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1
Mui, Chi Seong. "Frequency domain approach to time series analysis". Thesis, University of Macau, 2000. http://umaclib3.umac.mo/record=b1446676.
Testo completo
2
Ho, C. "Nonlinear vibration control : a frequency domain approach". Thesis, University of Sheffield, 2014. http://etheses.whiterose.ac.uk/5157/.
Testo completoAbstract (sommario):
A vibration isolator, sometimes called an isolating mount, is the device situating between the vibration source and the sensitive system preventing the transmission of undesired disturbances. The performance is measured by the force or the displacement transmissibility, both functions of frequency. A good vibration isolation system has three main properties - a low resonant peak, a large isolation range and low transmissibility at non-resonant regions. Unfortunately, these characteristics cannot be achieved simultaneously by a simple linear vibration isolation system. The thesis addresses this problem for single-degree-of-freedom (sdof) vibration isolation systems by introducing nonlinear damping and stiffness devices into the system. First, theoretical studies were carried out to rigorously reveal the benefits of the proposed nonlinear vibration isolation systems over linear ones. Next, the performance of these nonlinear systems were analysed by simulations. Then, experimental studies were conducted to verify the theoretical and simulations results. Finally, a systematic approach was developed to design the parameters of the nonlinear damping and stiffness devices in order to satisfy specific vibration isolation requirements. Many vibration isolators can be modelled as a single-degree-of-freedom mass-spring-damper system. Many researchers have attempted to enhance the vibration isolation performance by designing springs with nonlinear stiffness. Others have focused on different types of damping nonlinearities. The new vibration isolation system proposed in the thesis combines both spring and damping nonlinearities in one system to exploit the advantages of both components while avoiding their undesirable effects. The theoretical properties of this proposed nonlinear vibration isolation system were analysed rigorously using the output frequency response function (OFRF) approach, a novel and unique method recently proposed at Sheeld. The stiffness nonlinearity is already a well researched area and can readily be realised in practice. Therefore, the implementation of the proposed nonlinear vibration suppression system focused on the realisation of the nonlinear damping component using commercially available magneto-rheological (MR) dampers which provide a damping force that is dependent on a control current. With feedback control, the force-velocity relationship of an MR damper can be shaped into a designed function. This implementation has been incorporated first in a vibration isolation system by simulation, then in a physical experimental rig which has a moving mass. The simulation and experimental data not only showed the successful realisation of a damping device with a particular nonlinear damping characteristic, but also confirmed the theoretical findings on the beneficial effects of nonlinear damping on a vibration isolation application. The final part of the thesis is devoted to the practical design of the proposed vibration isolation system. Given specific transmissibility requirements at certain critical frequencies, the values of the linear parameters are first designed, then the OFRF approach is applied to determine the nonlinear parameters. This pragmatic method simplifies the design of a complicated nonlinear system, which was traditionally difficult to work with, into a step-by-step guide and, therefore, has significant potential of industrial applications. The thesis has exploited the special effects of two nonlinear components on the performance of a passive sdof vibration isolation system. With the support of theoretical, simulation and experimental studies, the newly proposed configuration has shown substantial benefits to many vibration isolation problems. The simple yet effective design and implementation has significant implications for a wide range of engineering applications such as car suspension designs and building protection against earthquakes.
3
Warburton, Niels Jamie. "Frequency domain approach to self-force calculations". Thesis, University of Southampton, 2012. https://eprints.soton.ac.uk/167481/.
Testo completoAbstract (sommario):
In this thesis, the problem of computing the back-reaction, or self-force, caused by a point particle interacting with its own field is studied. In particular, motivated by the prospect of detecting gravitational waves from extreme mass ratio inspiral systems, we consider the motion of the particle in black hole spacetimes. As a toy model for the most astrophysically relevant scenario of orbits about a rotating black hole we first study the scalar-field self-force (SSF)experienced by a scalar charge moving on a fixed geodesic in Kerr spacetime for a variety of orbits. Our approach is to work in the frequency domain, fully decomposing the scalar field into spheroidal harmonic and frequency modes and numerically solving for the retarded field mode-by-mode. Regularization of the retarded field is performed using the standard mode-sum technique which requires spherical harmonic modes as input, which we obtain by projecting the spheroidal harmonic modes on to a basis of spherical harmonics. We find for circular, equatorial orbits that the black hole spin can have a pronounced effect on the conservative piece of the SSF, causing it to (with respect to the Schwarzschild scalar-field self-force) change sign for certain spins and orbital radii. For eccentric orbits in the equatorial plane, we make use of the recently introduced method of extended homogeneous solutions to overcome the Gibbs phenomenon associated with a naive approach. As an application of our work we compute the shift to the innermost stable circular orbit due to the conservative piece of the scalar-field self-force for a variety of black hole spins. We also present some preliminary results for the SSF along circular, inclined geodesics. As well as studying the toy model SSF, we also consider the gravitational self-force (GSF) problem in the context of orbits around a Schwarzschild black hole. Our approach is again to work in the frequency domain, and we perform a complete decomposition of the metric perturbation in tensor spherical harmonics and frequency modes. The ten metric perturbation fields decouple with respect to the multipole indices but remain coupled within each spherical harmonic mode. We solve the resulting coupled sets numerically with a code set up to run on a computer cluster. Regularization is again performed using the mode-sum technique. Our resulting code is extremely efficient for low eccentricity orbits, and using it we compute the GSF for a great many points in the orbital parameter space. With these results we fit an analytic model to our numerical data and then use a relativistic osculating elements scheme to evolve the orbital inspiral. This allows us, for the first time, to assess the contribution to a complete inspiral from the conservative piece of the gravitational self-force. Finally, as an aside, we investigate the recently discovered phenomenon of isofrequency orbits, whereby it is possible to have pairs of physically distinct bound geodesics about a Kerr black hole that share the same three orbital frequencies.
4
Chao, Chi-Shun. "A frequency domain based approach to on-line system identification". Thesis, Monterey, California. Naval Postgraduate School, 1991. http://hdl.handle.net/10945/28237.
Testo completo
5
Vaudrey, Michael A. "A novel approach to multiple reference frequency domain adaptive control". Thesis, This resource online, 1996. http://scholar.lib.vt.edu/theses/available/etd-08292008-063731/.
Testo completo
6
Schamel, Andreas. "A frequency domain approach to the analysis and optimization of valve spring dynamics". Thesis, Loughborough University, 1993. https://dspace.lboro.ac.uk/2134/14724.
Testo completoAbstract (sommario):
In this thesis a method is derived and presented, for the efficient analysis of the steady state response of dynamic systems with time variant propenies. The method is especially attractive for the simulation of the steady state response of lightly damped systems with low numbers of degree of freedom which are forced by a periodic excitation. A major feature of the method is that the system non-linearities can be successfully modelled as time variant propenies. An ideal application for this approach is the calculation of the dynamic response of a modal model for progressive valve springs in the frequency domain. The solution method is explained and derived using this example. The differences, drawbacks, and advantages are assessed by comparison with both a linear modal model and a discrete time-domain model; correlation with actual measurement is also shown. The extreme efficiency of the method allows its application in a more general study of the dynamic propenies of valve springs. This analysis is initially discussed and examined using statistical methods. Then the frequency domain solution method is employed to perform an automatic optimization of the spring frequency characteristic for a 16 valve prototype engine application. The spring design obtained from this study has been manufactured and the resulting hardware is discussed. The measured response of this hardware is compared with simulation results for the same configuration, verifying the fmdings from the statistical investigation and the optimization. Finally open issues and further envisaged work in the area of damping mechanisms in valve springs and manufacturing issues are diScussed and an approach for the next steps to take is outlined.
7
Jun, Jonathan Ho. "An abductive approach to Design Structure Matrix (DSM) partitioning using frequency domain scoring". Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/118547.
Testo completoAbstract (sommario):
Thesis: S.M. in Engineering and Management, Massachusetts Institute of Technology, System Design and Management Program, 2018.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 65-66).
A key benefit of the DSM representation is that it gives a visual interpretation of relationships between its elements. The array format allows us to sort the elements using clustering algorithms which try to group the relationships into modules which are as independent as possible. There are a number of clustering algorithms available which may each end up sorting the DSMs differently using different objectives, for example, activities in a time-based DSM can be sequenced to reduce iterations or to improve concurrency. However, most of these algorithms take a deductive approach which results in only one 'optimal' output. If an abductive approach is used instead, multiple solutions can be generated for the user to evaluate, some which may provide insight on useful configurations that he or she may have overlooked. In electrical engineering, we often make use of transforms to convert time domain signals into frequency domain signals in order to glean additional information which may not have been initially apparent. In this respect, using a frequency domain transform on a DSM matrix gives us additional insights into the relationships represented. An example of one such insight would be into the sorted-ness of a DSM to which module cuts can be defined. By applying a frequency transform to a pixel representation of the DSM and examining the transform coefficients, we gain an understanding of what image patterns exist in the DSM. Rules pertaining to these coefficients could then be defined which would classify a DSM as well sorted (with the dependencies being grouped up) or being unsorted (with the dependencies being scattered). This thesis demonstrates the above technique to rank each permutation of an 8x8 matrix on their conformance to certain rules or behaviors in order to filter out useful configurations in an abductive approach. When comparing the highest-ranking hypotheses against the optimal result from other clustering and sequencing algorithms, this algorithm performed on par with them to reduce external dependencies and iterations respectively. The frequency based scoring was also shown to be a useful metric when determining the optimal module cut of a system.
by Jonathan Ho Jun.
S.M. in Engineering and Management
8
MacKay, Cameron. "An optimisation approach to the frequency-domain inverse problem for a nonuniform transmission line". Thesis, University of Strathclyde, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.410242.
Testo completo
9
Thein, Christoph Oliver [Verfasser]. "A frequency domain approach to synchronization of filterbank multicarrier systems in practice / Christoph Oliver Thein". Hannover : Technische Informationsbibliothek und Universitätsbibliothek Hannover (TIB), 2015. http://d-nb.info/106892425X/34.
Testo completo
10
FLADUNG, JR WILLIAM A. "A GENERALIZED RESIDUALS MODEL FOR THE UNIFIED MATRIX POLYNOMIAL APPROACH TO FREQUENCY DOMAIN MODAL PARAMETER ESTIMATION". University of Cincinnati / OhioLINK, 2001. http://rave.ohiolink.edu/etdc/view?acc_num=ucin990800667.
Testo completo
11
Selander, Keith N. "A function space approach to the generalized nonlinear model with applications to frequency domain spectral estimation". Diss., This resource online, 1992. http://scholar.lib.vt.edu/theses/available/etd-06062008-172034/.
Testo completo
12
Tatossian, Charles A. "Aerodynamic shape optimization via control theory of helicopter rotor blades using a non-linear frequency domain approach". Thesis, McGill University, 2008. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=112586.
Testo completoAbstract (sommario):
This study presents a discrete adjoint-based aerodynamic optimization algorithm for helicopter rotor blades in hover and forward flight using a Non-Linear Frequency Domain approach. The goal is to introduce a Mach number variation into the Non-Linear Frequency Domain (NLFD) method and implement a novel approach to present a time-varying cost function through a multi-objective adjoint boundary condition. The research presents the complete formulation of the time dependent optimal design problem. The approach is firstly demonstrated for the redesign of a NACA 0007 and a NACA 23012 helicopter rotor blade section in forward flight. A three-dimensional inviscid Aerodynamic Shape Optimization (ASO) algorithm is then employed to validate and redesign the Caradonna and Tung experimental blade. The results in determining the optimum aerodynamic configurations require an objective function which minimizes the inviscid torque coefficient and maintains the desired thrust level at transonic conditions.
13
Wilzeck, Andreas. "A software defined radio approach for high data rate multi-antenna wireless communications with frequency domain processing". Aachen Shaker, 2009. http://d-nb.info/997951338/04.
Testo completo
14
SALAM, ABDUL. "Model-based and data-based frequency domain design of fixed structure robust controller: a polynomial optimization approach". Doctoral thesis, Politecnico di Torino, 2022. https://hdl.handle.net/11583/2972836.
Testo completo
15
FERNANDEZ, BARRERO DIEGO. "Dynamic Soil-Structure Interactionof Soil-Steel Composite Bridges : A Frequency Domain Approach Using PML Elements and Model Updating". Thesis, KTH, Bro- och stålbyggnad, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-256033.
Testo completoAbstract (sommario):
This master thesis covers the dynamic soil structure interaction of soil-steel culverts applyinga methodology based on the frequency domain response. At the first stage of this masterthesis, field tests were performed on one bridge using controlled excitation. Then, themethodology followed uses previous research, the field tests, finite element models (FEM)and perfectly matched layer (PML) elements.Firstly, a 2D model of the analysed bridge, Hårestorp, was made to compare the frequencyresponse functions (FRF) with the ones obtained from the field tests. Simultaneously, a 3Dmodel of the bridge is created for the following purposes: compare it against the 2D modeland the field tests, and to implement a model updating procedure with the particle swarmalgorithm to calibrate the model parameters. Both models use PML elements, which areverified against previous solution from the literature. The verification concludes that thePML behave correctly except for extreme parameter values.In the course of this master thesis, relatively advanced computation techniques were requiredto ensure the computational feasibility of the problem with the resources available.To do that, a literature review of theoretical aspects of parallel computing was performed, aswell as the practical aspects in Comsol. Then, in collaboration with Comsol Support and thehelp given by PDC at KTH it was possible to reduce the computational time to a feasiblepoint of around two weeks for the model updating of the 3D model.The results are inconclusive, in terms of searching for a perfectly fitting model. Therefore,further research is required to adequately face the problem. Nevertheless, there are some accelerometerswhich show a considerable level of agreement. This thesis concludes to discardthe 2D models due to their incapability of facing the reality correctly, and establishes a modeloptimisation methodology using Comsol in connection with Matlab.
16
Ljung, Jonathan. "Parametric Studies of Soil-Steel Composite Bridges for Dynamic Loads, a Frequency Domain Approach using 3D Finite Element Modelling". Thesis, KTH, Bro- och stålbyggnad, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-254343.
Testo completoAbstract (sommario):
In this thesis, parametric studies have been performed for a soil-steel compositebridge to determine and investigate the most influential parameters on the dynamicresponse.High-speed railways are currently being planned in Sweden by the Swedish TransportAdministration with train speeds up to 320 km/h. According to the European designcodes, bridges must be verified with respect to dynamic resonance behaviour for trainspeeds exceeding 200 km/h. However, there are no guidelines or design criterion forperforming dynamic verifications of soil-steel composite bridges. The aim of thisthesis has therefore been to investigate the influence of the geometry and materialproperties of soil-steel composite bridges on their dynamic response.This thesis is based upon the frequency domain approach for dynamic analysis ofa soil-steel composite bridge using finite element software. In 2018, field measurementswere performed on a soil-steel composite bridge in Hårestorp, Sweden. Areference finite element model was developed based on previous research and wasverified against these field measurements. Parametric studies where performed byextrapolating the geometry of the reference model, focusing primarily on the crownheight, culvert span width and the location of the bedrock. Sensitivity analyses ofthe density- and stiffness of the soil was also performed.The parametric studies showed that the crown height was the most influential parameterwith respect to the amplitude of the resonance peak. Increasing it from 1 mto 3 m reduced the amplitude by approximately 70 %. An increased span width ofthe culvert was found to reduce the frequency and amplitude of the resonance peak,however increasing the stiffness of the culvert increased the resonance frequency.The position of the rock layer also reduced the amplitude of the resonance peak iflowered, likely because of lessened wave reflection. The lowest rock level investigatedshowed a significant decrease of more than 70 % in amplitude. However, the modelused to calculate this response was heavily extrapolated and thus difficult to verify.The sensitivity analyses showed that the soil density- and stiffness was negativelyand positively correlated with the resonance frequency, respectively. Additionally,the soil density lowered the amplitude of the resonance peak if increased.
17
Lui, Man Leung. "A new 2-dimensional full-wave frequency-domain approach for direct dispersion analysis of arbitrarily shaped wave-guiding structures". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape8/PQDD_0020/MQ48279.pdf.
Testo completo
18
Wilzeck, Andreas [Verfasser]. "A Software Defined Radio Approach for High Data-Rate Multi-Antenna Wireless Communications with Frequency Domain Processing / Andreas Wilzeck". Aachen : Shaker, 2009. http://d-nb.info/1159836337/34.
Testo completo
19
Dizemen, Ilke Evrim. "Assessment Of An Iterative Approach For Solution Of Frequency Domain Linearized Euler Equations For Noise Propagation Through Turbofan Jet Flows". Master's thesis, METU, 2008. http://etd.lib.metu.edu.tr/upload/12609095/index.pdf.
Testo completoAbstract (sommario):
This study, explores the use of an iterative solution approach for the linearized Euler equations
formulated in the frequency domain for fan tone noise propagation and radiation through bypass
jets. The aim is to be able to simulate high frequency propagation and radiation phenomena
with this code, without excessive computational resources. All computations are performed
in parallel using MPI library routines on a computer cluster. The linearized Euler equations
support the Kelvin-Helmholtz type convective physical instabilities in jet shear flows. If these
equations are solved directly in frequency domain, the unstable modes may be filtered out for
the frequencies of interest. However, direct solutions are memory intensive and the reachable
frequency is limited. Results provided shown that iterative solution of LEE is more efficient
when considered memory requirement and might solve a wider scope of frequencies, if the
instabilities are controlled.
20
Smith, Austin Gregory. "Characterization and Quantification of Early Stages for Organic Coatings Applied on AA2024/AA7075 by Correlating Frequency Domain Approach in Real Time". University of Akron / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=akron1399125698.
Testo completo
21
Baby, Arun Paul. "Comparison of Modal Parameter Estimation using State Space Methods (N4SID) and the Unified Matrix Polynomial Approach". University of Cincinnati / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1613731964598438.
Testo completo
22
Bzikha, Ihssane. "Comparison and development of advanced wiring fault detection methods on coaxial cables". Thesis, Limoges, 2019. http://www.theses.fr/2019LIMO0119.
Testo completoAbstract (sommario):
Dans cette thèse, nous présentons de nouvelles approches pour la détection de défauts sur des structures filaires plus ou moins complexes. L’idée est de trouver une nouvelle approche pour surmonter les difficultés des techniques de réflectométrie standards. Tout d’abord, des techniques de débruitage doivent être appliquées, telles que la décomposition en mode empirique (EMD), la décomposition moyenne locale (LMD), ou la transformée des ondelettes discrète (DWT). Ces trois méthodes décomposent un signal en plusieurs niveaux de reconstruire un signal utile. On montre dans ce manuscrit que l’EMD est la méthode la plus efficace, bien que limitée par les effets de bords. Ensuite, l’analyse temps fréquence est utilisée afin de détecter et localiser les défauts sur le câblage. Cette approche, basée sur la transformation de Fourier, ne permet de détecter les défauts de câblage que si le niveau de bruit est faible d’où l’intérêt de la première étape de débruitage. Par ailleurs, on propose aussi une approche bayésienne utile notamment lorsque la complexité du système augmente. Sa réponse est basée sur l’estimation des paramètres et des distributions à priori. Dans ce manuscrit, l’approche bayésienne est décrite mathématiquement puis les résultats validant l’approche sont présentés en analysant en particulier les paramètres qui affectent la performance de la méthode. Enfin, nous utilisons une approche de la réflectométrie chaotique temporelle basée sur les propriétés du signal chaotique. Les résultats montrent que cette méthode est capable de synthétiser des signaux et de localiser les défauts de câblage sans prétraitement ou informations a prioriIn this thesis, we present new approaches of soft fault detection and location in simple andcomplex wire networks. The idea is to find a new approach to overcome the difficulties withstandard reflectometry techniques. We prove that before applying post-treatment methods,denoising techniques should be applied, such as empirical mode decomposition (EMD), localmean decomposition (LMD), or the discrete wavelet transform (DWT). These three methodsdecompose a signal into multiple levels to threshold them before signal reconstruction.Testing several applications shows that EMD is the most efficient method, although it hassome limitations as side effects. After the denoising step, the wiring faults can be detected.Time–frequency analysis is employed at this step. This approach, based on the FourierTransform, is able to detect wiring faults only if the noise level is low. To overcome thisdifficulty, the Bayesian approach is beneficial when system complexity increases. Its responseis based on estimation of prior parameters and prior distributions. In this work, the Bayesianapproach is applied via a formal mathematical study followed by simulation results validatingthe proposed approach, with analysis of the parameters that affect the method’s performance.In the domain of soft fault location, we derive a chaos time domain reflectometry approachbased on chaotic signal properties. Our simulation and experimental results prove that thismethod can synthesize signals and localize the soft fault position without the need forsupplemental methods
23
Trad, Farah. "Stability of some hyperbolic systems with different types of controls under weak geometric conditions". Electronic Thesis or Diss., Valenciennes, Université Polytechnique Hauts-de-France, 2024. http://www.theses.fr/2024UPHF0015.
Testo completoAbstract (sommario):
Le but de cette thèse est d'étudier la stabilisation de certaines équations d'évolution du second ordre. Tout d’abord, nous nous concentrons sur l’étude de la stabilisation d’équations d’évolution du second ordre de type hyperbolique localement faiblement couplées, caractérisées par un amortissement direct dans une seule des deux équations. Comme de tels systèmes ne sont pas exponentiellement stables, nous souhaitons déterminer les taux de décroissance de l’énergie polynomiale. Nos principales contributions concernent les propriétés abstraites de stabilité forte et polynomiale, qui sont dérivées des propriétés de stabilité de deux problèmes auxiliaires : l'équation avec amortissement unique et l'équation avec amortissement liée à l'opérateur de couplage. La principale nouveauté est que les taux de décroissance d'énergie polynomiale sont obtenus dans plusieurs situations importantes non abordées auparavant, y compris le cas où l'opérateur de couplage n'est ni partiellement coercitif ni nécessairement limité. Les principaux outils utilisés dans notre étude sont l’approche du domaine fréquentiel combinée à une nouvelle technique de multiplicateurs basée sur les solutions des équations résolvantes des problèmes auxiliaires susmentionnés. Le cadre abstrait développé est ensuite illustré par plusieurs exemples concrets non traités auparavant. Ensuite, la stabilisation d'une équation de plaque de Kirchhoff bidimensionnelle avec des conditions aux limites acoustiques généralisées est examinée. En employant une approche spectrale combinée à un critère général d'Arendt-Batty, nous établissons d'abord la forte stabilité de notre modèle. Nous prouvons ensuite que le système ne se dégrade pas de façon exponentielle. Cependant, à condition que les coefficients des conditions aux limites acoustiques satisfassent à certaines hypothèses, nous prouvons que l'énergie satisfait à différents taux de décroissance de l'énergie polynomiale en fonction du comportement de notre système auxiliaire. Nous étudions également le taux de décroissance sur les domaines satisfaisant aux conditions aux limites du multiplicateur. De plus, nous présentons quelques exemples appropriés et montrons que nos hypothèses ont été correctement définies. Enfin, nous considérons un problème de transmission d'ondes avec des conditions aux limites acoustiques généralisées dans un espace unidimensionnel, dont nous étudions la stabilité théoriquement et numériquement. Dans la partie théorique nous prouvons que notre système est fortement stable. Nous présentons ensuite divers taux de décroissance d'énergie polynomiale, à condition que les coefficients des conditions aux limites acoustiques satisfassent certaines hypothèses, nous donnons des exemples pertinents pour montrer que nos hypothèses sont correctes. Dans la partie numérique, nous étudions une approximation numérique de notre système utilisant la discrétisation en volumes finis dans un schéma à variables spatiales et différences finies dans le tempsThe purpose of this thesis is to investigate the stabilization of certain second order evolution equations. First, we focus on studying the stabilization of locally weakly coupled second order evolution equations of hyperbolic type, characterized by direct damping in only one of the two equations. As such systems are not exponentially stable , we are interested in determining polynomial energy decay rates. Our main contributions concern abstract strong and polynomial stability properties, which are derived from the stability properties of two auxiliary problems: the sole damped equation and the equation with a damping related to the coupling operator. The main novelty is thatthe polynomial energy decay rates are obtained in several important situations previously unaddressed, including the case where the coupling operator is neither partially coercive nor necessarily bounded. The main tools used in our study are the frequency domain approach combined with new multipliers technique based on the solutions of the resolvent equations of the aforementioned auxiliary problems. The abstract framework developed is then illustrated by several concrete examples not treated before. Next, the stabilization of a two-dimensional Kirchhoff plate equation with generalized acoustic boundary conditions is examined. Employing a spectrum approach combined with a general criteria of Arendt-Batty, we first establish the strong stability of our model. We then prove that the system doesn't decay exponentially. However, provided that the coefficients of the acoustic boundary conditions satisfy certain assumptions we prove that the energy satisfies varying polynomial energy decay rates depending on the behavior of our auxiliary system. We also investigate the decay rate on domains satisfying multiplier boundary conditions. Further, we present some appropriate examples and show that our assumptions have been set correctly. Finally, we consider a wave wave transmission problem with generalized acoustic boundary conditions in one dimensional space, where we investigate the stability theoretically and numerically. In the theoretical part we prove that our system is strongly stable. We then present diverse polynomial energy decay rates provided that the coefficients of the acoustic boundary conditions satisfy some assumptions. we give relevant examples to show that our assumptions are correct. In the numerical part, we study a numerical approximation of our system using finite volume discretization in a spatial variable and finite difference scheme in time
24
Giuliani, Corrado. "Automatic analysis of electrocardiographic repolarization: innovative approaches in the time and frequency domains". Doctoral thesis, Università Politecnica delle Marche, 2015. http://hdl.handle.net/11566/242935.
Testo completoAbstract (sommario):
La morte cardiaca improvvisa (SCD) rappresenta la causa principale di morte nei paesi industrializzati. Conseguentemente, a scopo preventivo, sono stati proposti numerosi indici, basati sull'onda T elettrocardiografica,cioè la ripolarizzazione cardiaca, tra i quali i più usati sono l'intervallo QT e la T-wave alternans. Tuttavia, nessuno di questi indici è stato in grado di fornire sensibilità e specificità sufficienti a giustificare terapie preventive. E' stato inoltre osservato che cambiamenti nella morfologia della ripolarizzazione si riflettono in variazioni del contenuto in frequenza delle onde T. Quindi gli obiettivi di questa tesi sono: (i) proporre indici basati sul contenuto in frequenza delle onde T e (ii) migliorare l'affidabilità dell'intervallo QT tramite una nuova procedura per l'identificazione della fine delle onde T (Toff).
(i) E' stata valutata la capacità di quattro nuovi indici, AUNE2-5, AUNE10-35, TCE10 e f99, sia nell'individuare la patologia sia come indici di rischio. L'indice f99 è risultato il più promettente: infatti, oltre a discriminare pazienti con patologie analogamente agli altri indici proposti, è anche utilizzabile come indice di rischio cardiovascolare.
(ii) L'onda T dominante (DTW), cioè un'onda globale di ripolarizzazione, è stata utilizzata per identificare i Toff tramite due algoritmi presenti in letteratura. La DTW è stata prima calcolata su tutte e 15 le derivazioni elettrocardiografiche, quindi su gruppi di derivazioni linearmente indipendenti per verificare se i risultati possano essere influenzati da ridondanza. L'identificazione dei Toff è risultata equivalente tra i due metodi quando la DTW è ottenuta usando le 15 derivazioni; Inoltre è stato verificato che non dipende dal numero di derivazioni usate per il calcolo della DTW, quando questo è superiore a 8.
In conclusione l'indice f99 e l'uso della DTW per migliorare l'affidabilità dell'intervallo QT sono un passo in avanti nell'analisi della ripolarizzazione cardiaca.Sudden cardiac death (SCD) is one of the leading causes of death in developed countries. Consequently, several noninvasive predictors of SCD based on the T-wave, that is the cardiac repolarization on electrocardiogram (ECG) tracings, have been proposed in the literature, such as the QT-interval and the T-wave alternans. However, none of these indexes has proven sufficient sensitivity and specificity to justify preventive treatments. Abnormalities in the repolarization morphology are reflected, in the frequency domain, in a variation of the T-wave frequency content. Thus, aims of the present thesis are: (i) to propose innovative frequency-based repolarization index (Toff) and (ii) to improve QT-interval reliability introducing a new procedure to help identify T-wave offsets (Toff). To aim (i), 4 new indexes are proposed, termed AUNE2-5, AUNE10-35, TCE10 and f99, and their ability to discriminate clinical to pathological condition or to assess cardiovascular risk is evaluated. As a result, the f99 is the most promising frequency-based repolarization index among all proposed, being able to assess cardiovascular risk, even though each of these indexes is able to discriminate clinical to pathological condition. To aim (ii), the dominant T-wave (DTW), which is a global repolarization waveform, is used to improve QT-interval reliability by identifying Toff on DTWs computed over all the clinical available 15 ECG leads and then over smaller, yet linear independent, leads' groups, to test if data redundancy could bias the analysis. As a result, Toff identification by two automatic methods is equivalent when performed on DTWs computed over 15 leads and results are not affected by data redundancy, being statistically comparable and strongly correlated when Toffs are identified on DTWs computed over 8 or more leads. In conclusion, the proposed innovative f99 index and the use of DTW to improve QT-interval reliability represent a step further in the ECG repolarization analysis.
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Lee, Kyungmi. "Effective Approaches to Extract Features and Classify Echoes in Long Ultrasound Signals from Metal shafts". Thesis, Griffith University, 2007. http://hdl.handle.net/10072/366794.
Testo completoAbstract (sommario):
Applications of machine learning demand exploration of feature extraction methods and classifier types in order to obtain systems with reliable highest accuracy. The industrial application discussed in this thesis is the classification of ultrasonic echoes in an A-scan. The application is particularly challenging as A-scans are taken from the end of long large complex metal shafts. Although several pattern analysis and machine learning techniques have been used with success in analyzing A-scan data [43, 89], they are typically in the context of very short signals produced from machine parts like plate surfaces or pipe surfaces. Those cases are usually much simpler; in particular, the task reduces to detecting the existence of an echo (indicating a fault in the material). When signals for testing come from long shafts, however, a major problem of mode-converted reflection emerges. These reflections are echoes that do not correspond to real faults (cracks), nor to characteristics in the shaft. These mode-converted echoes may cause misjudgement of the position of cracks on shafts as some critical faint echoes from a cracked surface may lie somewhere among the multiple secondary echoes. Consequences of misclassification are catastrophic with enormous cost in downtime, consequential damage to associate equipment and potential injury to personnel [23]. The problem is then, to discriminate efficiently the different types of reflectors amongst the large volumes of digitalized ultrasonic shaft defect information. As the relationship between ultrasonic signal characteristics and flaw classes is not straightforward, we need to identify and extract informative sets of signal features from which classification might be performed more efficiently and accurately. Among various methods for extracting signal features, the Fast Fourier Transform (FFT) is a useful scheme for extracting frequency-domain signal features [23, 62]. This seems natural when dealing with ultrasound since the traditional representation of these types of signals is by mathematical Fourier series that identify physically meaningful features, like frequency and phase. But recent studies on the ultrasonic flaw classification employ the Discrete Wavelet Transform (DWT) as part of their feature extraction scheme. DWT provides effective signal compression and time-frequency presentation [69, 86]. Many researchers have compared these two feature extraction schemes (FFT and DWT), and most comparisons showed a superiority of DWT to FFT in discriminating the type of flaw (or its non-existence) [74, 78, 90]. However, these previous reported studies have compared the DWT based features with the FFT with limited feature components. Typically, short signals have been reported, with little attention to phase components of FFT sequences. This thesis is the first study analyzing feature extraction in more complex ultrasonic signals from shafts. In particular, we introduce a new FFT-based feature extraction scheme FFT_Magpha which effectively represents both magnitude and phase components of FFT sequences. By employing this state-of-the-art FFT feature extraction scheme, we have more extension and reliability in the investigation about the feasibility of FFT as a better feature extraction scheme than other types of feature extraction schemes such as DWT. On the other hand, the time-variance problem exhibited in DWT has resulted in reservations about its wide acceptance even though DWT coefficients provide effective time-frequency representation of non-stationary signals, and thus are considered useful features for input into classifiers. To solve this, we study a new preprocessing technique for time-domain A-scans, which offer consistent extraction of a segment of the signal from long signals that occur in the NDT of shafts. We compare the performance of this new echo-gating technique with other previously developed methods and investigate that we can use DWT more efficiently as a feature extraction scheme for ultrasonic signal classification by employing this new method in the preprocessing stage. In addition, our investigation in this thesis finds the potential of DWT to be a more reliable feature extraction scheme, through the more stable classification results in different runs of cross validation tests than the results produced in the tests using FFT-based feature extraction scheme. This potential is especially beneficial for the practical NDT for shafts, where we can train a classifier with arbitrary training data and then use the classifier for in-field ultrasonic shaft signal test. We also demonstrate the superiority of using DWT as the feature extraction scheme in the ultrasonic shaft signal classification involving not only ANN hut also SVM. These results dissipate any doubt that the DWT feature extraction methodology is too far suited for ANN which has been popularly employed previously in many similar experimental scenarios. Through these experimental comparisons employing various learning algorithms, we find a certain facility when specific classes of echoes are concerned with different combinations of feature extraction (FFT or DWT) and classifier (ANN or SVM), though DWT is superior to FFT and SVM is superior to ANN in terms of the overall classification accuracy. This
finding leads into a hybrid classifier that will improve overall performance by giving more weight to the more trustworthy sub-classifier. Based on those experimental analysis, we design an Integrated SVM classifier (ISVM) which is a combined classification system efficiently employing benefits from each of two SVM classifiers using two feature extraction schemes, FFT aud DWT. The outcomes of a classifier based on FFT is not totally dismissed in this system although the DWT-based classifier has been shown to be superior. This property of ISVM enables us to combine classifiers considering the misclassification cost, to obtain a more informative classification for its application in the field. We also explore the diverse possibilities of heterogeneous and homogeneous ensembles by combining the classifiers along the dimension of feature extraction mechanism, along the dimension of combination method and along the dimension of type of classifier. The experimental result suggests guidelines for designing an integrated multi-classifier system for shaft test data by way of selectively employing the combining structure.Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Information and Communication Technology
Full Text
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El, Hellani Doha. "Approche LMI pour l'analyse et la synthèse de filtres H∞ dans un domaine fréquentiel fini". Electronic Thesis or Diss., Amiens, 2018. http://www.theses.fr/2018AMIE0021.
Testo completoAbstract (sommario):
Ce mémoire aborde la synthèse de filtres H∞ sur des domaines fréquentiels finis pour différentes classes de systèmes dynamiques, tels que les systèmes linéaires avec incertitudes paramétriques, les systèmes à retard, les systèmes non linéaires de type Takagi-Sugeno (TS) et les systèmes sous contraintes de communication. Les contributions portent sur le développement de nouveaux outils d'analyse et de synthèse de filtres H∞, qui sont moins restrictifs par rapport aux résultats existants dans la littérature et permettent de réduire le conservatisme de celles-ci tout en garantissant que les méthodes proposées soient numériquement efficaces. Les conditions de stabilité et de synthèse de filtres pour les différentes classes de systèmes dynamiques sont formulées en des problèmes d'optimisation convexe sous contraintes d'inégalités matricielles linéaires (LMIs). Des exemples numériques et des comparaisons avec des résultats récents de la littérature sont également présentés afin de montrer les avantages et l'intérêt des approches proposéesThis work is concerned with the H∞ filtering problem in a finite frequency domain for different types of dynamic systems, such that uncertain systems, nonlinear systems via TS fuzzy model, time delay systems and systems with communication constraints. The main contribution is the development of new H∞ filter analysis and design approaches which reduce the conservatism of results found in the literature. The filter stability and design problems, for different classes of dynamic systems, are formulated as optimization problems with Linear Matrix Inequality (LMI). Simulation examples are presented to demonstrate the effectiveness and the less conservatism of the proposed approaches in comparison with other solutions that appear in the literature
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Lamara, Abderrahim. "Approche CRONE multivariable : développement et application à la régulation de bancs d'essais moteur haute dynamique". Thesis, Bordeaux, 2015. http://www.theses.fr/2015BORD0069/document.
Testo completoAbstract (sommario):
Le travail de cette thèse s'inscrit dans le cadre du développement de la méthodologie CRONE (Commande Robuste d'Ordre Non Entier) multivariable. Il porte plus précisément sur la simplification de sa mise en oeuvre pour la synthèse de régulateurs multivariables robustes, avec une application au contrôle de bancs d'essais moteur haute dynamique, notamment ceux développés par l'entreprise D2T. Le premier chapitre présente les différents types de bancs d'essais, leur fonctionnement et leur problématique. Le deuxième chapitre présente tout d'abord une modélisation physique simple des bancs d'essais qui en permet ensuite leur simulation, puis est dédié à leur identification fréquentielle avec une application à un banc d'essais équipé d'un moteur Diesel. Le troisième chapitre présente la méthodologie CRONE multivariable et différents développements permettant d'en simplifier la mise en oeuvre notamment grâce à l'optimisation d'un nouveau paramètre. Illustrant ces développements, la boite à outils CRONE multivariable qui a été développée est alors utilisée pour la synthèse de la loi de commande d'une maquette de banc d'essais constituée de deux moteurs asynchrones. Finalement, le quatrième chapitre est dédié à la validation des développements présentés par leur application à un banc d'essais haute dynamique équipé d'un moteur Essence. Ce chapitre présente également les différents outils logiciel développés pour faciliter l'intégration de la méthodologie CRONE full MIMO aux produits D2TThe work presented in this Thesis is part of the CRONE (robust control with fractional integration order) multivariable methodology development. It deals with the simplification of the robust multivariable control system implementation with application to the control of high dynamic engine test-benches, including those developed by the D2T company. The first chapter introduces different kind of test-benches and gives a general idea about how those systems work while explaining their problems. While the first part of chapter II presents a simple method for test-benches modeling which then allows their simulation, the second part is dedicated to their frequency-domain system identification. The defined identification procedure is applied to a test-bench equipped with a Diesel engine. The third chapter presents the CRONE multivariable methodology and different developments to simplify its use. Reflecting these developments, the developed CRONE multivariable toolbox is used to design a control system for a test-bench consists of two asynchronous motors. The fourth chapter is dedicated to validate the presented work by applying these developments to a high dynamic test-bench with a spark ignition engine. This chapter presents the various software tools developed to simplify the implementation to D2T products of the CRONE full MIMO methodology
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Zarudniev, Mykhailo. "Synthèse de fréquence par couplage d'oscillateurs spintroniques". Phd thesis, Ecole Centrale de Lyon, 2013. http://tel.archives-ouvertes.fr/tel-00804561.
Testo completoAbstract (sommario):
La tendance actuelle dans le domaine des télécommunications mène à des systèmes capables de fonctionner selon plusieurs standards, et donc plusieurs fréquences porteuses. La synthèse de la fréquence porteuse est un élément clef, dont les propriétés reposent essentiellement sur les performances de l'oscillateur employé. Pour assurer le fonctionnement de systèmes compatibles avec plusieurs standards de télécommunication, la solution conventionnelle consiste à intégrer plusieurs oscillateurs locaux. Cette solution est coûteuse, d'autant plus que, malgré le fait que les technologies actuelles atteignent des niveaux d'intégration très importants, la surface occupée par des oscillateurs traditionnels de type LC ne peut pas être diminuée, alors que le coût de fabrication au millimètre carré devient de plus en plus élevé. Il serait donc très intéressant de remplacer les oscillateurs LC, ce qui nous amène à rechercher des solutions alternatives parmi de nouvelles technologies. L'oscillateur spintronique (STO) est un nouveau dispositif issu des études sur les couches minces magnétiques. Il apparait comme un candidat potentiel de remplacement des oscillateurs LC du fait de sa grande accordabilité en fréquence et de son faible encombrement. Toutefois des mesures effectuées sur les STOs ont montré que la performance en puissance et en bruit de phase d'un oscillateur seul ne permet pas de remplir les spécifications pour des applications de télécommunication. Nous proposons de remplir ces spécifications en couplant un nombre d'oscillateurs spintroniques important. Dans ce cadre se posent plusieurs questions qui concernent les procédures de modélisation, d'analyse et de synthèse des systèmes interconnectés. Les procédures de modélisation incluent la démarche de recherche de modèles à complexité croissante qui décrivent les propriétés entrée-sortie d'un oscillateur spintronique, ainsi que la démarche de généralisation des modèles des oscillateurs dans le cadre du réseau. Les procédures d'analyse cherchent à vérifier la stabilité et évaluer la performance des systèmes interconnectés. Les procédures de synthèse permettent de concevoir des interconnexions sophistiquées pour les oscillateurs afin d'assurer toutes les spécifications du cahier des charges. Dans ce document, nous établissons tout d'abord le problème de la synthèse de fréquence par couplage avec un cahier des charges formalisé en termes de gabarits fréquentiels sur des densités spectrales de puissance. Le cahier des charges posé amène la nécessité de modéliser l'oscillateur spintronique pour pouvoir simuler et analyser son comportement. Ici, nous proposons une modélisation originale selon des degrés de complexité croissante. Ensuite, nous discutons de la structure de la commande de l'ensemble des oscillateurs afin de remplir les spécifications du cahier des charges. La structure de commande proposée nécessite de développer une méthode de conception des interconnexions du réseau d'après les critères de performance. Dans les deux derniers chapitres, nous proposons deux méthodes fréquentielles de synthèse originales pour résoudre le problème de synthèse de fréquence par couplage. La première méthode de synthèse permet de prendre en compte un critère mathématique du cahier des charges, qui correspond à un gabarit fréquentiel à respecter, et permet d'obtenir une matrice d'interconnexion des sous-systèmes, telle que le module de la réponse fréquentielle du réseau approxime le gabarit imposé par le cahier des charges. La deuxième méthode de synthèse permet de prendre en compte plusieurs gabarits fréquentiels à la fois. La solution obtenue est une matrice d'interconnexion des sous-systèmes, qui résout le problème de la synthèse de fréquence par couplage d'oscillateurs spintroniques.
29
Yang, Li Tung, e 李東陽. "Nonlinear System Identification: Time-Frequency Domain Approach". Thesis, 2003. http://ndltd.ncl.edu.tw/handle/93307553240433948283.
Testo completoAbstract (sommario):
碩士國立臺灣大學
土木工程學研究所
91
This dissertation presents the development of structural identification procedures for a nonlinear SDOF system. It consists of three parts: i) Test of the system nonlinearity using input/output data or only using output data, ii) Reconstruct the nonlinear system restoring force mathmatical model, iii) Reconstruct system NARX model. The tests of nonlinearity conclude HTD test and bispectrum test. The restoring force mathematical model is established by chebyshev polynomials. And the system NARX model is solved by orthogonal least square method. Finally, a numerical simulation of inelastic SDOF system with Bouc-Wen model and an experimental study of 3-Story RCS frame were used to test the applicability of the proposed methods.
30
LIAO, WEI-LIANG, e 廖威量. "Flutter analysis of an oscillating airfoil by frequency domain approach". Thesis, 1989. http://ndltd.ncl.edu.tw/handle/71646600072201712337.
Testo completo
31
Sha, Shaoshu. "A frequency domain approach for time-reversal of microwave impulses". 2009. http://hdl.handle.net/10106/1787.
Testo completo
32
Chen, Chi-Hsiao, e 陳基孝. "Frequency Domain Approach for Multiple Narrowband Interference Cancellation in GPS Receivers". Thesis, 2013. http://ndltd.ncl.edu.tw/handle/80206365751356834513.
Testo completoAbstract (sommario):
碩士國立臺灣大學
電子工程學研究所
101
Nowadays, GPS (Global Positioning System) has been widely integrated into consumer electronics products. The harmonic frequencies caused by other components may interfere with the GPS receivers. Therefore, GPS receivers need to implement an interference excision mechanism to deal with the issue. In this thesis, we propose using the consecutive mean excision (CME) algorithm, which is a frequency-domain-based digital signal processing (DSP) approach, to implement an anti-jamming filter. The CME algorithm leverages the fact that the magnitude spectrum of the un-jammed GPS signal should have a Rayleigh distribution to adaptively adjust an excision threshold. By excising all the frequency bins whose magnitudes are above the threshold, the resulting magnitude spectrum ideally becomes Rayleigh distribution again. Therefore, the narrow band jamming signals can be eliminated. Moreover, the impaction of the proposed anti-jamming filter on the acquisition and tracking loops in the GPS receiver is analyzed. Finally, we compare the approach in this thesis with one related previous work. Our method can handle more than two times the number of interference and at most eight jamming signals with jamming-to-signal ratio (JSR) of 25 dB. In this case, the anti-jamming filter does not affect the acquisition of C/A code phase and the resulting detection probability is over 90%; the resulting tracking errors are 10-3 chips, 0.5 Hz, and 0.20, with respect to the code phase, carrier frequency, and carrier phase.
33
Huang, Kuen-Yu, e 黃堃宇. "A Time Domain Approach to High-Frequency Circuit Simulation of Semiconductor Devices". Thesis, 2005. http://ndltd.ncl.edu.tw/handle/16133979209925385508.
Testo completoAbstract (sommario):
博士國立交通大學
電子工程系所
94
In order to solve the radio-frequency (RF) steady-state, that is ,high-frequency periodic circuit problem, such as intermodulation distortion, we develop a new numerical solution technique in this dissertation to simulate circuits in time-domain. Traditional transient analysis in SPICE-like time-domain solver is not suitable for RF steady-state solution. The tough criteria for solving steady-state problem in time- domain drive us to build our own time-domain circuit solver. This solver should be stable, efficient, and able to handle strongly nonlinear circuits, for instance, the large-signal models for semiconductor devices. Combining the waveform relaxation (WR) method, monotone iterative (MI) method, and Runge-Kutta (RK) method, we succeeded in solving the circuit ordinary differential equations (ODEs) in time domain that satisfies the criteria of the RF steady-state analysis. The convergence of our developed algorithms has been proved and demonstrated in this dissertation. We also perform subsequent analysis, such as the discrete Fourier transform (DFT), to extract the frequency-domain information from simulated time-domain data. In this dissertation, we use our numerical solution techniques to simulate the characteristics of heterojunction bipolar transistors (HBTs) with the Gummel-Poon (GP) model. The results of DC circuit calculation, time-domain simulation, frequency-domain analysis and intermodulation distortion characterization are presented. Furthermore, we compare the results of various simulators (our solver, HSPICE and ADS) with measured data to show the accuracy and efficiency of the developed method. For HBTs under high bias and high power operation, the thermal effects dominate the behavior of the device. Therefore, we include the electrical-thermal interactive equations in our numerical solution technique to further improve the reality of the simulation. The difference between the simulations with and without thermal effects is well discussed in the context of this dissertation. In additional, we describe the thermal coupling effects of an multi-finger HBT and its influence on DC, RF power and intermodulation distortion characteristics. In the appendixes, the EPFL-EKV compact model of the metal-oxide semiconductor field-effect transistors (MOSFETs) is discussed and the related circuits are simulated by the proposed method and HSPICE. The convergence properties of the utilized algorithms are presented in these appendixes. According to the discussion in this dissertation, the developed approach is not only an alternative computational technique for the time-domain solution of nonlinear circuit ODEs but also can be generalized for high-frequency circuits simulation including more and variant kind of semiconductor devices.
34
Chevallier, Arnaud Michel. "A probabilisitc approach to the frequency domain analysis of drill-string lateral vibrations". Thesis, 1998. http://hdl.handle.net/1911/17161.
Testo completoAbstract (sommario):
Drill-string failure is recognized by the drilling community as one of its most costly and frequently encountered problems. In order to diminish the frequency of such failures, the drilling community has been focusing on the modeling of the static and dynamic behaviors of drill-strings, towards increasing efficiency. Drill-string dynamics involves complex phenomena with excitations in axial, lateral and torsional directions, and coupling of these three and other factors such as mass imbalance, whirling, or stick-slip motion of the bit.
The present study focuses on one aspect which has not been studied in detail by the drilling community, namely the consideration of random loads on the BHA studied by a frequency domain approach. A comprehensive literature survey is attempted and elucidating numerical results are provided.
35
Moghadam, Amin. "A signal-processing-based approach for damage detection of steel structures". Thesis, 2019. http://hdl.handle.net/2097/39465.
Testo completoAbstract (sommario):
Master of ScienceDepartment of Civil Engineering
Hani G. Melhem
This study reports the results of an analytical, experimental and a numerical study (proof of concept study) on a proposed method for extracting the pseudo-free-vibration response of a structure using ambient vibration, usually of a random nature, as a source of excitation to detect any change in the dynamic properties of a structure that may be caused by damage. The structural response contains not only a random component but also a component reflecting the dynamic properties of the structure, comparable to the free vibration for a given initial condition. Structural response to the arbitrary excitation is recorded by one or several accelerometers with a desired data-collection frequency and resolution. The free-vibration response of the structure is then extracted from this data by removing the random component of the response by the method proposed in this study. The features of the free-vibration response of the structure extracted by a suitable method, namely Fast Fourier Transform (FFT) in this study, can be used for change detection. Possible change of the pattern of these features is dominantly linked to the change in dynamic properties of the system, caused by possible damage. To show the applicability of the concept, besides an analytical verification using Newmark’s linear acceleration method, two steel portal frames with different flexural stiffness were made in the steel workshop of the structural laboratory for an experimental study. These structures were also numerically modeled using a finite element software. A wireless accelerometer with a sampling frequency rate of 2046 Hz was affixed on the top of the physical structure, at the same location where the acceleration was recorded for the corresponding numerical model. The physical structure was excited manually by an arbitrary hit and the response of the structure to this excitation, in terms of the acceleration on the top of the structure, was recorded. The pseudo-free-vibration response was extracted and transferred into frequency domain using FFT. The frequency with the largest magnitude which is the fundamental frequency of the structure was traced. This was repeated for several independent excitations and the fundamental frequencies were observed to be the same, showing that the process can correctly identify the natural frequencies of the structure. Similarly, the numerical model was excited and for several base excitation cases, the fundamental frequencies were found to be the same. Considering the acceptable accuracy of the results from the two numerical models in simulating the response of their corresponding physical models, additional numerical models were analyzed to show the consistency and applicability of the proposed method for a range of flexural stiffness and damping ratio. The results confirm that the proposed method can precisely extract the pseudo-free-vibration response of the structures and detect the structural frequencies regardless of the excitation. The fundamental frequency is tied to the stiffness and a larger stiffness leads to a higher frequency, as expected, regardless of the simulated ambient excitation.
36
Wu, Chang-Yen, e 吳昌晏. "Applying Causality Frequency-Domain Approach to Test Housing Bubble-The Case of Japan and America". Thesis, 2013. http://ndltd.ncl.edu.tw/handle/26850939197044872734.
Testo completoAbstract (sommario):
碩士逢甲大學
財務金融學系碩士班
101
This paper uses OECD and AMECO annual databases to investigate frequency domain causality between personal disposable income and house price index from 1970 to 2011 to determine whether there is housing bubble in Japan and USA. We find that the personal disposable income in long-term and short-term has no Granger causality with house price index in USA, but house price index has Granger causality with personal disposable income in USA. After adding stock price index as control variable, we find that both personal disposable income to house price and house price to personal income have no long-term relationship, After adding interest rate as control variable, we find that personal disposable income to house price index has middle-term Granger causality , but house price to personal disposable income has no Granger causality Before adding stock or interest rate as control variable, Japanese personal disposable income to house price has middle and short-term Granger causality and house price index to personal disposable income exists Granger causality. After adding stock price index as control variable, we find that personal disposable income to house price index has more power of Granger causality in short-term, but house price to personal disposable income has no Granger causality, After adding interest rate as control variable, both personal disposable income to house price and house price to personal income have no long-term relationship.
37
Wang, Chih-liang, e 王志良. "A Frequency-Domain Approach to the Design of 2-D Quadratic Filters and its Application to Image Processing". Thesis, 1997. http://ndltd.ncl.edu.tw/handle/75167769426155470073.
Testo completoAbstract (sommario):
碩士國立海洋大學
電機工程學系
85
Two-dimensional(2-D) quadratic filters have been found very effective in image processing problems such as edge preserving smoothing, edge extraction, texturediscrimination, prediction of image sequences and interpolatrion of image sequences.The relation between the input and output od 1 2-D quadratic filter can be describedby a 2-D second-order Volterra series. The advantage od a quadratic filter overa traditional linear filter is derived from its more elaborate modeling capabilityin describing nonlinear effects of engineering applications. However, there is a lackof guidelines on finding an appropriate 2-D quadratic filter for a certain task. Therefore, how to design 2-D quadrat, efficiently is a bottleneck to be broken through. A solution, which was suggested by previous researchers, to this problem is to use an optimization technique. More explicity, the optimum 2-Dquadratic filter is obtained by minimizing an objective function(for example, themean square error) subject to the required I/O relation. As recorded in the literatures, conventional methods, including the steepestdescent method, the Powell's direction method, and the simulated annealing, havebeen developed. All of these methods design 2-D quadratic filters in the space-domainand obtain acceptable results. However, sometimes these methods may not lead to satisfactory results because they may consume a lot of time just to reach a localoptimum---the repayment is far behind the investment. In this thesis, a novel design methodlogy is presented. By working in the frequency-domain,the proposed method is shown to be able to determine the optimum(in the sense of minimummean square error) filter coefficients of the 2-D quadratic filter. We show that, in the frequency-domain, the constrained optimization task in the conventional approach can beconverted to an unconventional problem with a quadratic objective function. Suchan objective function guarantees that the global optimum, instead of a local optimum, can be easily obtained. The feasibility of the novel technique will be verified by an applicationexample.
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Chen, Ying Hao, e 陳英儫. "The link between expenditure for Police Service and Number of fraud or Number of theft--A frequency-domain approach". Thesis, 2013. http://ndltd.ncl.edu.tw/handle/92132344544741569262.
Testo completo
39
Ying, Chen-Ling, e 應誠霖. "Design of Quantitative Robust Control Systems Using Frequency Domain Approaches". Thesis, 2002. http://ndltd.ncl.edu.tw/handle/98601375305746057819.
Testo completoAbstract (sommario):
博士元智大學
電機工程學系
90
In this dissertation, the equivalent disturbance rejection (EDR) design method is introduced to achieve quantitative robust control performance. Using this design method, the maximum variations of the uncertain plant can be transferred to an equivalent disturbance, and the maximum variations of the system tolerance can be transferred to a specified output response. The quantitative specification is then formulated in the inverse Nichols chart by calculating the values of bound functions at some specified frequencies using the sensitivity concept. Previous EDR design method is extended to handle stable and unstable systems plus both minimum and non-minimum phase multivariable systems in this dissertation. Finally, by loop shaping in the inverse Nichols chart, a robust controller can be designed to achieve quantitative robust performance. This dissertation also presents a design algorithm of involving robust decoupled control of uncertain multivariable feedback systems. For two-degree-of-freedom (2-DOF) system, quantitative feedback theory (QFT) is applied for feedback compensator design to achieve quantitative robustness. A decoupled model matching approach is employed for prefilter design to achieve input-output decoupling performance. On the other hand, the synthesis methodology of multivariable quantitative robust linear quadratic optimal control system is developed. Wiener-Hopf linear quadratic optimal control is introduced and is then incorporated with quantitative feedback theory robust control design technique to achieve the quantitative robust optimal control. Finally, an integrated control and diagnostic design method is proposed which uses the four-degree-of-freedom scheme. The robust controller presents a two-degree-of-freedom structure including the feedback controller and the prefilter. For failure diagnosis, the diagnostic filters are chosen to perform the fault detection. The adjoint technique is applied for threshold value determination to meet the diagnostic performance.
40
Ghosh, Rupak. "Effect of top tensioned risers (TTR) on the spar responses: Time domain and frequency domain approaches". Thesis, 2005. http://hdl.handle.net/1911/18766.
Testo completoAbstract (sommario):
The effect of top tension risers on the spar marine structure responses is studied by using time domain as well as frequency domain approaches. A simplified model of the combined dynamic system consisting of a spar, a mooring line system, and top tension risers is established. The top tension of a riser is provided by a buoyancy-can that is laterally supported by a preloaded compliant guide. The overall system is nonlinear due to the mooring line restoring force, the friction between the buoyancy-can and the compliant guides, and the friction between the risers and guides at the spar keel. The friction between the spar and riser system is represented via a continuous Coulomb model.
The simplified model is numerically integrated using input time histories of force and moment that are compatible with a random representation (Jonswap spectrum) of a typical extreme environmental loading in the Gulf of Mexico. For validation, the dynamic responses of the simplified system are compared with the related responses of the combined system. The effect of the top tensioned risers on the spar responses is studied by using nonlinear time domain analysis. The responses of the simplified model are also determined by using a frequency domain approach based on the statistical linearization technique. Several parametric studies are conducted to investigate the sensitivity of the spar responses to different design parameters.
41
Wood, Sean. "Non-negative matrix decomposition approaches to frequency domain analysis of music audio signals". Thèse, 2009. http://hdl.handle.net/1866/3769.
Testo completoAbstract (sommario):
On étudie l’application des algorithmes de décomposition matricielles tel que la Factorisation Matricielle Non-négative (FMN), aux représentations fréquentielles de signaux audio musicaux. Ces algorithmes, dirigés par une fonction d’erreur de reconstruction, apprennent un ensemble de fonctions de base et un ensemble de coef- ficients correspondants qui approximent le signal d’entrée. On compare l’utilisation de trois fonctions d’erreur de reconstruction quand la FMN est appliquée à des gammes monophoniques et harmonisées: moindre carré, divergence Kullback-Leibler, et une mesure de divergence dépendente de la phase, introduite récemment. Des nouvelles méthodes pour interpréter les décompositions résultantes sont présentées et sont comparées aux méthodes utilisées précédemment qui nécessitent des connaissances du domaine acoustique. Finalement, on analyse la capacité de généralisation des fonctions de bases apprises par rapport à trois paramètres musicaux: l’amplitude, la durée et le type d’instrument. Pour ce faire, on introduit deux algorithmes d’étiquetage des fonctions de bases qui performent mieux que l’approche précédente dans la majorité de nos tests, la tâche d’instrument avec audio monophonique étant la seule exception importante.We study the application of unsupervised matrix decomposition algorithms such as Non-negative Matrix Factorization (NMF) to frequency domain representations of music audio signals. These algorithms, driven by a given reconstruction error function, learn a set of basis functions and a set of corresponding coefficients that approximate the input signal. We compare the use of three reconstruction error functions when NMF is applied to monophonic and harmonized musical scales: least squares, Kullback-Leibler divergence, and a recently introduced “phase-aware” divergence measure. Novel supervised methods for interpreting the resulting decompositions are presented and compared to previously used methods that rely on domain knowledge. Finally, the ability of the learned basis functions to generalize across musical parameter values including note amplitude, note duration and instrument type, are analyzed. To do so, we introduce two basis function labeling algorithms that outperform the previous labeling approach in the majority of our tests, instrument type with monophonic audio being the only notable exception.