基于面搭接多重网格技术的全机增升装置绕流数值模拟

文章在多块结构化框架下,采用面积加权平均的方法进行通量守恒传递,并成功地应用于存在"剪刀差"的全机增升装置复杂外形绕流N-S方程数值分析。通过对某民机全机低速构形所进行的气动力数值分析,计算结果与风洞实验结果吻合良好,表明该方法可以比较好地模拟如此复杂外形的流动细节,从而验证了文中所采用的面搭接多重网格技术、网格生成策略及流场计算方法的有效性。     

基于改进型类间方差分割的红外目标提取算法

文章对最大类间方差法进行了改进,利用计算图像类间方差的约束条件,通过构造罚函数,把求最大类间方差问题转换为求带约束条件的函数最优解问题,再用迭代法对图像进行分割,从而有效地弥补了最大类间方差法对图像噪音和目标大小敏感不足。仿真实验结果表明,该方法效果良好。     

Application of polymerizable surfactant in the preparation of polystyrene/nano-Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> composite

Monooctadecyl maleate, as a polymerizable surfactant, was synthesized by the mono-esterification of maleic anhydride and octadecanol, and was utilized to surface-modify nano-Fe₃O₄ particles. A polymerizable magnetic fluid was obtained by directly dispersing modified nano-Fe₃O₄ particles into styrene monomer, and the polystyrene/nano-Fe₃O₄ composite was prepared through free radical polymerization of polymerizable magnetic fluid. The structure and dispersion status in different dispersion phases of modified nano-Fe₃O₄ particles were studied by Fourier transform infrared (FTIR) spectrometry, X-ray diffraction (XRD) and transmission electron microscopy (TEM), respectively. The experimental results show that the nano-Fe₃O₄ particles modified by monooctadecyl maleate with the size of about 7–10 nm can be uniformly dispersed into styrene and fixed in the composite during the procedure of polymerization. Thermogravimetric analysis (TGA) and vibrating sample magnetometry (VSM) indicate that the thermal stability of polystyrene/nano-Fe₃O₄ composite is improved compared to that of pure polystyrene, and the composite is a sort of superparamagnetic materials.     

一种多地球物理特征匹配自主导航方法

针对地球物理场具有多个特征和匹配可操作性较强的特点,文中提出了一种多地球物理特征匹配的自主导航方法,研究了导航方法的实现方式和对应的匹配算法。导航方法通过同步测量航迹上的地磁场的多个特征和重力梯度,采用固定点数的滑动窗口构造测量序列后与基准图匹配,最后对匹配结果做融合,得到实时位置信息。匹配算法设计了基于"初始位置+初速度+加速度"实值编码的遗传算法作为搜索策略,采用平均平方差准则(MSD)作为每个特征的匹配相似性度量,并使用加权最大值原则融合所有特征的相似性度量。最后由仿真算例验证了方法的可行性,表明了导航方法具有良好的匹配精度,可用于低空、低速运动载体的导航。     

水下航行器高速斜入水冲击的探索仿真研究

文章基于大型非线性瞬态动力软件MSC.dytran,对某型号圆盘尖拱头型的水下航行器4种姿态角的高速斜入水冲击进行了探索性的数值仿真研究。在仿真中,对MSC.dytran在高速入水冲击方面数值仿真模型的建立进行了详细论述,并对模型中欧拉网格和拉格朗日网格的尺寸比对收敛性的影响进行了测试。得到了此水下航行器高速斜入水冲击的运动学参数,例如速度时间历程和速度变化量以及过载和载荷等力学参数。这些仿真结果对水下航行器高速入水的后续弹道设计以及头部壳体强度的设计都具有很重要的参考意义。     

叶盘结构频率转向特征的量化分析研究

研究叶盘结构频率转向的曲线特征,是预测叶盘结构的失谐敏感性及振动局部化程度的重要前提。文章基于叶盘系统的集中参数模型,分析了频率转向曲线特征参数(频率曲线转向处曲率、频率曲线斜率、两频率曲线转向处最小距离)与叶盘系统结构参数(耦合刚度,轮盘质量)之间的内在联系,仿真研究了频率转向曲线特征参数随叶盘系统结构参数的变化规律。研究结果表明:频率曲线转向处曲率越大(或斜率越大),系统失谐敏感性越大;频率转向曲线间隙处附近的系统模态局部化变化剧烈,该区域模态对结构失谐非常敏感。     

Study on the characteristics of erbium-doped waveguide ring laser

A theoretical model of the erbium-doped waveguide ring laser is established according to the theory of erbium-doped waveguide amplifier and the transmission matrix of waveguide directional coupler. The influence of bend radius, coupling coefficient and doped erbium ion concentration on the characteristics of waveguide ring laser is investigated. It is shown that due to the co-action of waveguide bend loss and other relevant loss there is an optimal bend radius which can provide simultaneously low threshold pumping power and high laser light output power. As one part of the resonator’s loss, the laser light coupling coefficient of directional coupler has an impact on the laser property. The analysis indicates that the laser achieves the high output power when the coupling coefficient is about 0.2. The threshold pumping power is the minimum when the doped erbium ion concentration is 0.85×10²⁶ m⁻³. Increasing the concentration of doped erbium ions will enhance the output power of laser light as long as the concentration doesn’t introduce remarkable up-conversion effect. The results give a good theoretical basis for the design and fabrication of erbium-doped waveguide ring laser devices. Supported by the National Natural Science Foundation of China (Grant No. 60807015), the Specialized Research Fund for the Doctoral Program of Higher Education (Grant No. 200801411037), the Young Teacher Cultivation Foundation of Dalian University of Technology (Grant No. 893210) and Doctor Start-up Foundation of Dalian University of Technology (Grant No. 893322)     

Numerical study on the restriction speed of train passing curved rail in cross wind

The results of numerical investigations of aerodynamic forces and moment coefficients of flow passing a simplified train geometry under different wind speeds are summarized. To compute numerically the different coefficients, the three-dimensional Reynolds-Averaged Navier-Stokes (RANS) equations, combined with the k-ε turbulence model, were solved using finite volume technique. The pres-sure-velocity fields were coupled using the SIMPLE algorithm. At each iteration the pressure correction was obtained by sol...     

Experiments and reaction characteristics of liquid phase simultaneous removal of SO<Subscript>2</Subscript> and NO

Experiments of simultaneous removal of SO₂ and NO from simulated flue gas, using NaClO₂ solution as the absorbent, were carried out in a self-designed bubble reactor, and high simultaneous removal efficiencies of SO₂ and NO were obtained under the optimal experimental conditions. The mechanism of simultaneous removal based on NaClO₂ acid solutions was proposed by analyzing the removal products. Possibility and limitation of the desulfurization and denitrification using NaClO₂ acid solutions were calculated by thermodynamic methods. Experimental results of reaction kinetics for simultaneous desulfurization and denitrification indicated that the oxidation-absorption processes of SO₂ and NO were divided into two zones, namely the fast and slow reaction zones. In the slow reaction zones both were zero order reactions, and in the fast reaction zones, the reaction order, rate constant and activation energy of SO₂ reaction with absorbent were 1.4, 1.22 (mol·L⁻¹)^−0.4·s⁻¹ and 66.25 kJ·mol⁻¹, respectively, and 2, 3.15×10³ (mol·L⁻¹) ⁻¹·s⁻¹, and 42.50 kJ·mol⁻¹ for NO reaction, respectively. Supported by the National High-Tech Research and Development Program of China (“863” Project) (Grant No. 2007AA061803)     

Restraint of mid-spatial frequency error in magneto-rheological finishing (MRF) process by maximum entropy method

In order to restrain the mid-spatial frequency error in magnetorheological finishing (MRF) process, a novel part-random path is designed based on the theory of maximum entropy method (MEM). Using KDMRF-1000F polishing machine, one flat work piece (98 mm in diameter) is polished. The mid-spatial frequency error in the region using part-random path is much lower than that by using common raster path. After one MRF iteration (7.46 min), peak-to-valley (PV) is 0.062 wave (1 wave =632.8 nm), root-mean-square (RM...