黏结剂含量对碳基材料性能和结构的影响

以沥青焦、炭黑、人造石墨粉为骨料,以硫改性沥青为黏结剂,通过浆涂混合冷压炭化工艺,制备了一系列碳基体材料.考察了黏结剂含量对碳材料的物理性能和微观结构的影响.结果表明,碳材料的物理性能和微观结构与黏结剂含量有重要的关系;随黏结剂含量的增加,材料的密度和强度呈增大的趋势,而开孔率则逐渐下降;当黏结剂质量分数为44%时,材料的弯曲强度和压缩强度分别达到42.6 MPa和187 MPa;当黏结剂质量分数超过44%时,材料在炭化过程中破裂.这些变化可归因于黏结剂与骨料颗粒在热混捏和炭化过程中的相互作用机理.     

月球探测中通信跟踪(C&T)技术遇到的新问题

以技术成熟的GEO以下近地轨道的C&T技术为参照点,提出月球探测遇到的新问题———长时间、远距离地月转移轨道测量、环月轨道段测量和月面登陆段测量中的新问题,给出解决这些问题的合理方法。     

降落伞充气时间的计算方法

文章介绍了各类降落伞充气时间的计算方法。对密致伞 ,将质量守恒方程与物 -伞系统的运动方程相结合推导出计算充气时间的数学模型并应用于一个算例。对开缝伞 ,提供了计算充气时间的经验公式。对采用收口技术的伞也提供了计算充气时间的经验公式。     

Analysis on capabilities of density-based solvers within OpenFOAM to distinguish aerothermal variables in difusion boundary layer

Open source feld operation and manipulation（OpenFOAM）is one of the most prevalent open source computational fluid dynamics（CFD）software.It is very convenient for researchers to develop their own codes based on the class library toolbox within OpenFOAM.In recent years,several density-based solvers within OpenFOAM for supersonic/hypersonic compressible flow are coming up.Although the capabilities of these solvers to capture shock wave have already been verifed by some researchers,these solvers still need to be validated comprehensively as commercial CFD software.In boundary layer where diffusion is the dominant transportation manner,the convective discrete schemes＇capability to capture aerothermal variables,such as temperature and heat flux,is different from each other due to their own numerical dissipative characteristics and from viewpoint of this capability,these compressible solvers within OpenFOAM can be validated further.In this paper,frstly,the organizational architecture of density-based solvers within OpenFOAM is analyzed.Then,from the viewpoint of the capability to capture aerothermal variables,the numerical results of several typical geometrical felds predicted by these solvers are compared with both the outcome obtained from the commercial software Fastran and the experimental data.During the computing process,the Roe,AUSM＋（Advection Upstream Splitting Method）,and HLLC（Harten-Lax-van Leer-Contact）convective discrete schemes of which the spatial accuracy is 1st and 2nd order are utilized,respectively.The compared results show that the aerothermal variables are in agreement with results generated by Fastran and the experimental data even if the1st order spatial precision is implemented.Overall,the accuracy of these density-based solvers can meet the requirement of engineering and scientifc problems to capture aerothermal variables in diffusion boundary layer.     

在UG中参数化设计齿轮创建零件库

通过使用UG/Open系列的UG二次开发工具,以直齿圆柱齿轮的参数化设计为例,研究构建UG的零件库的新方法。在分析了标准渐开线直齿轮设计模型的基础上,建立了直齿齿轮的三维参数化模型。     

一种新型高选择性微带带通滤波器设计

介绍了一种通过在微带开环谐振滤波器中引入交叉耦合,产生一对传输极点,从而提高通带选择性的滤波器设计方法。讨论了这种滤波器的综合方法和实现流程。实际设计了一个六阶开环谐振滤波器,并给出了全波仿真结果。分析和仿真都表明这种滤波器具有体积紧凑、选择性高的优点。     

开放式计算机试题库系统

本文通过对开放式计算机试题库系统设计的阐述，介绍了开放式计算机试题库系统的基本特点，并阐述了计算机系统设计计算机试题库的基本环节、难点问题及解决方法，并给出了程序流程图。     

Reynolds number effect on compressible cylindrical cavity flow

Presence of a cavity changes the mean and fluctuating pressure distributions inside and near the cavity. For cylindrical cavity flow, the diameter-to-depth ratio is the dominant factor. In this study, flow is naturally developed along a flat plate with two different lengths, resulting in different incoming boundary layer thicknesses ahead of the cavity. The effect of Reynolds number based on incoming boundary layer thickness on characteristics of mean and fluctuating pressure distributions is addressed. Pressure sensitive paint was also used to visualize the mean surface pressure patterns. The effect of Reynolds number on the classification of compressible cylindrical cavity flow and self-sustained oscillating frequency is not significant. An increase in Reynolds number results in a reduction in the value of differential pressure or momentum flux near the rear edge.     

一种可容错的无刷直流电机驱动控制方法

针对反电势为梯形波的永磁无刷直流电机断路故障,提出了一种可容错的驱动控制方法,利用电流传感器对故障进行检测和定位,对发生的一相断路故障,通过在传统三相全桥驱动电路基础上增加一路半桥,并将电机星型连接点引出与之相连,实现故障状态下的容错驱动。在Simulink中建立正常运行模型和容错运行模型,对所提出的驱动方案进行验证和分析。最后,通过实验证明了该方案的可行性以及理论分析和仿真的正确性。     

减速板对水平尾翼的干扰研究

在ＮＨ－２风洞中对某机放减速板产生较大抬头力矩的机理进行了研究，通过减速板分离涡场的测量和测力试验表明，抬头力矩主要是由减速板分离涡在平尾处产生在的诱导下洗角所致，诱导下洗角涡机身轴线向后逐渐减小，减速板前移可以消除抬头力矩。保持原减速板位置不动时，减速板开孔减小涡强度可以减小抬头力矩，选择适当的减速板开孔率和开孔位置能使抬头力矩减小到可以接受的程度并且保持具有足够的阻力。