组件与非组件式热阴极的热特性分析

利用ANSYS软件研究了组件式热阴极与非组件式热阴极在阴极温度分布和启动时间等特性上的异同,并与实验结果进行对比。结果表明：组件与非组件式结构的阴极表面温度分布都十分均匀,组件式阴极钼筒外表面的温差与热子输入功率成正比;组件式阴极的钼筒外温度、阴极温度高于非组件式的,而热子温度明显低于非组件式的,但非组件式阴极启动更快;非组件式阴极通过增加阴极下表面发射率可以显著升高阴极温度,增加热子发射率可以显著降低热子温度,从而热性能也能达到与组件式阴极相近水准。     

组件与非组件式热阴极的热特性分析

 利用ANSYS软件研究了组件式热阴极与非组件式热阴极在阴极温度分布和启动时间等特性上的异同,并与实验结果进行对比。结果表明：组件与非组件式结构的阴极表面温度分布都十分均匀,组件式阴极钼筒外表面的温差与热子输入功率成正比;组件式阴极的钼筒外温度、阴极温度高于非组件式的,而热子温度明显低于非组件式的,但非组件式阴极启动更快;非组件式阴极通过增加阴极下表面发射率可以显著升高阴极温度,增加热子发射率可以显著降低热子温度,从而热性能也能达到与组件式阴极相近水准。     

离子推力器栅极组件温度场仿真分析及试验研究

栅极组件热变形是影响离子推力器工作性能及工作寿命的主要因素,为研究栅极组件升温过程中温度场分布及变化规律,探索能较准确模拟栅极温度场的方法,建立了栅极组件1/12全尺寸有限元模型进行温度场仿真计算。同时,基于实验室搭建的温度测量平台,测量了大气环境下加热时栅极组件的瞬态温度变化。对比有限元分析求解与试验过程中的温度场,加速栅平均误差为14.4%,屏栅平均误差为9.7%,双栅最大误差不超过18.4%,验证了有限元模型及方法的可信度和合理性。     

海洋环境下光电设备控制电机选型分析与研究

光电设备设计要求结构紧凑、体积小、质量轻、工作精度高、响应速度快、可靠性高。传统的电机选型会留有较多余量,导致伺服驱动电机的尺寸过大,进而导致整个系统的尺寸和质量增大。因此在对电机的选型时应充分考虑其搭载的平台。分析了在海洋环境下某光电设备伺服控制电机克服外界环境时需要考虑各项因素,如在复杂海况环境下载体摇摆,参考电机机械性能指标,选取合适电机,并通过摇摆试验和实际使用验证了该电机选择的合理性。     

空间遥感相机长条反射镜组件的动力学特性分析

空间遥感相机长条反射镜较圆反射镜的整体刚度相差很大,整个组件在随火箭发射过程中因力学环境引起的自身位置改变导致面形的微小畸变从而对成像质量造成严重影响。因此,反射镜组件的设计就成为整个相机系统研制的重点与难点之一。对其进行科学、严谨的力学环境仿真是设计中的有效辅助手段。对某相机的长条反射镜组件动力学响应进行了较为深入的研究,借助MSC-patran,用有限元法进行了求解。获得了组件的动力学特性。     

某航空光电稳定平台方位框架设计和分析

直升机载光电稳定平台载荷近红外相机在垂直成像过程中会产生像旋,为了消除像旋,同时满足载机对光电稳定平台的体积尺寸要求,提出悬臂式方位框架的结构方案,建立了方位框架结构的三维模型。利用有限元方法建立仿真模型,分别进行静力学分析和模态分析,研究方位框架悬臂结构的合理性。在24.5 kg负载情况下,设计的方位框架最大变形量为0.025 4 mm,满足指向精度误差分配要求;框架结构一阶频率为42.99 Hz,满足系统伺服带宽要求。     

全工况下光伏组件输出特性的预测建模与研究

在光生电流远大于二极管反向饱和电流,并联电阻为无穷大且二极管反向饱和电流与光强无关的假设条件下,理论上推导出全工况光伏组件输出特性预测模型,并采用Matlab/Simulink搭建了仿真系统.对单(多)晶硅光伏组件的实验与预测对比,表明模型可以准确预测组件在任意光强与温度下的输出特性,预测误差在6%以下.研究结果发现,相对于光强变化,温度变化对组件输出特性预测影响更大;多晶硅组件预测难于单晶硅组件.对实际环境中单位光强与单位温度实时改变时的预测表明,组件输出主要由所受辐照总光强决定,而不是器件温度;且需要根据外界情况调整组件的输出电压,以实现最大功率输出.     

基于ANSYS的高温超导直线感应电机仿真分析

随着直线感应电机在地铁等城市轨道交通中的不断应用和高温超导带材技术的不断完善,文中提出一种新型高温超导直线感应电动机的设计思路,依据直线感应电机电磁设计原理,对高温超导直线感应电机进行了研究和设计;利用大型有限元软件ANSYS对电机的电磁场、电磁力等进行仿真,给出仿真结果;并对仿真结果进行简要说明。最后通过对普通铜绕组直线感应电机和高温超导直线感应电机的理论和仿真分析对比,验证了高温超导直线感应电机将具有更大的优越性。     

基于Maxwell/RMxprt的超导电机设备参数特性分析

与常规电机相比,超导电机具备功率密度和体积优势。当今,实际制作超导电机的成本非常巨大,若设计有误,会给设计方和开发方造成巨大的经济损失。而Maxwell仿真软件的RMxprt模块,可以利用可视化模窗口模拟出超导电机的尺寸和电磁特性,以及各项性能参数,得到的计算结果可以为超导电机设计提供有效参考,降低设计时间与成本。提供了超导电机的主要流程,可以较为清晰地分析超导电机性能变化的规律,为最佳方案设计提供可信参考。并解决了电机效率低下,避免磁场饱和过剩等问题。     

小型传导冷却低温系统热分析与实验研究

传导冷却型低温系统中,各结构组件间的热平衡过程是以固体间热传导的形式向制冷机实现热量传递。由于各冷却部件降温条件的差异,会导致系统内部温度分布不均匀,影响被测样品性能测量,需对系统结构开展热分析与实验研究。借助ANSYS软件,建立了小型低温系统三维模型并进行了热分析,结果显示,预期系统最低温度为2.38 K,冷屏最大温差不超过1.0 K,样品台最大温差不超过0.1 K。同时,采用一套2.2 W@4.2 K双级制冷机作为冷源,完成了低温系统降温与精准控温实验。实验结果表明,冷屏误差不超过1.5 K,样品台误差不超过0.01 K,与模拟分析结果吻合良好,满足系统要求,验证了传导冷却低温系统热分析方法的准确性以及实验装置测温的可靠性,为类似装置的热分析及其设计提供了参考。     

光电吊舱大速率平稳跟踪补偿技术研究

针对某型号光电吊舱大速率跟踪时的不平稳现象，提出了一种改进的滤波滞后超前补偿网络。运用MATLAB软件建立了系统机械传动装置的数学模型，分析了该滤波网络对系统动态性能的改进效果。相对于常规滤波器，该滤波网络既考虑了中心谐振频率对系统动态性能的影响，又兼顾了其他谐振点对系统性能的影响。实验结果表明：采用该滤波网络能显著提高系统的动态性能，有效抑制抖动幅度，且数字滤波更易于实现。     

Lattice-controlled electron transport characteristics in quantized surface layers at low temperature

A theory of intravalley acoustic scattering of the carriers in a non-degenerate two-dimensional electron gas is developed here under the condition of low lattice temperature when the assumptions of the well-known traditional theory are not valid. The scattering rates thus obtained are then used to estimate the zero-field mobility characteristics in an n-channel Si inversion layer. It is found that the finite energy of the phonons makes the energy and lattice temperature dependence of the scattering rate, and consequently the lattice temperature dependence of the mobility, significantly different from what follows, in the light of traditional theory which assumes equipartition law for the phonon distribution and neglects the phonon energy in comparison to the carrier energy.     

Quantum friction of micromechanical resonators at low temperatures

Dissipation of micro- and nanoscale mechanical structures is dominated by quantum-mechanical tunneling of two-level defects intrinsically present in the system. We find that at high frequencies-usually, for smaller, micron-scale structures-a novel mechanism of phonon pumping of two-level defects gives rise to weakly temperature-dependent internal friction, Q-1, concomitant to the effects observed in recent experiments. Because of their size, comparable to or shorter than the emitted phonon wavelength, these structures suffer from superradiance-enhanced dissipation by the collective relaxation of a large number of two-level defects contained within the wavelength.     

Noise-induced transitions in a double-well potential at low friction

A new integral representation of the transition rate holds for any friction and is shown to allow a feasible evaluation in a wide friction range. Analytic approximations include the (high-friction) Kramers result with the leading correction, as well as a low-friction case. The method is complementary to a recent one of Melnikov and Meshkov.     

The thermal characteristics of a closed two-phase thermosyphon at low temperature difference

The applications of closed two-phase thermosyphons are increasing in heat recovery systems because of their high effective conductivity. However, their range of application is limited by the need for some minimum temperature difference between the evaporator and condenser sections to initiate nucleate boiling. In the project described, the steady state heat transfer characteristics for vertical two-phase closed thermosyphons at low temperature differences with R11, R22, and water as working fluid were studied experimentally. From these experimental results, the minimum temperature differences required to initiate and sustain boiling in the low temperature thermosyphons have been established for the above working fluids. A method for improving the performance at low temperature difference was devised on the basis of a thermal triggering system. Triggering could also be achieved by mechanical vibration.     

Theory of mutual friction in superfluid He at low temperatures

We review the microscopic theory of the mutual friction in superfluid ³He. This theory suggests that the dynamics of vortices is governed by the interaction between the quasiparticles localized in the vortex core and excitations outside the vortex. The mutual friction parameters are determined by the ratio of the distance between the energy levels of quasiparticles localized in the vortex and the relaxation rate of these quasiparticles.     

New crystalline phases of an equiatomic K-Cs alloy at low temperature

Solid equiatomic K-Cs alloys have been investigated by X-ray diffraction throughout the temperature range 300-100K. The results indicate that a phase separation occurs below 185K accompanied by the appearance of an ordered phase in this range. This phase has a hexagonal lattice with parameters: a = 9.32(1) Å and c = 11.80(2) Å (at 170K). Evidence from our other studies [7] indicates that its composition is K₂Cs. Another phase transformation in this ordered crystal is observed below 120K. There is no change of lattice symmetry but the unit cell constants shrink to the values: a = 9.11(1) Å and c = 10.86(2) Å (at 100K). The transformation can be ascribed to a rearrangement of the electronic structure of Cs.     

Johnson noise at low temperature

It has long been accepted that Johnson noise in metals is proportional to absolute temperature, and is materials-independent. This is a semi-classical result, based on the equipartition of energy. Johnson noise in copper below 10 mK suggests a departure from this relation. The data have been fitted empirically to T_J = T_o coth $\text{T}{}_{\mathrm{<mtext>o</mtext>}}\text{T}$, where T_J is the “Johnson noise” temperature, T is measured by CMN, and T_o is chosen for best fit and is about 2 mK. T_o is now identifiable with a zero-point frequency of electronic charge imbalance, which moves with average Fermi velocity ν from end to end of the resistor of length l. $\text{T}{}_{\mathrm{<mtext>o</mtext><mtext>\; =\; </mtext><mtext>h\nu </mtext><mtext>2kl\; \approx \; 2\; </mtext><mtext>mK</mtext>}}$, and so is materials- and geometry-dependent.     

Quantum tunneling at zero temperature in the strong friction regime

In the large damping limit we derive a Fokker-Planck equation in configuration space (the so-called Smoluchowski equation) describing a Brownian particle immersed into a thermal environment and subjected to a nonlinear external force. We quantize this stochastic system and survey the problem of escape over a double-well potential barrier. Our finding is that the quantum Kramers rate does not depend on the friction coefficient at low temperatures; i.e., we predict a superfluidity phenomenon in overdamped open systems. Moreover, at zero temperature we show that the quantum escape rate does not vanish in the strong friction regime. This result, therefore, is in contrast with the work by Ankerhold et al. [Phys. Rev. Lett. 87, 086802 (2001)]] in which no quantum tunneling is predicted at zero temperature.