High Levels Of Distortion Research Articles

Reverse Thrust Aerodynamics of Variable Pitch Fans with Inlet Distortion

Abstract Variable pitch fans can improve the operability of low pressure ratio fan systems by re-pitching the rotor blades. If a variable pitch fan can generate sufficient reverse thrust on landing it also eliminates the need for heavy, cascade-type thrust reversers. However, any reverse thrust generation is impacted by high levels of inlet distortion generated as air is drawn into the exhaust nozzle. This paper uses RANS computations and low-speed rig experiments to explore how a representative inlet distortion from the engine installation affects the aerodynamics and performance of a variable pitch fan operating in reverse thrust mode. The simulations and the experiments show that the distortion from the engine installation leads to a highly three-dimensional flow field with a large recirculation region within the bypass duct. The distortion substantially redistributes the mass flow, thrust and power in the engine. Streamline tracking combined with a power balance analysis reveals highly radial flow within the fan rotor, with almost all the fan power used to drive the recirculating flow in the bypass duct, generating high loss and high total temperature. The recirculation reduces the net mass flow through the engine to around 5% of a uniform inflow case and greatly reduces the effective reverse thrust. With uniform inflow, the net reverse thrust was found to be 35% of the nominal takeoff thrust. With inlet distortion, this was reduced to 20%. This demonstrates the importance of designing and operating variable pitch fan systems to minimise reverse thrust inlet distortion.

SUIVI DE LA QUALITÉ DE PUISSANCE MAXIMALE D'UN GÉNÉRATEUR D'INDUCTION À DOUBLE ALIMENTATION BASÉ SUR UN CONTRÔLEUR DE RÉSEAU NEURONAL ARTIFICIEL POUR SYSTÈME DE CONVERSION D'ÉNERGIE ÉOLIENNE

Renewable energy sources are playing a crucial role in satisfying the upcoming energy source needs for the world. The current power system is power electronics converter based, with several non-linear loads and spotted generations of renewable energy sources, resulting in many power quality issues. Most existing research analyzed MATLAB simulations and presented a high Total Harmonics Distortion (THD) level. This research work proposed an artificial neural network (ANN) control technique for a doubly fed induction generator (DFIG) based wind energy conversion systems (WECSs). To decrease chattering phenomena during the excitation arrangement, an advanced controller works for adaptive modification of the irregular power gain, even preserving the strength of the closed-loop scheme. The proposed PI controller one step forward improves reliability and tracks maximum voltage from the pulse width modulation rectifier. At primary, the modeling of the DFIG was presented. Then, using the proposed ANN controller, the rotor magnitude was tuned to recognize vector control of active and reactive power. The converter intends to activate at unity power factor and provide input currents with adequate harmonic content. The interface between the power’s electronic converter and the DFIG pulls out the most real power potential. The proposed prototype hardware model and simulation results are verified.

Investigating the Power Quality of an Electrical Distribution System Stressed by Non-Linear Domestic Appliances

: Power quality has become a matter of growing concern in recent years owing to a daily rise in use of non-linear loads at domestic level. In addition, fast growing technologies like distributed generation and electric vehicles are emerging as part of modern distribution systems. Therefore, it is necessary to evaluate and analyze the power quality issues due to various non-linear home appliances to give a clear picture of the current scenario. So that future technologies can be accommodated in the distribution systems while coping with existing power quality issues. The experimentally developed harmonic models, of various commonly deployed domestic appliances, are used for the simulation of a practical distribution system in Electrical Transient Analyzer Program (ETAP). Experimental results combined with simulation results show an alarmingly high level of harmonic distortion, breaching the recommended standard practices, in both current and voltage at not only point of common coupling (PCC) but also at the consumer’s end. In addition to increase in losses, this also degrades power factor giving rise to distortion power. While discussing other impacts of harmonic distortion, true power factor (PFtrue) and distortion power (D) has also been evaluated at PCC.

A novel framework for enhancing the power quality of electrical vehicle battery charging based on a modified Ferdowsi Converter

A DC–DC converter in an EV charging station is to regulate the DC voltage from the rectifier to the required voltage for battery charging. This ensures that a constant, stable, and safe charging voltage is provided to the battery However, if the EV charging is done only with a DC–DC​ converter, it results in poor Power Quality (PQ), with high levels of harmonic distortion and a low power factor. This can lead to longer charging times, increased energy costs, decreased battery performance and life, and introduce serious PQ issues. To address these issues, the Ferdowsi Converter is proposed is a combination of two interleaved Buck-Boost converters with a common input inductor as a solution with simplified PT control strategy presented, operated in operating in discontinuous conduction mode (DCM) is presented, which can achieve nearly unity power factor (PF) over universal input voltage range studied. The converter performs with fewer components, providing a charger input current that is in phase with the mains voltage, reducing the THD to below 5% under steady state and during variations in line and load side.

Deep Learning OFDM Receivers for Improved Power Efficiency and Coverage

In this article, we propose multiple machine learning (ML) based physical-layer receiver solutions for demodulating orthogonal frequency-division multiplexing (OFDM) signals that are subject to high level of nonlinear distortion. Specifically, three novel deep learning based convolutional neural network receivers are devised, containing layers in time- and/or frequency-domains, allowing to demodulate and decode the transmitted bits reliably despite the high error vector magnitude (EVM) in the transmit signal. Applicable training procedures are also described, such that the learned layers in the receiver processing properly generalize over different nonlinear distortion and multipath channel characteristics. Extensive set of numerical results is provided, in the context of 5G NR uplink (UL) incorporating also measured terminal power amplifier (PA) characteristics. The obtained results show that the proposed receiver systems are able to clearly outperform the classical linear minimum mean-squared error (LMMSE) receiver as well as the existing ML receiver approaches, especially when the EVM is high compared to modulation order. This is particularly so when the devised ML receiver is of hybrid nature with layers both in time and frequency. The proposed ML receivers can thus facilitate pushing the terminal PA systems deeper into saturation, and thereon improve the terminal power-efficiency, radiated power and network coverage. Through combining the obtained radio link performance results with link budget calculations, all carried out at the 28 GHz mmWave band, it is shown that the proposed ML receivers can enhance the network coverage in terms of maximum UL link distances by close to 100%, when compared to classical LMMSE receiver based networks.

Harmonic injection of domestic nonlinear loads in Ghana's power distribution system: analysis and mitigation using a low-cost notch filter

Due to global efforts to save energy, digital light processing (DLP) and direct view televisions (DVTVs) are being replaced by energy-efficient liquid crystal display (LCD) and light emitting diode (LED) televisions. However, these energy-efficient appliances cause harmonics to be injected into the power distribution system, posing a threat to power quality. This study investigates the harmonics generated by common domestic appliances, particularly LCD and LED TVs used in homes in Ghana. Field harmonic measurements were taken using a C.A. 8335 Power Quality Analyzer at a selected facility and were then replicated in a simulation using MATLAB/SIMULINK to model the facility's area network capacity of 100-kVA, 11kV/433V. The study proposes a notch filter as a harmonic mitigation technique, which is integrated into the simulation design and found to be effective at reducing total harmonic distortion current to 0.05 % when applied in parallel to nonlinear loads. The study also compares the harmonic distortion generated by LED TVs and LCD TVs, finding that both types generate high levels of distortion.

Evaluation of a Framework for Robust Image Reversible Watermarking

In the literature, robust reversible watermarking schemes (RWSs) allow the extraction of watermarks after the images have suffered attacks; however, the modified images are compromised. On the other hand, self-recovery schemes will restore the compromised regions of the images, but no secret messages are inserted in these schemes. A framework for robust reversible watermarking with signal restoration capabilities was previously proposed in the literature. This study selects four fragile reversible watermarking techniques and two self-recovery schemes to design different framework configurations. These configurations are evaluated to test the framework’s performance and determine the structure that yields better results in terms of perceptual transparency using a well-known image database as the signal input. It was found that fragile reversible watermarking schemes hold low perceptual distortion, while self-recovery schemes produce high perceptual distortion levels. The inherent characteristics of each algorithm determine, a priori, the behavior of the framework, which is approximated by a proposed equation.

Exciton-Phonon Coupling of Chiral One-Dimensional Lead-Free Hybrid Metal Halides at Room Temperature.

The interaction between organic cations and inorganic metal halide octahedral units strongly affects the properties of organic-inorganic hybrid metal halides. The "soft" property of the lattice provides the possibility of its strong exciton-phonon interaction. Here we report one-dimensional (1D) lead-free chiral organic-inorganic hybrid metal halide single crystals of (R/S)-methylbenzylamine bismuth iodide (R/S-MBA)2Bi2I8, which exhibits a high level of octahedral bond distortion. The introduction of chiral amines leads to a strong chiroptical response in the range of 200-600 nm. The strong exciton-phonon coupling can be observed through the coherent oscillation spectrum of transient absorption dynamics at room temperature. The coherent phonon oscillation frequencies are ∼97 and ∼130 cm-1, corresponding to the symmetrical stretching or bending of the Bi-I octahedron. Our work provides new insights for the study of exciton-phonon coupling in 1D chiral hybrid metal halides.

Impact assessment of grid tied rooftop PV systems on LV distribution network

Due to the high demand for electricity in the world today and the need to reduce carbon footprint, the power system is undergoing a profound change and this change is paving way for renewable electricity generation into the traditional grid, making the conventional network become smarter. The convention which has been in existence over several decades has changed; thus, consumers of electricity have now become prosumers; generating and feeding electricity into the low voltage network. Despite the benefits of prosuming, some researchers say their presence create stability, reliability and power quality (over and under-voltages, and high harmonic distortion levels) problems which in effect lead to overloading of transformers and feeders, extreme line losses, and failure in network protection exceeding the limits in the low voltage grid.The objective of this paper is to evaluate the effect of rooftop PV generations on distribution losses (power losses) and network voltage profile (voltage regulation on LV network) in a typical traditional grid setup. The study employs an empirical analysis of the power system, forward/backward sweep based on BIBC and BCBV matrices and python simulation to arrive at its conclusion under two different scenarios, nine different loading conditions and six PV (from 1kWp to 6kWp) injections.The results obtained show that a grid connected with rooftop PV systems have the potential of reducing distribution losses substantially and also do not violate standardized voltage limits. The net power loss recorded on the network with PV injections from 1kWp to 6kWp were in the range of 1.1kW–88.9kW at poor power factors and 0.7kW and 89.1kW at improved power factors, respectively. The variation in the voltage profile ranges between 0.97pu and 1.05pu for both the conventional and prosumer grids.

Impacts of Harmonic Voltage Distortions on the Dynamic Behavior and the PRPD Patterns of Partial Discharges in an Air Cavity Inside a Solid Dielectric Material

The monitoring of partial discharges (PDs) is one of the main methods used worldwide for evaluation and diagnosis of the insulation conditions in equipment powered by medium and high voltages. The occurrence of PDs is usually an indication of the appearance of insulation defects, which over time can compromise the dielectric withstand of the material used, increasing the probability of complete breakdown. In general, laboratory tests for detecting and registering PDs are carried out using purely sinusoidal voltages. However, it is very common for an electrical asset to be subjected at some point in its operating life to voltages distorted by harmonic components. Some studies reported in the literature reveal that harmonic distortions can affect the PDs’ characteristics, nevertheless, the effects of individual harmonic components on PDs still need to be analyzed. In this context, this paper proposes to evaluate the impacts of harmonic voltage distortions on the dynamic behavior and the phase-resolved partial discharge (PRPD) patterns of PDs in an air cavity within a solid dielectric material. For this, a simulation model was implemented, which was used to analyze the effects of applying distorted voltages composed of different harmonic orders (third, fifth, and seventh) and distinct levels of distortion (1%, 3%, 5%, 10%, 15%, and 20%). In addition, the influence of the third harmonic phase angle on PDs is also analyzed. The results extracted from the simulations revealed that the harmonic distortions caused changes in the numbers of PDs per cycle, in the mean apparent charges of the PDs per cycle, and in the PRPD patterns’ characteristics. These changes were very significant for higher distortion levels, which in practice may impair the interpretation of PD measurement records for the diagnosis of the condition of the insulation system.

Experimental and numerical characterization of twisting response of thin glass

The use of new generation thin, lightweight and damage-resistant glass, originally conceived for electronic displays, is moving its first steps in the built environment, in particular for adaptive and movable skins and façades. Its experimental characterization represents pearhaps one of the main open problems in glass research and engineering. Indeed, standard methods to test the glass strength cannot be used, due to geometrical nonlinearities, thwarting the correct procedure and the strenght calculation. Here, an innovative test procedure is proposed, where a rectangular thin glass element is twisted with high distortion level, while rigid elements constrain two opposite plate edges to remain straight. A dedicated experimental apparatus, that can be used to test specimens with different size and thickness, has been designed and used to test, up to rupture, chemically tempered thin glass with thickness of 1.1 mm and 2.1 mm. Experimental results have been compared to those of numerical analyses, with particular regard to the influence of different constrain conditions on the plate response.

Tutorial on the Use of Deep Learning in Diffuse Optical Tomography

Diffuse optical tomography using deep learning is an emerging technology that has found impressive medical diagnostic applications. However, creating an optical imaging system that uses visible and near-infrared (NIR) light is not straightforward due to photon absorption and multi-scattering by tissues. The high distortion levels caused due to these effects make the image reconstruction incredibly challenging. To overcome these challenges, various techniques have been proposed in the past, with varying success. One of the most successful techniques is the application of deep learning algorithms in diffuse optical tomography. This article discusses the current state-of-the-art diffuse optical tomography systems and comprehensively reviews the deep learning algorithms used in image reconstruction. This article attempts to provide researchers with the necessary background and tools to implement deep learning methods to solve diffuse optical tomography.

Multipoint Aerodynamic Design of Ultrashort Nacelles for Ultrahigh-Bypass-Ratio Engines

This paper presents a newly developed methodology for multipoint aerodynamic design of ultrashort nacelles for ultrahigh-bypass-ratio turbofan engines. An integrated aerodynamic framework, based on parametric geometry generation and flowfield solution via three-dimensional Reynolds-averaged Navier–Stokes equations, was built and used for designing several ultrashort nacelle shapes and to evaluate their aerodynamic performance. An approach for modeling the inlet–fan coupling is presented and validated. A design strategy is introduced, and various test cases are evaluated under the following critical operating conditions: midcruise, low speed/high angle of attack, and pure crosswind. The major design parameters are highlighted and their influence in the flowfield is discussed in detail for all the chosen flight conditions. Performance was evaluated by assessing inlet flow distortion and by bookkeeping of thrust and drag. The framework has proven to be suitable for designing high-performance nacelles capable of operating under critical flight conditions, without flow separation or high levels of distortion. Drooping the inlet by 4 deg is shown to reduce the drag at cruise by 1.9%, which also has a large beneficial impact on internal lip separation at high-incidence conditions. Furthermore, crosswind was identified as the most severe of the conditions, requiring a drastic reshaping of the nacelle to avoid internal lip separation. Two final nacelle designs were compared: the first allowed inlet separation under a 90 deg crosswind condition, whereas the second was reshaped to be separation-free under all operating conditions. Reshaping to avoid separation has increased drag by 5.1% at cruise.

Characterization of Supraharmonic Emission from Three Different Electric Vehicle Charging Infrastructures in Time and Frequency Domain

With the recent proliferation of electric vehicles (EVs), maintaining power quality within acceptable limits in future distribution grids will become a challenging task. A specific concern is the spread of Supraharmonics in the range from 2 to 150 kHz, generated by modern power electronic devices. In this paper, the long term Supraharmonic distortion from three differently sized electric vehicle charging infrastructures is analyzed in frequency and time domain. At the monitored sites several interruptions of EV charging processes were observed due to poor power quality. It was found that vehicles disconnect when exposed to high levels of harmonic distortion. Moreover, the impact of the charging EVs on the Supraharmonic distortion and the interaction with the background distortion for the individual sites is discussed. Results show that a general increase in Supraharmonics emission can be expected due to the rising number of EVs. However, measurements also indicate that damping effects can occur for certain load configurations.

Design of Compressive Sensing Adaptive Taylor-Fourier Comb Filters for Harmonic Synchrophasor Estimation

In modern power systems, phasor measurements are expected to deal with challenging conditions, e.g. fast dynamics and high distortion levels. Taylor-Fourier Multifrequency models represent a promising solution, but their performance is strongly related to the accurate extraction of the signal spectral support. In this context, this paper proposes an enhanced method for support recovery that exploits the inherent block-sparsity properties of electrical signals. The proposed method is fully characterized in diverse and distorted test conditions, inspired by reference standards and real-world scenarios. The comparison against another Compressive Sensing based approach confirms the significant improvement in terms of both recovered support exactness and synchrophasor measurement accuracy.

A Method of Image Quality Assessment for Text Recognition on Camera-Captured and Projectively Distorted Documents

In this paper, we consider the problem of identity document recognition in images captured with a mobile device camera. A high level of projective distortion leads to poor quality of the restored text images and, hence, to unreliable recognition results. We propose a novel, theoretically based method for estimating the projective distortion level at a restored image point. On this basis, we suggest a new method of binary quality estimation of projectively restored field images. The method analyzes the projective homography only and does not depend on the image size. The text font and height of an evaluated field are assumed to be predefined in the document template. This information is used to estimate the maximum level of distortion acceptable for recognition. The method was tested on a dataset of synthetically distorted field images. Synthetic images were created based on document template images from the publicly available dataset MIDV-2019. In the experiments, the method shows stable predictive values for different strings of one font and height. When used as a pre-recognition rejection method, it demonstrates a positive predictive value of 86.7% and a negative predictive value of 64.1% on the synthetic dataset. A comparison with other geometric quality assessment methods shows the superiority of our approach.

Power Quality and Performance Analysis of Grid-Connected Solar PV System Based on Recent Grid Integration Requirements

The electrical energy demand is steadily growing, and hence, the integration of photovoltaic system to the distribution networks is also dramatically increasing though it has a significant effect on the network’s power quality. The purpose of this paper is to analyze the impact of solar PV integration on the power quality of distribution networks. The study is conducted using ETAP software, taking one of the radial distribution networks available in Bahir Dar city during the peak of connected loads which has the least voltage profile. Furthermore, the optimal location of the PV in the network is done using particle swarm optimization. Accordingly, the appropriate location of the PV system is determined to be the farthest end bus (bus 34). Also, the impact in terms of voltage and current harmonic distortion on the distribution feeder network is comparatively discussed by comparing the distribution system parameters with different penetration levels of solar PV system. The simulation results obtained demonstrate that high harmonic distortion level is injected correspondingly as the penetration capacity of PV system increased which indicates that the solar PV system should be integrating only up to a maximum possible capacity the network can carry. The integration of the PV system beyond this maximum penetration level causes production of high harmonic distortion which adversely affects the system performance. At the maximum penetration level which allows the acceptable harmonic distortion limit, the total voltage harmonic distortion and current demand distortion are found to be 4.97% and 14.98%, respectively.

Rectifilter for electric arc plasma plant

This article presents the results of the development and research of a new type of AC-DC converter - a filter-rectifier (or rectifilter). The object of application of the proposed device is an industrial plant of electric arc plasma processing, the operation of which requires maintaining a constant value of the arc current and is accompanied by a high level of harmonic distortion and consumed reactive energy. From the point of view of the reactive power compensation and harmonic filtering strategy, the rectifilter can be attributed to active electric power filters and FACTS, however, from the position of the main function performed, it is a direct current source, an AC to DC converter, an active rectifier. This work describes in detail the principles of operation of the control system and the hardware architecture of the device. Mathematical modeling of the rectifilter and analysis of the graphs of the consumed alternating current, rectified current, analysis of the harmonic composition and power factor in comparison with the thyristor rectifier of an electric arc plasmatron were carried out.

A spatial analysis of corruption, misallocation, and efficiency.

Political corruption is considered one of the major obstacles to achieving high-quality economic development in developed and developing countries. This study first calculates the ecological footprints of 29 provinces in China based on China's provincial panel data from 2006 to 2015. The provinces' ecological efficiencies were then calculated. The relationship between government corruption and ecological efficiency is researched, and the result shows that such a relationship is not linear. At different levels of ecological efficiency, government corruption has different effects on ecological efficiency. Finally, the resource misallocation index is introduced, and the spatial error model is used to further test the impact of government corruption and resource misallocation on ecological efficiency. The regression results show that high levels of government corruption and resource allocation distortion will cause a decrease in regional ecological efficiency, which adversely affects the sustainable development of the economy.

Effect of high-energy ball milling on the magnetocaloric properties of La0.7Ca0.2Sr0.1MnO3

We report an experimental–theoretical analysis of the large magnetocaloric effect observed in the compound La0.7Ca0.2Sr0.1MnO3, synthesized by high-energy ball milling assisted by heat treatment. We demonstrated that this method induces crystal structure distortions and defects, which are responsible for the excellent MC properties. X-ray diffraction and Rietveld refinement allowed quantification of the high levels of microstrain and distortion of the synthesized orthorhombic structure (Pnma). Temperature-dependent magnetization measurements reveal a Curie temperature of approximately 310 K; furthermore, a large value of magnetic entropy change |ΔSM|= 4.11 Jkg−1 K−1 and relative cooling power of 61.12 Jkg−1 were estimated by means of Maxwell's equations under an applied field (H) of 18 kOe, making this manganite a promising material for refrigeration applications. Electron paramagnetic resonance spectra of the doped manganite show the presence of Mn4+ ions, which strengthen the double-exchange interaction (ferromagnetic). It is demonstrated that the high-energy ball milling process assisted by heat treatment is an easy, economic, and fast method for synthesizing doped manganites, showing improved magnetocaloric properties compared to those of the same material synthesized by other methods.