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Old August 13th, 2013, 11:46 PM   #41
ramanujann
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So, the tube is needed to create a low pressure system:

Quote:
Short Annotateof figuring out real teleportation, which would of course be awesome (someone please do this), the only option for super fast travel is to build a tube over or under the ground that contains a special environment. This is where things get tricky.

At one extreme of the potential solutions is some enlarged version of the old pneumatic tubes used to send mail and packages within and between buildings. You could, in principle, use very powerful fans to push air at high speed through a tube and propel people-sized pods all the way from LA to San Francisco. However, the friction of a 350 mile long column of air moving at anywhere near sonic velocity against the inside of the tube is so stupendously high that this is impossible for all practical purposes.

Another extreme is the approach, advocated by Rand and ET3, of drawing a hard or near hard vacuum in the tube and then using an electromagnetic suspension. The problem with this approach is that it is incredibly hard to maintain a near vacuum in a room, let alone 700 miles (round trip) of large tube with dozens of station gateways and thousands of pods entering and exiting every day. All it takes is one leaky seal or a small crack somewhere in the hundreds of miles of tube and the whole system stops working.

However, a low pressure (vs. almost no pressure) system set to a level where standard commercial pumps could easily overcome an air leak and the transport pods could handle variable air density would be inherently robust. Unfortunately, this means that there is a non-trivial amount of air in the tube and leads us straight into another problem.
And the compressor on the nose of the capsule is to overcome the Kantrowitz limit and to supply
air to air bearings:

Quote:
Whenever you have a capsule or pod (I am using the words interchangeably) moving at high speed through a tube containing air, there is a minimum tube to pod area ratio below which you will choke the flow. What this means is that if the walls of the tube and the capsule are too close together, the capsule will behave like a syringe and eventually be forced to push the entire column of air in the system. Not good.

Nature’s toAnnotatep speed law for a given tube to pod area ratio is known as the Kantrowitz limit. This is highly problematic, as it forces you to either go slowly or have a super huge diameter tube. Interestingly, there are usually two solutions to the Kantrowitz limit – one where you go slowly and one where you go really, really fast.
Quote:
The approach that I believe would overcome the Kantrowitz limit is to mount an electric compressor fan on the nose of the pod that actively transfers high pressure air from the front to the rear of the vessel. This is like having a pump in the head of the syringe actively relieving
pressure.


It would also simultaneously solve another problem, which is how to create a low friction suspension system when traveling at over 700 mph. Wheels don’t work very well at that sort of speed, but a cushion of air does. Air bearings, which use the same basic principle as an air hockey table, have been demonstrated to work at speeds of Mach 1.1 with very low friction. In this case, however, it is the pod that is producing the air cushion, rather than the tube, as it is important to make the tube as low cost and simple as possible.
Quote:
One important feature of the capsule is the onboard compressor, which serves
two purposes. This system allows the capsule to traverse the relatively narrow
tube without choking flow that travels between the capsule and the tube walls
(resulting in a build-up of air mass in front of the capsule and increasing the
drag) by compressing air that is bypassed through the capsule. It also supplies
air to air bearings that support the weight of the capsule throughout the
journey.
http://www.spacex.com/sites/spacex/f...a-20130812.pdf

Last edited by ramanujann; August 14th, 2013 at 12:01 AM.
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Old August 14th, 2013, 12:27 AM   #42
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Thanks. I started reading the PDF but never got that far. I jumped the gun a bit.
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Old August 14th, 2013, 05:26 PM   #43
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How could it only cost $6 billion? Property acquisition alone would be more than that. Sure he plans to use the Interstate median but Caltrans isn't going to give that away. They will require the Hyperloop team to purchase that property. In addition to that Caltrans will require extensive new property acquisitions adjacent to the freeway for future freeway expansion that would have otherwise used the median.
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Old August 14th, 2013, 08:19 PM   #44
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it has decelerating panels only every 70km

so imagine

earthquake
a pod hits the wall, get anihilated

air rushes in destabilizing all other pods in tunnel and all pods that are in last 70km get crashed horrendesly, since there is nothing to decelerate them, probably even only one accelerating ramp is not enough to get them to stop


this is such a silly idea it is hard to comprehend
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Old August 15th, 2013, 06:54 AM   #45
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Quote:
Originally Posted by Shenkey View Post
it has decelerating panels only every 70km

so imagine

earthquake
a pod hits the wall, get anihilated

air rushes in destabilizing all other pods in tunnel and all pods that are in last 70km get crashed horrendesly, since there is nothing to decelerate them, probably even only one accelerating ramp is not enough to get them to stop


this is such a silly idea it is hard to comprehend
Yeah, because a high speed train doing 300kmh would fare much better in an earthquake

There are other safety features that may get considered or built in, pressure sensors that trigger emergency brakes...or whatever...you don't discard the whole idea because of smaller design or construction issues...you work through them.
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Old August 15th, 2013, 11:37 AM   #46
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Quote:
Originally Posted by Shenkey View Post
it has decelerating panels only every 70km

so imagine

earthquake
a pod hits the wall, get anihilated

air rushes in destabilizing all other pods in tunnel and all pods that are in last 70km get crashed horrendesly, since there is nothing to decelerate them, probably even only one accelerating ramp is not enough to get them to stop


this is such a silly idea it is hard to comprehend
I take it you didn't even open the alpha paper they released right? We'll i'm sure you don't need to. You clearly know more about this than the dozen engineers from SpaceX and Tesla who's been working on this for a year.
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Old August 15th, 2013, 02:51 PM   #47
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This looks very realistic and there is a 69% chance that it will be built.
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Old August 15th, 2013, 03:34 PM   #48
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I think that's an accurate guess. Musk confirmed that he will build the hyperloop technology demonstrator himself, which raises the odds in it's favor.
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Old August 15th, 2013, 04:02 PM   #49
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I don't care if the plans were delivered to us by aliens or a god. I think the concept sounds rather risky and isn't worth scratching all our existing infrastructure plans for.
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Old August 15th, 2013, 08:38 PM   #50
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Quote:
Originally Posted by Econ77 View Post
You clearly know more about this than the dozen engineers from SpaceX and Tesla who's been working on this for a year.
I really doubt they had much to do with this. Otherwise, they would have warned Elon not go public with such half-baked gadgetbahn proposal.
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Old August 16th, 2013, 12:53 AM   #51
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It's not a finished project ready to be build tomorrow. It's an open source project -- everyone can participate by proposing improvements, finding solutions to the problems etc. To do this you have at first read the pdf that was published...
All the non-constructive criticism has nothing to offer...
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Old August 16th, 2013, 06:26 AM   #52
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Just finished reading Elon's PDF of the project. Here are some highlights. Here is a link to the entire PDF. http://www.spacex.com/sites/spacex/files/hyperloop_alpha-20130812.pdf

Quote:

Passenger Capsule


The maximum width is 4.43 ft (1.35 m) and maximum height is 6.11 ft (1.10
m). With rounded corners, this is equivalent to a 15 ft2 (1.4 m2) frontal area,
not including any propulsion or suspension components.
The aerodynamic power requirements at 700 mph (1,130 kph) is around only
134 hp (100 kW) with a drag force of only 72 lbf (320 N), or about the same
force as the weight of one oversized checked bag at the airport. The doors on
each side will open in a gullwing (or possibly sliding) manner to allow easy
access during loading and unloading. The luggage compartment will be at the
front or rear of the capsule.
The interior of the capsule is specifically designed with passenger safety and
comfort in mind. The seats conform well to the body to maintain comfort
during the high speed accelerations experienced during travel. Beautiful
landscape will be displayed in the cabin and each passenger will have access
their own personal entertainment system.

The Tube

The main Hyperloop route consists of a partially evacuated cylindrical tube
that connects the Los Angeles and San Francisco stations in a closed loop
system (Figure 2). The tube is specifically sized for optimal air flow around the
capsule improving performance and energy consumption at the expected travel
speed. The expected pressure inside the tube will be maintained around 0.015
psi (100 Pa, 0.75 torr), which is about 1/6 the pressure on Mars.

In order to keep cost to a minimum, a uniform thickness steel tube reinforced
with stringers was selected as the material of choice for the inner diameter
tube Tube sections would be pre-fabricated and installed between pillar
supports spaced 100 ft (30 m) on average, varying slightly depending on
location. This relatively short span allows keeping tube material cost and
deflection to a minimum.
The steel construction allows simple welding processes to join different tube
sections together. A specifically designed cleaning and boring machine will
make it possible to surface finish the inside of the tube and welded joints for a
better gliding surface. In addition, safety emergency exits and pressurization
ports will be added in key locations along the length of the tube.
A tube wall thickness between 0.8 and 0.9 in. (20 to 23 mm) is necessary to
provide sufficient strength for the load cases considered such as pressure
differential, bending and buckling between pillars, loading due to the capsule
weight and acceleration, as well as seismic considerations.
The expected cost for the tube is expected to be less than $650 million USD,
including pre-fabricated tube sections with stringer reinforcements and
emergency exits.
The spacing of the Hyperloop pillars retaining the tube is critical to achieve the
design objective of the tube structure. The average spacing is 100 ft (30 m),
which means there will be near 25,000 pillars supporting both tubes and solar
panels. The pillars will be 20 ft (6 m) tall whenever possible but may vary in
height in hilly areas or where obstacles are in the way. Also, in some key areas,
the spacing will have to vary in order to pass over roads or other obstacles.
Small spacing between each support reduces the deflection of the tube keeping
the capsule steadier and the journey more enjoyable. In addition, reduced
spacing has increased resistance to seismic loading as well as the lateral
acceleration of the capsule.

In order to avoid bend radii that would lead to uncomfortable passenger
inertial accelerations and hence limit velocity, it is necessary to optimize the
route. This can be achieved by deviating from the current highway system,
earth removal, constructing pylons to achieve elevation change or tunneling.
The proposed route considers a combination of 20, 50, and 100 ft (6, 15, and 30
m, respectively) pylon heights to raise and lower the Hyperloop tube over
geographical obstacles. A total tunnel length of 15.2 miles (24.5 km) has been
included in this optimization where extreme local gradients (>6%) would
preclude the use of pylons. Tunneling cost estimations are estimated at $50
million per mile ($31 million per km). The small diameter of the Hyperloop
tube should keep tunneling costs to a far more reasonable level than traditional
automotive and rail tunnels.

Safety

The vast majority of the Hyperloop travel distance is spent coasting and so the
capsule does not require continuous power to travel. The capsule life support
systems will be powered by two or more redundant lithium ion battery pack
and so would be unaffected by a power outage. In the event of a power outage
occurring after a capsule had been launched, all linear accelerators would be
equipped with enough energy storage to bring all capsules currently in the
Hyperloop tube safely to a stop at their destination. In addition, linear
accelerators using the same storage would complete the acceleration of all
capsules currently in the tube. For additional redundancy, all Hyperloop
capsules would be fitted with a mechanical braking system to bring capsules
safely to a stop.

Cost

The total cost of the Hyperloop passenger transportation system as outlined is
less than $6 billion USD (Table 8). The passenger plus vehicle version of
Hyperloop is including both passenger and cargo capsules and the total cost is
outlined as $7.5 billion USD. Transporting 7.4 million people each way and amortizing the
cost of $6 billion over 20 years gives a ticket price of $20 for a one-way trip for
the passenger version of Hyperloop. The passenger plus vehicle version of the
Hyperloop is less than 9% of the cost of the proposed passenger only high speed
rail system between Los Angeles and San Francisco.
After reading the entire proposal I take back what I said earlier. He clearly thought this through very well. If it is in fact possible to build this for the cost he claims it would be a damn shame not to build it. This is where I expect people like Bill Gates and other billionaires to jump in and do something usefully with their money. This could easily be financed by private investors and made profitable in the long term. Lets hope that there are more wise rich men out there, than just one.

To Elon Musk.
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Old August 16th, 2013, 12:15 PM   #53
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Quote:
Originally Posted by AnOldBlackMarble View Post
After reading the entire proposal I take back what I said earlier. He clearly thought this through very well.
No he did not.

One obvious thing that every structural engineer would spot immediately that he just handwaves away thermal expansion.

For example, for the entire length of the tube, there are no expansion joints. He only mentions that thermal expansion is accommodated for at the end points. But this only works if you have perfectly straight tube all the way. Otherwise, at every curve you will end up with huge misalignments up to the order of tens of meters. And since your tube geometry has to be maintained laser sharp in order not to turn people in capsules to pulp this wont fly.

There is plenty of constructive criticism on curve geometries, headway times, acceleration, capacity (which is ridiculous even if you accept that joke of price estimate) and so on...

http://pedestrianobservations.wordpr...-entrepreneur/
http://stopandmove.blogspot.de/2013/...r-attempt.html
http://greatergreaterwashington.org/...doesnt-add-up/

And on the topic of price it is just ridiculous. For example trans alaska pipeline cost $33bn in todays dollars (that's excluding terminal costs) at twice the length of proposed Hyperloop. And mind you, this is just meant to transport liquid and not people at almost Mach 1, so you dont need big fancy pipes and fancy pylons to support everything. And it was built over land where you did not have anyone.

It is not my intention to denigrate Elon Musk, since he did some very impressive stuff, but with hyperloop he either drank too much of his own kool-aid or this was just marketing stunt to keep him in public eye.

Last edited by tomkeus; August 16th, 2013 at 01:29 PM.
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Old August 16th, 2013, 02:12 PM   #54
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And one thing I forgot. Onion got things straight:

New Super-Fast Transport System Powered By Passengers’ Screams
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Old August 16th, 2013, 02:38 PM   #55
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I'm no engineer (fascinating how everyone suddenly seems to be), but wouldn't a system able to survive severe earthquakes be able to cope with thermal expansion? From the alpha paper:
Quote:
4.5.5. Earthquakes
California is no stranger to earthquakes and transport systems and all built with
earthquakes in mind. Hyperloop would be no different with the entire tube
length built with the necessary flexibility to withstand the earthquake motions
while maintaining the Hyperloop tube alignment.
Additionally, how much does concrete expand? I assume it's nowhere near what's seen in metal.
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Old August 16th, 2013, 03:14 PM   #56
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Quote:
Originally Posted by Econ77 View Post
I'm no engineer (fascinating how everyone suddenly seems to be), but wouldn't a system able to survive severe earthquakes be able to cope with thermal expansion? From the alpha paper:

Additionally, how much does concrete expand? I assume it's nowhere near what's seen in metal.
Single solid steel tube would indeed be able to resists earthquakes very well. But mechanical stress is not the same as thermal stress. Steel simply changes volume under effect of temperature. You cannot escape that.

Concrete does not suffer from much thermal expansion, and if it did it would not be a problem for Hyperloop, since slight expansion of every pylon would not make a lot of difference (probably)

But single 600km steel tube, since it is very long would expand tremenduously. Thermal expansion coefficient of steel is around 13e-6m/(m K) which means that 600km of tube would expand by around 400m between temperature extremes, which would cause huge misalignments in curves. The way oil pipelines deal with thermal expansion is by doing something like on the picture below



and allowing bends to deform slightly. In this way thermal expansion does not accumulate along the length of entire pipeline. This obviously wont work for Hyperloop.

Possible solutions for Hyperloop are to prestress the pipe (as is done for continuously welded rail) or to put expansion joints. Either of these is going to complicate construction and raise the prices immensely.

I mean, none of engineering problems with Hyperloop is unsolvable. The problems is that solving them is very expensive.

Evacuated tube transport is very old idea. Hyperloop is one of them and not particularly original and inventive at that. And the same reasons that have stopped earlier proposals from being built will stop the Hyperloop also.

Maybe, at certain point in the future, it will be possible to do this kind of construction at reasonable cost, and we will see mass transport based on evacuated tubes, but at this point, it is not close to being competitive to established forms of transport in price, reliability or capacity.
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Old August 16th, 2013, 05:46 PM   #57
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Interesting.. They would clearly need some type of solution, not catered for in the alpha paper. Why not write them at [email protected] and ask? You clearly understand the problem
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Old August 16th, 2013, 08:01 PM   #58
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Quote:
Originally Posted by tomkeus View Post
Single solid steel tube would indeed be able to resists earthquakes very well. But mechanical stress is not the same as thermal stress. Steel simply changes volume under effect of temperature. You cannot escape that.

Concrete does not suffer from much thermal expansion, and if it did it would not be a problem for Hyperloop, since slight expansion of every pylon would not make a lot of difference (probably)

But single 600km steel tube, since it is very long would expand tremenduously. Thermal expansion coefficient of steel is around 13e-6m/(m K) which means that 600km of tube would expand by around 400m between temperature extremes, which would cause huge misalignments in curves. The way oil pipelines deal with thermal expansion is by doing something like on the picture below



and allowing bends to deform slightly. In this way thermal expansion does not accumulate along the length of entire pipeline. This obviously wont work for Hyperloop.

Possible solutions for Hyperloop are to prestress the pipe (as is done for continuously welded rail) or to put expansion joints. Either of these is going to complicate construction and raise the prices immensely.

I mean, none of engineering problems with Hyperloop is unsolvable. The problems is that solving them is very expensive.

Evacuated tube transport is very old idea. Hyperloop is one of them and not particularly original and inventive at that. And the same reasons that have stopped earlier proposals from being built will stop the Hyperloop also.

Maybe, at certain point in the future, it will be possible to do this kind of construction at reasonable cost, and we will see mass transport based on evacuated tubes, but at this point, it is not close to being competitive to established forms of transport in price, reliability or capacity.
He does mention expansion joints in several places in the paper and claims to have a solution for the problem. I was also surprised that he wanted to build the tubes from steel, while the pylons from concrete because it is cheaper. It might be smarter to build the tube from concrete as well and directly onto the ground with pylons only as viaducts where the land requires it. I also don't understand his claim that building the tubes on 20,000 pylons is "cheaper" than building rail tracks on the ground? After reading his paper I assumed that because he has already spent money on building Tesla, and SpaceX he has a good idea on costs, but if a rail line is going to cost 30b I don't understand how a more complex tube will only cost 6b???

And what do you think the situation would be if the tubes were build from carbon fiber or some other similar material?
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Old August 19th, 2013, 01:48 PM   #59
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Quote:
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Steel simply changes volume under effect of temperature. You cannot escape that.

Concrete does not suffer from much thermal expansion
Concrete also suffers thermal expansion.
Actually, the expansion coeficient is similar to that of steel. It's this property which allows structures to be built with steel reinforced concrete, without having the steel and concrete rip each other apart due to thermal expansion.
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Old August 20th, 2013, 01:52 AM   #60
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Yeah, because a high speed train doing 300kmh would fare much better in an earthquake

There are other safety features that may get considered or built in, pressure sensors that trigger emergency brakes...or whatever...you don't discard the whole idea because of smaller design or construction issues...you work through them.
yeah it is

its touching ground so it actualy has brakes, only possible ones for this would be to stop stucking air in in the front, which would make pod touch the ground, since cusion would dissapear

dont get me started on accesability

start thinking and stop sucking musk's dick
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