磁悬浮控制力矩陀螺的高速转子模态分析及实验研究

采用通用有限元软件包ANSYS7．0，建立了控制力矩陀螺结构的有限元模型，对磁悬浮飞轮转子组件以及陀螺整体组合结构进行了模态分析。通过与实验结果对比，验证了模型的合理性和精确性，指出了盘轴相对弯曲模态是系统工作带宽内的主要模态，也是影响飞轮转子系统稳定性的主要原因之一，必须进行有效陷波处理。分析结果为电磁轴承控制器参数的选取以及陀螺框架的设计提供了依据；采用ANSYS参数设计语言APDL建立的有限元模型也为下一步的优化设计奠定了基础。     

磁悬浮挠性转子系统模型复合辨识方法

针对磁悬浮挠性转子的纯有限元分析模型精度低的问题,提出一种磁悬浮挠性转子系统模型复合辨识方法。该方法首先采用有限元方法把磁悬浮挠性转子划分为多个Timoshenko梁单元,建立磁悬浮挠性转子系统模型,并对其挠性临界频率、阻尼、刚度和振型等关键参数进行分析,进而得到磁悬浮挠性转子的等效降阶数学模型;然后采用鲁棒自适应方法分析磁悬浮挠性转子系统的动态特性;最后,采用变LEVY方法从动态特性分析数据中对磁悬浮挠性转子进行系统辨识,校正有限元分析得到的降阶数学模型。实验结果表明,本方法可以得到磁悬浮挠性转子较为准确的系统模型。     

陶瓷刀具切削区温度场的计算机模拟

在切削金属过程中所消耗的能量几乎９０％以上都转化为热，致使工件，切屑和刀具的温度都上升，其中刀具的温升与切削机理及切削参数密切相关，并且直接影响刀具磨损及其全用寿命。为了研究陶瓷刀具切削温度分布对其磨损规律和机理的影响，根据传热理论建立了数学模型，用计算机模拟编制出陶瓷刀具切削区温度场计算的专业软件，可以得出不同陶瓷料刀具在不同切削条件下切步同工件材料过程中的温度分布曲线图，而且实际测量值与模拟值     

短脉冲激光加热分数阶导热及其热应力研究

短脉冲激光加热引起材料内部复杂的传热过程及热变形,现有的以Fourier定律或Cattaneo-Vernotte松弛方程结合弹性理论为框架建立起来热应力理论在刻画其热物理过程存在严重缺陷.本文基于分数阶微积分理论,以半空间为研究对象,建立了分数阶Cattaneo热传导方程和相应的热应力方程,给出了问题的初始条件和边界条件,采用拉普拉斯变换方法,给出了非高斯时间分布激光热源辐射下温度场和热应力场的解析解,研究了短脉冲激光加热的温度场及热应力场的热物理行为.数值计算中,首先对理论解进行数值验证,然后取分数阶变量p=0.5研究温度场和热应力场的变化特点及激光参数对温度和热应力的影响,最后数值计算分数阶参数对温度和热应力场的影响.计算结果表明,分数阶Cattaneo传热方程和热应力方程描述的温度和热应力任然具有波动特性,与经典的Fourier传热模型和标准的Cattaneo传热模型相比,分数阶阶次越大,热波波速越小,热波波动性越明显;反之,则热波波速越大,热扩散性越强.激光加热和冷却的速度越快,温度上升和下降的速度越快,压应力和拉应力交替变化越快,温度变化幅值越小,热应力幅值影响不明显.     

数控机床电机散热温度场的数值模拟研究

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.     

CPU散热片温度场模拟分析及其材料和尺寸选择的研究

对CPU的Cu—Al散热片进行了数值模拟热分析，研究了在室温、强迫对流的条件下的温度分布及散热片材料和几何尺寸对其传热性能的影响，并计算出模块较佳的材料和尺寸参数。有限元数值模拟分析值与实验测试值的比较结果表明，采用有限元热分析技术对CPU散热片进行数值模拟是可行的，为CPU散热片的设计提供了有效的方法。     

空间薄壁管结构瞬态温度场、热变形有限元分析

对于辐射换热的薄壁杆件航天结构，为分析其在太空中不同时刻的姿态下的温度场和热变形，构造了一种相对自由度矩形管单元。其基本思想是从2维非线性瞬态热传导方程出发，假设沿矩形管横截面上每边的温度为线性分布，用4个角点的平均温度和温差来表示矩形管横截面上的温度分布，构造了一种1维2结点温度杆单元，该单元每个结点包含平均温度，上下面温差，左右面温差3个自由度；在计算热变形时，此三个广义温度参数分别对应热轴力和2个热弯矩载荷。经与三维有限元计算结果的比较，证明用该单元计算的矩形管温度场和位移场是可靠的。利用这种新型的薄壁矩形管单元和本文作者在其他文章中提出的薄壁圆管单元，可以对非线性换热条件下的复杂空间结构进行比较准确的温度场和热变形有限元分析，最后本文计算了考虑遮挡的太阳能帆板的瞬态温度场和热变形以说明其应用价值。     

高速磁悬浮转子稳定性研究及其在控制力矩陀螺中应用

磁悬浮支承应用于控制力矩陀螺具有高精度，长寿命的优点。高速转子的陀螺效应导致的失稳制约了其在CMG中的应用，尤其是章动造成的磁悬浮转子高速失稳问题。该文分析了由于陀螺效应产生的章动造成系统失稳的根本原因，提出了控制系统的解决方案。研究结果表明，章动失稳的主要原因是系统的相位延迟造成的，尤其对数字控制系统，相位延迟更为严重，使用简单交叉解耦控制不能解决问题，需要对现有的控制器进行优化才能保证系统在高速下的稳定性。     

采用包络-准则法优化考虑瞬态传热的薄板结构

刚度和强度是薄板结构的两个主要性能。在瞬态传热过程中,考虑热-力耦合,随时间和空间变化的非均匀温度场在结构中会引起热变形和热应力,温度场随时间变化的规律和空间分布依赖于板的厚度变化,进而影响板的刚度和强度。因此,考虑瞬态传热的薄板优化问题具有更强的非线性,更加难以求解。本文给出一种包络-准则方法处理这类结构优化问题。首先,针对外力荷载,进行一个结构柔顺性的优化设计;以这一设计为基础,通过瞬态热-力耦合分析及优化准则,计算多个时刻的优化设计变量并取其包络,对上述优化结果进行迭代修正,以消除瞬态温度场作用下较高的局部应力。优化算例表明,该方法对于考虑瞬态传热薄板优化问题有效。     

热流密度/对流换热边界下双向梯度板的瞬态温度场分析

采用有限单元-有限差分法研究了热流密度/对流换热边界条件下双向梯度板的瞬态热传导问题。采用细观力学方法结合混合律准则描述了材料的热物理属性,通过推导一种8节点高阶双向梯度单元建立了结构的连续梯度有限元模型。计算给出了在考虑组份属性的温度效应下,温度场的时间响应历程以及不同时刻温度场的空间分布形式,并与材料属性温度无关时的计算结果进行了比较,最后讨论了相关参数对瞬态温度场的影响规律。结果表明：温度较低时,组份属性的温度效应对瞬态温度场影响很小;在 y 方向热流密度载荷的作用下,温度场沿 x、y 方向均存在明显的梯度;x 方向组份体积分布系数的增大,延长了温度场达到稳态需要的时间,绝对温度梯度沿 x、y 方向均增大,稳态温度场升高;增大 y 方向组份体积分布系数的值,情况相反。     

Analysis of maximum radial stress location of composite energy storage flywheel rotor

The relatively low radial tensile strength of a composite circumferential wound flywheel rotor is a crucial factor to restrict the maximum allowable rotation speed and energy storage capability of the flywheel system. In this paper, based on plane stress assumption, the stress analysis of the anisotropic flywheel rotor under the high-speed rotation was performed firstly, and the radial and circumferential stress distributions of the flywheel rotor were obtained. Then, the maximum radial stress location equation was derived by extreme point method and calculated by Newton iteration method. Finally, the effects of the anisotropy degree of the flywheel rotor material, the ratio of inner and outer radii and the rotation speed on the maximum radial stress location were systematically studied. Results provide a valuable reference for the designing of a high-performance composite flywheel rotor.     

Effect of Moisture Movement on Tested Thermal Conductivity of Moist Aerated Autoclaved Concrete

The purpose of this work was to study both theoretically and experimentally the process of moisture redistribution and heat transfer due to phase changes during the tests of thermal conductivity in aerated autoclaved concrete (AAC) moist specimens. The different moisture contents of the test samples were obtained in climatic chamber at equilibrium conditions reached with constant air temperature and variable relative humidity. The moist specimens were sealed inside highly impermeable polyethylene bag, as required by UNI 10051, and placed in a heat flow meter apparatus. During the experimental thermal conductivity measurements, the temperature and heat flow rate were measured under transient and steady state conditions. A theoretical analysis of the heat and mass transfer process was performed and then a suitable numerical model was used to predict the moisture redistribution and heat transfer due to the phase changes. The theoretical model has been compared against the experimental data. Substantial agreement between numerical results and experimental data was found. Then several numerical simulations have been performed to study the influence of the errors due to phase changes and non-uniform moisture distribution during the test of thermal conductivity of moist AAC specimens.     

Bifurcations in the response of a rigid rotor supported by load sharing between magnetic and auxiliary bearings

Auxiliary bearings are utilized in practical installations of magnetically suspended rotating machines with the main functions to provide support to the rotating machines during their non-operational period, and to protect the magnetic bearings and the rotating assembly from being damaged due to power loss during operation. The relatively small clearances of these bearings, which are typically half of that of the magnetic bearings, may at time cause contact between the rotor and these bearings to occur even during normal operation of the rotating machines. The work presented herein examines the bifurcations in the response of a rigid rotor supported by load sharing between magnetic and auxiliary bearings, which occurs during contact between the rotor and the auxiliary bearings. Numerical results revealed the occurrence of period-doubling bifurcation resulting in vibrations of period-2, -4, -8, -16 and -32, as well as quasi-periodic and chaotic vibrations. The results further showed that for a relatively small rotor imbalance magnitude, which is within the prescribed level of certain classes of practical rotating machinery, such nonlinear dynamical phenomena would not have been discovered had the auxiliary bearings forces been omitted in the model of the rotor-bearing system. As these bearings are essential elements in practical installations of magnetically supported rotating machines, failure to include them in the rotor-bearing model may result in incorrect prediction of the rotor’s vibration response.     

Effects of thermal dispersion on heat transfer in cross-flow tubular heat exchangers

Effects of thermal dispersion on heat transfer and temperature field within cross-flow tubular heat exchangers are investigated both analytically and numerically, exploiting the volume averaging theory in porous media. Thermal dispersion caused by fluid mixing due to the presence of the obstacles plays an important role in enhancing heat transfer. Therefore, it must be taken into account for accurate estimations of the exit temperature and total heat transfer rate. It is shown that the thermal dispersion coefficient is inversely proportional to the interstitial heat transfer coefficient. The present analysis reveals that conventional estimations without consideration of the thermal dispersion result in errors in the fluid temperature development and underestimation of the total heat transfer rate.     

Sensitivity analysis of thermal design parameters for focal plane assembly in a space spectral imaging instrument

There are deviations between real parameters and thermal design parameters on thermophysical attribute of focal plane assembly (FPA). The parameters are difficult to be determined accurately and the thermal design scheme will be affected with the values of the parameters. The thermal design problem of FPA is described by means of system sensitivity theory. The in-orbit heat balance equations are established, and the thermal design parameters, which might affect the temperature distribution of the FPA, are given. As an example, the sensitivity of thermal design parameters is analyzed for a FPA in a space spectral imaging instrument. A basis to determine the structural and thermophysical parameters for FPA is gotten, furthermore, an analytical method is provided for reliability validation of thermal design and operating reliability on orbit. It is shown that contact heat-transfer coefficient between mounted surfaces and surface emissivity are the main parameters affecting mean temperature of Charge converse device (CCD). The power of the inner heat source, thermal conductivity and inner contact heat-transfer coefficient are the primary parameters affecting temperature difference between CCD and the heat-transfer block. The thermal test is set up, and it is illuminated that the sensitivity analysis strategy based on the thermal design scheme is effective and feasible.     

磁头/磁盘滑动接触下磁盘温度及热退磁临界条件的研究

采用二维轴对称有限元模型计算磁头/磁盘滑动接触下,铝质磁盘的稳态温度和热应力场以及热退磁临界条件.结果表明:磁盘温度在极短时间内升至摩擦稳态值,然后缓慢线性升高到最终稳态值;经过充分热传导和热交换后磁盘的温度梯度较小,此时磁层内的热应力集中分布于磁盘固定端边缘附近;磁盘的稳态温度和热应力均随速度增大而增大,且载荷越大其值增大越快;热应力小于1.2 GPa时所对应的速度和载荷为安全工况;温升大于373 K时所对应的工况将导致磁盘退磁.     

混合润滑下螺旋锥齿轮抗胶合能力分析

针对螺旋锥齿轮重载下热胶合失效问题,对螺旋锥齿轮在混合润滑条件下的摩擦热行为进行分析. 通过混合弹流润滑数值计算方法和基于有限元的热分析方法,综合考虑螺旋锥齿轮的表面粗糙度、载荷分担、速度矢量和真实接触几何等因素建立点接触混合润滑分析模型,计算啮合轨迹上的连续摩擦系数变化和摩擦热流率,采用有限元分析软件进行齿面热载荷的加载,考虑轮齿导热和齿面与环境的热对流,分析轮齿本体温度场分布和啮合过程中闪温变化. 根据齿面最大接触温度与国际标准ISO 6336-20中齿轮抗胶合能力计算方法进行比较分析. 结果表明:有限元热分析得到的齿面温度与ISO所得变化规律十分接近,其最大温度低于ISO标准计算温度,使用ISO标准计算出螺旋锥齿轮抗胶合安全系数小于有限元法. 在混合润滑下求解的齿面热流率和温度变化,并且考虑了齿轮热传导和热对流影响,从理论上来说有限元法更加符合实际工作情况. ISO方法在处理上述问题以及计算本体温度上仍有不足,但其在齿轮抗胶合能力校核上具有广泛的适用性,可考虑结合有限元热分析法解决传热问题同时进行抗胶合能力综合评价.      

高温仪器化压入测试中热接触对位移测量漂移的影响

基于对室温压头和热试样接触后传热过程的分析, 重点研究热接触引起的压头基托热膨胀对高温仪器化压入测试中位移测量漂移的影响. 首先, 通过热传导理论分析, 获得热接触后基托内温度场分布的解析解, 进而研究基托热膨胀引起的位移测量漂移量; 然后, 建立有限元分析模型, 数值模拟高温仪器化压入过程, 验证理论模型的准确性. 研究发现, 压头与热试样接触面间的热传导性质显著影响基托内的温度场分布; 对于不同材料的试样, 接触面间传热性能不同, 基托的热膨胀量差异可以达到几个数量级. 研究结果有助于优化高温压入测试程序, 提高测试的可靠性.      

Thermal reliability analysis of a BLDC motor in a high-speed axial fan by the accelerated-life test and numerical methods

The thermal reliability of a closed-type BLDC motor for a high-speed fan is analyzed by an accelerated-life testing and numerical methods in this paper. Since a module and a motor part are integrated in a closed case, heat generated from a rotor in a motor and electronic components in the PCB module cannot be effectively removed to the outside. Therefore, the module will easily fail due to high temperature. The experiment for measuring the temperature and the surface heat flux of the electronic components is carried out to predict their surface temperature distributions and main heat sources. The accelerated-life test is accomplished to formulate the life equation depending on the environmental temperature. Moreover, the temperature of the PCB module is different from the environmental temperature since the heat generated from the motor cannot be effectively dissipated owing to the motor’s structure. Therefore a numerical method is used to predict the temperature of the PCB module, which is one of the life equation parameter, according to the environment. By numerically obtaining the maxima of the thermal stress and strain of the electronic components according to the operation environments with the temperature results, the fatigue cycle can be estimated.