Research Paper
Fluid Mechanics
M. Alemi; R. Maia
Abstract
The present study aimed to investigate two numerical solutions of the Navier-Stokes equations. For this purpose, the mentioned flow equations were written in two different formulations, namely (i) velocity-pressure and (ii) vorticity-stream function formulations. Solution algorithms and boundary conditions ...
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The present study aimed to investigate two numerical solutions of the Navier-Stokes equations. For this purpose, the mentioned flow equations were written in two different formulations, namely (i) velocity-pressure and (ii) vorticity-stream function formulations. Solution algorithms and boundary conditions were presented for both formulations and the efficiency of each formulation was investigated by considering a two-dimensional low laminar flow around a square pile in a rectangular computational domain. Simulations under the same conditions were conducted to assess the difference between results generated by both formulations. Furthermore, the accuracy of the results was analyzed through a comparison of the results with the available reference data. In addition, computational efficiency of both formulations was investigated in term of computation time. The corresponding results indicated that both formulations are adequate to the case used in the present study. Moreover, performed simulations showed that solving the vorticity-stream function form of the flow equations is faster than solving the velocity-pressure form of those equations for simulating a two-dimensional laminar flow around a square pile.
Research Paper
Composite Materials
A. Niknami; M. Shariyat
Abstract
In the present research, in contrast to the available papers, not only the superelasticity but also the shape memory effects are taken into account in determination of the impact responses. At the same time, in addition to modifying Brinson’s model for the shape memory alloys (SMAs), to include ...
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In the present research, in contrast to the available papers, not only the superelasticity but also the shape memory effects are taken into account in determination of the impact responses. At the same time, in addition to modifying Brinson’s model for the shape memory alloys (SMAs), to include new parameters and loading events, and Hertz contact law, distributions of the SMA phases are considered to be both localized and time-dependent. Furthermore, effects of the impact-induced heat generation and mechanical energy on the resulting histories of the martensite phase volume fraction, stress-strain, temperature, lateral deflection, and contact force are investigated. The generated heat in the SMA wires during the impact is determined through using a Helmholtz free energy function including the latent heat of the phase transformation. The resulting governing equations are solved by the finite element method. The nonlinear refined constitutive laws are solved through a return-mapping Newton-Raphson procedure. Results reveal that incorporation of the heat generation effects is significant in medium/high-velocity impacts or when the stress field is almost uniform.
Research Paper
Heat and Mass Transfer
L. Ramamohan Reddy; M. C. Raju; G. S. S. Raju; S. M. Ibrahim
Abstract
The paper aims at investigating the effects of chemical reaction and thermal radiation on the steady two-dimensional laminar flow of viscous incompressible electrically conducting micropolar fluid past a stretching surface embedded in a non-Darcian porous medium. The radiative heat flux is assumed to ...
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The paper aims at investigating the effects of chemical reaction and thermal radiation on the steady two-dimensional laminar flow of viscous incompressible electrically conducting micropolar fluid past a stretching surface embedded in a non-Darcian porous medium. The radiative heat flux is assumed to follow Rosseland approximation. The governing equations of momentum, angular momentum, energy, and species equations are solved numerically using Runge-Kutta fourth order method with the shooting technique. The effects of various parameters on the velocity, microrotation, temperature and concentration field as well as skin friction coefficient, Nusselt number and Sherwood number are shown graphically and tabulated. It is observed that the micropolar fluid helps the reduction of drag forces and also acts as a cooling agent. It was found that the skin-friction coefficient, heat transfer rate, and mass transfer rate are decreased, and the gradient of angular velocity increases as the inverse Darcy number, porous medium inertia coefficient, or magnetic field parameter increase. Increases in the heat generation/absorption coefficient caused increases in the skin-friction coefficient and decrease the heat transfer rate. It was noticed that the increase in radiation parameter or Prandtl number caused a decrease in the skin-friction coefficient and an increase in the heat transfer rate. In addition, it was found that the increase in Schmidt number and chemical reaction caused a decrease in the skin-friction coefficient and an increase in the mass transfer rate.
Research Paper
Forming
S. Izadpanah; S. H. Ghaderi; M. Gerdooei
Abstract
This paper investigates the earing phenomenon in deep drawing of AA3105 aluminum alloy, experimentally and numerically. Earing defect is mainly attributed to the plastic anisotropy of sheet metal. In order to control such defect, predicting the evolution of ears in sheet metal forming analyses becomes ...
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This paper investigates the earing phenomenon in deep drawing of AA3105 aluminum alloy, experimentally and numerically. Earing defect is mainly attributed to the plastic anisotropy of sheet metal. In order to control such defect, predicting the evolution of ears in sheet metal forming analyses becomes indispensable. In this regard, the present study implements the advanced yield criterion BBC2003. Based on this yield function and the associated flow rule of plasticity, the constitutive model is derived. Accordingly, a user material VUMAT subroutine is developed and adopted in the commercial finite element software ABAQUS/Explicit. Several plane stress loading problems are designed, through which, the accuracy of the developed subroutine is verified. In addition, cylindrical cups of AA3105 aluminum alloy are fabricated using a deep drawing die. The earing defect was clearly observed on the recovered parts. Using the experimentally obtained constants of BBC2003 yield criterion for this alloy in VUMAT, deep drawing of the cylindrical cups was simulated. The results demonstrate that the earing profile can successfully be predicted using BBC2003 yield function.
Research Paper
Fatigue
J. Amirian; H. Safari; M. Shirani; M. Moradi; S. Shabani
Abstract
Generally, fatigue failure in an element happens at the notch on a surface where the stress level rises because of the stress concentration effect. The present paper investigates the effect of a notch on the fatigue life of the HSLA100 (high strength low alloy) steel which is widely applicable in ...
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Generally, fatigue failure in an element happens at the notch on a surface where the stress level rises because of the stress concentration effect. The present paper investigates the effect of a notch on the fatigue life of the HSLA100 (high strength low alloy) steel which is widely applicable in the marine industry. Tensile test was conducted on specimens and mechanical properties were obtained. Rotating bending and axial fatigue tests were performed at room temperature on smooth and notched specimens and S-N curves were obtained. Using the obtained S-N curve for smooth specimens, the fatigue strength factor for the notched specimens were predicted by Weibull's weakest-link, Peterson, Neuber, stress gradient and critical distance methods and compared with experimental results. It was found that the critical distance and also Weibull’s weakest-link methods have the best agreement with experimental results.
Research Paper
Fluid Mechanics
F. Khalighi; A. Ahmadi; A. Keramat
Abstract
Four explicit finite difference schemes, including Lax-Friedrichs, Nessyahu-Tadmor, Lax-Wendroff and Lax-Wendroff with a nonlinear filter are applied to solve water hammer equations. The schemes solve the equations in a reservoir-pipe-valve with ...
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Four explicit finite difference schemes, including Lax-Friedrichs, Nessyahu-Tadmor, Lax-Wendroff and Lax-Wendroff with a nonlinear filter are applied to solve water hammer equations. The schemes solve the equations in a reservoir-pipe-valve with an instantaneous and gradual closure of the valve boundary. The computational results are compared with those of the method of characteristics (MOC), and with the results of Godunov''s scheme to verify the proposed numerical solution. The computations reveal that the proposed Lax-Friedrichs and Nessyahu-Tadmor schemes can predict the discontinuities in fluid pressure with an acceptable order of accuracy in cases of instantaneous and gradual closure. However, Lax-Wendroff and Lax-Wendroff with nonlinear filter schemes fail to predict the pressure discontinuities in instantaneous closure. The independency of time and space steps in these schemes are allowed to set different spatial grid size with a unique time step, thus increasing the efficiency with respect to the conventional MOC. In these schemes, no Riemann problems are solved; hence field-by-field decompositions are avoided. As provided in the results, this leads to reduced run times compared to the Godunov scheme.
Research Paper
Robotics
k. Alipour; m. Ghiasvand; B. Tarvirdizadeh
Abstract
In this paper, the important formation control problem of nonholonomic wheeled mobile robots is investigated via a leader-follower strategy. To this end, the dynamics model of the considered wheeled mobile robot is derived using Lagrange equations of motion. Then, using ADAMS multi-body simulation software, ...
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In this paper, the important formation control problem of nonholonomic wheeled mobile robots is investigated via a leader-follower strategy. To this end, the dynamics model of the considered wheeled mobile robot is derived using Lagrange equations of motion. Then, using ADAMS multi-body simulation software, the obtained dynamics of the wheeled system in MATLAB software is verified. After that, in order to generate and keep the desired formation, a Fuzzy Logic Controller is designed. In this regard, the leader mobile robot is controlled to follow a reference path and the follower robots use the Fuzzy Logic Controller to keep constant relative distance and constant angle with respect to the leader. The efficiency of the suggested dynamics-based formation controller has been proved using several computer simulations under different situations and desired trajectories. Also, the performance of the follower robot in path tracking is checked in the presence of receiving noisy data from the leader robot.
Research Paper
Vibration
M. Moradi; M. Bagheri Nouri
Abstract
In this paper, a new algorithm for studying elastic wave propagation in the phononic crystals is presented. At first, the displacement-based forms of elastic wave equations are derived and then the forms are discretized using finite difference method. So the new algorithm is called the displacement-based ...
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In this paper, a new algorithm for studying elastic wave propagation in the phononic crystals is presented. At first, the displacement-based forms of elastic wave equations are derived and then the forms are discretized using finite difference method. So the new algorithm is called the displacement-based finite difference time domain (DBFDTD). Three numerical examples are computed with this method and the results are compared with experimental measurements and the conventional FDTD method. Also, the computational cost of the new approach is compared with the conventional FDTD method. The comparison showed that the calculation time of the DBFDTD method is 37.5 percent less than that of the FDTD method.
Research Paper
Vibration
M. Talebitooti; M. Ghasemi; S. M. Hosseini
Abstract
In the present work, study of the vibration of a functionally graded (FG) cylindrical shell made up of stainless steel, zirconia, and nickel is presented. Free vibration analysis is presented for FG cylindrical shells with simply supported-simply supported and clamped–clamped boundary condition ...
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In the present work, study of the vibration of a functionally graded (FG) cylindrical shell made up of stainless steel, zirconia, and nickel is presented. Free vibration analysis is presented for FG cylindrical shells with simply supported-simply supported and clamped–clamped boundary condition based on temperature independent material properties. The equations of motion are derived by Hamilton’s principle. Material properties assume to be graded in the thickness direction according to a simple power law distribution in terms of the volume fraction of the constituents. Effects of boundary conditions and volume fractions (power law exponent) on the natural frequencies of the FG cylindrical shell are studied. Frequency characteristics of the FG shell are found to be similar to those of isotropic cylindrical shells. Furthermore, natural frequencies of these shells are observed to be dependent on the constituent volume fractions and boundary conditions. Strain displacement relations from Love's and first-order shear deformation theories are employed. Galerkin method is used to derive the governing equations for clamped boundary conditions. Further, analytical results are validated with those reported in the literature and excellent agreement is observed. Finally, in order to investigate the effects of the temperature gradient, functionally graded materials cylindrical shell with high temperature specified on the inner surface and outer surface at ambient temperature,1D heat conduction equation along the thickness of the shell is applied and the results are reported.
Research Paper
Fatigue
M. Jooybari; J. Shahbazi Karami; M. Sheikhi
Abstract
In the present study, mechanical properties and low cycle fatigue behavior of a solid-solutionized AA6061 aluminum alloy produced by equal channel angular pressing (ECAP) process were investigated. The grain refinement after two passes of ECAP significantly increased the yield stress and ultimate tensile ...
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In the present study, mechanical properties and low cycle fatigue behavior of a solid-solutionized AA6061 aluminum alloy produced by equal channel angular pressing (ECAP) process were investigated. The grain refinement after two passes of ECAP significantly increased the yield stress and ultimate tensile stress and decreased the ductility of the alloy. However, the improvement of low cycle fatigue strength was not as remarkable as expected. Post-ECAP aging heat treatment to the peak-aging condition imposed a notable change in the strength and ductility of the alloy so that its fatigue strength partly enhanced. An optimized combination of grain refinement and distributed fine precipitates in the matrix of the alloy was achieved by conducting aging heat treatment between passes of ECAP. The proposed procedure was proved to yield the best combination of strength and ductility, better distribution and size of precipitates, and thus a remarkable improvement in the low cycle fatigue response of the investigated material.
