钛基稀土激光熔覆层组织细化机制及性能

采用通快TruDisk 4002光纤激光器在TC4合金表面分别制备了0wt% Y₂O₃和3wt% Y₂O₃的TC4+Ni45+Co-WC钛基耐磨复合涂层。利用XRD、SEM、EDS、EPMA、显微硬度计和摩擦磨损试验机等分析了涂层组织、显微硬度和摩擦学性能。结果表明，两种涂层表面均无裂纹孔隙等缺陷，且生成相一致，主要包括TiC、TiB₂、Ti₂Ni、WC和α-Ti；0wt% Y₂O₃涂层组织存在明显偏析，析出相尺寸粗大且方向性明显；3wt% Y₂O₃涂层组织呈均匀弥散状态分布，细化特征明显；经Bramfitt二维点阵错配度计算，（100）_Y2O3和（100）_Ti2Ni、（111）_Y2O3和（110）_TiC、（110）_Y2O3和（1010）_TiB2间的错配度分别为5.75%、6.72%和10.10%，Y₂O₃作为异质形核核心对Ti₂Ni、TiC和TiB₂的细化能力依次为Ti₂Ni > TiC > TiB₂；0wt% Y₂O₃和3wt% Y₂O₃涂层显微硬度分别为600~630 HV_0.5和470~480 HV_0.5，较基材分别提高了约62%和26%；3wt% Y₂O₃涂层耐磨减摩性最优，其磨损体积和摩擦系数较0wt% Y₂O₃涂层分别下降了约47.8%和5.0%，磨损机制主要为磨粒磨损。     

LARGE-EDDY SIMULATIONS OF TURBULENT CAVITY FLOWS WITH DYNAMIC SGS MODEL AND LBM ALGORITHM

INTRODUCTIONLarge- eddy simulation ( LES) method is apowerfull tool in numerical simulations of turbu-lence. On the other hand,lattice Boltzmannmethod( LBM) is a new method in computationalfluid dynamics ( CFD) ,especially when used inlarge scale parallel applications.Therefore it isuseful to build the dynamic SGS model intoLBM.In this paper the new method of dynamicSGS model with LBM is described in detail andsome results using the method to numericallysimulate the two and three…     

二维三角晶格的Peierls相变前后的声子色散曲线的研究

利用品格动力学理论计算了二维三角品格的Peimrls相变前后的声子能谱。并且在第一布里渊区绘制了主要的对称点、线上的声子色散曲线。通过对Peierls相变前后的声子能谱比较可知，随其对称性降低，声子能谱的简并度被破缺。二维三角品格的Peierls相变前只有两支声频支声子能谱，Peierls相变后有两支声频支声子能谱与两支光频支声子能谱，并且声频支声子能谱及光频支声子能谱不相交，两支光频支声子沿ky轴平缓地变化。     

半刚性模型风洞试验荷载谱的处理方法

高频测力天平试验模型要求质量尽量小,频率足够高.然而,对于一些特殊的结构,由于结构本身的特殊性,很难制作出满足频率要求的刚性模型.对于频率不够高的半刚性模型,其一阶振型频率处于结构荷载谱频带以内,因而共振作用比较明显,对结构动力荷载的影响不可忽视.通过半刚性格构式塔架模型的高频测力天平风洞试验,得到了模型在风荷载作用下的基底弯矩和扭矩.进而根据结构动力学和随机振动理论,推导了一种实用计算公式,消除了模型共振对基底力谱的影响,得到了格构式塔架的一阶广义荷载谱.     

一种新的并行检测算法下的信道分组方法

在发射天线数为NT、接收天线数为NR的MIMO系统中,并行检测算法可达到最优的检测性能,但现有系统中用到的信道分组方法是计算NT次矩阵广义逆来完成信道分组,随着天线数量的不断增加,矩阵求逆计算量会快速增加,从而进一步加剧并行检测算法计算复杂度。针对该问题,文章证明了:在并行检测算法中,只须一次矩阵广义逆的计算即可完成信道分组。仿真结果表明,应用新的信道分组方法的格归约并行检测算法的性能不变。     

高雷诺数下的翼型绕流LBM数值模拟

采用格子Boltzmann方法(LBM)的二维9速度(D2Q9)模型和贴体网格,通过引入非均匀网格插值方法和非平衡态外推边界处理,分别结合Baldwin-Lomax(B-L)湍流模型和Spalart-Allmaras(S-A)湍流模型,对高雷诺数Re≥5×105下的NACA0012翼型绕流进行了数值模拟和对比研究,两者的结果与CFL3D的结果和实验结果均吻合的很好,相比之下,采用S-A模型能更好地预测失速迎角,其处理分离流动的能力要强于B-L模型。改进后的LBM适用于非均匀贴体网格,曲边边界,计算简单,并可应用于更复杂的高雷诺数流动中。     

TiC-TiB2复合相钛基稀土激光熔覆层组织与性能

采用通快同轴送粉4002光纤激光器,在TC4表面熔覆制备了不同含量Y₂O₃的TC4+Ni45+Co-WC+Y₂O₃钛基复合耐磨涂层。采用XRD、SEM、EDS、EPMA测试研究了涂层微观组织,利用显微硬度计、摩擦磨损实验机和白光轮廓仪分析评价了涂层的显微硬度和摩擦学性能。结果表明,涂层生成相不随Y₂O₃含量变化而改变,主要包括Ti₂Ni、TiC、TiB₂以及α-Ti;未添加Y₂O₃涂层,生成相尺寸粗大,方向性明显;随着Y₂O₃的加入,涂层组织逐步细化,生成相方向性减弱;当Y₂O₃为3wt%时,涂层析出相以颗粒和短棒状相为主,合成了大量TiC-TiB₂依附生长复合相,经二维点阵错配度计算,TiB₂（0001）与TiC （111）错配度δ为0.912%,TiC与TiB₂形成了共格界面,可有效增加涂层组织分布均匀性;Y₂O₃含量为0wt%、1wt%和3wt%时,涂层显微硬度逐渐减小,磨损体积先增大后减小,摩擦系数逐渐降低;在TiC-TiB₂复合相的作用下,3wt% Y₂O₃涂层的耐磨、减摩性最优,涂层磨损机理为磨粒磨损。     

Static aeroelastic analysis of very flexible wings based on non-planar vortex lattice method

A rapid and efficient method for static aeroelastic analysis of a flexible slender wing when considering the structural geometric nonlinearity has been developed in this paper. A non-planar vortex lattice method herein is used to compute the non-planar aerodynamics of flexible wings with large deformation. The finite element method is introduced for structural nonlinear statics analysis. The surface spline method is used for structure/aerodynamics coupling. The static aeroelastic characteristics of the wind tunnel model of a flexible wing are studied by the nonlinear method presented, and the nonlinear method is also evaluated by comparing the results with those obtained from two other methods and the wind tunnel test. The results indicate that the traditional linear method of static aeroelastic analysis is not applicable for cases with large deformation because it produces results that are not realistic. However, the nonlinear methodology, which involves combining the structure finite element method with the non-planar vortex lattice method, could be used to solve the aeroelastic deformation with considerable accuracy, which is in fair agreement with the test results. Moreover, the nonlinear finite element method could consider complex structures. The non-planar vortex lattice method has advantages in both the computational accuracy and efficiency. Consequently, the nonlinear method presented is suitable for the rapid and efficient analysis requirements of engineering practice. It could be used in the preliminary stage and also in the detailed stage of aircraft design.     

A new non-linear vortex lattice method:Applications to wing aerodynamic optimizations

This paper presents a new non-linear formulation of the classical Vortex Lattice Method (VLM) approach for calculating the aerodynamic properties of lifting surfaces. The method accounts for the effects of viscosity, and due to its low computational cost, it represents a very good tool to perform rapid and accurate wing design and optimization procedures. The mathematical model is constructed by using two-dimensional viscous analyses of the wing span-wise sections, according to strip theory, and then coupling the strip viscous forces with the forces generated by the vortex rings distributed on the wing camber surface, calculated with a fully three-dimensional vortex lifting law. The numerical results obtained with the proposed method are validated with experimental data and show good agreement in predicting both the lift and pitching moment, as well as in predicting the wing drag. The method is applied to modifying the wing of an Unmanned Aerial System to increase its aerodynamic efficiency and to calculate the drag reductions obtained by an upper surface morphing technique for an adaptable regional aircraft wing.     

基于三维格子Boltzmann铝点蚀动态数值模拟

铝作为目前最经济且应用最为广泛的材料之一,具有重量轻、耐腐蚀、导热性好、导电性好等优点。然而,金属铝在氯离子环境中容易发生点蚀。根据中性溶液中铝表面点蚀反应机理,结合液体流动和相变特性,建立了三维格子Boltzmann铝点蚀模型,研究了中性溶液中铝表面的点蚀现象,弥补了传统实验方法的不足。采用建立的腐蚀模型对整个铝点蚀过程进行了模拟,得到了不同组分的浓度分布以及不同参数与腐蚀程度的关系。结果表明：铝的腐蚀程度随接触时间的增加而增加。随着初始氯离子浓度的增加和腐蚀反应速率的增大,铝被腐蚀得更严重。三维格子Boltzmann铝点蚀模型为金属腐蚀数值研究提供了新的思路。