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CONTENTS
Volume 8, Number 1, January 2020
 

Abstract
In order to develop a new adsorbent for removal of formaldehyde from aqueous solution, surface modification of TiO2 nanoparticles was performed with 2,4-Dinitrophenylhydrazine (DNPH) that have a strong affinity to the formaldehyde. Sodium dodecyl sulfate (SDS) surfactant was used to improve the DNPH grafting to TiO2 surface. Modified adsorbents were characterized by SEM, TEM, XRD, EDX and FTIR. Since the COD level in wastewaters including formaldehyde is considerable, it is necessary to determine the COD content of the synthetic wastewater. In order to determine the optimal removal conditions, the effect of contact time (60-210 min), pH (4-10) and adsorbent dosage (0.5-1.5 g/L) on adsorption and COD removal efficiencies were studied, using response surface method. EDX and FTIR analysis confirmed the presence of nitrogen-containing functional groups on the modified TiO2 surface. The maximum formaldehyde adsorption and COD removal efficiencies by modified TiO2 were about 15.65 and 7.35% higher than the unmodified nanoparticles respectively. Therefore, the grafting of nano-TiO2 with DNPH would greatly improve its formaldehyde adsorption efficiency. The optimum conditions determined for a maximum formaldehyde removal of 99.904% and a COD reduction of 94.815% by TiO2/SDS/DNPH nanocomposites were: adsorbent dosage 1.100 g/L, pH 7.424 and the contact time 183.290 min.

Key Words
titanium dioxide nanoparticles; DNPH; formaldehyde; aqueous solution; adsorption; COD

Address
Department of Chemical Engineering, Quchan Branch, Islamic Azad University, Quchan, Iran.


Abstract
In this paper, for the first time based on the nonlocal strain gradient theory the effect of size dependency in torsional vibration of bi-direction functionally graded (FG) nonlinear nano-cone is study. The material properties were assumed to vary according to the arbitrary function in radial and axial directions. The Navier equation and boundary conditions of the size-dependent bidirectional FG nonlinear nano-cone were derived by Hamilton's principle. These equations were solved by employing the generalized differential quadrature method (GDQM). The presented model can turn into the classical model if the material length scale parameters are taken to be zero. The effects of some parameters, such as inhomogeneity constant, cross-sectional area parameter and small-scale parameters, were studied. As an essential result of this study can be stated that an FG nano-cone model based on the nonlocal elasticity theory behaves softer and based on the strain gradient theory behaves harder.

Key Words
torsional vibration; bi-directional FGMs; nano-cone; GDQM; nonlocal strain gradient elasticity

Address
(1) Reza Noroozi, Amin Kazemi, Saeed Norouzi:
School of Mechanical Engineering, College of Engineering, University of Tehran, Tehran, Iran;
(2) Abbas Barati:
Department of Mechanical Engineering, University of Guilan, Rasht, Iran;
(3) Amin Hadi:
Cellular and Molecular Research Center, School of Medicine, Yasuj University of Medical Sciences, Yasuj, Iran.

Abstract
Rotating systems concern with torsional vibration, and it should be considered in vibration analysis. To do this, the time-dependent torsional vibrations in a single-walled carbon nanotube (SWCNT) under the linear and harmonic external torque, are investigated in this paper. Eringen's nonlocal elasticity theory is considered to demonstrate the nonlocality and constitutive relations. Hamilton's principle is established to derive the governing equation of motion and consequently related boundary conditions. An analytical method, called the Galerkin method, is utilized to discretize the driven differential equations. Linear and harmonic torsional loads, along with determined amplitude, are applied to the SWCNT as the external torques. SWCNT is considered under the clamped-clamped end supports. In free vibration, analysis of small scale effect reveals the capability of natural frequencies in different modes, and this results desirably are in coincidence with another study. The forced torsional vibration in the time domain, especially for carbon nanotubes, has not been done before in the previous works. The previous forced studies were devoted to the transverse vibrations. It should be emphasized that the dynamical analysis of torsion is novel, workable, and at the beginning of the path. The variations of nonlocal parameter, CNT's thickness, and the influence of excitation frequency on timedependent angular displacement and nondimensional angular displacement are investigated in the context.

Key Words
forced vibration; SWCNT; torsional vibration; linear and harmonic; exact solution

Address
(1) Seyyed A.H. Hosseini:
Department of Industrial, Mechanical and Aerospace Engineering, Buein Zahra Technical University, Buein Zahra, Qazvin, Iran;
(2) Farshad Khosravi:
Department of Aerospace Engineering, K.N. Toosi University of Technology, Tehran, Iran.

Abstract
This work focuses on the behavior of non-local shear deformation beam theory for the vibration of functionally graded (FG) nanobeams with porosities that may occur inside the functionally graded materials (FG) during their fabrication, using the nonlocal differential constitutive relations of Eringen. For this purpose, the developed theory accounts for the higher-order variation of transverse shear strain through the depth of the nanobeam. The material properties of the FG nanobeam are assumed to vary in the thickness direction. The equations of motion are derived from Hamilton's principle. Analytical solutions are presented for a simply supported FG nanobeam with porosities. The validity of this theory is verified by comparing some of the present results with other higher-order theories reported in the literature, the influence of material parameters, the volume fraction of porosity and the thickness ratio on the behavior mechanical P-FGM beam are represented by numerical examples.

Key Words
nanobeam; non-local elasticity theory; vibration; functionally graded; porosity coefficient

Address
(1) Youcef Gafour:
University Djillali Liabes- Faculty of Technology, Sidi-Bel-Abbès, BP 89, Sidi Bel Abbès 22000 Algeria;
(2) Abdelillah Benahmed:
Laboratory of Modeling and Multi-Scale Simulation, Department of Physics, Faculty of Exact Science, University of Sidi Bel Abbes, Algeria;
(3) Ahmed Hamidi:
Civil Engineering and Hydraulic Department, Faculty Technology, University of Bechar, P.O. Box 417, Street of Independence 08000, Algeria;
(4) Mohamed Zidour, Tayeb Bensattalah:
University of Tiaret, BP 78 Zaaroura, 14000 Tiaret, Algeria;
(5) Mohamed Zidour, Tayeb Bensattalah:
Laboratory of Geomatics and Sustainable Development, University of Ibn Khaldoun-Tiaret, Algeria.

Abstract
This paper investigates the vibration characteristics of flexoelectric nanobeams resting on viscoelastic foundation and subjected to magneto-electro-viscoelastic-hygro-thermal (MEVHT) loading. In this regard, the Nonlocal strain gradient elasticity theory (NSGET) is employed. The proposed formulation accommodates the nonlocal stress and strain gradient parameter along with the flexoelectric coefficient to accurately predict the frequencies. Further, with the aid of Hamilton\'s principle the governing differential equations are derived which are then solved through Galerkin-based approach. The variation of the natural frequency of MEVHT nanobeams under the influence of various parameters such as the nonlocal strain gradient parameter, different field loads, power-law exponent and slenderness ratio are also investigated.

Key Words
transient damping vibration; magneto-electro-viscoelastic-hygro-thermal; nanobeam; Visco-Pasternak foundation; nonlocal strain gradient elasticity

Address
(1) Ali Shariati:
Division of Computational Mathematics and Engineering, Institute for Computational Science, Ton Duc Thang University, Ho Chi Minh City, Vietnam;
(2) Ali Shariati:
Faculty of Civil Engineering, Ton Duc Thang University, Ho Chi Minh City, Vietnam;
(3) Farzad Ebrahimi, Mahsa Karimiasl:
Department of Mechanical Engineering, Faculty of Engineering, Imam Khomeini International University, Qazvin, Iran;
(4) M. Vinyas:
Department of Aerospace Engineering, Indian Institute of Science, Bangalore-560012, India;
(5) Ali Toghroli:
Institute of Research and Development, Duy Tan University, Da Nang 550000, Vietnam.

Abstract
In the present study, buckling analysis of sandwich composite (carbon nanotube reinforced composite and fiber reinforced composite) Euler-Bernoulli beam in two configurations (core and layers material), three laminates (combination of different angles) and two models (relative thickness of core according to peripheral layers) using differential quadrature method (DQM) is studied. Also, the effects of porosity coefficient and different types of porosity distribution on critical buckling load are discussed. Using sandwich beam, it shows a considerable enhancement in the critical buckling load when compared to ordinary composite. Actually, resistance against buckling in sandwich beam is between two to four times more. It is also showed the critical buckling loads of laminate 1 and 3 are significantly larger than the results of laminate 2. When Configuration 2 is used, the critical buckling load rises about 3 percent in laminate 1 and 3 compared to the results of configuration 1. The amount of enhancement for laminate 3 is about 17 percent. It is also demonstrated that the influence of the core height (thickness) in the case of lower carbon volume fractions is ignorable. Even though, when volume fraction of fiber increases, differences grow smoothly. It should be noticed the amount of decline has inverse relationship with the beam aspect ratio. Among three porosity patterns investigated, beam with the distribution of porosity Type 2 (downward parabolic) has the maximum critical buckling load. At the end, the first three modes of buckling will be demonstrated to investigate the effect of spring constants.

Key Words
nano composite sandwich Euler-Bernoulli beam; buckling analysis; various porosity distributions; DQM

Address
Department of Solid Mechanics, Faculty of Mechanical Engineering, University of Kashan, Kashan, Iran.


Abstract
In this study, the free and forced vibration analysis of micro sandwich plate with porous core layer and magnetoelectric face sheets based on modified couple stress theory and first order shear deformation theory under simply supported boundary conditions is illustrated. It is noted that the core layer is composed from balsa wood and also piezo magneto-electric facesheets are made of BiTiO3-CoFe2O4. Using Hamilton's principle, the equations of motion for micro sandwich plate are obtained. Also, the Navier's method for simply support boundary condition is used to solve these equations. The effects of applied voltage, magnetic field, length to width ratio, thickness of porous to micro plate thickness ratio, type of porous, coefficient of porous on the frequency ratio are investigated. The numerical results indicate that with increasing of the porous coefficient, the non-dimensional frequency increases. Also, with an increase in the electric potential, the non–dimensional frequency decreases, while and with increasing of the magnetic potential is vice versa.

Key Words
free and forced vibration; electric and magnetic fields; micro sandwich plate; Balsa wood; porous material

Address
Department of Solid Mechanics, Faculty of Mechanical Engineering, University of Kashan, P.O. Box 87317-53153, Iran.


Abstract
An analytical formulation and solution process for the buckling analysis of porous magneto-electro-elastic functionally graded (MEE-FG) beam via different thermal loadings and various boundary conditions is suggested in this paper. Magneto electro mechanical coupling properties of FGM beam are taken to vary via the thickness direction of beam. The rule of power-law is changed to consider inclusion of porosity according to even and uneven distribution. Pores possibly occur inside FGMs due the result of technical problems that lead to creation of micro-voids in these materials. Change in pores along the thickness direction stimulates the mechanical and physical properties. Four-variable tangential-exponential refined theory is employed to derive the governing equations and boundary conditions of porous FGM beam under magneto-electrical field via Hamilton

Key Words
buckling analysis; magneto-electro-elastic porous FG beam; thermal loading; refined beam theory

Address
(1) Farzad Ebrahimi, Ali Jafari:
Department of Mechanical Engineering, Faculty of Engineering, Imam Khomeini International University, Qazvin, Iran;
(2) Rajendran Selvamani:
Department of mathematics, Karunya Institute of Technology and Sciences, Coimbatore, India.


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