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-   -   Impose transeint force (http://www.cfd-online.com/Forums/star-ccm/85668-impose-transeint-force.html)

 Henry Arrigo March 3, 2011 17:52

Impose transeint force

Hello,
How can I impose a sinusoidal force on a body. In the external force node there is no possibility to bind a Field function. What s your suggestions please?

Thank you.

 Henry Arrigo March 3, 2011 17:54

any one can help me please?

 alastormoody11 March 4, 2011 00:29

If the field function is not available you need to write a macro.

A simple strategy is to record a macro where you set a value for the external force with a numeric value.

Use this macro as a initial construct and instead of the numeric value replace it with your function.

 Henry Arrigo March 4, 2011 10:07

thank you
this is not gonna work since I need to impose a continuous force while this case would result in a discrete one. more over I want to come up with solution in a single run.

 alastormoody11 March 7, 2011 00:28

Hi,

As long as you are using CFD for your simulation you cannot apply continuous force.

Whatever you do, even if you manage to get your BCs via a field function you will be using a finite time step and hence your profile will always be implemented in discrete time steps and not in a continuous fashion as you have envisioned.

So the only remedy to the above problem is to use a smaller time step while applying the acceleration profile.

Hope you got that

 Henry Arrigo March 7, 2011 10:01

Hi,
Thank you Alastormoody.
Did you mean applying acceleration to the fluid field? Did I get it right.

In the wall node and in the Physics Conditions sub-node, there is an option which is named Tangential Velocity Specification. It has this possibility to use a field function as a vector field. Have you ever use that? I guess that could be a remedy too...

Thanks.
Henry

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