Effect of promoter in the oxidative coupling of methane over synthesized Mn/SiO2 nanocatalysts via incipient wetness impregnation

S. Mahmoodi,M.R. Ehsani,S.M. Ghoreishi 한국공업화학회 2010 Journal of Industrial and Engineering Chemistry Vol.16 No.6

The M–Na–Mn/SiO2 nanocatalysts (M =W, Mo, Nb, V, Cr) were synthesized with the size of 12–92 nm by incipient wetness impregnation method to study the effect of different promoters on the catalytic performance in the oxidative coupling of methane. The results at 1 atm, 1048 K, 2500 ml h1 g1, and CH4/O2/N2 = 2/2/1 revealed that C2 selectivity was significantly increased (31.6%) in the order of W> Mo > Nb > Cr > V whereas moderate enhancement (12.6%) was observed in the CH4 conversion in the order of W> Cr > Nb > Mo > V. The results of the characterization techniques (Raman, FT-IR, BET,TGA/DTA and XRD) demonstrated that Mn2O3 and a-cristobalite were the predominant species and active sites in the nanocatalyst surface and Na2MoO4, Na2WO4 and Mn2O3 crystalline phases contributed to achieving high selectivity of C2 products. The redox mechanism involving two metal sites such as Mn3+/2+ and W6+/5+ or Mn3+/2+ and Mo6+/5+ was found to be the most compatible route with the OCM reaction path in which CH4 and O2 adsorption was the controlling step. 2010 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.

Nonlinear response of a resonant viscoelastic microbeam under an electrical actuation

M. Zamanian,S.E. Khadem,S.N. Mahmoodi 국제구조공학회 2010 Structural Engineering and Mechanics, An Int'l Jou Vol.35 No.4

In this paper, using perturbation and Galerkin method, the response of a resonant viscoelastic microbeam to an electric actuation is obtained. The microbeam is under axial load and electrical load. It is assumed that midplane is stretched, when the beam is deflected. The equation of motion is derived using the Newton's second law. The viscoelastic model is taken to be the Kelvin-Voigt model. In the first section, the static deflection is obtained using the Galerkin method. Exact linear symmetric mode shape of a straight beam and its deflection function under constant transverse load are used as admissible functions. So, an analytical expression that describes the static deflection at all points is obtained. Comparing the result with previous research show that using deflection function as admissible function decreases the computation errors and previous calculations volume. In the second section, the response of a microbeam resonator system under primary and secondary resonance excitation has been obtained by analytical multiple scale perturbation method combined with the Galerkin method. It is shown, that a small amount of viscoelastic damping has an important effect and causes to decrease the maximum amplitude of response, and to shift the resonance frequency. Also, it shown, that an increase of the DC voltage, ratio of the air gap to the microbeam thickness, tensile axial load, would increase the effect of viscoelastic damping, and an increase of the compressive axial load would decrease the effect of viscoelastic damping.

Nonlinear response of a resonant viscoelastic microbeam under an electrical actuation

Zamanian, M.,Khadem, S.E.,Mahmoodi, S.N. Techno-Press 2010 Structural Engineering and Mechanics, An Int'l Jou Vol.35 No.4

In this paper, using perturbation and Galerkin method, the response of a resonant viscoelastic microbeam to an electric actuation is obtained. The microbeam is under axial load and electrical load. It is assumed that midplane is stretched, when the beam is deflected. The equation of motion is derived using the Newton's second law. The viscoelastic model is taken to be the Kelvin-Voigt model. In the first section, the static deflection is obtained using the Galerkin method. Exact linear symmetric mode shape of a straight beam and its deflection function under constant transverse load are used as admissible functions. So, an analytical expression that describes the static deflection at all points is obtained. Comparing the result with previous research show that using deflection function as admissible function decreases the computation errors and previous calculations volume. In the second section, the response of a microbeam resonator system under primary and secondary resonance excitation has been obtained by analytical multiple scale perturbation method combined with the Galerkin method. It is shown, that a small amount of viscoelastic damping has an important effect and causes to decrease the maximum amplitude of response, and to shift the resonance frequency. Also, it shown, that an increase of the DC voltage, ratio of the air gap to the microbeam thickness, tensile axial load, would increase the effect of viscoelastic damping, and an increase of the compressive axial load would decrease the effect of viscoelastic damping.

Assessment the Effect of Skewness and Number of Spans in Seismic Behavior of Bridges with Continuous Multiple Spans Using MPA

S. M. Rasouli,M. Mahmoodi 대한토목학회 2018 KSCE JOURNAL OF CIVIL ENGINEERING Vol.22 No.4

The seismic behavior of skewed bridges compared to straight bridges is not well recognized and need more study to investigate itsunique behavior under seismic forces. Much more damage have seen from skewed bridges particularly when its deck rotates in theearthquake. Many causes are involved in this behavior such as columns and piers nonlinear deformation patterns. Through a ModalPushover Analysis (MPA) we will assess the inelastic seismic behavior of reinforced concrete bridges those have skew-angled seattypeabutments. The angle of skewness will change the seismic behavior of this kind of bridges and in this paper this change isexplored with special attention. Maximum nonlinear displacement is sensitive to increase the number of spans and the skew angle ofabutments and piers, but the amount of effects are up to number of spans and angle of skewness. This study showed that as thenumber of spans increases, the deck rotation responses at abutments will be deducted and the adverse effect of skew would subtractedin the bridge.

Linear and nonlinear approaches towards amplitude modulation atomic force microscopy

Aidin Delnavaz,S. Nima Mahmoodi,Nader Jalili,Hassan Zohoor 한국물리학회 2010 Current Applied Physics Vol.10 No.6

Frequency response behavior of microcantilever is analytically and experimentally investigated in amplitude modulation Atomic Force Microscopy (AFM). AFM microcantilever probe is modeled as a continuous beam, and tip-sample interaction force is considered to include both attractive and repulsive force regimes. The developed model is compared with the linear lumped-parameters model that has been extensively used in the literature so far. Experimental measurements are also provided for the frequency response of a typical microcantilever-sample system to demonstrate the advantages of the developed model over the linear formulation. The results indicate that the nonlinear continuous model is more accurate, particularly in the estimation of the saturated amplitude value and frequency zone in which the tip-sample contact happens.

A Review On Active Wind Energy Harvesting Designs

Andrew Truitt,S. Nima Mahmoodi 한국정밀공학회 2013 International Journal of Precision Engineering and Vol. No.

This paper aims to review various designs and effects of vibrations generated by fluids, different bluff bodies, aeroelastic instabilities,and study the methods for harvesting their energies by means of piezoelectric materials. Wind based energy harvesting is increasingly pursued due to the ubiquitous nature of excitation source as well as the strong correlation with other types of excitation. Vortexinduced vibrations (VIV), as well as vibrations induced by bluff bodies, and the effect of their own shape on potential gains has been investigated. In addition, the effect of aeroelastic instability phenomenon such as fluttering and galloping on energy generation is investigated. The energy generation density of various methods is evaluated by comparing the gains of different approaches. The study results show that energy densities and peak power outputs vary widely depending on device configuration and instability phenomenon. Additionally, peak power output versus bandwidth varies greatly between the phenomena suggesting specialized applications for a given phenomenon. Through these study results, new research paths to move forward in this field are suggested when paired with the latest examples at active energy harvesting.

Effect of a Magnetic Field on Mixed Convection of a Nanofluid in a Square Cavity

G. A. Sheikhzadeh,S. Mazrouei Sebdani,M. Mahmoodi,Elham Safaeizadeh,S. E. Hashemi 한국자기학회 2013 Journal of Magnetics Vol.18 No.3

The problem of mixed convection in a differentially heated lid-driven square cavity filled with Cu-water nanofluid under effect of a magnetic field is investigated numerically. The left and right walls of the cavity are kept at temperatures of Th and Tc respectively while the horizontal walls are adiabatic. The top wall of the cavity moves in own plane from left to right. The effects of some pertinent parameters such as Richardson number (ranging from 0.1 to 10), the volume fraction of the nanoparticles (ranging 0 to 0.1) and the Hartmann number (ranging from 0 to 60) on the fluid flow and temperature fields and the rate of heat transfer in the cavity are investigated. It must be noted that in all calculations the Prandtl number of water as the pure fluid is kept at 6.8, while the Grashof number is considered fixed at 104. The obtained results show that the rate of heat transfer increases with an increase of the Reynolds number, while but it decreases with increase in the Hartmann number. Moreover it is found that based the Richardson and Hartmann numbers by increase in volume fraction of the nanoparticles the rate of heat transfer can be enhanced or deteriorated compared to the based fluid.