Vector Boundary Research Articles

Thrust ripple suppression analysis of moving-magnet-type linear synchronous motor based on independent coil

In this paper, a novel thrust ripple suppression method for multi-secondary permanent magnet synchronous linear motor based on independent coil structure is proposed. Independent coil structure can realize independent power supply for each coil by changing the driving mode of the coils. Combined with the new power supply strategy, the detent and electromagnetic force fluctuation can be suppressed. Firstly, the cogging and end force of moving-magnet-type linear motor are separated by periodic and vector boundary conditions and harmonic analysis is carried out. An analytical model of air gap magnetic field based on virtual magnetic poles is established to solve the back EMF and electromagnetic force fluctuation of the motor. The generation mechanism and harmonic of electromagnetic force fluctuation are analyzed. A multi-secondary PMLSM based on independent coil is proposed, the principle of suppressing motor thrust ripple is expounded, and the coupling effect between modules is analyzed. Finally, a zero-crossing power supply strategy is proposed. The simulation and experimental results show that multi-secondary independent coil PMLSM can effectively suppress the detent and electromagnetic force fluctuation.

A novel immersed boundary approach for irregular topography with acoustic wave equations

Irregular terrain has a pronounced effect on the propagation of seismic and acoustic wavefields but is not straightforwardly reconciled with structured finite-difference (FD) methods used to model such phenomena. Accurate wavefield simulation is paramount in subsurface imaging applications such as reverse time migration and full-waveform inversion, requiring suitable topography handling. Methods currently detailed in the literature generally are limited in scope application-wise or nontrivial to apply to real-world geometries. A general immersed boundary treatment capable of imposing a range of boundary conditions in a relatively equation-agnostic manner has been developed, alongside a framework implementing this approach to complement emerging code-generation paradigms. The approach is distinguished by the use of N-dimensional Taylor-series extrapolants constrained by boundary conditions imposed at some suitably distributed set of surface points. The extrapolation process is encapsulated in modified derivative stencils applied in the vicinity of the boundary, using hyperspherical support regions. This method ensures boundary representation is consistent with the FD discretization. Furthermore, high-dimensional and vector boundary conditions can be applied without approximation prior to discretization. A consistent methodology can thus be applied across free and rigid surfaces with first- and second-order acoustic wave equation formulations. Application to both equations is demonstrated, and numerical examples based on analytic and real-world topography implementing free and rigid surfaces in 2D and 3D are presented. Numerical examples and convergence tests demonstrate the accuracy of boundary treatments devised by the prescribed approach, their suitability to practical applications, and the feasibility of automatically generating treatments to suit each case.

The spatiotemporal epidemiological study on human brucellosis in shenyang, China from 2013 to 2022

BackgroundEpidemiological characteristics of human brucellosis (HB) have changed over the last decade. In this study, we depicted the spatiotemporal features of HB in Shenyang, China, from 2013 to 2022 and the objective was to visualise spatiotemporal patterns and identify high-risk regions with the purpose to provide evidence for HB prevention and control. MethodsWe performed an observational epidemiological study using HB data obtained from the National Notifiable Disease Reporting System (NNDRS). Joinpoint regression analysis was employed to determine the changing trends in the annual incidence. A vector boundary map of Shenyang was used to visualise spatial distribution. Spatial autocorrelation was identified using both global and local Moran's autocorrelation coefficients, while hotspot areas were determined using the Getis-Ord statistic. ResultsA combined sum of 4103 HB cases were analysed, and the average level of annual incidence of HB was 5.52 per 100,000. The incidence of HB showed obvious seasonality, with a notable peak observed from April to July (summer peak). The annual incidence in Shenyang has been on the rise since 2013, with an annual percentage change (APC) of 6.39% (95%CI 1.29%, 12.39%). Xinmin County exhibited the most elevated average annual incidence rate, with Faku County ranking second. The average annual incidence in rural areas exhibited a significantly greater disparity compared to suburban areas (P < 0.001), whereas the incidence rate in suburban areas demonstrated a significantly higher contrast when compared to urban areas (P < 0.001). A clustered distribution of the annual incidence of HB was observed for all years from 2013 to 2022. Abnormally high values were found in suburban areas, and no abnormally high values were found after 2017. The low-low clustering areas were found in urban as well as suburban areas from 2013 to 2022. Hotspots (P < 0.05) were located in rural areas, while cold spots (P < 0.05) were found in both urban and suburban areas. Since 2020, there have been no hotspots in Shenyang. ConclusionsRural areas are high-risk areas for HB and may be key to controlling HB epidemics. Although the annual incidence of HB in rural areas has increased, owing to the stability of spatial relationships and the disappearance of hotspots, there is little possibility of outbreaks; however, stricter monitoring should be applied in rural areas to prevent the emergence of new transmission routes.

Cooperation of multi-task segmentation and a graph convolutional network for object vector boundary extraction in remote-sensing imagery

ABSTRACT Identifying and vectorizing the object in the image is an important part of producing high-precision vector maps. Deep learning can automatically extract vector boundaries accurately, but it still does not satisfy the application requirements for boundaries. Clearer boundaries and more concise vector points are also important components that cannot be neglected in vectorization. Taking buildings as the research object, we introduce a cooperative neural network of multi-task segmentation and graph convolution to improve the extraction of buildings by strengthening the boundaries and strategically selecting key points. We design a multi-task neural network to extract and optimize the vector boundaries, whose key points can be selected and refined with a graph convolutional network. In addition, to improve the coherence between features and jointly multi-information, we design a mutual-supervision loss for our method. Our experimental results show that our method effectively extracted buildings and outperformed several equal methods on the different public datasets.

Polarization-dependent boundary modes in nonlinear mechanical metamaterials

The boundary modes of highly distorted mechanical metamaterials exhibit obvious nonlinear effects. However the characteristics of vector boundary modes (boundary modes with two coupled components—translation and rotation) of nonlinear mechanical metamaterials have not been revealed, which severely limits their applications in vector deformation controls of robots and intelligent structures. In this work, by building the continuous and discrete models of nonlinear mechanical metamaterials with vector couplings, an analytical framework for soft modes of rotation-cross vector metamaterial chains is proposed. An anomalous nonlinear phenomenon is found, namely, the polarization indices (the ratio of displacement to the increment of rotation angle) of all nodes are equal, which is further verified by the experiment. Specially, the results show that the morphology of the vector boundary mode can be tuned through adjusting the polarization index. Based on this, existence conditions of static-topological-soliton boundary modes under couplings of translation and rotation are revealed explicitly, and the results further show that the vector boundary modes based on static-topological-solitons are robust and immune to structural imperfections, which is crucial to achieve precise vector deformation controls. These novel rules and phenomena presented in this work can provide new ideas and important bases for vector deformation controls of nonlinear mechanical metamaterials and their applications in lightweight robots and intelligent structures.

On contact problems with a deformable punch and variable rheology

The paper presents for the first time one of the methods for studying and solving contact problems with a deformed stamp for those cases when there is a need to change the rheology of the stamp material. It is based on a new universal modeling method previously published by the authors, which is used in boundary value problems for systems of partial differential equations. With its help, solutions of complex vector boundary value problems for systems of differential equations can be decomposed into solutions of scalar boundary value problems for individual differential equations. Among them, the Helmholtz equations are the simplest. Solutions to scalar boundary value problems are represented as fractals, self-similar mathematical objects first introduced by the American mathematician B. Mandelbrot. The role of fractals is performed by packed block elements. The transition from systems of differential equations in partial derivatives to individual equations is carried out using the transformation of academician B. G. Galerkin or representation by potentials. It is known that the solutions of dynamic contact problems with a deformable stamp of complex rheology are cumbersome, and their study is always difficult. The problem is complicated by the presence of discrete resonant frequencies in such problems, which were once discovered by Academician I. I. Vorovich.

Inversion of Glacier 3D Displacement from Sentinel-1 and Landsat 8 Images Based on Variance Component Estimation: A Case Study in Shishapangma Peak, Tibet, China

Offset tracking technology is widely studied to evaluate glacier surface displacements. However, few studies have used a cross-platform to this end. In this study, two heterogeneous data sources, Sentinel-1 and Landsat 8, from January 2019 to January 2021, were used to estimate the offset, and then the optimal estimation of the 3D deformation rate of a Himalayan glacier was obtained based on the joint model of variance component estimation. The results show that the maximum deformation rates of the glacier in the east–west direction, north–south direction, and vertical direction are 85, 126, and 88 mm/day, respectively. The results of the joint model were compared and analyzed with the results of simultaneous optical image pixel offset tracking. The results showed that the accuracy of the joint solution model increased by 41% in the east–west direction and 36% in the south–north direction. The regional flow velocity of the moraine glacier after the joint solution was consistent with the vector boundary of the glacier cataloging data. The time-series results of the glacier displacement were calculated using more images. These results indicate that the joint solution model is feasible for calculating temporal glacier velocity. The model can improve the time resolution of the monitoring results and obtain further information on glacier characteristics. Our results show that the glacier velocity is affected by local terrain slope and temperature. However, there is no absolute positive correlation between glacier velocity and slope. This study provides a reference for the joint acquisition of large-scale three-dimensional displacement of glaciers using multi-source remote sensing data and provides support for the identification and early warning of glacier disasters.

Integration of the modified double layer potential of the vector boundary element method for eddy current problems

The boundary element method for the eddy current problem (BEM-ECP) was proposed in a number of papers and is applicable to important tasks such as the problem of inductive heating and transmission of electromagnetic energy. BEM-ECP requires the construction of a system of linear algebraic equations in which the matrix is inherently dense and is constructed out of element matrices. For the process of the element matrix computation, two cases are normally considered: far-field interaction and near-field interaction, because the construction of element matrices requires integration of a singular function. In this article, we suggest a transform that allows computing the matrix components of the near-singular interaction part while implementing only the single and double layer potentials. The previously suggested modified double layer potential (MDLP) can be integrated by means of this transform, which simplifies the program implementation of BEM-ECP significantly. Solving model problems, we analyse the drawbacks of the previously suggested approach. This analysis includes the proof of the MDLP singularity that makes the integration of this potential a rather difficult task without the help of our transform. The previously suggested approach does not work well with surfaces that are not smooth. Our approach does consider such cases, which is its main advantage. We demonstrate this on the model problems with known analytical solutions.

Rapid monitoring of abandoned farmland and information on regulation achievements of government based on remote sensing technology

Farmland abandonment has become a worldwide phenomenon, and remote sensing technology has been used to monitor this phenomenon. However, information on only the final net change in abandoned farmland can be obtained based on existing methods, and the various components and contributions of government regulation cannot be identified. These methods therefore cannot meet the needs for the management of abandoned farmland or related policy-adjustments. Therefore, this study uses Longyan Prefecture in China as the study area, and GF-1 satellite images as the main data source, to propose a new rapid monitoring method for abandoned farmland that can reflect and separate the government's regulatory contribution to changes in farmland abandonment. The results show that the abandoned farmland in the study area generally expanded from 2015 to 2019. Despite this observation, government regulation has made some achievements. In 2015–2017 and 2017–2019, 41.72% and 41.67% of the new increased abandoned farmland was offset, respectively, delaying the process of farmland-abandonment. However, the achievement of government regulation decreased by 23.86% in 2017–2019 compared with that during 2015–2017. The results show that our method can reflect the process of farmland abandonment and the contribution of government regulation, can be applied on a large scale, and provides comparable results among regions. Offsetting the newly increased abandoned farmland by improving the contribution of government regulation is an important and direct way to curb farmland abandonment, but special attention should be given to the scientific nature and full implementation of policies in actual management practices. Data AvailabilityThe Chinese GF-1 Satellite images were downloaded from the China Center for Resources Satellite Date and Application website (http://www.cresda.com/EN/). The Advanced Land Observing Satellite (ALOS) data downloaded from the National Aeronautics and Space Administration (NASA) (https://search.asf.alaska.edu/#/). The vector boundary of the research area was obtained from the Chinese Resource and Environment Science and Data Center (https://www.resdc.cn/). Most of the field samples for evaluating the accuracy of the land classification results downloaded from Global Change Data & Discovery (http://www.geodoi.ac.cn/WebEn/doi.aspx?Id=1502).

Intelligent Diagnosis Method for New Diseases Based on Fuzzy SVM Incremental Learning.

The diagnosis of new diseases is a challenging problem. In the early stage of the emergence of new diseases, there are few case samples; this may lead to the low accuracy of intelligent diagnosis. Because of the advantages of support vector machine (SVM) in dealing with small sample problems, it is selected for the intelligent diagnosis method. The standard SVM diagnosis model updating needs to retrain all samples. It costs huge storage and calculation costs and is difficult to adapt to the changing reality. In order to solve this problem, this paper proposes a new disease diagnosis method based on Fuzzy SVM incremental learning. According to SVM theory, the support vector set and boundary sample set related to the SVM diagnosis model are extracted. Only these sample sets are considered in incremental learning to ensure the accuracy and reduce the cost of calculation and storage. To reduce the impact of noise points caused by the reduction of training samples, FSVM is used to update the diagnosis model, and the generalization is improved. The simulation results on the banana dataset show that the proposed method can improve the classification accuracy from 86.4% to 90.4%. Finally, the method is applied in COVID-19's diagnostic. The diagnostic accuracy reaches 98.2% as the traditional SVM only gets 84%. With the increase of the number of case samples, the model is updated. When the training samples increase to 400, the number of samples participating in training is only 77; the amount of calculation of the updated model is small.

Fine Object Change Detection Based on Vector Boundary and Deep Learning With High-Resolution Remote Sensing Images

Remote sensing (RS) image change detection analyzes and determines the difference of surface states at different times. Polygons are common vector data to express the surface states in geographic information systems. However, the production and updating of polygons typically depend on manual procedures, which costs significant time and human resources. This article proposes an automatic polygon change detection method based on high-resolution RS images and deep learning image classification. First, bitemporal images are segmented by boundary-preserved masking simple linear iterative clustering based on the boundaries and categories of polygons. Then, the labeled dataset is automatically generated by adaptively cropping image segments according to the center-to-boundary distance. Date-1 data are used to train the model and purified by two different classifiers to improve the model performance. Date-2 data, whose categories are predicted, are the basic units of change detection analysis. Furthermore, an improved bilinear convolutional neural network with a reduced number of parameters and training time is applied to fine-grained classification. Finally, the changed polygons can be retrieved based on category comparison and post-processing. In our experiments, two real datasets with high-resolution RS images and land-use polygons are employed to validate the effectiveness of our proposed method. The results are examined by visual interpretation and show that the precision and recall rates for dataset 1 are 90.5% and 93.1%, respectively, while those for dataset 2 are 87.6% and 90.8%. Through our method, the existing polygons can be used appropriately, and the difficulty of data updating can be reduced.

Boundary Extraction of Urban Built-Up Area Based on Luminance Value Correction of NTL Image

Nighttime light image (NTL) is an effective data for urban built-up area. Due to the shortcomings of low resolution and the blooming effect of NTL, the extraction result of the original NTL image is not ideal. We combined point of interest (POI), road network, and land surface temperature (LST) data to propose the POI, road density, and LST-adjusted NTL Index (PRLANI) to correct the luminance value of the NTL image. The proposed index was verified by NTL images of different developed areas and different spatial resolutions. The threshold segmentation method was used to obtain the result of the built-up area extraction from the original NTL and the image modified by the PRLANI. Then, we generated the vector boundary from the built-up area. Taking Changchun urban area as an example, the kappa coefficient based on PRLANI-VIIRS is 0.802, which is 0.293 higher than of NTL-VIIRS. The kappa coefficient based on PRLANI-LJ is 0.838, which is 0.179 higher than that of NTL-LJ. The results show that: the PRLANI can effectively suppress the blooming effect and improve the overestimation of the built-up area caused by light dimming; the PRLANI can enhance the weak light signal in the original NTL image and compensate for the missing information of the built-up area; and the fusion of road network data improves the extraction accuracy and refines the internal structure of built-up area, especially the NPP/VIIRS. The vector boundary was consistent with the built-up area range of reference data, and the visualization effect was good.

On the properties of topological discretization of solutions to boundary value problems

This paper seems to show for the first time that Packed block elements used in solving a boundary value problem by the block element method are elements of a discrete topological space. Since the solutions to boundary value problems belong to a discrete topological space instead of equations, it is possible to obtain a solution in a new coordinate system without having to study the boundary value problem. The block element method used in problems of continuum mechanics, which has a connection with topology, can become more effective in applications if the General properties of topological spaces studied in detail are used more deeply. One of the important properties of topology is the existence of discrete topological spaces. Their characteristic property is that an element that represents the Union of any set of elements in a topological space belongs to a discrete topological space. Belonging of discrete block elements to a topological space means that it is possible to completely cover any area with a piecewise smooth boundary and, thus, an exact solution of the boundary problem in it. In topological space, continuous geometric transformations and transitions to new coordinate systems are possible. In this paper, it is shown that Packed block elements generated by the boundary value problem for the Helmholtz equation, are elements of a discrete topological space. Given that scalar solutions of the Helmholtz equation can describe solutions to a fairly wide set of vector boundary value problems, this property also applies to solutions of more complex boundary value problems. The constructions made for the homogeneous Helmholtz equation remain valid for the inhomogeneous one.

Stress state of an elastic rectangular domain under steady load

The dynamic elasticity problem for rectangular domain is presented at this paper. The conditions of ideal contact are given at the lateral sides and bottom edge of the domain; the upper edge is loaded by normal stress. Problem is formulated as the boundary value problem in steady-state case. It was necessary to find the wave field of the rectangular domain. The Fourier transform was applied to formulated problem and reduced it to one dimensional vector boundary problem. The last one was solved with the method based on matrix differential calculations which was successfully applied earlier to solve the analogous static problem Pozhylenkov O. V. (2019). According to this procedure of the solving the exact solution of the vector boundary problem was constructed in transform domain in the explicit form. Application of the inverse Fourier transform finalized the deriving of the stated problem solution. The analyses of wave field of rectangular domain depending on different load types, frequency values and domain size was done.

Block element method in solving vector boundary problems using scalar

Block element method in solving vector boundary problems using scalar

Топологическая дискретизация решений граничных задач механики сплошных сред

This paper seems to show for the first time that Packed block elements used in solving a boundary value problem by the block element method are elements of a discrete topological space. Since the solutions to boundary value problems belong to a discrete topological space instead of equations, it is possible to obtain a solution in a new coordinate system without having to study the boundary value problem. The block element method used in problems of continuum mechanics, which has a connection with topology, can become more effective in applications if the General properties of topological spaces studied in detail are used more deeply. One of the important properties of topology is the existence of discrete topological spaces. Their characteristic property is that an element that represents the Union of any set of elements in a topological space belongs to a discrete topological space. Belonging of discrete block elements to a topological space means that it is possible to completely cover any area with a piecewise smooth boundary and, thus, an exact solution of the boundary problem in it. In topological space, continuous geometric transformations and transitions to new coordinate systems are possible. In this paper, it is shown that Packed block elements generated by the boundary value problem for the Helmholtz equation, are elements of a discrete topological space. Given that scalar solutions of the Helmholtz equation can describe solutions to a fairly wide set of vector boundary value problems, this property also applies to solutions of more complex boundary value problems.

Application of the Block Element Method in a Certain Boundary Value Problem of Academician I.I. Vorovich

By the example of the boundary value problems—the vector problem (set of differential equations) and the scalar problem (single equation)—the features of their solutions by the block element method are demonstrated. In this method, the solutions can be presented in packed and unpacked forms. Here, these properties are explained in comparison by the example of two problems, the vector and scalar boundary value problems, solved for the first time exactly by the block element method. The vector boundary value problem was formulated previously by Academician I.I. Vorovich to a student, and its exact solution is given in this study.

Influence of rotor solidity on trailing edge noise from wind turbine blades

Noise prediction from streamlined bodies such as wind turbine blades can be predicted accurately using CFD computations that use spatio-temporal turbulence models at the expense of high computational power. In this work, empirical methods proposed from BPM, Grosveld and Lowson are used to compute numerically to analyse the influence of rotor solidity factor on broadband trailing edge noise from a 2 MW horizontal axis wind turbine with a blade length of 37 m. Inputs to acoustic solver are the velocity vector field and boundary layer data which are obtained using blade element momentum and X-Foil. The outputs from acoustic solver are directivity and far field sound pressure on a receiver located at distance of 120 m from tower base. The results have shown that for a wind speed of 10 m/s measured at 10 m above ground, sound power level was found to increase between mid-bands to high frequencies for all three methods. Rotor solidity effect was illustrated at constant rotational speed of 17 RPM and receiver height of 0.5 m located in downwind position. A minimum difference of 1.5dBA was found at f ~ 100 Hz for Lowson method and maximum of ~ 2.8dBA at 1 kHz between two and three blade rotor. For BPM and Grosveld methods however, the sound levels were ~ 5dBA lower for two blade rotor than three blade rotor between f ~ 100 Hz and f ~ 1 kHz. The study also demonstrated that as number of blades increase by integral multiples, the effect on noise radiation from trailing edge of blades increase by 2-5dBA due to amplitude modulation.

Stability of mathematical models of the main problems of the anisotropic theory of elasticity

The boundary problems of the complex-variable function theory are effectively used while investigating equilibrium of homogeneous elastic mediums. The most complicated systems of the boundary value problems correspond to the case when an elastic body exhibits anisotropic properties. Anisotropy of the medium results in the drift of boundary conditions of the function that in general disrupts analyticity of the functions of interest. The paper studies systems of the boundary value problems with drift for analytic vectors corresponding to the primal elastic problems (first, second and mixed problems). Systems of analytic vectors with drift are reduced to equivalent systems of Hilbert boundary value problems for analytic functions with weak singularity integrators. The obtained general solution of the primal boundary value problems for the anisotropic theory of elasticity allows us to check the above problems for stability with respect to perturbations of boundary value conditions and contour shape. The research is relevant as there is necessity to apply approximate numerical methods to the boundary value problems with drift. The main research result comes to be a proof of stability of the systems of the vector boundary value problems with drift for analytic functions on the Hölder space corresponding to the primal problems of the elastic theory for anisotropic bodies in the case of change in the boundary value conditions and contour shape.

The existence, uniqueness and asymptotic estimates of solutions for third-order full nonlinear singularly perturbed vector boundary value problems

In this paper, we discuss third-order full nonlinear singularly perturbed vector boundary value problems. We first present the existence of solutions for the nonlinear vector boundary value problems without perturbation by using the upper and lower solutions method and topological degree theory. Then the existence, uniqueness and asymptotic estimates of solutions for the singularly perturbed vector boundary value problems are established by constructing appropriate a lower solution–upper solution pair, as well as analysis technique. Some known results are extended.