Key wordsControl of elliptic variational inequalities, functionally graded plates, optimal design of plates, finite element approximations.Optimal design of a simply supported functionally graded axisymmetric circular plate resting on several inner rigid rings is presented in Part I. The variable thickness and the exponent of the power-law of the grading function are to be optimized.In Part II the approximate state problem and approximate optimal design problems are introduced, using spaces of linear and cubic Hermite splines, respectively. We prove the existence of approximate solutions and the convergence of a subsequence of the solutions to a solution of the original continuous optimal design problem.In Part II of the present paper we propose and analyse numerical approximate solutions of the four Optimal Design Problems introduced in Part I [2]. The procedure is based on simple finite element approximations of both the state and design variables.The core of the numerical analysis is represented by a general Theorem 3.1 on two-parametric approximations of elliptic variational inequalities. In Sect. 2 we introduce approximations of the set of admissible state variables, of the elliptic operators and of the designed thickness by means of linear and cubic Hermite splines.A general theorem on two-parametric approximations is proved in Sect. 3 and applied in Sect. 4. Approximate cost functionals are introduced in Sect. 5. In Sect. 6 we prove that there exists a subsequence of approximate optimal designs, which converges to a solution of the original Optimal Design Problem, if the mesh-size tends to zero.
Approximate solution of the state problemWe introduce simple discretizations of the spaces, sets, and operators defined in Part I - [2].x m ] be a partition of the interval Ω ≡ [0, R], (x 0 = 0, x M = R), such that the points r 1 , . . . , r N , corresponding to the radii of rigid circular supports, belong to the nodes x m of T