The SolidWorks Blog

You Can’t Prototype This: The Power of Mechatronic Design

Yesterday I took the family to the airport for their semiannual flight back to the UK to visit friends and family.  And as I watched the luggage go down the conveyor belt I started to wonder what went on behind those black plastic doors.  Now we’ve all heard of stories where you fly to Madrid but your luggage ends up in Beijing, but have you ever thought of what happens in such an automated system?  From a systems point of view, it’s just one giant mechatronic sorting machine, but from a design point of view it’s a machine that you cannot prototype.  It’s a one-off--it’s large and expensive, and any issues you have with it could well only turn up at the time of installation.

If you have a one-off design the importance and impact of design analysis and verification becomes even greater.  The cost of redesign is huge at the time of installation, but the delay in putting your product into service can also have a dramatic impact on cost.  So thinking back to my baggage sorting machine at the airport, how would I design and test this inside SolidWorks?  Well as I said the sorting machine is a mechatronic design where the mechanical, control and electrical aspects of design are closely coupled.  If one aspect of the mechatronic design doesn’t work then the machine fails, you need to test each aspect of the design before you build. 

Let’s consider the small conveyor system below.  A product, in this case a pallet with two engine cylinder blocks, moves down one conveyor and then is lifted onto the second shorter conveyor (the image showing the end of the simulation).  We can build this simple behavior with Event Based Motion (the lower part of the image).  In event based motion analysis, sensors trigger action in the same way that a light beam or micro switch sensor would in the real world, allowing the designer to try different sensor locations. Once the sensor locations are set routing can then be used to layout the cable runs thoughout the conveyor.

 

But what about the controls design?  Well, as a result of the event based approach, one of the outputs is a Gant chart of the event interactions (bottom right of the image).  This is the first part of the controls design, but you can go so much further by using either Motion Analyzer from Rockwell Automation or LabView from National Instruments.  These partner products allow you to control your machine using virtual controls software so you can create a true virtual prototype of your machine.

Just as important as the motion verification is the stress analysis--you want to make sure that your machine can withstand the operational loads.  So with the event based motion analysis calculated, you can transfer the motion loads to structural simulation and evaluate stresses and displacements to ensure that there is an adequate factor of safety. If the factor of safety is too high, then parts can be redesigned, the motion analysis re-run and the stresses re-calculated.  SolidWorks Simulation can then go one step further and calculate the expected service life of the components, helping the design team set the correct maintenance schedule.

With SolidWorks and its partners a true mechatronic design approach is possible.  The three aspects of modern machine design, mechanical, electrical and controls, are brought together inside of SolidWorks allowing a holistic approach to machine design.  When you cannot prototype, developing a true lifelike virtual design is central to minimizing the risk of design.  Simulation gives the designer information to make better design decisions, and ultimately better products.

Ultimate Igloos and Cool Engineering

Last year, a former colleague at SolidWorks built himself an igloo, and my children deemed it ‘totally awesome’ and demanded one. I never managed to finish that particular project, but the thought of building an igloo has never really gone away, and with the cold weather we are (finally) having in New England right now, it’s got me thinking about it again.  More specifically as I have two small children, it’s got me thinking of igloo structural safety.  The last thing I want is an igloo I build collapsing on the neighborhood kids.  So can SolidWorks help me design a safe igloo??

The classic igloo is a tessellated dome created from packed snow blocks, and it stays up because its internal forces are in balance with the external loads.  If we keep things simple and ignore any wind loading, the only load is the snow blocks self-weight and the frictional force between the block resisting the blocks wanting to push apart and collapse the dome.

The geometry, with its 4 meter diameter and 20cm wall thickness, is relatively simple to analyze. But because friction plays such a big part in keeping the structure together, this will have to be a non-linear analysis.  Capturing the material behavior of snow blocks is a bigger challenge, and a trawl of the Internet suggests that using a either Drucker Prager material model, or if the strain rates are low, a simple brittle failure model.  As the igloo loading is static, we can use the simpler material model of a with the yield point at the stress at which dry packed snow will fail. 

As I first want to get a safe dome design, I am not considering the entrance to the igloo initially.  This means I can use the SolidWorks Simulation 2D simplification tool and run this problem as an axisymmetric analysis.  The advantage of 2D simplification is that the problem solves very quickly with no loss of accuracy.

 

The initial results look promising, but there is a small region of possible failure between the first two blocks of the wall, so we need a design change.  We need thicker walls, but if we uniformly increased the wall thickness, there would be greater weight bearing down, giving rise to greater load.  So let’s consider a new design with a tapered wall thickness. A nice feature of 2D simplification is that the results can be viewed in 3D which makes it easy to explain the results

 

The new design has a maximum stress well below the snow block failure stress.  Our basic dome structure is ‘safe,’ so let’s consider the entrance.  Adding the entrance invalidates the assumptions behind the 2d simplification, so a 3D analysis has to be carried out using symmetry to reduce the computational load.  The run time increases, reminding me how useful 2D simplification is for a lot of problems, but eventually we get our solution.  Now there are two ‘hot spots’ where the stress looks to be too high, but I am not overly concerned about then because they occur at sharp intersections and they can easily be smoothed out by a judicious addition of some extra snow.

I now have a safe igloo design--all I need is the snow to build it.

Student Teams Tout Their Punkin' Chunkin' Trebuchets

What’s more competitive than a Halloween costume contest? A punkin' chunkin' contest! As we announced today, Team ETHOS, a SolidWorks hobbyist team, is a contender in The World Championship Punkin Chunkin Association (WCPCA). The team used SolidWorks 3D design software to create its catapult for World Championship Punkin' Chunkin' Contest in Delaware this week.

You can check out the release for more details—but while we’re on the topic of punkin' chunkin', we want to give a shout out to a couple of our student users.

The Mt. Olive High School Robotics Team of Flanders, NJ, won the Grand Champion’s Award for the longest shot in the annual New Jersey Last Fling Pumpkin Sling in 2011, for the second year running. This year, the team won with a distance of 959 feet—an impressive showing—with a catapult designed in SolidWorks. Next up is the World Championship Punkin' Chunkin' Contest, where the Mt. Olive team will face off against other student teams from around the country.

This Wall Street Journal article chronicles the team’s journey and even gives SolidWorks some love in the slide show. Thanks to David Bodmer of Mt. Olive High School for keeping us up to date on the team’s accomplishments, and how SolidWorks helped make them happen. Best of luck to you in November!

You may remember Assabet Valley Technical High School of Marlboro, Mass. from Let’s Go Design Project 2. The students of the precision machining and automated manufacturing department, led by Bryant LaFlamme, are back with a catapult of their own—check out the attached video testing the height and reach of 400 lbs of weight (click through to the article for a video). Pretty impressive work, profiled last weekend in the Milford Daily News, and also we’re rooting for the team at Assabet Valley at the World Championship Punkin' Chunkin' Contest this week!

We’d love to hear about your homemade catapults, trebuchets, slingshots and whatever else you’ve created to fling things—tell us in the comments!

 

P.S - If you want to see how SolidWorks and SolidWorks Simulation could help you design your own punkin' chunkin' machine, check out the new video on our website.

New in SolidWorks Flow Simulation 2012: Tracer Study

With a new tracer feature found in SolidWorks Flow Simulation 2012, you can quickly simulate concentration source, surface condensation, or evaporation of an admixture fluid (for example, water vapor or toxic gas) in the carrier fluid (for example, air). The presence of the admixture has negligible influence on the carrier fluid flow.

Tracer is an admixture presented at low mass fraction in a carrier fluid with no influence (passive) on this carrier fluid. If concentration of a gas admixture is low you can consider it as a tracer (examples of tracers in air: water vapor, H2, CO, NO, NO2, Cl2, HCl, NH3, H2S, SO2). The tracer feature is available in the HVAC module only.

This is only one of the over 200 enhancements added to our 20th release of SolidWorks. Want to learn more? Just visit the SolidWorks 2012 website to learn about the rest of the updates for our 20th release.

New for 2012: Import Flow Simulation Data to Shells

New for 2012 is the ability to import results from Flow Simulation analyses performed with thin solid or sheet metal parts to shells in SolidWorks Simulation. Imported data include temperature, pressure, shear stresses, and convection coefficient. You can view a graphic plot of the imported data in SolidWorks Simulation.

1. In the Simulation study tree, right-click External Loads, and select Flow Effects.
2. Select Include fluid pressure effects from SolidWorks Flow Simulation, and browse to select the Flow Simulation results file (.fld).
   If your model consists of thin solid parts, before you import the Flow Simulation results, define shells from selected solid faces with thickness equal to the thickness of the solids.
3. To view the imported Flow Simulation data, mesh the model, right-click the flow data definition under External Loads, and select Show Plot.

You can also view Flow Simulation data imported from solids in Simulation study trees. New plots for fluid shear stresses are now included.

This is only one of the over 200 enhancements added to our 20th release of SolidWorks. Want to learn more? Just visit the SolidWorks 2012 website to learn about the rest of the updates for our 20th release.

The Leaning Tower of...Parliament?

As an Englishman, there are certain things that one expects to remain constant:

1. There will always be a royal family;
2. The summer sun will shine as England plays cricket at Lords;
3. Big Ben will chime every hour, every day.

So it is somewhat disconcerting to hear that the Palace of Westminster’s (also known as the House of Parliament) bell tower, housing Big Ben (Big Ben is the bell, not the tower) is mimicking the Tower of Pisa and is slowly leaning over. How can this be? We all know new buildings "settle," but the Palace of Westminster was finished around 1870, so what is happening?

Simply put, time is happening. We all imagine that the materials we use every day will remain in the shape we make them into, unless they corrode or otherwise degrade due to an outside agent. But time will affect many materials under load through the phenomenon known as creep. Creep is the tendency of solid materials to deform (or flow) under load. Generally speaking, engineering materials creep very slowly, unless the material is operating above 30% of its melting temperature--but if the time period is very long, creep is noticeable even at ambient temperatures. Stained glass windows in medieval churches are a good example of low-temperature creep in a material we would otherwise consider stable and unchanging.

So is this happening to the Palace of Westminster? Yes, but not only to the Palace, but also to its foundations and the ground it sits upon. So we have the classic recipe for a creep problem: a long time and a large load. Using a "building block approach" we can study the effects of creep inside SolidWorks Simulation. Below is a simple representation of the Palace of Westminster with the bell tower on the right and the foundations hidden (I hope Charles Barry isn’t too offended).

 

To carry out a simulation of how the palace would creep over time, we need to define a nonlinear analysis. The only load is gravity, but the trick is in defining the creep material parameters which are used to calculate the creep strain (ε^C ) and hence the structures deformation over time.

        C₁>1 and 0 <C₂ ≤ 1

Where                  T = temperature

                                C_T = creep temperature dependency

                                C₀, C₁ and C₂ are the three creep constants

Now for the Palace of Westminster the temperature dependency is not a big issue, but varying moisture around and in the foundation can have a big impact on the support strength, and hence the creep rate. But if we model the varying moisture as a pseudo temperature, this effect can also be modeled. Getting the creep data can be hard but I have estimated some figures, and the results look reasonable.

So if your product life is measured in decades, or it's operating at high temperatures, you might want to consider a creep analysis to make sure your design is fit for purpose over its complete life span.

Luckily the creep rate is very low, so we have plenty of time (pun intended) to save Big Ben.

New in SolidWorks Simulation 2012: Beams in Linear Dynamics

SolidWorks Simulation 2012 brings several enhancements with regard to beams. In particular, Beam elements are now supported in Linear Dynamic studies, which include: Modal Time History, Harmonic, Random Vibration, and Response Spectra analyses. You can use beams to simplify problems with weldments or structural members, improve simulation performance, and reduce the file size of results.

To perform a linear dynamic analysis for models that include beams:

1. Create a Linear Dynamic study, and select one of the study options depending on the loading and response parameters you want to access after running the study.

   You can also copy an existing frequency study to a new dynamic study.

2. Set the frequency and dynamic properties of the study.
3. Define material. You can apply only Linear Elastic Isotropic material type to beams.
4. Define restraints. Fixed Geometry, Immovable (No translation), and Use Reference Geometry are available for beams.
5. Define Loads. You can choose from the following options:

   • Time-dependent force or torque

     Available for modal time history analysis studies. Select beam joints or the entire beam length to apply force or torque values.

     Frequency-dependent force or torque

     Available for harmonic and random vibration studies. Select beam joints or the entire beam length to apply force or torque values.

   • Uniform and selected base excitations

     For Random Vibration and Response Spectra Analysis, you can apply base excitation only in the global X, Y, Z directions.

   • Initial conditions

     Available for modal time history analysis studies. Displacements, velocities, or accelerations at time = 0. You can apply initial conditions to beam joints or the entire beam length.

6. Define damping.
7. Define contact. You can select Bonded or Allow Penetration.
8. Mesh the model and run the study.
9. View the results:
   • You can generate time history graphs at selected nodes. Right-click Results, and select Define Response Graph.
   • You can plot stresses (axial, bending, highest axial and bending, torsional, and shear), displacements, velocities and accelerations for a specified solution step, or extreme values across all solution steps. Right-click Results, and select from the plot options.

Want to see more? Just visit the SolidWorks 2012 website to learn about the rest of the updates for our 20th release.

SolidWorks Simulation On Umbrellas and Mary Poppins

Last weekend saw me and the family at our favorite lake. While the kids swam and fished I sat under a beach umbrella trying to keep my pallid English skin out of the strong New England sun.  I don’t tan, ladies and gentlemen--I just go a disconcerting and painful shade of red.  Luckily for me, there was a cool breeze blowing across the beach, but every so often it blew quite strongly, threatening to pull the umbrella out of the sand or flip the shade inside out. 

At one point while holding on to my umbrella (and watching every family doing the same), an image of Mary Poppins floating over the rooftops of London came into my head.  I wondered how strong would the wind--and umbrella--would have to be to pick me up and deposit me in the lake. Much to the amusement of my kids I’m sure.

I didn’t think much more about it until I got home, and then my curiosity got the better of me.  A quick email to my colleagues at work soon resulted in a SolidWorks model of the "classic" English black umbrella, and I quickly had my virtual test ready to go with SolidWorks Flow Simulation.  So if I was foolish enough to hold the umbrella above my head at a 45-degree angle, allowing the wind into the umbrella, what wind speed would pick up my 200lbs? 

Setting up the problem was very straightforward once I had the umbrella-holding mannequin on my digital beach--all I had to do was set the wind speed and measure the force on the umbrella.  But what is the best way to find the wind speed that would pick me up??  I could set up multiple studies at different wind speeds and run them one after another, but SolidWorks Flow Simulation has a really nice tool called a Parameter Study.  In the parameter study you can change the flow parameters (such as wind speed) to achieve a desired goal, in this case the umbrella lift force.  Once I had set it up it was time to hit run and get the kids ready for bed.

The results where soon in and I was both pleased and disappointed to find out that it would require a wind speed of 61.2 mph to lift me off the ground. At that speed, I doubt I would be outside.  Now, the umbrella creates drag as well as lift, and Flow Simulation calculates that the umbrella creates a drag force that is roughly equal to two thirds of the lift.  So at the same time the wind is lifting me off my feet its also trying to push me on my rear.

I guess the next step is to design an umbrella that can withstand such extreme winds.  Time to fire up SolidWorks and Simulation again and see what I can come up with...

Meet the Let’s Go Design Team: Stephen Endersby

Regular readers of this blog will recognize Stephen Endersby as a regular contributor, writing about SolidWorks Simulation and interesting analysis problems. But Stephen is also a core member of the Let's Go Design team, helping Jeremy on every project to date. In the video below, Stephen talks about his role as a product manager at SolidWorks, his involvement in the project, as well as his choice of wardrobe.

Stay tuned for the next episode of Let's Go Design, coming later this month.

New in SolidWorks 2012: Automated Motion Optimization & Other Simulation Enhancements

The SolidWorks 2012 product line includes lots of new enhancements in the area of simulation and design validation. Some of these include the ability to:

• Optimize complex flows of fluids and gases with SolidWorks Flow Simulation
• Easily apply bearing loads, forces, pressures, and torques to find stress points
• Evaluate forces and stresses, including friction, between parts to optimize assemblies
• Investigate motion characteristics, such as actuator force, joint loads, and part displacements to help source the best components for your design

Check out the video below to see these enhancements in action, then visit the SolidWorks 2012 website to learn about the rest of the updates for our 20th release.