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"Cloud" condensation (Read 4878 times)
frankuitaalst
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"Cloud" condensation
09/22/07 at 11:05:52
 
Wondering how a cloud of rocks condensates I simulated the accretion in the following sim :  
800 bodies circling a body of equal mass in 1AU +/- 90% .  
Doing this the bodies have almost zero velocity . So one might think the cloud of bodies should condensate.  
In order to get some action the bodies al had 1 Earth mass and diameter 10000 km. Then the mass of the central body is set on 10 Earth masses ( in order to stabilise the focus ) .  
Hereunder is the screenshot of the sim . Sim was run at 2000 seconds for more than 2 years . A screenshot was made every 10 days.  
The cloud condenses , some clusters are formed , some planets merge , but what I didn't expect is that so many bodies are ejected ....
At the end of the sim the system seems to move ; this is because the focus planet moves .
Is there some way to focus on the barycenter of the system ?
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Cloud800-2.gif
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Tony
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Re: "Cloud" condensation
Reply #1 - 09/22/07 at 12:27:49
 
Press the "F" button on Graphics Options to focus on the barycenter.
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frankuitaalst
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Re: "Cloud" condensation
Reply #2 - 09/22/07 at 13:39:08
 
Thanks , this works . I reduced the timestep to 2000 instead of 4000 . Less or no planets are ejected now. Will try to post again tomorrow if my PC doesnt get overheated  Smiley
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Re: "Cloud" condensation
Reply #3 - 09/22/07 at 13:56:15
 
With this many objects, remember to go to Preferences and set the DoEvents interval to 1, and the Update Graphics Interval to something large like 100 or 500.
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frankuitaalst
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Re: "Cloud" condensation
Reply #4 - 09/22/07 at 14:12:48
 
ok this works : sim is running faster . Whats the meaning of both (seconds ? ) .
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frankuitaalst
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Re: "Cloud" condensation
Reply #5 - 09/22/07 at 14:26:24
 
Able to "stabilze" the system thanks to youur advice.  
I should reduce the primary mass to stablise the view more I guess .  
Heres the sim for 2 years .  
Clumps are being build . But the system should contract and eventually get some rotation ...
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cloud800-2.gif (attachment deleted)  
 
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Re: "Cloud" condensation
Reply #6 - 09/22/07 at 14:47:41
 
Quote from frankuitaalst on 09/22/07 at 14:12:48:
ok this works : sim is running faster . Whats the meaning of both (seconds ? ) .

DoEvents means how often should the simulation return control to the rest of the program.  With the number set low, your simulation runs slow, but the rest of the program is very responsive.  With the number set high, the simulation runs faster, but the rest of the program is very non-responsive.  For example, if it is set very high, you might click on a menu option and it just doesn't accept your click.  With lots of objects, the time to complete a single iteration is very high, so setting DoEvents to a low number doesn't slow it down by much.
 
Graphics Interval tells it to update the graphics once every N number of iterations.  So the higher the number, the faster the simulation runs, as it is not wasting CPU time plotting points.  But too fast makes it appear jumpy.
 
The objects that escape are effecting the total center of mass of the system.  To keep the system better centered, delete the objects that have escaped.  They're not significantly affecting the simulation anymore.  The easiest way to do this is to zoom way out to see the escaped objects, turn on the Labels (the L button), then right click on an object, and choose delete.  This brings the barycenter back into the remaining cluster, and makes the sim run faster since there are fewer objects.
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frankuitaalst
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Re: "Cloud" condensation
Reply #7 - 09/22/07 at 14:55:14
 
ok thanks , understood .  
anxious how the system will evolve . Reduced the timestep to 1000 . This gives lesser ejections
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frankuitaalst
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Re: "Cloud" condensation
Reply #8 - 09/23/07 at 00:17:32
 
Running the above system (800 Earth Planets at rest , within 1AU+/-80%) gives the following frame :
Screenshots were made every 30 days ; timestep 1024s.  
First one can see a clustering , later a condensation of the system which finally results in an expansion .  
This expansion amazes me . Looks as if the potential energy is converted in kinetic energy driving the system outwards . Sim was in total run for 120 years ( only the first 10 years are shown here ) . In this time the system was already expanded to 500 AU .  
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Cloud800-3.gif
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frankuitaalst
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Re: "Cloud" condensation
Reply #9 - 09/23/07 at 05:35:30
 
Reducing the size of the system to 100 "planetesimals" , each with the size of earth , using the same initial conditions as above gives a more "calm" situation .  
The sim herunder covers more than 30 years .
At the end of the sim (120 y) the system was still slowly expanding , but a mini solar system was formed near the barycenter consisting of : 1 Sun (Mass 24 ) , and three planets resp. 9,2,1  Earth masses !  
In the outreaches of the system even more binaries were created .
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Re: "Cloud" condensation
Reply #10 - 10/19/07 at 19:28:55
 
What I generally do for these "cloud" simulations is to create a reference object with a mass of one kilogram and create all the other objects orbiting it, and then delete the reference object. That ensures the planetesimals' movement at the start of the simulation is essentially zero; I have found in the past that even slow rotation about an Earth-sized initial object influences the evolution of the system.
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