Here is my test apparatus which is my first shot at making a tsunami
simulator. It consists of three layers of 1/4 inch plexiglass.
The middle layer is cut out so that the result is a very thin
wave tank. I learned alot about tsunami simulations tonight.
Here
is a map of what occured in the Indian Ocean. An area of sea floor
40,000 square kilometers pops up by 5 to 15 feet, which pushes the
ocean above it up into the air. The water slides off but it makes a
huge wave. Not huge in height, but huge in area and speed. Out on
the water, the wave would not even be noticable to boats. The wave
would take 1/2 to 1 hour to pass, and it would only be feet or inches
high. It is only when this huge wave approaches shallow water, where it
piles up and turns into a deadly nightmare.
The Tsunami
This tsunami was created by simulating the sea floor bursting upwards in deep water.
Here
you can see the water is basically level on the beach. However,
off on the right you can just see the water level starting to drop off
to the far right. This is the first sign of the tsunami. Note where the
water level is.
A very short time later, you can now see the whole wave. The first sign is that the water gets sucked away from the beach. This made the disaster worse, because people walked out onto the beach because it was so strange that all the water pulled away.
If
you take the average water level over the whole white line, the water
level is still the same. However, that water on the top is moving very
fast towards shore. And this is where the destructive power comes from.
Not from the height of the wave, but from the speed and the huge amount
of water piled up behind the wavefront.
Here a dotted line shows the size of a regular ocean wave. The Tsunami moves much faster,
and has tons more water behind it. A tsunami wave could extend up for
miles out to sea, and all that water is headed towards shore with
momentum.
Right
now the tsunami wave has reached what was dry land before. A
normal wave would have crashed and expended all its energy by now. But
the tsunami is still moving ashore like a truck with no brakes going up
an emergency ramp.
And
finally, the water has run up the hill, and only stopped in this
picture because it hit the wall of the tank. But the water is not
level, you can see the slope in. Once this water stops going
inland, it is going to turn around and start running back down hill,
carrying cars, buildings, and people with it. Everything gets swept
back out to sea, as the beach drains yet again for the next wave. It
would be still draining 1/2 hour later when the next wave hit.
Observations Regarding Making a Tsunami Simulator
1.) Tsunami Simulators are very very messy.
2.) If you want to have two fluid layers, then you must have a top on your tsunami simulator, else everthing just splashes out the top and you don't get any waves on the interface layer.
3.) If you don't want your liquid spilled all over the place, you need to have a sensible system for filling and draining the tank.
What was Cool
The tank itself did not leak at all, and my little 5-minute legs worked great for holding it upright. It was very fun to play with, although it was not as cool as I had hoped it would be. I also did not die from the fumes from mixing paint thinner, isopropyl alcohol, and mineral oil!
What was Lame
I could reproduce tsunami's in my tank, but they were very unimpressive ones. They are unimpressive because they are
a.) Too Fast. All the action is over in about 1/2 sec.
b.) Too Small. With a tank only 1/4 inch wide, all the energy of my wave is used up due to friction with the sides. I.E. with such a thin amount of water, the momentum behind the waves isn't very much. Waves die out very quickly. By making the tank 10 times wider, the friction should remain about the same, but the wave will have 10x the energy. Therefore the dying out problem should be reduced.
I did some experimentation with layers of non-mixing fluids, to see if I could get much slower motion. Unfortunately, it became clear right away that since the tank did not have a top, that all my energy went into water waves on the surface. I could not see much of a slow-motion effect like I wanted. I tried the following:
Stuff I tried
- Mineral Spirits on top, water on bottom. - Separated nicely, but the waves didn't look much different that water and air.
- Mineral Oil on top, 91% isopropyl alchohol on bottom - densities are almost equal. The waves were so slow it was almost static. All motion was dominated by the oil-surface waves at the top. Also, the oil was so viscous that the energy was damped out.
- Miniral spirits on top, isopropyl alchohol on bottom - Just a big cloudy mess.
My Next Prototype
I'm interested in exploring the two-fluid system further. If I could solve some of the problems, perhaps it could work. My next prototype will be:
- 2.5 inches wide instead of .25 inches wide
- It will have a top, with only a small tube on top where air makes contact.
- An easy way to fill or drain it.
- It will need to be longer. That means a much bigger piece of material...
13Jan2005
I modified the simulator to put a top on it. Then I tried the mineral-oil water boundary again. Extremely messy, and the viscosity of the oil killed any wave I tried to make. So I cleaned that out and tried mineral spirits and water.
Again, the wave's energy damps out very quickly, but the waves were working, and the boundary between water and the mineral spirits was excellent. No bubbles, and the boundary was shiny like a mirror. Just to see what would happen, I poured some 91% isopropyl alcohol in. The alcohol made the mineral spirits go cloudy, but most of it poured down onto the layer between the two other fluids. Interestingly enough, my waves seemed to work alot better, as if the alcohol reduced the friction with the walls.
Anyway, it is much more clear to me that I will need to go about 10x wider to reduce the amount of friction. I will not be able to get a tsunami in slow motion unless the energy of my earthquake is enough to get a wave to travel the length of the tank and still have enough umph to make an exciting finish.