电力变压器铁芯温度场的数值解法与实施

本文系统地介绍了求解电力变压器铁芯温度场的三维数值方法,较好地解决了流体—构件耦合场的数值求解问题,并采用有限元法对若干影响铁芯温升的相关因素进行了大量的数值模拟研究。     

Evaluation of temperature characteristics of high-efficiency InGaP/InGaAs/Ge triple-junction solar cells under concentration

Temperature characteristics of the open-circuit voltage (V_oc) were investigated in the temperature range from 30°C to 240°C for the InGaP/InGaAs/Ge triple-junction cells. Also, single-junction cells that had the similar structure to the subcells in the triple-junction cells were studied. In the high-temperature range (from 170°C to 240°C), the temperature coefficients of V_oc of the InGaP/InGaAs/Ge triple-junction solar cell (dV_oc/dT) were different from those in the low-temperature range (from 30°C to 100°C). This is because photo-voltage from the Ge subcell becomes almost 0 V in the high-temperature range. It was found that the open-circuit voltage of a Ge single-junction cell reduced to almost 0 V temperatures over 120°C under 1 sun condition.     

Two-dimensional thermal analysis of a polygonal fin with two tubes on a square pitch

The boundary element method (BEM) has been used to investigate the two-dimensional temperature distribution and the flow of heat from a polygonal fin with two tubes on a square pitch. This numerical method is shown to be convergent, stable and consistent. The resultant heat flows from the fin and the tubes are presented in the form of fin performance ratios. The values of the two-dimensional fin performance ratios are almost identical to those obtained for a single radial rectangular fin of equivalent surface area. The one-dimensional fin performance indicators, fin performance ratio or fin efficiency can be used to predict the heat flows. However, the two-dimensional temperature distributions have revealed the existence of conductive paths between the two tubes depending upon the fin dimensions, the values of the heat transfer and material thermal conductivity, and the magnitude of the temperature differences between the two tubes and the surrounding air.     

贯流式机组水电站厂房底板施工期温度场仿真分析

对于水电站厂房这样结构复杂的大型水工结构,提出了将国外著名的大型有限元计算软件与自主开发的温度场、温度应力仿真计算程序相结合的方法,解决了在仿真中实现三维空间内混凝土跳仓浇筑的困难,并对某水电站厂房底板进行了仿真计算分析。利用此方法,工程人员可以根据具体的施工方案、浇筑顺序方便地进行温度场、温度应力仿真分析,掌握温度分布情况,及时采取减小温度应力的相应温控措施。     

3-D Elasticity Solutions of Layered Rectangular Plates Subjected to Thermo-Loads

According to the exact three-dimensional (3D) thermoelasticity theory, the elasticity solution of the simply-supported layered rectangular plates subjected to steady temperature loads was studied. An analytical method was developed to solve the temperature, stress and displacement fields in the plate. Firstly, the general solutions of the temperature, displacements and stresses in a simply-supported isotropic layer were obtained by solving the 3-D heat conduction equation and the 3-D equations of elasticity respectively, which were expressed in the form of double Fourier series. Then, the temperature, displacement and stress relationships between the upper surface and the lower surface of the isotropic layer were derived. Based on the continuity of the temperature, the heat flux, the displacements and the stresses on the interface of two adjacent layers with different material properties, the recursive formulae of temperature, displacements and stresses between the bottom layer and the top layer of the layered plate were obtained by using the transfer matrix method. The unknown coefficients in the solutions for every layer were uniquely determined by the upper surface and lower surface conditions of the plate. The distributions of the temperature, displacements and stresses in the plate were given by substituting the unknown coefficients obtained back to the recurrence formulae and the solutions. The convergence of the solutions was checked with respect to the number of the terms of series. Comparing the results with those obtained from the finite element method, the correctness of the present method was verified. Finally, the effects of surface temperatures, plate thickness, layer number and material properties of each layer on the distributions of the temperature, displacements and stresses in the plates were discussed in detail.     

Two-Dimensional Green's Function for Thermal Stresses in a Semi-Layer Under a Point Heat Source

We present specific new expressions for thermal stresses as Green's functions for a plane boundary value problem of steady-state thermoelasticity for a semi-layer. We also obtain new integration formulas of Green's type, which determine the thermal stresses in the form of integrals of the products of the given distributed internal heat source, boundary temperature, and heat flux and derived kernels. Elementary functions results obtained are formulated in a theorem, which is proved using the harmonic integral representations method to derive thermal stresses Green's functions, which are written in terms of Green's functions for Poisson's equation. A new solution to particular two-dimensional boundary value problem for a semi-layer under a boundary constant temperature gradient is obtained in explicit form. Graphical presentations for thermal stresses Green's functions created by a unit heat source (line load in out-of-plane direction) and by a temperature gradient are also included.     

利用有限差分法计算空间目标红外特征

空间目标的红外辐射特性是对空间目标进行探测与识别的重要依据.首先分析了空间目标与外界环境的热交换关系,确定了目标表面的边界条件,推导出边界单元的有限差分形式,针对空间目标的遮挡问题.开展了判断方法的讨论,为准确计算目标的表面温度场奠定了基础.其次利用有限差分法求解其导热微分方程,获得了目标表面温度场分布特性;将总红外辐射分解为自发辐射和反射辐射两部分,分别给出了计算自发辐射强度和反射辐射强度的计算式.最后以某空间目标为例,利用数值方法计算表面温度场,并在此基础上计算了红外辐射强度的空间分布,对计算结果进行了分析.     

内热式多级连续真空炉炉温均匀性的测定及改善

内热式多级连续真空炉广泛应用于二元合金的分离中,但由于炉膛冷凝罩内温度均匀性差而影响了产品质量。真空炉温度控制水平不高是导致真空炉炉温均匀性差,制约真空炉广泛应用和发展的重要原因。本文以内热式多级连续真空炉温度控制为研究对象,利用模糊算法离线整定PID（由比例单元P、积分单元I和微分单元D组成的控制器）参数,得到了较为理想的控制效果。同时利用有限元法分析真空炉温度场分布规律并依此安装测量热电偶,在未加料的情况下测量结果表明：利用模糊算法整定PID参数后炉膛内各测试点温度偏差较改善前明显缩小,偏差降低率最小为2.38％,最大为6.35％。提高了真空炉冶炼合金的种类范围和产品质量。     

土壤相对湿度与电容相关性探究

土壤相对湿度是农业自动化灌溉技术的关键性指标,也是当前农田领域研究的热点问题。为了探索土壤电容与土壤相对湿度的相关性,设计了一种测量土壤电容值的方法,通过烘干法对不同湿度点进行了较为精准的电容值检测,最后通过matlab7.1作数据拟合。结果表明,土壤电容值与土壤相对湿度在30%-100%之间存在很好的对数关系,考虑温度补偿,得到任意温度t的湿度t=(17.53ln Cx-5.773)*(100+0.05075*(20-t))%,判定系数R2=0.975。     

A process-tolerant out-of-band blocker rejection technique for SAW-less receivers

In this paper, an active filtering technique is presented which is capable of filtering the out-of-band blockers in wireless receivers. The concept is based on the feedforward cancellation technique where a blocker replica is subtracted at the output of the low-noise amplifier (LNA). In contrast to the previously reported feedforward cancellation methods, exact gain and phase matching are easily obtained in the proposed architecture to produce a highly selective narrowband frequency response at the output of the LNA with wide rejection bandwidth. For the proof of concept, the system is implemented in a 65 nm CMOS technology. It occupies a total area of 0.8 mm² and the current consumption is 24 mA from a 1.2 V supply. The system post-layout simulations showed a blocker rejection of more than 33 dB for blocker signals 100 MHz away from the desired signal when the feedforward path is activated. The noise figure (NF) of the entire system is 3.8 dB that degrades to 5.8 dB when the feedforward path is activated.