
Hyperloop lets you travel on a resonant acoustic wave? - bjornsing
http://conscienceofanentrepreneur.blogspot.com/2013/07/hyperloop-lets-you-travel-on-resonant.html
======
speeq
"Elon Musks final invention will be a time machine. It will only work once
before exploding. Before entering it, Elon will turn around and tell us he has
done his duty and given us many gifts, and now we must use those gifts to
advance mankind. He hopes great things for us.

We beg for him to stay and aid us further. He smiles sadly, He looks at us
with his tired but happy eyes, shakes his head, and steps into the machine. He
returns to an early 21st century earth...and begins his work once again. As it
has always been, as it always shall be."

~~~
beagle3
Reminds me of Silverberg's amazing short story "absolutely inflexible".

~~~
wallflower
Excellent story. Thanks!

[http://www.sblib.com/book/silverberg-robert-absolutely-
infle...](http://www.sblib.com/book/silverberg-robert-absolutely-inflexible/)

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niels_olson
As a surfer, let me volunteer that it's a bit like a highway onramp: you want
to match speed exactly when the front arrives. Tiny adjustments in speed,
pitch, yaw, roll, and center of gravity make the difference between making it,
falling off the back, and getting eaten.

Mistiming your drop leads to bad outcomes that are directly proportional to
the kinetic energy of the wave and are inversely proportional to the depth of
the water. This is huge kinetic energy with a distance to the wall of,
probably, microns. I want to see how this thing works, but oh, Nelly, what a
wipe-out!

~~~
pedalpete
I'm somewhat new to surfing but am thinking this is slightly different than
what you are imagining. I also know next to nothing about acoustics and wave
forms.

Wouldn't the wave be the height of the tube, and the vehicle be near that same
height? That way you can't "miss" the wave. Unlike surfing their is no room
below the wave for the vehicle do dive and throw the surfer off, and unlike
surfing , a soundwave (to my knowledge) doesn't break, so there is no tumble.
If you enter at the point where you're off the back of the wave, you're
positioned to be picked up by the next wave, which because your vehicle height
is near equal to the height of the wave, your vehicle automatically gets
pushed along.

That's how I'm visualizing it, but I could be wrong.

~~~
johnpmayer
(experienced body boarder/body surfer, novice actual surfer ;-)

I think the point is that, regardless of which wave you decide to catch,
whether it be the first or second one, at some point to need to sync-up. If
you miss the first one, then you still have to speed up or you're going to
miss the second one too.

There's definitely an optimal timing that takes the minimum amount of energy
to accelerate and synchronize with the "sweet spot" of the wave; beginners
need to paddle early and paddle hard, whereas an expert has a better feel for
it and will exploit his or her experience with the timing to expend less
effort catching a wave.

When you surf, paddling up to speed and the timing will make or break catching
a _particular_ wave - which is very important is the "good waves" are rarer.
With an acoustic loop, it's may be more predictable, but you still probably
want to get it right the first time, while you're still in the main
accelerator section of the tube.

------
moomin
Not to be funny, but it seems like every other day has another "hyperloop uses
acoustic waves" article. It's a good guess, but it doesn't even contain new
speculation (another article went into detailed theorising about how cars
would accelerate and decelerate).

Seriously, until we have a solid info, or even a new guess, can we lay off
Hyperloop?

~~~
foobarqux
I wouldn't mind the article if it contained some kind of real analysis as to
feasibility from a physics and engineering perspective. That type of analysis
would be interesting independent of hyperloop.

~~~
PaulHoule
Worst of all this article is just a rip-off (a paraphrasing) of another
article. He is kind enough to point to the original article, but he isn't
adding anything new, just putting the old wine in new bottles.

~~~
gliese1337
No, it's not. The pointed-to article says that if you travel with the density
peak of a sound wave, you get reduced drag, but you'll need some other system
(like a railgun / gauss gun) to actually provide propulsion. This article says
"I bet it's more than that, I bet the sound waves are actually providing the
driving force like in this cool YouTube video of acoustic levitation."

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bencoder
The hyperloop is feeling like the segway at the moment. I remember the hype
before the reality of the segway and everyone being disappointed when they
found out it was just a slightly altered scooter.

~~~
ricardobeat
The hype before the Segway was so immense, that even if they announced
something exactly like the Hyperloop people would have felt disappointed.
People _actually considered anti-gravity belts to be a possibility_ at the
time.

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kyro
For someone who has taken nothing more than undergraduate physics as a
requirement for my degree, can someone explain the benefits/risks of using an
acoustic wave system over others? Has anyone previously looked at this sort of
system for travel? If the wave were to be disrupted and these capsules come to
a screeching halt, how fast of a deceleration are we talking about? Never more
have I wanted to crack open my physics texts again.

And how will this affect the elephants?

~~~
jessriedel
This depends entirely on the drag coefficient of the train car. If the engines
on a supersonic jet cut off, it's essentially a rock traveling at the speed of
sound through still air. I don't believe the acceleration is cataclysmic for
the occupants (although probably jolting). Remember also that normal
commercial gets travel at like 80% of the speed of sound, and they can easily
handle a loss of engine power. (Although maybe typical engine cut-outs are
more gradual than a suddenly ruptured hyperloop tunnel?)

So the train car need only have aerodynamics similar to an air plane in order
to avoid bad stopping forces. An aerodynamic design makes sense anyways since
you want to avoid drag.

~~~
manmal
If the passenger cabin were smaller than the capsule, the cabin's movement
could be softened by hydraulic dampers. This could also prevent casualties
(e.g. through brain trauma, as often happens in train crashes) in case of an
instant halt.

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radarsat1
> the tunnel would be opened up to the outside atmosphere. That would
> immediately ruin the resonance and all capsules should come to a screeching
> halt.

Correct me if I'm wrong, but my intuition is that this would also lead to
quite a bad explosion. I mean, the amount of energy I imagine it would take to
initiate a standing wave between LA and NY should be massive, (and certainly
not a small amount to maintain it either, though far less than the initial
amount if it truly stores the energy well). But if it is _storing_ this
energy, then any rupture should release it quite... quickly. No?

A standing wave is not nothing.. it is a huge amount of pressure oscillating
back and forth in an underground cavity. A controlled hole in the cavity wall
could release it properly, but a crack in the side could effectively lead to
rupture, couldn't it?

Another thing, if the air pressure inside the tunnel is indeed quite high, the
train cars would also need to be pressurized. This leads to some other
potential dangers.. not to mention the time to pressurize would be added to
the total trip time.

~~~
ethanbond
It doesn't need to be a standing wave, it doesn't need to be from LA - NY (it
only needs to be the length of the train), and it doesn't need to be in an
enclosed tube.

------
VLM
A Hyperloop sounds to me like a marketed trademarked copyrighted patented
implementation of a traditional Launch Loop aka Space Fountain. A wiki link:

[http://en.wikipedia.org/wiki/Launch_loop](http://en.wikipedia.org/wiki/Launch_loop)

[http://en.wikipedia.org/wiki/Space_fountain](http://en.wikipedia.org/wiki/Space_fountain)

You could buy a kids toy circa 2005 implementing a model of the design using
what looks like a shoelace and a blacklight. My kids thought it was pretty
cool.

So, take a magnetically controllable loop, like a wagon wheel tire. It'll
collapse under its own weight it stood up. Turns out if you spin a rope
ridiculously fast it inevitably turns into a circle and can support well over
its own weight. Basically you build a linear induction motor to get dragged
along and remove the clamps at the appropriate time. Think of how you can ride
upside down in a roller coaster as long as you exceed critical speed (too slow
and you fall out, whoops)

Compared to a space elevator its well within modern current day tech to build
one. I donno if its economically within modern day ability.

Three major problems, if that dude splits at the wrong time its an unholy mess
as it augers in, and there's something of a dynamic stability puzzle to
stabilize movement and temperature, and finally you need a plan of sorts if
the clamp or whatever you call it sticks and hauls the first stage back for
another go of it.

One optional problem is to build a loop that stores energy by spinning a bit
fast, faster than a vehicle re-entering for a second loop can handle nose
first. That makes the "stuck clamp" hollywood disaster even worse. Of course a
smart engineer would never do that... would they?

There's a fixation on SSTO, of course. However, aside from economic issues,
you can make a real loop thats as worthless as you want, and any delta-v it
gives for free to a launch vehicle is a net win. So make a "mere" 10 mile
diameter one that only replaces the first stage of a launcher, thats cool. How
about reducing the mass fraction for a "SSTO" from 95% to maybe 50%? That
would still be cool, even if its not "SSTO".

If you can't mentally handle this rotating stuff, think of it like a really
long aircraft carrier catapult... so long it can loop back on itself no
problemo. And think of cablecars, although it'll probably be magnetic not
literally clamping onto a cable, although that would be a charming steampunk
aesthetic.

~~~
tommypalm
Except that Musk has said it's the 5th mode of Earth Transport after Trains,
Cars, Airplanes and Boats.

~~~
bjornsing
Excellent point! Throwing in space travel would be obvious feature creep.

------
kineticfocus
There's been a lot of speculation on the hyperloop without accounting the
'air-hockey table' comment from Elon. I personally thought it meant using the
ground effect.

------
jessriedel
I can't figure out how the OP proposal differs from Charles Alexander's. Low
frequency (long wavelength) waves travel around the tube at the speed of
sound. By traveling at the same speed, and correctly choosing a point along
the wavefront, one can take advantage of significantly reduced apparent drag.
It's implicit in Alexander's suggestion that either (a) the total length of
the loop is an integer multiple of the wavelength of the waves, so they are
"resonant" in that sense, or (b) the envelope of the wave is much less than
the length of the loop. (If neither (a) or (b) held, the wave could not be
formed in the first place.)

So what distinction is OP making? That it's resonant, and so definitely (a)
and not (b)? I think it would require a calculation of how fast the wave would
disperse in the tube, which OP has not done.

~~~
lnanek2
I don't think there is any distinction. He's just reblogging. He did link the
original at least.

~~~
bjornsing
Not so, I felt it with my own gut!

Another difference is in Charles' model you would have to travel at the speed
of sound. Due to the shape not being a perfect line airflow will have to be
supersonic somewhere over the surface of the craft. That's generally not good
for energy efficient travel. My "design" allows for the capsule traveling at
subsonic speeds.

~~~
moocowduckquack
I suspect that design by gut is not necessarily a reliable approach to this.

~~~
bjornsing
Yea? Why do you think so? Did you look it up in a book? You should have felt
it, with your gut! [1]

1\.
[http://www.youtube.com/watch?v=OBRKPoAPXEQ](http://www.youtube.com/watch?v=OBRKPoAPXEQ)

~~~
moocowduckquack
and my gut tells me that's how our nervous system works... :)

------
kolev
I can't wait for Elon Musk to silence all the low self-esteem full-of-envy
idiots talking shit about him and mentioning "vaporware" without even
understanding how vaporware works! I bet $100 he'll have a prototype to
showcase given the engineering power at his disposal.

~~~
sachingulaya
I'll take that $100 bet.

~~~
bdamm
And I'll hold your money. Bitcoin, anyone?

------
jboydyhacker
How might one get on and off this thing at these speeds? Perhaps a 2nd loop
near entry/exit points?

~~~
ethanbond
Just like a normal train would - you route off the main track. As far as
actually stopping it, it could just be a "rail gun in reverse" which would
allow it to regain a huge portion of its energy upon deceleration.

------
xd
[http://www.youtube.com/watch?v=qy1w6rTpC2g](http://www.youtube.com/watch?v=qy1w6rTpC2g)

------
asselinpaul
Whatever it ends up being, this is exciting!

------
Tloewald
If the solution involves a tunnel or tube from SF to LA then I fail to see how
it can be as cheap as has been claimed. I suggest it's an accelerator that
launches capsules ballistically, "skips" them to maintain velocity, and
recaptures a good deal of energy on arrival.

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monk_e_boy
Do you ever think that Elon has no plan, but he's just put this idea of a plan
out there and let us crowd source a solution. That would be neat way to solve
an 'impossible' problem.

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dhughes
6,437km/h (4,000mph) to zero is going to be one hell of a stop.

~~~
dkrich
Yeah, where did you get those numbers? The distance from SF to LA is about 380
miles, and the speed of sound is about 760 mph. Whether or not the principles
of sound movement are involved in Musk's plan, the speed is roughly equivalent
if we're talking traveling back and forth in half an hour. Still a jolt, but
you're talking about six times that.

~~~
rorrr2
Either way, pretty much any accident will result in everyone's death.

Car accidents at 50 MPH result in 80% death.

760 MPH is much much much more, considering the amount of energy needed to be
dispersed grows quadratically (E = 0.5 * m * v^2)

~~~
VLM
"Car accidents at 50 MPH result in 80% death."

Actual stats from Great Britain in 2008 on motorways, presumably always speed
limit above 50 MPH, "6% of the total killed, 3% of total seriously injured, 5%
of total with slight injuries." at least per wikipedia.

So there's about a 9 in 10 chance if you crash on a GB motorway, at least in
2008, you'll walk away without a scratch, rather than your 1 in 5 stat.

Also all minor aircraft accidents involve flying faster than 50 MPH although
death from anything but fire is relatively rare. True though, that controlled
flight into terrain at cruise speed doesn't usually leave many large pieces on
the mountainside.

~~~
bigfudge
Given traffic in the UK, I don't think it's a safe assumption all those
accidents were at > 50mph.

------
enko
Like most titles that end with a question mark - "no". Why would you use some
kind of acoustic wave system over tried and true maglev?

~~~
bjornsing
Drag?

And by the way - the title doesn't end in a question mark. ;)

~~~
enko
It does on HN : P

Well, the acoustic idea wouldn't solve drag at all. The craft would still have
to move through air.

~~~
pjscott
I refer you to Charles Alexander's idea, which goes through a bit of the math
for why traveling with the peak of an intense, low-frequency sound wave would
give freakishly low drag.

[http://charlesalexander2013.wordpress.com/2013/07/18/hyperlo...](http://charlesalexander2013.wordpress.com/2013/07/18/hyperloop-
riding-sounds-density-peak-to-exploit-the-drag-equation/)

~~~
enko
Ah, I see. That's an interesting idea. Sounds impractical - if you're going to
do all that engineering work, might as well just get rid of the air in the
first place - but cool concept.

~~~
pjscott
Do you know how difficult it is to build and maintain an evacuated tube of
that size? Not all loopy tubes are created equal.

~~~
enko
As opposed to building this thing, filling it (perfectly) with ultra-high-
power resonant soundwaves of the precise characteristics, and flinging in
shuttles and hoping nothing goes wrong? I don't know, the evacuated maglev is
sort of sounding like the safe, easy option?

The reason evacuated tubes are expensive and difficult is because of the tube,
not because of the evacuation. Once you have a great big tube, reducing the
air inside isn't going to be that big a deal. You don't even need to get rid
of all the air, just maintaining 90% vacuum would be fine, you could whiz down
there at 1000kph as easy as kiss my hand.

Anyway, I'm not a physicist, I am just wondering if people have a full
understanding of the forces involved flinging stuff around at 1000kph+ in an
enclosed space at full air density. It is some serious shit. People are
comparing it to aeroplanes, but at sea level it would be 3x the shockwave a
plane has to deal with. High speed trains in Europe and Japan already match or
exceed the air-displacement issues faced by airlines - and that's one third
the proposed speed of this device. I don't know, man. Sure, in ideal
circumstances you might be able to engineer some low drag trick. Still sounds
like unicycling along the edge of a cliff to me. Near mach 1 in a fully
pressurised tunnel? Dear christ.

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dsrguru
> it's not an evacuated tunnel

Really? I thought it was already established that the Hyperloop is a vactrain
([http://en.wikipedia.org/wiki/Vactrain](http://en.wikipedia.org/wiki/Vactrain)).
Using small cars (say, six passengers) accomplishes the "leaves when you
arrive" and putting solar panels on top of the tunnel accomplishes the storing
energy part. I wonder what the alternative would be and what its advantages
over a vactrain would be.

~~~
jessriedel
He's said explicitly that it's not, although I can't find a primary source for
this quote.

~~~
moogleii
[https://twitter.com/elonmusk/status/224406502188916739](https://twitter.com/elonmusk/status/224406502188916739)

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jengomangofun
Thats clearly nothing to think of :P

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tootie
I have a flight to LA tomorrow. Any chance this will be ready by tonight?

~~~
ctdonath
You're not flying to LA tomorrow. They haven't built the plane yet.

