Identical Steady-State Results for a Kalman Tracker

It is shown that the analytical results presented in [2, 3] for determining the steady state gain and error covariance matrices of the two state Kalman tracker [1] are identical although they appear to be different.     

随机声载荷时域信号门限自回归模型研究

利用航空发动机燃烧室噪声测试数据[1],采用门限自回归分析方法建立随机声载荷门限自回归模型SETAR(2;2;30,30),得到令人满意结果,并将拟合和预测均方误差与文献[1]非门限的自回归滑动平均模型ARMA(17,16)的结果进行了比较.     

Comments on "on Probability of Error in Decision Feedback Equalizer"

The above-mentioned paper [1] derives bounds on the error probability of a decision feedback equalizer (DFE) which are claimed to be significantly tighter than the earlier upper bound of [2]. Unfortunately, [1] makes an unsupportable assumption which reddars the conclusions incorrect. We show that valid bounds can be obtained by the methods of [1], but that for the numerical example of [2] , the resulting upper bound is never tighter than, and sometimes significantly weaker than, that derived in [2]. Similarly, a lower bound derived by the method of [1] is shown for the same numerical example to be very close to the error-free past lower bound previously known.     

A General Steepest Descent Algorithm

The following paper derives a general gradient process for extremization ion by imposing an " exponential decay" condition on the controlled variable. The general process is applied to two adaptive linear filter problems; a sonar application by Widrow [3] and a radar problem of Brennan & Reed [4]. The results are discussed in sections 11 and Ill, respectively. A central feature of the Fletcher-Powell process [1] is a matrix modification algorithm due to Davidon [2]. It is shown in Appendix A that this algorithm may be derived using the same exponential condition imposed on the proper error term.     

剩余柔度模态与附着模态在模态综合法中的等价性

在早期的模态综合法中,引起计算误差的主要原因是由于截去了高阶模态。文献[1～4]从不同角度揭示,剩余柔度模态和附着模态可以有效地补偿这种截断误差。在此基础上,已派生出两类新的自由界面模态综合法。第一类方法的特点是将子结构位移用自由界面模态与剩余柔度模态来表示,第二类方法的特点是用自由界面模态与附着模态来表示子结构位移。本文将指出,这两类方法是等价的。其等价性表现在剩余柔度模态与附着模态可以相互替换而不影响模态综合的最终结果。本文将以文献[4]提出的方法为例来证明该等价性,并在文末给出一个数值算例。     

2-D wavelet image transforms extended to 3-D with applications

Mallet and Zhong [1992] have derived some elegant results on 1-D and 2-D wavelet transforms. The objective here is to extend the 2-D results of Mallet and Zhong to 3-D. Illustrated here is how these results can be applied to the feature analysis of 2-D images with time t as the third dimension. An algorithm for extending 2-D to 3-D wavelets is presented     

Comments on "Computationally Efficient Bank of Rectangular Digital Filters"

In [1] a scheme for forming a rectangular FIR filter bank is described using only a few percent of the number of multiplications required by straightforward procedures. The sidelobe level suffers degradation. Attention is drawn to a different scheme published in [2] and [3] which needs even fewer multiplications without degradationvof the sidelobe level.     

非对称铺层复合材料板室温形状的非线性有限元分析

由于一般铺层复合材料板壳存在拉伸-弯曲、拉伸-扭转等耦合效应,在温度变化时将出现垂直于中面方向的翘曲变形,给工程使用和理论分析带来了极大的不便。但另一方面,利用非对称铺层复合材料板壳可以有效地减轻结构的重量,并可能提供利用平面模具制造曲面层合壳的新工艺。     

复合材料层板等强最优设计方法

 本文对复合材料无矩对称层板的最优设计,提出了一种概念直观、方法简便、收敛迅速、效果较好的等强最优设计方法。给出了几个算例的结果,并与文献[1、2]的方法作了对比,结果表明,本文的方法具有显著的优越性。     

Analysis of friction and heat flux on a sphere in the turbulent supersonic flow

The results of calculating the heat flux and local friction coefficient at the supersonic velocities of a flow past an impermeable spherical surface are presented for the case when the viscosity-temperature dependence is determined according to the Sutherland law. The mathematical model of a turbulent boundary layer for compressible gas [1, 2] is used. The heat flux and local friction coefficient are analyzed assuming that the turbulence regime starts from a critical point. Use is made of Dorodnitsyn’s method of generalized integral relations [3]. The results of computational experiments are compared with the data of [1, 4].     

发动机支点柔性圆周炭石墨密封材料PV值试验

根据高空长航时航空发动机支点柔性圆周炭石墨密封材料的实际服役工况,从高摩擦线速度（60～130 m/s）、轻载（30～400 kPa）和温度（25～600 ℃）的角度出发,自主设计动态试验测试台,评测国内部分现役机型用炭石墨密封材料的PV值,并通过装机论证PV值试验的可行性。试验结果表明:采用80 m/s恒速,逐级增加载荷测得XX1#-1、XX2#-1、XX3#-1、XX4#-1和XX5#-1的许用[PV]值分别为4.8、5.9、6.9、9.1、12.3 MPa·m/s。采用300 kPa定载,逐级增加线速度测得XX2#-2、XX3#-2、XX4#-2和XX5#-2的许用[PV]值分别为6.0、8.0、10.0、12.0 MPa·m/s。经某研究所装机论证发现当试验样的许用[PV]值小于发动机的许用[PV]值时,易出现异常磨损,并伴随燃气泄漏;当试验样的许用[PV]值大于发动机的许用[PV]值时,能为发动机支点炭石墨密封材料选型提供材料特性数据,为发动机炭石墨密封材料的研究提供鉴别方法。此外,该试验方法将大大节约发动机用石墨封严材料选型的时间成本、人力成本和上机论证经费的投入成本。      

Study on Compressive Properties of Z-pinned Laminates in RTD and Hygrothermal Environment

Compressive tests of [0] 12 and [90] 12 unidirectional laminates and [45/0/-45/90] 2S quasi-isotropic laminates are accomplished in both room-temperature and dry (RTD) and hygrothermal environment. And simulation studies on the compressive strength of Z-pinned laminates of [0] 12 and [45/0/-45/90] 2S are conducted by using finite element analysis (FEA). A microstructural unit cell for FEA is created to simulate a representative laminates unit with one pin. Within the unit cell, the first directions of the elements’ material coordinate systems are changed to simulate the fibres’ deflecting around the pin. The hygrothermal effect is simulated by the material properties’ adjustments which are determined by the compressive tests of non-pined laminates. The experimental results indicate that the percentage of reduction in the compressive modulus of Z-pinned laminates caused by Z-pin becomes smaller with the percentage of 0° fibres decreasing in the laminates; the compressive strength of quasi-isotropic laminates reduces and the percentage of the reduction in the compressive strength declines with Z-pin volume content increasing, and the moisture absorption ratio of the Z-pinned specimens is greater than that of the non-pinned specimens, because the cracks around Z-pin increase the moisture absorption. In addition, the simulations show that the deflection of fibres around Z-pin is the main factor for the reduction in the compressive strength of Z-pinned unidirectional laminates, the dilution of fibre volume content caused by resin-rich pocket is the principal factor for the decline in the compressive strength of Z-pinned quasi-istropic laminates, and the compressive strength of Z-pinned specimens in hygrothermal environment reduces as the result of superimposition of some factors, including the changes in material properties caused by hygrothermal environment, the deflection of fibres and the resin-rich pocket caused by Z-pin.     

碳纤维复合材料层压板低速冲击试验研究

为研究复合材料不同铺层结构的抗冲击性能,采用碳纤维预浸料制备了单向[0°]8和正交[0/90]2s铺层2种不同结构的碳纤维复合材料层压板,并使用Instron 9250落锤冲击测试仪测试其低速冲击性能,得到了载荷-时间曲线,分析了2种不同铺层方式的复合材料层压板的低速冲击加载力学性能,得到复合材料层压板的破坏形态来分析其破坏方式。结果表明:2种铺层方式产生了不同的破坏模式,正交[0/90]2s的复合材料层压板的抗低速冲击能力要优于单向[0°]8铺层的。     

基于筏化的镍基单晶合金高温蠕变模型

采用应力法以及界面能法对不同取向的镍基单晶合金在950℃下的筏化类型进行了预测.上述两种方法的筏化预测结果一致,[001]取向为N型筏化,[011]取向为P型筏化,[111]取向不筏化.进一步,根据筏化预测结果以及晶体滑移理论,结合Kachanov-Robotnov（K-R）损伤演化公式,建立了一个镍基单晶合金蠕变模型,采用该模型并结合商用有限元软件Abaqus的用户材料子程序（UMAT）二次开发接口,对[001],[011]和[111]取向下的CMSX-4镍基单晶合金,在950℃,180~450MPa应力条件下的蠕变变形行为进行了模拟.该模型能够准确预测镍基单晶合金的筏化类型以及滑移系开动规律,更加符合材料的蠕变变形物理机制,因此模型可以对镍基单晶合金的高温蠕变曲线的第2,3阶段进行很好的模拟,并得到了试验的验证.      

叶片空间造型的计算几何方法

 本文把新近发展起来的计算几何中的几种典型方法（包括Bézier曲面、B样条曲面和Bézier-B样条混合曲面等）,同航空发动机叶片空间造型结合起来,形成一套计算机辅助叶片外形设计的新方法。扭曲叶片由三二次混合曲面片拼接而成,型面有完整的数学模型。因此有利于叶片三元流场性能和有限元强度计算分析以及与数控加工相结合。实例表明该方法简单、灵活、计算量小,对大弯度叶片设计亦行之有效。     

A. M. Hubert and C. Jaschek (eds.), B[e] Stars

The B[e] stars are early type stars with hydrogen emission lines, forbidden [FeII] and [OI] emission lines, and with an IR excess due to circumstellar dust. These properties may occur in stars of quite different evolutionary stages. In fact, the group of B[e] stars is very inhomogeneous, and contains pre-main sequence stars, supergiants with disks, compact planetary nebulae, symbiotic stars, and a group of stars with unclear evolutionary phase. The book gives the proceedings of a workshop in Paris in 1997 in which the properties and evolutionary phases of the B[e] stars are discussed. It contains chapters on: (1) the definition of B[e] stars, (2) distances, kinematics and the distribution in our Galaxy, (3) spectroscopy, (4) infrared properties, (5) photometry, polarimetry and variability, (6) models for winds and disks, (7) evolutionary stages, (8) revised classification of B[e] stars. The book ends with an object list of all B[e] stars. The book is very useful for students and researchers of hot star winds and gives nice overviews of the observations and theories and remaining puzzles of these strange objects with winds and outflowing dust-forming disks. This revised version was published online in August 2006 with corrections to the Cover Date.     

Analysis of shells of revolution under symmetrical loading using the quadrature method

The application of the quadrature method [1] to analyzing the shells of revolution under symmetrical loading relative to the zero meridian is considered. The method can be treated as a generalization of the method presented in [2] to solve the Volterra integral equation of the second kind.     

Orthogonalization of a Direction Cosine Matrix by Iterative Techniques

It is shown that the ?first inversion, transposition, and averaging? technique [1] is, assuming convergence, quadratically convergent, since it can be developed very simply by the use of quasilinearization. Only the three-dimensional case is considered; the art of matrix orthogonalization is practiced in more general settings [2] than considered here.     

B-样条函数的一种快速递推法

 本文提出了常用的等距结点B-样条函数的一种快速递推法及递推计算格式和程序设计。阐明了此法具有计算简便、递推快速和更为直观的特点。它为B-样条函数的数学分析和推广应用提供了方便。此法将易于为一般工程技术人员掌握和运用。     

Comments on "Angular Spectra in Radar Applications"

In [1], we proposed using "data adaptive" spectrum estimation techniques (e.g., maximum likelihood and maximum entropy) for radar problems such as separating low angle returns from ground reflections. W. White suggests [2] that these techniques will be of little value due to the correlation between the various received signals. In this rebuttal, we present additional conceptual arguments, simulation results and field data which support the utility of the techniques set forth in [1].