大功率IGBT器件及其组合多时间尺度动力学表征研究综述

在提出电力电子器件及其组合多时间尺度动力学表征需求的前提下,以目前常用的全控型电力电子器件——绝缘栅双极晶体管(Insulated Gate Bipolar Transistor,IGBT)为例,系统分析并归纳了目前在IGBT及其组合多时间尺度动力学表征研究方面的进展和成果,包括作为基础的大功率IGBT及其组合多时间尺度电热瞬态建模方法、基于模型的大功率IGBT模块失效量化表征方法以及用于辅助分析的IGBT组合多速率仿真方法。此外,介绍了基于IGBT多时间尺度模型的装置应用设计案例。从建模方法、可靠性评估、仿真手段以及应用设计四个方面系统全面地阐述了大功率IGBT及其组合多时间尺度的动力学表征方法,可为电力电子混杂系统的精确设计提供电力电子器件层面的理论和技术支撑。     

Real-time prediction of projectile penetration to laminates by training machine learning models withfinite element solver as the trainer

Studies on ballistic penetration to laminates is complicated, but important for design effective protection of structures. Experimental means of study is expensive and can often be dangerous. Numerical simu-lation has been an excellent supplement, but the computation is time-consuming. Main aim of this thesis was to develop and test an effective tool for real-time prediction of projectile penetrations to laminates by training a neural network and a decision tree regression model. A large number of finite element models were developed;the residual velocities of projectiles fromfinite element simulations were used as the target data and processed to produce sufficient number of training samples. Study focused on steel 4340tpolyurea laminates with various configurations. Four different 3D shapes of the projectiles were modeled and used in the training. The trained neural network and decision tree model was tested using independently generated test samples using finite element models. The predicted projectile velocity values using the trained machine learning models are then compared with thefinite element simulation to verify the effectiveness of the models. Additionally, both models were trained using a published experimental data of projectile impacts to predict residual velocity of projectiles for the unseen samples. Performance of both the models was evaluated and compared. Models trained with Finite element simulation data samples were found capable to give more accurate predication, compared to the models trained with experimental data, becausefinite element modeling can generate much larger training set, and thus finite element solvers can serve as an excellent teacher. This study also showed that neural network model performs better with small experimental dataset compared to decision tree regression model.     

An interface shear damage model of chromium coating/steel substrate under thermal erosion load

The Cr-plated coating inside a gun barrel can effectively improve the barrel's erosion resistance and thus increase the service life.However,due to the cyclic thermal load caused by high-temperature gun-powder,micro-element damage tends to occur within the Cr coating/steel substrate interface,leading to a gradual deterioration in macro-mechanical properties for the material in the related region.In order to mimic this cyclic thermal load and,thereby,study the thermal erosion behavior of the Cr coating on the barrel's inner wall,a laser emitter is utilized in the current study.With the help of in-situ tensile test and finite element simulation results,a shear stress distribution law of the Cr coating/steel substrate and a change law of the interface ultimate shear strength are identified.Studies have shown that the Cr coating/steel substrate interface's ultimate shear strength has a significant weakening effect due to increasing temperature.In this study,the interfacial ultimate shear strength decreases from 2.57 GPa(no erosion)to 1.02 GPa(laser power is 160 W).The data from this experiment is employed to establish a Cr coating/steel substrate interface shear damage model.And this model is used to predict the flaking process of Cr coating by finite element method.The simulation results show that the increase of coating crack spacing and coating thickness will increase the service life of gun barrel.     

超级电容起动动态过程分析与建模仿真

为了改进装甲车辆起动性能,提出了用超级电容替代蓄电池起动的方案。介绍了超级电容的特性,建立了起动系统模型并进行了仿真研究,对仿真结果进行了实验验证。结果表明:仿真与实验的结论基本吻合,显示了该方案的可行性。     

新型防空武器系统抗击CM建模与仿真

在分析巡航导弹技术、战术特点的基础上,给出了抗击CM的基本要求,结合新型武器系统的特点提出了抗击作战的数学模型,并通过仿真实验验证了武器系统抗击巡航导弹作战的可用性与高效性,为我新型防空武器系统抗击CM作战的效能评估提供了必要的方法和依据。     

基于有限元模型的机枪结构动态特性仿真

在对机枪进行结构设计时,了解机枪的固有频率和射击载荷作用下的动态响应特性对整个武器射击精度的影响十分必要。利用有限元分析软件对某机枪模型进行模态仿真分析,进而得出该武器对射击精度影响较大的部件。同时对机枪在射击载荷作用下的动力响应特性进行仿真计算,阐述了在机枪结构设计时频率匹配、射向一致的必要性,为机枪结构动力修改提供了理论依据。     

某型舰炮火控系统建模与仿真

简要介绍了某型舰炮火控仿真系统的训练、教学和和科研功能设计方案,硬件组成和必需的软件模块.在对一批空中目标拦截的战术设定情况下,给出了作战仿真流程图,列出了我舰及目标运动状态和姿态、噪声仿真、系统解命中、射击效果在线评估等数学模型.最后指出在建立数学模型时新的跟踪机制、解命中体制和滤波外推算法是三个技术难点,而在仿真过程中必须注意分布式、可视化和时钟统一等关键技术.     

反潜飞机对潜搜索法研究

反潜飞机使用吊放声纳对潜搜索具有不连续性.针对该特点,提出一种在实际搜索中能方便执行并且具有一定实用价值的搜索法.该法的基本思想是:通过增大或者减小取整的方法来保证起始相遇点在起始点,终止相遇点在该搜索段的终止点.算例验证该法正确可信.     

基于接触的捞雷具夹紧爪接触面形状优化

介绍了在捞雷具夹紧爪设计过程中引入的基于接触的有限元形状优化设计方法.传统的机械设计方法仅考虑了零件的几何尺寸,而对其形状的设计却考虑不够,导致设计结果不理想.文中将基于接触的有限元形状优化方法应用于传统的机械设计过程.对捞雷具夹紧爪建立基于有限元分析的优化设计模型,使夹紧爪既能满足打捞鱼雷的要求,又得到了优化的形状.结构的特性与受力状况均得到改善.     

破片模拟弹侵彻钢板的有限元分析

根据破片模拟弹侵彻钢板的实验研究,采用MSC.Dytran对破片模拟弹侵彻钢板的侵彻过程、侵彻特性、钢板的破坏模式以及弹体的侵彻速度、靶板的侵彻阻力进行了有限元分析,并将分析结果与实验结果进行了比较.分析结果表明,破片模拟弹冲击钢装甲的侵彻过程可大致分为初始接触、弹体侵入、剪切冲塞和穿甲破坏4个阶段.有限元分析的破片模拟弹侵彻特性及靶板破坏模式与实验观测结果有较好的一致性,在靶板破口的正面,与弹体平面凸缘两端接触的部分,变形以剪切为主,而与切削面接触的部分,以挤压变形为主;靶板破口背面为剪切冲塞破坏;有限元模拟的弹体剩余速度与实验结果吻合较好,弹体侵彻过程中弹靶作用界面的速度和侵彻速度近似呈线性变化.有限元分析结果还表明,采用适当的模型,有限元法能较好地模拟破片模拟弹侵彻钢板的侵彻过程、侵彻特性以及钢板的破坏模式.