# Impose transeint force

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 March 3, 2011, 17:52 Impose transeint force #1 Senior Member   Henry Arrigo Join Date: Jun 2010 Location: Italy Posts: 100 Rep Power: 8 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. Last edited by Henry Arrigo; March 3, 2011 at 18:51.

 March 3, 2011, 17:54 #2 Senior Member   Henry Arrigo Join Date: Jun 2010 Location: Italy Posts: 100 Rep Power: 8 any one can help me please?

 March 4, 2011, 00:29 #3 Senior Member   Join Date: Jun 2009 Posts: 100 Rep Power: 9 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.

 March 4, 2011, 10:07 #4 Senior Member   Henry Arrigo Join Date: Jun 2010 Location: Italy Posts: 100 Rep Power: 8 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.

 March 7, 2011, 00:28 #5 Senior Member   Join Date: Jun 2009 Posts: 100 Rep Power: 9 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

 March 7, 2011, 10:01 #6 Senior Member   Henry Arrigo Join Date: Jun 2010 Location: Italy Posts: 100 Rep Power: 8 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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