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Tracking collar and infrastructure for leopard researchWarnich, Dirk J. 12 1900 (has links)
Thesis (MScEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: This project targeted the development of a new tracking collar, trap telemetry system
and supporting infrastructure, to aid researchers from the Cape Leopard Trust. Previously
used collar products had all proven insu cient in some capacity and remote monitoring of
trap sites was also required. Tracking collars are used to identify the movement patterns
of the leopards and through the resulting research, assist in protecting this threatened
species. In the development of the tracking collar and trap telemetry system, a high level
system design was rst formulated, identifying major components that would be required.
Alternative methods for implementation were then considered and the most optimal chosen.
Two di erent modes of communication with the collar were envisioned and designed for.
These would be used to transmit logged coordinates obtained from a GPS receiver back to
researchers. A VHF terrestrial radio link was investigated, but an Iridium Satellite based
solution was ultimately selected. An Iridium Satellite communications system was also used
for transfer of trap state data. Ultimately, a working trap telemetry system was delivered
for use by researchers. The tracking collar system had progressed to a working prototype,
requiring miniaturisation and packaging before deployment. A possible packaging solution
was also identi ed. The trap telemetry system, although displaying certain de ciencies,
provided a capability previously unavailable to researchers. With further development, there
is potential for the tracking collar to provide accurate satellite tracking and communications
in a mass and price combination not previously available. / AFRIKAANSE OPSOMMING: Hierdie projek het as doel die ontwikkeling van 'n nuwe opsporingshalsband, 'n lokval
telemetriese stelsel en die nodige ondersteunende infrastruktuur daarvoor. As hulpmiddels
vir navorsers van Cape Leopard Trust. Geen van die halsband produkte wat tot nou toe
gebruik is, het voldoen aan al die nodige behoeftes nie, en dit was ook nodig om die
lokvalterreine van 'n afstand te kan monitor. Die opsporingshalsbande word gebruik om
die bewegingspatrone van luiperds vas te stel en die navorsing wat daarop volg, help dat
'n bedreigde spesie bewaar word. Die ontwikkeling van die opsporingshalsband en lokval
telemetriese stelsel het begin met die formulering van 'n ho evlak stelselontwerp waarin
die hoofkomponente wat benodig sou wees ge denti seer is. Alternatiewe metodes van
bewerkstelling is daarna oorweeg en die optimale hiervan is gekies. Twee verskillende
metodes van kommunikasie met die halsband is voorgestel en ontwerp. Hierdie sou gebruik
word om die vasgelegte koordinate wat van 'n GPS ontvanger verkry is, na navorsers terug
te versend. 'n Terrestriale radioverbinding is ondersoek, maar 'n Iridium Satelliet-baseerde
oplossing is uiteindelik verkies. 'n Iridium Satelliet kommunikasie stelsel is ook gebruik
vir die oordrag van data aangaande die lokvaltoestand. Uitendelik is 'n werkende lokval
telemetriese stelsel gelewer vir dir gebruik van navorsers. Die opsporingshalsband stelsel
was nou 'n werkende prototipe, wat slegs verklein en toepaslik verpak moes word voor dit
in gebruik geneem kon word. 'n Moontlike oplossing tot die verpakkingsprobleem is ook
identi seer. Die lokval telemetriese stelsel, hoewel dit steeds tekorte toon, voorsien die
navorsers van voorheen onbekombare inligting. Met verder ontwikkeling is daar potensiaal
vir die opsporingshalsband om akkurate satellietopsporing en kommunikasie te voorsien in
'n kombinasie van laer massa, sowel as prys, soos nog nooit voorheen beskikbaar nie.
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An analysis and comparison of two methods for UAV actuator fault detection and isolationOdendaal, Hendrik Mostert 12 1900 (has links)
Thesis (MScEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: Fault detection and isolation (FDI) is an important aspect of effective fault tolerant control
architectures. The Electronic System Laboratory at Stellenbosch University identified the
need to study viable methods of FDI. In this research two FDI methods for actuator failures
on the Meraka Modular UAV are investigated.
The Meraka Modular UAV is an unmanned aircraft that was developed by the CSIR. A
simple six degree of freedom non-linear mathematical model is developed that presents a
platform on which the two FDI methods are formulated. The theoretical model is used in
a simulation environment to extensively test and compare the performance of the proposed
FDI methods in different types of flight conditions.
The first method investigated is a multiple model adaptive estimator (MMAE), which incorporates
a bank of Kalman filters. Each Kalman filter in the MMAE is conditioned for
each expected actuator fault scenario. The limitations of using linear Kalman filters are explained
and they are replaced by extended Kalman filters, whose associated advantages and
disadvantages are discussed. Each filter in the bank of Kalman filters produces a residual
vector and residual covariance matrix. This information is subjected to a Bayes classifier to
determine the fault scenario which will have the highest likelihood of being active.
The second method that is studied incorporates the parity space approach for FDI. The
parity space consists of the parity relations that quantify all the analytical redundancies
available between the sensors’ outputs and actuator inputs of a system. A transformation
matrix is then optimised to transform these parity relations into residuals that are specially
sensitive to specific actuator faults. Actuator faults cause the parity space residuals’ variance
to increase. A cumulative summation procedure is used to determine when the residuals’
variance has changed sufficiently to indicate an actuator fault. A pseudoinverse actuator
estimation scheme is used to extract the actuator deflections from the parity relations.
The FDI performance is tested by deliberately failing specific actuators of the Meraka Modular
UAV in-flight. The flight test data is then used to analyse and compare the performance
of the two FDI methods investigated in the research. It is found that, for the specific
Meraka Modular UAV, the FDI performs as expected with disturbance effects and actuator
excitation influencing the FDI effectiveness. The research shows that the bank of Kalman
filters creates less false alarms whereas the parity space FDI is more sensitive to faults. It
is illustrated that FDI can be improved with active actuator excitation and process noise
estimation techniques, delivering promising results. / AFRIKAANSE OPSOMMING: Fout-deteksie en -isolasie (FDI) is belangrik vir ’n stelsel se beheerder om foute te kan
hanteer. Die Elektroniese Stelsellabaratorium (ESL) by die Universiteit van Stellenbosch
het die behoefte geïdentifiseer om te gaan kyk na moontlike FDI-stelsels wat gebruik kan
word op hul onbemande vliegtuie (OV). In hierdie navorsing is daar na twee FDI-metodes
gekyk wat op die Meraka Modulêre OV toegepas kan word.
Die Meraka Modulêre OV is ’n vliegtuig wat deur die WNNR ontwikkel is. ’n Eenvoudige sesgrade-
van-vryheid, nie-liniêre wiskundige model van die Meraka Modulêre OV is ontwikkel,
en die FDI-metodes is rondom hierdie model geformuleer. Die teoretiese model is gebruik
in ’n simulasie-omgewing en die werkverrigting van die twee FDI-metodes is in verskillende
vlug-omstandighede getoets en vergelyk.
Die eerste metode waarna gekyk is, was ’n multi-model aanpasbare afskatter (MMAA), wat
’n bank van Kalman-filters gebruik. Elke Kalman-filter in die MMAA is gekondisioneer
vir elke denkbare aktueerder-fout. Die beperkinge rondom liniêre Kalman-filters is uitgelig
en vergelyk met uitgebreide Kalman-filters, waarvan die voor- en nadele bespreek is. Elke
filter in die MMAA produseer ’n residu-vektor en residu-kovariansiematriks. Hierdie informasie
is na ’n Bayes-klassifiseerder gestuur om te bepaal watter fout-senario die grootste
waarskynlikheid het om aktief te wees.
Die tweede metode waarna gekyk is, het die pariteitsruimte vir FDI gebruik. Die pariteitsruimte
is uit al die pariteitsverwantskappe opgebou wat die verhoudings tussen al die insette
en uitsette van ’n sisteem kwantifiseer. ’n Transformasie-matriks is geoptimaliseer om hierdie
pariteitsverwantskappe te transformeer na residue wat elkeen sensitief is tot ’n spesikiefe
aktueerderfout. ’n Spesifieke aktueerderfout veroorsaak dat ’n spesifieke residu se variansie
verhoog. ’n Kummulatiewe sommeringsproses is dan gebruik om te bepaal of die variansie
genoegsaam toegeneem het. Sodoende kon daar bepaal word of ’n fout ontstaan het. ’n
Pseudo-inversaktueerder-afskattingstegniek is gebruik om die afgeskatte aktueerderdefleksie
uit die pariteitsverwantskappe te onttrek.
Die FDI-werkverrigtinge van die twee metodes is getoets deur sekere aktueerders met opset
te laat faal gedurende vlugtoetse. Die vlugtoetsdata is gebruik om die werkverrigting van die
FDI-metodes te analiseer en met mekaar te vergelyk. Met die spesifieke Meraka Modulêre
OV is, soos te wagte, bevind dat versteurings en aktueerderopwekking ’n groot invloed op
die FDI’s se werkverrigtinge toon.
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Satellite communications strategy selection for optimal LEO satellite communicationBezuidenhout, Quintus 12 1900 (has links)
Thesis (MScEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: A low earth orbit satellite system can be useful in numerous communication applications
where physical connections are not possible. Communication time available from any point on
earth to the satellite is less than one hour per day. This one hour is fragmented into smaller
time slots due to the satellite orbiting. This is not much time to transfer data and there is
even less time available to transfer data when there are other external factors affecting the
system. It is thus crucial to optimise the satellite communications link so that more data can
be transferred per orbit.
The goal of this thesis is to improve the performance of a low earth orbit satellite communication
channel by varying certain parameters of the system, such as the protocol used,
modulation scheme, packet size, transmission power etc. and then to observe how these
parameters influence the system. The protocols that were chosen to be implemented are
CSMA-CA, CSMA-CA with DSSS technology and Round-Robin Polling.
A simulator for each protocol was designed with the Opnet platform, so that specific parameters
could be changed and the results observed, in order to optimise the communications link
between the satellite and ground stations.
The results showed that there is no particular configuration of modulation scheme, packet
size, transmission power etc. presenting the best overall solution for LEO satellite communications.
It must be considered what the specific LEO satellite application would be used for and
the characteristics required by that specific application. A suitable configuration must subsequently
be chosen from the set of configurations available to satisfy most of the application
requirements. / AFRIKAANSE OPSOMMING: ’n Satelliet met ’n lae wentelbaan kan gebruik word in verskeie kommunikasie toepassings
waar fisiese verbindinge nie noodwendig moontlik is nie. Die kommunikasietyd van enige
punt van aarde af na die satelliet, is minder as een uur per dag. Hierdie tyd word nog verder
verklein omdat die satelliet besig is om, om die aarde te wentel. ’n Uur is glad nie baie tyd
om data oor te dra nie en in realiteit is daar nog minder tyd beskikbaar as daar eksterne
faktore op die sisteem inwerk. Dus is dit baie belangrik om die satelliet kommunikasiekanaal
te optimiseer sodat soveel moontlik data as moontlik oorgedra kan word per omwenteling.
Die doel van hierdie tesis is om die deurset van die kommunikasiekanaal van n lae wentelbaan
satelliet te optimiseer, deur verskeie parameters te verander soos, protokol wat gebruik word,
modulasie skema, pakkie grootte, transmissiekrag ens. en dan waar te neem hoe dit die
sisteem beïnvloed. Die protokolle wat geïmplementeer is, is CSMA-CA, CSMA-CA met DSSS
tegnologie en Round-Robin Polling.
’n Simulator vir elke protokol was ontwerp in die Opnet simulasie platform, sodat die spesifieke
parameters verander kon word om die resultate te bestudeer met die doel om die kommunikasiekanaal
tussen die satelliet en grond stasies optimaal te benut.
Die resultate het bewys dat daar geen spesifieke konfigurasie van modulasie skema, pakkie
grootte, transmissiekrag ens. is wat die algehele beste oplossing is nie. Die spesifieke applikasie
waarvoor die lae wentelbaan satelliet gaan gebruik word moet geanaliseer word sowel
as die spesifieke karakteristieke van daai applikasie. Daarvolgens moet n unieke konfigurasie
opgestel word wat meeste van die applikasie se behoeftes bevredig.
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Kinodynamic planning for a fixed-wing aircraft in dynamic, cluttered environments : a local planning method using implicitly-defined motion primitivesCowley, Edwe Gerrit 03 1900 (has links)
Thesis (MScEng)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: In order to navigate dynamic, cluttered environments safely, fully autonomous Unmanned
Aerial Vehicles (UAVs) are required to plan conflict-free trajectories between two states
in position-time space efficiently and reliably. Kinodynamic planning for vehicles with
non-holonomic dynamic constraints is an NP-hard problem which is usually addressed
using sampling-based, probabilistically complete motion planning algorithms. These algorithms
are often applied in conjunction with a finite set of simple geometric motion
primitives which encapsulate the dynamic constraints of the vehicle. This ensures that
composite trajectories generated by the planning algorithm adhere to the vehicle dynamics.
For many vehicles, accurate tracking of position-based trajectories is a non-trivial
problem which demands complicated control techniques with high energy requirements.
In an effort to reduce control complexity and thus also energy consumption, a generic
Local Planning Method (LPM), able to plan trajectories based on implicitly-defined motion
primitives, is developed in this project. This allows the planning algorithm to construct
trajectories which are based on simulated results of vehicle motion under the
control of a rudimentary auto-pilot, as opposed to a more complicated position-tracking
system. The LPM abstracts motion primitives in such a way that it may theoretically be
made applicable to various vehicles and control systems through simple substitution of
the motion primitive set.
The LPM, which is based on a variation of the Levenberg-Marquardt Algorithm (LMA),
is integrated into a well-known Probabilistic Roadmap (PRM) kinodynamic planning algorithm
which is known to work well in dynamic and cluttered environments. The complete
motion planning algorithm is tested thoroughly in various simulated environments,
using a vehicle model and controllers which have been previously verified against a real
UAV during practical flight tests. / AFRIKAANSE OPSOMMING: Ten einde dinamiese, voorwerpryke omgewings veilig te navigeer, word daar vereis dat
volledig-outonome onbemande lugvoertuie konflikvrye trajekte tussen twee posisie-tydtoestande
doeltreffend en betroubaar kan beplan. Kinodinamiese beplanning is ’n NPmoeilike
probleem wat gewoonlik deur middel van probabilisties-volledige beplanningsalgoritmes
aangespreek word . Hierdie algoritmes word dikwels in kombinasie met ’n
eindige stel eenvoudige geometriese maneuvers, wat die dinamiese beperkings van die
voertuig omvat, ingespan. Sodanig word daar verseker dat trajekte wat deur die beplaningsalgoritme
saamgestel is aan die dinamiese beperkings van die voertuig voldoen.
Vir baie voertuie, is die akkurate volging van posisie-gebaseerde trajekte ’n nie-triviale
probleem wat die gebruik van ingewikkelde, energie-intensiewe beheertegnieke vereis.
In ’n poging om beheer-kompleksiteit, en dus energie-verbruik, te verminder, word ’n generiese
plaaslike-beplanner voorgestel. Hierdie algoritme stel die groter kinodinamiese
beplanner in staat daartoe om trajekte saam te stel wat op empiriese waarnemings van
voertuig-trajekte gebaseer is. ’n Eenvoudige beheerstelsel kan dus gebruik word, in
teenstelling met die meer ingewikkelde padvolgingsbeheerders wat benodig word om
eenvoudige geometriese trajekte akkuraat te volg. Die plaaslike-beplanner abstraeer
maneuvers in so ’n mate dat dit teoreties op verskeie voertuie en beheerstelsels van
toepassing gemaak kan word deur eenvoudig die maneuver-stel te vervang.
Die plaaslike-beplanner, wat afgelei is van die Levenberg-Marquardt-Algoritme (LMA),
word in ’n welbekende “Probabilistic Roadmap” (PRM) kinodinamiese-beplanningsalgoritme
geïntegreer. Dit word algemeen aanvaar dat die PRM effektief werk in dinamiese, voorwerpryke
omgewings. Die volledige beplanningsalgoritme word deeglik in verskeie, gesimuleerde
omgewings getoets op ’n voertuig-model en -beheerders wat voorheen vir
akkuraatheid teenoor ’n werklike voertuig gekontroleer is tydens praktiese vlugtoetse.
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Online system identification for fault tolerant control of unmanned aerial vehiclesAppel, Jean-Paul 03 1900 (has links)
Thesis (MScEng)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: In this thesis the strategy for performing System Identification on an aircraft is presented. The
ultimate aim of this document is to outline the steps required for successful aircraft parameter
estimation within a Fault Tolerant Control Framework.
A brief derivation of the classical 6 degree-of-freedom aircraft model is firstly presented. The
derivation gives insight into the aircraft dynamics that are to be used to estimate the aircraft
parameters, and provides a basis for the methods provided in this thesis.
Different techniques of System Identification were evaluated, resulting in the choice of the
Regression method to be used. This method, based on the Least-Squares method, is chosen
because of its simplicity of use and because it does not require as much computational time as
the other methods presented. Regression methods, including a recursive algorithm, are then
applied to aircraft parameter estimation and practical considerations such as Identifiability and
corrupted measurements are highlighted.
The determination of unknown measurements required for System Identification of aircraft
parameters is then discussed. Methods for both estimating and measuring the Angle-of-Attack
(AoA) and angular accelerations are presented. The design and calibration of an AoA probe
for AoA measurements, as well as a novel method that uses distributed sensors to determine
the angular accelerations is also presented.
The techniques presented in this thesis are then tested on a non-linear aircraft model. Through
simulation it was shown that for the given sensor setup, the methods do not provide
sufficiently accurate parameter estimates. When using the Regression method, obtaining
measurements of the angle-of-attack solely through estimation causes problems in the
estimation of the aerodynamic lift coefficients.
Flight tests were performed and the data was analyzed. Similar issues as experienced with
estimation done on the non-linear aircraft simulation, was found. Recommendations with
regards to how to conduct future flight tests for system identification is proposed and possible sources of errors are highlighted. / AFRIKAANSE OPSOMMING: In hierdie tesis word die strategie vir die uitvoering van Stelsel Identifikasie op 'n vliegtuig
aangebied. Die uiteindelike doel van hierdie document is om die stappe wat nodig is vir 'n
suksesvolle vliegtuig parameter beraming, binne 'n Fout Tolerante Beheer Raamwerk, uit
eente sit.
'n Kort afleiding van die klassieke 6 graad-van-vryheid vliegtuig model word eerstens
aangebied. Die afleiding gee insig in die vliegtuig dinamika wat gebruik moet word om die
vliegtuig parameters te beraam, en bied 'n basis vir die metodes wat in hierdie tesis verskyn.
Verskillende tegnieke van Stelsel Identifikasie is geëvalueer, wat lei tot gebruik van die
regressie-metode. Hierdie metode is gekies as gevolg van sy eenvoudigheid en omdat dit nie
soveel berekening tyd as die ander metodes vereis nie. Regressie metodes, insluitend 'n
rekursiewe algoritme, word dan toegepas op vliegtuig parameter beraming en praktiese
orwegings soos identifiseerbaarheid en korrupte metings word uitgelig.
Die bepaling van onbekende afmetings wat benodig is, word vir Stelsel Identifisering van die
vliegtuig parameters bespreek. Metodes om die invalshoek en hoekige versnellings te meet en
beraam, word aangebied. Die ontwerp en kalibrasie van 'n invalshoek sensor vir invalshoek
metings, sowel as 'n nuwe metode wat gebruik maak van verspreide sensore om die
hoekversnellings te bepaal, word ook aangebied.
Die tegnieke wat in hierdie tesis aangebied is, word dan op 'n nie-lineêre vliegtuig model
getoets. Deur simulasie is dit getoon dat die metodes vir die gegewe sensor opstelling nie
voldoende akkurate parameters beraam nie. Dit is ook bewys dat met die gebruik van die
Regressie metode, die vekryging van metings van die invalshoek slegs deur skatting,
probleme in die beraming van die aerodinamiese lug koëffisiente veroorsaak.
Die tegnieke wat in hierdie tesis verskyn, word dan op werklike vlug data toegepas.Vlugtoetse
is uitgevoer en die data is ontleed. Aanbeveling met betrekking tot hoe om toekomstige vlug
toetse vir Stelsel Identifikasiete word voorgestel, en moontlike bronne van foute word uitgelig.
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Robust multi-H2 output-feedback approach to aerial refuelling automation of large aircraft via linear matrix inequalitiesClaase, Etienne H. 03 1900 (has links)
Thesis (MScEng)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: In recent years the aviation industry has shown an interest in the airborne refuelling
of large transport aircraft to enable increased payload mass at take-off and
to extend aircraft range. Due to the large volume of fuel to be transferred, a boom
and receptacle refuelling system with a larger fuel transfer rate is employed. The
refuelling operation is particularly difficult and strenuous for the pilot of the receiver
aircraft, because the position of the receptacle relative to the tanker aircraft must
be maintained within a narrow window for a relatively long period of time. The
airborne refuelling of a large aircraft is typically much more difficult than that of a
fighter aircraft, since the large aircraft is more sluggish, takes much longer to refuel,
and has a relatively large distance between its refuelling receptacle and its centre of
mass. These difficulties provide the motivation for developing flight control laws for
Autonomous In-Flight Refuelling (AIFR) to alleviate the workload on the pilot.
The objective of the research is to design a flight control system that can regulate
the receptacle of a receiver aircraft to remain within the boom envelope of a tanker
aircraft in light and medium turbulence. The flight control system must be robust
to uncertainties in the aircraft dynamic model, and must obey actuator deflection
and slew rate limits.
Literature on AIFR shows a wide range of approaches, including Linear Quadratic
Regulator (LQR), μ-synthesis and neural-network based adaptive control, none of
which explicitly includes constraints on actuator amplitudes, actuator rates and
regulation errors in the design/synthesis. A new approach to designing AIFR flight
control laws is proposed, based on Linear Matrix Inequality (LMI) optimisation.
The relatively new LMI technique enables optimised regulation of stochastic systems
subject to time-varying uncertainties and coloured noise disturbance, while simultaneously
constraining transient behaviour and multiple outputs and actuators to
operate within their amplitude, saturation and slew rate limits. These constraints
are achieved by directly formulating them as inequalities. / AFRIKAANSE OPSOMMING: Die lugvaart industrie toon huidiglik ’n belangstelling in die brandstof oordrag
tussen twee groot vervoervliegtuie gedurende vlug, met die doel om die maksimum
opstyggewig kapasiteit sowel as die maksimum ononderbroke vlugafstand vermoë
van die hervulde vliegtuig te vermeerder. ’n Boom hervulling-stelsel word geïmplementeer
om die hoë spoed van brandstof oordrag te voorsien. Die verrigting van
vluggebonde hervulling van ’n groot, trae vliegtuig is moeiliker en meer veeleisend
as bv. van ’n vegvliegtuig, veral vir die vlieënier van die hervulde vliegtuig, wat
sy boom-skakel moet reguleer binne ’n relatiewe klein boom bewegingsruimte vir ’n
relatiewe lang tydperk. Die kinematika betrokke speel ook ’n groter rol in ’n groot
hervulde vliegtuig a.g.v. die langer afstand tussen die boom-skakel en die massa middelpunt/
draaipunt. Hierdie bied die motivering om ’n beheerstelsel te ontwikkel wat
die taak outomaties uitvoer.
Die doel van die navorsing is om ’n beheerstelsel te ontwerp wat die boom-skakel
van die hervulde vliegtuig outomaties reguleer binne die bewegingsruimte van die
boom, gedurende ligte en matige turbulensie. Daar word van die beheerder vereis
om robuust te wees teen onsekerhede in die vliegtuig se meganika, sowel as om die
beheer oppervlaktes en turbines van die vliegtuig binne hul defleksie-, wringkrag- en
sleurtempo-perke te hou.
Daar bestaan reeds ’n groot verskeidenheid van benaderings tot die outomatisering
van luggebonde hervulling, onder andere LQR, μ-sintese en neurale-netwerk
gebaseerde aanpasbare beheer, waarvan geeneen perke op aktueerders en regulasie
foute direk in die ontwerp insluit nie. ’n Nuwe benadering word voorgestel wat
gebaseer is op Linear Matrix Inequality (LMI) optimering. Die LMI tegniek is relatief
nuut in die gebruik van beheerstelsel ontwerp. Dit stel die ontwerper in staat
om ’n stogastiese stelsel, onderworpe aan tydvariante-stelsel-variasie en gekleurde
ruis versteurings, optimaal te reguleer, terwyl aktueerders en stelsel gedrag direk
beperk word.
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An attitude control system for the deployment and stabilisation of a tethered dual CubeSat missionKearney, Mike-Alec 03 1900 (has links)
Thesis (MScEng)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: The use of electrodynamic tethers on-board satellites is an exciting scientific prospect. These conductive tethers provide the means for satellites to generate power and to do propulsion by electrodynamic interaction with the geomagnetic field. Although well researched in theory, the concept has not enjoyed much success in practice. This study aims to utilise low-cost CubeSats as experimental tool to verify many of the theoretical principles that govern the behaviour of conductive tethers in orbit. The study provides a theoretical background of the concept by evaluating past tether missions and analysing existing theory. A feasible application of an electrodynamic tether within the size and weight limitations of a Nano-satellite is formulated. Existing theoretical work is adapted to model the dynamics and electrodynamics of specifically Nano-satellites. Using these mathematical models, control and estimation algorithms are designed which would provide stable deployment of a tethered CubeSat pair and stable control of the orientation of the tethered system. To be able to implement these algorithms on a satellite mission, a prototype of a sensor capable of measuring the angle of the tether using a CMOS camera is designed and built. A hardware platform is built to test the deployment of the tether using an electric motor. Electronics are designed to control the operation of the camera, to do motor control, and to run control and estimation algorithms. Using the results obtained from the practical tests done on the hardware, and using the theoretical models and control algorithms designed, a full orbital simulation of the deployment was done. This simulation includes the performance of the deployment system, the electrodynamic performance of the tether in earth‟s plasmasphere, and the estimation and control algorithms to control the system. Different deployment strategies are analysed and their performance are compared. / AFRIKAANSE OPSOMMING: Die gebruik van elektrodinamiese toue aanboord satelliete is 'n opwindende wetenskaplike vooruitsig. Hierdie geleidende toue verleen aan die satelliete die vermoë om krag op te kan wek en propulsie deur elektriese interaksie met die geomagnetiese veld te kan doen. Alhoewel dit goed nagevors is in teorie, het die konsep nog nie veel sukses in die praktyk geniet nie. Hierdie studie het dit ten doel om lae-koste CubeSats aan te wend as 'n eksperimentele instrument om baie van die teoretiese beginsels wat geld vir die gedrag van geleidende toue in wentelbane te verifieer. Die studie bied 'n teoretiese agtergrond van die konsep deur die evaluering van vorige tou-missies sowel as die analise van bestaande teorie. 'n Uitvoerbare toepassing van 'n elektrodinamiese tou binne die grootte- en gewigsbeperkinge van 'n Nano-satelliet is geformuleer. Bestaande teoretiese werk is aangepas om die dinamika en elektrodinamika spesifiek van toepassing op Nano-satelliete, te modelleer. Deur hierdie wiskundige modelle te gebruik, is beheer- en afskattingsalgoritmes ontwerp wat stabiele ontplooiing van 'n verbinde CubeSat-paar en stabiele beheer van die oriëntasie van die verbinde stelsel sal verseker. Om hierdie algoritmes te implementeer op 'n satelliet-sending, is 'n prototipe van 'n sensor wat in staat is om die hoek van die tou met behulp van 'n CMOS kamera te meet, ontwerp en gebou. 'n Hardeware platform is gebou om die ontplooiing van die tou met behulp van 'n elektriese motor te toets. Elektronika is ontwerp om die kamera te beheer, motor beheer te doen asook om beheer- en afskattingsalgoritmes uit te voer. Deur gebruik te maak van die resultate wat verkry is tydens die praktiese toetse wat gedoen is op die hardeware, en deur gebruik te maak van die teoretiese modelle en beheeralgoritmes wat ontwerp is, is 'n volle wentelbaan-simulasie van die ontplooiing gedoen. Hierdie simulasie sluit die gedrag van die ontplooiingstelsel, die elektriese gedrag van die geleidende tou in die aarde se plasmasfeer, en die afskatting- en beheeralgoritmes om die stelsel te beheer in. Verskillende ontplooiingstrategieë word ontleed en hul gedrag word vergelyk.
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Motion planning algorithms for autonomous navigation for a rotary-wing UAVBeyers, Coenraad Johannes 03 1900 (has links)
Thesis (MScEng)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: This project concerns motion planning for a rotary wing UAV, where vehicle controllers are
already in place, and map data is readily available to a collision detection module. In broad
terms, the goal of the motion planning algorithm is to provide a safe (i.e. obstacle free)
flight path between an initial- and goal waypoint. This project looks at two specific motion
planning algorithms, the Rapidly Exploring Random Tree (or RRT*), and the Probabilistic
Roadmap Method (or PRM).
The primary focus of this project is learning how these algorithms behave in specific environments
and an in depth analysis is done on their differences. A secondary focus is the
execution of planned paths via a Simulink simulation and lastly, this project also looks at
the effect of path replanning.
The work done in this project enables a rotary wing UAV to autonomously navigate an
uncertain, dynamic and cluttered environment. The work also provides insight into the
choice of an algorithm for a given environment: knowing which algorithm performs better
can save valuable processing time and will make the entire system more responsive. / AFRIKAANSE OPSOMMING: ’n Tipiese vliegstuuroutomaat is daartoe in staat om ’n onbemande lugvaartvoertuig (UAV)
so te stuur dat ’n stel gedefinieerde punte gevolg word. Die punte moet egter vooraf beplan
word, en indien enige verandering nodig is (bv. as gevolg van veranderinge in die omgewing)
is dit nodig dat ’n menslike operateur betrokke moet raak. Vir voertuie om ten volle
outonoom te kan navigeer, moet die voertuig in staat wees om te kan reageer op veranderende
situasies. Vir hierdie doel word kinodinamiese beplanningsalgoritmes en konflikdeteksiemetodes
gebruik.
Hierdie projek behels kinodinamiese beplanningsalgoritmes vir ’n onbemande helikopter,
waar die beheerders vir die voertuig reeds in plek is, en omgewingsdata beskikbaar is vir
’n konflikdeteksie-module. In breë terme is die doel van die kinodinamiese beplanningsalgoritme
om ’n veilige (d.w.s ’n konflikvrye) vlugpad tussen ’n begin- en eindpunt te vind.
Hierdie projek kyk na twee spesifieke kinodinamiese beplanningsalgoritmes, die “Rapidly
exploring Random Tree*” (of RRT*), en die “Probabilistic Roadmap Method” (of PRM).
Die primêre fokus van hierdie projek is om die gedrag van hierdie algoritmes in spesifieke
omgewings te analiseer en ’n volledige analise te doen op hul verskille. ’n Sekondêre fokus is
die uitvoering van ’n beplande vlugpad d.m.v ’n Simulink-simulasie, en laastens kyk hierdie
projek ook na die effek van padherbeplanning.
Die werk wat gedoen is in hierdie projek stel ’n onbemande helikopter in staat om outonoom
te navigeer in ’n onsekere, dinamiese en besige omgewing. Die werk bied ook insig in die
keuse van ’n algoritme vir ’n gegewe omgewing: om te weet watter algoritme beter uitvoertye
het kan waardevolle verwerkingstyd bespaar, en verseker dat die hele stelsel vinniger kan
reageer.
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Mathematical and numerical analysis of electrospraying electrodynamics / Wiskundige en numeriese analiese van elektrosproei elektrodinamikaPieterse, Cornelius Louwrens 12 1900 (has links)
Thesis (MEng) -- Stellenbosch University, 2014 / ENGLISH ABSTRACT: The electrodynamics of arbitrary, point-to-plane electrospraying geometries,
were investigated in this research both analytically and numerically. Electrospraying
is the process during which particles of sizes in the nanometre range
are simultaneously generated and charged by means of an applied electrostatic
field. A high electrostatic potential is applied to a conductive capillary needle,
which overcomes the force exerted by the liquid surface tension. One of the
primary limitations of this process are corona discharges. The effect of corona
discharges have not been studied quantitatively, even though it is frequently
reported in the electrospraying literature.
The main objective of this research was to understand the corona discharge
thresholds associated with electrospraying. Previously, only one theoretical,
and two empirical investigations studied this phenomenon, over a time period
of approximately forty years. It was clear that by better understanding these
thresholds, electrospraying could be applied much more effectively.
A corona discharge threshold model is proposed, using either a numerical
or analytical model for the calculation of polarization fields. When compared
with the experimental results of other researchers, both these two models have
average relative percentage errors of approximately 15%. These are the first
models proposed in the literature for the calculation of electrospraying corona
thresholds. A new method to determine surface tension using electrospraying
is described theoretically. In addition to this method, the calculation of corona
discharge thresholds have various applications. For example, the dynamics of
electrostatic ion thrusters are much better described, powder production by
means of electrospraying can be optimised, and pattern generation using pulsed
electrospraying cone-jets can be optimised as well. / AFRIKAANSE OPSOMMING: Die elektrodinamika van arbitrêre, punt-tot-vlak elektrosproei geometrieë was
beide analities en numeries ondersoek in hierdie tesis. Dit is die proses waartydens
nanodeeltjies gelyktydig gegenereer en elektrostaties gelaai word. Deur 'n
hoë elektriese potensiaal aan te lê tot 'n geleidende kapillêr, is dit moontlik om
die krag van die oppervlakte spanning te oorkom. Een van die primêre beperkings
van elektrosproei is corona ontladings. Die effek van corona ontladings
was nog nie kwantitatief bestudeer nie, selfs al word dit dikwels rapporteer in
die elektrosproei literatuur. Die primêre doel van hierdie navorsing was om die
corona ontlading drempels te verstaan wat geassosieer word met elektrosproei.
In die verlede was daar nog net een teoretiese, en twee empiriese ondersoeke
gewees wat hierdie verskynsel bestuur het, oor 'n tydperk van ongeveer veertig
jaar. Dit was duidelik dat deur 'n beter begrip te hê van hierdie elektrosproei
drempels, kan hierdie proses baie meer doeltreffend toegepas word.
In hierdie tesis word 'n corona ontlading drempel model voorgestel, wat
gebruik maak van 'n analitiese of numeriese model om die polarisasie velde te
bereken. Wanneer vergelyk met die resultate van ander navorsers, het beide die
modelle 'n gemiddelde relatiewe persentasie fout van ongeveer 15%. Hierdie is
die eerste modelle wat voorgestel word vir die berekening van corona ontlading
drempels. Deur gebruik te maak van elektrosproei, word 'n nuwe metode ook
voorgestel om die oppervlakte spanning te bereken. In byvoeging tot hierdie,
het die berekening van corona ontlading drempels vele ander toepassings. As
'n voorbeeld, die dinamika van elektrostatiese ioon stuwers word beter beskryf,
en poeier produksie deur middel van elektrosproei kan optimeer word.
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Optimal estimation and sensor selection for autonomous landing of a helicopter on a ship deckIrwin, Shaun George 12 1900 (has links)
Thesis (MEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: This thesis presents a complete state estimation framework for landing an unmanned
helicopter on a ship deck. In order to design and simulate an optimal state estimator,
realistic sensor models are required. Selected inertial, absolute and relative sensors
are modeled based on extensive data analysis. The short-listed relative sensors include
monocular vision, stereo vision and laser-based sensors.
A state estimation framework is developed to fuse available helicopter estimates, ship
estimates and relative measurements. The estimation structure is shown to be both
optimal, as it minimises variance on the estimates, and flexible, as it allows for varying
degrees of ship deck instrumentation. Deck instrumentation permitted ranges
from a fully instrumented deck, equipped with an inertial measurement unit and differential
GPS, to a completely uninstrumented ship deck. Optimal estimates of all
helicopter, relative and ship states necessary for the autonomous landing on the ship
deck are provided by the estimator. Active gyro bias estimation is incorporated into
the helicopter’s attitude estimator. In addition, the process and measurement noise
covariance matrices are derived from sensor noise analysis, rather than conventional
tuning methods.
A full performance analysis of the estimator is then conducted. The optimal relative
sensor combination is determined through Monte Carlo simulation. Results show
that the choice of sensors is primarily dependent on the desired hover height during
the ship motion prediction stage. For a low hover height, monocular vision is
sufficient. For greater altitudes, a combination of monocular vision and a scanning
laser beam greatly improves relative and ship state estimation. A communication
link between helicopter and ship is not required for landing, but is advised for added
accuracy. The estimator is implemented on a microprocessor running real-time Linux. The
successful performance of the system is demonstrated through hardware-in-the-loop
and actual flight testing. / AFRIKAANSE OPSOMMING: Hierdie tesis bied ’n volledige sensorfusie- en posisieskattingstruktuur om ’n onbemande
helikopter op ’n skeepsdek te laat land. Die ontwerp van ’n optimale posisieskatter
vereis die ontwikkeling van realistiese sensormodelle ten einde die skatter
akkuraat te simuleer. Die gekose inersie-, absolute en relatiewe sensors in hierdie
tesis is op grond van uitvoerige dataontleding getipeer, wat eenoogvisie-, stereovisieen
lasergegronde sensors ingesluit het.
’n Innoverende raamwerk vir die skatting van relatiewe en skeepsposisie is ontwikkel
om die beskikbare helikopterskattings, skeepskattings en relatiewe metings te kombineer.
Die skattingstruktuur blyk optimaal te wees in die beperking van skattingsvariansie,
en is terselfdertyd buigsaam aangesien dit vir wisselende mates van skeepsdekinstrumentasie
voorsiening maak. Die toegelate vlakke van dekinstrumentasie
wissel van ’n volledig geïnstrumenteerde dek wat met ’n inersiemetingseenheid en ’n
differensiële globale posisioneringstelsel (GPS) toegerus is, tot ’n algeheel ongeïnstrumenteerde
dek. Die skatter voorsien optimale skattings van alle vereiste helikopter-,
relatiewe en skeepsposisies vir die doeleinde van outonome landing op die skeepsdek.
Aktiewe giro-sydige skatting is by die posisieskatter van die helikopter ingesluit. Die
proses- en metingsmatrikse vir geruiskovariansie in die helikopterskatter is met behulp
van ’n ontleding van sensorgeruis, eerder as gebruiklike instemmingsmetodes,
afgelei. ’n Volledige werkingsontleding is daarna op die skatter uitgevoer. Die optimale relatiewe
sensorkombinasie vir landing op ’n skeepsdek is met Monte Carlo-simulasie
bepaal. Die resultate toon dat die keuse van sensors hoofsaaklik van die gewenste
sweefhanghoogte gedurende die voorspellingstadium van skeepsbeweging afhang.
Vir ’n lae sweefhanghoogte is eenoogvisie-sensors voldoende. Vir hoër hoogtes het
’n kombinasie van eenoogvisie-sensors en ’n aftaslaserbundel ’n groot verbetering in
relatiewe en skeepsposisieskatting teweeggebring. ’n Kommunikasieskakel tussen helikopter
en skip is nie ’n vereiste vir landing nie, maar word wel aanbeveel vir ekstra
akkuraatheid.
Die skatter is op ’n mikroverwerker met intydse Linux in werking gestel. Die suksesvolle werking van die stelsel is deur middel van hardeware-geïntegreerde simulasie
en werklike vlugtoetse aangetoon.
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