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An analysis of harbor seal (Phoca vitulina) and gray seal (Halichoerus grypus) haul-out patterns, behavior budgets, and aggressive interactions on Mount Desert Rock, Maine /Renner, Steven C., January 2005 (has links) (PDF)
Thesis (M.S.) in Wildlife Ecology--University of Maine, 2005. / Includes vita. Includes bibliographical references (leaves 60-64).
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The behavioral response of harbor seals to seasonal prey pulses of spawning Pacific herring /Thomas, Austen C. Acevedo-Gutiérrez, Alejandro. January 2010 (has links)
Thesis (M.S.)--Western Washington University, 2010. / Includes bibliographical references (leaves 45-53). Also issued online.
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Self-induced flow circulation by enclosed rotorsDaneshmandi, Mohsen January 1995 (has links)
No description available.
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INVESTIGATION OF AN AXIAL FLOW ROTARY VALVE SEALStieha, Joseph K. 01 January 2017 (has links)
This thesis investigates potential materials to be used in the rotary sealing industry that provide low power loss and minimize cost. The studied rotary valve utilizes slots that act as timing valves to allow for flow axially, through the seal face, at particular times within a heat pump cycle. This investigation examines various combinations of multiple PTFE materials, plastics, and soft metals that have been proven to provide low friction coefficients. Leakage and wear requirements are stated for the future use of the rotary valve and are used to determine the effectiveness of sealing the fluid while examining the power loss. In conclusion, the study finds the combination of a modified PTFE stationary ring and Aluminum Bronze rotating face to provide the lowest power loss. Numerical analysis was completed to verify the lubrication regime to be partial lubrication and was also used to investigate geometry changes and impact on the power loss.
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Impact of Rotor Surface Velocity, Leakage Models and Real Gas Properties on Rotordynamic Force Predictions of Gas Labyrinth SealsThorat, Manish R. 2010 May 1900 (has links)
Rotordynamic coefficients of a gas labyrinth seal are assumed to be frequency independent. However, this assumption loses its validity as rotor surface velocity approaches Mach 1. The solution procedure of 1CV model by Childs and Scharrer which assumes frequency independent force coefficients is modified to allow for calculating frequency dependent force coefficients. A comparative study of the impact of using frequency-dependent model and the original frequency-independent model on stability analysis is made. The results indicate that frequency dependency of force coefficients should be accounted for in stability analysis as rotor surface velocity approaches a significant fraction of Mach number. The bulk flow rotordynamic analysis model by Childs and Scharrer is modified to investigate the impact of leakage-flow models on predictions. A number of leakage models are incorporated in the one-control volume model, and a comparative study is made. Kinetic energy carryover factor of a leakage equation is one of the dominant factors in seal cross-force generation. A leakage equation based on a model proposed by Gamal which uses Hodkinson?s kinetic energy carryover factor is found to improve predictions of direct damping and cross-coupled stiffness. A test case is implemented to study the impact of variation of seal axial radial clearance on stability characteristics. The 1CV model by Childs and Scharrer and subsequent bulk flow models are based on the assumption of isothermal flow across the labyrinth seal. The 1CV model by Childs and Scharrer is modified to include energy equation, and the flow process is assumed to be adiabatic. However, predicted cross-coupled stiffness and direct damping coefficients using the new model do not compare well with the experimental results by Picardo as compared to the isothermal model. The impact of using real gas properties on static and rotordynamic characteristics of the seal is studied.
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Test versus predictions for rotordynamic and leakage characteristics of a convergent-tapered, honeycomb-stator/smooth-rotor annular gas sealVan Der Velde Alvarez, Daniel Eduardo 15 May 2009 (has links)
This thesis presents the results for measured and predicted rotordynamic
coefficients and leakage for a convergent-tapered honeycomb seal (CTHC). The test
seals had a diameter of 114.968 mm (4.5263 in) at the entrance, and a diameter of
114.709 mm (4.5161 in) at the exit. The honeycomb cell depth was 3.175 mm (0.125
in), and the cell width was 0.79 mm (0.0311 in). Measurements are reported with air as
the test fluid at three different speeds: 10,200, 15,200, and 20,200 rpm; with a supply
pressure of 69 bar (1,000 psi), with exit-to-inlet pressure ratios from 20% to 50%, and
using two rotors that are 114.3 mm (4.500 in) and 114.5 mm (4.508 in) respectively; this
enables the same seals to be tested under two different conditions.
The q factor, which is just a simple way to quantify taper is defined as the taperangle
seal parameter and is calculated using the inlet and exit radial clearance. Two
taper-angles parameters were calculated; q = 0.24 for the 114.3 mm (4.500 in) rotor,
and q = 0.386 for the 114.5 mm (4.508 in) rotor. The q = 0.24 condition was compared
to a constant clearance honeycomb seal (CCHC q = 0) because both sets of data were
taken with the same rotor diameter.
The direct stiffness, effective stiffness, and direct damping coefficients were
larger for q = 0.24. The CTHC q = 0.24 eliminates the direct negative static stiffness
obtained with CCHC ( q = 0). The cross-coupled stiffness and damping also were larger
for q = 0.24, especially at low frequencies.
Effective damping is one of the best indicators in determining the stability of a
roughened stator annular gas seal. The frequency at which it changes sign is called the cross-over frequency. In applications, this frequency needs to be lower than the rotorsystem’s
first natural frequency. Otherwise, the seal will be highly destabilizing instead
of highly stabilizing. The magnitude of effective damping and the cross-over frequency
also increases with q for all frequencies.
Constant clearance honeycomb seals have less leakage than convergenttapered
honeycomb seals. CTHC ( q = 0.24), has approximately 20 percent more
leakage than CCHC ( q = 0).
The experimental results for rotordynamic characteristics and leakage were
compared to theoretical predictions by the two-control-volume developed by Kleynhans
and Childs. All rotordynamic coefficients were reasonably predicted for all cases. The
model does a better job predicting the cross-coupled stiffness and damping coefficients
rather than the direct stiffness and damping coefficients. Also, the two-control-volume
model predicts the dynamic characteristics of CCHC ( q = 0) better, and does not predict
well the effective stiffness and damping for CTHC q = 0.386.
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Impact of Rotor Surface Velocity, Leakage Models and Real Gas Properties on Rotordynamic Force Predictions of Gas Labyrinth SealsThorat, Manish R. 2010 May 1900 (has links)
Rotordynamic coefficients of a gas labyrinth seal are assumed to be frequency independent. However, this assumption loses its validity as rotor surface velocity approaches Mach 1. The solution procedure of 1CV model by Childs and Scharrer which assumes frequency independent force coefficients is modified to allow for calculating frequency dependent force coefficients. A comparative study of the impact of using frequency-dependent model and the original frequency-independent model on stability analysis is made. The results indicate that frequency dependency of force coefficients should be accounted for in stability analysis as rotor surface velocity approaches a significant fraction of Mach number. The bulk flow rotordynamic analysis model by Childs and Scharrer is modified to investigate the impact of leakage-flow models on predictions. A number of leakage models are incorporated in the one-control volume model, and a comparative study is made. Kinetic energy carryover factor of a leakage equation is one of the dominant factors in seal cross-force generation. A leakage equation based on a model proposed by Gamal which uses Hodkinson?s kinetic energy carryover factor is found to improve predictions of direct damping and cross-coupled stiffness. A test case is implemented to study the impact of variation of seal axial radial clearance on stability characteristics. The 1CV model by Childs and Scharrer and subsequent bulk flow models are based on the assumption of isothermal flow across the labyrinth seal. The 1CV model by Childs and Scharrer is modified to include energy equation, and the flow process is assumed to be adiabatic. However, predicted cross-coupled stiffness and direct damping coefficients using the new model do not compare well with the experimental results by Picardo as compared to the isothermal model. The impact of using real gas properties on static and rotordynamic characteristics of the seal is studied.
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Experimental measurement and analysis of wall pressure distribution for a 50% eccentric whirling annular sealSuryanarayanan, Arun 15 November 2004 (has links)
In any rotating machinery, the geometry of the seal influences the extent of systemleakage. The path taken by the flow in the clearance volume is dependent on the seal and rotor profile. The clearance between a new "seal-rotor" combination is uniform except for small variations during manufacturing and assembly. With time this annular cross section undergoes further physical changes causing non-uniform flow in the annular volume. This azimuthally varying leakage through the seal-rotor annulus creates unbalanced forces on the rotor causing it to whirl. It is essential to identify the reasons for these unwanted forces. Velocity profiling of the clearance volume flow was performed by Morrison et al. (1992) using 3-D LDA measurements on annular and labyrinth seals operating with 50% dynamic eccentricities and a whirl ratio of one. However, this alone does not provide a complete matrix of data for the conditions prevailing in the clearance zone. Additional information of mean and instantaneous wall pressure distributions for 0%, 10%, 25% and 50% rotor dynamic eccentricity for whirl ratios of zero and one, with positive pre-swirl, no pre-swirl and negative pre-swirl conditions were measured by Robic (1999). The data collected showed that the pressure field on the seal walls reversed itself between the whirling and non-whirling conditions. As a continuance of the earlier works, the present effort investigates the effect of whirl ratio variation for a 50% eccentric smooth annular seal at a leakage Reynolds number of 24000. An attempt has been made to collect pressure data for negative whirl ratios also under similar test conditions.
A seal test rig capable of handling different eccentricities and whirl ratios simultaneously was designed and constructed for this purpose. Mean and instantaneous wall pressure data were recorded for 50% eccentricity with whirl ratios between ? 1 for a rotor speed of 1800. For a rotor speed of 2700, whirl ratios tested were between ? 0.6 and for 3600 rotor speed, whirl ratios ranging between ? 0.5 were tested. From the collected data a detailed analysis of wall pressures along the seal surface is performed following the technique described by Winslow (1994) and Robic (1999).
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Windback seal design for gas compressors: a numerical and experimental studyAl-Ghasem, Adnan Mahmoud 17 September 2007 (has links)
Seals are considered one of the important flow elements of a turbomachinery device.
Traditional labyrinth seals have proven their performance functionality by reducing leakage
rates. Significant improvements on labyrinth seal functionality were obtained through altering
the design geometry of labyrinth seals to prevent contamination across a seal and maintaining
small leakage flowrates. This results in a windback seal that has only one tooth which
continuously winds around the shaft like a screw thread. These seals are used in gas compressors
to isolate the gas face seal from bearing oil. A purge gas is passed through the seal into the
bearing housing. The helical design allows the seal to clear itself of any oil contamination.
Windback seal performance is controlled through changing the seal geometry. A 2D graphical
design tool for calculating the total and cavity leakage flowrates for windback seals is
introduced.
The effectiveness of the Fluent CFD (Computational Fluid Dynamics) commercial code
to accurately predict the leakage rate for windback seals was evaluated. The objective is to
determine if CFD simulations can be used along with a few experimental tests to study windback
seals of this design with air as the working fluid. Comparison of measurement and predictions
for a windback seal using the ú-õ turbulence model with enhanced wall treatment functions show
predictions and measurements comparing very well with a maximum difference of 5% for
leakage rate. Similarly, the leakage rate of the tested smooth seal compares favorably with two
dimensional CFD predictions, with a difference of 2%-11% and 8%-15% using laminar and ú-õ
turbulent flow models, respectively. The variation of leakage with shaft speed and pressure ratio
across the seals is accurately predicted by the CFD simulations. Increasing the rotor speed to
15000 rpm increases the measured leakage flowrate for the windback seal by 2% at high
differential pressure and 4.5% at low differential pressure, and decreases it by 10 % for the
smooth seal. The effects of seal clearance, tooth pitch, cavity depth and the tooth number of starts on
leakage flowrate, velocity and pressure distributions were studied numerically for three
differential pressures and four rotor speeds.
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Prey selection in Gulf of Maine harbor seals (Phoca vitulina) in relation to fish abundance and fish mercury concentrations /Kopec, Audrey Dianne, January 2009 (has links)
Thesis (Ph.D.) in Biological Sciences--University of Maine, 2009. / Includes vita. Includes bibliographical references (leaves 136-165).
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