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Position sensorless control of a transverse-laminated reluctance synchronous machineBarnard, Francois Jacobus Wessels 12 1900 (has links)
Thesis (MEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: The focus of this thesis is position sensorless control of a transverse-laminated reluctance
synchronous machine. Rotor position information is required for high-performance closedloop
control of the reluctance synchronous machine and is conventionally supplied by
unreliable hardware position resolvers. In addition a FPGA-based rapid prototyping
system is completed as part of the research term for control of the machine drive system.
For the first time the unified active-
ux (AF) method is investigated and implemented
for position sensorless control of the transverse-laminated reluctance synchronous machine
in this study. The method is based on the torque equation of the machine and is basically
the same for any AC machine. The estimation scheme is implemented for closed-loop
position sensorless control from low- to rated speed in the entire rated load range with
simulation and measured results confirming its capabilities. A number of characteristics
of the machine (including generator operation) have implications for implementation of
the active-
ux (AF) method and are therefore investigated.
Another position estimation method investigated is the arbitrary injection (AI) scheme
which is derived to be completely machine parameter independent. The method simply
requires a current progression at each calculation step allowing use of a smaller injection
voltage. This method is implemented again on the reluctance synchronous machine
and is shown to be capable of position sensorless current and speed control of the drive
from standstill to rated speed with simulation and measured results. However, when the
machine is operating above low speeds it is shown that this technique is only capable of
position sensorless control at low loads.
To deliver position sensorless control in the entire rated speed and load range a new
hybrid controller scheme is designed and implemented. The hybrid scheme is speed and
load dependent with hysteresis regions for stability at specific working points. The active-
ux (AF) method is implemented in the low to rated speed range at medium to rated
loads while the arbitrary injection (AI) method is implemented elsewhere. Measured
results show that the scheme is capable of position sensorless control in the entire rated
speed and load range with some limitations on dynamics.
Because of the limitations on dynamics of the hybrid scheme an assisted fundamental
model position estimation scheme was investigated. Simulation results show that this
controller requires further investigation. / AFRIKAANSE OPSOMMING: Die fokus in hierdie tesis is die posisie-sensorlose beheer van 'n transvers-gelamineerde
reluktansie sinchroonmasjien. Rotor posisie inligting word benodig vir geslote-lus beheer
van die reluktansie sinchroonmasjien met ho e-werkverrigting, en word normaalweg deur
onbetroubare hardeware sensors verskaf. As deel van die navorsings-termyn is 'n FPGAgebaseerde
beheerstelsel vir die masjien stelsel voltooi.
Die \aktiewe-vloed" posisie-afskattings metode is ondersoek en vir die eerste keer
ge mplementeer vir posisie-sensorlose beheer van die transvers-gelamineerde reluktansie
sinchroonmasjien. Die metode is dieselfde in konsep vir alle WS masjiene en word basseer
op die vergelyking vir wringkrag van die masjien. Vollas geslote-lus posisie-sensorlose
beheer van die masjien in die lae tot ho e spoedbereik is suksesvol ge mplementeer met
simulasie en gemete resultate. Verkskeie inherente eienskappe van die masjien het implikasies
vir gebruik van die \aktiewe-vloed" metode (insluitend generator werking) en is
dus ondersoek.
Die \arbitr^ere injeksie" metode wat afgelei is om onafhanklik van masjien parameters
te wees is ook odersoek. Hierdie metode verlang slegs 'n stroom-afgeleide by elke tydstip
en benodig dus 'n kleiner injeksie-spanning. Hierdie metode is weer ge mplementeer op die
reluktansie sinchroon masjien met suksesvolle posisie-sensorlose beheer in die hele spoed
bereik getoon in simulasie en praktiese resultate. Dit word egter getoon dat hierdie metode
slegs onder lae-las toestande posisie sensorlose beheer bo lae-spoed kan bewerkstellig.
Ten einde posisie-sensorlose beheer in die hele spoed en wringkrag bereik te verkry
is 'n nuwe hibriede beheerskema ontwerp en ge mplementeer. Die skema is spoed en
las afhanklik met histerese vir stabiliteit by 'n spesi eke werkpunt. Die \aktiewe-vloed"
metode word gebruik bo lae spoed teen 'n minimum las terwyl die \arbitr^ere injeksie"
andersins ge mplementeer word. Gemete resultate toon dat die skema posisie-sensorlose
beheer van die masjien in die hele spoed en las bereik toelaat met sommige beperkings
op dinamika.
Met inagneming van die beperkings op die hibriede metode is 'n ondersteunde fundamentele
model afskattingskema ondersoek. Simulasie resulate toon dat hierdie beheerder
verdere ondersoek benodig.
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Design and implementation of generic flight software for a CubeSatHeunis, Andre Emile 12 1900 (has links)
Thesis (MEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: The main on-board computer in a satellite is responsible for ensuring the correct
operation of the entire system. It performs this task using flight software. In order to
reduce future development costs, it is desirable to develop generic software that can
be re-used on subsequent missions. This thesis details the design and implementation
of a generic flight software application for CubeSats.
A generic, modular framework is used in order to increase the re-usability of the flight
software architecture. In order to simplify the management of the various on-board
processes, the software is built upon the FreeRTOS real-time operating system.
The Consultative Committee for Space Data Systems’ telemetry and telecommand
packet definitions are used to interface with ground stations. In addition, a number
of services defined in the European Cooperation for Space Standardisation’s Packet
Utilisation Standard are used to perform the functions required from the flight
software.
The final application contains all the command and data handling functionality
required in a standard CubeSat mission. Mechanisms for the collection, storage and
transmission of housekeeping data are included as well as the implementation of
basic fault tolerance techniques. Through testing it is shown that the FreeRTOS
scheduler can be used to ensure the software meets hard-real time requirements. / AFRIKAANSE OPSOMMING: Die hoof aanboordrekenaar in ’n satelliet verseker die korrekte werking van die hele
stelsel. Die rekenaar voer hierdie taak uit deur van vlugsagteware gebruik te maak.
Om toekomstige ontwikkelingskostes te verminder, is dit noodsaaklik om generiese
sagteware te ontwikkel wat hergebruik kan word op daaropvolgende missies. Hierdie
tesis handel oor die besonderhede van die ontwerp en implementering van generiese
vlugsagteware vir ’n CubeSat.
’n Generiese, modulêre raamwerk word gebruik om die hergebruik van die sagteware
te verbeter. Ten einde die beheer van die verskillende aanboordprosesse te
vereenvoudig, word die sagteware gebou op die FreeRTOS reëletyd bedryfstelsel.
Die telemetrie- en telebevelpakket definisies van die “Consultative Committee for
Space Data Systems” word gebruik om met grondstasies te kommunikeer. Daarby
is ’n aantal dienste omskryf in die “Packet Utilisation Standard” van die “European
Cooperation for Space Standardisation” gebruik om die vereiste funksies van die
vlugsagteware uit te voer.
Die finale sagteware bevat al die bevel en data-hantering funksies soos wat vereis
word van ’n standaard CubeSat missie. Meganismes vir die versameling, bewaring en
oordrag van huishoudelike data is ingesluit sowel as die implementering van basiese
fouttolerante tegnieke. Toetse het gewys dat die FreeRTOS skeduleerder gebruik
kan word om te verseker dat die sagteware aan harde reëletyd vereistes voldoen.
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Design of a reluctance synchronous machine for an electric vehicle with a multi speed gearboxVorster, Christiaan Willem 12 1900 (has links)
Thesis (MEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Conventional electrical vehicles (EVs) favour mostly permanent magnet
machines with single speed gearboxes. This is understandable, the PM machine
has a high power density making the electrical machine smaller in size.
The PM machine also has a favourable field weakening capability combining
this with a single speed gearbox nearly perfectly matches the required traction
curve. However the dependency of rare earth metals from China and the
environmental issues raised by mining these metals raise concern. Therefore
alternatives should be considered. Induction -, switch reluctance - and wound
rotor machines are all gaining ground as favourable traction machines to power
vehicles. The reluctance synchronous machine (RSM) is known for it’s robustness
and high efficiency, however the machine has a limited field-weakening
capability. To overcome this short coming a multi gearbox from an internal
combustion engine (ICE) is suggested.
By combining the RSM and multi speed gearbox it is possible to match the
traction curve. There are numerous advantages offered by using this system,
especially from an performance and efficiency point of view. However there
are also numerous challenges faced by using the suggested powertrain, however
the focus of this study is mainly on performance and efficiency of the motor
and the powertrain.
As a case study a Corsa 140i is used and the design specifications is taken
from the ICE. The aim is to design a RSM that meets the specifications of
the ICE. The RSM structure is mathematically modelled then optimized using
commercial optimization and 2D finite element software. To evaluate the design of the RSM, the motor is then tested. The powertrain is then tested by
connecting the motor onto the gearbox of the Corsa and the efficiency of the
powertrain is evaluated.
The test results it shown that the RSM can be used as a traction motor.
There are two motors built one with NO20 and the other with M530-65A
lamination steel. Both motors perform well throughout the speed and torque
spectrum. The measured efficiency at the rated condition for the motor with
the NO20 steel is above 91% and the motor with the M530-65A laminations
above 89%. The power train is is tested in 4th and 5th gear. The efficiency of
4th and 5th gear is approximated and the efficiency is above 90% . This high
efficiency makes the multi speed gearbox a competitor for the EV power train. / AFRIKAANSE OPSOMMING: Elektrisie voertuie (EVe) het meestal permanent magneet motors met ’n
enkel spoed ratkas. Dit is verstaanbaar, die PMS masjien het ’n hoë krag
digtigheid wat die masjien kleiner maak in grote. Die PMS masjien het ’n
baie goeie vloed veld verswakkings gebied en as dit gekombineer word met
’n enkel spoed ratkas, volg dit die velangde traksie kurwe amper perfek. Die
nadeel is dat die PMS motor skaars aard metale nodig het vir die magnete
van China af. Die probleem is dat daar baie omgewings probleme gepaard
gaan om die metale te myn en China beheer die mark. As gevolg hiervan
moet ander tipe motors oorweeg word as traksie motors vir voertuie. Skakel
reluktansie, induksie en ’n wikkel rotor motors is almal besig om vordering te
maak as traksie motors vir EV’e. Die sinchroon reluktansie motor (RSM) is
bekend as ’n robuuste en effektiewe motor. Die probleem met die RSM is dat
dit nie ’n goeie vloed veld verswakkings gebied het nie. Om die probleem te
oorkom, word ’n veranderlike spoed ratkas van ’n binnebrand engin voorgestel.
Deur om die RSM en die veranderlike spoed ratkas as ’n dryfstelsel te gebruik
kan die verlangde traksie kurwe ook verkry word. Daar is talle voordele
om ’n veranderlike spoed ratkas te gebruik, veral van af ’n draaimoment verrigting
en effektiwiteits oogpunt. Daar is ongelukkig ook baie uitdagings wat
gepaard gaan as ’n veranderlike spoed ratkas gebruik wil word in die dryfstelsel.
Alhoewel daar baie uitdagings is kyk die studie slegs na die draaimoment verrigting en die effektiwiteit van die dryfstelsel.
’n Corsa 140i word as ’n gevallestudie gebruik en die spesifikasies vir die
elektrisie motor word vanaf die spesifikasies van die binnebrand engin geneem.
Die doel is om ’n motor te ontwerp wat dieselfde spesifikasies het as die binnebrand
engin. Die RSM strukstuur word wiskundig gemodelleer en dan geoptimeer
deur gebruik te maak van kommersiele optimering en 2D eindige element
sagteware. Om die ontwerp te verifieer word die motor getoets. Die dryfstelsel
word dan getoets deur om die motor met die raktas te konnekteer. Die draaimoment
verrigting en die effektiwiteit word dan ge-evalueer.
Twee motors word gebou, een met NO20 laminasies en een met M530-65A
laminasies. Beide motors het goeie verrigting deur die spoed en draaimoment
gebied. Die gemeete effektiwiteit van die motor met die NO20 laminasies is bo
91% en die motor met die M530-65A laminasies het ’n gemeete effektiwiteit
bo 89%. Die toets resultate wys dat die RSM as ’n traksie motor gebruik
kan word. Die dryfstelsel word in 4de en 5de rat ge-evalueer. Die effektiwiteit
van die ratkas in 4de en 5de word benader en ’n effektiwiteit bo 90% is verkry.
Hierdie hoë effektiwiteit maak die veranderlike spoed ratkas ’n lewensvatbare
mededinger in die EV dryfstelsel.
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Time domain metrology for MeerKAT systemsMatthysen, Nardus 12 1900 (has links)
Thesis (MEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: This work in this study covers a powerful technique to derive propagation and scattering information
in an expedient fashion. Expedient because time-domain (TD) data gathers a broad spectrum
in a single transmitted pulse. TD has been criticised because of a lack of dynamic range, which has
now been overcome by the direct sampling system, RATTY and RTA. This study focuses on the investigation
of a TD metrology system, to assist with the characterisation of MeerKAT systems. The
elementary components of the system include a fast-rising impulse generator that was coupled with
an impulse radiating antenna (IRA). The system was calibrated and tested before practical measurements
and preliminary testing in the Karoo were done.
For TDmetrology a larger bandwidth accelerates measurements without the loss of accuracy. The
pulse generator’s (PG’s) fundamental components are an avalanche transistor and a step recovery
diode (SRD), to sharpen the leading edge of the pulse. Improving the rise-time of a pulse increases its
bandwidth in the spectrum. The external circuitry around these components is pivotal and it determines
the shape, amplitude and rise-time of the pulse. In the course of the investigation, the general
circuitry around the PG was improved to obtain the best possible pulse for measurements inside a
reverberation chamber (RC) and for measurements in the Karoo. In light of this, a second and third
PG source were obtained. For measurements in the Karoo, a larger amplitude pulse was required to
increase the spectral content and this is essential for propagation measurements over distance and
the shielding effectiveness (SE) of structures. Stacking avalanche transistors allow larger amplitude
pulses and it improves the dynamic range of the spectrum. A PG incorporating stacked avalanche
transistors, was designed, built and measured to assist with RC and small-scale field measurements
in the Karoo. The third PG was bought for the practical measurements in the Karoo. The PG produces
kilovolt pulses with pico-second rise-times that extend the spectral range of the current PGs at our
disposal.
With these PGs, an antenna is required for the radiation of impulse-like transients. The IRA is a
high-gain large-bandwidth antenna. The IRA consists of a parabolic reflector, conical-plate transmission
lines that are terminated through resistors onto the dish, and a feeding balun. The IRA design
was thoroughly discussed and a first model for metrology was designed, measured and optimised.
The IRA was also simulated with computation software code, FEKO.
Before deployment of theTDsystem, calibration and characterisation measurements are required.
The measuring devices used within this study were sampling oscilloscopes and direct sampling systems.
The limitations of each device were explored and are discussed. The final measurements that were conducted contribute to work related to the SKA. This incorporated antenna pattern calibration,
propagation over distance and the SE of a berm built from Karoo soil. The system investigated the
propagation attenuation over the Karoo soil and vegetation, with great promise. A broad spectrum
was measured over a few kilometres and compared to free-space loss. The SE of the berm covered
the same spectral bandwidth. In this measurement, scattering effects and knife-edge diffraction were
observed. / AFRIKAANSE OPSOMMING: Die werk in hierdie studie dek ’n kragtige tegniek wat gebruik kan word om die voortplanting en
die verstrooiingsinligting van elektromagnetiese golwe op ’n voordelige manier af te lei. Dit is voordelig,
want tydgebieddata versamel ’n wye spektrum in ’n enkele oordraagbare puls. Tydgebied is
in die verlede baie gekritiseer omdat dit ’n dinamiese reikwydte kortkom en dit is nou oorwin deur
die direkte steekproefnemingstelsel, RATTY en RTA. Hierdie studie fokus op die ondersoek van ’n
tydgebiedmetingssisteem en dit help met die karakterisering van MeerKAT sisteme. Die elementêre
komponente van die sisteem bestaan uit ’n vinnig-stygende impulsgenerator wat gekoppel is aan ’n
impulsuitstralende-antenna (IRA). Die sisteem is gekalibreer en getoets voordat praktiese metings en
toetse in die Karoo uitgevoer kon word.
Vir tydgebiedmetings versnel ’n groter bandwydte die metings sonder om die akkuraatheid daarvan
te beïnvloed. Die pulsgenerator se fundamentele komponente is ’n stortvloedtransistor en ’n
stap-herstel diode (SRD) wat die voorpunt van die puls verskerp. Die eskterne stroombaan rondom
hierdie komponente is noodsaaklik en dit bepaal die vorm, amplitude en die stygtyd van die puls.
Deur die loop van hierdie ondersoek is die algemene stroombaan rondom die puls verbeter, om die
beste moontlike puls vir metings binne in die weerkaatsingskamer en vir metings in die Karoo, te
verkry. Na aanleiding van dit is ’n tweede en derde pulsgenerator bron verkry. Vir die metings in
die Karoo is ’n puls met ’n groter amplitude vereis om die spektrale inhoud te vermeerder. Dit is
noodsaaklik vir elektromagnetiese golf voortplantingsmetings oor afstand asook die beskermings effektiwiteit
(SE) van die strukture. Stapel-stortvloed transistors skep pulse met groter amplitudes en
dit verbeter die dinamiese reikwydte van die spektrum. ’n Pulsgenerator wat gestapelde stortvloedtransistors
insluit is ontwerp, gebou en gemeet om te help met metings in die weerkaatsingskamer en
kleinskaal veldmetings in die Karoo. Die derde pulsgenerator is gekoop vir praktiese metings in die
Karoo. Die pulsgenerator vervaardig kilovolt pulse met pikosekond stygtye, wat die reikwydte van die
spektrum van ons huidige puls uitbrei.
Hierdie pulsgenerators vereis ’n antenna vir die uistraling van impulsagtige seine. Die IRA is ’n
hoë-wins, groot-bandwydte antenna. Die IRA bestaan uit ’n paraboliese weerkaatser, konieseplaat
transmissielyne wat deur weerstande op die skottel getermineer word, asook ’n voedings "balun".
Die IRA ontwerp is deeglik bespreek en ’n model is ontwerp, gemeet en verbeter. Die IRA is ook gesimuleer
met behulp van ’n rekenaarsagtewareprogram, FEKO. Voordat die tydgebiedsisteem benut kan word, moet dit gekalibreer word en karakteriseringsmetings
moet ook daarmee uitgevoer word. Die meetinstrumente wat in hierdie studie gebruik is,
is steekproefneming-ossilloskope en direkte steekproefneming-sisteme. Die tekortkominge van elke
instrument is ondersoek en bespreek. Die finale meting wat uitgevoer is, dra by tot die werk wat
geassosieer word met die SKA. Dit behels antennapatroonkalibrasie, voortplanting van elektromagnetiese
golwe oor afstand en die SE van ’n "berm"wat gebou is uit Karoo-grond. Hierdie sisteem is
gebruik om die voortplantings-verswakking oor die Karoo-grond en plantegroei te ondersoek en dit
lyk baie belowend. ’nWye spektrumis oor ’n paar kilometer gemeet en dit is met wrywinglose ruimte
vergelyk. Die SE van die "berm"het dieselfde spektrale bandwydte gedek. In hierdie meting is verstrooiingseffekte
en mespunt-diffraksie waargeneem.
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Intelligent elevator control based on adaptive learning and optimisationJordaan, Edzard Adolf Biermann 12 1900 (has links)
Thesis (MEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Machine learning techniques have been around for a few decades now and
are being established as a pre-dominant feature in most control applications.
Elevators create a unique control application where traffic flow is controlled
and directed according to certain control philosophies. Machine learning techniques
can be implemented to predict and control every possible traffic flow
scenario and deliver the best possible solution. Various techniques will be implemented
in the elevator application in an attempt to establish a degree of
artificial intelligence in the decision making process and to be able to have
increased interaction with the passengers at all times.
The primary objective for this thesis is to investigate the potential of machine
learning solutions and the relevancy of such technologies in elevator control
applications. The aim is to establish how the research field of machine learning,
specifically neural network science, can be successfully utilised with the
goal of creating an artificial intelligent (AI) controller. The AI controller is
to adapt to its existing state and change its control parameters as required
without the intervention of the user.
The secondary objective for this thesis is to develop an elevator model that represents
every aspect of the real-world application. The purpose of the model
is to improve the accuracy of existing theoretical and simulated models, by
modulating previously unknown and complex variables and constraints. The
aim is to create a complete and fully functional testing platform for developing
new elevator control philosophies and testing new elevator control mechanisms. To achieve these objectives, the main focus is directed to how waiting time,
probability theory and power consumption predictions can be optimally utilised
by means of machine learning solutions. The theoretical background is provided
for these concepts and how each subject can potentially influence the
decision making process. The reason why this approach has been difficult to
implement in the past, is possibly mainly due to the lack of adequate representation
for these concepts in an online environment without the continuous
feedback from an Expert System. As a result of this thesis, the respective
online models for each of these concepts were successfully developed in order
to deal with the identified shortcomings.
The developed online models for projected waiting times, probability networks
and power consumption feedback were then combined to form a new Intelligent
Elevator Controller (IEC) structure as opposed to the Expert System
approach, mostly used in present computer based elevator controllers. / AFRIKAANSE OPSOMMING: Masjienleertegnieke bestaan al vir 'n paar dekades en is 'n oorwegende kenmerk
in hedendaagse beheertoestelle. Hysbakke skep 'n unieke beheertoepassing,
waar verkeersvloei beheer en gerig kan word volgens sekere beheer loso e.
Masjienleertegnieke kan geïmplementeer word om elke moontlike verkeersvloei
situasie te voorspel en te beheer en die beste moontlike oplossing te lewer.
Verskeie tegnieke sal in die tesis ondersoek word in 'n poging om 'n mate van
kunsmatige intelligensie in die besluitneming proses te skep asook verhoogte
interaksie met die passasiers te alle tye.
Die prim^ere doel van hierdie tesis is om die potensiaal van 'n masjienleer oplossing
en die toepaslikheid van dit in hysbakbeheertoepassings te ondersoek.
Die doel is om vas te stel hoe die navorsing in die veld van die masjienleer,
spesi ek in neurale netwerk wetenskappe, suksesvol aangewend kan word met
die doel om 'n kunsmatige intelligente beheerder te skep. Die kunsmatige intelligente
beheerder moet kan aanpas by sy onmidelike omgewing en sy beheer
parameters moet kan verander soos nodig sonder die ingryping van die gebruiker.
Die sekond^ere doelwit vir hierdie tesis is om 'n hysbakmodel, wat elke aspek
van die werklike w^ereld verteenwoordig, te ontwikkel. Die doel van die
model is om die akkuraatheid van die bestaande teoretiese en gesimuleerde
modelle te verbeter deur voorheen onbekende en komplekse veranderlikes en
beperkings in ag te neem. Die doel is om 'n funksionele toetsplatform te skep vir die ontwikkeling van
nuwe hysbakbeheer loso e en vir die toets van nuwe hysbakbeheermeganismes.
Om hierdie doelwitte te bereik, is die hoo okus gerig om wagtyd, waarskynlikheidsteorie
en kragverbruik voorspellings optimaal te gebruik deur middel
van die masjienleer oplossings. Die teoretiese agtergrond is voorsien vir hierdie
konsepte en hoe elke konsep potensieel die besluitneming kan beïnvloed. Die
rede waarom hierdie benadering moeilik was om te implementeer tot hede, is
moontlik te wyte aan die gebrek aan voldoende verteenwoordiging vir hierdie
konsepte in 'n aanlynomgewing sonder die voortdurende terugvoer van 'n Deskundige
Stelsel. As gevolg van hierdie tesis word die onderskeie aanlynmodelle
vir elk van hierdie konsepte suksesvol ontwikkel om die geïdenti seerde tekortkominge
te oorkom.
Die ontwikkelde aanlynmodelle vir geprojekteerde wagtye, waarskynlikheidsnetwerke
en kragverbruik terugvoer is dan gekombineer om 'n nuwe intelligente
hysbakbeheerder struktuur te skep, in teenstelling met die Deskundige Stelsel
benadering in die huidige rekenaar gebaseerde hysbakbeheerders.
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The design and implementation of a prototype digital video watermarking scheme with dynamic traitor tracingSalotto, Antony 12 1900 (has links)
Thesis (MEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: We design and implement a prototype digital watermarking scheme that uses
spread-transform dither modulation to embed hidden binary message signals
into uncompressed digital video signals. The hidden messages are intended
to identify the original recipient of a particular copy of a digital video, so
that in the event that a pirate copy of that video is found, the recipient can be
incriminated as a pirate. We test the ability of the watermark signal to survive
various modifications to the watermarked video, including lossy compression,
frame deletion, and amplitude scaling. We find that the scheme performs
well when watermarked videos remain uncompressed, but the scheme is not
sufficiently robust against lossy compression. We also implement a dynamic
traitor tracing scheme based on the scheme of Fiat and Tassa, which is designed
to identify a group of pirates who combine their watermarked videos in an
attempt to defeat the watermarking scheme. We test the traitor tracing scheme
in a simulated digitally watermarked video broadcast system where a pirate
rebroadcast is monitored. We find that when the pirate rebroadcast is delayed,
our traitor tracing scheme identifies and disconnects the pirates more quickly
than the scheme of Fiat and Tassa. / AFRIKAANSE OPSOMMING: Ons ontwerp en implementeer ’n digitale watermerkskema-prototipe wat
strektransform-bibbermodulasie gebruik om binêre boodskapseine in digitale
videoseine te verskuil. Die doel van die versteekte boodskappe is om die oorspronklike
ontvanger van ’n bepaalde digitale video-afskrif te identifiseer. Indien
’n onwettige afskrif van die video ontdek word, kan die oorspronklike
ontvanger daarvoor verantwoordelik gehou word. Ons toets die vermoë van
die watermerksein om verskeie veranderinge aan die gewatermerkte video te
oorleef, byvoorbeeld kompressie, die verwydering van videorame, en amplitudeskalering.
Die skema vaar goed in die afwesigheid van videokompressie,
maar is nie robuus wanneer die video beduidend saamgepers word nie. Ons
implementeer ook ’n dinamiese skema vir verraaier-opsporing, gebaseer op ’n
tegniek deur Fiat en Tassa. Die doel van hierdie skema is om groepe gebruikers
te identifiseer wat saamwerk om ’n watermerkskema te kul deur gewatermerkte
videos te kombineer. Ons toets die verraaier-opsporingskema in ’n
simulasie van ’n gewatermerkte video-uitsendingstelsel wat ’n roofuitsending
monitor. Wanneer die roofuitsending vertraag is, vind ons dat die voorgestelde
verraaier-opsporingskema die skuldige gebruikers vinniger uitwys as die skema
van Fiat en Tassa.
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Design and development of a satellite ground station for water resource monitoringMafukidze, Harry D. 12 1900 (has links)
Thesis (MEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: The SU Department of Forestry has the responsibility to monitor, assess and suggest
management processes for water resources in some remote areas. The researchers need
information on wind speed, wind direction, soil run-o , absorption and soil drainage.
Most of the areas they are targeting have no form of GSM/GPRS coverage. This thesis
presents the design and development of a Zigbee based wireless sensor network to send
data from distributed sensor nodes to a ground station, all in a remote area. The ground
station in turn uses a global commercial satellite communications system to send the
eld data to a centralised host computer. This was accomplished through the integration
of the most common and popular open source and commercial electronics prototyping
platforms, namely, Arduino, Digi XBee radio, Raspberry Pi and Iridium modem. The
system relies on an Arduino Uno working as a sensor node, Digi XBee radios for forming
wireless mesh and multi-hop networks, Raspberry Pi being the heart of the ground
station and the Iridium modem to send data to the master station through the Iridium
gateway. A comprehensive literature study was conducted and a prototype of the system
implemented. Various tests were conducted to determine and prove the feasibility of the
system. / AFRIKAANSE OPSOMMING: Die Departement van Bosbou het die verantwoordelikheid om water hulpbronne in
afgele e areas te monitor, evalueer en voorstelle te maak tov. die bestuur daarvan. Die
navorsers benodig inligting oor windspoed, windrigting, grondwater a
oop, -opname
en -dreinering. Die meeste van die gebiede ter sprake het geen vorm van GSM /
GPRS-dekking nie. Hierdie tesis beskryf die ontwerp en ontwikkeling van 'n Zigbee
gebaseerde radio sensornetwerk om data vanaf verspreide sensornodes te stuur na 'n
grondstasie. Die grondstasie op sy beurt maak gebruik van 'n globale kommersiele
satelliet-kommunikasiestelsel om data van 'n afgele e plek in die veld te stuur na 'n
gesentraliseerde rekenaarstelsel. Dit is gedoen deur van die mees algemene en gewilde
prototipe oopbron en kommersiele platforms, naamlik Arduino, Digi XBee radio, Raspberry
Pi en Iridium modem te integreer. Die sensornodes is gebaseer op 'n Arduino Uno,
met Digi XBee radio's vir die radio- multihop netwerk. Die grondstasie is gebou om die
Raspberry Pi en stuur data aan na die meesterstasie, via die Iridium modem en satellietstelsel.
Na 'n omvattende literatuurstudie, is 'n prototipe van die stelsel ontwerp en
geimplementeer. Omvattende toetse is gedoen om die korrekte werking en bruikbaarheid
van die stelsel te bewys.
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Development of a satellite network simulator tool and simulation of AX.25, FX.25 and a hybrid protocol for nano-satellite communicationsLe Roux, Jan-Hielke 12 1900 (has links)
Thesis (MEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Nano-satellites are mostly used in lower earth orbit applications, where communication
intervals are limited, often to a combined total of less than one hour per day. With these type
of inherent limitations of lower earth orbits, there are also the physical size and equipment
restriction of nano-satellites to consider, especially those of the CubeSat specification. It is
of critical importance to use the limited time and communication resources as effectively as
possible.
The network protocol has a huge influence on reliability and throughput of a satellite network.
An important requisite for designing, comparing and improving network protocols is
a network protocol simulator, that is able to envisage the design results. Simulation can
facilitate rapid development and unforeseen discoveries. Very little information is currently
available regarding communication protocols used in nano-satellites. This thesis aims to
explore and improve the current status of nano-satellite network simulation, as well as to
demonstrate the development of an improved communication protocol strategy.
It was found that there is a lack of proper simulation tools for satellite networks, which led
to the development of SatSim. SatSim is a discrete event network simulation tool, developed
in Python, which can be used to develop and analyse network protocols. SatSim was verified
by comparing simulation results with other published results, which made use of different
software tools and theoretical throughput calculations.
AX.25 is one of the most commonly used network protocols in the nano-satellite industry.
It was implemented in SatSim and verified with theoretical throughput calculations, as
no other simulation data on AX.25 was available. AX.25 was used as a baseline protocol
to improve upon. FX.25 was developed by the Stensat Group in an attempt to improve
AX.25. FX.25 adds forward error correction to AX.25, by wrapping additional data around
the AX.25 frames. This method maintains backward compatibility with AX.25. FX.25 was
implemented in SatSim and the simulation results proved that FX.25 was a more reliable
protocol than AX.25, as it can communicate at lower elevations and over noisier communication
channels. However, the drawback of the additional forward error correction is the
increased overhead, which reduces the overall payload data throughput.
A modular AX/FX.25 protocol was then implemented in SatSim, to exploit the strengths of
both protocols. This hybrid protocol yielded significant improvements to data throughput
and can enable future software defined radio or hardware developments. / AFRIKAANSE OPSOMMING: Nano-satelliete word hoofsaaklik gebruik in lae-aard wentelbaan toepassings waar kommunikasietyd
beperk is, soms tot minder as een uur per dag. Gepaardgaande met hierdie inherente
beperking van lae-aard wentelbane, is daar ook die verminderde omvang en kapasiteit
van nano-satelliete, veral ten opsigte van die CubeSat spesifikasie. Effektiewe aanwending
van die beperkte tyd en kommunikasie-hulpbronne is dus noodsaaklik.
Die keuse van netwerk protokol het ’n beduidende invloed op die betroubaarheid en data
deurset van ’n satelliet netwerk. ’n Belangrike voorvereiste vir die ontwerp, vergelyking
en verbetering van netwerk-protokolle, is ’n netwerk simulator. Beperkte inligting is tans
beskikbaar oor kommunikasie protokolle in nano-satelliet toepassings. Hierdie tesis fokus
op die verbetering van nano-satelliet netwerk-simulasie, asook die ontwikkelling van ’n verbeterde
netwerk-protokol strategie vir nano-satelliet toepassings.
Dit het na vore gekom dat daar ’n leemte is in die beskikbaarheid van simulasie sagteware
wat gerig is op die ondersoek van satelliet netwerke. Hierdie waarneming het die ontwikkeling
van SatSim genoop. SatSim is ’n diskrete-gebeurtenis netwerk-simulasie sagtewarepakket
wat in die Python programmeertaal ontwikkel is om netwerk protokolle te ontwikkel en te
analiseer. SatSim was geverifieer deur simulasies te vergelyk met die resultate van ander
navorsingspublikasies, wat van verskillende sagtewarepakkette gebruik gemaak het, sowel as
teoretiese deursetberekeninge.
AX.25 is een van die netwerk protokolle wat mees algemeen in die nano-satelliet bedryf
voorkom. AX.25 was geïmplementeer in SatSim en geverifieer met teoretiese deursetberekeninge.
AX.25 was gebruik as ’n grondslag om op te verbeter. FX.25 was ontwikkel
deur die Stensat Group in ’n poging om op AX.25 te verbeter. FX.25 voeg vorentoefoutkorreksie
by tot AX.25, deur addisionele data tot die AX.25 netwerk pakkies te voeg.
Hierdie benadering bewerkstellig agteruit-verenigbaarheid met AX.25. FX.25 was geïmplementeer
in SatSim en simulasieresultate dui daarop dat FX.25 ’n meer betroubare protokol
is as AX.25, omdat dit teen laer elevasiehoeke en oor swakker kommunikasiekanale kan
kommunikeer. Die verbeterde betroubaarheid is ten koste van datadeurset, as gevolg van
die toevoeging van die vorentoe-foutkorreksiedata.
’n Modulêre AX/FX.25 protokol was geïmplemeteer om te kapitaliseer op die sterk eienskappe
van beide protokolle. Hierdie hibriede protokol het ’n beduidende verbetering gelewer
ten opsigte van data deurset en kan toekomstige sagteware-gedefinieerde radio en hardewaretoepassings
stimuleer.
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A 3-axis attitude control system hardware design for a CubeSatGerber, Jako 12 1900 (has links)
Thesis (MScEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: With CubeSats becoming popular as a cheap alternative to larger satellites, the need
for advanced miniature attitude determination and control systems (ADCS) arises to
meet the pointing requirements of satellite operations such as earth imaging and orbit
maintenance. This thesis describes the design of a complete ADCS for use on CubeSats.
A previously designed CubeSat on-board-computer, CubeComputer, and ne sun and
nadir sensor, CubeSense, is incorporated in the design. The remaining requirements with
regard to sensors and actuators were met by CubeControl, an additional module, the
design, manufacturing and testing of which are described. CubeControl can implement
magnetic control with the use of a magnetometer and three magnetorquers. It is also
capable of driving three reaction wheels for accurate active 3-axis stabilization. / AFRIKAANSE OPSOMMING: Met CubeSats wat gewild raak as 'n goedkoop alternatief tot groter satelliete ontstaan
die behoefte vir gevorderde miniatuur ori entasiebepaling en -beheerstelsels wat satelliet
operasies soos aardwaarneming en wentelbaan korreksies moontlik maak. Hierdie tesis
beskryf die ontwerp van 'n volledige ori entasiebepaling en -beheerstelsel vir CubeSats. 'n
Voorheen ontwikkelde CubeSat aanboordrekenaar, CubeComputer, en 'n fyn sonsensor en
nadirsensor, CubeSense, is ingesluit in die ontwerp. Die orige benodighede met verband
tot sensors en aktueerders word vervul deur CubeControl, 'n addisionele module waarvan
die ontwerp, vervaardiging en toetsing beskyf word. CubeControl kan magnetiese beheer
implementeer deur gebruik te maak van 'n magnetometer en drie magneetstange. Dit kan
ook drie reaksiewiele aandryf vir akkurate aktiewe 3-as stabilisering.
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Low Earth orbit satellite constellation control using atmospheric dragDu Toit, Daniel N.J. 03 1900 (has links)
Thesis (PhD (Electrical and Electronic Engineering))--University of Stellenbosch, 1997. / This dissertation considers the feasibility of using atmospheric drag to control
constellations of micro-satellites in low Earth orbits. The constellation control
requirements include an acquisition phase and a maintenance phase. Optimal
strategies are designed to control the relative positions of the satellites during these
two phases. It is shown that the feasibility and success of the strategies depend on
many factors, including the satellite properties and orbital configuration. A nominal
test constellation is presented and used as a generic example for the application of the
control strategies.
The dissertation also focuses on the accurate modelling and simulation of a typical
low Earth orbit satellite, moving under the influence of a variety of significant orbit
perturbation forces. The simulations form an integral part of the study and are used to
verify the application of all the proposed control strategies.
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