Influence of TiB2 particles on machinability and machining parameter optimization of TiB2/Al MMCs

In situ formed TiB₂ particle reinforced aluminum matrix composites (TiB₂/Al MMCs) have some extraordinary properties which make them be a promising material for high performance aero-engine blade. Due to the influence of TiB₂ particles, the machinability is still a problem which restricts the application of TiB₂/Al MMCs. In order to meet the industrial requirements, the influence of TiB₂ particles on the machinability of TiB₂/Al MMCs was investigated experimentally. Moreover, the optimal machining conditions for this kind of MMCs were investigated in this study. The major conclusions are: (1) the machining force of TiB₂/Al MMCs is bigger than that of non-reinforced alloy and mainly controlled by feed rate; (2) the residual stress of TiB₂/Al MMCs is compressive while that of non-reinforced alloy is nearly neutral; (3) the surface roughness of TiB₂/Al MMCs is smaller than that of non-reinforced alloy under the same cutting speed, but reverse result was observed when the feed rate increased; (4) a multi-objective optimization model for surface roughness and material removal rate (MRR) was established, and a set of optimal parameter combinations of the machining was obtained. The results show a great difference from SiC particle reinforced MMCs and provide a useful guide for a better control of machining process of this material.     

A coupling VWM/CFD/CSD method for rotor airload prediction

A coupling fluid-structure method with a combination of viscous wake model(VWM),computational fluid dynamics(CFD) and comprehensive structural dynamics(CSD) modules is developed in this paper for rotor unsteady airload prediction. The hybrid VWM/CFD solver is employed to model the nonlinear aerodynamic phenomena and complicated rotor wake dynamics;the moderate deflection beam theory is implemented to predict the blade structural deformation; the loose coupling strategy based on the ‘delt method' is used to couple the fluid and structure solvers.Several cases of Helishape 7A rotor are performed first to investigate the effect of elastic deformation on airloads. Then, two challenging forward flight conditions of UH-60 A helicopter rotor are investigated, and the simulated results of wake geometry, chordwise pressure distribution and sectional normal force show excellent agreement with available test data; a comparison with traditional CFD/CSD method is also presented to illustrate the efficiency of the developed method.     

试飞员能力模型研究

在飞行器研制和人类飞行探索中,试飞员的能力至关重要。针对以往对试飞员能力的评价基本停留在"客观、正确、诚信、能力以及尊重他人"等主观、感性层面,分析了试飞员在飞行器研制试验与鉴定中的作用和任务,给出了试飞员能力模型和"百分制"对试飞员的计划、飞行、评价、报告和建议等基本能力的量化分配。将试飞员能力显性化,有利于试飞员能力的客观评价。     

语篇分析理论指导下的高级英语教学

高级英语是高校针对英语专业三四年级学生开设的一门学科,目的是训练和提高学生的综合英语技能。将语篇分析理论运用到高级英语课堂教学中来,以具体课文为例,对其标题、结构、衔接和连贯进行分析,对高级英语的课程建设有很大的推动作用。     

基于LMS Virtual. Lab的系留气球仿真与优化

系留气球在近地面收放过程中存在俯仰角过大的问题，为了更全面地了解收放过程中不同因素对球体俯仰角的影响，采用LMS Virtua1. Lab建立了带滑轮索具系统的系留气球三维动力学模型进行仿真分析，结果表明，仿真结果与理论计算、测量数据都有较高的符合度。进而运用试验设计( DOE)方法，探索典型风速下球体俯仰角的响应区间。最后基于响应面模型的优化技术，对滑轮索具系统设计进行优化，有效改善了球体在收放过程中俯仰角过大的问题。仿真模型对系留气球系统设计及收放控制有一定的指导作用。     

一种卫星信道的反馈优化接入机制

提高卫星信道资源利用率，探索高效可行的端站接入机制是卫星通信发展亟待解决的问题之一。当前卫星通信DVB-RCS标准基于带宽预先规划的接入机制与端站随遇接入的需求矛盾凸显，因此提出一套信道反馈优化接入机制，综合考虑各端站数据业务需求，在不改变原有协议信令特征的基础上，探索性地引入谦虚度激励方法，创造性地构造动态协商反馈模型并加以求解，达到提高端站接入数量、满足随遇接入需求、提升信道利用效率、最大化整体带宽通信业务效益的目的。通过试验验证，带宽分配反馈优化机制比传统模式提高近1倍接入率，最大端站数接入时算法耗时约只有0.67s，可为卫星信道使用提供技术参考。     

黄渤海晴空像元下雾霾识别的机器学习算法

为实时有效地识别和监测雾霾，选取2013年10月4日与10月5日的两景MODIS遥感图像，利用不同类型像元的光谱差异，基于神经网络模型，建立海上雾霾的遥感识别机器学习算法。经检验表明，在晴空条件下，机器学习算法反演精度相对较高，已超过98%，利用算法可以实现对中国近海上空雾霾的监测。     

基于ANSYS Workbench的行星滚柱丝杠动态特性分析

通过Pro/Engineer建立行星滚柱丝杠三维模型，基于ANSYS Workbench有限元分析技术进行模态与谐响应分析，得到前六阶固有频率与各阶模态振型，确定共振频率，掌握对应频率下的位移峰值响应，并研究螺母处于不同工作位置时对固有频率的影响，为基于行星滚柱丝杠传动的舵系统抗振设计提供数据支撑。     

EPDM包覆层热解状态下的力学行为及本构模型

为了准确描述固体火箭发动机三元乙丙(EPDM)包覆层在不同热解状态下的力学特性,通过热重分析的方法得到EPDM的热解温度范围,并采用准静态单轴拉伸实验的方法获得EPDM在不同热解温度下的应力-应变曲线。以Ogden(n=2)模型为基础,分别对不同热解状态下的力学曲线进行建模,并通过对实验数据的拟合获得模型参数。结果表明,在初始热解状态下,材料只发生了少量的失水和气体的逃逸,其力学行为可通过粘超弹本构模型进行描述;随着材料热解程度增加,基体材料和填充纤维均遭到破坏,其力学行为表现为超弹脆性材料特性。