二维编织C／SiC复合材料高温拉伸性能研究

对二维编织C／SiC复合材料在1300℃高温氩气、湿氧环境下拉伸性能进行了实验,结合断口观察分析了其在拉伸载荷下的损伤和破坏机理。试验结果表明,二维编织C／SiC复合材料在高温氩气、湿氧环境下表现为非线性特征,通过对比发现,由于氧化作用,高温氩气环境下拉伸强度、破坏应变和比例极限均高于高温湿氧环境。断口观察表明,基体开裂、层间分层以及纤维和纤维束的断裂拔出是材料拉伸破坏的主要形式。     

An inversion approach for lunar regolith layer thickness using optical albedo data and microwave emission simulation

An approach to inversion of the lunar regolith layer thickness by using multi-channel brightness temperature observation in passive microwave remote sensing is developed. To first make simulation of brightness temperature from the lunar layered media, the lunar regolith layer thickness (d) is proposed being constructed by available lunar DEM (digital elevation mapping) and on site measurements. The physical temperature distribution (T) over the lunar surface is also empirically assumed as a monotonic function of the latitude. Optical albedo of the lunar nearside from the telescopic observation is employed to construct the spatial distribution of the FeO+TiO₂ content (S) in the lunar regolith layer. A statistic relationship between the DEM and S of the lunar nearside is further extended to construction of S of the lunar farside. Thus, the dielectric permittivity (ε) of global lunar regolith layer can then be determined. Based on all these conditions (d,T,ε), brightness temperature of the lunar regolith layer in passive microwave remote sensing, which is planned for China's Chang-E lunar project, is numerically simulated by a parallel layering model using the strong fluctuation theory of random media.Then, taking these simulations with random noise as observations, an inversion method of the lunar regolith layer thickness is developed by using three- or two-channels brightness temperatures. When the S is low, and the four channels brightness temperatures in China's Chang-E project are well distinguishable, the regolith layer thickness and physical temperature of the underlying lunar rock media can be inverted by the three-channels approach. When the S becomes high that the brightness temperature at high frequency channels such as 19.35, 37 GHz are saturated, the regolith layer thickness is alternatively inverted only by the two-channels approach.Numerical simulation and inversion approach in this paper make an evaluation of the performance for lunar passive microwave remote sensing, and for future data calibration and validation.     

工业化生产中大规格2D70铝合金棒材淬透性的实验方法

采用多路温度控制仪监测材料淬火过程不同部位的温度变化的试验方法,通过对材料硬度和力学性能指标的测试分析,描绘出大规格2D70铝合金棒材截面上距离边部不同距离的硬度和力学性能变化曲线,对比分析了该试验条件和工业化生产条件下合金的硬度和力学性能变化曲线,探讨了本试验方法应用到工业化生产中检测材料淬透性的可能性。研究结果表明,淬火过程中2D70铝合金Ф250mm×250mm的棒材边部和心部的温度基本均匀,淬火过程中总的冷却速率为4℃／s,可满足合金充分固溶的要求,工业化生产的250mm棒材已经完全淬透。     

三种热喷涂工艺制备NiCr/Cr_3C_2-BaF_2·CaF_2涂层的结构与性能

采用大气等离子喷涂、爆炸喷涂和超音速火焰喷涂三种热喷涂技术制备了NiCr／Cr3C2-BaF2·CaF2涂层,分析比较了涂层的显微组织、物相组成、孔隙率、硬度、结合强度及其摩擦学性能。结果表明,与大气等离子喷涂相比,超音速火焰喷涂和爆炸喷涂技术制备的涂层具有更高的致密度、硬度和结合强度。采用包覆法制备的粉末进行喷涂,碳化物失碳明显减少,涂层中氧化物含量低。三种NiCr／Cr3C2-BaF2·CaF2热喷涂涂层的摩擦系数都随着温度的升高而减小,爆炸喷涂和超音速火焰喷涂涂层的摩擦系数比等离子喷涂涂层的摩擦系数更低,耐磨性得到提高。高温下BaF2·CaF2润滑膜的形成均可有效降低三种涂层的摩擦系数,从而降低涂层和对磨球Si3N4的磨损率。     

基于自校正模糊神经控制的无刷直流传动系统

提出了一种自校正模糊神经网络控制器(SCFNNC)来实现无刷直流电动机起动、调速、制动等各运行阶段的性能指标.该SCFNNC是采用调整系统增益参数的方法完成较完善的控制规则的.重点研究了系统自校正增益参数的确定方法,模糊控制器的设计,人工神经网络实现模糊控制规则的方法等.自校正增益参数是根据系统对超调量、转速稳态误差、动态速降的期望值来确定的.设计模糊控制器时是根据系统的性能指标,确定出合适的模糊控制规则表,用于训练神经网络.为使系统的性能达到最佳,采用了自校正模糊神经控制、开关控制和比例控制相结合的复合控制方法,通过数学仿真证实配备SCFNNC的系统具有优良的动、静态特性,及较强的鲁棒性.     

拦截机动目标的模糊导引律研究

使用模糊方法研究了三维实际追逃问题的最小能量导引律问题。首先,通过对一些状态变量的定义域进行在线模糊分区,一方面,将非线性模型变为模糊T-S线性模型;另一方面,又能方便地处理目标的任意机动而引起的目标运动方向的变化。其次,利用RH（Receding Hori-zon）控制方法和伴随技术,在目标作对抗性机动条件下,获得了一个有效拦截的导引律。数值仿真结果表明,由这种导引律导引的导弹能够精确拦截任意机动的目标。     

基于特征点的颅面复原技术

介绍了用人工神经网络算法确定待复原颅面的软组织厚度及颅面特征点的方法。在计算机辅助颅面复原过程中,通常只能根据颅骨上少数特征点及其所在部位的法向软组织厚度的统计值进行运算。由于现有统计值指标涵盖的年龄较宽泛,导致复原结果缺乏个性。在测定待复原颅骨骨龄的基础上,通过神经网络训练,确定软组织厚度随年龄的变化规律,较精确地计算出与拟复原对象的骨龄相适应的特征点软组织厚度值,并用最小二乘法及曲面法线原理建立数学模型,计算出颅面特征点。最后用基于Delaunay三角剖分的wavelet插值法复原出面貌雏形。     

基于QAR的PW4077D发动机放气活门与N1的关系

航空发动机的放气活门调节规律是一个较为复杂的控制过程。依据大量QAR数据,采用数学分析的方法初步探索了PW4077D型发动机2.5级放气活门开度控制规律。通过对大量数据的统计分析可知,放气活门开度与低压转子转速N1关系最为密切。首先通过数据解码和修正得到各航班标准状态下的N1值;采用非线性回归的数理统计方法分段拟合,得到2.5级放气活门开度与N1的数学模型。经检验,该模型在一定范围内良好地反映了该型发动机2.5级放气活门开度大小的调节规律。     

基于网络的《工程力学》实验系统初探

实验教学是学生获得知识和能力训练的重要途径,工程力学实验是工科院校学生的一门技术基础课。尝试利用现代网络技术和3Dmax软件,结合我校的力学实验课教学,开发一套基于网络的工程力学实验教学系统,作为对理论教学和实验室教学的补充,取得很好效果。     

New He neutron monitor for Chilean Cosmic-Ray Observatories from the Altiplanic zone to the Antarctic zone

We present the results of three years of continuous operations and the principal characteristics of our new ³He neutron monitors installed in the Chilean Network of Cosmic-Ray Observatories. During the years 2004 and 2005, we began the construction of this International Geophysical Year (IGY)-type ³He neutron monitor, with the intention of replacing the older proportional tubes of the BF₃. These new monitors are installed in stations at locations ranging from the near-equatorial zone to the Antarctic zone. As a reference system, we used our own BF₃ neutron monitors and previously complemented the collected data with a Monte Carlo simulation for the proton-yield function response of the Putre neutron monitor. Herein, we present for the first time the data obtained from our new high-mountain observatory located in the Altiplanic zone.