# Thread Subject: Crater function plot.

 Subject: Crater function plot. From: Kallol Das Date: 29 Jan, 2009 17:43:02 Message: 1 of 10 Hello, I need to plot a crater function. Suppose you are hitting a surface with an iron ball. Now the direction will be varied by a 5 degree interval from normal to the surface to 85 degree off normal. Depending upon the angle of impact the shape of the surface will change. Can anyone help me produce a function in the form of Z = f (x,y, theta, h) that takes angle of impact theta as input and the value 'h' as the maximum ripple amplitude? I want to plot a 3D surface with this function. Thanks
 Subject: Crater function plot. From: Roger Stafford Date: 29 Jan, 2009 18:10:18 Message: 2 of 10 "Kallol Das" wrote in message ... > Hello, > I need to plot a crater function. Suppose you are hitting a surface with an iron ball. Now the direction will be varied by a 5 degree interval from normal to the surface to 85 degree off normal. Depending upon the angle of impact the shape of the surface will change. > Can anyone help me produce a function in the form of Z = f (x,y, theta, h) that takes angle of impact theta as input and the value 'h' as the maximum ripple amplitude? > I want to plot a 3D surface with this function. > Thanks   There is no way to answer your question until it is known what assumptions are being made about the impact conditions. How realistic is it expected to be? What is the velocity of impact? How much resistance is to be expected from the surface material? Is momentum imparted to the surface causing it to spread apart from contact with the ball. Etc., etc., etc. ...   In any case, this is hardly the appropriate newsgroup for this sort of question. Roger Stafford
 Subject: Crater function plot. From: David Date: 29 Jan, 2009 18:28:01 Message: 3 of 10 "Roger Stafford" wrote in message ... > "Kallol Das" wrote in message ... > > Hello, > > I need to plot a crater function. Suppose you are hitting a surface with an iron ball. Now the direction will be varied by a 5 degree interval from normal to the surface to 85 degree off normal. Depending upon the angle of impact the shape of the surface will change. > > Can anyone help me produce a function in the form of Z = f (x,y, theta, h) that takes angle of impact theta as input and the value 'h' as the maximum ripple amplitude? > > I want to plot a 3D surface with this function. > > Thanks > > There is no way to answer your question until it is known what assumptions are being made about the impact conditions. How realistic is it expected to be? What is the velocity of impact? How much resistance is to be expected from the surface material? Is momentum imparted to the surface causing it to spread apart from contact with the ball. Etc., etc., etc. ... > > In any case, this is hardly the appropriate newsgroup for this sort of question. > > Roger Stafford agreed... they use supercomputers to model this kind of stuff and years and years of work... there is no simple 'function' to predict it. consider the extreme differences, hit glass with a slow moving ball and you get nothing, but hit a powdery surface with a supersonic ball and you get a huge effect, hit water with anything and you get nothing after some time period, but initially you get some kind of movement.
 Subject: Crater function plot. From: David Date: 29 Jan, 2009 19:22:01 Message: 5 of 10 "Kallol Das" wrote in message ... > Thanks Roger and David for your reply. > > I agree what you all have said. Actually I am modeling a molecular dynamics simulation. I need some sample crater functions as the input files. The momentum, velocity and other stuffs are included in my MD code. I just need some crater functions as a input to the code. well, if you already are modeling the molecular dynamics of your surface just hit it with a point impulse and let your simulation do the work.
 Subject: Crater function plot. From: Walter Roberson Date: 29 Jan, 2009 19:23:02 Message: 6 of 10 Kallol Das wrote: > Actually I am modeling a molecular dynamics simulation. I need some sample crater functions as > the input files. The momentum, velocity and other stuffs are included in my MD code. I just > need some crater functions as a input to the code. > The crater functions that I am looking for is something like a predicted shape of surface if > it is hit by an atom. I just need the surface shape. And some variables namely theta, > maximum height of the ripple, and a decaying factor by which I can change the shape of the surface. > The surface will look very similar to the craters made on the earth surface by the meteors? Hmmm, something doesn't sound right. If you are doing this for molecular dynamics then you need to take into account the electrostatic repulsion or attraction between the atom and the molecular surface. And your molecular surface will, on the scale of an atom, be quite bumpy, and on that scale it is *not* going to move like earth does. For one thing, with meteors (or the like) hitting the earth, the meteor embeds itself in the earth (unless the shockwave of compressed air is enough to push most of it back out of the hole), but an atom hitting a molecular surface has a non-negligible chance of bouncing out again, possibly after having knocked an atom or a chain out of the molecule. And the reaction of the molecule to having an atom or chain knocked out is going to depend upon the chemistry of the molecule. "Atom hitting a molecule or surface leading to a molecular change" is a fair description of normal chemical reactions involving gases or (simple) liquids around the target molecule. When you are working at the level of single atom interaction with something, you need to ask whether there will be quantum effects or relativistic effects or wave-particle duality effects. Are you trying to model something like "sputtering"?
 Subject: Crater function plot. From: Kallol Das Date: 29 Jan, 2009 20:10:18 Message: 7 of 10 Walter, You made the right guess. Actually I have run some codes and I have found that the atomic bombardment on the surface behaves very similarly like the meteors hitting the earth. There are some differences though. But if you take an average of the heights made by hundreds of impacts, you will get a structure that closely matches with the craters made by the meteors. So I just need a function that can produce surfaces like those of the craters with a few parameters like angle of impact, maximum height or depth created. There is going to be some exponential decay of the height or depth of the crater as you go radially out of the point of impact. Can you help? Thanks. Walter Roberson wrote in message <8mngl.724\$Xi1.317@newsfe16.iad>... > Kallol Das wrote: > > > Actually I am modeling a molecular dynamics simulation. I need some sample crater functions as > > the input files. The momentum, velocity and other stuffs are included in my MD code. I just > > need some crater functions as a input to the code. > > > The crater functions that I am looking for is something like a predicted shape of surface if > > it is hit by an atom. I just need the surface shape. And some variables namely theta, > > maximum height of the ripple, and a decaying factor by which I can change the shape of the surface. > > > The surface will look very similar to the craters made on the earth surface by the meteors? > > Hmmm, something doesn't sound right. > > If you are doing this for molecular dynamics then you need to take into account the > electrostatic repulsion or attraction between the atom and the molecular surface. > And your molecular surface will, on the scale of an atom, be quite bumpy, and on > that scale it is *not* going to move like earth does. For one thing, with meteors > (or the like) hitting the earth, the meteor embeds itself in the earth (unless > the shockwave of compressed air is enough to push most of it back out of > the hole), but an atom hitting a molecular surface has a non-negligible chance > of bouncing out again, possibly after having knocked an atom or a chain out of > the molecule. And the reaction of the molecule to having an atom or chain knocked > out is going to depend upon the chemistry of the molecule. "Atom hitting a molecule > or surface leading to a molecular change" is a fair description of normal chemical > reactions involving gases or (simple) liquids around the target molecule. > > When you are working at the level of single atom interaction with something, you > need to ask whether there will be quantum effects or relativistic effects or > wave-particle duality effects. > > Are you trying to model something like "sputtering"?
 Subject: Crater function plot. From: ImageAnalyst Date: 30 Jan, 2009 19:12:32 Message: 10 of 10 The sinc function [sin(x)/x] and Bessel functions look similar - big pit with lots of side ripples - but I'm not sure how to skew them to simulate a particle coming in at an angle. And if the particle goes really deep, you'll have a tube extending into your surface, possibly at an oblique angle. I have no idea how to model that.

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