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Dissertations / Theses on the topic 'Frequency response analysis'
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Troeng, Tor. "Frequency Response Analysis using Component Mode Synthesis." Thesis, Umeå universitet, Institutionen för matematik och matematisk statistik, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-37809.
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Solutions to physical problems described by Differential Equationson complex domains are in except for special cases almost impossibleto find. This turns our interest toward numerical approaches. Sincethe size of the numerical models tends to be very large when handlingcomplex problems, the area of model reduction is always a hot topic. Inthis report we look into a model reduction method called ComponentMode Synthesis. This can be described as dividing a large and complexdomain into smaller and more manageable ones. On each of thesesubdomains, we solve an eigenvalue problem and use the eigenvectorsas a reduced basis. Depending on the required accuracy we mightwant to use many or few modes in each subdomain, this opens for anadaptive selection of which subdomains that affects the solution most.We cover two numerical examples where we solve Helmholtz equationin a linear elastic problem. The first example is a truss and the othera gear wheel. In both examples we use an adaptive algorithm to refinethe reduced basis and compare the results with a uniform refinementand with a classic model reduction method called Modal Analysis. Wealso introduce a new approach when computing the coupling modesonly on the adjacent subdomains.
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Li, Jie. "High frequency power transformer modelling for frequency response analysis (FRA) diagnosis." Thesis, University of Manchester, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.538489.
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Transformer fault diagnosis through Frequency Response Analysis (FRA) has been receiving a great deal of attention in recent years. As a comparative technique, FRA has good capability and sensitivity in detecting mechanical faults that are difficult to identify by conventional condition assessment techniques. Power transformers are among the most expensive equipment owned by electric utilities, and it is not reasonable to produce deformation on actual transformers and carry out measurement sensitivity studies. On the other hand, simulation models, which can accurately reproduce transformer high frequency behaviours, are flexible tools for performing FRA deformation type sensitivity studies for deriving FRA interpretation rules. The main objective of this thesis is to develop appropriate simulation models for use in FRA diagnosis and to improve the interpretation of FRA responses through simulation studies. The transformer models developed at the University of Manchester (then UMIST) were by far the best representation of state-of-art modelling techniques; the inductance and the capacitance of the basic model unit were calculated using winding geometry and material properties, the frequency dependent conductive and dielectric losses were also included. In addition, mutual capacitive and inductive couplings between units were carefully considered to ensure the accuracy of the model. However, there is still some room for improvement on these models and during this PhD research, major contributions are made on as. follows: firstly take core effect into consideration to reproduce valid FRA characteristic representation in the low frequencies, secondly status of network terminal nodes are uniformed represented by externally connecting an impedance so that during FRA deformation sensitivity study, it is flexible to change the terminal condition, thirdly reconfigure the network node and unit relationship so that tap winding connection are precisely represented as the design, finally convert the single-phase model to a three-phase model and by developing a reduced matrix model, keep the simulation accuracy intact for a three-phase transformer up to 2 MHz, at the same time reduce computational time significantly. In detail, this PhD thesis describes the following three parts of my research: Firstly a transformer model incorporating a magnetic core based on the Principle of Duality is established to interpret low frequency characteristics of FRA responses (from 10Hz to up to 1 kHz). This model includes leakage inductances and capacitances of windings and can explain FRA low frequency differences caused by asymmetry of magnetic paths in three-limb and five-limb core transformers. Secondly, FRA characteristics were studied systematically using a component-system approach through building models for single windings, a one-phase winding set and finally the three-phase transformer. In this way the effects of winding structure, inductive and capacitive coupling among windings, among phases and terminal connection effect on FRA characteristics were studied. FinaUya complete three-phase transformer reduced matrix model is built, that can flexibly represent winding terminal connection and precisely describe tap positions. Using this modelling strategy, transmission power transformers at 2751132 kVand 275/33 kV voltage levels are simulated and numerous deformation sensitivity studies are performed, in order to gain better understanding on their FRA characteristics and to identify FRA features of different winding deformation types on these transformers. The research indicates that the overall approach used to develop these simulation models has helped in improving interpretation of FRA responses. The transformer modelling techniques being developed, with further refinement, can be a useful tool for FRA diagnosis and benefit the test engineers from the industry.
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Elvik, Gary G. "Frequency response analysis of T-ACS experimental data." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2000. http://handle.dtic.mil/100.2/ADA384673.
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Visser, Wilhelmina Josefine. "Updating structural dynamics models using frequency response data." Thesis, Imperial College London, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.262548.
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El-Hajjar, Houssam Ziad. "Identification of transformer mechanical faults using frequency response analysis." Thesis, University of Manchester, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.540009.
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Mahmoodi, Seyed Nima. "Nonlinear vibration and frequency response analysis of nanomechanical cantilever beams." Connect to this title online, 2007. http://etd.lib.clemson.edu/documents/1193080354/.
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Ahmed, Ibrahim. "Use of frequency response analysis to detect transformer winding movement." Thesis, Ahmed, Ibrahim (2013) Use of frequency response analysis to detect transformer winding movement. Other thesis, Murdoch University, 2013. https://researchrepository.murdoch.edu.au/id/eprint/21677/.
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In this thesis, a study of continuous disc type 6.6kV transformer winding was utilised to investigate winding deformation by means of frequency response analysis (FRA). The equivalent electrical circuit is based on the lumped parameter model. Transformer elements include series capacitance, ground capacitance and inductance. The calculation were based on 6.6kV transformer design specification data sheet.
The values of the parameters were changed in order to simulate a likelihood of failure on the windings, which would correspond to unique frequency range spectrum. The FRA simulation range is from 10 kHz to 2 MHz. Then sensitivity analyses were performed to assess the accuracies of the two types of measurand: transfer function (Vout/Vin ) and trans impedance ( Vin/Iout).
Matlab/simpowersystem software was used for simulation analysis and the bodeplot command was implemented to graph the magnitude and phase of the equivalent circuit (healthy circuit) and circuit with introduced fault. A linear frequency scale was utilised in order to compare the small differences at certain frequency bands. This thesis presents FRA which includes sweep frequency response analysis (SFRA), the measurement techniques and interpretation of SFRA measurement.
In this thesis, a simulation model of a continuous disc type 6.6kV transformer was utilised to study frequency response analysis (FRA) which includes SFRA. The model was based on lumped parameters using circuit elements of series capacitance, inductance and ground capacitance. Faults were simulated through change in value of series capacitance, inductance and ground capacitance. . It was found that an increase of 20% in inductance, which corresponds to disc deformation and local breakdown faults etc. alters the FRA signature over the entire frequency range (10 Hz-2 MHz). On the other hand a change in series capacitance and ground capacitance which correlates to disc movement faults occurs only at frequencies above 400 kHz.
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Mohseni, Bahar. "Noise Detection and Elimination in Online Impulse Frequency Response Analysis." Thesis, Curtin University, 2017. http://hdl.handle.net/20.500.11937/57444.
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One of the main problems associated with implementing transformer impulse frequency response (IFRA) test online is coupling of external interferences and noise with measured signals, which can lead to misinterpretation of the results. To resolve this issue, in this study, initially, the distribution properties of different types of noise and their impact on the transformer online IFRA signature are investigated and secondly, a filtering technique for elimination of external interferences and noise is proposed.
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Kaplan, Matthew Frederick. "Implementation of automated multilevel substructuring for frequency response analysis of structures." Access restricted to users with UT Austin EID Full text (PDF) from UMI/Dissertation Abstracts International, 2001. http://wwwlib.umi.com/cr/utexas/fullcit?p3037508.
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Ware, Brenton R. "Frequency response based permittivity sensors for measuring air contaminants." Thesis, Kansas State University, 2012. http://hdl.handle.net/2097/14190.
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Master of Science<br>Department of Biological and Agricultural Engineering<br>Naiqian Zhang<br>Permittivity, displayed when a dielectric material is exposed to an electric field, is a useful property for measuring impurities in a dielectric medium. These impurities often have a dipole moment different from the pure material, and the dipoles align through polarization and impede electric current. By measuring the resulting impedance in a known geometry, the permittivity can be determined.
Four permittivity sensors were utilized to measure contaminants that are associated with biofuels, specifically glycerol, ethanol, and ammonia. These sensors were based around either stainless steel or aluminum plates to ensure durability and reliability. By connecting each of these sensors to a signal generating control box, the gain and phase can be measured at 609 frequencies, from 10 kHz up to 120 MHz.
Data from each of the three contaminants were run through a method for detection. Measurements for ambient air and air with the contaminants were compared with a statistical analysis. Glycerol, ethanol, and ammonia each had significantly different measurements in the gain and phase data at a unique set of frequencies. Using a neural network analysis for detection resulted in a 95.8%, 93.9%, and 97.1% success rate for detecting glycerol, ethanol, and ammonia, respectively.
For ethanol and ammonia, where multiple concentrations were measured, regression methods were used to relate the frequency response data to the contaminant concentration. Stepwise regression, wavelet transformation followed by stepwise regression, partial least squares regression, and neural network regression were the four methods used to establish these relationships. Several regressions over-fit the data, showing coefficient of determination (R[superscript]2) values of 1.000 for training data, yet very low R[superscript]2 values for validation data. However, the best R[superscript]2 values of all the regressions were 1.000 and 0.996 for the training and validation data, respectively, from measuring ammonia.
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Bedford, T. J. "Calculation of operational inductances of turbogenerators and their use in frequency domain transient analysis." Thesis, University of Newcastle Upon Tyne, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.383925.
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Roebuck, C. A. "Testing and frequency response analysis of an electric vehicle traction drive." Thesis, Coventry University, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.384599.
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Shafiei, Ziaedin. "Design and analysis of robust control systems by frequency response methods." Thesis, University of Liverpool, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.317391.
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Hashemnia, Naser. "Characterization of Power Transformer Frequency Response Signature using Finite Element Analysis." Thesis, Curtin University, 2014. http://hdl.handle.net/20.500.11937/731.
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Power transformers are a vital link in electrical transmission and distribution networks. Monitoring and diagnostic techniques are essential to decrease maintenance and improve the reliability of the equipment.This research has developed a novel, versatile, reliable and robust technique for modelling high frequency power transformers. The purpose of this modelling is to enable engineers to conduct sensitivity analyses of FRA in the course of evaluating mechanical defects of power transformer windings. The importance of this new development is that it can be applied successfully to industry transformers of real geometries.
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Gao, Zhen. "Stochastic Response Analysis of Mooring Systems with Emphasis on Frequency-domain Analysis of Fatigue due to Wide-band Response Processes." Doctoral thesis, Norwegian University of Science and Technology, Department of Marine Technology, 2008. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-2020.
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<p>Mooring systems are widely used in the offshore industry to limit the horizontal excursions of a floating structure from desired position in order for the structure to fulfill the required tasks. Safety of mooring systems is therefore crucial for successful marine operations.</p><p>Under the environmental actions of waves, wind and current, large dynamic tension in mooring lines can be excited at both wave frequency (WF) and low frequency (LF). Due to the nonlinearities of environmental loads and mooring systems, both WF and LF tension are non-Gaussian random processes. In this thesis, stochastic nonlinear mooring line tension has been modeled in an efficient way, by which, motion-induced WF tension is approximated by a simplified dynamic model, while LF tension is evaluated based on a quasi-static analysis. Especially, non-Gaussian fatigue of each frequency component has been explicitly estimated in the frequency domain, and fatigue induced by the combined tension, so-called bimodal fatigue problem, has been dealt with. The frequency-domain method for fatigue analysis has been exemplified by mooring analysis of a semi-submersible and validated by time-domain simulations and rainflow cycle counting method.</p><p>The degrading mechanism of e.g. corrosion has an influence on mooring system reliability, since mooring lines are normally submerged in sea water for a long period of interest. A time-variant reliability problem is formulated herein using a probabilistic analysis of corrosion. The problem is solved by a piece-wise constant model of line strength and the effect of corrosion on mooring safety has been analyzed in terms of annual failure probability increasing with time.</p><p>Another problem discussed in this thesis is mooring system responsein a partially damaged condition. Extensive mooring analyses have been carried out using varying long-term environmental conditions and considerable increases of tension loads in the neighboring mooring lines have been obtained due to failure of one line. Significant variations in the yearly and even seasonal wave conditions and the induced extreme and fatigue responses of mooring systems together with other marine vessels, like an FPSO and a semi-submersible, have been analyzed. These variations could have a notable effect on the safety assessment of these structures.</p><p>In addition, an efficient method for estimating the damping of LF vessel motions caused by mooring systems has been proposed based on the simplified dynamic model of mooring lines. The accuracy of the calculated damping coefficients in surge and sway including the cross terms has been verified by time-domain simulations using a finite element method.</p><p>As an interesting extension of bimodal fatigue analysis, a novel frequency-domain method for estimating trimodal fatigue damage has been developed considering the interaction between the high, intermediate and low frequency components. Such a process might occur for combined responses of moored structures involving vortex induced vibrations. The proposed method has been verified to be accurate and practically acceptable by rainflow counting algorithm based on time-domain simulations of a series of ideal trimodal Gaussian processes.</p><p>Furthermore, this method has been generalized and applied to Gaussian processes with general wide-band spectra. In this way, three equivalent processes have been first defined based on the division of the response spectrum into three parts with the same variances. The wide-band fatigue damage is then estimated using the same procedure as for ideal trimodal processes. Extensive time series have been simulated for different kinds of wide-band processes, including typical marine structural responses induced by waves and wind. It is noted that the narrow-band approximation can be applied to estimate the wide-band fatigue damage if the Vanmarcke’s bandwidth parameter is less than 0.5. The proposed method has been validated with the simulation results and compared with other empirical methods. Although the idea of the proposed method is simple, it seems to be applicable for a wide range of spectral types.</p><p>Moreover, previous research work on frequency-domain fatigue analysis has mainly focused on single-slope SN curves. In this thesis, fatigue analysis considering two-slope SN curves has been carried out and especially the methods of bimodal fatigue analysis have been generalized and the accuracy has been verified by time-domain simulations.</p><br>Paper I, II and III reproduced with kind permission of Elsevier, sciencedirect.com
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Deshpande, Anirudh Gururaj. "Parameter study of bodywork attachments influencing the chassis dynamics by vibration response analysis." Thesis, KTH, Maskinkonstruktion (Inst.), 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-232452.
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Bilindustrin är i ständig utveckling och är väl medvetna om de ökande kraven från kundermed avseende på körkomfort och körupplevelse. Lastbilar med tunga laster är ofta utrustademed en påbyggnad, till exempel en låda för pallar och gods, en sopsamlare eller en stödram förbärning av timmer. SCANIA Bodybuilding Center utvecklar riktlinjer för val av olika typer avkarosseri, dvs typ av stödram och antal , fästpunkter. Målet med detta arbete är att utvecklaen bättre förståelse för hur det stödjande ramverket och dess infästningar i en lastbil påverkarrammens dynamik och sedan föreslå förbättringar till dessa riktlinjer.Viktiga parametrar som påverkar chassisdynamiken identifierades och beskrivs från början.Fysisk vibrationstestning av chassiet och påbyggnadsram med fasthållningsfäste utfördes vidi testrigg på Scania R&D. Frekvensresponsfunktionerna från mätningarna användes för attbestämma modala parametrar. Olika test utfördes genom att ändra parametrarna och upptagningenav mätningarna. Testresultaten användes för att studera egenfrekvenser egna frekvenser,modifieringsformer och dämpning i systemet. Även en ny metod för att bygga en dynamiskfinit element (FE) modell eller chassi och påbyggnadsram är presenterad i denna undersökning.Modalanalys av chassi-påbygnadsramssystemet gjordes för att studera FEMs egna frekvenseroch modeformer. Den föreslagna metoden för koppling av chassit och delramen i FEM är kritisktbedömd genom att korrelera FE-simuleringen med de experimentella resultaten. Baserat på deutförda experimenten och den numeriska simuleringen föreslås från experiment och numerisksimulering, föreslås nya rekommendationer med avseende på påbyggnadsanslutningarnas konfigurationi lastbil.<br>The automotive sector is continuously evolving and the companies are well aware of therising demands from customers with regard to driving comfort and experience. Trucks carryingheavy loads are often equipped with on-built bodywork, for example a box for pallets and goods, agarbage collector device or a supporting frame for carrying timber. SCANIA bodybuilding centredevelops guidelines for selecting different types of bodywork, i.e. the type of supporting frame,design and number of attachment brackets, attachment points. The purpose of this master thesisis to develop a better understanding of how the supporting frame and its attachments in a truckinfluence the chassis frame dynamics and to propose improvements to these guidelines.Major parameters influencing the chassis dynamics were identified and described from theoutset. Physical vibration testing of the chassis-subframe assembly was carried out at roadsimulator. The frequency response functions from the measurements were used to determinethe modal parameters. Several tests were performed by altering the parameters and recordingthe measurements. The results from the test cases were used to study and analyse the eigenfrequencies, mode shapes and damping in the system. Also, a new method to build a dynamicfinite element (FE) model of chassis and subframe is presented in this study. Modal analysisof the chassis-subframe assembly was done to study the eigen frequencies and mode shapes byFEM. The proposed method of coupling the chassis and the subframe is critically assessed bycorrelating the results from FE simulation with the experimental results. Based on the resultsfrom experiment and numerical simulation, new recommendations are proposed with regard tothe bodywork attachments’ configuration in the truck.
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Dolasa, Anaita Rustom. "Computer-Aided Design Software for the Undamped Two-Dimensional Static and Dynamic Analysis of Beams and Rotors." Thesis, Virginia Tech, 1999. http://hdl.handle.net/10919/32283.
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The objective of this research work was to develop a design tool to analyze and design undamped beam and rotor systems in two dimensions. Systems modeled in two dimensions, such as beams with different moments of inertia, could produce varying responses in the each direction of motion. A coupling between the vertical and horizontal motions also exists in rotor systems mounted of fluid film bearings.
The computer program called 2DBEAM has been developed to model and provide analyses of such systems in two dimensions. The tool has been based on an existing design package, BEAM9, which in its present state provides the response of beams and rotors in one plane of motion. The 2DBEAM program has the capability of performing the static response, free vibration, forced dynamic response, and frequency response analyses of a system.
The Transfer Matrix Method has been used in the development of the software and an explanation of the method is included in this thesis. Mathematical problems and solutions encountered while developing 2DBEAM are also documented in this study. The code has been tested against analytical and published solutions for the types of analysis mentioned above and on coupled and uncoupled system models.<br>Master of Science
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McGraw, John M. "An Investigation into Classification of High Dimensional Frequency Data." Thesis, Virginia Tech, 2001. http://hdl.handle.net/10919/35487.
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We desire an algorithm to classify a physical object in ``real-time" using an easily portable probing device. The probe excites a given object at frequencies from 100 MHz up to 800 MHz at intervals of 0.5 MHz. Thus the data used for classification is the 1400-component vector of these frequency responses.
The Interdisciplinary Center for Applied Mathematics (ICAM) was asked to help develop an algorithm and executable computer code for the probing device to use in its classification analysis. Due to these and other requirements, all work had to be done in Matlab. Hence a significant portion of the effort was spent in writing and testing applicable Matlab code which incorporated the various statistical techniques implemented.
We offer three approaches to classification: maximum log-likelihood estimates, correlation coefficients, and confidence bands. Related work included considering ways to recover and exploit certain symmetry characteristics of the objects (using the response data). Present investigations are not entirely conclusive, but the correlation coefficient classifier seems to produce reasonable and consistent results. All three methods currently require the evaluation of the full 1400-component vector. It has been suggested that unknown portions of the vectors may include extraneous and misleading information, or information common to all classes. Identifying and removing the respective components may be beneficial to classification regardless of method. Another advantage of dimension reduction should be a strengthening of mean and covariance estimates.<br>Master of Science
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Rutherford, Robert Chad. "A design methodology for control of a belt-driven robot using frequency response analysis." Thesis, Georgia Institute of Technology, 1997. http://hdl.handle.net/1853/19072.
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Harting, Nina [Verfasser], Ulrike [Akademischer Betreuer] Krewer, and Uwe [Akademischer Betreuer] Schröder. "Nonlinear Frequency Response Analysis of Lithium-Ion Batteries / Nina Harting ; Ulrike Krewer, Uwe Schröder." Braunschweig : Technische Universität Braunschweig, 2019. http://d-nb.info/119454620X/34.
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Hall, Melissa A. "Characterization of Vibration Test Fixtures using Modal Analysis." University of Cincinnati / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1627664784639955.
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Jacobs, William. "Bayesian non-linear system identification and frequency response analysis with application to soft smart actuators." Thesis, University of Sheffield, 2016. http://etheses.whiterose.ac.uk/13824/.
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Newly emerging classes of next generation soft-smart actuators are set to have a huge impact on the fields of robotics, orthotics and prosthetics due to their lightweight, high-strain and muscle-like properties. Like muscle, these actuators can be used in multiple roles, e.g. both as actuators and brakes, due their variable compliance. One important class of soft actuator is the dielectric elastomer actuator (DEA). However, DEAs are extremely difficult to control due to their non-linear and time varying dynamics. A crucial step in the advancement of this technology is the development of techniques for systems level modelling and analysis, which is the focus of this thesis. In the first part of the thesis, a set of DEAs are identified and analysed using standard methods from the field of system identification, obtaining non-linear autoregressive with exogenous input (NARX) models. These provide a benchmark against which later methods are evaluated. The key novelty in this part is the development of NARX models of DEAs for use in non-linear frequency-domain analysis. This result provides insight for the first time into how a set of similarly fabricated DEAs vary in different ways. A further aspect of DEA behaviour is their unexplained time varying behaviour. The system identification approach used to identify NARX models of DEAs is in a convenient form such that it can be easily extended to cater for this time varying behaviour. There are however very few available methods for the frequency domain analysis of time varying systems. A novel method for time varying frequency domain analysis of NARX systems is developed in this work and applied to the DEAs. The analysis procedure is used to provide insight on how the dynamic behaviour of DEAs change over time. In the second part of the thesis a novel approach to the joint structure detection and parameter estimation of NARX models is developed using a sparse Bayesian method. The Bayesian framework allows for the estimation of posterior distributions over model parameters, characterising the model uncertainty. Analytic solutions are found that describe model uncertainty in the frequency-domain as confidence bounds on both linear and higher order frequency response functions. The sparse Bayesian identification algorithm is applied to the DEA data sets and is used to give the first non-linear dynamic model of DEAs with uncertainty bounds plus the first description of DEA dynamics in the frequency-domain, again with uncertainty bounds.
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Pålsson, Emma. "Vibration analysis of a fast response brushless excitation system." Thesis, Uppsala universitet, Elektricitetslära, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-394098.
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The aim of this study is to measure and analyze vibrations on a fast response brushless exciter (FRBE) at a real hydropower plant and identify vibration origins through frequency analysis. Moreover, the observed vibrations are evaluated in relation to generator vibration standards and estimated tangential eigenfrequencies of the studied FRBE. It is concluded that the pulsations in the air gap torque, originating from the rotating thyristor bridge rectifier, is the source of the strongest vibrations. Some additional vibration sources are also identified. The requirements of the generator vibration standards are mostly fulfilled and no tangential eigenfrequencies are triggered in the vibration recordings. For further studies it is recommended that alternative control strategies and optimization of the FRBE mechanical design, with respect to its ability to withstand vibrations, should be investigated.
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Seuaciuc-Osório, Thiago. "On the modeling of energy harvesters and analysis of their response under time-varying frequency excitations." Connect to this title online, 2009. http://etd.lib.clemson.edu/documents/1252423883/.
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Zhu, Chuanbin. "Improving one-dimensional ground response analysis by incorporating basin effects." Thesis, Queensland University of Technology, 2018. https://eprints.qut.edu.au/118146/2/Chuanbin%20Zhu%20Thesis.pdf.
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This project is an engineering-orientated investigation on earthquake hazard estimations in urban sedimentary basins which accommodate many significant metropolitan areas, such as Los Angeles, San Francisco, Tokyo, Mexico City, and Taipei. It develops and disseminates a practical and robust approach to mitigate seismic risks of safety-critical buildings and infrastructure, such as tall buildings, long-span bridges and nuclear power plants.
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Tavakoli, Hanif. "A High Frequency Transformer Winding Model for FRA Applications." Licentiate thesis, Stockholm : Skolan för elektro- och systemteknik, Kungliga Tekniska högskolan, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-11178.
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Bandara, Arachchillage Rupika Priyadarshani. "Damage identification and condition assessment of building structures using frequency response functions and neural networks." Thesis, Queensland University of Technology, 2013. https://eprints.qut.edu.au/61196/4/Rupika_Bandara_Thesis.pdf.
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This thesis investigated the viability of using Frequency Response Functions in combination with Artificial Neural Network technique in damage assessment of building structures. The proposed approach can help overcome some of limitations associated with previously developed vibration based methods and assist in delivering more accurate and robust damage identification results. Excellent results are obtained for damage identification of the case studies proving that the proposed approach has been developed successfully.
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Abbas, Ghulam. "Analysis, modelling, design and implementation of fast-response digital controllers for high-frequency low-power switching converters." Thesis, Lyon, INSA, 2012. http://www.theses.fr/2012ISAL0055.
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L'objectif de la thèse est de concevoir des compensateurs discrets qui permettent de compenser les non-linéarités introduites par les différents éléments dans la boucle de commande numérique, tout en maintenant des performances dynamiques élevées, des temps de développement rapide, et une structure reconfigurable. Ces compensateurs discrets doivent également avoir des temps de réponse rapide, avoir une déviation de la tension minimale et avoir, pour un étage de puissance donné, un temps de récupération rapide de la tension. Ces performances peuvent être atteintes par des compensateurs discrets conçus sur la base de techniques de contrôle linéaires et non linéaires. Pour obtenir une réponse rapide et stable, la thèse propose deux solutions : La première consiste à utiliser des techniques de contrôle linéaires et de concevoir le compensateur discret tout en gardant la bande passante la plus élevée possible. Il est communément admis que plus la bande passante est élevée, plus la réponse transitoire est rapide. L‘obtention d’une bande passante élevée, en utilisant des techniques de contrôle linéaires, est parfois difficile. Toutes ces situations sont mises en évidence dans la thèse. La seconde consiste à combiner les techniques de contrôle linéaires avec les techniques de contrôles non linéaires tels que la logique floue ou les réseaux de neurones. Les résultats de simulations ont permis de vérifier que la combinaison des contrôleurs non-linéaires avec les linéaires ont un meilleur rendement dynamique que les contrôleurs linéaires lorsque le point de fonctionnement varie. Avec l'aide des deux méthodes décrites ci-dessus, la thèse étudie également la technique de l’annulation des pôles-zéros (PZC) qui annule la fonction de transfert du convertisseur. Quelques modifications des techniques classiques de contrôle sont également proposées à partir de contrôleurs numériques afin d’améliorer les performances dynamiques. La thèse met également en évidence les non-linéarités qui dégradent les performances, propose les solutions permettant d'obtenir les meilleures performances, et lève les mystères du contrôle numérique. Une interface graphique est également introduite et illustrée dans le cas de la conception d'un convertisseur abaisseur de tension synchrone. En résumé, cette thèse décrit principalement l'analyse, la conception, la simulation, l’optimisation la mise en œuvre et la rentabilité des contrôleurs numériques. Une attention particulière est portée à l'analyse et l'optimisation des performances dynamique à haute fréquence et pour de faibles puissances des convertisseurs DC-DC abaisseur de tension. Ces convertisseurs fonctionnent en mode de conduction continue (CCM) à une fréquence de commutation de 1 MHz et s’appuie sur des techniques de contrôle linéaires et non linéaires de façon séquentielle<br>The objective of the thesis is to design the discrete compensators which counteract the nonlinearities introduced by various elements in the digital control loop while delivering high dynamic performance, fast time-to-market and scalability. Excellent line and fast load transient response, which is a measure of the system response speed, with minimal achievable voltage deviation and a fast voltage recovery time for a given power stage can be achieved through the discrete compensators designed on the basis of linear and nonlinear control techniques. To achieve a stable and fast response, the thesis proposes two ways. One way is to use linear control techniques to design the discrete compensator while keeping the bandwidth higher. It is well-known fact that the higher the bandwidth, the faster is the transient response. Achieving higher bandwidth through linear control techniques sometimes becomes tricky. All those situations are highlighted in the thesis. The other way is to hybridize the linear control techniques with the nonlinear control techniques such as fuzzy logic or neural network based control techniques. Simulation results verify that hybridization of nonlinear controllers with the linear ones have better dynamic performance over linear controllers under the change of operating points. Along with using the two methodologies described above, the thesis also investigates the pole-zero cancellation (PZC) technique in which the poles and zeros of the compensator are placed in such a way that they cancel the effect of the poles or zeros of the buck converter to boost the phase margin at the required bandwidth. Some modifications are also suggested to the classical control techniques based digital controllers to improve the dynamic performance. The thesis highlights the nonlinearities which degrade the performance, a cost-effective solution that achieves good performance and the mysteries of digital control system. A graphical user interface is introduced and demonstrated for use with the design of a synchronous-buck converter. In summary, this thesis mainly describes the analysis, design, simulation, optimization, implementation and cost effectiveness of digital controllers with particular focus on the analysis and the optimization of the dynamic performance for high-frequency low-power DC-DC buck converter working in continuous conduction mode (CCM) operating at a switching frequency of 1 MHz using linear and nonlinear control techniques in a very sequential and comprehensive way
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Shehata, Hisham. "Unsteady Aerodynamic/Hydrodynamic Analysis of Bio-inspired Flapping Elements at Low Reynolds Number." Diss., Virginia Tech, 2020. http://hdl.handle.net/10919/97567.
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The impressive kinematic capabilities and structural adaptations presented by bio-locomotion continue to inspire some of the advancements in today's small-scaled flying and swimming vehicles. These vehicles operate in a low Reynolds number flow regime where viscous effects dominate flow interactions, which makes it challenging to generate lift and thrust. Overcoming these challenges means utilizing non-conventional lifting and flow control mechanisms generated by unsteady flapping body motion. Understanding and characterizing the aerodynamic phenomena associated with the unsteady motion is vital to predict the unsteady fluid loads generated, to implement control methodologies, and to assess the dynamic stability and control authority of airborne and underwater vehicles. This dissertation presents experimental results for forced oscillations on multi-element airfoils and hydrofoils for Reynolds numbers between Re=104 and Re=106. The document divides the work into four main sections: The first topic presents wind tunnel measurements of lift forces generated by an oscillating trailing edge flap on a NACA-0012 airfoil to illustrate the effects that frequency and pitching amplitude have on lift enhancement. The results suggest that this dynamic trailing edge flap enhances the mean lift by up to 20% in the stalled flow regime. Using frequency response approach, it is determined that the maximum enhancement in circulatory lift amplitude occurs at stalled angles of attack for lower pitching amplitudes. The second topic presents wind tunnel measurements for lift and drag generated by a sinusoidal and non-sinusoidal oscillations of a NACA-0012 airfoil. The results show that 'trapezoidal' pitching enhances the mean lift and the RMS lift by up to 50% and 35% in the pre-stall flow regime, respectively, whereas the 'reverse sawtooth' and sinusoidal pitching generate the most substantial increase of the lift-to-drag ratio in stall and post-stall flow regimes, respectively. The third topic involves a study on the role of fish-tail flexibility on thrust and propulsive efficiency. Flexible tails enhance thrust production in comparison to a rigid ones of the same size and under the same operating conditions. Further analysis indicates that varying the tail's aspect ratio has a more significant effect on propulsive efficiency and the thrust-to-power ratio at zero freestream flow. On the other hand, changing the material's property has the strongest impact on propulsive efficiency at non-zero freestream flow. The results also show that the maximum thrust peaks correspond to the maximum passive tail amplitudes only for the most flexible case. The final topic aims to assess the unsteady hydrodynamic forces and moments generated by a three-link swimming prototype performing different swimming gaits, swimming speeds, and oscillatory frequencies. We conclude that the active actuation of the tail's first mode bending produces the most significant thrust force in the presence of freestream flow. In contrast, the second mode bending kinematics provides the most significant thrust force in a zero-freestream flow.<br>Doctor of Philosophy<br>It is by no surprise that animal locomotion continues to inspire the design of flying and swimming vehicles. Although nature produces complex kinematics and highly unsteady flow characteristics, simplified approximations to model bio-inspired locomotion in fluid flows are experimentally achievable using low degrees of freedom motion, such as pitching airfoils and trailing edge flaps. The contributions of this dissertation are divided into four primary foci: (a) wind tunnel force measurements on a flapped NACA-0012 airfoil undergoing forced pitching, (b) wind tunnel measurements of aerodynamic forces generated by sinusoidal and non-sinusoidal pitching of a NACA-0012 airfoil, (c) towing tank measurements of thrust forces and torques generated by a one-link swimming prototype with varying tail flexibilities, and (d) towing tank measurements of hydrodynamic forces and moments generated by active tail actuation of a multi-link swimming prototype. From our wind tunnel measurements, we determine that lift enhancement by a trailing edge flap is achieved under certain flow regimes and oscillating conditions. Additionally, we assess the aerodynamic forces for a sinusoidal and non-sinusoidal pitching of an airfoil and show that 'trapezoidal' pitching produces the largest lift coefficient amplitude whereas the sinusoidal and 'reverse sawtooth' pitching achieve the best lift to drag ratios. From our towing tank experiments, we note that the role of tail flexibility enhances thrust generation on a swimming device. Finally, we conclude that different kinematics on an articulating body strongly affect the hydrodynamic forces and moments. The results of the towing tank measurements are accessible from an online public database to encourage research and contribution in underwater vehicle design through physics-based low-order models that can accommodate hydrodynamic principles and geometric control concepts.
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Mondal, Abrez. "ANALYSIS AND MITIGATION OF FREQUENCY DISTURBANCES IN AN ISLANDED MICROGRID." The Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1492563068162654.
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Hang, Huajiang Engineering & Information Technology Australian Defence Force Academy UNSW. "Prediction of the effects of distributed structural modification on the dynamic response of structures." Awarded by:University of New South Wales - Australian Defence Force Academy. Engineering & Information Technology, 2009. http://handle.unsw.edu.au/1959.4/44275.
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The aim of this study is to investigate means of efficiently assessing the effects of distributed structural modification on the dynamic properties of a complex structure. The helicopter structure is normally designed to avoid resonance at the main rotor rotational frequency. However, very often military helicopters have to be modified (such as to carry a different weapon system or an additional fuel tank) to fulfill operational requirements. Any modification to a helicopter structure has the potential of changing its resonance frequencies and mode shapes. The dynamic properties of the modified structure can be determined by experimental testing or numerical simulation, both of which are complex, expensive and time-consuming. Assuming that the original dynamic characteristics are already established and that the modification is a relatively simple attachment such as beam or plate modification, the modified dynamic properties may be determined numerically without solving the equations of motion of the full-modified structure. The frequency response functions (FRFs) of the modified structure can be computed by coupling the original FRFs and a delta dynamic stiffness matrix for the modification introduced. The validity of this approach is investigated by applying it to several cases, 1) 1D structure with structural modification but no change in the number of degree of freedom (DOFs). A simply supported beam with double thickness in the middle section is treated as an example for this case; 2) 1D structure with additional DOFs. A cantilever beam to which a smaller beam is attached is treated as an example for this case, 3) 2D structure with a reduction in DOFs. A four-edge-clamped plate with a cut-out in the centre is treated as an example for this case; and 4) 3D structure with additional DOFs. A box frame with a plate attached to it as structural modification with additional DOFs and combination of different structures. The original FRFs were obtained numerically and experimentally except for the first case. The delta dynamic stiffness matrix was determined numerically by modelling the part of the modified structure including the modifying structure and part of the original structure at the same location. The FRFs of the modified structure were then computed. Good agreement is obtained by comparing the results to the FRFs of the modified structure determined experimentally as well as by numerical modelling of the complete modified structure.
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Kadyk, Thomas Verfasser], and Kai [Akademischer Betreuer] [Sundmacher. "Nonlinear frequency response analysis for the diagnosis of polymer electrolyte membrane fuel cells / Thomas Kadyk. Betreuer: Kai Sundmacher." Magdeburg : Universitätsbibliothek, 2012. http://d-nb.info/1053914431/34.
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Chronopoulos, Dimitrios. "Prediction of the vibroacoustic response of aerospace composite structures in a broadband frequency range." Phd thesis, Ecole Centrale de Lyon, 2012. http://tel.archives-ouvertes.fr/tel-00787864.
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During its mission, a launch vehicle is subject to broadband, severe, aeroacoustic and structure-borne excitations of various provenances, which can endanger the survivability of the payload and the vehicles electronic equipment, and consequently the success of the mission. Aerospace structures are generally characterized by the use of exotic composite materials of various configurations and thicknesses, as well as by their extensively complex geometries and connections between different subsystems. It is therefore of crucial importance for the modern aerospace industry, the development of analytical and numerical tools that can accurately predict the vibroacoustic response of large, composite structures of various geometries and subject to a combination of aeroacoustic excitations. Recently, a lot of research has been conducted on the modelling of wave propagation characteristics within composite structures. In this study, the Wave Finite Element Method (WFEM) is used in order to predict the wave dispersion characteristics within orthotropic composite structures of various geometries, namely flat panels, singly curved panels, doubly curved panels and cylindrical shells. These characteristics are initially used for predicting the modal density and the coupling loss factor of the structures connected to the acoustic medium. Subsequently the broad-band Transmission Loss (TL) of the modelled structures within a Statistical Energy Analysis (SEA) wave-context approach is calculated. Mainly due to the extensive geometric complexity of structures, the use of Finite Element(FE) modelling within the aerospace industry is frequently inevitable. The use of such models is limited mainly because of the large computation time demanded even for calculations in the low frequency range. During the last years, a lot of researchers focus on the model reduction of large FE models, in order to make their application feasible. In this study, the Second Order ARnoldi (SOAR) reduction approach is adopted, in order to minimize the computation time for a fully coupled composite structural-acoustic system, while at the same time retaining a satisfactory accuracy of the prediction in a broadband sense. The system is modelled under various aeroacoustic excitations, namely a diffused acoustic field and a Turbulent Boundary Layer (TBL) excitation. Experimental validation of the developed tools is conducted on a set of orthotropic sandwich composite structures. Initially, the wave propagation characteristics of a flat panel are measured and the experimental results are compared to the WFEM predictions. The later are used in order to formulate an Equivalent Single Layer (ESL) approach for the modelling of the spatial response of the panel within a dynamic stiffness matrix approach. The effect of the temperature of the structure as well as of the acoustic medium on the vibroacoustic response of the system is examined and analyzed. Subsequently, a model of the SYLDA structure, also made of an orthotropic sandwich material, is tested mainly in order to investigate the coupling nature between its various subsystems. The developed ESL modelling is used for an efficient calculation of the response of the structure in the lower frequency range, while for higher frequencies a hybrid WFEM/FEM formulation for modelling discontinuous structures is used.
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Du, Zhaobin. "Area COI-based slow frequency dynamics modeling, analysis and emergency control for interconnected power systems." Click to view the E-thesis via HKUTO, 2008. http://sunzi.lib.hku.hk/hkuto/record/B4175783X.
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Gurney, Michael Lynn. "Peri-implant Indices of Remodeling as a Response to Mechanical Loading." The Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1337800531.
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Cairns, Nicola J. "The feasibility of vibration analysis as a technique to detect osseointegration of transfemoral implants." Thesis, Queensland University of Technology, 2010. https://eprints.qut.edu.au/38874/1/Nicola_Cairns_Thesis.pdf.
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One of the main causes of above knee or transfemoral amputation (TFA) in the developed world is trauma to the limb. The number of people undergoing TFA due to limb trauma, particularly due to war injuries, has been increasing. Typically the trauma amputee population, including war-related amputees, are otherwise healthy, active and desire to return to employment and their usual lifestyle. Consequently there is a growing need to restore long-term mobility and limb function to this population.
Traditionally transfemoral amputees are provided with an artificial or prosthetic leg that consists of a fabricated socket, knee joint mechanism and a prosthetic foot. Amputees have reported several problems related to the socket of their prosthetic limb. These include pain in the residual limb, poor socket fit, discomfort and poor mobility.
Removing the socket from the prosthetic limb could eliminate or reduce these problems. A solution to this is the direct attachment of the prosthesis to the residual bone (femur) inside the residual limb. This technique has been used on a small population of transfemoral amputees since 1990. A threaded titanium implant is screwed in to the shaft of the femur and a second component connects between the implant and the prosthesis. A period of time is required to allow the implant to become fully attached to the bone, called osseointegration (OI), and be able to withstand applied load; then the prosthesis can be attached.
The advantages of transfemoral osseointegration (TFOI) over conventional prosthetic sockets include better hip mobility, sitting comfort and prosthetic retention and fewer skin problems on the residual limb. However, due to the length of time required for OI to progress and to complete the rehabilitation exercises, it can take up to twelve months after implant insertion for an amputee to be able to load bear and to walk unaided. The long rehabilitation time is a significant disadvantage of TFOI and may be impeding the wider adoption of the technique. There is a need for a non-invasive method of assessing the degree of osseointegration between the bone and the implant. If such a method was capable of determining the progression of TFOI and assessing when the implant was able to withstand physiological load it could reduce the overall rehabilitation time.
Vibration analysis has been suggested as a potential technique: it is a non destructive method of assessing the dynamic properties of a structure. Changes in the physical properties of a structure can be identified from changes in its dynamic properties. Consequently vibration analysis, both experimental and computational, has been used to assess bone fracture healing, prosthetic hip loosening and dental implant OI with varying degrees of success. More recently experimental vibration analysis has been used in TFOI. However further work is needed to assess the potential of the technique and fully characterise the femur-implant system.
The overall aim of this study was to develop physical and computational models of the TFOI femur-implant system and use these models to investigate the feasibility of vibration analysis to detect the process of OI.
Femur-implant physical models were developed and manufactured using synthetic materials to represent four key stages of OI development (identified from a physiological model), simulated using different interface conditions between the implant and femur.
Experimental vibration analysis (modal analysis) was then conducted using the physical models. The femur-implant models, representing stage one to stage four of OI development, were excited and the modal parameters obtained over the range 0-5kHz. The results indicated the technique had limited capability in distinguishing between different interface conditions. The fundamental bending mode did not alter with interfacial changes. However higher modes were able to track chronological changes in interface condition by the change in natural frequency, although no one modal parameter could uniquely distinguish between each interface condition. The importance of the model boundary condition (how the model is constrained) was the key finding; variations in the boundary condition altered the modal parameters obtained. Therefore the boundary conditions need to be held constant between tests in order for the detected modal parameter changes to be attributed to interface condition changes.
A three dimensional Finite Element (FE) model of the femur-implant model was then developed and used to explore the sensitivity of the modal parameters to more subtle interfacial and boundary condition changes. The FE model was created using the synthetic femur geometry and an approximation of the implant geometry. The natural frequencies of the FE model were found to match the experimental frequencies within 20% and the FE and experimental mode shapes were similar. Therefore the FE model was shown to successfully capture the dynamic response of the physical system.
As was found with the experimental modal analysis, the fundamental bending mode of the FE model did not alter due to changes in interface elastic modulus. Axial and torsional modes were identified by the FE model that were not detected experimentally; the torsional mode exhibited the largest frequency change due to interfacial changes (103% between the lower and upper limits of the interface modulus range). Therefore the FE model provided additional information on the dynamic response of the system and was complementary to the experimental model. The small changes in natural frequency over a large range of interface region elastic moduli indicated the method may only be able to distinguish between early and late OI progression. The boundary conditions applied to the FE model influenced the modal parameters to a far greater extent than the interface condition variations. Therefore the FE model, as well as the experimental modal analysis, indicated that the boundary conditions need to be held constant between tests in order for the detected changes in modal parameters to be attributed to interface condition changes alone.
The results of this study suggest that in a clinical setting it is unlikely that the in vivo boundary conditions of the amputated femur could be adequately controlled or replicated over time and consequently it is unlikely that any longitudinal change in frequency detected by the modal analysis technique could be attributed exclusively to changes at the femur-implant interface. Therefore further development of the modal analysis technique would require significant consideration of the clinical boundary conditions and investigation of modes other than the bending modes.
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Dahl, Jason F. "Time Aliasing Methods of Spectrum Estimation." Diss., CLICK HERE for online access, 2003. http://contentdm.lib.byu.edu/ETD/image/etd157.pdf.
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Aljohani, Omar Maqbul. "A Novel Digital Image Processing Technique to Detect Power Transformers Internal Faults using Frequency Response Analysis Polar Plot Signature." Thesis, Curtin University, 2017. http://hdl.handle.net/20.500.11937/53045.
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This thesis introduces a new application, which aims to improve the current approach to interpretation of the Frequency Response Analysis (FRA) signature. In contrast to current FRA practice (conventional approach), the newly proposed application develops various Digital Image Processing techniques to overcome most of the drawbacks of the conventional FRA approach. By automating and standardising FRA interpretation, its detection accuracy is enhanced so that incipient mechanical and non-mechanical faults within power transformers can be detected.
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Abraham, Etimbuk. "Adaptive supervisory control scheme for voltage controlled demand response in power systems." Thesis, University of Manchester, 2018. https://www.research.manchester.ac.uk/portal/en/theses/adaptive-supervisory-control-scheme-for-voltage-controlled-demand-response-in-power-systems(3e64537d-52c7-4eb5-87f2-b73fe920b9cb).html.
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Radical changes to present day power systems will lead to power systems with a significant penetration of renewable energy sources and smartness, expressed in an extensive utilization of novel sensors and cyber secure Information and Communication Technology. Although these renewable energy sources prove to contribute to the reduction of CO2 emissions into the environment, its high penetration affects power system dynamic performance as a result of reduced power system inertia as well as less flexibility with regards to dispatching generation to balance future demand. These pose a threat both to the security and stability of future power systems. It is therefore very important to develop new methods through which power system security and stability can be maintained. This research investigated the development of methods through which the contributions of on-load tap changing transformers/transformer clusters could be assessed with the intent of developing real time adaptive voltage controlled demand response schemes for power systems. The development of such a scheme enables more active system components to be involved in the provision of frequency control as an ancillary service and deploys a new frequency control service with low infrastructural investment, bearing in mind that OLTC transformers are already very prevalent in power systems. In this thesis, a novel online adaptive supervisory controller for ensuring optimal dispatch of voltage-controlled demand response resources is developed. This novel controller is designed using the assessment results of OLTC transformer impacts on steady-state frequency and was tested for a variety of scenarios. To achieve the effective performance of the adaptive supervisory controller, the extensive use of statistical techniques for assessing OLTC transformer contributions to voltage controlled demand response is presented. This thesis also includes the use of unsupervised machine learning techniques for power system partitioning and the further use of statistical methods for assessing the contributions of OLTC transformer aggregates.
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Du, Zhaobin, and 杜兆斌. "Area COI-based slow frequency dynamics modeling, analysis and emergency control for interconnected power systems." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2008. http://hub.hku.hk/bib/B4175783X.
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Vittal, Eknath. "A static analysis of maximum wind penetration in Iowa and a dynamic assessment of frequency response in wind turbine types." [Ames, Iowa : Iowa State University], 2008.
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Guimarães, Rogério Coelho. "Modelo elétrico da impedância do transformador baseado em células RLC passivas." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2010. http://hdl.handle.net/10183/38778.
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No novo contexto do setor elétrico brasileiro, as concessionárias passam a ter uma nova postura quanto à gestão. A energia elétrica, como produto, como negócio, deve levar lucro às empresas concessionárias. Começam a dar mais importância aos custos, entendendo que vários aspectos técnicos devem ser analisados, visando reduzir perdas substanciais. Assim sendo, o transformador de potência assume uma posição destacada, considerando sua posição estratégica no sistema elétrico, fundamental no processo de transporte e entrega de energia elétrica. Por este motivo vem despertando o interesse no desenvolvimento de estudos e pesquisas no sentido de aumentar sua vida útil. O método de Análise da Resposta em Frequência da impedância do transformador permite obter a “assinatura” do mesmo, a fim de verificar futuras degradações. Este método é adotado por várias empresas em todo o mundo, há mais de três décadas. Embora sua ampla aplicação entre muitas técnicas utilizadas na monitoração e análise de falhas em equipamentos, até agora não houve consenso na interpretação dos resultados obtidos por este método. A dificuldade de correlacionar parâmetros com prováveis falhas tem suscitado pesquisas para obtenção de resultados confiáveis e de interpretação fácil. Este trabalho objetiva determinar um modelo elétrico que represente a característica da resposta em frequência para fins de armazenamento de dados e simulações. A partir de dados reais do teste de resposta em frequência da impedância inseridos no modelo proposto, através de um programa computacional, foi verificada a confiabilidade nas respostas obtidas, comparadas com as reais. Os resultados obtidos asseguram que o modelo proposto é viável de ser aplicado.<br>In the new context of the Brazilian electric industry, the electric power provider companies have adopted a new administration posture. The electric power, as a product and business, should make the companies profitable. They have been paying more attention to the costs, .learning that many technical aspects should be analyzed in order to reduce substantial losses. Therefore, the power transformer takes an outstanding position, considering its strategic position in the electric system and being essential in the process of transport and delivery of the electric power. For this reason, there has been an interest in the development of studies and research in order to increase its useful life. The method of Frequency Response Analysis of impedance of the power transformer permits to obtain reference parameters of this one, in order to verify future degradations. This method has been adopted by many companies throughout the world for over three decades. Despite its wide application among several techniques used in the supervision and analysis of faults of equipments, there has been no consensus in the interpretation of the results obtained by this method so far. The difficulty of correlating the parameters with probable faults have increased research in order to obtain reliable results and of easy interpretation. This study aims to determine an electric model that represents the characteristic of the frequency response in order to store data and simulations. Starting from the real data of the FRA test inserted in the proposed model through a computer program, the reliability of the obtained responses were verified and compared with the real data. The obtained results assure that the proposed model is viable and can be applied.
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Tavakoli, Hanif. "An FRA Transformer Model with Application on Time Domain Reflectometry." Doctoral thesis, KTH, Elektroteknisk teori och konstruktion, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-48568.
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Frequency response analysis (FRA) is a frequency-domain method which is used to detect mechanical faults in transformers. The frequency response of a transformer is determined by its geometry and material properties, and it can be considered as the transformer’s fingerprint. If there are any mechanical changes in the transformer, for example if the windings are moved or distorted, its fingerprint will also be changed so, theoretically, mechanical changes in the transformer can be detected with FRA. A problem with FRA is the fact that there is no general agreement about how to interpret the measurement results for detection of winding damages. For instance, the interpretation of measurement results has still not been standardized.The overall goal of this thesis is to try to enhance the understanding of the information contained in FRA measurements. This has been done in two ways: (1) by examining the FRA method for (much) higher frequencies than what is usual, and (2) by developing a new method in which FRA is combined with the ideas of Time Domain Reflectometry (TDR). As tools for carrying out the above mentioned steps, models for the magnetic core and the winding have been developed and verified by comparison to measurements.The usual upper frequency limit for FRA is around 2 MHz, which in this thesis has been extended by an order of magnitude in order to detect and interpret new phenomena that emerge at high frequencies and to investigate the potential of this high-frequency region for detection of winding deteriorations.Further, in the above-mentioned new method developed in this thesis, FRA and TDR are combined as a step towards an easier and more intuitive detection and localization of faults in transformer windings, where frequency response measurements are visualized in the time domain in order to facilitate their interpretation.<br>QC 20111122
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Harmachova, Karolina. "Vibration performance of hybrid steel-CLT floors." Thesis, KTH, Byggnadsmaterial, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-192475.
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In the light of today’s effort to achieve sustainable future of the planet, timber as building material makes a comeback on the construction market. Since the requirements on the buildings and the internal comfort increase, there is a need for finding new solutions and products; one of them is cross-laminated timber (CLT), which has the potential to be used for high-rise buildings due to its mechanical properties. The aim of this work was to study the vibration performance of CLT floors as it is often the governing factor in design of CLT structures unlike for other common building materials. The orthotropic mechanical properties of CLT were determined by the shear analogy method and verified with a finite element (FE) model of a simply supported beam compared to hand calculations of shear forces, bending moments and deflections. The properties based on Timoshenko’s approach were evaluated as less precise regarding the deflection. The non-composite structural behaviour of a steel-CLT hybrid floor structure was predicted for FE dynamic analysis based on a comparison between modelling exercise and hand calculations. Two different methods, the Concrete Society (SC) and Steel Construction Institution (SCI) methods, both seemed to be applicable for determination of the response factor first since the mechanical properties are not used as input in the calculations. These two methods differ in certain aspects, and based on FE analysis of simply supported slab even the resulting response factor for the CLT differs significantly. Moreover, the hand calculation results were similar to those of the FE analysis for the CS method, but in less agreement for the SCI method. Nevertheless, it is not recommended to reject the latter method based on this study and further studies should be performed on real structures with response factor known from on-site measurements. A part of the first floor of Canary Wharf College was modelled and analysed, and previous measurements of the frequency and response factors enabled a validation of some assumptions. The SCI approach showed to be inadequate for this type of structure and therefore only the CS method was applied further. Analysis of the floor structures supported by walls demonstrated similar results from both the measurements and the dynamic analysis. However, if the floor slab was supported by beams, the response factor was significantly overestimated although on the conservative side. This difference suggests that the modelling of such conditions are not satisfactory. The CS method appears to assess correctly the magnitude of the response factor for CLT floors supported by walls but overestimates it in case of beam supports. The first finding shall be confirmed through analysis of other structures and a more extensive research should focus on the latter one to determine more exact behaviour of the model under different conditions.
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Kim, Tae-Chung. "Analysis of Clearance Non-linearities and Vibro-impacts in Torsional Systems." The Ohio State University, 2003. http://rave.ohiolink.edu/etdc/view?acc_num=osu1053634349.
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SONDKAR, PRAVIN BANDU. "A Hearing-Based, Frequency Domain Sound Quality Model for Combined Aerodynamic and Power Transmission Response With Application To Rotorcraft Interior Noise." University of Cincinnati / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1203968025.
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Wiberg, Niklas, and Jasmin Halilovic. "Train Induced Vibration Analysis of an End-frame Bridge : Numerical Analysis on Sidensjövägen." Thesis, KTH, Bro- och stålbyggnad, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-231911.
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Higher speeds and higher capacity will cause the Swedish rail network to be exposed to disturbing dynamic effects. Higher speeds cause higher vertical acceleration levels of the bridge deck. In this thesis, a numerical analysis of a three span end-frame bridge subjected to train induced vibrations is performed. The aim is to identify which structural components and boundary conditions that affect the dynamic behavior of the bridge. Furthermore, the influence of soil structure interaction (SSI) will be investigated as it may have contribution to the stiffness and damping of the structural system. In order to capture the dynamic response of the bridge, an analysis in the frequency domain was preformed where frequency response functions (FRF) and acceleration envelopes were obtained. For this purpose, a detailed FE-model in 3D was created. Three different cases were studied, model subjected to ballast, model subjected to soil and model subjected to both ballast and soil in coherence. A high speed load model (HSLM) was used to create simulation of train passages at different speeds and applied to all cases so that the bridge deck accelerations could be studied. A simplified 2D-model with impedance functions representing the soil-structure interaction was created to validate the results from the detailed 3D-model and for practical design purposes. The result of this numerical analysis showed that the vertical accelerations were within acceptable levels of the maximum allowed limits given in governing publications. Considering the surrounding soil, the results revealed an increase of the dynamic response in the midspan at resonant frequency. However, it was identified that this behavior is not explained by the influence of soil structure interaction but rather the change in boundary conditions of the end-shields. The same dynamic behavior was identified for the simplified 2D-model, with a slight underestimation of the vertical accelerations at resonance.
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Esposito, Roberta. "Application of Magnetotelluric Method in sedimentary environments and analysis of the resistivity dispersion in presence of 3D polarizable structures." reponame:Repositório Institucional da UFC, 2016. http://www.repositorio.ufc.br/handle/riufc/22898.
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ESPOSITO, Roberta. Application of Magnetotelluric Method in sedimentary environments and analysis of the resistivity dispersion in presence of 3D polarizable structures. 2016. 106 f. Tese (Doutorado em Geologia)-Universidade Federal do Ceará, Fortaleza, 2016.<br>Submitted by Jairo Viana (jairo@ufc.br) on 2017-05-29T20:43:16Z
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Previous issue date: 2016<br>O Método magnetotelúrico permite a determinação da distribuição de resistividade elétrica na subsuperfície, a fim de diferenciar as estruturas presentes. Com os procedimentos de inversão de dados é possível obter valores de resistividade de algumas dezenas de metros até centenas de quilómetros. Como acontece com todos os métodos de prospecção geofísica, o método MT está sujeito a ambiguidades por causa do fenômeno da dispersão da resistividade. Este fenómeno pode deformar as curvas de resposta MT e pode conduzir a uma interpretação errónea. Uma conclusão geral é que os efeitos de dispersão pode influenciar a resposta MT em forma reconhecível ou sutil. Em ambos os casos, sem considerar os efeitos de distorção a interpretação pode levar a conclusões enganosas sobre as propriedades físicas das estruturas pesquisadas. Este trabalho trata com diferentes aspectos do Método Magnetotelúrico. Em primeiro lugar a dispersão da resistividade é estudada teoricamente realizando, pela primeira vez, simulações de um modelo 3-D da Terra (caso 1-D é apresentado a partir de um trabalho anterior de Esposito e Patella, 2009 e o caso 2-D é reconstruído baseando a simulação sobre um trabalho de Mauriello et al., 1996), com um estudo de caso em uma área geotérmica (Snake River Plain, Idaho, USA). Mostra-se uma aplicação do MT na área do Pecém (Ceará, Brasil), desconsiderando a dispersão da resistividade, a fim de mostrar a eficiência do método para resolver contrastes de resitividade na subsuperfície e, finalmente, são realizadas as simulações teóricas que mostram a aplicação do método MT para pesquisa de Oléo e Gás na porção emersa da Bacia Potiguar (Rio Grande do Norte, Brasil), a fim de considerar a MT como um apoio em áreas onde a sísmica, usada principalmente para esses fins, pode ser logisticamente difícil de aplicar ou precisa de uma comparação com outros métodos de prospecção geofísica.<br>O Método magnetotelúrico permite a determinação da distribuição de resistividade elétrica na subsuperfície, a fim de diferenciar as estruturas presentes. Com os procedimentos de inversão de dados é possível obter valores de resistividade de algumas dezenas de metros até centenas de quilómetros. Como acontece com todos os métodos de prospecção geofísica, o método MT está sujeito a ambiguidades por causa do fenômeno da dispersão da resistividade. Este fenómeno pode deformar as curvas de resposta MT e pode conduzir a uma interpretação errónea. Uma conclusão geral é que os efeitos de dispersão pode influenciar a resposta MT em forma reconhecível ou sutil. Em ambos os casos, sem considerar os efeitos de distorção a interpretação pode levar a conclusões enganosas sobre as propriedades físicas das estruturas pesquisadas. Este trabalho trata com diferentes aspectos do Método Magnetotelúrico. Em primeiro lugar a dispersão da resistividade é estudada teoricamente realizando, pela primeira vez, simulações de um modelo 3-D da Terra (caso 1-D é apresentado a partir de um trabalho anterior de Esposito e Patella, 2009 e o caso 2-D é reconstruído baseando a simulação sobre um trabalho de Mauriello et al., 1996), com um estudo de caso em uma área geotérmica (Snake River Plain, Idaho, USA). Mostra-se uma aplicação do MT na área do Pecém (Ceará, Brasil), desconsiderando a dispersão da resistividade, a fim de mostrar a eficiência do método para resolver contrastes de resitividade na subsuperfície e, finalmente, são realizadas as simulações teóricas que mostram a aplicação do método MT para pesquisa de Oléo e Gás na porção emersa da Bacia Potiguar (Rio Grande do Norte, Brasil), a fim de considerar a MT como um apoio em áreas onde a sísmica, usada principalmente para esses fins, pode ser logisticamente difícil de aplicar ou precisa de uma comparação com outros métodos de prospecção geofísica.
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Fong, Peng Shiang, and 彭向逢. "Loudspeaker System Frequency Response Analysis." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/40047265800555147087.
Full textAbstract:
碩士<br>中華科技大學<br>機電光工程研究所碩士班<br>102<br>In this research the ARTA software, a collection of programs for audio measurements and analysis, was used to measure the frequency response and the Thiele/Small parameters for loudspeaker drivers. The WinISD Pro software was used to calculate the box volume and the vent tube of a vented cabinet system for designated speaker drivers. Frequency responses were simulated.
For a vented loudspeaker cabinet, resonant frequency and damping factor were dominated by the volume and the geometry of the vent tube. The cabinet’s resonant frequency, damping factor and the loudspeaker driver’s Thiele/Small parameters determine the frequency response and efficiency of the loudspeaker system. To achieve the best result for a loudspeaker system, experiments and adjustments may be needed in addition to the theoretical analysis. In order to study influences of the resonant frequency and the damping factor on the impedance and the frequency response, a loudspeaker system with different lengths of the round vent tubes for a fixed volume cabinet was tested. By comparing the measured results, relationships between vent tubes, impedance curves and frequency responses curves were discussed. Better design parameters were therefore suggested.
Notch filter is considered as a good tool for designing a modern high-end loudspeaker. To find a loudspeaker driver with flat frequency response is very difficult and the driver could be implausibly expensive. Notch filter, used to remove the rise in the frequency curve for a specified stopband, is an excellent and budget way for a loudspeaker system to achieve flatter frequency response. In this research, a parallel notch filter was designed for the experimental loudspeaker system to attenuate the rise between 500 Hz and 2000 Hz. Experiments showed that the notch filter has attenuated the curve between 800 Hz and 1600 Hz for about 4 dB. Since only the first order of decaying was used for the filter, frequency response at 500 Hz and 2000 Hz also have been attenuated for about 2 dB. This means that filter’s function to flatten the frequency response is not very effective. Meanwhile the filter, serially connected between the amplifier and the loudspeaker, has also acted as an factor to lower the loudspeaker’s efficiency during the most musical range. Therefore to successfully design a notch filter, the stopband, parallel or serial schematics, and the order of attenuation are important factors to consider.
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LEE, HSIANG-LUNG, and 李湘龍. "The Frequency Response Analysis of Buck Converter." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/44849144664763351425.
Full textAbstract:
碩士<br>大葉大學<br>電機工程學系碩士在職專班<br>96<br>Recently the energy question was more serious, when the electric power, the petroleum and non-renewable was in danger. When it became international society economy problem. The power of development solar energy resource become economical development question. The switch loss of the resonant converter is lower than traditional switch converter, and the technique of zero-voltage-switch is more effective in reducing the temperature of active switch. Finally , we will compare the case of switch with the resonant type and traditional type