S.A. Vera

Transverse vibrations of circular annular plates with edges elastically restrained against rotation, used in acoustic underwater transducers

Abstract Simply supported or clamped boundary conditions are rather ideal situations difficult to satisfy from a physical viewpoint. This paper considers a more “moderate” restriction: the case of edges elastically restrained against rotation for which no exact solution appears in the open literature. Eigenvalues corresponding to a wide range of the intervening geometric and mechanical parameters are determined. Good agreement is obtained with frequency coefficients determined two decades ago by means of a variational method. Obviously the problem is of basic interest in many ocean engineering applications: from the design of certain underwater acoustic transducers to pump and compressor elements passing through the design of naval vehicles and ocean structures.

Numerical experiments on dynamic stiffening of beams and plates

Abstract By introducing continuous or discontinuous variations in the thickness of beams, arches and plates, it is possible in many practical situations to raise the value of the fundamental frequency and, at the same time, to lower the weight of the structural element. This is a beneficial situation, especially in those cases where weight reduction and large dynamic stiffness are of interest. The present paper surveys some recent practical accomplishments in this area. The rigorous procedure consists, from a general structural optimization viewpoint, of minimizing an objective function (for instance, total volume) subject to constraints on the geometry and behavior (natural frequencies, buckling loads, etc.). In many instances it is convenient to reverse the problem: one fixes or limits the weight or volume and constructs some quantity which describes the desired behavior of the system e.g. the fundamental frequency. The problems under study in the present paper are considerably more modest in scope, since the procedure is performed by numerical experiments.

A Note on the Solution of Very Basic Vibrations Problems Obtained from a Generalised Situation

Two forced vibrations problems are fundamental from academic and technological viewpoints; the suddenly applied constant-value force, and the situation where a sinusoidally varying excitation acts on the system. It is shown that both problems are particular cases of a more general excitation. The resonance stage is studied in detail.

A computer-aided modelling analogue for lattice dynamics

A useful methodology to study lattice dynamics is presented in this paper. Our method is based on the analogous behaviour of electromagnetic waves in transmission lines. The parameters analysed include the optical and acoustical branches and the frequency gap. The electrical circuit is solved using commercial software (MicroCap ); therefore, our methodology would be easily implemented on different systems. Resumen. En este trabajo se presenta una metodologia util para estudiar dinamica de redes. Nuestro metodo se basa en el comportamiento analogo de las ondas electromagneticas en las lineas de transmicion. Los parametros analizados incluyen las ramas optica y acustica y el gap de frecuencia. El circuito electrico es resuelto utlizando un software comercial (MicroCap ); por lo que nuestra metodologia puede ser facilmente implementada en diferentes sistemas.