电弧式触发器中银片阻值模型建立与计算分析

电弧式触发器作为混合型限流熔断器中重要的短路电流信号检测元件因其具有可靠性高、分断能力强、体积小、成本低等优点成为电力系统保护领域中重要的研究内容。触发器的额定通流能力强弱是衡量触发器性能优劣的重要指标之一。触发器中银片的阻值正是限制触发器通流能力提升的重要瓶颈。目前，绝大多数电气领域工作者利用MALAB软件与ANASYS软件对设计银片进行阻值计算。然而，大部分从事着并没有深入地了解软件建模过程中数学方法与物理原理的结合过程。目前，现有文献也对软件建模过程背后的原理概念解释不深，过程不详。本文利用差分方程和欧姆定律介绍了电弧式触发器的银片阻值的数学建模过程，详尽地揭示了仿真软件进行阻值计算的原理、步骤。对深入了解触发器工作原理和改进触发器性能具有一定借鉴意义。

A novel approach to conductive EMI noise source modeling

A new approach to conductive electromagnetic interference （EMI） noise source modeling, i. e. the source internal impedance extraction, is presented. First, the impedance magnitude is achieved through an exciting probe and a detecting probe, or through calculations based on insertion loss measurement results when inserting a series nigh-value known impedance or a shunt low-value known impedance in the circuit. Then the impedance phase is extracted by the Hilbert transform （HT） of the logarithm of the obtained impedance magnitude. Performance studies show that the estimated phase error can increase greatly at a zero frequency in the Hilbert transform because of the existence of a singular point, and this effect can be eliminated by introducing a zero-point when the noise source does not include a series-connected capacitive component. It is also found that when the frequency is nigher than 150 kHz, the estimated phase error is not sensitive to the inductive source but sensitive to the capacitive source. Finally, under the conditions of the same measurement accuracies for impedance magnitude, the accuracy of complex impedance based on the HT can be improved about 10 times when compared with the accuracy of estimated parameters based on the impedance magnitude fitting method （IMFM）.

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.

Multiple linear system techniques for 3D finite element method modeling of direct current resistivity

The strategies that minimize the overall solution time of multiple linear systems in 3D finite element method (FEM) modeling of direct current (DC) resistivity were discussed. A global stiff matrix is assembled and stored in two parts separately. One part is associated with the volume integral and the other is associated with the subsurface boundary integral. The equivalent multiple linear systems with closer right-hand sides than the original systems were constructed. A recycling Krylov subspace technique was employed to solve the multiple linear systems. The solution of the seed system was used as an initial guess for the subsequent systems. The results of two numerical experiments show that the improved algorithm reduces the iterations and CPU time by almost 50%, compared with the classical preconditioned conjugate gradient method.

Modeling of Magneto-Rheological Damper with Neural Network

With the revival of magnetorheological technology research in the 1980’s, its application in vehicles is in- creasingly focused on vibration suppression. Based on the importance of magnetorheological damper modeling, non- parametric modeling with neural network, which is a promising development in semi-active online control of vehicles with MR suspension, has been carried out in this study. A two layer neural network with 7 neurons in a hidden layer and 3 inputs and 1 output was established to simulate the behavior of MR damper at different excitation currents. In the neural network modeling, the damping force is a function of displacement, velocity and the applied current. A MR damper for vehicles is fabricated and tested by MTS; the data acquired are utilized for neural network training and vali- dation. The application and validation show that the predicted forces of the neural network match well with the forces tested with a small variance, which demonstrates the effectiveness and precision of neural network modeling.

Thermal-hydraulic modeling and analysis of hydraulic system by pseudo-bond graph

To increase the efficiency and reliability of the thermodynamics analysis of the hydraulic system, the method based on pseudo-bond graph is introduced. According to the working mechanism of hydraulic components, they can be separated into two categories: capacitive components and resistive components. Then, the thermal-hydraulic pseudo-bond graphs of capacitive C element and resistance R element were developed, based on the conservation of mass and energy. Subsequently, the connection rule for the pseudo-bond graph elements and the method to construct the complete thermal-hydraulic system model were proposed. On the basis of heat transfer analysis of a typical hydraulic circuit containing a piston pump, the lumped parameter mathematical model of the system was given. The good agreement between the simulation results and experimental data demonstrates the validity of the modeling method.

2014年北京高考物理压轴题的评析与启示

根据2014年北京高考理综第24题的考核内容,对电流的微观物理图像、动生电动势的物理本质、电阻的建模过程等进行评析和拓展。探讨了该题的设计理念对高中物理教与学、未来选拔性考试命题的启示作用。

Simulation of inter atrial block based on a human atrial model

Inter atrial block(IAB) is a prevailing cardiac conduction abnormality that is under-recognized in clinical practice. IAB has strong association with atrial arrhythmia, left atrial enlargement, and electromechanical discordance, increasing the risk of atrial fibrillation(AF) and myocardial ischemia. IAB was generally believed to be caused by impaired conduction along the Bachmann bundle(BB). However, there are three other conduction pathways, including the fibers posteriorly in the vicinity of the right pulmonary veins(VRPV), transseptal fibers in the fossa ovalis(FO), and muscular bundles on the inferior atrial surface near the coronary sinus(CS). We hypothesized that the importance of BB on IAB might have been overestimated. To test this hypothesis, various combinations of conduction pathway blocks were simulated based on a realistic human atrial model to investigate their effects on the index of clinical diagnosis standard of IAB using a simulated 12-lead electrocardiogram(ECG). Firstly, the results showed that the BB block alone could not generate typical P wave morphology of IAB, and that the combination of BB and VRPV pathway block played important roles in the occurrence of IAB. Secondly, although single FO and CS pathways play subordinate roles in inter atrial conduction, their combination with BB and VRPV block could also produce severe IAB. In summary, this simulation study has demonstrated that the combinations of different inter atrial conduction pathways, rather than BB alone, resulted in ECG morphology of IAB. Attention needs to be paid to this in future pathophysiological and clinical studies of IAB.