Harmonic generation in transition metal dichalcogenides and their heterostructures

Few layered transition metal dichalcogenides (TMD), with an absence of crystal inversion symmetry and outstanding optical characteristics, are frequently applied in studies of nonlinear optics (NLO) for harmonic generation. Related materials are regarded as potential candidates for many optoelectronics applications. In order to enhance and manipulate the intrinsically weak NLO responses, TMD’s have been fabricated into heterostructures in recent years. The basic physics of harmonic generation and of TMD optical responses, as well as the interactions in TMD hybrid structures are introduced briefly, and the current state-of-the-art in the performance of TMDs in harmonic generation are reviewed. A particular focus is made on heterostructure studies to enhance and manipulate the response, which represent the core issues for devices and applications.     

A multi-objective approach to optimal placement and sizing of multiple active power filters using a music-inspired algorithm

This paper proposes a new multi-objective framework for optimal placement and sizing of the active power filters (APFs) with satisfactory and acceptable standard levels. total harmonic distortion (THD) of voltage, harmonic transmission line loss (HTLL), motor load loss function (MLLF), and total APFs currents are the four objectives considered in the optimization, while harmonic distortions within standard level, and maximum allowable APF size, are modeled as constraints. The proposed model is one of non-convex optimization problem having a non-linear, mixed-integer nature. Since, a new modified harmony search algorithm (MHSA) is used and followed by a min–max technique in order to obtain the final optimal solution. The harmony search algorithm is a recently developed optimization algorithm, which imitates the music improvisation process. In this process, the Harmonists improvise their instrument pitches searching for the perfect state of harmony. The newly developed method has been applied on the IEEE 18-bus test system and IEEE 30-bus test system by different scenarios and cases to demonstrate the feasibility and effectiveness of the proposed method. The detailed results of the case studies are presented and thoroughly analyzed. The obtained results illustrate the sufficiency and profitableness of the newly developed method in the placement and sizing of the multiple active power filters, when compared with other methods.     

轻载装载机变速箱振动特性分析与试验

为了给装载机变速箱减振降噪提供依据,通过集中参数和有限元法相结合的方式对变速箱进行振动分析。综合考虑液力变矩器激励、齿轮系统内部激励等因素,建立装载机变速箱传动系统的弯-扭耦合动力学模型,求解得到各轴承的动态支反力;建立箱体有限元模型,进行模态分析,以轴承动态支反力为激励,在模态的基础上进行箱体谐响应分析,得到箱体在激励下的振动响应,选择箱体表面的振动测点,分析测点的振动加速度,找到并分析振动峰值及对应振型;最后进行变速箱振动试验,验证仿真的正确性。结果表明：传动系统的激励主要集中在输入和输出平行轴齿轮处,传动系统和箱体振动的峰值频率均和齿轮啮合频率相近,变速箱箱体振动较大的位置位于箱体的底部。试验与仿真对比,试验中存在和仿真相近的峰值频率,仿真和试验所得的振动加速度均方根误差值小于20%,验证了仿真的正确性。     

环形配电网的分频调节阻性有源电力滤波器位置策略

通过理论分析环形配电网的谐波放大原理,对比安装在线路中点且阻抗匹配的阻性有源电力滤波器(RAPF)和对称安装在不同位置的分频调节RAPF的抑制效果,提出了一种适用于环形配电网的分频调节RAPF的位置策略。若线路长度小于谐波波长的1/2,靠近线路中点的对称位置为最优安装位置;若线路长度大于谐波波长的1/2,距谐波源1/4波长的对称位置为最优安装位置。与安装在线路中点且阻抗匹配的RAPF相比,安装在最优位置的分频调节RAPF,当其电导增益≥匹配的电导时,均能有效地衰减谐波,获得更好的抑制效果;且电导增益越大,谐波抑制效果越好。同时,该方案对线路参数的改变具有更好的适应性。仿真和实验结果验证了该方案的有效性。     

基于ANSYS有限元法的某型车床主轴振动频率响应分析

Making an analysis for vibration modal and frequency response of the lathe spindle, respectively by using finite element method based on ANSYS and experiment of CA6140 type lathe in machining, and the calculation results are compared and analyzed, which verified the accuracy of ANSYS method. Numerical simulation and experimental results show that: Spindle in the first order and fifth order are prone to resonance, but did not reach resonance, the low order natural frequency have more effect than the high order natural frequency of the spindle vibration; by the experiments can conclude that the maximum vibration of the main shaft in the working state is mainly concentrated in the vicinity of its two ends, therefore, the improved bearing is an important way to reduce the vibration of the main shaft and ensure the machining accuracy, and the research results can provide a theoretical reference for the structural optimization design of the lathe.     

基于ABAQUS的三轴立式镗铣加工中心动态特性分析

以辛辛那提750为例,研究三轴立式镗铣加工中心的动态特性,根据有限元模型分析方法建立模型后进行模态特性分析机床各阶振动模态的特点,找到了机床结构上薄弱环节;在此薄弱环节上选取一点进行谐响应分析,计算出机床上最大激振力误差以及相应的特征频率。结果表明:机床结构的主轴箱位移量较大,激振力频率与机床结构第十阶固有频率接近时容易发生共振。     

基于范成原理的CTC谐波齿轮传动柔轮齿廓的参数化设计与仿真

主要对圆弧-渐开线-圆弧(CTC)齿形谐波齿轮传动的柔轮进行参数化设计与仿真。首先对刀具的基准齿形进行设计,其次根据范成原理可得出与之共轭的柔轮齿形,最终基于MATLAB软件实现了柔轮齿形的参数化设计与仿真。     

某汽车座椅骨架的动态特性分析

为获得某汽车座椅骨架结构的动态特性,利用Pro/E软件建立其三维模型,基于Ansys Workbench软件进行模态分析,并考虑路面和整车的影响对其进行了随机振动分析和谐响应分析,得到汽车座椅骨架的前六阶模态值和振型,以及随机振动和谐响应条件下汽车座椅骨架和座垫骨架的响应值。分析结果表明该汽车座椅骨架避开了人体不同器官的共振频率范围,并给出了座垫骨架具有较大位移响应的频率值,为后续汽车座椅骨架的结构设计和整车动态特性的优化设计提供了参考依据。     

配电网半绝缘电磁式PT加装消谐器后损坏原因分析研究

研究了铁磁谐振机理和特点,得出了铁磁谐振简化等效电路和PT承受电压计算方法,分析了半绝缘PT加装一次消谐器后的损坏原因,提出了改进措施。     

Analysis of non-linear singular system from fluid dynamics using extended runge-kutta methods

A non-linear singular system from fluid dynamics has been analysed by considering various possibilities using three different fourth order extended Runge–Kutta (RK) methods based on arithmetic mean, harmonic mean and heronian mean. It is observed that the extended RK methods suit well for the nuclear reactor core problem, when compared to the Single Term Walsh Series (STWS) method [1,10]. The simple and direct methods presented here can easily be implemented in a digital computer.