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February 14, 2006, 12:57 
Force on body by velocity compared to force_y@...

#1 
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Dear posters, it would really help me if anyone could give me a hint with this:
in order to calculate the Force on a bluff body normaly one uses force_y@bluffBodyName. This shuould calculate the y component of Integral(sigma dot normal)*dS this integral is equal to areaInt((p+2*Dynamic Viscosity*(Velocity u.Gradient X))*Normal X)@bluffBodyName + areaInt(Dynamic Viscosity*(Velocity u.Gradient Y+Velocity v.Gradient X)*Normal Y)@bluffBodyName + areaInt(Dynamic Viscosity*(Velocity u.Gradient Z+Velocity w.Gradient X)*Normal Z)@bluffBodyName But they are not equal! Question: Why? (I need to calculate the Integral this way, because in my application I need to direcly acsess the memory of the solver with Fortran routines and map forces from a deformed to a reference configuration) 

February 14, 2006, 13:08 
Re: Force on body by velocity compared to force_y@

#2 
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Dear Stefan,
I assume you are using a laminar model because otherwise you cannot assume that the shear force is visc*(grad vel + gradT vel).. Recall that the turbulence models use wall functions, and the expression for wall shear is C * (Vel Node  Vel Wall) or something in that direction.. Good luck, Opaque.. 

February 15, 2006, 10:27 
Re: Force on body by velocity compared to force_y@

#3 
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Thank's a lot for your answer.
Yes I am using a laminar model the reynolds number is only 20. no wall function or anything like that is used. using f_x@cylinder I get 5.56847e005 [N] and using visc*(grad vel + gradT vel) leads to 5.48238e005 [N] which is not the same and I need it to be exact. Really looks like I foregot something. Can you think of anything else that went wrong? greetings Stefan 

February 15, 2006, 10:29 
Re: Force on body by velocity compared to force_y@

#4 
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Foregot to say that the fluid is visous and incompressible


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