Kelly Cordell-Morris’ Blog

Interesting and amusing anecdotes on the application of CFD in engineering/design problems. Plus whatever takes my fancy and may be of interest to the world as a whole!

24 September, 2009

There’s been talk for a while that Moore’s Law is no longer applicable. The law is based on the idea that as transistors get smaller they get better. But with silicon based components the insulating layer in the gates is getting thinner as the transistors become smaller and the all important electrons can find ways through the too thin insulator. Then there’s the doping problem. No it’s nothing to do with sports participation but the process by which the silicon substrate is manufactured. Doping introduces impurities into the pure silicon to “tune” microscopic circuits, but as more transistors are packed onto the ICs the circuits get smaller and doping becomes problematic. The belief that we are reaching the limits of what silicon can support has been around for a while and the race has been on for some time to find a new material to support the microelectronics industry’s quest for smaller, faster, better.

Today though on the BBC website I found a report that Intel has shown a wafer using transistors just 22nm across, showing that there is still life in Moore’s Law yet. How much remains to be seen.


14 August, 2009

This week I was in our Nottingham office to help deliver some internal training. One of the subjects of the training course was setting up transient analysis in FloTHERM. The example model we used was a detailed model of a TO220 on a PCB in free air. We set the heat source in the die to pulse on for 50ms, off for 50ms and repeat for 1s total. The idea was to show how a transient model can be set up, things to look out for, solver settings pertinent to transient analysis in free convection and how to post process those results afterward. With a mini competition for the best looking animation that the trainees could come up with. Note: Simple often works better, trying to be too clever and do too much normally means that your processor and/or graphics card just can’t keep up!

Anyway whilst showing the post processing we noticed a cool bit of physics going on. Now the TO220 model we had has 7 leads, but only 1 was directly connected to the die, the other 6 were connected to the encapsulant.

Our TO220 FloTHERM model

Our TO220 FloTHERM model

When the die first powered on, the heat traveled through the die to the die flag and out to the top signal layer of the board, it also traveled from the die to the centre lead.

Heat flux through centre lead at 10ms

Heat flux through centre lead at 10ms

Heat was able to pass along the signal layer and back up into the base of the lead for a short time

Heat flux through centre lead at 20ms

Heat flux through centre lead at 20ms

until the heat traveling down the lead finally caught up and overrode it.

Heat flux through centre lead at 70ms

Heat flux through centre lead at 70ms

Now in the centre lead this took a very short time, however in the outer leads, heat was still traveling in the opposite direction up the leads at the end of 1s.

Heat flux through outer lead at 1s

Heat flux through outer lead at 1s

So what does this teach us – mainly that conduction paths may not be as simple as they first appear. But also that FloTHERM is a great tool for finding out what exactly is going on with your thermal design – sweet!

Just to finish off, here’s an animation of the whole analysis. See how the die cools down in the “off” cycle while the heat still spreads throughout the rest of the model.

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28 July, 2009

Browsing through the BBC website today I found this little snippet. The Toucan has a disproportionately large bill for its body size compared with other birds. It seems the Toucan uses its bill to dissipate heat much like a heatsink on an electronics component.
Of course the Toucan’s bill is much smarter than a block of aluminium as the bird is able to restrict blood flow to the bill in cooler temperatures and so retain its body heat. However it’s not often that a design engineer wants a chip to retain heat so I guess it doesn’t matter that we are dumber than a Toucan ;)

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25 July, 2009

My new toy has arrived a Garmin Forerunner 405 so that I can see just how hard (or not) I’m working when out running. I’m very excited by it in all its gadgety-ness. It will tell me how far I run, how fast, my heart rate. It will even show me the way back to the van should I need it to – that’s a whole other story for another time perhaps. Suffice to say my 30min run-before-work turned into a 90min will-I-ever-find-the-van-again quest, still the dogs were happy.

Whilst fiddling with my new toy this morning, uploading training programmes to it for my upcoming runs I realised just how much I use technology unthinkingly these days.

My iPod that I never go anywhere without, my eBook that I’ve only had a few months but that too has become a permanent fixture. My laptop and wireless router that between me and my husband are probably used almost 24-7. Not to mention my mobile and Bluetooth headset, and that’s without considering TV, the Sky+ box etc.

On a recent journey to college up near Hull I had the iPod plugged in to the van’s stereo, mobile with headset so I could talk during my loooong drive, eBook and laptop packed away along with the mobile broadband usb stick so I could still surf the net in the B&B. Obviously on any future trips the Garmin will be along for the ride too. Writing it all down it seems slightly ridiculous but I can’t imagine going away for a few days and not taking any of those things. I truly am reliant on technology and it forms a significant part of my everyday life without me even thinking about it, I’m sure I can’t be the only one.

When I get asked what I do for a living I usually try to brush the enquiry off with a reply like “oh just engineering stuff”. Depending on the person I either get the reply “so you work on cars?” or “oh right what kind of engineering?” or thankfully less often the but-you’re-a-woman! look (yes, well done, full marks for observation).

For now I’m just going to ignore the state of affairs concerning the word engineer in the UK which to so many people means you must be a mechanic (maybe that’s a topic for another time). Or indeed that it is still possible to drop the bombshell that women are engineers too every now and then.

What should my reply be to those that are (possibly feigning) interest in my career. How do I explain it without the oh so common assumption “you work with computers then? Can you help with my PC?” – No Robin it’s not just you. Say CFD to most and after you’ve explained what CFD is (while their eyes glaze over) they assume that it is only used in Formula 1 or for designing aircraft and it offers so much more than that. Fortunately for us, most engineers (in whatever industry) realise that. Which means I get to help other engineers use our software so that consumers everywhere can enjoy technology without having to think about it.

Today I’m kinda pleased that I play a very small part in an industry that so many people take for granted. I’m also resigned to the fact that if my husband thinks my job is “something to do with computers” I’m never going to convince others any differently.

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16 July, 2009

So I haven’t written anything in a little while. Whilst many may be sighing in relief at that fact, a little birdie told me that maybe I should just post a snippet of “why I have had no ideas” recently.

I am in training for some running events – a 10k in September and an 8mile in December. I’ve been questioning my sanity somewhat especially on Tuesday when I was running hill intervals at 5.30am with two of my dogs showing just how easy it is when you are young, fit and have four legs.

That same Tuesday evening, because I’m slightly deranged, I took one of those two dogs to agility training where I proceeded to sprint around an indoor equestrian arena, trying to remember what direction to go in, in what order, how to direct the dog and BREATHE all at the same time. At one point I almost brained my poor Springer during a run. In a heroic attempt to avoid kicking him in the head, I lunged sideways and half jumped/fell over the jump I was supposed to be directing him over. After laughing at me for a while my trainer remarked that I need to pay more attention to where I’m going whilst still looking at the dog. I think I need to get me some chameleon eyes or something.

So my attention is somewhat diverted from all things CFD at the moment as the time normally devoted to pondering blog content – early morning dog walks, has been replaced by early morning torture sessions. Although I’ll admit half way through this morning’s torture I did think “this isn’t so bad” at least until the final hill. Note to self: find an off road route with no hills.

I’m also just finishing off my foundation degree (three assignments to go and counting). I’m obviously concentrating on agility training in readiness for our competition debut in 2010, and then there’s the other training with the other three dogs – I did mention I was mental right? So contemplation time in the evenings is in short supply also.

So there you have it, I’m sure normal service will be resumed soon. Just as soon as I get some chameleon eyes and new lungs that breathe without me having to consciously think about it.

1 July, 2009

So Murray played under the roof on Monday. It was a pretty intense match and I got absolutely nothing done that evening as I couldn’t drag my eyes away from the TV.

I’ve been thinking about the design, and the fact that the humidity needs to be kept at around 50% RH to avoid condensation or the grass sweating. Humidity can effect the speed of the ball though and certainly Murray has claimed that he needed to change his game to cope with the changed conditions and that if felt very humid to play in.

FloVENT can be used to predict the temperature and humidity levels within a model. FloVENT can output a percentage saturation therefore telling you where condensation will occur. FloVENT would allow you to model the centre court structure, the spectators and players as well as the air conditioning systems and the solar loading through the material roof. FloVENT allows you to investigate comfort temperatures and indices for occupants, and make quick changes to your HVAC design and see the impact it makes. You could even use the analysis to determine whether you could have a system with a lower humidity and allow Murray to play his normal game.

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15 June, 2009

Did you see the MotoGP race yesterday? I’m not sure how he managed it but Valentino Rossi’s final overtaking maneuver that secured the win also secured his hero status in my eyes. Awesome!

Despite the great race result yesterday was frustrating for me. I was attempting to write an assignment for my college course. Attempting because my laptop kept overheating and switching off – even with the cooling mat whatsit that I have already bought for it. The technique I discovered to ensure that the laptop remained on was to sit it (on cooling mat) on a flat surface (so not my lap then) and then prop up the front to increase the gap below the vents on the underside. This made typing more difficult but did mean it stayed on for longer.

As I was typing with my wrists at odd angles (carpel tunnel here I come) I got to thinking that my laptop cooling design must be very sensitive. Some days I can sit with it on my lap whilst lounging on the sofa without issue, and yet on other days like yesterday I wonder if there is any cooling going on at all.

That led me to thinking about who on earth designed my laptop and would I ever buy one from the same manufacturer again (I don’t know, looking more and more unlikely though). That in turn got me to thinking about how they had designed my laptop and that really they should have used the Response Surface Optimisation tool in FloTHERM.

The RSO allows a user to change variables within his (or her!) model and to see where the optimum lies. Of course you could do that with the plain ol’ sequential optimiser in FloTHERM too – so why is the RSO special?

Well for starters it allows you to see if your optimum solution is lying in a well.

well

A well is bad news as any deviation in the variable(s) will cause a rise in the cost function that you as a designer are trying so hard to minimise. An optimum solution that is in a well, may not be the best choice if you cannot guarantee the required degree of accuracy in manufacture for instance.

The RSO also allows you to see just how sensitive your design goal is to changes in the design itself. For instance how sensitive is your cooling solution to the ambient air temperature, how much the vents may be covered or indeed how sensitive your laptop may be to being placed on a lap!

A typical example is a heat sink, with the variable inputs as base thickness, internal fin height, and the thermal paste resistivity.
Here we can see that the cost function (which in this case was a component temperature target) is pretty sensitive to the internal fin height but not sensitive to the heat sink base thickness.

sensitivity1

For those of us who enjoy our widgets the response surface viewer allows you to change the 3rd variable (ie the one not on an axis) and see how the response changes – nice :)

For those who also enjoy getting real results there are 2D graphs. Below are graphs for the same design with the same variables. The first show the response with an internal fin height at around 5mm – here you can see that you will need an expensive low resistance thermal paste to get your low cost function.

graph1

The second is with the fin height at around 15mm, here you can have a cheaper higher resistance thermal paste – and still get a lower cost function.

graph2

So my advice to my laptop manufacturer (no I’m not going to tell you who it is) is this – get FloTHERM and use the RSO your customers will appreciate it ;)

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14 June, 2009

I had a long weekend this weekend and was looking forward to having it all to myself – well in as much that I didn’t have any work to bring home with me. However a certain someone asked me to blog this weekend.

I have a lot of ideas as to what this particular post should be about but since I have declared this weekend a work free zone this is it.

I have been often criticised in my life – my career, my hobbies, my choice in music to name but a few, but this weekend it was brought home to me that we are nothing if we are not ourselves.

Metallica said it well – Life is ours, we live it our way….. Forever trusting who we are, and nothing else matters.

8 June, 2009

So before I was talking about bike racing and whether teams used CFD. So do they? Could they? What exactly could they do with CFD?

Well I’m thinking that if you had a model of bike and rider you could vary the angle of lean on the bike for a start and see the resultant forces to give you an idea of stability. Remember that stability is important for rider confidence. It’s pretty hard to pull this kind of move – part 1, part 2, if you aren’t confident.

Now of course motorcycle dynamics is a complicated thing, you only have to watch a few races with the riders throwing the bikes around corners to see how the things move around underneath them, but if you had the nous I reckon it would be doable to take the resultant forces and feedback to the chassis and suspension setup to see how the geometry would change/deform. So stability probably doable in some form or other but what about the rest of it?

Well there’s the electronics systems used for engine control, traction control, telemetry etc etc, all squished onto these small bikes. Cooling has got to be an issue surely? Well CFD could help with that. Then there’s the engine itself, the exhaust system, engine cooling etc etc all common applications for CFD. So is the bike industry using CFD rather than the racing teams?

Well apparently they are!
Buell has reportedly used CFD to design the fairing and windshield to help optimise the airflow over and around the rider to reduce drag and increase rider comfort.

They also used CFD to design the ram-air system, on cowling design to help improve heat transfer at the radiator and shield the rider from the hot air. It seems Buell have embraced all that CFD can offer.

Now I have no idea what CFD code Buell use but what I do know is that FloEFD is setup to do just the kind of analysis you would need in motorcycle design. The parametric setup of the tool makes doing quick design changes easy with the added bonus that recreating the mesh is just not necessary, so what could be a few weeks worth of work in a traditional CFD code to model the geometry, mesh and solve, becomes a few hours in FloEFD. With the batch run capabilities you could set up a number of different models (varying the bike lean angle perhaps) run it all overnight and come back to the office to review all your results – cool huh?

So if there are any motorcycle racing teams out there who are interested in using CFD to improve their performance let me know. Obviously it will involve me spending an inordinate amount of time in the pits during races – but you knew that right? ;)

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2 June, 2009

It was a weekend filled with bike racing this weekend – British Superbikes at Thruxton, World Superbikes in the US and MotoGP in Italy. I spent much of the weekend watching it all, qualifying, practise then a whole days racing at the Thruxton circuit, then watching all the races we had recorded on Sky when we got home.

I love bikes, my whole family love bikes. I remember riding pillion on my Dad’s bike as a kid, willing him to go faster, lean harder – getting your knee down as a pillion would be awesome!

As soon as I could afford one I bought a bike. I was at Uni and I bought an old dilapidated Honda CG125. I loved that bike, although I had been driving for a while I didn’t have my own car and still used my Mum’s, so having my own bike equalled freedom to me. I had bruises and lumps all up my right calf from starting the damn thing with a kick start that kicked back. The seat was held together with tape and my Dad insisted on getting the cylinder (yes single) re-bored as it smoked terribly. I rode that bike (on L plates) into Uni up the A4 everyday, weaving my way through the traffic, dodging courier bikes, I loved it and that joy of riding a bike has never left me.

I’ve had a couple of bike since those heady days, a Suzuki Bandit 600 when I passed my test, then a Suzuki SV650s which sat unused much of the time I’m afraid to say. I was bike-less for almost a whole year after the SV – trying to be practical I sold it since I wasn’t riding much. Frankly it was depressing being without a bike so I went and got my current toy a Triumph Street Triple.

Isn’t it pretty?

Check out the nosy dog in the background!

I’m glad to report that quite possibly I’ve never liked biking more than I do right now. I hardly ever have time to ride it, but I’m working on changing that. But every time I do go out on it I remember why I fell in love with bikes in the first place – the freedom, the alone-ness. My perfect ride is never about my top speed or whether I got my knee down, or how fast I took that bend. My perfect rides are always the ones where everything just flowed, where for those few minutes or hours I was smooth and controlled and everything just floated past, no worries or thoughts about my to do list. Just me and my machine, as one. That’s why I love biking.

That’s not to say I don’t appreciate speed – but I’m just not that good a rider. But that’s why I watch bike racing, to see what is possible if you aren’t afraid of crashing! So this weekend I watched bike racing. And I also watched the first ever female bike racer to qualify for World Supersport race – Melissa Paris. Unfortunately a mechanical problem forced early retirement but what an achievement – and not just because she is a woman (although hey its worthy of mention since there really are very few at World level although a few are coming on through the British series’ now see here) but also because it was only her second pro race.

Whilst watching all this racing I got to wondering just how many teams use CFD – if any? Bike racing is slightly different to Formula 1 in that the race teams don’t often design their own bikes – they get the manufacturers bikes. So it’s the manufacturers that would be using CFD for the design of the bikes rather than the team. Bike racing is not all about the top speed, stability is important. A stable bike gives a rider confidence. A confident rider pushes the bike further, takes the bigger chances, has the faster corner speed, opens the throttle earlier exiting corners. So how can CFD help bike design?

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