Browsing by Subject "seal"
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Item An evaluation of the impacts of aging on skeletal muscle performance in several mammalian divers(2009-05-15) Hindle, Allyson GayleBased on the ?free radical theory of aging,? I hypothesized that hypoxia caused by the mammalian dive response induces free radical production which could modulate or accelerate cellular aging. On the other hand, to prevent free radical ?stress? (pro- /antioxidant imbalance), divers could display elevated protective mechanisms. Additionally, the unusual connection between diving physiology and foraging ecology implies that aging physiology is significant to our understanding of ecology for divers. This study examines three aspects of aging in representative diving mammals. First, gracilis muscle morphology was analyzed for old/young shrews (water shrew, Sorex palustris (diver); short-tailed shrew, Blarina brevicauda (non-diver)). Extracellular space was elevated in old animals (10% diver, ~70% non-diver; P=0.021), which corresponded to a larger extracellular collagen component of old muscle (~60%; P=0.008). Muscle was dominated by Type I collagen, and the ratio of collagen Type I: III more than doubled with age (P=0.001). Second, oxidative stress markers, protective antioxidant enzymes and apoptosis were examined in muscle of the two shrew species. The activities of antioxidant enzymes catalase and glutathione peroxidase were statistically identical at each age in both species. The Cu,Zn superoxide dismutase isoform was, however, elevated in older animals (115% diver, 83% non-diver, P=0.054). Only one indicator of oxidative stress (lipid peroxidation) increased with age (P=0.009), whereas the other markers declined (4-hydroxynonenal content, P=0.008, dihydroethidium oxidation, P=0.025). Apoptosis occurred in <1% of myocytes, and did not change with age. On balance, diving water shrews did not have adaptations to combat oxidative stress, yet they do not display excessive oxidative tissue damage. Apoptosis was similar between species. The third study component was the development of a predictive simulation model for the energetics of old/young foraging Weddell seals, Leptonychotes weddellii. With advancing age, the model predicts declining net energy gain associated with a decrease in muscle contractile efficiency. The effects of age are exacerbated when good prey patches are scarce. In such cases, declines in old seal energy gain caused by increased buoyancy and decreased aerobic dive limit become apparent. The model also addresses the idea that behavioral plasticity may allow older animals to compensate for age-related performance constraints.Item Coastal Microstructure: From Active Overturn to Fossil Turbulence(2012-02-14) Leung, Pak TaoThe Remote Anthropogenic Sensing Program was a five year effort (2001- 2005) to examine subsurface phenomena related to a sewage outfall off the coast of Oahu, Hawaii. This research has implications for basic ocean hydrodynamics, particularly for a greatly improved understanding of the evolution of turbulent patches. It was the first time a microstructure measurement was used to study such a buoyancy-driven turbulence generated by a sea-floor diffuser. In 2004, two stations were selected to represent the near field and ambient conditions. They have nearly identical bathymetrical and hydrographical features and provide an ideal environment for a control experiment. Repeated vertical microstructure measurements were performed at both stations for 20 days. A time series of physical parameters was collected and used for statistical analysis. After comparing the data from both stations, it can be concluded that the turbulent mixing generated by the diffuser contributes to the elevated dissipation rate observed in the pycnocline and bottom boundary layer. To further understand the mixing processes in both regions, data were plotted on a Hydrodynamic Phase Diagram. The overturning stages of the turbulent patches are identified by Hydrodynamic Phase Diagram. This technique provides detailed information on the evolution of the turbulent patches from active overturns to fossilized scalar microstructures in the water column. Results from this study offer new evidence to support the fossil turbulence theory. This study concluded that: 1. Field Data collected near a sea-floor outfall diffuser show that turbulent patches evolve from active (overturning) to fossil (buoyancy-inhibited) stages, consistent with the process of turbulent patch evolution proposed by fossil turbulence theory. 2. The data show that active (overturning) and fossil (buoyancy-inhibited) patches have smaller length scales than the active+fossil (intermediate) stage of patch evolution, consistent with fossil turbulence theory and with laboratory studies. 3. Compared to a far-field reference, elevated dissipation rates near the diffuser were found in the seasonal pycnocline as well as in the bottom boundary layer. 4. More than 90% of the turbulent patches observed in the water column were non-overturning (active+fossil and fossil). Such patches can provide significant mixing in the interior of the ocean, far from surface and bottom boundary layers.Item Measurements of leakage, power loss and rotordynamic force coefficients in a hybrid brush seal(2009-05-15) Baker, Jose EnriqueThis 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 ?m) 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 ( ?) and dry friction coefficient ( ?). 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.Item The Effect of High Rotational Speed on the Performance of Straight-through Labyrinth Seals for Compressible and Incompressible Flow(2012-07-16) Obidigbo, Ekene R.The leakage flow through straight through labyrinth seals with tooth on stator was investigated by performing CFD simulations .ANSYS Fluent is used to simulate the fluid flow through straight through Labyrinth seals. The effect of seal geometry on discharge coefficient, carry over coefficient and expansion factor is studied by varying clearance, pitch, tooth height, tooth width ,Reynolds number and rotor speed. Derived quantities Such as carry over coefficient, coefficient of discharge and expansion factor are analyzed as a function of the tooth with preceding cavity to predict the effectiveness of the seal. To understand the effect of varying seal geometries and swirl, 2D CFD simulations were performed. It was found that the clearance to pitch ratio is a strong geometry factor which affect the performance of the seal. The carryover coefficient which describes the portion of kinetic energy carried over from one cavity to the next is also examined. It was found to be a function of Reynolds number and shaft speed. Discharge coefficient describes the losses which occur when fluid flows through the cavity and under the tooth. Just like the carryover coefficient, it is also discovered that it is a strong function of Reynolds number and shaft speed.