Even in the times of 8-bit CPUs you'd see absolutely awful circuit designs and layouts that radiated and conducted hash like crazy, and then when the EMI tests were done they had to work around poor PCB layouts etc., adding shielding, chokes and whatnot. All the while someone who knew what they were doing could have likely designed everything to pass at the first attempt. I've had industrial drive systems pass emissions at the level called for in medical equipment. As an end user, you'd be glad you used those instead of something that passed emissions with a nod and a wink and corrupted the signals from any analog sensor located in its vicinity.
And that's why I do my own data acquisition, because if all I wanted was cookbook designs, I could have just bought a DAQ card. It's only when you need something that is better than cookbooks that you need to look inwards, and if you want to be competitive you often need something better than a cookbook.
Heck, when you're validating high speed interconnects on your PCB, you are also looking at the digitized form of the analog signal present on the differential data pairs. This requires some rather specialist knowledge to be done properly, if for nothing else than not to destroy the multi-$k differential probes used in such setups. Never mind the oscilloscopes that can actually do something useful with the signals the probes feed them. I don't do any bleeding-edge work in this area, but even I have a few probes that were $800 used, and it was an exceedingly good deal for them, too. Oh, and a $500 signal source needed to make sure that the probes actually work, even if in a pinch I could have just probed a few "standard" signals on the motherboard of my desktop.
I didn't know the body fluids had a timer and had to wait until it expires. Surface moisture on all of our body's surfaces exposed to the atmosphere evaporates plenty even in standard conditions. At pressures below the Armstrong limit , there'll be boiling of water at the surface, but that's not the end of the world. Some of the critical fluids inside of your body most definitely are not at ambient pressure. Hypotension let loose will kill you:)
Your lungs certainly don't take lightly to the surface boiling "treatment", but that's a reversible effect. When exposed to vacuum, it's really anoxia that kills you. The oxygen in your blood, circulating through the lungs, will off-gas into the vacuum in the airway. That's the primary mechanism of oxygen loss when exposed to vacuum. That's why you can hold your breath for minutes at atmospheric pressure - nothing is removing the dissolved oxygen from your blood. Yet, in vacuum, you'll pass out from hypoxia in ~10 seconds.
If you were, prior to being exposed to vacuum, to evacuate your lungs and then fill them with an oxygenated buffer liquid like perflubron, you'd probably stay conscious for much longer than the ballpark 10 seconds. Yeah, your skin would be swelling like crazy, and you'd be frothing from the nose, but so what - it's reversible. My rear-end-sourced estimate is that you'd have 20 seconds of ambulation for airlock-to-airlock stroll on Mars with such pre-treatment, assuming you'd be trained not to get too excited about it.
This isn't about travel, and isn't about corporate world. The guy is doing teaching. As I've said, good luck with getting the bureaucracy of an academic institution let you "use" any sort of a credit card. The modus operandi is to do expense reimbursement. As in: you front the expense, and they will, if you bow low enough, maybe, refund it a month or two later. You better not have cash flow problems when working in academia. I have heard first hand from tenured people in Big 10 institutions whose salary checks have bounced once or twice.
Oh, so I see you've never had the "pleasure" of attempting to get any bureaucracy to give you a credit card, nor of subsequently getting said bureaucracy to agree with your charges on such card. You know, after all you could defraud them of a $7 latte, so it's obviously better they spend hundreds of manhours micromanaging you. Bureaucrats cost the bureaucracy nothing - it wouldn't exist without them.
TL;DR: Good fucking luck getting the "institution" to "foot the bill" for anything in the form of providing a credit card for it. LOL. Good for you that you don't have to deal with any of that.
In a place that serves a lot of coffee, so that it's always freshly brewed, into low thermal mass, insulating cups - heck yes, they will be very close together, within 10F or so.
There's no single paper. There's a lot of papers that refine the technique and apply it to different problems. To even begin to understand it, you must have a good grasp of network coding as it's actually applied in real life. The butterfly network is but a starting point.
The reason that the S-N graph is slightly deceptive is this: I can give you a pre-cracked steel part where the material is perfectly sound except that there is a crack, and I can size the crack so that the part will fail at an arbitrarily low load, in just one half-cycle of loading (you only load up, it fails before you cycle load back to zero). It looks as if I gave you "weaker" steel, but the steel is fine, it's the geometry of the part that's wrong. It may appear to the naked eye that the geometry is fine, because I can make the crack in such a way that you won't see it.
When aluminum fails due to fatigue, the tensile yield stress appears to be lowered, and thus we talk of fatigue "weakening", but only because you ignore the presence of cracks. Say you have a 1 inch square aluminum rod under a 20,000lb normal load, so you think the longitudinal tensile stress in the rod is 20ksi. But in fact it's not, it's very high, at the level of a yield stress, since there are cracks in the material, and the crack surface is a stress-free boundary. So the load has to find elsewhere to go, figuratively speaking. So it looks as if you had a weak rod. But then you can apply a compressive load just under the nominal yield (not any weakened yield), and guess what, if the rod doesn't buckle, nothing else will happen. So the material is not weaker. The part is. That's a subtle difference.
So, there's a very easy way to tell if a material is weaker, or just the part is precracked and thus weaker on average: just apply compressive load instead of a tensile one. In metals, the compressive and tensile strength should be similar. When it isn't, you have a precracked part. When it is, and both are low, you have true material weakening at the microscopic level.
This shows the bulk stress needed to fail the part. It will fail by a fatigue crack. The effect is that of a "weakening" but only if you view it in bulk. The effect is as if the material was weaker, but it's really a material that's not set up the same anymore. It has new internal surfaces that didn't exist before.
You're correct, but even then I find the video rather weird. They're supposed to be braking from 160mph down to 0mph. They don't freaking need to apply the brakes at 5000RPM or anything like that, even though they seem to do just that in the video. To me, that's silly, or the superimposed numbers are someone's fantasy. The testing regime for their brakes is spinup to 10kRPM, the dyno braking down to 1600RPM to simulate air drag, then actual braking down to 0RPM at ~1MW braking power, if my assumption of 15s braking is correct, and the assumption that 1000mph = 10kRPM. The highest I've ever recorded my SUV braking at was 1.2MW IIRC, during some emergency braking tests. Of course the brakes probably wouldn't last if I could keep at it for 15 seconds, but for 3 second they were just fine (that was 100mph to 0mph).
I hope that you do realize that the braking job described here is something done routinely by disc brakes in large trucks, and occasionally done by disc brakes in run-of-the-mill SUVs. The stuff that happens at the braking speeds is inconsequential. You got taken by a very inaccurate and misleading article. What they worry about is what the disc does when it's not braking at all and is merely spun fast without any braking action. An emergency braking on my SUV dissipates as much power as a 15 second braking would on their vehicle. You can't look at those things without running some numbers. The video is also rather misleading since it overlays thermal imagery on visible image. Nothing is really glowing in visible light. The brake testing that they do is also slightly over-the-top: the brakes will not be used at 5kRPM at all.
"when aluminum flexes, it weakens." Nope. The finite fatigue life of aluminum has nothing to do with weakening, unless you simply use the wrong term to really mean fatigue. Fatigue has little to do with strength of the material itslef. A typical fatigue failure mode is fatigue cracking, and it most definitely doesn't make the material weaker. The part gets weaker, but that's because it changes shape. Cracking produces new surfaces and thus changes the shape of the part. A part with a crack in it is not the same part as one without a crack, even if the material is no weaker.
There are specific terms for it. Aluminum generally has finite fatigue life no matter what the cyclic stress amplitude is. That means that in presence of cyclic stresses, it will always eventually fail. If you really overdesign things, it may take a very, very large number of cycles - so large that they won't occur in a human lifetime, but still, if you keep cycling the stress, you'll get failure. Many kinds of steel, though, have infinite fatigue life at sufficiently small cyclic stress amplitudes. If you design things properly out of steel, they'll literally "last forever" - or at least they won't fail due to fatigue.
There's no 4.6 anything. A 15 second braking of a 6 ton vehicle from 160mph to a stop dissipates 1MW (1,000 kilo Watts) on average. The vehicle energy at 160mph is 15MJ (15,000,000 Joules). The energy at 1000mph is 0.6GJ (600,000,000 Joules). The 4.6 is someone's figment of imagination.
It wouldn't solve anything, because you have no clue about mechanics of such composite assemblies. Just forget it. There is no rotor issue. Remember that the article doesn't mention any issues at all. They managed to shatter a carbon disk that wasn't designed for the job. Big deal. There are no other problems at all. It's just sensationalism and innuendo. Get over it.
So, to anyone dumb enough to propose regen braking: take a good look at the size and weight of a 1MW generator, even a small duty cycle one, even water-cooled.
A well-loaded SUV doing pedal-to-the-metal ABS emergency braking from 100mph on dry pavement with summer tires can easily hit 1MW total braking power. A passenger car doing some only mildly distracted late braking in city traffic easily pulls off 50kW braking power. An old grandma's scooter can easily exceed 5kW of braking power in city traffic.
The 4.6kW figure is a typo, and anyone who takes it on face value is silly. I don't know where the heck it came from. A 6 ton vehicle doing 15 second braking from 160mph to stop needs to dissipate 1MW.
All figures are average power per vehicle, not per brake. Uneven braking will produce higher peak power.
So, let me think. A simple chunk of metal that heats itself by friction, vs. a generator and a bunch of resistor coils. Yes, I thought so. Proposing regen braking for this project is insane. BTW, who the heck told you that heating is a problem? Disc brakes work just fine. On my wife's car, on dry pavement, I can hit 1MW of braking power for a second or two, no biggie. Braking a 6 ton vehicle from 160mph is no problem for disc brakes. Let me repeat: braking is not a problem at all. It's the survivability of a brake disc that wasn't necessarily designed for operation in enterprise hard drive spindle type of a job. A major problem with off-the-shelf brake discs in this application is fatigue cracking. They have various holes and radii that are not designed for the hard drive spindle operation called for here. The whole article is IMHO a big fat decoy, most likely an inadvertent one - due to ignorance, not malice.
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Even in the times of 8-bit CPUs you'd see absolutely awful circuit designs and layouts that radiated and conducted hash like crazy, and then when the EMI tests were done they had to work around poor PCB layouts etc., adding shielding, chokes and whatnot. All the while someone who knew what they were doing could have likely designed everything to pass at the first attempt. I've had industrial drive systems pass emissions at the level called for in medical equipment. As an end user, you'd be glad you used those instead of something that passed emissions with a nod and a wink and corrupted the signals from any analog sensor located in its vicinity.
And that's why I do my own data acquisition, because if all I wanted was cookbook designs, I could have just bought a DAQ card. It's only when you need something that is better than cookbooks that you need to look inwards, and if you want to be competitive you often need something better than a cookbook.
Heck, when you're validating high speed interconnects on your PCB, you are also looking at the digitized form of the analog signal present on the differential data pairs. This requires some rather specialist knowledge to be done properly, if for nothing else than not to destroy the multi-$k differential probes used in such setups. Never mind the oscilloscopes that can actually do something useful with the signals the probes feed them. I don't do any bleeding-edge work in this area, but even I have a few probes that were $800 used, and it was an exceedingly good deal for them, too. Oh, and a $500 signal source needed to make sure that the probes actually work, even if in a pinch I could have just probed a few "standard" signals on the motherboard of my desktop.
I didn't know the body fluids had a timer and had to wait until it expires. Surface moisture on all of our body's surfaces exposed to the atmosphere evaporates plenty even in standard conditions. At pressures below the Armstrong limit , there'll be boiling of water at the surface, but that's not the end of the world. Some of the critical fluids inside of your body most definitely are not at ambient pressure. Hypotension let loose will kill you :)
Your lungs certainly don't take lightly to the surface boiling "treatment", but that's a reversible effect. When exposed to vacuum, it's really anoxia that kills you. The oxygen in your blood, circulating through the lungs, will off-gas into the vacuum in the airway. That's the primary mechanism of oxygen loss when exposed to vacuum. That's why you can hold your breath for minutes at atmospheric pressure - nothing is removing the dissolved oxygen from your blood. Yet, in vacuum, you'll pass out from hypoxia in ~10 seconds.
If you were, prior to being exposed to vacuum, to evacuate your lungs and then fill them with an oxygenated buffer liquid like perflubron, you'd probably stay conscious for much longer than the ballpark 10 seconds. Yeah, your skin would be swelling like crazy, and you'd be frothing from the nose, but so what - it's reversible. My rear-end-sourced estimate is that you'd have 20 seconds of ambulation for airlock-to-airlock stroll on Mars with such pre-treatment, assuming you'd be trained not to get too excited about it.
This isn't about travel, and isn't about corporate world. The guy is doing teaching. As I've said, good luck with getting the bureaucracy of an academic institution let you "use" any sort of a credit card. The modus operandi is to do expense reimbursement. As in: you front the expense, and they will, if you bow low enough, maybe, refund it a month or two later. You better not have cash flow problems when working in academia. I have heard first hand from tenured people in Big 10 institutions whose salary checks have bounced once or twice.
Oh, so I see you've never had the "pleasure" of attempting to get any bureaucracy to give you a credit card, nor of subsequently getting said bureaucracy to agree with your charges on such card. You know, after all you could defraud them of a $7 latte, so it's obviously better they spend hundreds of manhours micromanaging you. Bureaucrats cost the bureaucracy nothing - it wouldn't exist without them.
TL;DR: Good fucking luck getting the "institution" to "foot the bill" for anything in the form of providing a credit card for it. LOL. Good for you that you don't have to deal with any of that.
This! I can't agree more.
In a place that serves a lot of coffee, so that it's always freshly brewed, into low thermal mass, insulating cups - heck yes, they will be very close together, within 10F or so.
But that's not U.S. In the U.S., I'd ballpark $1500 for a completely new house for permits in an incorporated metro area.
The linear algebra isn't even fancy. They need to do a lot of linear equation solving, that's about it.
There's no single paper. There's a lot of papers that refine the technique and apply it to different problems. To even begin to understand it, you must have a good grasp of network coding as it's actually applied in real life. The butterfly network is but a starting point.
What I mean is: anyone able to pull off such a feat is on way to getting rich, rich, rich.
The reason that the S-N graph is slightly deceptive is this: I can give you a pre-cracked steel part where the material is perfectly sound except that there is a crack, and I can size the crack so that the part will fail at an arbitrarily low load, in just one half-cycle of loading (you only load up, it fails before you cycle load back to zero). It looks as if I gave you "weaker" steel, but the steel is fine, it's the geometry of the part that's wrong. It may appear to the naked eye that the geometry is fine, because I can make the crack in such a way that you won't see it.
When aluminum fails due to fatigue, the tensile yield stress appears to be lowered, and thus we talk of fatigue "weakening", but only because you ignore the presence of cracks. Say you have a 1 inch square aluminum rod under a 20,000lb normal load, so you think the longitudinal tensile stress in the rod is 20ksi. But in fact it's not, it's very high, at the level of a yield stress, since there are cracks in the material, and the crack surface is a stress-free boundary. So the load has to find elsewhere to go, figuratively speaking. So it looks as if you had a weak rod. But then you can apply a compressive load just under the nominal yield (not any weakened yield), and guess what, if the rod doesn't buckle, nothing else will happen. So the material is not weaker. The part is. That's a subtle difference.
So, there's a very easy way to tell if a material is weaker, or just the part is precracked and thus weaker on average: just apply compressive load instead of a tensile one. In metals, the compressive and tensile strength should be similar. When it isn't, you have a precracked part. When it is, and both are low, you have true material weakening at the microscopic level.
So, you made a 1 megawatt inductive brake that was smaller than this disc brake was? You must be filthy rich then :)
This shows the bulk stress needed to fail the part. It will fail by a fatigue crack. The effect is that of a "weakening" but only if you view it in bulk. The effect is as if the material was weaker, but it's really a material that's not set up the same anymore. It has new internal surfaces that didn't exist before.
You're correct, but even then I find the video rather weird. They're supposed to be braking from 160mph down to 0mph. They don't freaking need to apply the brakes at 5000RPM or anything like that, even though they seem to do just that in the video. To me, that's silly, or the superimposed numbers are someone's fantasy. The testing regime for their brakes is spinup to 10kRPM, the dyno braking down to 1600RPM to simulate air drag, then actual braking down to 0RPM at ~1MW braking power, if my assumption of 15s braking is correct, and the assumption that 1000mph = 10kRPM. The highest I've ever recorded my SUV braking at was 1.2MW IIRC, during some emergency braking tests. Of course the brakes probably wouldn't last if I could keep at it for 15 seconds, but for 3 second they were just fine (that was 100mph to 0mph).
I hope that you do realize that the braking job described here is something done routinely by disc brakes in large trucks, and occasionally done by disc brakes in run-of-the-mill SUVs. The stuff that happens at the braking speeds is inconsequential. You got taken by a very inaccurate and misleading article. What they worry about is what the disc does when it's not braking at all and is merely spun fast without any braking action. An emergency braking on my SUV dissipates as much power as a 15 second braking would on their vehicle. You can't look at those things without running some numbers. The video is also rather misleading since it overlays thermal imagery on visible image. Nothing is really glowing in visible light. The brake testing that they do is also slightly over-the-top: the brakes will not be used at 5kRPM at all.
"when aluminum flexes, it weakens." Nope. The finite fatigue life of aluminum has nothing to do with weakening, unless you simply use the wrong term to really mean fatigue. Fatigue has little to do with strength of the material itslef. A typical fatigue failure mode is fatigue cracking, and it most definitely doesn't make the material weaker. The part gets weaker, but that's because it changes shape. Cracking produces new surfaces and thus changes the shape of the part. A part with a crack in it is not the same part as one without a crack, even if the material is no weaker.
There are specific terms for it. Aluminum generally has finite fatigue life no matter what the cyclic stress amplitude is. That means that in presence of cyclic stresses, it will always eventually fail. If you really overdesign things, it may take a very, very large number of cycles - so large that they won't occur in a human lifetime, but still, if you keep cycling the stress, you'll get failure. Many kinds of steel, though, have infinite fatigue life at sufficiently small cyclic stress amplitudes. If you design things properly out of steel, they'll literally "last forever" - or at least they won't fail due to fatigue.
There's no 4.6 anything. A 15 second braking of a 6 ton vehicle from 160mph to a stop dissipates 1MW (1,000 kilo Watts) on average. The vehicle energy at 160mph is 15MJ (15,000,000 Joules). The energy at 1000mph is 0.6GJ (600,000,000 Joules). The 4.6 is someone's figment of imagination.
It wouldn't solve anything, because you have no clue about mechanics of such composite assemblies. Just forget it. There is no rotor issue. Remember that the article doesn't mention any issues at all. They managed to shatter a carbon disk that wasn't designed for the job. Big deal. There are no other problems at all. It's just sensationalism and innuendo. Get over it.
So, to anyone dumb enough to propose regen braking: take a good look at the size and weight of a 1MW generator, even a small duty cycle one, even water-cooled.
Let's get some perspective.
A well-loaded SUV doing pedal-to-the-metal ABS emergency braking from 100mph on dry pavement with summer tires can easily hit 1MW total braking power.
A passenger car doing some only mildly distracted late braking in city traffic easily pulls off 50kW braking power.
An old grandma's scooter can easily exceed 5kW of braking power in city traffic.
The 4.6kW figure is a typo, and anyone who takes it on face value is silly. I don't know where the heck it came from. A 6 ton vehicle doing 15 second braking from 160mph to stop needs to dissipate 1MW.
All figures are average power per vehicle, not per brake. Uneven braking will produce higher peak power.
So, let me think. A simple chunk of metal that heats itself by friction, vs. a generator and a bunch of resistor coils. Yes, I thought so. Proposing regen braking for this project is insane. BTW, who the heck told you that heating is a problem? Disc brakes work just fine. On my wife's car, on dry pavement, I can hit 1MW of braking power for a second or two, no biggie. Braking a 6 ton vehicle from 160mph is no problem for disc brakes. Let me repeat: braking is not a problem at all. It's the survivability of a brake disc that wasn't necessarily designed for operation in enterprise hard drive spindle type of a job. A major problem with off-the-shelf brake discs in this application is fatigue cracking. They have various holes and radii that are not designed for the hard drive spindle operation called for here. The whole article is IMHO a big fat decoy, most likely an inadvertent one - due to ignorance, not malice.
Do you really need to write like an american teenager?
brakes, not breaks
braking, not breaking
their, not there
Sheesh :)