High Frequency Phenomena Research Articles

740 拘束条件式を近似したマルチボディ車両モデルのリアルタイム解析

In this paper, the performance of the real-time multibody dynamic simulation with linearized constraint equation is discussed. It is well known that a small step size of numerical integration is required for the simulation of a system with high stiffness elements such as a rubber bush or a system with high frequency phenomena. The amount of the calculation can be reduced by linearizing the constraint equation of the system, and a real-time multibody dynamic analysis with smaller step size of numerical integration can be realized. On the other hand, it is important to understand how much accuracy was lost by the linearization. In this study, we compared the real-time simulation result with the linearized and the non-linearized multibody model in the case of the vehicle dynamic simulation. The calculation speed was evaluated on a real-time analysis environment, and the accuracy of the simulation result was examined.

Modelagem de aterramentos elétricos para fenômenos de alta frequência e comparação com resultados experimentais

Este artigo apresenta os fundamentos físicos e matemáticos de uma metodologia de cálculo de transitórios eletromagnéticos em aterramentos elétricos, solicitados por fenômenos de alta frequência, por exemplo, aqueles associados à incidência de descargas atmosféricas. As equações resultantes são oriundas da aplicação direta das equações básicas do eletromagnetismo no domínio da frequência, cuja solução é obtida mediante aplicação da técnica numérica Método dos Momentos. Os resultados advindos do modelo proposto são comparados com dados de medição e com resultados de outro modelo, considerado referência na literatura técnica especializada. De tais comparações verifica-se a consistência da modelagem proposta.

Cosine lobes for interactive direct lighting in dynamic scenes

Cosine functions have been widely used for representing Bidirectional Reflection Distribution Functions (BRDF) such as Lambert, Phong and Lafortune models. They are well suited to represent both high and low frequency signals. However, they are difficult to use with visibility and incident radiance. In most systems, the rendering equation terms are thus estimated using various methods. Several interactive rendering systems rather rely on the projection of each term onto orthonormal basis functions such as spherical harmonics or wavelets. These methods are easier to handle since the integration becomes a dot product. However, these functions are also subject to several drawbacks. For instance the number of coefficients is high for the representation of high frequency phenomena; the pre-computation time required for projecting each term of the rendering equation cannot be neglected. This paper demonstrates that cosine lobes can be generalized to visibility and incoming radiance with several advantages. First, cosine lobes do not form an orthonormal basis of functions and the number of parameters remains naturally adapted to the signal. This is very interesting for complex and high frequency functions: glossy BRDF or small light sources for instance. We also use this property for reducing the number of parameters as the computation goes along. Second, Lambert, Phong and Lafortune BRDF models are already used in many rendering systems. Since they already rely on this representation, no transformation into other types of model is necessary. This paper shows how it is possible to rapidly integrate the product of cosine lobes. As a demonstration of our methodology, we propose an interactive rendering system for direct lighting, including soft shadows and spatially varying materials.

Time Domain Techniques in Computational Electromagnetics [book review

This book is part of the Advanced in Electrical and Electronic Engineering Series. The purpose of the book is to "present the state of the art in the field of time-domain numerical modeling of high frequency and transient electromagnetic phenomena." The text consists of five chapters: a formulation of the MOMTD (method of moments time domain) approach; the application of MOMTD; Fourier transform procedure for obtaining frequency-domain information from TD results; an overview of finite time domain analysis; and two hybrid time domains methods. This relatively short book is a compilation of five self-contained papers. The depth, notation, and style of presentation varies widely from chapter to chapter. The main drawback of the book is that time domain computational electromagnetics is an active research field that demands more coverage.

Wavelet coefficients for window width and subsequent harmonics estimation – Case study

This paper is an extended version of the original author’s work presented during XIV IMEKO TC-4 Symposium [T. Tarasiuk, Estimation of measurement window width by interpolation based on wavelet coefficients – case study, in: Proceedings of 14th IMEKO TC-4 International Symposium, Poland, Gdynia/Jurata 2005, pp. 352–357]. Especially, new results have been added. This paper deals with the problem of reliable width estimation of a measurement window and its impact on harmonic analysis of chosen signals. The simple method of window width estimation is detection of a zero-crossing instant of a given signal by the analysis of sample polarisation changes. But the method is sensitive to waveform distortions, especially analysed signal multiple zero-crossings. So, the idea of implementing a discrete wavelet transform for risk reduction of measurement results corruption by the higher frequency phenomena has been proposed and preliminarily tested [T. Tarasiuk, Interpolation based on wavelet coefficients for frequency measurement, in: Proceedings of XVII IMEKO World Congress, June 22–27, 2003, Dubrovnik, Croatia, pp. 895–898]. In this paper, the concept has been further developed, especially the analysis of real voltages with multiple zero-crossing has been carried out. Then, the consequences of the chosen methods for the subsequent harmonics analysis have been laid and discussed.

The NCAR CCM as a Numerical Weather Prediction Model

Abstract The NCAR Community Climate Model (CCM, version 3.6) is evaluated as a numerical weather prediction model. The model was run in real-time mode at relatively high resolution (T126 or approximately 1°) to produce 10-day forecasts over a 1-yr period ending 1 March 2004. The evaluation of the performance of the CCM could be useful for both the climate modeling community as well as the operational forecast centers. For climate modelers, the higher-resolution, short-range forecasts can be used to diagnose deficiencies in the physical parameterizations in the model. While climate models may produce good mean climatologies, they may fail to simulate important higher-frequency phenomena that may be important to climate. For operational centers, the examination of an open, well-developed, and studied model could provide insights that could lead to improvement in their own models. Furthermore, the CCM could be considered a candidate as a member for a suite of models for use in an operational context. And, finally, as operational centers gradually extend their forecast range, and climate scientists are paying more attention to the subseasonal time scales, the study of a climate model in the short range becomes more appropriate.

The Rossi X-ray timing explorer: Capabilities, achievements and aims

The prime scientific objectives of the Rossi X-Ray Timing Explorer (RXTE) were the study of astrophysical compact objects: black holes (galactic and extragalactic), many types of neutron stars, and accreting white dwarfs. RXTE was successful in achieving its original observing objectives of large area and high time resolution observations with broadband (2-200 keV) spectra, scheduled flexibly enough to enable observations of targets of opportunity on any timescale greater than a few hours. These capabilities enabled qualitatively new discoveries about dynamical timescale phenomena related to neutron stars and black holes, phenomena which probe basic physics in the most extreme environments of gravity, density, and magnetic fields. RXTE has extended its lifetime by applying the proportional counter area selectively and maintains schedule flexibility by making use of the distribution of targets around the sky. Proposed future observations emphasize opportunity to discover and study additional millisecond pulsars, pursue the high frequency quasi-periodic oscillations in black hole transients, and connect high frequency phenomena with longer term characteristics. RXTE will continue to strongly support, for both galactic and extragalactic targets, combining RXTE observations with other wavelengths (from IR to TeV) or with other capabilities, such as high spectral resolution.

Dynamics of oscillator chains from high frequency initial conditions: Comparison of ϕ4 and FPU-β models

The dynamics of oscillator chains are studied, starting from high frequency initial conditions (h.f.i.c.). In particular, the formation and evolution of chaotic breathers (CB's) of the Klein-Gordon chain with quartic nonlinearity in the Hamiltonian (the phi(4) model) are compared to the results of the previously studied Fermi-Pasta-Ulam (FPU-beta) chain. We find an important difference for h.f.i.c. is that the quartic nonlinearity, which drives the high frequency phenomena, being a self-force on each individual oscillator in the phi(4) model is significantly weaker than the quartic term in the FPU-beta model, which acts between neighboring oscillators that are nearly out-of-phase. The addition of a self-force breaks the translational invariance and adds a parameter. We compare theoretical results, using the envelope approximation to reduce the discrete coupled equations to a partial differential equation for each chain, indicating that various scalings can be used to predict the relative energies at which the basic phenomena of parametric instability, breather formation and coalescence, and ultimately breather decay to energy equipartition, will occur. Detailed numerical results, comparing the two chains, are presented to verify the scalings.

Observation of magnetohydrodynamic instability and direct measurement of local perturbed magnetic field using motional Stark effect diagnostic

The local oscillating component of the poloidal magnetic field in plasma associated with magnetohydrodynamic (MHD) instabilities has been measured using the motional Stark effects (MSE) diagnostic on the DIII–D tokamark. The magnetic field perturbations associated with a resistive wall mode rotated by internal coils at 20 Hz was measured using the conventional MSE operation mode. These first observations of perturbations due to a MHD mode were obtained on multiple MSE channels covering a significant portion of the plasma and the radial profile of the amplitude of the perturbed field oscillations was obtained. The measured profile is similar to the profile of the amplitude of the electron temperature oscillation measured by electron cyclotron emission (ECE) measurements. In a new mode of measurement, the amplitude of a tearing mode rotating at a high frequency (∼7 kHz) was observed using the spectral analysis of high frequency MSE data on one channel. The spectrum consists of the harmonics of the light modulation employed in the MSE diagnostics, their mutual beat frequencies and their beat frequencies with the rotation frequency of the tearing mode. The value and time variation of the frequency of the observed perturbations is in good agreement with that measured by Mirnov probes and ECE. The article demonstrates that the MSE diagnostic can be used for observing low and high frequency phenomena such as MHD instabilities and electromagnetic turbulence.

Three Approaches for Elastodynamic Contact in Multibody Systems

In machine dynamics impacts may occur by interaction of solid bodies. There is no doubt that the method of multibody systems is most efficient for the dynamical analysis of the overall motion. However, during impact energy is lost macromechanically measured by the coefficient of restitution. This coefficient has to be estimated from experiments and experience but cannot be computed within the multibody system approach. The impacts, on the other hand, are generating waves in the bodies which are propagating until they are vanishing due to material damping. These high frequency phenomena are analyzed using wave propagation, modal approach and finite elements. The results of the simulation on the fast time scale are used to compute the coefficient of restitution which is then fed back to the multibody system equations and the solution continues on the related slow time scale. The efficiency of the approach presented is shown for the impact of a steel sphere on four different shaped aluminum bodies of comparable mass. The simulation results are verified with experiments performed on different time scales, too. Using the impact of a double pendulum on a stop as example, the application of the multiscale approach to a multibody system is shown.

The impact of switching strategies on power quality for integral cycle controllers

Integral cycle controllers (ICCs) are used for load power control. ICCs are switched at an integral number of cycles to effect this control. The load current for such controllers has an impact on the distribution supply bus: the impact occurs for low frequency (subsynchronous) phenomena and high frequency (supersynchronous) phenomena. Subsynchronous impact includes flicker on the distribution bus, and supersynchronous phenomena includes supply transformer core loss. The management of these power quality issues is discussed in terms of selecting the controller switching strategy. An innovative concept of group frequencies is discussed.

Modelling high frequency phenomena in the rotor of induction motors under no-load test conditions

The paper aims to deep the electromagnetic phenomena in the rotor of induction motors produced during the no-load test by the high-order harmonics of the spatial distribution of magnetic flux . The analysis is carried out by a flux driven finite element procedure, which can take into account the hysteresis of magnetic material, the induced currents in rotor cage and the eddy currents in the laminations. The computed results, including losses and local waveforms of electrical and magnetic quantities, are finally discussed.

Measurement techniques for unsteady flows in turbomachines

The growing interest for unsteady flows in turbomachines over the last two decades has led to an intensive development of fast response measurement techniques, capable of resolving with high frequency phenomena related to inlet distortion, rotating stall and blade row interference effects with blade passing frequencies ranging from 3 to 30 kHz. This development was favoured by major advances in sensor technology and data acquisition systems. The paper reviews the progress in fast response measurement techniques for high speed turbomachinery and application with emphasis on fast response pressure and temperature probes and blade surface sensors including pressure, heat transfer and shear stress determination.

High resolution photothermal imaging of high frequency phenomena using a visible charge coupled device camera associated with a multichannel lock-in scheme

We have developed a technique using a photothermal microscope from which we can make a thermal image of an electronic component working at a “high frequency” using a charge coupled device (CCD) camera and a multichannel lock-in scheme. To do this, we have created an electronic “stroboscope”: the frequency F of the thermal signal induced by a high frequency electrical excitation and the frequency of the light F+f that illuminates the device are next to each other; the signal reflected at the surface of the device whose amplitude is proportional to the variation of reflectivity and hence to the variation of temperature and whose frequency is the blinking one f is analyzed by a visible CCD camera. Amplitude and phase images of the high frequency thermal phenomenon can then be made. Moreover, this technique presents a great advantage: the spatial resolution is better than 1 μm. The amplitude and phase images presented show, with a very good spatial resolution, Joule and Peltier heating of a polycrystalline silicon 2.5 kΩ resistor across which a sinusoidal current is forced.

On the Modeling of Friction and Rolling in Flexible Multi-Body Systems

This paper is concerned with the dynamic analysis of flexible, nonlinear multi-body systems undergoing contact involving friction and rolling. A continuous friction law is used to model the friction forces between contacting bodies. This avoids the numerical problems associated with the discontinuity inherent to Coulomb's friction law and eliminates the need for different sets of equations modeling sliding and rolling as distinct phenomena. On the other hand, continuous friction laws eliminate specific physical phenomena implied by Coulomb's friction law. The condition of vanishing relative velocity between two contacting bodies is not possible: sticking or rolling are replaced by creeping with a small relative velocity. Discrete events such as transition from slipping to rolling or rolling to slipping are eliminated, together with the high frequency phenomena they are likely to cause. The computational issues associated with the continuous friction law and with the enforcement of the non-holonomic rolling constraint are addressed in this paper. This work is developed within the framework of energy preserving and decaying time integration schemes that provide unconditional stability for nonlinear, flexible multi-body systems undergoing contact involving friction and rolling.

A New and Powerful Real Time Digital Transient Network Analyser

Abstract Power systems rely more and more on a wide range of equipment that regulate power plants, voltage and reactive power, or protect the grid against malfunctions. To test these various equipment, such as relays, controls or power electronic devices, analog simulators have been developed over the years. However, the poor flexibility and the maintenance costs of these simulators opened up the way for fully digital real-time simulators able to simulate high frequency phenomena: the real-time Digital Transient Network Analysers (DTNA). Up to now, DTNA's used mainly hybrid or non-standard technologies that limited their assets compared to analog simulators. This paper presents a new and fully digital real-time DTNA that can perform real-time tests on a standard multi-purpose parallel computer: ARENE. This new facility will be used to test all kinds of equipment from protective relays to generator controllers, HVDC or FACTS prototypes or controllers.

Interlock/friction model for dynamic shear response in natural jointed rock

A system identification approach is used to formulate a discrete element analytical model to predict the behavior of natural jointed rock specimens subject to static normal stress and dynamic shear in a compliant loading apparatus. Model parameters are synthesized to correspond to various low and high frequency physical phenomena that are observed to occur in available experimental data for welded tuff specimens subject to harmonic shear. An approximate interlock/friction model is postulated for the rock interface dynamics, while various spring/mass and damper systems represent the loading apparatus. Furthermore, it is found that primary and secondary asperities of the joint interface roughness must be characterized in order to provide an adequate model of the observed experimental behavior. It is found that the fundamental jointed rock behavior can be related to basic excitation frequency and primary joint asperities, while higher frequency phenomena are associated with compliant mode responses of the loading apparatus that are excited by secondary joint asperities. Recommendations are given for impact of the results on current joint friction model theories.

High Frequency Phenomena in Regurgitant Jets

Color Doppler echocardiography is accepted as a useful tool for evaluating valvular regurgitation but, so far, it does not allow for a precise quantification of the regurgitant volume since it is limited by the combination of velocity ambiguities, a limited resolution, and a low frame rate. The low frame rate is imposed by the sector angle, the packet size, the pulse repetition rate, the line density, and the sequential analysis of the ultrasound emissions. On the other hand, the images are supposed to depict pulsatile jets surrounded by high frequency pulsatile vortices. The present study was designed to search for the presence of high frequency phenomena in turbulent jets and to analyze the influence of the low frame rate on the jet images. An in vitro study using an aliasing‐free laser Doppler and a hydraulic model simulating intracardiac jets was carried out. An analysis of flow events with a high bandwidth (500 Hz) was conducted using M‐mode color displays of the velocities. It showed: (1) on the centerline, a slow propagation of the front of the jet, and low frequency velocity fluctuations (< 50 Hz); and (2) at the opposite, in the boundary layer of the jet, very rapid fluctuations with frequencies comprised between 50 and 500 Hz. On two‐dimensional color images of laser Doppler data, the size of the central laminar core appeared strongly modified by a decrease in frame rate up to the maximum one commonly used in color Doppler (30 frames / sec) as well by a decrease in line density. These data demonstrate that higher frame rate could improve the accuracy of ultrasound color Doppler flow mapping.

Fiber Optics

On looking back to the beginnings of Physical Review it is interesting to find that the very first paper in volume 1, number 1, 1893, addressed the “transmission spectra of certain substances in the infrared.” The article, authored by Ernest Nichols, included quartz and glass as materials of interest. The same volume offers a review of Nikola Tesla's book Light and Other High-Frequency Phenomena. It is therefore fitting that this celebration of the 100th anniversary of Physical Review includes a discussion of a technology that is based on fundamental principles of physics addressed in the journal's first issue and countless numbers of later issues and that has profoundly transformed the telecommunications infrastructure of our society.

Détermination des paramètres du schéma équivalent discrétisé des enroulements d'un transformateur

Dans cet article, nous presentons le calcul des parametres inductifs et capacitifs d'un transformateur de puissance a l'aide de methodes numeriques utilisant les elements finis en trois dimensions. La modelisation, basee sur un calcul par elements finis du champ electromagnetique, permet d'aborder sous un nouvel angle l'etude des phenomenes haute frequence se propageant dans les enroulements d'un transformateur. La methode est appliquee a un transformateur de puissance de type cuirasse a l'aide du logiciel FLUX3D.