Vibrations of a simply supported plate carrying an elastically mounted concentrated mass

A large number of papers and technical reports are available on the technically important problem of structural elements executing transverse vibrations and carrying concentrated masses. In general it is assumed that the attachment is perfectly rigid. On the other hand, a rather limited amount of published work is available when the mass is elastically connected to the structure. The system then exhibits a more complex behavior than in the case of rigid attachment. The present study deals with the solution of the title problem using the well-known normal mode, sinusoidal eigenfunction expansions.     

Analytical and experimental investigation on vibrating rectangular plates with two opposite free edges and internal supports while the remaining are elastically restrained against rotation

This paper deals with the determination of an approximate fundamental frequency equation for a rectangular plate with two edges (y = 0, b) elastically restrained against rotation while the edges x=0, a are free but internal supports parallel to the free edges are present in the structural system. The algorithmic procedure can be easily implemented on a micro computer or even a hand, programmable calculator.Good engineering agreement with experimental results is shown to exist in the case of a plate with edges y=0,b rigidly clamped.     

A unified, polynomial approach for the approximate solution of thermoelastic problems in rectangular plates

The present paper, of a tutorial nature, solves two different thermoelastic problems using a unified approach: (a) thermoelastic stresses and deflections in thin, rectangular plates with edges elastically restrained against rotation when small-deflection theory is used and stress resultants in the middle plane of the plates are neglected; and (b) thermoelastic plane stress situations in rectangular plates with stress-free edges subjected to a two-dimensional temperature distribution.The first problem is attacked using polynomial coordinate functions which identically satisfy the governing boundary conditions, and the Ritz method is used to determine the plate response. When the flexibility coefficients approach zero (clamped edge conditions) the calculated results practically coincide with the exact solution for the test case treated in this paper. On the other hand this degenerate solution turns out to be a very convenient approximation for obtaining a solution to Airy's problem described in the second place and which is also solved in a straightforward manner using a variational approach.     

Dynamic response of the leg of a tension leg platform subjected to an axial, suddenly applied load at one end

This paper deals with the solution of the problem of the dynamic response of the leg of a tension leg platform subjected to an axial, suddenly applied load at one end, considering a highly simplified model but taking into account several complicating factors. The problem is solved by means of a non-harmonic Fourier expansion in terms of eigenfunctions obtained from a non-regular Sturm-Liouville system.     

Kirsch problem and the lower natural frequencies of a clamped square-plate

A clamped square-plate is subjected to a uniform state of stress in the x-direction. The present study deals with the basic question of determining the variation of the lower natural frequencies of transverse vibration of a plate as a small diameter, central hole is made in it, introducing a stress concentration field.     

Transverse vibrations of a rectangular cantilever plate with thickness varying in a discontinuous fashion

A numerical solution is obtained for the title problem by means of the popular finite element method. An experimental investigation of the problem is also presented for plates of square planform. The agreement between theoretical and experimental values is very good in the case of the fundamental frequency, and reasonably good when the second and third normal modes of transverse vibration are considered. It is concluded that beneficial effects are obtained in the sense that one generates a lighter structural element with higher fundamental frequency of transverse vibration. Hence, dynamic stiffening is achieved.     

Monitoring the status of a mechanical cable while in operation by means of the acoustic emission method

The mechanical cable is an essential element in towing operations, remote control of equipment, salvage operations, civil engineering applications, etc.Failure of these cables can result in loss of life and loss of equipment worth hundreds of thousands of dollars. Obviously then, sensors that can indicate the condition of these cables so that the risk to their continued use and their remaining safe life can be determined when in operation are very important from the point of view of commercial and military interest.This paper presents a brief review of research into failure mechanisms of various cables and the acoustic emission signatures of the various cables under simulated loading. The development of a specific operational monitor for a towed cable system is also given.     

Oxidative stress in Laeonereis acuta (Polychaeta, Nereididae): environmental and seasonal effects

Laeonereis acuta was seasonally collected in an industrially polluted site (P) and in an unpolluted site (UP) at the Patos Lagoon estuary (southern Brazil). Glutathione S-transferase (GST), superoxide dismutase (SOD) and catalase (CAT) activity (U/mg protein) was determined in five groups of worms from each site. Metallothionein (MT - mol GSH/g ww) and lipid peroxides content (LPO - nmoles of cumene hydroperoxide/g ww) were also measured. Annual mean values for CAT (UP=3.7+/-0.3; P=5.7+/-0.6), GST (UP=0.034+/-0.003; P=0.045+/-0.004) and MT (UP=0.15+/-0.02; P=0.23+/-0.03) were higher (p<0.05) in worms from the P site. In autumn, CAT activity was higher (p<0.05) in worms from the P site (7.6 +/- 1.3) than in those from the UP site (3.6 +/- 0.4). In summer, MT concentration was higher in worms from the P site (0.37 +/- 0.03) than in those from the UP site (0.19 +/- 0.01). No significant difference (p>0.05) in the LPO content was observed in worms from the different sites or collected in different seasons. These results indicate that worms from the polluted site showed higher antioxidant responses than those from the unpolluted site, sufficient to prevent oxidative damage in terms of LPO.