基于似然比检验的橡胶密封件加速试验机理一致性判别方法

加速退化试验广泛应用于橡胶密封件等长寿命产品的可靠性评估,试验过程中需要将高应力水平下的试验结果外推到正常应力水平。要获得准确的产品可靠性评估结果,需要保证加速应力下的退化失效机理与正常应力下的退化失效机理一致。基于似然比检验原理,提出加速退化试验机理一致性判别方法及流程。针对失效机理一致与失效机理变化两种场合,提出对数线性及非对数线性两类加速模型,并结合混合效应模型描述产品退化过程。利用似然比检验判断加速模型参数是否变化,完成失效机理一致性判别。仿真算例和应用实例表明,该方法能够有效判别橡胶密封件失效机理是否变化,并找到失效机理不变的应力水平边界。     

浮式振荡立轴叶轮的三维效应影响

为研究振荡运动下立轴水轮机的三维效应影响,采用ANSYS CFX软件三维模拟立轴水轮机在不同展弦下的振荡运动（横荡、纵荡）,并与二维模拟的立轴水轮机作对比,通过最小二乘法拟合计算得到水轮机推力和侧向力系数时域结果,分析得到不同展弦比下水轮机阻尼系数和附加质量系数。结果表明：随着展弦比增大,叶轮潮流能的转换效率逐渐增大;三维振荡叶轮的水动力载荷与叶轮展长呈正相关,当展弦比达到10时其水动力载荷及能量转换效率和二维的计算结果相当;三维水轮机水动力系数常数项和阻尼项随展弦比增大而增大。     

星载双基地SAR系统模糊性

针对星载双基地SAR由双基地几何关系引入的新问题,提出了计算其模糊比的新方法和近似分解方法。利用此方法通过仿真计算对星载双基地SAR模糊性变化规律做了进一步研究。结果表明,因接收天线的面积限制,与其伴随飞行的大卫星SAR相比,模糊性问题更为严重,但变化规律基本一致。比较而言,由于小卫星天线尺寸在高度上更接近大卫星天线,在距离模糊比上相对大卫星SAR抬高得不多,而在方位模糊比上抬高较大。     

Dynamic signatures and their use in comparing the reliability of new and used systems

The signature of a system with independent and identically distributed (i.i.d.) component lifetimes is a vector whose ith element is the probability that the ith component failure is fatal to the system. System signatures have been found to be quite useful tools in the study and comparison of engineered systems. In this article, the theory of system signatures is extended to versions of signatures applicable in dynamic reliability settings. It is shown that, when a working used system is inspected at time t and it is noted that precisely k failures have occurred, the vector s [0,1]^n‐k whose jth element is the probability that the (k + j)th component failure is fatal to the system, for j = 1,2,2026;,n ‐ k, is a distribution‐free measure of the design of the residual system. Next, known representation and preservation theorems for system signatures are generalized to dynamic versions. Two additional applications of dynamic signatures are studied in detail. The well‐known “new better than used” (NBU) property of aging systems is extended to a uniform (UNBU) version, which compares systems when new and when used, conditional on the known number of failures. Sufficient conditions are given for a system to have the UNBU property. The application of dynamic signatures to the engineering practice of “burn‐in” is also treated. Specifically, we consider the comparison of new systems with working used systems burned‐in to a given ordered component failure time. In a reliability economics framework, we illustrate how one might compare a new system to one successfully burned‐in to the kth component failure, and we identify circumstances in which burn‐in is inferior (or is superior) to the fielding of a new system. © 2009 Wiley Periodicals, Inc. Naval Research Logistics, 2009     

A note on necessary and sufficient conditions for ordering properties of coherent systems with exchangeable components

We give necessary and sufficient conditions based on signatures to obtain distribution‐free stochastic ordering properties for coherent systems with exchangeable components. Specifically, we consider the stochastic, the hazard (failure) rate, the reversed hazard rate, and the likelihood ratio orders. We apply these results to obtain stochastic ordering properties for all the coherent systems with five or less exchangeable components. Our results extend some preceding results. © 2011 Wiley Periodicals, Inc. Naval Research Logistics, 2011     

基于Laguerre滤波的雷达通道均衡方法

传统雷达通道均衡采用自适应FIR滤波器作为均衡器,当理想脉冲响应序列很长时,其逼近效果不理想,计算量大。Laguerre滤波器兼具FIR和IIR结构的优点,通过在单位圆内固定一极点保证了系统的稳定,又因为引入了全通滤波环节,使其能够用较少的阶数逼近长脉冲序列响应。推导了Laguerre滤波器的自适应算法,并将其应用于雷达通道均衡中,仿真实验也证明了它与传统的FIR结构相比,用更少的系数获得了更优的对消比,达到了更好的均衡效果。     

滑翔增程弹滑翔弹道优化设计分析

针对鸭式布局的滑翔增程弹,建立了滑翔增程弹滑翔弹道的模型,采用使滑翔弹道上每一点的升阻比最大的设计思想进行弹道优化设计,导出了俯仰舵偏角与平衡攻角的表达式,并对滑翔飞行弹道特性进行了仿真计算分析.仿真计算表明,滑翔弹道与常规弹道降弧段相比下降趋缓,增程效果显著.     

论短肢剪力墙的轴压比限值

在理论方面,短肢剪力墙的研究尚处在探索阶段,缺少系统的研究,有关短肢剪力墙结构的轴压比对抗剪性能的影响分析还很不完善。在理论分析的基础上,确定了用以判断构件大、小偏压状态的界限轴压比,得到了为保证T形截面短肢剪力墙构件具有一定延性的轴压比限值。     

层次分析法的水下航行器维修性指标分配方法

基于层次分析法的水下航行器维修性指标分配方法把层次分析法应用到水下航行器维修性指标分配方法中,即邀请专家对故障的检测和隔离方式、可达性、可更换性和测试的困难等级进行两两比较,得到评价矩阵,据此,可以得到分配结果.这种方法克服了按故障率和设计特性分配法在设计特性相差不大时存在的缺陷,把定性分析与定量分析相结合.在设计初期即明确设计目标,除了考虑到单元的故障率还兼顾了初期设计过程中的不确定性.将这种方法应用于某水下航行器的维修性分配,结果表明,该方法具有实用价值.     

助推-滑翔飞行器可达区域影响因素研究

利用Radau伪谱法将连续的助推-滑翔飞行器轨迹优化问题转化为非线性规划问题,通过仿真得到了飞行器完整的可达区域,着重分析了升阻比、终端速度以及终端倾角对飞行器可达区域的影响.研究结果表明,可达区域呈现出类椭圆结构,其地理区域覆盖能力由助推火箭关机点速度决定;与终端倾角对飞行器可达区域的影响相比,飞行器升阻比特性和终端速度的影响相对较大.