CFX Expression Language–Part 3: Applying Boundary Conditions Using CEL

In two previous entries we introduced CFX Expression Language, CEL:

Part 1: Accessing CFD Simulation Information in CFX (and FLUENT)

Part 2: Augmenting Material Property Assignments in ANSYS CFX

In this third installment we will see how to use CEL to apply boundary conditions as equations rather than constant values. For example, if a non-constant velocity profile can be defined as an equation, we can use CEL to define as well as apply the profile.

Let’s look at an example in which the velocity profile is a function of y coordinate:

u(y) = 6 * Umax * y / H * (1 – y/H) (m/s)

Using the procedure we learned in part 1 of this series, in CFX Pre we have defined expressions for H and Umax. We then defined the equation for the velocity profile as Uprofile:

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Next we go to the Plot tab within the Expressions editor to verify that our velocity profile matches expectations:

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To use our new expression in CFX Pre, we just enter the expression name in the appropriate field when defining the inlet velocity:

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Finally, this velocity plot from CFD Post shows that indeed our desired velocity profile was applied at the inlet.

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Hopefully this demonstrates how easy it can be to use CFX Expressions to define non-constant boundary conditions. In the next part of the series, we will look at using expressions to ramp or step apply loads.

CFX Expression Language – Part 2: Augmenting Material Property Assignments in ANSYS CFX

In a previous entry we introduced CFX Expression Language, CEL.  You can view that post here

Before we get started, there are some key things to remember:

  1. Expressions can be easily created by right-clicking in the Expressions tab after double clicking on Expressions in the CFX Pre object tree.
  2. Expressions and their contents are case sensitive.

In this next part of the series, we’ll show how to use CEL to augment your material property definitions in CFX. If material properties are constants then their input is straightforward. However, if the properties are defined as equations, we can use CEL to input those equations in CFX.

For example, if viscosity is defined as a function of shear strain rate, we need to define viscosity using an equation that captures that relationship, such as

m = K * gn-1

Below are shown two ways in which that equation can be captured using CFX Expression Language, visc1 and visc2. The second equation, visc2, is more flexible in that we have defined the constant terms as expressions themselves.

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It’s always a good idea to verify the input. Most expressions can be easily plotted by clicking on the Plot tab in the Details view. Here is a plot of the viscosity vs. shear strain rates between 0 and 1, as calculated by expression visc2:

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Similarly, the Evaluate tab can be used to evaluate the expression for desired values of the inputs.

So, we have defined an expression for a material property, viscosity in this case. How do we get CFX to use that expression? In the material property input, we click on the expression icon to the right of the particular material property we are defining, then enter the name of the expression, as shown here for expression visc2:

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Summing it up, we can use CFX Expression Language to define material property equations for non-constant material values. In the next installment we will look at how to use CEL to define changing boundary conditions, such as a ramped load.

Monster in the Closet: PADT Goes Live with 512 Core HVPC CUBE Cluster

imageThere is a closet in the back of PADT’s product development lab. It does not store empty boxes, old files, or obsolete hardware.  Within that closet is a monster.  Not the sort of monster that scares little children at night.  No, this is a monster that puts fear into the heart of those who try to paint high performance computing as a difficult and expensive task only to be undertaking by those who are in the priesthood.  It makes salespeople who earn fat commissions by selling consulting services and unnecessary add-ons quake in fear.

This closet holds PADT’s latest upgrade to our compute infrastructure: a 512 core CUBE HVPC Cluster.  No data center, no special consultants, no expensive add-ons. Just 512 cores chugging away at solving FLUENT and CFX problems, and pumping a large amount of heat up into the ceiling.

Here are the specifics:

CUBE C512 Columbia Class Cluster

  • 512 AMD 2.4GHz Cores (in 8 nodes, 4 sockets per node, 16 cores per socket)
  • 2TB RAM (256 GB per node of DDR3 1600 ECC RAM)
  • Raid Controller Card (1 per node)
  • 24TB Data Disk Space (3TB per node of SAS2 15k drives in RAID0)
  • Infiniband (8 Port switch, 40 Gbps)
  • 52 Port GIGE switch connected to 2 GIGE ports per node
  • 42 U Rack with thermal convection ducting (chimney)
  • Keyboard, monitor, mouse in drawer
  • CENTOS (switching to RedHat soon)

We built this system with CFD simulation in mind.  The original goal was to provide a proof of concept to expand our CUBE HVPC offering, showing that you can create a cluster of this size, with very good speed, for a price that small and medium sized companies can afford.  We also needed a way to run large problems for benchmarks in support of our ANSYS sales efforts and to provide faster technical support our FLUENT and CFX customers.  We already have a growing queue of benchmarks waiting to get into the machine.

The image above is the glamour shot.  Here is what it looks like in the closet:

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Keeping with our theme of High Value Performance Computing we stuck it into this closet that was built for telephone equipment and networking equipment back at the turn of the century when Motorola had this suite.  We were able to fit a modern rack in next to an old rack that was in there. We then used the included duct to push the air up into our ceiling space and moved the A/C ducting to duct right into the front of the units.  We did need to keep the flow going into the rack instead of into the area under the networking and telephone switches, so we used an old video game poster:

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Anyone remember Ratchet and Clank? 
Best PS2 games ever.

It works well and adds a little color to the closet.

So far our testing has shown some great numbers. Not the fastest cluster out there, but if you look at the cost, it offers incredible performance.   You could add a drive array over Infiniband, faster chips, and some redundant power. And it will run faster and more reliably, but it will cost much more.  We are cheap so we like this solution.

Oh yea, with the parts from our old CFD cluster and some new bits, we will be building a smaller mini-cluster using INTEL chips, a GPU or two, and a ton of fast disk and RAM as our FEA cluster.  Look for an update on that in a couple of months.

Interested in getting a cluster like this for you computing pleasure?  A system configured like this one will run about $150,000 (video game poster is extra). Visit our CUBE page to learn more or just shoot an email to sales@padtinc.com.  Don’t worry, we don’t sell these with sales people, someone from IT will get back with you.

The Reality of Simulation Driven Product Development

A note to our regular readers: This is not a normal Focus post. No info on how to use an obscure new ANSYS command. This may be something our regular readers (the people who do simulation) might find useful to share with their management. And maybe a CEO/CTO/COO or two might stumble across it and “see the light” that we have all been working in for years.

I’ve been involved in planning or attending a couple of what we call “C” level visits in the past month or so. A “C” level visit is where we talk with the CEO, CFO, CTO, COO, or some sort of high level executive at a company.  These visits are very different than sitting in a room with a bunch of engineers showing off what ANSYS software can do, or talking about what services PADT can offer.

In the “C” level visits we are there for two reasons. The first is to understand what the high level product development needs are for the company from a business perspective.  Once we know that, we like to articulate how the products we sell or the services we offer can help the company meet those goals faster and with less effort and cost. And when simulation fits into their needs, we talk about Simulation Driven Product Development (SDPD).

Many people in the simulation software business talk about SDPD a lot.  They use SDPD as buzz word and they surround it with buzz words: time to market, rapid product development, stage gates, decision tree, etc…  In such a discussion you talk about the vagaries of “enabling your enterprise” and “collaborative global solutions.”  All of this is oriented towards a single message: buy our tools.

The Real World

PADT is fortunate enough to not only be a company that sells simulation tools, we use them as a service to help our customers drive product development. We also use simulation to drive product development that we do here at PADT. (WAH? PADT does product development? Yes we do. And rapid prototyping. Click the links to learn more.)

Top this off with the technical support and mentoring that we offer our simulation customers and we are able to get a pretty good idea about the reality of SDPD. And that reality is that SDPD really works, it can make a huge difference in many areas.  But the reality is also that SDPD needs to be done correctly to make it effective.

Why SDPD is Effective

To understand the real world impact of SDPD you have to step back and look at what developing a product is about. There are a lot of different processes, and people get all “burn the heretic at the stake” over there particular flavor.  But they all share some common characteristics:

  1. Define what you want the product to do (specifications)
  2. Come up with and capture all of the things that define the product (design)
  3. See if you ideas work (test)
  4. Fix stuff that didn’t work (iterate)
  5. Make it (manufacture)

Every step in the process involves people asking questions and answering them.  How big, how strong, how long, how much this or that?  And each question can be answered in many different ways. Things like experience, calculations, comparison to existing solutions, statistical studies, testing, and many more.  The cost and correctness of how those questions are answered has a direct impact on the cost and speed of a development project.  Also, many studies have shown that the sooner in the schedule that you answer those questions, the more efficient your project is.

What is great about simulation is that it allows you to answer questions quickly and accurately.  Working in a virtual environment on the computer you can combine comparisons, testing, calculations, and statistics in one place with speed and very little capital investment. The fact that you can do it so fast also allows you to avoid making assumptions and simplifications that reduce the accuracy of the answer.

The most comprehensive study on the effectiveness of simulation for driving product development can be found in “The Impact of Strategic Simulation on Product Profitability” from the Aberdeen Group.  It shows that best-in-class companies across industries are companies that use simulation to drive their product development.

The study finds that:

There is no point in the design process where companies do not profit from intelligent decision-making. By integrating simulation analysis from the earliest stages of design, the Best-in-Class are able to make better decisions through the process. This enables these leaders to drive higher quality and lower cost products, as well as deliver the innovations and features that differentiate their products.

Making SDPD Effective for Your Organization

So companies make more money using simulation to drive their product development.  It would be nice if it was true that all companies that use simulation automatically see a benefit.  But we are talking about the reality of SDPD and that reality is you have to have the proper simulation tools, and you have to use them effectively.

The Right Tools

As far as tools go, you should know where I stand.  ANSYS, Inc’s products. If you are reading this you are probably an ANSYS, Inc. product user or you got this posting from someone who is.  Why are these tools the leaders across the industry? Because they have breadth and depth so you are not limited by your simulation tools, they are accurate, and they work together so you do not have to jump through hoops to work as a team.  That is really all there is to it.

If you can not use this tool set for some reason, say your senior manager is married to the competition’s local rep (which is maybe one of the few valid reasons) you still need to make sure you stay high end.  Do not cheap out on a CAD based tool or a low end tool that is “good enough for what we need.”  Anything other than a full function tool suit will limit your ability to get accurate solutions, or to model your product completely.  That $20,000 you saved will get eaten up in about a week of fumbling around trying to get useful information.

Yes these tools cost a lot more than the low cost or CAD based alternatives. But there is a reason for that.  It is the army of developers, support engineers, and product managers that work day in and day out to improve the speed, accuracy, and capability of their simulation tools.  The reality of simulation is having 80% is only good 80% of the time. When you need that extra 20% of functionality, you need it. And when you do not have it, your project bleeds cash.

Effective Application

Deciding to drive you product development with simulation: easy.  Deciding on the right tool set: a bit of work, unless you just go with ANSYS products, then it is easy.  Now you have to make it work.

This is such a big topic that we did a seminar on it about two years ago.  I’ve uploaded a PDF of the presentation if you would like more details.

The gist of it is the following four rules:

  1. Establish goals for SDPD in general and establish goals for each project that uses simulation.  Without goals it is easy to do too much simulation or to do the wrong simulation.
  2. You must have the right type of users doing the right tasks: experts and mainstream users. Also, do not turn good engineers into bad users by violating the other rules.
  3. Use the right tools. Not just the simulation software, we covered that.  You need the right hardware, the right support, and the right utility software to support your efforts.
  4. Design the right flexible process for your team and constantly improve on it.

Mainstream

I have been driving product development with simulation for over 25 years, and many people who read this blog have been doing it for longer. Once a secret of the aerospace and automotive industry, SDPD is now mainstream. We have customers that use it to design ear buds, mining equipment, coolers for organ transplants, and toys.  It is used to make almost every electronic device around us more reliable, cooler, and faster.  And we still have people that use it to design Turbine Engines, space craft, and automotive components.

In fact the industries that are long time users are increasing their seat count and the size of the computing systems.  Many that we know of are making multi-million dollar investments every year and growing that investment year over year for a simple  reason, they see results from driving more and more of their design process with simulation.

If you are not using simulation, or some portion of your company is not using simulation, than something is wrong. You or they are literally leaving money on the table and giving a competitive edge to the competition.  If you would like to learn more about how PADT and many of our customers have been successful with simulation, feel free to contact me. Or just get out there and start evangelizing something that has already been proven to work.

PADT has an Immediate Opening for a CFD Engineer

We just posted a new job opening on our website for an Experienced CFD Analysis Engineer.

The bottom line is that we are looking for someone who really likes variety, who really knows their stuff, and who likes doing both services and support work.  This position will join the rest of PADT’s CFD team in conducting CFD consulting, training, mentoring, support, and application engineering. Lots of fun, very challenging, and rewarding.

If you are interested, or if you know someone that is interested, send a resume to jobs@padtinc.com.  Put [PADTJOB] in the title.