运用MATLAB对高速卧式加工中心进行可靠性建模

针对国内还没有对高速立卧式加工中心的故障间隔时间指标进行量化考核,提出一种高速立卧式加工中心故障间隔时间的可靠性建模方法:以经验建模和MATLAB软件为基础,运用MAT-LAB软件对4台同型号的加工中心故障间隔时间进行可靠性建模,即模型的参数估计和检验模型服从Weibull分布的合理性,最终确定加工中心故障间隔时间服从Weibull分布的数学模型。这将为高速卧式加工中心的可靠性评估、维修策略制定提供依据,并对加工中心整机的可靠性预测提供理论支撑。     

采用平均风速参与因子法的区域风资源评估

目前多依据风能特征指标对单个风电场进行风资源评估,评估结果对区域能源规划所起到的参考作用比较有限。对此,提出了基于平均风速参与因子的区域风资源评估方法。按照风速观测站的位置进行地理划分,在各站风速历史数据中合理取样;在假设风速服从2参数威布尔(Weibull)分布的基础上,采用矩量法计算出各样本的风速分布参数;之后建立多维自回归模型,求得各样本风速序列的相互影响系数,应用所提平均风速参与因子方法求得区域等效风速分布参数,进行区域风资源评估。以某地10个风速观测站实测数据为样本,进行了算例分析。结果表明,所提风资源评估方法计算结果与实测数据统计结果较为接近,能有效解决区域风能能源规划中风资源评价的瓶颈问题。     

含风电场的互联发电系统可靠性评估

为得到更准确的风速序列,建立了小时级的时序风速概率分布模型,并根据该模型进行抽样获得时序风速序列。考虑风电机组的功率输出特性、尾流效应等因素,建立了风电场可靠性模型。采用分区的方法,结合增加了由25台风电机组组成的风电场的IEEE-RTS 24节点算例,利用时序蒙特卡洛模拟法对含风电场的互联发电系统进行可靠性评估。所提模型考虑了风速和负荷的时序相关性以及风电机组的功率输出特性、尾流效应等影响风电场出力的因素,使风电场接入系统后的可靠性评估更为客观、准确。     

Performance analysis of multiple-antenna cooperative networks under Weibull fading

In wireless communications, cooperative relaying is well-known to enhance the overall system performance, but implementation and cost constraints stand against its wide deployment. This paper investigates the performance of cooperative relays with and without multiple antennas under independent and identically distributed (i.i.d.) Weibull faded channels in a two-hop wireless network. We consider the Weibull fading channel model due to its flexibility in describing the radio propagation environment more than the classical Rayleigh model. Our study relies on applying selection combining (SC) along with threshold decode and forward (TDF) protocol at the cooperative relays as a good compromise between cost and performance. In addition, maximal ratio combining (MRC) is used at the destination. We derive analytical expressions for the end-to-end (E2E) error performance of the network under such scenario and provide simulation results to confirm the validity of the obtained analytical expressions.     

Serial relaying communications over generalized‐gamma fading channels

In this paper, a study on the end‐to‐end performance of multi‐hop non‐regenerative relaying networks over independent generalized‐gamma (GG) fading channels is presented. Using an upper bound for the end‐to‐end signal‐to‐noise ratio (SNR), novel closed‐form expressions for the probability density function, the moments, and the moments‐generating function of the end‐to‐end SNR are presented. Based on these derived formulas, lower bounds for the outage and the average bit error probability (ABEP) are derived in closed form. Special attention is given to the low‐ and high‐SNR regions having practical interest as well as to the Nakagami fading scenario. Moreover, the performance of the considered system when employing adaptive square‐quadrature amplitude modulation is further analyzed in terms of the average spectral efficiency, the bit error outage, and the ABEP. Computer simulation results verify the tightness and the accuracy of the proposed bounds. Copyright © 2011 John Wiley & Sons, Ltd.     

基于粗糙表面模型的微波波导连接的无源互调研究

提出了一种计算微波波导连接产生的无源互调(PIM)的新模型.考虑到实际波导表面微凸体高度分布的非对称性,采用威布尔分布来描述波导表面的微观形貌,具有更广泛的适用性.依据波导连接的MIM(金属绝缘体-金属)界面粗糙模型对其等效电路参数的影响规律,采用泰勒级数法较为系统地研究了矩形波导的三阶PIM对表面粗糙度、绝缘层厚度、接触载倚等因素的依赖关系.研究结果表明:波导加工所致的表面粗糙度越大、表面绝缘层越厚、施加的接触载荷越小,PIM则越严重;理论预测表明:当波导连接的接触载荷从104Pa增加到106Pa时,三阶PIM可降低约50dB.     

考虑围压影响的非均质岩石剪胀扩容模型

为了描述围压对非均质岩石剪胀扩容行为的影响,通过扩容指数建立了剪胀角和围压之间的关系式.利用Weibull分布考虑岩石力学参数的非均质性,假设岩石为理想弹塑性材料,建立了考虑围压影响的非均质岩石剪胀扩容模型,并在FLAC软件下利用Fish函数法予以实现.数值算例按3种方案研究了不同侧限下平面应变煤样的破坏行为,结果表明...     

Bayesian calculation of optimal burn‐in time using the joint criteria of cost and delivered reliability

Burn‐in is a quality control process used to minimize the warranty cost of a product by screening out defective products through prior operation for a period of time before sale. Two decision criteria used to determine the optimal burn‐in time are the maximization of the reliability of the delivered product and the minimization of the total cost, which are composed of the cost of burn‐in process and the cost of warranty claims. Because of uncertainty regarding the underlying lifetime distribution of the product, both the product reliability and the total cost are random variables. In this paper, the uncertainty in reliability and cost is quantified by use of Bayesian analysis. The joint distribution of reliability and cost is inferred from the uncertainty distribution of the parameters of the product lifetime distribution. To incorporate the uncertainty in reliability and cost as well as the tradeoff between them into the selection of optimal burn‐in time, the joint utility function of reliability and cost is constructed using the joint distribution of reliability and cost. The optimal burn‐in time is selected as the time that maximizes the joint utility function. Copyright © 2010 John Wiley & Sons, Ltd.     

On the upper truncated Weibull distribution and its reliability implications

The characteristics and application of the truncated Weibull distribution are studied in this paper. This distribution is applicable to the situation where the test data are bounded in an interval because of test conditions, cost and other restrictions. An important property of the truncated Weibull distribution is that it can have bathtub-shaped failure rate function. In this paper, the parametric analysis and parameter estimation methods of the distribution are investigated. Both the graphical approach and the maximum likelihood estimation are considered. The applicability of this distribution to modeling lifetime data is illustrated by an example and the results of comparisons to other competitive models in modeling the given data are also presented. Moreover, the possible application of the distribution to modeling component or system failure is discussed.     

碳/碳复合材料纤维束/基体界面强度的表征

为了获得准确表征纤维束界面强度的方法,对影响纤维束界面强度的因素进行了研究.通过顶出方法对纤维束界面强度进行表征,利用SEM和Micro-CT研究了纤维束界面层微结构对纤维束界面强度的影响,并通过有限元分析方法对纤维束界面的断裂行为进行分析.结果表明：在纤维束界面层含有不同程度的脱粘和裂纹缺陷结构,影响了纤维束的界面强...