Angle section members, used in open engineering structures, have been known to experience large amplitude oscillations when exposed to normal atmospheric winds, and in a few instances failure has been reported. The bluff geometry together with low natural frequency makes these members susceptible to aeroelastic vibrations of a vortex resonant or galloping nature. The thesis aims at studying the nature of the aerodynamic forces and the resulting instabilities for the safe design of the structures. It presents information on the aerodynamics and dynamics of the angle section during stationary, plunging, torsional and combined plunging-torsional conditions. From the measurements on stationary angle models, it is possible to predict the critical vortex resonant wind speeds for various angles of attack. The large variations of the unsteady aerodynamic coefficients indicate the dependence of the resonant instability on model orientation. Incorporating the stationary aerodynamic loadings, the quasi-steady analysis is able to predict the galloping instability and resulting amplitude and buildup time response. The absence of torsional galloping during the experiment is substantiated by the theory which shows the instability to occur only at high wind speeds or for systems with very low damping. The dynamical study demonstrates that structural angle sections are susceptible in general, to combined plunging and torsional vibrations. The nature of the instability depends on such system parameters as damping, natural frequency, angle of attack, section size, etc. However, due to the existence of two distinct families of virtual hinge points, it is possible to represent the motion as predominantly plunging or torsion. Furthermore, the frequency of the coupled motion as well as the type and range of the instability are found to be similar to those in the single degree of freedom. This makes it possible to obtain pertinent information by studying, both experimentally and theoretically, the plunging and torsional degrees of freedom, separately. During plunging resonance, the angle section experiences a vortex capture phenomenon where the shedding frequency is controlled by the cylinder motion over a finite wind speed range. On the other hand, the torsional vibration shows a vortex control condition over a large velocity range where the vortex shedding governs the frequency of oscillation and follows the stationary model Strouhal curve. Compared to the stationary and torsional results, the fluctuating pressures on the angle surface during plunging resonance are substantially larger in magnitude with less amplitude modulation and phase variation. Consequently, the unsteady aerodynamic coefficients increase with this instability. During resonance in either degree of freedom, the vortex velocity and longitudinal spacing remain essentially unaltered, however, the wake width experiences substantial increase with plunging motion. It appears that the torsional resonance has virtually no effect on the vortex shedding or wake characteristics. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

The use of optical techniques for the study of vibrating surfaces has thus far been limited to measuring small amplitudes on the order of a few hundred microinches. To extend the measuring range to much larger amplitudes a completely new technique is sought. In this thesis optical vibration methods are presented that allow amplitudes of .001" and up to be investigated, the upper limit being determined solely by the prohibitive size and cost of the equipment. The study is based on a combination of the shadow moire deflection measuring method and the Salet-Ikeda slope measuring method which, as far as the author knows, have been applied only to the study of static situations. It is shown how these two methods may be applied to the dynamic case to permit the direct visualization of nodal and antinodal locations and displacements in vibrating plates. Three specimens are studied: a cantilever beam, a square cantilever plate and a circular free plate. Complete photographic results along with theoretical or experimental solutions are given for each specimen. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

Uniform water flow past cylinders of various cross-sections produces oscillating lift and drag forces. In the tests made in this investigation the cylinders were elastically mounted on a cantilever of known stiffness. The experiments were carried out to obtain a series of two-dimensional vibration records which were then analysed to find: i) the variation of the types of lateral and longitudinal vibrations, ii) the variation of the amplitude of lateral and longitudinal vibrations with respect to Reynolds numbers, iii) the relation between frequency of lateral and longitudinal vibrations and the velocity of flow, iv) Strouhal number for both lateral and longitudinal vibrations and to relate them with the corresponding Reynolds numbers of the flow, v) Coefficient of lift and drag allowing for magnification factor. The range of investigation was within Re = 2.1 × 10³ and Re = 7.25 × 10⁴. The cantilever system including the model was 38 inches long, cylinders of various cross-sectional shapes, such as circular, truncated-conical, D-shaped, square and rectangular were tested. For the circular cylinders, the natural frequency of vibration was found to vary between 2.78 to 3.57 cycles/sec. and the damping coefficients varied between 0.068 to 0.12. For circular cylinders, the resonance of longitudinal vibration occured at [V] / [Vy res] = 0.42. The most interesting result, which has not been reported elsewhere, is that the longitudinal amplitude was re-excited by the lateral vibration and started rising again to a second maximum. For the circular cylinders, maximum values of coefficient of drag and of coefficient of lift were found to be 3.50 and 4.70 respectively even after allowing for magnification, Strouhal number variation in the lateral direction was found to be between 0.185 and 0.14. For circular cylinders, up to the point where lateral resonance occured, the frequency of the excitation in the longitudinal direction was found to be twice that in the lateral direction. Although the natural frequency of vibration was the same for both lateral and longitudinal direction, the Strouhal number was not constant, but varied within a narrow range. Thus, the velocity of resonance in the lateral direction was not twice that of the velocity of resonance in the longitudinal direction but was 2.3 times instead. For the D-section, the flat face normal to flow was found to be the most unstable of all orientations. The flat face parallel to flow gave the least coefficients of drag and lift out of all the various shapes investigated. The Strouhal number variation in the lateral direction for the circular cylinders, for the D-shaped cylinder with flat face parallel to the flow, and for rectangular cylinders with 2" face normal to the flow was the same. The maximum value of the coefficient of lift was higher for circular cylinders than that for any other shapes investigated. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

One of the major limitations on productivity in metal cutting is chatter. Chatter is a form of unstable self-excited vibration which causes poor surface finish, as well as cutter and machine tool damage. The investigation of chatter suppression in milling using continuously variable spindle speed is presented in this thesis. The fundamental mechanism in regenerative chatter is due to favorable phasing between the inner and outer modulations on the chip thickness. In this thesis, the spindle speed is sinusoidally varied to prevent the dynamic cutting process from locking on to a constant phase shift and causing unstable cutting, or chatter. Because of the nonlin-earities and complexities of the process, time domain simulation of the dynamic cutting process has been modelled. The influence of various parameters, such as axial depth of cut, process damping from flank interference, and amplitude and frequency of speed variation have been investigated using the simulation model. The trends predicted by simulation results have been experimentally verified using cutting tests on a milling machine. It has been concluded from simulation and milling tests that a variable spindle speed can partially increase the chatter limit, but can never totally prevent chatter. The variable spindle speed strategy is incorporated into a proposed in-process chatter detection and avoidance algorithm. The milling process is monitored using the sound pressure signal measured by a microphone. When the amplitude of the sound spectrum near the natural frequency exceeds a threshold value, chatter has been detected and the spindle speed is oscillated until stability is regained. The proposed algorithm is implemented on line and experimental results are presented. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

Self-excited chatter is a basic performance limitation in the machining of metals. Self-excited chatter was investigated both experimenttally and theoretically in the present research. An experimental lathe was constructed so as to obtain orthogonal one degree of freedom cutting. An experimental method developed by Brockley and Ko which enables the recording of a phase plane diagram and the force-velocity curve of one cycle of vibration was used. Experiments were carried out on 70-30 lead free brass workpiece disc with a high speed steel tool at surface speeds ranging from 2 in/sec to 20 in/sec. The results revealed that the force-velocity curve was 'loop' shaped. The chatter vibration was quasi-harmonic and the growth and decay of vibration amplitude with variation in surface speed was observed. Frictional quasi-harmonic vibration was observed to occur in the same speed range which suggested the concept that metal-cutting chatter could be friction actuated. The experimental force-velocity curve was employed in a graphical construction of the phase plane representation of the vibration. The constructed phase plane was in close agreement with the experimental recording. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

Ambient energy harvesting has attracted significant attention over the last years for applications such as wireless sensors, implantable devices, health monitoring systems, and wearable devices. The methods of vibration-to-electric energy conversion can be included in the following categories: electromagnetic, electrostatic, and piezoelectric. Among various techniques of vibration-based energy harvesting, piezoelectric transduction method has received the most attention due to the large power density of the piezoelectric material and its simple architectures. In contrast to electromagnetic energy harvesting, the output voltage of a piezoelectric energy harvester is high, which can charge a storage component such as a battery. Compared to electrostatic energy harvester, the piezoelectric energy harvester does not require an external voltage supply. Also, piezoelectric harvesters can be manufactured in micro-scale, where they show better performance compared to other energy harvesters, owing to the well-established thick-film and thin-film fabrication techniques. The main drawback of the linear piezoelectric harvesters is that they only retrieve energy efficiently when they are excited at their resonance frequencies, which are usually high, while they are less efficient when the excitation frequency is distributed over a broad spectrum or is dominant at low frequencies. High-frequency vibrations can be found in machinery and vehicles could be used as the energy source but, most of the vibration energy harvesters are targeting at low-frequency vibration sources which are more achievable in the natural environment. One way to overcome this limitation is by using the frequency-up-conversion technology via impacts, where the source of the impacts can be one or two stoppers or more massive beams. The impact makes the piezoelectric beam oscillate in its resonance frequency and brings nonlinear behavior into the system.

With this thesis the research at the engineering department is continued, based on previous thesis projects. These projects were considering the possibility of simulation gears with rigid bodies. After researches with different emphasizes on the rigid body simulation, the gained knowledge showed limitations of the rigid body model. Gear failures are very diverse and the actual simulation technique could not represent all necessary failure modes that can occur. That led to this thesis as a research project to find a way to detect and analyze the failure modes that cannot be considered with the current rigid body approach. With the flexible body theory and simulation tools (MSC:Adams) this gap of gear failure detection simulation can be closed. The objective is, making it possible to simulate all failure modes of a gear that can occur. Additionally the previous project on this topic were using gears of small laboratory conditions. An industry sector has been picked to work on a practical application. This application is a wind turbine gearbox. These gearboxes have common run-time errors which influences the profitability of the power generation. To model this system a gear design guide for wind turbine gearboxes is elaborated.

Essentially there are three types of vibration machines mechanical, electrodynamic, and electrohydraulic (hydraulic). Each of these machines has characteristics which make it suitable for particular areas of use.

The performance of a flexible structure as a breakwater is investigated numerically. The structure is a hemicylinder and is filled with water of uniform pressure. It is anchored along the sides. Only flexural modes are present. The structure is modeled as an elastic shell using the finite element program ABAQUS. The fluid is assumed to be inviscid and incompressible. The fluid flow is analyzed using a boundary integral method and the integral equation is solved numerically by a panel method. The vibration characteristics of the structure are analyzed both in the absence and presence of water. The hydrodynamic coefficients, forces, and the dynamic response of the structure in waves are obtained as a function of the wave number. Two different water depths of 5 m and 6 m are considered. For each water depth, normal and oblique incident waves are considered. The free surface elevation in front of and behind the structure is evaluated for different wave frequencies and directions. The results indicate that the flexible structure is effective in reducing the incident wave intensity over a wide range of frequencies. / Master of Science

Southern pine (SP) lumber is the primary softwood material in the United States. The main procedure during lumber grading process is the identification of the strength reducing characteristics that impacts the modulus of rupture (MOR). Non-destructive evaluation technology can be used to identify higher-stiffness material. This study investigated the use of vibration methods to evaluate the mechanical properties of southern pine lumber. Significant correlations between the properties determined by non-destructive techniques and the static MOE were found. No strong correlations were found for MOR because it is related to the ultimate strength of material, often associated with the existence of localized defects, such as a knot. Non-destructive measurements, visual characteristics, and lumber density were used as independent variables. Linear models were constructed to indirectly estimate the MOE and MOR. The variables selected was dynamic modulus of elasticity (dMOE) to predict MOE. Adding density and knot diameter ratio to the model it was possible to develop a prediction model for MOR. It was possible to improve predictability of strength (MOR) with a combination of non-destructive and knot evaluation.