Applying boundary conditions to PDE

Question

Can anyone help me on how to define the following BC for a PDE in Maple or Mathematica:

\begin{equation} Diff(f(t,r,\theta),r) \ \ \ when \ \ \ r=a \ \ \ equals \ \ \ V \cdot a^2 \cdot sin\theta\\ Diff(f(t,r,\theta),\theta) \ \ \ when \ \ \ r=a \ \ \ equals \ \ \ V \cdot a \cdot sin^2\theta \end{equation}

Answer 1

In Mathematica,

Derivative[0,1,0][f][t,a,\[Theta]]==V a^2 Sin[\[Theta]]
Derivative[0,0,1][f][t,a,\[Theta]]==V a Sin[\[Theta]]^2