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Ecology of the ringed seal (Phoca hispida Schreber) in the fast-ice of Barrow Strait, Northwest TerritoriesHammill, Michael O. January 1987 (has links)
No description available.
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Animal bones and human society in the late Younger Stone Age of Arctic NorwayHodgetts, Lisa Maye January 1999 (has links)
In recent decades anthropologists and archaeologists have divided hunter-gatherer groups into two types; "simple" and "complex". However, many documented foraging communities display traits associated with both types, and the placement of past and present hunter-gatherers into either category is problematic. The substantial house remains of the late Younger Stone Age hunter-gatherers of Varangerfjord, North Norway, have been connected by many archaeologists with sedentism and, by extension, with "complexity" and permanent social hierarchies. This analysis takes a more direct approach social organisation, using faunal remains to better define the social relationships between households within this community. The large mammal remains from a series of houses are compared to determine whether all households had equal access to prey species and to different parts of large mammal carcasses. Towards this end, the climate and available resources are established for North Norway during the Younger Stone Age. Previous interpretations of the archaeology of the period, including the argument for "complexity" are then discussed. The study sites and associated faunal assemblages are presented. Seal hunting patterns are compared between households in terms of both the choice of species and the age breakdown of each hunted seal population. Local differences in the numbers of ringed seal are attributed to the preference of ringed seal for certain types of coastline. Strong similarities are noted between all sites in terms of both the season of seal hunting activity and the selection of adult versus juvenile harp seal and ringed seal. Distribution of seal and reindeer body parts are also compared between and within houses. Again, there are more similarities than differences between households. Seals were returned whole to all houses and reindeer body part representation appears to be mediated by the utility of each part for artefact manufacture. The implication of these results are discussed in terms of the structure of social relationships, symbolic behaviour and territoriality. The utility of this approach in a broader context is also considered.
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Improving performance and rotordynamic characteristics of injection compressors via much longer balance-piston and division-wall sealsRodrigues Rodrigues, Margarita 15 May 2009 (has links)
Predictions are presented for a selected compressor using longer hole-pattern seals with L/D ratios from 0.5 to 2.5. Results were obtained for back-to-back and in-line compressors with the seal located at mid-span and at 82% of rotor span respectively, considering different seal lengths, radial seal clearances, as well as constant clearance and convergent-tapered seal geometries. Predictions of the synchronous rotordynamic coefficients and leakage were estimated using a code developed by Kleynhans and Childs with zero preswirl and constant pressure ratio of 0.5. This code does not include moment coefficients; which can affect the results. Results of all configurations show an increase of stiffness and damping coefficients with increasing seal length. In addition, a significant reduction in leakage (approximately 47 percent) as L/D increases is exhibited for constant clearance and convergent-tapered hole-pattern seals. For the back-to-back compressor, the stability analysis predicts that the system is stable for all speeds and L/D ratios. In fact, the rotor cylindrical-bending mode becomes more stable with lengthening the seals, for both constant clearance and convergent-tapered hole-pattern seals. For constant clearance seals (Case A), the synchronous response at mid-span show a critical speed at 8,000 rpm (cylindrical-bending mode) for all L/D ratios, while a reduction of 85 percent in the peak response is exhibited as L/D increases. Case B, in which the radial clearance is increased as L/D increases to have the same leakage as case A, slightly increases the synchronous response of the model compared to case A. For convergent-tapered seals (Case C), the synchronous response at mid-span shows a higher critical speed (9,000 rpm) for all L/D ratios, and a larger reduction (89 percent) in peak response with increasing L/D, compared to Case A. However, the magnitude of the peak response is larger for convergent-tapered seals than that for constant clearance seals, for all L/D ratios. For in-line compressor, the stability analysis predicts two critical speeds at 6,000 (conical mode) and 18,000 rpm (first bending mode) respectively. Both modes are predicted to be stable for all speed and L/D ratios. Synchronous response at the mid-span for Case A shows the peak response at the first critical speed is slightly reduced as L/D increases while the response at the second critical speed is increased for most of the cases. In addition, the second critical speed is reduced from 18,000 to 13,000 rpm, which is not a concern because it remains above the running speed. This was also the trend for convergent-tapered hole-pattern seal. In addition, the increase of radial clearance in Case B slightly increases the amplitude of vibration, compared to Case A.
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Improving performance and rotordynamic characteristics of injection compressors via much longer balance-piston and division-wall sealsRodrigues Rodrigues, Margarita 15 May 2009 (has links)
Predictions are presented for a selected compressor using longer hole-pattern seals with L/D ratios from 0.5 to 2.5. Results were obtained for back-to-back and in-line compressors with the seal located at mid-span and at 82% of rotor span respectively, considering different seal lengths, radial seal clearances, as well as constant clearance and convergent-tapered seal geometries. Predictions of the synchronous rotordynamic coefficients and leakage were estimated using a code developed by Kleynhans and Childs with zero preswirl and constant pressure ratio of 0.5. This code does not include moment coefficients; which can affect the results. Results of all configurations show an increase of stiffness and damping coefficients with increasing seal length. In addition, a significant reduction in leakage (approximately 47 percent) as L/D increases is exhibited for constant clearance and convergent-tapered hole-pattern seals. For the back-to-back compressor, the stability analysis predicts that the system is stable for all speeds and L/D ratios. In fact, the rotor cylindrical-bending mode becomes more stable with lengthening the seals, for both constant clearance and convergent-tapered hole-pattern seals. For constant clearance seals (Case A), the synchronous response at mid-span show a critical speed at 8,000 rpm (cylindrical-bending mode) for all L/D ratios, while a reduction of 85 percent in the peak response is exhibited as L/D increases. Case B, in which the radial clearance is increased as L/D increases to have the same leakage as case A, slightly increases the synchronous response of the model compared to case A. For convergent-tapered seals (Case C), the synchronous response at mid-span shows a higher critical speed (9,000 rpm) for all L/D ratios, and a larger reduction (89 percent) in peak response with increasing L/D, compared to Case A. However, the magnitude of the peak response is larger for convergent-tapered seals than that for constant clearance seals, for all L/D ratios. For in-line compressor, the stability analysis predicts two critical speeds at 6,000 (conical mode) and 18,000 rpm (first bending mode) respectively. Both modes are predicted to be stable for all speed and L/D ratios. Synchronous response at the mid-span for Case A shows the peak response at the first critical speed is slightly reduced as L/D increases while the response at the second critical speed is increased for most of the cases. In addition, the second critical speed is reduced from 18,000 to 13,000 rpm, which is not a concern because it remains above the running speed. This was also the trend for convergent-tapered hole-pattern seal. In addition, the increase of radial clearance in Case B slightly increases the amplitude of vibration, compared to Case A.
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A linear fluid inertia model for improved prediction of force coefficients in grooved squeeze film dampers and grooved oil seal ringsDelgado-Marquez, Adolfo 15 May 2009 (has links)
In Squeeze Film Dampers, (SFD), grooves (deep or shallow) are used to feed oil into
the damper and prevent oil starvation within the fluid film lands. In oil seals with film
land of clearance c, short shallow grooves (depth ≤ 15c, length ≤ 30c) are machined to
reduce the cross-coupled stiffness coefficients, and thus improve the seal stability
characteristics. Moreover, test stands for these devices can also incorporate grooves or
recesses as part of oil feeding/ discharge arrangements. A common assumption is that
these grooves do not influence the test system forced response. However, unexpected
large added mass coefficients are reported in these configurations and not adequately
predicted. In the case of grooved oil seals, experimental results also show that
circumferential grooves do aid to reduce cross-coupled force coefficients but to a lesser
extent than predictions otherwise indicate.
A linear fluid inertia model for analysis of multiple-groove SFD or oil seal
configurations is advanced. A perturbation analysis for small motion about a journal
centered and off-centered position yields zeroth and first order flow equations defined at
each individual flow region (land and grooves) of constant clearance ( c ).The analysis
considers both the circumferential and axial dynamic pressure variations across the
groove and land regions. At the groove regions, an effective groove depth ( dη ) and
effective clearance (c d c η η = + ) are defined based on qualitative observations of the
laminar flow pattern through annular cavities. This depth differs from the actual physical
groove depth. The boundary conditions at the inlet and exit plane are a function of the geometric configuration. Integration of the resulting dynamic pressure fields on the
journal surface yields the force coefficients (stiffness, damping, and inertia).
Comparisons between predicted and experimental force coefficients for a grooved
oil seal and a SFD show excellent correlation over a narrow range of effective groove
depths. The results confirm that large added mass coefficients are associated to the
feed/discharge grooves in the scrutinized test configurations. Furthermore, predictions,
benchmarking experimental data, corroborate that short inner land grooves in an oil seal
do not isolate the pressure field of the adjacent film lands, and hence contribute greatly
to the force response of the seal.
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Experimental Dynamic Forced Performance of a Centrally Grooved, End Sealed Squeeze Film DamperMahecha Mojica, Lady Paola 2011 August 1900 (has links)
Squeeze film dampers (SFDs) provide viscous damping to attenuate excessive vibrations and enhance system stability in turbomachinery. SFDs are of special importance in aircraft engines which use rolling element support bearings that, by themselves, do not provide enough damping to ensure safe operation.
A modular test rig capable of simulating actual operating conditions in aircraft jet engines is used to test two centrally grooved, end sealed, SFDs. Both SFDs have diameter D and nominal radial clearance c and consist of two parallel squeeze film lands separated by a deep circumferential groove of length LG and depth dG. A short length damper with film land lengths L and a long damper with land lengths 2L are tested.
Piston rings seal the damper lands. An ISO VG2 lubricant is supplied to the SFD via three radial holes that discharge lubricant into the central groove. The lubricant passes through the damper lands and across the piston ring seals to finally exit the damper at ambient pressure.
Circular orbit tests of amplitude ~0.5c and for static eccentricities varying from 0 to ~0.36c are conducted on the two sealed dampers. The instrumental variable filter method (IVFM) serves to identify the SFD dynamic force coefficients. The parameter identification range is 50Hz to 210Hz for the short damper and 110Hz to 250Hz for the long damper.
Large amplitude dynamic pressures measured in the central groove demonstrate that the central groove does not divide the damper in two separate film lands, but the lubricant in the groove interacts with the squeeze film lands, hence contributing significantly to the SFD forced response. Dynamic pressures in the film lands and in the central groove reveal that both dampers operate free of air ingestion or cavitation for the tested static eccentricities and amplitudes of motion.
Comparisons to test results for the same SFD configurations but with open ends demonstrate the effectiveness of the end seals on increasing the direct damping coefficients. For the sealed ends short length damper, the added mass coefficients are ~2 times larger and the damping coefficients are ~3.8 times larger than the respective coefficients of the open ends long damper. For the sealed ends long damper, the damping coefficients are ~2.8 times, and the added mass coefficients are ~3.1 times larger than coefficients from the open ends configuration.
The identified SFD direct stiffness coefficients are nearly zero except at the maximum static eccentricity for the long damper.
Predictions from a novel computational model that include the effects of the central groove, the lubricant feed holes and the end seals are in excellent agreement with results from the short length damper. For the long damper, the predicted damping coefficients are in good agreement with the test results, while the added mass coefficients are under predicted by ~25 percent.
Experimental results from the two sealed SFD configurations lead to a better understanding of the effects of end seals as well as central feed groves on the SFD forced performance. The results presented in this thesis will help improve the effectiveness of SFDs aircraft jet engines.
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The Effect of High Rotational Speed on the Performance of Straight-through Labyrinth Seals for Compressible and Incompressible FlowObidigbo, Ekene R. 2012 May 1900 (has links)
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.
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A novel isolation curtain to reduce turbine ingress heating and an advanced model for honeycomb labyrinth sealsChoi, Dong Chun 16 August 2006 (has links)
A combination of 3-D and 2-D computational fluid dynamics (CFD) modeling
as well as experimental testing of the labyrinth seal with hexagonal honeycomb cells on
the stator wall was performed. For the 3-D and 2-D CFD models, the hexagonal
honeycomb structure was modeled using the concept of the baffle (zero-thickness wall)
and the simplified 2-D fin, respectively. The 3-D model showed that even a small axial
change of the tooth (or honeycomb wall) location, or a small circumferential change of
the honeycomb wall location significantly affected the flow patterns and leakage
characteristics especially for small tooth tip clearance. Also, the local details of the flow
field were investigated.
The seven basic procedural steps to develop a 2-D axisymmetric honeycomb
labyrinth seal leakage model were shown. Clearly demonstrated for varying test
conditions was the 2-D model capability to predict the 3-D honeycomb labyrinth flow
that had been measured at different operating conditions from that used in developing the
2-D model. Specifically, the 2-D model showed very close agreement with measurements. In addition, the 2-D model greatly reduced the computer resource
requirement needed to obtain a solution of the 3-D honeycomb labyrinth seal leakage.
The novel and advanced strategy to reduce the turbine ingress heating, and thus
the coolant requirement, by injecting a Âcoolant isolation curtain was developed
numerically using a 3-D CFD model. The coolant isolation curtain was applied under the
nozzle guide vane platform for the forward cavity of a turbine stage. Specifically, the
isolation curtain serves to isolate the hot mainstream gas from the turbine outer region.
The effect of the geometry change, the outer cavity axial gap clearance, the
circumferential location of the injection curtain slot and the injection fluid angle on the
ingress heating was investigated. Adding the chamfer to the baseline design gave a
similar or higher maximum temperature T*
max than did the baseline design without
chamfer, but implementation of the injection curtain slot reduced substantially T*
max of
the outer region. In addition, a more desirable uniform adiabatic wall temperature
distribution along the outer rotor and stator surfaces was observed due to the presence of
the isolation curtain.
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Anatomical observations on the river otter, sea otter and harp seal with reference to those structures that are of known significance in thermal regulation and diving.Tarasoff, Frederick John. January 1972 (has links)
No description available.
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Automatic seal control in regenerative air preheaters in power stationsGraham, John A. January 1986 (has links)
No description available.
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