Symmetric Imperfections Research Articles

The effect local geometric imperfections of rotational shell on its natural frequencies and models

In this paper, an additional stiffness matrix of meridional geometric imperfections was formed by considering the geometric imperfections as initial displacements based on reference [7]. Then, natural frequencies and models of rotational shell with symmetric geometric imperfections were analysed by perturbation method. From the computed example, it was known that the effect of geometric imperfections of frequencies is to increase them, and the larger the range of imperfection, the more the frequencies would be increased.

Geometrically Nonlinear Finite Element Analysis of Imperfect Laminated Shells

Formulations and computational procedures are presented for the finite element analysis of laminated anisotropic composite thin shells including imperfections. The derivations of the nonlinear geometric element stiffness matrices were based on the total Lagrangian description. A 48 degree-of-freedom (d.o.f.) general curved shell element with arbitrary distribution of curvatures was used to model the shell middle- surface. Numerical results include the large deflection behavior of a variety of perfect plate and shell examples; buckling of a spherical shell with an axially symmetric im perfection ; and buckling of a cylindrical panel using measured initial transverse im perfections. A good comparison with existing results is obtained.

Effect of a small deviation in the form of the shells of revolution from axial symmetry on their state of stress

The effect of small, non-axially symmetric imperfections of the middle surface in shells of revolution on their stresses and displacements is studied. A strong dependence on them is found both in statics as well as thermoelasticity. The general theoretical results are confirmed by a numerical study of the displacement and stress fields in cylindrical and conical shells with small imperfections of the type f( z) cos mφ.

Plastic Symmetry of Roorda's Frame

Abstract The well-known Roorda frame displays an asymmetric postbuckling behavior in the elastic case, and it is therefore sensitive to asymmetric geometric imperfections. By contrast it is shown here that an elastic-plastic frame displays practically symmetric imperfection sensitivity since the maximum load is attained by a basically different mechanism that only to an insignificant degree invokes that part of the geometric nonlinearity which induces the asymmetry.

Nonlinear Stability Analysis of Pressure-Loaded imperfect Stiffened Cylinders

This paper deals with the buckling of imperfect, thin, circular, cylindrical, stiffened shells under the application of external pressure. The methodology is based on the smeared technique, the Von Karmgn-Donnellnonlinear kinematic relations, and linearly elastic behavior, and it considers both axisymmetric and symmetric imperfections. Numerical results for various configurations are presented. These include some optimal stiffened configurations which exemplify submarine hull designs for operating depths of 1000 and3000 ft (305 and 915 m).

Asymmetric Buckling of Imperfect Spherical Shells

A study is presented concerning the buckling characteristics of spherical shells with small initial symmetric and asymmetric imperfections in the geometry. The governing nonlinear partial differential equations are formulated using general relations with no restriction on shallowness. The effect of initial geometric imperfections is included in the equations. The shell material is assumed to be linearly elastic. The solution of the differential equations is carried out numerically using the method of L.V. Kantorovich in combination with finite differences. Numerical results are obtained by means of a digital computer, for spherical shells clamped at the boundary and subjected to uniform external pressure. Buckling pressures are determined from the load deflection relationship. The cases of asymmetric imperfections, and symmetric imperfections are studied. A wide range of shell geometries and imperfections is covered. Comparison with earlier experimental results shows good agreement.