FINITE ELEMENT ANALYSIS AND DESIGN OF LARGE SHELLS

Abstract

It is well known from the theory of shells that classical solutions of shells subjected to different types of loads involves tedious calculations and is extremely difficult especially for shells of arbitrary shapes. The finite element method is very much suitable for the analysis of shells of general shape because of its flexibility in accounting arbitrary geometry, loading and variation in the material properties. Also in these modern days of supercomputers numerous numbers of softwares are available for finite element analysis viz. ANSYS, COSMOS, NASTRAN, ABEQUES...etc. In present work, the three dimensional theory of continuum mechanics has been briefly reviewed. The process of degeneration of a three dimensional solid into more simpler element has been discussed. Some comments on the different theories developed so far on plate or shell elements are given. A brief review of finite shell elements is also given. The problems of cylindrical shells with and without edge beams (Single, intermediate and outer cylindrical shells) and hyperbolic paraboloid shells were taken for analysis purpose. ANSYS, finite element analysis software was employed for the analysis. The basics of finite element analysis and ANSYS features also had been discussed separately. Three types of elements namely 4-noded, 8-noded degenerated shell elements and 3-D beam elements had been employed for the analysis purpose, however, 3-D brick element with six degrees of freedom per node also has been employed for some problems to verify the performance of different elements. As obviously, solid modeling for thin shells yields less accurate results as compared to surface modeling. The mathematical formulation of a degenerated shell element also has been discussed. To understand the behavior of cylindrical and hyperbolic paraboloid shells a parametric study has been carried out and the effect of various parameters on their behavior has been studied and the results have been discussed. Later to understand the basic concepts of designing of the shells and to have knowledge about the reinforcement details, one problem of single cylindrical shell with edge beam and hyperbolic paraboloid shell (inverted umbrella type) has been and designed.