Dunn, Stanley E.

A method of analysis is presented which employs a two-dimensional
plate test to determine the dynamic modulus of elasticity and loss
factor of viscoelastic damping materials. This method is based on an
energy approach to the free vibration of plates. The results derived
from the two-dimensional plate test procedure are compared to values
from conventional beam tests. This comparison indicates that the
material properties determined from the plate test method are in good
agreement with values determined from the beam test method. Thus,
the dynamic modulus of elasticity and loss factor of viscoelastic
damping materials can be determined from either beam or plate tests
and these values can be used in the two-dimensional plate equations
to evaluate the effectiveness of the damping material. In light of
this study, it is suggested that beam tests be performed to derive
viscoelastic material properties because of the simplicity of the
beam test procedure compared to that of the plate test procedure.

In this investigation acoustic emission techniques were employed to
detect deterioration of reinforced concrete. As a result of various
laboratory tests, acoustic emission activity was found to be due to
development of cracking only. Acoustic emission techniques were able
to locate cracks in a specimen by linear location. Various acoustic
emission parameters such as amplitude, signal shape and frequency
were also analyzed and discussed. It was concluded that acoustic
emission techniques provided a feasible method for detection of deterioration
and cracking of steel reinforced structures in laboratory
studies as well as in a field environment.

This report presents the results of an experimental investigation
of the effects of using different source measurement techniques in
implementing the coherence function for source identification purposes.
Frequency domain measurements leading to the coherence
function are developed with regard to providing a causal relation
for a single input, single output, linear system. The use of a
near microphone or accelerometer for source measurements is
presented with particular interest paid to the effect of introducing
noise into the input measurement. Experimental results show
that while a near microphone provides a more accurate coherence
statement than an accelerometer, the input of correlated noise may
be a problem. The possibility of an empirical criteria for the
source to noise signal difference at the near microphone is raised
as a means to help avoid this problem.

This investigation presents the development of an acoustical model
for the study of the reaction of a diving mask on the human vocal
tract. The vocal tract and mask cavity are approximated by simplified
acoustic elements of uniform geometry within which undamped
plane wave motion is assumed. Equations for the impedance at the
mouth opening both with and without a theoretical mask cavity are
developed from the one-dimensional wave equation. The results are
compared with an analysis of the same system using the lumped parameter
technique. The impulse response of the mouth opening is
found by numerical methods and the extension of the technique to
the study of theoretical and actual diving masks is discussed.

A method of on-line monitoring AUV onboard systems is described. This algorithm determines deviations from normal operating conditions based on a damage level calculated from recursive least squares system identification performed on the system under consideration, followed by a gradient detection technique which extracts significant changes in identified model parameters System damage types are characterized together with likely system responses to such failures. Extensive testing of the algorithm is performed using several simulated AUV on-board systems undergoing different types of failures while carrying out different mission scenarios.