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排序方式: 共有415条查询结果,搜索用时 31 毫秒
71.
Farzad Bazdidi-Tehrani Mohsen Kiamansouri Mohammad Jadidi 《Journal of Building Performance Simulation》2016,9(6):680-698
The present paper investigates the performance of various inflow turbulence generation techniques (ITGT) for large eddy simulation (LES) of flow and dispersion around a model building in a turbulent atmospheric boundary layer. Four different ITGT comprising 1 – no fluctuations, 2 – spectral method, 3 – vortex method and 4 – internal mapping, based on two basic methodologies (i.e. precursor and synthetic turbulence methods), are employed. These techniques are evaluated by considering their prediction accuracy, computational costs, complexity of implementation, inflow information required to operate and impacts on the flow downstream of the inlet, particularly in the wake region of the model building. Results indicate that the accuracy of LES predictions is greatly reliant on ITGT. It is shown that ITGT not only have significant effects on flow field vortical structures, but also influence frequency contents of velocity fluctuations, recirculation regions and plume shapes in the wake region. 相似文献
72.
We propose a multiscale approach to study the influence of carbon nanotubes’ agglomeration on the stability of hybrid nanocomposite plates. The hybrid nanocomposite consists of both macro- and nano-scale reinforcing fibers dispersed in a polymer matrix. The equivalent material properties are calculated by coupling the Eshelby-Mori-Tanaka model with the rule of mixture accounting for effects of CNTs inside the generated clusters. Furthermore, an energy based approach is implemented to obtain the governing equations of the problem utilizing a refined higher-order plate theorem. Subsequently, the derived equations are solved by Galerkin’s analytical method to predict the critical buckling load. The influence of various boundary conditions is studied as well. After validation, a set of numerical examples are presented to explain how each variant can affect the plate’s natural frequency. 相似文献
73.
Investigation of rare earth sealing of porous micro-arc oxidation coating formed on AZ91D magnesium alloy 总被引:1,自引:0,他引:1
Magnesium and its alloys have been used in many industries, but they are reactive and require protection against aggressive envi-ronments. In this study, oxide coatings were applied on AZ91D magnesium alloy using micro-arc oxidation (MAO) process. Then, in order to seal the pores of the MAO coatings, the samples were immersed in cerium bath for different times. The surface morphologies and composi-tions of the coatings were analyzed by scanning electron microscopy (SEM) and X-ray energy dispersive spectroscopy (EDS), respectively. The corrosion behavior of the coatings was investigated with electrochemical impedance spectroscopy (EIS) and potentiodynamic polariza-tion tests in 3.5 wt.% NaCl solution. The amount of the porosity of the coating was measured by electrochemical method. It was found that the sealing treatments by immersion in cerium bath successfully sealed the pores of the MAO coatings. The results of the corrosion tests showed that the MAO coating which was sealed in Ce bath for 10 min enhanced the corrosion resistance of the substrate significantly. Fur-thermore, this coating had the lowest amount of the porosity among the coatings.) 相似文献
74.
Javad Foroughi Bahram KimiaghalamShaban Reza Ghorbani Farzad SafaeiMehran Abolhasan 《Thin solid films》2012,520(24):7049-7053
Experiments were conducted to measure the electrical conductivity in three types of pristine and carbon nanotube-polypyrrole (CNT-PPy) composite yarns and its dependence on over a wide temperature range. The experimental results fit well with the analytical models developed. The effective energy separation between localized states of the pristine CNT yarn is larger than that for both the electrochemically and chemically prepared CNT-PPy yarns. It was found that all samples are in the critical regime in the insulator-metal transition, or close to the metallic regime at low temperature. The electrical conductivity results are in good agreement with a Three Dimensional Variable Range Hopping model at low temperatures, which provides a strong indication that electron hopping is the main means of current transfer in CNT yarns at T < 100 K. We found that the two shell model accurately describes the electronic properties of CNT and CNT-PPy composite yarns in the temperature range of 5-350 K. 相似文献
75.
In this paper a new algorithm for allocating energy and determining the optimum amount of network active power reserve capacity and the share of generating units and demand side contribution in providing reserve capacity requirements for day-ahead market is presented. In the proposed method, the optimum amount of reserve requirement is determined based on network security set by operator. In this regard, Expected Load Not Supplied (ELNS) is used to evaluate system security in each hour. The proposed method has been implemented over the IEEE 24-bus test system and the results are compared with a deterministic security approach, which considers certain and fixed amount of reserve capacity in each hour. This comparison is done from economic and technical points of view. The promising results show the effectiveness of the proposed model which is formulated as mixed integer linear programming (MILP) and solved by GAMS software. 相似文献
76.
Farzad Ebrahimi Mohammad Hassan Naei Abbas Rastgoo 《Journal of Mechanical Science and Technology》2009,23(8):2107-2124
A theoretical model for geometrically nonlinear vibration analysis of piezoelectrically actuated circular plates made of functionally
grade material (FGM) is presented based on Kirchhoff’s-Love hypothesis with von-Karman type geometrical large nonlinear deformations.
To determine the initial stress state and pre-vibration deformations of the smart plate a nonlinear static problem is solved
followed by adding an incremental dynamic state to the pre-vibration state. The derived governing equations of the structure
are solved by exact series expansion method combined with perturbation approach. The material properties of the FGM core plate
are assumed to be graded in the thickness direction according to the power-law distribution in terms of the volume fractions
of the constituents. Control of the FGM plate’s nonlinear deflections and natural frequencies using high control voltages
is studied and their nonlinear effects are evaluated. Numerical results for FG plates with various mixture of ceramic and
metal are presented in dimensionless forms. In a parametric study the emphasis is placed on investigating the effect of varying
the applied actuator voltage as well as gradient index of FGM plate on vibration characteristics of the smart structure.
This paper was recommended for publication in revised form by Associate Editor Eung-Soo Shin
Farzad Ebrahimi received his B.S. and M.S. degree in Mechanical Engineering from University of Tehran, Iran. He is currently working on his
Ph.D. thesis under the title of “Vibration analysis of smart functionally graded plates” at Smart Materials and Structures
Lab in Faculty of Mechanical Engineering of the University of Tehran. His research interests include vibration analysis of
plates and shells, smart materials and structures and functionally graded materials. 相似文献
77.
In many production environments where demand and lead times are variable, significant levels of safety stock inventory are required to assure timely production and delivery of the final product. Traditional models to determine the appropriate safety stock level may result in more safety stocks at sub-assembly and finished goods levels than necessary and thus lead to higher inventory carrying costs than desired. Such models generally incorrectly assume that the demand during the lead time follows a normal distribution. This paper revisits and analyses a re-ordering point inventory model developed by Estes (1973) that accounts for demand and lead time variability without making any particular distributional assumptions. Instead, it focuses on historical data to determine the possible outcomes of the replenishment cycle. We compare the proposed model with the traditional model by conducting simulation analysis using three data sets obtained from an electronics manufacturer. The results indicate that the proposed model yields much closer to target service levels and lower inventory carrying costs than the traditional model, regardless of the data set used. 相似文献
78.
Eklavya Singh Zongping Chen Farzad Houshmand Wencai Ren Yoav Peles Hui‐Ming Cheng Nikhil Koratkar 《Small (Weinheim an der Bergstrasse, Germany)》2013,9(1):75-80
The static and dynamic wetting properties of a 3D graphene foam network are reported. The foam is synthesized using template‐directed chemical vapor deposition and contains pores several hundred micrometers in dimension while the walls of the foam comprise few‐layer graphene sheets that are coated with Teflon. Water contact angle measurements reveal that the foam is superhydrophobic with an advancing contact angle of ~163 degrees while the receding contact angle is ~143 degrees. The extremely water repellent nature of the foam is also confirmed when impacting water droplets are able to completely rebound from the surface. Such superhydrophobic graphene foams show potential in a variety of applications ranging from anti‐sticking and self‐cleaning to anti‐corrosion and low‐friction coatings. 相似文献
79.
Seyed Jalal Hashemi Hassan Moslemi Naeini Gholamhosein Liaghat Roohollah Azizi Tafti Farzad Rahmani 《Journal of Materials Engineering and Performance》2013,22(1):57-63
Reduction of weight and increase of corrosion resistance are among the advantageous applications of aluminum alloys in automotive industry. Producing complicated components with several parts as a uniform part not only increases their strength but also decreases the production sequences and costs. However, achieving this purpose requires sufficient formability of the material. Tube hydroforming is an alternative process to produce complex products. In this process, the higher the material formability the more uniform will be the thickness distribution. In this research, tube hydroforming of aluminum alloy (AA1050) at various temperatures has been investigated numerically to study temperature effect on thickness distribution of final product. Also a warm hydroforming set-up has been designed and manufactured to evaluate numerical results. According to numerical and experimental results in the case of free bulging, unlike the constrained bulging, increase of the process temperature causes more uniform thickness distribution and therefore increases the material formability. 相似文献
80.
Nasser Safari Saeed Rayati Akbar Ghaemi Farzad Bahadoran Hamid Reza Khavasi 《Inorganic chemistry communications》2008,11(12):1459-1461
Tetramesitylporphyrin platinum(VI) dihydroxo complex, TMPPt(OH)2 · 2 benzoate was synthesized by addition of two equivalent of meta-chloroperbenzoic acid molecules to the tetramesitylporphyrin platinum(II). This complex was characterized by X-ray diffraction and spectroscopic methods, and is capable to convert two molecules of triphenylphosphine to triphenylphosphine oxide. 相似文献