Ripple Amplitude Research Articles

Analytical scalings of the linear Richtmyer-Meshkov instability when a shock is reflected.

When a planar shock hits a corrugated contact surface between two fluids, hydrodynamic perturbations are generated in both fluids that result in asymptotic normal and tangential velocity perturbations in the linear stage, the so called Richtmyer-Meshkov instability. In this work, explicit and exact analytical expansions of the asymptotic normal velocity (δv_{i}^{∞}) are presented for the general case in which a shock is reflected back. The expansions are derived from the conservation equations and take into account the whole perturbation history between the transmitted and reflected fronts. The important physical limits of weak and strong shocks and the high/low preshock density ratio at the contact surface are shown. An approximate expression for the normal velocity, valid even for high compression regimes, is given. A comparison with recent experimental data is done. The contact surface ripple growth is studied during the linear phase showing good agreement between theory and experiments done in a wide range of incident shock Mach numbers and preshock density ratios, for the cases in which the initial ripple amplitude is small enough. In particular, it is shown that in the linear asymptotic phase, the contact surface ripple (ψ_{i}) grows as ψ_{∞}+δv_{i}^{∞}t, where ψ_{∞} is an asymptotic ordinate different from the postshock ripple amplitude at t=0+. This work is a continuation of the calculations of F. Cobos Campos and J. G. Wouchuk, [Phys. Rev. E 90, 053007 (2014)PLEEE81539-375510.1103/PhysRevE.90.053007] for a single shock moving into one fluid.

Study of an all-fiber interleaver with flattop wavelength response

An interleaver with three cascaded 3×3 single-mode fiber couplers and one 2×2 single-mode fiber coupler is presented. Under certain values of physical length differences of the interferometer arms, 3-dB passband in odd channels and in even channels of the interleaver can realize an asymmetric passband wavelength response. Through a mathematical algorithm, the optimum splitting ratios, which are the relationship among the splitting ratios of the four couplers, were determined to achieve a flattop response within the passband for the interleaver. Based on the optimum splitting ratios, the output spectrums of the interleaver were analyzed and discussed. The results indicate that the amplitude of ripples in the “flat” region of the flattop passband wavelength response in odd channels and even channels are almost zero, the interleaver can achieve a perfect smoothing flattop response and good uniform channel passband, and the tolerance characteristics of the splitting ratios is favorable. In fabrication recipe, splitting ratios of the four couplers in the interleaver can be accurately controlled, so the degree of manufacturing difficulty is reduced.

Shaped Beam Synthesis of Real Antenna Arrays via Finite-Element Method, Floquet Modal Analysis, and Convex Programming

A shaped beam synthesis methodology for planar arrays with control of the ripple amplitude in the shaped region, and constraints on the sidelobe and cross-polar levels, is proposed in this paper. A previously developed synthesis formulation for designing finite impulse response (FIR) filters by transforming a nonconvex synthesis problem to a convex optimization scheme enforcing conjugate symmetric excitation weights, is extended to real and coupled radiating elements of complex geometry, taking into account mutual coupling effects. The optimization procedure is integrated with a finite array approach simulating different array environments. This approach is based on the infinite array model through a Floquet modal- and general scattering matrix (GSM)-based analysis, where the periodic radiating element is characterized from a hybrid and full-wave analysis procedure combining the FEM, modal analysis, and domain decomposition technique. Numerical results of different synthesized beam patterns are presented for arrays of open-ended apertures and microstrip antennas.

Influence of current ripple on the tungsten cathode erosion

The erosion of a thermionic tungsten cathode is studied. Arc burning conditions under which gas–vapor erosion causes cathode mass losses are determined. It is shown that erosion does not depend on the current ripple amplitude and is roughly equal to 2 ng/C. In experiments, the current ripple amplitude ranges from ±1% to ±50%.

Calculating Arbitrarily Located Sampling Data From Quiet Zone Spherical Near-Field Scanning Measurements

Amplitude and phase distribution inside the quiet zone (QZ) of a far-field antenna measurement chamber are important indicators for the quality of antenna measurements therein. Both amplitude and phase can be further subdivided into intuitive quality parameters such as linear taper, parabolic taper, and ripple. In order to retrieve these parameters from QZ spherical near-field measurements, the transmission formula is adapted to the case where the output signal of a virtually positioned output probe-antenna can be calculated on arbitrary locations inside the QZ. The output probe-antenna can be a measured or theoretically defined antenna and can be rotated in any direction of interest. This paper will show that this method provides similar results as industry standard linear field-probing by comparing amplitude taper and ripple extracted from both measurements. Further the advantages of using QZ spherical near-field scanning (QZSNFS) in combination with the adapted output transmission formula will be shown by calculating multiple projections not available by standard field-probing.

Serrated Edge Design and Field Analysis in Spatial, Time, and Angular Domains for Improving the Field Uniformity of Beam Combiner

Edge diffraction of a beam combiner will adversely affect the field uniformity in the observation plane. In order to suppress the edge diffraction, the serrated edge design method is proposed. According to the equivalence principle, a field uniformity analysis method was proposed to compute the spatial field distribution radiated from the aperture of a beam combiner. In order to separate the direct wave from diffracted wave, the spatial field is transformed into the time- and angular-domain spectrum by inverse Fourier transform. First, the height of serrations is designed by analog of the equivalent trapezoidal amplitude taper. Then, the number of serrations was designed by the assumption of isosceles and right triangles. Finally, the shape of serrations was designed by changing the interior angle of serrations. A serrated edge design example is also proposed and analyzed. By comparing the field uniformity in spatial, time, and angular domains before and after serrating the edges, the amplitude and phase ripples decrease from 1.85 dB and 12.16° to 0.53 dB and 3.98°, respectively. The results show that the field uniformity is significantly improved.

Medium-energy ion irradiation of Si and Ge wafers: studies of surface nanopatterning and signature of recrystallization in 100 keV Kr+ bombarded a-Si

We report new and exciting experimental results on ion-induced nanopatterning of a-Si and a-Ge surfaces. The crystalline Si (100) and Ge (100) wafers were amorphized and an a/c interface was developed by pre-irradiation with a 50 keV Ar+ beam at normal incidence with an ion fluence of 5.0 × 1015 ions cm−2. These amorphized surfaces were post-irradiated with Ar+ and Kr+ beams at an angle of 60°. The post irradiation was done with ion fluences of 1.0 × 1017 ions cm−2. For each beam, two energies (50 and 200 keV for Ar+, 100 and 250 keV for Kr+) were chosen to ensure ion stopping in both sides of the a/c interface. Regular nanopatterning (in the form of ripples) is observed on the Ge surface only with the post irradiation of the Kr+ beam. The Si surface showed regular nanopatterning with the irradiation of both beams with two energies. For the ion beams crossing the a/c interface, ripples of higher amplitude and longer wavelength were formed. Further, the irradiation with a heavy beam yielded surface ripples of relatively larger amplitudes. The Raman measurements confirm amorphization of the pre-irradiated surfaces. Surprisingly, the post-irradiated Si surface with the 100 keV Kr+ beam showed evidence of recrystallization. In the paper we discuss the physics at the interface and explain the experimental findings.

A CMOS Ripple Detector for Voltage Regulator Testing

This paper presents an RMS based ripple sensor for testing of fully integrated voltage regulators. A DC signal which is proportional to the input ripple amplitude is generated. Final digital pass/fail signal is obtained with a clocked comparator. The sensor can detect a peak-to-peak ripple voltage of up to 50 millivolts on the 1.2 V supply rail and has 220 MHz bandwidth. The sensor is designed using IBM 90 nm CMOS technology and its functionality is verified in Cadence Virtuoso simulation environment.

RETRACTED ARTICLE: Tokamak Coils Materials and Toroidal Field Ripples Calculation Using the Comsol Multiphysics

The ITER superconducting magnet systems consists of four main sub-systems: toroidal field (TF) coils, central solenoid coils, poloidal field coils, and correction coils. Like many other ITER systems, the magnet components are supplied in-kind by six domestic agencies. The technical specifications, manufacturing processes and procedures required to fabricate these components are particularly challenging. The management structure and organization to realize this procurement within the tight ITER construction schedule is very complex. On the other hand, toroidal magnetic field ripple in tokamak is an important issue in plasma equilibrium and stability studies. Toroidal magnetic field is created by toroidal torus with finite number of coils, therefore the field has a ripple in torus space. In this paper, we have reviewed the ITER magnetic coils materials, and also we have estimated the amplitude of TF ripples and its dependence to numbers of coils using the “Comsol Multiphysics” software. The calculations which performed for three: 8, 16 and 32 toroidal coils, indicates that increasing the number of toroidal coils lead to reduction of magnetic field ripple and lead to more stable plasma, but diagnostic access to plasma is reduces.

電圧形PWM変換器のデッドタイムに起因する電圧誤差補償法の系統連系時の動作特性

This paper discusses the performance of compensation methods for dead-time voltage error in voltage-source grid-connection PWM converters. The theoretical analysis in this paper reveals the relationship between the voltage error and the current ripples through the converter. The analytical results imply that the voltage error is strongly affected by the amplitude of the current ripples as well as the source power factor. This paper proposes a new compensation method which makes it possible to use two lookup tables to reduce the calculation time in the controller. The compensation characteristics are compared by using a 200-V 5-kW three-phase grid-connection converter. As a result, conventional approximation-based compensation methods exhibit an acceptable performance in a restricted power-factor operation range. In contrast, the turn-off transition-based compensation method and the proposed method have a good compensation performance all over the power-factor.

Mechanical Torque Ripple From a Passive Diode Rectifier in a 12 kW Vertical Axis Wind Turbine

The influence of passive rectification on the mechanical torque of a permanent magnet generator for a directly driven vertical axis wind turbine has been studied. Passive diode rectification introduce electromagnetic torque ripple from the generator. The conversion of electromagnetic torque ripple into mechanical torque ripple and rotational speed ripple has been modeled, analytically evaluated, and simulated. The simulations have been compared to measurements on an open site 12 kW prototype. A parameter study with the model illustrates the impact of shaft torsional spring constant, generator rotor inertia, generator inductance, and dc-link capacitance. The results show that the shaft and generator rotor can be an effective filter of electromagnetic torque ripple from diode rectification. The measured mechanical torque ripple amplitude on the prototype is less than $\pm$ 0.9% of nominal turbine torque. The measurements compare well with the simulations.

Effect of Intrinsic Ripples on Elasticity of the Graphene Monolayer.

The effect of intrinsic ripples on the mechanical response of the graphene monolayer is investigated under uniaxial loading using molecular dynamics (MD) simulations with a focus on nonlinear behavior at a small strain. The calculated stress-strain response shows a nonlinear relation through the entire range without constant slopes as a result of the competition between ripple softening and bond stretching hardening. For a small strain, entropic contribution is dominant due to intrinsic ripples, leading to elasticity softening. As the ripples flatten at increasing strain, the energetic term due to C–C bonds stretching competes with the entropic contribution, followed by energetic dominant deformation. Elasticity softening is enhanced at increased temperature as the ripple amplitude increases. The study shows that the intrinsic ripple of graphene affects elasticity. This result suggests that a change of ripple amplitudes due to various environmental conditions such as temperature, and substrate interactions can lead to a change of the mechanical properties of graphene. The understanding of the rippling effect on the mechanical behavior of 2D materials is useful for strain-based ripple manipulation for their engineering applications.

Sand Ripple Characterization Using an Extended Synthetic Aperture Sonar Model and Parallel Sampling Method

The aim of this work is to characterize the seafloor by estimating invariant sand ripple parameters from synthetic aperture sonar (SAS) imagery. Using a hierarchical Bayesian framework and a known sensing geometry, a method for estimating sand ripple frequency, amplitude, and orientation values from a single SAS image, as well as from sets of SAS imagery over an area, is presented. This is accomplished through the development of an extended model for sand ripple characterization and a Metropolis-within-Gibbs sampler to estimate sand ripple frequency, amplitude, and orientation characteristics for multiaspect high-frequency side-look sonar data. Results are presented on synthetic and measured SAS imagery that indicate the ability of the proposed method to estimate desired sand ripple characteristics.

Modelling ac ripple currents in HTS coated conductors

Dc transmission using high temperature superconducting (HTS) coated conductors (CCs) offers a promising solution to the globally growing demand for effective, reliable and economic transmission of green energy up to the gigawatt level over very long distances. The credible estimation of the losses and thereby the heat dissipation involved, where ac ripples (introduced in rectification/ac–dc conversion) are viewed as a potential source of notable contribution, is highly essential for the rational design of practical HTS dc transmission cables and corresponding cryogenic systems to fulfil this demand. Here we report a targeted modelling study into the ac losses in a HTS CC subject to dc and ac ripple currents simultaneously, by solving Maxwell’s equations using the finite element method (FEM) in the commercial software package COMSOL. It is observed that the instantaneous loss exhibits only one peak per cycle in the HTS CC subject to sinusoidal ripples, given that the amplitude of the ac ripples is smaller than approximately 20% of that of the dc current. This is a distinct contrast to the usual observation of two peaks per cycle in a HTS CC subject to ac currents only. The unique mechanism is also revealed, which is directly associated with the finding that, around any local minima of the applied ac ripples, the critical state of −Jc is never reached at the edges of the HTS CC, as it should be according to the Bean model. When running further into the longer term, it is discovered that the ac ripple loss of the HTS CC in full-wave rectification decays monotonically, at a speed which is found to be insensitive to the frequency of the applied ripples within our targeted situations, to a relatively low level of approximately 1.38 × 10−4 W m−1 in around 1.7 s. Comparison between this level and other typical loss contributions in a HTS dc cable implies that ac ripple currents in HTS CCs should only be considered as a minor source of dissipation in superconducting dc transmission.

Evaluations of CFETR ripple and optimization analyses of ferromagnetic inserts

Toroidal field ripple (TFR) amplitude of CFETR (China Fusion Engineering Test Reactor) was evaluated by ANSYS, and its profile at the plasma region was presented in MATLAB environment. The amplitude of the TFR is about 0.3% at the edge of plasma region, while it will reach 0.5% if the plasma radius is supposed to be larger. In order to investigate the effect of ferromagnetic materials on ripple reduction, ferromagnetic inserts with applicable material, various quantity and different toroidal angle in the shadow of each toroidal field coil were installed between the vacuum vessel shells by simulation and the results indicate ripple reduction is obtained when the angle was proper. By contrast, the ferromagnetic inserts were also installed on the inside of the inner shell and the outside of the outer shell. It shows that the effect on ripple reduction is better as the inserts are closer to plasma. Through the study we can conclude that it is feasible to install ferromagnetic inserts to reduce the TFR amplitude, but not necessary for CFETR at present parameters, while the method of installing ferromagnetic inserts could be developed if experiments with larger radius of plasma were to be done in the future.

Influence of Plugging DC Offset Estimation Integrator in Single-Phase EPLL and Alternative Scheme to Eliminate Effect of Input DC Offset and Harmonics

In this paper, the dynamic expressions of the amplitude and frequency estimated by the standard enhanced phase-locked loop (EPLL) and the ones with input dc offset estimation integrator (DCEI) are derived originally and reveal that the DCEI enlarges the amplitude of the periodic ripples caused by the dynamic disturbances and prolongs the dynamic process. To achieve correct estimation when the input signal contains dc offset and harmonics but without deteriorating the dynamic performance, an improved EPLL combined with delayed signal cancellation (DSC) is proposed. A DSC operator is employed to the input of the EPLL to eliminate dc offset and even-order harmonics. A cascaded DSC (CDSC) module is applied in both frequency and amplitude loops to remove the effect of most of the residual odd-order harmonics. The structure of the CDSC module and delay coefficients are designed in detail. Experimental results of all the three PLLs are presented and compared to validate the theoretical analysis results and the proposed EPLL.

Comparison of Output Current Ripple in Single and Dual Three-Phase Inverters for Electric Vehicle Motor Drives

The standard solution for the traction system in battery powered electric vehicles (EVs) is a two-level (2L) inverter feeding a three-phase motor. A simple and effective way to achieve a three-level (3L) inverter in battery-supplied electric vehicles consists of using two standard three-phase 2L inverters with the open-end winding connection of standard three-phase ac motors. The 3L inverter solution can be usefully adopted in EVs since it combines several benefits such as current ripple reduction, increment of phase motor voltage with limited voltage ratings of the two battery banks, improvement in system reliability, etc. The reduction in current ripple amplitude is particularly relevant since it is a source of electromagnetic interference and audio noise from the inverter-motor power connection cables and from the motor itself. By increasing the inverter switching frequency the ripple amplitude is reduced, but the drive efficiency decreases due to the proportionally increased switching losses. In this paper the peak-to-peak ripple amplitude of the dual-2L inverter is evaluated and compared with the corresponding ripple of the single-2L inverter, considering the same voltage and power motor ratings. The ripple analysis is carried out as a function of the modulation index to cover the whole modulation range of the inverter, and the theoretical results are verified with experimental tests carried out by an inverter-motor drive prototype.

Numerical and experimental verification of a trireflector compact antenna test range in the terahertz band

ABSTRACTNumerical and measured results of the quiet zone performance of a trireflector compact antenna test range (CATR) system in the terahertz band are presented in this letter. A modular Gaussian beam (GB) analysis method, which consists of frame‐based Gabor transformation, GB reflection and a 3D GB diffraction technique, was implemented to evaluate the quiet zone performance. Compared to geometrical optics method, this method is valid in predicting the field distribution in the caustic region. Moreover, simulation results of the CATR system demonstrated a superior efficiency to the physic optics method, especially in the terahertz range. Measured results show that 70% quiet zone usage can be achieved with amplitude and phase ripples less than 1.2 dB and 15°, respectively in the central frequencies. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:1686–1689, 2015

Hippocampal sharp waves and ripples: Effects of aging and modulation by NMDA receptors and L-type Ca2+ channels

Aging is accompanied by a complicated pattern of changes in the brain organization and often by alterations in specific memory functions. One of the brain activities with important role in the process of memory consolidation is thought to be the hippocampus activity of sharp waves and ripple oscillation (SWRs). Using field recordings from the CA1 area of hippocampal slices we compared SWRs as well as single pyramidal cell activity between adult (3–6-month old) and old (24–34-month old) Wistar rats. The slices from old rats displayed ripple oscillation with a significantly less number of ripples and lower frequency compared with those from adult animals. However, the hippocampus from old rats had significantly higher propensity to organized SWRs in long sequences. Furthermore, the bursts recorded from complex spike cells in slices from old compared with adult rats displayed higher number of spikes and longer mean inter-spike interval. Blockade of N-methyl-d-aspartic acid (NMDA) receptors by 3-((R)-2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CPP) increased the amplitude of both sharp waves and ripples and increased the interval between events of SWRs in both age groups. On the contrary, CPP reduced the probability of occurrence of sequences of SWRs more strongly in slices from adult than old rats. Blockade of L-type voltage-dependent calcium channels by nifedipine only enhanced the amplitude of sharp waves in slices from adult rats. CPP increased the postsynaptic excitability and the paired-pulse inhibition in slices from both adult and old rats similarly while nifedipine increased the postsynaptic excitability only in slices from adult rats. We propose that the tendency of the aged hippocampus to generate long sequences of SWR events might represent the consequence of homeostatic mechanisms that adaptively try to compensate the impairment in the ripple oscillation in order to maintain the behavioral outcome efficient in the old individuals. The age-dependent alterations in the firing mode of pyramidal cells might underlie to some extent the changes in ripples that occur in old animals.

Versions of Switched Reluctance Generatior Design at a Constant Stator Configuration

The investigation of the influence of the number of phases of switched reluctance generator (SRG) to the pulse of electromagnetic torque was carried out. The computer model was created. The amplitude of torque ripples reduces to 6 times with increasing of the ripple frequency to 5 times, that is more acceptable in terms of requirements.