Harmonic Line Research Articles

Evidence of nuclear motion in H2-like molecules by means of high harmonic generation

The dynamics of hydrogen-like molecules is investigated beyond the usual fixed nuclei approximation. The nuclear motion introduces in the familiar spectrum of emitted radiation additional regular lines whose separation is essentially given by the vibrational frequency of nuclear motion. A wavelet analysis of the emitted spectrum shows that the intensity of the harmonic lines is modulated with the same period of the nuclear motion; this suggests the possibility of the real-time control of the nuclear dynamics.

Boundary element model to study sound transmission provided by a single panel in the presence of an elastic interlayer

In this paper the Boundary Element Method is applied to develop a numerical model which may be used to study the airborne and impact sound insulation provided by a single panel of infinite extent bounded by two fluid media, with an elastic interlayer (joint) inserted into the partition. The elastic interlayer is placed in the panel, perpendicular to the its surfaces and fully occupying the panel thickness. When the interlayer assumes the properties of a resilient material, it is able to reduce the wave propagation through the elastic medium of the partition. The model is excited by a harmonic line load that acts either in the fluid medium or in the elastic medium in the direction perpendicular to the panel's surface. The model is developed following a direct frequency domain formulation which assumes full coupling between the fluid media and the elastic media. Analytical Green's functions for an elastic single layer bounded by fluid media are used to avoid having to discretize the horizontal surfaces of the partition. Numerical simulations are displayed in order to illustrate the applicability of the proposed model to the analysis of airborne and impact sound insulation when an elastic interlayer is inserted into a single partition.

Control Strategy for Discontinuous Conduction Mode Boost Rectifier with Low Total Harmonic Distortion and Improved Dynamic Response

Due to its simplicity, the discontinuous conduction mode boost rectifier is potentially the least expensive active line-harmonics reducing circuit. Problem statement: The line current however, shows considerable distortion when the peak input voltage is close to the output voltage, As a result, the input power factor is poor. This study proposes a simple, low-cost method to reduce the line harmonics. Approach: A periodic voltage signal was injected in the control circuit to vary the duty cycle of the boost switch within a line cycle so that the third-order harmonic of the input current is reduced and the THD is improved. The proposed technique eliminates the additional harmonic generator, phase detecting and phase-locking circuits, which was proposed in the literature. Instead we can utilize the bridge rectifier's output voltage of the boost converter to modulate the duty cycle of the boost switch. As a result, the injected signal is naturally synchronized with line current. In addition, to obtain nearly constant harmonic content over a wide range of load variation, a modulation index m is used to update the injected signal with a fraction of duty cycle which reflects the load changes. Results: The results proved that third-order harmonic, which was the Lowest Order Harmonic (LOH), can be attenuated by adjusting the modulation index of the injected signal. Moreover, the rectifier shows a good transient performance where the converter's output voltage overshoots during load and input voltage transients is reduced. Conclusions/Recommendations: The proposed circuit can be used as a front-end converter for DC/DC or DC/AC converters in order to improve the power factor of the input current. Also the proposed control circuit could be integrated in a single chip in order to reduce the cost of the industrial implementation.

Ground vibrations due to underground trains considering soil-tunnel interaction

A brief review of the research works on ground vibrations caused by trains moving in underground tunnels is first given. Then, the finite/infinite element approach for simulating the soil-tunnel interaction system with semi-infinite domain is summarized. The tunnel is assumed to be embedded in a homogeneous half-space or stratified soil medium. The train moving underground is modeled as an infinite harmonic line load. Factors considered in the parametric studies include the soil stratum depth, damping ratio and shear modulus of the soil with or without tunnel, and the thickness of the tunnel lining. As far as ground vibration is concerned, the existence of a concrete tunnel may somewhat compensate for the loss due to excavation of the tunnel. For a soil stratum resting on a bedrock, the resonance peak and frequency of the ground vibrations caused by the underground load can be rather accurately predicted by ignoring the existence of the tunnel. Other important findings drawn from the parametric studies are given in the conclusion.

Ground vibrations due to underground trains considering soil-tunnel interaction

A brief review of the research works on ground vibrations caused by trains moving in underground tunnels is first given. Then, the finite/infinite element approach for simulating the soil-tunnel interaction system with semi-infinite domain is summarized. The tunnel is assumed to be embedded in a homogeneous half-space or stratified soil medium. The train moving underground is modeled as an infinite harmonic line load. Factors considered in the parametric studies include the soil stratum depth, damping ratio and shear modulus of the soil with or without tunnel, and the thickness of the tunnel lining. As far as ground vibration is concerned, the existence of a concrete tunnel may somewhat compensate for the loss due to excavation of the tunnel. For a soil stratum resting on a bedrock, the resonance peak and frequency of the ground vibrations caused by the underground load can be rather accurately predicted by ignoring the existence of the tunnel. Other important findings drawn from the parametric studies are given in the conclusion.

Quantum path contribution to high-order harmonic spectra

Ultrashort pulses of uv and soft x-ray radiation with durations ranging from femtoseconds to attoseconds can be produced as high-order harmonics of the fundamental frequency of a laser beam focused into gas. Applications to fields such as spectroscopy and attosecond metrology require the control and characterization of spectral and spatial properties of the emitted radiation. These are determined by both single atom and macroscopic response of the interaction medium to the laser field. Here we present evidence that microscopic effects have a larger influence than previously thought, and can induce a splitting and a frequency shift of the harmonic lines. These results not only offer a direct diagnostic for high-order harmonic generation, but also enable us to better tune the parameters of the produced radiation, while giving a deeper insight into the fundamental physics underlying this nonlinear optical process.

Power Flow Control of a Single Distributed Generation Unit

This research addresses power flow control problem of a grid-connected inverter in distributed generation applications. A real and reactive power control solution is proposed on the basis of an existing voltage control strategy developed for island operations. The power control solution takes advantage of a newly designed system parameter identification method and a nonlinear feedforward algorithm, both of which are based on Newton-Raphson iteration method and implemented in real time. The proposed power control solution also performs grid-line current conditioning and yields harmonic free grid-line current. A phase locked loop based algorithm is developed as a part of the solution to handle possible harmonic distorted grid-line voltage and maintain harmonic free line current. The effectiveness of the proposed techniques is demonstrated by both simulation and experimental results.

Poroelastic acoustic wave trains excited by harmonic line tractions

A two-dimensional boundary-value problem for a porous half-space with an open boundary, described by the widely recognized Biot's equations of poroelasticity, is considered. Using complex analysis techniques, a general solution is represented as a superposition of contributions from the four different types of motion corresponding to P1, P2, S and Rayleigh waves. Far-field asymptotic solutions for the bulk modes, as well as near-field numerical results, are investigated. Most notably, this analysis reveals the following: (i) a line traction generates three wave trains corresponding to the bulk modes, so that P1, P2 and S modes emerge from corresponding wave trains at a certain distance from the source, (ii) bulk modes propagating along the plane boundary are subjected to geometric attenuation, which is found quantitatively to bex−3/2, similar to the classical results in perfect elasticity theory, (iii) the Rayleigh wave is found to be predominant at the surface in both the near (due to the negation of the P1 and S wave trains) and the far field (due to geometric attenuation of the bulk modes), and (iv) the recovery of the transition to the classical perfect elasticity asymptotic results validates the asymptotics established herein.

Three-phase phase-lock loop for distorted utilities

A novel three-phase phase-locked loop (PLL) structure suitable for phase and angular frequency derivation from distorted ac utility voltages is presented. The proposed PLL has a simple structure; a conventional three-phase PLL followed by a proportional-integral (PI)-controlled moving average filter together with a phase-locking algorithm. The objective of the proposed technique is to capture the fundamental phase angle and angular frequency of three-phase clean, distorted, balanced or unbalanced ac utilities. The PLL gives fast, accurate angular frequency and phase locking and is robust to utility distortion such as line notching, random noise, voltage imbalance, phase loss, phase imbalance, harmonics, dc offsets and frequency variation. The analysis presented substantiates the immunity of the proposed PLL to unbalanced and distorted utility conditions. The PLL technique is simulated and digital signal processor (DSP)-implemented for a three-phase system to verify the analytical results. The simulated and experimental results, for numerous utility conditions, demonstrate its phase-tracking ability, whereas the conventional technique fails to lock accurately in highly distorted, three-phase grid-connected operation.

Simultaneous observation on board a satellite and on the ground of large‐scale magnetospheric line radiation

Very Low Frequency (VLF) spectrograms show sometimes sets of lines called MLR (Magnetospheric Line Radiation) with frequency spacing close to 50 or 60 Hz. It is very tempting to attribute these MLR to Power Line Harmonic Radiation (PLHR). PLHR are the ELF and VLF waves radiated by electric power systems at the harmonic frequencies of 50 or 60 Hz. Here we show for the first time large scale MLR observed simultaneously on ground and on board a low altitude satellite which is flying over the same zone. This two hours event is observed over a large area in the Northern hemisphere (∼7,400,000 km2) and in the conjugate region. It is hypothesized that these MLR are due to PLHR propagating in the ionosphere and the magnetosphere. When they cross the equator, the PLHR undergo a nonlinear interaction with particles and may play a role in the dynamics of the radiation belts.

Interaction of Circular Lining and Interior Linear Crack by Incident SH-Wave

In this paper, the method of Green’s function is used to investigate the problem of dynamic stress concentration of circular lining and interior linear crack impacted by incident SH-wave. The train of thought for this problem is that: Firstly, a Green’s function is constructed for the problem, which is a fundamental solution of displacement field for an elastic space possessing a circular lining while bearing out-of-plane harmonic line source force at any point in the lining. In terms of the solution of SH-wave’s scattering by an elastic space with a circular lining, anti-plane stresses which are the same in quantity but opposite in direction to those mentioned before, are loaded at the region where the crack existent actually, we called this process “crack-division”. Finally, the expressions of the displacement and stress are given when the lining and the crack exist at the same time. Then, by using the expressions, some example is provided to show the effect of crack on the dynamic stress concentration around circular lining.

Input power flow in a submerged infinite cylindrical shell with doubly periodic supports

A submerged cylindrical shell reinforced by supports of rings and bulkheads is the primary structure of submarine, torpedo and all kinds of submerged aircrafts, so it is significant to study its characteristics of structure-borne sound. By means of periodic structure theory, the input power flow from a cosine harmonic line force into a submerged infinite cylindrical shell, reinforced by doubly periodic supports of rings and bulkheads, is studied analytically. The harmonic motion of the shell and the sound pressure field in the fluid are described by Flügge shell equations and Helmholtz equation, respectively. Since the fluid radical velocity and the shell radical velocity must be equal at the interface of the outer shell wall and the fluid, the motion equations of this coupled system are obtained. Both four kinds of forces (moments) between rings and shell and four kinds of forces (moments) between bulkheads and shell are considered. The solution is obtained in series form by expanding the system responses in terms of the space harmonics of the spacings of both stiffeners and bulkheads. The input vibrational power flow into the structure is obtained and the influences of different structural parameters on the results are analyzed. The analytic model is close to engineering practice, and it will give some guidelines for noise reduction of this kind of shell.

4U 0115+63 from RXTE and INTEGRAL data: Pulse profile and cyclotron line energy

We analyze the observations of the transient X-ray pulsar 4U 0115+63 with the RXTE and INTEGRAL observatories in a wide X-ray (3-100 keV) energy band during its intense outbursts in 1999 and 2004. The energy of the fundamental harmonic of the cyclotron resonance absorption line near the maximum of the X-ray flux from the source (luminosity range 5x10^{37} - 2x10^{38} erg/s) is ~11 keV. When the pulsar luminosity falls below ~5x10^{37} erg/s, the energy of the fundamental harmonic is displaced sharply toward the high energies, up to ~16 keV. Under the assumption of a dipole magnetic field configuration, this change in cyclotron harmonic energy corresponds to a decrease in the height of the emitting region by ~2 km, while other spectral parameters, in particular, the cutoff energy, remain essentially constant. At a luminosity ~7x10^{37} erg/s, four almost equidistant cyclotron line harmonics are clearly seen in the spectrum. This suggests that either the region where the emission originates is compact or the emergent spectrum from different (in height) segments of the accretion column is uniform. We have found significant pulse profile variations with energy, luminosity, and time. In particular, we show that the profile variations from pulse to pulse are not reduced to a simple modulation of the accretion rate specified by external conditions.

Direct theoretical evidence of nuclear motion in H+2 by means of high harmonic generation

The numerical solution of the time-dependent Schrödinger equation for vibrating hydrogen molecular ions in many-cycle laser pulses shows that high-order harmonic generation is sensitive to laser-induced molecular vibrations. In particular, the odd harmonic lines in the emitted spectra are surrounded by additional regular peaks whose spacing is given by the vibrational frequency of the nuclei motion. Analytical theory relates these satellite peaks to the molecular vibrations in terms of an approximated effective potentials. These results are not affected by the dimensionality of the system.

Fuzzy Logic Controller Based Three-phase Shunt Active Filter for Line Harmonics Reduction

Harmonic distortion is a form of electrical noise. It is a superposition of signals, which are of multiples of fundamental frequency. Proliferation of large power electronic systems results in increased harmonic distortion. Harmonic distortion results in reduction of power quality and system stability. This paper presents fuzzy control applicable for active power filter for three-phase systems, which are comprised of nonlinear loads. The active filter is based on a three-phase inverter with six controllable switches. The AC side of the inverter is connected in parallel with the other nonlinear loads through a filter inductance. The DC side of the inverter is connected to a filter capacitor. The Fuzzy Controller (FC) is used to shape the current through the filter inductor such that the line current is in phase with and of the same shape as the input voltage. The results of the computer simulation prove that the injected harmonics are greatly reduced, system efficiency and power factor are improved.

Vibrational power flow analysis of thin cylindrical shell with a circumferential surface crack

In the view of structure-borne sound, the structural wave and power flow characteristics of infinite thin cylindrical in vacuo shell with a circumferential surface crack are investigated. In this paper, the equivalent distributed line spring is designed to model the surface crack in the shell. The local compliance matrix due to the presence of the crack is deduced from fracture mechanics and three modes of the crack stress intensity factors and their coupling are considered in the local compliance matrix. The vibration of the thin shell is described by the Flügge shell equations. Under the excitation of radial harmonic line force, the input power flow and transmitted power flow of uncracked and cracked shells are obtained. The results show that the vibrational power flow of cracked shell changes substantially due to the presence of crack, and the change is strongly related to the depth and location of crack. Contours of input power flow at different frequencies are constructed to identify the location and depth of the crack. It is revealed that the power flow in the cylindrical shell structures can be used as an alternative defect information carrier. This research provides theoretical basis for the crack detection by measuring the vibrational power flow in cracked shell structures.

Modified FBD Method in Active Power Filters to Minimize the Line Current Harmonics

Harmonic line currents due to nonlinear loads cause nonsinusoidal grid voltages in electrical power systems. Shunt active power filters (SAPFs) can be employed to improve the system efficiency but their design must consider nonsinusoidal conditions. The Fryze, Buchholz, and Depenbrock method has been applied to controllers in SAPFs, allowing the compensation of the load nonactive power. A drawback of this method is a resultant line current with harmonic components which contributes to maintain the grid voltage distortion. This letter proposes a new definition of conductance for SAPF controllers in case of nonlinear loads and nonsinusoidal grid voltages which minimize the line current distortion

An Improved Adaptive Power Line Interference Canceller for Electrocardiography

Power line interference may severely corrupt a biomedical recording. Notch filters and adaptive cancellers have been suggested to suppress this interference. We propose an improved adaptive canceller for the reduction of the fundamental power line interference component and harmonics in electrocardiogram (ECG) recordings. The method tracks. the amplitude, phase, and frequency of all the interference components for power line frequency deviations up to about 4 Hz. A comparison is made between the performance of our method, former adaptive cancellers, and a narrow and a wide notch filter in suppressing the fundamental power line interference component. For this purpose a real ECG signal is corrupted by an artificial power line interference signal. The cleaned signal after applying all methods is compared with the original ECG signal. Our improved adaptive canceller shows a signal-to-power-line-interference ratio for the fundamental component up to 30 dB higher than that produced by the other methods. Moreover, our method is also effective for the suppression of the harmonics of the power line interference.

Coupled integral equations for sound propagation above a hard ground surface with trench cuttings

A set of coupled integral equations is formulated for the investigation of sound propagation from an infinitesimal harmonic line source above a hard ground surface corrugated with cuttings. Two half-space Green's functions are employed in the formulation. The first one defined for the upper half space is used to reduce the problem size and eliminate the edge effect resulting from the boundary truncation; the other one for the lower half space is to simplify the representation of the Neumann-Dirichlet map. As a result, the unknowns are only distributed over the corrugated part of the surface, which leads to substantial reduction in the size of the final linear system. The computational complexity of the Neumann-Dirichlet map is also reduced. The method is used to analyze the behavior of sound propagation above textured surfaces the impedance of which is expectedly altered. The effects of number and opening of trench cuttings, and the effect of source height are investigated. The conclusions drawn can be used for reference in a practical problem of mitigating gun blast noise.

Detection of Stator Faults in Induction Machines Using Residual Saturation Harmonics

Stator fault is one of the most commonly occurring faults in ac machines. Recent estimates suggest that 30%-40% of all reported induction machine faults are stator fault related. Going by the number of occurrences, the position of stator faults is only second to bearing-related faults. Third harmonic line currents, which are caused by the interaction of a reverse-rotating field and saturation-related permeance variation, the third harmonic component in the line voltage, and the speed ripple consequent to the reverse-rotating field, have been reported to increase under stator fault conditions. Since the reverse-rotating field is produced by voltage unbalance as well as stator faults, the measurement of third harmonic in the line current may not be a reliable estimator of stator faults, particularly at an incipient stage. The third and the other triplen-related harmonics are however found to be a very decisive indicator of the fault if measured in the machine terminal voltages just after switch-off. The fault-detection technique is independent of machine parameters and supply unbalances. Simulation and experimental results with very few shorted turns show that not only the presence of stator fault but also the phase in which the fault has occurred can be detected reliably. However, because of the nature of detection, it should strictly be called an offline method that can only validate existing online schemes, unless used for motors operating continuously in transient modes or form-wound machines