The general solution was obtained for the free flexural vibrations in the plane of a thin circular ring containing a point mass. As a degenerate case of the general solution, the solution for a uniform ring alone was derived from the general solution by taking the point mass to be zero. Numerical calculations of the frequencies and mode shapes of the first and second flexural modes were made for values of the point mass in the range from zero to infinity. The results are presented in graphical form. The predominant feature of the investigation was the difference in frequency and mode shape found in the symmetrical and antisymmetrical modes, and the particular orientation of the nodes with respect to the point mass. It was noted that similar phenomena were observed experimentally for vibrations of imperfect bodies of revolution. In conclusion, it was brought out that a ring with a point mass offers a convenient mathematical model for a preliminary theoretical investigation of the vibrations of imperfect bodies of revolution. / Master of Science

This dissertation presents techniques for using adaptive trusses for active vibration isolation in flexible structures. Passive methods have been used almost exclusively in the past for vibration isolation, although in the more recent literature active techniques have been proposed in an attempt to achieve greater isolation performance. Most of the active techniques, however, require either detailed knowledge of the system or of the disturbance to be isolated. This work focuses on techniques in which knowledge of the disturbance is minimal, and in some cases, knowledge of the system is not necessary. Two new active vibration isolation methods are presented which are based on feedback of transmitted forces in the system. The methods include force feedback through a high gain, and state feedback using the LQR method with disturbance modelling. A third method which has been demonstrated in the literature, force feedback through a classical compensator, is also presented for comparison. For the purpose of discussion, each of the methods is applied to a system which includes a single active mount. The methods are then applied analytically to an adaptive truss, which essentially contains multiple mounts, to demonstrate multi-degree-of-freedom active vibration isolation. It is shown that force feedback provides two-way isolation, and its effects are independent of the type of active mount used (whether it is a force- or displacement-commanded mount). The most promising technique proves to be the simplest, the high-gain feedback method. This technique is a stable, model-free method of vibration isolation which places no restrictions on the type of system disturbance, other than that it must be within the actuator’s bandwidth. The high-gain approach is applied experimentally and shown to agree with the simulated results. / Ph. D.

Call number: LD2668 .T4 1978 A94 / Master of Science

published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

This work incorporates previous work done by Guerra and the application of fluid dynamics. The structure attached to the turbine will cause unsteady fluctuations in the flow, and ultimately affect the acoustic pressure. The work of Guerra is based on a lot of assumptions and simplifications to the geometry of the turbine and structure. This work takes the geometry of the actual turbine, and uses computational fluid dynamic software to numerically model the flow around the turbine structure. Varying the angle of the attack altered the results, and as the angle increased the noise levels along with the sound pulse, and unsteady loading increased. Increasing the number of blades and reducing the chord length both reduced the unsteady loading. / by Renee' Lippert. / Thesis (M.S.C.S.)--Florida Atlantic University, 2012. / Includes bibliography. / Mode of access: World Wide Web. / System requirements: Adobe Reader.

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A typical failure in a heat exchanger is the breakdown of a tube due to impact-sliding wear. We investigate the dynamic behavior of a tube subjected to cross flow and study the stability of periodic solutions, bifurcations, and the route to chaos. The fluid-stiffness-controlled mechanism is chosen to represent the fluid forces and the impact forces are modeled by a piece-wise-Iinear spring. A two-point boundary-value algorithm is used to calculate periodic solutions and Floquet theory is used to study their stability. Poincare sections and bifurcation diagrams are used to study non-periodic solutions. Furthermore. for this autonomous system, the method of harmonic balance appears to be less suited than the two-point boundary-value algorithm for calculating periodic motions. For the case of a single-mode approximation. the results show that the tube undergoes relaxation oscillations and hence no bifurcations occur for fluid velocities ranging from 1.1 Ve to 3.0 Ve, where Ve is the critical fluid velocity. For the cases of two- and three-mode approximations. the results show that periodic solutions undergo bifurcations leading to chaos. Consequently. we conclude that chaos is the result of modal interactions. Observing the details of impacts. we also conclude that chaos appears when a second impact occurs on the same stopper. We also found intermittent chaos alternating with transient periodic motions. Lastly, we estimate the mean impact forces and mean impact-sliding wear work rates and compare them with previous results. / Master of Science

The nonlinear differential equations describing the motion of a crawler crane in a plane are formulated by applying Lagrange's equation to the system kinetic energy, potential energy and virtual work. The transient response of the crane system due to the vertical drop of the suspended load is simulated by numerically integrating the equations of motion. The crane model includes the vertical translation and rotation of the crane body, the rotation of the boom, the stretch and pendulation of the load line, and two discrete boom displacements. The model includes the effects of tilting of the crane tracks, shortening of the boom length, and loss of tension in the elastic cables. The model has been carefully developed to include the important effects which influence the crane system motion without loosing the simplicity which allows auxiliary control systems to be added with relative ease. A hydraulic valve-controlled piston actuator is adapted to the crawler crane pendent line to reduce the boom-tip excursions which excite the motion of the suspended load. Three proportional feedback compensation techniques, which detect the error between the desired crane state and the actual crane state, are used to describe the pendent actuator's valve position. The transient response of the system generalized coordinates for both the uncompensated crane and the compensated crane is presented subject to three sets of initial conditions and crane configurations. One controller which measures the deflection at a single point in the crane boom is able to attenuate the entire crane system response due to a 7.6 cm vertical drop of the 13,600 Kg load with only 13 Kw of hydraulic source power. / Master of Science

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