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581.
目前对沿岸流不稳定研究比较成熟的理论基础是线性不稳定理论,该理论假定增长率最大的不稳定模式决定着沿岸流的波动特性,但实验分析结果表明对有些情况下该假定难以解释实验中观测到的情况.利用沿岸流不稳定运动的多模式理论分析了实验中观测到的情况.结果表明沿岸流速度剖面对于沿岸流不稳定运动模式影响很大,特别是速度剖面的变化会导致不稳定模式出现多个模式的情况,即增长率曲线出现多于两个峰的情况.用解析的速度剖面分析了速度剖面前剪切和后剪切同时变化及单独变化对于沿岸流不稳定多模式运动的影响.结果表明对于坡度为1:100的平直斜坡的情况用前剪切不稳定理论可以解释其观测到的现象. 相似文献
582.
583.
1.75W线性分置式斯特林制冷机基于故障模式的持续改进 总被引：1，自引：0，他引：1
通过对线性分置式斯特林制冷机在实际应用过程中产生的故障进行研究分析,提出了解决故障的方案及持续改进的措施. 相似文献
584.
585.
大位移井钻井风险灰元故障树原理研究 总被引：2，自引：0，他引：2
大位移井钻井技术是国外90年代发展起来的高新钻井技术,但钻井风险和钻井事故越来越引起人们的重视。因此本文在故障树分析基础上,结合灰元概念,对大位移钻井风险,首次提出了灰元故障树原理,成功地解决了大位移钻井风险预测和防范等问题。实例表明结果与其它方法吻合很好,符合实际,不仅对测算大位移井钻井风险适用,而且对于评估工程和经济领域的风险也适用,用途十分广泛。 相似文献
586.
In this paper we study the persistent current (PC) of a staggered Harper model, close to the half-filling. The Harper model is different than other one dimensional disordered systems which are always localized, since it is a quasi-periodic system with correlated disorder resulting in the fact that it can be in the metallic regime. Nevertheless, the PC for a wide range of parameters of the Harper model does not show typical metallic behavior, although the system is in the metallic regime. This is a result of the nature of the central band states, which are a hybridization of Gaussian states localized in superlattice points. When the superlattice is not commensurate with the system length, the PC behaves as an insulator. Thus even in the metallic regime a typical finite Harper model may exhibit a PC expected from an insulator. 相似文献
587.
Mobile edge computing (MEC) is a key feature of next-generation mobile networks aimed at providing a variety of services for different applications by performing related processing tasks closer to the users. With the advent of the next-generation mobile networks, researchers have turned their attention to various aspects of edge computing in an effort to leverage the new capabilities offered by 5G. So, the integration of software defined networking (SDN) and MEC techniques was seriously considered to facilitate the orchestration and management of Mobile Edge Hosts (MEH). Edge clouds can be installed as an interface between the local servers and the core to provide the required services based on the known concept of the SDN networks. Nonetheless, the problem of reliability and fault tolerance will be of great importance in such networks. The paper introduced a dynamic architecture that focuses on the end-to-end mobility support required to maintain service continuity and quality of service. This paper also presents an SDN control plane with stochastic network calculus (SNC) framework to control MEC data flows. In accordance with the entrance processes of different QoS-class data flows, closed-form problems were formulated to determine the correlation between resource utilization and the violation probability of each data flow. Compared to other solutions investigated in the literature, the proposed approach exhibits a significant increase in the throughput distributed over the active links of mobile edge hosts. It also proved that the outage index and the system’s aggregate data rate can be effectively improved by up to 32%. 相似文献
588.
The existence of thermoelectric currents (TECs) in workpieces during the laser welding of metals has been common knowledge for more than 15 years. However, the time-dependent evolutions of TECs in laser welding remain unclear. The present study developed a novel three-dimensional theoretical model of thermoelectric phenomena in the fiber laser welding of austenite stainless steel and used it to observe the time-dependent evolutions of TECs for the first time. Our model includes the complex physical effects of thermal, electromagnetic, fluid and phase transformation dynamics occurring at the millimeter laser ablated zone, which allowed us to simulate the TEC, self-induced magnetic field, Lorentz force, keyhole and weld pool behaviors varying with the welding time for different parameters. We found that TECs are truly three-dimensional, time-dependent, and uneven with a maximum current density of around 107 A/m2 located at the liquid-solid (L/S) interface near the front or bottom part of the keyhole at a laser power of 1.5 kW and a welding speed of 3 m/min. The TEC formed three-dimensional circulations moving from the melting front to solidification front in the solid part of workpiece, after which the contrary direction was followed in the liquid part. High frequency oscillation characteristics (2.2–8.5 kHz) were demonstrated in the TEC, which coincides with that of the keyhole instability (2.0–5.0 kHz). The magnitude of the self-induced magnetic field and Lorentz force can reach 0.1 mT and 1 kN/m3, respectively, which are both consistent with literature data. The predicted results of the weld dimensions by the proposed model agree well with the experimental results. Our findings could enhance the fundamental understanding of thermoelectric phenomena in laser welding. 相似文献
589.
590.
The problem of fault identification in hybrid systems is investigated. It is assumed that the hybrid systems under consideration consist of a finite automaton, the set of nonlinear differential equations, and so-called mode activator that coordinates the action of these two parts. To solve the fault identification problem, sliding mode observers are used. The suggested approach for constructing sliding mode observers is based on the reduced order model of the original system. This allows to reduce complexity of sliding mode observers and relax the limitations imposed on the original system. Examples illustrate details of the solution. 相似文献