Eigenoscillations for PWR-core barrel - comparison between various theoretical results for the HDR geometry

In this paper the results of three approaches to the eigensolutions of a cylindrical shell are compared. The first method, code CYLDY3, is based on analytical solutions of the full partial differential equations for thin-walled cylindrical shells derived by Fluegge. This method gives exact results for eigenfrequencies and mode shapes in the framework of the theory. The given boundary conditions are matched exactly. On the other hand, as the differential equations as well as the boundary conditions enter the computer program, it is difficult to take into account any irregularities with respect to the geometry or the material of the shell. The code CYLDYFE, representing the second approach, is confined to cylindrical shells, too. It yields the eigensolutions by means of the finite element method, using ring type elements where the mode shape functions in azimuthal direction are given analytically. The elastic law for each element is based on Timoshenko's theory for cylindrical shells or, optionally, on Fluegge's simplified equations. Since geometrical and material properties may be defined separately for each element, it is easy to treat irregularities of the shell like changes in wall thickness, for example, as long as they remain axisymmetrically. In the third approach the shell is modelled using the standard finite element program STRUDL/DYNAL. Its advantage is the adaptability to various geometrical configurations. Its disadvantage arises from the computational effort and from limitations in spatial resolution. (orig./GL)