Local convergence and active constraint identification theorems are proved for gradient-projection iterates in the cone of nonnegative ${\cal L}^2$ functions on $[0,1]$. The theorems are based on recently established infinite-dimensional extensions of the Kuhn-Tucker sufficient conditions and are directly applicable to a large class of continuous-time optimal control problems with smooth nonconvex nonquadratic objective fractions and Hamiltonians that are quadratic in the control input $u$.