Optimisation of a fed-batch fermentation process typically uses the calculus of variations or Pontryagin's maximum principle to determine an optimal feed rate profile. This often results in a singular control problem and an open loop control structure. The singular feed rate is the optimal feed rate during the singular control period and is used to control the substrate concentration in the fermenter at an optimal level. This approach is supported by biological knowledge that biochemical reaction rates are controlled by the environmental conditions in the fermenter; in this case, the substrate concentration. Since an accurate neural net-based on-line estimation of the substrate concentration has recently become available and is currently employed in industry, we are therefore able to propose a method which makes use of this estimation. The proposed method divides the optimisation problem into two parts. First, an optimal substrate concentration profile which governs the biochemical reactions in the fermentation process is determined. Then a controller is designed to track the obtained optimal profile. Since the proposed method determines the optimal substrate concentration profile, the singular control problem is therefore avoided because the substrate concentration appears nonlinearly in the system equations. Also, the process is then operated in closed loop control of the substrate concentration. The proposed method is then called "closed loop optimal control". The proposed closed loop optimal control method is then compared with the open loop optimal feed rate profile method. The comparison simulations from both primary and secondary metabolite production processes show that both methods give similar performance in a case of perfect model while the closed loop optimal control provides better performance than the open loop method in a case of plant/model mismatch. The better performance of the closed loop optimal control is due to an ability to compensate for the modelling errors using feedback.

The objective of this thesis is to develop a strategy that allows robots to safely execute open-loop motion patterns for pre-computed time durations when facing interruptions in communication. By computing the time horizon in which collisions with other robots are impossible, this method allows the robots to move safely despite having no updated information about the environment. As the complexity of multi-robot systems increase, communication failures in the form of packet losses, saturated network channels and hardware failures are inevitable. This thesis is motivated by the need to increase the robustness of operation in the face of such failures. The advantage of this strategy is that it prevents the jerky and unpredictable motion behaviour which often plague robotic systems experiencing communication issues. To compute the safe time horizon, the first step involves constructing reachable sets around the robots to determine the set of all positions that can be reached by the robot in a given amount of time. In order to avoid complications arising from the non-convexity of these reachable sets, analytical expressions for minimum area ellipses enclosing the reachable sets are obtained. By using a fast gradient descent based technique, intersections are computed between a robot’s trajectory and the reachable sets of other robots. This information is then used to compute the safe time horizon for each robot in real time. To this end, provable safety guarantees are formulated to ensure collision avoidance. This strategy has been verified in simulation as well as on a team of two-wheeled differential drive robots on a multi-robot testbed.

Τα τελευταία χρόνια η ενεργειακή κρίση έχει αρχίσει και γίνεται ορατή σε όλες τις εκφάνσεις της καθημερινής ζωής, επηρεάζοντάς την σε σημαντικό βαθμό. Τα αποθέματα πετρελαίου λιγοστεύουν με ταχύτατους ρυθμούς ενώ η ζήτηση αυξάνεται με φρενήρεις ρυθμούς. Ταυτόχρονα, οι φυσικές καταστροφές, σημαντικό μέρος των οποίων αποδίδεται στην κλιματική αλλαγή, που με τη σειρά της αποδίδεται –εν μέρει- στην ρύπναση εξαιτίας της παραγωγής και χρήσης συμβατικών μορφών ενέργειας, και στη συνεχιζόμενη μόλυνση του περιβάλλοντος κατέστησαν αναγκαία την εύρεση και εφαρμογή εναλλακτικών μορφών παραγωγής ηλεκτρικής ενέργειας, φιλικές προς αυτό. Λύση στο αδιέξοδο αυτό φαίνεται να δίνουν οι Ανανεώσιμες Πηγές Ενέργειας καθώς σιγά-σιγά κατακτούν ολοένα και περισσότερο έδαφος στο χώρο της ενέργειας. Μορφές Ανανεώσιμων Πηγών Ενέργειας αποτελούν η αιολική ενέργεια, η ηλιακή, η υδροηλεκτρική, η ενέργεια από βιομάζα, η γεωθερμία, η παλιρροιακή ενέργεια, κ.α. οι οποίες αναπτύσσονται.Η παρούσα διπλωματική εργασία ασχολείται με την μελέτη της χρησης μιας καινοτόμας τεχνολογιας των φωτοβολταικών μονάδων με το όνομα ηλιακοί ιχνηλάτες.Αρχικά πραγματοποιείται εκτενής αναφορά στην βασική θεωρία της φωτοβολταικής τεχνολογίας δηλαδή στο φωτοβολταικό φαινόμενο,στα φωτοβολταικά κύταρρα και στην μοντελοποίηση του φωτοβολταικού κυτάρρου με την βοήθεια του προγραμματιστικού περιβάλοντος ΜΑTLAB.Στην συνέχεια παρουσιάζονται βασικές γνώσεις πάνω στην ηλιακή ακτινοβολία και την θέση του ηλίου σε σχέση με την γη που ειναι απαραίτητες αφου σε αυτες στηρίζονται οι βασικοί αστρονομικοί αλγόριθμοι που χρησιμοποιούν τα συστήματα ιχνηλάτισης του ηλίου που μελετώνται.Ακολουθεί εκτενής αναφορά στην θεωρία των συστημάτων ιχνηλάτισης ανοιχτού και κλειστού βρόχου καθως και στους σημαντικότερους αστρονομικούς αλγορίθμους που εχουν επινοηθεί μεχρι σήμερα.Επίσης γίνεται συγκριτική μελέτη με την βοήθεια προσομοιώσεων του ΜΑΤLAB μεταξύ των σταθερών πάνελ και αυτών με ιχνηλάτιση ανοιχτού βρόχου.Επίσης πραγματοποιείται η διάκριση μεταξύ μονοαξονικών και διαξονικών ηλιακών ιχνηλατών ανοιχτού και κλειστού βρόχου.Στο κεφάλαιο 5 παρατίθενται οι 2 αλγόριθμοι που κατασκευάσθηκαν ετσι ωστε να προσομοιώσουμε μέσω του ΜΑΤLAB την θέση του ηλίου κατα την διάρκεια μιας ολόκληρης ημέρας για οποιαδήποτε χρονολογία και τοποθεσία επυθημούμε καθως και για να υπολογίσουμε την ολική ευθεία, διάχυτη και ανακλώμενη ηλιακή ακτινοβολία εκείνης της ημέρας!Τρέχοντας λοιπόν μια ολοήμερη προσομοίωση λαμβάνουμε τα απαραίτητα στοιχεία(μετρήσεις) ωστε να να πραγματοποιήσουμε μια συγκριτική μελέτη μεταξύ των συστημάτων ιχνηλάτισης ανοιχτού βρόχου που χρησιμοποιούν τον αστρονομικό αλγόριθμο που δημιουργήσαμε και των ηλιακών ιχνηλατών κλειστού βρόχου που με την βοήθεια πυρανομέτρου μετρούν την ηλιακή ακτινοβολία. Παράλληλα χρησιμοποιώντας τον αλγόριθμο που κατασκευάσαμε για προσομοίωση της τροχιάς του ηλίου δημιουργήσαμε ενα πρόγραμμα στο MATLAB με το οποιο εισάγοντας τις γεωγραφικές συντεταγμένες του τόπου που μας ενδιαφέρει αλλα και την παγκόσμια ημερομηνία και ώρα παίρνουμε μια τρισδιάστατη απεικόνιση της θέσης στην οποία πρέπει να τοποθετήσουμε το σταθερό φωτοβολταικό μας πλαίσιο εαν θέλουμε να επυτήχουμε την μέγιστη απόδοση.Αυτή είναι μια πολυ σημαντική λεπτομέρεια αφου ετσι πραγματοποιείται και σύγκριση ολων των προηγούμενων με τα σταθερά πάνελ που ομως εχουν την δυνατότητα εποχιακής ρύθμισης.Τελος προτείνεται η βέλτιστη οικονομικά αλλα και ενεργειακά λύση ωστε να επυτήχουμε την υψηλότερη απόδοση. Ολοι οι αλγόριθμοι που χρησιμοποιήθηκαν περιγράφονται και επεξηγούνται αναλυτικά σε κάθε κεφάλαιο. / This analysis deals with the study of the use of an innovative technology for photovoltaic modules named Solar trackers.Initially it is being made extensive referaince to the basic theory of photovoltaic technology as the photovoltaic effect, the photovoltaic cells simulated with the help of programming environment of MATLAB.Also the basic knowledge of solar radiation and the position of the sun in relathion to earth are being illustrated since these are based on the astronomical algorithms that tracking systems use.There is also an extensive raiference to open and closed loop tracking systems as well as the most important astronomical algorithms have been devised up to now.Also a comparative study with the help of MATLAB simulations between fixed panels and with an open loop tracking system has been made.Last we made the distinction between single-axle and two axles solar trackers open and closed loop.At Chapter 5 lists the 2 algorithms constructed so as to simulate with MATLAB the position of the sun during a whole day for any date and location we desire and to estimate the total direct, diffuse and reflected sunlight that day!

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In this study a real-time open loop estimate of the disturbance displacement input to the tire and an external disturbance force, representing handling and aerodynamic forces, acting on the sprung mass of a quarter-car suspension test rig was generated. This information is intended for use in active control methods applied to vehicle suspensions. This estimate is achieved with two acceleration measurements as inputs to the estimator; one each on the sprung and unsprung masses. This method is differentiated from current disturbance accommodating control, bilinear observers, and preview control methods. A description of the quarter-car model and the experimental test rig is given. The equations of motion for the quarter-car model are derived in state space as well as a transfer function form. Several tests were run in simulation to investigate the performance of three integration techniques used in the estimator. These tests were first completed in continuous time prior to transforming to discrete time. Comparisons are made between the simulated and estimated displacement and velocity of the disturbance input to the tire and disturbance force input to the sprung mass. The simulated and estimated dynamic tire normal forces are also compared. This process was necessary to select preliminary values for the integrator transfer function to be implemented in real-time. Using the acceleration measurements from the quarter-car test rig, a quarter-car parameter optimization for use in the estimator was performed. The measured and estimated tire disturbance input, disturbance input velocity, and dynamic tire normal force signals are compared during experimental tests. The results show that the open loop observer provides estimates of the tire disturbance velocity and dynamic tire normal force with acceptable error. The results also indicate the quarter-car test rig behaves linearly within the frequency range and amplitude of the disturbance involved in this study. The resultant access to the disturbance estimate and dynamic tire force estimate in real-time enables pursuit of novel control methods applied to active vibration control of vehicle suspensions. / Master of Science

Maintenance of stable arterial blood pressure during orthostatic challenges is a major problem after spinal cord injury (SCI). Since early participation in rehabilitation is critically important in reducing long term morbidity, recovering the ability to regulate blood pressure during therapy is essential for individuals with SCI. The objective of our study was to investigate short term cardiovascular function of able-bodied (AB), paraplegic (PARA) and tetraplegic (TETRA) subjects in response to head up tilt (HUT) as an early indicator of autonomic damage that might forewarn of future orthostatic regulatory problems. We acquired cardiovascular variables from able-bodied (AB; n=11), paraplegic (PARA; n=5) and tetraplegic (TETRA; n=5) subjects in response to HUT. The SCI patients in both groups were in their first two months post injury. Data were recorded at rest and during 7 min each at 20??, 40??, 60?? and 80?? HUT. Techniques used to estimate regulatory capability and reflex activity included: Mean values and spectral power of heart rate (HR) and arterial blood pressure (BP), baroreflex sequence measurements and cross correlation between HR and systolic blood pressure (SBP). An index of baroreflex sensitivity (BRS), baroreflex effectiveness index (BEI), and the percentage occurrence of systolic blood pressure (BP) ramps and baroreflex sequences were calculated from baroreflex sequence measurements. The spectral power of HR and BP, the cross correlation of systolic BP and heart rate (HR) were examined in low frequency (LF: 0.04-0.15 Hz) and high frequency (HF: 0.15-0.4 Hz) ranges. The BRS index was significantly (p andlt; 0.05) decreased from supine to 80o HUT in AB and TETRA. This index in PARA was the lowest at each tilt position in the three groups, and decreased with tilt. The percentage of heart beats involved in systolic BP ramps and in baroreflex sequences significantly (pandlt;0.05) rose from supine to 80o HUT in AB, was relatively unchanged in PARA and declined in TETRA. Both of these indexes were significantly (pandlt;0.05) lowerin the SCI than in the AB group at each tilt level. The BEI values were greatest in AB, and declined with tilt in all groups. Spinal cord injured patients had less power of BP and HR fluctuations than AB in both LF and HF regions. The LF spectral power of BP and HR increased with tilt in AB, remained unchanged in PARA and decreased in TETRA. The HF spectral power of HR decreased in all three groups. The peak HR / BP cross correlation in the LF region was greatest in AB, and significantly (pandlt;0.05) increased during HUT in AB, remained fairly constant in PARA, and declined in TETRA. The peak cross correlation in the HF region significantly (pandlt;0.05) decreased with tilt in all groups, and the SCI group had lower values than AB at each tilt level. We conclude that both PARA and TETRA had a smaller percentage of SBP ramps, BRS, and lower BEI than AB, likely indicating decreased stimulation of arterial baroreceptors, and less engagement of feedback control. The mixed sympathetic, parasympathetic innervations of paraplegics, or their elevated HR, may contribute to their significantly lower BRS. Our data indicate that the pathways utilized to evoke baroreflex regulation of HR are compromised by SCI and this loss may be a major contributor to the decrease in orthostatic tolerance following injury.

Le thème général exploré dans cette recherche doctorale est "la Concurrence et la Convergence Fiscales". Examiner les concepts de concurrence et convergence fiscales d'une manière intégrée constitue un objectif important en soi. Cela permet, jusqu'à un certain point, d'apporter une vision innovatrice au problème étudié. Jusqu'ici, la littérature sur la concurrence fiscale ne suggère pas que les taux d'imposition convergent dans l'une ou l'autre direction. Les résultats principaux d'un modèle de concurrence fiscale classique avec des pays symétriques sont que, 1- la mobilité du capital induit un taux d'imposition trop bas par rapport à l'optimum social ; 2- il existe une corrélation négative entre la mobilité du capital et le taux d'imposition sur le capital ; 3- une harmonisation vers le haut des taux d'imposition des capitaux peut produire une amélioration au sens de Pareto. Bien que ces trois points représentent une vision simplificatrice et réductrice d'une longue et riche littérature, ils sont globalement corrects. Un deuxième objectif du travail est de confronter la théorie à la réalité empirique. Cette thèse est composée de "chapitres". Les chapitres 2 à 5 sont constitués, chacun d'un article dans son intégralité. Ceci signifie que le lecteur va retrouver dans chaque chapitre un papier avec introduction, développement et conclusions, et en cas de publication de l'article, une copie de celui-ci dans son format de présentation original. Le chapitre 6 contient les conclusions finales. Bien que chacune des parties constitue un composant isolé, l'enchainement garde un développement logique. Le chapitre 2 définit l'impôt sur lequel on souhaite travailler et présente la littérature sur les taux d'imposition effective avec quelques extensions. Une fois défini l'impôt sur le capital comme l'instrument sur lequel on centre notre attention, le chapitre 3 développe un modèle de concurrence fiscale. Le chapitre 4 observe la concurrence fiscale entre pays et fait un lien avec les mesures de convergence présentées dans le chapitre suivant. D'une manière similaire, le chapitre 5 tente d'observer la convergence fiscale entre pays d'une façon empirique.

Multiphase flow is associated with concurrent flow of more than one phase (gas-liquid, liquid-solid, or gas-liquid-solid) in a conduit. The simultaneous flow of these phases in a flow line, may initiate a slug flow in the pipeline. Hydrodynamic slug flow is an alternate or irregular flow with surges of liquid slug and gas pocket. This occurs when the velocity difference between the gas flow rate and liquid flow rate is high enough resulting in an unstable hydrodynamic behaviour usually caused by the Kelvin-Helmholtz instability. Active feedback control technology, though found effective for the control of severe slugs, has not been studied for hydrodynamic slug mitigation in the literature. This work extends active feedback control application for mitigating hydrodynamic slug problem to enhance oil production and recovery. Active feedback Proportional-Integral (PI) control strategy based on measurement of pressure at the riser base as controlled variable with topside choking as manipulated variable was investigated through Olga simulation in this project. A control system that uses the topside choke valve to keep the pressure at the riser base at or below the average pressure in the riser slug cycle has been implemented. This has been found to prevent liquid accumulation or blockage of the flow line. OLGA (olga is a commercial software widely tested and used in oil and gas industries) has been used to assess the capability of active feedback control strategy for hydrodynamic slug control and has been found to give useful results and most interestingly the increase in oil production and recovery. The riser slugging was suppressed and the choke valve opening was improved from 5% to 12.65% using riser base pressure as controlled variable and topside choke valve as the manipulated variable for the manual choking when compared to the automatic choking in a stabilised operation, representing an improvement of 7.65% in the valve opening. Secondly, implementing active control at open-loop condition reduced the riser base pressure from 15.3881bara to 13.4016bara.

Boom cranes are one of the most dynamically complicated types of cranes because they possess rotational joints as opposed to the linear tracks of bridge and gantry cranes. In addition, if the boom crane is placed on a mobile base, additional complexity is added to the system. However, mobile boom cranes have huge potential benefits as they can be quickly transported from one location to another. Furthermore, if they utilize their mobile base during lifting operations, then they can have an extremely large workspace. All cranes share the same limiting weakness; the payload oscillates when the crane moves. A command-generation approach is taken to control the payload oscillation. Input shaping is one such command-generation technique that modifies the original reference command by convolving it with a series of impulses. The shaped command produced by the convolution can then move the crane without inducing payload oscillation. Input shaping can accommodate parameter uncertainties, nonlinearities, multiple modes of vibration, and has been shown to be compatible with human operators. This thesis focuses on three aspects of mobile boom cranes: 1) dynamic analysis, 2) input-shaping control, and 3) experimental testing. A majority of the thesis focuses on analyzing and describing the complicated dynamics of mobile boom cranes. Then, various input-shaping controllers are designed and tested, including two-mode shapers for double-pendulum dynamics. In order to experimentally verify the simulation results, a small-scale mobile boom crane has been constructed. The details of the mobile boom crane and its important features are presented and discussed. Details of the software used to control the crane are also presented. Then, several different experimental protocols are introduced and the results presented. In addition, a set of operator performance studies that analyze human operators maneuvering the mobile boom crane through an obstacle course is presented.

The marine boundary layer (MBL) is the region where energy, momentum and masses are exchanged between the ocean surface and the free troposphere. The lack of observations with high vertical resolution over the ocean significantly restricts the understanding of the complex physical processes that occur inside the MBL. The relatively short vertical extent of the MBL (average about 1~2 km) and the frequent cloudiness at its top make probing the MBL extremely difficult from the space. Several features of the Global Positioning System (GPS) radio occultation (RO) technique suggest that it has a great potential for sensing the MBL. These features include global coverage, high vertical resolution, and the ability of GPS signals to penetrate clouds.Over moist marine areas, a large negative moisture gradient often exists across the thermal inversion capping the MBL, which can cause super-refraction (SR) or ducting. A large number of high-resolution soundings have shown that SR occurs about 90% of the time in a year over the subtropical and tropical oceans and even 50% at high-latitudes during the summer. In the presence of SR, the reconstruction of refractivity from RO data becomes an ill-posed inverse problem, i.e., a given RO bending angle profile is consistent with a continuum (an infinite number) of refractivity profiles. The standard Abel retrieval gives the minimum refractivity solution of the continuum and thus produces the largest negative bias, consistent with a negative bias that is often present in the retrieved refractivity profiles in the moist lower troposphere. Simulation studies indicate a large variation of the negative refractivity biases (could be over -15%). The impact of diffraction effects and the open-loop receiver tracking on the bending angle and refractivity retrievals are assessed. A novel approach is developed and tested to reconstruct the vertical refractivity structure within and below the SR layer, which yields a much-improved retrieval, especially below the SR layer (less than 0.5% error). Such a reconstruction method should greatly enhance our ability to measure the MBL globally using the GPS RO technique as well as to improve the MBL parameterizations used in weather and climate models.