but lately with smart materials we see that we can manipulate
seismic waves just like electromagnetic waves (manipulate light to
make "invisibility cloak")
Metamaterials and The Science of Invisibility | John Pendry |
TEDxImperialCollege
here in this TED lecture he talks about manipulating the seismic
wave by reshaping ordinary materials:
Metamaterials matter: smart material of future | Nicolò Maccaferri |
TEDxUniversityofLuxembourg
https://www.youtube.com/watch?v=FAF9EJJ9Xm8
so my idea is to take the dangerous Rayleigh wave and guide it away
from the city, like a lightning rod takes the dangerous energy
of the lightning (electromagnetic wave) and transfer it to the
ground.
SEISMIC "LIGHTNING ROD"
we know roughly where the waves will come from, by looking at
geology maps that show fault lines.
for example in this map by the USGS from Wikipedia
(San Andreas fault line), wherever there is a red-orange color
(danger) next to a green color (dense population) we want to take
the guide the red away from the green. so i added the yellow
"lightning" to show in what direction we need to direct the energy
away from dense population:
HOW DOES THIS WORK? COUPLED PENDULUMS
if you've never seen coupled pendulums, i'm putting a few videos
here:
Coupled Pendulums - Sixty Symbols
https://www.youtube.com/watch?v=izy4a5erom8
Coupled Pendulum (minus the bagpipe music) by Dan Russell
https://www.youtube.com/watch?v=CjJVBvDNxcE
the last one is "how does it work" to the "how does it work"
section:
Footnote †: Double Pendulums Are Crazy
by minutephysics
https://www.youtube.com/watch?v=gbJYK7q5ejY
in our case instead of 2 pendulums close to each other, we have 2
masses of land close to each other, let's say this hill and the
neighboring hill.
suppose we can connect them with something, let's say a tunnel with
a paved road inside, that will convey the vibrations between them,
like in the demos you saw with the pendulums.
what will happen with the 2 hills?
the first one will start to shake because the earthquake hit it
first, and normally (without the tunnel) it will transfer energy to
all it's neighboring hills equally.
but once we have the tunnel then almost all the vibrations move fast
into the second hill, and then back and forth, because the walls of
the tunnel are more solid then the surrounding ground, and it's
easier for the vibrations to travel inside a solid medium.
WHAT MATERIALS DO WE NEED? REINFORCED CONCRETE!
so what we need is something like a coil spring that can conduct the
vibration from one "block" of area on the map (with many people)
into another neighboring "block" (with few people). let's say 100
kilometers away.
because there is a lot of energy to transfer i suggest our spring
will actually be a straight metal bar, i think steel is the best.
where do we get 100 kilometer (km) long steel bar? we need to cast
the metal on the spot.
we first dig a long ditch 100 km long, because we need to steel bar
to be buried underground in the depth where this kind of waves
travel. i couldn't find this depth anywhere but from this article:
Dobrin, M. B., Simon, R. F., & Lawrence, P. L. (1951). Rayleigh
waves from small explosions. Transactions, American Geophysical
Union, 32(6), 822. doi:10.1029/tr032i006p00822
i guesstimate about we need to put the steel bar buried under 20
feet of earth, which is 6 meters.
the wave will "want" to travel through the bar because it travels
faster which means more easily there:
Rayleigh waves have a speed slightly less than shear waves by a
factor dependent on the elastic constants of the material.[1] The
typical speed of Rayleigh waves in metals is of the order of 2–5
km/s, and the typical Rayleigh speed in the ground is of the order
of 50–300 m/s.
the Golden Gate Bridge contains about 88,000 tons of steel which is
75,000 metric tons of steel.
1 metric ton equals 1000 kilograms (kg)
so the Golden Gate Bridge weight is 75,000,000 kg.
so if our steel bar is shaped like a cylinder of 100 km height which
is 100,000 meters, and a radius of 1 meter, it's volume would be PI
* radius^2 * height.
volume would be 3.14 * 1 * 100000 = 314,000 cubic meters of steel.
the weight of 1 cubic meter of steel is 7850 kilograms.
so a steel bar would have a weight of 2,464,900,000 kilograms.
so we need almost 33 Goldlen Gate Bridges for one steel bar.
but in a bridge we have a limiting constraint which is the weight
because it needs to hold it's heavy weight above the water so that
ships can pass below the bridge.
here we do not have this limiting constraint, so we can use
reinforced concrete which is concrete with very thin steel bars
inside it, and it has compressive strength (strong against pushing),
and because of the thin steel bars inside it it's also strong
against tensile strength (strong against pulling).
So how much steel do we need now?
The relative cross-sectional area of steel required for typical
reinforced concrete is usually quite small and varies from 1% for
most beams and slabs to 6% for some columns.
so the 95% of the mass of our "lighting rod" is made from concrete
which is 50 times cheaper than steel!
so i think the best way is to dig one long 100 big ditch for the
concrete, and running alongside it one furrow for each steel rod
that we want, then cast the steel rods and let them harden.
after we have the steel rods ready, we cast simultaneously all along
the ditch some concrete, and then lower a rod simultaneously into
the mix, and repeat this concrete-rod-concrete-rod etc.
CUTTING OFF THE ENERGY SO IT DOESN'T RETURN BACK
but remember we said the energy will travel back and forth between
the two neighboring "hills" or blocks of land, and we want to send
the energy away with a one-way-ticket and disperse there, we don't
want it to come back!
so what we need is to engage at the beginning, normally we have 45
seconds or so, in the beginning of the earthquake.
we need something that with a switch of a button will connect our
"lightning rod" to the ground, and with a flick or a button will
disconnect, once the energy moved away from the city.
it also must be very strong against pushing, ideally as strong as
the concrete and the steel that we're using, because the vibrations
("the pushes") will pass through this thing.
THERMAL EXPANSION - THINK OF GAPS IN TRAIN RAILWAY
https://en.wikipedia.org/wiki/Expansion_joint
Why Bridges Move... by Practical Engineering (this effect can be
seen in minute 4:00 of the video)
so in long straight sections of the "lightning rod" we need to make
gaps so that our one "lightning rod" is built from a series of many
"lightning rods" that almost touch.
when we make the "lightning rod", before we bury it in the ground we
need to connect electrodes to both sides of each section, so that we
can run electricity through the thin steel rods inside the concrete.
this will cause the steel to heat up and expand and also the
concrete will expand because it takes heat from the steel and
concrete has almost the same thermal expansion as steel.
so when we "activate" the rod all its parts are touching and
connected so they are pressed hard against each other and they
transfer the vibrations.
when the energy was transferred far away, we quickly disconnect the
electricity, the rods cool down and shorten, they are separated by
gaps, and the energy cannot return.
P.S. - WAVES UNDER THE SEA
you might ask yourself about the two "lightning rods" nearest to San
Francisco in the picture, that are located in the sea.
how can we cast steel and concrete on the bottom of the sea?
for drilling we can use all the oil and gas rigs that are pumping
carbon into the air from off shore drilling. instead of killing
people let's use them to save people.
"Rayleigh wave" can not travel in the ocean, but there is something
similar called "Scholte wave"
i think we should build this at first from some soft material, like
the baloon that you see here:
Michael Lombardi: Inventions Enable Diving to New Depths | Nat Geo
Live by National Geographic (you can skip over the first 10
minutes)
https://www.youtube.com/watch?v=VVxGa3AZJ2U
so we can connect this kind of baloons and anchor them to the
seafloor, and make a tunnel of air where people (or better yet
robots because it's dangerous) can work and cure a half pipe of
concrete. basically do what we did on ground but under this long
tent. the problem is that we are limited to how long a tent we
managed to stitch together. for this we need to make a process which
is not all in once but instead it's an "assembly line"
we have a "tent of air" that covers the length of 2 kilometers
(units one and two), and under its cover the robots are curing the
first kilometer, and after they move on to work on the second
kilometer meanwhile the first kilometer is hard enough to be exposed
to water, and now we advance the "tent of air" forward to cover the
next two units (unit two and three). and so on.
