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NSVineCopula: R package for modeling non-stationary multivariate dependence

Environmental Modelling and Software 2025年 190卷

作者： Zhang, Q. Li, Y.P. Huang, G.H. Huang, X.M. Wang, H. Wang, Z. Xu, Z.P. Wang, Y.Y. Shen, Z.Y. State Key Joint Laboratory of Environmental Simulation and Pollution Control School of Environment Beijing Normal University Beijing100875 China Department of Earth System Science Ministry of Education Key Laboratory for Earth System Modeling Institute for Global Change Studies Tsinghua University Beijing100875 China Institute for Energy Environment and Sustainable Communities University of Regina ReginaSKS4S0A2 Canada

A vine copula is a flexible method for multivariate dependence simulations that assumes stationarity. However, only a few studies have focused on non-stationarity and comprehensively developed nonstationary vine copula functions. In this study, a novel R package, NSVineCopula was developed and presented. Canonical-vine and Drawable-vine structure with 36 bivariate copula functions were considered in NSVineCopula. This package is capable of capturing non-stationary multivariate dependence, providing time-varying parameters for each bivariate copula, and quantifying the conditional probability. Notably, NSVineCopula provides a simple way for sampling non-stationary vine copulas. The capability of NSVineCopula was evaluated through two case studies: (1) agricultural drought risk assessment under compound dry-hot extreme conditions and water level prediction. The results demonstrate the advantages of NSVineCopula in non-stationary multivariate dependence analysis, and highlights the potential of NSVineCopula in many fields. Overall, NSVineCopula can provide valuable and robust functionalities for modeling nonstationary multivariate dependence. © 2025 Elsevier Ltd

关键词： Copula Multivariate dependence Non-stationarity R package Vine copula

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A Projection Method With Modular Grad-Div Stabilization for Inductionless Magnetohydrodynamic Equations Based on Charge Conservation

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Mathematical Methods in the Applied Sciences 2025年

作者： Yang, Yun-Bo Xia, Yande Department of Mathematics Yunnan Normal University Kunming China Yunnan Key Laboratory of Model Analytical Mathematics and Application Yunnan Normal University Kunming China Key Laboratory of Complex System Modeling and Application for Universities in Yunnan Yunnan Normal University Kunming China

In this paper, we proposed a fully discrete projection method with modular grad-div stabilization for solving the time-dependent inductionless magnetohydrodynamic equations. The method incorporates a minimally intrusive module into the classical projection method, serving as a postprocessing step, thereby enhancing solution accuracy and improving mass conservation. Additionally, a decoupled strategy is employed to separate the magnetic and fluid field functions from the original system. Since we only need to solve several linear subsystems at each time step, the numerical solutions can be obtained efficiently. In the spatial discretization, (Formula presented.) -conforming finite element pair is used to approximate the current density and electric potential, ensuring that the discrete current density is exactly divergence-free. Therefore, the designed numerical scheme maintains the features of linearization, decoupling, unconditional energy stability, charge conservation, and improved mass conservation. The unconditional energy stability and convergence of the algorithm are rigorously analyzed and proven. Numerical results are presented to verify the robustness of the algorithm with respect to the stabilization parameters and to demonstrate the performance of the scheme, particularly in terms of its stability and accuracy. © 2025 John Wiley & Sons Ltd.

关键词： Stabilization

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Error correction iterative finite element method based on charge-conservative for the stationary inductionless magnetohydrodynamic system

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ZAMM Zeitschrift fur Angewandte Mathematik und Mechanik 2025年第5期105卷

作者： Xia, Yande Yang, Yun-Bo Department of Mathematics Yunnan Normal University Kunming China Yunnan Key Laboratory of Model Analytical Mathematics and Application Yunnan Normal University Kunming China Key Laboratory of Complex System Modeling and Application for Universities in Yunnan Yunnan Normal University Kunming China

In this paper, we propose and analyze a new error correction iterative finite element method (FEM) based on charge-conservative for solving the stationary inductionless magnetohydrodynamic (MHD). The method consists of first solving the inductionless MHD equations by the Oseen iterative scheme to obtain an approximate solution, and then an error correction strategy is applied to control the error arising from the linearization of the nonlinear inductionless MHD equations. The proposed method not only retains the advantages of the classical Oseen iterative scheme but also leads to a rapid rate of convergence. It is shown that the convergence rate of the new method is greatly improved under the uniqueness condition. Stability analysis and error estimates are provided. Numerical results are presented to verify the applicability and effectiveness of the new method. © 2025 Wiley-VCH GmbH.

关键词： Nonlinear equations

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Dynamic analysis of rigid-flexible coupling spacecraft based on Euler parameters

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Scientific Reports 2025年第1期15卷 1-12页

作者： Ji, Yi Zhang, Huan School of Astronautics Harbin Institute of Technology Harbin 150001 China Frontier Science Center for Interaction between Space Environment and Matter Harbin 150001 China National Key Laboratory of Modeling and Simulation for Complex Systems Harbin 150001 China MOE Key Laboratory of Dynamics and Control of Flight Vehicle Beijing Institute of Technology Beijing 100081 China

With the development of aerospace technology, rigid-flexible coupling spacecraft with strong nonlinearity dominates, bringing huge challenges for numerical tools. This paper aims to accurately and quickly analyze the dynamic behavior of rigid-flexible coupling spacecraft. In our work, rigid body and flexible body are both described by Euler parameters for avoiding singular angles. Then, for this type of strong nonlinear dynamic system, the BN-stable method that is unconditionally stable for nonlinear initial value problems proposed by the first author is introduced to solve the transient responses. To keep the accuracy of the numerical rotation matrix, the relation between the angular velocity and Euler parameters, and the constraint in the level of velocity, are introduced to reformulate the original BN-stable method. Through the dynamic analysis for rigid satellite bodies and flexible solar wings, we find that the proposed strategy can effectively simulate the dynamic responses of spacecraft, and compared to the currently popular strategy, our strategy enjoys considerable advantages in accuracy, stability, and dissipation. © The Author(s) 2025.

关键词： BN-stability Dynamic analysis Euler parameters Rigid-flexible coupling Rotation matrix

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Evolutionary neural architecture search for automatically designing CNN-GRU-Attention neural networks for turntable servo systems

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Expert systems with Applications 2025年 283卷

作者： Xie, Cheng Xue, Bing Yang, Mingyi Zhang, Mengjie Xu, Zhigang Wang, Junyi Chen, Songlin Liu, Yang Shenyang Institute of Automation Chinese Academy of Sciences Liaoning Shenyang110169 China Centre for Data Science and Artificial Intelligence & School of Engineering and Computer Science Victoria University of Wellington Wellington6140 New Zealand University of Chinese Academy of Sciences Beijing101408 China National Key Laboratory of Modeling and Simulation for Complex Systems Harbin Institute of Technology Heilongjiang Harbin150001 China

Turntable servo systems are important experimental devices utilized in the semi-physical simulation and testing of aircraft. Building a model for turntable servo systems, which can accurately predict their operating states or behaviors, is important for the development and debugging of the whole servo control system. However, servo systems usually have complex nonlinear characteristics and external disturbances, which brings challenges to the accurate modeling of them. Therefore, this paper develops a modeling method for turntable servo systems by using CNN-GRU-Attention hybrid neural network models. The CNN-GRU-Attention model is used for compensating the nonlinear terms of the known dynamics model, thus effectively improving the modeling accuracy. Considering the complex architectures of the above hybrid model, an evolutionary neural architecture search (ENAS) algorithm is proposed accordingly, which can automatically design the architecture of the CNN-GRU-Attention models. During the designing process, a variable-length encoding strategy is proposed to represent the possible architectures, and novel crossover and mutation operators are proposed accordingly for the evolution of individuals. In addition, the real-time constraints are considered in the design of the search space, so that all the searched models can meet the real-time requirements. The experimental results show the CNN-GRU-Attention models obtained by the proposed ENAS algorithm achieve superior prediction performance over the peer competitors in most tasks. The effectiveness of the proposed method is further verified by analyzing the convergence and the search results. © 2025

关键词： Synchros

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A constructive method for approximating trigonometric functions and their integrals

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Applied Mathematics(A Journal of Chinese Universities) 2020年第3期35卷 293-307页

作者： CHEN Xiao-diao WANG Long-quan WANG Yi-gang Key Laboratory of Complex Systems Modeling and Simulation Hangzhou Dianzi UniversityHangzhou 310027China

This paper presents an interpolation-based method(IBM)for approximating some trigonometric functions or their integrals as *** provides two-sided bounds for each function,which also achieves much better approximation effects than those of prevailing *** principle,the IBM can be applied for bounding more bounded smooth functions and their integrals as well,and its applications include approximating the integral of sin(x)/x function and improving the famous square root inequalities.

关键词： Padéapproximant trigonometric function constructive method interpolation-based method two-sided bounds

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Intrinsic mode characteristic analysis and extraction in underwater cylindrical shell acoustic radiation

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Science China(Physics,Mechanics & Astronomy) 2013年第7期56卷 1339-1345页

作者： LIU QingYu FANG ShiLiang CHENG Qiang CAO Jin AN Liang LUO XinWei Complex Ship System Simulation Laboratory Key Laboratory of Underwater Acoustic Signal Processing (MoE) Southeast University

Target dimension is important information in underwater target classification. An intrinsic mode characteristic extraction method in underwater cylindrical shell acoustic radiation was studied in this paper based on the mechanism of shell vibration to gain the information about its dimension instead of accurate inversion processing. The underwater cylindrical shell vibration and acoustic radiation were first analyzed using mode decomposition to solve the wave equation. The characteristic of acoustic radiation was studied with different cylindrical shell lengths, radii, thickness, excitation points and fine structures. simulation results show that the intrinsic mode in acoustic radiation spectrum correlates closely with the geometry dimensions of cylindrical shells. Through multifaceted analysis, the strongest intrinsic mode characteristic extracted from underwater shell acoustic radiated signal was most likely relevant to the radiated source radius. Then, partial information about unknown source dimension could be gained from intrinsic mode characteristic in passive sonar applications for underwater target classification. Experimental data processing results verified the effectiveness of the method in this paper.

关键词： cylindrical shell mode decomposition acoustic radiation characteristic

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Optimization of All-Fiber Calibration-Free Wavelength-Modulated Laser Heterodyne system for Methane (CH4) Atmospheric Detection

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Microwave and Optical Technology Letters 2025年第5期67卷

作者： Sun, Chunyan Pan, Xueping Qiu, Chencheng Zhang, Bowen Bai, Jin Zhang, Liwei Cheng, Peng Cheng, WangPing School of Mathematics and Physics Anqing Normal University Anqing China Anhui Institute of Optics and Fine Mechanics Chinese Academy of Science Hefei China Key Laboratory of Modeling Simulation and Control of Complex Ecological model in Dabie Mountains of Anhui Higher Education Institutes Anqing China Hangzhou Dahua Apparatus Manufacture Co. Ltd Hangzhou China Fine Chemical Manufacturing Co. Ltd Dongguan China

This paper presents a calibration-free wavelength-modulated laser heterodyne radiometer (CF-WM-LHR) system, including the LabVIEW-designed software signal generator and software digital lock-in amplifier, monitors atmospheric methane (CH4) column concentration in real-time. Hefei Institute of Physical Sciences experiments with specific laser and SR830 settings acquire six signals per measurement. The 2 f signal of CH4 reaches near its maximum at a 0.28 V optimal modulation voltage. A 395–520 MHz bandpass achieves 250 MHz (0.0083 cm−1) spectral resolution. Compared with SR830, the software digital lock-in amplifier can demodulate multiple signals and attain an improved 2 f/1 f SNR of 429.3. The CF-WM-LHR system provides new greenhouse gas detection methods, and the software digital lock-in amplifier is crucial for inversion. © 2025 Wiley Periodicals LLC.

关键词： Mode-locked fiber lasers

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An efficient adaptive space partitioning algorithm for electromagnetic scattering calculation of complex 3D models

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Journal of systems Engineering and Electronics 2021年第5期32卷 1071-1082页

作者： HUANG Minjie ZHOU Yaoming WANG Yongchao LIU Zhongtie School of Aeronautic Science and Engineering Beihang UniversityBeijing 100191China Key Laboratory of Complex Aviation System Simulation Beijing 100076China

The space partitioning algorithm based on the rounding and addressing operations has been proved to be an efficient space partitioning algorithm with the potential for real-time *** improvement on this kind of space partitioning algorithms for solving complex 3D models is *** examples show that the efficiency of the improved algorithm is better than that of the original *** the size of most target elements is smaller than the size of spatial grids,the efficiency of the improved method can be more than four times of that of the original *** adaptive method of space partitioning based on the improved algorithm is developed by taking the surface element density or the curvature as the threshold for deep partitioning and conducting the deep partitioning using the octree method.A computer program implementation for applying the method in some typical applications is discussed,and the performance in terms of the efficiency,reliability,and resource use is *** testing shows that the results of the adaptive spacing partitioning are more convenient for the follow-up use than that of the basic uniform space ***,when it is used to calculate the electromagnetic scattering of complex targets by the ray tracing(RT)method,the adaptive space partitioning algorithm can reduce the calculation time of the RT process by more than 40%compared with the uniform space segmentation algorithm.

关键词： adaptive space partitioning computer graphics binary space partitioning ray tracing(RT)method stealth technology

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Diffusion mechanism simulation of cloud manufacturing complex network based on cooperative game theory

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Journal of systems Engineering and Electronics 2018年第2期29卷 321-335页

作者： GENG Chao QU Shiyou XIAO Yingying WANG Mei SHI Guoqiang LIN Tingyu XUE Junjie JIA Zhengxuan Economics and Management School Harbin Institute of Technology at Weihai Beijing Complex Product Advanced Manufacturing Engineering Research Center Beijing Simulation Center State Key Laboratory of Intelligent Manufacturing System Technology Beijing Institute of Electronic System Engineering Science and Technology on Space System Simulation Laboratory Beijing Simulation Center

Cloud manufacturing is a specific implementation form of the "Internet + manufacturing" strategy. Why and how to develop cloud manufacturing platform(CMP), however, remains the key concern of both platform operators and users. A microscopic model is proposed to investigate advantages and diffusion forces of CMP through exploration of its diffusion process and mechanism. Specifically, a three-stage basic evolution process of CMP is innovatively proposed. Then, based on this basic process, a more complex CMP evolution model has been established in virtue of complex network theory, with five diffusion forces identified. Thereafter, simulations on CMP diffusion have been conducted. The results indicate that, CMP possesses better resource utilization,user satisfaction, and enterprise utility. Results of simulation on impacts of different diffusion forces show that both the time required for CMP to reach an equilibrium state and the final network size are affected simultaneously by the five diffusion forces. All these analyses indicate that CMP could create an open online cooperation environment and turns out to be an effective implementation of the "Internet + manufacturing" strategy.

关键词： complex network cloud manufacturing innovation diffusion network effect Gale-Shapley algorithm cooperative game theory

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