[nwpukaka]

Dear OpenFoamer,

I've tried to write this cyclic or periodic boundary condition code by myself. For the velocity between two connected surface, I use the transformation matrix to change the direction of velocity. In order to calculate this matrix, the normal and tangent vectors of surface should be inputted. For instance,

nA = [-sin(theta_A), cos(theta_A), 0.0]
t1A = [cos(theta_A), sin(theta_A), 0.0]

however, there is certain error between real value of nA and calculated one. if theta_A = 30 degree. cos(theta_A) should be equal to sqrt(3)/2, but for the double type value in C++, the calculated result of cos(theta_A) is slightly different from real value, and then make the mass flux through two connected surfaces different.

So how can I fix this bug?

Thanks in advance