Russ's Crater Links: No Sense in Splash

[russ_watters]

That doesn't make any sense: a crater is quite literally a splash.

 

[russ_watters]

Really? what is the surface tension of a planet?

Nonexistant, but surface tension actually reduces splashes. A splash is a Newtonian collision of particles. Surface tension (and viscocity) just makes the collision more inelastic (try some cooking oil...).

I know its tough to consider a solid a fluid, but that's really looking at the issue backwards - a fluid is a collection of solids when dealing with a splash.

No, it isn't a coincidence that a meteor impact looks exactly like a splash: it is a splash.

(I'll try to find some computer simulations and pics... we had a splash thread a few months ago)

Just guessing here, but I suspect the reason the splash "disappears" has something to do with it being so close to the boiling point. The article doesn't mention the temperature the drop was at. If it were as warm as 140 F, the water would have boiled.

I thought of that, but unless the splashes were very small, that's a lot of water to boil without noticing, particularly with the rebound drop.

I agree with you and the others though - nowhere near enough information to tell what happened, much less why. It doesn't describe the observations at all.

 

[russ_watters]

Two links to splash simulation/visualization, from a previous discussion on tsunamis compared to splashes:

http://www.cc.gatech.edu/gvu/animation/Areas/secondary/closeUpDiveSplash.html

http://courses.ncssm.edu/hsi/splashes/PAGES/dcsplash/4-29-01.htm

From the first site:

A deformable mesh is mapped onto the surface of the fluid to model surface effects. The forces resulting from impacts to this surface are propagated to the volume model as pressure changes. As the net upward velocity of a column increases particles are spawned to model the spray from the splash. The initial positions of the particles are distributed over the area of the surface mesh that corresponds to the rising column. Initial velocities are determined by summing the velocity vectors of the fluid flowing in the pipes under the surface and the upward velocity of the column.

Paraphrased, a splash is caused by an extremely high pressure spike and propagates as a high amplitude pressure wave. If the amplitude is high enough to break surface tension and acceleration due to gravity, particles fly off the top of the propagating wave.

So then, the size of a crater is determined by how far the wave propagates before its energy is reduced to the point where it no longer throws off particles.

 

[Integral]

Russ,
I will grant your analogy as soon as I see a drop of water gouge a hole in the surface of my table splashing wood fragments across the surface. The difference in density between the involve materials is enough to make them completely different phenomena.

Seems that experimental evidence is not enough for you.

Sure a meteor striking a planet creates a form of a splash, but you certainly will not model a water droplet hitting a solid surface in the same fashion that you model a meteor impact.

In a water droplet surface tension is a KEY factor. I did not say HOW it effects the process, just that is AN effect. Are you capable of understand that?

I would also think that another key factor will be how the liquid wets the surface it impacts. Again there is no analogous parameter in a meteor impact.

As for your quote, that is nearly unintelligible. Are sure that is what it is saying? Frankly after reading that I would search for another source.

 

[russ_watters]

Russ,
I will grant your analogy as soon as I see a drop of water gouge a hole in the surface of my table splashing wood fragments across the surface. The difference in density between the involve materials is enough to make them completely different phenomena.

Again, its just a matter of the energy of the collision. Your wood table analogy doesn't work because you are using too low of an energy level collision. But water jets are, in fact, used to gouge holes - even in metal. http://www.waterjets.org/ Its just when the energy is very low compared to the integrity of the surface, you don't get a splash. Obviously, it takes a lot of energy to pulverize your table, and you only get a splash in a solid when the solid is pulverized. But you also only get a splash in water if there is enough energy to liberate small particles of water. So try dropping a BB a quarter of an inch into some water and see if it splashes...

Seems that experimental evidence is not enough for you.

Enough for whom? You have observed a splash and seen photos and simulations (both computer and physical) of crater formation, right? If I tell you I own a Ford car, you can't show me a picture of a Ford truck and tell me Ford doesn't make cars.

Sure a meteor striking a planet creates a form of a splash, but you certainly will not model a water droplet hitting a solid surface in the same fashion that you model a meteor impact.

You absolutely do. I happened to have the links available for water, but I'll need to find some for the crater.

In a water droplet surface tension is a KEY factor. I did not say HOW it effects the process, just that is AN effect. Are you capable of understand that?

We're not in disagreement that surface tension has an effect - just on how much. It may be a key factor when comparing the splash you get from dropping a BB into a barrel of water and a barrel of cooking oil, but its not a key factor when dropping a bowling ball into the same barrel.

I would also think that another key factor will be how the liquid wets the surface it impacts.

Huh?

As for your quote, that is nearly unintelligible. Are sure that is what it is saying? Frankly after reading that I would search for another source.

I translated it for those not familiar with computer 3d modeling. My paraphrase is accurate. And its tough to argue against a model that uses known physics and works.

 

[russ_watters]

http://www.lpl.arizona.edu/~jmelosh/impact_crater_collapse.pdf

Page 9 discusses crater modelling and mentions water simulations and scaling. I'll keep looking for more.

Incidentally, I was wrong about something I said above: crater splashes do exhibit rebound like water splashes do (depending on the size of the crater).

 

[Integral]

Again, its just a matter of the energy of the collision. Your wood table analogy doesn't work because you are using too low of an energy level collision.

BINGO! you have proven my point. These are complexly different energy levels. While I am sure the models you are looking at are excellent. Will they predict the behavior seen in the main topic of this thread? I doubt it... Therefor you are barking up the wrong tree. For all the similarities, there are factors in a low energy fluid collision which simply make it different from a high energy collision solid collision.

Would please cease making off topic posts in this thread.

 

[Integral]

There 'ya go Russ, now you have you own impact crater modleing thread. Have a ball.