Multi-field dynamic modeling and numerical simulation of aluminum alloy resistance spot welding

In order to explore the influence of welding parameters and to investigate the Al alloy (AA) nugget formation process, a comprehensive model involving electrical-thermal-mechanical and metallurgical analysis was established to numerically display the resistance spot welding (RSW) process within multiple fields and understand the AA-RSW physics. A multi-disciplinary finite element method (FEM) framework and a empirical sub-model were built to analyze the affecting factors on weld nugget and the underlying nature of welding physics with dynamic simulation procedure. Specifically, a counter-intuitive phenomenon of the resistance time-variation caused by the transient inverse virtual variation (TIVV) effect was highlighted and analyzed on the basis of welding current and temperature distribution simulation. The empirical model describing the TIVV phenomenon was used for modifying the dynamic resistance simulation during the AA spot welding process. The numerical and experimental results show that the proposed multi-field FEM model agrees with the measured AA welding feature, and the modified dynamic resistance model captures the physics of nugget growth and the electrical-thermal behavior under varying welding current and fluctuating heat input.

On Transient Simulation of Field Equations

We investigate under what conditions transient simulation could be used to integrate backward in time so that the initial field could be recovered from later histories. In this paper we use realistic examples and find that, in long histories, traces of the initial field would be present only in the exact analytical solutions. We conclude that the recovery of initial field is possible only if the equations could be solved analytically or only short time periods are involved. In practice, it is not possible to detect those traces by measurements or observations. If numerical procedures are used, truncation and discretization errors are always present. Fine-tuning of system parameters used or transforming time into another pseudo time frame may allow numerical integration to be carried out backward in time. But numerical instability is still a problem. Large spurious increases found by numerical procedures are most likely due to numerical inaccuracy and instability.

Nonlinear Switching Transient Field Simulation of Cable Joint without Residual Charge

The analysis of the impulse voltage on the internal electric field of the cable joint plays a key role in studying the breakdown of the joint. Based on the finite element method, a three-dimensional electromagnetic field simulation model of the cable joint is established in this paper. Simulation results show that the voltage at the head of the cable joint reaches about twice the impulse voltage. The increase of the conductivity of semi-conductive material also leads to the increase of electric field intensity. Then, several points and curves at different positions are selected for further analysis in this paper. Among them, the electric field distortion at the edge of the high voltage shield is the most serious and the electric field in the air gap is the least.

Comparative Study on Electromagnetic and Electrome-chanical Transient Model for Grid-connected Photovoltaic Power System

With the development of new energy technology, there are increasing applications of grid-connected photovoltaic power generation system. However, there is little research on development of electromechanical model of large scale photovoltaic power station. The computational speed will be very slow if electromagnetic transient model is used for stability study because of its complexity. Therefore, study on electromechanical transient model of grid-connected photovoltaic power generation system is of great meaning. In this paper, electromagnetic transient model of photovoltaic power generation system is introduced first, and then a general electromechanical transient model is proposed. These two kinds of simulation model are set up in PSCAD. By comparing the simulation results of two models, the correctness and validity of the electromechanical transient model is verified. It provides reference model for efficient simulation and modeling of grid-connected photovoltaic power station in large-scale power systems.

An Energy Balance Simulation of the Universe

We have developed an energy balance equation for the universe. The two system parameters involved in the equation could be “fine-tuned” so that the predicted temperature histories all lead to what is observed in the present cosmic microwave background. We have shown that various combinations of these two parameters are possible;in particular, the present background temperature needs not be the remnant of a very hot temperature in the far distance past. We also solved for the propagation of vortex solitons in optical fibres as contrasting examples to show how electromagnetic wave could be transmitted in a particular waveform under strictly controlled conditions. To avoid singularity, all vortexes have a black centre. We conclude that while numerical techniques can be used to account for an infinite quantity, it is unlikely that such a quantity could exist in reality.

基于MATLAB/SIMULINK的三相异步起动永磁同步电动机的建模与仿真

三相异步起动永磁同步电动机的磁路结构和起动过程都比较复杂.基于MATLAB/SIMULINK并利用坐标变换中的park方程建立了三相异步起动永磁同步电动机的瞬态仿真模型,并在三相对称电压供电时进行了仿真试验.

基于Modelica的电力系统电磁暂态仿真平台研究

本文建议使用面向对象的建模语言Modelica可构建一个模型代码完全开放的电力系统电磁暂态仿真环境。利用面向对象技术确定仿真平台的基本框架,仿真平台由若干个电力系统元件包和基包组成。该平台能够对连续动态、离散事件动态和混杂动态系统进行建模和仿真。此外,也可用于多域系统建模和仿真。文中给出发电机、OLTC控制器和多域系统模型的建模过程。并通过一个简单算例及其仿真结果,验证该仿真平台的合理性和有效性。

Enhanced quasi-three-dimensional transient simulation technique incorporating component volume effects for aero engine

Current transient analysis predominantly relies on zero-dimensional/one-dimensional tools,proficient at capturing aerothermodynamic variations across critical engine stations but insufficient for analyzing the internal flow field evolution during transients.Addressing this gap,the study presents an enhanced quasi-three dimensional(quasi-3D)transient simulation technique that integrates component volume effects,offering a significant leap from the preceding quasi-3D transient simulation method based on quasi-steady assumption.By embedding the component volume effects on density,momentum,and energy within the physical temporal dimension of the Navier-Stokes equations,the refined quasi-3D transient model achieves a closer representation of physical phenomena.Validation against a single-shaft turbofan engine’s experimental data confirms the model’s accuracy.Average errors for key performance indicators,including shaft speed,thrust,mass flow rate,and critical component exit temperature and pressure,remain below 0.41%,5.69%,2.55%,3.18%and 0.67%,respectively.Crucially,the model exposes a discernible temporal lag in the compressor outlet pressure and temperature response due to volume effects—previously unquantified in quasi-3D transient simulations.And further exploration of the meridional flow field emphasizes the consequential role of volumes in transient flow field evolution.Incorporating volume effects within quasi-3D transient simulations enhances engine modeling and is pivotal for precise transient analysis in engine design and optimization.

Power World Simulator软件的电力系统暂态稳定性仿真

将可视化软件Power World Simulator应用于电力系统暂态稳定性仿真,介绍了仿真的步骤和发电机模型库,建立IEEE-3机9节点系统,先求得系统的潮流分布,然后选择发电机、励磁系统和稳定器的类型,设置三相短路故障,完成暂态稳定性仿真。通过分析和对比发电机6阶、5阶实用模型和经典2阶数学模型时的仿真结果,验证了暂态稳定性仿真结果的有效性。

基于SIMULINK/FLUENT的PEMFC系统的协同仿真

提出了基于SIMULINK/FLUENT的质子交换膜燃料电池系统协同仿真方法,结合SIMULINK和FLUENT各自的功能,利用SIMULINK的S-函数及FLUENT的日志文件开发了两者的接口,通过共享数据文件的方式实现了两程序之间数据的同步传递,初步建立了燃料电池模拟系统的三维协同仿真平台。最后,通过数值算例仿真在质量守恒的意义下验证了协同仿真平台的动态数学模型的正确性。

Mathematical model for iron corrosion that eliminates chemical potential parameters

Iron corrosion in acidic media is a natural phenomenon that converts elemental iron to a more chemically-stable form,i.e.its oxide and hydroxide.In this study,the iron corrosion process is modeled as a completely implicit problem,solved by a novel finite difference model to provide insight into the ionic aspects of corrosion behavior.This new mathematical model eliminates the chemical potential parameters from the corrosion process equations,thereby reducing the need for experimental determination of chemical potentials.The eliminatedchemical-potential-parameters model predicts and quantifies key parameters(concentrations of conjugate base ion,iron(Ⅱ)ion,hydrogen ion,anodic and cathodic potentials,and the electrical current density)associated with the iron corrosion process in acidic solutions.The rigorous derivation and novel application of the eliminated-chemical-potential-parameters model and its results provide new insights into the iron corrosion process.The present model is also applicable in any industrial process which is associated with metal corrosion.The model helps to guide the design of future corrosion resistant systems,and various experimental studies pertaining to corrosion inhibition techniques.

基于SIMULINK/FIRE的PEMFC系统联合仿真

针对PEMFC三维动态数值仿真,结合SIMULINK和FIRE各自的功能,利用SIMULINK的S-函数及FIRE的USERFUNCTION开发了两者的接口,通过共享数据文件的方式实现了SIMULINK和FIRE之间的数据同步通讯,初步建立了PEMFC系统的空间三维动态联合仿真平台。并以单流道PEMFC三维数值模拟为例,在质量守恒的意义下用数值算例验证了联合仿真动态计算的有效性。

Resolution of the Computational Diffusion Hydrodynamic Model into Partial Differential Equation Form

Computational modeling continues to evolve in applications of hydrology and hydraulics, and the field of Computational Hydrology and Hydraulics has grown into a significant technology in both engineering and computational mathematics. In this paper, the fundamental issue of assessment of computational error is addressed by determination of an “equivalent” mathematical statement, as a partial differential equation (“PDE”) that describes the original mathematical PDE statement and computational solution of it. In other words, given that the computational model does not exactly solve the governing PDE and that the computational processes used to approximate the governing PDE further moves the computational outcome away from the exact solution, what “alternate” or “equivalent” PDE does the resulting computational model exactly solve? In this paper it is shown that development of such an equivalent PDE enables an assessment of computational error by direct comparison of the equivalent PDE to the original PDE targeted to being solved. As an example, the USGS Diffusion Hydrodynamic Model (“DHM”) is examined as to development of an equivalent PDE that describes the DHM computational modeling outcome, which is then compared to the actual outcomes resulting from application of the DHM model.

基于Transient Thermal的回流焊温度曲线仿真技术研究

回流焊工艺是表面组装技术SMT的重要一环,决定了电子器件焊接的质量与速度。作为回流焊工艺重要环节,回流焊温度曲线直接影响PCB板的质量。本文针对某回焊炉,通过热传导模型求解出稳定工作时炉内温度曲线,建立了基于Transient Thermal的回流焊温度曲线仿真模型,优化包括温区温度设定以及传送带速度的因素。根据得到的仿真实验数据,通过逐步回归,分析出制程界限与各因素的关系,在制程界限下通过仿真建模,求解出最优的回流温度曲线。最后求出传送带速度为82.44 cm/s,五大温区温度设置分别为165℃、185℃、225℃、265℃、25℃,进一步优化了回流焊温度曲线。对比传统的反复实验调整,基于Transient Thermal的仿真建模方法可以在更高效率下得到更精确地优化控制。该方法能以其高效率与低能耗的优势,更好为回焊炉参数设置提供决策支持。

Power system transient stability simulation under uncertainty based on Taylor model arithmetic

The Taylor model arithmetic is introduced to deal with uncertainty.The uncertainty of model parameters is described by Taylor models and each variable in functions is replaced with the Taylor model(TM).Thus,time domain simulation under uncertainty is transformed to the integration of TM-based differential equations.In this paper,the Taylor series method is employed to compute differential equations;moreover,power system time domain simulation under uncertainty based on Taylor model method is presented.This method allows a rigorous estimation of the influence of either form of uncertainty and only needs one simulation.It is computationally fast compared with the Monte Carlo method,which is another technique for uncertainty analysis.The proposed method has been tested on the 39-bus New England system.The test results illustrate the effectiveness and practical value of the approach by comparing with the results of Monte Carlo simulation and traditional time domain simulation.

适应并离网模式切换的DFIG电磁暂态仿真建模

目前,常用的商业仿真软件中的双馈式感应发电机(double-fed Induction Generator,DFIG)模型通常不支持离网运行模式,难以实现风力发电系统由离网到并网的全过程电磁暂态仿真,对电力系统仿真分析工作带来极大不便。研究适应并离网模式切换的DFIG电磁暂态仿真建模方法。基于模块化思想分别对风力机、异步电机、变流器以及断路器进行建模,在系统组装形成DFIG风力发电系统电磁暂态仿真模型。提出了适应并离网模式切换的DFIG受控源等效电路模型和离散时间域实现方法,通过设计状态变量矩阵元素的截取和扩充算法实现了模型在并离网模式下的无缝衔接。在MATLAB/Simulink中搭建DFIG发电系统模型对所提方法和模型进行验证,仿真结果表明,所提建模方法能够很好地支持DFIG离网运行模式,实现DFIG由离网到并网的全过程电磁暂态仿真。

基于多核CPU的风光新能源场站全拓扑实时仿真建模方法

风光新能源场站在构建新型电力系统中占据重要地位,其电磁暂态实时仿真愈发受到关注。由于新能源场站网络解算十分复杂,串行逻辑冗长,难以在目前开发较为成熟的多核CPU仿真机上实时仿真。因此提出了一种基于多核CPU的风光新能源场站全拓扑实时仿真建模方法。该方法基于电网络等效原理,建立发电单元四端子等效模型,依据该模型的仿真流程设计适用于多核CPU的并行仿真架构,实现新能源场站的实时仿真。所建场站模型利用内部电压的计算可保留高精度的全拓扑信息,同时通过降阶有效降低网络解算资源占用,缩短串行逻辑。经仿真测试,相较于RTDS模型,该方法所建模型在保证精度误差小于4%的同时可实时仿真的场站规模扩大3倍,有效降低实时仿真硬件成本。

新型省级电网电磁暂态实时仿真建模方法

为了解决大规模省级电网电磁暂态仿真效率低下的问题,研究了一种适用于省级电网的电磁暂态实时仿真建模方法。分析了大电网电磁暂态建模难点,通过子系统建模和任务优化方法建立了省级电网模型,对各子网内部进行功率调节,实现了首次功率平衡;基于输电线路模型法原理完成了各子网之间输电线接口的联络,在预设平衡点的基础上,通过在线调节潮流的方法使得所建模型运行在合理平衡点上。为验证该方法的有效性,基于自主研发的实时仿真器(universal real-time experimental platform,UREP-300)对某新型省级电网进行实时仿真。仿真结果表明,所提方法能提高仿真效率,扩大了系统的仿真规模,减小了实时仿真机的计算负担,可为各类大规模系统的仿真与建模提供一种参考。

基于NSGA-Ⅱ的锂电池液冷扁管结构设计与热性能优化研究

文中提出了一种锂电池模组蛇形液冷扁管空间并行交叉液冷结构,对液冷结构参数进行了优化。以电池最高温度和最大温差为优化目标,以液冷扁管高度为优化变量,采用拉丁超立方法(Latin Hypercube Sampling,LHS)对优化变量建立80组参数化组合样本,以CFD瞬态数值仿真计算,结合Kriging代理模型与NSGA-Ⅱ(Non-dominated Sorting Genetic AlgorithmⅡ)多目标遗传算法对液冷结构参数进行寻优求解,并进一步研究了冷却液入口速度对液冷结构散热性能的影响。结果显示:相对单层蛇形液冷扁管结构,蛇形液冷扁管空间并行交叉结构有更好的冷却性能,在冷却液入口流速为0.02 m/s时,电池1C放电工况下最高温度和最大温差分别下降3.2%和19.3%,电池2C放电工况下最高温度和最大温差分别下降6.4%和18.3%;在冷却液入口流速降低时,蛇形液冷扁管空间并行交叉结构的散热性优势更明显。

复杂地形瞬变电磁三维正演模拟与地形效应分析

目前,地面瞬变电磁法凭借其优势已被广泛用于煤矿水文地质勘查中,然而,在野外实际勘探中,复杂地形环境常导致发射源几何形状的改变与信号接收偏差,降低了勘探精度。为此,采用理论分析、数值模拟和实际地形数据分析相结合的方式,系统研究了复杂地形条件下电性源与磁性源瞬变电磁场的响应特征。首先,基于二阶后退欧拉离散的矢量有限元正演模拟技术,详细探讨了山峰和山谷地形位于接收点和发射源位置时,对两种源系统的影响规律。结果表明:电性源系统会出现响应变号现象,源导线位置高于周围地形时响应增强,反之则被削弱;而磁性源无变号现象,但响应变化规律与电性源类似。其次,利用实测地形数据,采用四面体网格建立与实际地形高度吻合的三维正演模型。模拟结果显示:早期响应曲线能够清晰反映地形细节,曲线形态与地形特征一致;而晚期响应则逐渐趋于平缓,体现了深部背景的影响。研究成果可为复杂地形条件下瞬变电磁法的勘探装置布设、数据采集、处理和解释提供理论指导,对提高煤矿水文地质勘探精度具有重要意义。