Influence of inserted sample on second harmonic component in a finite-amplitude focused sound.

This study contributes to an improved understanding of the stability of the boundary layer generated at the bottom of a propagating surface wave of small but finite amplitude such that both a second harmonic component and a steady streaming component, which are superimposed on the main oscillatory flow, assume significant values. A linear stability analysis of the laminar flow is made to determine the conditions leading to transition and turbulence appearance. The Reynolds number of the phenomenon is assumed to be large and a ‘momentary’ criterion of stability is used. The results show that, at a given location, the laminar regime becomes unstable when the flow close to the bottom reverses its direction from the onshore to the offshore direction and the Reynolds number exceeds a first critical value $R_{\delta ,c1}$ . However, close to the critical condition, the flow is expected to relaminarize during the other phases of the cycle. Only when the Reynolds number is increased does turbulence tend to appear also after the passage of the wave trough when the flow close to the bottom reverses from the offshore to the onshore direction. When the Reynolds number is further increased and becomes larger than a second ‘threshold’ value, the growth rate of the perturbations becomes positive over the entire wave period. The obtained results suggest the existence of four different flow regimes: the laminar regime, the disturbed laminar regime, the intermittently turbulent regime and the fully developed turbulent regime.

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On resonant over-reflexion of internal gravity waves from a Helmholtz velocity profile

Journal of Fluid Mechanics ◽

10.1017/s0022112079002123 ◽

1979 ◽

Vol 90 (1) ◽

pp. 161-178 ◽

Cited By ~ 11

Author(s):

R. H. J. Grimshaw

Keyword(s):

Velocity Profile ◽

Gravity Waves ◽

Second Harmonic ◽

Phase Speed ◽

Internal Gravity Waves ◽

Finite Amplitude ◽

Weakly Nonlinear ◽

Velocity Discontinuity ◽

Interface Displacement ◽

Boussinesq Fluid

A Helmholtz velocity profile with velocity discontinuity 2U is embedded in an infinite continuously stratified Boussinesq fluid with constant Brunt—Väisälä frequency N. Linear theory shows that this system can support resonant over-reflexion, i.e. the existence of neutral modes consisting of outgoing internal gravity waves, whenever the horizontal wavenumber is less than N/2½U. This paper examines the weakly nonlinear theory of these modes. An equation governing the evolution of the amplitude of the interface displacement is derived. The time scale for this evolution is α−2, where α is a measure of the magnitude of the interface displacement, which is excited by an incident wave of magnitude O(α3). It is shown that the mode which is symmetrical with respect to the interface (and has a horizontal phase speed equal to the mean of the basic velocity discontinuity) remains neutral, with a finite amplitude wave on the interface. However, the other modes, which are not symmetrical with respect to the interface, become unstable owing to the self-interaction of the primary mode with its second harmonic. The interface displacement develops a singularity in a finite time.

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Control Strategy Based on Arm-Level Control for Output and Circulating Current of MMC in Stationary Reference Frame

Energies ◽

10.3390/en14144160 ◽

2021 ◽

Vol 14 (14) ◽

pp. 4160

Author(s):

Waqar Uddin ◽

Tiago D. C. Busarello ◽

Kamran Zeb ◽

Muhammad Adil Khan ◽

Anil Kumar Yedluri ◽

...

Keyword(s):

Reference Frame ◽

Control Method ◽

Second Harmonic ◽

Harmonic Component ◽

Effective Control ◽

Level Control ◽

Circulating Current ◽

Stationary Reference Frame ◽

Pr Controller ◽

Dc Component

This paper proposed a control method for output and circulating currents of modular multilevel converter (MMC). The output and circulating current are controlled with the help of arm currents, which contain DC, fundamental frequency, and double frequency components. The arm current is transformed into a stationary reference frame (SRF) to isolate the DC and AC components. The AC component is controlled with a conventional proportional resonant (PR) controller, while the DC component is controlled by a proportional controller. The effective control of the upper arm and lower arm ultimately controls the output current so that it delivers the required power to the grid and circulating current in such a way that the second harmonic component is completely vanished leaving behind only the DC component. Comparative results of leg-level control based on PR controller are included in the paper to show the effectiveness of the proposed control scheme. A three-phase, five-level MMC is developed in MATLAB/Simulink to verify the effectiveness of the proposed control method.

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A more general model equation of nonlinear Rayleigh waves and their quasilinear solutions

Modern Physics Letters B ◽

10.1142/s0217984916500962 ◽

2016 ◽

Vol 30 (08) ◽

pp. 1650096 ◽

Cited By ~ 4

Author(s):

Shuzeng Zhang ◽

Xiongbing Li ◽

Hyunjo Jeong

Keyword(s):

Rayleigh Waves ◽

General Equation ◽

Wave Motion ◽

Numerical Solutions ◽

Second Harmonic ◽

Approximate Equation ◽

Finite Amplitude ◽

Sound Beam ◽

Quasilinear Theory ◽

Sound Beams

A more general two-dimensional wave motion equation with consideration of attenuation and nonlinearity is proposed to describe propagating nonlinear Rayleigh waves of finite amplitude. Based on the quasilinear theory, the numerical solutions for the sound beams of fundamental and second harmonic waves are constructed with Green’s function method. Compared with solutions from the parabolic approximate equation, results from the general equation have more accuracy in both the near distance of the propagation direction and the far distance of the transverse direction, as quasiplane waves are used and non-paraxial Green’s functions are obtained. It is more effective to obtain the nonlinear Rayleigh sound beam distributions accurately with the proposed general equation and solutions. Brief consideration is given to the measurement of nonlinear parameter using nonlinear Rayleigh waves.

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Control of MMC-Based STATCOM as an Effective Interface between Energy Sources and the Power Grid

Electronics ◽

10.3390/electronics8111264 ◽

2019 ◽

Vol 8 (11) ◽

pp. 1264 ◽

Cited By ~ 1

Author(s):

Fatemeh Shahnazian ◽

Ebrahim Adabi ◽

Jafar Adabi ◽

Edris Pouresmaeil ◽

Kumars Rouzbehi ◽

...

Keyword(s):

Reactive Power ◽

Control Method ◽

Second Harmonic ◽

Power Grid ◽

Harmonic Component ◽

Current Control ◽

Energy Sources ◽

Stable Operation ◽

Multilevel Converters ◽

Steady State Operation

This paper presents a dynamic model of modular multilevel converters (MMCs), which are considered as an effective interface between energy sources and the power grid. By improving the converter performance, appropriate reactive power compensation is guaranteed. Modulation indices are calculated based on detailed harmonic evaluations of both dynamic and steady-state operation modes, which is considered as the main contribution of this paper in comparison with other methods. As another novelty of this paper, circulating current control is accomplished by embedding an additional second harmonic component in the modulation process. The proposed control method leads to an effective reduction in capacitor voltage fluctuation and losses. Finally, converter’s maximum stable operation range is modified, which provides efficiency enhancements and also stability assurance. The proficiency and functionality of the proposed controller are demonstrated through detailed theoretical analysis and simulations with MATLAB/Simulink.

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A new system for in vivo assessment of the degree of nonlinear generation using the second harmonic component in echo signals

Ultrasound in Medicine & Biology ◽

10.1016/j.ultrasmedbio.2004.08.016 ◽

2004 ◽

Vol 30 (11) ◽

pp. 1511-1516 ◽

Cited By ~ 9

Author(s):

Yasutomo Fujii ◽

Nobuyuki Taniguchi ◽

Iwaki Akiyama ◽

Jing-Wen Tsao ◽

Kouichi Itoh

Keyword(s):

Second Harmonic ◽

Harmonic Component ◽

Nonlinear Generation ◽

In Vivo Assessment ◽

New System

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Second‐harmonic component in the focused beam transmitted through a weakly dispersive liquid layer

The Journal of the Acoustical Society of America ◽

10.1121/1.425774 ◽

1999 ◽

Vol 105 (2) ◽

pp. 957-957

Author(s):

Shigemi Saito

Keyword(s):

Liquid Layer ◽

Second Harmonic ◽

Harmonic Component ◽

Focused Beam

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Line Frequency Instability of One-Cycle-Controlled Boost Power Factor Correction Converter

Electronics ◽

10.3390/electronics7090203 ◽

2018 ◽

Vol 7 (9) ◽

pp. 203 ◽

Cited By ~ 4

Author(s):

Rui Zhang ◽

Wei Ma ◽

Lei Wang ◽

Min Hu ◽

Longhan Cao ◽

...

Keyword(s):

Power Factor ◽

Power Factor Correction ◽

Second Harmonic ◽

Harmonic Component ◽

Input Voltage ◽

Frequency Instability ◽

Control Circuit ◽

Line Frequency ◽

Control Loops ◽

Non Linear

Power Factor Correction (PFC) converters are widely used in engineering. A classical PFC control circuit employs two complicated feedback control loops and a multiplier, while the One-Cycle-Controlled (OCC) PFC converter has a simple control circuit. In OCC PFC converters, the voltage loop is implemented with a PID control and the multiplier is not needed. Although linear theory is used in designing the OCC PFC converter control circuit, it cannot be used in predicting non-linear phenomena in the converter. In this paper, a non-linear model of the OCC PFC Boost converter is proposed based on the double averaging method. The line frequency instability of the converter is predicted by studying the DC component, the first harmonic component and the second harmonic component of the main circuit and the control circuit. The effect of the input voltage and the output capacitance on the stability of the converter is studied. The correctness of the proposed model is verified with numerical simulations and experimental measurements.

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Development of lateral interactions in the infant visual system

Visual Neuroscience ◽

10.1017/s095252380000643x ◽

1992 ◽

Vol 8 (1) ◽

pp. 3-8 ◽

Cited By ~ 8

Author(s):

Samuel Sokol ◽

Vance Zemon ◽

Anne Moskowitz

Keyword(s):

Visual System ◽

Long Range ◽

Short Range ◽

Second Harmonic ◽

Harmonic Component ◽

Frequency Component ◽

Human Infants ◽

Long Range Interactions ◽

Harmonic Components ◽

Inhibitory Interactions

AbstractThe development of lateral inhibitory interactions in the infant visual system, as reflected by the visual-evoked potential (VEP), was studied using a radial, asymmetrical windmill-dartboard stimulus. This contrast-reversing stimulus generates VEP responses with a strong fundamental frequency component and an attenuated second harmonic component (relative to that obtained using a symmetrical stimulus). These two harmonic components reflect distinct phenomena, and appear to be the result of short-range (the fundamental) and long-range (attenuated second harmonic) lateral inhibitory interactions elicited by differential luminance-modulation of contiguous spatial regions. We studied the development of the short-and long-range interactions at 100% and 30% contrast in human infants using both VEP amplitude and phase measures. Attenuation of the second harmonic (long-range interactions) was adult-like by 8 weeks of age while the strength of the fundamental (short-range interactions) was adult-like by 20 weeks suggesting a differential development of long-range and short-range interactions. In contrast, corresponding phase data indicated significant immaturities at 20 weeks of age for both the short-and long-range components.

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