Search

Electrical power conversions are common in a large variety of engineering applications. With reference to AC/DC and DC/AC power conversions, a strong research interest resides in multilevel converters, thanks to the many advantages they provide over standard two-level converters. In this paper, a power-oriented model of single-phase Modular Multilevel Converters (MMCs) is first provided, followed by a detailed harmonic analysis. The model is given in the form of a Power Oriented Graphs block scheme that can be directly implemented in the Matlab/Simulink environment. The performed harmonic analysis gives a deep and exact understanding of the different terms affecting the evolution of the voltage trajectories in the upper and lower arms of the converter. Next, a new model-based cascade control architecture for MMCs is proposed. Combined with the real-time calculation of the ideal average capacitor voltages reference, the proposed control architecture allows to properly track the desired load current while minimizing the tracking error and the harmonic content in the generated load current itself. [Display omitted] • Power-Oriented Modeling of Modular Multilevel Converters. • Full Harmonic Analysis of Modular Multilevel Converters. • Calculation of the Ideal Voltage Tracking Reference for the Capacitors Voltages. • Model-Based Cascade Control of Modular Multilevel Converters. • Load Current Tracking Error and Harmonic Content Reduction. [ABSTRACT FROM AUTHOR]

Abstract: This paper focuses on main principles of high speed imaging used for motion analysis of microscopic biomechanical objects represented by cilia of respiratory apparatus epithelium. Frequency based analysis (FFT and its derivates) is used for searching regions with dominant movement which brings more objectivity for acquired videosequences analysis and segmentation. 3D image information (videosequence) is projected to 2D frequency maps for evaluation. Paper brings basic mathematical apparatus and elementary approaches how to solve this tasks. Results of experiments are successfully built-in to medical and pharmacological research. [Copyright &y& Elsevier]

Highlights • Vibration monitoring is applied for speed estimation of rotating machinery. • Vibration spectrum with sample of short duration produces large error in speed estimation. • Speed estimation using harmonic component improve its accuracy. However, higher harmonics component are found to be absent in many cases. • An algorithm is proposed to generate artificially higher order harmonic components of the fundamental rotational frequency, for speed estimation. • Accurate speed estimation using the proposed algorithm reduces error in estimating speed by 16 times. Abstract The use of vibration sensors for rotational speed estimation has been found to be an effective and reliable technique. In general, the fundamental rotational frequency (f) component observed in the vibration spectrum represents the rotational speed. However, for a better accuracy of estimation, large sample duration is required which results in a higher data acquisition time, computational time and data storage. Hence, the estimation of speed accuracy with the vibration signal of a short duration is a challenging task. This paper proposes an algorithm, which requires extraction of the fundamental rotational frequency component and later, the artificial generation of its corresponding harmonic components, for the accurate estimation of speed. The proposed algorithm can be used to estimate the speed of any rotating machinery. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, we prove two general theorems on monotone Boolean functions which are useful for constructing a learning algorithm for monotone Boolean functions under the uniform distribution. A monotone Boolean function is called fair if it takes the value 1 on exactly half of its inputs. The first result proved in this paper is that a single variable function has the minimum correlation with the majority function among all fair monotone functions. This proves the conjecture by Blum et al. (1998, Proc. 39th FOCS, pp. 408–415) and improves the performance guarantee of the best known learning algorithm for monotone Boolean functions under the uniform distribution they proposed. Our second result is on the relationship between the influences and the average sensitivity of a monotone Boolean function. The influence of variable on f is defined as the probability that differs from where x is chosen uniformly from and means x with its ith bit flipped. The average sensitivity of f is defined as the sum of the influences over all variables . We prove that a somewhat unintuitive result which says if the influence of every variable on a monotone Boolean function is small, i.e., for some constant , then the average sensitivity of the function must be large, i.e., . We also discuss how to apply this result to the construction of a new learning algorithm for monotone Boolean functions. [Copyright &y& Elsevier]

Harmonic pollution is one of the challenging problems facing power networks recently due to the widespread non-linear loads and inverter-based renewables. In this regard, this work presents the optimal design of damped and undamped passive filters using a solver called Mixed-Integer Distributed Ant Colony Optimisation (MIDACO). This solver is employed to obtain an optimal design strategy for single-tuned passive power filters by investigating three primary criteria – minimisation of active power losses of the Thevenin's resistor, maximisation of the true power factor, and maximisation of the transmission efficiency. Several constrictions associated with the designed filters have been considered, in which the global maximum or minimum criterion was attained by retaining the quality factors of the designed filters within a particular range, damping harmonic resonance, achieving a permissible range of the power factor, limiting voltage harmonic distortion by complying with IEEE Std. 519–2014 restrictions. Besides, the performance limits of capacitors operating in distorted systems have been met while complying with IEEE Std. 18–2012. Further, the results obtained using the MIDACO solver in four different case studies are compared to those obtained using particle swarm optimisation and genetic algorithm. In addition, this work depicts the damping resistor of the inductance in the single-tuned filters. The benefits and drawbacks of damping over an undamped filter are discussed. Finally, the results validate the effectiveness of the MIDACO solver employed in this paper. [ABSTRACT FROM AUTHOR]

Signals and systems is a complex subject and effective teaching even at the introductory level requires a means of communicating complex concepts to students. One of the difficulties in teaching this topic is because of the advanced mathematics involved. At the Near East University in Cyprus we teach the signals and systems course at the undergraduate level to electrical/electronic engineering students. Although the students in general are interested in learning the concepts, they usually have difficulty in understanding the complex theory. To address this issue, we have introduced extensive practical work in the form of simulation and laboratory sessions. This paper discusses our experiences of teaching the signals and systems course with the successful implementation and integration of the theory, simulation, and practical sessions. [ABSTRACT FROM AUTHOR]

In this paper station coordinate time series from three space geodesy techniques that have contributed to the realization of the International Terrestrial Reference Frame 2014 (ITRF2014) are compared. In particular the height component time series extracted from official combined intra-technique solutions submitted for ITRF2014 by DORIS, VLBI and GNSS Combination Centers have been investigated. The main goal of this study is to assess the level of agreement among these three space geodetic techniques. A novel analytic method, modeling time series as discrete-time Markov processes, is presented and applied to the compared time series. The analysis method has proven to be particularly suited to obtain quasi-cyclostationary residuals which are an important property to carry out a reliable harmonic analysis. We looked for common signatures among the three techniques. Frequencies and amplitudes of the detected signals have been reported along with their percentage of incidence. Our comparison shows that two of the estimated signals, having one-year and 14 days periods, are common to all the techniques. Different hypotheses on the nature of the signal having a period of 14 days are presented. As a final check we have compared the estimated velocities and their standard deviations (STD) for the sites that co-located the VLBI, GNSS and DORIS stations, obtaining a good agreement among the three techniques both in the horizontal (1.0 mm/yr mean STD) and in the vertical (0.7 mm/yr mean STD) component, although some sites show larger STDs, mainly due to lack of data, different data spans or noisy observations. [ABSTRACT FROM AUTHOR]

In this paper we present an analytical model of Perfectly Matched Layers for flexural waves within elongated beam structures. The model is based on transformation optics techniques and it is shown to work both in time harmonic and transient regimes. A comparison between flexural and longitudinal waves is detailed and it is shown that the bending problem requires special interface conditions. A connection with transformation of eigenfrequencies and eigenmodes is given and the effect of the additional boundary conditions introduced at the border of the Perfectly Matched Layer domain is discussed in detailed. Such a model is particularly useful for Finite Element analyses pertaining propagating flexural waves in infinite domain. [ABSTRACT FROM AUTHOR]

• Structural multidisciplinary design and optimization are achieved. • Stress optimization model of structure under harmonic load is proposed. • Sensitivity of stress optimization under harmonic excitation are derived. • Stress concentration effects are effectively solved. • Strength of engineering structure under harmonic load is improved. In this paper, a new optimization method for the maximum von Mises stress minimization design of continuum structures subjected to harmonic force excitation is proposed. By using an extended Bi-directional Evolutionary Structural Optimization (BESO) method, the intermediate density elements with high stress state are avoided. To reduce the computational cost, the global von Mises stress is approximately measured by using a global stress measure based on the p -norm. Both sensitivities and topological variables are filtered to overcome the highly nonlinear stress behavior and stabilize the optimization procedure. A series of comparisons have been conducted to validate the effectiveness and practicability of the method on two-dimensional and three-dimensional benchmark design problems. The influence of varying excitation frequencies, damping and boundary conditions on the optimized results and the mode shapes are considered. The optimized results indicate that the proposed approach has good convergence and can achieve a reasonable design that effectively reduces the stress concentration effect at the critical stress areas. Strength of engineering structure under harmonic load is improved. [ABSTRACT FROM AUTHOR]

Estimating damping in structure composed of different materials (steel, brass, aluminum) and processes still remains as one of the most extremely vast challengers. The paper presents Structural damping effect on beam vibration by impact hammer. Structural damping contributes to about 10-15% of total system damping. The main objective of this work is to estimate the natural frequency and damping ratio of cantilever beams of Aluminum, Brass, and Steel by LabVIEW software and validate the result with vibration analysis and Harmonic analysis utilizing ANSYS. Free vibration analysis was carried out for identifying the natural frequencies and the harmonic analysis was carried out for obtaining frequency replication curves from which damping ratios were estimated utilizing Half- power Band Width Method. It is observed that damping ratio is higher for brass than steel than aluminum. [ABSTRACT FROM AUTHOR]

Appropriate Tidal level data is indispensable requirement for planning and safe execution of harbour projects, other coastal structures and also for optimal movement of ships. Tidal currents are also used in deciding the orientation of berthing structures and in identifying the area, dominated by eddy currents. Conventional tidal forecasting using least squares method for the prediction of long-term tidal levels requires large number of parameters for harmonic analysis. Accuracy of results depends on the length of measured samples. This paper presents an Artificial Neural Network (ANN) model for forecasting the tidal-levels using the limited measured data as an alternative to conventional harmonic analysis. ANN model developed for forecasting the tidal data is trained with different learning algorithms, number of neurons in its hidden layer and number of epochs (iterations). The aim was to develop a network, which provides a simulated tide which would be in well agreement with the actual tide. Efforts were made to forecast the time series of tidal levels based on the previous data. Study shows that the Feed-Forward Back Propagation (FFBP) network with Levenberg-Marquardt (LM) algorithm provides good correlations as compared to other algorithms. Results were compared using statistical techniques such as correlation coefficients, RMSE and Nash-Sutcliff efficiency. ANN is found to be efficient technique in forecasting the tidal data time series for a short duration. This method can be used for short term predictions of tidal time series, however model developed would remain site specific. This model was also used for predicting the tide at a far distance tidal station using the tide at the local station. It was observed that prediction of tidal levels at the far distant station is not accurately done by the neural network and shall not be used for such purposes. [ABSTRACT FROM AUTHOR]

Solar activity, as measured by the yearly revisited time series of sunspot numbers (SSN) for the period 1700–2014 (Clette et al., 2014), undergoes in this paper a triple statistical and econometric checkup. The conclusions are that the SSN sequence: (1) is best modeled as a signal that features nonlinearity in mean and variance, long memory, mean reversion, ‘threshold’ symmetry, and stationarity; (2) is best described as a discrete damped harmonic oscillator which linearly approximates the flux-transport dynamo model; (3) its prediction well into the 22nd century testifies of a substantial fall of the SSN centered around the year 2030. In addition, the first and last Gleissberg cycles show almost the same peak number and height during the period considered, yet the former slightly prevails when measured by means of the estimated smoother. All of these conclusions are achieved by making use of modern tools developed in the field of Financial Econometrics and of two new proposed procedures for signal smoothing and prediction. [ABSTRACT FROM AUTHOR]

Monitoring residual stress relaxation due to mechanical loading has the capability to retrieve a component's load history. So far, these changes are determined by X-ray diffraction using the sin 2 ψ-method going along with high effort regarding specimen preparation, measurement time and costs. The presented paper evaluates harmonic analysis of eddy current measurements as an alternative technology to determine alterations of a component's subsurface due to fatigue. Transferring this approach to a wide range of machined components and mass production bears the potential to gain access to large databases of service life information, representing an important enabling technology for cyber-physical systems. [ABSTRACT FROM AUTHOR]

• Investigating and revealing potential risks of poor energy quality for shipboard microgrids. • Providing a clear view of the importance of selecting the accurate algorithms for analyzing the quality of energy and delivering a comparative study. • Proposing a developed algorithm, which is an offline-based energy quality analyzing technique developed for the short-term protective action stage to assess the energy quality of shipboard microgrids. • Proposing an enhanced algorithm, which is an online-based energy quality assessing technique, Which is very suitable for the long-term preventive action stage. Retrofitting of shipboard microgrids is receiving much attention nowadays due to the flexibility it offers to adapt existing ships with rapid market variations to move towards all-electric ships (A-ESs). This modernity mainly relies on incorporating the power electronics converters that unfortunately draw a large number of harmonics, which affect the energy quality and threaten the system stability and crew/passengers safety. The contribution of this paper lies in proposing two developed open-loop algorithms to assess the harmonics distortion of A-ESs without relying on signal periodicity. The first algorithm is an offline-based analyzing technique developed for the short-term protective action stage, which incorporates the eigenvalue solution inside the short-time fast Fourier transform (ST-FFT) to adapt its window size. Consequently, this algorithm can provide a comprehensive harmonics analysis with a fast transient response even under large system frequency drifts. The second algorithm is an online-based assessing technique, which is very suitable for the long-term preventive action stage to provide accurate harmonics distortion assessment with the fast transient response and efficient computation burden. This approach relies on cascading three moving average filters (MAFs) with particular window sizes to filter and estimate the mean value inside the discrete Fourier transform and the true RMS blocks without the need of frequency information. Hence, it results in enhancing the harmonics rejection capability of the algorithm even under the existence of non-characteristic harmonics and frequency drifts. Simulation and experimental results are provided to validate the efficacy of the proposed algorithms and the results are compared with traditional methods. [ABSTRACT FROM AUTHOR]

In view of increasing concerns about climate change and global warming, various renewable energy sources are widely adopted in power systems to reduce greenhouse gas emissions. However, the widespread adoption of renewable energy sources exacerbates the problem of harmonics pollution. In order to improve power quality, it is urgent to develop a new approach for monitoring harmonics. By leveraging the structured sparsity and spatial sparsity of harmonic sources, this paper proposes a group sparse Bayesian learning method for solving harmonic state estimation problems. The proposed algorithm can employ a small number of measurements less than the number of state variables to pinpoint harmonic sources and to estimate the harmonic magnitudes and angles. Moreover, the proposed method achieves automatic hyperparameter adjustments and solves the system states in complex domain without splitting them into real and imaginary parts. Extensive results on a benchmark IEEE 14-bus system are presented to substantiate the superiority of the proposed method in terms of localization accuracy and harmonic magnitude and phase angle estimation. • A group sparse Bayesian learning method is proposed for harmonic state estimation. • The proposed algorithm achieves automatic hyperparameter adjustments. • The proposed method can directly handle the measurements in the complex domain. • Using a small number of measurements pinpoints the harmonic sources. • The proposed method has high localization precision and small estimation error. [ABSTRACT FROM AUTHOR]

Abstract: The acoustic signal of gas pipeline leakage has advantage in short delay time and carries physical information of the leakage, so it can be used for the diagnosis and localization of the pipeline leakage. In the long distance pipeline, collecting vibration signal caused by sound field has important significance to research of acoustic leakage detection technology. In order to get sound signal, first, this paper researches on the phonation principle of the pipeline leakage and the characteristic of the sound source, and the sound field is established on the basis of aero acoustics. Second, the vibration of the pipeline wall is analyzed with the harmonic analysis technology of the ANSYS software when the leak wall bears broadband harmonic sound pressure. Finally, the field experiment demonstrates that this approach can improve detection ability of small leakage with low false alarm rate. [Copyright &y& Elsevier]

Abstract: Solving harmonic estimation problems in power quality signals has attained significant importance in recent times. Stochastic optimization algorithms have been successfully employed to determine magnitude of this information in an unknown signal contaminated with noise or containing additive dc decaying components. The present paper shows how a recently proposed stochastic optimization algorithm, called artificial bee colony algorithm, can be hybridized with least square algorithm to solve these problems effectively. The proposed algorithm has been tested for a series of case studies employing different benchmark environment situations and our extensive simulation tests validate the usefulness of the proposed algorithm and it could largely outperform several competing simulation algorithms, proposed in the recent past. The effectiveness of the proposed algorithm is further demonstrated for those situations where the number of harmonics present in the signal is also not known, along with the magnitude and phase of each harmonic. [Copyright &y& Elsevier]

Abstract: Targeting at the new type data called gravity gradient, the basic formulae and equations of the global virtual line mass model and harmonic analysis are made in this paper. The virtual line mass models based on radius real component, horizontal complex component and full tensor are studied. So are the least squares solutions. The harmonic analysis formulae of virtual line mass models are shown completely, which have various advantages such as eliminating the disperse errors and dealing with multi-types data compared with virtual point mass harmonic analysis. With consideration of different depths, the virtual line mass method is better than the virtual point mass method with various frequencies. Finally, the availability and validity are made through simulation experiments. [Copyright &y& Elsevier]

Abstract: This paper describes not only the hardware architecture of the servo system composed by self-made inverter and permanent magnet synchronous motor, but also its measurement and control system software features. A communication system is built based on the Modbus-RTU protocols which contain the CRC data verification between IPC and the inverter. The measurement and control software of servo system which consists of self-made inverter and PMSM is realized. The results compare with the servo system which consists of Schindler''s ATV31 inverter and SIMO''s asynchronous motor. The experiment parameters include harmonic content which is contained by phase current and voltage, and also the motor speed. The results show that the measurement and control system is stable and reliable. Both the harmonic content of the Inverter output and the motor speed meet the requirements. [Copyright &y& Elsevier]

Abstract: The paper presents an iterative method for obtaining footprint, pressure distribution, local deformation and sub-surface stress field for the contact between a rigid cylindrical indenter and an elastic flat substrate. The methodology is applicable for semi-infinite, as well as for thin or thick bonded elastic layered solids with high or low elastic moduli. All findings are in accord with the observed behaviour of hard wear resistant and soft solid lubricating coatings. It is shown that the decomposed contact pressure distribution into a series of harmonic waves induces sub-surface stress fields that decay into the depth of the solid according to their wavelengths. Consequently, conditions vis-à-vis fatigue spalling and adhesion performance may be predicted for given thickness of layered bonded elastic solids. [Copyright &y& Elsevier]

The aim of this paper is to investigate the possibility of applying a nonlinear frequency response (FR) method described by Ilić et al. [2007b. Nonlinear frequency response method for estimation of single solute adsorption isotherms. Part I. Theoretical basis and simulations, this volume, doi:10.1016/j.ces.2007.05.004] to determine single solute adsorption isotherms. The method is based on the analysis of the nonlinear FR of a chromatographic column to a periodical change of the inlet concentration around several steady-state concentrations. The first, second and third local derivatives of single solute isotherms are estimated from the low-frequency asymptotic behaviour of the corresponding FR functions. The adsorption of 4-tert-butylphenol and ethyl benzoate as single solutes is studied on octadecyl silica from methanol–water mixture (60:40). Experiments are performed using a standard gradient HPLC unit capable to realize inlet concentration changes in a nearly sine waveform. Small injections of compounds into the not preloaded column, as well as conventional frontal analysis experiments are performed for rough estimation of the adsorption isotherm coefficients and comparison with the results obtained using the nonlinear FR method. [Copyright &y& Elsevier]

Abstract: This paper presents a methodology for determination of harmonic iron losses in laminated iron cores under non sinusoidal excitation. The methodology adopted is based on a particular 3D finite element model by using a reduced scalar potential formulation. Eddy currents in iron laminations are considered by means of convenient surface current densities. Experimental verification is performed by comparing computed and measured leakage field in an E-shape laminated core case. A convenient modification of induction motor equivalent circuit parameters is proposed enabling consideration of switching frequency iron losses in case of inverter supply. [Copyright &y& Elsevier]

Barometric pressure changes can induce airflow in an open borehole or well screened in the vadose zone, thereby ventilating the soil surrounding the borehole. This paper presents an analytic model of the induced airflow and compares the predictions of the model with experimental measurements. This model may be useful for the design of passive soil vapor extraction as applied to the remediation of soil contaminated by volatile organic compounds (VOCs). Based on harmonic analysis, the model predicts the time-dependent flow in agreement with measurements at a borehole in strata of differing permeability. The model uses no adjustable parameters, but proceeds from first principles based upon known or estimated values of soil properties as a function of depth. In an approximation, the calculated flow is determined by the difference between barometric pressure and the attenuated pressure that would propagate vertically into the vadose zone in the absence of an open borehole. The attenuated vertical propagation of pressure can be calculated by a corresponding harmonic method presented previously. The model reveals that the flow in the borehole is approximately proportional to the horizontal permeability in the formation, and depends only weakly on the soil porosity and borehole radius. [Copyright &y& Elsevier]

Accurate tidal prediction and supplement is an important task in determining constructions and human activities in coastal and oceanic areas. The harmonic tidal level is conventionally used to predict tide levels. However, determination of the tidal components using the spectral analysis requires a long-term tidal level record (more than one year [Handbook of coastal and ocean engineering 1 (1990) 534]). In addition, calculating the coefficients abbreviated of tide component using the least-squares method also requires a large database of tide measurements. This paper presents an application of the artificial neural network for predicting and supplementing the long-term tidal-level using the short term observed data. On site, tidal-level data at Taichung Harbor in Taiwan will be used to test the performance of the artificial neural network model. The results show that the tidal levels over a long duration can be efficiently predicted or supplemented using only a short-term tidal record. [Copyright &y& Elsevier]

This paper documents a technique for investigating one-dimensional airflow in the vadose zone. Variations in pore gas pressures resulting from barometric cycles were measured at depths as great as 180 m in several gas monitoring wells. The data were transformed to the frequency domain, enabling comparison with closed-form analytic expressions of one-dimensional pressure transport in layered porous media. The data reveal evidence for vertical fracture flow that was not apparent from in situ measurements of permeability. The data also reveal that the basalt underlying the site at depths greater than 100 m has permeability exceeding 1000 darcies, and is vented to the atmosphere at an estimated distance of a few kilometers from the site. [Copyright &y& Elsevier]

• A technology based on integral parameters method is applied to assess EM loads of EAST PFCs. • EM loads of EAST PFCS during MD events are obtained by simple algebraic calculation with gained integral parameters. • Results indicated that the method can be efficiently used for multi-scenarios and real-time EM analysis of Tokamak PFCs. A method of simplification of analysis for assessing the electromagnetic (EM) loads of the blanket components in tokamaks has been reported [ 1 , 2 ]. The method simplified calculation by extracting the characteristic parameters of the local conducting structure. This paper explored the feasibility of applying the new method to EM loads assessment of EAST Plasma Facing Components (PFCs). Firstly, the integral parameters of EAST PFCs were calculated using harmonic analysis technique. Then EM loads could be gained by simple linear calculation using the pre-obtained integral parameters and external magnetic field. The results comparison with finite element analysis (FEA) validated the efficiency of the method, and this method will be used for the future real-time EM analysis of EAST PFCs. [ABSTRACT FROM AUTHOR]