高耐蚀锌铁合金电沉积研究

利用电沉积的方法获取含Fe0.4％～0.8％的锌铁耐蚀合金镀层。结果表明:工艺因素对镀层含Fe量影响很大。而镀层中的含Fe量又直接影响镀层的耐蚀性。含Fe0.4％～0.8％的锌铁合金镀层其耐蚀性大大优于普通镀锌层。少量的铁元素可以大大延迟镀层出白锈、出红锈的时间。     

亚、超音喷管中声传播的数值模拟

采用计算气动声学方法研究了管道近音速区的声传播和声波与激波的相互作用问题。空间离散采用高阶DRP格式,时间离散采用低耗散低频散的龙格库塔方法,边界条件采用Giles的特征变量一维非定常无反射边界条件。计算结果和解析解的精确吻合表明,计算中应用的这种高阶的DRP格式有很高的分辨率和很好的稳定性,适合声传播的计算。      

进口畸变下非定常数值模拟进口边界数学模型

进口畸变下压气机内存在的不同空间和时间尺度的非定常流动之间的相互作用是进口畸变对压气机性能影响的重要流动机理.介绍了一种用于周向进口总压畸变下单转子通道内非定常数值模拟的进口边界简化模型,并基于该模型进行了三维非定常数值模拟.数值模拟结果显示了进口周向总压畸变的大尺度总压脉动和压气机转子通道非定常分离流场的相互作用过程.该模型为周向进口畸变的三维非定常数值模拟提出了一种简化方法.      

不同飞行工况下的某高超飞行器流道特征及气动力特性研究

对一种类似于X-43A飞行器的一体化构形进行了全三维数值仿真模拟,将前体下表面侧沿程静压分布的计算结果与实验结果进行了对比,二者吻合较好,表明数值模拟方法正确,结果可信.在此基础上研究了不同飞行工况下飞行器流道特征及气动力特性的变化.研究结果表明:①研究范围内来流马赫数的变化对全流道的流动结构和全机气动力特性有着一定影响,使得飞行器全机的升阻比略有下降;②随着飞行攻角的改变,全流道的流动结构和升力系数变化显著,而阻力系数的变化并不明显;③侧滑角导致了不对称的流动结构,但在本文的研究范围内其进气道以及全机的气动特性的不利影响并不明显.      

High order optimal control of space trajectories with uncertain boundary conditions

A high order optimal control strategy is proposed in this work, based on the use of differential algebraic techniques. In the frame of orbital mechanics, differential algebra allows to represent, by high order Taylor polynomials, the dependency of the spacecraft state on initial conditions and environmental parameters. The resulting polynomials can be manipulated to obtain the high order expansion of the solution of two-point boundary value problems. Since the optimal control problem can be reduced to a two-point boundary value problem, differential algebra is used to compute the high order expansion of the solution of the optimal control problem about a reference trajectory. Whenever perturbations in the nominal conditions occur, new optimal control laws for perturbed initial and final states are obtained by the mere evaluation of polynomials. The performances of the method are assessed on lunar landing, rendezvous maneuvers, and a low-thrust Earth–Mars transfer.     

Lovász条件下LLL算法最简复Givens矩阵形式的研究

为了解决复数域下基于QR分解的LLL（A．K．Lenstra,H．W．Lenstraand L．Lovasz）算法中复Gives旋转矩形式不统一的问题,文章从复数域下原始LLL算法中Gram—Schmidt系数与QR分解的上三角矩阵胄中元素之间的关系出发,证明了上三角矩阵R的元素与Gram—Schmidt系数以及Lovasz条件之间的等价的关系;从复数的指数形式出发,推导出2种适合LLL算法的复Givens旋转矩阵形式,并证明只有其中一种符合Lovasz条件下复Givens旋转矩阵形式。仿真结果表明,采用基于QR分解的复数域LLL算法的MIMO系统相比采用基于Gram—Schmidt正交化LLL算法的MIMO系统具有更好的误比特率性能。     

Adaptive-surrogate-based robust optimization of transonic natural laminar flow nacelle

Natural Laminar Flow (NLF) technology is very effective for reducing the skin friction drag of aircraft engine nacelle, but the aerodynamic performance of NLF nacelle is highly sensitive to uncertain working conditions. Therefore, it’s imperative to incorporate uncertainties into the design of NLF nacelle. In this study, for a robust optimization of NLF nacelle and for improving its efficiency, an adaptive-surrogate-based robust optimization strategy is established, which is an iterative optimization process where the surrogate model is updated to obtain the real Pareto front of multi-objective optimization problem. A case study is carried out to validate its feasibility and effectiveness. The results show that the optimization increases the favorable pressure gradient region and the volume ratio of the nacelle by increasing its lip radius and reducing its maximum diameter. And the aerodynamic robustness of the NLF nacelle is mainly determined by the lip radius, maximum diameter of nacelle and location of the maximum diameter. Compared to the initial nacelle, the optimized nacelle maintains a wide range of low drag and high laminar flow ratio in the disturbance space, which extends the average laminar flow region to 21.6% and facilitates a decrease of 1.98 counts in the average drag coefficient.     

弹性薄圆板混合边界问题的解析解法：分区联合解法

板的混合边界问题的解析解法长期未能满意解决，对这方面所做的工作很少。近年来我国力学工作者做出了不少成绩，但都是有效的近似解法。设弹性薄圆析周边支承与板内受载周期性地改变，可将板假想地分成若干以圆心为顶点的扇形，每一块扇形内只有一种支承方式，再设载荷对称于各该扇形的中线，在以上条件下，根据天津大学严送教授首先系统地提出的“加补充项的广义Ｆｏｕｒｉｅｒ－Ｂｅｓｓｅｌ双重级数法”提出了“分区联合解法”即     

Oscillatory thermocapillary flows in simulated floating-zones with time-dependent temperature boundary conditions

This study deals with numerical simulations of the Maxus sounding rocket experiment on oscillatory Marangoni convection in liquid bridges. The problem is investigated through direct numerical solution of the non-linear, time-dependent, three-dimensional Navier-Stokes equations. In particular, a liquid bridge of silicon oil 2[cs] with a length L = 20 [mm] and a diameter D = 20 (mm) is considered. A temperature difference ΔT = 30 [K] is imposed between the supporting disks, by heating the top disk and cooling the bottom one with different rates of ramping. The results show that the oscillatory flow starts as an ‘axially running wave’, but after a transient time the instability is described by the dynamic model of a ‘standing wave’, with an azimuthal spatial distribution corresponding to m = 1 (where m is the critical wave number). After the transition, the disturbances become larger and the azimuthal velocity plays a more important role and the oscillatory field is characterized by a travelling wave. The characteristic times for the onset of the different flow regimes are computed for different rates of ramping.     

航空子母弹时序抛撒散布效果数值仿真(英文)

对采用时序抛撒的航空子母弹工作过程、子弹外弹道初始条件、落点散布模型进行了探讨,建立了时序抛撒外弹道初始条件模型和落点散布模型,并进行了数值仿真。根据仿真结果分析了影响落点散布的主要因素,验证了时序抛撒对改善散布效果的可行性。采用时序抛撒,并通过优化各空投参数,可使系统达到更佳的作战效能,而且可为时序抛撒机构结构设计、结构优化及散布效果分析提供理论指导。