*2.1. Description of the Model*

As shown in Figure 1, a doubly curved FG-CNTRC shell panel in the orthogonal curvilinear coordinate system (*x, y, z*) is considered as the modal analysis. The panel has curvilinear length *a* in the *x-*direction, curvilinear width *b* in the *y*-direction, thickness *h* in the *z*-direction. In the middle surface of the panel, the principal radii of curvature, denoted by *Rx* and *Ry*, are assumed as constants. This results in unit Lamé parameters. Here, four special kinds of the doubly curved shell panels are investigated such as plate (PLA, *Rx* = *Ry* = ∞), cylindrical (CYL) panel (*Rx* = *R* and *Ry* = ∞), spherical (SPH) panel (*Rx* = *Ry*), and hyperbolic paraboloid (HPR) panel (*Rx* = −*Ry*).

**Figure 1.** Schematic of the laminated functionally graded carbon nanotube-reinforced composite (FG-CNTRC) doubly curved panel.
