El benestar psicològic, entès com la vessant psicològica que forma part del concepte més ampli de qualitat de vida, constitueix un àmbit d'estudi en expansió. Tot i tenir un passat més breu en comparació amb d'altres constructes psicosocials, cada vegada investigadors de les més diverses disciplines s'afegeixen a la llista d'estudiosos que fan del benestar psicològic un dels seus objectes d'investigació. Amb tot, l'estudi del benestar psicològic en l'adolescència constitueix probablement un dels àmbits en els quals la necessitat de seguir avançant es fa més evident. El seu estudi en subjectes adolescents té, a més, un doble interès. Per una part, els canvis i transicions que nois i noies experimenten durant l'adolescència comporten amb freqüència que sigui un període estressant per a molts d'ells/es, amb implicacions importants per al seu benestar psicològic. Aprofundir en el seu coneixement durant aquest període té un interès més enllà de l'estrictament científic i permet el disseny de programes de prevenció més ajustats a les problemàtiques que els/les adolescents puguin estar experimentant. L'exploració dels elements del benestar psicològic constitueix una de les estratègies d'aproximació al seu estudi. En aquesta tesi doctoral s'han seleccionat alguns dels elements que de la literatura científica es desprèn que tenen una connexió més estreta amb el benestar psicològic i que són la satisfacció amb la vida globalment i amb àmbits específics de la vida, l'autoestima, el suport social percebut, la percepció de control i els valors. Tot i que existeix un consens elevat en considerar que l'exploració d'aquests elements és de primera necessitat de cares a aprofundir en l'estructura del benestar psicològic, generalment han estat estudiats de forma separada, malgrat no falten intents d'integració teòrica. Les limitacions més importants que presenta l'estudi del benestar psicològic i el dels seus elements en l'actualitat són bàsicament de caràcter epistemològic i fan referència a la dificultat de trobar visions comunes (tant a nivell de definicions com de teories explicatives) compartides per una majoria d'investigadors socials. Aquestes limitacions justifiquen l'interès per dirigir l'atenció vers un altre tipus d'explicacions del benestar psicològic, qualitativament diferents a les disponibles, que no es refugiïn ni en reduccionismes ni en explicacions causals rígides. Les teories de la complexitat suposen una alternativa productiva en aquest sentit ja que aquelles característiques a través de les quals la complexitat ve donada (borrositat de límits, punts de catàstrofe, dimensions fractals, processos caòtics i no lineals), són, en definitiva, les mateixes propietats que caracteritzen als fenòmens psicosocials. I això inclou el de benestar psicològic. Les dades de les que disposem, obtingudes mitjançant un estudi transversal, impedeixen fer una aproximació al benestar psicològic des de totes les propietats de la complexitat esmentades a excepció de la característica de la no linealitat. L'objectiu general de la tesi ha estat el de construir un model de benestar psicològic a partir de les dades obtingudes que permetés: 1) Evidenciar relacions entre variables que fins aquests moments no han pogut ser massa explorades, 2) Contemplar aquestes relacions més enllà de la seva unidireccionalitat, i 3) Entendre el benestar psicològic en l'adolescència des d'un punt de vista més integrador i holista i, consegüentment, oferir una manera més comprehensiva d'aproximar-se a aquest fenomen. Aquesta tesi ha de ser entesa com un primer pas, fonamentalment metodològic, per l'elaboració futura de conceptualizacions sobre el benestar psicològic en l'adolescència que es basin en els principis que ens aporten les ciències de la complexitat. Malgrat els resultats obtinguts no estan absents de limitacions, obren noves perspectives d'anàlisi del benestar psicològic en l'adolescència. / Psychological well-being is the psychological dimension of quality of life and a growing field of study. It has a shorter past compared to other psychosocial concepts. However, researchers coming from many diverse displicines are every day enlarging the list of those who take psychological well-being as their object of study. The study of adolescent psychological well-being is probably one of the fields where the need of moving forward is more evident.Its study in adolescent population has a double interest. On the one hand, boys and girls deal with different changes and transitions at these ages and this leads adolescence frequently to be an stressful period of time, with important consequences for their psychological well-being. On the other hand, the fact of deeping in its knowledge during this period has also an interest which goes beyond the scientifical one, and allows the designing of more adjusted to the specific problems adolescents are living prevention programs. The exploration of psychological well-being elements is one of the approximation strategies to its study. In this thesis, we have selected some of the elements it is considered by the scientific literature to have a stronger connection to psychological well-being. They are the following: satisfaction with life as a whole, satisfaction with specific life dimensions, self-esteem, social suport, perception of control and values. There is an important consensus in considering that the exploration of this elements is of vital need to deepen in the psychological well-being structure. They have generally been studied in a separated way, however, it is possible to find some theoric integration attempts.The most important limitations that psychological well-being and also its elements have nowadays are basically epistemological, and refer to the difficulty of finding common visions (at the definitions level and at explanatory theories as well), shared by a majority of social researchers. These limitations justify the interest of directing attention towards other type of qualitatively different explanations, while avoding those being reductionistic and based on rigid causal explanations. Complexity theories can be a valid alternative as those properties that characterise complexity (fuzziness of limits, catastrophical points, fractal dimensions, chaotic and non linear processes) are, at the end, the same features psychosocial phenomena have. This including psychological well-being. The data we had, obtained through a transversal study, do not allow us to approximate to psychological well-being from each of the above properties with the exception of non linearity.The general objective of the thesis has been constructing a psychological well-being model from the obtained data which should be able of: 1) Making evident some up-to-now still non-explored relationships among variables, 2) Comprehending these relationships beyong their unidirectionality, and 3) Understanding psychological well-being in adolescence from a more integrative and holistic point of view and, thus, offering a more comprehensive way of approaching to these phenomenon.This thesis must be understood as a first step, specially a methodological one, to elaborate in the future conceptualisations about psychological well-being in adolescence based on complexity theories principles. Although the obtained results have some limitations, they also open to new analysis perspectives in the study of psychological well-being in adolescence.

The rapidly expanding wireless market requires low cost, high integration and high performance of wireless communication systems. CMOS technology provides benefits of cost effectiveness and higher levels of integration. However, the design of highly efficient linear CMOS power amplifier that meets the requirement of advanced communication standards is a challenging task because of the inherent difficulties in CMOS technology. The objective of this research is to realize PAs for wireless communication systems that overcoming the drawbacks of CMOS process, and to develop design approaches that satisfying the demands of the industry. In this dissertation, a cascode bias technique is proposed for improving linearity and reliability of the multi-stage cascode CMOS PA. In addition, to achieve load variation immunity characteristic and to enhance matching and stability, a fully-integrated balanced PA is implemented in a 0.18-m CMOS process. A triple-mode balanced PA using switched quadrature coupler is also proposed, and this work saved a large amount of quiescent current and further improved the efficiency in the back-off power. For the low losses and a high quality factor of passive output combining, a transformer-based quadrature coupler was implemented using integrated passive device (IPD) process. Various practical approaches for linear CMOS PA are suggested with the verified results, and they demonstrate the potential PA design approach for WCDMA applications using a standard CMOS technology.

Forced response analysis of bladed disk assemblies plays a vital role in rotor blade design and has been drawing a great deal of attention both from research community and engine industry for more than half a century. However because of the phenomenon called &lsquo / mistuning&rsquo / , which destroys the cyclic symmetry of a rotor, there have been several difficulties related to forced response analysis ever since, two of which are addressed in this thesis: efficient non-linear forced response analysis of mistuned bladed disks and mistuning identification. On the nonlinear analysis side, a new solution approach is proposed studying the combined effect of non-linearity and mistuning, which is relatively recent in this research area and generally conducted with methods whose convergence and accuracy depend highly on the number of degrees of freedom where non-linear elements are attached. The proposed approach predicts nonlinear forced response of mistuned bladed disk assemblies considering any type of nonlinearity. In this thesis, special attention is given to the friction contact modeling of bladed disks which is the most common type of nonlinearity found in bladed disk assemblies. In the modeling of frictional contact a friction element which enables normal load variation and separation of the contact interface in three-dimensional space is utilized. Moreover, the analysis is carried out in modal domain where the differential equations of motions are converted to a set of non-linear algebraic equations using harmonic balance method and modal superposition technique. Thus, the number of non-linear equations to be solved is independent of the number of non-linear elements used. On the mistuning identification side, a new method is enclosed herein which makes use of neural networks to assess unknown mistuning parameters of a given bladed disk assembly from its assembly modes, thus being suitable for integrally bladed disks. The method assumes that a tuned mathematical model of the rotor under consideration is readily available, which is always the case for today&rsquo / s realistic bladed disk assemblies. A data set of selected mode shapes and natural frequencies is created by a number of simulations performed by mistuning the tuned mathematical model randomly. A neural network created by considering the number of modes, is then trained with this data set for being used to identify mistuning of the rotor from measured data. On top of these, a new adaptive algorithm is developed for harmonic balance method, several intentional mistuning patterns are investigated via excessive Monte-Carlo simulations and a new approach to locate, classify and parametrically identify structural non-linearities is introduced.

Community Climate Model 3 (CCM3) is run on an idealized all land zonally symmetric planet (Terra Blanda) with no seasonality, no snow and fixed soil moisture to obtain a stationary time series effectively much longer than conventional runs with geography and seasons. The surface temperature field generated is studied to analyze the spatial and temporal spectra, estimate the length scale and time scale of the model, and test the linearity of response to periodic and steady heat source forcings. The length scale of the model is found to be in the range of 1000-2000 km and the time scale is estimated to be 24 days for the global average surface temperature field. The response of the global average temperature is found to be fairly linear to periodic and the steady heat source forcings. The results obtained are compared with the results of a similar study that used CCM0. Fluctuation Dissipation theorem is also tested for applicability on CCM3. The response of the surface temperature field to a step function forcing is demonstrated to be very similar to the decay of naturally occurring anomalies, and the auto-correlation function. Return period of surface temperature anomalies is also studied. It is observed that the length of the data obtained from CCM3, though sufficient for analysis of first and second moments, is significantly deficient for return period analysis. An AR1 process is simulated to model the global averaged surface temperature of Terra Blanda 3 to assess the sampling error associated with short runs.

Analog-to-digital converter (ADC) is the main workhorse in a digital waveform recorder. Strictly speaking, an ADC is supposed to perform uniformly, irrespective of the characteristics of the signal to be acquired. However, because of certain hardware related inconsistencies, its performance declines, particularly, when acquiring non-repetitive, fast-rising, high frequency signals. The error and distortion contributed due to its declining performance, for the entire range of signals, can be comprehensively characterized by the static and dynamic nonlinearities. Actual testing of ADCs is the only way of estimating these indices. These characteristics reveal information at the microscopic level, such as bit-level aberrations, code transitions, response and settling trends, etc. These tests attain greater significance, when the digitizer is part of a reference measuring or a calibration system, because, the levels of accuracies to be achieved in such a setup may become comparable to the error introduced by the ADC. Hence, testing ADCs is a priority. International and national standards exist for testing digital waveform recorders and ADCs. For several years, the matter related to reducing static test time of high-resolution ADCs was highlighted through many publications. A critical examination of the literature indicates the major schools-of-thought pursued so far, are, (i) refinements to ramp/triangular signal based static testing, (ii) proposals for use of alternative methods and/or test signals for static test, (iii) innovative ways of achieving a relaxation in signal source requirements and, (iv) efforts to combine static and dynamic test into a single test with an appropriate test signal. As a consequence of the literature review, objectives of the thesis were formulated. They attempt to resolve- (i) Conceive a suitable test signal for simultaneous estimation of static and dynamic nonlinearity through a single test (ii) Explore possibility of employing a low-linearity ramp signal to estimate static nonlinearity (iii) Estimating static nonlinearity by exploiting linearity property of a sine signal • In the first part of the thesis, a method is proposed for the concurrent estimation of static and dynamic nonlinearity characteristics of an ADC, with the application of a single test signal. The novelty arises from the fact that the test signal proposed is new, and so is the concept of extracting the static and dynamic nonlinearity from the ADC output. This was achieved by conceiving a test signal, comprising of a high frequency sinusoid (which addresses the dynamic requirement), modulated by a low frequency ramp (which addresses the static requirement). • Static characteristics of an ADC can be determined directly from the histogram-based quasi-static approach by measuring the ADC output, when excited by an ideal ramp/triangular signal of sufficiently low frequency. This approach requires only a fraction of time compared to the conventional DC test, is straightforward, easy to implement, and, in principle is an accepted method as per the revised IEEE-1057. However, the only drawback is that ramp signal sources are not ideal. Thus, nonlinearity present in the ramp signal gets superimposed on the measured ADC characteristics, which renders them, as such, unusable. The second part of the work describes a proposal to get rid of the ramp signal nonlinearity, before it is applied to the ADC. A simple method is presented which employs a low-linearity ramp signal, but yet causes only a fraction of influence on the measured ADC static characteristics. • The third part of the thesis describes a novel method to estimate the actual static characteristics of an ADC using a low frequency sine signal, say, less than 10 Hz, by employing the histogram-based approach. It is based on the well known fact that variation of sine signal is ‘reasonably linear,’ when the angle is small. In the proposed method, the ADC under test has to be ‘fed’ with this ‘linear’ portion of the sine wave. Due to harmonics and offset in input excitation, this ‘linear’ part of the sine signal is marginally different, compared to an ideal ramp signal of equal amplitude. However, since it is a sinusoid, this difference can be accurately determined and later compensated from the measured ADC output. Thus, the corrected ADC output will correspond to the true ADC static nonlinearity. The proposed approach successfully addresses all the three concerns while estimating static linearity, i.e. it is time-efficient, excites all the ADC code-bins reasonably uniformly and tackles the source linearity issue quite nicely. These proposals are novel, simple, easy to implement, time-efficient and importantly static nonlinearity characteristics determined from them are in good agreement with that estimated by the original DC-based technique. Implementation of each method is discussed along with experimental results, for two 8-bit digital oscilloscopes and a 10-bit real time digitizer. Further details are presented in the thesis.

Ziel der vorliegenden Dissertation war die Erweiterung der Kenntnisse über das nichtlinear-elastische Spannungs-Verformungsverhalten von Tragschichten ohne Bindemittel (ToB). Ein analytisches Bemessungsverfahren ist aufgrund der schwierigen Modellierbarkeit des Verformungsverhalten der einzelnen Straßenbaustoffe bisher nicht existent. Die Dissertation soll einen Beitrag zur Entwicklung eines solchen Bemessungsverfahrens leisten. Eine Literaturrecherche zum Verformungsverhalten von ToB bildet die Grundlage für die Festlegung der Vorgehensweise. Basis der weiteren Untersuchungen sind Triaxialversuche, die an der Universität Nottingham an verschiedenen Gesteinskörnungen durchgeführt wurden. Mit Hilfe der Shakedown-Theorie konnte belegt werden, dass sich ToB in unterschiedlichen Beanspruchungsbereichen nach verschiedenen Gesetzmäßigkeiten verhalten und dass Modelle zur Beschreibung des Verformungsverhaltens von ToB bereichsweise verschieden formuliert werden müssen. Somit ist es möglich, Gültigkeitsgrenzen für elastische Stoffmodelle zu ermitteln sowie Beanspruchungsgrenzen für ToB festzulegen. Mit ausgewählten Stoffmodellen erfolgten Beanspruchungsberechnungen nach der Finite-Elemente Methode (FEM). Die beste Annäherung zwischen Messwerten und Rechenergebnissen ergibt sich bei Anwendung des DRESDNER Modells. Berechnungen für Befestigungen nach den RStO 01 haben gezeigt, dass die Beanspruchungen auf den ToB bei Anwendung des DRESDNER Modells stark von denen bei Anwendung linearer Elastizität abweichen können. Durch unterschiedliche Überbauungsdicken der ToB besitzen diese einen verschieden hohen Anteil am Tragverhalten der Befestigung. Abschließend wird eine Methode zur Ermittlung von Sicherheitsniveaus vorgestellt. Bei Kenntnis der entsprechenden Schichtparameter lassen sich die Beanspruchungen jeder beliebigen Bauweise mit denen von Bauweisen nach RStO vergleichen. Als Ergebnis kann festgehalten werden, dass das Sicherheitsniveau einer bestimmten Bauweise nach RStO genauso groß ist, wie eine Befestigung mit einer dünneren Asphalttragschicht, dafür jedoch einer steiferen ToB. / The aim of this thesis was the extension of the knowledge about the resilient stress-deformation behaviour of unbound granular materials (UGM). Due to difficulties in modelling the behaviour of the single materials an analytical design method does not exist at present. Therefore this thesis makes a contribution for developing such a design method. A study of international publications about the current knowledge of the stress-deformation behaviour of UGM and repeated load triaxial tests, which have been performed at Nottingham University, were the base for all further investigations. With the shakedown concept it could be shown that materials behave in a different manner depending on the applied stress level and that material laws for describing the resilient deformation behaviour of UGM have to be formulated separately for different stress ranges. Within this thesis a method is introduced which helps to find boarders for the applicability of different material laws and limiting stress lines where below the lines stable behaviour and admissible deformations for the material are expected. Applying selected material laws finite element calculations have been performed. Comparing calculation results with measurement results it can be shown that the Dresden model offers the best approach. Calculations for pavement constructions applying the Dresden model have resulted that the vertical stresses differ very much in comparison with elastic behaviour for the UGM. It can be concluded that the thickness of the covering bounded layers have an effect to the contribution of the unbound granular layers at the complete deformation behaviour of the pavement construction. Finishing a method is introduced to determine the safety levels of pavement constructions. It seems to be possible to compare the stress-strain levels of any pavement construction with those from the german standard RStO 01. Existing functions could be modified to determine safety coefficients, i. e. ratios between admissible and existing numbers of load cycles. It can be concluded that there are the same safety levels for different pavement constructions ? a thinner asphalt layer can be compensated with a stiffer UGM.

No description available.

<p>This thesis contains three papers investigating problems of interest for noise control in ducts.</p><p>The first part of this thesis treats the sound propagation in rectangular ducts with flexible walls. Various experimental techniques are performed to measure the internal sound propagation and radiation to the surrounding. An analytical model is derived to calculate the coupled propagation wavenumber and radiated sound power. The two-port formalism is used.</p><p>The second part starts with the sound propagation in open ended circular straight pipe with airflow (a tailpipe). Various aspects such as: acoustic damping, reflection and transmission at the open termination are investigated. Sound absorption due to vorticity shed at the opening is also treated. The geometry of the opening is then modified (oblique cuts, diffusers) and comparisons with the reference straight pipe is made for the sound transmission and flow induced noise generation. The effect of an upstream bend close to the opening is also investigated.</p><p>In the third part the acoustic impedance of perforated plates are investigated. In particular the application to small perforation ratios ( ≈ 1% ) and holes or slits with apertures of sub-millimetre size, so called micro-perforated plates, are of interest. Linear and non-linear regimes are investigated. A model is derived to calculate the linear acoustic impedance of perforated elements.</p>

This work investigates the fundamental device limits related to operational voltage constraints and linearity in state-of-the-art silicon-germanium (SiGe) heterojunction bipolar transistors (HBTs) in order to support the design of robust next-generation high-frequency transceivers. This objective requires a broad understanding of how much "usable" voltage exists compared to conventionally defined breakdown voltage specifications, so the role of avalanche-induced current-crowding (or "pinch-in") effects on transistor performance and reliability are carefully studied. Also, the effects of intermodulation distortion are examined at the transistor-level for new and better understanding of the limits and trade-offs associated with achieving enhanced dynamic range and linearity performance on existing and future SiGe HBT technology platforms. Based on these investigations, circuits designed for superior dynamic range performance are presented.

O σχεδιασμός και η ανάπτυξη οικονομικών προϊόντων, με ταυτόχρονη ικανοποίηση των αναγκών για υψηλές επιδόσεις και ασφάλεια αποτελεί μια από τις μεγαλύτερες προκλήσεις για τους ερευνητές μηχανικούς και τη βιομηχανία. Ειδικότερα στους τομείς της κατασκευαστικής βιομηχανίας (αεροναυπηγική, ναυπηγική, αυτοκινητοβιομηχανία, διαστημική) των οποίων τα προϊόντα παράγονται σύμφωνα με τις τεχνολογίες αιχμής, επιζητείται από το μηχανικό να σχεδιάζει νέα προϊόντα με υψηλότερες επιδόσεις, χωρίς να αγνοεί την απαίτηση για μείωση του κόστους και του χρόνου ανάπτυξης αυτών. Η τάση αυτή βρίσκει εφαρμογή κατά κύριο λόγο στην αεροναυπηγική, όπου η μείωση του αξιοσημείωτου κόστους ανάπτυξης νέων αεροσκαφών, χωρίς υποβάθμιση της ασφαλούς και υψηλής ποιότητας τους, αποτελεί βασικό και μόνιμο στόχο. Ο κυριότερος παράγοντας που επιβαρύνει σημαντικά την ανάπτυξη νέων αεροσκαφών, τόσο από πλευράς κόστους, όσο και χρονικά, είναι οι πειραματικές δοκιμές πλήρους κλίμακας η μεγάλης κλίμακας σε συνθήκες λειτουργίας, οι οποίες επηρεάζουν σημαντικά το κόστος και το χρόνο ανάπτυξης. Οι συγκεκριμένες δοκιμές συμπεριλαμβάνονται στη διαδικασία του σχεδιασμού, με σκοπό να επαληθεύσουν τα αποτελέσματα των αντίστοιχων δομικών αναλύσεων. Η σημασία των πειραματικών δοκιμών και συγκεκριμένα εκείνων της πλήρους κλίμακας ενισχύεται από το γεγονός ότι επιβάλλονται κατά την πιστοποίηση από τις αρχές Αδειοδότησης, με δεδομένο ότι οι δομικές αναλύσεις της αντίστοιχης κλίμακας (πολύ μεγάλης η πλήρους) δεν παρέχουν ικανοποιητική αξιοπιστία. Η παραπάνω αδυναμία να εξαχθούν ικανοποιητικά αποτελέσματα από τις δομικές αναλύσεις οφείλεται σε δύο βασικά χαρακτηριστικά της ανάλυσης των κατασκευών μεγάλης κλίμακας. Η πρόβλεψη της αστοχίας στις αεροναυπηγικές και άλλες κατασκευές απαιτεί μη-γραμμική ανάλυση, λόγω αιτιών που σχετίζονται με τη συμπεριφορά υλικού (μη-γραμμική συμπεριφορά λόγω ελαστοπλαστικής συμπεριφοράς μεταλλικών υλικών η λόγω αστοχίας συνθέτων υλικών) ή με τη συμπεριφορά της δομής (γεωμετρική μη-γραμμικότητα, προβλήματα επαφής, κλπ/). Επιπρόσθετα, στις κατασκευές αυτές υπάρχει μεγάλη διαφορά κλίμακας μεταξύ των διαστάσεων της περιοχής έναρξης και αρχικής διάδοσης της τοπικής βλάβης με τις συνολικές διαστάσεις της δομής, οι οποίες σχετίζονται με την τελική αστοχία της κατασκευής. Η προσομοίωση με αριθμητικές μεθόδους, με έμφαση στη μέθοδο των Πεπερασμένων Στοιχείων, της δομικής συμπεριφοράς μεγάλης κλίμακας κατασκευών με τα παραπάνω χαρακτηριστικά, οδηγεί σε αριθμητικά πρότυπα εκατομμυρίων βαθμών ελευθερίας, τα οποία απαιτείται να επιλυθούν με μη-γραμμικές μεθόδους. Ο συνδυασμός του μεγέθους των προτύπων αυτών με το μη-γραμμικό χαρακτήρα τους, καθιστά το πρόβλημα δυσεπίλυτο έως σήμερα με χρήση συμβατικών μεθόδων και ουσιαστικά αποτελεί την αιτία μη-αξιοποίησης των εικονικών δοκιμών (αριθμητικών αναλύσεων), στην ελαχιστοποίηση ή και την ολοκληρωτική αποφυγή των εκτενών και δαπανηρών πειραματικών δοκιμών. Βάσει των ανωτέρω, σκοπός της παρούσας διατριβής είναι η ανάπτυξη νέων, αξιόπιστων και ολοκληρωμένων μεθοδολογιών για τη μη-γραμμική ανάλυση κατασκευών μεγάλης κλίμακας, με κύριο στόχο την ικανοποιητική πρόβλεψη τοπικών φαινομένων που συνδέονται με την έναρξη της βλάβης, αλλά και την ικανότητα να εκτείνονται έως την κατάλληλη κλίμακα (ίσως και την πλήρη), ώστε να καθίσταται δυνατός ο υπολογισμός της δομικής συμπεριφοράς της κατασκευής μέχρι την τελική αστοχία. Στη βάση αυτή, γίνεται ανάπτυξη νέων μεθοδολογιών δομικής μη-γραμμικής ανάλυσης και προτείνονται κατάλληλες τροποποιήσεις σε ήδη καθιερωμένες μεθόδους, με σκοπό την εφαρμογή τους σε κατασκευές μεγάλης κλίμακας. Λόγω των πλεονεκτημάτων που παρέχονται από την ταχεία και συνεχόμενη εξέλιξη των ηλεκτρονικών υπολογιστών (ταχύτητα, μνήμη, λογισμικό) και την ευρεία χρήση εμπορικών πακέτων που βασίζονται στη θεωρία των πινάκων (Πεπερασμένα Στοιχεία, Συνοριακά Στοιχεία, κλπ.), οι παραπάνω μεθοδολογίες χρησιμοποιούνται ευρέως στην πρόβλεψη της δομικής συμπεριφοράς των κατασκευών στη βάση της φιλοσοφίας της ‘εικονικής δοκιμής’. Με δεδομένο ότι οι αριθμητικές μέθοδοι επίλυσης μη-γραμμικών προβλημάτων σε κατασκευές μεγάλης κλίμακας δεν παρέχουν ικανοποιητικά αποτελέσματα, όπως προαναφέρθηκε, στην παρούσα εργασία αναζητήθηκαν εναλλακτικές μεθοδολογίες και τεχνικές, για την προσέγγιση του τεχνολογικού προβλήματος από τη σκοπιά του μηχανικού και προτάθηκαν αξιόπιστες λύσεις με δυνατότητα εφαρμογής σε βιομηχανικό περιβάλλον. Η διαδικασία που ακολουθήθηκε αποτελείται από τέσσερις βασικούς άξονες, την γραμμική αριθμητική ανάλυση των τάσεων ολόκληρης της δομής μεγάλης κλίμακας, τον έλεγχο για πιθανή εμφάνιση τοπικής μη-γραμμικής συμπεριφοράς, την τοπική ανάλυση αστοχίας (μη-γραμμική ανάλυση) και μια σειρά κατάλληλων τεχνικών για τον προσδιορισμό της συνεισφοράς των περιοχών με τοπική μη-γραμμικότητα στη δομική συμπεριφορά ολόκληρης της δομής. Όλα τα βήματα της διαδικασίας πραγματοποιήθηκαν στη βάση της μεθόδου των Πεπερασμένων Στοιχείων. Η γραμμική αριθμητική ανάλυση τάσεων της κατασκευής έγινε με χρήση αριθμητικών προτύπων που προσομοιώνουν ολόκληρη την κατασκευή, χωρισμένων σε τμήματα, ανάλογα με την γεωμετρική επαναληψιμότητα που πιθανώς εμφανίζει η γεωμετρία. Οι τάσεις που υπολογίστηκαν χρησιμοποιήθηκαν στην πρόβλεψη τα εμφάνισης τοπικής μη-γραμμικότητας με τη βοήθεια κατάλληλα ανεπτυγμένων κριτηρίων, ανάλογα με το είδος της μη-γραμμικότητας που μπορεί να εμφανιστεί. Οι περιοχές μη-γραμμικότητας που ανιχνεύονται, ταξινομούνται σε σειρά κρισιμότητας και ανάλογα με το κρίσιμο επίπεδο φορτίου καθεμιάς από αυτές, επεξεργάζονται τοπικά με μη-γραμμικές αναλύσεις για την προσομοίωση της έναρξης και εξέλιξης της τοπικής μη-γραμμικότητας. Για τον υπολογισμό της συνεισφοράς των μη-γραμμικών υποπεριοχών στη δομική συμπεριφορά ολόκληρης της κατασκευής, αναπτύχθηκαν κατάλληλες τεχνικές περιγραφής της τοπικής μη-γραμμικότητας και εισαγωγής τους στα δομικά χαρακτηριστικά του αριθμητικού προτύπου της ολικής κατασκευής. Για την προσομοίωση της εξέλιξης της τοπικής μη-γραμμικότητας, από την πρώτη ανίχνευση μέχρι την τελική εξέλιξη, η διαδικασία εκτελείται βηματικά και επαναληπτικά. Αποδεικνύεται ότι κάτω από συγκεκριμένες παραδοχές, οι μεθοδολογίες για τη δομική μη-γραμμική ανάλυση κατασκευών μεγάλης κλίμακας είναι εφικτό να παρέχουν αξιόπιστα αποτελέσματα αντίστοιχα με εκείνα των πειραματικών δοκιμών πλήρους κλίμακας. Ταυτόχρονα είναι και αποτελεσματικές, δεδομένου ότι έχουν αναπτυχθεί κατάλληλα, ώστε να εστιάζουν τους διαθέσιμους υπολογιστικούς πόρους μόνο στις κρίσιμες περιοχές, μέσω της κατά απαίτησης εφαρμογής τοπικών μη-γραμμικών αναλύσεων. / The design and development of low-cost products, with simultaneous fulfilment of the requirements for higher performance and safety, is one of the biggest challenges for the research engineers and the industry. Especially in the sectors of the structural industry (aeronautics, shipbuilding, automotive, space industry) where the products are being produced according to the latest achievements of the technology, the engineer is obliged to design new products with higher proficiency, without neglecting the need for lower cost and development time. This trend has great application mainly in the aeronautical industry, where the reduction of the remarkable cost for the development of a new aircraft, without downgrading the level of safety and the quality of service comprises the main target of the current research effort. The main factor that weighs down the development of new aircrafts, as far as the cost and the time is concerned, is the required experimental tests of the full / large scale under service loads, which affect significantly the development cost and the time to market. These tests are included in the design process, in order to verify the results of the corresponding structural analyses. The importance of the experimental tests and specifically these of the full scale level is amplified by the fact that they are being imposed during the certification process by the Airworthiness Authorities, since the structural analyses of the corresponding scale (full scale) do not provide adequate results. The above mentioned inability of the structural analyses of providing adequate results is based on two main characteristics of the large scale structures. Firstly, the failure prediction in aeronautical (among others) structures requires non-linear analysis, for reasons related to the material behaviour (non-linear behaviour due to composite material damage, elastoplastic behaviour of metallic materials) and the structural behaviour (geometrical non-linearity, contact problems). Secondly, in these structures there is great difference between the dimensions of the local damage initiation region and the dimensions of the whole structure, with the latter being related with the total collapse. The simulation with numerical methods, especially with the use of Finite Elements, of the structural behaviour of large scale structures with the above characteristics, leads to million DOFs (Degrees Of Freedom), whose solution requires non-linear numerical methods. The combination of the size of these models with their non-linear nature renders the problem non-solvable using conventional methodologies and is in fact the reason for the, up to now, not thoroughly utilization of virtual testing (numerical simulations), that would lead to the minimization of the number or even to the complete avoidance of the extensive and costly experimental tests. Based on the above, main objective of this Thesis is the development of new, reliable and integrated methodologies for the non-linear analysis of large scale structures, targeting mainly in the satisfactory prediction of phenomena related to the initiation of local damage, but also being able to evolute up to the appropriate scale (maybe full scale), in order to account the structural behaviour of the whole structure up to the total collapse. On this basis, innovative methodologies are being developed for the structural non-linear analysis and appropriate modifications are proposed for already well-established techniques, in order to be applied on large scale structures. Due to the advantages offered from the rapid and constant progress of computers (speed, memory, software) and the wide usage of commercial tools that are based on the matrix theory (Finite Elements, Boundary Elements), the above mentioned methodologies were developed based on the philosophy of ‘virtual testing’. Due to the fact that the numerical solution methods for non-linear problems in large scale structures are not able to provide adequate results, as mentioned previously, in the present work alternative methodologies and techniques were investigated, approaching the technological problem from the engineer’s view and reliable solutions applicable to an industrial environment were proposed. The procedure that was followed consists of four basic keystones: the linear numerical stress analysis of the whole structure, the check for possible local non-linear behaviour, the local damage analysis (non-linear analysis) and a series of appropriately configured sub-routines, able to redefine the contribution of the regions exhibiting local damage in the structural behaviour of the whole structure. All the routines of the proposed methodologies were accomplished using the commercial Finite Element code ANSYS. The linear numerical stress analysis of the structure was carried out with the use of numerical models simulating the whole structure, divided into suitable parts, based on the geometrical repeatability. The calculated stresses were utilized for the prediction of the local damage, using properly developed damage criteria, depending on the type of non-linearity. The corresponding regions detected, were classified according to the criticality level (critical load) and were elaborated with local analyses of non-linear nature for the simulation of local damage initiation. For the accumulation of the contribution of the local damage in the structural behaviour of the whole structure, appropriate techniques were developed for the description of the local damage and its incorporation in the structural features of the numerical model of the structure. For the determination of the damage evolution, from the first detection up to the final failure, the procedure was performed in an incremental and iterative way. It was proved, that under specific assumptions, the proposed methodologies simulating the non-linear phenomena of large scale structures are capable of providing accurate results, in accordance with those of the experimental tests of full scale level. Simultaneously, the proposed methodologies become also efficient, providing that they have been developed appropriately, in order to focus the available computer resources on the non-linearly behaving regions by the ‘on demand’ application of the non-linear analyses.