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Note: This discussion is about an older version of the COMSOL Multiphysics® software. The information provided may be out of date.

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Free Fall

Posted Nov 2, 2011, 8:34 a.m. EDT Version 3.5a 4 Replies

Stefan Herzog
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Hi,

I am trying to simulate the situation, where a object is falling due to gravity.
I want to neglect air (and with this: friction).
I have chosen the module "Plane stress (2d)" and have succeeded in inserting the gravity force as an body load.
My main problem is now, how to choose the surrounding geometry and its boundary condition. I would prefer vacuum as environment.
I have added a fixed block made of glass, which lies 1m beneath the starting point of the falling object.
After solving the problem and plotting the displacement of the falling object, it seems that it falls directly THROUGH the solid block, as if the block is made of air???

So, what I want is summed up in the following sentence: How can I model a falling object, which hits a solid surface, in vacuum.

Thanks a lot!

Stefan

4 Replies Last Post Nov 2, 2011, 11:57 a.m. EDT
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Nov 2, 2011, 11:07 a.m. EDT
Hi

COMSOl is not really a multibody simulation system, even if you can do some multi body solving.

So if you go in 2D, structural time stepping solving, and draw a rectangle, give it some Young modulus (1000 , poisson (0) and density (2000). Then add a body load Fy = "-g_const*solid.rho" (or whatever it was called in 3.5, it was different) and solve you will see the device "fall", no need for anything else

--
Good luck
Ivar
Hi COMSOl is not really a multibody simulation system, even if you can do some multi body solving. So if you go in 2D, structural time stepping solving, and draw a rectangle, give it some Young modulus (1000 , poisson (0) and density (2000). Then add a body load Fy = "-g_const*solid.rho" (or whatever it was called in 3.5, it was different) and solve you will see the device "fall", no need for anything else -- Good luck Ivar
Stefan Herzog
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Posted: 1 decade ago Nov 2, 2011, 11:11 a.m. EDT
Hi,

thank you for quick answer.
However, this solution won't do.
I want to add a AC/DC module afterwards, since the falling object should be a magnet, which should levitate above a coil and I want to determine the steady state distance between magnet and coil.

Greetings

Stefan
Hi, thank you for quick answer. However, this solution won't do. I want to add a AC/DC module afterwards, since the falling object should be a magnet, which should levitate above a coil and I want to determine the steady state distance between magnet and coil. Greetings Stefan
Edgar Kaiser
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Posted: 1 decade ago Nov 2, 2011, 11:34 a.m. EDT
Hi Stefan,

you will need to find out how to model the interactions between the bodies.

In the case of the falling object hitting a solid surface this interaction might be modelled by a contact pair? Maybe, I am not that much a solid mechanics specialist.

In the other case you will have to introduce the magnetic forces into your model.

Cheers
Edgar
Hi Stefan, you will need to find out how to model the interactions between the bodies. In the case of the falling object hitting a solid surface this interaction might be modelled by a contact pair? Maybe, I am not that much a solid mechanics specialist. In the other case you will have to introduce the magnetic forces into your model. Cheers Edgar
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Nov 2, 2011, 11:57 a.m. EDT
Hi all

That is correct. but then to get a magnetic field you need a air/vacuum volume + to let the object "fall" therein, hence moving mesh to cope for the free displacement, it starts to become tricky

--
Good luck
Ivar
Hi all That is correct. but then to get a magnetic field you need a air/vacuum volume + to let the object "fall" therein, hence moving mesh to cope for the free displacement, it starts to become tricky -- Good luck Ivar

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