# Force of sphere due to doublet

1. Nov 2, 2012

### shaowei

1. The problem statement, all variables and given/known data
Consider ideal 3D flow. Let the center of a sphere of radius "a" be on the reference axis at the origin. Let a doublet of strength "m" be on the reference axis to the right of the sphere at a distance L=3a. Find the force acting on a sphere due to the doublet

2. Relevant equations
Force due to doublet: F = -ρm$\frac{\partial u_{i}}{\partial x}$

3. The attempt at a solution
I'll be honest, at this point my classmates and I are at a complete loss. I know I need to calculate the velocity potential in terms of r & θ and then take the derivative of the velocity potential to obtain the velocity. With the velocity I can plug it into the equation above. Any guidance or ideas would be great! Thank you in advance!