直线振动筛相似模拟动应力研究

对27m2大型直线振动筛的相似试验模型进行了动应力测试,得到了试验模型筛筛体梁、板关键点处的最大动应力应变值。根据量纲分析法和方程分析法推导的工作状态参数相似关系,通过对原型筛与缩小的相似试验模型筛的试验结果对比分析,验证了相似模型与原型试验数据的一致性及可靠性,证实了利用缩小的相似试验模型进行动态测试及分析的有效性。本文结果为提高直线振动筛的使用寿命及结构的优化设计提供了理论依据,也为相似试验模型的发展研究提供了参考。     

制动器非线性动态特性的动力学仿真

本文通过制动器力学分析模型的建立研究了制顺的非线性动态特性及其对车轮防滑制动的瞬态响就这数值仿真曲线的比较和讨论，为制动器的动态设计提供了若干理论依据和设计准则。     

飞机风挡结构抗鸟撞一体化设计技术研究

结合大型非线性有限元分析软件，实践了飞机风挡结构由初步设计、数值仿真以及实验验证的一体化设计过程，建立了适于风挡结构材料的非线性黏弹性本构计算接口程序，对合理选取单元类型、材料模型、边界条件影响以及试验设计等工作细节进行了深入研究，通过实验与仿真计算结果的对比，验证了数值仿真计算模型的精度．为飞机风挡的抗鸟撞结构设计-数值仿真-实验验证一体化技术提供了支持论证．     

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通过对惯性振动筛工作原理和噪声测试结果的分析，认为来自激振器的高频干扰力是引起振动筛高噪声的根本原因之一，在此基础上提出了用双质体结构降低振动筛噪声的新措施，说明该结构的降噪原理，并利用试验结果验证了该方法的有效性．     

基于软件GPS接收机的高动态跟踪环路设计

介绍了三阶载波跟踪环路的设计方法,并在MATLAB软件上通过低动态实验和高动态仿真实验对设计的跟踪环路性能进行验证。低动态实验采用中频信号采样器采集的真实GPS信号,高动态实验采用GPS信号仿真器生成的高动态仿真信号。实验结果表明,基于软件GPS接收机设计的二阶载波跟踪环路可满足一般低动态要求,而三阶载波环路则可满足载体相对于卫星加速度为10个g的高动态要求。     

沥青搅拌设备振动筛系统动力学分析及其参数影响研究

基于牛顿法建立了沥青搅拌设备振动筛系统的动力学模型,考虑了实际生产中的机械振动方向与支撑弹簧方向的不完全一致性和支撑轴承及筛板刚度对振动筛系统的影响。求解了不同激振器频率和安装倾角下,振动筛质心的振动位移变化情况。对振动筛进行稳态有限元数值分析,获得了振动筛不同位置测点的振幅分布,并探究了不同的振动方向角对振动筛振幅和应力的影响。结果表明,振动筛的振动幅值随激振器频率的增大而增大,亦随振动筛倾角的减小而增大;当振动方向角β在0°~90°范围内变化时,振动筛的主振幅和主应力都随着振动方向角β的增大而增大;在振动筛沿筛体长度方向上,进料口附近振幅大于出料口附近振幅。     

非线性特征方程的重根特征灵敏度

在大型结构工程的控制工程中，对非线性特征方程的需求将愈来愈多，在以非线性特征方程分析结构或控制系统的动态特性，进而指导系统的动态设计时，其特征灵敏度是不可缺少的信息。为此，本文针对具有生根的非线性特征方程的特征导数计算提出了一种较为实用的方法。     

大型客机后缘襟翼操纵与非对称控制

针对大型客机后缘襟翼操纵与非对称控制的复杂结构及运动机构动力学仿真问题,通过零部件模态综合法建立刚柔混合多体动力学模型，替代传统的有限元法，综合考虑结构柔性、关节轴承摩擦、滑轮架摩擦、机翼盒段变形协调支持边界影响，实现了大型客机后缘襟翼在空中多状态/多工况载荷综合作用下的仿真分析．总体上看，仿真计算的各作动器驱动载荷变化规律与试飞结果一致，驱动载荷最大值误差小于10 %．受内襟翼靠近机身部分的翼面风洞测压数据及机身变形支持边界等不确定因素影响，初始启动和襟翼小偏度时各作动器操纵载荷仿真结果与试飞结果相对误差偏大．通过数值仿真，进行后缘襟翼单作动器脱开故障的非对称控制需求及其交联装置动态冲击过程分析，仿真结果表明内外襟翼交联装置可以有效减小后缘襟翼单作动器脱开故障非对称变形影响．     

惯性平台稳定回路的变结构控制

本文讨论了惯性平台稳定回路的变结构滑模控制规律的设计问题。在二自由度陀螺稳定平台中，稳定回路通常按角度输入进行设计，但是这种系统的动态误差主要来自舰船摇摆时轴上的摩擦力矩引起的稳定误差，因此，用经典方法设计的控制规律在实际使用中动态误差较大。本文用变结构滑模控制方法设计了控制规律，仿真结果表明变结构稳定回路的抗干扰能力和跟踪性能得到了较大的改善，提高了惯性稳定平台的可靠性和精度。     

大型精密离心机光栅测角系统的设计与实现

对JML－1大型精密离心机主轴光栅测角系统的关键技术进行了研究，给出了如何解决光栅测角系统的精度问题。抗干扰问题和动态测角问题的设计方法及测试结果。     

Coupled fluid structure analysis for wing 445.6 flutter using a fast dynamic mesh technology

The flow around wing 445.6 was modelled using Navier–Stokes equations and S-A model. The wing vibration and flow mesh deformation were computed using a fast dynamic mesh technology proposed by our own group. Wing 445.6 flutter was analysed through a strong coupling between the wing vibration and flow. The reduced flutter velocity was predicted and results are in good agreement with the experimental data. It is found that the subsonic flutter is mainly induced by the flow separation and the transonic and supersonic flutter are mainly caused by the oscillating shock wave and its induced flow separation. The positive aerodynamic work increases due to the oscillating shock wave when the subsonic flow becomes transonic reducing the flutter velocity. While the positive aerodynamic work induced by the oscillating shock wave decreases when the transonic flow becomes supersonic increasing the flutter velocity. That is why the transonic dip exists.     

Experimental investigation on using the piezoelectric and electromagnetic vibration absorbers in milling

The paper presents an active control system that counteracts the development of chatter vibration. The vibration amplitude depends on the dynamic properties of the machine tool, cutting tool and work-piece. In the paper we analyze the case when the loss of machining stability is caused by the work-piece. The proposed active control system employs electromagnet or piezoelectric actuator to suppress vibration during milling. The active control introduces damping into the system, thereby raising the critical depth of cut and reducing forced vibration amplitude. It enables stable cutting under a much wider range of cutting parameters that for the uncontrolled system. Cutting tests are performed on JAFO FYN-50 machine with mill DIN 845 B-25 K-N HSS to demonstrate an effectiveness of the proposed systems.     

PARALLEL FINITE ELEMENT ANALYSIS OF HIGH FREQUENCY VIBRATIONS OF QUARTZ CRYSTAL RESONATORS ON LINUX CLUSTER

Quartz crystal resonators are typical piezoelectric acoustic wave devices for frequency control applications with mechanical vibration frequency at the radio-frequency （RF） range. Precise analyses of the vibration and deformation are generally required in the resonator design and improvement process. The considerations include the presence of electrodes, mountings, bias fields such as temperature, initial stresses, and acceleration. Naturally, the finite element method is the only effective tool for such a coupled problem with multi-physics nature. The main challenge is the extremely large size of resulted linear equations. For this reason, we have been employing the Mindlin plate equations to reduce the computational difficulty. In addition, we have to utilize the parallel computing techniques on Linux clusters, which are widely available for academic and industrial applications nowadays, to improve the computing efficiency. The general principle of our research is to use open source software components and public domain technology to reduce cost for developers and users on a Linux cluster. We start with a mesh generator specifically for quartz crystal resonators of rectangular and circular types, and the Mindlin plate equations are implemented for the finite element analysis. Computing techniques like parallel processing, sparse matrix handling, and the latest eigenvalue extraction package are integrated into the program. It is clear from our computation that the combination of these algorithms and methods on a cluster can meet the memory requirement and reduce computing time significantly.     

P波作用下衬砌混凝土的爆破安全振动速度研究

隧洞爆破开挖诱发的爆破地震会对邻近的衬砌混凝土产生不利影响，利用应力波(P波)在混凝土与基岩结合面处的透、反射规律研究结合面处的应力状态，并通过结合面的抗拉强度分析，提出了一种确定衬砌混凝土安全振动速度的理论计算方法。计算结果表明，新浇筑衬砌混凝土极限振动速度随着基岩弹模的增大而降低，而爆破地震波频率的影响非常有限。我国现行采用的新浇筑大体积混凝土基础面上的爆破安全振动速度有一定的安全储备。     

Analysis of Machining Stability for a Parallel Machine Tool

Abstract

Machine tool chatter is a self-excited vibration generated by chip thickness variation. It severely degrades the quality of the machined surface. The incidence of chatter is greatly affected by the dynamic characteristics of machine tool structure. This article extends chatter stability analysis to a machine tool equipped with a parallel mechanism. The vibration model of a parallel machine tool is derived, in which the legs of the parallel mechanism are considered as spring-damper systems. Then, the regenerative cutting dynamics is combined with the vibration model and stability analysis is performed. The chatter stability charts for various machining parameters are examined, with the example of the cubic parallel mechanism that is specially designed for machine tool use.     

Vibration of two beams connected by nonlinear isolators: analytical and experimental study

To study the coupling vibration of nonlinear isolators and flexible bodies, test rigs of two flexible beams connected by wire mesh isolators are constructed and investigated both experimentally and analytically. A five-parameter polynomial model of wire mesh isolators is derived by identifying parameters in the frequency domain with the sine-sweep test. For obtaining the parameters that are valid in a wide range of frequency, a numerically assisted identification method is developed. With this model, the vibration of two flexible beams connected by wire mesh isolators is studied. The frequency response is obtained analytically by employing the Green’s function method and harmonic balance method. Sine-sweep test results with three test rigs show good coherence with the corresponding numerical results. With obtained experimental results and numerical results, effect of connection parameters is studied in detail. It is found that traditional design rules for isolators are no longer effective and the coupling vibration must be investigated in the design phase. Another phenomenon is that the damping has a function of weakening the effect of nonlinear stiffness. Nonlinear stiffness and nonlinear damping can decrease the transmissibility along with the increase of the excitation level.     

新浇筑基础混凝土爆破安全震动速度的确定

针对以往完全依据工程经验来确定新浇筑混凝土爆破安全震动速度这一现状 ,通过爆破地震波(Rayleigh波 )作用下的新浇筑基础混凝土中的震动速度及动拉应变的分布计算并结合不同龄期下新浇筑混凝土的允许极限拉应变分析 ,提出了一种确定新浇筑基础混凝土安全震动速度的理论计算方法。理论分析结果和计算实例表明 ,所提出的理论计算方法是合理可行的 ,新浇筑基础混凝土的极限震动速度随混凝土龄期的缩短及基岩对新浇筑混凝土的基础约束程度的提高而降低。我国现行采用的新浇筑大体积混凝土基础面上的质点安全震动速度具有较大的安全储备。     

交流电动机启动过程的扭振及电震荡

本文建立了电机的扭振方程和电路方程相耦联的统一数学系统,得到了它的解.研究了电源电压、扭转刚度等参数对启动过程的扭振、电磁力矩、电流等的影响,得到了一些有工程实际价值的规律和消除这种大扭振的途径,理论结果和实验结果吻合很好.     

基于机器学习的非结构网格阵面推进生成技术初探

网格生成和自适应是制约计算流体力学未来发展的瓶颈问题之一,网格生成自动化和智能化仍是一个需要持续研究的领域.随着高性能计算算力的提升和大数据时代的到来,以机器学习为代表的人工智能方法已经成功应用于包括流体力学在内的多个领域,革命性地推动了这些领域的发展.本文首先简要综述机器学习方法在非结构网格生成领域的研究进展,分析基于机器学习进行非结构网格生成的关键问题;其次,设计非结构网格样本数据格式并实现了样本数据集的自动提取,通过结合人工神经网络和阵面推进法,初步发展了一种基于人工神经网络的二维非结构网格阵面推进生成方法;最后,采用新发展的方法生成了几个典型二维各向同性非结构三角形网格(二维圆柱、二维NACA0012翼型和30p30n三段翼型),进一步采用合并法生成了相应的三角形/四边形混合网格,并测试了网格质量和生成耗时,结果显示本文方法生成的网格质量可以达到商业软件的水平,且生成效率较传统阵面推进法提高30%.      

大型冷锯机切噪声声功率的预估

通过对大型冷锯机锯切过程中主要声源及受力分析，明确了主要锯切噪声是由锯齿脉冲激励引起锯片和工件的局部高频振动所产生的。并用大型有限元结构分析软件ANSYS计算得到的单元速度值，根据结构振动声辐射理论，对冷锯机的锯切噪声进行了定量预估。从理论预估值与现场锯切噪声实测结果的比较可见，本文所建立的大型冷锯机锯切噪声分析及预估理论是正确的。