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电机作为数控机床的核心部件,其性能影响着机床主轴系统的精度、电机效率和使用寿命.因此,合理设计高速电机的结构使其处于最佳的温度场,了解电机在运行过程中各空气区域内的速度及温度分布非常重要.本文以某机床的电机定转子作为研究对象,利用CFD软件对转子通风道的设计方案进行数值模拟,通过数值模拟分析电机内部的流场温度场及流场分布.根据模拟结果进行优化设计,在转子和定子之间进行单排孔和双排孔的优化方案设计,通过温度分布确定最佳设计方案,为电机转子通风道的散热优化设计提供有意义的参考. 相似文献
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采用电惯量替代机械飞轮模拟车辆摩擦制动过程的能量转化,是制动试验台的发展趋势,电惯量控制算法就成为制动试验台模拟车辆载荷的关键。针对列车制动试验台,基于转矩控制计算方法存在的惯量模拟偏差及波动大的问题,提出了惯量偏差控制算法。该算法将制动能量方程引入平均惯量计算中,将平均惯量及瞬时模拟惯量值与目标值的偏差,直接作为算法输入量,控制电机转矩。通过惯量偏差控制方程,实现了基于不同偏差量的电机转矩控制策略,达到了提高模拟精度、减小惯量波动的目的。将提出的惯量偏差控制算法与转矩控制法进行了比较试验。结果显示,惯量偏差控制法模拟的瞬时惯量,偏差超过5 kg?m2以上的时间占总制动时间的比例,比转矩控制法小60%,惯量模拟误差从10%降到了1%。相对于转矩控制算法,基于惯量偏差的电惯量控制算法,克服了模拟精度易受角减速度计算时滞、摩擦材料性能变化、机械阻力等因素影响的缺陷。 相似文献
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基于LS-DYNA软件中的ALE算法,对近水面水下爆炸气泡脉动过程进行数值模拟并与实验结果进行对比,验证了近水面近壁面混合边界有限元模型和参数设置的正确性。设置不同爆炸工况,对气泡及其破碎兴波对浮动冲击平台影响进行探究,结果表明:在水下爆炸过程中,气泡、自由面、浮动冲击平台会发生强烈的耦合作用,在气泡脉动阶段,气泡会诱导出涌流和水冢效应,影响浮动冲击平台的安全性和使用性;冲击波是影响浮动冲击平台冲击环境的主要因素,由于气泡的低频性,气泡脉动及水冢对浮动冲击平台的直接冲击作用,会小幅度增加浮动冲击平台冲击环境的谱速度值、谱位移值,对谱加速度值几乎无影响;水冢抨击水面所形成的波浪和气泡破碎兴波,对浮动冲击平台造成的激励载荷呈周期性,其周期与波浪周期相同。波浪的激励载荷仅通过激励其对应频率的浮动冲击平台共振来改变平台的冲击环境。波浪载荷很小,对浮动冲击平台的冲击环境影响较小。 相似文献
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动力UH模型及其有限元应用 总被引:1,自引:0,他引:1
饱和砂土在循环载荷下具有复杂的应力应变关系, 通常表现出液化过程中的大变形以及往返活动性现象. 为简单有效地模拟上述特性, 在超固结UH模型的基础上, 将其扩展为可考虑砂土动力加载下的本构模型. 具体做法有3点: (1)改变屈服面椭圆长短轴之比, 将比值定义为反映应力诱导各向异性转轴斜率的函数; (2)引入旋转硬化规则, 用来反映应力诱导各向异性; (3)建立一个与旋转硬化规则以及临界状态特性相协调的统一硬化参数. 模型预测结果表明, 所提动力模型可简单、有效地用于砂土在动力载荷下应力应变关系的模拟. 最后将该动力UH模型嵌入到有限元软件中, 三维地基的动力加载模拟结果表明, 动力UH模型可方便地应用于岩土工程实践中. 相似文献
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高速列车车轮多边形磨耗是一种沿车轮周向的不均匀磨耗,是列车服役过程中常见的车轮失效现象,其产生的剧烈轮轨激励严重威胁车辆系统服役可靠性. 制动系统作为保障高速列车服役安全的核心部件,其界面摩擦学行为直接受到轮轨激励的影响. 为探究车轮多边形激励下的制动界面摩擦学行为,建立了刚柔耦合车辆动力学模型和制动系统热机耦合有限元模型,并分别通过线路试验和台架试验验证了模型的正确性. 然后,提出一种考虑车轮多边形激励的制动界面摩擦学行为分析方法,能够真实地反映服役过程中制动界面摩擦学行为. 基于此,研究了不同车辆运行速度下车轮多边形激励对制动系统动态接触、温度以及振动特性的影响规律. 结果表明:车轮多边形磨耗导致系统接触面积、摩擦热、接触应力和振动等摩擦学行为更为复杂且剧烈. 此外,系统接触面积标准差和振动加速度均方根值随速度的增加而增大. 因此,车轮多边形磨耗对制动界面摩擦学行为具有不可忽略的影响. 该研究成果可为制动系统界面摩擦学行为研究及结构优化设计提供有效方法与工程指导. 相似文献
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多轴随机载荷下的疲劳寿命估算方法 总被引:5,自引:0,他引:5
现代工业的发展使得更多的构件承受着复杂的载荷形式, 将单轴疲劳模型应用到多轴载荷情况已不能满足现代工业的设计要求, 多轴随机载荷下的疲劳寿命计算日益引起人们的重视. 多轴随机载荷的寿命预测中, 如何计算载荷循环次数是其基础,目前广泛使用的是雨流计数方法, 现在已能成功的应用于多轴载荷的情况. 累积的疲劳损伤分析在各种构件和结构的载荷历史中都起着重要的作用. 自从线性损伤律提出以来已发展了数十种损伤律, 变幅载荷引起的疲劳损伤可以由许多不同的累积损伤律来计算, 虽然发展了许多损伤模型, 由于问题的复杂性, 每个模型的应用范围也是随具体情况而定. 线性损伤律方法尽管有很多不足之处, 但在设计使用中仍占有重要的位置. 两载荷水平及模式下的损伤累积以及损伤与物理机制的关系在本文中也做了介绍. 针对近年来提出的描述多轴随机载荷下疲劳寿命估算方法进行了详细的评述, 对各模型的应用范围和预测能力进行了讨论, 并对今后的工作提出了建议. 相似文献
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Menghua Zhang Xin Ma Xuewen Rong Rui Song Xincheng Tian Yibin Li 《Nonlinear dynamics》2017,89(3):1779-1791
For underactuated overhead cranes with payload hoisting/lowering, a partially saturated adaptive controller subject to unknown or uncertain system parameters is presented in this paper. To decrease the convergence time in the case of the overhead crane parameters already experienced by the system, the learning component is added to the proposed partially saturated adaptive controller. By introducing hyperbolic tangent functions into the control methods, the proposed controllers can guarantee soft trolley start even in the case of high initial velocities of trolley and cable. The convergence and stability performance of the closed-loop system is proven by Lyapunov techniques and LaSalle’s invariance theorem. Simulation results are listed to verify the adaptive performance with reduced actuating forces and strong robustness with respect to different external disturbances of the proposed controllers. 相似文献
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《International Journal of Solids and Structures》2006,43(2):376-389
Dynamic response of tower cranes coupled with the pendulum motions of the payload is studied in this paper. A simple perturbation scheme and the assumption of small pendulum angle are applied to simplify the governing equation. The tower crane is modeled by the finite element method, while the pendulum motion is represented as rigid-body kinetics. Integrated governing equations for the coupled dynamics problem are derived based on Lagrange’s equations including the dissipation function. Dynamics of a real luffing crane model with the spherical and planar pendulum motions is analyzed using the proposed formulations and computational method. It is found that the dynamic responses of the tower crane are dominated by both the first few natural frequencies of crane structure and the pendulum motion of the payload. The dynamic amplification factors generally increase with the increase of the initial pendulum angle and the changes are just slightly nonlinear for the planar pendulum motion. 相似文献
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This paper is concerned with modelling of the behaviour of container cranes under seismic loadings. For this purpose, physical and mathematical models are prepared. A six degrees-of-freedom non-linear mathematical model is developed in order to understand the dynamic behaviour of cranes under the seismic loadings. In order to determine the seismic behaviour of the container cranes against earthquakes, a 1/20 scaled crane model was designed and constructed. For the comparison of the models, the real earthquake records were used. The results are used to observe the destructive effects and compared with the period values of the most critical sections on the crane structure. When time and frequency domains are compared, it is seen that mathematical modelling of the container crane structure shows reasonable results under dynamic loadings. It will be available to take precautions and to increase seismic performance of cranes with the help of the developed dynamic model. Also, the developed mathematical model will be able to be used as a crane model in active vibration control studies in order to decrease the structural vibrations on container cranes. 相似文献
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Nonlinear Dynamics of Floating Cranes 总被引:7,自引:0,他引:7
The nonlinear dynamic responses of moored crane vessels to regular wavesare investigated experimentally and theoretically. The main subject ofinterest are nonlinear phenomena like bifurcations and the existence ofmultiple attractors. In the experimental part of the work, a mooredmodel of a crane vessel has been excited by regular waves in a wavetank. A special mechanism has been developed to model the nonlinearbehavior of real mooring systems. The theoretical part of the workconcerns the mathematical modeling of the floating cranes. Twomathematical models of different levels of complexity are presented. Twodifferent tools are used to systematically determine the responses ofthe systems to periodic forcing of waves. Firstly, the path-followingtechniques in combination with numerical integration of equations ofmotion applied to a full nonlinear model give insight into the dynamicsin time domain. Secondly, the multiple scales method allows for ananalytical investigation of simplified nonlinear models in frequencydomain. Many results of computations for two crane vessels, barge andship, are presented. Special attention is paid to oscillations near thefrequencies of primary resonances and to subharmonic motions. Anexcellent agreement is found between the results of time-domain andfrequency-domain analysis. The computational examples chosen correspondto the models used not only in the present experiments but in theexperiments of others as well. The results presented in the work allow usto draw several important conclusions concerning the dynamic behavior offloating cranes during offshore operations. Both the developed modelsand the analytical tools can be used to identify the limits of theoperating range of floating cranes. 相似文献
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Ziyad N. Masoud 《Nonlinear dynamics》2009,58(1-2):129-140
Oscillation frequency of crane payloads is the main and most important factor in crane anti-sway control systems design. In the summer of 2005, a Smart Sway Control system (SSC) was installed on a 65-ton quay-side container crane at Jeddah Port. During the calibration phase of the installation, it was observed that heavy payloads combined with the dynamic stretch of the hoist cables had a significant impact on the configuration of the hoisting mechanism and the pattern of oscillation. This introduced considerable change in the oscillation frequency of the payload, which resulted in a significant impact on the performance of the anti-sway control system. Empirical formulas had to be used to compensate for the change in the frequency approximation used in the controller algorithm. In this work, an analytic approximation of the oscillation frequency of the hoisting mechanism of a quay-side container crane is developed, which takes into consideration the elasticity of the hoisting cables. A parametric study is performed to investigate the extent of the effect of the hoisting cables stretch on the system behavior for a typical range of payload masses and cable lengths. The performance of the delayed feedback control system used in the SSC controller is simulated on an elastic cables model using both the elastic and rigid cable frequency approximations. 相似文献
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When a tower crane is handling payload via rotation and moving the carriage simultaneously the jib structure and the payload can be modeled as a system consisting of a slewing flexible clamed-free beam with the spherical payload pendulum that moves along the beam. The present work completes the dynamic modeling of the system mentioned above. The clamed-free beam attached to a rotating hub is modeled by Euler–Bernoulli beam theory. The payload is modeled as a sphere pendulum of point mass attached to via massless inextensible cable the carriage moving on the rotating beam. Non-linear coupled equations of motion of the in- and out-of-plane of the beam and the payload pendulum are derived by means of the Hamilton principle. Some remarks are made on the equations of motion. 相似文献
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J. Ubbink 《Applied Scientific Research》1970,22(1):442-448
For an electrostatic motor consisting of a rotor of insulating material covered with a slightly conducting surface layer,
and a ring of electrodes fed with phase-shifted ac voltages that generate a rotating electric field acting on the rotor, the
maximum torque on the rotor and the corresponding surface resistance are determined theoretically under the condition that
the amplitude of the ac voltages on the electrodes is constant. 相似文献