Not sure which trails you went on, but glad you enjoyed them.:) They're of course mixed quality - the Reykjadalur one used to be a "mud bog" trail, but they've since fixed it because it got popular. But in general we do a good job, I think. Especially given that "mud bog" is kind of the default state around here;)
And your whales are really tasty - like filet mignon.
Anyway, spoiling it for those who didn't see it: nice clean landing (despite the stormy weather at the landing ship and the new experimental titanium grid fins), SECO completed as nominally, awaiting startup 2 after the S2 coast phase (40 mins).
Reminds me of news in Iceland. I remember one time reading an article about how two Icelanders were at an episode of the Tonight Show or something like that. Not on the show, just in the audience;) Checking the news right now, I see one article about an unattended rooster seen walking around a national park.
The expansion joints thing is just another example of why you don't turn to a biochemist for a lecture on engineering. Most HSR doesn't have expansion joints either. Lots of things don't have expansion joints. There are three standard ways in industry to deal with thermal expansion: 1) resist it, 2) let it expand by increased bend radii, 3) let it expand by increased linear length. All three are widely used. In HSR, it's common practice to use the "resist" approach - they generally lay the track hot, so that when it cools it contracts and there's built-in tension on all but the hottest days. They usually use heavy and/or anchored ties (commonly concrete) to resist track movement. Pipelines generally use some combination of #1 (e.g. overburden anchoring), #2 (e.g. expansion loops) or #3 (e.g. slip-type expansion joints). Hyperloop wants to use #3, with the dampers as slip joints (e.g. like teflon shoes on pipelines). Whoop-de-doodle-doo. Even if that sort of thing wasn't already a common solution for thermal expansion, they could always just switch to resisting expansion, with a pretensioned tube, like the rail on HSR.
Not as comfortable or convenient, though. Shinkansen is a great way to travel. Arrive, buy your ticket, walk straight onto the platform, catch whatever train happens to be next and going in the right direction, take whatever seat (much roomier and more comfortable than airplane seats), then relax and enjoy the ride.
Hyperloop itself isn't designed for journeys of that length - it's designed to be optimal for intermediary length trips, with trains better for shorter journeys and aircraft better for longer journeys. That said, it is possible to make Hyperloop have a higher top speed (and thus reduced long-distance travel time) by increasing the sonic velocity of the gas - aka, via either increasing the temperature of the (highly rarified) gas inside the tube, or by using a (rarified) light gas such as hydrogen or helium. The latter requires increased tube evacuation pumping to minimize the fraction of leaked-in-air in the tubes. The former may happen to some extent on its own due to compression heating from passing Hyperloop capsules (the tube itself will be an effective thermal radiator, but the gas inside (due to its very low density) will not be very effective at transferring heat into the tube). Both lighter and hotter gases not only increase the sonic velocity, but also decrease air resistance (particularly using light gases). The low densities mean that you don't use great quantities of gases - meaning that the amounts of helium are affordable and loss rates acceptable, while hydrogen would not be prone to embrittling the tube or presenting a tube explosion hazard even when mixed with leaked-in air (although its behavior inside the capsule compressors / air bearings / etc needs consideration). Rarified water vapour, ammonia or methane atmospheres would also allow improved speeds of sound vs. air, although not to the degree of hydrogen or helium.
Another issue for long-distance travel via Hyperloop is that the faster you go, the greater the minimum bend radius. Not so much of an issue when you're going over flat plains, but once you start getting into uneven terrain it can present problems. "Floating Hyperloop" is particularly appealing for when dealing with very high speed travel due to the ability to sculpt bend radii as gently as you want over open ocean.
The Hyperloop design document doesn't consider that other technology can't or won't advance as well. But for at least intermediate-distance travel, they argue - convincingly, in my opinion - that increased aircraft speed, even if associated with improved economics, can't beat out Hyperloop. This is because of the simple reason that increasing aircraft speed means increasing altitude (to reduce the velocity-squared drag and to avoid sonic boom effects on the surface), which means increased subsonic climbing and descent times. Not a problem for long journeys, but for intermediate hops, that looks like a fairly fundamental barrier.
VDUs are also much higher diameter, which makes them harder to design, not easier. And the feed lines can have very high length to diameter ratios.
It's the same engineering principles. The amount of structural reinforcement - both wall thickness, and reinforcing rings - to resist implosion is very well understood engineering and there are standard guidelines for it. Thunderf00t's ignorant nonsense to the contrary headlined with comic sans text done in what looks like MS Paint notwithstanding.
You should also know the kind of energy they are talking about to create such a thing.
The share of vacuum-related energy required equates to pennies worth of electricity per passenger-trip. And the energy density of the tube is orders of magnitude less than a tube full of typical hydrocarbon fuels (aka a pipeline). The maximum instantaneously deliverable power at a point of rupture is also orders of magnitude less than that of a collision of a loaded passenger train.
Right. Because when I want an engineering analysis, I always turn to an organic chemist.
Meanwhile, in the real world, mild or hard vacuum lines and chambers are widely used in industry (for example, see VDUs), and designing a structure to be stable against vacuum, including in catastrophic-rupture scenarios is basic engineering. Believe me, the VDU and its low pressure lines are not what people at refineries fear ruptures in - if you want to see some alarm, rupture a line for a hydrocracker.
That's not in the slightest "how they're selling it". Read the design document. To reiterate that which for some inexplicable reason has to be repeated in every thread about Hyperloop: the Hyperloop Alpha design:
* Is not a pneumatic tube
* Is not a vacuum train
* Would not even work in a hard vacuum
* Is not maglev
* Is a ground-effect aircraft / air-bearing suspended vehicle in a highly rarified atmosphere, utilizing a battery-powered compressor to shunt the air built up ahead of the vehicle to the suspension and behind the vehicle.
Your failure to read anything about how it works is nobody's fault but your own.
He prepared them on government computers on government time (while he was being paid by us), so he was not authorized to release government owned material, whether classified or not
"Waaaah, someone is saying something mean about my president, waaaaah! He's saying that it looks more and more like obstruction of justice and treason and that that several people involved in the campaign and administration already have grand juries against them while the investigation expands every several weeks to include new persons of interest as investigation keeps turning up new evidence of wrongdoing, waaaaah! Somebody stop the big mean liberal, he's hurting my feelings!"
Personnel records and work product are not classified, though they remain the property of the employer.
I'd be very surprised if the offloading policy of the FBI permits walking off with any asset whatsoever.
Which Comey didn't do. Comey does not have the memos, and did not leak the memos. He leaked a description of their contents. Which was made very clear during the hearing, where he stated that he hopes that the FBI gives the investigation the actual memos.
For your argument to work, you'd need to be arguing that "talking about non-classified matters is prohibited, because your knowledge of said non-classified matters remains the property of the employer". By all means argue that.
Also made clear was the fact that the memos weren't classified, and they were deliberately written to not contain information that was classified, so that they specifically could be made public if the FBI needed to defend itself against charges of what Comey perceived to be a White House attempt to influence an investigation.
Comparing this to the leaking of classified information is silly and bordering on clickbait. And what the heck is this crappy site that Slashdot is linking to as its article source?
I totally get it. I don't want a car until they can stop them from breaking down
I've seen so many cars (people I know) break down (farm equipment, too) after just a few years, but I've had the same horse for thirty years and the same mule for twenty.
Composites are cheap in small volumes relative to metal stamping because of the low tooling costs; you can carve a mould out of styrofoam if you want. But metal stamping is generally cheaper in large volumes; there's more steps in making a composite part, there's the curing times, there's often a higher defect rate, automated production equipment is more complex, and so forth. There's a lot of work trying to achieve lower mass-production costs for composites, and I really do think they're the future. But the future is not quite here.
I really respect what Boeing has been doing with the Dreamliner. They've taken a real risk, and it's costing them a lot of money. But anything to push forward large-scale composite usage production is good in my book.
BTW, your mention specifically of CF: one thing that's kind of neat that you're starting to see now is carbon/dyneema weaves. And it took me a bit to really catch onto the point of it, but I really like it. Basically, dyneema = UHMWPE = ultra high molecular weight polyethylene. Low density (even floats in water), but still with a good tensile strength; its specific tensile strength (aka strength per unit mass) is nearly as good as carbon fibre's. It's not frequently used in laminates however because it's extremely slick and doesn't adhere well with most resins. It's also UV sensitive, but additives and coatings can work around that. Its specific compressive strength is also worse than carbon fibre's - but on the upside it's also much better at energy absorption than carbon fibre (aka not likely to shatter). So combining the two into a single weave, you still get excellent mechanical properties, but it's not brittle.
But here's the neat part: yes, UHMWPE has a slightly lower specific tensile strength vs CF. But that's not the figure that actually matters. Because the density is lower, a sheet of equivalent tensile strength is thicker if there's spectra in the weave. And thickness matters hugely when it comes to bending resistance - that's why sandwich composites are so much stronger than single layers, why you use trusses in large structures rather than just simple beams, and why you use hollow beams or I-beams rather than solid ones. If I recall the formulae correctly, stress is proportional to the distance from the centreline to the third power, while deflection is proportional to its fourth power. So the fact that the composites are less dense adds an unexpectedly large amount of strength. And that strength carries over when you use these stronger layers in sandwich composites, trusses, tubes, etc.
More specifically, motor wear increases significantly as you go into the high end of the RPM range. Most EVs don't use a multi-gear transmission, so to get more top-end speed you have to choose a different gear ratio, which reduces your low-end torque. EVs are excellent on low-end torque in general, but it's not unlimited; as you keep dropping the RPM, eventually torque flatlines, due to either mechanical or electrical limitations. And most customers would rather have fast accel that they can actually use instead of crazy top speeds that they never get to experience. Unless they're buying it as a track car, that is.
Technically it's possible to reduce wear at high RPMs, which provides another way to get a higher top speed - and EV motors have been moving in this direction. But the torque / top speed tradeoff will always remain, unless you add in the weight, cost and maintenance of a multi-gear transmission.
And costs an insane amount per shot, with very restrictive (and predictable) "firing" windows due to orbital dynamics. If you really want kinetic energy weapons, there's a much better way: railguns. The goal is to be able to fire a dozen or so rounds per minute, many tens to hundreds of kilometers, with precision hits having the ability to penetrate any armour and almost any traditional fortification, with ammunition being cheap (~$25k per shot) and able (due to its small size) to be stored onboard in great quantities with no risk of inadvertent explosion. Fragmenting shells should also make for superb air defense systems. The rail lifespan problem seems to have been largely solved; they should be able to get a thousand or so shots off between replacements.
You'll never manage that sort of price performance with an orbital system.
Now, there's somewhat of a chicken-and-egg problem with kinetic energy penetrators... the same problem that hit the Zumwalts' guns when the ship production numbers were slashed. GPS-guided artillery shells are certainly possible; see for example the M982 Excalibur, which has a CEP of around 5 meters, based on tech that's now over 10 years old. The issue is cost. You can get the ammunition down to just a couple tens of thousands of dollars per shot, since there's nothing fundamentally expensive about it - but you need to order it in huge quantities to do so. Meaning you have to make a big gamble that widespread deployment of all aspects of the system will work in order to justify such large purchases. If you purchase it in small quantities, you end up having to pay cruise missile-prices per shot, defeating a lot of the purpose. Widespread deployment doesn't come without a cost; you have to remove other combat systems to make space for the gun, its ammunition and capacitor buffer. Only the Zumwalt and Ford classes (3 ships total at present, and not many more in the near future) have enough power to run one directly; all other ships also require a battery bank.
One may note that what the average person thinks "looks aerodynamic" often doesn't correspond to what actually is aerodynamic. The Saturn Sky sure "looks" aerodynamic (top up), but its drag coefficient is 0.42. The Dodge Viper is even worse, at 0.45, and the Ford Mustang ranges from 0.44-0.48. Meanwhile, the definitely not-sleek looking Ford Escape has a drag coefficient of 0.29. The SUV has a much larger cross-sectional area, of course, but that's beside the point -cross-sectional area is useful, but a high drag coefficient is not. Well, with one exception: a number of "sporty" cars get deliberately bad drag coefficients by being designed to create downforce (for an ideal streamlined shape you want no net lift); a Formula 1 car can have a drag coefficient of over 1.0, deliberately, in order to get as much downforce as possible to maximize its grip on the road. But for the most part, when a mass-market car has a bad drag coefficient, it's to play to people's style preferences, not for any functional reason.
Parent makes the right response. Aerodynamics doesn't care what you think of how it looks; it is what it is. If you want to know what the extreme end of aerodynamic streamlining looks like, the Aptera 2e was a pretty close example to maximizing it for a road vehicle. There's various decisions one can make about how they'd like their internal area laid out, and this affects the particulars of the optimal shape, but in general: front end like a deformed egg, all surfaces highly smooth with as few panel gaps as possible, air intakes as small as possible, steady transition from hood to windshield, wiper hidden, mirrors small and streamlined (or ideally, absent and replaced with cameras), maximum diameter reached relatively quickly (no fat front end pretending there's a huge engine inside) followed by a long gradual taper; taper ends at a line or point (line usually allows for a better use of internal space), wheels small and shrouded, exposed all struts shaped as airfoils, and as little exposed hardware as possible. Cabin air ejected through whatever flat rear surfaces you have can help reduce the wake. Where you can't taper to a line or point (aka, you want to have a space that's both tall and wide behind the front seats for additional passengers), an abrupt cutoff (kammback-style) is better than a steep taper; if your taper is too steep, you get flow separation, and you start dragging a low pressure wake from that point. Deliberate vortex generation at the point of expected flow separation can help reduce the size of the wake; this is often done with overhangs, vortex-generating spikes, or in some unusual cases, golfball-like dimples. Higher driving speeds, as well as crosswinds, require a shallower tapering angle to avoid flow separation; concerning crosswinds, a bit of a lateral taper can help as well.
Once you get into extreme streamlining, however, you have to become more of a niggler for details. A traditional exposed set of windshield wiper would double the drag of an Aptera-like vehicle, for example. If you let snow and ice accumulate on the vehicle, you've totaled the drag coefficient. On the upside, those smooth curves and slick composite surfaces help resist accumulation. A funny thing with the Aptera was that if the vehicle was out in the rain or you sprayed it with a hose, almost all of the water ran off the same point, in the bottom centre of the vehicle.:)
Just in case that all these ideas aren't clear to you, note that there is a (mechanical) engineering sub-field called material resistance (by assuming that I am not making a bad translation from Spanish), a closely-related branch is structural mechanics. Unlikely dynamics/kinematics, these branches deal with deformable solids (as your pylons do)
In English, concerning physics, "resistance" generally means electrical resistance, thermal resistance, or drag (e.g. "air resistance"). How bodies deform under stress is studied via finite element analysis (FEA / FEM).
with material properties and more realistic conditions what means that a bullet doesn't behave as a stream of water with the same mass
And as was pointed out to you, the issue has nothing to do with the bullet or the water, it's that in a gun you're dealing with several thousand atmospheres of pressure. It's like if someone said "this house would collapse if the roof has to bear five meters of snow but not one meter of snow", and you said, "but what if the one meter of snow was moving at a good fraction the speed of light?" It's not at all relevant to the problem at hand.
If you remove the completely-inapplicable-to-Hyperloop thing you're adding to the conversation (the pressure from the exploding gunpowder), then yes, you can directly compare a bullet sitting in a gun vs. water sitting in a water gun, as simple mass loadings.
You didn't get that point right. I was trying to give a graphical example about the kind of differences which theoretical analyses ignore.
Your comparison was different to the point of being ludicrous.:)
Let me put it in a different way: imagine that you can shoot water at the same speed than a steel bullet, would both of them do the same damage?
The same mass of water? Actually the water would do a pretty damned good job. Ever seen what a non-abrasive water jet cutter does? That's what happens when water moves at bullet-speeds, even tiny amounts of water. The faster the object, the more it's just the kinetic energy that matters and the less that the object's structural integrity matters. If you had a bullet's mass worth of water moving at bullet speeds, it'd cut deep into a person, if not right through. High speed liquid jets are how shaped charges pierce through armour. As a matter of fact, water charges are shaped charges that use water as their piercing fluid.
Now, I'm pretty sure that you're in a weird way trying to make some sort of point about how the distribution of loads matters - am I understanding you correctly? Good. Except that as I pointed out, the distribution of loads is similar for a Hyperloop capsule and a fluid - most on the bottom, less on the sides, little on the top. The exact distribution depends on the final choice of ski locations and the ratio of ski pressure vs. compression pressure**, and it is more uneven than carrying a fluid - but nearly an inch of steel will have zero difficulty whatsoever distributing such loads from an object that only weighs a few tonnes. Image how much an arch of inch-thick steel would deform if you drove a loaded pickup onto it. Basically nothing, right? Exactly. The only relevant potential for deformation is linear, along the pipe's length - so it doesn't matter whether the mass is a fluid or a capsule, it just becomes simple mass loadings - and only the amount of mass, not the type, matters.
** - And if you don't think it's even enough? Just add more skis.
The only practical difference is that the Hyperloop loads are transient, while the fluid loads are permanent. But transient loads are generally to a structure's favour. As noted previously, even if the added loads weren't borne at all and the pipe went into free fall every time a capsule passed, it would only drop a couple centimeters.
Back to the beginning: versus a pipeline and HSR, Hyperloop's loads peak loadings are dramatically lower, and they're transient. Elevation costs are directly proportional to mass loadings.
First off, thanks for actually reading the document. These discussions are a lot more enjoyable when 90% of responses aren't just "RTFM";)
Their earthquake proofing (and safety in the event of an accident, e.g. a truck going into one of the pylons in a road median) is not nearly good enough. The PDF they put out suggests that they will simply put adjustable dampers in the pylons... But such things react relatively slowly and have a limited range of movement.
They actually have calculations of the track response to impulses like earthquakes (figures 15 through 20 illustrate peak deflections, stress, and shear). Dampers responding slowly is exactly the point; they don't move immediately when they face a jolt, but slowly react to it, giving time for the control system to compensate (see hysteric dampers and base isolation dampers). Also note that simply shifting the tube around a couple millimeters one way or the other does not create a meaningful deflection for the vehicles, even at Hyperloop vehicle speeds. Also note that the capsule skis are mounted on a suspension system designed for ~10hz jolts, and that air bearings have a highly nonlinear response to float height changes.
In a hyperloop, tens of millimetres of offset between two sections of the pipe will cause enormous, injury inducing g-forces on the occupants of the vehicle.
This is not true. Let's take the suspension system out of the equation for a minute. Let's say 20 millimeters, sound good? 30 meters per pylon, so at 340m/s that's 89ms. 20mm in 89ms is ~0,22m/s average velocity (in one direction for the first 30m, then reversed for the next 30m). Which means an acceleration of about ~0,45 m/s^2, or 0,046g. An insignificant amount.
I've actually done the calculations before for the complete loss of all support from a tower, how much sag that would impose on a pipe as described, and how much g-forces that would translate to. The short of it: not all that much.
It might be possible to overcome this by making the pipe larger relative to the vehicle, but then the whole thing becomes less efficient.
I think you've misunderstood something. Increasing the pipe diameter makes it more efficient, not less. The skis remain in close proximity to the wall regardless of the size, but you're reducing the ram air effect by having a larger bypass, and thus reducing the compressor load (as well as enabling a longer suspension deflection stroke). The pipe isn't small to make it efficient, it's small to save construction costs.
Compare this to the maglev trains developed in Japan.
It's not really a proper comparison, now is it? Japanese rail tracks aren't damped. If you want to compare to damped systems, damped bridges are your best comparison point.
To be honest, the whole document is a bit... For example, it talks about how a quiet supersonic aircraft would solve all the long distance problems, apparently unaware of the high cost in terms of fuel consumption / pollution and smaller cabins.
It's not the only problem with supersonic travel, but it is the limiting factor for Hyperloop-length journeys (for reasons which are accurately stated in the document): you have to spend so much time flying subsonic to get to altitude that you lose much of the advantage of the high peak cruise speeds. Other issues are addressable. What you refer to in terms of fuel consumption / pollution and cabin size by and large all come down to drag. There is a huge wave drag at transonic speeds, but it drops with increasing speed. Subsonic cruise is fundamentally more efficient than supersonic, but not prohibitively so for supersonic travel. There's lots of other issues that can be added to the list of problems, mind you -
Slashdot Mirror
Not sure which trails you went on, but glad you enjoyed them. :) They're of course mixed quality - the Reykjadalur one used to be a "mud bog" trail, but they've since fixed it because it got popular. But in general we do a good job, I think. Especially given that "mud bog" is kind of the default state around here ;)
Speaking of that... ;)
I actually watch and enjoy them all. But Slashdot does not.
Anyway, spoiling it for those who didn't see it: nice clean landing (despite the stormy weather at the landing ship and the new experimental titanium grid fins), SECO completed as nominally, awaiting startup 2 after the S2 coast phase (40 mins).
Slow news day.
Reminds me of news in Iceland. I remember one time reading an article about how two Icelanders were at an episode of the Tonight Show or something like that. Not on the show, just in the audience ;) Checking the news right now, I see one article about an unattended rooster seen walking around a national park.
The expansion joints thing is just another example of why you don't turn to a biochemist for a lecture on engineering. Most HSR doesn't have expansion joints either. Lots of things don't have expansion joints. There are three standard ways in industry to deal with thermal expansion: 1) resist it, 2) let it expand by increased bend radii, 3) let it expand by increased linear length. All three are widely used. In HSR, it's common practice to use the "resist" approach - they generally lay the track hot, so that when it cools it contracts and there's built-in tension on all but the hottest days. They usually use heavy and/or anchored ties (commonly concrete) to resist track movement. Pipelines generally use some combination of #1 (e.g. overburden anchoring), #2 (e.g. expansion loops) or #3 (e.g. slip-type expansion joints). Hyperloop wants to use #3, with the dampers as slip joints (e.g. like teflon shoes on pipelines). Whoop-de-doodle-doo. Even if that sort of thing wasn't already a common solution for thermal expansion, they could always just switch to resisting expansion, with a pretensioned tube, like the rail on HSR.
Not as comfortable or convenient, though. Shinkansen is a great way to travel. Arrive, buy your ticket, walk straight onto the platform, catch whatever train happens to be next and going in the right direction, take whatever seat (much roomier and more comfortable than airplane seats), then relax and enjoy the ride.
Hyperloop itself isn't designed for journeys of that length - it's designed to be optimal for intermediary length trips, with trains better for shorter journeys and aircraft better for longer journeys. That said, it is possible to make Hyperloop have a higher top speed (and thus reduced long-distance travel time) by increasing the sonic velocity of the gas - aka, via either increasing the temperature of the (highly rarified) gas inside the tube, or by using a (rarified) light gas such as hydrogen or helium. The latter requires increased tube evacuation pumping to minimize the fraction of leaked-in-air in the tubes. The former may happen to some extent on its own due to compression heating from passing Hyperloop capsules (the tube itself will be an effective thermal radiator, but the gas inside (due to its very low density) will not be very effective at transferring heat into the tube). Both lighter and hotter gases not only increase the sonic velocity, but also decrease air resistance (particularly using light gases). The low densities mean that you don't use great quantities of gases - meaning that the amounts of helium are affordable and loss rates acceptable, while hydrogen would not be prone to embrittling the tube or presenting a tube explosion hazard even when mixed with leaked-in air (although its behavior inside the capsule compressors / air bearings / etc needs consideration). Rarified water vapour, ammonia or methane atmospheres would also allow improved speeds of sound vs. air, although not to the degree of hydrogen or helium.
Another issue for long-distance travel via Hyperloop is that the faster you go, the greater the minimum bend radius. Not so much of an issue when you're going over flat plains, but once you start getting into uneven terrain it can present problems. "Floating Hyperloop" is particularly appealing for when dealing with very high speed travel due to the ability to sculpt bend radii as gently as you want over open ocean.
The Hyperloop design document doesn't consider that other technology can't or won't advance as well. But for at least intermediate-distance travel, they argue - convincingly, in my opinion - that increased aircraft speed, even if associated with improved economics, can't beat out Hyperloop. This is because of the simple reason that increasing aircraft speed means increasing altitude (to reduce the velocity-squared drag and to avoid sonic boom effects on the surface), which means increased subsonic climbing and descent times. Not a problem for long journeys, but for intermediate hops, that looks like a fairly fundamental barrier.
VDUs are also much higher diameter, which makes them harder to design, not easier. And the feed lines can have very high length to diameter ratios.
It's the same engineering principles. The amount of structural reinforcement - both wall thickness, and reinforcing rings - to resist implosion is very well understood engineering and there are standard guidelines for it. Thunderf00t's ignorant nonsense to the contrary headlined with comic sans text done in what looks like MS Paint notwithstanding.
The share of vacuum-related energy required equates to pennies worth of electricity per passenger-trip. And the energy density of the tube is orders of magnitude less than a tube full of typical hydrocarbon fuels (aka a pipeline). The maximum instantaneously deliverable power at a point of rupture is also orders of magnitude less than that of a collision of a loaded passenger train.
Right. Because when I want an engineering analysis, I always turn to an organic chemist.
Meanwhile, in the real world, mild or hard vacuum lines and chambers are widely used in industry (for example, see VDUs), and designing a structure to be stable against vacuum, including in catastrophic-rupture scenarios is basic engineering. Believe me, the VDU and its low pressure lines are not what people at refineries fear ruptures in - if you want to see some alarm, rupture a line for a hydrocracker.
That's not in the slightest "how they're selling it". Read the design document. To reiterate that which for some inexplicable reason has to be repeated in every thread about Hyperloop: the Hyperloop Alpha design:
* Is not a pneumatic tube
* Is not a vacuum train
* Would not even work in a hard vacuum
* Is not maglev
* Is a ground-effect aircraft / air-bearing suspended vehicle in a highly rarified atmosphere, utilizing a battery-powered compressor to shunt the air built up ahead of the vehicle to the suspension and behind the vehicle.
Your failure to read anything about how it works is nobody's fault but your own.
You've got that backwards. Unclassified content created by the government is automatically public domain .
"Waaaah, someone is saying something mean about my president, waaaaah! He's saying that it looks more and more like obstruction of justice and treason and that that several people involved in the campaign and administration already have grand juries against them while the investigation expands every several weeks to include new persons of interest as investigation keeps turning up new evidence of wrongdoing, waaaaah! Somebody stop the big mean liberal, he's hurting my feelings!"
Which Comey didn't do. Comey does not have the memos, and did not leak the memos. He leaked a description of their contents. Which was made very clear during the hearing, where he stated that he hopes that the FBI gives the investigation the actual memos.
For your argument to work, you'd need to be arguing that "talking about non-classified matters is prohibited, because your knowledge of said non-classified matters remains the property of the employer". By all means argue that.
Also made clear was the fact that the memos weren't classified, and they were deliberately written to not contain information that was classified, so that they specifically could be made public if the FBI needed to defend itself against charges of what Comey perceived to be a White House attempt to influence an investigation.
Comparing this to the leaking of classified information is silly and bordering on clickbait. And what the heck is this crappy site that Slashdot is linking to as its article source?
I totally get it. I don't want a car until they can stop them from breaking down
I've seen so many cars (people I know) break down (farm equipment, too) after just a few years, but I've had the same horse for thirty years and the same mule for twenty.
Also, re: my lawn? Get off it.
Composites are cheap in small volumes relative to metal stamping because of the low tooling costs; you can carve a mould out of styrofoam if you want. But metal stamping is generally cheaper in large volumes; there's more steps in making a composite part, there's the curing times, there's often a higher defect rate, automated production equipment is more complex, and so forth. There's a lot of work trying to achieve lower mass-production costs for composites, and I really do think they're the future. But the future is not quite here.
I really respect what Boeing has been doing with the Dreamliner. They've taken a real risk, and it's costing them a lot of money. But anything to push forward large-scale composite usage production is good in my book.
BTW, your mention specifically of CF: one thing that's kind of neat that you're starting to see now is carbon/dyneema weaves. And it took me a bit to really catch onto the point of it, but I really like it. Basically, dyneema = UHMWPE = ultra high molecular weight polyethylene. Low density (even floats in water), but still with a good tensile strength; its specific tensile strength (aka strength per unit mass) is nearly as good as carbon fibre's. It's not frequently used in laminates however because it's extremely slick and doesn't adhere well with most resins. It's also UV sensitive, but additives and coatings can work around that. Its specific compressive strength is also worse than carbon fibre's - but on the upside it's also much better at energy absorption than carbon fibre (aka not likely to shatter). So combining the two into a single weave, you still get excellent mechanical properties, but it's not brittle.
But here's the neat part: yes, UHMWPE has a slightly lower specific tensile strength vs CF. But that's not the figure that actually matters. Because the density is lower, a sheet of equivalent tensile strength is thicker if there's spectra in the weave. And thickness matters hugely when it comes to bending resistance - that's why sandwich composites are so much stronger than single layers, why you use trusses in large structures rather than just simple beams, and why you use hollow beams or I-beams rather than solid ones. If I recall the formulae correctly, stress is proportional to the distance from the centreline to the third power, while deflection is proportional to its fourth power. So the fact that the composites are less dense adds an unexpectedly large amount of strength. And that strength carries over when you use these stronger layers in sandwich composites, trusses, tubes, etc.
More specifically, motor wear increases significantly as you go into the high end of the RPM range. Most EVs don't use a multi-gear transmission, so to get more top-end speed you have to choose a different gear ratio, which reduces your low-end torque. EVs are excellent on low-end torque in general, but it's not unlimited; as you keep dropping the RPM, eventually torque flatlines, due to either mechanical or electrical limitations. And most customers would rather have fast accel that they can actually use instead of crazy top speeds that they never get to experience. Unless they're buying it as a track car, that is.
Technically it's possible to reduce wear at high RPMs, which provides another way to get a higher top speed - and EV motors have been moving in this direction. But the torque / top speed tradeoff will always remain, unless you add in the weight, cost and maintenance of a multi-gear transmission.
And costs an insane amount per shot, with very restrictive (and predictable) "firing" windows due to orbital dynamics. If you really want kinetic energy weapons, there's a much better way: railguns. The goal is to be able to fire a dozen or so rounds per minute, many tens to hundreds of kilometers, with precision hits having the ability to penetrate any armour and almost any traditional fortification, with ammunition being cheap (~$25k per shot) and able (due to its small size) to be stored onboard in great quantities with no risk of inadvertent explosion. Fragmenting shells should also make for superb air defense systems. The rail lifespan problem seems to have been largely solved; they should be able to get a thousand or so shots off between replacements.
You'll never manage that sort of price performance with an orbital system.
Now, there's somewhat of a chicken-and-egg problem with kinetic energy penetrators... the same problem that hit the Zumwalts' guns when the ship production numbers were slashed. GPS-guided artillery shells are certainly possible; see for example the M982 Excalibur, which has a CEP of around 5 meters, based on tech that's now over 10 years old. The issue is cost. You can get the ammunition down to just a couple tens of thousands of dollars per shot, since there's nothing fundamentally expensive about it - but you need to order it in huge quantities to do so. Meaning you have to make a big gamble that widespread deployment of all aspects of the system will work in order to justify such large purchases. If you purchase it in small quantities, you end up having to pay cruise missile-prices per shot, defeating a lot of the purpose. Widespread deployment doesn't come without a cost; you have to remove other combat systems to make space for the gun, its ammunition and capacitor buffer. Only the Zumwalt and Ford classes (3 ships total at present, and not many more in the near future) have enough power to run one directly; all other ships also require a battery bank.
And of course, because you can find everything on the internet...
One may note that what the average person thinks "looks aerodynamic" often doesn't correspond to what actually is aerodynamic. The Saturn Sky sure "looks" aerodynamic (top up), but its drag coefficient is 0.42. The Dodge Viper is even worse, at 0.45, and the Ford Mustang ranges from 0.44-0.48. Meanwhile, the definitely not-sleek looking Ford Escape has a drag coefficient of 0.29. The SUV has a much larger cross-sectional area, of course, but that's beside the point -cross-sectional area is useful, but a high drag coefficient is not. Well, with one exception: a number of "sporty" cars get deliberately bad drag coefficients by being designed to create downforce (for an ideal streamlined shape you want no net lift); a Formula 1 car can have a drag coefficient of over 1.0, deliberately, in order to get as much downforce as possible to maximize its grip on the road. But for the most part, when a mass-market car has a bad drag coefficient, it's to play to people's style preferences, not for any functional reason.
Parent makes the right response. Aerodynamics doesn't care what you think of how it looks; it is what it is. If you want to know what the extreme end of aerodynamic streamlining looks like, the Aptera 2e was a pretty close example to maximizing it for a road vehicle. There's various decisions one can make about how they'd like their internal area laid out, and this affects the particulars of the optimal shape, but in general: front end like a deformed egg, all surfaces highly smooth with as few panel gaps as possible, air intakes as small as possible, steady transition from hood to windshield, wiper hidden, mirrors small and streamlined (or ideally, absent and replaced with cameras), maximum diameter reached relatively quickly (no fat front end pretending there's a huge engine inside) followed by a long gradual taper; taper ends at a line or point (line usually allows for a better use of internal space), wheels small and shrouded, exposed all struts shaped as airfoils, and as little exposed hardware as possible. Cabin air ejected through whatever flat rear surfaces you have can help reduce the wake. Where you can't taper to a line or point (aka, you want to have a space that's both tall and wide behind the front seats for additional passengers), an abrupt cutoff (kammback-style) is better than a steep taper; if your taper is too steep, you get flow separation, and you start dragging a low pressure wake from that point. Deliberate vortex generation at the point of expected flow separation can help reduce the size of the wake; this is often done with overhangs, vortex-generating spikes, or in some unusual cases, golfball-like dimples. Higher driving speeds, as well as crosswinds, require a shallower tapering angle to avoid flow separation; concerning crosswinds, a bit of a lateral taper can help as well.
Once you get into extreme streamlining, however, you have to become more of a niggler for details. A traditional exposed set of windshield wiper would double the drag of an Aptera-like vehicle, for example. If you let snow and ice accumulate on the vehicle, you've totaled the drag coefficient. On the upside, those smooth curves and slick composite surfaces help resist accumulation. A funny thing with the Aptera was that if the vehicle was out in the rain or you sprayed it with a hose, almost all of the water ran off the same point, in the bottom centre of the vehicle. :)
A male Falcon rocket is technically known as a "tercel".
Indeed. And I'm sure they have quite a bit of money wrapped up in the X-37B.
In English, concerning physics, "resistance" generally means electrical resistance, thermal resistance, or drag (e.g. "air resistance"). How bodies deform under stress is studied via finite element analysis (FEA / FEM).
And as was pointed out to you, the issue has nothing to do with the bullet or the water, it's that in a gun you're dealing with several thousand atmospheres of pressure. It's like if someone said "this house would collapse if the roof has to bear five meters of snow but not one meter of snow", and you said, "but what if the one meter of snow was moving at a good fraction the speed of light?" It's not at all relevant to the problem at hand.
If you remove the completely-inapplicable-to-Hyperloop thing you're adding to the conversation (the pressure from the exploding gunpowder), then yes, you can directly compare a bullet sitting in a gun vs. water sitting in a water gun, as simple mass loadings.
Your comparison was different to the point of being ludicrous. :)
The same mass of water? Actually the water would do a pretty damned good job. Ever seen what a non-abrasive water jet cutter does? That's what happens when water moves at bullet-speeds, even tiny amounts of water. The faster the object, the more it's just the kinetic energy that matters and the less that the object's structural integrity matters. If you had a bullet's mass worth of water moving at bullet speeds, it'd cut deep into a person, if not right through. High speed liquid jets are how shaped charges pierce through armour. As a matter of fact, water charges are shaped charges that use water as their piercing fluid.
Now, I'm pretty sure that you're in a weird way trying to make some sort of point about how the distribution of loads matters - am I understanding you correctly? Good. Except that as I pointed out, the distribution of loads is similar for a Hyperloop capsule and a fluid - most on the bottom, less on the sides, little on the top. The exact distribution depends on the final choice of ski locations and the ratio of ski pressure vs. compression pressure**, and it is more uneven than carrying a fluid - but nearly an inch of steel will have zero difficulty whatsoever distributing such loads from an object that only weighs a few tonnes. Image how much an arch of inch-thick steel would deform if you drove a loaded pickup onto it. Basically nothing, right? Exactly. The only relevant potential for deformation is linear, along the pipe's length - so it doesn't matter whether the mass is a fluid or a capsule, it just becomes simple mass loadings - and only the amount of mass, not the type, matters.
** - And if you don't think it's even enough? Just add more skis.
The only practical difference is that the Hyperloop loads are transient, while the fluid loads are permanent. But transient loads are generally to a structure's favour. As noted previously, even if the added loads weren't borne at all and the pipe went into free fall every time a capsule passed, it would only drop a couple centimeters.
Back to the beginning: versus a pipeline and HSR, Hyperloop's loads peak loadings are dramatically lower, and they're transient. Elevation costs are directly proportional to mass loadings.
First off, thanks for actually reading the document. These discussions are a lot more enjoyable when 90% of responses aren't just "RTFM" ;)
They actually have calculations of the track response to impulses like earthquakes (figures 15 through 20 illustrate peak deflections, stress, and shear). Dampers responding slowly is exactly the point; they don't move immediately when they face a jolt, but slowly react to it, giving time for the control system to compensate (see hysteric dampers and base isolation dampers). Also note that simply shifting the tube around a couple millimeters one way or the other does not create a meaningful deflection for the vehicles, even at Hyperloop vehicle speeds. Also note that the capsule skis are mounted on a suspension system designed for ~10hz jolts, and that air bearings have a highly nonlinear response to float height changes.
This is not true. Let's take the suspension system out of the equation for a minute. Let's say 20 millimeters, sound good? 30 meters per pylon, so at 340m/s that's 89ms. 20mm in 89ms is ~0,22m/s average velocity (in one direction for the first 30m, then reversed for the next 30m). Which means an acceleration of about ~0,45 m/s^2, or 0,046g. An insignificant amount.
I've actually done the calculations before for the complete loss of all support from a tower, how much sag that would impose on a pipe as described, and how much g-forces that would translate to. The short of it: not all that much.
I think you've misunderstood something. Increasing the pipe diameter makes it more efficient, not less. The skis remain in close proximity to the wall regardless of the size, but you're reducing the ram air effect by having a larger bypass, and thus reducing the compressor load (as well as enabling a longer suspension deflection stroke). The pipe isn't small to make it efficient, it's small to save construction costs.
It's not really a proper comparison, now is it? Japanese rail tracks aren't damped. If you want to compare to damped systems, damped bridges are your best comparison point.
It's not the only problem with supersonic travel, but it is the limiting factor for Hyperloop-length journeys (for reasons which are accurately stated in the document): you have to spend so much time flying subsonic to get to altitude that you lose much of the advantage of the high peak cruise speeds. Other issues are addressable. What you refer to in terms of fuel consumption / pollution and cabin size by and large all come down to drag. There is a huge wave drag at transonic speeds, but it drops with increasing speed. Subsonic cruise is fundamentally more efficient than supersonic, but not prohibitively so for supersonic travel. There's lots of other issues that can be added to the list of problems, mind you -