Cuschieri, Joseph M.

A Statistical Energy Analysis (SEA) approach is used to investigate the vibrational behavior of a journal bearing. In developing the SEA model, consideration is given to the determination of coupling loss factors between non-conservatively coupled substructures. In the case of the journal bearing, the oil film between the rotating shaft and the bearing liner represents non-conservative coupling. The coupling loss factors are estimated using experimentally measured point mobility functions. The internal loss factors are directly measured with the bearing structure disassembled. Additionally, estimates for the coupling and internal loss factors are obtained in-situ using an energy ratio approach. Using the determined coupling and internal loss factors in an SEA model, estimates for the average mean square velocities on the surface of the bearing subcomponents are obtained for both static and dynamics conditions. The SEA estimates match well with directly measured results for the spatial average surface velocities at medium to high frequencies.

In thick structures, vibrational power can propagate by both in-plane and out-of-plane waves. In performing measurements of power flow or structural intensity, it would be required that the components associated with the in-plane or out-of-plane waves be identified. Using a frequency wavenumber approach, the measured structural intensity can be decomposed into its different wave components. In this thesis, simulated structural intensity measurements are presented to demonstrate the use of this frequency wavenumber technique. The results obtained show the distribution of the structural intensity into the wave components. The implementation of this technique using a laser based instrument is discussed. The required characteristics of the instrument, the number of channels, the spacing between the channels, and the phase accuracy, are described. Also, a table to perform the scanning for the frequency wavenumber analysis is presented.

In this thesis the flow of vibration power between two coupled, finite plates of arbitrary thicknesses is considered using a Mobility Power Flow (MPF) approach. The plate structure is divided into substructures and mobility functions are determined for the independent substructures. Power flow expressions are derived based on continuity of forces and displacements. The solution presented here considers the effects of both in-plane waves and out-of-plane waves. The solution is applicable to frequencies below the first mode of thickness-shear vibration. The results obtained show that at low frequencies, the out-of-plane waves dominate in the transmission of vibrational power. However, at high frequencies or for thick plates, the in-plane waves play a significant role in the power transmission through the plate.

Structural intensity is propagated through a thick structure by both in-plane and out-of-plane (transverse) waves. These waves propagate at different phase speeds and therefore it is important to distinguish the components of the structural intensity associated with each wave type. To show the presence of these different wave components, experimental results are performed on a thick beam. Using a frequency-wavenumber analysis, the different waves and contributions to the structural intensity are identified. The significance of the contributions to the structural intensity are a function of both frequency and thickness of the structure. Using simulated measurements on a thick L-shaped plate, the relative importance between the in-plane and out-of-plane contributions to structural intensity as a function of frequency and thickness is demonstrated. It is shown that in-plane wave contributions increase in importance as frequency or thickness increases.

An analytical and experimental investigation of the flow of vibrational power in a thin, L-shaped, finite plate structure subjected to mechanical and acoustic excitation is presented. In the analytical approach, mobility functions are used to determine the structural intensity vectors at various locations on the plate structure. Simulation results of intensity vectors estimated using three different measurement schemes are compared. The experimentally measured intensity vectors, for the case of mechanical excitation, using a four accelerometer array, are presented. They are found to match well with the results from the corresponding simulation. Similar results are obtained for the case of acoustic excitation of the L-shaped plate. The general pattern of the structural intensity vectors is found to be in agreement with the expected results.

An analytical investigation based on the Power Flow Method is presented for the prediction of vibrational Power Flow in simple connected structures subjected to various forms of distributed excitations. The principle of the power flow method consists of dividing the global structure into a series of substructures which can be analyzed independently and then coupled through the boundary conditions. Power flow expressions are derived for an L-shaped plate structure, subjected to any form of distributed mechanical excitation or excited by an acoustic plane wave. In the latter case air loading is considered to have a significant effect on the power input to the structure. Fluid-structure interaction considerations lead to the derivation of a corrected mode shape for the normal velocity, and the determination of the scattered pressure components in the expressions for the Power Flow.

A computer algorithm is developed to provide real-time cross range spatial quantization for a single beam forward look SONAR similar in operation to a typical sidescan SONAR. This involves the computer simulation of return time signals generated by scanning a surface profile. The time signals are normalized with respect to the scanning altitude to simulate the application of a time varying gain, and then are used as input to the surface estimation algorithm. The algorithm requires two time signals acquired from adjacent scanning positions and solves a stereoscopic geometry in arriving at the surface estimate. Final estimates have an error of less than 1% in target height determination within a set range of operation.

A Power Flow approach, where the vibrational Power Flow is expressed in terms of mobility functions is analytically investigated for simple connected structures. Using a Power Flow approach the global structure is divided into a series of substructures and the vibrational Power Flow between the substructures expressed in terms of input and transfer mobilities. Depending on the type and shape of the junction, line or point mobilities may be used. While in the case of point joints, the mobility functions are only functions of frequency, for line joints the mobility functions are variables of not just the frequency but also of space. In this thesis the application of the Power Flow method is first demonstrated for an L-shaped beam and the method is then extended to the application of a line junction between two plates forming an L-shaped plate. The results obtained in the two cases are compared to results obtained using Finite Element Analysis or Statistical Energy Analysis.

The objective of this thesis is the investigation of the transmission of vibrational power between beam-like and plate-like structures with joints using Statistical Energy Analysis (SEA) and an experimental approach. In the case of the L-shaped plate the influence of different structure parameters is investigated to determine possible ways to reduce both the transmitted power and the noise radiated by the receiver structure. The total transmitted power is measured and compared to theoretical predictions. Also power maps are generated which show the transmission of vibrational power from the source beam to the receiver beam. In the power flow measurements three different techniques are implemented with similar results which all match the analytical results.

Of the many methods of introducing damping in
vibrating structures, the dissipation of energy due to
interfacial slip can significantly increase the damping loss
factor. However, because of the lack of understanding and
other phenomena such as fretting corrosion and loss of
structural rigidity, friction damping is rarely used. A
study was thus undertaken to investigate this complex
phenomenon, with emphasis on trying to gain a better
understanding of friction damping with certain parameters
such as clamping pressure, frequency, magnitude of
excitation and surface finish. Although the non-linearities
associated with friction makes this mechanism difficult to
model mathematically, finite element (FE) analysis shows
some promise. Although the results obtained using an FE
model were not exactly comparable to the experimental
results, these analytical results did show the same general
trends as observed in the experiments.