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991.
通过对中原油田注水站应用高压大功率变频调速节能技术的原理及效果分析,揭示了油田注水系统应用变频实施节能改遗的巨大潜力. 相似文献
992.
993.
Hai-Yin Xu Author Vitae Hon Yuen Tam Author Vitae Author Vitae Li’an Hu Author Vitae 《Computer aided design》2009,41(6):432-440
The intersecting path is an important tool path generation method. This paper proposes an approach for the quart-parametric interpolation of intersecting paths. The objective of our approach is that the intersecting paths for surface machining can be directly interpolated within the computer numerical control (CNC) system. This enables the CNC interpolator to process the intersecting paths without geometric approximation as in existing approaches and take into consideration any specific feedrate profiles and further machining dynamical issues along the path.The interpolation of the intersection of two general parametric surfaces is transferred into interpolation of its projection curves and the time trajectories of four parameters along the intersecting curves are obtained. Our strategy is to carry out the quart-parametric interpolation based on the projection interpolation. The feedrate control method is developed, and then the interpolation algorithms for two projection curves are proposed. An error reduction scheme is presented to alleviate point deviation from the drive parametric surface. Simulations of quart-parametric interpolation have been carried out to verify the effectiveness of the proposed algorithm. 相似文献
994.
A (t, n) threshold proxy signature scheme allows any t or more proxy signers to cooperatively sign messages on behalf of an original signer, but t ? 1 or fewer proxy signers cannot. In a recent work [C.H. Yang, S.F. Tzeng, M.S. Hwang, On the efficiency of nonrepudiable threshold proxy signature scheme with known signers, Systems and Software 73(3) (2004) 507–514], C.H. Yang, S.F. Tzeng and M.S. Hwang proposed a new threshold proxy signature scheme (called as YTH scheme), which is more efficient in algorithm and communication than Hsu et al.'s scheme proposed in 2001. However, YTH scheme still has some security weaknesses. In this paper, we show that YTH scheme cannot resist frame attack and public-key substitute attack. A new improvement with high safety and efficiency is proposed. The new scheme remedies the weaknesses of YTH scheme, especially, it can resist public-key substitute attack successfully by Zero-Knowledge Proof. Furthermore, the system doesn't need a security channel and computational complexity can be lowered. 相似文献
995.
Online updating belief rule based system for pipeline leak detection under expert intervention 总被引:1,自引:0,他引:1
Zhi-Jie Zhou Chang-Hua Hu Jian-Bo Yang Dong-Ling Xu Dong-Hua Zhou 《Expert systems with applications》2009,36(4):7700-7709
A belief rule base inference methodology using the evidential reasoning approach (RIMER) has been developed recently, where a new belief rule base (BRB) is proposed to extend traditional IF-THEN rules and can capture more complicated causal relationships using different types of information with uncertainties, but these models are trained off-line and it is very expensive to train and re-train them. As such, recursive algorithms have been developed to update the BRB systems online and their calculation speed is very high, which is very important, particularly for the systems that have a high level of real-time requirement. The optimization models and recursive algorithms have been used for pipeline leak detection. However, because the proposed algorithms are both locally optimal and there may exist some noise in the real engineering systems, the trained or updated BRB may violate some certain running patterns that the pipeline leak should follow. These patterns can be determined by human experts according to some basic physical principles and the historical information. Therefore, this paper describes under expert intervention, how the recursive algorithm update the BRB system so that the updated BRB cannot only be used for pipeline leak detection but also satisfy the given patterns. Pipeline operations under different conditions are modeled by a BRB using expert knowledge, which is then updated and fine tuned using the proposed recursive algorithm and pipeline operating data, and validated by testing data. All training and testing data are collected from a real pipeline. The study demonstrates that under expert intervention, the BRB expert system is flexible, can be automatically tuned to represent complicated expert systems, and may be applied widely in engineering. It is also demonstrated that compared with other methods such as fuzzy neural networks (FNNs), the RIMER has a special characteristic of allowing direct intervention of human experts in deciding the internal structure and the parameters of a BRB expert system. 相似文献
996.
Liang Kong Yunzhuan Zhao Kaijin Hu Dehua Li Hongzhi Zhou Ziyan Wu Baolin Liu 《Advances in Engineering Software》2009,40(7):474-478
In this paper, effects of the implant thread pitch on the maximum Von Mises stresses were evaluated in jaw bones and implant–abutment complex by a finite element method. The thread pitch ranged from 0.5 mm to 1.6 mm. Results suggested that under axial load, the maximum equivalent stresses in cortical bone, cancellous bone and implant–abutment complex decreased by 6.7%, 55.2% and 22.3%, respectively with the variation of thread pitch; and under buccolingual load, 2.7%, 22.4% and 13.0%, respectively. When thread pitch exceeded 0.8 mm, minimum stresses were obtained. Data indicated that cancellous bone was more sensitive to thread pitch than cortical bone did; thread pitch played a great role in protecting dental implant under axial load than under buccolingual load; and thread pitch exceeding 0.8 mm were optimal selection for a screwed implant by biomechanical consideration. 相似文献
997.
998.
提出复杂产品虚拟样机协同开发平台的体系结构和功能框架,设计统一数据访问接口,自主开发了“复杂产品虚拟样机协同开发平台”软件。该软件包括个人工作空间管理、仿真建模、数据管理、过程管理、模型库管理和仿真评估等功能模块,能够支持复杂产品从设计、仿真、分析和优化的整个多学科协同开发过程,实现了对协同开发相关的项目、人员、模型、数据和工作流等资源的集成化管理,为复杂产品虚拟样机的实施提供了设计、仿真和资源管理的分布式支撑环境。 相似文献
999.
首先从混合式P2P网络拓扑结构出发,结合DHT思想,提出了基于DHT的层次化P2P网络模型.其次根据在文档集巨大的情况下,用户提交的查询不可能"面面俱到",实际用来回答查询的文档仅仅是文档集中很小的一部分这一思想,在层次化P2P模型的超级节点中建立了分布式缓存,运用分布式索引与缓存技术,提出一种新的方法来解决多项查询问题.即由多项查询中的某个关键字key,根据hash函数定位到负责该key的超级节点,查询该节点上的分布式索引得到缓存具体存储位置,最终将结果返回给用户,如若缓存中没有所要查询的内容,则广播该查询,同时根据系统中的历史广播查询信息来计算某个待选缓存项的利益值,利益最大的待选项加入缓存.一般针对多项查询的泛洪算法往往会造成巨大的网络信息量,提出的方法牺牲了超级节点上一小部分的存储力,缓解了多项查询造成的网络拥挤现象.同时,基于DHT的层次化P2P模型也具有很好的稳定性,不会因为大量节点的动态加入或者退出而无法进行多项查询. 相似文献
1000.
When paths share a common congested link, they will all suffer from a performance degradation. Boolean tomography exploits these performance-level correlations between different paths to identify the congested links. It is clear that the congestion of a path will be distinctly intensive when it traverses multiple congested links. We adopt an enlarged state space model to mirror different congestion levels and employ a system of integer equations, instead of Boolean equations, to describe relationships between the path states and the link states. We recast the problem of identifying congested links into a constraint optimization problem, including Boolean tomography as a special case. For a logical tree, we propose an up-to-bottom algorithm and prove that it always achieves a solution to the problem. Compared with existing algorithms, the simulation results show that our proposed algorithm achieves a higher detection rate while keeping a low false positive rate. 相似文献