Particles moving on a surface! Please Help!
 

Hello all, Im new to the forum and have joined because I'm in dire need of help. I have a medical animation deadline but don't know how to get the effect I need to execute.

I need to simulate the surface of a cell, particularly just the phospholipid bilayer. So basically I need particles to move on a nurbs surface whose surface curvature will be animated, which will instance geometry of individual phospholipids on that surface (I know how to instance already). To get a better idea of what I'm talking about, I've attached a picture of a cell surface, and each of those circles are phospholipids. I'm trying to simulate the natural lateral movement of those on a cell's surface.

I have no problem getting the particles on the surface by using surface flow, but the problem is I don't want them to flow in any particle direction. I want the particles to be crowded on the surface and to tightly and randomly move about (as phospholipids do) and at the same time, they have to appear to be colliding, not going through each other or else the scene would be a mess. I've tried applying a radial field to each particle so that they would avoid each other, but it doesn't seem to do anything, they still flow right through each other (yes ive selected "apply per vertex".

To go into more detail on the movement of each particle, I need the particles to be very crowded and slipping past each other slowly and randomly along the surface without any particular direction. My guesses would be to do a runtime expression to randomly change goals per particle but I don't know how to do that (too new to expressions). I also need to make sure my particles are pointing in the right direction as the animated surface's curvature is changed. I know how to do this by asigning the aimdirection to "velocity" when I use surface flow but,again, the problem is that with surface flow Im not getting the crowded, random movement that I need.

ANyone who would be able to help get this section of the animation ironed out will be of GREAT help to me. If anything requires expressions, it would really help if I know exactly what I need to enter in) I've been stressing greatly over this, and it's really important to get all these points I've mentioned to work at the same time:

-particles on surface (surface will be animated), and particles must move stay on the surface as the surface is animated
-particles are randomly moving on the surface (a turbelent movement is fine)
-particles are crowded next to each other and are colliding (stay away from each other so that the geometry doesn't overlap)
-instanced geometry for the particles are facing up to the normal of the surface they reside on (so that when I animate the surface and change it's curvature, the instanced geometry is always oriented correctly).

THANK YOU!

Maybe I should make it simpler
 

It doesn't seem that anyone wants to reply to lengthy posts.
Perhaps if I make it simpler.

How do I constrain particles onto a surface and have them stay on the surface as the surface is animated? And how do I make sure the instanced geometry on the particles are pointing up from the surface at all times as the surface is animated.

I've tried painting particles on a nurbs surface and parenting them, but when I animate the CV's on the surface, the particles don't stay with it.

Sounds like a job for softbody dynamics. I don't think you'll ever get good results with particle instancing looking at the requirements you outlined. And to be honest, what you described isn't easy to do. Hope you don't have too tight deadline.

i suppose it is silly to suggest a composite of some kind?

Theres a section in Maya 6 Killer tips for having partcles "Crawl" about on a surface, dont know if this would be any help?