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排序方式: 共有1685条查询结果,搜索用时 15 毫秒
91.
L. C. Chow Y. K. Cheung C. L. Tien 《Numerical Heat Transfer, Part B: Fundamentals》2013,63(3):417-423
Abstract In two-dimensional convective transport, the vorticity at a wall is usually not well specified. There exist several representations to relate the vorticity at a wall to the stream function and interior vorticity values. These are shown to be inadequate when suction occurs at the wall. A new representation is proposed and shown to be significantly superior to the existing ones. The analysis can also be applied to heat transfer calculations at a wall with suction. 相似文献
92.
Uncertainty Management in the Unit Commitment Problem 总被引:2,自引:0,他引:2
Ruiz P.A. Philbrick C.R. Zak E. Cheung K.W. Sauer P.W. 《Power Systems, IEEE Transactions on》2009,24(2):642-651
Uncertainty in power systems operations has been traditionally managed by multistage decision making and operating reserve requirements. A familiar example of multistage decisions is day-ahead unit commitment and real-time economic dispatch. An alternate approach for managing uncertainty is a stochastic formulation, which allows the explicit modeling of the sources of uncertainty. This paper compares stochastic and reserve methods and evaluates the benefits of a combined approach for the efficient management of uncertainty in the unit commitment problem. Numerical studies show that unit commitment solutions obtained for the combined approach are robust and superior with respect to the traditional approach in terms of both economics and reliability metrics. 相似文献
93.
Most advanced manufacturing processes require precise motions for material transfer, packaging, assembly, and electrical wiring. To achieve precise linear motions, most of these high-performance manufacturing machines use X-Y sliding tables with permanent-magnet rotary motors and rotary to linear couplers. Though this method is the most widely used, it has disadvantages of low accuracy, complex mechanical adjustments, high cost, and low reliability. This paper describes the position control of a linear switched reluctance motor for high-performance motions in manufacturing automation. The proposed actuator has a very simple structure and it can be manufactured easily. There is no need for magnets and no limitation on the travel distance. The actuator is extremely robust and can be used in a hostile environment. A novel current-force-position lookup table is first developed to perform the force linearization. Then, a plug-in robust compensator using H/sub /spl infin// loop-shaping design is employed to improve the system robustness and the tracking performance. Experimental results of the motion system indicate that the system has fast tracking responses with good accuracy. 相似文献
94.
An investigation has been performed of the cell nucleation and initial growth behaviors in the foam processing of polypropylene (PP) in both the linear and branched forms. These materials were foamed in extrusion with the two blowing agents, CO2 and isopentane. The cell density generally increased with an increased content of the blowing agent, for both CO2 and isopentane. The effect of processing pressure on the cell density was distinct when CO2 was used, whereas no pressure effect was observed in the foam processing with isopentane. The cell morphologies for the two PPs were found to be significantly different. A slightly lower nuclei density was observed in the branched PP foams than in the linear PP foams. However, the phenomenon of cell coalescence was observed much less in the branched PP foams. Most cells in the branched PP foams were closed, whereas in the linear PP foams they were connected to each other. The experimental results indicated that the branched structure played an important role in determining the cell morphologies through its effects on the melt strength and/or melt elasticity. 相似文献
95.
Jian Zhou Chenyu Zhu Lihua Li Man Cheung Ng Kun Liu 《Journal of the American Ceramic Society》2021,104(1):243-255
The glass-to-mold adhesion in precision glass molding could severely degrade the quality of molded optics and shorten the lifespan of the precious molds. Since the consequences of adhesion take effect during the separation between glass and molds, it is important to investigate the debonding behaviors of a typical glass molding interface. To this end, here we perform a probe tack test procedure for borosilicate glass BK7, where debonding is conducted at molding temperature and specific velocity. We fully characterize the debonding behaviors using the peak adhesion stress σmax and the work of debonding Wdeb. Experiments show that when temperature is decreased from 690°C to 655°C at 10 μm/s, σmax continuously increases, while Wdeb first increases but then sharply decreases. When the debonding velocity is increased from 10 to 50 μm/s at 680°C, σmax also increases while Wdeb overall decreases. Therefore, the debonding behaviors are highly temperature and rate dependent. More importantly, depending on the debonding conditions, three debonding types are identified, that is, the cohesive bulk deformation, the cohesive-interfacial transition and the interfacial fracture. The cohesive type can be converted into the interfacial fracture, by either decreasing temperature or increasing the debonding velocity. Based on the Wdeb criterion, the three debonding regimes can be clearly distinguished. Finally, analyses on the temperature and velocity experimental results are unified by incorporating the reduced crack velocity aTvc. The dependences of both viscoelasticity and Wdeb on aTvc qualitatively explain the transition condition for different debonding types. Concerning these findings, the work of debonding not only supplements the characterization of adhesion strength, but also throws insightful light on revealing the debonding mechanisms. 相似文献
96.
Blends of polysulfone (PSF) and poly-phenylene sulfide (PPS) exhibit ductile behavior, below 35% by weight PPS, under tensile loading conditions. However, the blends are notch sensitive to Izod impact. The use of a core-shell type rubber-modifier effectively toughens the blends. Notched Izod impact strength rises, from ~ 50 J/m to about 900 j/m, by increasing rubber content from 0% to 10–15%. It remains constant at a rubber content > 10–15%. Scanning electron microscopy (SEM) is used to study the morphology of the fracture surfaces. At low modifier content (5%), smooth or mesa-like fracture surfaces are observed. Voids and interfacial debonding are revealed. With a higher concentration of toughening agent (> 10%), some crazing is evidence but not consistent. However, matrix yielding and extensive plastic flow of the PSF/PPS matrix are seen throughout, with a higher level of rubber modifier. 相似文献
97.
98.
Xinghou Gong Cheng Cheng Chak Yin Tang Wing‐Cheung Law Xueting Lin Yehuang Chen Ling Chen Gary Chi Pong Tsui Nanxi Rao 《Polymer Engineering and Science》2019,59(3):608-615
Iron oxide nanoparticle (Fe3O4) has gained remarkable research interest for various applications, from environmental to biological, because of its superparamagnetic properties and good biocompatibility. In this work, the nucleation effect of Fe3O4 in a polylactide (PLA) matrix under an influence of an alternating magnetic field was studied. The nanocomposite films that is, containing different concentrations of Fe3O4 (~8 nm) which were uniformly dispersed in the PLA matrix, were prepared via a solution casting method. The amplitude and frequency of the magnetic field impose great effects on the morphology and nucleation rate of PLA crystallization. Thermogravimetric analysis was used to study the thermal stability of Fe3O4/PLA and it showed that the thermal stability of Fe3O4/PLA was affected by the Fe3O4 content. Fourier transform infrared spectroscopy and X‐ray diffractometry indicated that Fe3O4 shows impeding effect to the crystallization of PLA. Based on the differential scanning calorimetry results, composite with 1% of Fe3O4 content could promote the crystallization of PLA but it would become an obstacle when 3% of Fe3O4 was added. The result of polarized optical microscopy also showed a good agreement that the incorporation of Fe3O4 could act as an effective nucleation regent to the composite film. POLYM. ENG. SCI., 59:608–615, 2019. © 2018 Society of Plastics Engineers 相似文献
99.
100.
基于相关向量机的短期风速预测模型 总被引:4,自引:0,他引:4
通过对风速的时间序列进行分析,表明该序列具有混沌特性。在此基础上,利用相空间重构理论建立基于相关向量机(RVM)的短期风速预测模型,并对不同的核函数进行分析,选出最优的核函数。与现有的风速预测模型相比,该模型具有高稀疏性、核函数选择灵活等优点。仿真结果表明,与BP神经网络和支持向量机(SVM)模型相比,RVM模型预测精度更高。 相似文献