import errors are regularly addressed, unlike with IGES.

You may also have licenses for Parasolid and/or ACIS readers, which can lead to some confusion as to which format to use. This is easily addressed by considering the underlying geometry kernel for the originating CAD tool*.

I said geometry kernel, not…oh never mind… mmmm… fried chicken….

For example, SolidEdge, NX, and Solidworks all use the Parasolid kernel. Therefore the most robust neutral format for geometry exported from these tools will generally be Parasolid (.x_t or .x_b extension), of course. Likewise, AutoCAD uses the ACIS kernel, indicating that ACIS (.sat file) will usually be the best neutral geometry format in this case. For CAD tools that use neither of these kernels, STEP will typically be the best neutral format.

As you can see, even though the IGES people know how to make acronyms, IGES is typically the last geometry format you want to try when importing or associating geometry to ANSYS. This doesn’t mean that IGES is always the worst option for reading in CAD files (especially compared to the CATIA connection), just that it usually is.

*Hat tip to Robin Steed of ANSYS, Inc. for this tip

## why does no1 respon to my request for help (Some Pointers to Students Looking for Help on Forums, Social Media, and Blogs)

[Note: I know I misspelled respond… that is the point] As many of you know, PADT hosts a very successful mailing list and forum called XANSYS.org. It is one of the most successful online community help places I have ever seen.  There are a lot of reasons for that success, but the biggest is the moderators and how strongly they enforce rules for those posting.  Especially on using complete sentences, punctuation, showing that you have tried, and fully identifying yourself.

I bring this up because I’ve seen several posts on Facebook and LinkedIn groups for ANSYS users that just don’t get many responses, or don’t get the quality of response that posts on XANSYS get. I thought it might not be a bad idea to make some comments on the subject and share this post on some of those other forums.  Although I’ll focus on the ANSYS community, what is said applies to any community that supports engineering and technology tools.

## Show Some Effort

The thing that posters need to remember is that they are often asking industry experts to take time out of their busy day to help them.  Those experts want to see some effort put in to the question.  It is very important that the requester form the question in proper English, or whatever language the forum uses.  Even if the poster is not a native speaker, an effort needs to be made to use full and complete sentences, even if grammar is a bit off. (I won’t comment about speling, because that is a my weakest area… so I’ll forgive others on that one)

The easiest way to show a lack of respect to the people you want to answer your question is to not use capitalization or punctuation. As someone commented one time on XANSYS

“If you can’t find the time to use a shift key, I don’t have the time to answer your question.”

The most famous “bad post” on XANSYS was something along the lines of:

“i have been told to model a turbine blade in ansys, can someone show me how to do this”

Needless to say, no one helped them.  Before you post a question you need to try and figure things out yourself. Read the manual, search the internet, talk to co-workers. Most importantly, just try it.  Trial and error is a great learning experience. If you can’t get that to work or you still can’t find the information you need, then post your question. But, make sure you let people know what you have already done and tried.

The people who can help you on forums want to help, they don’t want to do your homework or your work for you.

The quote above is not just notorious  because it is asking someone to do their work for them, it is also well known because the question is insanely too general.  Questions that are very specific are the ones that are answered the quickest and with the most useful information.  Even if you have lots of questions, break them up – solve one, then try and solve the next.

## Identify Yourself

Saying who you are and where you go to work or school is huge. It is a professional courtesy that says “I have nothing to hide.”  When you hide your identity, people assume you are trying to get someone else to do your work and that you don’t want your professor or boss to know. Or, more seriously, you could be posting from an embargoed country or using illegal copies of the software.

## Give Back

This is obvious.  Many people who answer a lot of questions also ask a lot of questions. Even if you are new to the tool you are asking about, share what you learned on the thread when you get it all working. And as you get better, go back and answer some other people’s questions. Remember, it is a community.