遗传算法对压气机叶片排序的应用

采用遗传算法研究压气机叶片装配中的排序优化问题。详细给出了遗传算法的计算步骤、计算过程中叶片序列可行解的编码、交叉算子、变异算子的选择方法,建立了对叶片排序问题的适应度函数及其优化的评估方法。具体算例表明所建立的方法对压气机叶片排序问题有较高的效率和满意的准确度。      

反求工程中经济型快速测量装置的研究

设计了结构简单经济实用的快速测量装置,采用分区域数据补偿方法进行误差补偿,提高了系统的测量精度,将有助于反求工程中测量效率的提高。     

风云四号卫星双程测距系统精密轨道确定

针对我国新一代静止轨道卫星风云四号高精度轨道计算需求，地面跟踪系统设计了多台站双频双程测距模式。详细给出了信号传播介质改正中的电离层与对流层处理方法，并给出了风云四号卫星动力学轨道确定策略。在非变轨期间，采用动力学定轨方法。轨道确定残差分析，测量噪声均方根优于0.5 m。通过轨道重叠分析，非变轨期间精度优于20 m。动量轮卸载期间，采用估计经验力的方法，其定轨残差优于1 m。对多弧段数据处理表明文中方法满足同步卫星双程测距模式下的高精度轨道跟踪问题。     

Hierarchical global search for fuel-optimal impulsive transfers between lunar libration orbits

The attention to the periodic orbit in the Earth-Moon restricted three-body system continues to grow due to its special environment and locations. This research investigates the feasibility of constructing fuel-optimal single and multiple impulse transfers between unstable periodic orbits at L₁ and L₂ points. Invariant manifolds, which could provide the appropriate initial trajectories for optimization, are analyzed deeply to enable previously unknown orbit options and potentially to reduce mission cost. A global search strategy based on comparing the orbital state of the unstable and stable manifolds, incorporated with low-thrust techniques, is performed to seek a suitable matching point for maneuver application. Then the sequential quadratic programming (SQP) is adopted to further optimize the velocity increment and obtain the single/multiple impulse optimal transfers. The associated constraint gradients are derived to achieve higher accuracy and rapidity of the algorithm. To highlight the effectivity of the transfer scheme, three-dimensional low-energy transfers between different types and spatial regions of performing single and multiple impulses are explored. The total Delta-V required varies between a few meters per second and tens of meters per second, and the related flight time is about several weeks, mainly depending on the energy of periodic orbits and the invariant manifold structure. The results obtained in this paper can provide a useful reference for the selection of escape and capture site along the manifolds, maneuver magnitude and transfer time.     

Direct Numerical Simulation of Secondary Breakup of Liquid Drops

This article studies numerically a familiar important phenomenon in spray combustion which is deformation and breakup of liquid drops in gas flow. The SIMPLER method is used to solve the two-dimensional (2D) unsteady axisymmetric Navier-Stokes equations for both the drop and the ambient gas flow. The level set method is applied to capturing the liquid/gas interface. Through calculation are obtained four typical breakup modes-oscillation, bag breakup, sheet stripping breakup and shear breakup governed by four non-dimensional numbers which are gas Weber number (Weg), liquid Reynolds number (Rel), gas Reynolds number (Reg) and density ratio (γ) . Their effects upon each mode are analyzed. The results indicate that among the four numbers, Weg is of the highest importance with Rel, Reg and γfollowing up. By widening the range of the density ratio up to 1 000, the breakup mode is discovered to be so complicated that a new one called multimode breakup mode turns up. This mode contains the shearing breakup and piercing breakup, which successively happen. The calculation results agree well with what is observed from the experiments.     

Dual Drive Curve Tool Path Planning Method for 5-axis NC Machining of Sculptured Surfaces

The problem of finished surface being not first-order continuous commonly exists in machining sculptured surfaces with a torus cutter and some other types of cutters. To solve this problem, a dual drive curve tool path planning method is proposed in this article. First, the maximum machining strip width of a whole tool path can be obtained through optimizing each tool position with multi-point machining (MPM) method. Second, two drive curves are then determined according to the obtained maximum machining strip width. Finally, the tool is positioned once more along the dual drive curve under the condition of tool path smoothness. A computer simulation and cutting experiments are carried out to testify the performance of the new method. The machined surface is measured with a coordinate measuring machine (CMM) to examine the machining quality. The results obtained show that this method can effectively eliminate sharp scallops between adjacent tool paths, keep tool paths smooth, and improve the surface machining quality as well as machining efficiency.     

游客非凡体验和一般体验对认知体系效用分析

在过去的近30年里,与体验相关的研究逐渐演变为经济管理领域的一个热点话题,事实上,全球经济中增长最快的行业都与体验消费相关。旅游体验是体验经济时代最为典型的体验形式之一,旅游业就是出售"舞台化"体验的行业,其核心生产活动就是创造游客体验。基于行为主义学习理论提出理论模型和研究假设,确认了游客非凡体验的效用,辨析非凡体验和一般体验对游客认知体系的不同影响效果,结果显示非凡体验能够显著影响游客的信念体系,而后者则不具备类似的功效。     

航空航天用纳米碳复合材料研究进展

对航空航天用纳米碳复合材料及其多功能特性的研究进展情况进行了综述，阐述了国内外研究者们在纳米碳复合材料及其多功能特性方面取得的重要成果，并系统地综述了纳米碳复合材料在多尺度增强、电磁屏蔽、智能驱动、隔热、传感方面的研究工作。最后展望了纳米碳复合材料在航空航天领域中的潜在应用。