This thesis is concerned with the free vibration analysis of stiffened
circular cylindrical and conical shells. The study was carried out with
a view to improving the accuracy and efficieny of various modelling
techniques for the prediction of the stiffened shells natural frequencies
and mode shapes.
A review of the existing literature covering various aspects of the shell
vibrations problem and modelling techniques has been given at the
beginning of each chapter with a critical appraisal of the assumptions
made and results obtained.
Initially the continuum energy approach was used for the analysis. The
developed method allows for discrete consideration of stiffeners having
arbitrary location and properties. Energy of bending in two planes and
rotary inertia have been included in the analysis. Various types of
stiffened shells with shear diaphragm ends condition were analysed using
this method for the prediction of their natural frequencies. The
predicted results have been compared with published experimental results.
The finite element technique was also used for the prediction of natural
frequencies and mode shapes of stiffened shells. Axisymmetric shell of
revolution element, Facet shell element, semi-100f element and various
types of beam elements, which are available within the PAFEC 75 suite of
programs, were used for these studies. An efficient modelling technique
has been introduced for ring stiffened cylindrical and conical shells by
the use of the shell of revolution element.
For improved accuracy of the predicted frequencies and a more economical
model, shell symmetry was utilized for the free vibration analysis of
unstiffened and stiffened shells. Half, quarter and one eighth models
were studied by developing the appropriate boundary conditions and are
discussed here. The free vibration characteristics of orthogonally stiffened cylindrical
shells and an orthogonally stiffened cylindrical panel have been studied.
An eight noded stiffened super shell element was developed for this
study. This element was used for modelling various other types of
stiffened shells and the predicted natural frequencies have been compared
with known published experimental and theoretical results.
Experimental verification of theoretical predictions of natural
frequencies and mode shapes of an orthogonally stiffened cylindrical
panel was carried out and is reported here.
A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.