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force on gmo with prescribed motion

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Old   April 14, 2011, 11:28
Default force on gmo with prescribed motion
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jiko
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I am analysing vertical force of water on a vertically (z, axis of gravity) oscillating GMO. the amplitude and frequency of the gmo is prescribed.
now since it is oscillating in still water I thought the initial force would be 0 at 0 time. but it is not. could someone please explain why the vertical force is not zero at zero time. or is something wrong in my simulation setup ?

thanks in advance.
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Old   April 26, 2011, 10:00
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Quote:
Originally Posted by jiko View Post
I am analysing vertical force of water on a vertically (z, axis of gravity) oscillating GMO. the amplitude and frequency of the gmo is prescribed.
now since it is oscillating in still water I thought the initial force would be 0 at 0 time. but it is not. could someone please explain why the vertical force is not zero at zero time. or is something wrong in my simulation setup ?

thanks in advance.

it's quite surprising that no one seems to have any idea of buoyancy
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Old   July 25, 2011, 13:45
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mohammad hossein shfiei
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Quote:
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it's quite surprising that no one seems to have any idea of buoyancy
i think u mast do 2 work:
1. simulate your model and calculate time for stability
2. add this time to general time and told to software start your own problem after calculate time for stability.
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Old   July 25, 2011, 17:02
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Jeff Burnham
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Force is calculated from acceleration (of the water on the object). If there is gravity, then the force is non-zero. If there is motion, then the force is non-zero. At t=0, when using the GMO harmonic oscillation model, acceleration is non-zero. Therefore, the initial state of the fluid is non-zero: although it is not 'in motion' (no advection is occurring), it is accelerating, correct? Therefore, the force on the GMO is also non-zero. Note that velocity works the same way, since it is also following a harmonic oscillation: GMO velocity at t=0 is not zero.
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Old   July 29, 2011, 00:21
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michael barkhudarov
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Quote:
Originally Posted by jiko View Post
I am analysing vertical force of water on a vertically (z, axis of gravity) oscillating GMO. the amplitude and frequency of the gmo is prescribed.
now since it is oscillating in still water I thought the initial force would be 0 at 0 time. but it is not. could someone please explain why the vertical force is not zero at zero time. or is something wrong in my simulation setup ?

thanks in advance.
It is the buoyancy force, like you said, that is computed at t=0. It should be close to the weight of the fluid displaced by the object
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