1. A computer-implemented method of forming a computer-based model of manufacturable product, the method comprising: in a hardware processor configured to implement a computer aided design (CAD) system: forming a CAD model modeling a subject product, including in the CAD model designing a surface of the subject product that is defined by guiding curves P(u) and Q(v) and a coupling curve s (t(s),w(s)); and improving the manufacture of the subject product as modeled by the formed CAD model and the designed surface by, in the CAD system: accessing data, in a memory or disk storage, that defines the guiding curves of the defined surface P(u) and Q(v) and a cost function ƒ(t,w); defining an objective function of the type J=J(ƒ,t,w), involving both the cost function ƒ(t,w) and coordinates t,w of the coupling curve of the designed surface s (t(s),w(s)); optimizing said objective function J to obtain a coupling curve of the designed surface s (t(s),w(s)) of parameter s; providing, at a user display, CAD system output of the CAD model including display of the subject product having the designed surface according to the guiding curves P(t(s)) and Q(w(s)), respectively composed with the coordinates t,w of the coupling curve obtained, wherein: at the steps of defining and optimizing the objective function, the objective function J=J(ƒ,t,w) is constrained such that arguments t,w of the cost function ƒ(t,w) are regulated by a regulation function μ; and enabling the improved manufacturing of the subject product represented by the CAD system output of the CAD model.