Dissertations / Theses on the topic 'Seals'
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1
Hadley, Gillian Louise. "Recruitment Probabilities and Reproductive Costs for Weddell Seals in Erebus Bay, Antarctica." Thesis, Montana State University, 2006. http://etd.lib.montana.edu/etd/2006/hadley/HadleyG0506.pdf.
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The study of life history traits such as age at first reproduction and the evaluation of recruitment probabilities and reproductive costs allow insight regarding the diverse factors and mechanisms shaping reproductive strategies. We investigated these mechanisms using a 26-year mark-resight dataset for Weddell seals (Leptonychotes weddellii) in Erebus Bay, Antarctica. Mean age at first reproduction was 7.62 years of age (SD=1.71), but varied from four to 14 suggesting the presence of important heterogeneity in quality among females. Survival rate was maximized for offspring of age-14 mothers (φ=0.70 [SÊ=0.08]), whereas recruitment probability was highest for pups born to youngest-breeding mothers. For example, probability of recruitment at age 7 was an average of 43% lower for seals born to age-14 mothers than for seals born to age-6 mothers. These results suggest the influence of countervailing selection (where favored genotypes for reproductive success are generally those that are selected against as juveniles). Sea-ice extent affected annual recruitment rates, likely due to cascading effects of oceanographic conditions on marine primary productivity and fluctuations in food availability for female Weddell seals. Results from the reproductive cost analysis strongly supported the presence of reproductive costs to survival (φ was 0.91 for breeders versus 0.94 for nonbreeders). Costs to fecundity were present for first-time breeders (mean probability of breeding the next year was 0.20 lower for first-time breeders than for experienced breeders). Females that delayed breeding until later in life experienced highest reproductive costs to fecundity, possibly due to their inferiority relative to other individuals in the population, again suggesting the influence of heterogeneity in individual quality. From these analyses we have gained insight into 1) the extent of within-population variation in important life-history characteristics for a long-lived species, and 2) the sources of this variation and potential linkages with environmental variables. Keys to future research will be 1) explaining variation in individual quality with random effects models or by using mass as an indicator variable, and 2) more detailed exploration of appropriate climate and sea-ice indices to elucidate linkages between this top trophic level predator and variation in the Antarctic marine environment.
2
Scholze, Stefan Andreas. "Development of Improved Performance Lip-Seals for Seal Clean Bearing Applications." Thesis, University of Wolverhampton, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.502824.
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Payne, John Wilson. "Feasibility study of a controllable mechanical seal for reactor coolant pumps." Thesis, Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/47632.
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In a nuclear power plant, one of the most important systems for both safety and performance is the reactor cooling system. The cooling system is generally driven by one or more very large centrifugal pumps. Most reactor coolant pumps utilize a multi-stage mechanical face seal system for fluid containment. As a result, these seal systems are critical to safe, continued operation of a nuclear reactor. Without adequate sealing, loss of coolant volume can occur, and a reactor may be forced to shut down, costing the operating utility significantly until it can be brought online again.
The main advantage of mechanical face seals is their self-adjusting properties. These seals are tuned so that they automatically adjust to varying fluid conditions to provide adequate leakage control. Because of the enormous pressures, complicated water chemistry, and possible large temperature transients, the mechanical seals inside a reactor coolant pump must be some of the most robust seals available. In addition, their long service life and continuous operation demand durability and the capability to adjust to a wide range of conditions. However, over time, wear, chemical deposition, or changing operating conditions can alter the face gap, which is the critical geometry between the sealing faces of a seal. An altered face gap can lead to undesirable conditions of too much or not enough leakage, which must be maintained within a certain range to provide lubrication and cooling to the seal faces without resulting in uncontrolled coolant volume loss. Nuclear power plants operate within strict leakage ranges, and long-term effects causing undesirable leakage can eventually necessitate a reactor shutdown if the seal cannot self-adjust to control the leakage.
This document will examine possible causes of undesirable leakage rates in a commonly-used reactor coolant pump assembly. These causes will be examined to determine the conditions which promote them, the physical explanation for their effect on the operation of a mechanical seal, and possible methods of mitigation of both the cause and its effect. These findings are based on previous publications by utilities and technical and incident reports from reactor stations which detail actual incidents of abnormal seal performance and their root causes as determined by the utilities. Next, a method of increasing the ability of a mechanical seal to adapt to a wider range of conditions will be proposed. This method involves modifying an existing seal face to include a method of active control. This active control focuses on deliberately deforming one face of the mechanical sealing face pair. This deformation alters the face gap in order to make the fluid conditions inside the face gap more preferable, generating more or less leakage as desired. Two methods of actuation, hydraulic pressure and piezoelectric deformation, will be proposed.
Finally, a model of the actively controlled seal faces will be introduced. This model includes a method of numerically solving the Reynolds equation to determine the fluid mechanics that drive the lubrication problem in the seal face and coupling the solution with a deformation analysis in a finite element model of a seal face. The model solves iteratively until a converged solution of a sealed pressure distribution, a resulting face deformation, and a calculated leakage rate is reached. The model includes a study of the effects of induced deformation in the seal via both hydraulic and piezoelectric actuation and the ability of this deformation to control the leakage rate.
4
Egan, Geoffrey. "Provenanced leaden cloth seals." Thesis, University College London (University of London), 1988. http://discovery.ucl.ac.uk/1349956/.
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This thesis considers the leaden seals which were attached to textiles from the late 14th- to the early 19th century in England as part of a system of industrial regulation and taxation. Almost all of the 1,345 seals and related items which are described here individually were recovered from the ground. This total comprises all the English seals examined which refer to their place of origin in the legends (many of these are alnage seals), all the known English seals of medieval date, and the English matrices for the cloth seals. The unsorted information about each item is presented, just as recorded, in Appendix 1. The historical context and development of cloth sealing in this country are discussed, and a chronological framework for the various stamped devices and forms of seal is proposed. Following a more detailed account of the known medieval seals are brief summaries of the main aspects of local textile industries and a synthesized description of the recorded seals county by county. A concluding section assesses the information provided by the known seals, and the degree of correspondence with data from historical sources. Directions for future studies are suggested. Further appendices provide statistical tables and maps of documentary-based information on levels of textile production at different periods, detailed discussions of the provenances and findspots of the recorded seals, an account of the largest known group of English seals, and documentary evidence for the dating of some of the seals from Norfolk. For the first time information has been presented systematically, and assessed in detail, both on the extent of survival and on the potential academic value of cloth seals found during excavations.
5
Gamal, Eldin Ahmed Mohamed. "Leakage and rotordynamic effects of pocket damper seals and see-through labyrinth seals." Texas A&M University, 2007. http://hdl.handle.net/1969.1/85848.
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This dissertation discusses research on the leakage and rotordynamic characteristics
of pocket damper seals (PDS) and see-through labyrinth seals, presents and evaluates
models for labyrinth seal and PDS leakage and PDS force coefficients, and compares
these seals to other annular gas seals. Low-pressure experimental results are used
alongside previously-published high-pressure labyrinth and PDS data to evaluate the
models. Effects of major seal design parameters; blade thickness, blade spacing, blade
profile, and cavity depth; on seal leakage, as well as the effect of operating a seal in an
off-center position, are examined through a series of non-rotating tests. Two
reconfigurable seal designs were used, which enabled testing labyrinth seals and PDS
with two to six blades.
Leakage and pressure measurements were made with air as the working fluid on
twenty-two seal configurations. Increasing seal blade thickness reduced leakage by the
largest amount. Blade profile results were more equivocal, indicating that both profile
and thickness affected leakage, but that the influence of one factor partially negated the
influence of the other. Seal leakage increased with increased eccentricity at lower
supply pressures, but that this effect was attenuated for higher pressure drops. While
cavity depth effects were minor, reducing depths reduced leakage up to a point beyond
which leakage increased, indicating that an optimum cavity depth existed. Changing
blade spacing produced results almost as significant as those for blade thickness,
showing that reducing spacing can detrimentally affect leakage to the point of negating the benefit of inserting additional blades. Tests to determine the effect of PDS partition
walls showed that they reduce axial leakage. The pressure drop was found to be highest
across the first blade of a seal for low pressure drops, but the pressure drop distribution
became parabolic for high pressure drops with the largest drop across the last blade.
Thirteen leakage equations made up of a base equations, a flow factor, and a kinetic
energy carryover factor were examined. The importance of the carryover coefficient
was made evident and a modified carryover coefficient is suggested. Existing fullypartitioned
PDS models were expanded to accommodate seals of various geometries.
6
Huang, Yuli. "Elastohydrodynamic model of hydraulic rod seals with various rod surfaces." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/53061.
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The reduction or elimination of leakage of hydraulic fluid from fluid power systems is considered a fundamental prerequisite for the expanded use of fluid power. There is also a need to reduce seal friction to both reduce energy dissipation and eliminate control problems. These seals are developed through empirical means at the present time, since the fundamental physics of seal operation has been unclear.
This research develops numerical models for analyzing reciprocating hydraulic rod seals with various rod surfaces. These models consist of coupled fluid mechanics, contact mechanics and deformation analyses. Both flooded and starved lubrication boundary conditions are applied.
For seals with a smooth rod and a plunge-ground rod, the model combines a 1-D finite volume Reynolds equation solver with a 2-D axisymmetric finite element deformation and static contact mechanics analyses, and a Greenwood-Williamson contact mechanics analysis with rod motion. Leakage and friction, along with sealing zone details with the plunge-ground rod are compared with those with the smooth rod. The influence of rod surface finish on seal performance is investigated and explained, under both flooded and starved conditions
For seals with a micro-patterned rod, the model consists of finite volume Reynolds equation solver, finite element deformation and static contact mechanics analyses and a Greenwood-Williamson dynamic contact mechanics analysis. This model is able to handle rod surface pattern with 3-dimensional geometrics. Simulations with different micro-pattern geometries are performed to analyze the fundamental mechanism of surface pattern effects on seal operation. Again, both flooded and starved conditions are applied and the results for both cases are compared and analyzed.
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Liu, Yin Miao. "Visually sealed and digitally signed electronic documents : building on Asian tradition." Thesis, Queensland University of Technology, 2004. https://eprints.qut.edu.au/15967/1/Yin-Miao_Liu_Thesis.pdf.
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E-commerce has developed through the use of digital signatures, employing various forms of Public Key Infrastructure (PKI) to ensure the secure usage of digital signatures. Digital signatures are designed to facilitate the functions of traditional seals and handwritten signatures for the purposes of authentication, data integrity, and non-repudiation within the e-commerce environment. Historically, the authenticity of documentation has always been verified by the application of a recognisable visual stimulus to the document; however, the current digital signature regime overlooks the importance of this analogous sense of visualisation. One of the primary problems with existing digital signatures is that a digital signature does not "feel" like, or resemble, a traditional seal to the human observer, as it does not have a personal, recognisable, or aesthetic sense of visualisation. Currently, digital signatures, such as the OpenPGP (Pretty Good Privacy) digital signature, are attached to the end of an electronic document as a stream of printable ASCII characters. (RFC2440) This appears to the average user as a long, incomprehensible string of random characters offering no sense of identity or ownership by simple visual inspection. Additionally, digital signatures change each time they are applied, in contrast to traditional seals that remain consistent personal identifiers associated with individual signatories. The goal of this research is to promote enhancements to existing digital signature schemes in order to bridge the cultural gap between traditional seals and digital signatures. Culturally friendly features integrated into the digital signature have the potential to increase user acceptability of global e-commerce. This research investigates traditional seal cultures within the context of modern digital signatures, identifying the need to develop a new, culturally friendly, visualised digital signature scheme. The principles behind digital signatures are reviewed and the essential roles and responsibilities of a PKI are addressed. A practical analysis of PKI implementation is also essential. Taiwan is selected as the focus of this research since its heritage is deeply rooted in, and strongly adheres to the Chinese seal culture. The Taiwanese government is in the process of adapting the traditional seal certificate system to the electronic digital signature system. Therefore it is pertinent to review the PKI implementation and digital signatures applications in Taiwan in this study. The purpose of this research is to make the intangible digital signature virtually tangible; i.e., to incorporate visualisation into the current digital signature practice. This research defines new private extensions to the X.509 v3 certificate, recommending that conforming visualised digital signature applications should then be developed to generate and/or recognise visual digital certificates in support of the proposed visualised digital signature scheme. The processes of visualised digital signature creation and of verification through the application of the visualised digital certificate are then explained. This is accompanied by a model of system analysis for developers of conforming implementations of this specification. This allows developers the freedom to select appropriate developing tools. An analysis of this research evaluates the quality of integrity, security, interoperability, performance, and flexibility offered by this proposal.Future directions for furthering research development conclude this dissertation.
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Liu, Yin Miao. "Visually sealed and digitally signed electronic documents: Building on Asian tradition." Queensland University of Technology, 2004. http://eprints.qut.edu.au/15967/.
Full textAbstract:
E-commerce has developed through the use of digital signatures, employing various forms of Public Key Infrastructure (PKI) to ensure the secure usage of digital signatures. Digital signatures are designed to facilitate the functions of traditional seals and handwritten signatures for the purposes of authentication, data integrity, and non-repudiation within the e-commerce environment. Historically, the authenticity of documentation has always been verified by the application of a recognisable visual stimulus to the document; however, the current digital signature regime overlooks the importance of this analogous sense of visualisation. One of the primary problems with existing digital signatures is that a digital signature does not "feel" like, or resemble, a traditional seal to the human observer, as it does not have a personal, recognisable, or aesthetic sense of visualisation. Currently, digital signatures, such as the OpenPGP (Pretty Good Privacy) digital signature, are attached to the end of an electronic document as a stream of printable ASCII characters. (RFC2440) This appears to the average user as a long, incomprehensible string of random characters offering no sense of identity or ownership by simple visual inspection. Additionally, digital signatures change each time they are applied, in contrast to traditional seals that remain consistent personal identifiers associated with individual signatories. The goal of this research is to promote enhancements to existing digital signature schemes in order to bridge the cultural gap between traditional seals and digital signatures. Culturally friendly features integrated into the digital signature have the potential to increase user acceptability of global e-commerce. This research investigates traditional seal cultures within the context of modern digital signatures, identifying the need to develop a new, culturally friendly, visualised digital signature scheme. The principles behind digital signatures are reviewed and the essential roles and responsibilities of a PKI are addressed. A practical analysis of PKI implementation is also essential. Taiwan is selected as the focus of this research since its heritage is deeply rooted in, and strongly adheres to the Chinese seal culture. The Taiwanese government is in the process of adapting the traditional seal certificate system to the electronic digital signature system. Therefore it is pertinent to review the PKI implementation and digital signatures applications in Taiwan in this study. The purpose of this research is to make the intangible digital signature virtually tangible; i.e., to incorporate visualisation into the current digital signature practice. This research defines new private extensions to the X.509 v3 certificate, recommending that conforming visualised digital signature applications should then be developed to generate and/or recognise visual digital certificates in support of the proposed visualised digital signature scheme. The processes of visualised digital signature creation and of verification through the application of the visualised digital certificate are then explained. This is accompanied by a model of system analysis for developers of conforming implementations of this specification. This allows developers the freedom to select appropriate developing tools. An analysis of this research evaluates the quality of integrity, security, interoperability, performance, and flexibility offered by this proposal.Future directions for furthering research development conclude this dissertation.
9
Gibbens, John Robert. "Demography of Australian fur seals (Arctocephalus pusillus doriferus)." Connect to thesis, 2009. http://repository.unimelb.edu.au/10187/5788.
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The Australian fur seal (Arctocephalus pusillus doriferus) population has displayed a relatively slow rate of recovery since being hunted by commercial sealers during the early 19th century. Despite this, population abundance doubled in the past 2 – 3 decades, indicating that the population growth rate has recently increased. Yet, the factors influencing the population’s dynamics are poorly understood, primarily because basic demographic rates are unknown.Female age, survival, fecundity, breeding and physiology were studied at Kanowna Island, Bass Strait, Australia, between 2003 – 2006 by conducting censuses and captures (n = 294). Mark-recapture estimates of pup production were used to validate direct pup counts, allowing a 9-year dataset to be used for calculation of the population growth rate (2.2% p.a.) and investigation of environmental influences on reproductive success. Annual pup production (x = 3108) was synchronous, with 90% of births occurring within 28 days of the median birth date of 23 November. Births occurred earlier in years when pup production and female body condition were high and these factors were correlated with local oceanographic indicators, suggesting that reproductive success is constrained by environmentally-mediated nutritional stress.
Pregnancy was assessed by blood plasma progesterone radioimmunoassay and the pupping status of the same females was observed during breeding season. Despite high mid-gestation pregnancy rates (x = 84%), the birth rate was lower than in other fur seals (x = 53%), suggesting that late-term abortion is common. Lactating females were less likely to pup, indicating that nutrition may be insufficient to support concurrent lactation and gestation.
Age and morphometric data were used to construct body growth, age structure and survivorship models. Adult female survival rates were similar to those of other fur seals (x = 88.5%). A life table was constructed and its age-specific survival and fecundity rates used in a Leslie-matrix model to project the population growth rate (2.2% p.a.) and determine the relative influence of each parameter. The abundance of female non-pups was 6 times greater than that of female pups, which is approximately 50% higher than previous conversion factors used to extrapolate population abundance from pup censuses in Australian fur seals. However, if the non-pup sex ratios of other otariids are considered, the pup:population conversion factor is 4.5.
Compared to a study performed before the recent population increase, the modern population displays similar body growth and fecundity rates but higher survival rates. This suggests that recent population growth resulted from a relaxation of hunting and/or predation mortality rather than from increased food availability. The low population growth rate is attributed to a low birth rate associated with nutritional stress, yet despite this, body growth occurs rapidly. Such characteristics are typical of sea lions rather than fur seals, perhaps because Australian fur seals employ the typical sea lion strategy of using benthic foraging to exploit a continental shelf habitat. The effect of ecological niche on population dynamics in the Otariidae is discussed.
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Page, Brad, and page bradley@saugov sa gov au. "Niche partitioning among fur seals." La Trobe University. Zoology Department, School of Life Sciences, 2005. http://www.lib.latrobe.edu.au./thesis/public/adt-LTU20060622.153716.
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At Cape Gantheaume, Kangaroo Island (South Australia), adult male, lactating female
and juvenile New Zealand (NZ) and Australian fur seals regularly return to the same
colony, creating the potential for intra- and inter-specific foraging competition in nearby
waters. I hypothesised that these demographic groups would exhibit distinct foraging
strategies, which reduce competition and facilitate their coexistence. I analysed the diet
of adult male, adult female and juvenile NZ fur seals and adult male Australian fur seals
and studied the diving behaviour of adult male and lactating female NZ fur seals and the
at-sea movements of juvenile, adult male and lactating female NZ fur seals. Female diet
reflected that of a generalist predator, influenced by prey availability and their
dependant pups� fasting abilities. In contrast, adult male NZ and Australian fur seals
used larger and more energy-rich prey, most likely because they could more efficiently
access and handle such prey. Juvenile fur seals primarily utilised small lantern fish,
which occur south of the shelf break, in pelagic waters. Juveniles undertook the longest
foraging trips and adult males conducted more lengthy trips than lactating females,
which perform relatively brief trips in order to regularly nurse their pups. Unlike lactating
females, some adult males appeared to rest underwater by performing dives that were
characterised by a period of passive drifting through the water column. The large body
sizes of adult males and lactating females facilitated the use of both benthic and pelagic
habitats, but adult males dived deeper and for longer than lactating females, facilitating
vertical separation of their foraging habitats. Spatial overlap in foraging habitats among
the age/sex groups was minimal, because lactating females typically utilised continental
shelf waters and males used deeper water over the shelf break, beyond female foraging
grounds. Furthermore, juveniles used pelagic waters, up to 1000 km south of the
regions used by lactating females and adult males. The age and sex groups in this
study employed dramatically different strategies to maximise their survival and
reproductive success. Their prey and foraging habitats are likely to be shaped by body
size differences, which determine their different physiological constraints and metabolic
requirements. I suggest that these physiological constraints and the lactation
constraints on females are the primary factors that reduce competition, thereby
facilitating niche partitioning.
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Page, Brad. "Niche partitioning among fur seals /." Access full text, 2005. http://www.lib.latrobe.edu.au/thesis/public/adt-LTU20060622.153716/index.html.
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Thesis (Ph.D.) -- La Trobe University, 2005.Submitted in total fulfilment of the requirements for the degree of Doctor of Philosophy to the Zoology Dept., School of Life Sciences, Faculty of Science, Technology and Engineering. Research. Includes bibliographical references (leaves 133-152). Also available via the World Wide Web.
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Khan, Mohammed Ajaz. "Leakage flow in labyrinth seals." Thesis, University of Bradford, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.482781.
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Franceschini, Gervas. "Shaft seals for turbine engines." Thesis, University of Oxford, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.531815.
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Reeves, Brian W. "Navy SEALs : theory vs. reality." Thesis, Monterey, California. Naval Postgraduate School, 1997. http://hdl.handle.net/10945/8728.
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Approved for public release; distribution in unlimited.The purpose of this thesis is to examine two books that advance alternate theories to explain the success or failure of special operations. The first book is Perilous Options: Special Operations as an Instrument of U.S. Foreign Policy, by Lucien S. Vandenbroucke. Vandeubroucke discusses recurrent problems with U.S. special operations and identifies what he believes are the causes of failure of such operations. The second book is Spec Ops, written by William H. McRaven. McRaven examines eight historic cases from around the globe and develops his theory on how to conduct successful special operations. From the analysis of three recent Navy SEAL special operations missions, both theories seem to provide a useful tool for thinking about the failure or success of special operations. Combining these theories provides a complete framework for senior planners and tacticians in formulating a plan for successfully conducting future special operations missions
15
Druecke, Benjamin Charles. "Mechanics of swellable elastomeric seals." Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/115609.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2018.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 129-134).
This thesis investigates the mechanics of swellable elastomeric seals for the purpose of hydraulic fracturing in oil and gas applications. The first component of the thesis is the development of a laboratory-scale apparatus for the visualization of swellable seals in situ up to the point of leakage. Experiments using this apparatus show that leakage is a result of large, nonuniform deformation that stretches the seal material tangential to the sealing surfaces and leads to a corresponding loss of traction normal to the sealing surfaces due to Poisson contraction. This phenomenon was investigated in two analogous seal systems - an O-ring and a rectangular swellable elastomer used to seal a rectangular channel. Both analog systems exhibit leakage due to the same mechanism. Corresponding finite element simulations predict a fluid leakage path that agrees qualitatively with experiments. The second part of this thesis consists of an experimental investigation of the eect of geometry and metal support rings on the performance of swellable seal systems. Although this work is highly applied, it reveals two interesting results. The first is that mechanical supports, in the form of rigid metal support rings, provide most of the support for the applied differential pressure. Secondly, in some seals, changing the length of the rubber part of the seal does not significantly affect the maximum differential pressure that the seal can support. Motivated by the experiments showing no dependence of critical leakage pressure on seal length, we conduct an analytic investigation of the combined effects of compressibility and aspect ratio on the performance of the seal system. We nd an approximate, linear elastic Saint-Venant type solution that agrees well with nonlinear (finite deformation neo-Hookean) finite element simulations, indicating nonlinear effects are unimportant in the bulk of the seal, and only important at the high-pressure and low-pressure ends. Using finite element simulations, we characterize the energy release rates for the growth of cracks in the regions of high stress concentration at the ends of the seal. We show that, despite the linear Saint-Venant solution not being valid at the ends, it correlates the energy release rates obtained in the nonlinear finite element solutions. Although the Saint-Venant solution enables understanding of the location where fracture will first occur, experimental observations indicate that fracture often happens on both ends of the seal. In order to understand this, we implement a user subroutine within the finite element software Abaqus to predict fracture initiation and propagation. Results indicate that, despite fracture initially occurring on either end, the growth of cracks leads to fracture on both ends of the seal, consistent with experimental observations.
by Benjamin C. Druecke.
Ph. D.
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Ayala, Hugo M. (Hugo Mario). "Soil ingestion by elastomeric seals." Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/46270.
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Thesis (Sc.D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1999.Includes bibliographical references (p. 157-160).
Studies of elastomeric seal failure have until recently focused on the erosion of the sealing interface. This has limited the improvements in seal life to the application of wear-resistant materials. The present work shows that three stages of particle ingestion precede seal erosion, and that seals designed to interfere with each stage exhibit substantially longer operational life. The three stages of failure preceding seal erosion are as follows. The first stage occurs when small soil particles creep into the contact gap. These particles are so small (< 0.1 microns) that they accumulate in the surface valleys of the seal without damaging it. The second stage occurs as the shearing motion of the seal pushes the increasing number of entering particles against each other and short-range forces bind the particles into clusters. As more particles enter the seal, the clusters grow in size. Eventually, the clusters become so large that they no longer fit in the surface valleys of the seal. The third stage occurs when the clusters start rolling between the seal and its mating surface. The rolling pushes clusters further into the contact band until they fall freely into the oil. It is at this point that material erosion becomes the rate-limiting mechanism leading to failure. This work contains a description of the apparatus and techniques used in investigating seal failure; results of test for various seal lip designs, material composition, and operating parameters; images showing results the oil-film thickness measurements by means of laser-induced fluorescent; and estimates of contact pressure by finite-element simulations.
by Hugo Mario Ayala.
Sc.D.
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Li, Qi. "Transmission loss of vehicle seals." Licentiate thesis, Stockholm : Farkost och flyg, Kungliga Tekniska högskolan, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-9792.
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Curtis, Caitlin. "Population Genetics of Antarctic Seals." Scholar Commons, 2009. https://scholarcommons.usf.edu/etd/1918.
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I developed and tested a protocol for determining the sex of individual pinnipeds using the sex-chromosome specific genes ZFX and ZFY. I screened a total of 368 seals (168 crabeater, Lobodon carcinophagus; 159 Weddell, Leptonychotes weddellii; and 41 Ross, Ommatophoca rossii) of known or unknown sex and compared the molecular sex to the sex assigned at the time of collection in the Ross and Amundsen seas, Antarctica. Discrepancies ranged from 0.0% - 6.7% among species. It is unclear, however, if mis-assignment of sex occurred in situ or in the laboratory. It also is possible, however, that the assigned morphological and molecular sex both are correct, owing perhaps to developmental effects of environmental pollution.
I sequenced a portion (ca 475 bp) of the mitochondrial control region of Weddell seals (N = 181); crabeater seals (N = 143); and Ross seals (N = 41). I resolved 251 haplotypes with a haplotype diversity of 0.98 to 0.99. Bayesian estimates of Θ from the program LAMARC ranged from 0.075 for Weddell seals to 0.576 for crabeater seals. I used the values of theta to estimate female effective population sizes (NEF), which were 40,700 to 63,000 for Weddell seals, 44,400 to 97,800 for Ross seals, and 358,500 to 531,900 for crabeater seals. Weddell seals and crabeater seals had significant, unimodal mean pairwise difference mismatch distributions (p = 0.56 and 0.36, respectively), suggesting that their populations expanded suddenly around 731,000 years ago (Weddell seals) and around 1.6 million years ago (crabeater seals). Both of these expansions occurred during times of intensified glaciations and may have been fostered by expanding pack ice habitat.
Autosomal microsatellite based NEs were 147,850 for L. Weddellii, 344,950 for O. rossii, and 939,600 for L. carcinophagus. I screened one X-linked microsatellite (Lw18), which yielded a larger NE estimate for O. rossii than the other two species. Microsatellite NE estimates are compared with previously published mitochondrial NE estimates and this comparison indicates that the Ross seal may have a serially monogamous system of mating. I find no sign of a recent, sustained genetic bottleneck in any of the three species.
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Cordes, Line Søltoft. "Demography and breeding phenology of a marine top predator." Thesis, University of Aberdeen, 2011. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=183669.
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Worldwide harbour seal populations are showing differing and fluctuating trends in abundance, but the drivers of change remain uncertain. Within the Moray Firth, NE Scotland, count surveys carried out over the last 20 years highlighted the development of a new breeding site, providing a unique opportunity to carry out an individual-based study of harbour seal demography and pupping phenology using photo-identification techniques within a mark-recapture framework. Sightings of individual seals suggested that a large proportion of harbour seals are year-round residents at haul-out sites. Both sexes displayed high levels of between-year breeding site fidelity as well as seasonal variation in their haul-out behaviour. Apparent sex-specific survival rates (0.89♂, 0.97♀) and birth rates (0.88) were high. There was a strong correlation between lactation durations and the timing of pupping, suggesting that shifts in pupping phenology are a result of energetic constraints. This highlights the potential for using the timing of pupping as an indicator of ecosystem conditions. This study provided the first concurrent real-time estimates of survival and fecundity in a naturally regulated population of harbour seals. Demographic parameters and physiological responses indicate that prevailing conditions within the Moray Firth are favourable, and that this population should be recovering. However, observed patterns may also be an artefact of the long-term decline having caused an increase in per capita food availability through the reduction in intra-specific competition. This study highlights the current and long-term importance of individual-based data in understanding population dynamics. Through the identification of sentinel sites around the world, harbour seals could provide a single-species indicator of coastal ecosystem conditions in the Northern Hemisphere.
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Gardiner, Karen J. "Some aspects of the reproductive endocronology of harbour seals (Phoca vitulina) and grey seals (Halichoerus grypus)." Thesis, University of Aberdeen, 1994. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU068319.
Full textAbstract:
This study describes annual hormone cycles in wild and captive harbour seals, considers hormonal changes in wild grey seals during their lactation period, investigates the changing responsiveness of the pituitary-gonad axis throughout the year to stimulation with small single doses of gonadotrophin releasing hormone (GnRH) and addresses the possible influence of the experimental techniques upon the results using plasma cortisol concentrations as an index of stress. In captive harbour seals, LH concentrations through the year were significantly different only in the pregnant female. Plasma FSH concentrations were significantly different throughout the year only in the two non-pregnant females, being highest during delayed implantation. Plasma progesterone concentrations were significantly different throughout the year in both the pregnant and non-pregnant females. In wild harbour seals, plasma FSH concentrations were not significantly different throughout the year in the adult females but were significantly different in the immature females between stage 1 and 4 (post-partum oestrus and late gestation for the mature females). Plasma progesterone concentrations were significantly different throughout the year only in the adult females. In wild male harbour seals plasma testosterone concentrations were significantly different in adults between the pre-breeding and breeding season, being highest in the pre-breeding season. In wild lactating grey seals, plasma progesterone and FSH concentrations were low throughout most of lactation but increased late on. Plasma prolactin concentrations were highest during mid-lactation decreasing at the time when behavioural oestrus was observed. In all captive harbour seals and wild and captive grey seals an increase in plasma LH concentration was measured following GnRH administration returning to pre-GnRH concentrations within ninety minutes. In lactating female grey seals the magnitude of the LH response was smaller than in the other animals but was more prolonged.
21
Baart, Pieter. "Grease lubrication mechanisms in bearing seals." Doctoral thesis, Luleå, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-26652.
Full textAbstract:
Rolling bearings contain seals to keep lubricant inside and contaminants outside the bearing system. These systems are often lubricated with grease; the grease acts as a lubricant for the bearing and seal and improves the sealing efficiency. In this thesis, the influence of lubricating grease on bearing seal performance is studied. Rheological properties of the grease, i.e. shear stress and normal stress difference, are evaluated and related to the lubricating and sealing performance of the sealing system. This includes the seal, grease and counterface. The grease velocity profile in the seal pocket in-between two sealing lips is dependent on the rheological properties of the grease. The velocity profile in a wide pocket is evaluated using a 1-dimensional model based on the Herschel-Bulkley model. The velocity profile in a narrow pocket, where the influence of the side walls on the velocity profile is significant, is measured using micro particle image velocimetry. Subsequently, the radial migration of contaminants into the seal pocket is modelled and related to the sealing function of the grease. Additionally, also migration in the axial direction is found in the vicinity of the sealing contact. Experimental results show that contaminant particles in different greases consistently migrate either away from the sealing contact or towards the sealing contact, also when the pumping rate of the seal can be neglected. Lubrication of the seal lip contact is dependent on several grease properties. A lubricant film in the sealing contact may be built up as in oil lubricated seals but normal stress differences in the grease within the vicinity of the contact may result in an additional lift force. The grease, which is being sheared in the vicinity of the contact, will also contribute to the frictional torque. It is important to maintain a lubricant film in the sealing contact to minimize friction and wear. Here the replenishment of oil separated from the grease, also referred to as oil bleed, is of crucial importance. A model is presented to predict this oil bleed based on oil flow through the porous grease thickener microstructure. The model is applied to an axial sealing contact and a prediction of the film thickness as a function of time is made. The work presented in the thesis gives a significant contribution to a better understanding of the influence of lubricating grease on the sealing system performance and seal lubrication conditions.Godkänd; 2011; 20110824 (andbra); DISPUTATION Ämnesområde: Maskinelement/Machine Elements Opponent: Georgia Power Distinguished Professor Richard F Salant, Georgia Institute of Technology, Atlanta, USA Ordförande: Professor Braham Prakash, Institutionen för teknikvetenskap och matematik, Luleå tekniska universitet, Luleå Tid: Torsdag den 22 september 2011, kl 09.30 Plats: E231, Luleå tekniska universitet
22
Farahani, Arash. "Gas turbine engine static strip seals." Thesis, University of Sussex, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.444118.
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Allcock, D. C. J. "Abradable stator gas turbine labyrinth seals." Thesis, Cranfield University, 1999. http://dspace.lib.cranfield.ac.uk/handle/1826/10702.
Full textAbstract:
This is a detailed
study into the internal aerodynamics of labyrinth seals, with pmic|
reference to the effects of abradable
honeycomb stators on labyrinth seal leakage.-
A extensive
experimental programme established tables of friction factor for three
different
grades of honeycomb used by industry, and examined the effect of both
Reynolds number and clearance on these friction factors. The friction factor associated
with a
aerodynamically smooth surface was also experimentally determined in order to
establish the
experimental method.
The
experimental data was used to model the different grades of honeycomb used as
stator material in numerical simulations of a number
labyrinth seals, and allowed for
comparison of the leakage associated with both smooth and abradable stator straight
through labyrinth seals. Step-up and step-down seal geometries were also considered,
and the effects of pressure ratio, clearance and rotation on labyrinth seal leakage was
examined on all modelled seal
types.
This
numerically generated leakage data was comprehensive enough to allow for the
creation of a
second-generation one-dimensional labyrinth seal leakage predictor tool of
the
type used by design engineers in network models. This tool accounts for stator
material, seal clearance, overall pressure ratio, rotation and seal geometry, and the
accuracy associated with this tool allows labyrinth seal leakage to b predicted to within
10%. Functions of discharge coefficient and carry-over factor obtained from the
numerical
predictions are used by this tool, and as such it is capable of dealing with a
large number of different operating conditions for all the seal types modelled.
24
Sagoo, Kamaljeet S. "Wear and corrosion of mechanical seals." Thesis, Aston University, 1988. http://publications.aston.ac.uk/11884/.
Full textAbstract:
Mechanical seals are used extensively to seal machinery such as pumps, mixers and agitators in the oil, petrochemical and chemical industries. The performance of such machinery is critically dependent on these devices. Seal failures may result in the escape of dangerous chemicals, possibly causing injury or loss of life. Seal performance is limited by the choice of face materials available. These range from cast iron and stellited stainless steel to cemented and silicon carbides. The main factors that affect seal performance are the wear and corrosion of seal faces. This research investigated the feasibility of applying surface coating/treatments to seal materials, in order to provide improved seal performance. Various surface coating/treatment methods were considered; these included electroless nickel plating, ion plating, plasma nitriding, thermal spraying and high temperature diffusion processes. The best wear resistance, as evaluated by the Pin-on-Disc wear test method, was conferred by the sprayed tungsten carbide/nickel/tungsten-chromium carbide deposit, produced by the high energy plasma spraying (Jet-Kote) process. In general, no correlation was found between hardness and wear resistance or surface finish and friction. This is due primarily to the complexity of the wear and frictional oxidation, plastic deformation, ploughing, fracture and delamination. Corrosion resistance was evaluated by Tafel extrapolation, linear polarisation and anodic potentiodynamic polarisation techniques. The best corrosion performance was exhibited by an electroless nickel/titanium nitride duplex coating due to the passivity of the titanium nitride layer in the acidified salt solution. The surface coating/treatments were ranked using a systematic method, which also considered other properties such as adhesion, internal stress and resistance to thermal cracking. The sealing behaviour of surface coated/treated seals was investigated on an industrial seal testing rig. The best sealing performances were exhibited by the Jet-Kote and electroless nickel silicon carbide composite coated seals. The failure of the electroless nickel and electroless nickel/titanium nitride duplex coated seals was due to inadequate adhesion of the deposits to the substrate. Abrasion of the seal faces was the principal wear mechanism. For operation in an environment similar to the experimental system employed (acidified salt solution) the Jet-Kote deposit appears to be the best compromise.
25
Baart, Pieter. "Grease lubrication in radial lip seals." Licentiate thesis, Luleå : Luleå University of Technology, 2009. http://pure.ltu.se/ws/fbspretrieve/2760890.
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26
Reyes, A. T. "The stamp-seals of ancient Cyprus /." Oxford : Oxford University School of Archaeology, 2001. http://catalogue.bnf.fr/ark:/12148/cb392631246.
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Tripovich, Joy Sophie. "Acoustic communication in Australian fur seals." Thesis, The University of Sydney, 2006. http://hdl.handle.net/2123/1690.
Full textAbstract:
Communication is a fundamental process that allows animals to effectively transfer information between groups or individuals. Recognition plays an essential role in permitting animals to distinguish individuals based upon both communicatory and non-communicatory signals allowing animals to direct suitable behaviours towards them. Several modes of recognition exist and in colonial breeding animals which congregate in large numbers, acoustic signalling is thought to be the most effective as it suffers less from environmental degradation. Otariid seals (fur seals and sea lions) are generally colonial breeding species which congregate at high densities on offshore islands. In contrast to the other Arctocephaline species, the Australian fur seal, Arctocephalus pusillus doriferus, along with its conspecific, the Cape fur seal, A. p. pusillus, display many of the behavioural traits of sea lions. This may have important consequences in terms of its social structure and evolution. The acoustic communication of Australian fur seals was studied on Kanowna Island, Bass Strait, Australia. Analysing the acoustic structure of vocalisations and their use facilitates our understanding of the social function of calls in animal communication. The vocal repertoires of males, females, pups and yearlings were characterised and their behavioural context examined. Call structural variations in males were evident with changes in behavioural context, indicating parallel changes in the emotive state of sender. For a call to be used in vocal recognition it must display stereotypy within callers and variation between them. In Australian fur seal females and pups, individuals were found to have unique calls. Mutual mother-pup recognition has been suggested for otariids and this study supports the potential for this process to occur through the use of vocalisations. Call structural changes in pup vocalisations were also investigated over the progression of the year, from birth to weaning. Vocalisations produced by pups increased in duration, lowered in both the number of parts per call and the harmonic band containing the maximum frequency as they became older, suggesting calls are changing constantly as pups grow toward maturity. It has been suggested through descriptive reports, that the bark call produced by males is important to vocal recognition. The present study quantified this through the analysis of vocalisations produced by male Australian fur seals. Results support descriptive evidence suggesting that male barks can be used to discriminate callers. Traditional playback studies further confirmed that territorial male Australian fur seals respond significantly more to the calls of strangers than to those of neighbours, supporting male vocal recognition. This study modified call features of the bark to determine the importance to vocal recognition. The results indicate that the whole frequency spectrum was important to recognition. There was also an increase in response from males when they heard more bark units, indicating the importance of repetition by a caller. Recognition occurred when males heard between 25-75% of each bark unit, indicating that the whole duration of each bark unit is not necessary for recognition to occur. This may have particular advantages for communication in acoustically complex breeding environments, where parts of calls may be degraded by the environment. The present study examined the life history characteristics of otariids to determine the factors likely to influence and shape its vocal behaviour. Preliminary results indicate that female density, body size and the breeding environment all influence the vocal behaviour of otariids, while duration of lactation and the degree of polygyny do not appear to be influential. Understanding these interactions may help elucidate how vocal recognition and communication have evolved in different pinniped species.
28
Tripovich, Joy Sophie. "Acoustic communication in Australian fur seals." University of Sydney, 2006. http://hdl.handle.net/2123/1690.
Full textAbstract:
Doctor of Philosophy(PhD)Communication is a fundamental process that allows animals to effectively transfer information between groups or individuals. Recognition plays an essential role in permitting animals to distinguish individuals based upon both communicatory and non-communicatory signals allowing animals to direct suitable behaviours towards them. Several modes of recognition exist and in colonial breeding animals which congregate in large numbers, acoustic signalling is thought to be the most effective as it suffers less from environmental degradation. Otariid seals (fur seals and sea lions) are generally colonial breeding species which congregate at high densities on offshore islands. In contrast to the other Arctocephaline species, the Australian fur seal, Arctocephalus pusillus doriferus, along with its conspecific, the Cape fur seal, A. p. pusillus, display many of the behavioural traits of sea lions. This may have important consequences in terms of its social structure and evolution. The acoustic communication of Australian fur seals was studied on Kanowna Island, Bass Strait, Australia. Analysing the acoustic structure of vocalisations and their use facilitates our understanding of the social function of calls in animal communication. The vocal repertoires of males, females, pups and yearlings were characterised and their behavioural context examined. Call structural variations in males were evident with changes in behavioural context, indicating parallel changes in the emotive state of sender. For a call to be used in vocal recognition it must display stereotypy within callers and variation between them. In Australian fur seal females and pups, individuals were found to have unique calls. Mutual mother-pup recognition has been suggested for otariids and this study supports the potential for this process to occur through the use of vocalisations. Call structural changes in pup vocalisations were also investigated over the progression of the year, from birth to weaning. Vocalisations produced by pups increased in duration, lowered in both the number of parts per call and the harmonic band containing the maximum frequency as they became older, suggesting calls are changing constantly as pups grow toward maturity. It has been suggested through descriptive reports, that the bark call produced by males is important to vocal recognition. The present study quantified this through the analysis of vocalisations produced by male Australian fur seals. Results support descriptive evidence suggesting that male barks can be used to discriminate callers. Traditional playback studies further confirmed that territorial male Australian fur seals respond significantly more to the calls of strangers than to those of neighbours, supporting male vocal recognition. This study modified call features of the bark to determine the importance to vocal recognition. The results indicate that the whole frequency spectrum was important to recognition. There was also an increase in response from males when they heard more bark units, indicating the importance of repetition by a caller. Recognition occurred when males heard between 25-75% of each bark unit, indicating that the whole duration of each bark unit is not necessary for recognition to occur. This may have particular advantages for communication in acoustically complex breeding environments, where parts of calls may be degraded by the environment. The present study examined the life history characteristics of otariids to determine the factors likely to influence and shape its vocal behaviour. Preliminary results indicate that female density, body size and the breeding environment all influence the vocal behaviour of otariids, while duration of lactation and the degree of polygyny do not appear to be influential. Understanding these interactions may help elucidate how vocal recognition and communication have evolved in different pinniped species.
29
Hammill, Michael O. "Ecology of the ringed seal (Phoca hispida Schreber) in the fast-ice of Barrow Strait, Northwest Territories." Thesis, McGill University, 1987. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=75684.
Full textAbstract:
The effects of habitat features on the distribution of ringed seals (Phoca hispada) in the fast ice of Barrow Strait were examined between March and June 1984 to 1986. Breathing hole density in thirty-two, 2-4 km$ sp2$ study plots provided an index of seal abundance. Densities of seal holes were determined using a combination of trained dogs to locate the subnivean breathing holes and removal sampling.Birth lairs were not seen before 4 April, but the incidence of these structures increased as the season progressed. Structures maintained by male seals were evident in late March, but were not found after mid-May. In 1984, densities of seal holes were correlated with ice thickness. In 1985, no relationship was detected between seal hole density and habitat. In 1986, the highest densities of subnivean structures including birth lairs, were associated with deep snow conditions located in areas of late consolidating ice. No relationship was identified between the density of male structures and any habitat variables.
The mean reproductive rate for females $>$7 years old was 0.64. Between March and June for adult males lost 204 g per day with 72% of this weight being lost from blubber. Pregnant females lost 467 g per day with 68% of the loss occurring from the blubber. In adult seals no differences in body condition were detected between sexes or between years, but juveniles collected in 1986 were in significantly better condition than juveniles collected in 1984 and 1985.
30
Lewis, Rebecca Mary Gwynne. "The coastal and pelagic foraging behaviour of grey seals and southern elephant seals : a stable isotope approach." Thesis, Durham University, 2003. http://etheses.dur.ac.uk/3739/.
Full textAbstract:
Whisker samples were collected from grey seals from North Rona and from Isle of May in 1997-1999, from southern elephant seals from Pensinsular Valdes, Patagonia, from 1998 and 1999 and from South American sea lions also from Pensinsular Valdes in 1999. The whiskers were sub-sampled along their length and analysed for stable isotopes of δ(^13)C and δ(^15)N. There were significant differences between the two populations of grey seal and between years for each of the populations. Isotopic variations seen along the length of some of the whiskers were greater than could be attributed to background variation, indicating some seasonal variation. Possible prey items were herring, sandeels, some species of flat fish and gadoids. A strong temporal shift in apparent prey choice was seen only for the Isle of May, and the shift over a period of three years diminished the difference between the two populations. This could reflect changing prey choice or prey abundance in the North Sea over this time period. Male and female southern elephant seals showed significant differences in their isotopic values, with the male seals showing three different isotopic clusters that were distinct from one another and from the female seals. Two of these groups showed higher S'^C and §'^N values than those of the females and the third group. South American sea lions showed significantly higher values of δ(^13)C and δ(^15)N than female and most male southern elephant seals, suggesting that they were feeding at a higher trophic level. The South American sea lions and the group of male southern elephant seals with the highest values of δ(^13)C and δ(^15)N were possibly eating similar prey species which could include various fish and elasmobranch species. The female seals were feeding on prey with an isotopic signature similar to that of krill.
31
Xi, Jinxiang. "Seal inlet disturbance boundary conditions for rotordynamic models and influence of some off-design conditions on labyrinth rotordynamic instability." Texas A&M University, 2005. http://hdl.handle.net/1969.1/4971.
Full textAbstract:
Systematic parametric studies were performed to better understand seal-inlet rotordynamics.
A CFD-perturbation model was employed to compute the seal-inlet flow
disturbance quantities. Seal inlet disturbance boundary condition correlations were
proposed from the computed seal-inlet quantities using the important parameters. It
was found that the cosine component of the seal-inlet swirl velocity disturbance W1C
has a substantial impact on the cross-coupled stiffness, and that the correlations for
W1C and W1S should be used to replace the historical guess that seal inlet W1C = 0
and W1S = 0. Also, an extremely precise relationship was found between the swirl
disturbance W1C and the seal-inlet swirl velocity (ÃÂRsh â ïW0). Thus, the number
of experiments or computer runs needed to determine the effect of spin speed, shaft
radius and/or inlet swirl velocity on the cross-coupled stiffness is greatly reduced by
plotting the simplified relationship of the cross-coupled stiffness against the swirl slip
velocity. The benefits of using the new seal-inlet boundary condition correlations
were assessed by implementing them into a CFD-perturbation model. Consistently
improved agreement with measurements was obtained for both liquid annular seals
and gas labyrinth seals.
Further, the well-established CFD-perturbation model with new boundary condition
correlations was employed to investigate the rotordynamics of two off-design situations. The first case considered the influence of labyrinth seal teeth damage on
the performance and the rotordynamic characteristics of impeller eye seals in centrifugal
compressors. The second case considered the influence of rotor-axial-shifting on
rotordynamic forces for high-low labyrinth seals in steam turbines during the start-up
and shut-down process. The results should provide useful information for labyrinth
seal design and fault diagnosis of stability problems in turbines and compressors.
32
Smith, Ian M. "An Experimental Investigation Into The Optimization of Padded Finger Seals." University of Akron / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=akron1195226720.
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33
Parihar, Shailendra S. "High Temperature Seals for Solid Oxide Fuel Cells." University of Cincinnati / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1172490697.
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34
Ireland, Darren Scott. "Mass estimation of Weddell Seals through photogrammetry." Thesis, Montana State University, 2004. http://etd.lib.montana.edu/etd/2004/ireland/IrelandD1204.pdf.
Full textAbstract:
Food resources of pelagic marine predators have traditionally been difficult to monitor and annual monitoring of food-resource availability is not currently feasible for the Weddell seal (Leptonychotes wedellii) population in Erebus Bay, Antarctica. Body mass measurements of parturient females, or their weaned pups, on an annual basis may be used as an indicator of food availability during the previous year and also provide a link between population vital rates and environmental fluctuation. Traditional methods of acquiring mass measurements, including physical restraint and/or chemical immobilization, limit the ability to sample adequately large numbers of individuals from the population of interest. Previous researchers have developed methods to estimate the mass of large seals using scaled photographs, but later application of these methods have not explicitly included uncertainty around estimates derived from predictive equations. I therefore developed the equipment and methods for estimating the mass of Weddell seals using digital photographs and image-analysis software. I then applied the method at a small scale to determine how prediction intervals may be incorporated into calculations based on mass estimates and what affect the explicit use of these intervals would have on the ability to detect differences between the mass of individuals or groups of seals. Scaled photographs of adult female and pup Weddell seals were taken from overhead, ground-level side, and ground-level head or tail perspectives. Morphometric measurements from scaled photographs (photogrammetric measurements) were then correlated using regression against the measured mass at the time of photography. Sampling occurred throughout the nursing period in order to build regression models over a wide range of masses. Resulting regression models predict the mass of adult female seals to within ±13.8% of estimated mass, and ±25.9% of estimated mass for pups. In an application of the method, differences in mass transfer between experienced and inexperienced maternal females and their pups were detected when prediction intervals were explicitly included. Detection of differences between individual seals may not be possible when prediction intervals are included with mass estimates, but estimated mass measurements should be useful for comparing mean differences across a population between years in relation to environmental variation.
35
Yang, Bo. "Elastohydrodynamic model of reciprocating hydraulic rod seals." Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/34747.
Full textAbstract:
Reciprocating rod seals are widely used in hydraulic systems to prevent the hydraulic fluid from leaking into and polluting the environment. In this research an elastohydrodynamic model of a generalized reciprocating hydraulic rod seal, including mixed lubrication and surface roughness, has been successfully developed. This model consists of coupled fluid mechanics, contact mechanics, thermal analysis and deformation analyses.
Such model is capable of predicting the key seal performance characteristics, especially net leakage and friction force. This allows evaluation of potential seal designs and serves as design tools. Also as this model has been developed, the basic physics of seal operation has been clarified, which stimulates the development of innovative seal concepts, such as seals with engineered sealing surfaces.
The results of this study indicate that in general, hydraulic rod seals operate in the mixed lubrication regime, although under certain conditions full film lubrication may occur over a portion of the sealing zone. The roughness of the seal surface and the rod speeds play important roles in determining whether or not a seal will leak. Cavitation during the outstroke and partial full film lubrication during the instroke tend to prevent net leakage. The behavior of a reciprocating hydraulic rod seal with a double lip or two seals in tandem arrangement can be very different from that of a similar seal with a single lip. For the double lip seal, the secondary lip can strongly affect the behavior of the primary lip by producing an elevated pressure in the interlip region. The same seal characteristics that promote effective sealing in a single lip seal and, in addition structural decoupling of multiple lips, are found to promote effective sealing in a multiple lip seal.
The model is validated through comparisons of model predictions with experimental measurements and observations by industry partners. The results have shown the predicted leakage and friction force for various seal and operation conditions are consistent with the measurements.
A seal with micro-pattern on the sealing surface also has been investigated. The results indicate that an elaborately designed pattern can improve the sealing characteristics of the seal, without significantly affecting the friction force.
In the end, the selection of the rod seal for a specific application using this analytical model is demonstrated. The best design can be picked up before a prototype being built.
36
Ertas, Bugra Han. "Rotordynamic force coefficients of pocket damper seals." Texas A&M University, 2005. http://hdl.handle.net/1969.1/2592.
Full textAbstract:
The present work describes experiments conducted on several pocket damper seal
(PDS) designs using a high pressure annular gas seal test rig. Both rotating and non-rotating
tests were conducted for a 12, 8, and 6 bladed PDS. The objective of the tests was to
determine the rotordynamic force coefficients and leakage for the different PDS while
varying parameters such as: (1) clearance ratio, (2) rotor surface speed, (3) PDS pressure
differential, and (4) excitation frequency. Two different methods were used to determine
frequency dependent force coefficients: (1) the impedance method, which involved using a
baseline subtraction and (2) the dynamic pressure response method, which comprised of
measuring seal cavity dynamic pressure and phase relationship to vibration. Both methods
were used to determine coefficients, but the dynamic pressure response method revealed
insights to the dynamics of the PDS that were the first of its kind and allowed the comparison
to the damper seal theory at the most fundamental of levels. The results indicated that the
conventional PDS possessed high positive damping, negative and positive stiffness, and same
sign cross-coupled coefficients. Another objective of the work is to investigate a new fully
partitioned PDS design and accompany experimental results with the development of a
modified damper seal theory. The new fully partitioned PDS design was shown to give twice
as much damping as the conventional design and revealed the ability to modify direct stiffness
without degradation in direct damping. Finally, both the conventional theory and the newly
proposed theory predictions are compared to experimentally determined force coefficients.
The last objective was to evaluate the leakage characteristics of the different designs and to
investigate the effect of blade profile on seal leakage. Results showed that beveled tooth blade
profiles yield higher mass flow leakage compared to rectangular blade profiles.
37
Wileman, James Michael. "Dynamic analysis of eccentric mechanical face seals." Diss., Georgia Institute of Technology, 1994. http://hdl.handle.net/1853/17343.
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38
Chen, Lihong. "Numerical and experimental modelling of brush seals." Thesis, University of Oxford, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.268200.
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O'Mahoney, T. S. D. "Large-eddy simulation of turbine rim seals." Thesis, University of Surrey, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.553681.
Full textAbstract:
This thesis describes the application of Large-Eddy Simulation (LES) to the internal flows within turbomachines. In particular, the work sought to investigate whether LES could give an improved predictive tool for flows through a turbine rim seal where other methods of modelling turbulence give disappointing results for the simulation of hot annulus gas ingestion into the rim seal cavity. The applicability of LES to flow regimes within a rotor-stator cavity were investigated with reference to two experimental studies, those of Daily & Nece [1] and of Itoh et al. [2]. LES simulations were run using the commercial Computational Fluid Dynamics (CFD) code FLUENT and the Rolls-Royce CFD code HYDRA. Both gave good agreement for the velocity field even when the boundary layer was not fully resolved. HYDRA was then used to simulate a turbine rim seal cavity with external flow through an annulus with NGV and rotor blades, modelled using a small sector with periodic boundary conditions in the circumferential direction. LES was found to predict higher levels of ingestion than Unsteady Reynolds- Averaged Navier-Stokes (URANS) simulations at a number of different values of cavity throughflow. This resulted in better, but not close, agreement with the experiments of Gentilhomme [3]. The sensitivity of the LES to changes in the size of the sector and to the resolution of the CFD grid were investigated. A larger sector simulation, corresponding to 40°, gave almost identical results to those on the smaller sector, 13.3°. Refinement to the CFD grid did lead to different results, particularly in the annulus flow, though critically the prediction of ingestion in the stator boundary layer was largely unaffected.
40
Davis, Karen Ann 1979. "Investigation of reverse plumbing in rotary seals." Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/89394.
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41
Omeru, Tuviere. "Mass transport deposits : implications for reservoir seals." Thesis, Cardiff University, 2014. http://orca.cf.ac.uk/64667/.
Full textAbstract:
This thesis uses a combination of two-dimensional (2D) and three-dimensional (3D) seismicreflection data to investigate the morphology and internal architecture of mass transport deposits (MTDs) from the west Nile delta, offshore Egypt and from the Deepwater Taranaki Basin, New Zealand. The overall aim of the project is to gain an improved understanding of the impact of MTDs on hydrocarbon seals. To this end a novel seismic based classification for MTDs that is directly mappable onto the problem of defining their potential as sealing sequences is proposed based on results of investigations from three core research chapters. In the first core chapter, the phases and mechanisms of failure of three main MTDs (termed A, B and C) in the western Nile delta (Eastern Mediterranean) was investigated using 3D seismic data. Analysis of the geometries of the MTDs suggests that they were emplaced in at least two main phases: Progressive failure occurred initially with MTD A cutting through MTDs B and C. Retrogressive failure then occurred due to the natural unbalance of the supposed headwall of MTD A. Reconstruction of the pre-seabed topography suggests a minimum total volume (residual and depleted) of remobilisation of the order of 750 km3, making this amongst the largest submarine landslide complexes documented to date. It is suggested that this giant slope failure might have posed a risk to the integrity of petroleum seals considering that the failure occurred in a gas rich province of the western Nile delta. In the second core chapter, six large scale MTDs, stacked and locally amalgamated making up c. 50% of the stratigraphic succession were recognised and mapped using 2D seismic data. Key kinematic features suggest a north-westerly transport direction for all of the MTDs with the exception of MTD 6, having a south-westerly transport direction. There is seismic stratigraphic evidence in the form of both lateral and basal truncations suggesting that the MTDs were erosive during their emplacement. Estimation shows that c 70% of the final volume of MTD 6 was contributed from substrate cannibalization greater than the other five MTDs in the study area. This work suggests that the rheology of the substrate immediately beneath the seafloor might not be the only factor controlling the degree of substrate cannibalisation during MTD emplacement and that the nature of any triggering mechanism might also play an important role. This has a bearing on the MTD content (sandy or muddy dominated MTD) and would in turn influence the seal integrity of MTD. The final core chapter presents insights into the dynamics of emplacement of MTD 6 using 3D seismic data. MTD 6 consists of five distinctive domains (labelled A – E). Domains A – C show evidence of deformation and remobilisation of c. 30% of a lower transparent interval while Domain D is characterised by a partial or complete loss of seismic character coupled with c. 30% reduction in thickness compared to adjacent domains. Based on the deformation styles, the transition across domain boundaries and the observed volume loss, a progressive stratal disaggregation is inextricably linked with gravity spreading as the mode of emplacement of MTD 6. This study highlights the power of 3D seismic data in unravelling the detailed processes involved during MTD emplacement and which may have significant implications as regards the translation and emplacement of other submarine slope failures in other continental margins.
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Menger, Christian. "Behaviour of sliding seals in abrasive fluids." Thesis, University of the West of England, Bristol, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.408040.
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Jahn, Ingo H. J. "Leaf seals for gas and steam turbines." Thesis, University of Oxford, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.670066.
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Linnik, K. S., and D. O. Marchenko. "Numerical modeling of reciprocating fluid power seals." Thesis, Видавництво СумДУ, 2011. http://essuir.sumdu.edu.ua/handle/123456789/13364.
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Chittora, Siddharth M. "Monitoring of Mechanical Seals in Process Pumps." Thesis, KTH, Skolan för industriell teknik och management (ITM), 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-236035.
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Kassfeldt, Elisabet. "Analysis and design of hydraulic cylinder seals." Doctoral thesis, Luleå tekniska universitet, Maskinelement, 1987. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-17192.
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Hydraulic cylinder seal performance is studied experimentally and theoretically. The seal performance is discussed in terms of friction force and oil leakage, which are due to the oil film build-up in the seal contact. The theoretical analysis is based both on calculated and measured contact pressure distributions. The compressibility of seal materials is determined experimentally, and it is shown that the compressibility is a pressure dependent material property. A method for calculation of the contact pressure distribution for a seal with an arbitrary cross-section is proposed, based on geometrical considerations and the experimentally determined compressibility. The pressure calculations are verified experimentally. Theoretically calculated oil film thicknesses in a seal contact are compared with measured film thicknesses. The increase of film thickness with increasing sliding velocity shows a good agreement between theory and experiment. The oil film is thicker in the experiments due to the surface roughness of the seal. A complete theoretical analysis of the seal performance is developed to be used as a design tool.Godkänd; 1987; 20070424 (ysko)
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Peterson, Erick. "The strategic utility of U.S. Navy Seals." Thesis, Monterey, Calif. : Naval Postgraduate School, 2009. http://edocs.nps.edu/npspubs/scholarly/theses/2009/Jun/09Jun%5FPeterson.pdf.
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Thesis (M.S. in Defense Analysis)--Naval Postgraduate School, June 2009.Thesis Advisor(s): Rothstein, Hy. "June 2009." Description based on title screen as viewed on July 13, 2009. Author(s) subject terms: U.S. Navy SEALs, SEALs, Naval Special Warfare, NSW, Special Operations Forces, SOF, SOCOM, SOF Culture, Comparative Advantage, Strategic Utility. Includes bibliographical references (p. 93-103). Also available in print.
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Palo, Jukka. "Genetic diversity and phylogeography of landlocked seals." Helsinki : University of Helsinki, 2003. http://ethesis.helsinki.fi/julkaisut/mat/ekolo/vk/palo/.
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Raja, Mohan Anandu, and Niranjan Sutar. "Characterization of Sealing Surface for Static Seals." Thesis, KTH, Skolan för industriell teknik och management (ITM), 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-263915.
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Leakages from seals are one of the important factors that are taken into consideration while designing any machining element. This is because leakages can affect the performance of any component and can also turn into a catastrophe. If looked into it, many parameters can be pointed out that can enhance leakages within the system, some of them may be pressure, temperature, clamping force and bolt distance etc. But the main parameter is the surface roughness, higher the roughness more the leakage and vice-versa. Thus, in this thesis an attempt has been made how the surface roughness can affect the performance of the sealing concept for metal bounded gasket with above four mentioned parameters. Also how leak proof surface can be defined using standard tribological parameters is the aim of this thesis. This report includes the results for methodologies implemented during the thesis and track down the leakages. The leaked surfaces were carefully studied and analyzed using different standards compared with the non leaked surfaces’ roughness parameters.Läckagerisk från tätande förband är en av de viktigaste faktorerna som beaktas vid utformning av konstruktionsartiklar. Detta på grund av att konsekvenserna kan bli förödande. Det tätande förbandet påverkas av många olika parametrar såsom till exempel tryck, temperatur, klämkraft, skruvavstånd och val av packning. En viktig faktor är ytans beskaffenhet; Generellt läcker en grov yta och vågig yta mer än en fin och plan yta. Således har i denna avhandling ytans beskaffenhet studerats tillsammans med en packning av typen metallburen gummipackning för att påvisa täthetfunktionen som en funktion av tryck, temperatur, klämkraft och skruvavstånd. Denna rapport innehåller resultat och analys av olika standardmetoder för de ytor som ingick i utredningen.
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MAGNESS-GARDINER, BONNIE SUE. "SEALS AND SEALING IN THE ADMINISTRATION OF THE STATE: A FUNCTIONAL ANALYSIS OF SEALS IN SECOND MILLENNIUM BC SYRIA." Diss., The University of Arizona, 1987. http://hdl.handle.net/10150/184217.
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Cylinder seal impressions occur in many contexts in the ancient Near East. This disssertation focuses specifically on the function of sealing in the manipulation of state resources (land, labor, and goods) in second millennium B.C. Syria. The sources of information utilized in this study include textual references to sealing practices, sealed documents, bullae, and the seals themselves. The archives of Mari, Alalah, and Ugarit are particularly important as they provide textual and archaeological information on seals and sealing within the physical and institutional context of the palace, the center of state administration. Chapter 1 surveys the previous research on seals and sealing and briefly outlines Syrian geography and political history in the second millennium B.C. Chapter 2 examines the physical qualities of the seals--materials, methods of production, distribution and style. Chapter 3 addresses the problem of the physical and institutional context of seal use. A functional division between legal and administrative texts is reflected in the use of seals on them. On both types of documents, however, the use of a seal acknowledges the obligation of the sealer. The nature of that obligation varies with the contents of the text itself. Chapter 4 evaluates the use of seals on legal texts in palace archives. Most of these sealed documents record land grants. The historical trend in second millennium Syria is to an increasing involvement of heads-of-state in granting state land. Other sealed legal documents were kept in palace archives because the participants were in some way associated with the palace. Chapter 5 details the administrative use of seals at Mari. Receipts and expenditures are the most common sealed documents. The use of seals on these texts signals the acceptance by the sealer of responsibility for the goods or actions described therein. The conclusions (Chapter 6) summarize the differences in sealing practices in Mari, Alalah and Ugarit in light of the different historical circumstances and political needs of each state.