试件水灰比和胶砂比对混凝土硫酸盐侵蚀速度影响

通过大量试验,采用强度指标研究了试件水灰比和胶砂比对硫酸盐侵蚀速度的影响.结果表明:试件的水灰比越大,胶砂比越小,侵蚀速度越快;为了加快硫酸盐侵蚀速度,宜采用大水灰比、小胶砂比的试件.在各种条件下,硫酸钠侵蚀破坏的速度比硫酸镁侵蚀快.对硫酸钠型侵蚀,采用抗折抗蚀系数作为判定指标较为合理,而对硫酸镁型侵蚀,应该综合考虑抗折抗蚀系数和抗压抗蚀系数.     

高重合度人字齿轮传动动态性能优化设计

对人字齿轮传动进行高重合度设计的分析,基于人字齿轮副承载接触分析技术,针对人字齿轮传动中主动小齿轮轴向浮动安装的特点,综合考虑齿轮时变啮合刚度、啮合冲击激励及误差激励等因素的影响,采用集中质量法建立了考虑修形的人字齿轮副弯-扭-轴耦合非线性振动模型,推导了系统无量纲运动微分方程,求解得到齿轮传动系统的振动加速度。以齿轮的振动加速度均方根值为优化的目标函数,针对该类复杂实际工程优化设计中适应值计算费时的缺点,提出了一种改进的具有适应值预测机制的遗传算法,优化得到了人字齿轮的基本设计参数及修形参数,提高了计算效率,通过实例分析验证了该优化方法的有效性。对加工的人字齿轮在减振降噪试验台上进行带载试验,对比优化前后的噪音分贝值,进一步验证了该优化方法对齿轮副减振降噪具有一定作用。     

基于不同叶片数目比的烟气涡轮多叶片通道数值模拟

基于定常假设,利用混合平面模型传递级间参数,运用Fluent软件对不同静动叶片数目比下的烟气涡轮多叶片通道流场进行了数值计算,得到了温度、压力、出口速度和马赫数等参数的变化规律,绘制了不同静动叶片数目比下各种参数的体积加权平均XY图,并通过数值分析确定了静动叶片最佳数目比为50∶74,最佳静叶安装角为35°。结果表明:叶片数目增减和静叶安装角的变化对烟气涡轮整体性能的影响须考虑多种因素,并不能以单一参数的变化来决定最佳叶片数目和静叶安装角。该结论可为烟气涡轮现有装备的科学管理和技术改进提供理论依据。     

一种锥比率数据包络分析模型及有关结论

本文研究一种锥比率数据包络分析模型,它既能反映各项输入或输出的相对重要性和对某些决策单元的偏好,又可单纯地评价决策单元间的相对技术有效性。本文着重讨论这一模型的DEA有效性与多目标规划非支配解的关系以及有效决策单元的存在性等问题,论证了有关结论。     

4点弯曲载荷作用下残余应力与弹性模量比对涂层/基体材料界面能量释放率的影响

采用有限元计算方法研究了在4点弯曲载荷作用下,残余应力、涂层与基体的弹性模量比(简称弹性模量比)对涂层/基体材料界面能量释放率及其相角的影响。结果表明:能量释放率随着残余拉应力、弹性模量比的增大而增大;能量释放率中的相角也随着残余拉应力的增大而增大,但并不敏感,其随着弹性模量比的增大而减小。研究结果可为评价涂层/基体材料界面结合性能提供理论依据,有助于深化对涂层/基体材料界面结合性能的认识。     

On the application and extension of system signatures in engineering reliability

Following a review of the basic ideas in structural reliability, including signature‐based representation and preservation theorems for systems whose components have independent and identically distributed (i.i.d.) lifetimes, extensions that apply to the comparison of coherent systems of different sizes, and stochastic mixtures of them, are obtained. It is then shown that these results may be extended to vectors of exchangeable random lifetimes. In particular, for arbitrary systems of sizes m < n with exchangeable component lifetimes, it is shown that the distribution of an m‐component system's lifetime can be written as a mixture of the distributions of k‐out‐of‐n systems. When the system has n components, the vector of coefficients in this mixture representation is precisely the signature of the system defined in Samaniego, IEEE Trans Reliabil R–34 (1985) 69–72. These mixture representations are then used to obtain new stochastic ordering properties for coherent or mixed systems of different sizes. © 2008 Wiley Periodicals, Inc. Naval Research Logistics, 2008     

Effect of particle gradation of aluminum on the explosion field pressure and temperature of RDX-based explosives in vacuum and air atmosphere

To optimize the energy output and improve the energy utilization efficiency of an aluminized explosive, an explosion device was developed and used to investigate the detonation pressure and temperature of R1 (Al6) aluminum powder and the aluminum powder particle gradation of R2 (Al6+Al13), R3 (Al6+Al24) and R4 (Al6+Al flake) in a confined space. By using gas chromatography, quantitative analysis and calculations were carried out to analyze the gaseous detonation products. Finally, the reaction ratios of the aluminum powder and the explosion reaction equations were calculated. The results show that in a confined space, the quasi-static pressures and equilibrium temperature of the aluminum powder in air are higher than in vacuum. In vacuum, the quasi-static pressures and equilibrium temperatures of the samples in descending order are R1>R3>R4>R2 and R3>R4>R1>R2, respectively. In air, the quasi-static pressures and equilibrium temperatures of the samples in descending order are R1>R2>R4>R3 and R1>R4>R2>R3, respectively. R4 (Al6+Al flake) and R3 (Al6+Al24) have relatively higher temperatures after detonation, which shows that the particle gradation method can enhance the reaction energy output of aluminum during the initial reaction stage of the explosion and increase the reaction ratio by 10.6% and 8.0%, respectively. In air, the reaction ratio of Al6 aluminum powder can reach as high as 78.16%, and the reaction ratio is slightly reduced after particle gradation. Finally, the reaction equations of the explosives in vacuum and in air were calculated by quantitative analysis of the explosion products, which provides a powerful basis for the study of RDX-based explosive reactions.     

高空平台通信系统中多波束天线辐射特性对系统性能的影响

高空平台通信系统中将采用多波束天线提供蜂窝覆盖，来提高系统容量。本文分析等波束宽度和等波束面积两种类型多波束天线辐射特性以及它们的几何模型，推导了载干比计算公式，通过仿真分析不同参数配置条件下多波束天线辐射特性对系统载干比性能的影响。研究表明等波束面积多波束天线比等波束宽度多波束天线具有更好的载干比分布特性。本文得出的结论对HAP通信系统规划具有重要的指导意义。     

高超声速变形飞行器翼面变形模式分析

为提高高超声速翼身组合式飞行器的射程,研究了采用不同翼面变形模式时,飞行器在马赫数3~8内的气动特性和翼面效率。针对典型的轴对称翼身组合式外形,采用Navier-Stokes方程进行数值模拟,对伸缩、变后掠和二维折叠三种变形模式下的外形在超声速及高超声速来流条件下进行模拟,并对升阻比、翼面单位面积升阻比和操稳特性进行分析。结果表明:在超声速及高超声速范围内,变后掠变形模式在宽速域内升阻比提高明显,同时具备优良的翼面效率及操稳特性,其在马赫数3~8范围内具有最优的综合性能。研究成果能对高超声速翼身组合式变形飞行器布局设计提供参考,具有一定的指导意义。     

基于辐照度标准传递的辐亮度校准系统

介绍了一种新型辐亮度校准系统,通过溯源至国家辐照度标准,构建了军用光辐射校准平台。对系统的测量不确定度分析表明,该系统可以满足装备计量保障对测试不确定度比的通用要求,适用于装备专用检测设备的辐亮度校准。