Hyperloop Bankrupt and Busted.

[CarlBar]

15 minutes ago, leadeater said:

That is the inverse situation though, you are containing a high pressure in a low pressure environment. Hyper loop is containing low pressure in a high pressure environment so the force acting on the structure is not the same. A spacecraft wants to "explode" and a hyperloop wants it "implode".

 

It's why SpaceX can use carbon fibre just fine while other recent example could not.

 

As i noted in my last reply, all it does is change the type of load. Compressive strength is generally lower than tensile for a given material, (exceptions like concrete exist), but so long as you account for that it's not a major issue. 

[leadeater]

7 minutes ago, CarlBar said:

As i noted in my last reply, all it does is change the type of load. Compressive strength is generally lower than tensile for a given material, (exceptions like concrete exist), but so long as you account for that it's not a major issue. 

Well it does matter a lot of carbon fibre though, not that they were intending to use that. Any composite material like that the difference in force is critical since none of them handle compression and delaminate or splay apart and critically fail. It's a really bad time when you use the wrong material for an application. We just don't often get such clear examples about that and reported so widely.

 

Composite materials like standard carbon fibre and fibre glass just aren't safe to use in applications like this because their rated capacity is not static or uniform across the structure and essentially they get weaker and weaker over time and will always fail. Metals will too, the time span is just many orders of magnitude longer.

[CarlBar]

7 minutes ago, leadeater said:

Well it does matter a lot of carbon fibre though, not that they were intending to use that. Any composite material like that the difference in force is critical since none of them handle compression and delaminate or splay apart and critically fail. It's a really bad time when you use the wrong material for an application. We just don't often get such clear examples about that and reported so widely.

 

Composite materials like standard carbon fibre and fibre glass just aren't safe to use in applications like this because their rated capacity is not static or uniform across the structure and essentially they get weaker and weaker over time and will always fail. Metals will too, the time span is just many orders of magnitude longer.

 

Oh absolutely, but given who else i'm replying to in the thread i felt it needed to be said specifically about what t means at the engineering level. i should note for your benefit the hoop stress calculation is still a fairly coarse one as material flex needs to be accounted for. It's not a major problem to do, but it's a more complex formulae and i'm not familiar with the specifics, (i can calculate the flex given the right material properties info, but feeding that back into the formulae for calculating strain is fundamentally a recursive problem, so some additional stuff will be needed).

[leadeater]

38 minutes ago, CarlBar said:

Oh absolutely, but given who else i'm replying to in the thread i felt it needed to be said specifically about what t means at the engineering level. i should note for your benefit the hoop stress calculation is still a fairly coarse one as material flex needs to be accounted for. It's not a major problem to do, but it's a more complex formulae and i'm not familiar with the specifics, (i can calculate the flex given the right material properties info, but feeding that back into the formulae for calculating strain is fundamentally a recursive problem, so some additional stuff will be needed).

My Solidworks usage stopped at 1st year Uni and we didn't do anything near that complicated, at this point my memory of how to even use Solidworks would be nothing more than "ooo pretty colours and, omg too many options!".

 

Definitely something for a computer simulations rather than basic formulaic evaluations though, good enough for general viability checking though.

 

Anyway pipes in a vacuum and pipes with pressure differentials, internal being lower, is not uncommon and there is actually what appears to be standard industry ratings and guidelines. Basically, this is not new and novel usage we are talking about.

 

Quote

Negative-pressure (vacuum) might develop in the following cases:

1. When a pipe is installed in vacuum-feeding pipelines.
2. When a pipe is installed in a steep inclination, causing rapid free flow.
3. Extreme temperature changes of the transported liquid.

If a Pexgol pipe collapses, it results in an oval deformation.

Note that when a Pexgol pipe collapses due to vacuum, it can be returned to its original round shape by applying internal pressure.

The amount of vacuum that a Pexgol pipe can withstand depends on the pipe’s SDR. A pipe with sufficient wall thickness must be selected in order to resist the collapsing forces generated by the vacuum.

Table 51.1 shows maximum rates of vacuum supported by Pexgol pipes of different classes and different design temperatures. These values are empirical.

 

 

Quote

* Tested under full vacuum conditions: -1 bar (g) 0 bar (a)

The values in the table are in bar (g) (Bar gauge). For example:
-0.8 bar (g) is equal to 0.2 bar (a) or Bar absolute.
Pexgol pipe class 10 is not recommend for use under full vacuum conditions.

Allowable external pressure

For pipe of uniform cross-section, applying a safety factor of 1.5 which includes the influence of pipe ovality, the maximum allowable external pressure Pc in bar can calculated from the following equation:

Pc = 2618/ (SDR-1)3

• For Pexgol class 10 SDR 13.6 Pc = 0.75 bar
• For Pexgol class 12 SDR 13.6 Pc = 1.0 bar
• For Pexgol class 15 SDR 11.0 Pc = 2.5 bar
• For Pexgol class 19 SDR 9.0 Pc = 5.0 bar
• For Pexgol class 24 SDR 7.3 Pc = 10.0 bar
• For Pexgol class 30 SDR 6.0 Pc = 21.0 bar

Underground Pexgol pipe under vaccum or external pressures

Vacuum, or external pressures, creates hoop stresses in the pipe wall which are combined with the external pressures of the soil. In extreme cases, these stresses can cause the pipe to collapse. Therefore, when a Pexgol vacuum pipeline is installed underground, the vacuum stresses have to be added to the total static and dynamic loads exerted by the soil and all the stresses must be considered. In this case, make sure that the soil around the pipe is compacted. When designing a vacuum pipeline at recommended vacuum conditions, please contact our engineer for consultation regarding installation of vacuum breakers.

https://www.pexgol.com/resources/design-considerations/vacuum-suction-pipelines/

 

Didn't have to go far to find this either, second result on Google 

 

As well as https://www.passuite.com/start & https://iopscience.iop.org/article/10.1088/1755-1315/49/5/052008/pdf

[Uttamattamakin]

4 hours ago, leadeater said:

That is the inverse situation though, you are containing a high pressure in a low pressure environment. Hyper loop is containing low pressure in a high pressure environment so the force acting on the structure is not the same. A spacecraft wants to "explode" and a hyperloop wants it "implode".

Exactly.  @CarlBar see above. 

 

3 hours ago, CarlBar said:

 

Let em unpack this for you.

 

1. A complete vacuum in a pipe still applies a force vector. 

Lets assume what you just said was true if it applied a force vector it would be directed inward not outward.  It would be a "force" or perhaps a fictitious force that would tend to crus the pipe.  

Proof of this suck all the air out of a Balloon.   

 

 

3 hours ago, CarlBar said:

 

2. All going from pressure inside to vacuum outside does from an engineering and physics standpoint is change the load from a tensile one to a compressive one. it's an identical problem in fact, it's just the final load vector that changes.

No it's not identical.  

 

Tensile strength  is strength when being stretched.  That is good for holding in pressure.  See a balloon.  They have a reasonable Youngs modulus and will bend a lot before they break.   This describes most metals. 

Compressive strength   This can describe metals but only in one direction or the other.  For example a metal pipe that might hold on a great deal of weight vertically would crush if force was applied perpendicular to its axis. (Because the bulk modulus is a tensor of rank 2)

 

3 hours ago, CarlBar said:

 

3. No Hyperloop concept is an actual complete vacuum, the all still have some small amount of pressure in them. In fact this applies even to very high end vacuum chambers and outer space. The pressure is so low you can treat it as zero in calculation but true absolute vacuum doesn't really exist as far as we know.

 

 

True absolute vacuum is not needed for this.  If your pressure is as low as it is in say  cislunar space then it is zero. 

As for the vacuum not existing thing you are mentioning that refers to particles being created and annihilated by quantum field theoretical fluctuations. We still call this  0 particle state a vacuum since the particles that pop in and out of existence only last less than a Planck time  

 

I should be writing the syllabus for calc physics right now.  I need to get back to it.  

[wanderingfool2]

3 hours ago, leadeater said:

That is the inverse situation though, you are containing a high pressure in a low pressure environment. Hyper loop is containing low pressure in a high pressure environment so the force acting on the structure is not the same. A spacecraft wants to "explode" and a hyperloop wants it "implode".

 

It's why SpaceX can use carbon fibre just fine while other recent example could not. Although even SpaceX is ditching carbon fibre for their really big stuff.

Well it's a material in compression instead of tension for strength; but the general idea is that you still don't need nearly as much material as being suggested.  (you can also design it so that the material is stressed in similar ways)

 

A massive thing though is that the comparison to something that has 400 atm is frankly a preposterous notion to entertain.  Any vessel that could survive under 10m depth of the ocean should be capable of withstanding a low vacuum.

 

From what I have seen, it seems like even at a 2m pipe you would need less than a 2cm of material (at full vacuum)...although that seems to assume just the material itself instead of designing for larger systems.  [There was a paper, can't find it at the moment that talked about the rule of thumb being about 1/100th for the diameter with safety factor included]

 

4 hours ago, Uttamattamakin said:

To see why you need to consider again the definition of pressure.  Force divided by area. 

400 atm = 5878 PSI

Even at full vacuum you get ~14.7 PSI

 

To make the comparison to a vessel that faces a delta of 400 atm is frankly not right; at half atmosphere that's ~7.34 PSI

 

5 hours ago, Uttamattamakin said:

Thermal expansion issues.  Materials would expand in every direction. 

Thermal expansion matters a lot less though when the proposed installation would be underground...where the exterior temperature fluctuates a lot less.

 

5 hours ago, Uttamattamakin said:

Low vacuum does not save it either.  Since that has almost the same problems as high vacuum along with air resistance.  Not having to deal with air resistance is the whole point of any vacuum at all.  The same savings can come by making your pods more aerodynamic and having them run on rail (high speed rail) or making them very aerodynamic and travel up where there is less air (like a Boeing 737 Max  Ok bad example).  

It's a whole lot easier pulling a partial vacuum than a high vacuum; so no it doesn't have the same problems.

 

As for air resistance, you can't see the forest through the trees; having a lower air resistance lowers the overall drag while going at the same speed.

 

I'm too lazy to look up all the equations and do a more precise thing; but drag is in relation to co-efficient of drag * density * v^2/2 * [something else I forget].  Reducing the density of air by half would reduce the drag by half...so if you say assume going 100km/h, you could go at roughly 142km/h using the same amount of energy.   If you were to pull it to reduce to 0.25 atm, you would be able to achieve speeds of 200 km/h for the same energy.

 

You can only optimize for the co-efficient of drag by so much.

 

5 hours ago, Uttamattamakin said:

As Thunderf00t who is a physicist who specializes in vacuum physics explained in his videos vacuum of even 1 ATM makes a huge difference.   

ThunderF00t has a history of shoddy, ill-chosen numbers based on terrible assumptions.  After all, ThunderF00t famously energy to boil water for tea to be defined as the energy it would take to boil the entire thing to steam

 

Almost everything that I have seen assumes the state to be pretty much a high vacuum

[Uttamattamakin]

In fact at @CarlBar  on the force you think that a vaccum or near vaccum would apply.  We can look at  why this force would have to be directed inward and tend to make the object implode as follows. 

Newton's third law ... in appropriate meme form. 

So for every action on a body, there is an equal and opposite reaction.  This applies to objects that are at rest or in motion in a straight line, neither accelerating or decelerating.    So an object moving in space in a straight line or resting on a table.  If the momentum is not changing the energy is not changing it will just stay in that state forever.  

 

One could object the pipe can resist the force.  Sure if it is an ideal material.  Real actual materials will if the contain a vaccum (or even if not) be crushed if enough force is applied.    A pipe that is 1 KM long may be fine.  One that is 10 KM long maybe not.  100km long and so  needs to take all of that force, and not crush. 

 

There is a reason that larger SSBN's don't really go that deep and the ones that go to the challenger deep are tiny.    The bigger the vacuum chamber the more force is trying to crush it.  (It can also be looked at as storing potential energy that would be released by the implosion of the vacuum chamber.  This is why the results of implosions and explosions tend to look just as gruesome. 

 

[Uttamattamakin]

3 minutes ago, wanderingfool2 said:

ThunderF00t has a history of shoddy, ill-chosen numbers based on terrible assumptions.  After all, ThunderF00t famously energy to boil water for tea to be defined as the energy it would take to boil the entire thing to steam

 

Almost everything that I have seen assumes the state to be pretty much a high vacuum

He also has the history of having a PhD and publications in this very topic.  I mean he certifiably,... literally certifiably... knows what he's talking about. 

 

As for his "shoddy numbers" in his examples in his videos.  Most people who watch those aren't looking to do rigorous calculations.  The idea is to give numbers that are nice, round, friendly and easy to think about. 

[wanderingfool2]

33 minutes ago, Uttamattamakin said:

As for his "shoddy numbers" in his examples in his videos.  Most people who watch those aren't looking to do rigorous calculations.  The idea is to give numbers that are nice, round, friendly and easy to think about. 

He again has a history of literally making up the numbers to fit his narrative [like estimating sizes/weights that are off by a factor of 10x].  It's why I stopped watching him, as he blatantly uses incorrect numbers too often.  Again the example I alluded to was he calculates boiling water for tea for an energy busting...but he assumes the number to boil an entire pot to steam [which requires considerably more energy].  He pretty much promotes himself as though it's educational, but when he misrepresents baseline numbers it becomes an issue.

 

33 minutes ago, Uttamattamakin said:

He also has the history of having a PhD and publications in this very topic.  I mean he certifiably,... literally certifiably... knows what he's talking about. 

There are people who can have a PhD in something and be very stupid when it comes to some basic things in it, I know of a couple...including a computer science doctorate who struggled with everyday computer stuff.

 

His PhD also appears to be in...drum roll please... chemistry...yes chemistry.  Don't confuse working with vacuums in a science based environment to actually KNOWING lets say practical vacuum applications within the world.

 

 

 

Again, the analysis by everyone seems to assume that you will be pulling a high vacuum etc (and assumes the stops will be in a relatively short time).

 

It brings me back to what I was saying earlier, the ability to dig tunnels cheaply is the biggest factor in regards to transportation.  If you could do that, then something like a version of hyperloop might make sense in that pulling a partial vacuum will increase your max speed...but overall I don't think it's viable, but people get caught up on the wrong types of arguments in why it's not necessarily practical.

 

[Sauron]

14 hours ago, wanderingfool2 said:

We've already created such things that can withstand vacuums, it's called spacecraft.

Uh... again... I never said it's impossible, I said it's expensive and impractical. If your mundane high volume public transport option is being compared to spacecraft in terms of technical and economical feasibility then you have a problem.

14 hours ago, wanderingfool2 said:

To address the trains crashing into each other, there would be the concept of block brakes.  Just like on roller coasters, how do they prevent trains from crashing into each other despite some having like 10 - 12 cars on the track at the same time.  I think there is a term for it in the railway already but I only know the roller coaster term.

Roller coasters go much slower, have direct contact with the rail allowing for high efficiency physical braking, only start when the operator decides it's safe for them to start, automatically slow down when they get close to the finish. They aren't on a specific schedule so individual small delays aren't a problem. They (generally) don't have multiple stops.

 

Normal trains have emergency air brakes triggered by the tracks if they aren't enabled for passage afaik, or something similar. It's a physical mechanism that wouldn't be possible, or at least would be much harder, to implement on a maglev.

[wanderingfool2]

50 minutes ago, Sauron said:

Uh... again... I never said it's impossible, I said it's expensive and impractical. If your mundane high volume public transport option is being compared to spacecraft in terms of technical and economical feasibility then you have a problem.

The part I was quoting is where you were referring to the thickness of the walls needing to be thick to the point of not being economically feasible.

 

I'm saying that that is realistically wrong in terms of how much thickness you are assuming you need...the amount of metal required for it I doubt would make it really non-viable when you consider the concept of it being in a tunnel.

 

A large chunk of what makes underground transportation is building the tunnel itself.  So the notion of claiming the cost to build a system that is partially vacuumed isn't correct.

 

I was comparing to a spacecraft to state that to hold back 1 atm of pressure doesn't actually require as much metal as you seem to think.

 

Again the cost to actually dig the tunnel itself and support the tunnel is probably a large chunk of any rail project that is meant for underground.  (And high speed rail, if you are going through cities will have to be either suspended in the air or buried in a tunnel (both of which are not cheap anyways)

 

[Sauron]

21 minutes ago, wanderingfool2 said:

The part I was quoting is where you were referring to the thickness of the walls needing to be thick to the point of not being economically feasible.

 

I'm saying that that is realistically wrong in terms of how much thickness you are assuming you need...the amount of metal required for it I doubt would make it really non-viable when you consider the concept of it being in a tunnel.

Not viable for something that's supposed to substitute a train. For a spaceship the numbers are quite different.

23 minutes ago, wanderingfool2 said:

A large chunk of what makes underground transportation is building the tunnel itself.  So the notion of claiming the cost to build a system that is partially vacuumed isn't correct.

The railway it was supposed to substitute would not have been underground. Subway systems don't generally span thousands of km.

24 minutes ago, wanderingfool2 said:

I was comparing to a spacecraft to state that to hold back 1 atm of pressure doesn't actually require as much metal as you seem to think.

Even a few cm thick steel tube that is multiple metres wide over thousands of km would get expensive quickly compared to literally a couple of beams and a few power poles.

[CarlBar]

10 hours ago, Uttamattamakin said:

Lets assume what you just said was true if it applied a force vector it would be directed inward not outward.  It would be a "force" or perhaps a fictitious force that would tend to crus the pipe.  

Proof of this suck all the air out of a Balloon. 

 

Vacuum does not suck. Any force applied by vacuum is due to a different volume adjacent to it having positive pressure. This is pressure 101.

 

And yes, and the formulae can handle the switch from a tensile to a force, it's a bi directional formulae. All (Pi-Po0)*D does is describe the force exerted on the pipe by the pressure differential. It produces a value in either direction. If the pressure differential is reversed from high inside-low outside it gives a negetive value, which indicates it's a compressive not a tensile load.

 

You are aware that Pi = pressure inside the pipe and Po = pressure outside the pipe? I know i didn't provide a key but it's really freaking obvious to me.

 

Assuming Pressure is measured in pascals and D and T are in meters you should get the resultant stress value out of it in pascals, (or more normally in engineering when i studied you'd use the longform of N per m^2).

 

10 hours ago, Uttamattamakin said:

No it's not identical.  

 

Tensile strength  is strength when being stretched.  That is good for holding in pressure.  See a balloon.  They have a reasonable Youngs modulus and will bend a lot before they break.   This describes most metals. 

Compressive strength   This can describe metals but only in one direction or the other.  For example a metal pipe that might hold on a great deal of weight vertically would crush if force was applied perpendicular to its axis. (Because the bulk modulus is a tensor of rank 2)

 

If a force is being exerted on a material that is under compression that is not in the direction of compression then that force is either a shear load or a tensile load. More usually if it's not at exactly 90 or 180 degrees to the compression load it will be a mixture of different loads. You have to work out the force vectors using basic trigonometry to make sense of it.

 

And engineering has formulas that can define the resultant material bearing capability in the face of all these loads. if it didn't we couldn't build large structures subject to high winds or seismic proofing. 

 

@leadeater Cheers for digging those up, i was probably using much more technical search terms than you when i tried. @Uttamattamakin you'll note there's no mention of length limitations in there. That is somthing you would see if such a thing was a issue.

[leadeater]

43 minutes ago, CarlBar said:

i was probably using much more technical search terms than you when i tried

"pipes under vacuum" 

 

Search engines suffer a lot from TMI so it's typically best to start basic as possible and then narrow in on more specifics or add more search modifiers.

[CarlBar]

9 minutes ago, leadeater said:

"pipes under vacuum" 

 

Search engines suffer a lot from TMI so it's typically best to start basic as possible and then narrow in on more specifics or add more search modifiers.

 

eah i know, i just tend to screw it up when i'm hyper focused on somthing. ASD for you.

[Uttamattamakin]

6 hours ago, CarlBar said:

 

Vacuum does not suck. Any force applied by vacuum is due to a different volume adjacent to it having positive pressure. This is pressure 101.

 

Carl I didn't say that vacuum "sucks" nor did I Imply it.  I just explained to you why car tires go flat, balloons deflate and even a metal / concrete tunnel will collapse if it has enough pressure applied to it.  1 ATM is enough to do that.  There are numerous real world examples of this and I have explained to you the theory on this. 

 

I will jus agree to agree with you.  Think as you like.  Experiments tell the tale. 

 

There you have a not perfect vacuum crushing a steel drum.    1 ATM does that.  

7 hours ago, Sauron said:

Even a few cm thick steel tube that is multiple metres wide over thousands of km would get expensive quickly compared to literally a couple of beams and a few power poles.

 Especially if it is buried.  Would anyone bet their life on that evacuated multi multi km tube maintaining integrity over all that distance?  

Imagine the security needs of such a system. 

Every above ground part  of it would need to be secured against sabotage.  Since if one were to punch a hole in part of it the whole thing will have the atmosphere rush in with enormous force, kin to a explosive device.     Even a small charge would result in mass destruction.  One of the big pluses of a train VS planes is that they need less security.  

 

That said of course one could derail A single train  .. but that wouldn't also derail every other train on the line. 

[wanderingfool2]

9 hours ago, Sauron said:

The railway it was supposed to substitute would not have been underground. Subway systems don't generally span thousands of km.

Again, you are oversimplifying it down to a specific usecase and declaring it's not ever feasible.  Longer distance travelled by trains has been a thing for hundreds of years.  We have overall gone towards things like cheap airlines etc now though; prior to that though we would have trains that connect cities together over hundreds of km.

 

Even stops at like 50 km distance would start making sense...and again many railway systems are going underground these days because you can't just push a railway through a city.

 

9 hours ago, Sauron said:

Not viable for something that's supposed to substitute a train. For a spaceship the numbers are quite different.

Cars aren't viable then because the cost to use a horse is so much less.  I used a space craft as an example in terms of a relative vessel that matched closer to the atm that would be exerted rather than Uta's 400 atm of pressure.

 

9 hours ago, Sauron said:

Even a few cm thick steel tube that is multiple metres wide over thousands of km would get expensive quickly compared to literally a couple of beams and a few power poles.

And you know what, the cost to build thousands of km is already insanely expensive.

 

If you want an example, Canada Line in Vancouver cost over $1 billion in total funding to make...it travels less than 20 km....literally costs $50,000/meter...and again the 2 cm was based on full vacuum, which again wouldn't be practical (but a low vacuum environment would be).

 

The whole thickness also ignores that you can also use concrete walls to help prevent collapse (the 2cm would be based on the metal supporting it entirely though).

 

But hey, lets do a bit of crude math.

 

Assume 2 cm, on a 2 meter tube full vacuum and 1 km of track

It's ~0.25m² of area for a cross section

It's 252m³ for the volume at 1 km.

Assuming carbon steel, which would be ~$5,000/m3

That's only an additional $1.26 million per km...or if you were to associate it with the cost to build the Canada line, it would equate to 2.5% of the build cost of the Canada Line.

 

Again, that assumes a full vacuum.  At 0.5 atm you wouldn't need nearly as much material; and again something that size you would likely also use concrete which is a whole lot cheaper to encompass the steel to allow it to maintain the vacuum with less steel required.

 

2 hours ago, Uttamattamakin said:

I will jus agree to agree with you.  Think as you like.  Experiments tell the tale. 

 

There you have a not perfect vacuum crushing a steel drum.    1 ATM does that.  

"Experiments tell the tale"; and yet all you can conclude from it is a steel barrel can collapse if enough air is sucked out of it.  It's like the companies that claim something is biodegradable, but conveniently leave out details like that the biodegradable means it has to be kept at temperatures above 40C.

 

No where does the experiment state the type of barrel they are using, how many inches of mercury there are, age of the barrel/condition of it, etc.

 

All you have shown is that at some level of vacuum a steel drum will implode.  You don't know if it's a high vacuum/low vacuum/etc.  For all we know, it could be 0.0001 atm before it implodes.

 

Based on the research I did though, a barrel of that size should maintain structural integrity until ~-10 in/hg...and even then that doesn't tell me the gauge of the barrel (it could be 24 gauge for all I know, but most likely below 16 gauge)

 

2 hours ago, Uttamattamakin said:

Every above ground part  of it would need to be secured against sabotage.  Since if one were to punch a hole in part of it the whole thing will have the atmosphere rush in with enormous force, kin to a explosive device.     Even a small charge would result in mass destruction.  One of the big pluses of a train VS planes is that they need less security.  

A shockwave would only be capable of travelling at the speed of sound.

 

No you wouldn't need to have every bit guarded; it's like me trying to say the water lines feeding the city should always be guarded.  It's a whole lot easier to poison a water supply than it would be to try sabotaging something like this.  Yes putting an explosion would create an issue, but I guarantee that if an explosion went off on the underground the line would be down for at least weeks while the damage is assessed and procedures in place to try catching the terrorist.

 

The biggest risk would be the people onboard the train when it happens but that also assumes you can open up the pipe to essentially let in all the air in one quick burst...you effectively have a choke point though which would be limiting the amount of air that could be entered at one time which would limit the overall effect.

[CarlBar]

@Uttamattamakin I'll settle for the agree to disagree but for that video, a 55 gallon drum according to a research paper, (i'll link below), can withstand a maximum overpressure of between 14 and 30 psi with the majority being towards the 14psi figure. Low tensile steels which is what i assume the drum is made of typically have a compressive strength around 60% that of their tensile so 14 psi burst equates to about -8.6 psi (relative to atmosphere, absolute internal would be aroudn 6.1 psi or 0.41 Bar). It's not a suprise it imploded, the drum's material strength is nowhere near enough to handle it. A higher grade steel or a greater thickness would handle it just fine.

 

Go to page 6: https://www.osti.gov/servlets/purl/1202902

 

@wanderingfool2 the problem is he's under the impression that if you double the length of a pipe you double the stress on it, (correct), but do not increase the ability to resist stress, (incorrect), so the maximum vacuum evacuated pipe length you can have is limited.

 

He also seems (hence my vacuum doesn't suck), to be under the impression that 2 atmospheres outside, 1 inside is a lower stress than 1 atmosphere outside 0 atmospheres inside. Without that i could describe a fairly basic home experiment i figure he could run to prove the first assumption false.

[leadeater]

46 minutes ago, CarlBar said:

@wanderingfool2 the problem is he's under the impression that if you double the length of a pipe you double the stress on it, (correct), but do not increase the ability to resist stress, (incorrect), so the maximum vacuum evacuated pipe length you can have is limited.

I believe length is a factor, that research paper on disasters talked about Length to Diameter ratios (L/D) but I didn't read it well enough since I'm not that interested, I know it's possible already so not going to destroy my brain with complicated formulas lol. Anyway ruling out "short pipe" from this since we are talking about "long pipe" (difference does matter) I know stiffening bands are required along the length to compensate for deflection and deformation to maintain the proper ability to withstand the pressure differential. I'm not sure if it's only that and it's purely the pipe thickness and material for the actual containment strength but either way an infinitely long pipe can withstand the same pressure, that's what a "long pipe" is and the mathematics behind it, just need those mention stiffening bands along it at the required interval distances based on the mathematical simulations.

 

tl;dr length of pipe as no effect on required pipe wall thickness far as I know, I know little and want to continue to know little lol.

[CarlBar]

1 hour ago, leadeater said:

I believe length is a factor, that research paper on disasters talked about Length to Diameter ratios (L/D) but I didn't read it well enough since I'm not that interested, I know it's possible already so not going to destroy my brain with complicated formulas lol. Anyway ruling out "short pipe" from this since we are talking about "long pipe" (difference does matter) I know stiffening bands are required along the length to compensate for deflection and deformation to maintain the proper ability to withstand the pressure differential. I'm not sure if it's only that and it's purely the pipe thickness and material for the actual containment strength but either way an infinitely long pipe can withstand the same pressure, that's what a "long pipe" is and the mathematics behind it, just need those mention stiffening bands along it at the required interval distances based on the mathematical simulations.

 

tl;dr length of pipe as no effect on required pipe wall thickness far as I know, I know little and want to continue to know little lol.

 

Basically yes. Making the pipe wall thick enough all the way along to resist the effects of flex on load, (flex stretches the material which thins the wall thickness which reduces load bearing capability), would require more material than putting specific stiffener rings, (basically points of low flex), in at specific intervals. I won't get more detailed than that :).

[HenrySalayne]

17 hours ago, Uttamattamakin said:

One could object the pipe can resist the force.  Sure if it is an ideal material.  Real actual materials will if the contain a vaccum (or even if not) be crushed if enough force is applied.    A pipe that is 1 KM long may be fine.  One that is 10 KM long maybe not.  100km long and so  needs to take all of that force, and not crush. 

???

The length of the pipe is completely irrelevant...

Do the math. You have a pipe with twice the length, twice the surface area and twice the force applied to it but twice the material to withstand this force. It doesn't matter...

[Uttamattamakin]

4 hours ago, HenrySalayne said:

???

The length of the pipe is completely irrelevant...

Do the math. You have a pipe with twice the length, twice the surface area and twice the force applied to it but twice the material to withstand this force. It doesn't matter...

The length of the pipe is not irrelevant. Same for you @CarlBar  and others. 

https://cds.cern.ch/record/1046848/files/p31.pdf

So says not I says cern. 

 

The SPAN (length) AND  Thickness matter.  Don't be mislead.  It matters.   There are many reasons we can't build a proton accelerator of arbitrary size.  Magnets and energy and funding being big ones.  The difficulty of making a very good long vacuum chamber is a real challenge.    

These are the people that built and run the Large Hadron Collider.   If their word isn't good enough then whose would be? 

 

These are a matter of what stress and strains will be applied given the size of the tube and if there is a material that can resist those.  To make all the above simpler.  Bigger chamber, harder to build, more likely to implode.  Not impossible just difficult to a point where it makes no sense to do it. 

 

[leadeater]

5 hours ago, Uttamattamakin said:

 

From what I see all of what you quoted is for a beam and not a tube, which is what I would assume a hyper loop internal would be with an outer that is not at low pressure or closer to atmosphere than the internal tube.

 

Quote

No length in the equation.

 

Quote

The buckling pressure can also be computed through analytical formulas, depending upon the geometrical parameters of the tube and the Young’s modulus of the material. The most conservative one is for an infinite length of the tube:

ν being the Poisson ratio and (1 – ν 2) could be generally approximated by 0.9. A rule of thumb is that the thickness of a stainless-steel circular tube should be at least one hundredth of its diameter (safety factor included).

 

 

I hope you can see from above the most appropriate discussion would be circular not non-circular and I would imagine any non-circular structures seen is most likely only the outer and there will be an inner circular tube that is the pressure vessel. 

 

So if we go off the stated rule of thumb a 2m diameter tube would need at least 20mm thickness.

[StDragon]

On 1/14/2024 at 6:37 PM, leadeater said:

Freedom trains? 2nd Amendment trains?

 

Is embracing the term bullet the answer to the perception change? lol

I would prefer a cannonball run. That's one way to shoot across the country. 

[CarlBar]

@Uttamattamakin as @leadeater points out what you provided covers non-circular tubes.

 

Also i'd need to dig through the source PDF in more than a quick glance through, but in the section you provided L  could be as interpreted as referring to what would normally be considered the width, i'm not sure without reading through in more detail, (Engineering formulas can be a bit weird like that, constants are often axis neutral and you have to determine which axis a constant refers to by the way it's used, niot the name or symbol of the constant).

 

I don't have time to dig through in more detail ATM, woke up to a boiler leak and got to move stuff so the repairman can get to it easily, typed this whilst coming round enough to function for that.