calculating force coefficents

achyutan · June 5, 2013, 05:24

Hi,

could someone tell me how to calculate force coefficients for a moving object (mesh motion) ?
I have experience in calculating forces and coefficients by using 'forces' object in controlDict. I want to know how to modify the vectors liftDir and DragDir based on the moving object (boundary). I want to make a script so that the calculation is automated.

regards,

achyutan

achyutan · June 7, 2013, 04:45

Hi,

I am waiting for some response to know if anybody has had experience in modifying vectors liftDir, dragDir in controlDict during run time for moving objects.

If reported unclear, i can explain in detail.
But, i am disappointed that nobody turns up with a response.

regards,

achyutan

kilroy · June 13, 2013, 18:02

achyutan,

If you can give more details about your case I can try to help. Why don't you calculate the forces with OpenFoam and calculate your force coefficients externally?

Sincerely,

Kilroy

achyutan · June 26, 2013, 07:15

Hi,

First of all, thanks for the reply which was encouraging for me.

I want to create a boundary condition for moving boundary which makes use of lift, drag forces/coefficients. so, i want to calculate lift, drag forces/coeffs at run-time and access them in my b.c for a moving wall. This implies that i need to change liftDir, dragDir according to the movement of solid boundary.

calculating these force/coeffs externally and feeding them back into openfoam at every time step is like creating an interface btw openfoam and external script. i want to avoid it and that's precisely why i went for such an implicit b.c

regards,

achyutan

kilroy · June 26, 2013, 09:45

achyutan,

I don't think OpenFoam have the capabilities that you need by default. The only way I can think of is to stop the simulation in each time step and edit the parameters that you want to edit. Then set startTime to latestTime and restart. Maybe you can accomplish what you have described by using an external python script or by modifying the OpenFoam source-code, but I have no experience on modifying OpenFoam code for the boundary conditions the way you want.

Hope this helps,

kilroy

June 5, 2013, 05:24	calculating force coefficents	#1
achyutan Member Join Date: Sep 2012 Posts: 60 Rep Power: 13	Hi, could someone tell me how to calculate force coefficients for a moving object (mesh motion) ? I have experience in calculating forces and coefficients by using 'forces' object in controlDict. I want to know how to modify the vectors liftDir and DragDir based on the moving object (boundary). I want to make a script so that the calculation is automated. regards, achyutan

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June 7, 2013, 04:45		#2
achyutan Member Join Date: Sep 2012 Posts: 60 Rep Power: 13	Hi, I am waiting for some response to know if anybody has had experience in modifying vectors liftDir, dragDir in controlDict during run time for moving objects. If reported unclear, i can explain in detail. But, i am disappointed that nobody turns up with a response. regards, achyutan

June 13, 2013, 18:02		#3
kilroy Senior Member Join Date: Mar 2013 Location: USA Posts: 120 Rep Power: 13	achyutan, If you can give more details about your case I can try to help. Why don't you calculate the forces with OpenFoam and calculate your force coefficients externally? Sincerely, Kilroy

June 26, 2013, 07:15		#4
achyutan Member Join Date: Sep 2012 Posts: 60 Rep Power: 13	Hi, First of all, thanks for the reply which was encouraging for me. I want to create a boundary condition for moving boundary which makes use of lift, drag forces/coefficients. so, i want to calculate lift, drag forces/coeffs at run-time and access them in my b.c for a moving wall. This implies that i need to change liftDir, dragDir according to the movement of solid boundary. calculating these force/coeffs externally and feeding them back into openfoam at every time step is like creating an interface btw openfoam and external script. i want to avoid it and that's precisely why i went for such an implicit b.c regards, achyutan

June 26, 2013, 09:45		#5
kilroy Senior Member Join Date: Mar 2013 Location: USA Posts: 120 Rep Power: 13	achyutan, I don't think OpenFoam have the capabilities that you need by default. The only way I can think of is to stop the simulation in each time step and edit the parameters that you want to edit. Then set startTime to latestTime and restart. Maybe you can accomplish what you have described by using an external python script or by modifying the OpenFoam source-code, but I have no experience on modifying OpenFoam code for the boundary conditions the way you want. Hope this helps, kilroy