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CONTENTS
Volume 6, Number 2, June 2017
 

Abstract
This paper proposes the idea to enhance the heat transfer in Gas Tungsten Arc Welding (GTAW) by using the azimuthal magnetic field. The azimuthal magnetic field generated by the external currents makes the Lorentz force stronger, and consequently improves the heat transfer by the faster flow movement. The enhanced heat transfer might improve the welding performance by increasing the temperature at the workpiece. To validate the proposed idea, a two-dimensional axi-symmetric model of GTAW is built, and the multiphysics simulation of GTAW is carried out. As the analysis result, the distributions of electric current, electromagnetic fields, arc flow velocity, and temperature are investigated. Then, the proposed idea for heat transfer enhancement is validated by comparing the Lorentz force, flow velocity, and temperature distribution with and without azimuthal magnetic fields.

Key Words
thermal plasma; finite element analysis; electromagnetic fields; fluid dynamics; heat transfer; azimuthal magnetic fields

Address
Yiseul Kim, Jaewook Lee, Xiaolong Liu and Boyoung Lee: Department of Aerospace and Mechanical Engineering, Korea Aerospace University,76 Hanggongdaehang-ro, Deogyang-gu, Goyang-si, Gyeonggi-do 412-791, Korea
Yunlong Chang: School of Materials Science and Engineering, Shenyang University of Technology, No.111,
Shenliao West Road, Economic & Technological Development Zone, Shenyang,110870, P.R.China

Abstract
During the last decades, Pendulum Bearings with one or more concave sliding surfaces have been dominating bridge structures. For bridges with relative small lengths, the use of classical pendulum bearings could be a simple and cheaper solution. This work attempts to investigate the effectiveness of such a system, and especially its behavior for the case of a seismic excitation. The results obtained have shown that the classical pendulum bearings are very effective, mainly for bridges with short or intermediate length.

Key Words
dynamics of bridges; pendulum bearings; seismic excitation

Address
Ioannis G. Raftoyiannis and George T. Michaltsos: National Technical University of Athens, Department of Civil Engineering, 9 Iroon Polytechneiou Str., Athens 15780, Greece

Abstract
We present relatively simple derivations of the Helfrich energy potential that has been widely adopted in the analysis of lipid membranes without detailed explanations. Through the energy variation methods (within the limit of Helfrich energy potential), we obtained series of analytical solutions in the case when the lipid membranes are excited through their edges. These affordable solutions can be readily applied in the related membrane experiments. In particular, it is shown that, in case of an elliptic cross section of a rigid substrate differing slightly from a circle and subjected to the incremental deformations, exact analytical expressions describing deformed configurations of lipid membranes can be obtained without the extensive use of Mathieu\'s function.

Key Words
lipid membranes; bilayers; shape equation; substrate-membrane interaction; elliptical contact domain; analytic solution

Address
Chun Il Kim: Department of Mechanical Engineering, University of Alberta, Edmonton, Alberta, T6G 2G8, Canada

Abstract
In the present investigation reflection and transmission of plane waves at an elastic half space and piezothermoelastic solid half space with fractional order derivative is discussed. The piezothermoelastic solid half space is assumed to have 6 mm type symmetry and assumed to be loaded with an elastic half space. It is found that the amplitude ratios of various reflected and refracted waves are functions of angle of incidence, frequency of incident wave and are influenced by the piezothermoelastic properties of media. The expressions of amplitude ratios and energy ratios are obtained in closed form. The energy ratios are computed numerically using amplitude ratios for a particular model of graphite and Cadmium Selenide (CdSe). The variations of energy ratios with angle of incidence are shown graphically. The conservation of energy across the interface is verified. Some cases of interest are also deduced from the present investigation.

Key Words
reflection; piezothermoelastic; fractional order; transmission; elastic; amplitude ratios

Address
Rajneesh Kumar and Poonam Sharma: Department of Mathematics, Kurukshetra University, Kurukshetra 136119, Haryana, India

Abstract
This paper deals with a uniform cantilever Euler-Bernoulli beam subjected to follower and transversal force at its free end as a model for a pipe conveying fluid under electromagnetic damper force. The electromagnetic damper is composed of a permanent-magnet DC motor, a ball screw and a nut. The main objective of the current work is to reduce the pipe vibration resulting from the fluid velocity and allow it to transform into electric energy. To pursue this goal, the stability and vibration of the beam model was studied using Ritz and Newmark methods. It was observed that increasing the fluid velocity results in a decrease in the motion of the free end of the pipe. The results of simulation showed that the designed semi-active electromagnetic damper controlled by on-off damping control strategy decreased the vibration amplitude of the pipe about 5.9% and regenerated energy nearly 1.9 (mJ/s). It was also revealed that the designed semi-active electromagnetic damper has better performance and more energy regeneration than the passive electromagnetic damper.

Key Words
stability; pipe; fluid; vibration; electromagnetic; damper

Address
Omid Kavianipour: Department of Mechanical Engineering, Damavand Branch, Islamic Azad University, Damavand, Iran

Abstract
Tanks are used to store a wide variety of liquids such as oil, gasoline and water. It is reported that, a large number of tanks have been damaged during severe earthquakes. Therefore, understanding their behavior under earthquake is an important subject for structural engineers. In this paper, a comprehensive study is presented on dynamic response of tanks. A parametric study has been completed on the rectangular storage tanks with aid of finite element method (FEM). Various parameters are investigated, such as; liquid height, density and earthquake with different peak ground acceleration (PGA). When investigating these parameters, modal and time history method is used. Six different earthquake records are used for time history analysis. The analysis results show that when the PGA increases by 10.7 times, the maximum displacements, stress, sloshing and base shear increase by 11.4, 22.6, 5.46 and 17.8 times, respectively and when the liquid height increases by two times, the absolute maximum values of stress, displacements, base shear and sloshing increase 1.65, 2.04, 2.05 and 1.34. Furthermore, values of sloshing increase with decrease in density.

Key Words
dynamic; rectangular tanks; time history; modal

Address
Mohsen Yazdanian: Young Researchers and Elite Club, Ahvaz Branch, Islamic Azad University, Ahvaz, Iran
Feng Fu: School of Mathematics, Computer Science & Engineering, Department of Civil Engineering,
City University London, Northampton Square, EC1V, 0HB, London, UK

Abstract
In this paper Timoshenko beam theory is employed to investigate the vibration characteristics of functionally graded carbon nanotube-reinforced composite (FG-CNTRC) Beams with a stiff core in thermal environment. The material characteristic of carbon nanotubes (CNT) are supposed to change in the thickness direction in a functionally graded form. They can also be calculated through a micromechanical model where the CNT efficiency parameter is determined by matching the elastic modulus of CNTRCs calculated from the rule of mixture with those gained from the molecular dynamics simulations. The differential transform method (DTM) which is established upon the Taylor series expansion is one of the effective mathematical techniques employed to the differential governing equations of sandwich beams. Effects of carbon nanotube volume fraction, slenderness ratio, core-to-face sheet thickness ratio, different thermal environment and various boundary conditions on the free vibration characteristics of FG-CNTRC sandwich beams are studied. It is observed that vibration response of FG-CNTRC sandwich beams is prominently influenced by these parameters.

Key Words
functionally graded carbon nanotube-reinforced composite; thermo-mechanical vibration; Hamilton

Address
Farzad Ebrahimi and Navid Farazamandnia: Department of Mechanical Engineering, Faculty of Engineering, Imam Khomeini International University, Qazvin, P.O.B. 16818-34149, Iran


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