Let’s discuss the difference between the linear solver and the dynamic solver with a case study. Take the example of an engineer slamming his head on his desk after getting poor simulation results from his linear solver.

In scenario #1, the engineer lightly places his head on his desk then proceeds to slowly press down with his body weight. The force value, F, represents the maximum amount of force he can transmit through his neck.

In scenario #2, the engineers head starts a distance of 2 feet from his desk. The engineer proceeds to accelerate his head towards his desk with the aforementioned force value, F. After he comes into contact with the desk, his neck continues to transmit the force until his head comes to a complete rest against the surface.

Now, in both scenarios, the engineer’s neck transmits the same amount of force, F. However, the second scenario will produce higher levels of cranial stress at specific instances in time. The higher stress is related to momentum. The engineer recognizes this and proceeds with scenario #2 until the desired level of masochistic indulgence is achieved.

If we were to simulate these events, design scenario #1 could be adequately achieved with either the static solver or the dynamic solver and the results would be the same. However, if we were to run scenario #2 with a static solver, we would get the same result as we would with scenario #1. Obviously, the static solver has limitations.

The linear solver only sees the last moment in time; when things are at rest. Thus, we have two data points, the beginning and the end.

On the other hand, the dynamic solver is aware of the time in-between the beginning and the end. As a result, we are left with a much more complete picture.

For a moment, let’s sidestep the slamming head on desk approach, as this practice is no longer necessary. Let’s use the example of a cantilever beam with a weight of one hundred pounds suspended from the end.

For the linear study, let’s consider the case of loading the end very slowly. The results of this simulation are shown below.
The maximum displacement is 58 mm.

For the dynamic study, let’s consider that the weight will take .05 seconds to reach its maximum value of 100 pounds and will then level out. The maximum displacement results of this simulation are shown below.
The maximum displacement is 93 mm. This is an enormous jump from 58mm. Obviously, we’d want to study the dynamic simulation results over the static.

To be a good simulation engineer, you need to ask “what if” questions. “What if we make this pipe longer?” “What if we change the thickness?” “What if we change the material?” However, if you have a complicated assembly or part, it’s easy to say, “I don’t want to model it again. That took forever.” Well, the solution has arrived: You need to become a better modeler.

Recently, I was introduced to parametric modeling by my partner in crime, Nick B (or #2, as I call him). It took a while before I realized its potential in regards to optimization and these so called “What if” scenarios.

Once a multi-body part or assembly is parametrically driven, changing values become much easier to do.

To illustrate my point, I’ll breeze through the modeling process for the design of a solar thermal unit. With a setup like this, a good engineer will ask questions like, “What if we add pipe passes?” and “What if we make the passes closer together?” If the model isn’t setup correctly, these changes are difficult to make. So, we’ll design with the intention of changing it later.

Let’s get started with the first pass of the copper tube. A sweep is done and the model is dimensioned and linked accordingly.

The next thing to do is create a linear pattern, linking the spacing value with the pass width and iteration values.

We then create “plane 1,” normal to the right plane and define its spacing with an equation, relating the number of pass iterations with the pass distance.

Plane Distance = (# of passes)*(pass distance)

At this point, the reason for the plane might seem unclear. However, the protective box and heat sink will reference this plane.

We then create merged pipe extensions using linked values while referencing the default right plane and plane 1.

When sunlight travels through the glass opening of our solar panel, only a small percentage of sunlight will actually hit the pipe. So, we need to create a heat sink which will capture radiation from the sunlight and transfer heat via conduction to the copper tubing. We’ll do this by creating a single sheet metal piece with linked values, then pattern it with linked values and equations.

Heat sink iterations = (# of passes)*2 +1

The next step is to create the protective box and glass cover. The geometry is defined using existing relations, similar to what we’ve already done.

Now, if I change values, like the number of tube pass iterations or tube space distance, the entire model updates automatically. This will come in handy when running optimization simulations and playing with other what if scenarios.

I very well could have had this conversation while doing tech support…
Dude: Well, I can see that this is some powerful software, but it’s taking a long time to solve and things shouldn’t be this complicated.

Me: Yeah… that’s a pretty… pretty big mesh. I can’t even see the part.

Me: What are you trying to study here?
Dude: The assembly. (Duhhh!)
Me: Yeah, but what about the assembly? Is there a particular part you’re worried about?
Dude: Well, now that you’ve mentioned it, I am pretty concerned about this part.

Me: Okay, we can eliminate these parts and apply equivalent forces on the faces.

Me: Alright, let’s get started! We can use a rough mesh to find the contact forces.

Me: Now, we can eliminate the top pieces from the assembly and create split lines where we would like to apply the equivalent forces.

Me: This is a perfect opportunity to use 2D simplification. Let’s create a new study.

Me: Now, we can afford a pretty heavy mesh control on the component of interest.

Me: If we go into properties and select the option for “Improve accuracy for no penetration contacting surfaces” we’ll get the same results as before with a fraction of the run time.
Dude: Thanks Nick! You’re the best!
Me: I know… I know.

What is nonlinear simulation? Most people don’t know. So, I’ll lay it out as simply as I can.

First, let’s talk about the linear solver. When the linear solver runs, it solves for the end result. Only the end result. The solver doesn’t recognize any of the in-between steps. Most people notice this when they create an animation where you would expect some intermediate interaction between parts. “Why didn’t the hook go over the latch?” Is a question I hear all too often when customers create animations from linear simulations. When you have a hook going over a latch, you would expect some interaction between the two components. The reason the two components don’t move like you would expect is because a linear solver only focuses on the end result. So, we only have two points to work with – The start point and the end point. The animation interpolates between the two. The middle is missing.

The nonlinear solver goes about the problem in a different way. Instead of having two points, A and B, the nonlinear solver will solve the in-between steps. The solver marches through time solving these intermediate steps. However, this time isn’t real time. It’s merely a parameter used to describe the relation between the intermediate steps. So, it’s often referred to as pseudo time. This approach comes in handy in a few different situations.

Boundary nonlinearity – Just like the latch example. You have two parts that interact with one another. When the situation arises where you would like to study the steps in-between start and finish, you might want to treat the simulation nonlinearly.

Geometric nonlinearity – When a part deforms so much that its spacial orientation significantly changes, it often helps to solve with little steps. This sort of nonlinear simulation can be dealt with using Simulation Standard. To turn this option on, click, “Large displacement” under properties.

Material nonlinearity – When a material doesn’t have a straight stress-strain curve, you can’t go from point A to point B without the in-between steps. This is because the path from point A to point B is crooked. Have you ever stretched rubber so far that it became easier to stretch? Well, how could you ever solve THAT with a linear solver? You have one force and two or more displacements. Think about it. There are a few different types of material non-linearity, so I won’t go into it too deeply. but they apply to rubbers, plastics, metals after yield and so forth.

So, when someone tells you, “This problem is nonlinear,” don’t change the subject. It’s not as complicated as it sounds.

A rubber band stretches over a can.  Simple, right?  But when the rubber band is half the size of the can, simulating that sort of expansion over a large body becomes an enormously complex task.   It was day one of Advanced Non- linear Simulation Training in Chicago.  By the dumb expressions on our faces, Jandra Novak, our Czechoslovakian instructor, knew that we were stumped.  “Try this.” He said.    

We watched as he proceeded to silently work.  We all leaned forward and closed our laptops.  He entered values into the software.  No words, just numerical values.  It’s a language we all speak.  

Without getting into too much detail, simulating the rubber band going over the can was not possible.  The size difference was too great for any simulation software to handle.  What Jandra did, was simple.  He shrank the can and placed it in the center of the rubber band.  Then, he made the can grow.  The rubber band expanded as it came into contact with the can.

To any non-super-nerd it was all just numbers.  But to us, it was physics.  Glorious physics.  (It’s as close to reading the code from The Matrix as I’ll ever get.)  

He clicked “Run” and we waited.  

As we reviewed the result, I leaned back in my chair and had only one simple thought:  I understood everything that just happened. 

I’m smart.

As I walked into O’Hare,  I grabbed my ticket and looked down.  C33.  Gate C33, I thought.  For those of you who have never been, O’Hare is one of the largest airports in the country.  Getting to gate C33 was no small chore.  It took 3 miles of walking to get to.  As I reached the end of the terminal, I read C30, C31, C32.  No C33.  Confused, to say the least, I asked, “Excuse me miss, where is gate C33?”  

“Let me see your ticket,”  she replied.

I passed it across the counter.  I watched her type for what felt like an eternity.  

“C33 is your seat number.  You’re 5 miles away from your gate.”   

Defeated, I plopped down in gate 32.  I leaned back and had only one simple thought:  I’ve got a lot to learn.

-Nick Luyster, Applications Engineer (Simulation)

In the past I have been asked to attend/present at the Twin Cities Simulation User Group meetings. Unfortunately, Simulation is not my area of expertise so I have not been much help for the group. But today I received an email from Anne Yust, the group leader, asking me to watch a video. This is something that I can do!!!

So what does a video about “Preparing your SolidWorks file for 3D printing” have to do with Simulation? Well, I can answer that with one word: sponsorship. Here’s the deal: in order for the Simulation User Group to gain a new sponsor, they’re required to have a certain number of people watch this short video.

Even if you do not currently use SolidWorks Simulation, helping them acquire this sponsor will help ensure the group is around when you start using Simulation.

Below is the link to the video. Please take a little time to help out Anne and the entire group.

Click Here to Watch the Video

Thank you,

Jason Schroeder

Well, it’s that time of year again.  SolidWorks has released Beta 3 of SolidWorks 2011 which means the official release must be right around the corner.

To help everyone get ready for the new release, Symmetry Solutions will be holding What’s New Events.  Please mark your calendar and plan on attending the event that’s closest to you.  Here is when and where the events will take place:

• New Richmond, WI – October 20th
• Owatonna, MN – October 21st
• Twin Cities – October 22nd

I will also be highlighting new features in this blog, so stay tuned and I hope to see you at the SolidWorks 2011 Roll Out.

Go Here to Register for Your Event!
 

The SolidWorks Flow Simulation can give you a message stating that authorization has failed. This is because on the client machine  the License Manager was opened and the License Order tab was selected. This changes a registry setting that needs to be corrected. Below is the work around for this and it has been corrected in 2010 SP3 which should be released in the middle of April.

Here is the workaround – please be sure you are comfortable editing the registry prior to attempting this procedure. Consider making a backup of the registry beforehand, in case you make a mistake.

National Instruments and SolidWorks Collaborate on a Virtual Prototyping Solution

National Instruments has begun shipping the production release of NI SoftMotion for SolidWorks, a pioneer mechatronics tool that helps mechanical and control engineers work together to lower the cost and risk of motion system design. Seamlessly connecting NI LabVIEW graphical system design software and SolidWorks® 3D CAD software, the new virtual prototyping solution helps engineers and scientists design, optimize, validate and visualize the real-world performance of machines and motion systems before incurring the costs of physical prototypes.

NI SoftMotion for SolidWorks requires SolidWorks Motion Simulation, included with SolidWorks Premium, SolidWorks Simulation Professional and SolidWorks Simulation Premium. Additional LabView modules may also be required.

National Instruments has an extremely information website with webcasts, whitepapers, getting started guides, etc. Check it out: http://www.ni.com/digitalprototyping/

As mentioned in a previous blog posting, Rockwell Automation is collaborating with SolidWorks on a very similar solution that will integrate RA Motion Analyser software with SolidWorks Motion Simulation. This software should be available later this fall. More info can be found at http://www.ab.com/motion/software/analyzer.html and http://www.rockwellautomation.com/partners/dassault.html

I was watching TV the other day, saw some radio-controlled helicopters and thought, “I want one!”  So $200 later, I’ve got a fully capable heli in my untrained hands. Not sure why I ever thought I knew the first thing about how to fly a chopper…

Much to my dismay, it was destroyed within 1 minute of installing the battery. Not very encouraging.  Back at the hobby shop, I spent nearly $40 in repair parts.  This time, though, my natural copter ability didn’t let me down. I managed to hover.  It was an amazing show of skill that lasted almost 2 seconds before a wall got in the way, resulting in the “wallet reach”, a crushed ego, and the reinforcement that I have no idea how to fly a helicopter. Things worked out better for my buddies who now have a funny story to tell. 

There’s got to be a better way, a cheaper way, maybe a virtual way?

SIMULATION

Right, can’t believe I didn’t buy the simulator first.  For starters, it’s fun. When I crash I don’t do the “wallet reach” I hit reset.  I can’t imagine what it would have cost to learn to fly with the real heli. I’m sure I’ve crashed at least $100,000 worth of remote-controlled choppers.  Best of all, within one week of simulation practice I was able to hover my real model through an entire battery. 

The simulator cost $100. I had already spent $80 after flying (if you call it that) for a total of 3 seconds.  It makes so much more sense to try things virtually before committing to the real thing, and it’s so much cheaper. 

Anyway, I wanted to share how we’re using simulation everywhere.   Time to get back to it. I’ve got to figure out the Idle-Up mode, inverted flight.