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Note: / This thesis deals with flow-induced ovalling oscillation and the mechanical characteristics of cylindrical shells. The experiments were conducted with epoxy shells which were either clamped at both ends or clamped at one end and free at the other end. The response of the shells in cross flow was studied in a wind tunnel. A mini-shaker and a fotonic sensor were used to determine the mechanical characteristics (including the natural frequencies, modal damping, and the axial and circumferentia1 mode shapes) of the shells. An analytical method was developed, with the use of potential flow theory for the aerodynamic force, to calculate the oscillation frequencies as well as the negative aerodynamic damping values of clamped-clamped shells. Theory and experiments prove that flow-induced ovalling vibration of a cylindrical shell is not a three-dimensional effect, but rather an aeroelastic phenomenon. Vibration of the shell does not depend on flow periodicity in the wakes and an integral relationship (f/fvs) between the shell frequency (f) and the vortex shedding frequency (fvs) is not necessary at the onset of ovalling. / Cette these traite des oscillations induites par ecoulements, incluant les characteristiques mecaniques de coques cylindriques. Un mini-vibrateur et un capteur optique (Fotonic) ont ete utilises pour determiner les characteristiques mecaniques (inc1uant les frequences naturelles: l'amortissement, et les formes modales axiales et circonferentielles) des coques. Une methode analytique a ete developpee pour le calcul des frequences d'oscillations, ainsi que les valeurs negatives de l'amortissement aerodynamique des coques fixes, faisant usage de la theorie des ecoulements potentiels pour les forces aerodynamiques. La theorie et les essais sur ces coques demontrent que la vibration induite par ecoulements est un phenomene aeroelastique bi-dimensionnel, plutot que tri-dimensionnel. Les vibrations de la coque ne dependent pas de la periodicite de ecoulement dans le sillage, et un rapport integral (f/f ) vs entre la frequence de la coque et la frequence du detachement de tourbillons n'existe pas necessairement, au seuil des vibrations.

This thesis presents a novel device for measuring the viscoelastic properties of biological tissue. The ability to measure the mechanical properties of tissue is of special interest for many medical applications; ranging from disease diagnostics to surgical operations and simulations. In practice, physicians use a technique called palpation to detect the presence of viscoelastic property changes which are associated with the healthiness of tissue. Palpation relies exclusively on the expertise and experience of the physician and is only effective if the difference in tissue stiffness is profound. Current technologies for the measurement of tissue healthiness, including ultrasound, have been shown to be incapable of detecting isoechoic lesions even though they were significantly stiffer than surrounding tissue. The new device presents a reliable, accurate and quantitative method for determining the mechanical properties of soft tissue. Consequently, the healthiness of the tissue or the presence of lesions can be found.

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