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991.
根据断裂力学和随机过程理论,提出了一个随机荷载作用下疲劳裂纹扩展的统计模型。在基于应变能密度因子变程的确定性疲劳裂纹扩展速率公式中引入材料内在的分散性和外部荷载的随机性,将疲劳裂纹扩展近似为连续型马尔可夫过程。应用随机平均法导出了裂纹扩展过程转移概率满足的向后Fokker-Planck方程,并得出相应的边界条件。采用本征函数法进行求解,以收敛的无穷级数表示出疲劳裂纹扩展寿命的分布函数。作为一个算例,具体计算出疲劳裂纹扩展寿命的分布密度曲线。 相似文献
992.
A general and complete methodology is presented to facilitate systematic modeling and design of polymer processes during the early development period. To capture and handle the subjective type of uncertainty, embedded in the preliminary process development, fuzzy theories are used as a basis to model and design the process in the presence of ambiguity and vagueness. Physical membership functions are developed for mapping the relation between process variables and the associated fuzzy uncertainties. Based on the qualitative results generated using our previously proposed “linguistic based preliminary design method,” the process modeling can be followed even in the absence of any process governing equations. The modeling is carried out by establishing an appropriate fuzzy reasoning system which provides a specific functional mapping that relates input process variables to one (or more than one) output performance parameter(s). A reduced yet feasible domain is generated by our qualitative design scheme to constrain the process variables. Now, any optimization routine can then be employed to search for a proper process design. We demonstrate the effectiveness of the proposed methodology by its application to a typical compression molding process. 相似文献
993.
This paper presents strategies for an automated control of distortion at the operational level of a production process chain, as well as first steps towards a combined implementation in heat‐treatment processes. In order to minimise the loss of production due to quality defects, the first quality control loop will be implemented on an in‐process level. The second control loop within the reach of operational control includes the feedback of post‐process measurements of quality features. As such, the post‐process control loop optimises the set‐values of the in‐process control loop. 相似文献
994.
996.
Harriet Black Nembhard Ming Shu Kao 《Quality and Reliability Engineering International》2001,17(4):307-321
Nonconforming parts are often produced when a process moves from one level to another due to transition events. Control charting, when applied to a stable state process, is an effective monitoring tool to continuously check for process shifts or upsets. However, the presence of transition events can impede the normal performance of traditional control chart with increased false alarms. The presence of autocorrelation also requires modification to the control charting procedure. We present a methodology for characterizing the process transition which involves a tracking signal statistic, based on the forecast‐based exponentially weighted moving average (EWMA). This test will supplement the forecast‐based EWMA control charting as a means of detecting when the transition event is complete. Such a procedure facilitates smooth application of the appropriate control chart by knowing when the transition is over. The transition characterization methodology also carries benefits in cost and material savings. We use a color transition process in plastic extrusion to illustrate a transition event and demonstrate our proposed methodology. Simulation is employed to evaluate the performance of the methodology. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
997.
998.
Yao Lu Minoru Inamura Maria del Carmen Valdes 《International journal of imaging systems and technology》2004,14(1):8-15
Numerous approaches to super‐resolution (SR) of sequentially observed images (image sequence) of low resolution (LR) have been presented in the past two decades. However, neural network methods are almost ignored for solving SR problems. This is because the SR problem traditionally has been regarded as the optimization of an ill‐posed large set of linear equations. A designed neural network based on this has a large number of neurons, thereby requiring a long learning time. Also, the deduced cost function is overly complex. These defects limit applications of a neural network to an SR problem. We think that the underlying meaning of the SR problem should refer to super‐resolving an imaging system by image sequence observation, instead of merely improving the image sequence itself. SR can be regarded as a pattern mapping from LR to SR images. The parameters of the pattern mapping can be learned from the imaging process of the image sequence. This article presents a neural network for SR based on learning from the imaging process of the image sequence. In order to speed up the convergence, we employ vector mapping to train the neural network. A mapping vector is composed of some neighbor subpixels. Such a well‐trained neural network has powerful generalization ability so that it can be used directly to estimate the SR image of the other image sequences without learning again. Our simulations show the effectiveness of the proposed neural network. © 2004 Wiley Periodicals, Inc. Int J Imaging Syst Technol 14, 8–15, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ima.20001 相似文献
999.
The paper proposes a robust Bayesian approach to support the replacement policy of low-pressure cast-iron pipelines used in metropolitan gas distribution networks by the assessment of their probability of failure. In this respect, after the identification of the factors leading to failure, the main problem is the historical data on failures, which is generally limited and incomplete, and often collected for other purposes. Consequently, effective evaluation of the probability of failure must be based on the integration of historical data and knowledge of company experts. The Analytic Hierarchy Process has been used as elicitation method of expert opinion to determine the a priori distribution of gas pipeline failures. A real world case study is presented in which the company expertise has been elicited by an ad hoc questionnaire and combined with the historical data by means of Bayesian inference. The robustness of the proposed methodology has also been tested. 相似文献
1000.