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The Impact of Micro-Surface Shaping of the Piston on the Piston/Cylinder Interface of an Axial Piston MachineWondergem, Ashley, Ivantysynova, Monika 02 May 2016 (has links) (PDF)
Axial piston machines of the swashplate type are commonly used in various hydraulic systems and with recent developments in displacement control, it is essential to maximize their efficiency further reducing operation costs as well as improving performance and reliability. This paper reports findings of a research study conducted for the piston-cylinder interface utilizing a novel fluid structure thermal interaction model considering solid body deformation due to thermal and pressure effects in order to accurately predict the transient fluid film within the gap. A large reduction in energy dissipation is possible due to reduced clearances allowable due to the surface shaping of the piston resulting in a reduction in leakage. From this study, it is shown that surface shaping of the piston in combination with a reduced clearance is not only beneficial by improving the efficiency of a machine, but also increases the reliability and the performance of the machine as the load support is enhanced.
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Implementation of a two-stream-fan in the CIRSTEL systemHeise, R. 12 1900 (has links)
Thesis (PhD (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2006. / This thesis describes the design and incorporation of a twin-stream fan into the CIRSTEL tail
boom. The Combined Infra-Red Suppression and Tail rotor Elimination (CIRSTEL) tail boom is a
system designed to replace the tail rotor on a conventional helicopter. It relies on the Coanda effect
to create circulation around the helicopter tail boom when exposed to the rotor downwash. This
generates sideways-directed lift to counter the main rotor torque, and a tail thruster adds extra
torque and directional control. A twin-stream fan supplies separate air streams to each of the
Coanda and tail thruster sections. The first section of the study describes the experimental tests
done on an 83% scale demonstrator of the twin-stream fan with the objective to verify the concept
and determine the fan section efficiencies. Subsequent modifications done to the fan stator blades
are also evaluated. The efficiencies of the design were shown to exceed the targets in both
sections. The section concludes with design recommendations for a future fan, based on the
findings of the experiments. A brief analysis of the CIRSTEL system is presented and by using
optimisation techniques the predicted power demand of the system could be significantly reduced
from a conventional tail rotor. The second section of the study details the conceptual design and
CFD evaluation of air intakes for the fan that can be fitted to the helicopter. The objective here was
to study the flow affecting helicopter intakes as well as to establish design considerations for a fan
intake. A basic intake concept was developed for the Alouette III/CIRSTEL combination and
modified according to results based on the CFD simulations. The intake design was evolved to the
point were it was shown that the concept is feasible. These CFD simulations were an initial effort
to design the fan intakes with the help of a simplified rotor flow field. The investigation was
subsequently extended to investigate helicopter intake design considerations in the presence of a
representative rotor, which was modelled as an actuator disk in the CFD simulations. In this
investigation top and side mounted intake concepts were compared and analysed for suitability as a
fan intake. Each intake concept showed its own advantages. Due to the proximity of the rotor hub
to the intake, distortion and total pressure levels at the fan face are influenced negatively. The
report is concluded with design recommendations for the intake as applied to the current
Alouette III configuration, as well as for implementation on helicopters in general.
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From turbo-machines to solar chimneysVon Backstrom, Theodor W. 12 1900 (has links)
Thesis (PhD)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: This dissertation is basically a summary, with some interpretation, of published research
by the author. The scope is limited to the fields of turbo-machinery, computational fluid
dynamics and solar chimney power plants.
The main contribution in the field of turbo-machinery in general is in the development
of a through-flow method that automatically satisfies mass conservation. Concerning
fan design, the contributions are the realization of the importance of the exit
kinetic energy in the determination of the efficiency of rotor-only axial flow fans, and
the quantification of the effect of off-axis inflow into cooling system fans on their performance.
In the field of centrifugal fans and compressors an original, unifying model
for the prediction of slip factor was developed. To investigate accident scenarios in
closed cycle gas turbine nuclear reactors, all possible operational modes of multi-stage
axial compressor operation caused by flow and rotation direction were investigated experimentally
and computationally. Spanning the fields of turbo-machinery and solar
chimneys, the basic theory of solar chimney turbines was developed, showing that high
turbine efficiency was possible.
In the field of solar chimneys, an original thermodynamic approach was developed
to predict the main relationships that govern solar chimney performance, and to solve
the through-flow equations for non-ideal systems with losses. Equations for the accurate
determination of all the thermodynamic variables in a solar chimney as dependent on
chimney height, wall friction, additional losses, internal drag and area change were
derived and solved. Coefficients of wall friction, bracing wheel loss and exit kinetic
energy were determined experimentally, and empirical equations were developed to
predict the loss coefficient of the collector to turbine transition section and and the
turbine inlet flow angle. A simple power law approach allowed the calculation of the
optimal turbine pressure drop in solar chimney power plants. A comparison of two sets
of equations used to calculate the heat fluxes into, inside and leaving the solar collector,
resulted in similar air temperature rises in the collector, and similar produced power.
It turned out however that the optimal flow for minimal turbine pressure drop was
dependent on the heat transfer models.
Investigation of the performance of various solar chimney turbo-generator layouts
using analytical models and optimisation techniques showed that the optimal number
of turbines varies with plant size, but the individual turbine size, the number of blades
and even the efficiency remains close to constant. It was found that the cost of a turbogenerator
system, however, varies significantly with size. A joint paper with several
German universities and institutions did a comparative cost analysis of solar chimney
power plants / AFRIKAANSE OPSOMMING: Hierdie verhandeling is basies ’n opsomming, met interpretasie, van gepubliseerde navorsing
deur die outeur. Die omvang is beperk tot die gebiede van turbomasjinerie,
berekeningsvloeidinamika en sonskoorsteenkragstasies.
Die hoof bydrae op die gebied van turbomasjinerie in die algemeen is in die ontwikkeling
van ’n deurvloeimetode wat outomaties massabehoud bevredig. Wat waaierontwerp
betref is die bydrae die besef van die belangrikheid van die uitlaat kinetiese
energie in die bepaling van waaierbenuttingsgraad, en die kwantifisering van die effek
van af-as invloei in verkoelingswaaiers op hulle gedrag. Op die gebied van sentrifugaalwaaiers
en -kompressors is ’n oorspronklike, samevattende model vir die voorspelling
van glipfaktor ontwikkel. Om ongeluk-scenario’s in geslote kringloop gasturbine kenreaktors
te ondersoek is al die moontlike werksmodusse veroorsaak deur vloei en rotasie
rigting van ’n multistadium aksiaalkompressor eksperimenteel en numeries ondersoek.
As brug tussen turbomasjinerie en sonskoorstene is die basiese teorie van sonskoorsteenturbines
ontwikkel met die aanduiding dat hoë turbine benuttingsgraad moontlik
is.
Op die gebied van sonskoorstene is ’n oorspronklike termodinamies benadering ontwikkel
om die hoofverwantskappe te voorspel wat sonskoorsteen gedrag bepaal, en
om die deurvloei vergelykings op te los vir nie-ideale stelsels met verliese. Vergelykings
vir die akkurate bepaling van al die termodinamiese veranderlikes in ’n sonskoorsteen
soos afhanklik van skoorsteenhoogte, wandwrywing, bykomstige verliese, interne
sleur en oppervlakte verandering is afgelei en opgelos. Koëffisiënte vir wandwrywing,
verstywingswiel-verlies en uitlaat kinetiese energie is eksperimenteel bepaal, en empiriese
vergelykings is ontwikkel om die verlieskoëffisiënt van die kollektor-tot-skoorsteen
oorgang en die turbine inlaatvloeihoek te bepaal. ’n Eenvoudige magswet benadering
het dit mootlik gemaak om die optimum turbine-drukval in sonskoorsteen aanlegte te
bepaal. ’n Verglyking van twee stelle vergelykings om warmtevloede in, binne en uit
die sonkollektor te bereken het gelei na soortgelyke temperatuurstygings en gelewerde
drywing. Die optimale vloei vir maksimum drywing was egter afhanklik van die warmteoordrag
modelle.
Ondersoek van die gedrag van verskeie turbo-generator uitlegte, deur gebruik van
analitiese modelle en optimeringstegnieke het getoon dat die optimale aantal turbines
wissel met aanleg grootte, maar die individuele turbine grootte, die aantal lemme en
selfs die benuttingsgraad bly feitlik konstant. Daar is egter gevind dat die koste van
’n turbogenerator stelsel beduidend wissel met grootte. ’n Gesamentlike artikel met
verskeie Duitse universiteite en instansies het ’n vergelykende koste analise van sonskoorstene
gedoen.
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Design and performance evaluation of a magnetically geared axial-flux permanent magnet generatorBronn, Lodewyk 03 1900 (has links)
Thesis (MScEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: This thesis is a description of how the first magnetically geared axial flux permanent magnet generator
(MGAFG) is designed, constructed and experimentally evaluated. Magnetic gears (MGs) allow for
contact-less power transfer and lubricant free operation, which may solve the reliability concerns with
current mechanically geared wind energy converters.
However, the complex structure of MGs may present serious challenges to its design. Thus, special
care should be given to the mechanical layout and the electromagnetic influence of every component.
The MGAFG can be configured to be magnetically coupled or decoupled. In the coupled configuration
the permanent magnets (PMs) of the MG contribute to the total flux linkage in the PM generator
(PMG). The coupled configuration is therefore more efficient. The processing time required to optimise
the decoupled configuration is however much faster, since the MG and the PMG can be optimised
separately.
The optimised results show that a torque density in excess of 100kNm/m3 could be achieved, which
is significantly higher than any of known electrical machines. However, owing to excessive losses in the
mechanical support structures, the prototype exhibited lower torque density and poor efficiency. The
design related aspects and issues are analysed and discussed in detail in an attempt to outline problem
areas in the design process. Relevant recommendations are also given for future design improvements.
The costs of magnetic material accounts for over fifty percent of the total cost of the prototype. Therefore
to make the manufacturing of the MGAFG more economically viable magnetic material should be
minimised in the design process. / AFRIKAANSE OPSOMMING: In hierdie tesis word die eerste magnetiese geratte aksiale vloed permanente magneet generator
(MGAVG) ontwerp, vervaardig en eksperimenteel geëvalueer. In magnetiese ratte (MR) is daar geen
kontak tussen werkende dele nie, daarom word geen smeermiddels benodig nie. Dit dra by tot die
betroubaarheid van die ratkaste in wind energie generators en kan onderhoud grotendeels uitskakel.
Die komplekse struktuur van magnetiese ratte kan egter die betroubaarheid van die ontwerp juis
verswak. Daarom moet die meganiese uitleg noukeurig beplan word sodat dit nie die elektromagnetiese
werking ondermyn nie.
Die magnetiese rat (MR) en die permanente magneet generator (PMG) van die masjien kan magneties
of sonder magnetiese koppeling verbind word. In die gekoppelde konfigurasie dra all die permanente
magnete van die MR gesamentlik by tot die totale vloed-koppeling in die PMG. Wat die magnetiese
gekoppelde konfigurasie meer doeltrefend maak. Minder tyd word benodig om die nie magnetiese
gekoppelde konfigurasie te optimaliseer omdat die MR en die PMG apart geoptimaliseer kan word.
Die optimale resultate toon dat ’n wringkrag van meer as 100kNm/3 bereik kan word, wat aansienlik
beter is as die van bekende elektriese masjiene.
Maar as gevolg van oormatige verliese in die meganiese strukture, toon die prototipe lae wringkrag
digtheid en swak doeltreffendheid. Die ontwerp probleme word ontleed en bespreek in ’n poging
om probleem areas in die ontwerp te identifiseer. Relevante aanbevelings word gegee vir toekomstige
ontwerp verbeterings.
Die koste van die magnetiese material verteenwoordig meer as vyftig persent van die vervaardigings
koste van die prototipe. Koste kan bespaar word op die vervaardiging van die MGAVG deur die
hoeveelheid magnete wat gebruik word te beperk.
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Effects of confinement and small axial load on flexural ductility of high-strength reinforced concrete beamsChau, Siu-lee., 周小梨. January 2005 (has links)
published_or_final_version / abstract / Civil Engineering / Master / Master of Philosophy
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A mechanical model of an axial piston machineLöfstrand Grip, Rasmus January 2009 (has links)
<p>A mechanical model of an axial piston-type machine with a so-called wobble plate and Z-shaft mechanism is presented. The overall aim is to design and construct an oil-free piston expander demonstrator as a first step to realizing an advanced and compact small-scale steam engine system. The benefits of a small steam engine are negligible NOx emissions (due to continuous, low-temperature combustion), no gearbox needed, fuel flexibility (e.g., can run on biofuel and solar), high part-load efficiency, and low noise. Piston expanders, compared with turbines or clearance-sealed rotary displacement machines, have higher mechanical losses but lower leakage losses, much better part-load efficiency, and for many applications a more favourable (i.e., lower) speed. A piston expander is thus feasible for directly propelling small systems in the vehicular power range. An axial piston machine with minimized contact pressures and sliding velocities, and with properly selected construction materials for steam/water lubrication, should enable completely oil-free operation. An oil-free piston machine also has potential for other applications, for example, as a refrigerant (e.g., CO<sub>2</sub>) expander in a low-temperature Rankine cycle or as a refrigerant compressor.</p><p> </p><p>An analytical rigid-body kinematics and inverse dynamics model of the machine is presented. The kinematical analysis generates the resulting motion of the integral parts of the machine, fully parameterized. Inverse dynamics is applied when the system motion is completely known, and the method yields required external and internal forces and torques. The analytical model made use of the “Sophia” plug-in developed by Lesser for the simple derivation of rotational matrices relating different coordinate systems and for vector differentiation. Numerical solutions were computed in MATLAB. The results indicate a large load bearing in the conical contact surface between the mechanism’s wobble plate and engine block. The lateral force between piston and cylinder is small compared with that of a comparable machine with a conventional crank mechanism.</p><p> </p><p>This study aims to predict contact loads and sliding velocities in the component interfaces. Such data are needed for bearing and component dimensioning and for selecting materials and coatings. Predicted contact loads together with contact geometries can also be used as input for tribological rig testing. Results from the model have been used to dimension the integral parts, bearings and materials of a physical demonstrator of the super-critical steam expander application as well as in component design and concept studies.</p>
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Investigation of acoustic source characterisation and installation effects for small axial fansBerglund, Per-Olof January 2003 (has links)
<p>Fans are often used in equipment such as home appliances andelectronic equipment where the margin of profit is small butcustomers demands on a low noise level are high. Therefore,methods for predicting the noise emitted by an applicationincluding one or several fans are desirable in order toimprove, accelerate and reduce the cost of low-noise design.The Noise Shaping Technology (NST) has been developed withinthe EC-project NABUCCO in order to fulfil the aboverequirements on a prediction method. According to NST, thenoise source (not necessary a fan) is described by one orseveral noise descriptors, CSSs, and the correspondingtransmission paths through the structure described by one orseveral transfer functions, ACFs. In this thesis, theapplicability of NST is evaluated on a cabinet for electronicequipment where small axial cooling fans constitute the primarysources of the airborne sound.</p><p>As an axial fan is a complex source of sound,simplifications are necessary when modelling its acousticproperties. Therefore, the sound radiation of an axial fan infree space was examined by expanding the generated soundpressure field into spherical harmonics. The conclusion on asource model for the cabinet example, where the fans are moreor less In-duct mounted, is a modified single axial dipole. Themodel is expected to be valid in the entire frequency range ofinterest except in the mid-frequency range where the modaldensity is low. In order to improve the source model in thisfrequency range, a future model based on a rotating dipole isproposed.</p><p>The sound power of a small axial fan is measured in an ISO10302 test-rig. In order to take account of flow conditions,acoustically transparent ducts have been developed. These shallbe attached to the test-rig when measuring the sound power ofthe fan. A simple but practical method of how to correct thesound power for the baffling effect of the test-rig has alsobeen developed. Finally, the sound power can be converted intodipole force, which is the airborne CSS corresponding to thesingle axial dipole model.</p><p>The corresponding airborne transfer function (ACF), i.e.,from dipole force at the source point to sound pressure at thereceiver point, is measured reciprocally by taking use ofLyamshevs reciprocity relation.</p><p>From multiplication of the CSS and the ACF, the soundpressure can be predicted. The prediction shows quite goodagreement with the measured values.</p><p><b>Keywords:</b>axial fan, airborne sound, sourcecharacterisation, transmission path analysis, In-duct,spherical harmonics, rotating dipole, installation effects, ISO10302, flow conditions, baffling effect, acousticallytransparent ducts, Lyamshevs reciprocity relation, reciprocity,CSS, ACF, GSM, NST.</p>
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Detailed Water Quality Modeling of Pressurized Pipe Systems and Its Effect on the Security of Municipal Water Distribution NetworksAustin, Ryan Glen January 2011 (has links)
The current study expands on the body of knowledge associated with water distribution system security. The three main chapters focus on 1) the effectiveness of an incomplete mixing model (AZRED-I) with respect to multi-objective sensor placement decisions; 2) risk assessment as a tool for evaluating vulnerability and making sensor placement decisions; and 3) experimental verification of a combined axial-dispersion and incomplete-mixing water quality model (AZRED-II). The study concludes that water quality models do impact sensor placement decisions, especially in highly interconnected networks; that risk assessment is a valuable evaluation tool for providing information concerning a system's vulnerability to contamination and also information that can affect sensor placement decisions; and that AZRED-II is superior to other water quality models at predicting the spatiotemporal pattern of a pulse through a distribution network with cross junctions under laminar flow. The other sections of the study describe the connection that exists between water distribution security and water quality models.
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Design and Analysis of Micro-electromechanical Resonant StructuresHassanpour Asl, Pezhman 20 January 2009 (has links)
Dynamics of a beam-based micro-electromechanical resonator is investigated theoretically and experimentally. The resonant structure comprises a micro-beam and two electrostatic comb-drives, one for exciting the vibration, and the other for detecting the response. Two identical resonators of this type can form a double-ended tuning fork.
An analytical linear model of these resonators is developed by assuming the beam to obey the thin beam theory subjected to an axial force. The comb-drives are initially treated as a point mass. The point mass is free to be placed anywhere along the beam span. The exact natural frequencies and mode shapes of vibration are obtained. Further, the mass is considered to have rotary inertia. The influence of the rotary inertia on the natural frequencies and mode shapes of vibration are investigated. Subsequently, the model of a beam with a guided mass is studied to determine the upper limit of the natural frequencies of the resonator. The advantage of this model over the previous ones is in providing detailed insight into the dynamics of the resonator, particularly when the comb-drives are placed at locations other than the mid-point of the beam. It has been shown that the mode shapes of vibration of these resonators are not orthogonal to each other under its classic definition. The orthogonality condition of the mode shapes of the beam-lumped mass system is introduced, and used for studying the forced vibration response.
The nonlinear vibration of the system due to stretching is considered for the case of free vibration and the primary resonance. The nonlinear model is used to investigate the effect of damping on the resonator response.
The interaction of the electrostatic governing equations and the mechanical model is studied. This model is employed for designing the experiment circuits for testing fabricated resonators. The fabrication processes used are explained, and the design parameters of each resonator are provided. The experimental results are reported, and used to find the axial force and stress of the resonant beams.
The model and results of this dissertation can be used in the design of beam-based micromachined resonators for different applications.
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Design and Analysis of Micro-electromechanical Resonant StructuresHassanpour Asl, Pezhman 20 January 2009 (has links)
Dynamics of a beam-based micro-electromechanical resonator is investigated theoretically and experimentally. The resonant structure comprises a micro-beam and two electrostatic comb-drives, one for exciting the vibration, and the other for detecting the response. Two identical resonators of this type can form a double-ended tuning fork.
An analytical linear model of these resonators is developed by assuming the beam to obey the thin beam theory subjected to an axial force. The comb-drives are initially treated as a point mass. The point mass is free to be placed anywhere along the beam span. The exact natural frequencies and mode shapes of vibration are obtained. Further, the mass is considered to have rotary inertia. The influence of the rotary inertia on the natural frequencies and mode shapes of vibration are investigated. Subsequently, the model of a beam with a guided mass is studied to determine the upper limit of the natural frequencies of the resonator. The advantage of this model over the previous ones is in providing detailed insight into the dynamics of the resonator, particularly when the comb-drives are placed at locations other than the mid-point of the beam. It has been shown that the mode shapes of vibration of these resonators are not orthogonal to each other under its classic definition. The orthogonality condition of the mode shapes of the beam-lumped mass system is introduced, and used for studying the forced vibration response.
The nonlinear vibration of the system due to stretching is considered for the case of free vibration and the primary resonance. The nonlinear model is used to investigate the effect of damping on the resonator response.
The interaction of the electrostatic governing equations and the mechanical model is studied. This model is employed for designing the experiment circuits for testing fabricated resonators. The fabrication processes used are explained, and the design parameters of each resonator are provided. The experimental results are reported, and used to find the axial force and stress of the resonant beams.
The model and results of this dissertation can be used in the design of beam-based micromachined resonators for different applications.
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