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Investigation Of Fluid Rheology Effects On Ultrasound PropagationOzkok, Okan 01 September 2012 (has links) (PDF)
In this study, a mathematical model is developed for investigating the discrete sound propagation in viscoelastic medium to identify its viscoelastic properties. The outcome of the model suggests that pulse repetition frequency is a very important parameter for the determination of relaxation time. Adjusting the order of magnitude of the pulse repetition frequency, the corresponding relaxation time which has similar magnitude with pulse repetition frequency is filtered while the others in the spectrum are discarded. Discrete relaxation spectrum can be obtained by changing the magnitude of the pulse repetition frequency. Therefore, the model enables to characterize the relaxation times by ultrasonic measurements.
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Cepstral Deconvolution Method For Measurement Of Absorption And Scattering Coefficients Of MaterialsAslan, Gokhan 01 January 2007 (has links) (PDF)
Several methods are developed to measure absorption and scattering coefficients of materials. In this study, a new method based on cepstral deconvolution technique is proposed. A reverberation room method standardized recently by ISO (ISO 17497-1) is taken as the reference for measurements. Several measurements were conducted in a physically scaled reverberation room and results are evaluated according to these two methods, namely, the method given
in the standard and cepstral deconvolution method. Two methods differ from each other in the estimation of specular parts of room impulse responses essential for determination of scattering coefficients. In the standard method, specular part
is found by synchronous averaging of impulse responses. However, cepstral deconvolution method utilizes cepstral analysis to obtain the specular part instead of averaging. Results obtained by both of these two approaches are compared for five different test materials. Both of the methods gave almost same values for absorption coefficients. On the other hand, lower scattering coefficient values
have been obtained for cepstral deconvolution with respect to the ISO method.
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Experimental And Theoretical Investigation Of Complex Flows By Ultrasound Doppler VelocimetryKoseli, Volkan 01 July 2009 (has links) (PDF)
Non-invasive and fast flow measurement techniques have had increasing importance
for the last decades. Scientists are looking for such quick techniques to be able to
monitor real velocities without disturbing flow itself. Ultrasound Doppler
velocimetry (UDV) being one of such techniques promising with advantages of
getting simultaneous velocity measurements from several points and of applicability
for opaque liquids as well. UDV is a technique which is still being developed for
new applications and analysis of complex flows.
In this study effect of sinusoidal oscillating, turbulent (random) and viscoelastic fluid
motions on UDV signals were investigated theoretically and experimentally.
Obtained mathematical relations for random and viscoelastic motions were utilized
to get statistics of flow and distribution of relaxation spectrum, respectively.
Analytical analysis and numerical simulation of sinusoidal oscillating flow depicted
that there is a critical value for the ratio of oscillation amplitude to oscillation
frequency for a specified set of measurement parameters of UDV. Above this critical
value UDV is not successful to determine mean flow velocity. Mathematical
relations between velocity probability density function (PDF) &ndash / velocity auto
correlation function (ACF) and UDV signal spectrum were obtained in the analysis
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of flow with random velocity. Comparison of velocity ACFs from direct velocity
measurements and from raw in-phase (I) and quadrature (Q) signals through derived
relation, revealed that time resolution of UDV technique is not enough for getting a
good velocity ACF and thus turbulence spectrum. Using I and Q signals rather than
measured velocities to get velocity ACF, increased the time resolution in the order of
number of pulses used for getting one velocity value (Nprn).
Velocity PDF obtained from UDV spectrum was compared with the one obtained
from measured velocities with the assumption of Gaussian PDF. Both velocity PDFs
were consistent. Also some parameters of pipe turbulence from literature were
compared with the presented findings from velocity ACF obtained from I and Q
signals through derived relation. Results showed good compatibility.
In the last part of the study, complex viscosity of a linear viscoelastic fluid
mathematically related to spectrum of UDV for a pipe flow with small-amplitude
oscillating pressure field. Generalized Maxwell model was employed to express
complex viscosity terms. Zero frequency (mean flow) component of UDV spectrum
was used to obtain an equation for relaxation viscosities of generalized Maxwell
model. Results have revealed that UDV technique can also be used to probe some of
viscoelastic material functions.
In conclusion, UDV is relatively new but a promising technique for the measurement
and analysis of complex flows in a non-invasive manner.
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Numerical And Experimental Analysis Of Dissipative Silencer Coupled With Quarter Wave TubeDincer, Ayse 01 January 2013 (has links) (PDF)
The study deals with investigation of acoustical characteristics of a hybrid silencer made up of a dissipative silencer and a quarter wave tube resonator. The theoretical and experimental analyses are performed to define acoustic characteristics of a simple expansion chamber and reactive perforated silencer, while the numerical and experimental solutions are presented for dissipative perforated silencer. Furthermore, the experiments and numerical solutions are extended to the hybrid silencer to find the effect of quarter wave tube resonator on the silencer performance. The experimental results of dissipative silencer are verified with theoretical solutions. The empirical expressions for acoustic impedance of perforation and filling material are presented in this study for use in a three-dimensional boundary element method (BEM). Besides, an experimental setup is also established to find the characteristic impedance and wavenumber of absorbing material to import BEM solution when the empirical expression cannot be used. The results found with BEM are compared by analytical and experimental results favorably.
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