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.

Domespace is creating the next generation of eco-friendly homes with SolidWorks

Many years ago, I had ambitions of being an architect. I worked at a firm, and even went to architecture school briefly, until I realized I didn't have the artistry needed for the job. If I had my way, every structure built today would be an angular Bauhaus affair. So I have something of a soft spot for anything related to building design, which is why I found it interesting that a French company called Domespace is now a SolidWorks customer.

Domespace International designs and builds dome-shaped, eco-friendly homes. According to the company, the dome shape is designed to be more in harmony with nature, takes advantage of solar radiation, and is less susceptible to seismic and cyclonic forces than traditional, angular designs. On some models, the exterior of the home actually rotates, following the sun in winter to take advantage of its warming rays, and the shade in summer for cooling.

Domespace uses SolidWorks Professional for concept development, SolidWorks Premium for structural design, and SolidWorks Flow Simulation for studying air flow and environmental conditions. They say they have cut time-to-market and development costs in half. In a case study on our website, Computational and R&D Head Benjamin Thoby discusses how 3D design and simulation technology is helping Domespace ramp up production of its world-class, ecologically sensitive homes. Even if you're not in the AEC space, it's worth checking out.

You can find it here.

 

 

Bend It Like a Football Star – With SolidWorks Simulation

Watching my son play indoor 6-a-side football (or soccer, as some of you might call it), is both an exhilarating and nerve-racking experience. The father in me wants him to enjoy ‘the beautiful game,’ the competitor in me wants him to win, and the coach in me wants him to play well. One of the skills the boys on the team are learning is to get the ball to curl by imparting the correct amount of spin.

Now, I can talk until I’m blue in the face about how the spinning ball creates a region of low pressure on one side, resulting in a sideways force which creates the curl, but it’s the doing and seeing of it that made it real for the boys. I started to wonder if SolidWorks and SolidWorks Simulation could help out, and in a cosmic sense of kismet, a colleague in France sent me a simulation of the ‘Perfect Free Kick.’

Julien’s model is the perfect example of how you can use Design Studies with Motion to solve complex multi-physics problems.  If we consider the ball in isolation, there are three sets of forces acting on it.

1. The impact force which determines the initial velocity and spin of the ball 
2. The aerodynamic forces, slowing the ball down and, partially, determining the path of the ball
3. Gravity, the other component that sets the path of the ball

Using the new motion function builder it is easy to apply the aerodynamic forces to the ball.

The motion analysis can now be run, and the ball dips and swerves over the defensive wall, beating the goalie and landing in the top left hand corner.

But that is only half the story. Using SolidWorks and Design Studies we can alter the both the position of the ball and the parameters of the ‘kick.’

The power of SolidWorks and Simulation is that you can run multiple versions of a design to determine the optimum configuration in the virtual world before you cut metal. But just as important as the optimum is the understanding of the design sensitivity, or how well your design performs ‘off optimum.’ 

The world isn’t perfect, and in the real world your design will have to perform over a wide range of loading conditions and environments.  The Design Study enables you to test for variation in geometric, environmental and loading conditions.  So in the case of the free kick, the robustness of the design can be measured by distance of ball center from the ‘ideal’ target center, and we can find many ‘correct’ solutions but only one robust solution.

By running an analysis on your design you not only gain insight to its current behavior but also its future behavior and how to improve it.  So I can now show my son how and why the ball bends, and that all he has to do is practice, practice, practice..

Applying dead loads to fatigue

I was recently asked how to apply a dead load in a fatigue study (a none varying load that is applied to a structure all of the time, as opposed to a live or dynamic load that generates an alternating stress).

The diagram below shows the definition of alternating stress (or stress amplitude) and mean stress, both of which are important in influencing the lifetime of a material.

The normal inputs to a fatigue study are the stress amplitudes, but as you can see in the next picture, mean stresses also have an impact on the lifetime of a material. The higher the mean stress, the lower the predicted lifetime.

Dead loads are not alternating but do contribute to the mean stress, so it is important that we can consider them in a fatigue study. But how do we do this?

Alternating load only case

In a normal fatigue study, the method takes the max stress, S_max from a static study loadcase and we use the loading ratio (R = S_min/S_max) to define S_min directly.

For example,

• Picking ‘zero based’ means we define S_max but S_min = 0.
• Picking ‘fully reversed’ means we define S_max and S_min = - S_max.
• Picking ‘loading ratio’ means we can define any arbitrary S_min from the S_max value.

The fatigue setup simply allows us to pick the relevant static study and along with the loading ratio this provides our alternating stress values. These are then compared to the S-N curve to get the lifetime or damage plots.

Dead load case

Dead loads however are constant and therefore by definition not alternating. This means they only apply a non-zero mean stress, which must be considered for the reasons argued above, but cannot be applied in SolidWorks Simulation in the normal way.

The method we use therefore is the ‘Find cycle peaks’ method. This method takes the peaks of multiple loads to find the damage so we must build our static studies with the ‘peaks’ in mind.

Therefore if we had one alternating stress and one dead load, we would need two studies:

• Static study 1 including S_max and the dead load.
• Static study 2 including S_min and the dead load.

You can see here that we are not using one study for S_max and implying S_min from the loading ratio, rather we are doing two separate studies with S_max in one and S_min in the other. However both include the dead load.

Finally, in the fatigue study you reference both of these studies using the ‘Find cycle peaks’ method. This then takes both S_max + dead load and S_min + dead load extremes and combines them to find the worst case for fatigue.

Technorati Tags: SolidWorks Simulation,Fatigue,Dead Loads

All buckled up!

I recently did a simulation product demo for a Norwegian customer and the question of buckling came up. I realised this was an excellent example of understanding the assumptions of the solutions you are producing plus the physical implications of your modelling methods.

We started off with a simple curved panel from a training example,

 

and used shell elements to perform a linear buckling study on a quarter of the model. You can see the edge restraint on the bottom right edge, and the other two symmetry restraints with a point load at one corner, equivalent to the centre of the full panel.

 

The output of interest from a buckling study is the buckling load factor, which was obtained by RMB on the Results folder, and was reported as 27.9. This means that the load must be increased by 27.9 times to make the panel buckle.

However this was a ‘linear’ buckling study, which assumes that the deformation occurring in the component before the onset of buckling must be small. If the panel shows large deflections before buckling occurs, then its stiffness may change. Our linear buckling study solves this in one step and has no opportunity to update the stiffness matrix, therefore giving us a potentially wrong answer.

To test this we ran a nonlinear buckling study on the same component, where the final load is applied in a series of incremental steps. This allows the stiffness matrix to be updated at each increment and so the stiffness of the panel is more realistic as it deforms.

In such a study we do not have a simple buckling load factor report, rather we can plot the displacement of the corner node where the load is applied in a Response Graph. The result looked like this:

where the curve needs to be read from right to the left since the displacement (on the x-axis) is in the negative Y direction, or downwards in our model.

What this shows is that the displacement increases as the load is applied up to a ‘snap-through’ point where it begins to change direction. This snap-through point provides the value of the incremental Load Factor at the onset of buckling and is equivalent to our buckling load factor. Here you can see that it is reading about 13.2, which is a lot less than the linear case of 27.9 above!

So you can see that with a nonlinear buckling study our model would buckle if we increased our load by 13.2 times, rather than 27.9 times; a much more sobering figure.

There is one final step that is worth considering too. Our model here is perfectly symmetrical and the solution is also symmetrical due to the way it has been constructed. However the real world is not symmetrical with manufacturing variations and real loads resulting in an asymmetrical setup.

To see what effect this has on our buckling load factors we re-ran the ‘full panel’ model with a slight offset of our load as an example of an inherent asymmetry. Here you can see a split line used to create a vertex on which the load is applied, slightly to one side of the middle of the panel.

The response graph of displacement at this point shows a different result again, however the buckling load factor is even lower, coming out around 11.7.

So you can see that buckling of ‘real-world’ structures should consider potential asymmetries that allow the structure to buckle sooner than in a symmetrical case.

All-in-all buckling is an interesting failure method and for an accurate solution you should consider both the real structure, your modelling methods, and the solution type to make sure it is as accurate as possible.

Technorati Tags: SolidWorks Simulation,Buckling

Naim Audio, creating a high-end audio component with SolidWorks

Naim Audio designs and manufactures a familiar range of audio equipment, but don’t look for Naim on the shelf at the mall electronics store. Naim’s tuners, amplifiers, CD players, loudspeakers and digital-audio converters are for high-end audiophiles, the kind of customers who can tell the difference between analog and digital sound, and who can tell if the harps in Mahler’s Third Symphony sound flat. Naim Audio’s customers want superior sound, and they’re willing to pay a premium for stereo equipment that can deliver it.

 

 

 

 

 

Challenge:

Develop a new high-end disk drive stereo component that cools itself “passively” by careful placement of internal assemblies and material choice.

Solution:

Use SolidWorks Flow Simulation software to model the airflow through the component and guide modifications that promote passive cooling.

Results:

· Reduced prototyping from as many as 10 prototypes to 2

· Final design is self-cooling up to 25° C (77 ° F)

· Hard drive manufacturer validated all analysis and testing results.

All of Naim’s products receive the same care in design and engineering, from a $30,000 CD player to the $4,000 Naim Uniti all-in-one unit. In designating Naim Uniti the best product in its class for 2009, Tone Audio magazine observed: “Naim  has packed the heart and soul of their famous NAIT 5i and CD5i onto one chassis, no cheesy class-D chip amps here.”

Naim has a policy – expressed on its Website – of not creating a new product “unless it has something genuinely new to offer and integrates perfectly into our product range.” In 2008, the sales and marketing departments decided that a hard disk player met that standard.

New product, new design challenge

Hard disk players store digitized music and play it through stereo systems. A hard disk player is just another stereo component in most regards, but the hard disk player had a complication that Naim’s other components didn’t. The hard drive itself. It presented one of the biggest challenges that Naim’s 30+ person design team faced in producing its hard disk player (HDX): how to keep the component cool enough to prevent the hard drive from failing prematurely. Naim products are sold worldwide in a variety of climates, so the HDX had to resist overheating even in tropical temperatures.

“We had to be very conscious of the temperature inside the unit. Hard drives have a temperature they like to turn at, and it reduces their life expectancy if they run too hot. The bearings wear out, for example,” said Naim Audio Mechanical Design Manager Paul Neville. “The HDX was our first product with a hard drive, and it also has significantly more software than anything else we’ve designed. A complex product means more electronics, and more electronics generate more heat. At the same time, they reduce the amount of room in the unit that allows heat to circulate through. We had to do a lot of thermal analysis before we went to market to make sure the unit wouldn’t overheat.”

Guarding against overheating required even more analysis than Naim Audio usually devotes to a new product, Neville said. Also complicating the task was Naim’s desire for the internal fan to operate only at extreme temperatures, not at regular room temperatures.

“We wanted the HDX to operate at ambient room temperature without the fan kicking in, so it had to be passively cooled,” Neville said. “That meant incorporating heat sinks into the design and using positioning of the interior components to promote airflow through the product.”

SolidWorks analysis provided fast answers

Naim has designed and analyzed its products using SolidWorks CAD, Simulation, and Product Data Management software since Neville came to the company 3½  years ago. He had worked with SolidWorks and a competing product in his previous job. Based on Naim’s size and its analysis requirements, he recommended switching to SolidWorks because of its integrated analysis tools and cost effectiveness. Also, because of SolidWorks’ growing footprint in the engineering community, Neville said switching to SolidWorks gave Naim access to a bigger talent pool to hire from in the future.

“We design all of the physical elements of our products in SolidWorks, except for PCB boards. We do those in a specialized PCB application then convert the results into a solid model. For everything else – chassis, knobs, buttons, connectors, internal components, cable accessories – we use SolidWorks CAD software. To validate our designs, we use SolidWorks Flow Simulation.”

Neville’s team used SolidWorks Flow Simulation to model the heat flow through the HDX. Flow Simulation enabled the Naim team to analyze:

• radiation heat transfer between high-temperature surfaces;
• heat flow between and around components;
• transient flow analysis for simulating unsteady flow over time;
• conduction and convection heat transfer.

HDX was the first time Naim used SolidWorks Flow Simulation in new product development. Designers used a CAD model of the HDX as a starting point to create a thermal analysis model in SolidWorks Flow Simulation. The model enabled them to predict the flow patterns and maximum temperatures inside the HDX. Designers modified the CAD models in response to the thermal analysis, then ran another analysis to ensure the modification would work.

“The SolidWorks Flow Simulation software worked very well at giving us comparative solutions,” Neville said. “For example, if we changed the material or thickness of a heat sink, we would run another analysis to see what effect that had on key components. Otherwise, we would have had to use physical prototypes, and that would have taken a lot of time. We ended up doing two prototypes to look at the thermal side of the design, but using the software we tried 10 different scenarios. If not for the software, we would have needed 10 prototypes.”

Neville said SolidWorks Flow Simulation’s ability to clone a project to compare two versions side-by-side and the setup wizards for starting tasks also helped cut time off the design process.

Analysis yields self-cooling product

Using SolidWorks Flow Simulation results as a guide, Naim settled on a design that includes a 5mm thick aluminum product case that provides a built-in heat sink for the components and a path to remove heat from product. Components were mounted to the case so their heat would radiate out of the product. Designers moved the primary hard drive close to the cover to shorten the path heat had to travel to get outside. The internal air flow keeps the fan off unless the temperature rises above 77 degrees.

The HDX went to market in late 2008 to praise from the audiophile press. “We didn't expect to be won over by a computerized box of tricks, but we have been,” said TechRadar U.K.

“Naim Audio, a name synonymous with high-end, has recently launched its very own hard drive-based music server, and on paper, it's a fairly mesmerizing piece of kit,” wrote Engadget.

Neville said Naim sent the HDX to hard drive manufacturer Seagate’s test center before it went into production, to double-check its test results.

“They confirmed all of our analysis and testing,” he said. “It’s a testament to how intuitive the SolidWorks Flow Simulation software is that we were able to achieve results like that our first time using it.”

For more information about Naim Audio’s HDX visit www.naimaudio.com

How long is the flow?

I was asked yesterday if it was possible to calculate how long the flow lasts inside the domain during a flow simulation? Think of this another way and it is easy to solve; how long does it take a particle to pass through the domain when it enters the flow inlet.

To do this, we therefore start off by performing a particle study:

1. Insert a new Particle Study
2. Define an injection of particles from the inlet
3. Run the Particle Study

Then, to find the time of a particle in the domain, simply RMB on the Particle Study created and View Results.

Hit the Summary button,

and you will get a table of results for each particle injected into the inlet.

 

The thing you are interested in here is the Residence Time, which is the “life time” of the particle, or how long it exists in the calculated domain.

However there are some other interesting details here too.

The Length is the physical distance travelled by the particle whilst in the domain. You will notice that each particle has a different length and residence time, and this is simply due to the fact that each particle will take different paths depending on their starting position in the flowstream.

The picture below shows this clearly as some of the inlet particles travel all around the circumference of the external pipe, whereas others travel more directly from inlet to outlet.

This means that you should consider if you need to know the min, max, or average of the residence times for your particular application.

You will also notice that the Summary table gives you the Fate of each particle and this leads us to another interesting option in Particle Studies.

If you go to the Boundary Conditions tab in the Particle Study setup and edit the default setup, you will see three options for the boundary conditions.

This determines what happens when the particles meet the walls of the domain, and the options are:

• Absorption - The particles are absorbed by the walls. This is typical for liquid particles.

• Ideal reflection - The particles are reflected from the walls. This is typical for solid particles.

• Reflection - Specify the normal and tangential restitution coefficients which are ratios of the absolute value of the normal and tangential velocity components correspondingly after and before the collision:

So the Fate of the individual particles may be to reach the opening, be absorbed, or possibly to end their time still within the domain when the calculation finishes.

Technorati Tags: SolidWorks Flow Simulation,Tips and Tricks,Particle Study,Residence Time

Welded to the spot – and now edge…

One of the most common questions from people who have welded structures is, “can you model welds?”. Well, obviously!

In 2010 we have a new edge weld connector, similar to the spot weld connector already available.

The tool allows you define a fillet or groove weld, either single or double sided between any two sheet metal parts or shell structures like the one below.

By picking two intersecting surfaces the edge weld is generated for you at the intersecting curve.

Now all you have to do is pick an electrode material from the list of steel and aluminium types, and provide an estimated weld size.

The weld is then ready to go!

Simply solve your simulation as usual and the forces and moments are automatically passed through the new weld onto the surrounding structure.

However the really neat bit comes next. Not only is the weld connector a new joint type, it currently compares the forces and moments through the weld to the AWS 1.1 standard and tells you if the weld size you have chosen is good enough!

To get this info, RMB the Results folder and chose Define Weld Check Plot. Hit the OK tick and you get a new dialog that lists all your welds into two groups, those that pass and those that fail according to the standard.

This allows you to browse each connector and see where you need to define a larger weld.

What is more, if you chose a weld in this dialog and hit the Details button, you get even more helpful info containing the required weld and throat size plus the forces and moments experienced by the weld in the particular configuration you tested.

And as a final benefit, you can also plot the required weld size and throat size along the weld length (from an indicated start point and direction) based upon the loads generated from the simulation.

 So you can see that with a few short steps it is possible to assess your design for weld sizes. In fact you could put any arbitrary weld size in, because the software then tells you what is ultimately needed, which is of course what you want to know!

Technorati Tags: SolidWorks Simulation,Simulation,Welds,Simulating Welds

The Future of SolidWorks Simulation?

It’s been a while since I’ve posted a simulation blog as I’ve been busy looking after my new daughter. As proof, here’s a picture showing just what a fan of SolidWorks she’s already become :-).

So enough about me, let’s get back into the swing of things with a couple of insights this week.

Firstly I received this fantastic video of a flow simulation showing a timing sequence of valves in an engine manifold.

I particularly like the simplicity with which the pressures can be switched on and off using the dependency button. Very impressive.

Up next, as part of our SolidWorks 2010 launch we have been showing some of the great new motion simulation features.

One of the main reasons for using motion simulation is to know the loads that your mechanism experiences when its moving. After all, as the mechanism moves, the loads will change at each moment in time putting varying strains on your design. How do you know if you have tested the worst case?

In 2010 we have a new tool, called stress recovery (because that is what it does). Notice the three new buttons on the motion dashboard…

The first button on the left provides a dialog allowing you to choose which components you want to see stressed, and of course which period of the motion you are interested in (perhaps the entire motion just in case you can’t decide when the worst case is!).

Having defined this and run a motion study as normal to generate the loads, the middle button    then launches the structural solver to calculate the displacements and stresses on your chosen part at each time step.

And the final button on the right let’s you pick which contour you want plotted.

So, with hardly any effort, and moving from right to left through these new buttons, it is simple to generate a proper understanding of the response of your mechanism to the changing loads generated in a motion study.

 

Technorati Tags: SolidWorks Simulation,Motion Simulation

 

Are you up to the challenge?

Challenge your knowledge on 6 common design problems:

 
Good luck and enjoy the quiz.