The paper outlines an approach to identifying the principal dynamic-instability domain for systems composed of shells of revolution with different shapes under axisymmetric periodic loading. The original problem is reduced to one-dimensional eigenvalue problems with respect to the meridional coordinate. Results of calculations for a specific shell system are presented Keywords: shell system, periodic load, dynamic instability domain Introduction. When in service, various shell systems or their components may be subjected to periodic loads that somehow change some characteristics of the system. These are, for example, aircrafts with pulsating thrust, underwater pipelines subjected to external pressure and conveying pulsating flows of oil and gas, mine hoists that periodically interact with the pit-shaft, etc. Problems of the stability of such systems under various loads are of interest for reasons of accident prevention. The theoretical treatment of these problems in the general case involves solution of nonlinear nonstationary dynamic problems for elastic systems and analysis of varying vibration modes and scenarios for the occurrence of irregular modes. The practically important dynamic problem of identifying the instability boundaries may be solved in the linear case. The results of previous relevant studies are covered in [12,13,20].The dynamic stability of plates and cylindrical shells was adequately studied in [5, 10, 16-19, 21, 22, 24, 25]. A considerably fewer publications are concerned with conical and spherical shells [7-9, 23]. Very few papers such as [2, 3] mention the possibility of examining compound shell systems with variable parameters, assuming the initial state momentless and homogeneous. The range of studies on such shells was extended because of the following complicating factors: layered structure [10,22,25], orthotropy and viscosity of elastic materials [10,[16][17][18]21], various boundary conditions and types of periodic loads [5,8,23], complex configuration of plates [19], etc. The longitudinally inhomogeneous mechanical characteristics of shells of revolution were taken into account in [2,3].Parametric vibrations were in most cases studied using the classical Kirchhoff-Love model of thin shells or simplified Donnell's model [2,3,8,9,23]. In the case of layered shells made of viscoelastic composites, the first-order Timoshenko-Reissner shear model [16,21,22] was sometimes used.Nonstationary nonlinear problems are traditionally reduced, by the Bubnov-Galerkin method, to solution of Cauchy problems for dynamic systems with several degrees of freedom and analysis of their solutions for stability. To this end, the finite-difference and finite-element methods may be used as well.Linear problems of identifying the dynamic-instability domains are reduced to a system of Mathieu-Hill equations whose properties are well known [11]. Another approach to identifying the dynamic-instability domains of shells of revolution with longitudinally (meridionally) variable parameters was proposed in [2,3], whe...