|Tsunami Simulation Part 2|
|Written by Administrator|
|Saturday, 16 May 2009 21:33|
Simulating a Tsunami Part 2
In my first experiment, I used water in a thin tank. The action went too quickly, and my wave lost a lot of their energy from friction with tank walls. I wanted to try building a wider tank, so the there would be more energy in the waves, while the energy lost due to friction with the walls would remain the same.
Above is the new tank. It is 4 feet long, 4 inches wide, and 8 inches deep. I choose 4 feet long because that was the biggest 1/4" thick plexiglass I could buy at Chase Pitken. In addition, if it were any longer it would not fit on my workbench. I made it 4 inches wide because otherwise I wouldn't be able to get my hands in there to get the nuts on the bolts, or to clean it. It is 8 inches deep, because that is how much material I had. In addition, this should be enough to experiment with different water depths.
I assembled it tonight. It has about 150 6-32 bolts. Surprise! Not all the bolts lined up with the holes I had drilled. An interesting problem to solve after one has already put the caulking on. I'm going to let it dry a few days before I try testing it for water tightness. It will be a miracle if it is; I cut the pieces with a circular saw on the floor of the garage. Not exactly a precise system.
I could not figure out a way to make a water-tight top which would still be removable. So I made a false ceiling which is not water-tight. It is adjustable via the two long bolts sticking out the top.
The dream is to make a simulation with time slowed down, so you can see exactly what is happening without needing to make a video and play it back frame by frame. It turns out from the physics of waves, what controls the speed at which the waves move and change has to do with the density of the liquid and how strong gravity is. The more gravity, the larger the forces will be on the water, and therefore the faster events will unfold.
We cannot easily change gravity, but we can do a trick to lower the forces. That is instead of just having water in the tank with air above it, we actually replace the air with another liquid that has a lower density than water, so it stays on top. The idea is that the force of gravity causing the waves will now act on the difference between the density of liquid1 verses liquid2. So for very slow waves, all you need is two non-mixing liquids with very similar densities.
Above is a diagram of what the false ceiling is for. I want to try having two non-mixing fluids of different densities. I'm hoping for slow-motion waves. However, my experience with prototype 1 showed that if you have no top to the tank, all the waves happen on the air-surface, and you don't get any slow motion. The false ceiling should be similar to having a tank with an adjustable depth.
Will mineral spirits eat the plexiglass and/or the silicon caulking? It didn't seem to hurt prototype 1 in the short time I left the stuff in it. Maybe I just let some sit for a few days to see what happens.
23Jan2005 - Tsunami Tests
Here is a video of the first test of the larger tank with a single fluid: Water. The source of the wave is a piece of aluminum tipped over the deep water end of the tank. The wave moves so quickly that it is difficult to catch on video.
Here is the same test but with the two fluid system. The bottom layer is the blue water. The top layer is clear mineral oil. The same metal piece is allowed to tip over.
Regular (non-tsunami) Water Waves
A Tsunami is a shallow-water wave. This means that the distance from one wave peak to the next is longer than the depth of the water. So if you have a wave that is so spread out that it is a hundred miles to the next peak, then you can have a shallow water wave in the deepest parts of the ocean. In this demonstration, I'm making short waves which are NOT tsunami-like. No matter how hard I drive the waves, they don't travel very far up the shore.
Now compare those waves which don't have any ability to climb up the shore, with the following long-wave.
The Surface Tension Problem
I have read in several places on the net that a drop of soap in the water will reduce the surface tension.
I tried it in a glass dish to see if that will reduce my problem in the two-fluid system. It appeared to help a great deal, but it does tend to make bubbles now. This may not be so bad, because the sea has bubbles when the water is turbulent.
Now here is the same test with some soap in the water:
I tried several experiments with Silicon Oil, isopropyl alcohol and other liquids, but not with much success.
Unfortunately, the mineral spirits turned my GE Silicon II caulking into a jelly-like substance. The tank didn't leak when the mineral spirits was in it. However, after I had drained the tank and tried refilling it with plain water, the caulking was falling out of the seams, and it leaked quite badly after a few minutes.
Efforts to repair the tank failed. I had a lot of fun but never got up enough motivation to redesign the tank in a way that didn't depending on RTV.
|Last Updated on Sunday, 17 May 2009 05:31|