Includes bibliography (p. 87) Thesis (doctoral)--Tartu University, 2004. / Vita.

Universiẗat, Diss., 1991--Bonn.

Thesis--Basel, 1952. / Vita. Bibliography: p. 221-231.

Köln, University, Diss., 1998.

The science of modelling the behaviour of natural phenomena and physical systems has grown significantly in importance in the last century. It helps us to understand and predict natural phenomena or improve and control all types of industrial processes. There are basically two approaches to system modelling: a model can be derived from physical knowledge of the system or by systematically testing it and estimating the model structure and parameters based on the test data. The method of system testing has gained importance due to the increasing complexity of modern industrial systems and processes. It also serves as a verification tool to the physical model. It has led to a rapid advance of a particular discipline within science generally referred to as system identification. This thesis deals with a frequency domain approach to identifying a particular class of nonlinear systems which can be modelled by the Volterra series. The methodology is based on the application of specially designed multisine test signals which allow second and third order terms of the Volterra series, so-called Volterra kernels, to be measured directly and the structure of the nonlinear system to be identified. In the first part of this thesis an introduction is given to system identification in the frequency domain and the analysis of a particular class of nonlinear systems using the Volterra series. Particular attention is given to the design of multisine signals and the development of a comprehensive software tool to aid with the identification task. The second part examines Volterra kernels and the application of block-oriented models to Volterra systems. A method is proposed for identifying the structure of such models based on Volterra kernels and in particular for the de-composition of a cascade structure into its linear dynamic components. The contributions made in this work include the development of a software tool for system identification, the measurement and representation of frequency domain Volterra kernels, as well as the classification and decomposition of block-oriented models by applying specially designed multisine signals.

Orientador: Hans Ingo Weber / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica / Made available in DSpace on 2018-07-18T20:03:29Z (GMT). No. of bitstreams: 1 Mattos_MarcioCoelhode_M.pdf: 4554853 bytes, checksum: c0466ccf4f68d65ae87f03b78d331ab2 (MD5) Previous issue date: 1993 / Resumo: Este trabalho apresenta um estudo sobre sistemas amortecidos com atrito viscoso/coulomb. Trata-se de um sistema de vários graus de liberdade onde apenas uma das coordenadas está sujeita ao efeito do atrito seco. As dificuldades encontradas durante o estudo do problema são apresentadas, bem como uma discussão sobr:e métodos para análise de sistemas não lineares e sua; aplicabilidade ao problema. Usa-se a solução exata no domínio do tempo para o estudo de sistemas com até 4 graus de liberdade.A influência do Atrito na resposta em freqüência de sistemas com determinados modelos é apresentada, bem como a redução na amplitude de vibração destes sistemas. Realiza-se uma comparação entre os sistemas de dois graus de liberdade amortecidos com atrito seco e o absorvedor dinâmico de vibrações convencional. Estuda-se o ,caso real de uma viga engastada em uma das extremidades, com massas concentradas e atrito seco na extremidade livre. O problema de modelamento discreto de sistemas contínuos no estudo de sistemas amortecidos com atrito seco é discutido / Abstract: In this work we present a study on systems with combined coulomb and viscous friction. It concernes systems with several degrees of freedom and coulomb damping actuating on only one coordinate. The difficulties encountered during this study are presented. Methods to analize non-linear systems and their applicabillity in the study of dry friction damped systems are dis-cussed. The exact solution in the time domain is used to study systems with 1 up to 4 degrees of freedom. The influence of dry friction on the frequency response oí systems with determinate models is studied as well as the reduction of amplitude of vib.ration in this systems. A comparision hetween 2DOF dry friction damped systems and conventional dynamic absorber of vibration is presented. The study of a real case of a clamped beam.on one end, distribuited masses and coulomb friction on the free end is realized. The problem of discrete modellingJ of continuous systems in the study of dry frictiondamped systems is discussed. / Mestrado / Mestre em Engenharia Mecânica

This work is a numerical study of a class of weakly singular neutral equations. The motivation for this study is an aeroelastic system. Numerical techniques are developed to approximate the singular integral equation component appearing in the complete dynamical model for the elastic motions of a three degree of freedom structure, an airfoil with trailing edge flap, in a two dimensional unsteady flow. The flap can be viewed as an active control surface to dampen vibrations that contribute to flutter. The goal of this work is to provide accurate approximations for weakly singular neutral equations using finite elements as basis functions for the initial function space. Several examples are presented in order to validate the numerical scheme. / Master of Science

[pt] Esta dissertação apresenta um desenvolvimento analítico que permite caracterizar as distorções produzidas na densidade espectral de potência de sinais OFDM devido à sua passagem através de sistemas não lineares. O processo estocástico que caracteriza a envoltória complexa de um sinal OFDM é odelado como um processo estocástico gaussiano complexo, próprio. A não linearidade do canal de transmissão é caracterizada pela expansão, em série de potências, de suas características de conversão AM/AM e AM/PM. Utilizando-se o Teorema dos Momentos para processos gaussianos complexos chega-se a expressões analíticas fechadas para a função autocorrelação e para a densidade espectral de potência do sinal produzido na saída da não- linearidade. As expressões obtidas são aplicadas a situações particulares nas quais 1, 2 e 3 sinais OFDM compartilham a não- linearidade permitindo quantificar, nestas situações específicas, as distorções correspondentes aos produtos de intermodulação de diferentes ordens e o efeito, nestas distorções, de variações no valor do back-off de entrada do sinal. / [en] This MSc dissertation presents a theoretical analysis that evaluates the distortion experienced by the power spectrum density of OFDM signals when they are transmitted through a non-linear channel. The complex envelope of the OFDM signals are modeled as a complex proper gaussian random process and the channel non-linearity is characterized through a power series expansion of its AM/AM and AM/PM distortion curves. Using the Moment Theorem for complex gaussian random processes, closed form expressions for the autocorrelation function and the power spectrum density of the signal produced at the non-linear channel output are obtained. These expressions are applied to specific situations in which 1, 2 and 3 OFDM signals share the nonlinear channel, producing results that quantify the distortions corresponding to intermodulation products of different orders and the effect of varying the signal input back-off value.

Είναι γνωστό ότι η ανάγκη για την ταυτοποίηση συστηµάτων εµφανίζεται σε πολλά προβλήµατα του ευρύτερου κλάδου της Επεξεργασίας Σηµάτων. Υπάρχουν πολλές εφαρµογές, στις οποίες είτε σήµατα προκύπτουν λόγω µη γραµµικών ϕαινοµένων, είτε σήµατα υπόκεινται σε µη γραµµική επεξεργασία. Παραδείγµατα τέτοιων εφαρµογών αποτελούν η µη γραµµική ακύρωση ηχούς, η εξίσωση καναλιών, η µοντελοποίηση ϕωνής, η προσαρµοστική ακύρωση ϑορύβου και η βελτίωση εικόνας. Σε τέτοιες περιπτώσεις, η ταυτοποίηση συστηµάτων χρησιµοποιώντας γραµµικά µοντέλα είναι εντελώς ακατάλληλη για τη µοντελοποίηση των αντιστοίχων ϕαινοµένων/διαδικασιών και τόσο η χρήση µη γραµµικών µοντέλων όσο και η ανάπτυξη σχετικών µεθόδων ταυτοποίησης είναι απαραίτητες. Στα πλαίσια της εν λόγω διπλωµατικής εργασίας, ϑα ασχοληθούµε µε το πρόβληµα της ταυτοποίησης µη γραµµικών συστηµάτων υψηλής τάξης µη γραµµικότητας, τα οποία επιδέχονται ανάπτυξη σε ισοδύναµες Σειρές Volterra. Αρχικά, ϑα ασχοληθούµε µε την ντετερµινιστική ταυτοποίηση µίας ειδικής µορφής διακριτού χρόνου πολυωνυµικών µη γραµµικών συστηµάτων, τα οποία περιγράφονται µέσω του λεγόµενου µοντέλου Volterra - Hammerstein. Πιο συγκεκριµένα, ϑα παρουσιάσουµε και ϑα αναλύσουµε µία σχετικά νέα µέθοδο ταυτοποίησης, η οποία βασίζεται στη διέγερση του υπό µελέτη συστήµατος χρησιµοποιώντας χρονικά µεταβαλλόµενα αρµονικά σήµατα πεπερασµένης διάρκειας, τα επονοµαζόµενα chirps, τα οποία διαθέτουν ορισµένες ενδιαφέρουσες χρονοσυχνοτικές ιδιότητες. Επιπλέον, παρουσιάζουµε καινούργια και ενδιαφέροντα αποτελέσµατα. Στη συνέχεια, εισάγουµε και αναλύουµε διεξοδικά το ϑεµελιώδες πρόβληµα της βέλτιστης στοχαστικής ταυτοποίησης συστηµάτων Volterra διακριτού χρόνου υπό την έννοια του ελάχιστου µέσου τετραγωνικού σφάλµατος, καθώς και το αντίστοιχο πρόβληµα της βέλτιστης ταυτοποίησης συστηµάτων Volterra διακριτού χρόνου υπό την έννοια των ελαχίστων τετραγώνων. Επιπλέον, ϑα επικεντρωθούµε στη διατύπωση των προαναφερθέντων προβληµάτων ελτιστοποίησης πάνω σε ισοδύναµους ορθοκανονικούς χώρους σηµάτων εισόδου. Ακόµα, εξετάζουµε αναλυτικά το πρόβληµα της βέλτιστης αναδροµικής και προσαρµοστικής ταυτοποίησης χρονικά µεταβλητών συστηµάτων Volterra διακριτού χρόνου υπό την έννοια του ελάχιστου µέσου τετραγωνικού σφάλµατος, µέσω του δηµοφιλούς ϕίλτρου Kalman. Χρησιµοποιώντας τη σχέση µίας ειδικής µορφής του ϕίλτρου Kalman µε τον εξίσου δηµοφιλή αλγόριθµο των εκθετικά σταθµισµένων αναδροµικών ελαχίστων τετραγώνων, αναπτύσσουµε προσαρµοστικά ϕίλτρα µε βελτιωµένες ικανότητες εντοπισµού. Τέλος, δοκιµάζουµε και συγκρίνουµε τις παραπάνω µεθόδους µέσω πειραµάτων και χρησιµοποιώντας δεδοµένα, τα οποία προέρχονται από περιβάλλοντα εξοµοίωσης. Επίσης, εξετάζουµε και συγκρίνουµε τη συµπεριφορά των µεθόδων υπό την επίδραση εξωτερικών διαταραχών µέτρησης στα αντίστοιχα σήµατα εξόδου. / -

The CDMA standard operating over the wireless environment along with various other wireless standards places stringent specifications on the RF Front end. Due to possible large interference signal tones at the receiver end along with the carrier, the Low Noise Amplifier (LNA) is expected to provide high linearity, thus preventing the intermodulation tones created by the interference signal from corrupting the carrier signal. The research focuses on designing a novel LNA which achieves high linearity without sacrificing any of its specifications of gain and Noise Figure (NF). The novel LNA proposed achieves high linearity by canceling the IM3 tones in the main transistor in both magnitude and phase using the IM3 tones generated by an auxiliary transistor. Extensive Volterra series analysis using the harmonic input method has been performed to prove the concept of third harmonic cancellation and a design methodology has been proposed. The LNA has been designed to operate at 900MHz in TSMC 0.35um CMOS technology. The LNA has been experimentally verified for its functionality. Linearity is usually measured in terms of IIP3 and the LNA has an IIP3 of +21dBm, with a gain of 11 dB, NF of 3.1 dB and power consumption of 22.5 mW.