How can I identify the action point for forces on a surface in CFX-11.0?




This can be done in CFX-Post, but not automatically. In the CFX-Post calculator you have to calculate the following expression for 2D space:

x_p = (area y * x * Pressure + area y * x * shear stress)/(area y * Pressure + area y * shear stress)

for each coordinate.

In 3D space, this becomes more complicated as you need to solve the matrix equation

r x F = Integral( r x (p+shear stress )*d_area )

where 'x' stands for vector product. The integral is available in CFX-Post as torque and forces are also there, but to get components of action point location 'r={x_p,y_p,z_p}', you will need to solve linear system of equations :

F_y*z_p - F_z*y_p = T_x
F_z*x_p - F_x*z_p = T_y
F_x*y_p - F_y*z_p = T_z

where T_x, T_y, T_z are components of torque.

Also, to obtain boundary values directly from the solver (which are much more accurate) you need to switch on "Output Boundary Flows" in the Boundary condition frame in CFX-Pre (descibed in CFX Help>Post>Post Tools Menu>Function Calculator).





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