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Periodic transonic flow simulation using fourier-based algorithm
Mohammad Reza Mohaghegh,Majid Malek-Jafarian 대한기계학회 2014 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.28 No.10
The present research simulates time-periodic unsteady transonic flow around pitching airfoils via the solution of unsteady Euler andNavier-Stokes equations, using time spectral method (TSM) and compares it with the traditional methods like BDF and explicit structuredadaptive grid method. The TSM uses a Fourier representation in time and hence solves for the periodic state directly without resolvingtransients (which consume most of the resources in a time-accurate scheme). Mathematical tools used here are discrete Fourier transformations. The TSM has been validated with 2D external aerodynamics test cases. These test cases are NACA 64A010 (CT6) andNACA 0012 (CT1 and CT5) pitching airfoils. Because of turbulent nature of flow, Baldwin-Lomax turbulence model has been used inviscous flow analysis with large oscillation amplitude (CT5 type). The results presented by the TSM are compared with experimentaldata and the two other methods. By enforcing periodicity and using Fourier representation in time that has a spectral accuracy, tremendousreduction of computational cost has been obtained compared to the conventional time-accurate methods. Results verify the smallnumber of time intervals per pitching cycle (just four time intervals) required to capture the flow physics with small oscillation amplitude(CT6) and large oscillation amplitude (CT5) as compared to the other two methods.
An Upper Bound for the Probability of Generating a Finite Nilpotent Group
Halimeh Madadi,Seyyed Majid Jafarian Amir,Hojjat Rostami 경북대학교 자연과학대학 수학과 2023 Kyungpook mathematical journal Vol.63 No.2
Let G be a finite group and let ν(G) be the probability that two randomly selected elements of G produce a nilpotent group. In this article we show that for every positive integer n > 0, there is a finite group G such that ν(G) =1/n We also classify all groups G with ν(G) = 1/2 Further, we prove that if G is a solvable nonnilpotent group of even order, then ν(G) ≤p+3/4p , where p is the smallest odd prime divisor of |G|, and that equality exists if and only if G/Z∞(G) is isomorphic to the dihedral group of order 2p where Z∞(G) is the hypercenter of G. Finally we find an upper bound for ν(G) in terms of |G| where G ranges over all groups of odd square-free order.
Javad Shabani-Shayeh,Ali Ehsani,Majid Jafarian 한국전기화학회 2014 한국전기화학회지 Vol.17 No.3
Methanol electro oxidation on the surface of carbon paste modified by NiCl2/6H2Owas studied in 1M NaOH by potentiostatic and potentiodynamic methods. Ni/C catalyst bythe concentration of 5% Ni showed about twice higher electro catalytic activity than Ni metal. The amount of monolayer’s on the surface of electrode is almost one order higher for Ni/Cthan Ni electrode. The kinetic parameters and the diffusion coefficient of methanol were derivedfrom chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS) measurements
Shabani-Shayeh, Javad,Ehsani, Ali,Jafarian, Majid The Korean Electrochemical Society 2014 한국전기화학회지 Vol.17 No.3
Methanol electro oxidation on the surface of carbon paste modified by $NiCl_2/6H_2O$ was studied in 1M NaOH by potentiostatic and potentiodynamic methods. Ni/C catalyst by the concentration of 5% Ni showed about twice higher electro catalytic activity than Ni metal. The amount of monolayer's on the surface of electrode is almost one order higher for Ni/C than Ni electrode. The kinetic parameters and the diffusion coefficient of methanol were derived from chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS) measurements.