Parameter identification for nonlocal phase field models for tumor growth via optimal control and asymptotic analysis

We introduce the problem of parameter identification for a coupled nonlocal Cahn-Hilliard-reaction-diffusion PDE system stemming from a recently introduced tumor growth model. The inverse problem of identifying relevant parameters is studied here by relying on techniques from optimal control theory of PDE systems. The parameters to be identified play the role of controls, and a suitable cost functional of tracking-type is introduced to account for the discrepancy between some a priori knowledge of the parameters and the controls themselves. The analysis is carried out for several classes of models, each one depending on a specific relaxation (of parabolic or viscous type) performed on the original system. First-order necessary optimality conditions are obtained on the fully relaxed system, in both the two and three-dimensional case. Then, the optimal control problem on the non-relaxed models is tackled by means of asymptotic arguments, by showing convergence of the respective adjoint systems and the minimization problems as each one of the relaxing coefficients vanishes. This allows obtaining the desired necessary optimality conditions, hence to solve the parameter identification problem, for the original PDE system in case of physically relevant double-well potentials.Comment: 39 page

On a Cahn--Hilliard--Brinkman Model for Tumor Growth and Its Singular Limits

In this work, we study a model consisting of a Cahn-Hilliard-type equation for the concentration of tumor cells coupled to a reaction-diffusion-type equation for the nutrient density and a Brinkman-type equation for the velocity. We equip the system with a Neumann boundary condition for the tumor cell variable and the chemical potential, a Robin-type boundary condition for the nutrient, and a "no-friction" boundary condition for the velocity, which allows us to consider solution-dependent source terms. Well-posedness of the model as well as existence of strong solutions will be established for a broad class of potentials. We will show that in the singular limit of vanishing viscosities we recover a Darcy-type system related to Cahn-Hilliard-Darcy-type models for tumor growth which have been studied earlier. An asymptotic limit will show that the results are also valid in the case of Dirichlet boundary conditions for the nutrient