A method of studying the natural vibrations of highly inhomogeneous shells of revolution is developed. The method is based on a nonclassical theory of shells that allows for transverse shear and reduction. By separating variables, the two-dimensional problem is reduced to a sequence of one-dimensional eigenvalue problems. The inverse iteration method is used to reduce these problems to a sequence of inhomogeneous boundary-value problems solved by the orthogonal sweep method. The capabilities of the method are illustrated by solving certain representative problems and comparing their solutions with those obtained using the three-dimensional theory of elasticity, the classical theory of shells, and the refined Timoshenko model Keywords: highly inhomogeneous shells of revolution, natural frequencies, transverse shear, reduction, solution technique, inverse iteration method, three-dimensional theoryIntroduction. General analysis of the frequency spectrum of elastic structures, as any linear system, has two interrelated subtasks: qualitative analysis of the behavior of this spectrum and quantitative dynamic analysis of a specific class of structures [1-3, 5, 7, 9, 10, 11, 16]. The present paper is concerned with the latter task and naturally continues the developments intended to determine the natural frequencies and modes of the elastic objects mentioned in [3]. Most studies in this area are based on two shell models: classical Kirchhoff-Love model and refined Timoshenko model. These models made it possible to accurately calculate the lowest frequencies for a wide class of thin and medium-thickness shells made of shearable materials. However, these models may fail to ensure required accuracy for shells highly inhomogeneous across the thickness, such as laminated shells with layers whose mechanical properties differ by more than an order of magnitude. In this connection, this paper proposes a method to calculate the dynamic characteristics of shells based on a nonclassical model that allows for all transverse strains. The capabilities of the method will be demonstrated by solving representative problems for a wide scope of assumptions on the inhomogeneity of shells across the thickness. The frequencies obtained by the three-dimensional theory of elasticity and by two-dimensional shell models of different degrees of accuracy will be compared. The nonclassical shell model that accounts for transverse shears and reduction was earlier tested by solving stress-strain problems for laminated shells under local loads and contact problems for shells of revolution on a rigid foundation [12,14,15].
Problem Formulation and SolutionTechnique. The subject of study is the class of inhomogeneous shells of revolution described, as three-dimensional bodies, in an orthogonal curvilinear coordinate system s, q, V (s is the meridional arc length, q is the cross-sectional central angle, and V is the thickness coordinate reckoned from some coordinate surface V = const). Shells of this class include an arbitrary number J of isotropic and ort...