Excessive Distortion Research Articles

Composite control of single-phase inverter based on SRFPI and reduced-order LADRC

One of the development trends of inverters is toward higher performance. Periodic and non-periodic disturbances will result in excessive harmonic distortion in the output voltage and reduce the performance of single-phase inverters. The linear active disturbance rejection control (LADRC) method is used in inverter control because of its good anti-interference ability. When compared to a full-order LADRC, the reduced-order LADRC (RLADRC) algorithm efficiently reduces the system’s phase lag, simplifies the control structure by reducing the order and the control parameters, and exhibits comparable disturbance rejection capabilities. In this paper, a composite voltage control scheme based on the combination of RLADRC, and the synchronous reference frame proportional–integral​ (SRFPI) control is explored for single-phase off-grid inverters. The basic idea is that the non-periodic disturbances of system can be efficiently eliminated by RLADRC, while the periodic disturbances can be restrained by SRFPI. The design of RLADRC is given in detail. Moreover, the Thevenin equivalent model of the inverter control system is derived for stability and robustness analysis. Finally, compared with SRFPI-LADRC based method, the comparative experimental results demonstrate that the inverter realizes fast transient response, good load regulation and lower total harmonic distortion (THD) with the proposed SRFPI-RLADRC based composite control strategy.

A homogenised anisotropic J-model for accelerating computations of screening current profile in large-scale HTS magnets

Owing to the induced excessive strain, plastic deformation, and distortion of the magnetic field in high-temperature superconducting (HTS) tapes, there is a rapidly growing research interest in the screening current profile in high-field superconducting magnets. The J-model was developed to calculate the current density distributions in HTS stacks and cables, which improves the calculation efficiency because no air domain is considered in the calculation regions. However, for a large-scale high-field magnet wound with hundreds and thousands of layers of HTS tapes, there is still a big challenge for J-model simulation involving prohibitive time consumption and memory requirements. This study proposes an improved J-model approach based on a homogenised anisotropic (HA) scheme for large-scale HTS magnet systems to decrease the number of elements and enhance calculation efficiency. The reliability of the improved HA J-model was verified by solving 2000-tape HTS stacks, and a significant improvement in computational performance was achieved. Furthermore, the HA J-model was applied to a large-scale scenario of a 32 T hybrid all-superconducting magnet at the National High Magnetic Field Laboratory to numerically capture the electromagnetic responses. The magnetic flux and current densities in the HTS insert coils were obtained completely, and the screen current induced field, which is the most concerning, showed a good agreement with the literature. Meanwhile, the time consumption by the HA J-model is approximately half that of the traditional J-model and even less than 1–2 orders of magnitude of the others, such as the traditional T-A model and H model, with acceptable accuracy. The improved HA J-model may provide an appropriate prior design with rapid and real-time calculations for large-scale magnet systems.

Pengaruh besaran arus dan kecepatan las terhadap angular distorsi pada SS304 dengan GMAW

SS304 is a steel with good corrosion resistance, so it is widely used in various industrial worlds. The stainless-steel fabrication process generally uses a joining process by welding. To get a good welding result, it is necessary to choose the correct parameters to reduce the potential for welding imperfections. In the ISO 6520-1-520 standard, excessive distortion is a welding imperfection that must be avoided because it can cause angular misalignment, namely ISO 6520-1-508 standard. In this research, an experiment was conducted to determine the effect of current strength and welding speed on the angular distortion generated using GMAW. The current strength is 115, 120, and 125 A, while the welding speed is 3.6, 3.9, and 4.2mm/s. The angular distortion of the weld results is measured using a CMM (Coordinate Measuring Machine) after the material has experienced natural cooling. From the research results obtained, it is known that the greater the current strength, the greater the resulting angular distortion. On the other hand, if the welding speed is greater, the width of the weld bead and the resulting angular distortion will be smaller.

EVALUATING THE ACCURACY OF A DIGITAL CORRELATION SYSTEM TO PREDICT THE FATIGUE FAILURE OF ADDITIVELY MANUFACTURED PARTS

Internal defects that occur during the additive manufacturing process of direct metal laser sintering can have a significant influence on the fatigue performance of Ti-6Al-4V additively manufactured parts compared with parts that are made using traditional manufacturing methods. For the adoption of additively manufactured parts in the medical, automotive, and aerospace industries, the expected fatigue life of parts must be predictable and repeatable for successful application. Micro-CT scanning is commonly used to provide insight into the expected fatigue life of parts by examining internal defects that have occurred during melting. However, using a micro-CT for every part in the supply chain is not always feasible, so alternatives must be considered. One approach would be to analyse parts by applying a short-run fatigue test coupled with a digital image correlation (DIC) system to detect areas on parts where excessive distortion is taking place. This study investigated the level of accuracy that a DIC system could obtain as an alternative non-destructive test to predict where and when a test specimen would fail. To determine whether this alternative was viable, tests were carried out until the specimens failed. The DIC images were analysed at 50% of the fatigue life and at the point just before failure to determine whether the DIC system accurately indicated the strain concentration at the same point where the specimens failed. Experimental data from the study shows that the DIC system could accurately predict the point of failure at the fatigue half-life in only 10% of the test specimens that were investigated. The DIC system was able accurately to predict the point of failure right before failure occurred in only 25% of the test specimens that were investigated.

A Differential Protection Scheme Based on Improved DTW Algorithm for Distribution Networks With Highly-Penetrated Distributed Generation

Differential protection has been introduced into the distribution network to address the ineffectiveness of traditional protection due to the uncertainties of power flow caused by the access of multiple inverter-interfaced distributed generation (IIDG). Designed for lower data synchronization costs, this paper proposes a novel differential protection scheme based on improved dynamic time warping (DTW) distance. The proposed algorithm can effectively alleviate the singularity caused by DTW’s excessive X-axis distortion through relaxation search and derivative estimation and minimize the impact of data synchronization errors and data loss. Based on the proposed algorithm, the protection scheme combined with the feeder terminal unit (FTU) for fast fault isolation is designed, which can make full use of the existing equipment and reduce costs. Moreover, multiple influencing factors considered in this scheme, including transition resistance, penetration rate, and output intermittency of IIDG, variable network topology, underground cables, and hybrid lines. The test results demonstrate that the proposed protection scheme can effectively isolate short-circuit faults in various scenarios.

Removal of strong noise in magnetotelluric data using grey wolf optimized wavelet threshold

AbstractTraditional magnetotelluric signal processing usually uses time–frequency transformation method. Wavelet is also a time–frequency transformation method that used to suppress the magnetotelluric noise. However, the selection of the threshold is very significant, and the unsuitable threshold will lead to excessive distortion of the reconstructed signal. Thus, we propose a method for magnetotelluric noise suppression using grey wolf optimized wavelet threshold. First, the magnetotelluric signal is decomposed by wavelet with appropriate wavelet basis and decomposition layers. The generalized cross‐validation criterion is used as the fitness function of grey wolf optimizer algorithm, which optimizes the threshold of each decomposition layer. Then, the detail coefficients of each layer and the maximum layer of the approximation coefficients are used in the optimized threshold. Next, the inverse wavelet transform is performed. Finally, the noise contour is obtained through iteratively searching for the optimal threshold, and the useful magnetotelluric signal is reconstructed. Simulation experiments and measured magnetotelluric data processing show that the large‐scale interference can effectively be suppressed, and the reconstructed magnetotelluric signal retains the more abundant low‐frequency of useful information. Compared with the remote reference method, fixed threshold method and Birge–Massart layered threshold method, the proposed method realizes the wavelet denoising with adaptive threshold selection in the magnetotelluric noise suppression. The results obtained show smoother and more continuous apparent resistivity–phase curves, which verifies the effectiveness of the optimization.

Simulation of the hemispherical forming process of a woven fabric with two different material models

The anisotropic hyperelastic model (MAT_249) and Non-Orthogonal Model (MAT_293) are the material models developed recently to simulate the forming process of dry fabric and fabric-reinforced thermoplastic prepregs. In this study, the prediction capabilities of these two models in terms of shear angle distribution and boundary profile of the deformed fabric are compared over a hemispherical forming simulation of a plain weave E-glass fabric reinforcement. According to the results, in the simulation performed with MAT_293, it is seen that excessive distortions occur in the meshes at the advanced stages of the deformation in the fabric. In addition, after a certain punch stroke, the shear angle distribution obtained with MAT_293 starts to deviate rapidly from realistic results. MAT_249 produces consistent results even in large deformations.

Investigations on the local structure and the spin Hamiltonian parameters for Cu2+ in xCuO-(68-x)V2 O5 -32TeO2 glasses.

The defect structure, spin Hamiltonian parameters (SHPs: anisotropic factors and and the hyperfine structure constants and ), and their compositional dependence of in ( = 5, 10, 20, 30 mol%) glasses are quantitatively analyzed by using the higher-order perturbation formula of octahedral complex with tetrahedral elongation distortion. Due to the Jahn-Teller effect, the group is subjected to tetragonal elongation distortion of varying degrees. , and show nonlinear changes with the concentrations of . When = 10 mol% CuO, the degree of distortion ( ) is the smallest; when = 30 mol% CuO, the degree of distortion ( ) is the largest, which indicates that excessive distortion leads to the appearance of -axis oxygen vacancies and the coordination number of copper ions from six to four. The increasing tendency of the evaluated and reveals decreasing covalency of the whole glass system. Present theoretical studies would be useful to the explore the structural properties and optical applications of glass with different concentrations.

Multi-scale Fusion of Stretched Infrared and Visible Images.

Infrared (IR) band sensors can capture digital images under challenging conditions, such as haze, smoke, and fog, while visible (VIS) band sensors seize abundant texture information. It is desired to fuse IR and VIS images to generate a more informative image. In this paper, a novel multi-scale IR and VIS images fusion algorithm is proposed to integrate information from both the images into the fused image and preserve the color of the VIS image. A content-adaptive gamma correction is first introduced to stretch the IR images by using one of the simplest edge-preserving filters, which alleviates excessive luminance shifts and color distortions in the fused images. New contrast and exposedness measures are then introduced for the stretched IR and VIS images to achieve weight matrices that are more in line with their characteristics. The IR and luminance components of the VIS image in grayscale or RGB space are fused by using the Gaussian and Laplacian pyramids. The RGB components of the VIS image are finally expanded to generate the fused image if necessary. Comparisons experimentally demonstrate the effectiveness of the proposed algorithm to 10 different state-of-the-art fusion algorithms in terms of computational cost and quality of the fused images.

Topology optimization of scale-dependent non-local plates

The main objective of this work is to extend finite element-based topology optimization problem to the two-dimensional, size-dependent structures described using weakly non-local Cosserat (micropolar) and strongly non-local Eringen’s theories, the latter of which finds an application for the first time, to the best of Authors’ knowledge. The optimum material layouts that minimize the structural compliance are attained by means of Solid Isotropic Material with Penalization approach, while the desired smooth, mesh-independent, binary solutions are obtained using density filter accompanied by volume preserving Heaviside projection method. The algorithms are enhanced by including an element removal and reintroduction strategy to reduce the computational cost, and to prevent spurious excessive distortion of elements with very low density. Example problems of practical importance are investigated under the assumption of linear elasticity to validate the code and to clearly demonstrate the influence of internal length scales and different non-locality mechanisms on final configurations. Obtained macro-scale optimum topologies admit the characteristics of corresponding continuum theories, and appear to be in agreement with the mechanical response governed by particle interactions in micro/nanoscale.

Understanding of scratch behavior of an automotive coating system: Experiments and finite element analysis

As one of the most important components of a vehicle, the automotive coating system is typically a multi-layer polymeric structure with complex scratch damage patterns. This work is the first one to systematically investigate the scratch performance of an automotive coating system via experimental and numerical approaches. To achieve this end, uniaxial tensile tests are firstly carried out to acquire the basic mechanical properties of paint films at different strain rates. Then, a series of scratch tests are conducted in accordance with ASTM D7027/ISO 19252 standards, and the damage features are identified. In addition, the effects of scratch speed, loading rate, and stylus type are experimentally investigated. Afterwards, a finite element approach for scratch simulations is developed, which includes a rate-dependent constitutive model calibrated using the uniaxial tensile tests, a tied interface algorithm for efficient connection between coating and substrate, and an interior contact method to avoid excessive element distortions. Eventually, with the aid of the presented numerical approach, the damage patterns observed in scratch tests are numerically explained, and the scratch damage process is reasonably surmised. The presented approaches and findings can contribute to the development of anti-scratch automotive coating structures.

Enhanced fatigue performance of tandem MIG 5083 aluminium alloy weld joints by heat sink and static thermal tensioning

In this work, tandem metal inert gas (MIG) welding using double torches with each torch contained a single wire feed was conducted to join AA5083 aluminium alloy plates. In order to minimise excessive welding distortion and residual stress and hence fatigue crack propagation rate due to high heat input, two methods for minimisation of welding distortion and residual stress, namely heat sink and static thermal tensioning (STT) treatments were applied during welding. The tandem MIG processes were conducted by locating two torches at a distance of 100 mm from each other with and without the treatments. Furthermore, welding distortion, residual stress, microstructure, hardness distribution, tensile strength and fatigue crack propagation were characterised and evaluated. Results showed that the use of heat sink effectively reduced fatigue crack propagation rate of the tandem weld, especially at low ΔK below 6 MPa√m. This fatigue crack propagation inhibition in the heat sink treated weld could be linked to its fine grained equiaxed structure and compressive residual stress. However, in term of welding distortion reduction, heat sink treatment seemed to be less effective compared to STT treatment. The beneficial effect of heat sink and STT in minimising welding distortion and residual stress was attributed to thermal tensioning due to temperature gradient and it is discussed in the present study.

Study on the effect of multi-point stretch-bending processing conditions on the section distortion of complex cross-sectional parts

Section distortion is a common defect in plastic forming, however, excessive section distortion will affect the actual use of the workpiece. In this paper, the finite element software ABAQUS is used to simulate the multi-point flexible stretch-bending process. Processing parameters are important factors in the forming process of the profile, so this paper discusses the effects of three processing parameters, namely the effects of pre-stretching amount, pro-stretching amount and friction coefficient on section distortion under different bending radius, taking the complex cross-sectional T-profile as an example. And the validity of the simulation results is verified by comparing with the experimental results and the simulation results. At the same time, the upper limit value of section distortion is given according to the actual assembly and use of aluminium profile components of high-speed train head frame, and the minimum bending radius (i.e., processing limit) for which the section distortion does not exceed the given value under different process parameters is explored and used for practical production guidance.

Forecasting of voltage disturbances at the beginning of ferroresonance phenomena in power systems using by a new approach of long-short term memory (LSTM): LSTM for Ferroresonance in power systems

Ferroresonance is an unexpected, continuous, and undesirable event that causes excessive growth and distortion in the voltage and current waveform, whose cause is unknown and suddenly develops in power systems. To take precautions against the ferroresonance phenomenon, it is necessary to be able to predict how the distortions in the ferroresonance voltage will continue. Today, the ferroresonance problem has not been fully solved yet and more scientific studies are still needed. In this study, a new approach of an LSTM network has been developed that predicts the irregular and excessively large-amplitude continuing behavioral disturbances of the phase voltage in a real electrical power network exposed to ferroresonance. As a result of the study, the ferroresonance-voltage continuing in distorted waveform was estimated with an error of 0.0346 according to the Mean Absolute Percent Error (MAPE). The training data used in the study is only about 5% of all predicted ferroresonance voltage data. The successful estimation of 95% of the Ferreroresonance voltage using only about 5%, proves the success of the LSTM model applied with a new approach for the study.

Automated Log Data Analytics Workflow – The Value of Data Access and Management to Reduced Turnaround Time for Log Analysis

The oil and gas industry of today is undergoing rapid digitalization. This implies a massive effort to transform standard work procedures and workflows into more efficient practices and implementations using machine learning (ML) and automation. This will enable geoscientists to explore and exploit vast amounts of data quickly and efficiently. To address these current industry challenges, we propose a pilot well-log database in HDF5 (Hierarchical Data Format version 5) format that can be continuously extended if new data become available. It also provides versatility for data preparation for further analysis. We show an alternative way to store and use log files in a hierarchical structure that is easy to understand and handle by research institutes, companies, and academia. We also touch upon well-log depth matching, a long-standing industry challenge, to synchronize data from different logging passes to a single depth reference. Having a robust automated solution for depth matching is important to facilitate the use of all available data in a depth interval for analysis by ML. We propose an automatic well-log depth-matching workflow capable of handling multiple log types simultaneously and its integration with the database. The updated depth-matched logs are added to the database with their corresponding metadata, giving the geoscientist full control. We implemented two algorithms—classical cross correlation combined with a scaling factor to simulate stretch-squeeze effects and a constrained dynamic time warping (DTW). Our results indicate that the classical cross correlation outperforms the warping for both robustness and speed when the DTW is constrained to avoid excessive signal distortion and when the number of processed curves increases, respectively. Some limitations of our approach are related to large changes in the log patterns between the runs, as well as the assumption of negligible depth shift between log types within the same run. The cross correlation also allows a consistent application of depth matching to the metadata. This prototype workflow is tested using two wells from the Norwegian North Sea. We see the potential for extending this automatic database-processing workflow to give geoscientists access to all the data to improve interpretation.

Mesoscopic scale simulation and wear investigation of self-lubricating fabric liner based on representative volume element

As the self-lubricating layer of self-lubricating spherical plain bearings, fabric liner shows obvious heterogeneous anisotropic characteristics, so it is a technical difficulty to predict its wear properties. In this paper, the continuous wear of self-lubricating fabric liner was simulated based on the mesoscopic scale wear model. The macroscopic wear properties of the fabric liner were characterized by establishing a representative volume element, and subsequently imposing periodic boundary restrictions on periodic surfaces. In order to avoid excessive mesh distortion, voxel grids meshing method was used, and then continuous wear of the heterogeneous material was realized by adjusting node coordinates and combining nodes. Detailed comparison between simulation prediction results and wear test data of fabric liner was made. The good correlation of the results confirmed that the mesoscopic scale wear model could be used in accurately predict the tribological performance of fabric composite.

Tailoring alloy 718 laser directed energy deposition process strategies for repair applications

Laser-based directed energy deposition (LDED) for repair and sustainment has become a viable alternative to replace or complement traditional repair applications. Many a time, thin-walled structures cannot be repaired because of the heat intensive repair operations, which lead to excessive distortion or degradation of the parent material. To overcome repair challenges related to thin-walled structures, a low-energy process strategy with powder feedstock has been developed to reduce the heat-affected zone, reduce distortion, and produce a microstructure yielding higher microhardness values. On the other side of the repair spectrum, much larger surfaces may also need attention. In this case, a high-deposition rate process strategy may be more suitable to reduce lead-time and cost. To accommodate larger repairs, a high-deposition rate process strategy using wire feedstock has been developed. The high-deposition rate strategy is shown to be more cost-effective provided the target application and part geometry can accommodate the high-energy process. Validating these LDED repair strategies has been accomplished by analyzing the resulting distortion, presence of flaws or defects, microhardness, microstructure, and tensile properties. The process control offered by LDED through the ability to tailor the process-structure-property relationships of a material system depending on component geometry and application has put a new tool in place addressing many concerns related to traditional arc-based repair processes.

Decentralization of environmental management and enterprises’ environmental technology innovation: evidence from China

ABSTRACT We construct an environmental decentralization index and use spatial econometric modeling to test the government’s role in promoting environmental technology innovation at the enterprise level. The results show that a moderate increase in the degree of environmental decentralization is conducive to promoting local enterprises’ environmental innovation and avoiding excessive distortions caused by externalities. Further investigation reveals that the effect is more pronounced when local tax competition is taken into account. However, administrative decentralization and supervision decentralization have different effects on enterprises’ environmental innovation. An increase in administrative decentralization has a negative impact on enterprise innovation, and environmental supervision should be more focused on the central government, which can help avoid excessive distortion caused by externalities. Our analysis is of certain reference value for understanding the influence of rational allocation of environmental protection functions among different levels of government on enterprises’ environmental innovation activities.

Enabling High-Fidelity Ultra-Wideband Radio Channel Emulation: Band-Stitching and Digital Predistortion Concepts

Channel emulators are the key instrument in radio performance testing. The fidelity of the emulated channel with respect to the target channel models directly affects the credibility of the testing result. In practice, due to some non-idealities of the radio-frequency (RF) components of the emulator, its intrinsic frequency response, i.e., the response of the bypass mode, may not be flat over the frequency band of interest, which leads to an excessive distortion over the target channel models, and hence a less accurate emulated channel. This problem could be even more profound when the emulator engages the band-stitching process for a wider-bandwidth emulation, especially in the transition frequency band between adjacent sub-bands. To enable high-fidelity band-stitched or even ultra-wideband channel emulation, we propose a novel digital pre-distortion concept in this work, where we pre-distort the target channel models according to the measured intrinsic response of the emulator to compensate for its effect on the emulated channel. The proposed method is numerically assessed with measured intrinsic responses of a commercial emulator, and the magnitude and phase variations of the stitched channel reduce by one order of magnitude in comparison to that of the conventional method.

Cost uncertainty in an oligopoly with endogenous entry

AbstractHow does cost uncertainty affect the welfare consequences of an oligopoly? To answer this question, we investigate a Cournot oligopoly in which firms produce a homogeneous commodity and market entry is feasible. Marginal costs are unknown ex ante, that is, prior to entering the market. They become public knowledge before output choices are made. We show that uncertainty induces additional entry in market equilibrium and also raises the socially optimal number of firms. Since the first change dominates, the excessive entry distortion is aggravated. This prediction is robust to various extensions of the analytical setup. Furthermore, the welfare loss due to oligopoly tends to increase with uncertainty.