Thèse de doctorat : Sciences. Turbomachines : Ecole Centrale de Lyon : 2003. / 73 réf.

Thèse doctorat : Sciences. Turbomachines : Ecole Centrale de Lyon : 2003. / Titre provenant de l'écran-titre. 73 réf.

Thèse doctorat : Mécanique : Villeurbanne, INSA : 2002. / Titre provenant de l'écran-titre. Bibliogr. p. 165-175.

Reproduction de : Thèse de doctorat : Acoustique : Le Mans : 2007. / Titre provenant de l'écran-titre. Bibliogr. p.203-209.

Thèse de doctorat : Sciences et techniques des activités physiques et sportives : Rennes 2 : 2007. / Bibliogr. f. 162-189. Annexes.

Licentiatavhandling (sammanfattning) Linköping : Linköpings universitet, 2009. / Härtill 2 uppsatser.

The pattern of mucosal blood flow in normal human stomachs, and benign gastric ulcers was assesed with laser Doppler flowmetry and the relationship between a single determination of ulcer blood flow and the systemic level of growth factors was investigated. A significant ascending gradient in mucosal blood flow from the antrum to fundus was demonstrated. Different levels of cellular activity in the regions of the stomach may explain this gradient. In the gastric ulcers that healed on standard medical therapy mucosal blood flow was significantly increased in comparison to normal stomachs. In the ulcers that were refractory to standard medical therapy mucosal blood flow was significantly lower than in normal stomachs and healing ulcers. Higher systemic levels of the growth factor bFGF were demonstrated in healing ulcers compared to non-healing ulcers. Gastric mucosal blood flow can increase in response to the increased metabolic demands of healing, however impairment of this response may be an important factor preventing healing of benign gastric ulcers. It would appear that non-healing of gastric ulcers can be predicted at initial diagnosis by reduced peri-ulcer gastric mucosal blood flow and low blood levels of bFGF. / Thesis (M.Med.Sc.)-University of Natal, Durban, 1999.

No description available.

Experimental aeroacoustic research was conducted on a wind turbine specific airfoil at low Reynolds numbers. The goal of this thesis was to study trailing edge noise generation from the airfoil and investigate correlations between the noise and the flow field. Before experiments were performed the current wind tunnel had to be modified in order to make it more suitable for aeroacoustic tests. Sound absorbing foam was added to the inside of the tunnel to lower the background noise levels and turbulence reduction screens were added which lowered the turbulence. An S822 airfoil was chosen because it is designed for low Reynolds flows attainable in the wind tunnel which are on the order of 104. Smoke wire flow visualization was used to gain insight into the airfoil wake development and oil film flow visualization was used to qualitatively assess the boundary layer development. Laser Doppler anemometry (LDA) was used to measure two components of velocity at high data rates in the airfoil wake. Wake profiles were measured in addition to single point measurements to determine the velocity spectrum. A microphone was mounted inside the test section in order to measure the trailing edge noise. Initial plans included measuring the trailing edge noise with a microphone array capable of quantifying and locating noise sources. Although an array was built and beamforming code was written it was only used in preliminary monopole source tests. Oil film results showed the behaviour of the boundary layer to be consistent with previous low Reynolds number experiments. LDA results revealed sharp peaks in the velocity spectra at 1100 Hz from U0 = 15–24 m/s, and 3100 and 3800 Hz, from U0 = 25–35 m/s, which were inconsistent with vortex shedding results of previous researchers. Also present were a series of broad peaks in the spectra that increase from 1200–1700 Hz in the U0 = 25–35 m/s range. The shedding frequency from the smoke wire flow visualization was calculated to be 1250 Hz at U0 = 26 m/s. These sharp peaks were also present in the acoustic spectrum. It was reasoned that these peaks are due to wind tunnel resonance which is a common occurrence in hard wall wind tunnels. In particular the tone at 1100 Hz is due to a standing wave with a wavelength equal to half the tunnel width. The shedding frequency from the smoke wire flow visualization was calculated to be 1100 Hz at U0 = 20 m/s. These tones exhibited a “ladder-like” relationship with freestream velocity, another aspect indicative of wind tunnel resonance. It was reasoned that the wind tunnel resonance was forcing the shedding frequency of the airfoil in the U0 = 15–24 m/s range, and in the U0 = 25–35 m/s range, the shedding frequency corresponded to the broad peaks in the LDA spectra.

The research effort in this thesis is devoted to develop techniques to accurately and rapidly identify the location, orientation, and magnitude of the defects by using structural health monitoring concepts that use Laser Doppler Vibrometer as a non-contact sensor with multi-point sensing capability. The first research area addresses the formulation and validation of an innovative Damage Measure that is based on the ratios of the strain energy distributions of the damaged and undamaged structure. The innovations include use of a single set of actuator/sensor pair to excite and detect the responses of a structure for low frequency vibrations as well as guided wave propagation studies. A second new capability is the estimation of the Damage Measure without requiring any knowledge of the undamaged baseline structure. This method is made possible because of the development of these new technologies: Spatial Decimation and Wavenumber/Frequency filtering. The third contribution is to develop analytical models for the structural dynamics of damaged structure and seek solutions that use perturbation methods to detect damage in a plate structure. The fourth contribution is the development of a comprehensive damage detection technique over a wide frequency dynamic range. The fifth topic of research involves automation in Structural Health Monitoring based on the comprehensive Damage Measure formulation. Under the control of software the Scanning Laser Doppler Vibrometer is used to acquire the low frequency vibration mode data for a coarse identification of all the suspect regions of damage using a threshold criterion on the Damage Measure. Each suspect region of damage is further investigated using the high frequency elastic wave propagation to clearly identify the location, orientation, and extent of the damage. The computer control of the Laser Doppler Vibrometer and a quantitative assessment of the damage provide the enabling technologies for the automation proof of concept. Finally the developed techniques of damage detection are successfully demonstrated on practical structures such as a turbine blade in the laboratory and an F-15 vertical tail in field maintenance conditions