Journal articles on the topic 'Combinational harmonics'
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Pineda Allen, Juan Carlos, and Ching Tai Ng. "Nonlinear Guided-Wave Mixing for Condition Monitoring of Bolted Joints." Sensors 21, no. 15 (July 27, 2021): 5093. http://dx.doi.org/10.3390/s21155093.
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Bolted joints are fundamental to numerous structural components in engineering practice. Nevertheless, their failure or even their loosening can lead to insufficient performance and reduced structural safety. This study presents a theoretical development and experimental investigation into nonlinear guided-wave mixing for integrity monitoring of bolted joints in plates. Combinational harmonics generated due to nonlinear Lamb wave mixing and contact acoustic nonlinearity at the bolted joints were used to evaluate the applied torque level in the joint. The area of the power spectral density in the region of the sum combinational harmonic bandwidth is found to be highly correlated to the applied torque level at the joint. Moreover, the effect of the number of cycles and thus the time duration of the excitation is investigated. The results show that the combinational harmonics remain robust for different numbers of cycles in detecting bolt loosening. The findings presented in this study also provide physical insight into the phenomena of nonlinear Lamb wave mixing for evaluating applied torque in bolted joints, and the results help further advance the use of nonlinear guided waves for damage detection.
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Abd Halim, Wahidah, and Nasrudin Abd Rahim. "Selective Harmonic Elimination Method for Cascaded H-Bridge Multilevel Inverter." Applied Mechanics and Materials 785 (August 2015): 122–26. http://dx.doi.org/10.4028/www.scientific.net/amm.785.122.
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This paper presents a selective harmonic elimination (SHE) modulation technique for cascaded H-bridge (CHB) multilevel inverter. The main advantage of the proposed SHE concept is its simple implementation to eliminate the specific order harmonics. The procedures used to achieve the appropriate switching angles are presented. The switching angles are offline computed using the Newton-Raphson method. The SHE scheme of the adopted inverter uses the relationship between the angles and a sinusoidal reference waveform through some combinational logic gates. Theoretical results are verified by the experimental work of a single-phase 7-level CHB inverter employing an Altera DE2 field-programmable gate array (FPGA). Results show the inverter producing an optimum stepped output voltage when selected low-order harmonics are eliminated and the voltage total harmonic distortion (THD) is improved.
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Xia, Yanwen, Yue Liang, Sen Li, Junpu Zhao, Zhitao Peng, Hongguang Li, Hua Liu, Zhihong Sun, Kuixing Zheng, and Xiaofeng Wei. "Energy measurement system of a large-aperture high power laser experiment platform." High Power Laser Science and Engineering 1, no. 3-4 (December 20, 2013): 126–31. http://dx.doi.org/10.1017/hpl.2013.21.
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AbstractAn energy measurement system in a Large-aperture high power laser experiment platform is introduced. The entire measurement system includes five calorimeters, which carry out the energy measurement of the fundamental frequency before the frequency conversion unit, remaining fundamental frequency, remain second-harmonics, third harmonics, as well as the energy balance measurement after the frequency conversion unit. Combinational indirect calibration and direct calibration are employed to calibrate the sampling coefficients of the calorimeters. The analysis of the data showed that, regarding the energy balance coefficients, combinational calibration approach gives a higher precision, and leads to an energy balance with 1%; and regarding the energy sampling coefficients for the various wavelengths after the frequency conversion, the results from direct and combinational calibration are consistent. The uncertainties for all energy sampling coefficients are within 3%, which guarantees the reliability of the energy measurement for the laser facility.
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Xi, Neng, Jia Jun Yang, Wen Wei Liu, Jing Fang Shen, and Yuan Xiong Cheng. "A Novel Approach of Thrust Ripple Minimization by Combinational Iron-Cored Primary in Permanent Magnet Linear Synchronous Motor." Applied Mechanics and Materials 190-191 (July 2012): 638–41. http://dx.doi.org/10.4028/www.scientific.net/amm.190-191.638.
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The paper presents a technique of combinational iron-cored primary for thrust ripple-free permanent magnet linear synchronous motor (PMLSM). Due to multiple end sides of primary iron-cores constructed, the low order harmonics of thrust ripple could be directly eliminated. At the same time, each phase of armature windings forms a circulating sequence at side edge, which enables the parameters of the armature windings to be symmetric and constant. Therefore, electromagnetic ripple caused by side effect will be directly removed. The theoretical analysis conducted reveals the basic characteristics of the proposed approach. Numeric simulation of the finite-element method and harmonic analysis verify the correctness of theoretic analysis and direct effects of the approach on eliminating thrust ripple.
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Yurikov, Alexey, Boris Gurevich, Konstantin Tertyshnikov, Maxim Lebedev, Roman Isaenkov, Evgenii Sidenko, Sinem Yavuz, et al. "Evidence of Nonlinear Seismic Effects in the Earth from Downhole Distributed Acoustic Sensors." Sensors 22, no. 23 (December 1, 2022): 9382. http://dx.doi.org/10.3390/s22239382.
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Seismic velocities and elastic moduli of rocks are known to vary significantly with applied stress, which indicates that these materials exhibit nonlinear elasticity. Monochromatic waves in nonlinear elastic media are known to generate higher harmonics and combinational frequencies. Such effects have the potential to be used for broadening the frequency band of seismic sources, characterization of the subsurface, and safety monitoring of civil engineering infrastructure. However, knowledge on nonlinear seismic effects is still scarce, which impedes the development of their practical applications. To explore the potential of nonlinear seismology, we performed three experiments: two in the field and one in the laboratory. The first field experiment used two vibroseis sources generating signals with two different monochromatic frequencies. The second field experiment used a surface orbital vibrator with two eccentric motors working at different frequencies. In both experiments, the generated wavefield was recorded in a borehole using a fiber-optic distributed acoustic sensing cable. Both experiments showed combinational frequencies, harmonics, and other intermodulation products of the fundamental frequencies both on the surface and at depth. Laboratory experiments replicated the setup of the field test with vibroseis sources and showed similar nonlinear combinations of fundamental frequencies. Amplitudes of the nonlinear signals observed in the laboratory showed variation with the saturating fluid. These results confirm that nonlinear components of the wavefield propagate as body waves, are likely to generate within rock formations, and can be potentially used for reservoir fluid characterization.
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KRIUCHKOVA, LARYSA, IVAN TSMOKANYCH, and MAKSYM VOVK. "ADVANCED METHOD OF PROTECTION OF CONFIDENTIAL INFORMATION FROM INTERCEPTION BY HIGH-FREQUENCY IMPOSITION METHODS." Computer systems and information technologies, no. 3 (April 14, 2022): 14–20. http://dx.doi.org/10.31891/csit-2021-5-2.
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The processes of formation of technical channels of leakage of confidential information on objects of information activity by methods of high-frequency imposition, physical essence of process of formation of dangerous signals by modulation of probing high-frequency signal by acoustic signals, conditions of formation of basic and auxiliary technical means and systems of dangerous signals are considered. As a basis for improvement, a method of blocking information interception channels by high-frequency imposition is used, in which target active noise protection signals are introduced into the medium used to supply probing oscillations, aimed at destroying informative parameters of dangerous signal with different types of carrier modulation. It is proposed to form a set of protective signals for the destruction of informative parameters of dangerous signals both on the fundamental frequency and on the combinational harmonics of the probing signal, which provides more effective protection of confidential information from interception. The parameters of effective noise protection signals, capable of destroying the informative parameters of dangerous signals of high-frequency imposition on the fundamental frequency and combinational harmonics of the probing signal, have been determined by mathematical and simulation modelling. Basic recommendations for the formation of protective signals are formulated.
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Mamedova, L. M. "On the Combination of Harmonics and Polynoms in Econometric Modeling of RUB/AZN Exchange Rate." Statistics and Economics 19, no. 5 (October 5, 2022): 48–58. http://dx.doi.org/10.21686/2500-3925-2022-5-48-58.
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Conducting a combinational polynomial and spectral analysis of time series formed on the basis of daily observations of changes in the RUB/AZN exchange rate with pronounced fluctuations for the period 11.05.2017- 02.11.2018 based on computer econometric modeling.The purpose of the research. The possibility of describing the global rate dynamics by approximation with a combination of a nonlinear polynomial trend and harmonic oscillations of various frequencies relative to this curve; the ability to calculate amplitudes and phases, which can be used to estimate the power spectrum of the Fourier approximation; the ability to develop a high-precision algorithm for predicting exchange rate changes in RUB/AZN.Materials and methodology. The official statistics of the State Statistics Committee of Azerbaijan were used; classical methods of mathematical analysis and economic analysis; methods of econometrics, harmonic (Fourier) analysis, statistical spectral analysis, “Fourier analysis” of the MS Excel add-in, tools of the Eviews 8 application package with the standard deviation and average approximation error being taken into account, the necessary statistical procedures required for identifying and estimating the parameters of the model and checking its adequacy and accuracy.Results. By breaking up the empirical analysis of given time series into time-scale polynomial and time-frequency components. Combinations of the optimal degree of variants of polynomials up to the 11th degree and the number of harmonics of sines and cosines of all possible discrete frequencies were revealed.Conclusion. This result allows us to reconsider the asymmetric impact of RUB/AZN exchange rate pressure on the foreign trade balance between Russia and Azerbaijan. An increase/decrease in exchange rate pressure affects the likelihood of a ruble-manat crisis, while this phenomenon may negatively/positively affect the foreign trade balance and may make it difficult/easier to import resources, goods and services between countries. This, in turn, adds significance to the task of further detailed structuring and analysis of exchange rate changes in RUB/AZN in the face of increased sanction pressures against Russia, thereby actualizing the development of the retrospective part of the study.
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U. Eya, Candidus, Ugwuanyi Oliver O., and Omeje Crescent O. "An Improved Conventional Diode-Clamped Multilevel Inverter Using Non-Zero Triangular- Based Unipolar Modulation Scheme." WSEAS TRANSACTIONS ON SYSTEMS AND CONTROL 17 (February 21, 2022): 91–100. http://dx.doi.org/10.37394/23203.2022.17.11.
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This paper presents an improved conventional diode-clamped multilevel inverter using non-zero triangular-based unipolar modulation scheme. The proposed scheme is meant to reduce the number of carrier waves, minimize the circuits of modulation scheme and obtain stabilized output voltage waveforms. Non-zero triangular-based unipolar modulation scheme is actualized by using two zero-free triangular wave carriers and two modulating sinewaves for line-to- line five level output voltage waveforms in single phase full bridge diode-clamped multilevel inverter unlike conventional multicarrier sinusoidal pulse width modulation that uses four triangular waves and one modulating sinewave for the same inverter type. The proposed system also used microcontroller in the combinational of its wave signals in order to generate the appropriate triggering signals for switching the power semiconductor switches. The proposed system has the following features: (i) It produces two distinct triggering trains (W1 and W2) meant to reduce the low and high harmonics unlike conventional modulation techniques (ii) All its carrier waves operate in continuous current mode which makes it unique from other multicarrier and other related modulation schemes (iii) it has low component counts. The proposed scheme on the conventional diode-clamped inverter produced the following results: voltage and current with total harmonic distortions of 0.4547%, stabilized 400V output voltage and 20A output current, probability results at each level of voltage and current occurrences are 0.10, 0.25, 0.25, 0.75 and 0.90; power output of 80kW, low component counts of modulation circuit scheme and experimental prototype.
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Kumar Dash, Srikanta, Byamakesh Nayak, and Jiban Ballav Sahu. "Selective Harmonic Elimination of an Eleven Level Inverter Using Whale Optimization Technique." International Journal of Power Electronics and Drive Systems (IJPEDS) 9, no. 4 (December 1, 2018): 1944. http://dx.doi.org/10.11591/ijpeds.v9.i4.pp1944-1951.
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Reduction of total harmonic distortion in multilevel inverters is a difficult optimization problem that includes nonlinear transcendent equations having more than one local minima.This paper deals with the harmonic elimination of cascaded multilevel inverter with equal D.C. sources using a new optimization technique. The objective of this paper is to find the best combination of switching angles to minimize the lower order harmonics and the total harmonic distortion is reduced. For this purpose, a new optimization techniques i.e. whale optimization technique is considered.This algorithm is applied to an 11-level cascaded H-bridge inverter.Results shows that WOA gives better results and effectively minimizes the THD and lower order harmonics
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Jin, Tao, Yiyang Chen, and Rodolfo C. C. Flesch. "A novel power harmonic analysis method based on Nuttall-Kaiser combination window double spectrum interpolated FFT algorithm." Journal of Electrical Engineering 68, no. 6 (November 1, 2017): 435–43. http://dx.doi.org/10.1515/jee-2017-0078.
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AbstractHarmonics pose a great threat to safe and economical operation of power grids. Therefore, it is critical to detect harmonic parameters accurately to design harmonic compensation equipment. The fast Fourier transform (FFT) is widely used for electrical popular power harmonics analysis. However, the barrier effect produced by the algorithm itself and spectrum leakage caused by asynchronous sampling often affects the harmonic analysis accuracy. This paper examines a new approach for harmonic analysis based on deducing the modifier formulas of frequency, phase angle, and amplitude, utilizing the Nuttall-Kaiser window double spectrum line interpolation method, which overcomes the shortcomings in traditional FFT harmonic calculations. The proposed approach is verified numerically and experimentally to be accurate and reliable.
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Vovos, Panagis N., and Konstantinos G. Georgakas. "Multipurpose Power Converter for Non-Grid-Connected Microsystems." International Journal of Emerging Electric Power Systems 16, no. 2 (April 1, 2015): 165–79. http://dx.doi.org/10.1515/ijeeps-2014-0129.
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Abstract The aim of this paper is to present a multipurpose converter, appropriate for non-grid-connected microsystems, which are prone to harmonic distortion. The converter suppresses harmonics by injecting mirror harmonics in the modulation stage. An important property is that it continuously monitors and significantly reduces the harmonic content without the use of active or passive low-frequency filters. This is under constant switching frequency, no matter if the harmonics are mainly created by the source, the loads or even its own operation. The converter is regulating output voltage using typical fuzzy control. The two types of control (harmonic and voltage) do not seem to affect each other during operation. Furthermore, it can supply either dc or ac loads from a dc source. The versatility of the converter is a useful property for remote or mobile micropower systems, where neither sources nor loads are of a single type. The converter has been tested successfully for a combination of harmonic-injecting electric appliances and various load step changes.
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Kudlicki, Andrzej, Małgorzata Rowicka, Mirosław Gilski, and Zbyszek Otwinowski. "An efficient routine for computing symmetric real spherical harmonics for high orders of expansion." Journal of Applied Crystallography 38, no. 3 (May 13, 2005): 501–4. http://dx.doi.org/10.1107/s0021889805007685.
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A numerically efficient method of constructing symmetric real spherical harmonics is presented. Symmetric spherical harmonics are real spherical harmonics with built-in invariance with respect to rotations or inversions. Such symmetry-invariant spherical harmonics are linear combinations of non-symmetric ones. They are obtained as eigenvectors of an appropriate operator, depending on symmetry. This approach allows for fast and stable computation up to very high order symmetric harmonic bases, which can be used in e.g. averaging of non-crystallographic symmetry in protein crystallography or refinement of large viruses in electron microscopy.
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Yao, Jianjun, Chenguang Xiao, Zhenshuai Wan, Shiqi Zhang, and Xiaodong Zhang. "Acceleration Harmonics Identification for an Electro-Hydraulic Servo Shaking Table Based on a Nonlinear Adaptive Algorithm." Applied Sciences 8, no. 8 (August 9, 2018): 1332. http://dx.doi.org/10.3390/app8081332.
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Since the electro-hydraulic servo shaking table came into existence, many nonlinear elements, such as, dead zone, friction and backlash, as well as its acceleration response has higher harmonics which result in acceleration harmonic distortion, when the electro-hydraulic system is excited by sinusoidal signal. For suppressing the harmonic distortion and precisely identify harmonics, a combination of the adaptive linear neural network and least mean M-estimate (ADALINE-LMM), is proposed to identify the amplitude and phase of each harmonic component. Specifically, the Hampel’s three-part M-estimator is applied to provide thresholds for detecting and suppressing the impulse noise. Harmonic generators are used by this harmonic identification scheme to create input vectors and the value of the identified acceleration signal is subtracted from the true value of the system acceleration response to construct the criterion function. The weight vector of the ADALINE is updated iteratively by the LMM algorithm, and the amplitude and phase of each harmonic, even the results of harmonic components, can be computed directly online. The simulation and experiment are performed to validate the performance of the proposed algorithm. According to the experiment result, the above method of harmonic identification possesses great real-time performance and it has not only good convergence performance but also high identification precision.
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Liang, Zhi Rui, and Meng Ya Zhao. "The Analysis and Suppression of Harmonics on the AC Side of HVDC Transmission System." Applied Mechanics and Materials 556-562 (May 2014): 1822–25. http://dx.doi.org/10.4028/www.scientific.net/amm.556-562.1822.
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The advantage of HVDC is large power of transmission, low cost and good control performance. Generation system has harmonic because of the nonlinear characteristics of the converter. It has very important significance for HVDC transmission system to accurate analysis and rational allocation of harmonic filtering device. This paper mainly studies the characteristics and suppression of harmonics on AC side in HVDC system, and the filtering effect of different filter combinations of simulation.
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Жуковский, К. В., and А. М. Калитенко. "Генерация когерентного рентгеновского излучения гармоник в однопроходном лазере на свободных электронах со сдвигом фаз электронов относительно фотонов." Журнал технической физики 90, no. 8 (2020): 1337. http://dx.doi.org/10.21883/jtf.2020.08.49545.280-18.
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Theoretical study of the radiated FEL power and bunching is conducted in single-pass free electron laser (FEL) with repetitive shift of the photon pulse with respect to the electron bunch in between the sections of the undulator with field harmonics. Using the analytical calculations, the asymmetric elliptic and planar undulator fields are identified for the undulators to be able to reduce the fundamental tone and enhance the harmonic radiation. This effect is amplified by the phase shift kπ/n, k=2,4,6… of the electrons and photons between the undulator sections. This allows n-th FEL harmonic reach its peak power beyond the fundamental saturation FEL length. It is not possible to achieve in a common FEL due to fast increase of the energy spread, induced by the fundamental tone along FEL and its early saturation. The phenomenological model of the FEL is used for the analysis of the bunching coefficients and harmonic powers evolution in the FEL. The model describes the debunching between the undulator sections, where the phase shift is imposed, and accounts for the higher sensitivity to losses of the electron-photon interaction at high harmonic wavelengths. The losses are due to the beam energy spread and emittance, deviation off the axis, diffraction etc. Explicit expressions for the Bessel coefficients of the planar and elliptic undulators with field harmonics are obtained and analyzed. The combination of the undulator field harmonics is identified, which reduces the fundamental tone and enhances the 3rd and 5th UR harmonics as compared with the radiation from a planar undulator. We propose the use of these undulators in a FEL with the electron-photon phase shift, which increases high harmonic powers in X-ray band by ~100 times with respect to common FELs.
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Fitzgerald, C. J., P. H. Taylor, R. Eatock Taylor, J. Grice, and J. Zang. "Phase manipulation and the harmonic components of ringing forces on a surface-piercing column." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 470, no. 2168 (August 8, 2014): 20130847. http://dx.doi.org/10.1098/rspa.2013.0847.
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A general phase-based harmonic separation method for the hydrodynamic loading on a fixed structure in water waves of moderate steepness is proposed. An existing method demonstrated in the experimental study described by Zang et al. (Zang et al. 2010 In Proc. Third Int. Conf. on Appl. of Phys. Modelling to Port and Coastal Protection. pp. 1–7.) achieves the separation of a total diffraction force into odd and even harmonics by controlling the phase of incident focused waves. Underlying this method is the assumption that the hydrodynamic force in focused waves possesses a Stokes-like structure. Under the same assumption, it is shown here how the harmonic separation method can be generalized, so that the first four sum harmonics can be separated by phase control and linear combinations of the resultant time-histories. The effectiveness of the method is demonstrated by comparisons of the Fourier transforms of the combined time-histories containing the harmonics of interest. The local wave elevations around the focus time are also visualized for the first three harmonics in order to reveal the local dynamics driving components within the wave force time-history.
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Wang, Wei-Teng, Yae-Lin Sheu, and Shih-I. Chu. "Bayesian approach for the optimal control of high-order harmonics for the generation of ultrashort attosecond laser pulses." Journal of Physics B: Atomic, Molecular and Optical Physics 54, no. 21 (November 3, 2021): 21LT02. http://dx.doi.org/10.1088/1361-6455/ac3b3e.
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Abstract We present an efficient and powerful method to optimize the production of high-order harmonic generation (HHG) and the synthesis of an isolated attosecond pulse. The system under investigation is the helium atoms that are exposed to the combination of chirped two-color mid-IR laser field and its 1s–2p transition frequency. An ab initio study is conducted by solving the three dimensional time-dependent Schrödinger equation accurately and efficiently by means of the time-dependent generalized pseudospectral method. We applied Bayesian optimization to obtain an optimal laser waveform to generated a HHG spectrum with enhanced harmonics and extended cutoff frequency. Harmonic phases are analysed by the wavelet transform. We demonstrated that an isolated 10 attosecond pulse can be synthesized using a sequence of consecutive and phase-locked harmonics in the plateau region.
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Saucier, Antoine, Matthew Marchant, and Michel Chouteau. "A fast and accurate frequency estimation method for canceling harmonic noise in geophysical records." GEOPHYSICS 71, no. 1 (January 2006): V7—V18. http://dx.doi.org/10.1190/1.2159063.
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The cancellation of harmonic noise from geophysical records can be achieved by subtracting an estimate of the harmonic noise. Estimating the harmonic noise consists of estimating the fundamental frequency and the amplitudes and phases of all harmonics. We propose a new frequency-estimation method that builds upon the estimator originally proposed by Nyman and Gaiser. This Nyman and Gaiser estimation (NGE) method exploits the fact that the noise fundamental frequency is known to be close to 60 Hz. The NGE method is based on solving a system of four equations that determine the amplitude, phase, and frequency of a given harmonic in the harmonic noise. Hence, NGE can produce frequency estimates for all harmonics. Our improved estimator uses a suitable linear combination of these NGE frequency estimates to produce a more accurate estimate of the fundamental frequency. Our method is more accurate than NGE, and its accuracy is comparable to least-squares estimation (LSE). The advantage of our method is that it is about two times faster than LSE. This speed gain can become valuable when processing large magnetotelluric (MT) data records. Applying our method to the restoration of MT data, we found that the harmonic noise amplitude in the periodogram is reduced by at least 60 dB to a level below that of MT data.
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Dunne, J. F. "Subharmonic-Response Computation and Stability Analysis for a Nonlinear Oscillator Using a Split-Frequency Harmonic Balance Method." Journal of Computational and Nonlinear Dynamics 1, no. 3 (February 20, 2006): 221–29. http://dx.doi.org/10.1115/1.2198875.
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A split-frequency harmonic balance method (SF-HBM) is developed to obtain subharmonic responses of a nonlinear single-degree-of-freedom oscillator driven by periodic excitation. This method is capable of generating highly accurate periodic solutions involving a large number of solution harmonics. Responses at the excitation period, or corresponding multiples (such as period 2 and period 3), can be readily obtained with this method, either in isolation or as combinations. To achieve this, the oscillator equation error is first expressed in terms of two Mickens functions, where the assumed Fourier series solution is split into two groups, nominally associated with low-frequency or high-frequency harmonics. The number of low-frequency harmonics remains small compared to the number of high-frequency harmonics. By exploiting a convergence property of the equation-error functions, accurate low-frequency harmonics can be obtained in a new iterative scheme using a conventional harmonic balance method, in a separate step from obtaining the high-frequency harmonics. The algebraic equations (needed in the HBM part of the method) are generated wholly numerically via a fast Fourier transform, using a discrete-time formulation to include inexpansible nonlinearities. A nonlinear forced-response stability analysis is adapted for use with solutions obtained with this SF-HBM. Period-3 subharmonic responses are obtained for an oscillator with power-law nonlinear stiffness. The paper shows that for this type of oscillator, two qualitatively different period-3 subharmonic response branches can be obtained across a broad frequency range. Stability analysis reveals, however, that for an increasingly stiff model, neither of these subharmonic branches are stable.
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Le Gia, Quoc T., Ming Li, and Yu Guang Wang. "Algorithm 1018: FaVeST—Fast Vector Spherical Harmonic Transforms." ACM Transactions on Mathematical Software 47, no. 4 (December 31, 2021): 1–24. http://dx.doi.org/10.1145/3458470.
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Vector spherical harmonics on the unit sphere of ℝ 3 have broad applications in geophysics, quantum mechanics, and astrophysics. In the representation of a tangent vector field, one needs to evaluate the expansion and the Fourier coefficients of vector spherical harmonics. In this article, we develop fast algorithms (FaVeST) for vector spherical harmonic transforms on these evaluations. The forward FaVeST evaluates the Fourier coefficients and has a computational cost proportional to N log √ N for N number of evaluation points. The adjoint FaVeST, which evaluates a linear combination of vector spherical harmonics with a degree up to ⊡ M for M evaluation points, has cost proportional to M log √ M . Numerical examples of simulated tangent fields illustrate the accuracy, efficiency, and stability of FaVeST.
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TRULSEN, KARSTEN, and CHIANG C. MEI. "Effects of weak wind and damping on Wilton's ripples." Journal of Fluid Mechanics 335 (March 25, 1997): 141–63. http://dx.doi.org/10.1017/s0022112096004478.
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A model for second-harmonic resonance between two gravity–capillary waves is derived, for the case where weak wind and laminar viscosity are of comparable importance. It is revealed that there exist two threshold wind speeds. For winds weaker than the lower threshold, waves are damped. For winds stronger than the upper threshold, the wave energy becomes unbounded and the spectrum cannot be confined to two resonating harmonics. In the intermediate range there exist steady progressive combination waves of the first and second harmonics. These are Wilton's ripples in equilibrium with wind input and viscous dissipation, and are probably physically observable.
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Wenstrup, Jeffrey J. "Frequency Organization and Responses to Complex Sounds in the Medial Geniculate Body of the Mustached Bat." Journal of Neurophysiology 82, no. 5 (November 1, 1999): 2528–44. http://dx.doi.org/10.1152/jn.1999.82.5.2528.
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The auditory cortex of the mustached bat ( Pteronotus parnellii) displays some of the most highly developed physiological and organizational features described in mammalian auditory cortex. This study examines response properties and organization in the medial geniculate body (MGB) that may contribute to these features of auditory cortex. About 25% of 427 auditory responses had simple frequency tuning with single excitatory tuning curves. The remainder displayed more complex frequency tuning using two-tone or noise stimuli. Most of these were combination-sensitive, responsive to combinations of different frequency bands within sonar or social vocalizations. They included FM-FM neurons, responsive to different harmonic elements of the frequency modulated (FM) sweep in the sonar signal, and H1-CF neurons, responsive to combinations of the bat's first sonar harmonic (H1) and a higher harmonic of the constant frequency (CF) sonar signal. Most combination-sensitive neurons (86%) showed facilitatory interactions. Neurons tuned to frequencies outside the biosonar range also displayed combination-sensitive responses, perhaps related to analyses of social vocalizations. Complex spectral responses were distributed throughout dorsal and ventral divisions of the MGB, forming a major feature of this bat's analysis of complex sounds. The auditory sector of the thalamic reticular nucleus also was dominated by complex spectral responses to sounds. The ventral division was organized tonotopically, based on best frequencies of singly tuned neurons and higher best frequencies of combination-sensitive neurons. Best frequencies were lowest ventrolaterally, increasing dorsally and then ventromedially. However, representations of frequencies associated with higher harmonics of the FM sonar signal were reduced greatly. Frequency organization in the dorsal division was not tonotopic; within the middle one-third of MGB, combination-sensitive responses to second and third harmonic CF sonar signals (60–63 and 90–94 kHz) occurred in adjacent regions. In the rostral one-third, combination-sensitive responses to second, third, and fourth harmonic FM frequency bands predominated. These FM-FM neurons, thought to be selective for delay between an emitted pulse and echo, showed some organization of delay selectivity. The organization of frequency sensitivity in the MGB suggests a major rewiring of the output of the central nucleus of the inferior colliculus, by which collicular neurons tuned to the bat's FM sonar signals mostly project to the dorsal, not the ventral, division. Because physiological differences between collicular and MGB neurons are minor, a major role of the tecto-thalamic projection in the mustached bat may be the reorganization of responses to provide for cortical representations of sonar target features.
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Wang, Jian, Tian Guan, and Da Tian Ye. "Pitch Perception of Medium-Rank Harmonic Complex Tones Based on Temporal Analysis." Advanced Materials Research 860-863 (December 2013): 2924–28. http://dx.doi.org/10.4028/www.scientific.net/amr.860-863.2924.
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Fundamental frequency difference limens were measured for a target harmonic complex tone (HCT) in the absence and presence of a masker HCT, which were filtered into the same bandpass frequency region and were gated on and off synchronously. There were three kinds of nominal fundamental frequencies (F0s) for target (200, 400, and 800 Hz), five kinds of F0 separations between target and masker (0, ±3, and ±6 semitones), and four kinds of phase combinations. Results found significant effects of nominal F0, phase combination, and F0 separation between target and masker. Analysis based on temporal profile proved that the significant effect of nominal F0 could be explained by peak height of target, and that the significant effects of F0 separation and phase combination could be explained by the ratio of temporal peak heights between target and masker. Thus it is suggested that F0 discrimination of medium-rank harmonics probably depends on the use of temporal fine structure information.
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Quy, Do Ngoc, Do Ba Phu, and Nguyen Kien Trung. "The new approach minimizes harmonics in a single-phase three-level NPC 400 Hz converter for airplanes." International Journal of Power Electronics and Drive Systems (IJPEDS) 12, no. 3 (September 1, 2021): 1738. http://dx.doi.org/10.11591/ijpeds.v12.i3.pp1738-1750.
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<span lang="EN-US">This paper provides a new approach to reducing high-order harmonics in 400 Hz inverter using a three-level neutral-point clamped (NPC) converter. A voltage control loop using the harmonic compensation combined with NPC clamping diode control technology. The capacitor voltage imbalance also causes harmonics in the output voltage. For 400 Hz inverter, maintain a balanced voltage between the two input (direct current) (DC) capacitors is difficult because the pulse width modulation (PWM) modulation frequency ratio is low compared to the frequency of the output voltage. A method of determining the current flowing into the capacitor to control the voltage on the two balanced capacitors to ensure fast response reversal is also given in this paper. The combination of a high-harmonic resonator controller and a neutral-point voltage controller working together on the 400 Hz NPC inverter structure is given in this paper.</span>
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Dhayanandh, S., and S. Manoharan. "Design and Implementation of GA Based Selective Harmonic Elimination in Modified Cascaded Multilevel Inverter." Applied Mechanics and Materials 573 (June 2014): 3–6. http://dx.doi.org/10.4028/www.scientific.net/amm.573.3.
Full textAbstract:
- The emergence of multilevel inverters has been in increase since the last decade. These new types of converters are suitable for high voltage and high power application due to their ability to synthesize waveforms with better harmonic spectrum. Numerous topologies have been introduced and widely studied for utility and induction billet applications. In this paper, proposed a Modified Multilevel Inverter (MMI) is eleven Levels. This proposed MMI consists of less number of switches to attain eleven levels when compared to the traditional cascaded multilevel inverter to attain the same level. As a result, voltage current stress across switches gets reduced, so that power loss gets reduced in the system. Secondly, an effective pulse width modulation (PWM) approach that can be utilized successfully with high control accuracy is combination of selective harmonic elimination and pulse width modulation (SHEPWM).This technique offers many advantages other PWM techniques including direct control over output waveform harmonics, and the ability to eliminate third, fifth and seventh order harmonics.
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Olsen, J. F., and N. Suga. "Combination-sensitive neurons in the medial geniculate body of the mustached bat: encoding of target range information." Journal of Neurophysiology 65, no. 6 (June 1, 1991): 1275–96. http://dx.doi.org/10.1152/jn.1991.65.6.1275.
Full textAbstract:
1. Delay-tuned combination-sensitive neurons (FM-FM neurons) have been discovered in the dorsal and medial divisions of the medial geniculate body (MGB) of the mustached bat (Pteronotus parnellii). In this paper we present evidence for a thalamic origin for FM-FM neurons. Our examination of the response properties of FM-FM neurons indicates that the neural mechanism of delay-tuning depends on coincidence detection and involves an interaction between neural inhibition and excitation. 2. The biosonar pulse (P) and its echo (E) produced and heard by the mustached bat consist of four harmonics; each harmonic contains a constant frequency (CF) component and a frequency modulated (FM) component. Thus the pulse-echo pair contains eight CF components (PCF1-4, ECF1-4) and eight FM components (PFM1-4, EFM1-4). The stimuli used in this study consisted of CF, FM, and CF-FM sounds: paired CF-FM sounds were used to simulate any two harmonics of pulse-echo pairs. The responses of FM-FM neurons in the MGB were recorded extracellularly. We found that FM-FM neurons respond poorly or not at all to single sounds, respond strongly to paired sounds, and are tuned to the frequency and amplitude of each sound of the pair and to the time interval separating them (simulated echo delay). 3. All FM-FM neurons are facilitated by paired FM sounds and most are facilitated by paired CF sounds. Best facilitative frequencies measured with paired CF sounds fall outside the frequency ranges of the CF components of biosonar signals, whereas best facilitative frequencies measured with paired FM sounds fall within the frequency ranges of the FM components of biosonar signals. Thus FM-FM neurons are expected to respond selectively to combinations of FM components in biosonar signals. The FM components of pulse-echo pairs essential to facilitate FM-FM neurons are the FM component of the fundamental of the pulse (PFM1) in combination with the FM component of the second, third, or fourth harmonic of an echo (EFM2, EFM3, EFM4; collectively, EFMn). 4. The frequency combinations to which FM-FM neurons are tuned reflect small deviations from the harmonic relationship such as occurs in combinations of FM components from pulses and Doppler-shifted echoes. Compared with CF/CF neurons, however, FM-FM neurons are broadly tuned to stimulus frequency. Thus FM-FM neurons are Doppler-shift tolerant and relatively unspecialized for processing velocity information in the frequency domain.(ABSTRACT TRUNCATED AT 400 WORDS)
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Wang, Li, Teng Qiao, Bin Zhao, Xiangjun Zeng, and Qing Yuan. "Modeling and Parameter Optimization of Grid-Connected Photovoltaic Systems Considering the Low Voltage Ride-through Control." Energies 13, no. 15 (August 2, 2020): 3972. http://dx.doi.org/10.3390/en13153972.
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The asymmetric faults often cause the power grid current imbalance and power grid oscillation, which brings great instability risk to the power grid. To address this problem, this paper presented a modeling and parameter optimization method of grid-connected photovoltaic (PV) systems, considering the low voltage ride-through (LVRT) control. The harmonics of the grid current under asymmetric faults were analyzed based on the negative-sequence voltage feedforward control method. The notch filter was added to the voltage loop to filter out the harmonic components of the DC bus voltage and reduce the harmonic contents of the given grid current value. The proportional resonant (PR) controller was added to the current loop. The combination of these two components could reduce the 3rd, 5th, and 7th harmonics of the grid current and the output power fluctuation. Then, the parameters of the inverter controller were identified by the adaptive differential evolution (ADE) algorithm based on the sensitivity analysis. The effectiveness of the proposed method was compared with two other strategies under the asymmetric grid faults. The suppression of DC bus voltage fluctuation, power fluctuation, and low-order harmonics of the grid current all had better results, ensuring the safe and stable operation of the PV plant under grid faults.
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Garner, Karen S., Maarten J. Kamper, and Andrew T. Loubser. "Performance Evaluation of Harmonic Reduced Non-Overlap Winding Wound Rotor Synchronous Machine." Energies 14, no. 22 (November 10, 2021): 7501. http://dx.doi.org/10.3390/en14227501.
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The analysis and performance evaluation of a harmonic reduction strategy of a non-overlap winding wound rotor synchronous machine is conducted in this paper. The harmonic reduction strategy utilizes phase-shifts between coil currents to reduce sub- and higher-order harmonics. The design is performed on a 3 MW wound rotor synchronous machine with a 16/18 pole/slot combination. The application results in a lowered torque ripple and an increased efficiency of the designed machine. The manufacturing and testing of a 3 kW prototype to ascertain the effectiveness of the design is also presented. The practical measurements correlate successfully with the theoretical results.
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Butler, Karl E., and R. Don Russell. "Cancellation of multiple harmonic noise series in geophysical records." GEOPHYSICS 68, no. 3 (May 2003): 1083–90. http://dx.doi.org/10.1190/1.1581080.
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We describe a procedure for the simultaneous estimation of multiple stationary sinusoidal contaminants in a time series and demonstrate its application to the cancellation of powerline noise in seismic and seismoelectric records. An estimate of the noise in each record is obtained by seeking a linear combination of sinusoids that are harmonics of one or more fundamental frequencies; this combination must fit the data in a least‐squares sense. The algorithm accommodates estimation windows of arbitrary length, including windows shorter than one fundamental period, without cross‐contamination between harmonic estimates. Provision is made for refining the fundamental frequencies, for which small errors (e.g., 0.01 Hz in 60 Hz) can result in significant residual noise near the ends of the record (beating). Our strategy is novel in that it uses all specified harmonics and iteratively searches frequency space for a best fit using numerical derivatives. This determination is very robust for at least two fundamentals (the limit of our investigation) and often converges rapidly to three or four decimal places. Cancellation of harmonic noise has been essential in our research to uncover seismoelectric signals that are often completely masked by powerline noise. We expect this procedure will be useful in other geophysical methods—especially exploration seismology, for which powerline contamination is a recognized problem.
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Khan, Rashid Ahmed, Shoeb Azam Farooqui, Mohammad Irfan Sarwar, Seerin Ahmad, Mohd Tariq, Adil Sarwar, Mohammad Zaid, Shafiq Ahmad, and Adamali Shah Noor Mohamed. "Archimedes Optimization Algorithm Based Selective Harmonic Elimination in a Cascaded H-Bridge Multilevel Inverter." Sustainability 14, no. 1 (December 28, 2021): 310. http://dx.doi.org/10.3390/su14010310.
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This paper presents the Archimedes optimization algorithm to eliminate selective harmonics in a cascaded H-bridge (CHB) multilevel inverter (MLI). The foremost objective of the selective harmonic elimination (SHE) is to eliminate lower order harmonics by finding the optimal switching angle combination which minimizes the objective function containing Total Harmonic Distortion (THD) and other specific harmonic terms. Consequently, the THD is also reduced. In this study, a recently proposed metaheuristic technique named the Archimedes optimization algorithm (AOA) is used to determine the optimal angles corresponding to the 5, 7 and 9 level CHB-MLI. AOA involves equations related to a physical law, the Archimedes Principle. It is based on the idea of a buoyant force acting upward on a body or object that is partially or completely submerged in a fluid, and the upward force is related to the weight of the fluid displaced. This optimization technique has been implemented on CHB-MLI to generate various level outputs, simulated on MATLAB™ R2021a version environment software. The simulation results reveal that AOA is a high-performance optimization technique in terms of convergence speed and exploitation-exploration balance and is well-suited to the solution of the SHE problem. Furthermore, the laboratory validated the simulation result on a hardware setup using DSP-TMS320F28379D.
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Yamansarin, Ildar, Mikhail Salikov, Alexander Padeev, and Dmitry Surkov. "An Approach to the Use of an External Magnetic Field As a Diagnostic Sign of an Asynchronous Motor Malfunction." Известия высших учебных заведений. Электромеханика 64, no. 3 (2021): 18–23. http://dx.doi.org/10.17213/0136-3360-2021-3-18-23.
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The article deals with the issues related to the possibility of diagnosing the technical condition of an asyn-chronous electric motor by an external magnetic field. The justification of the problems associated with the di-agnosis of electric motors is given. The difficulties that arise when measuring the external magnetic field of electric motors, as well as the devices with which it is possible to carry out measurements, are described. The re-lationship between the EMF of the sensor and the external magnetic field is shown. The results of processing the EMF waveforms induced by an external magnetic field in an inductive sensor for various electric motors are presented. The processing was carried out by the fast Fourier transform method. The external magnetic field contains the first harmonic and various harmonics that are multiples of the combination of the stator teeth, or the sum of the stator and rotor teeth that fall on one pair of poles. The ratio of the amplitudes of the first and tooth harmonics is affected by the measurement location and the orientation of the sensor. Diagrams showing the ratio of the main and tooth harmonics at different points of the motor body are constructed. The depend-ences of the harmonic amplitudes on the magnitude of the magnetizing current of the stator are given. Changes in the amplitudes and spectrum of harmonics in the presence and absence of an inter-turn short circuit in the stator winding are shown. Diagrams of the circular external magnetic field for the main and higher harmonics are constructed. The study shows the possibility of using an external magnetic field to detect inter-turn short circuits of the stator winding.
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Liu, H., L. Q. Feng, and R. M. Sani. "Effects of inhomogeneous laser field in time and space on the generation of broad spectral continuum and ultrashort attosecond pulse." Modern Physics Letters B 34, no. 13 (February 28, 2020): 2050131. http://dx.doi.org/10.1142/s0217984920501316.
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The inhomogeneous effects of laser field in time and space on the generations of high-order harmonic spectra and attosecond pulses from He atom have been investigated with the assistance of the frequency-chirping technique and the metallic nanostructure. We find that in different combinations of chirps and spatial inhomogeneous effects, not only can the harmonic cutoff be extended, but the single harmonic emission peak (HEP) can also be selected to contribute to the spectral continuum. In detail, with the combinations of (i) symmetric chirp in frequency and positive inhomogeneous effect in space or (ii) asymmetric down chirp in frequency and negative inhomogeneous effect in space, two broad spectral continua with bandwidths of 496 eV and 480 eV can be obtained. Further, by properly adding IR or UV controlling pulse, the harmonic emission efficiency can be enhanced by several orders of magnitude. The enhancement of harmonic yield from adding UV pulse is higher than that from adding IR pulse. Moreover, the difference of harmonic enhancement between UV combined field and IR combined field is much more obvious at lower controlling laser intensity. Through analyzing the ionization probability, we find that the higher enhancement of harmonic yield from UV combined field is because of UV-resonance-enhancement-ionization between the ground state and the excited state of He atom. Finally, by properly superposing some harmonics, a number of attosecond pulses with pulse durations of 45 as can be obtained.
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Penangsang, Ontoseno, Muhammad Daffa Cahyonoputra, Dimas Fajar Uman Putra, Muhira Dzar Faraby, Sofyan Sofyan, and Akhyar Muchtar. "Determination of location and capacity of distributed generations with reconfiguration in distribution systems for power quality improvement." International Journal of Electrical and Computer Engineering (IJECE) 13, no. 1 (February 1, 2023): 28. http://dx.doi.org/10.11591/ijece.v13i1.pp28-38.
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The use of non-linear loads and the integration of renewable energy in electricity network can cause power quality problems, especially harmonic distortion. It is a challenge in the operation and design of the radial distribution system. This can happen because harmonics that exceed the limit can cause interference to equipment and systems. This study will discuss the determination of the optimal location and capacity of distributed generation (DG) and network reconfiguration in the radial distribution system to improve the quality of electric power, especially the suppression of harmonic distribution. This study combines the optimal location and capacity of DG and network reconfiguration using the particle swarm optimization method. In addition, this research method is implemented in the distribution system of Bandar Lampung City by considering the effect of using nonlinear loads to improve power quality, especially harmonic distortion. The inverter-based DG type used considers the value of harmonic source when placed. The combination of the proposed methods provides an optimal solution. Increased efficiency in reducing power losses up to 81.17% and %total harmonic distortion voltage (THDv) is below the allowable limit.
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Vashisht, Rajiv Kumar, and Qingjin Peng. "Adaptive hybrid control of unbalanced vibrations of a rotor/active magnetic bearing system with coupling misalignment using low cost instrumentation." Journal of Vibration and Control 25, no. 15 (June 12, 2019): 2151–74. http://dx.doi.org/10.1177/1077546319852221.
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An adaptive hybrid controller is proposed for reducing the unbalanced vibration response of a flexible rotor/active magnetic bearing system. It is observed that conventional adaptive feedforward controller (AFFC) normally used in the active noise control is very sensitive in performance for changes in rotor spin frequencies. Although frequency updating is a part of its architecture, a small practical variation in the rotor spin frequency can reduce its effectiveness drastically. A smart combination of adaptive notch filter and Goertzel filter is proposed for the frequency estimation. During changes of the rotor spin frequency, fundamental harmonics of the flexible rotor are excited. By using hybrid controllers that combine feedback control and AFFC, the amplitude of these fundamental harmonics is reduced significantly. By applying the multi-harmonic hybrid control, the multiple harmonics generated due to coupling misalignment are compensated efficiently. Fourier transform of the control signal is further used to detect the presence of the coupling misalignment.
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Minh Khoa, Ngo, and Le Van Dai. "Detection and Classification of Power Quality Disturbances in Power System Using Modified-Combination between the Stockwell Transform and Decision Tree Methods." Energies 13, no. 14 (July 14, 2020): 3623. http://dx.doi.org/10.3390/en13143623.
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The detection, mitigation, and classification of power quality (PQ) disturbances have been issues of interest in the power system field. This paper proposes an approach to detect and classify various types of PQ disturbances based on the Stockwell transform (ST) and decision tree (DT) methods. At first, the ST is developed based on the moving, localizing, and scalable Gaussian window to detect five statistical features of PQ disturbances such as the high frequency of oscillatory transient, distinction between stationary and non-stationary, the voltage amplitude oscillation around an average value, the existence of harmonics in a disturbance signal, and the root mean square voltage at the internal period of sag, swell or interruption. Then, these features are classified into nine types, such as normal, sag, swell, interruption, harmonic, flicker, oscillatory transient, harmonic voltage sag, and harmonic voltage swell by using the DT algorithm that is based on a set of rules with the structure “if…then’’. This proposed study is simulated using MATLAB simulation. The IEEE 13-bus system, the recorded real data based on PQube, and the experiment based on the laboratory environment are applied to verify the effectiveness.
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Wang, Ji Zhong, Chao Nan Tong, and Rui Li. "Harmonic Analyses of Power Grid in Large-Capacity Groups of AC-DC-AC Frequency Speed Drag System." Applied Mechanics and Materials 448-453 (October 2013): 1988–93. http://dx.doi.org/10.4028/www.scientific.net/amm.448-453.1988.
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Based on the synchronous machine in AC-DC-AC Frequency speed drag System, a new power supply method of phase shifting combination is proposed by a detailed study of the impact in the power grid harmonics. With regard to the main Motor drive system of hot-rolling finishing mills, a large number of varying parameters quantitative analysis is made respectively for power load, LC filter, pulse-width modulation circuit and transformer, in which the grid side harmonic rate and waveform distortion rate is focused on. The simulation results show that the power supply method with reasonable parameters design of the drag system can be drastically reduce the grid side harmonic interference that the total harmonic distortion is suppressed within 4.0%. Results of this study provides an effective method for the design of the factory drag system, reactive power compensation system as well as fault diagnosis of electric drag system.
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Kurtz, D. W. "Nonlinear, Nonradial Pulsation in Rapidly Oscillating Ap Stars." International Astronomical Union Colloquium 134 (1993): 207–14. http://dx.doi.org/10.1017/s0252921100014214.
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AbstractThe rapidly oscillating Ap stars pulsate in high-overtone, low degree p-modes with their pulsation axes aligned with their oblique magnetic axes. They show non-linearity in their pulsation in three ways: 1)The harmonics of the basic pulsation frequency are detectable.2)The pulsation phase seems to vary stochastically on a time scale of days to years depending on the star.3)The form of the nonradial surface distortion is not constant with time.These three effects are illustrated with HR 3831, the best studied of the roAp stars. HR 3831 pulsates in distorted dipole mode which can be modelled as a linear sum of axisymmetric l = 0, 1, 2, and 3 spherical harmonics aligned with the magnetic axis. This gives rise to a 7-frequency multiplet split by exactly the rotation frequency. The form of the distortion shows small changes on a time-scale of years. HR 3831 shows a 5-frequency rotationally split first harmonic multiplet, a 3-frequency rotationally split second harmonic multiplet, and a single third harmonic frequency has probably been detected at an amplitude of 0.065 mmag. The first harmonic has changed its form significantly over the last 10 years. A technique for decomposing the fundamental frequency septuplet into its component spherical harmonics is used to fit the pulsation phase as a function of rotation phase. This allows a unique O-C to be defined for any length of light curve. The long term behaviour of the O-C diagram cannot be modelled adequately with a combination of periodic (Doppler shift) and quadratic (evolution) terms; there seems to be a significant stochastic component. The direction of the pulsation phase reversal at rotational phase 0.747 is indeterminate; sometimes it is a positive-going reversal, sometimes negative-going. At present it is not known whether this is a numerical artifact, or a physical effect in the star. If it is a physical effect, it means that small non-periodic differences in pulsation amplitude between the bipolar hemispheres have been detected.
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Huybrechts, Nicolas, Lan Anh Van, Jean-Michel Hervouet, and Catherine Villaret. "REFINED HYDRODYNAMIC MODELLING OF THE GIRONDE ESTUARY, FRANCE." Coastal Engineering Proceedings 1, no. 32 (January 31, 2011): 3. http://dx.doi.org/10.9753/icce.v32.posters.3.
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In the centre of the Gironde estuary, EDF exploits a power plant. A hydrodynamic model is required to prevent different risks. Indeed, accurate water levels and velocity field are needed for flood control, sediment transport and associated deposition and transport of algae or pollutant. In order to enhance the accuracy of the hydrodynamic results and to tend to a fully predictive model, two attempts have been envisaged. The first one focuses on the tide imposed at the border by a combination of different harmonic waves whose constant harmonics are extracted from a tide model. Harmonic constants from different tide models have been compared and the influence of the harmonics number have been studied. The second attempt focuses on the friction coefficient. The values of the friction coefficient have been calibrated and compared to values predicted by the equation of van Rijn 2007.
With the calibrated values, the differences between the measured and computed water levels are less than 10 cm.
With the predictive friction formula, limited accuracy losses have been observed, which demonstrates the feasibility of using van Rijn formula for a configuration such as the Gironde.
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van Vondelen, Aemilius A. W., Sachin T. Navalkar, Alexandros Iliopoulos, Daan C. van der Hoek, and Jan-Willem van Wingerden. "Damping identification of offshore wind turbines using operational modal analysis: a review." Wind Energy Science 7, no. 1 (January 24, 2022): 161–84. http://dx.doi.org/10.5194/wes-7-161-2022.
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Abstract. To increase the contribution of offshore wind energy to the global energy mix in an economically sustainable manner, it is required to reduce the costs associated with the production and operation of offshore wind turbines (OWTs). One of the largest uncertainties and sources of conservatism in design and lifetime prediction for OWTs is the determination of the global damping level of the OWT. Estimation of OWT damping based on field measurement data has hence been subject to considerable research attention and is based on the use of (preferably operational) vibration data obtained from sensors mounted on the structure. As such, it is an output-only problem and can be addressed using state-of-the-art operational modal analysis (OMA) techniques, reviewed in this paper. The evolution of classical time- and frequency-domain OMA techniques has been reviewed; however, the literature shows that the OWT vibration data are often contaminated by rotor speed harmonics of significantly high energy located close to structural modes, which impede classical damping identification. Recent advances in OMA algorithms for known or unknown harmonic frequencies can be used to improve identification in such cases. Further, the transmissibility family of OMA algorithms is purported to be insensitive to harmonics. Based on this review, a classification of OMA algorithms is made according to a set of novel suitability criteria, such that the OMA technique appropriate to the specific OWT vibration measurement setup may be selected. Finally, based on this literature review, it has been identified that the most attractive future path for OWT damping estimation lies in the combination of uncertain non-stationary harmonic frequency measurements with statistical harmonic isolation to enhance classical OMA techniques, orthogonal removal of harmonics from measured vibration signals, and in the robustification of transmissibility-based techniques.
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Wang, Jian, Tian Guan, Da Tian Ye, and Zhi Peng Chen. "Effect of Several Parameters on Pitch Perception of Unresolved Harmonics." Applied Mechanics and Materials 427-429 (September 2013): 1928–33. http://dx.doi.org/10.4028/www.scientific.net/amm.427-429.1928.
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This paper studied the effect of several parameters on pitch perception of unresolved harmonics by measuring fundamental frequency difference limens. The parameters included roving fundamental frequency or not, type of background noise, and cutoff frequency of lowpass pink noise. Results found that performance was significantly worse when the fundamental frequency was roved than the constant case, lowpass pink noise had similar ability to mask combination tones as threshold equalizing noise, and that combination tones could be masked if the cutoff frequency of the lowpass pink noise was not lower than the frequency of the tenth harmonic. This paper proposed a set of appropriate parameters for experiments of pitch perception, which suggested that roving fundamental frequency, using threshold equalizing noise with the level of about 8-13 dB below the level per component of the stimuli, or using lowpass pink noise with the cutoff frequency not lower than the frequency of the tenth harmonic, can achieve effective performance for pitch perception.
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Geng, Qiang, Jiahe Feng, Haojie Sha, Weixi Zhou, and Zhanqing Zhou. "Harmonic Analysis and Attenuation Strategy for a Two-Stage Matrix Converter Fed by Dual-Inverter Based on Pulse Barycenter Method." Energies 15, no. 12 (June 18, 2022): 4447. http://dx.doi.org/10.3390/en15124447.
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Since the DC-link of the dual-inverter two-stage matrix converter (TSMC) has no energy storage element, its grid-side current waveform is closely related to the load-side condition. The conventional modulation strategy of the dual-inverter TSMC is only the stack of the double inverters, without considering the cooperation between both modulation strategies. Thus, the fluctuations in the grid-side currents synthesized by both load-side currents will be obvious. To solve this problem, this paper analyzes the effect of the current pulse position on the grid-side current waveform quality, and relevant relationship between the pulse position and current harmonics is obtained according to Fourier transform. On this basis, the harmonic attenuation strategy for the dual-inverter TSMC is proposed. In the proposed strategy, the grid-side current harmonic is reduced based on the optimal duty-cycle combination, obtained from the harmonic optimization problem. The simulation and experimental results are provided to verify that the theoretical analysis of grid-side current harmonic content is consistent with the actual condition, and the proposed modulation strategy can effectively reduce the grid-side current harmonic.
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Domagk, Max, Irene Yu-Hua Gu, Jan Meyer, and Peter Schegner. "Automatic Identification of Different Types of Consumer Configurations by Using Harmonic Current Measurements." Applied Sciences 11, no. 8 (April 16, 2021): 3598. http://dx.doi.org/10.3390/app11083598.
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Power quality (PQ) is an increasing concern in the distribution networks of modern industrialized countries. The PQ monitoring activities of distribution system operators (DSO), and consequently the amount of PQ measurement data, continuously increase, and consequently new and automated tools are required for efficient PQ analysis. Time characteristics of PQ parameters (e.g., harmonics) usually show characteristic daily and weekly cycles, mainly caused by the usage behaviour of electric devices. In this paper, methods are proposed for the classification of harmonic emission profiles for typical consumer configurations in public low voltage (LV) networks using a binary decision tree in combination with support vector machines. The performance of the classification was evaluated based on 40 different measurement sites in German public LV grids. This method can support network operators in the identification of consumer configurations and the early detection of fundamental changes in harmonic emission behaviour. This enables, for example, assistance in resolving customer complaints or supporting network planning by managing PQ levels using typical harmonic emission profiles.
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Shin, Homin, and Junghwan Chang. "Efficiency Improvement Strategy for Multiple Operating Points in Doubly Fed Magnetic Geared Motor." Applied Sciences 10, no. 7 (April 3, 2020): 2456. http://dx.doi.org/10.3390/app10072456.
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The doubly fed magnetic geared motor, which has dual AC windings, can be operated with different frequencies in the inner and outer windings. However, the inner and outer windings have different numbers of pole pairs to meet the pole combination derived by the magnetic gearing effect, and hence undesirable space harmonic components of the magnetic flux are produced at the air gaps. These space harmonics affect the iron losses at each core, and the resultant iron loss and efficiency are varied by the frequencies of the inner and outer windings. Thus, in this paper, first, the effect of the space harmonic components of the air gap magnetic flux density in the inner stator, outer stator, and the modulating pieces is separately investigated. In addition, the iron loss characteristics of each ferromagnetic material are presented according to the frequency combinations in the inner and outer windings. Secondly, the iron loss maps and the efficiency maps according to the frequency conditions of the inner and outer windings are drawn, and the causes of the characteristic differences in each map are analyzed. Thirdly, the frequency control sequence and the roles of the inner and outer windings as the armature and field parts are changed, and the analysis of the iron loss map and efficiency map is repeated. Finally, the results in the inner-armature case and the outer-armature case are compared with each other, and the possibility of improving the overall operating efficiency over the multiple operating points by using the individual frequency control and frequency combination selection is proved.
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Habibović, Dino, and Dejan B. Milošević. "Ellipticity of High-Order Harmonics Generated by Aligned Homonuclear Diatomic Molecules Exposed to an Orthogonal Two-Color Laser Field." Photonics 7, no. 4 (November 12, 2020): 110. http://dx.doi.org/10.3390/photonics7040110.
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We investigate emission rate and ellipticity of high-order harmonics generated exposing a homonuclear diatomic molecule, aligned in the laser-field polarization plane, to a strong orthogonally polarized two-color (OTC) laser field. The linearly polarized OTC-field components have frequencies rω and sω, where r and s are integers. Using the molecular strong-field approximation with dressed initial state and undressed final state, we calculate the harmonic emission rate and harmonic ellipticity for frequency ratios 1:2 and 1:3. The obtained quantities depend strongly on the relative phase between the laser-field components. We show that with the OTC field it is possible to generate elliptically polarized high-energy harmonics with high emission rate. To estimate the relative phase for which the emission rate is maximal we use the simple man’s model. In the harmonic spectra as a function of the molecular orientation there are two types of minima, one connected with the symmetry of the molecular orbital and the other one due to destructive interference between different contributions to the recombination matrix element, where we take into account that the electron can be ionized and recombine at the same or different atomic centers. We derive a condition for the interference minima. These minima are blurred in the OTC field except in the cases where the highest occupied molecular orbital is modeled using only s or only p orbitals in the linear combination of the atomic orbitals. This allows us to use the interference minima to assess which atomic orbitals are dominant in a particular molecular orbital. Finally, we show that the harmonic ellipticity, presented in false colors in the molecular-orientation angle vs. harmonic-order plane, can be large in particular regions of this plane. These regions are bounded by the curves determined by the condition that the harmonic ellipticity is approximately zero, which is determined by the minima of the T-matrix contributions parallel and perpendicular to the fundamental component of the OTC field.
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El Mehdi Belkacem, Riadh, Redha Benzid, and Noureddine Bouguechal. "Multilevel inverter with optimal THD through the firefly algorithm." Archives of Electrical Engineering 66, no. 1 (March 1, 2017): 141–54. http://dx.doi.org/10.1515/aee-2017-0010.
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Abstract Reduction of the Total Harmonic Distortion (THD) in multilevel inverters requires resolution of complex nonlinear transcendental equations; in this paper we propose a combination of one of the best existing optimized hardware structures with the recent firefly algorithm, which was used to optimize the THD, through finding the best switching angles and guaranteeing the minimization of harmonics within a user defined bandwidth. The obtained THD through the simulation of the thirteen-level symmetric inverter has been reduced down to 5% (FFT of 60 harmonics). In order to validate the simulation results, a thirteen-level symmetric inverter prototype has been made, and practically experimented and tested with different loads. Consequently, the measured THD with resistive load was 4.7% on a bandwidth of 3 kHz. The main advantage of the achieved work is the reduction of the THD.
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Wang, Tao, and Jinchun Song. "Harmonic Detection Method Based on Particle Swarm Optimization and Simulated Annealing Algorithm of Electrohydraulic Servo System." Journal of Robotics 2022 (November 28, 2022): 1–13. http://dx.doi.org/10.1155/2022/7483427.
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Due to the comprehensive influence of many nonlinear coupling factors within a system, when the input signal provided by an electrohydraulic servo shaker is sinusoidal, it often leads to the existence of high-order harmonic components of the system, which makes the output servo signal parameters exist extremely serious. Therefore, the detection of harmonics of the electrohydraulic servo shaker has very important application significance. In this paper, by using simulated annealing (SA) based harmonic detection, a kernel function is introduced to study area influence-based particle swarm optimization (PSO). Using a super accurate and fast global convergence brought by the combination of hybrid particle swarm optimization algorithm and simulated annealing algorithm, it can quickly jump out of the trap of traditional local optimization algorithms and a more stable, high-precision, as well as fast global convergence optimal solution can be obtained. Through the detection and simulation of the amplitude and phase of the harmonics in the system, by comparing the PSO-SA detection with PSO detection, it is proved that the PSO-SA algorithm can well satisfy the accuracy of the detection system, which has advantages such as a fast convergence speed, a high search accuracy, etc.; meanwhile, it is simple and easy to implement.
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Kotzé, Pieter Benjamin. "Spectral analysis of auroral geomagnetic activity during various solar cycles between 1960 and 2014." Annales Geophysicae 34, no. 12 (December 6, 2016): 1159–64. http://dx.doi.org/10.5194/angeo-34-1159-2016.
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Abstract. In this paper we use wavelets and Lomb–Scargle spectral analysis techniques to investigate the changing pattern of the different harmonics of the 27-day solar rotation period of the AE (auroral electrojet) index during various phases of different solar cycles between 1960 and 2014. Previous investigations have revealed that the solar minimum of cycles 23–24 exhibited strong 13.5- and 9.0-day recurrence in geomagnetic data in comparison to the usual dominant 27.0-day synodic solar rotation period. Daily mean AE indices are utilized to show how several harmonics of the 27-day recurrent period change during every solar cycle subject to a 95 % confidence rule by performing a wavelet analysis of each individual year's AE indices. Results show that particularly during the solar minimum of 23–24 during 2008 the 27-day period is no longer detectable above the 95 % confidence level. During this interval geomagnetic activity is now dominated by the second (13.5-day) and third (9.0-day) harmonics. A Pearson correlation analysis between AE and various spherical harmonic coefficients describing the solar magnetic field during each Carrington rotation period confirms that the solar dynamo has been dominated by an unusual combination of sectorial harmonic structure during 23–24, which can be responsible for the observed anomalously low solar activity. These findings clearly show that, during the unusual low-activity interval of 2008, auroral geomagnetic activity was predominantly driven by high-speed solar wind streams originating from multiple low-latitude coronal holes distributed at regular solar longitude intervals.
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Apostolakis, Apostolos, and Mauro F. Pereira. "Superlattice nonlinearities for Gigahertz-Terahertz generation in harmonic multipliers." Nanophotonics 9, no. 12 (July 6, 2020): 3941–52. http://dx.doi.org/10.1515/nanoph-2020-0155.
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AbstractSemiconductor superlattices are strongly nonlinear media offering several technological challenges associated with the generation of high-frequency Gigahertz radiation and very effective frequency multiplication up to several Terahertzs. However, charge accumulation, traps and interface defects lead to pronounced asymmetries in the nonlinear current flow, from which high harmonic generation stems. This problem requires a full non-perturbative solution of asymmetric current flow under irradiation, which we deliver in this paper within the Boltzmann-Bloch approach. We investigate the nonlinear output on both frequency and time domains and demonstrate a significant enhancement of even harmonics by tuning the interface quality. Moreover, we find that increasing arbitrarily the input power is not a solution for high nonlinear output, in contrast with materials described by conventional susceptibilities. There is a complex combination of asymmetry and power values leading to maximum high harmonic generation.
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Kuznetsov, Sergey, and Yana Saprykina. "SECONDARY WAVES IN COASTAL ZONE: PHYSICAL MECHANISMS OF FORMATION AND POSSIBLE APPLICATION FOR COASTAL PROTECTION." Coastal Engineering Proceedings 1, no. 33 (October 25, 2012): 12. http://dx.doi.org/10.9753/icce.v33.waves.12.
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The formation of secondary wave in a coastal zone was investigated on the base of field, laboratory and numerical experiments. It was found that formation of secondary waves is essentially part of weakly nonlinear-dispersive wave transformation and determined by a periodic exchange of energy between the first and second harmonics. The formation of secondary waves depends on a stage of wave transformation and defined by amplitude of secondary harmonic and by phase shift between first and second harmonics. On the base of numerical modeling and laboratory experiments an idea of combination of underwater structures with floating breakwater is investigated. Waves propagating above submerged bar generate secondary waves that decrease the mean period of waves. Each additional bar reinforces and stabilizes this effect. Behind the bars the floating breakwater can be applied, because it suppresses successfully only short waves. Advantages and disadvantages of this idea are discussed.
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LEUNG, A. Y. T., H. X. YANG, and P. ZHU. "NEIMARK BIFURCATIONS OF A GENERALIZED DUFFING–VAN DER POL OSCILLATOR WITH NONLINEAR FRACTIONAL ORDER DAMPING." International Journal of Bifurcation and Chaos 23, no. 11 (November 2013): 1350177. http://dx.doi.org/10.1142/s0218127413501770.
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A generalized Duffing–van der Pol oscillator with nonlinear fractional order damping is introduced and investigated by the residue harmonic homotopy. The cubic displacement involved in fractional operator is used to describe the higher-order viscoelastic behavior of materials and of aerodynamic damping. The residue harmonic balance method is employed to analytically generate higher-order approximations for the steady state responses of an autonomous system. Nonlinear dynamic behaviors of the harmonically forced oscillator are further explored by the harmonic balance method along with the polynomial homotopy continuation technique. A parametric investigation is carried out to analyze the effects of fractional order of damping and the effect of the magnitude of imposed excitation on the system using amplitude-frequency curves. Jump avoidance conditions are addressed. Neimark bifurcations are captured to delineate regions of instability. The existence of even harmonics in the Fourier expansions implies symmetry-breaking bifurcation in certain combinations of system parameters. Numerical simulations are given by comparing with analytical solutions for validation purpose. We find that all Neimark bifurcation points in the response diagram always exist along a straight line.