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.     

纤维增韧陶瓷基复合材料的比例极限应力与残余热应力关系

从细观力学角度分析并建立了纤维增韧陶瓷基复合材料从制备温度冷却到室温过程中产生的残余热应力与复合材料的比例极限应力的关系模型。该模型表明,减少复合材料的残余热应力或提高复合材料的纤维与基体的模量比,均可提高复合材料的比例极限应力。通过单调拉伸实验测试了先驱体浸渍裂解法(PIP)制备的2D SiC/SiC复合材料的比例极限应力,并采用文中建立的比例极限应力与残余热应力关系模型,计算出复合材料SiC基体的残余热应力为-19.5 MPa。分析表明,该结果是合理的。此外,引用了公开文献报道的5种复合材料体系数据,用于验证文中所建立的比例极限应力与残余热应力关系模型的适应性和可靠性,计算结果与实验结果最大误差为18.6%,表明该模型具有较好的适应性和可靠性,可为纤维增韧陶瓷基复合材料的研究提供新思路。     

强不确定系统“全系数之和等于1”的实现方法

摘要： 研究强不确定系统“全系数之和等于1”的实现方法，强不确定系统指的是系统的静态增益及其界不完全确知且范围较大.“全系数之和等于1”是吴宏鑫院士20世纪80年代发现的，该原理表明，对于未知连续系统，其离散化系统的系数的和在一定条件下是1.该原理的发现对于解决闭环辨识和自适应控制的瓶颈问题具有关键作用.“全系数之和等于1”是在一定条件下成立的.为了实现系统的“全系数之和等于1”，需要对系统进行一定的变换，以满足所需条件.其中，采用静态增益的标称值的倒数进行输入变换的方法在实际中得到了广泛应用.但是，当系统的不确定性较大时，该变换将带来较大偏差.针对该问题开展了深入研究，明确给出了系统静态增益的不确定性与标称值的比值的关系对于实现“全系数之和等于1”的影响.当不确定性与标称值的比值较小时，可以近似实现“全系数之和等于1”；当比值较大时，进一步给出了通过选取合适的采样周期，近似实现“全系数之和等于1”的方法.本文的研究对于特征模型理论在实际中的应用提供了一定的基础.     

可控曲率半径的圆柱形叶片逐点绘型方法

针对中低比转速离心泵,根据叶片进出口边界条件,以逐点绘型方法为基础,提出了一种新的曲率半径可控的叶片绘型方法。该方法的主要特点是曲率半径比值可作为设计常量由设计人员根据需要事先给定,随后分析了曲率半径及比例因子对叶片安放角、叶片包角、相对速度及速度矩等的影响。结果表明,不同曲率半径比值下的叶型参数及流动参数变化范围很大,曲率半径比值较大时,节流损失较大,泵扬程较低,曲率半径比值较小时,脱流损失较大,泵效率较低,存在较优的曲率半径比值区间[1.4,2.4],使叶片安放角平滑变化,泵的综合性能较优,在该优化区间内,取较大的曲率半径比值有利于获得较优的汽蚀性能,比例因子为0时叶片安放角的变化较为平稳,可用于开展离心泵的初步设计。     

Fault Estimation and Accommodation for a Class of Nonlinear System Based on Neural Network Observer

The problem of fault estimation and accommodation of nonlinear systems with disturbances is studied using adaptive observer and neural network techniques.A robust adaptive learning algorithm based on switchingβsmodification is developed to realize the accurate and fast estimation of unknown actuator faults or component faults.Then a fault tolerant controller is designed to restore system performance.Dynamic error convergence and system stability can be guaranteed by Lyapunov stability theory.Finally,simulation results of quadrotor helicopter attitude systems are presented to illustrate the efficiency of the proposed techniques.     

LENS风洞试验返回器模型气动热特性模拟

国家数值风洞高超声速流动模拟软件HyFLOW的研制对打破国外同类软件的技术壁垒具有重要意义。与国外DPLR软件进行了对比研究，同时系统介绍了HyFLOW软件求解器的数值方法、物理化学模型以及壁面催化特性计算模型等主要方法，采用典型算例对有限催化模型进行了数值验证，最后基于LENS风洞试验146 mm返回器标模外形开展了高超声速气动热特性数值模拟。研究结果表明，HyFLOW软件在高超声速热化学非平衡流动模拟与评估方面的气动力计算精度高，与国外同类软件DPLR相当，同时其壁面催化条件下的气动热计算精度可靠，可信度高。     

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。     

A surface parametric control and global optimization method for axial flow compressor blades

An aerodynamic optimization method for axial flow compressor blades available for engineering is developed in this paper. Bezier surface is adopted as parameterization method to control the suction surface of the blades, which brings the following advantages:(A) significantly reducing design variables;(B) easy to ensure the mechanical strength of rotating blades;(C) better physical understanding;(D) easy to achieve smooth surface. The Improved Artificial Bee Colony(IABC) algorithm, which significantly increases the convergence speed and global optimization ability, is adopted to find the optimal result. A new engineering optimization tool is constructed by combining the surface parametric control method, the IABC algorithm, with a verified Computational Fluid Dynamics(CFD) simulation method, and it has been successfully applied in the aerodynamic optimization for a single-row transonic rotor(Rotor 37) and a single-stage transonic axialflow compressor(Stage 35). With the constraint that the relative change in the flow rate is less than0.5% and the total pressure ratio does not decrease, within the acceptable time in engineering, the adiabatic efficiency of Rotor 37 at design point increases by 1.02%, while its surge margin 0.84%,and the adiabatic efficiency of Stage 35 0.54%, while its surge margin 1.11% after optimization, to verify the effectiveness and potential in engineering of this new tool for optimization of axial compressor blade.