用“参数多项式方法”确定风力透平叶片的失速振荡流

用“参数多项式方法”确定风力透平叶片的失速振荡流陈佐一,孙永忠,杨玲（清华大学热能工程系北京１０００８４）关键词：参数多项式方法,风力透平,颤振在现代各类流动诱导振动问题的研究中,流体激振的安全性分析与诊断,要求在较短的时间内,对大量的复杂流动工况进...     

Study of micro‐channel geometries for internally cooled Si monochromators

Rocking curves of micro‐channel (MC) water‐cooled monochromators are broadened by stresses introduced during fabrication and under X‐ray thermal load. This is a problem which will be even more serious with the rise of the fourth‐generation synchrotron sources, i.e. the free‐electron lasers. The X‐ray optics group at the Institute of Physics at the ASCR v.v.i. in Prague is designing, testing and, with company Polovodi?e a.s., fabricating novel internally water‐cooled Si monochromators. Here three new micro‐channel geometries are introduced which reduce rocking‐curve enlargement owing to the fabrication to less than 2.5 µrad (～0.5 arcsec). All three MC designs show less rocking‐curve enlargement and smoother topographic images. The designs also show better cooling efficiencies than the classical MC design in finite‐element analysis calculations.     

Structural response of stiffened plates in similitude under a turbulent boundary layer excitation

In structural dynamics, similitude laws usually deal with simple configurations as thin flat plates with point forces. Only recently, few papers have analyzed stiffened shells or stochastic pressure loads.This research activity extends the applicability of some similitude laws, developed for thin flat plates under a turbulent boundary layer load, to ribbed plates forced by the same wall pressure fluctuations.The work addresses the problem of designing a scaled experimental test-article and, successively, of re-modulating the measured data in order to get the structural response of an original (unscaled) configuration.Due to the complexity of the structural domain, the design of a scaled configuration leads to a distorted similitude. Then, a simple approach, to circumvent the distortion effects, is proposed.     

无轴承旋翼柔性梁载荷特性研究

应用Hamilton原理建立了双路传力的无轴承旋翼运动方程。采用均匀入流模型,基于直升机飞行平衡条件,建立了无轴承旋翼柔性梁载荷的计算模型,并通过算例验证了模型的精度。利用该模型,研究了全机重心位置、机身气动阻力以及平尾安装角对柔性梁载荷特性的影响,给出了各因素对柔性梁载荷的影响趋势,得出了降低柔性梁载荷的方法。数值结果表明:2cm左右重心位置的变化能够引起9%~11%的柔性梁载荷变化量,15%气动阻力的增加会导致约9%的柔性梁载荷的增大;2°平尾安装角的变化引起约10%柔性梁载荷的变化量,3°平尾安装角的变化引起约26%柔性梁载荷的变化。     

The Application of Fractal Transform and Entropy for Improving Fault Tolerance and Load Balancing in Grid Computing Environments

This paper applies the entropy-based fractal indexing scheme that enables the grid environment for fast indexing and querying. It addresses the issue of fault tolerance and load balancing-based fractal management to make computational grids more effective and reliable. A fractal dimension of a cloud of points gives an estimate of the intrinsic dimensionality of the data in that space. The main drawback of this technique is the long computing time. The main contribution of the suggested work is to investigate the effect of fractal transform by adding R-tree index structure-based entropy to existing grid computing models to obtain a balanced infrastructure with minimal fault. In this regard, the presented work is going to extend the commonly scheduling algorithms that are built based on the physical grid structure to a reduced logical network. The objective of this logical network is to reduce the searching in the grid paths according to arrival time rate and path’s bandwidth with respect to load balance and fault tolerance, respectively. Furthermore, an optimization searching technique is utilized to enhance the grid performance by investigating the optimum number of nodes extracted from the logical grid. The experimental results indicated that the proposed model has better execution time, throughput, makespan, latency, load balancing, and success rate.     

相干多普勒测风激光雷达

 鉴于多普勒测风激光雷达在航空航天、遥感遥测、气象观测等军事及民用领域中的广泛应用,结合相干探测工作原理,介绍了国外几种典型波段相干多普勒测风激光雷达系统,重点分析了激光发射机/接收机、空间扫描、数据处理等关键技术,并对相干多普勒激光雷达的广阔应用前景进行了展望。指出国内相干多普勒测风激光雷达研究已取得的一些重要进展。     

相干激光雷达中最大似然离散谱峰值估计及Monte Carlo仿真

相干测风激光雷达中一个核心的问题是从微弱的气溶胶后向散射信号中估计出风速。基于零均值复高斯随机过程协方差矩阵统计模型的后向散射信号,首先讨论了最大似然（ML）离散谱峰值（DSP）风速估计算法的克拉美-罗下界（CRLB）与由Fisher信息矩阵论得到的精确CRLB之间的关系。其次,对于ML DSP估计应用于相干测风激光雷达中协方差矩阵统计模型的后向散射信号时,使用计算机Monte Carlo仿真的方法研究了风速估计的概率密度函数。分别讨论了信噪比、激光脉冲累积发数和发射激光脉冲宽度对ML DSP风速估计性能的影响。计算仿真结果表明：ML DSP风速估计的CRLB低于精确的CRLB;在信噪比为－20 dB,100发激光脉冲累积和信噪比为－30 dB,10 000发激光脉冲累积条件下,ML DSP风速估计中坏的估计值所占的比例都为0,好的估计值的标准差分别为0.62 m/s和0.50 m/s。     

Simulation of the inherent turbulence and wake interaction inside an infinitely long row of wind turbines

The turbulence in the interior of a wind farm is simulated using large eddy simulation and the actuator line technique implemented in the Navier–Stokes equations. The simulations are carried out for an infinitely long row of turbines simulated by applying cyclic boundary conditions at the inlet and outlet. The simulations investigate the turbulence inherent to the wind turbines as no ambient turbulence or shear is added to this idealised case. The simulated data give insight into the performance of the wind turbines operating in the wake of others as well as details on key turbulent quantities. One of the key features of wakes behind wind turbines is the dynamic wake meandering, which is shown to be related to the wind turbine spacing and the vortex shedding from the turbine as a bluff body. The flow is analysed and reconstructed by applying proper orthogonal decomposition.     

Load-Carrying Capacity of Circular Plates Made of a Fiber-Reinforced Composite

The load-carrying capacity of circular plates made of a fiber-reinforced composite and loaded with axisymmetric transverse forces under axisymmetric boundary conditions is investigated. The plates can be freely supported or clamped along their contour. To the known yield condition used, in the plane of main bending moments, there correspond irregular hexagons, which depend on the mechanical properties of composite constituents and some characteristic geometrical parameters. It is shown that, depending on the ratio of ultimate radial and circumferential bending moments, in the plastic state, the circular plates (the central part of the clamped plates) take the form of a cone or a frustum of cone. For each of the cases, the limit load is found, which is a function of the above-mentioned mechanical parameters. The statically allowable fields of bending moments and the corresponding allowable fields of deflection rates are determined. The solutions found are exact. Special cases for the freely supported plates are analyzed, and the results obtained are presented in the form of graphs.__________Translated from Mekhanika Kompozitnykh Materialov, Vol. 41, No. 2, pp. 177–192, March–April, 2005.     

自适应光学对大气扰动波前的补偿效果研究：I.理论推导

在采用冻结湍流假设和几何光学近似的条件下，得到了经自适应光学系统校正后的剩余波前相位扰动的结构函数，进而根据剩余相位结构函数与系统Ｓｔｒｅｈｌ比的关系，求出自适应光学系统的补偿效果受系统的时空传递函数，大气湍流，光波传播路径上的横向风，观察目标的旋转角速度以及系统时间延迟影响情况的解析表达式。