Ellipticity of the Koiter and Naghdi models for nonhomogeneous anisotropic shells

We show that the bilinear forms associated to the linear thin shell models of Koiter and Naghdi, for a nonhomogeneous and anisotropic material are elliptic. We essentially use the fact that these bilinear forms are deduced from the three dimensional elasticity tensor, which is positive defined and also some techniques already used for homogeneous and isotropic shells. The ellipticity assures the existence and uniqueness of solution for these modelsAvailable from Departamento de Matematica, Universidade de Coimbra, 3000 Coimbra, Portugal / FCT - Fundação para o Ciência e a TecnologiaSIGLEPTPortuga