面向对象的发动机曲柄连杆机构动力学仿真

基于面向对象的多物理领域联合仿真平台SimulationX,建立了发动机工作过程和曲柄连杆机构的统一物理模型,该模型实现了发动机一维燃烧和运动机构三维动力学联合仿真.通过对某型号发动机曲柄连杆机构的多刚体系统动力学仿真分析,得到了相关载荷参数,为后续发动机的热力学和结构动力学分析提供了边界条件,也为发动机数字化的虚拟设计和仿真分析提供了依据.     

公路隧道竖井一集热棚一烟囱三段式自然通风节能模型及应用

为了降低公路隧道通风费用,实现隧道运营节能,自然风的利用是隧道通风发展的方向。但是由于自然风向随机,并且不能准确确定风量大小,隧道自然风的有效利用率低。为了加强公路隧道竖井自然通风的效果,控制竖井口自然风风向,实现隧道通风节能,设计了一种竖井-集热棚-烟囱的三段式自然风增强模型。利用数值模拟的方法,分析太阳能烟囱不同温度下,太阳能烟囱内部不同位置的温度、压力和风速分布情况,从而确定自然风向。结果表明：在太阳能烟囱的不同温度下,设计的三段式太阳能烟囱的通风量与集热棚-烟囱的温度差呈线性相关,并且环境温度越高,线性相关性越强。在环境温度低于15℃时,太阳能烟囱的风向保持向上,起到抽吸的作用。根据该模型的设计思想,陕西省雷家坡一号隧道建成了太阳能烟囱自然风通风系统,观测数据表明该通风系统可以补充隧道机械动力通风,为黄土高原及类似地形地区公路隧道的自然风利用提供借鉴意义。     

基于层次动态灰色关联分析的配电网运行状态评价指标体系的构建与应用

配电网现行评价指标数量多、指标体系复杂、随机性强、指标间信息冗余问题凸显,针对这些问题提出一种基于层次动态灰色关联分析的评价指标体系构建方法。首先找出影响配电网运行状态的初始指标;然后通过提出的层次动态灰色关联分析法得到初始指标间的综合关联度,将综合关联度向量内的元素进行动态筛选,筛选出更准确的评价指标;再以指标的信息贡献率来验证筛选后评价指标的有效性和合理性,建立最终评价指标体系。最后通过实例进行分析,构建的评价指标体系得到的评价结果与配电网实际运行情况相符,证明了所构建指标体系的可靠性和合理性,可为配电网优化运行提供有效指导。     

二级物流服务供应链的契约协调机制研究

研究一个物流服务集成商和一个物流服务提供商所组成的二级物流服务供应链的系统协调问题。分别建立了集中控制模型、批发价格契约下的Stackelberg主从协调模型、收益共享契约下的协调模型,得到不同协调方法下的最优解所满足的条件。通过模型间的对比,证明了收益共享契约可使得该物流服务供应链达到整体最优的状态,相对于批发价格契约,实现了Pareto改进。最后,用数值试验的方式进一步验证了收益共享契约在协调物流服务供应链运作的有效性。     

Non-linear electromechanical response of 1–3 type piezocomposites

Domain switching in piezoelectric materials is caused by external loads such as electric field and stress that leads to non-linear behaviour. A study is carried out to compare the non-linear behaviour of 1–3 piezocomposites with different volume fractions and bulk piezoceramics. Experiments are conducted to measure the electrical displacement and strain on piezocomposites and bulk ceramics under high cyclic electrical loading and constant compressive prestress. A thermodynamically consistent uni-axial framework is developed to predict the nonlinear behaviour by combining the phenomenological and micromechanical techniques. Volume fractions of three distinct uni-axial variants (instead of six variants) are used as internal variables to describe the microscopic state of the material. In this model, the grain boundary effects are taken into account by introducing the back fields (electric field and stress) as non-linear kinematic hardening functions. An analytical model based on equivalent layered approach is used to calculate effective properties such as elastic, piezoelectric, and dielectric constants for different volume fractions of piezocomposites. The predicted effective properties are incorporated in the proposed uni-axial model and the dielectric hysteresis (electrical displacement versus electric field) as well as butterfly curves (strain versus electric field) are simulated. Comparison between the experiments and simulations show that this model can reproduce the characteristics of non-linear response. It is observed that the variation in fiber volume fraction and compressive stress has a significant influence on the response of the 1–3 piezocomposites.     

Analysis of resistive switching behaviors of vanadium oxide thin film

We demonstrated the polarization of resistive switching for Cu/VO_x/Cu memory cell. Switching behaviors of Cu/VO_x/Cu cell were tested by semiconductor device analyzer (Agilent B1500A), and the relative micro-analysis of I-V characteristics of VO_x/Cu was characterized by conductive atomic force microscope (CAFM). The I-V test results indicated that both forming and the reversible resistive switching between low resistance state (LRS) and high resistance state (HRS) can be observed under either positive or negative sweep. The CAFM images for LRS and HRS directly exhibited evidences of the formation and rupture of filaments based on positive or negative voltage. Cu/VO_x/Cu sandwiched structure exhibits a reversible resistive switching behavior and shows potential applications in the next generation nonvolatile memory field.     

Analysis and modeling of resistive switching mechanisms oriented to resistive random-access memory

With the progress of the semiconductor industry,the resistive random-access memory(RAM) has drawn increasing attention.The discovery of the memristor has brought much attention to this study.Research has focused on the resistive switching characteristics of different materials and the analysis of resistive switching mechanisms.We discuss the resistive switching mechanisms of different materials in this paper and analyze the differences of those mechanisms from the view point of circuitry to establish their respective circuit models.Finally,simulations are presented.We give the prospect of using different materials in resistive RAM on account of their resistive switching mechanisms,which are applied to explain their resistive switchings.     

基于因素-时间变权模型的公路隧道群运营期安全性评价研究

公路隧道群运营期安全保障工程相较于单体隧道更为复杂,面临的大量不确定性和安全风险直接威胁着隧道安全运营。从“人-车-隧道-交通环境-管理”五个要素构建运营安全评价因子集,结合变权理论对开展动态评价研究,形成因素-时间变权方法的双动态权重计算模型以体现指标的时变特点,结合模糊综合评价模型进行等级评价,以某高速隧道群开展评价工作。通过上述研究表明：因素-时间变权模型对于运营期的隧道群安全评价指标的权重控制具有极强的针对性,能很好的弥补常规评价方法中对隧道运营期安全因时变性的特点造成的评价结果失真的缺点;变权理论的利用为开展风险的动态管控提供了重要的理论支撑。     

异步电机低开关频率的模型预测直接电流控制

针对二极管箝位型(neutral point clamped, NPC) 三电平逆变器驱动异步电机的低开关频率控制, 提出了一种新颖的模型预测直接电流控制(model predictive direct current control, MPDCC) 方法. 基于推导的传动系统离散时间内部预测模型, 控制器预测了每个容许开关位置对应的电流输出轨迹、外推输出轨迹, 并根据评估平均开关频率的价值函数在线滚动优化实时求取最优开关矢量, 使得逆变器平均开关频率最小化, 且保持电流轨迹在给定的滞环范围内. 相对于已有的单步预测电流控制方法, 该方法在保持基本相同谐波性能的同时显著降低了开关频率. 仿真结果表明, 低开关频率模型预测电流控制算法可将三电平逆变器的平均开关频率降低至500 Hz 以下, 并且具有较理想的电流谐波畸变和动态响应性能.     

New Generalizations of Migdal-Kadanoff Bond-Moving Recursion Procedures and Their Applications

Considering in symmetrical half-length bond operations,we present in this paper two types of newlydeveloped generalizations of the remarkable Migdal-Kadanoff bond-moving renormalization group transformation recursion procedures.The predominance in application of these generalized procedures are illustrated by making use of them to study the critical behavior of the spin-continuous Gaussian model constructed on the typical translational invariant lattices and fractals respectively.Results such as the correlation length critical exponents obtained by these means are found to be in good conformity with the classical results from other previous studies.