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Frequency domain unsteady transonic aerodynamics for flutter and limit cycle oscillation prediction

GRECO JR., Paulo C.; LAN, Chuan-Tau E.
Fonte: Associação Brasileira de Engenharia e Ciências Mecânicas - ABCM Publicador: Associação Brasileira de Engenharia e Ciências Mecânicas - ABCM
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
66.05%
The purpose of this study was to develop new approaches for predicting transonic flutter and limit cycle oscillations (LCO) using computational methods. The TSD equation is separated into the in-phase and out-of-phase components through a nonlinear harmonic averaging method. It is then solved in the frequency domain to obtain the aerodynamic forcing function which is needed in the flutter and LCO analyses. To predict flutter, equations are developed using the concept of generalized coordinates. The flutter speed is determined by examining the frequency-domain matrix equation eigenvalues. Flutter characteristics of the AGARD I-445.6 wing are analyzed. Flutter speed and frequency are well predicted in subsonic speed, but are overestimated in supersonic flow. To predict limit cycle oscillations, the frequency-domain aerodynamic coefficients are used to obtain a nonlinear time-domain expression for the aerodynamic force. Limit cycle oscillation characteristics of the DAST ARW-2 wing are analyzed. The results show LCO for Mach numbers ranging from 0.915 to 0.940.

Frequency Domain Connectivity Identification: An Application of Partial Directed Coherence in fMRI

SATO, Joao R.; TAKAHASHI, Daniel Y.; ARCURI, Silvia M.; Sameshima, Koichi; MORETTIN, Pedro A.; Baccala, Luiz Antonio
Fonte: WILEY-LISS Publicador: WILEY-LISS
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
65.94%
Functional magnetic resonance imaging (fMRI) has become an important tool in Neuroscience due to its noninvasive and high spatial resolution properties compared to other methods like PET or EEG. Characterization of the neural connectivity has been the aim of several cognitive researches, as the interactions among cortical areas lie at the heart of many brain dysfunctions and mental disorders. Several methods like correlation analysis, structural equation modeling, and dynamic causal models have been proposed to quantify connectivity strength. An important concept related to connectivity modeling is Granger causality, which is one of the most popular definitions for the measure of directional dependence between time series. In this article, we propose the application of the partial directed coherence (PDC) for the connectivity analysis of multisubject fMRI data using multivariate bootstrap. PDC is a frequency domain counterpart of Granger causality and has become a very prominent tool in EEG studies. The achieved frequency decomposition of connectivity is useful in separating interactions from neural modules from those originating in scanner noise, breath, and heart beating. Real fMRI dataset of six subjects executing a language processing protocol was used for the analysis of connectivity. Hum Brain Mapp 30:452-461...

Patellofemoral pain syndrome: Electromyography in a frequency domain analysis

Catelli, D. S.; Kuriki, H. U.; Polito, L. F.; Azevedo, F. M.; Filho, R.F. Negrão; Alves, Neri
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Conferência ou Objeto de Conferência
Português
Relevância na Pesquisa
65.99%
The Patellofemoral Pain Syndrome (PFPS), has a multifactorial etiology and affects approximately 7 to 15% of the population, mostly women, youth, adults and active persons. PFPS causes anterior or retropatelar pain that is exacerbated during functional motor gestures, such as up and down stairs or spending long periods of time sitting, squatting or kneeling. As the diagnostic evaluation of this syndrome is still indirect, different mechanisms and methodologies try to make a classification that distinguishes patients with PFPS in relation to asymptomatic. Thereby, the purpose of this investigation was to determine the characteristics of the electromyographic (EMG) signal in the frequency domain of the vastus medialis oblique (VMO) and vastus lateralis (VL) in patients with PFPS, during the ascent of stairs. 33 young women (22 control group and 11 PFPS group), were evaluated by EMG during ascent of stairs. The VMO mean power frequency (MPF) and the VL frequency 95% (F95) were lower in symptomatic individuals. This may be related to the difference in muscle recruitment strategy exerted by each muscle in the PFPS group compared to the control group.

A frequency domain extraction procedure of low-pass equivalent behavioural models of microwave PAs

Siviero, C.; Lavrador, P.M.; Pedro, J.C.
Fonte: Universidade de Aveiro Publicador: Universidade de Aveiro
Tipo: Conferência ou Objeto de Conferência
Português
Relevância na Pesquisa
65.97%
This paper reports on a novel extraction procedure of low-pass equivalent behavioral models of microwave power amplifiers. The proposed approach is based on the use of the discrete-time Volterra Series model and on the complex envelope of a multisine as stimulus. The model extraction procedure is formulated using an alternative orthogonal model representation in the frequency domain, providing a methodology which successfully leads to an optimal model identification not affected by the ill-conditioning of typical learning methods. © 2006 EuMA.; IST-1-507893-NOE - TARGET

Iterative frequency-domain receivers for the uplink of cellular systems with base station cooperation

Ribeiro, F.; Dinis, R.; Cercas, F. C.; Silva, Adão
Fonte: IEEE Publicador: IEEE
Tipo: Conferência ou Objeto de Conferência
Português
Relevância na Pesquisa
65.97%
In this paper we consider the uplink transmission in BS (Base Station) cooperation schemes where users in adjacent cells share the same physical channel and the signals received by each BS are sent to a CPU (Central Processing Unit) that combines the different received signals associated to a given user and/or performs the user separation. We consider SC-FDE signals (Single-Carrier with Frequency-Domain Equalization) combined with iterative frequency-domain receivers based on the IB-DFE concept (Iterative Block Decision Feedback Equalization). Our performance results show that the proposed receivers allow significant macro-diversity gains as well as an efficient user separation, with performance close to the MFB (Matched Filter Bound), making these techniques an excellent choice for the uplink transmission in future broadband wireless systems employing BS cooperation schemes.

A frequency-domain pseudo-force method for dynamic structural analysis nonlinear systems and nonproportional damping

Ferreira,W.G.; Claret,A.M.; Venancio-Filho,F.; Mansur,W.J.
Fonte: The Brazilian Society of Mechanical Sciences Publicador: The Brazilian Society of Mechanical Sciences
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2000 Português
Relevância na Pesquisa
65.99%
A frequency-domain method for nonlinear analysis of structural systems with viscous, hysteretic, nonproportional and frequency-dependent damping is presented. The nonlinear effects and nonproportional damping are considered through pseudo-force terms. The modal coordinates uncoupled equations are iteratively solved. The treatment of initial conditions in the frequency domain which is necessary for the treatment of the uncoupled equations is initially adressed.

Frequency domain analysis of core inflation measures for Brazil

Araújo,Eurilton; Fiorencio,Antonio
Fonte: Fundação Instituto de Pesquisas Econômicas - FIPE Publicador: Fundação Instituto de Pesquisas Econômicas - FIPE
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/03/2005 Português
Relevância na Pesquisa
65.94%
This paper analyses the frequency domain properties of two well-known measures of core inflation: the trimmed mean estimator and the SVAR estimator. It also investigates whether a small modification of the trimmed mean estimator enhances its capacity of filtering high‑frequency noise. We find that the two versions of the trimmed estimator are rather similar. They work as imperfect approximations for low pass filters. Therefore, they are capturing very well trend inflation. The SVAR estimator, however, is quite different from both of them. It emphasizes intermediate frequencies rather than low frequencies, indicating that cyclical movements associated with excess demand pressures are very important in the medium run.

Frequency domain unsteady transonic aerodynamics for flutter and limit cycle oscillation prediction

Greco Jr.,Paulo C.; Lan,Chuan-Tau E.
Fonte: Associação Brasileira de Engenharia e Ciências Mecânicas - ABCM Publicador: Associação Brasileira de Engenharia e Ciências Mecânicas - ABCM
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/12/2010 Português
Relevância na Pesquisa
66.05%
The purpose of this study was to develop new approaches for predicting transonic flutter and limit cycle oscillations (LCO) using computational methods. The TSD equation is separated into the in-phase and out-of-phase components through a nonlinear harmonic averaging method. It is then solved in the frequency domain to obtain the aerodynamic forcing function which is needed in the flutter and LCO analyses. To predict flutter, equations are developed using the concept of generalized coordinates. The flutter speed is determined by examining the frequency-domain matrix equation eigenvalues. Flutter characteristics of the AGARD I-445.6 wing are analyzed. Flutter speed and frequency are well predicted in subsonic speed, but are overestimated in supersonic flow. To predict limit cycle oscillations, the frequency-domain aerodynamic coefficients are used to obtain a nonlinear time-domain expression for the aerodynamic force. Limit cycle oscillation characteristics of the DAST ARW-2 wing are analyzed. The results show LCO for Mach numbers ranging from 0.915 to 0.940.

Spectral discrimination of breast pathologies in situ using spatial frequency domain imaging

Laughney, Ashley M; Krishnaswamy, Venkataramanan; Rizzo, Elizabeth J; Schwab, Mary C; Barth, Richard J; Cuccia, David J; Tromberg, Bruce J; Paulsen, Keith D; Pogue, Brian W; Wells, Wendy A
Fonte: BioMed Central Publicador: BioMed Central
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
65.96%
Introduction: Nationally, 25% to 50% of patients undergoing lumpectomy for local management of breast cancer require a secondary excision because of the persistence of residual tumor. Intraoperative assessment of specimen margins by frozen-section analysis is not widely adopted in breast-conserving surgery. Here, a new approach to wide-field optical imaging of breast pathology in situ was tested to determine whether the system could accurately discriminate cancer from benign tissues before routine pathological processing. Methods: Spatial frequency domain imaging (SFDI) was used to quantify near-infrared (NIR) optical parameters at the surface of 47 lumpectomy tissue specimens. Spatial frequency and wavelength-dependent reflectance spectra were parameterized with matched simulations of light transport. Spectral images were co-registered to histopathology in adjacent, stained sections of the tissue, cut in the geometry imaged in situ. A supervised classifier and feature-selection algorithm were implemented to automate discrimination of breast pathologies and to rank the contribution of each parameter to a diagnosis. Results: Spectral parameters distinguished all pathology subtypes with 82% accuracy and benign (fibrocystic disease, fibroadenoma) from malignant (DCIS...

Frequency-domain hypothesis testing approach to leak detection in a single fluid line

Zecchin, A.; White, L.; Lambert, M.; Simpson, A.
Fonte: University of Exeter, Centre for Water Systems; Exeter, UK Publicador: University of Exeter, Centre for Water Systems; Exeter, UK
Tipo: Conference paper
Publicado em //2005 Português
Relevância na Pesquisa
65.96%
The detection of leakage is of great importance in the reliable operation and management of fluid line systems. This paper, presents a novel technique for the detection of leaks within a single line system. Based on the Laplace-domain transmission line framework, system transfer functions are derived using a basic block diagram approach. A frequency domain detection and estimation procedure is then formulated under the assumption of white Gaussian noise. Numerical experiments are conducted showing promising results; http://www.projects.ex.ac.uk/CCWI2005/Final%20detailed%20presentation%20schedule%20STK5a.pdf; Aaron C. Zecchin, Langford B. White, Martin F. Lambert, and Angus R. Simpson

Frequency-domain modeling of transients in pipe networks with compound nodes using a Laplace-domain admittance matrix

Zecchin, A.; Lambert, M.; Simpson, A.; White, L.
Fonte: ASCE-Amer Soc Civil Engineers Publicador: ASCE-Amer Soc Civil Engineers
Tipo: Artigo de Revista Científica
Publicado em //2010 Português
Relevância na Pesquisa
66.04%
An alternative to modeling the transient behavior of pipeline systems in the time domain is to model these systems in the frequency domain using Laplace transform techniques. A limitation with traditional frequency-domain pipeline models is that they are only able to deal with systems of a limited class of configuration. Despite the development of a number of recent Laplace-domain network models for arbitrarily configured systems, the current formulations are designed for systems comprised only of pipes and simple node types such as reservoirs and junctions. This paper presents a significant generalization of existing network models by proposing a framework that allows not only complete flexibility with regard to the topological structure of a network, but also, encompasses nodes with dynamic components of a more general class (such as air vessels, valves, and capacitance elements). This generalization is achieved through a novel decomposition of the nodal dynamics for inclusion into a Laplace-domain network admittance matrix. A symbolic example is given demonstrating the development of the network admittance matrix and numerical examples are given comparing the proposed method to the method of characteristics for 11-pipe and 51-pipe networks.; Aaron C. Zecchin...

Frequency domain analysis of linear and nonlinear structures with applications to impact force identification and micro-resonator design

Ghaderi, Pooya
Fonte: Universidade Rice Publicador: Universidade Rice
Português
Relevância na Pesquisa
66.04%
The modeling and analysis of structures using frequency-domain methods simplify the procedure of the modeling and analysis and provides better understanding of the response of the structures. There are different applications in frequency-domain structural modeling and analysis such as modeling and analysis in impact engineering, wave propagation in structures, and micro-resonators. The identification of the impact force and the impact location in structures are important for monitoring the condition of the structures and also for the design of the future structures. The complexity and nonlinearity of the impact incident makes it impractical to measure the impact force directly. In this study, a new method that uses the spectral finite element method (SFEM) is introduced in order to identify and locate the applied impact force. Using SFEM facilitates for the successfully identification of the high frequency content in the impact forces. Also, using SFEM allows for the identification of the impact force independent of the location of the impact force. The impact force identification and localization method is verified by experimental results. For designing and analyzing micro-resonators, it is required to do the frequency-analysis of these structures which provide the frequency characteristics and the frequency-response of the structures. In this study...

Frequency domain modelling of random wound motor windings for insulation stress analysis

Martínez-Tarifa, Juan Manuel; Amarís Duarte, Hortensia; Sanz Feito, Javier
Fonte: Springer Publicador: Springer
Tipo: info:eu-repo/semantics/acceptedVersion; info:eu-repo/semantics/article Formato: application/pdf
Publicado em /06/2006 Português
Relevância na Pesquisa
66.04%
The use of conventional low voltage induction motors fed by pulse width modulated (PWM) inverters has begun to present important problems. These waveforms consist of steep-fronted pulses having very short rise times (about 100 ns in modern IGBT bridges) and high frequency repetition rates (up to 20 kHz) whose immediate consequences are additional electrical stresses in an induction motorrsquos insulation system. In this paper a frequency domain model for the analysis and characterization of the internal voltage distribution in random wound coils is presented. The model allows voltage prediction in time domain when an inverse fast Fourier transform (FFT) transformation is performed, and requires only a few frequency domain impedance measurements. This methodology will be useful for accurately predicting the voltage distribution in motor windings during the design stage, and reducing the risk of premature failure in motor insulation. Experimental and theoretical results are presented and compared and model effectiveness using different approximations is studied.; This research has been suported by the Spanish Science and Technology Ministry under contract MAT 2002 03210, and the Madrid Regional Government under the Initiative for Regional R&D Laboratoy Network.

Rule Based Design Optimization of Cradle Structures Using Frequency Domain Structural Synthesis

Gordis, Joshua H.; Healy, Anthony J.; Cook, Ronald E.
Fonte: Monterey, California. Naval Postgraduate School Publicador: Monterey, California. Naval Postgraduate School
Tipo: Relatório Formato: 1 v. (various pagings) : ill. ; 28 cm.
Português
Relevância na Pesquisa
65.97%
Approved for public release; distribution is unlimited.; This work investigates the use of frequency domain structural synthesis and an expert system rule based design methodology for automating the design of the submarine machinery cradle. The expert system provides 'intelligent' automated executive control of the design process. Frequency domain structural synthesis provides the means to rapidly alter the structural configuration of the cradle design and calculate dynamic response. The goal is the minimization of structural dynamic transmissibility.; Program Executive Office - Submaries; http://archive.org/details/rulebaseddesigno00gord; N0002493WX70233

An adaptive wavenumber sampling strategy for 2.5D seismic-wave modeling in the frequency domain

Zhou, B.; Greenhalgh, S.
Fonte: Birkhauser Verlag Ag Publicador: Birkhauser Verlag Ag
Tipo: Artigo de Revista Científica
Publicado em //2006 Português
Relevância na Pesquisa
66.05%
Simulation of seismic waves from a 3D point-source in a 2D medium may be performed in the frequency-wavenumber domain (called 2.5D modelling). It involves computing the Fourier-transformed Green's function for a number of frequency (ω) and strike direction wavenumber (ky) values and doubly inverse transforming to convert to the traveltime and distance space. Such modeling produces a wavefield with 3D features but the computation becomes pseudo 2D (i.e., in the xz-plane) rather than 3D (in the xyz-frame). The common sampling strategy for the wavenumber is inefficient for 2.5D wave modeling because it employs a large number of wavenumbers (ky). This leads to a high cost of computer time in the linear-equation-solving processing, which detracts from the advantages of 2.5D modeling. In this paper, we use two analytic frequency-wavenumber-domain solutions for seismic waves in a homogeneous medium and an inhomogeneous media (two semi-infinite media in contact) to investigate the properties of the solutions and an efficient sampling strategy for choosing the wavenumbers. We have carried out analytic and numerical experiments with these solutions, and present adaptive Gauss–Legendre abscissae for the wavenumber sampling in terms of a modeling situation. We show that the effective range and the number of sampling points of the wavenumber define the adaptive sampling strategy...

Joint time/frequency-domain inversion of reflection data for seabed geoacoustic profiles

Dettmer, Jan; Dosso, S.E.; Holland, Charles W.
Fonte: Acoustical Society of America Publicador: Acoustical Society of America
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
65.97%
This paper develops a joint time/frequency-domain inversion for high-resolution single-bounce reflection data, with the potential to resolve fine-scale profiles of sediment velocity, density, and attenuation over small seafloor footprints (∼100 m). The

A holistic approach to inversion of frequency-domain airborne EM data

Brodie, Ross; Sambridge, Malcolm
Fonte: Society of Exploration Geophysicists Publicador: Society of Exploration Geophysicists
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
65.97%
We have developed a holistic method for simultaneously calibrating, processing, and inverting frequency-domain airborne electromagnetic data. A spline-based, 3D, layered conductivity model covering the complete survey area was recovered through inversion

Frequency-domain modelling of floating wind turbines

Lupton, Richard
Fonte: University of Cambridge; Department of Engineering; Pembroke College Publicador: University of Cambridge; Department of Engineering; Pembroke College
Tipo: Thesis; doctoral; PhD
Português
Relevância na Pesquisa
65.94%
The development of new types of offshore wind turbine on floating platforms requires the development of new approaches to modelling the combined platform-turbine system. In this thesis a linearised frequency-domain approach is developed which gives fast but approximate results: linearised models of the structural dynamics, hydrodynamics, aerodynamics and control system dynamics are brought together to find the overall response of the floating wind turbine to harmonic wind and wave loading. Initially, a nonlinear flexible multibody dynamics code is developed and verified, which is then used to provide reference nonlinear simulation results. The structural dynamics of a wind turbine on a moving platform are shown to be nonlinear, but for realistic conditions the effects are small. An approximate analysis of the second-order response of floating cylinders to hydrodynamic loads suggests slow drift motion may be relatively small for floating wind turbines, compared to other floating offshore structures. The aerodynamic loads are linearised using both harmonic and tangent linearisation approaches; the harmonic linearisation gives improved results when stall occurs. The wake dynamics can also be included. The control system behaviour is linearised using the same method...

Robust entropy-enhanced frequency-domain genomic analysis under uncertainties

Lyshevski, Sergey; Krueger, Frank
Fonte: IEEE Publicador: IEEE
Tipo: Proceedings
Português
Relevância na Pesquisa
65.97%
Here, we report the application of an entropy-enhanced frequency-domain analysis method to examine large-scale genomic data. This ensures superior coherency for qualitative and quantitative analysis. Different statistical methods are used to analyze large-scale data produced and attempts have been made to perform data mining. These efforts have been partially successful due to sequence gaps, noncoding and low complexity regions, inaccuracy, etc. In contrast, we report a novel robust method that is based on frequency-domain analysis. Our paradigm complements a number of far-reaching perceptions that new concepts emerge to comprehend complex large-scale genomic data under uncertainties.; Copyright 2004 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE.

Quantification of frequency domain error bounds with guaranteed confidence level in prediction error identification

Bombois, Xavier; Anderson, Brian; Gevers, Michel
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
65.99%
This paper considers prediction error identification of linearly parametrized models in the situation where the system is in the model set. For such situation it is easy to construct a confidence ellipsoid in parameter space in which the true parameter lies with an a priori fixed probability level, α. Surprisingly perhaps, the construction of a corresponding uncertainty set in the frequency domain, to which the true system belongs with probability α, is still an open problem. We show in this paper how to construct such frequency domain uncertainty set with a probability level of at least α.