Σκοπός της παρούσας διδακτορικής διατριβής είναι η ανάπτυξη προτύπων πεπερασμένων στοιχείων ικανών να προσομοιώσουν την μορφική και δυναμική απόκριση ευφυών δοκών με διαστρωματική αποκόλληση. Έμφαση δίνεται στη χρήση πιεζοηλεκτρικών διεγερτών και αισθητήρων. Στη πρώτη ενότητα πραγματοποιούνται πειραματικές μετρήσεις σε δοκούς με αποκόλληση χρησιμοποιώντας διάφορες μεθοδολογίες διέγερσης και δειγματοληψίας, οι οποίες περιλαμβάνουν πιεζοηλεκτρικά στοιχεία (actuators,sensors) εκτός των κλασικών μεθόδων (shaker, accelerometer). Από τις πειραματικές μετρήσεις διαπιστώνονται οι δυνατότητες χρήσης πιεζοηλεκτρικών στοιχείων ενώ ανιχνεύεται και ποσοτικοποιείται η επίδραση της ύπαρξης και έκτασης αποκόλλησης στα μορφικά χαρακτηριστικά των δοκών. Στη συνέχεια διατυπώνονται μοντέλα μεσομηχανικής αποσκοπώντας στη προσομοίωση της ηλεκτρομηχανικής συμπεριφοράς ευφυών δοκών με αποκόλληση. Τα πρότυπα αυτά είναι συζευγμένα ηλεκτρομηχανικά και με τη χρήση κατάλληλου πεπερασμένου στοιχείου δοκού οδηγούν στο ηλεκτρομηχανικό σύστημα το οποίο χρησιμοποιείται για να προβλέψει τη στατική και μορφική απόκριση δοκών με διαστρωματική αποκόλληση. Στην επόμενη ενότητα τα πρότυπα μεσομηχανικής καθώς και το πεπερασμένο στοιχείο επεκτείνονται, έτσι ώστε να επιβάλλονται με φυσικό τρόπο συνθήκες επαφής και περιορισμού της οριζόντιας κίνησης (τριβής) μεταξύ των δύο μερών της αποκόλλησης. Το συζευγμένο μη‐γραμμικό ηλεκτρομηχανικό σύστημα που προκύπτει χρησιμοποιείται για να προσδιορίσει τη μεταβατική απόκριση δοκών με αποκόλληση και επαληθεύεται με πειραματικές μετρήσεις. Τέλος παρουσιάζεται ένα δισδιάστατο πρότυπο πεπερασμένο στοιχείο ευφυούς δοκού με αποκόλληση. Στο πρότυπο αυτό τα μοντέλα μεσομηχανικής επεκτείνονται περιλαμβάνοντας μεταβλητό πεδίο επίπεδων και εγκάρσιων αξονικών μετατοπίσεων, αποτελώντας τις δύο διαστάσεις του μοντέλου ώστε να προβλέψει τη στατική, μορφική και δυναμική απόκριση δοκών μεγάλου πάχους με αποκόλληση σε υψηλές συχνότητες. Χρησιμοποιείται για να προσομοιάσει συμμετρικές κατά το πάχος ιδιομορφές και την κυματική διάδοση υψηλών συχνοτήτων ευφυών δοκών με αποκόλληση. Τέλος τα μοντέλα εφαρμόζονται για τον περαιτέρω προσδιορισμό της βλάβης μέσα από την απόκριση χρόνου‐συχνότητας. / -

During this thesis, it has been proved that the electrical conductivity of multilayered and electrically anisotropic carbon fiber materials can be expressed by an equivalent second order tensor, which is equal to sum of each layer’s electrical conductivity tensor. The aforementioned equivalent electrical conductivity tensor is valid assuming that the material’s thickness is negligible compared to the other dimensions of the body. The mathematical expression for the prediction of the electrical conductivity of a multilayered material for any stacking sequence, is based on the electric current conservation, and was validated using different methods. Each layer’s electrical conductivity was experimentally studied at the two principal directions. Transverse to the fibers’ direction, an empirical model was developed for the prediction of the electrical conductivity as a function of the layer’s thickness, of the fibre volume fraction and of temperature. All cases involved the study of multidirectional and unidirectional carbon fiber materials without the presence of matrix (porous form – CF preform) as well as in the presence of polymeric matrix (CFRP). The validation of the equivalent tensor was achieved through three different ways: a) through the measurement of the electric resistance, for various stacking sequences, b) through the Joule heating effect, by recording and comparing the developing temperature field to the respective numerically calculated, c) through 3D numerical models which approximate the analytical solution of the 2D domain problem. Moreover using the finite difference method, certain electrothermal models were developed in order to study the temperature field for different stacking sequences. The electrical problem can be expressed by an elliptic PDE, for the case where the material is electrically anisotropic and homogeneous, or non-homogeneous. On the other hand, the transient heat transfer problem involves the case where the material is thermally anisotropic and homogeneous. Using the equivalent tensor, the 3D domain problem is simplified to a 2D domain problem resulting in less computational requirements for the solution of the problem. The present research study could be used in a plethora of application, such as the development of carbon fibre reinforced heating elements (direct heating CFRP molds) as well as damage detection in multidirectional composite materials with electrical conductive reinforcement. / Κατά τη διάρκεια της παρούσας διδακτορική διατριβής, αποδείχθηκε ότι η ηλεκτρική αγωγιμότητα των πολύστρωτων και ηλεκτρικά ανισότροπων υλικών με ίνες άνθρακα, μπορεί να εκφραστεί από έναν ισοδύναμο τανυστή δεύτερης τάξης, ο οποίος είναι το άθροισμα των τανυστών κάθε στρώσης. Ο ισοδύναμος τανυστής ισχύει υποθέτοντας ότι το πάχος συγκριτικά με τις υπόλοιπες διαστάσεις του υλικού είναι πολύ μικρό. Η μαθηματική έκφραση με την οποία μπορεί να προβλεφθεί η ηλεκτρική αγωγιμότητα ενός πολύστρωτου υλικού για οποιαδήποτε αλληλουχία στρώσεων αποδείχτηκε με συστηματικό τρόπο και βασίζεται στην αρχή διατήρησης του ηλεκτρικού φορτίου. Η ηλεκτρική αγωγιμότητα κάθε στρώσης μελετήθηκε πειραματικά στις δύο κύριες διευθύνσεις. Κάθετα στη διεύθυνση των ινών αναπτύχθηκε ένα εμπειρικό μοντέλο πρόβλεψης της ηλεκτρικής αγωγιμότητας συναρτήσει του πάχους της στρώσης, της περιεκτικότητας σε ίνες άνθρακα και της θερμοκρασίας. Σε όλες τις περιπτώσεις μελετήθηκαν πολύστρωτα υλικά ινών άνθρακα χωρίς μήτρα (πορώδης μορφή-CF preforms) και με πολυμερική μήτρα (CFRPs). Η επιβεβαίωση της εγκυρότητας του ισοδύναμου τανυστή έγινε με τρεις διαφορετικούς τρόπους: α) μέσω μετρήσεων της ηλεκτρικής αντίστασης, για διαφορετικές αλληλουχίες στρώσεων, β) μέσω του φαινομένου Joule, καταγράφοντας και συγκρίνοντας το αναπτυσσόμενο θερμοκρασιακό πεδίο με το θερμοκρασιακό πεδίο που υπολογίζεται αριθμητικά, γ) μέσω τρισδιάστατων αριθμητικών μοντέλων όπου τείνουν στην αναλυτική λύση του δισδιάστατου προβλήματος. Στη συνέχεια αναπτύχτηκαν ηλεκτροθερμικά μοντέλα με τη μέθοδο των πεπερασμένων διαφορών με σκοπό τη μελέτη του θερμοκρασιακού πεδίου για διαφορετικές αλληλουχίες στρώσεων. Το ηλεκτρικό πρόβλημα εκφράζεται από μία ελλειπτική διαφορική εξίσωση όπου το υλικό είναι ηλεκτρικά ανισότροπο και ομογενές ή μη ομογενές ενώ το θερμικό πρόβλημα είναι θερμικά ανισότροπο και ομογενές. Χρησιμοποιώντας τον ισοδύναμο τανυστή το τρισδιάστατο πρόβλημα μετατρέπεται σε ένα δισδιάστατο πρόβλημα με αποτέλεσμα να απαιτούνται λιγότεροι πόροι για την επίλυση του προβλήματος. Η συγκεκριμένη εργασία μπορεί να χρησιμοποιηθεί σε μία πληθώρα εφαρμογών όπως στην ανάπτυξη και στη λειτουργία θερμαινόμενων στοιχείων ενισχυμένων με ίνες άνθρακα (καλούπια όπου το θερμαντικό στοιχείο το αποτελούν οι ίνες άνθρακα) αλλά και στην ανίχνευση βλάβης συνθέτων υλικών με αγώγιμη ενίσχυση.

Plusieurs industries manipulent des substances liquides et gazeuses qui circulent souvent dans de longues canalisations. La technique d'ondes guidées est couramment utilisée dans ce domaine. Cette technique est en progrès continu. Dans cette thèse, un système d'inspection a été conçu et développé. Il est basé sur des transducteurs piézoélectriques qui génèrent des ondes guidées de torsion pouvant se propager le long du tube testé. Les signaux réfléchis des défauts et singularités rencontrés sont détectés aussi par des capteurs piézoélectriques. Des simulations numériques utilisantpar la méthode d'éléments finis standard et la méthode Wave Finite Element(WFEM) ont été effectuées afin de vérifier et de visualiser le phénomène de propagation des ondes dans des tubes intacts et endommagés. Un ensemble de tests a été mis en place sur des tubes droits et courbés avec deux matériaux différents: PVC et acier. L'interaction entre les ondes générées et les défauts usinés a été prouvée.Les résultats numériques et expérimentaux confirment certaines caractéristiques spécifiques concernant le coefficient de réflexion de l'onde. Par la suite, un pipeline industriel d'environ soixante mètres de long et contenant plusieurs défauts et singularités a été testé par le système d'inspection. Les signaux enregistrés ont soumis certains traitements numériques afin de les rendre exploitables. Les signaux traités sont analysés afin d'identifier et de distinguer les réflexions des défauts de celles des singularités structurés. La méthode WFEM a été employée pour construire une base de données numérique des coefficients de réflexion en variant la profondeur et les extensions axiale et circonférentielle du défaut modélisé. Le calcul a été établi en fonction de la fréquence. La corrélation des tailles des défauts est effectuée en balayant la base de données numérique pour trouver la combinaison appropriée de dimensions pour un défaut donné. Les réflexions à partir des singularités structurées (coudes, blocs de béton, colliers, et les soudures) sont traitées ainsi en comparant des coefficients de réflexion obtenus par WFEM à ceux évalués expérimentalement. Enfin, on a étudié numériquement l'effet de la position angulaire d'un défaut sur les coefficients de réflexion et de transmission tout en excitant à différents types d'ondes. La méthode WFE est aussi utilisée pour effectuer le calcul. Cette étude donne un guide à la localisation circonférentielle des défauts dans les tubes. / Long pipelines are widely used in several industries transporting liquid or gas. The guided wave technique is commonly used in this field and it is under continuing progress. In this thesis, an inspection system has been designed and developed. Piezoelectric transducers are employed to generate torsional guided waves that could propagate along the tested pipe; and receive reflected signals from encountered features and damages. Numerical simulations using standard FE and Wave Finite Element methods have been carried out in order to verify and visualize the wave propagation phenomenon in both intact and damaged pipes. A set of tests has been performed on straight and curved pipes with two different materials: PVC and steel. The interaction between generated waves and machined defects has been proven. Numerical and experimental results confirm some specific features in the wave reflection coefficient. Thereafter, an industrial pipeline of about sixty meters long and containing several features has been tested by the inspection system.Recorded signals had submitted some numerical treatments in order to make them interpretable. Processed signals are analyzed to identify defects reflections from structured singularities echoes. The Wave Finite Element Method (WFEM) has been used to construct a numerical database of reflection coefficients from modelled defects by varying thickness, axial and circumferential extents. Calculation was made depending on frequency. The approximation of defect sizes is carried out by sweeping the numerical database to find the suitable combination of dimensions fora given defect. Reflections from structural singularities (elbows, concrete blocks,clamps, and welds) are treated as well by comparing reflection coefficients obtained by WFEM to those evaluated experimentally. Finally, a numerical investigation deals with the effect of defect angular-position on reflection and transmission coefficients while exciting by different types of waves. The spectral method Wave Finite Element has been used to carry out calculation. This study gives guidance to circumferential localization of defects in pipes.

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Loss or partial loss of eye sight can have major effect on quality of person's life. One of the most common diseases, which causes loss or partial loss of eye sight are diabetic retinopathy and age releated macular degeneration. Both of these diseases can be prevented or mediated by early detection and proper treatment. The fundus camera, which is used to capture eye retina, has had major effect on increasing quality and speed of early detection. Images captured by fundus camera can be automatically analyzed in order to detect any possible signs of retina damage. This thesis proposes one possible way of automating this process. First part of this thesis describes eye, its diseases and capturing technology. Second part then proposes way of automating detection process and its implementation. Lastly, the results are evaluated.

In this Diploma Thesis, an interaction of genotoxic environmental pollutant 2-nitrofluorene with a double-stranded calf thymus DNA has been studied using a hanging mercury drop electrode (HMDE) as an electrochemical sensor. Two types of DNA damage were investigated and electrochemically detected (using cyclic voltammetry and differential pulse voltammetry): (i) The DNA damage caused by the direct interaction with 2-nitrofluorene and (ii) the DNA damage caused by short-lived radicals generated by the electrochemical reduction of the nitro group in 2-nitrofluorene. For the study of direct interaction, HMDE was modified by DNA and the interaction of DNA with 2-nitrofluorene was studied, after their incubation, right at the HMDE surface (adsorptive transfer stripping technique) or the DNA was preincubated with 2-nitrofluorene and, subsequently, the interaction was studied voltammetrically (DNA titration technique). Using both detection techniques, the formation of DNA - 2-nitrofluorene complex was observed and the mutual interaction was interpreted as an intercalation between the DNA base pairs, although such interaction was not clearly confirmed by UV-visible absorption spectroscopy. An electrostatic binding of 2-nitrofluorene on DNA sugar-phosphate backbone was partially formed at low concentrations of...

Structural health monitoring (SHM) is damage detection strategy for aerospace, civiland mechanical infrastructure. This project tries to show that Lamb waves, that are being generated and sensed with piezoelectric transducers, can be used for damage detection in a SHM system. For these piezoelectric transducers to work, filtering and amplification circuits needs to be connected to them. This report include the design,simulation, assembly and testing of these circuits. Due to lack of time, it was not possible to generate and sense actual Lamb waves. The result of the thesis is thatsimulations and tests show that it is possible to generate and sense Lamb waves for damage detection in a SHM system / Structural health monitoring (SHM) är en skadedetekteringsstrategi för flyg-,civil- och mekanisk infrastruktur. Detta projekt försöker visa att Lambvågor, som genereras och avkänns med piezoelektriska givare, kan användas för skadedetektering i ett SHM-system. För att dessa piezoelektriska givare ska fungera krävs att filtrerings- och förstärkningskretsar är anslutna till dem. Denna rapport inkluderar design, simulering, montering och testning av dessa kretsar. På grund av tidsbrist var det inte möjligt att generera eller avkänna Lambvågor. Resultatet av examensarbetet är att simuleringar och tester visar att det är möjligt att generera och avkänna Lambvågor för skadedetektering i ett SHM-system.

[pt] Dentre as diversas metodologias de detecção de danos, destacam-se os métodos de identificação de danos baseados na resposta da vibração (Vibration-based damage identification - VBDI), uma vez que a deterioração presente em elementos estruturais influencia diretamente na resposta dinâmica global e local da estrutura ocasionando alterações nos parâmetros dinâmicos. As diferentes abordagens encontradas na revisão de literatura para detecção dinâmica de danos focam principalmente em estruturas unidimensionais ou retas, que, por sua vez, podem não representar o comportamento dinâmico real de estruturas arrojadas como pontes e passarelas com geometria diferenciada. Alguns índices modais, nomeadamente curvatura modal, flexibilidade modal e energia de deformação modal, foram avaliados para uma passarela de aço com geometria curva. Para isso utilizou-se um modelo de elementos finitos da mesma, de onde foram extraídos os modos de vibração tridimensionais. Além disso, um índice recentemente proposto, denominado vetor resultante, que incorpora coordenadas modais tridimensionais, também é avaliado e comparado aos índices mencionados anteriormente. Os resultados mostram que a precisão dos índices na localização de danos está correlacionada com a região da estrutura onde o dano se encontra. Conclui-se então que para detecção de dano em uma estrutura real, é necessário que se utilize mais de um índice de dano. O impacto da magnitude do dano na acurácia dos índices é também estudado. A influência do dano nas vigas adjacentes e como isso se reflete nos índices também é investigada, a fim de evitar ambiguidade na localização de danos, e para direcionar corretamente programas de inspeção e monitoramento da integridade estrutural. / [en] Among the various damage detection methodologies, the Vibration-based damage identification (VBDI) methods stand out, since the deterioration present in structural elements directly influences the global and local dynamic response of the structure, causing changes in the dynamic parameters. The different approaches found in the literature review for dynamic damage detection focus mainly on one-dimensional or straight structures, which in turn may not represent the actual dynamic behavior of bold structures such as bridges and footbridges with different geometry. Some modal indices, namely modal curvature, modal flexibility, and modal strain energy were evaluated for a steel footbridge with curved geometry. For this purpose, a finite element model of it was used, from which the three-dimensional mode shapes were extracted. In addition, a recently proposed index, called resultant vector, which incorporates three-dimensional modal coordinates, is also evaluated and compared to the aforementioned ones. The results show that the accuracy of the indices for damage localization is correlated with the region of the structure where the damage is located. It is then concluded that for damage detection in a real structure, it is necessary to use more than one damage index. The impact of the damage magnitude on the accuracy of the indices is also studied. The influence of damage in adjacent beams and how this is reflected in the indices is also investigated in order to avoid ambiguity in damage location, and to correctly direct inspections and structural integrity monitoring programs.

[pt] As estruturas civis durante toda a sua vida útil estão sujeitas a diversas ações de deterioração, desgastes ou corrosão de seus membros, que podem gerar variações em suas características físicas. Estas ações podem causar danos ao seu funcionamento, podendo chegar até ao colapso, em casos mais extremos. Além disso, o avanço tecnológico que permite a concepção de estruturas cada vez mais esbeltas, e que geram assim possíveis vibrações excessivas, elevam o monitoramento estrutural a um patamar de extrema importância e atenção na ótica dos gestores desses sistemas. Particularmente, no caso de obras de infraestrutura como pontes e passarelas, as grandes dimensões são características significativas que tornam as práticas de monitoramento e inspeção mais difíceis. Dessa forma, com o objetivo auxiliar no monitoramento estrutural e direcionar inspeções visuais, diversos métodos de identificação de danos são estudados com base nas características dinâmicas das estruturas, como as frequências naturais e os modos de vibração. A revisão de literatura, porém, demonstra que há uma dificuldade na aplicação desta identificação em estruturas mais complexas de grande porte. Assim, este trabalho visa estudar esta dificuldade e propor uma solução baseada na construção de um índice, composto pelos modos de vibração. Além disso, através da aplicação de algoritmos de aprendizado de máquina e de reconhecimento de padrões, como as Redes Neurais Artificiais (RNAs), propõese aumentar a eficiência do processo de localização espacial e quantificação dos danos. Em seguida, a metodologia proposta é, então, aplicada em um modelo de passarela metálica inspirado em uma estrutura real presente na região do Terminal Centro Olímpico da cidade do Rio de Janeiro – RJ. A identificação de danos é estudada através da aplicação do índice proposto, incorporando as redes neurais e avaliando do impacto da variação dos parâmetros da RNA na eficiência global da detecção. / [en] Civil structures are subjected to different deterioration and corrosion actions throughout their entire service life, which can generate variations in their physical characteristics. These actions can cause damage to its functioning, and possibly leading to collapse in more severe cases. In addition, technology development which allows the design of increasingly slender structures, can produce excessive vibrations, which elevates the importance ofstructural monitoring to a higher level from the perspective of infrastructure managers. Particularly, in the case of bridges and walkaways, due to their large dimensions make monitoring and inspection even more difficult. Thus, with the aim of providing methods to assist in structural monitoring and facilitate visual inspections, several damage identification methods are investigated, which are based on structures dynamic characteristics, such as natural frequencies and mode shapes. The conducted literature review revealed that there is a difficulty in applying these identification methods in large-scale and complex structures. Thus, this research aims to study these barriers and propose a solution based on the development of a new damage index based on the structure s mode shapes. Furthermore, through the application of machine learning algorithms and pattern recognition, such as Artificial Neural Networks (ANN), it is proposed to increase the efficiency of the damage identification and quantification process. Then, the proposed methodology is tested numerically on a steel footbridge model inspired by a real structure located in the region of the Olympic Center Terminal, in the city of Rio de Janeiro – RJ. The damage identification method is studied through the application of the proposed damage index, incorporating the neural network and assessing the impact of ANNs parameters variation in the global efficiency of the damage detection method.

No description available.