空间光学镜头可适应边界温度的CAE计算方法

提出了空间遥感器温度场的描述方法,建立了某空间遥感器光学镜头的热光学分析模型,计算得到了该空间光学遥感器温度水平和温差要求的热控指标。在对遥感器在轨运行热载荷状态进行假定描述的基础上,用有限元方法进行了温度场及热弹性变形分析,得出假定温度载荷作用下光学遥感器各光学表面的变形量及刚体位移量。利用Zernike多项式进行波前差拟合,得到Zernike多项式系数,代入光学系统,利用CODEV光学计算软件计算热载荷作用下光学镜头的传递函数(MTF)。通过迭代,得到光学系统满足传递函数指标＞0.4要求的各温度场临界值,完成了从光学指标到热控指标的转换,避免了热控设计的过设计或设计不足, 可以在设计方案阶段作为遥感器结构的热适应性设计的参考,同时为制定合理的热控设计指标提供数据依据。     

测绘相机的温度适应性

分析了温度对三线阵测绘相机传递函数和交会角的影响,通过热光学计算确定了测绘相机的热控指标.首先,在设定测绘相机热载荷状态的基础上,用有限元方法分析了温度场及热弹性变形;利用Zernike多项式进行波面拟合,代入光学软件考察温度对光学系统传递函数的影响,得到测绘相机光学传递函数在假定温度场作用下的下降系数.然后,进行了测绘基座的热尺寸稳定性分析.并在此基础上考察了温度对测绘相机交会角的影响.实验显示,上述分析避免了热控设计的过设计或设计不足,为制定合理的热控设计指标提供了数据依据.     

退火工艺过程光学玻璃热力学特性的计算机仿真

退火是光学玻璃加工的重要工艺过程.用于空间光学遥感器的平板光学玻璃的热特性及热控措施具有特殊的要求,因此其退火过程也具有一定的特殊性.本文的重点工作是利用有限元法、针对全部镀膜后的光学玻璃在退火工艺过程中的温度场及热弹性变形进行分析计算,旨在探索合理的退火工艺参数及其改进措施.     

离合器温度场计算中摩擦热流密度模型的比较研究

温度场计算是离合器设计与控制的重要依据,摩擦热模型是温度场计算准确性的关键。针对热流均布和压力均布两种主流的摩擦热流密度模型,将其分别引入离合器热分析的有限元模型,计算在持续滑摩的极端工况下温度场随时间和空间的变化过程,从温度分布云图、温度沿半径方向的变化、最高温度以及温度梯度等方面对两种模型的计算结果进行比较,给出了两种模型的适用范围。     

二氧化碳探测仪的热控系统

根据二氧化碳探测仪所处的空间环境、结构特点和工作模式,采用被动热控和主动热控相结合的方法设计了它的热控系统。首先,介绍了探测仪结构及内热源,同时分析了探测仪的外热流,从而得到了热控任务难点。然后,对探测仪的各个部分进行了热设计,采用被动热控与主动热控相结合的方式进行了热隔离、热疏导和热补偿;根据探测仪所处的空间环境和采取的热控措施利用TMG软件进行了热分析。仿真分析结果表明,光学系统主体框架的温度为13.3~21.7℃,满足了设计要求。最后,通过真空条件下的热平衡试验对热设计进行了试验验证,试验结果显示光学系统主体框架的温度为13.0~20.3℃,试验值与计算值基本一致,满足热控指标要求。得到的数据表明提出的热设计方案合理可行。     

城市轨道交通车辆踏面制动热应力仿真分析

分析了城轨列车在踏面制动方式下车轮踏面热疲劳裂纹产生的机理,并建立了车轮制动过程瞬态温度场三维有限元模型,采用整体输入热流和对流换热的简化模式为基础的传统理论的热应力计算方法,计算车轮在连续两次紧急制动工况下的热温度场及热应力场,为确定城轨列车制动方式及列车制动距离等技术规范提供计算依据。     

复杂热环境下连接接头的温度场和热应力研究

复杂热环境下结构连接接头起到热连通器的作用,研究接头在复杂温度场条件下的温度场和热应力对于工程设计具有实用意义.利用有限元方法,通过热/力有限元模型的建立以及边界条件的处理,应用数值计算对接头温度、温度梯度和热应力的变化规律进行了分析研究,得出了复杂热环境下接头的稳态温度及热应力分布.计算结果表明,热短路中螺栓根部产生一定量的热应力,设计阶段必须适当其热强度分析问题.     

柴油机气缸套三维温度场数值计算与分析

建立了完整的气缸套温度场计算模型,用FLUENT软件计算得到了S195柴油机在标定工况下的气缸套温度场.计算结果表明:最高温度位于气缸套的内壁顶端,达到498K,最低温度位于气缸套的下部,缸套温度场分布自上而下降低,热负荷不大.对气缸套的强度设计、热设计具有参考价值.     

关节轴承摩擦温度场计算方法

以推力型关节轴承为研究对象,分析了轴向载荷下的接触应力,并根据试验所得摩擦力矩反推出了动态摩擦因数。结合接触应力及摩擦因数求出了摩擦热流率,并将其作为第二类边界条件进行了轴承非定常温度场有限元分析,最后利用红外热像仪拍摄了摩擦过程中轴承侧表面温度分布,检验仿真结果的可靠性。仿真与试验结果表明：该计算方法解决了球面摩擦副摩擦因数的精确计算和热流率的空间分配问题,建模时忽略球面间隙会直接影响接触应力分布并造成温度场分布出现较大误差,考虑球面间隙可以更精确地计算轴承摩擦温度场。     

空间光学系统的热分析

利用有限元方法对空间光学系统在各种空间热环境下的传热学及热力学响应进行了模拟仿真,通过对温度梯度分布的分析,采取了相应的热控手段,使系统的温度响应明显减小.     

Quantification of extreme thermal gradients during in situ transmission electron microscope heating experiments

Studies on materials affected by large thermal gradients and rapid thermal cycling are an area of increasing interest, driving the need for real time observations of microstructural evoultion under transient thermal conditions. However, current in situ transmission electron microscope (TEM) heating stages introduce uniform temperature distributions across the material during heating experiments. Here, a methodology is described to generate thermal gradients across a TEM specimen by modifying a commercially available MEMS-based heating stage. It was found that a specimen placed next to the metallic heater, over a window, cut by FIB milling, does not disrupt the overall thermal stability of the device. Infrared thermal imaging (IRTI) experiments were performed on unmodified and modified heating devices, to measure thermal gradients across the device. The mean temperature measured within the central viewing area of the unmodified device was 3–5% lower than the setpoint temperature. Using IRTI data, at setpoint temperatures ranging from 900 to 1,300°C, thermal gradients at the edge of the modified window were calculated to be in the range of 0.6 × 10⁶ to 7.0 × 10⁶°C/m. Additionally, the Ag nanocube sublimation approach was used, to measure the local temperature across a FIB-cut Si lamella at high spatial resolution inside the TEM, and demonstrate “proof of concept” of the modified MEMS device. The thermal gradient across the Si lamella, measured using the latter approach was found to be 6.3 × 10⁶°C/m, at a setpoint temperature of 1,000°C. Finally, the applicability of this approach and choice of experimental parameters are critically discussed.     

The output window of a large-area accelerator with an increased electron-beam current density

The results of theoretical and experimental investigations of a large-area accelerator with a new type of output window are presented. With this window, it is possible to increase the current density of the extracted electron beam, reduce the operating temperature of the foil, and extend its service life. A two-level support structure with cooling of each level is used for this purpose. The heat load of the foil mounted on the second level of the support structure that carries the main mechanical load is reduced by partial interception of the thermal power due to direct loss of the electron beam, which is released on the first level experiencing no mechanical load. The current loss at the structural elements of the output window is estimated, and the hydraulic characteristics and foil temperature in the output device are calculated. A higher current density of the beam extracted over the foil is attained in comparison with the conventional design of the support structure.     

A finite element model of thermal evolution in laser micro sintering

Laser micro sintering (LMS) is a promising technique for micro-additive manufacturing. During LMS of metallic powder, the material property variation and the heat input energy profile are important to understand physical phenomena involved. This paper presents a finite element temperature distribution profile in LMS of nickel powder on 304 stainless steel substrate. The simulation considered the transition of powder-to-dense sub-model which involves effective thermal conductivity, volumetric enthalpy, and absorptance change; and a moving volumetric Gaussian distribution heat source sub-model. It is found that, for a specified cross section, the mechanism of preheating the nickel powder changes for the heat source from previous laser-irradiated substrate region to molten nickel as the laser beam approaches, while the center of molten pool slice is slightly shifted toward the reverse direction of laser scanning when the laser moves away due to the thermal accumulation effect. Simulated sintered widths showed very good agreement with experimental measurement, and relative prediction errors are below 16 % within the process window.     

4Cr5MoSiV1热作模具钢的热变形行为与热加工图

利用Gleeble-3500型热模拟试验机对4Cr5MoSiV1热作模具钢进行单道次等温压缩试验,研究了其在变形温度750~1050℃,应变速率0.001~0.1s^-1条件下的热变形行为,并观察变形后的显微组织;根据试验得到的真应力-真应变曲线,构建了03真应变下的Arrhenius高温本构模型,并在动态材料模型基础上绘制了热加工图,从而得到该钢的合理热加工区间。结果表明:4Cr5MoSiV1钢的变形抗力随变形温度的升高或应变速率的降低而显著降低;4Cr5MoSiV1钢的热变形激活能为59452 kJ·mol^-1;在试验参数范围内,4Cr5MoSiV1钢合理的热加工区间为变形温度1050℃、应变速率0.001~0.01s^-1,此时组织中的碳化物细小且弥散分布,第二相强化效果显著。     

空间光学遥感器轨道外热流的计算与软件设计

简述了采用离散平面假设,计算空间光学遥感器的太阳辐射、地球红外辐射及地球阳光反照角系数和轨道外热流的方法。结合空间工程的结构、轨道参数和工况要求,设计开发了其实用计算软件以及与PATRAN软件进行数据传递的接口软件。该方法和软件已在实际工程的热分析计算中得到应用,适用于空间飞行器轨道外热流的计算。     

An experimental investigation of temperature distribution and flooding phenomena of cathode flow fields in a proton exchange membrane (PEM) fuel cell

Water management is considered to be one of the main issues to be addressed for the performance improvement of proton exchange membrane (PEM) fuel cells. In this paper, to investigate cathode flooding and its relationship with temperature distribution, an experimental study was carried out on cathode sides of an operating single PEM fuel cell. For the direct visualization of temperature fields and water transport in cathode flow channels, a transparent cell was designed and manufactured using quartz window. Liquid water transport and distribution in the flow channels were investigated experimentally. Also, the visualization of temperature distributions in the cathode channels was made by using an IR (infra-red) camera. Results indicate that the temperature rise near the exit of cathode flow channels was found. It is expected that this study can effectively contribute to get the detailed data on water transport linked with thermal management during the operation of a PEM fuel cell.     

Fully automated measurement setup for non-destructive characterization of thermoelectric materials near room temperature

A measurement setup is presented that allows for a complete and non-destructive material characterization of electrochemically deposited thermoelectric material. All electrical (Seebeck coefficient α, electrical conductivity σ), thermal (thermal conductivity λ), and thermoelectric (figure of merit ZT) material parameters are determined within a single measurement run. The setup is capable of characterizing individual electrochemically deposited Bi(2+x)Te(3-x) pillars of various size and thickness down to a few 10 μm, embedded in a polymer matrix with a maximum measurement area of 1 × 1 cm(2). The temperature range is limited to an application specific window near room temperature of 10?°C to 70?°C. A maximum thermal flux of 1 W∕cm(2) can be applied to the device under test (DUT) by the Peltier element driven heat source and sink. The setup has a highly symmetric design and DUTs can be mounted and dismounted within few seconds. A novel in situ recalibration method for a simple, quick and more accurate calibration of all sensors has been developed. Thermal losses within the setup are analysed and are mathematically considered for each measurement. All random and systematic errors are encountered for by a MATLAB routine, calculating all the target parameters and their uncertainties. The setup provides a measurement accuracy of ±2.34 μV∕K for α, ±810.16 S∕m for σ, ±0.13 W∕mK for λ, and ±0.0075 for ZT at a mean temperature of 42.5?°C for the specifically designed test samples with a pillar diameter of 696 μm and thickness of 134 μm, embedded in a polyethylene terephthalate polymer matrix.     

Three-dimensional numerical modeling of an induction heated injection molding tool with flow visualization

Using elevated mold temperature is known to have a positive influence of final injection molded parts. Induction heating is a method that allow obtaining a rapid thermal cycle, so the overall molding cycle time is not increased. In the present research work, an integrated multi-turn induction heating coil has been developed and assembled into an injection molding tool provided with a glass window, so the effect of induction heating can directly be captured by a high speed camera. In addition, thermocouples and pressure sensors are also installed, and together with the high speed videos, comparison of the induction heating and filling of the cavity is compared and validated with simulations. Two polymer materials ABS and HVPC were utilized during the injection molding experiments carried out in this work. A nonlinear electromagnetic model was employed to establish an effective linear magnetic permeability. The three-dimensional transient thermal field of the mold cavity was then calculated and compared with the experiments. This thermal field was transferred to an injection molding flow solver to compare simulations and experimental results from the high speed video, both with and without the effect of induction heating. A rapid thermal cycle was proved to be feasible in a mold with an integrated induction coil. Furthermore, it was shown that the process can be modeled with good accuracy, both in terms of the thermal field and of the flow pattern.     

基于MAP估计的复小波域局部自适应绝缘子红外热像去噪方法

为了从强白噪声干扰的红外热像中提取真实的绝缘子盘面温度场信息,提出一种基于MAP估计的复小波域局部自适应去噪方法.首次证实了绝缘子红外热像双树复小波变换(DT-CWT)系数服从拉普拉斯分布,并对不同滤波器组采用各自最精细分解层子带系数估计噪声方差,利用待估计点圆形邻域系数估计信号方差,且随分辨率变化调整圆形邻域半径,使得MAP估计的无噪声系数更为准确,提高了去噪图像质量.实验结果表明,该方法比传统的Wiener滤波法、基于离散小波变换和DT-CWT的贝叶斯阈值去噪方法具有更高的信噪比,在有效去除图像噪声的同时,图像细节信息保留更完好.     

智能化窗户的设计

本文设计了一种智能化的窗户,该窗户可通过对室内室外的湿度、风速、光线强度、温度、煤气含量和二氧化碳含量等参数的测量,实现自动开启或关闭,或者通过通信模块向上级控制系统发出警报,从而实现窗户的智能化控制.