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Binary Eccentricity Test - volunteers needed! (Read 30209 times)
EDG
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Re: Binary Eccentricity Test - volunteers needed!
Reply #60 - 10/28/06 at 19:03:20
 
Quote from Tony   on 10/28/06 at 18:59:57:
Aren't you going to continue until you reach max ecc? It looks like you're getting close.

Why weep? It's possible you've found a problem with their formulas. Maybe they break down at certain values. If so, that would be very important to the study of exo-solar planets.

Or its possible that Gravity Simulator is the culprit. In any case, you've certainly proven the case that more study needs to be done in this area.

 
EDIT: I managed to restart the simulation using the final values from the saved output file from the crashed sim. I'll use the Mean Anomalies that I started with - hopefully that won't make too much of a difference. I should be able to add the output to the existing text file.  
 
I guess the resume.gsim didn't save because the program wasn't closed down manually - since it crashed, all it had to go on were the initial parameters.
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Re: Binary Eccentricity Test - volunteers needed!
Reply #61 - 10/28/06 at 19:19:45
 
Hm, doesn't look like it's going to be too bad after all - after the first 40,000 years the values are still doing what they were doing before (inc and ecc are still increasing, AoP and LAN still decreasing). Phew. Looks like the show is still on! Smiley
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Re: Binary Eccentricity Test - volunteers needed!
Reply #62 - 10/28/06 at 19:27:12
 
oops, I missed your "crash post".  Tough way to learn to autosave.  Hmmm, I could make Gravity Simulator create a backup sim every few minutes like Microsoft Word does:  "backup.gsim".
 
I'm glad you could reconstrut it.  I doubt that the anomolies will affect your results since nothing is locked into resonance.
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Re: Binary Eccentricity Test - volunteers needed!
Reply #63 - 10/28/06 at 19:32:41
 
Quote from Tony   on 10/28/06 at 19:27:12:
oops, I missed your "crash post". Tough way to learn to autosave. Hmmm, I could make Gravity Simulator create a backup sim every few minutes like Microsoft Word does: "backup.gsim".

 
Well, I'm autosaving every million years now, just in case! That said, an autosaved backup.gsim file wouldn't be a bad idea...!
 
Quote:
I'm glad you could reconstrut it. I doubt that the anomolies will affect your results since nothing is locked into resonance.

 
Yeah, it looks like it'll be OK. The only pain will be merging the text files into one file that I can plot a graph from, but it's no big problem. I've duly edited my "wailing and gnashing of teeth" posts accordingly Smiley
 
I'll remove the simulation1.zip file for now. It ain't over yet! Smiley
 
(and er, I guess this is now the longest thread ever on this forum? Wink)
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Re: Binary Eccentricity Test - volunteers needed!
Reply #64 - 10/28/06 at 20:30:58
 
Got a reply from Genya Takeda which was rather interesting. Apparently the inclination is also supposed to oscilate between the starting relative inclination and that critical value of about 40 degrees! This isn't happening in the GravSim simulation - the relative inclination is already well below the critical value. So something is still not right here in GravSim- either the algorithm used here isn't accurate enough or the timestep is still too large. More experiments are due, I guess!
 
However, he also mentioned that the Arg of Peri is either going to be circling around 360° or it's going to be oscillating around 90°, and it does look like this might be happening here! Remember, the sim did vary wildly around 360° at first, and now it looks like it's partway through a long period oscillation around 90°...
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Re: Binary Eccentricity Test - volunteers needed!
Reply #65 - 10/28/06 at 23:38:24
 
In measuring the inclination, you can't go by what Gravity Simulator tells you because that's inclination from the ecliptic.  I think what you want is inclination from the plane of the secondary.  And it's not as easy as subtracting one from the other.
 
If you gave the planet 75 degrees of inclination and the secondary 0 degrees, then the inclination of the planet that Gravity Simulator gives you would be useful since the secondary orbits in the ecliptic plane.
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Re: Binary Eccentricity Test - volunteers needed!
Reply #66 - 10/28/06 at 23:50:15
 
Quote from Tony   on 10/28/06 at 23:38:24:
In measuring the inclination, you can't go by what Gravity Simulator tells you because that's inclination from the ecliptic. I think what you want is inclination from the plane of the secondary. And it's not as easy as subtracting one from the other.

If you gave the planet 75 degrees of inclination and the secondary 0 degrees, then the inclination of the planet that Gravity Simulator gives you would be useful since the secondary orbits in the ecliptic plane.

 
Erm, wait a minute... the ecliptic can be anything you want if there's two bodies orbiting the star. You can set the planet at 0 degrees inclination and the companion at 75, and the planet's orbit will be the ecliptic. Or you can set the companion's orbit at 0 degrees and the planet's at 75 and the companion's orbit will be the ecliptic. It only gets fixed if you have a several bodies orbiting in roughly the same plane and one or two well outside it - in which case the plane that most of the bodies orbits in is the ecliptic. (technically, the Ecliptic in the solar system is the plane of Earth's orbit around the sun, but the other seven planets orbit roughly in that plane)
 
Of course the difference in orientation of the orbits is probably a problem, because I guess then you're talking about dog-leg angles when calculating the difference in inclinations. That I could understand being a problem.
 
Unless I've completely missed the point of what you're saying Wink.
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Re: Binary Eccentricity Test - volunteers needed!
Reply #67 - 10/28/06 at 23:02:09
 
25 million year update:
 
Interesting, the eccentricity looks like it's starting to flatten out, and it's nowhere 0.900. I'm also not entirely sure that the Arg of Peri is going to oscillate around 90° here.... and inclination is still increasing.  
 
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« Last Edit: 10/29/06 at 09:58:52 by EDG »  

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Re: Binary Eccentricity Test - volunteers needed!
Reply #68 - 10/29/06 at 01:27:36
 
Hi Mal , inclination will grow rapîdly as e wil go to 1 .  
I have the same experience with the 5-earths sim .  
I'll try to upload the images .  
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Re: Binary Eccentricity Test - volunteers needed!
Reply #69 - 10/29/06 at 07:28:54
 
27.857 million years:
 

 
Well, something's definitely gone pear-shaped. Eccentricity peaked at 0.35 at 26.5 million years and is now falling. Inclination is now 74.8 degrees. Arg of Peri is now 71 degrees and falling dropping. This is not supposed to be happening.
 
 
Oh, and here's what the companion orbit has been doing. Note that there's a kink where I restarted the graph after the crash. I don't know if this affected the outcome, I can't see a similar break in the planet  data.  
 

 
 
 
I'll let this run a little longer, but it looks like a bust - it's not doing anything like what it's supposed to be doing. I'll try another simulation after this - a 0.9 solar mass companion at 250 AU, with a 1MJ planet at 5 AU, everything else as before. Period should be about 300k years, which means I can run it at a slower timestep without dying of old age. I'll try at a 4k timestep and see what happens - that surely can't be too fast for this.
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Re: Binary Eccentricity Test - volunteers needed!
Reply #70 - 10/29/06 at 07:36:44
 
Quote from frankuitaalst   on 10/29/06 at 01:27:36:
Hi Mal , inclination will grow rapîdly as e wil go to 1 .
I have the same experience with the 5-earths sim .
I'll try to upload the images .

 
Hm, that shouldn't be happening - the relative inclination is supposed to be going between the starting value and 40 degrees.
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Re: Binary Eccentricity Test - volunteers needed!
Reply #71 - 10/29/06 at 09:58:25
 
OK, that's it, I've given up Smiley.  
 

 
Final time: 28.561 million years.  
Eccentricity dropping
Inclination 76° and still increasing
Arg of Peri and LAN still decreasing
 
So something's obviously not as it should be here.  
 
Gonna try the quicker one - I'll start a new thread. I think actually I'll make it simple by having the orbits starting off oriented in the same way (arg of peri and LAN both at 0) with the mean anomalies being different. See what happens then.  
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Re: Binary Eccentricity Test - volunteers needed!
Reply #72 - 10/29/06 at 11:26:42
 
here some results for the 5-earth sim .  
I ran them for about 400 years .  
Timestep = 128 sec .  
Tilmestep was perhaps too big for the 4 inner planets , as they lost their moons . The 5th earth kept his moon .  
 
Interesting is the following :  
1. Time before the Kozai becomes "visible" rises about exponentially with AU ( see last Excel-graph ) . This means that the moons of the outer planets must be protected by "time" .  
2. Inclination changes slowly in the beginning , but increases rapidly as the ecc. goes to 1.  
3. After reaching the max ecc the system gets in a cycle with decreasing ecc and decreasing incl , rising again , a.s.o.  
 
It is further interesting to run the sim with a smaller time step in order to obtain the frequency of the fluctations of incl . ( avoiding the moons are lost ) .  
I tried to correlate the frequency of oscillation tothe time needed to obtain full ecc , but data are to few . Such a link must exist surely .  
 
Note : running the sim I observed that the moon of the first earth changed the orientation at ecc=1 , meaning she returned to the earth in the some direction as she come from , meaning rotating clockwise instead of anti-clockwise .  
Really surprising !!!  
 

 






 

 
** modified by Tony -- added img tags.
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« Last Edit: 10/29/06 at 12:35:56 by Tony »  
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Re: Binary Eccentricity Test - volunteers needed!
Reply #73 - 10/29/06 at 13:29:23
 
The 3rd one is surprising.  It looks like eccentricity has a double peak.
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Re: Binary Eccentricity Test - volunteers needed!
Reply #74 - 10/29/06 at 14:14:03
 
In order to "save" the moons I started the sim with reduced timestep ( 32 instead of 128) . I lost already 3 moons ( also for 2Au , the one with the double peaks ) . I wonder how the results will be ... Keep you informed .  
BTW : the integration is done by Runge Kutta 4 or another method ?  
Frank
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