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RISS 인기검색어
- 검색키워드
- 저자 : Vahid Esfahanian (검색결과 5 건)
- 무료
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Improvement of the instability of compressible lattice Boltzmann model by shockdetecting sensor
Vahid Esfahanian,Mohsen Ghadyani 대한기계학회 2015 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.29 No.5
Recently, lattice Boltzmann method (LBM) has drawn attention as an alternative and promising numerical technique for simulatingfluid flows. The stability of LBM is a challenging problem in the simulation of compressible flows with different types of embeddeddiscontinuities. This study, proposes a complementary scheme for simulating inviscid flows by a compressible lattice Boltzmann modelin order to improve the instability using a shock-detecting procedure. The advantages and disadvantages of using a numerical hybrid filteron the primitive or conservative variables, in addition to, macroscopic or mesoscopic variables are investigated. The study demonstratesthat the robustness of the utilized LB model is improved for inviscid compressible flows by implementation of the complementaryscheme on mesoscopic variables. The validity of the procedure to capture shocks and resolve contact discontinuity and rarefaction wavesin well-known benchmark problems is investigated. The numerical results show that the scheme is capable of generating more robustsolutions in the simulation of compressible flows and prevents the formation of oscillations. Good agreements are obtained for all testcases.
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Design parameter study on the performance of lead-acid batteries
Vahid Esfahanian,Amir Babak Ansari,Hassan Bahramian,Pooyan Kheirkhah,Goodarz Ahmadi 대한기계학회 2014 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.28 No.6
The investigation of design parameters is very helpful for optimizing the capacity of an electrochemical cell, which can be done byboth experimental and numerical methods. In this study, a lead-acid battery has been simulated numerically using the CFD commercialsoftware package FLUENT. The governing equations, including conservation of charge in solid and liquid phases and conservation ofspecies, are solved by developing several user defined functions (UDF). The effect of some basic parameters such as electrode porosity,discharge current density, and width of the electrodes and separator on the cell voltage behavior of a lead-acid battery is investigated. Ithas been shown that increasing the width and porosity of separator has both positive and negative effects on the performance parametersof battery. Furthermore, a thicker PbO2 electrode has a more pronounced effect than a thicker Pb one.
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Masoud Masih-Tehrani,Mohammad-Reza Ha’iri-Yazdi,Vahid Esfahanian,Hossein Sagha 대한기계학회 2012 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.26 No.12
In this paper, a hybrid energy storage sizing algorithm for electric vehicles is developed to achieve a semi-optimum cost-effective design. Using the developed algorithm, a driving cycle is divided into its micro-trips and the power and energy demands in each micro-trip are determined. The battery size is estimated because the battery fulfills the power demands. Moreover, the ultra-capacitor (UC) energy (or the number of UC modules) is assessed because the UC delivers the maximum energy demands of the different micro-trips of a driving cycle. Finally, a design factor, which shows the power of the hybrid energy storage control strategy, is utilized to evaluate the newly designed control strategies. Using the developed algorithm, energy-saving loss, driver satisfaction criteria, and battery life criteria are calculated using a feed-forward dynamic modeling software program and are utilized for comparison among different energy storage candidates. This procedure is applied to the hybrid energy storage sizing of a series hybrid electric city bus in Manhattan and to the Tehran driving cycle. Results show that a higher aggressive driving cycle (Manhattan) requires more expensive energy storage system and more sophisticated energy management strategy.
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Effect of flow conditions on spray cone angle of a two-fluid atomizer
Maziar Shafaee,Sayed Abdolhossein Banitabaei,Mehdi Ashjaee and Vahid Esfahanian 대한기계학회 2011 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.25 No.2
A visual study is conducted to determine the effects of operating conditions on the spray cone angle of a two-fluid atomizer. The liquid (water) jets exit from peripheral inclined orifices and are introduced into a high-speed gas (air) stream in the gravitational direction. Using a high-speed imaging system, the spray cone angle is determined for Reynolds numbers ranging from 4×10⁴ to 9×10⁴ and different Weber numbers up to 140. The droplet sizes (Sauter mean diameter) and their distributions are determined using a Malvern Mastersizer X. The results show that the spray cone angle depends on the operating conditions, especially in lower values of Reynolds and Weber numbers. An empirical correlation is also obtained to predict the spray cone angle in terms of these two parameters.
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Maziar Shafaee,Sayed Abdolhossein Banitabaei,Mehdi Ashjaee and Vahid Esfahanian 대한기계학회 2011 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.25 No.12
A visual study is conducted to determine the effect of geometrical parameters of a two-fluid atomizer on its spray cone angle. The liquid (water) jets exit from six peripheral inclined orifices and are introduced to a high speed gas (air) stream in the gravitational direction. Using a high speed imaging system, the spray cone angle has been determined in constant operational conditions, i.e., Reynolds and Weber numbers for different nozzle geometries. Also, the droplet sizes (Sauter mean diameter) and their distributions have been determined using Malvern Master Sizer x. The investigated geometrical parameters are the liquid jet diameter, liquid port angle and the length of the gas-liquid mixing chamber. The results show that among these parameters, the liquid jet diameter has a significant effect on spray cone angle. In addition, an empirical correlation has been obtained to predict the spray cone angle of the present two-fluid atomizer in terms of nozzle geometries.
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