Antenna pattern control of planar arrays for long distance communications

As an alternative to standard antennas and due to the advent of low-cost digital processors and materials, adaptive antenna arrays are increasingly considered for applications in long distance communications. The pattern beam control potentialities provide the performance improvement of the communication systems. In this context, this work presents a technique that permits to synthesize the antenna pattern of a planar array. Considering that the relationship between the array factor and the array excitations for the far field region is a Fourier transform in the appropriate variables, the non-uniform sampling procedure is extended for planar arrays. These arrays permit a further control of the antenna pattern since two dimensions of space are used. The technique considers a number of array factor points equal to the array size, which is used to impose appropriated values in the antenna pattern. The produced array factor passes through those points with the desired values, which allows the synthesis of antenna patterns with appropriated characteristics. The theory is presented in order to develop the necessary direct expressions to calculate the array excitation. The array factor can be obtained using the inverse Fourier transform. As application examples, with this technique it is possible to define the level of each sidelobe of the antenna pattern, to control the main beam and to impose nulls in prescribed directions of the pattern.     

管理效率、技术进步与生产率增长——基于中美航空公司的比较

运用Malmquist生产率指数方法，对中美15个航空公司2000～2006年期间的全要素生产率的变化作了测算与对比。分析结果显示，2000—2006年这些公司的生产效率总体上都有所提高，中国航空公司的全要素生产率的平均增长率为4.3％，美国的平均增长率为6．1％；综合效率改善与技术进步对中美两国航空公司生产率的影响程度并不相同，美国航空公司的主要驱动因素为技术变革与创新，中国航空公司的发展动力主要为对已有技术的运用以及组织管理效率的提升。中国航空公司全要素生产率水平的提高，除继续强调综合效率的重要性之外，也要进一步加强对技术进步的重视。     

Applications of structural efficiency assessment method on structural-mechanical characteristics integrated design in aero-engines

In the design process of advanced aero-engines, it is necessary to carry out an effective analysis method between structural features and mechanical characteristics for a better structural optimization. Based on the structural composition and functions of aero-engines, the concept and contents of structural efficiency can reflect the relation between structural features and mechanical characteristics. In order to achieve the integrated design of structural and mechanical characteristics, one quantitative analysis method called Structural Efficiency Assessment Method (SEAM) was put forward. The structural efficiency coefficient was obtained by synthesizing the parameters to quantitatively evaluate the aero-engine structure design level. Parameterization method to evaluate structural design quality was realized. After analyzing the structural features of an actual dual-rotor system in typical high bypass ratio turbofan engines, the mechanical characteristics and structural efficiency coefficient were calculated. Structural efficiency coefficient of high-pressure rotor (0.43) is higher than that of low-pressure rotor (0.29), which directly shows the performance of the former is better, there is room for improvement in structural design of the low-pressure rotor. Thus the direction of structural optimization was pointed out. The applications of SEAM shows that the method is operational and effective in the evaluation and improvement of structural design.     

驻涡燃烧室前钝体燃料喷射性能数值分析

为研究驻涡燃烧室在前钝体燃料喷射状况下的燃烧性能,采用3维数值仿真模拟方法,对驻涡燃烧室前钝体燃料喷射 状况下的燃烧效率及燃烧室性能与无前钝体燃料喷射状况下的燃烧性能进行了对比分析,并对驻涡燃烧室的冷流以及燃烧状态 下的燃烧室性能进行了系统研究。燃烧室温度分布表明：前钝体顶部燃料喷射在0.2~0.7的喷射系数范围内,缩短了燃烧室火焰 长度,提高了燃烧室在相同轴向长度下的燃烧效率,使燃烧室更加紧凑;驻涡燃烧室前钝体顶部燃料喷射孔的孔径在一定范围内 的变化对燃烧室的燃烧效率、出口温度分布系数以及总压损失影响较小。     

涡轮动叶表面换热特性的试验研究

航空发动机性能的提高对涡轮叶片耐热极限提出了更高的要求,为了更准确地分析涡轮叶片的传热特性,选取某型气冷涡轮动叶10%、50%和90%叶高的特征型面通过低导热光敏树脂材料经过3D打印而成,通过叶片表面粘贴厚度为0.02mm康铜加热膜接通恒定电流加热,使用红外热像系统精确测量叶片壁面温度,在平面叶栅中研究了吹风比(M)和雷诺数(Re)对气膜绝热冷却效率和努塞尔数(Nu)的影响(试验中基于弦长的进口雷诺数Re为8.0×10⁴-16.7×10⁴,吹风比M为1-3)。试验结果表明：M=1时气膜能够较好附着在叶片表面,叶片表面得到较好冷却;随着主流雷诺数的增加,绝热壁面温度逐渐升高,绝热效率逐渐降低;吹风比对涡轮叶片的传热特性的影响与气膜孔出流角度有关,随着吹风比的增大,压力面绝热冷却效率逐渐增大,由于吸力面的气膜孔出流角较大,吹风比增大使得吸力面的绝热冷却效率逐渐减小;随着吹风比的增加,对流换热系数增大。     

机匣沟槽对微型轴流涡轮叶尖泄漏流动的影响

本文通过对某微型涡喷发动机的单级轴流式涡轮进行机匣设计,采用剪切应力输运(SST)模型求解定常黏性雷诺平均Navier-Stokes方程,研究了不同机匣沟槽结构对其叶尖泄漏流动的影响。计算结果说明：当全机匣沟槽结构的叶顶浸入沟槽即d/c＞1.0时,封严效果较好;相较于全机匣沟槽结构,后开式机匣沟槽结构的封严效果更好, 随着沟槽前缘间隙的增大,封严效果减弱;沟槽深度a/c=1时,封严效果最佳,即泄漏流明显减弱,同时效率减小量较小。     

自适应复合材料薄壁梁形状控制

针对翼面和桨叶等升力面结构,以单闭室薄壁梁为典型结构模型,讨论自适应复合材料薄壁梁的弯曲和扭转,探讨控制结构形状的途径     

复合材料层合梁分层问题中应力强度因子与守恒积分的解析变分解法

利用虚功原理导出了涉及两种不同介质的守恒积分表达式以及守恒积分J_Ⅰ与应力强度因子K_Ⅱ的关系式。对于对称正交铺层复合材料层合梁的分层问题,在利用分区广义变分原理确定了应力强度因子K_Ⅱ以及应力与位移本征展开式中的所有待定系数的基础上,进一步求出守恒积分值。最后,作为验证,由J_Ⅰ求出K_Ⅱ,并与由解析变分方法求出的K_Ⅱ相比较。计算表明,本方法前期准备工作少,计算节省机时,结果收敛迅速;沿不同积分路径求出的守恒积分保持恒定,并且用两种方法求出的K_Ⅱ具有很好的一致性。     

一种高效卫星赋形波束用圆极化馈源

本文介绍了一种賦形波束天线用的圆极化馈源。讨论了形成賦形波束的多馈源天线的特殊问题,通过理论及其实验以及它们的相互比较,说明了十字膜片馈源对于解决这类问题的适用性。比较了不同种类馈源对天线覆盖区增益的影响,从而进一步证明了十字膜片馈源的优点。     

基于表面再现 Marching cubes算法改进与实现

从医学体数据中得到对象的三维可视图像有广泛的应用领域,例如医学诊断、法医学、古人类学等.本文讨论并分析了一种基于表面再现的 Marching cubes算法的优点及存在的不足,给出了算法在时空开销、不确定性等方面的改进和解决方案,改进后的算法在实际系统中取得了良好的效果.