Local quadratic convergence of the SQP method for an optimal control problem governed by a regularized fracture propagation model

Abstract

We prove local quadratic convergence of the sequential quadratic programming (SQP) method for an optimal control problem of tracking type governed by one time step of the Euler-Lagrange equation of a time discrete regularized fracture or damage energy minimization problem. This lower-level energy minimization problem contains a penalization term for violation of the irreversibility condition in the fracture growth process and a viscous regularization term. Conditions on the latter, corresponding to a time step restriction, guarantee strict convexity and thus unique solvability of the Euler Lagrange equations. Nonetheless, these are quasilinear and the control problem is nonconvex. For the convergence proof with L∞ localization of the SQP-method, we follow the approach from Tröltzsch [SIAM J. Control Optim. 38 (1999) 294–312], utilizing strong regularity of generalized equations and arguments from Hoppe and Neitzel [Optim. Eng. 22 (2021)] for L2-localization.