Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

Thesis (M.S.)--Western Washington University, 2008. / Includes bibliographical references (leaves 75-82). Also available in electronic format.

Thesis (master's)--Göteborg University, 2000. / Title from PDF t.p. (viewed on Dec. 5, 2007). "18 Januari 2000." Includes bibliographical references (p. 16-19).

This thesis presents measurements of power loss and leakage in a hybrid brush seal (HBS) for increasing pressure differentials and over a range of rotor speeds. The test HBS, Haynes-25 bristle pack [~850 bristles/cm] and 45o lay angle, is 166.4 mm in diameter and integrates 20-arcuate pads connected with thin EDM-webs to the seal casing. The measured drag power at low rotor speeds (< 11 m/s at 1,300 rpm) decreases as the pressure differential across the seal increases. At a fixed rotor speed, a significant drop in drag torque (and drag power) ensues as the supply pressure increases, thus demonstrating a gas film separates the rotor from the seal pads. A constant operating temperature (~24oC) at the rotor/seal interface during tests with shaft rotation also indicates the absence of intermittent contact between the seal pads and rotor. Flow rate measurements at room temperature (25oC) show an improved sealing ability with a leakage reduction of about 36%, when compared to a 1st generation shoedbrush seal. The HBS predicted effective clearance (~50 μm) is a small fraction of that in an equivalent one-tooth labyrinth seal. Identified HBS direct stiffness coefficients decrease (~15%) as function of rotor speed for an increasing supply pressure condition (Pr = 1.7 and 2.4). The identified cross-coupled stiffness is at least one or two orders of magnitude smaller than the direct stiffness coefficient. The cross-coupled mass is negligible for all tested rotor speeds and supply pressures. The HBS energy dissipation mechanism is characterized in terms of a loss factor ( γ) and dry friction coefficient ( μ). The direct HBS viscous damping coefficient is strongly dependent on the excitation frequency, while showing minimal dependence on rotor speed or supply pressure. The HBS novel configuration incorporates pads contacting on assembly the shaft; and which under rotor spinning; lift off due to the generation of a hydrodynamic pressure. Experimental results obtained show that hybrid brush seals (HBS) are a viable alternative to overcoming the major drawbacks of labyrinth seals; namely excessive leakage and potential for rotordynamic instability. Additionally, during operation a gas film in HBS eliminates rotor and bristle wear, as well as thermal distortions; which are commonly known limitations of conventional brush seals.

Results are presented for measured and predicted rotordynamic coefficients and leakage for hole-pattern seals with a hole depth that varies axially along the seal. Testing was done to discover how pressure ratio, inlet preswirl, and rotor speed affect the seals’ rotordynamic characteristics and leakage. The results were compared to a constant hole depth hole-pattern seal. Experimental results show that the seals’ rotordynamic characteristics are not strongly influenced by pressure ratio. There were three preswirl conditions tested, each separated by a 6.9 bar (100 psi) difference in inlet pressure. Therefore, normalized preswirl results were compared. The normalized results indicate that introducing inlet fluid preswirl affects the crosscoupled stiffness and effective damping coefficients. Inlet preswirl increases the magnitude of cross-coupled stiffness. Effective damping decreases with inlet preswirl, as well as the effective damping cross-over frequency increasing. These results indicate that swirl brakes would be of great value. Rotor speed had a significant effect on the cross-coupled coefficients; both increased with speed. Experimental results were compared to results for a constant hole depth holepattern seal. The variable hole-depth seal has higher direct damping. The crosscoupled stiffness and cross-coupled damping coefficients were very similar. The direct stiffness was always lower at lower frequencies and higher at higher frequencies for the variable hole depth hole-pattern seal. This was also the case for effective stiffness. The effective damping of the variable hole-depth seal was not only larger than for the constant hole depth seal, it also had a drastically lower cross-over frequency. The difference in cross-over frequency was 40 percent on average. Experimental results for rotordynamic characteristics and leakage were compared to theoretical predictions by ISOTSEAL 2, a modified version of ISOTSEAL. Both cross-coupled stiffness and damping are reasonably predicted. Direct damping is always under-predicted. ISOTSEAL 2 does a poor job of predicting direct stiffness. Direct stiffness is over-predicted at lower frequencies and under-predicted at higher frequencies. This is also the case for effective stiffness. ISOTSEAL 2 under-predicts the direct damping, but does an excellent job of predicting the direct damping crossover frequency. Seal leakage is well predicted by ISOTSEAL 2.

Graduation date: 1981

Thesis (M.S.)--Western Washington University, 2008. / Includes bibliographical references (leaves 62-77). Also issued online.

Thesis (M.Phil) - University of St Andrews, October 2007.

Thesis (M.S.) in Wildlife Ecology--University of Maine, 2006. / Includes vita. Includes bibliographical references (leaves 119-128).

Phoca vitulina uses a variety of shallow coastal and freshwater habitats, is non-migratory and rarely found more than fifteen miles from shore. The seal possesses a complete mammalian hair system (less the erector pili muscle) consisting of guard hairs, underhairs, sebaceous and sweat glands. The hair provides primarily mechanical protection for the skin rather than insulation against heat loss. A foetal moult, normally intrauterine (except in P. v. largha, which may not be a harbour seal) differs in pattern sequence from the adult moult. The adult moult occurs during August - October for most specimens. There is some moult activity among adults during almost every month of the year. Distribution of two colour patterns, black and common, indicate locations of discrete populations whose existence has management implications. / Science, Faculty of / Zoology, Department of / Graduate