Simulating a Tsnunami PDF Print E-mail
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Saturday, 16 May 2009 19:57

Simulating a Tsunami

Jack and the Tsunami Simulator

   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 a lot about tsunami simulations tonight.

 

Map of 2005 Tsunami   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.

   On the shore, the water first receded, exposing the ocean bottom along the entire coast, causing some curious people to start walking out to sea to poke around at the sea floor.    Then later, they see the wall of water coming at them.    The water crashes up an over the coast going miles and miles inland, destroying builds and drowning people.

   When the water runs out of momentum, it drains back out to sea, dragging along people, cars and buildings.



 The Experiment

Water Lifter At Rest

 This tsunami was created by simulating the sea floor bursting upwards in deep water.  In the picture at the left, in the deep end of the tank, I have a water lifter device ready to be lifted straight up, thereby mimicking what happened in the ocean in 2005.



 

 

Water Lifter in Action Here is the tsunami water lifter device in action.  You can see the water lifted above its normal height.   Once lifted, it will run off to either side of the lifter, thus starting the tsunami.



 

The Tsunami Demonstrated

Tsunami Simulation t0

Imagine that the far left of the picture is the shore, and that the what looks like a few inches of dry tank floor is actually thousands of feet.  It would be a ten minute walk from the left tank wall to where the water starts.  That scale implies that you would be very tiny indeed.

   Here you can see the water is basically level on the beach, where the water is meeting the bottom of the tank.   However, off on the right you can see that the water level is not exactly flat on the far right.  This is the first indication of the coming tsunami.  In deep water, the wave is barely noticeable.  It is slow and not very high.



Tsunami Wave t1 with LineNow as that big long wave comes into shallow water,  it begins to change form.    There is a gentle draining of the water away from the shore, but out to sea (miles away) a wall of water is building up.

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.

 

Tsunami Wave t2

 Here a dotted line shows the shape of a regular ocean wave. The Tsunami moves much faster, and has millions of tons water behind it. A tsunami wave could extend up for miles out to sea, and all that water is headed towards shore with momentum.

 



Tsunami Wave t3

 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.



 

Tsunami Wave t4And finally, the water has run up the hill, and only stopped in this picture because it hit the wall of the tank.  Note how much has changed since the last video frame!  The speed of the wave as zoomed up the beach was incredible.

  All that land with people, homes, and trees are now under a hundred feet of fast moving water.

But it is not over yet, for the water is not level; You can see the slope in it, with the highest water level on the far left.  Once this water loses its momentum and stops moving 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.

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Last Updated on Friday, 29 January 2010 16:45
 

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