Sum of energy increase

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Sum of energy increase

Postby vk4 » Wed Apr 30, 2014 5:41 pm

Hi,

I have a problem, sum of energy of a free system in space increase more and more. I tested with a lot of scenes. The bug appears only when there is friction. Energy is higher with a spring. With friction the energy increase around 0.1 J each second. I send the scene.

If you have any idea what I need to do in my scene for have a realistic energy ?

thanks
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tests resssorts v1 - start - avec forces - envoi Al.phz
File to test where energy increase more and more
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Re: Sum of energy increase

Postby Kilinich » Sun May 04, 2014 8:29 pm

I've just set 1x sim speed and energy stops increasing.
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Re: Sum of energy increase

Postby vk4 » Mon May 05, 2014 3:28 pm

I downloaded my own file and tested it, the speed of simulation (0.1X or 1X) don't change the result. I tested this better scene more stable. The scene watch y/x position for each object and sum of energy. Like trajectories are differents, the force from spring don't give the same energy to the object 1 compare to object2.


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ste22 al.phz
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Re: Sum of energy increase

Postby vk4 » Tue May 13, 2014 8:03 am

I tested this new case with only a rotation. The sum of energy move. I try to find the error and it seems the trajectory of the center of gravity are not the same for Object1 and 2.

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Re: Sum of energy increase

Postby Kilinich » Tue May 13, 2014 8:24 am

Interesting research :ugeek:

I believe energy leak/increase is a limitation of step by step calc of contacts. Nothing you can do to stops it.
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Re: Sum of energy increase

Postby vk4 » Tue May 13, 2014 10:01 am

I tested with a range of frequency (900 to 1800 Hz) and the result don't change until forces are stable. I think I understood the error of Algodoo. Center of gravity of Object1 (green color) has a force perpendicular to its movement. In the contrary, the force on Object2 (red+orange) has a force that works. I compute the power = 0.026/2 (radius) * 88*cos(60°) (force) * 18.5 (angular velocity) = 10.5 W. Algodoo find 6.5 W. I added an axis on object 1, this don't change the result. Look at image :

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I added the scene.

I optimized the result and I can have more than 30 W on the second scene. I think the sum of force on big object act on the linear trajectory and add more and more energy because the system increase its angular velocity in the same time. Small object (2 objects) has a different trajectory, it's a rotation and the last translation. The rotation increase more and more due to the difference of distance I think.

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cc7-masses4-good parameters-2.zip
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cv6 - Al.phz
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Re: Sum of energy increase

Postby Kilinich » Wed May 14, 2014 12:14 am

Aaaaand ? :crazy:
It''s an approximation. What we should do now? :|
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Re: Sum of energy increase

Postby vk4 » Wed May 14, 2014 10:43 am

It's not an approximation, the torque exist. I understood where the energy come from and why Algodoo give more energy. Center of gravity of Object1 (green) is not the same than Object2 (red/orange). This create a torque in the direction of rotation. Now, what is the compensation of this torque ? And why Algodoo don't find it ? I tested from 800 to 5000 Hz (after forces are unstable), the energy is very stable. I added the scene and an animated gif file.

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cc7-masses4-good parameters-3-fr - Alf.zip
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Re: Sum of energy increase

Postby vk4 » Sat May 17, 2014 5:13 pm

This is the phase angle the problem. The center of gravity of green object in not at 180° in front of red object. Click on image please, they are larger than the site can do.

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The center of gravity don't move, it is very stable, move sometimes of 0.1 mm. The phase angle is in this example of 16.5°.

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Re: Sum of energy increase

Postby Xray » Sun May 18, 2014 2:52 am

WOW! I don't recall anyone putting this much time and energy into researching an issue in Algodoo! I don't understand all of it, but I am totally impressed by it! :clap:
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Re: Sum of energy increase

Postby vk4 » Tue May 20, 2014 1:39 pm

In this scene if I compute the error it's 1 cm ! The energy added each second is 26 J at 12000 Hz so with the sum of forces at 151 N and an angular velocity of 19 rd/s this give 26/151/19 = 0.9 cm. It's a great error. Sure the system has energy but it's only a kinetics energy. With big distance Algodoo give error ?

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