Characterisation of electrohydrodynamic fluid accelerators comprising highly asymmetric high voltage electrode geometries

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University London.Electrohydrodynamics (EHD) is a promising research field with several trending applications. Even though the phenomenon was first observed centuries ago, there is very little research until the middle 20th century, as the mechanisms behind it were very poorly understood. To this date, the majority of research is based on the development of empirical models and the presentation of laboratory experiments. This work begins with an extensive literature review on the phenomenon, clarifying conflicts between researchers throughout the history and listing the findings of the latest research. The literature review reveals that there are very few mathematical models describing even the most important parameters of the EHD fluid flow and most are either empirical or greatly simplified. As such, practical mathematical models for the assessment of all primary performance characteristics describing EHD fluid accelerators (Voltage Potential, Electric Field Intensity, Corona Discharge Current and Fluid Velocity) were developed and are begin presented in this work. These cover all configurations where the emitter faces a plane or another identical electrode and has a cylindrical surface. For configurations where the emitter faces a plane or another identical electrode and has a spherical surface, Corona Discharge Current and Fluid Velocity models have been presented as well. Laboratory experiments and computer simulations were performed and are being thoroughly presented in Chapter 4, verifying the accuracy and usability of the developed mathematical models. The laboratory experiments were performed using two of the most popular EHD electrode configurations - wire-plane and needle-grid. Finally, the findings of this research are being summarized in the conclusion, alongside with suggestions for future research. The step-by-step development of the equipotential lines mathematical model is presented in Appendix A. Appendix B covers the mathematical proof that the proposed field lines model is accurate and that the arcs are perpendicular to the surface of the electrodes and to all of the equipotential lines

An open learning environment for the diagnosis, assistance and evaluation of students based on artificial intelligence

The personalized diagnosis, assistance and evaluation of students in open learning environments can be a challenging task, especially in cases that the processes need to be taking place in real-time, classroom conditions. This paper describes the design of an open learning environment under development, designed to monitor the comprehension of students, assess their prior knowledge, build individual learner profiles, provide personalized assistance and, finally, evaluate their performance by using artificial intelligence. A trial test has been performed, with the participation of 20 students, which displayed promising results

Analytical Estimation of the Electrostatic Field in Cylinder-Plane and Cylinder-Cylinder Electrode Configurations

This work presents analytical formulas for the estimation of the electrostatic field in cylinder-plane and cylinder-cylinder electrode configurations. Assuming a predefined potential difference between the electrodes and given their geometrical characteristics, these could be useful for the solution of numerous problems involving such electrode sets. Moreover, the voltage distribution around the electrodes is defined by providing equations either for the equipotentials at a given voltage ratio, or the exact estimation of the potential at any point in the surrounding space. Simplified expressions for critical engineering parameters such as the peak electric field and the field enhancement factor are also given

An Advanced eLearning Environment Developed for Engineering Learners

Monitoring and evaluating engineering learners through computer-based laboratory exercises is a difficult task, especially under classroom conditions. A complete diagnosis requires the capability to assess both the competence of the learner to use the scientific software and the understanding of the theoretical principles. This monitoring and evaluation needs to be continuous, unobtrusive and personalized in order to be effective. This study presents the results of the pilot application of an eLearning environment developed specifically with engineering learners in mind. As its name suggests, the Learner Diagnosis, Assistance, and Evaluation System based on Artificial Intelligence (StuDiAsE) is an Open Learning Environment that can perform unattended diagnostic, evaluation and feedback tasks based on both quantitative and qualitative parameters. The base architecture of the system, the user interface and its effect on the performance of postgraduate engineering learners are being presented

Evaluation of an intelligent open learning system for engineering education

In computer-assisted education, the continuous monitoring and assessment of the learner is crucial for the delivery of personalized education to be effective. In this paper, we present a pilot application of the Student Diagnosis, Assistance, Evaluation System based on Artificial Intelligence (StuDiAsE), an open learning system for unattended student diagnosis, assistance and evaluation based on artificial intelligence. The system demonstrated in this paper has been designed with engineering students in mind and is capable of monitoring their comprehension, assessing their prior knowledge, building individual learner profiles, providing personalized assistance and, finally, evaluating a learner's performance both quantitatively and qualitatively by means of artificial intelligence techniques. The architecture and user interface of the system are being exhibited, the results and feedback received from a pilot application of the system within a theoretical engineering course are being demonstrated and the outcomes are being discussed

Χαρακτηρισμός ηλεκτροϋδροδυναμικών επιταχυντών ρευστών που περιλαμβάνουν ηλεκτρόδια υψηλής τάσης ιδιαίτερα ασύμμετρων γεωμετριών

Electrohydrodynamics (EHD) is a promising research field with several trending applications. Even though the phenomenon was first observed centuries ago, there is very little research until the middle 20th century, as the mechanisms behind it were very poorly understood. To this date, the majority of research is based on the development of empirical models and the presentation of laboratory experiments. This work begins with an extensive literature review on the phenomenon, clarifying conflicts between researchers throughout the history and listing the findings of the latest research. The literature review reveals that there are very few mathematical models describing even the most important parameters of the EHD fluid flow and most are either empirical or greatly simplified. As such, practical mathematical models for the assessment of all primary performance characteristics describing EHD fluid accelerators (Voltage Potential, Electric Field Intensity, Corona Discharge Current and Fluid Velocity) were developed and are being presented in this work. These cover all configurations where the emitter faces a plane or another identical electrode and has a cylindrical surface. For configurations where the emitter faces a plane or another identical electrode and has a spherical surface, Corona Discharge Current and Fluid Velocity models have been presented as well. Laboratory experiments and computer simulations were performed and are being thoroughly presented in Chapter 4, verifying the accuracy and usability of the developed mathematical models. The laboratory experiments were performed using two of the most popular EHD electrode configurations - wire-plane and needle-grid. Finally, the findings of this research are being summarized in the conclusion, alongside with suggestions for future research. The step-by-step development of the equipotential lines mathematical model is presented in Appendix A.Η Ηλεκτροϋδροδυναμική (EHD) είναι ένα πολλά υποσχόμενο ερευνητικό πεδίο με αρκετές τάσεις εφαρμογών. Παρόλο που το φαινόμενο παρατηρήθηκε για πρώτη φορά πριν από αιώνες, υπάρχει πολύ λίγη έρευνα μέχρι τα μέσα του 20ου αιώνα, καθώς οι μηχανισμοί πίσω από αυτό ήταν πολύ ελάχιστα κατανοητοί. Μέχρι σήμερα, η πλειονότητα της έρευνας βασίζεται στην ανάπτυξη εμπειρικών μοντέλων και στην παρουσίαση εργαστηριακών πειραμάτων. Αυτή η εργασία ξεκινά με μια εκτενή βιβλιογραφική ανασκόπηση για το φαινόμενο, διευκρινίζοντας τις συγκρούσεις μεταξύ των ερευνητών σε όλη την ιστορία και παραθέτοντας τα ευρήματα της τελευταίας έρευνας. Η βιβλιογραφική ανασκόπηση αποκαλύπτει ότι υπάρχουν πολύ λίγα μαθηματικά μοντέλα που περιγράφουν ακόμη και τις πιο σημαντικές παραμέτρους της ροής ρευστού EHD και τα περισσότερα είναι είτε εμπειρικά είτε πολύ απλοποιημένα. Ως εκ τούτου, αναπτύχθηκαν και παρουσιάζονται σε αυτή την εργασία πρακτικά μαθηματικά μοντέλα για την αξιολόγηση όλων των πρωταρχικών χαρακτηριστικών απόδοσης που περιγράφουν επιταχυντές υγρών EHD (Δυναμικό, Ένταση Ηλεκτρικού Πεδίου, Ρεύμα Εκκένωσης Κορώνας και Ταχύτητα Ρευστού). Αυτά καλύπτουν όλες τις διαμορφώσεις όπου ο εκπομπός βλέπει ένα επίπεδο ή άλλο πανομοιότυπο ηλεκτρόδιο και έχει κυλινδρική επιφάνεια. Για διαμορφώσεις όπου ο πομπός βλέπει σε ένα επίπεδο ή άλλο πανομοιότυπο ηλεκτρόδιο και έχει σφαιρική επιφάνεια, έχουν επίσης παρουσιαστεί μοντέλα Ρεύματος Εκκένωσης Κορώνας και Ταχύτητας Ρευστού. Πραγματοποιήθηκαν εργαστηριακά πειράματα και προσομοιώσεις υπολογιστή και παρουσιάζονται διεξοδικά στο Κεφάλαιο 4, επαληθεύοντας την ακρίβεια και τη χρηστικότητα των αναπτυγμένων μαθηματικών μοντέλων. Τα εργαστηριακά πειράματα πραγματοποιήθηκαν χρησιμοποιώντας δύο από τις πιο δημοφιλείς διαμορφώσεις ηλεκτροδίων EHD - αγωγός-επιφάνεια και βελόνα-πλέγμα. Τέλος, τα ευρήματα αυτής της έρευνας συνοψίζονται στο συμπέρασμα, μαζί με προτάσεις για μελλοντική έρευνα. Η ανάπτυξη βήμα προς βήμα του μαθηματικού μοντέλου ισοδυναμικών γραμμών παρουσιάζεται στο Παράρτημα Α

Star-delta switches evaluation for use in grid-connected wind farm installations

Electrical generators are designed to perform best under permanent rotation velocity and fixed loads conditions. However, such ideal conditions are not practically feasible during the operation of real wind turbines. Generally, the voltage output of electrical generators can be regulated without redesigning the electrical or/and mechanical parts constituting such a system, by simply changing the connection of the generator to the grid from Star to Delta or by using combined windings. The present work attempts to investigate the behavior of grid-connected wind turbines with Star-Delta, Delta, and Star connection switches in a variety of simulation scenarios, by taking into consideration the influence of both internal and external factors such as the inertia factor and the wind speed