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Xiao, Weidong. "Improved control of photovoltaic interfaces." Thesis, University of British Columbia, 2008. http://hdl.handle.net/2429/2393.
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Photovoltaic (solar electric) technology has shown significant potential as a source of practical and sustainable energy; this study focuses on increasing the performance of photovoltaic systems through the use of improved control and power interfaces. The main objective is to find an effective control algorithm and topology that are optimally suited to extracting the maximum power possible from photovoltaic modules. The thesis consists of the following primary subjects: photovoltaic modelling, the topological study of photovoltaic interfaces, the regulation of photovoltaic voltage, and maximum power tracking.
In photovoltaic power systems both photovoltaic modules and switching mode converters present non-linear and time-variant characteristics, resulting in a difficult control problem. This study applies in-depth modelling and analysis to quantify these inherent characteristics,s pecifically using successive linearization to create a simplified linear problem. Additionally, Youla Parameterisation is employed to design a stable control system for regulating the photovoltaic voltage. Finally, the thesis focuses on two critical aspects to improve the performance of maximum power point tracking. One improvement is to accurately locate the position of the maximum power point by using centred differentiation. The second is to reduce the oscillation around the steady-state maximum power point by controlling active perturbations. Adopting the method of steepest descent for maximum power point tracking, which delivers faster dynamic response and a smoother steady-state than the hill climbing method, enables these improvements. Comprehensive experimental evaluations have successfully illustrated the effectiveness of the proposed algorithms. Experimental evaluations show that the proposed control algorithm harvests about 1% more energy than the traditional method under the same evaluation platform and weather conditions without increasing the complexity of the hardware.
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Vedin, Jonas, and Robert Widén. "Stochastic Knock Control for Improved Efficiency." Thesis, Linköpings universitet, Fordonssystem, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-158635.
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Increasing the efficiency and performance of internal combustion engines is always of interest in the automotive industry. One limiting factor to achieve this in gasoline combustion engines is the ignition timing which can not always be set where optimal ignition efficiency and performance is obtained. This is due to the knock phenomenon which is an abnormal combustion process that can damage the engine. Due to knock, a feedback controller which sets the ignition timing at the best possible value without the risk of harming the engine is required. In this thesis, a statistically driven knock intensity simulation environment based on the Burr Type XII distribution model was set up. In the simulation environment, different stochastic knock feedback controllers were implemented along with background noise estimation techniques used in the knock detection system. The feedback controllers were evaluated against the conventional knock controller commonly used in today’s engines in terms of ignition angle and transient response. The results from the simulation environment showed that a more advanced mean ignition angle can be achieved with stochastic based knock control strategies with the same knock-rate and without lessening the fast transient response achieved from the conventional strategy. To evaluate the results, some of the controllers were implemented in a four cylinder two-liter four stroke Volvo engine with similar results.
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Borndalen, Philip. "Automation and Improved control of Bundle pusher : Automation control." Thesis, Uppsala universitet, Institutionen för teknikvetenskaper, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-353933.
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Newspapers are often bundled and packet on pallets to secure transport. Packing thebundles on pallets are often done with an automatic palletizer. For reliable operation,the bundle needed to have a correct position and orientation on the infeed conveyor.Wrong orientation can happen when the bundle is pushed from conveyor to thepalletisers conveyor. The main to reasons is wrong timing that leads to rotation of thebundle and to high pushing force that leads to tumbled bundles. The goal of thisproject is to make a prototype of a system that automatically adapts the pressure andsignal when to push using two laser sensors. One sensor sends a digital signal if laserbreaks, the other measure distance, e.g. bundle hight. The software was developed onan Arduino Uno board, and two interface board was made for voltage levelconversions. The prototype system managed to change pressure for different bundlesizes and timed the pushing signal correctly.
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Edwan, Talal A. "Improved algorithms for TCP congestion control." Thesis, Loughborough University, 2010. https://dspace.lboro.ac.uk/2134/7141.
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Reliable and efficient data transfer on the Internet is an important issue. Since late 70's the protocol responsible for that has been the de facto standard TCP, which has proven to be successful through out the years, its self-managed congestion control algorithms have retained the stability of the Internet for decades. However, the variety of existing new technologies such as high-speed networks (e.g. fibre optics) with high-speed long-delay set-up (e.g. cross-Atlantic links) and wireless technologies have posed lots of challenges to TCP congestion control algorithms. The congestion control research community proposed solutions to most of these challenges. This dissertation adds to the existing work by: firstly tackling the highspeed long-delay problem of TCP, we propose enhancements to one of the existing TCP variants (part of Linux kernel stack). We then propose our own variant: TCP-Gentle. Secondly, tackling the challenge of differentiating the wireless loss from congestive loss in a passive way and we propose a novel loss differentiation algorithm which quantifies the noise in packet inter arrival times and use this information together with the span (ratio of maximum to minimum packet inter arrival times) to adapt the multiplicative decrease factor according to a predefined logical formula. Finally, extending the well-known drift model of TCP to account for wireless loss and some hypothetical cases (e.g. variable multiplicative decrease), we have undertaken stability analysis for the new version of the model.
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Costa, R. J. "Improved solutions for zebra mussel control." Thesis, University of Cambridge, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.598014.
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The aim of the project presented in this dissertation was to develop improved chemical solutions for zebra mussel control. Three solution concepts were explored: (i) the combination of toxins; (ii) the encapsulation of toxins; and (iii) the exploitation of the seasonality of the species’ tolerance to toxins. The potential of binary mixtures of potassium chloride and poly(diallyldimethyl ammonium chloride) (polyDADMAC) as well as quaternary mixtures containing these chemicals and niclosamide ethanolamine salt and 2-(thiocyanomethylthio)benzothiazole (TCMTB) as assessed. Potassium chloride and polyDADMAC were observed to act more than additively on adult zebra mussels. The examination of the joint effects of these two toxins also suggested that potassium chloride dosages as low as 10mg/l impair the ability of the zebra mussels to perceive the presence of other biocides in the water column, and as a result inhibit protective valve closure responses. This study indicated that the combined application of potassium chloride and polyDADMAC (and possible other pairs of toxins) is likely to be of great practical value. The study of the performance of the quaternary antagonised in the presence of the others. Furthermore, the joint action of the four toxins was observed to be less than additive, and the sensitivity of the animals to potassium chloride and polyDADMAC decreased in the presence of niclosamide ethanolamine salt and TCMTB. These results seriously compromise the potential of the quaternary mixture for zebra mussel control. A promising polyDADMAC-loaded formulation was developed. The encapsulated biocide was shown to double the polymer toxic effects (even under rather unfavourable laboratory testing conditions).
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Bridger, Lee. "Improved control of fed-batch fermenters." Thesis, University of Exeter, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.288001.
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Carl, Jochen. "Improved dynamic testing by impedance control." Connect to online resource, 2008. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3303835.
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Marple, Steven Robert. "Improved error control techniques for data transmission." Thesis, Lancaster University, 2000. http://eprints.lancs.ac.uk/8074/.
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Error control coding is frequently used to minimise the errors which occur naturally in the transmission and storage of digital data. Many methods for decoding such codes already exist. The choice falls mainly into two areas: hard-decision algebraic decoding, a computationally-efficient method, and soft-decision combinatorial decoding, which although more complex offers better error-correction. The work presented in this Thesis is intended to provide practical decoding algorithms which can be implemented in real systems. Soft-decision maximum-likelihood decoding of Reed-Solomon codes can be obtained by using the Viterbi algorithm over a suitable trellis. Two-stage decoding of Reed-Solomon codes is presented. It is an algorithm by which near-optimum performance may be achieved with a complexity lower than the Viterbi algorithm. The soft-output Viterbi algorithm (SOVA) has been investigated as a means of providing soft-decision information for subsequent decoders. Considerations of how to apply SOVA to multi-level codes are given. The use of SOVA in a satellite downlink channel is discussed. The results of a computer simulation, which showed a 1.8dB improvement in coding gain for only a 20% increase in decoding complexity, are presented. SOVA was also used to improve the decoding performance when applied to an RS product code. Several different decoding methods were evaluated, including cascade decoding, and a method where the row and columns were decoded alternately. A complexity measurement was developed which allows accurate comparisons of decoding complexity for trellis-based and algebraic decoders. With this technique the decoding complexity of all the algorithms implemented are compared. Also included in the comparison are the Euclidean and Berlekamp-Massey algorithms.
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Miller, James J., and Philip H. Tannenholz. "AN IMPROVED DRONE TRACKING CONTROL SYSTEM TRANSPONDER." International Foundation for Telemetering, 1990. http://hdl.handle.net/10150/613789.
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International Telemetering Conference Proceedings / October 29-November 02, 1990 / Riviera Hotel and Convention Center, Las Vegas, Nevada<br>Improved performance has been achieved in the new Herley design of the Model MD700C-1 Drone Tracking and Control System, C-band Command and Control Transponder. The approach for obtaining better radio frequency rejection, automatic gain control, local oscillator stability, and power supply efficiency is described. New hybrid microwave integrated circuit application techniques were used to design a small local oscillator, tunable over the 5400 to 5900 MHz range with a frequency drift of less than ± 1 MHz. This low frequency drift allowed the use of a 4 pole immediate amplifier filter, 60 dB down, at 40 MHz bandwidth, which, when coupled with the three cavity radio frequency preselector filter, provides 7 pole out of band rejection for unwanted radar signals operating at close frequencies. To augment the out of band rejection, a new form of 75 dB dynamic range automatic gain control was used, which combines signal attenuation with a circuit that reduces immediate frequency noise with increasing signal. This allows rejection of the radars own in-band multipath signals by reducing the gain and threshold sensitivity. To reduce power consumption and heat while operating over a wide voltage range, a switching mode regulator and a nonsaturating core power supply was designed to operate at 80% efficiency.
Compared to units in field use over the past 10 years, the new design shows improvements of 400 percent in local oscillator frequency stability, 30 percent in out of band frequency rejection, 66 percent in the automatic gain
control dynamic range, and 60 percent in power supply efficiency.
The MD700C-1 was developed by Herley Industries for the USAF SMALC, and is currently in production.
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Altube, Vázquez Patricia. "Procedures for improved weather radar data quality control." Doctoral thesis, Universitat de Barcelona, 2016. http://hdl.handle.net/10803/400398.
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Weather radar data and its downstream products are essential elements in weather surveillance and key parameters in the initialisation and validation of hydrological and meteorological models, among other downstream applications. Following the quality standards established by the European and global weather radar networking referents, the present thesis aims for the improvement of the base data quality control in the regional weather radar network operated by the Meteorological Service of Catalonia, the XRAD. This objective is accomplished through the analysis, development and implementation of new or existing procedures and algorithms for radar data quality assessment and improvement. Attending to the current radar technology and to the already implemented quality control procedures for the XRAD, the work is focused on the continuous evaluation of the radar system calibration status and on the correction of Doppler velocity data. The quality control algorithms and recommendations presented are easily translatable to any other operative weather radar networking environment.
A Sun-based, fully automatic procedure for online monitoring the antenna alignment and the receiver chain calibration is adapted and operationally implemented for the XRAD. This Sun-monitoring technique was developed at the Royal Netherlands and Finnish Meteorological Institutes and is included in the quality control flow of numerous weather radar networks around the world. The method is modified for a robust detection and characterisation of solar interferences in raw data at all scan elevations, even when only data at relatively short ranges is available. The modified detection algorithm is also suitable for detecting interferences from wireless devices, which are stored for monitoring their incidence in the XRAD. The solar interferences detected, in turn, are input observations for the inversion of a two-dimensional Gaussian model that yields estimates of the calibration parameters of interest. A complete theoretical derivation of the model establishes its validity limits and provides analytical estimates of the effective solar widths directly from radar parameters. Results of application of this Sun-monitoring methodology to XRAD data reveal its ability to determine the accuracy of the antenna pointing and to detect changes in receiver calibration and radar system operation status.
In order to facilitate the usage of the Sun-monitoring technique and the interpretation of its estimates, the methodology is reproduced under controlled conditions based on the distributions of solar observations collected by two of the XRAD radars. The analysis shows that the accuracy of the estimated calibration parameters is conditioned by the precision, number and distribution of the solar observations which constitute key variables that need to be controlled to ensure reliable estimates. In addition, the Sun-monitoring technique is compared under actual operative conditions with two other common techniques for quantifying the antenna azimuth and elevation pointing offsets. Pointing bias estimates gathered in a dedicated short-term campaign are studied in a direct inter- comparison of the methods that reflects the advantages and limitations in each case. The analysis of the bias estimates reported by the methods in the course of a one-year period reveals that the performance of the techniques depends on the antenna position at the time of the measurement. After this study, a reanalysis of the Sun-monitoring method results is proposed, which allows to additionally quantify the antenna pedestal levelling error.
Finally, a post-processing, spatial image filtering algorithm for identification and correction of unfolding errors in dual-PRF Doppler velocity data is proposed. The correction of these errors benefits the usage of radar velocity data in downstream applications such as wind- shear and mesocyclone detection algorithms or assimilation in numerical weather prediction models. The main strengths of the proposed algorithm, in comparison with existing correction techniques, are its robustness to the presence of clustered unfolding errors and that it can be employed independently of post-processing dealiasing algorithms. By means of simulated dual-PRF velocity fields, the correction ability of the algorithm is quantitatively analysed and discussed with particular emphasis on the correction of clustered errors. The quality improvement in real dual-PRF data brought out by the new algorithm is illustrated through application to three selected severe weather events registered by the XRAD.<br>Seguint els estàndards de qualitat establerts per a les xarxes de radars meteorològics de referència a nivell europeu i global, la present tesi té com a objectiu la millora del control de qualitat de les dades de la xarxa regional de radars meteorològics operada pel Servei Meteorològic de Catalunya (la XRAD). Atenent als procediments de control de qualitat ja implementats per a la XRAD, el treball es centra en l'avaluació contínua de l'estat del calibratge del sistema radar i en la correcció de les dades de velocitat Doppler.
Es presenta l'adaptació i aplicació d’un procediment totalment automàtic basat en el Sol, que permet la quantificació remota dels errors d'alineació de l'antena i de calibratge en recepció del radar a la XRAD. El mètode ha estat modificat per a la detecció i caracterització robusta d'interferències solars a les dades primàries de radar. Les interferències solars són utilitzades per a la inversió d'un model físic que proporciona estimacions dels paràmetres de calibratge d'interès. L'algoritme de detecció modificat també és adequat per a la identificació d'interferències procedents de dispositius electrònics externs. Aquestes interferències són emmagatzemades per al seguiment de la seva incidència a la XRAD.
La metodologia solar esmentada es modelitza en condicions controlades a partir de la distribució de les observacions solars recollides per dos dels radars de la XRAD. L'anàlisi mostra que la precisió, el nombre i la distribució de les observacions solars constitueixen variables clau que necessiten ser controlades per garantir estimacions fiables dels paràmetres de calibrage. A més, la tècnica solar es compara, sota condicions operatives reals, amb altres dues tècniques habitualment emprades per a la quantificació de l'error d'apuntament de l'antena. A partir d'aquest estudi, es proposa un nou mètode d'anàlisi de les interferències solars, el cual permet quantificar l'error d'anivellament del pedestal de l'antena.
Finalment, es desenvolupa i valida un algoritme de filtrat d'imatges per a la identificació i correcció dels errors característics que es donen lloc a les dades dual-PRF de velocitat Doppler. Els punts forts de l'algoritme proposat, en comparació amb les tècniques de correcció existents, són la seva robustesa en la correció d'errors agrupats i que pot emprar- se amb independència dels algoritmes de dealiasing. La millora de la qualitat de les dades reals de velocitat s'il·lustra mitjançant l'aplicació de l’algoritme a tres episodis de temps sever enregistrats per la XRAD.
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Johnson, Jay H. "AUV steering parameter identification for improved control design." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2001. http://handle.dtic.mil/100.2/ADA397498.
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Thesis (M.S. in Mechanical Engineering) Naval Postgraduate School, June 2001.<br>Thesis advisor(s): Healey, Anthony J. "June 2001." Includes bibliographical references (p. 55). Also Available in print.
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Hofmann, Martin. "Improved control for multilevel inverters in grid applications." Doctoral thesis, Universitat Politècnica de Catalunya, 2018. http://hdl.handle.net/10803/663181.
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Control systems for three-phase grid connected voltage source inverters (VSI) play an important role in energy transformation systems . They are expected to be stable, robust and accurate during steady state as well as different grid faults and disturbances like voltage sags or unbalanced conditions. Caused by increasingly rising grid standards and efficiency requirements the use of multilevel inverter systems in grid connected low voltage applications are getting more and more attention. Nevertheless, the use of these inverter types leads to increased complexity of the control system and the hardware components.
This thesis presents an improved control scheme for multilevel inverters in grid applications. The system combines a robust and high-dynamic direct current control scheme called scalar hysteresis<br>En molts casos i, cada cop més, els sistemes de transformació energètica estan basats en convertidors en font de tensió connectats a la xarxa elèctrica trifàsica. Aquests convertidors necessiten de sistemes de control per controlar els fluxos energètics. Els sistemes de control han de ser estables, però també robustos i precisos durant el seu funcionament normal, però també en condicions on la xarxa pot presentar defectes, com curtcircuits, sots de tensió o desequilibris en la tensió. Degut a l'increment dels requeriments tècnics de connexió i d'eficiència energètica, els convertidors multinivell estan guanyant molt d'interès en aquest tipus d'aplicacions connectades a la xarxa tot i que el seu control i els seus components siguin més complexes. Aquesta tesi presenta un mètode de control per convertidors multinivell connectats a la xarxa elèctrica. El mètode combina la robustesa davant de canvis en el sistema així com una alta capacitat dinàmica per controlar el corrent injectat a la xarxa. El mètode presentat esta basat en l'anomenat Scalar Hysteresis Control (SHC) i incorpora un sistema feedforward que li permet seleccionar acuradament el punt de treball i seleccionar al millor estat de commutació en cada moment. La combinació del SHC amb el feedforward garanteix un comportament robust amb una alta dinàmica en totes les condicions de funcionament. El concepte bàsic del mètode feedforward proposat no usa sensors i està basat en detectar la tensió de l'inversor que inclou les components harmòniques. El mètode està basat en l'ús d'integradors generalitzats de segon ordre (second order generatlized integrators, SOGI) per tal de detectar les components harmòniques de la tensió de sortida de l'inversor. El sistema pot operar sense sensor de tensió, fins i tot en situacions de defecte de la tensió. Fins i tot, la informació extreta del SOGI es pot usar per altres llaços de control d'ordre superior com el control de la potencia usant les components simètriques. Per a determinar els millors estats de commutació de l'inversor amb el menor esforç s'usa en el mètode proposat en aquesta tesi un canvi de coordenades que usa valor enters. Aixo permet l'ús de relacions matemàtiques senzilles que es poden implementar fàcilment i que requereixen una menor potencia de càlcul. A més, el mètode és fàcilment generalitzable . En la tesi es presenten simulacions i resultats experimentals en convertidors multinivell de tres i cinc nivells per tal d'investigar i demostrar les funcionalitats del sistema de control proposat. Tant les simulacions com els resultats experimentals es realitzen en totes les condicions possibles de la xarxa elèctrica, estat estacionari, sots i distorsions harmòniques
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Guy, Nicholas J. H. "Ion-selective electrode dynamics for improved pH control." Thesis, University of Nottingham, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.362853.
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Okumus, Halil Ibrahim. "Improved direct torque control of induction machine drives." Thesis, University of Bristol, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.364958.
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Ahmad, Shah Shahrul. "Improved autogyro flying qualities using automatic control methods." Thesis, University of Glasgow, 2018. http://theses.gla.ac.uk/39052/.
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An autogyro or Autogiro is a unique type of rotary-wing aircraft that was successfully flown in the 1920s, many years before the first helicopter came to service. As far as the rotorcraft technology is concerned, the technical issues addressed by autogyros were eventually rectified and paved the way for the success of helicopter development. When helicopter became more popular and accepted in the civil aviation industry in the 1940s, autogyros were nearly forgotten and the popularity slowly diminished. The re-emergence of autogyros in the last two decades in hobby and sports flight activities, however, coincides with bad safety records due to stability issues. At the time of this writing, there are no specific flying qualities standards to be em- ployed as guidelines to design a light autogyro with good stability attributes. The only requirements available are addressed in the BCAR Section T airworthiness standard for light autogyros which only prescribes some basic dynamic stability requirements for the vehicle. For existing conventional light autogyros which mostly of 'home-built' type, complying with the airworthiness standards would be an issue as most of them were built beforehand. From these concerns, this Thesis aims to improve the flying qualities performance of existing light autogyros through automatic flight control methods, as one of the ways to practically achieve the required performance. Consequently, specific flying qualities requirements for light autogyros must first be proposed as preliminary guidelines for design and flying qualities improvement. A generic mathematical model of light autogyros named ARDiS is developed based on the 'multiblade' simulation ap- proach which is computationally cost-effective. This model was successfully validated against real autogyro flight data and later implemented in the control enhancement of the vehicle. The control enhancement was developed using classical approaches with limitation in size and simplicity of the vehicle as a light aircraft. Proper actuation control hard- ware was separately modelled and deployed into the autogyro to demonstrate a higher dynamics in the control mechanism so that a more realistic attitude behaviour of the vehicle is presented. This control enhancement was successfully evaluated with both, linear and nonlinear simulations according to the proposed autogyro flying qualities attributes. All presented results signify a higher possibility of improving the flying qualities of currently used and future built light autogyros through control enhance- ment.
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Zaitcev, Aleksandr. "EEG source imaging for improved control BCI performance." Thesis, University of Sheffield, 2017. http://etheses.whiterose.ac.uk/17155/.
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Brain-computer interfaces (BCIs) provide means for direct braincomputer interaction, based solely on the user's brain neural activity, commonly captured by Electroencephalography (EEG), and do not rely on any degree of physical movement. From a general perspective the function of BCIs is to discriminate between a limited set of mental states, which the user enters voluntarily or unconsciously. This represents a foundation for various BCI applications such as assistive technologies, including neuroprosthetics and computer control BCIs for disabled users or mental state monitoring systems aimed for emotion, fatigue or workload recognition. A commonly used type of mental tasks for BCI control is imagination of physical movement or motor imagery, which is characterized by the local power deviation occurring in the brain areas responsible for muscles involved in the executed task. This PhD manuscript is dedicated to the design of motor imagery EEG BCIs with a particular focus on signal processing and classification approaches that incorporate the background knowledge about biophysics and EEG signal generation. These aspects are considered in the EEG source reconstruction process, which estimate the cortical currents during the EEG voltage measurements from head surface. In this work it is shown that the application of the source reconstruction in a BCI signal processing scheme effectively decreases the negative effects of EEG electrode coupling providing for an increase in class separability, given that the cortical areas involved in motor imagery are anatomically segregated. Based on these observations a novel BCI feature extraction method based on source analysis and common spatial patterns (CSP) was proposed and its performance was investigated with a common motor imagery dataset and our own real-time BCI implementation. Our results show that EEG source reconstruction reduces the influence of noise and muscular artifacts, and thus the proposed approach consistently outperforms the conventional BCI sensor feature extraction methods.
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Ninaber, Deidre. "Improved control of Rhododendron ponticum for environmental management." Thesis, Bangor University, 2009. https://research.bangor.ac.uk/portal/en/theses/improved-control-of-rhododendron-ponticum-for-environmental-management(74c9f052-2a41-4837-94bf-b75b253126aa).html.
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Rhododendron ponticum is an invasive non-native shrub that represents a significant threat to productive land use, biodiversity conservation in priority habitats and potentially other ecosystem services in Britain and Ireland. Management actions that reduce the spread and impacts of invasive species require knowledge of their ecological characteristics as well as best control methods. A series of glasshouse experiments was carried out to investigate the effect of microhabitat on R. ponticum germination and seedling survival rates. Light environment in the form of different shade treatments, watering regime and seedbed substrate were manipulated in a factorial design to test their effects and interactions. Short-growing moss, bare soil and sown lawn grass produced a combination of high germination and seedling survival rates, with much lower rates in tall growing moss, leaf litter and grassland turf. Periodic droughting had a large negative effect on R. ponticum seed germination, especially in the more exposed seedbed substrates. The presence of additional canopy shade above a vegetated ground layer was very detrimental to R. ponticum establishment and this effect was found to be due to a reduction in light quality (ratio of red to far red light) and not light quantity (photosynthetic photon flux density). The use of chemical control methods with herbicides, in particular glyphosate, dominates current practice in the removal of R. ponticum from invaded habitats. In order to optimize the efficacy of glyphosate, a series of experiments were designed to improve knowledge of the effect on glyphosate absorption and translocation, of its dose in combination with application at different times of the year in the field, and of foliar application and light level in the glasshouse. Glyphosate applied to the foliage of R. ponticum plants less than 1.5 m in height, was most readily translocated when the plants were more metabolically active. Plants treated in August and May showed greater rates and extent of crown damage than those treated in November and February. 14C-labelled glyphosate applied to the lower leaf surface of R. ponticum plants was rapidly absorbed over the first six hours with maximum absorption after three days. Translocation to other parts of the plant (measured as glyphosate concentration) was greatest to the stem adjacent to the treated leaves and then to the roots, concentrations were lower in untreated leaves over 30 days. Supplemental lighting did not increase the foliar absorption of the 14C but did increase the amount translocated to the other parts of the plant. This study has brought a new understanding to the invasion dynamics of R. ponticum that can be used in identifying habitats vulnerable to invasion and in developing a post clearance management strategy for preventing reinvasion of sites. It has also brought a basic knowledge to glyphosate absorption and translocation patterns that could have profound implications in improving practical application techniques of invasive woody plant species.
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Overboe, Paul David. "Optimizing log truck payload through improved weight control." Thesis, Virginia Tech, 1987. http://hdl.handle.net/10919/43887.
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Trucking of forest products is a very important segment of the harvesting process and it is monitored relatively closely by external sources. Load weight is the focal point of the attention received by log hauling. The optimization of load weights is therefore very important to a logging operation's success and this can be achieved only through adequate gross vehicle weight control. Methods of load weight control are reviewed and possible applications discussed in this report. Studies were conducted to evaluate the adequacy of load weight control achieved utilizing two quite different methods. A reporting technique which provided loader operators with information about trends in the delivery weights of trucks which they loaded was used to heighten their awareness of problem areas in load weight distributions. This study was conducted at two southern paper mills with substantially different truck weight regulation environments. Two separate case studies were conducted on Virginia loggers utilizing on-board electronic truck scales.
Results of the loading study indicated that the passive treatment had affected the behavior of some of the producers studied. The behavioral changes observed generally improved the economic optimization of load delivery weights. The on-board scale studies indicated that the scale systems did perform well in the applications observed. However, the economic benefits associated with use of the scales were negligible for the two producers studied due to a reduction in delivery weights after installation of the scales.<br>Master of Science
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Hamersma, H. A. (Herman Adendorff). "Longitudinal vehicle dynamics control for improved vehicle safety." Diss., University of Pretoria, 2013. http://hdl.handle.net/2263/40829.
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An autonomous vehicle is a vehicle that is capable of navigating and driving with no human intervention whatsoever through the utilization of various sensors and positioning systems. The possible applications of autonomous vehicles are widespread, ranging from the aerospace industry to the mining and military sectors where the exposure of human operators to the operating conditions is hazardous to their health and safety. Automobile accidents have become the leading cause of death in certain segments of the world population. Removing the human driver from the decision-making process through automation may result in significantly safer highways. Although full autonomy may be the ultimate goal, there is huge scope for systems that aid the driver in decision making or systems that take over from the driver under conditions where the human driver fails.
The aim of the longitudinal control system to be implemented on the Land Rover test vehicle in this study is to improve the vehicle’s safety by controlling the vehicle’s longitudinal behaviour. A common problem with sports-utility-vehicles is the low rollover threshold, due to a high centre of gravity. Rather than modifying the vehicle to increase the rollover threshold, the aim of the control system presented here is to prevent the vehicle from exceeding speeds that would cause the vehicle to reach its rollover threshold.
In order to develop a control system that autonomously controls the longitudinal degree of freedom, a model of the test vehicle (a 1997 Land Rover Defender 110 Wagon) was developed in MSC.ADAMS/View and validated experimentally. The model accurately captures the response of the test vehicle to supply forces as generated by the engine and demand forces applied through drag, braking and engine braking. Furthermore, the model has been validated experimentally to provide reliable simulation results for lateral and vertical dynamics.
The control system was developed by generating a reference speed that the vehicle must track. This reference speed was formulated by taking into account the vehicle’s limits due to lateral acceleration, combined lateral and longitudinal acceleration and the vehicle’s performance capabilities. The control system generates the desired throttle pedal position, hydraulic pressure in the brake lines, clutch position and gear selection as output. The MSC.ADAMS\View model of the test vehicle was used to evaluate the performance of the control system on various racetracks of which the GPS coordinates were available. The simulation results indicate that the control system performs as expected.
Finally, the control system was implemented on the test vehicle and the performance was evaluated by conducting field tests in the form of a severe double lane change manoeuvre. The results of the field tests indicated that the control system limited the acceleration vector of the vehicle’s centre of gravity to prescribed limits, as predicted by the simulation results.<br>Dissertation (MEng)--University of Pretoria, 2013.<br>gm2014<br>Mechanical and Aeronautical Engineering<br>unrestricted
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Swanson, Davin Karl. "Dynamic simulation of an improved passive haptic display." Thesis, Georgia Institute of Technology, 1999. http://hdl.handle.net/1853/17292.
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Wong, Wallace Shung Hui. "Improved direct torque control and robust adaptive control of induction motor drives." Thesis, University of Bristol, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.271811.
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Smith, Anthony Paul. "Improved axis synchronisation in a distributed machine control interpolator." Thesis, Nottingham Trent University, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.261374.
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Bjenning, Lovisa. "Implementation of improved fat standardization using statistical process control." Thesis, Linnéuniversitetet, Institutionen för kemi och biomedicin (KOB), 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-86215.
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The aim of this project was to apply statistical process control (SPC) and measure the variation of fat content in milk in order to improve the standardization, so that the fat content does not change more than 0.03 percentage units from target. Recommendations of how to adjust the standardization should also be developed. The standardization takes place together with pasteurization in one of the three pasteurizers. Thereafter, the milk goes to a common product tank with all the pasteurizers. Samples from the three pasteurizers and the product tank were collected and analyzed on MilkoScan FT2 and the fat content was plotted into Shewhart and cumulative sum (CUSUM) charts. Sampling on the pasteurizers from startup showed that samples should be taken after about 20 minutes, because then the variation is in general smaller. The data from the product tank showed a smaller variation than the pasteurizers. Because the milk from all the pasteurizers is transported into one product tank, it is impossible to know which pasteurizer that is out of control and need to be adjusted. Therefore, the conclusion is that samples should be taken after the pasteurizer and plotted into Shewhart and CUSUM charts. Action limits were achieved from the Shewhart and CUSUM charts, respectively. These are the limits that should be used to determine when adjustments of the pasteurizers are needed, and not the brand limits that are considerably wider. If the measurements fall outside the second limit in the Shewhart chart (three times the standard deviation) or outside the limits (H) in the CUSUM chart, the standardization before the pasteurizer in question should be considered. It is not known if using SPC will improve the fat content to be within 0.03 percent units from target, because the recommendation has not been applied in the process yet, but it going to be that soon.<br>Syftet med detta arbete var att implementera statistisk processtyrning och mäta variationen i mjölkens fetthalt för att kunna förbättra standardiseringen. Detta skulle medföra att fetthalten inte förändras mer än 0,03 procentenheter från målet. Rekommendationer om hur standardiseringen bör justeras av fetthalten i mjölk ska också utvecklas. Standardiseringen sker tillsammans med pastöriseringen i en av de tre pastörerna. Därefter går mjölken till en gemensam produkttank för pastörerna. Prover från de tre pastörerna samt produkttank samlades in om analyserades på MilkoScan FT2 och fetthalten plottades in i Shewhart och Kumulativsumma (CUSUM) diagram. Provtagning från produktstart på pastörerna visade att prover skulle tas efter 20 minuter, eftersom variationerna då är mindre. Data från produkttank visade en lägre variation än hos de tre pastörerna. Eftersom mjölken från pastörerna transporteras till en produkttank är det omöjligt att veta vilken av de tre pastörerna som är utom kontroll och bör justeras. Därför är slutsatsen att proverna ska tas efter pastörerna och plottas in i Shewhart och CUSUM diagram. Åtgärdsgränser togs fram för både Shewhart och CUSUM diagram. Dessa är gränserna som ska användas för att bestämma när justeringar bör göras på pastörerna och inte varumärkesgränserna som är avsevärt bredare. Om ett mätvärde faller utanför den andra gränsen i Shewhart diagrammet eller utanför gränserna (H) i CUSUM diagrammet bör standardiseringen innan pastören i fråga justeras. Det är ännu oklart om standardiseringen kommer förbättras eftersom rekommendationerna inte har applicerats i processen än. Men kommer att göra det i den närmsta framtiden.
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Kite, David John. "Improved current control in thyristor drives for d.c. machines." Thesis, University of Bath, 1985. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.767552.
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The accurate and versatile control of a direct current machine's speed using a thyristor converter has led to its use for many industrial applications. However, as will be demonstrated, the current gain characteristic of such a device is not linear and under certain operating conditions can lead to an unacceptable degradation in performance. In order to develop a method of adaptive control that can compensate for the gain changes, the key features and theory of phase controlled thyristor converters are described and used to develop a digital computer simulation of a single phase converter. The d.c. gain of the device as a function of firing angle is then determined and the model used as the basis of a larger simulation of the machine's armature current control loop. The latter is used to investigate a number of control strategies, one of which is developed practically using a combination of analogue and digital electronics. The performance of the adaptive control system is then investigated by means of a comparison with the responses predicted by the software model and also by comparing the responses of the adaptive controller with the current loop responses obtained from a purely linear commercial drive. These show that the implementation of the chosen control strategy, although being very complex, does not achieve ideal responses. However, those obtained are seen under most conditions to be an improvement on the conventional system. Finally, the effect of the different armature current controllers on the speed response of d.c. machines using both linear and variable structure speed controllers is investigated. This is done purely in software following the development of a digital simulation of the speed loop. These show the adaptive qualities of VSS speed control, especially when used with the "faster" adapted current loop.
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Sokola, Matija. "Vector control of induction machines using improved machine models." Thesis, Liverpool John Moores University, 1998. http://researchonline.ljmu.ac.uk/4899/.
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Phung, Chi Dung. "Enriching the internet control-plane for improved traffic engineering." Thesis, Sorbonne université, 2018. http://www.theses.fr/2018SORUS017/document.
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L'un des défis majeurs de l'évolution de l'architecture Internet est la définition d'une architecture protocolaire permettant d'améliorer le routage, et en particulier (i) conserver un système de routage gérable avec les technologies actuelles et futures c'est-à-dire, avec quelques millions d'états, (ii) offrir une architecture apte à faciliter la programmabilité du plan de transfert, (iii) proposer un système de routage évolutif pouvant être régulièrement optimisé avec uniquement les informations sur les flux actifs, (iv) fournir une séparation entre localisateurs et identificateurs pour la mobilité IP avancée, (v) faciliter un déploiement incrémental, (vi) mieux servir les services applicatifs "over-the-top". Le protocole LISP (\textit{Locator/Identifier Separation Protocol}) a été identifié comme l'un des protocoles émergents à cet égard. Dans son état actuel, il répond très bien aux besoins susmentionnés. Cependant, il subit des limitations lorsqu'il s'agit de prendre en compte la résilience et la capacité à réagir rapidement aux mises à jour de l'état du réseau. Ces inconvénients peuvent être compensés en améliorant l'architecture du plan de contrôle et ses algorithmes de routage. Dans cette thèse, nous proposons une nouvelle architecture réseau-système et expérimentons de nouvelles primitives de plan de contrôle, ainsi que d'algorithmes de diffusion des états, en testant son passage à l'échelle avec différentes conditions de réseau. Nous concevons et construisons d'abord un nœud de plan de données et de plan de contrôle LISP open source. Nous le comparons avec d'autres implémentations en montrant que notre implémentation atteint des performances adaptées aux vrais déploiements. Nous montrons comment notre implémentation a permis la mise en oeuvre d'une plateforme d'expérimentation à grande échelle, la plate-forme LISP-Lab, en opération aussi bien les fonctions de plan de transfert que les fonctions de plan de contrôle. En suite, nous proposons une nouvelle solution pour les migrations à chaud de machines virtuelles à travers des centres de données géographiquement répartis sur des réseaux IP étendus. Des tests dans un testbed réel connecté nativement à Internet montrent qu'avec notre approche, nous pouvons facilement atteindre des temps d'arrêt inférieurs à la seconde lors de la migration sur une grande échelle, même pour des clients très distants. En outre, nous avons étudié des protocoles d'optimisation de réseau multicouche, en particulier en relation avec le protocole MPTCP (Multipath Transport Control Protocol), auquel LISP peut offrir une diversité de chemins pour l’agrégation de bande passante, ainsi qu’une plus grande confidentialité et fiabilité des connexions. Bien que nous ne puissions bénéficier que de quelques nœuds de réseau superposés, nous avons pu évaluer expérimentalement nos propositions en montrant l'impact positif de notre solution, l'impact négatif des longs temps d'aller-rétour sur certains sous-flux MPTCP, et la forte corrélation entre le temps d'aller-retour différentiel et le débit. Enfin, nous avons travaillé sur une refonte du plan de contrôle de LISP afin d’améliorer son fonctionnement du à l'échelle d’Internet, en facilitant la coopération entre les systèmes de mapping LISP et en introduisant plus d'automatisation dans la procédure de fourniture de services de connectivité LISP. Nous croyons qu'une telle optimisation pourrait sensibiliser la communauté des fournisseurs de services, générant de nouvelles opportunités commerciales liées aux services de cartographie LISP et l'application de politiques d'ingénierie de trafic interdomaines avancées dans le but d'obtenir de meilleures garanties de qualité de service<br>One of the major challenges in the evolution of the Internet architecture is the definition of a protocol architecture that allows to solve the following major issues in Internet routing and traffic forwarding capabilities, (i) keeping a routing state that is manageable with current and forthcoming computing infrastructure – i.e., with few millions of states, (ii) offering a scalable pull architecture in support of data-plane programmability, (iii) offering a scalable forwarding plane able to be regularly optimized with only active flows information, (iv) offering locator/identifier separation for advanced IP mobility, (v) is incrementally deployable, (vi) can enhance the support of over-the-top services. The Locator/Identifier Separation Protocol (LISP) has been identified as one of the rising protocols in this respect. In its current status, it supports the above mentioned requirements at a level that is acceptable for basic networking environments. However, it shows too limited capacities when it comes to take into consideration fault resiliency and capability to react fast to network state updates. These shortcomings can be compensated by enhancing the control-plane architecture, and the routing algorithms therein. In this dissertation, we propose new protocol features and experiment novel control-plane primitives, as well as hybrid distributed-centralized routing state dissemination algorithms, to scale with different network conditions. We first design and build own open source LISP data-plane and control plane node, comparing it with other implementations, showing how our implementation can scale for large networks and reach performances suitable for real deployments. We present how our implementation served to operate all network nodes (data-plane and control-plane nodes) of a large scale experimentation testbed, the LISP-Lab testbed. Then we propose a novel LISP-based solution for VM live migrations across geographically separated datacenters over wide area IP networks. Experimenting it at large scale, we show that with our approach we can easily reach sub-second downtimes upon Internet-wide migration, even for very distant clients. Moreover, we investigate cross-layer network optimization protocols, in particular in relation with the Multipath Transport Control Protocol (MPTCP) to which LISP can deliver path diversity in support of bandwidth increase, confidentiality support and connection reliability, also using LISP traffic engineering network overlays. Despite we could benefit from only few overlay network nodes, we could experimentally evaluate our proposals showing the positive impact by using our solution, the negative impact of long round-trip times on some MPTCP subflows, and the strong correlation between the differential round-trip time among subflows and the throughput performance. Finally, we worked on a framework to improve LISP operation at the Internet scale, by facilitating cooperation between LISP Mapping Systems and introducing more automation in the LISP connectivity service delivery procedure. We believe such optimization could raise awareness among the service providers’ community, yielding new business opportunities related to LISP mapping services and the enforcement of advanced inter-domain traffic engineering policies for the sake of better quality of service guarantees
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Issa, Walid R. M. "Improved control strategies for droop-controlled inverter-based microgrid." Thesis, University of Exeter, 2015. http://hdl.handle.net/10871/17435.
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The main focus of this PhD thesis is fundamental investigations into control techniques of inverter-based microgrids. It aims to develop new and improved control techniques to enhance performance and reliability. It focuses on the modelling, stability analysis and control design of parallel inverters in a microgrid. In inverter-based microgrids, the paralleled inverters need to work in both grid-connected mode and stand-alone mode and should be able to transfer seamlessly between the two modes. In grid-connected mode, the inverters control the amount of power injected into the grid. In stand-alone mode, however, the inverters control the island voltage while the output power is dictated by the load. This can be achieved using droop control. Inverters can have different power set-points during grid-connected mode but in stand-alone mode they all need their power set-points to be adjusted according to their power ratings. However, during sudden unintentional islanding (due to loss of mains), transient power can flow from inverters with high power set-points to inverters with low power set-points, which can raise the DC link voltage of the inverters causing them to shut down. This thesis investigates the transient circulating power between paralleled inverters during unintentional islanding and proposes a controller to limit it. The controller monitors the DC link voltage and adjusts the power set-point in proportion to the rise in the voltage. A small signal model of an island microgrid has been developed and used to design the controller. The model and the controller design have been validated by simulation and practical experimentation. The results confirmed the performance of the proposed controller for limiting the DC link voltage and supporting a seamless mode transfer. The limitation of the droop controller, that is utilized to achieve load sharing between parallel-operated inverters in island mode, has also been addressed. Unequal output impedances among the distribution generation (DG) units lead to the droop control being inaccurate, particularly in terms of reactive power sharing. Many methods reported in the literature adopt low speed communications to achieve efficient sharing. However, the loss of this communication could lead to inaccuracy or even instability. An improved reactive power-sharing controller is proposed in this thesis. It uses the voltage at the point of common coupling (PCC) to estimate the inductance value of the output impedance including the impedance of the interconnecting power cables and to readjust the voltage droop controller gain accordingly. In an island microgrid consisting of parallel-connected inverters, the interaction between an inverter’s output impedance (dominated by the inverter’s filter and voltage controller) and the impedance of the distribution network (dominated by the other paralleled inverters’ output impedances and the interconnecting power cables) might lead to instability. This thesis studies this phenomenon using root locus analysis. A controller based on the second derivative of the output capacitor voltage is proposed to enhance the stability of the system. Matlab simulation results are presented to confirm the validity of the theoretical analysis and the robustness of the proposed controller. A laboratory-scale microgrid consisting of two inverters and local load has been built for the experimental phase of the research work. A controller for a voltage source inverter is designed and implemented. A dSPACE unit has been used to realize the controller and monitor the system in real time with the aid of a host computer. Experimental results of the two voltage source inverters outputs are presented.
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Sandmark, David. "Navigation Strategies for Improved Positioning of Autonomous Vehicles." Thesis, Linköpings universitet, Reglerteknik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-159830.
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This report proposes three algorithms using model predictive control (MPC) in order to improve the positioning accuracy of an unmanned vehicle. The developed algorithms succeed in reducing the uncertainty in position by allowing the vehicle to deviate from a planned path, and can also handle the presence of occluding objects. To achieve this improvement, a compromise is made between following a predefined trajectory and maintaining good positioning accuracy. Due to the recent development of threats to systems using global navigation satellite systems to localise themselves, there is an increased need for methods of localisation that can function without relying on receiving signals from distant satellites. One example of such a system is a vehicle using a range-bearing sensor in combination with a map to localise itself. However, a system relying only on these measurements to estimate its position during a mission may get lost or gain an unacceptable level of uncertainty in its position estimates. Therefore, this thesis proposes a selection of algorithms that have been developed with the purpose of improving the positioning accuracy of such an autonomous vehicle without changing the available measurement equipment. These algorithms are: A nonlinear MPC solving an optimisation problem. A linear MPC using a linear approximation of the positioning uncertainty to reduce the computational complexity. A nonlinear MPC using a linear approximation (henceforth called the approximate MPC) of an underlying component of the positioning uncertainty in order to reduce computational complexity while still having good performance. The algorithms were evaluated in two different types of simulated scenarios in MATLAB. In these simulations, the nonlinear, linear and approximate MPC algorithms reduced the root mean squared positioning error by 20-25 %, 14-18 %, and 23-27 % respectively, compared to a reference path. It was found that the approximate MPC seems to have the best performance of the three algorithms in the examined scenarios, while the linear MPC may be used in the event that this is too computationally costly. The nonlinear MPC solving the full problem is a reasonable choice only in the case when computing power is not limited, or when the approximation used in the approximate MPC is too inaccurate for the application.
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Reed, Matthew Robert. "Development of an Improved Dissipative Passive Haptic Display." Thesis, Georgia Institute of Technology, 2003. http://hdl.handle.net/1853/5284.
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This project focuses on the design and modeling of a two degree-of-freedom dissipative passive haptic display. Haptic displays are man-machine interfaces that transmit forces to the human operator. A dissipative passive haptic display is one that may only remove energy from the system using actuators such as brakes and dampers, thus ensuring the safety of the human operator. These devices may be used to implement virtual constraints such as desired paths and obstacles. Traditional friction brakes have previously been used as dissipative and coupling elements in a two degree-of-freedom parallel manipulator, resulting in undesired effects such as vibration, stiction, and slow response times. Alternatively, the new robot is actuated by rheological brakes, which feature fast response times and smooth application of torque. This approach aims to improve upon the accuracy and feel of the previous design.
A commercial magnetorheological (MR) fluid brake was selected and put through an extensive series of tests. The data was used to develop a model that characterizes MR fluid behavior in low speed braking applications. A parallel five bar linkage was designed and built that has separate configurations corresponding to 3-brake and 4-brake operation. The length of each arm was chosen by means of a geometrical optimization that weighs the size and area of the workspace and actuator effects. A simulation was then developed by incorporating the brake model into the equations of motion of the robot. Next, two forms of path following velocity control were devised and tested in simulation. Finally, the accuracy, workload, and smoothness of both controllers and both configurations were examined in preliminary tests with human operators.
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Krauss, Ryan Walter. "An Improved Technique for Modeling and Control of Flexible Structures." Diss., Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/11519.
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Control design for flexible robots is a challenging problem. Part of the difficulty comes from a lack of controls-focused modeling tools. Practical flexible robots have several aspects that make them difficult to model: continuous elements, complicated actuators, multiple feedback loops, non-collocated sensors and actuators, and the ability to take on arbitrary three-dimensional poses. Even if existing techniques for modeling flexible structures could model the closed-loop response of a hydraulically-actuated flexible robot with a vibration suppression controller, how would such a model be used for control design?
This work presents the development of a modeling approach that meets the needs of a controls engineer. The approach is based on the transfer matrix method (TMM). The TMM has been expanded in several ways to enable it to accurately model practical flexible robots. Quantitative agreement is shown between model and experiment for the interaction of a hydraulic actuator and a flexible structure as well as for the closed-loop response of a system with vibration suppression.
Once the ability to model the closed-loop response of the system has been demonstrated, this work focuses on using the model for control design. Control design is facilitated by symbolic implementation of the TMM, which allows closed-form expressions for the closed-loop response of the system to be found without discretization. These closed-form expressions will be transcendental transfer functions for systems with continuous elements. These transfer functions can then be used in various optimization approaches for designing the closed-loop system response.
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Srinivasan, Ravichandra. "Improved understanding and control of high-speed jet interaction flows." Texas A&M University, 2005. http://hdl.handle.net/1969.1/3055.
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A numerical study of the flow field generated by injection through diamondshaped
orifices into a high-speed flow is presented in this document. Jet interaction
flows have a wide range of applications in the field of engineering. These
applications include the use of jets for fuel injection in scramjets, for reaction control
of high-speed aerodynamic bodies and as cooling jets for skins of high-speed
vehicles. A necessary requirement in the use of transverse jets for these and other
applications is a thorough understanding of the physics of the interaction between
the jet and freestream. This interaction generates numerous flow structures that
include multiple shocks, vortices, recirculation regions and shear layers. This study
involves diamond-shaped orifices that have the advantage of generating weaker or
attached interaction shocks as compared to circular injectors. These injectors also
negate the effects due to the recirculation region that is formed upstream of the
injector. This study was undertaken in order to gain further understanding of the
flow features generated by diamond-shaped injectors in a high-speed flow.
Numerical simulations were performed using two different levels of turbulence
models. Reynolds Averaged Navier-Stokes (RANS) simulations were performed
using the GASP flow solver while Detached-Eddy Simulation (DES) runs were performed
using the Cobalt flow solver. A total of fifteen diamond injector simulations
were performed using the RANS model for a 15 half-angle diamond injector. The fifteen simulations spanned over five different injection angles and three jet total
pressures. In addition to these, two circular injector simulations were also performed.
In addition, low pressure normal injection through diamond and circular
orifices simulations were performed using DES. Results obtained from CFD were
compared to available experimental data. The resulting flow structure and the turbulent
properties of the flow were examined in detail. The normal injection case
through the diamond-shaped orifice at the lowest jet total pressure was defined
as the baseline case and is presented in detail. In order to study the effect of different
components of the vorticity transport equation, an in-house code was used
post-process the results from the RANS runs.
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Burzo, Andrea Mihaela. "Improved control of single cycle pulse generation by molecular modulation." Texas A&M University, 2005. http://hdl.handle.net/1969.1/5010.
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Generation of reproducible attosecond (10-18s) pulses is an exciting goal: in the
same way as femtosecond pulses were used to make "movies" of the atomic motion
in molecules, attosecond pulses could "uncover" the motion of electrons around nuclei.
In this dissertation, we have suggested new ideas that will allow improving one
scheme for obtaining such ultra-short pulses: the molecular modulation technique. In
a theoretical proposal called Raman Additive technique, we have suggested a method
that will allow (with a proper phase stabilization of generated sidebands) to obtain
reproducible waveforms of arbitrary shape. An exciting range of possibilities could
open up - not only for absolute phase control or sub-cycle shape control, but also for
investigation of multiphoton ionization rates as a function of the sub-cycle shape. We
have elaborated on the latter subject in another theoretical project, where we have
exploited the unique feature of such ultrashort laser pulses, which is synchronization
with molecular motion (rotational or vibrational), in order to investigate photoionization
of molecules. From experimental point of view, a different construction of driving
lasers than previously employed led to establishment of larger molecular coherences
at higher operating pressure than in previous experiments. This resulted in simultaneous
generation of rotational and vibrational sidebands with only two fields applied.
In another experimental proposal using rotational transition in deuterium we have shown that employing a hollow waveguide instead of normal Raman cell improves
the efficiency of the generation process. By optimizing gas pressure and waveguide
geometry to compensate the dispersion, the method can be extended to efficiently
generate Raman sidebands at a much lower energy of driving fields than previously
employed. At the end, a very exciting possibility for controlling the molecular motion
in a Raman driven system will be shown. Based on the interference effects (EITlike)
that take place inside of a molecule, selectivity of different degrees of freedom
can be achieved (for example switching from rotational-vibrational motion to pure
rotational).
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Francis, Breeson. "Enhancing TCP Congestion Control for Improved Performance in Wireless Networks." Thèse, Université d'Ottawa / University of Ottawa, 2012. http://hdl.handle.net/10393/23254.
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Transmission Control Protocol (TCP) designed to deliver seamless and reliable end-to-end data transfer across unreliable networks works impeccably well in wired environment. In fact, TCP carries the around 90% of Internet traffic, so performance of Internet is largely based on the performance of TCP. However, end-to-end throughput in TCP degrades notably when operated in wireless networks. In wireless networks, due to high bit error rate and changing level of congestion, retransmission timeouts for packets lost in transmission is unavoidable. TCP misinterprets these random packet losses, due to the unpredictable nature of wireless environment, and the subsequent packet reordering as congestion and invokes congestion control by triggering fast retransmission and fast recovery, leading to underutilization of the network resources and affecting TCP performance critically. This thesis reviews existing approaches, details two proposed systems for better handling in networks with random loss and delay. Evaluation of the proposed systems is conducted using OPNET simulator by comparing against standard TCP variants and with varying number of hops.
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Knox, E. "Improved property control of hot rolled carbon manganese steel grades." Thesis, Swansea University, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.637816.
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The work is in the form of a project aimed at furthering the understanding of metallurgical interactions during the processing of hot rolled CMn (-Si) steel grades. The aim has been achieved through a number of complimentary investigations. Through-coil mechanical testing and metallographic examination, coupled with detailed analyses of relevant process parameters, have highlighted the typical properties and property variations within Corus' CMn (-Si) products. Deformation dilatometry experiments have allowed the transformation behaviour of CMn (-Si) compositions to be assessed and compared with that predicted by transformation theory. Laboratory-scale rolling and cooling experiments have demonstrated the effects of composition and process variations on steel properties. These combined discoveries have contributed to a deeper understanding of the metallurgy of CMn (-Si) steel manufacture. The project has illustrated where product design changes can contribute to enhanced properties, helping Corus to ensure the long-term success of its CMn (-Si) steels within the automotive market.
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Subak, Susan Elizabeth. "Methane policy perspectives : towards improved emissions estimation, projection and control." Thesis, University of East Anglia, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.318093.
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Stout, Adrian John. "Instrumentation techniques and improved control of stepper motor driven machinery." Thesis, Open University, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.312262.
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Frist, Duane C. "Improved beam jitter control methods for high energy laser systems." Thesis, Monterey, California : Naval Postgraduate School, 2009. http://edocs.nps.edu/npspubs/scholarly/theses/2009/Dec/09Dec%5FFrist.pdf.
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Thesis (M.S. in Astronautical Engineering)--Naval Postgraduate School, December 2009.<br>Thesis Advisor(s): Agrawal, Brij ; Kim, Jae Jun. "December 2009." Description based on title screen as viewed on January 28, 2010. Author(s) subject terms: High Energy Laser (HEL), beam control, Fast Steering Mirror (FSM), two axis gimbal, stabilization, video tracking, feedforward control, adaptive filter. Includes bibliographical references (p. 69). Also available in print.
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Choi, Myeonggeun. "Thermal control of gas turbine casings for improved tip clearance." Thesis, University of Oxford, 2015. https://ora.ox.ac.uk/objects/uuid:14a9ce6a-2af6-4187-afe7-8c6f8e113855.
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A thermal tip clearance control system provides a robust and flexible means of manipulating the closure between the casing and the rotating blade tips in a jet engine, reducing undesirable tip leakage flows. This may be achieved using an impingement cooling scheme on the external casing of the engine in conjunction with careful thermal management of internal over-tip seal segment cavity. For a reduction in thrust specific fuel consumption, the mass flow rate of air used for cooling must be minimised, be at as low a pressure as possible and delivered through a light weight structure surrounding the rotating components in the turbine. This thesis first characterises the effectiveness of a range of external impingement cooling arrangements in typical engine casing closure system. The effects of jet-to-jet pitch, number of jets, inline and staggered alignment of jets, arrays of jets on flange, on an engine representative casing geometry are assessed through comparison of the convective heat transfer coefficient distributions in a series of numerical studies. A baseline case is validated experimentally. The validation data allowed the suitability of different turbulence closure models to be assessed using a commercial RANS solver. Importantly for each configuration the thermal contraction of an idealised engine casing is predicted using thermo-mechanical finite element models, at a series of operating conditions representing engine idle to maximum take-off conditions. Cooling is provided by manifolds attached to the outside of the engine. The assembly tolerance of these components leads to variation in the standoff distance between the manifold and the casing. For cooling arrangements with promising performance, the study is extended to characterise the variation in closure with standoff distance. It is shown that where a sparse array of non-interacting jets is used the system can be made tolerant of large build misalignments. The casing geometry itself contributes to the thermal response of the system, and, in an additional study, the effect of casing thickness and circumferential thermal control flanges are investigated. Restriction of the passage of heat into the flanges was seen to be dramatically change their effectiveness and slight necking of the flanges at their root was shown to improve the performance disproportionally. High temperature secondary air flowing past the internal face of the engine casing tends to heat the casing, causing it to grow. Experimental and numerical characterisation of a heat transfer within a typical over-tip segment cavity heat transfer is presented in this thesis for the first time. A simplified modelling strategy is proposed for casing and a means to reduce the casing heat pickup by up to 25 % was identified. The overall validity of the modelling approach used is difficult to validate in the engine environment, however limited data from a test engine temperature survey became available during the course of the research. By modelling this engine tip clearance control system it was shown that good agreement to the temperature distribution in the engine casing could be achieved where full surface external heat transfer coefficient boundary conditions were available.
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Nelson, Timothy. "Margrave: An Improved Analyzer for Access-Control and Configuration Policies." Digital WPI, 2010. https://digitalcommons.wpi.edu/etd-theses/203.
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As our society grows more dependent on digital systems, policies that regulate access to electronic resources are becoming more common. However, such policies are notoriously difficult to configure properly, even for trained professionals. An incorrectly written access-control policy can result in inconvenience, financial damage, or even physical danger. The difficulty is more pronounced when multiple types of policy interact with each other, such as in routers on a network. This thesis presents a policy-analysis tool called Margrave. Given a query about a set of policies, Margrave returns a complete collection of scenarios that satisfy the query. Since the query language allows multiple policies to be compared, Margrave can be used to obtain an exhaustive list of the consequences of a seemingly innocent policy change. This feature gives policy authors the benefits of formal analysis without requiring that they state any formal properties about their policies. Our query language is equivalent to order-sorted first-order logic (OSL). Therefore our scenario-finding approach is, in general, only complete up to a user-provided bound on scenario size. To mitigate this limitation, we identify a class of OSL that we call Order-Sorted Effectively Propositional Logic (OS-EPL). We give a linear-time algorithm for testing membership in OS-EPL. Sentences in this class have the Finite Model Property, and thus Margrave's results on such queries are complete without user intervention.
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Sharon, Andre. "The macro/micro manipulator : an improved architecture for robot control." Thesis, Massachusetts Institute of Technology, 1988. http://hdl.handle.net/1721.1/14434.
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Fan, Frank H. (Frank Hsiao). "Improved continuous-time higher harmonic control using H [infinity] methods." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/79343.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2013.<br>This thesis was scanned as part of an electronic thesis pilot project.<br>In title on title-page, "[infinity]" appears as the symbol. Cataloged from PDF version of thesis.<br>Includes bibliographical references (p. 171-181).<br>The helicopter is a versatile aircraft that can take-off and land vertically, hover efficiently, and maneuver in confined space. This versatility is enabled by the main rotor, which also causes undesired harmonic vibration during operation. This unwanted vibration has a negative impact on the practicality of the helicopter and also increases its operational cost. Passive control techniques have been applied to helicopter vibration suppression, but these methods are generally heavy and are not robust to changes in operating conditions. Feedback control offers the advantages of robustness and potentially higher performance over passive control techniques, and amongst the various feedback schemes, Shaw's higher harmonic control algorithm has been shown to be an effective method for attenuating harmonic disturbance in helicopters. In this thesis, the higher harmonic disturbance algorithm is further developed to achieve improved performance. One goal in this thesis is to determine the importance of periodicity in the helicopter rotor dynamics for control synthesis. Based on the analysis of wind tunnel data and simulation results, we conclude the helicopter rotor can be modeled reasonably well as linear and time-invariant for control design purposes. Modeling the helicopter rotor as linear time-invariant allows us to apply linear control theory concepts to the higher harmonic control problem. Another goal in this thesis is to find the limits of performance in harmonic disturbance rejection. To achieve this goal, we first define the metrics to measure the performance of the controller in terms of response speed and robustness to changes in the plant dynamics. The performance metrics are incorporated into an H [infinity] control problem. For a given plant, the resulting H [infinity] controller achieves the maximum performance, thus allowing us to identify the performance limitation in harmonic disturbance rejection. However, the H [infinity] controllers are of high order, and may have unstable poles, leading us to develop a design method to generate stable, fixed-order, and high performance controllers. Both the H [infinity] and the fixed-order controllers are designed for constant flight conditions. A gain-scheduled control law is used to reduce the vibration throughout the flight envelope. The gain-scheduling is accomplished by blending the outputs from fixed-order controllers designed for different flight conditions. The structure of the fixed-order controller allows the usage of a previously developed anti-windup scheme, and the blending function results in a bumpless full flight envelope control law.<br>by Frank H. Fan.<br>Ph.D.
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Tzianetopoulou, Theodora 1974. "Design of an improved piezoelectric actuator for helicopter rotor control." Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/82197.
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Snell, Jared James. "Improved modeling and optimal control of an electric arc furnace." Thesis, University of Iowa, 2010. https://ir.uiowa.edu/etd/741.
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This thesis centers around an electric arc furnace (EAF) at a steel mini-mill in Wilton, IA. First, the thesis replicates previous optimization attempts. Next, the modeling is greatly altered to produce a much improved steel-melting model. Then, a new optimal control system is created and used to reduce energy and fuel costs over the melting process. Finally, results are presented. This thesis shows that when the new optimal control is simulated, the system shows significant energy and fuel savings.
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Oyegbami, Morenike. "Achieving Improved Glycemic Control Among Hispanic Type 2 Diabetic Adults." ScholarWorks, 2019. https://scholarworks.waldenu.edu/dissertations/6940.
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Type 2 diabetes is a major chronic health disease in the United States. A main concern of clinicians treating patients with Type 2 diabetes is poor glycemic control. The goal of this project was to improve glycemic control in Type 2 diabetic Hispanic adult patients in a private family practice clinic through the implementation of biweekly telephonic intervention focused on diabetes management by an advanced practice nurse/nurse practitioner. The project was guided by the chronic care model as a framework. The intervention was conducted over a 12-week period with 50 patients, ages 18 to 65. Data were collected from chart and log reviews, personal interviews, telephone calls, and use of questionnaires. Data were de-identified and used for secondary analyses. The interviews and telephone calls focused on self-care activities and daily practices related to the disease management. There were statistically significant reductions in fasting blood sugar (p=.042) and glycated hemoglobin results (p=.002) as well as improvement in diabetes self-care activities over the 12-week project timeframe. Qualitative data supported patients' recommitment to diabetes self-care management through daily blood sugar testing, attention to diet, exercise, and daily journaling. This project might lead to positive social change through improved disease management and better glycemic control. The project might also enable the Type 2 diabetic patients to make health and lifestyle choices that positively influence their day-to-day health.
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Lindahl, Oskar, and Viktor Dahlgren. "Powertrain Control for Improved Driver Comfort During Automated Gear Shifts." Thesis, Linköpings universitet, Fordonssystem, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-140132.
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Driveability is an important issue in the development of modern trucks. Comfort and sense of control are key for the driver. During a gear shift, the flywheel torque is lowered to zero before disengaging the clutch and then increased again after engaging the clutch. Lowering and increasing the flywheel torque creates movements in the cab. The previous developments of the gear shift functionality has had the purpose to maintain a good behaviour in the powertrain. This Master’s thesis has instead investigated whether it was possible to improve the cab comfort during autonomous gear shifts by altering the way it is performed. A measure of cab comfort has been developed through experiments and cooperation a test driver. The main differences between good and bad gear shifts were identified as the amplitudes of cab accelerations and jerk. Therefore, the goal was to minimize acceleration and jerk in order to improve the cab comfort. A model of how the powertrain affects the cab movements has been developed. Sub models of the powertrain, chassis and cab were developed individually and combined into one large model. The models performed well individually and the combined model was judged to be good enough for developing a controller. At the time of writing the existing controller had the purpose of preventing oscillations and jerk in the driveline. To avoid having to consider behaviour in the powertrain the developed controller were to control the existing controller. Two approaches have been investigated, open loop control and feedback control. The functionality of the open loop controller was to low pass filter inputs to the existing controller. The other approach was a feedback controller using the z-acceleration (upwards) as feedback. The purpose was to keep the acceleration low using a reference developed with experience from the comfort experiments. Simulations of the open loop controller showed that it was possible to alter the cab comfort by altering the engine torque. The comfort was improved in most parts of the gear shift and worsend in some parts. The feedback controller showed promising results in simulations. It was problematic to combine the existing controller with the developed controller since they have different purposes. By a fusion of the controllers there would be good opportunities to improve the gearshift with respect to both powertrain behaviour and cab comfort.
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Kritzinger, Pierre. "Improved nonparametric control charts for location based on runs-rules." Diss., University of Pretoria, 2011. http://hdl.handle.net/2263/31132.
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Numerous nonparametric or distribution-free control charts have been proposed and studied in
recent years; see, for example, the overview articles by Chakraborti et al. (2001), Chakraborti and
Graham (2007) and Chakraborti et al. (2010). Among the various nonparametric charts, the basic
Shewhart-type sign chart for case K (i.e. when the process parameters are known) proposed by Amin
et al. (1995) and the basic Shewhart-type precedence chart for case U (i.e. when the process
parameters are unknown) proposed by Chakraborti et. al. (2004) have received a lot of attention. For
example, Human et al. (2010) and Chakraborti et al. (2009a) extended the basic Shewhart-type sign
and precedence charts (which signals when the first plotting statistic plots on or outside the control
limits), respectively by incorporating runs-rules.
In this dissertation the focus is specifically on the nonparametric Shewhart-type sign and
precedence control charts. The goal is to further generalize these two charts by introducing improved
runs-rules in an attempt to enhance the out-of-control performance of these charts; specifically for
large (or larger) shifts. To evaluate the benefits of these new improved runs-rules sign and precedence
charts, their in-control and out-of-control run-length distributions are evaluated and studied; this is
done predominantly by using a Markov chain approach (for both case K and case U) coupled with the
idea of conditioning by expectation and the unconditioning (for case U, see, for example the work of
Chakraborti et al. (2009a), Chakraborti et al. (2004) and Chakraborti (2000)).
The dissertation consists of five chapters, a brief description of the contents is provided below:
Chapter 1 provides a brief introduction to Statistical Process Control. This will aid in familiarizing
the reader with concepts and terminology that are helpful to the following chapters.
Chapter 2 is dedicated to a discussion on the different methods to calculate the run-length
distribution of a control chart. The focus is on the Markov chain approach, since the Markov chain
approach is used in this dissertation to calculate the run-length distribution of the sign and precedence
charts with improved runs-rules incorporated.<br>Dissertation (MSc)--University of Pretoria, 2011.<br>Statistics<br>MSc<br>Unrestricted
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Gibson, Scott Brian. "Improved Dynamic Modeling and Robust Control of Autonomous Underwater Vehicles." Diss., Virginia Tech, 2018. http://hdl.handle.net/10919/84468.
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In this dissertation, we seek to improve the dynamic modeling and control of autonomous underwater vehicles (AUVs). We address nonlinear hydrodynamic modeling, simplifying modeling assumptions, and robust control for AUVs. In the literature, various hydrodynamic models exist with varying model complexity and with no universally accepted model. We compare various hydrodynamic models traditionally employed to predict the motion of AUVs by estimating model coefficients using least-squares and adaptive identifier techniques. Additionally, we derive several dynamic models for an AUV employing varying sets of simplifying assumptions. We experimentally assess the efficacy of invoking typical assumptions to simplify the equations of motion.
For robust control design, we develop a procedure for designing robust attitude controllers based on loop-shaping ideas. We specifically address the challenge of adjusting the desired actuator bandwidth in a loop-shaping design framework. Finally, we present a novel receding horizon H-infinity control algorithm to improve the control of autonomous vehicle systems working in high-disturbance environments, employing a Markov jump linear system framework to model the stochastic and non-stationary disturbances experienced by the vehicle. Our main results include a new Bounded Real Lemma for stability analysis and an output feedback H-infinity control synthesis algorithm.
This work uses numerical simulations and extensive field trials of autonomous underwater vehicles to identify and verify dynamic models and to validate control algorithms developed herein.<br>Ph. D.
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Marathe, Amar Ravindra. "Improved decoding for brain-machine interfaces for continuous movement control." Case Western Reserve University School of Graduate Studies / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=case1301667321.
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Zim, Bret E. "Improved Fabrication and Quality Control of Substrate Integrated Microelectrode Arrays." Thesis, University of North Texas, 2000. https://digital.library.unt.edu/ark:/67531/metadc2484/.
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Spontaneously active monolayer neuronal networks cultured on photoetched multimicroelectrode plates (MMEPs) offer great potential for use in studying neuronal networks. However, there are many problems associated with frequent, long-term use of MMEPs. The major problems include (1) polysiloxane insulation deterioration and breakdown, (2) and loss of gold at the gold electroplated indium-tin oxide (ITO) electrodes. The objective of this investigation was to correct these major problems. Quality control measures were employed to monitor MMEP fabrication variables. The phenotypes of polysiloxane degradation were identified and classified. Factors that were found to contribute most to insulation deterioration were (1) moisture contamination during MMEP insulation, (2) loss of the quartz barrier layer from excessive exposure to basic solutions, and (3) repetitive use in culture. As a result, the insulation equipment and methods were modified to control moisture-dependent insulation deterioration, and the KOH reprocessing solution was replaced with tetramethylguanidine to prevent damage to the quartz. The problems associated with gold electroplating were solved via the addition of a pulsed-DC application of gold in a new citrate buffered electroplating solution.
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Nguyen, Minh Nguyet. "Dengue virus transmission and case management for improved disease control." Thesis, Open University, 2016. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.702417.
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Dengue is the major arboviral disease in humans and is primarily transmitted through Aedes aegypti mosquitoes' bites. Better understanding of dengue virus (DENY) transmission and case management is needed to reduce morbidity and mortality. This thesis aimed to bridge existing knowledge gaps by investigating three main topics: The factors associated with human-to-mosquito DENV transmission remains poorly understood. We conducted the Ae. aegypti-feeding experiments on 208 laboratory-confirmed dengue patients: Plasma viremia levels were positively associated with DENV transmission, while illness day and antibody titers were independently correlated with a reduced risk of DENV transmission to mosquitoes. Physicians attending to dengue patients at outpatient clinics are ideally placed to communicate measures to limit DENV transmission in and around households. We explored knowledge, attitudes and practices of 50 physicians and 49 patients/caregivers on DENY transmission and prevention using semi-structured questionnaires. Both physicians and patients had an incomplete understanding of DENY transmission, leading to their inadequate attitudes and preventative practices. We measured the effectiveness of a 13% DEET-based repellent ·on febrile dengue patients compared to matched healthy controls (n=19 experiments). The repellent provided ~ 1 hour of Ae. aegypti repellency and no difference in protection between patients and controls, suggesting that while providing some benefit, duration of protection was limited and needed fi'equent reapplication. Early diagnosis and proper management are a prerequisite for reducing dengue mortality. We retrospectively described 55 fatal dengue cases at the Hospital for Tropical Diseases between 2008 and 2012. Females were predominant in study population (68%). Majority of patients (91 %) hospitalized with dengue shock syndrome. Other complications included respiratory distress (100%); severe bleeding (85%); severe liver involvement (76%); and renal failure (64%). The findings described manifestations associated with fatal outcome and identified knowledge gaps in dengue management. Overall, this thesis provided new insights into DENY transmission and clinical features of fatal dengue. The results also identified issues for public health that need improvement, e.g. opportunities for physicians to contribute more to public health by educating deng~e-affected families to perform relevant vector control.