AUT Journal of Mechanical EngineeringAUT Journal of Mechanical Engineering
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Feed provided by AUT Journal of Mechanical Engineering. Click to visit.Residual Stresses Measurement in UIC 60 Rail by Ring-Core Method and Sectioning Technique
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Articles in Press, Accepted Manuscript , Available Online from 18 December 2017<br><br>Measurement of residual stress in rail foot, according to manufacturing standards is mandatory. In this study, the ring-core method and the sectioning technique are used to measure the residual stresses. A calibration technique for the ring-core method has been explained and simulated by the finite element analysis. The calibration coefficient for certain parameters and various depths of the annular groove has been determined. The ring-core method has been simulated for the uniaxial residual stress field and it is observed that the maximum error in maximum principal residual stress was about 13% which is about 5% of material yield stress. The residual stresses have been measured at the UIC 60 rail foot by the ring-core method and the sectioning technique, and the results are in good agreement with earlier investigations in this field. Also, it has been indicated that maximum residual stresses on the rail foot are not in the longitudinal direction and in the subsurface of the rail foot the maximum principal direction about coincides with the longitudinal direction. Both methods indicated tensile residual stresses on the rail foot, but the ring-core method predicted 27% higher longitudinal residual stress on the rail foot in comparing with the sectioning technique.Sun, 17 Dec 2017 20:30:00 +0100Numerical Analysis of Critical Heat Flux Phenomenon in a Nuclear Power Plant Core Channel in ...
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Volume 1, Issue 2, Summer and Autumn 2017, Page 119-130<br><br>The necessity and importance of a high heat removal potential in various areas particularlyin nuclear applications are in a direct relationship with the excessively applied heat flux level. One wayto increase the heat transfer performance and subsequently enhance the threshold of the critical heatflux is to employ spacer grids accompanied by mixing vanes. In this study, the effect of the spacerswith mixing vanes on the critical heat flux characteristics in the dryout condition has been numericallyinvestigated employing the benefits of the Eulerian-Eulerian framework. In the current research, severalvane angles, including vane with 0, 15 and 25 degrees in comparison with the effect of the bare spacerwithout any mixing vanes on the flow characteristics were examined. It was shown that the existence ofthe spacer alone, delays the temperature jump under critical heat flux conditions. It was also concludedthat increasing the angle of the mixing vanes, further improves the heat transfer performance of thesystem by postponing the sudden temperature jump occurring in the channel; however, the presence ofthe spacers and vanes in the flow field imposes an increase of the pressure drop due to the constrictionon the coolant flow area.Thu, 30 Nov 2017 20:30:00 +0100The Buckling Analysis of Conical Sandwich Shells with Temperature Dependent Properties and an ...
http://ajme.aut.ac.ir/article_2738_0.html
Articles in Press, Accepted Manuscript , Available Online from 18 December 2017<br><br>In this study, an improved higher-order theory is used for buckling analysis of sandwich conical shells with thin functionally graded face sheets and homogenous soft core and with temperature-dependent properties. In-plane and transverse displacements of the core are assumed by cubic functions, and displacements of the FG face sheets are assumed by first-order shear deformation theory. The linear variation of temperature is assumed in the face sheets and the core. The material properties of the FG face sheets are assumed to be temperature-dependent by a third-order function of temperature and vary continuously through the thickness according to a power-law or an exponential distribution in terms of the volume fractions of the constituents. The nonlinear Von-Karman relations are used. Analytical solution for static analysis of simply supported sandwich conical shells under axial in-plane compressive loads and thermal conditions is performed by using Galerkin’s solution. The results show that the values of the critical dimensionless static axial load are affected by the configurations of the constituent materials, compositional profile variations, semi-vertex angle, thermal condition and the variation of the sandwich geometry. The comparisons show that the present results are in a good agreement with those in the literature.Sun, 17 Dec 2017 20:30:00 +0100An Exact Analytical Solution for Convective Heat Transfer in Elliptical Pipes
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Volume 1, Issue 2, Summer and Autumn 2017, Page 131-138<br><br>In this paper, an analytical solution for convective heat transfer in straight pipes withthe elliptical cross section is presented. The solution is obtained for steady-state fluid flow and heattransfer under the constant heat flux at walls using the finite series expansion method. Here, the exactsolution of Nusselt number as well as temperature distribution in terms of aspect ratio is presented as thecorrelation in the Cartesian coordinate system and validated with the previous investigations. It is shownthat the minimum amount of Nusselt number, as well as the maximum absolute value of dimensionlesstemperature at the center of the cross section, are related to the aspect ratio equal to 1 (circular pipe). Thesolution indicated that the amount of Nusselt number is increased by changing the geometry of crosssection from circular to an elliptical shape and it finally tends to 4356/833 at large enough aspect ratios.Our results also show that 95% of the increase in Nusselt number to the circular cylinder is related toaspect ratio equal to 18.36. The present method of solution could be used to obtain the exact solution ofconvective heat transfer in elliptical pipes for other thermal boundary conditions and fluid rheologicalbehaviors.Thu, 30 Nov 2017 20:30:00 +0100A fluid-structure interaction study on vulnerability of different coronary plaques to blood ...
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Articles in Press, Accepted Manuscript , Available Online from 18 December 2017<br><br>Pathological studies have shown that coronary atherosclerotic plaques are more prone to rupture under physical exercise. In this paper, using a fully coupled fluid-structure interaction (FSI) analysis based on arbitrary Lagrangian-Eulerian (ALE) finite element method, the effect of the coronary blood flow rate increase during physical exercise on the plaque rupture risk is investigated for different plaque types. It is proved that increase of coronary blood flow rate during physical exercise considerably increases the maximum stress in the plaque fibrous cap which can potentially lead to plaque rupture. The issue is investigated for different plaque shapes and their vulnerability to exercise condition is compared. It is observed that the diffused plaque type which experiences the maximum stress of 187.9 kPa at rest and 544 kPa at exercise is the most critical plaque type. Because it is subjected to the highest stress in both of these conditions. However, the descending plaque type exhibits the highest susceptibility to physical activity, since its maximum stress increases from 68.9 kPa at rest to 280.5 kPa at exercise which means an increase of about 308%.Sun, 17 Dec 2017 20:30:00 +0100A Unified Velocity Field for Analysis of Flat Rolling Process
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Volume 1, Issue 2, Summer and Autumn 2017, Page 139-148<br><br>The subject of this paper is analysis of the flat rolling process by upper bound method.In this analysis the arc of contact has been replaced by a chord and the inlet and outlet shear boundariesof the deformation zone have been assumed as arbitrarily exponential curves. A unified kinematicallyadmissible velocity field has been proposed that permits the possible formation of internal defects. Byminimizing the required total power with respect to the neutral point position and the shape of the inletand outlet shear boundaries, the rolling torque has been determined. The velocity components obtainedfrom the upper bound method have been compared with the FE simulation. The analytical results havebeen showed a good agreement between the upper bound data and the FE results. A criterion has beenpresented to predict the occurrence of the split ends and central bursts defects during flat rolling process.Comparison of analytically developed approach for rolling torque and internal defects with publishedtheoretical and experimental data have been showed a good agreement. Finally, the effects of processparameters on the safe and unsafe zones sizes have been investigated. It is shown that with increasing ofthe friction factor, the safe zone size is decreased.Thu, 30 Nov 2017 20:30:00 +0100Simulation of natural convection in eccentric annulus: A combined Lattice Boltzmann and ...
http://ajme.aut.ac.ir/article_2740_0.html
Articles in Press, Accepted Manuscript , Available Online from 18 December 2017<br><br>In present study, a hybrid method of thermal lattice Boltzmann and smoothed profile methods has been applied to simulate free convection in an eccentric annulus with constant temperature wall. Smoothed profile method employs an Eulerian approach to consider the fluid solid interaction without using an extra mesh for capturing solid boundary. As a result of this property, the combination of this method and Lattive Boltzmann method can be considered as an efficient method to simulate free convection in complex geometries like annulus. In order to investigate the effect of inner cylinder position on natural convection, inner cylinder was placed in different horizontal, vertical and diagonal positions. Influences of the Rayleigh number (103 ≤ Ra ≤ 105), eccentricity (-0.75 ≤ e ≤ 0.75)) and radial ratio (Ro/Ri=2, 2.6 and 3.2) on the streamlines, isotherms and Nusselt number were studied. It was found that the Nusselt number has a positive relationship with Rayleigh number and radial ratio. Also, it can be confirmed that Nusselt number in the case with negative eccentricity (e=−0.75) was larger than the others. It was found that a very good agreement exists between the present results and those from the open literature.Sun, 17 Dec 2017 20:30:00 +0100On the Elastic Field of Al/SiC Nanocomposite
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Volume 1, Issue 2, Summer and Autumn 2017, Page 149-158<br><br>This study aims to analyze the linear elastic behavior of an aluminum matrixnanocomposite reinforced with SiC nanoparticles. Once, a representative volume element was consideredfor the nanocomposite with a cuboidal inclusion. The elastic moduli of the matrix and the inclusion werethe same, but it contained eigenstrain. The stress and the strain fields were obtained for the inclusionand the aluminum by Galerkin vector method. The stress and the strain fields in the inclusion problemwere in a good agreement with the results in the literature. A similar representative volume element wasconsidered for the nanocomposite with a cuboidal inhomogeneity. The elastic moduli of the matrix andthe inhomogeneity were different, but it did not have any eigenstrain. For the calculation of the Eshelbytensor and the elastic fields for the inhomogeneity problem, the equivalent inclusion method (EIM) wasapplied. In the EIM, the uniform and equivalent eigenstrain were considered. The stress and the strainfields within the inhomogeneity and the matrix were obtained. Results showed that the stress and thestrain in the cuboidal inclusion were less than the cuboidal inhomogeneity due to the difference betweenthe matrix and the reinforcement materials.Thu, 30 Nov 2017 20:30:00 +0100Influence of Burner Head Design on Its Thermal and Environmental Characteristics
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Articles in Press, Accepted Manuscript , Available Online from 18 December 2017<br><br>در این مقاله، برای اولین بار، چهار تابع هدف حرارتی و آلودگی به صورت همزمان به منظور طراحی بهینه یک مشعل دیفیوژن با سوخت گاز طبیعی مورد توجه قرار می گیرند. توابع هدف در نظر گرفته شده در مطالعه حاضر عبارت اند از بازده حرارتی مشعل، و میزان نشر مونواکسید کربن، اکسید نیتروژن، و متان نسوخته. در مرحله اول، مشعل به صورت عددی مدل می شود و نتایج عددی از طریق مقایسه با نتایج تجربی موجود صحت سنجی می گردند. سپس، مدلسازی به ازای تنظیمات متفاوتی از متغیرهای طراحی (اندازه ورودیهای سوخت و هوا، و نسبت هم ارزی کلی) انجام می پذیرد و طرح بهینه با استفاده از مفهوم جبهه پارتو انتخاب می گردد. مقاله نشان خواهد داد که به دنبال فرایند ذکر شده، بازده حرارتی مشعل 29.4% افزایش می یابد، و میزان نشر مونواکسید کربن، اکسید نیتروژن، و متان نسوخته به ترتیب 81.2%، 98.6%، و 83.9% کاهش می یابند. مقاله با جزییات به بررسی دلایل برتری طرح بهبود یافته نسبت به طرح مرجع می پردازد.Sun, 17 Dec 2017 20:30:00 +0100A New Method to Investigate the Progressive Damage of Imperfect Composite Plates Under In-Plane ...
http://ajme.aut.ac.ir/article_2745_112.html
Volume 1, Issue 2, Summer and Autumn 2017, Page 159-168<br><br>Numerous studies have been conducted for failure criteria of fiber reinforced composites.The aim of this study is to present a new computational and mathematical method to analyze theprogressive damage and failure behavior of composite plates containing initial geometric imperfectionsunder uniaxial in-plane compression load. A new methodology is presented based on collocation methodin which the interested domain is discretized with Legendre-Gauss-Lobatto nodes. In order to avoid anexcessive number of nodes, an appropriate weight coefficient is considered for each node. The method isbased on the first order shear deformation theory and small displacement theory. Several failure criteria,including Maximum stress, Hashin and Tsai-Hill, are used to predict the failure mechanisms. The stiffnessdegradation is carried out by instantaneous and complete ply degradation model. Two different types ofboundary conditions are considered in this study. The effects of thickness, initial imperfections, andboundary conditions are studied, as well. The results are compared with the previously published data.It is found that the boundary conditions have significant effects on the ultimate strength of imperfectcomposite plates.Thu, 30 Nov 2017 20:30:00 +0100Numerical Investigation of Water/〖Al〗_2 O_3 Nanofluid Dryout Phenomenon in a Vertical Channel
http://ajme.aut.ac.ir/article_2742_0.html
Articles in Press, Accepted Manuscript , Available Online from 18 December 2017<br><br>Critical heat flux (CHF) phenomenon has been recognized as the upper limit for the safe operation of many cooling systems which may lead to the occurrence of dryout causing a large temperature gradient in the heated wall. One way to increase the level of the CHF is to add certain nanoparticles such as Al_2 O_3 to the base fluid. The present paper concerns the effect of nanoparticles on dryout phenomenon within computational fluid dynamics (CFD). Wall boiling phenomena are modeled using the mechanistic nucleate boiling model developed in Rensselaer Polytechnic Institute (RPI) which is extended to simulate the critical heat flux phenomena by partitioning wall heat flux to liquid and vapor phases. It was shown that the dryout phenomenon can be delayed by increasing the nanoparticles concentration, and in certain concentration of nanoparticles (5 percent), film boiling phenomenon would not occur and for the formation of dryout phenomenon in such concentrations, exerted wall heat flux should be increased to about 13 percent of the base heat flux magnitude.Sun, 17 Dec 2017 20:30:00 +0100Analysis and Optimization of Mining Truck Operation Based on the Driver Whole Body Vibration
http://ajme.aut.ac.ir/article_2757_112.html
Volume 1, Issue 2, Summer and Autumn 2017, Page 169-178<br><br>The present paper studies the whole body vibration of a three-axle dump truck duringvarious operational conditions in Zonuz Kaolin Mine of Iran. At first, the root mean square of vibrationsat different speeds, as well as in payloads and distribution qualities of materials in the truck dump bodyand also on different haul road qualities are experimentally obtained. Then, the vibrational health riskin all operational conditions is statistically analyzed based on ISO 2631-1 standard. As a result of thisanalysis, an optimization problem is constructed and solved to obtain the optimum operating conditionsof the truck. In the proposed problem, at first, regression analysis in terms of RMS of vibrationsand truck speed is applied. Then, the total RMS at the consequential working phases of the truck isminimized in the presence of some constraints related to the health risk and productivity levels. Solvingthe proposed constrained optimization problem determines the optimum payload and truck speed invarious conditions to keep materials hauling at the lowest possible vibrational health risk level while themine productivity at the planned level remains.Thu, 30 Nov 2017 20:30:00 +0100The effect of impact energy parameters on the closed-cell aluminum foam crushing behavior using ...
http://ajme.aut.ac.ir/article_2743_0.html
Articles in Press, Accepted Manuscript , Available Online from 18 December 2017<br><br>The present study is devoted to numerical and experimental investigation of influence of dominant impact parameters, including inertia and impact velocity, on the closed-cell aluminum foam behavior. In order to access 3D modeling of the internal microstructure of the foam samples, a new technique based on computerized tomography (CT) of 2D images is utilized. Influence of the abovementioned influential parameters are studied for three different foam densities. In order to validate finite element results, low velocity impact tests were conducted. The results demonstrates that for a constant level of impactor energy, two primary impact quantities of interest, i.e. maximum stress and energy absorption, are highly dependent to values of impactor momentum. In contrast, increasing the value of impactor inertia results in negligible variations of energy absorption for different foam densities. Similarly, increasing inertia at a constant foam density shows no significant variation in peak stress and a slight change in energy absorption. On the other hand, the velocity of impactor at a constant level of impactor energy plays such a crucial role such that for all three different foam sample densities, the case of higher impactor velocity causes greater values of peak stress as well as energy absorption.Sun, 17 Dec 2017 20:30:00 +0100Natural Frequency Analysis of Composite Skew Plates with Embedded Shape Memory Alloys in ...
http://ajme.aut.ac.ir/article_2747_112.html
Volume 1, Issue 2, Summer and Autumn 2017, Page 179-190<br><br>In this study, free vibration analysis of laminated composite skew plates with embeddedshape memory alloys under thermal loads is presented. The plates are assumed to be made of NiTi/Graphite/Epoxy with temperature-dependent properties. The thermo-mechanical behavior of shape memory alloywires is predicted by employing one-dimensional Brinson’s model. The governing equations are derivedbased on first-order shear deformation theory and solved using generalized differential quadraturetechnique as an efficient and accurate numerical tool. Some examples are provided to show the accuracyand efficiency of the applied numerical method by comparing the present results with those availablein the literature. A parametric study is carried out to demonstrate the influence of skew angle, pre-strainand volume fraction of shape memory alloys, temperature, and stacking sequence of layers on the naturalfrequencies of the structure. Results represent that shape memory alloys can change the vibrationalcharacteristics of shape memory alloy hybrid composite skew plates by a considerable amount. Thenumerical results also reveal that the effect of shape memory alloy wires on natural frequencies ofcomposite plates with simply supported boundaries is higher than those with clamped boundaries.Thu, 30 Nov 2017 20:30:00 +0100Energy and Exergy Analysis and Optimization of a Heat Sink Collector Equipped with Rotational ...
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Articles in Press, Accepted Manuscript , Available Online from 18 December 2017<br><br>In this paper, forced convection flow in a heat sink collector equipped with stationary and rotational obstacles are studied numerically. Three-dimensional governing equations are solved by control volume approach based on the SIMPLE algorithm and k‒ε turbulence model. Reynolds numbers are considered in laminar-turbulent range of 50<Re<12,000. The optimization was carried out by variation of related parameters. It is concluded that using heat sink, instead of customary instrument, increase the outlet temperature from the collector and exergy efficiency due to longer installing the fluid inside the collector. Also, it is realized that using the stationary and rotational obstacles enhance the outlet fluid temperature (about 2.5°C), energy efficiency and exergy efficiency. Nevertheless, using the rotational obstacles is more effective than the stationary obstacles. While the trend of exergy efficiency variation with effective parameters is increasing, applying the obstacles precipitate the efficiency increment (from 4% to 5.3%). In addition, for the case that the trend of exergy efficiency variation with changing these parameters is decreasing, the decreasing trend gets slow. There is a unique mass flow rate (0.005 kg/s) that the exergy efficiency gets maximum value and for higher mass flow rates, the efficiency decreases slightly and then remains unchanged.Sun, 17 Dec 2017 20:30:00 +0100A Parametric Study on Flutter Analysis of Cantilevered Trapezoidal FG Sandwich Plates
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Volume 1, Issue 2, Summer and Autumn 2017, Page 191-210<br><br>In this paper, supersonic flutter analysis of cantilevered trapezoidal plates composed oftwo functionally graded face sheets and an isotropic homogeneous core is presented. Using Hamilton’sprinciple, the set of governing equations and external boundary conditions are derived. A transformationof coordinates is used to convert the governing equations and boundary conditions from the originalcoordinates into the new dimensionless computational ones. Generalized differential quadrature method(GDQM) is employed as a numerical method and critical aerodynamic pressure and flutter frequenciesare derived. Convergence, versatility, and accuracy of the presented solution are confirmed usingnumerical and experimental results presented by other authors. The effect of power-law index, thicknessof the core, total thickness of the plate, aspect ratio and angles of the plate on the flutter boundaries areinvestigated. It is concluded that any attempt to increase the critical aerodynamic pressure leads to adecrease in lift force or rise in total weight of the plate.Thu, 30 Nov 2017 20:30:00 +0100An Analytical Procedure for Buckling Load Determination of an Axisymmetric Cylinder with ...
http://ajme.aut.ac.ir/article_2751_112.html
Volume 1, Issue 2, Summer and Autumn 2017, Page 211-218<br><br>In this article, the buckling load of an axisymmetric cylindrical shell with a variablethickness is determined analytically by using the perturbation method. The loading is axial and thematerial properties are defined by the Hooke’s law. The displacement field is predicted by using thefirst order shear deformation theory and the nonlinear von-Karman relations are used for the kinematicdescription of the shell. The stability equations, which are the system of nonlinear differential equationswith variable coefficients, are derived by the virtual work principle and are solved using the perturbationtechnique. Also, the buckling load is determined by using the finite element method and it is comparedwith the analytical solution results, the classical shell theory, and other references. The effects of linearand nonlinear shell profiles variation on the axial buckling load are investigated. Also, we studied theeffects of geometric parameters on the buckling load results. The results show that the first order sheardeformation theory is more useful for buckling load determination of thicker shells.Thu, 30 Nov 2017 20:30:00 +0100Computational Investigation of Unsteady Compressible Flow over a Fixed Delta Wing Using ...
http://ajme.aut.ac.ir/article_2750_112.html
Volume 1, Issue 2, Summer and Autumn 2017, Page 219-232<br><br>Unsteady compressible flows over a stationary 60-degree swept delta wing with a sharpleading edge were computationally simulated at different Mach numbers and moderate angles of theattack. An unstructured grid, Spalart-Allmaras Detached Eddy Simulation turbulence model, and adual-time implicit time integration were used. Vortical flow structures associated with various freestreamconditions are displayed and their variations versus time are studied. Variations of flow fieldparameters, such as u velocity component and pressure coefficient with the flow time are demonstratedat several point probes in the flow field. A Power Spectral Density frequency analysis is performed forsuch unsteady behaviours to identify the dominant frequencies which exist in each flow condition. Thefrequency analyses show that low frequencies associated with vortex breakdown oscillation are the mostdominant frequencies in all cases where vortex breakdown occurs. Dominant frequencies associated withhelical mode instability are also present at the probes downstream of breakdown. Dominant frequenciesrelated to the shear layer instabilities were observed for the low subsonic regime.Thu, 30 Nov 2017 20:30:00 +0100Dynamic Response of a Red Blood Cell in Shear Flow
http://ajme.aut.ac.ir/article_2749_112.html
Volume 1, Issue 2, Summer and Autumn 2017, Page 233-242<br><br>Three-dimensional simulation of a red blood cell deformation in a shear flow isperformed using immersed boundary lattice Boltzmann method for the fluid flow simulation, as well asfinite element method for membrane deformation. Immersed boundary method has been used to modelinteraction between fluid and membrane of the red blood cell. Red blood cell is modeled as a biconcavediscoid capsule containing fluid with an elastic membrane. Computations are performed at relativelysmall and large shear rates in order to study the dynamic behavior of red blood cell, especially tumblingand swinging modes of its motion. A rigid-body-like motion with the constant-amplitude oscillationof deformation parameter and continuous rotation is observed for red blood cell at its tumbling mode.However, at a relatively large shear rate, red blood cell follows a periodic gradual deformation andelongation with a final ellipsoidal shape. The effect of different initial orientations of red blood cell isalso investigated in the present paper. Results show that the dynamic response of red blood cell is notsensitive to this parameter.Thu, 30 Nov 2017 20:30:00 +0100Phase Field Method to the Interaction of Phase Transformations and Dislocations at Nanoscale
http://ajme.aut.ac.ir/article_2759_112.html
Volume 1, Issue 2, Summer and Autumn 2017, Page 243-246<br><br>In this paper, a new phase field method for the interaction between martensitic phasetransformations and dislocations is presented which is a nontrivial combination of the most advancedphase field methods to phase transformations and dislocation evolution. Some of the important points inthe model are the multiplicative decomposition of deformation gradient into elastic, transformational andplastic parts, defining a proper energy to satisfy thermodynamic equilibrium and instability conditions,including phase-dependent properties of dislocations. The system of equations consists of coupledelasticity and phase field equations of phase transformations and dislocations. Finite element methodis used to solve the system of equations and applied to study the growth and arrest of martensitic plateand the evolution of dislocations and phase in a nanograined material. It is found that dislocations playa key role in eliminating the driving force of the plate growth and their arrest which creates athermalfriction. Also, the dual effect of plasticity on phase transformations is revealed; due to dislocationspile-up and its stress concentration, the phase transformation driving force increases and consequently,martensitic nucleation occurs. On the other hand, the dislocation nucleation results in decreasing thephase transformation driving force and consequently, the phase transformation is suppressed.Thu, 30 Nov 2017 20:30:00 +0100Robustness of Controlled Lagrangian method to the Structured Uncertainties
http://ajme.aut.ac.ir/article_2753_0.html
Articles in Press, Accepted Manuscript , Available Online from 18 December 2017<br><br>Controlled Lagrangian method uses the inherent geometric structure of the energy of the mechanical systems to provide a stabilizing algorithm for underactuated mechanical systems. The presented method belongs to a larger family of nonlinear control algorithms, namely energy shaping methods in which the controller is designed by providing necessary modifications in the mechanical energy of the system. This paper presents sensitivity analysis of Controlled Lagrangian method. It is shown that the method presents a suitable performance under the effect of structured (or parametric) uncertainties such as masses values, their positions and their influence on the inertia tensor. Then, the sequel investigates the robustness level of the designed controller in the presence of structured uncertainties. A detailed robustness proof of the scheme is established in this paper. Simulations are provided for a linear inverted pendulum cart system to validate analytical results of robustness to parametric uncertainties. Simulation results confirm that the designed controller for the inverted pendulum, which is unstable and underactuated, is well robust against parametric uncertainties as the analytical studies predicted. The method was also compared with the sliding mode approach, and showed a superior robustness against parametric uncertainties and a more practical control input value.Sun, 17 Dec 2017 20:30:00 +0100Exact closed-form solution for vibration analysis of beams carrying lumped masses with rotary ...
http://ajme.aut.ac.ir/article_2754_0.html
Articles in Press, Accepted Manuscript , Available Online from 18 December 2017<br><br>In this paper, an exact closed-form solution is presented for free vibration analysis of Bernoulli–Euler beams carrying attached masses with rotary inertias. The proposed technique explicitly provides frequency equation and corresponding mode as functions with two integration constants which should be determined by external boundary conditions implementation and leads to solution of a two by two eigenvalue problem. The concentrated masses and their rotary inertia are modeled using Dirac’s delta generalized functions without implementation of continuity conditions. The non-dimensional inhomogeneous differential equation of motion is solved by applying integration procedure. Using the fundamental solutions which are made of the appropriate linear composition of trigonometric and hyperbolic functions leads to make the implementation of boundary conditions much easier. The proposed technique is employed to study effects of quantity, position and translational and rotational inertia of the concentrated masses on the dynamic behavior of the beam for all standard boundary conditions. Unlike many of previous exact approaches, presented solution has no limitation in number of concentrated masses.Sun, 17 Dec 2017 20:30:00 +0100Thermal Analysis Circular Couette Flow of Non-Newtonian Fluid with Viscous Dissipation
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Articles in Press, Accepted Manuscript , Available Online from 18 December 2017<br><br>The forced convection heat transfer in rotational flow of pseudoplastic fluids between concentric cylinders is examined when the inner cylinder is rotated at a constant angular velocity and the outer cylinder is stationary. The viscosity of fluid is considered simultaneously dependent on temperature and shear rate. Exponential dependence of viscosity on temperature is modeled with the Nahme law and the shear dependency is modeled according to the Carreau equation. The Viscous dissipation is adding complexity to the already highly correlated set of governing motion and energy equations. The perturbation method has been applied to the problem of finding an approximate solution for highly nonlinear governing equations in the narrow gap limit and steady state base flow. The effect of governing parameter such as Brinkman numbers and Deborah number on the thermal stability is investigated. Moreover, the study illustrated that the Nusselt number of outer cylinder increases as the fluid elasticity increases. It, however, decreases with increasing Brinkman number. The pseudoplastic fluid between concentric cylinders is heated as Brinkman number increases due to frictional dissipation and it is cooled as Deborah number increases which is due to the pseudoplasticity behavior of the fluid.Sun, 17 Dec 2017 20:30:00 +0100Nonlinear Free Transverse Vibration Analysis of Beams Using Variational Iteration Method
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Articles in Press, Accepted Manuscript , Available Online from 18 December 2017<br><br>In this study, Variational Iteration Method (VIM) is employed so as to investigate the linear and non-linear transverse vibration of Euler-Bernoulli beams. This method is a very powerful approach with high convergence speed which gives analytical and semi-analytical solution to the linear equations and is able to be extended to present semi-analytical solution to the non-linear ones. In this method, firstly, Lagrange`s multiplier and Initial Function should be chosen. Suitable choice of these two elements would effectively affect the convergence speed. In this attempt, in addition to presenting a discussion on how to choose these two functions appropriately, the calculated frequencies in non-linear state are compared with those obtained from DQM and FEM approaches, and the accuracy and convergence speed are studied as well. The proper choice of Lagrange`s multiplier and Initial Function will play a key role in this method. Semi analytical results presented in linear state show that the obtained values will converge to the accurate values quickly in a way that the first and second frequencies will reach the accuracy of four point decimal after four and six iterations respectively.Sun, 17 Dec 2017 20:30:00 +0100Multi-objective Optimization of Surface Roughness and Material Removal Rate Using an Improved ...
http://ajme.aut.ac.ir/article_2769_0.html
Articles in Press, Accepted Manuscript , Available Online from 02 January 2018<br><br>Surface roughness is one of the main characteristics of a work piece in the quality control process. Several parameters such as cutting tool material and geometry, cutting parameters, work piece material properties, machine tool and coolant type affect the surface quality. An important task of process planners is the proper selection of three main cutting parameters: cutting speed, feed rate, and depth of cut in order to not only have low surface roughness, but also to perform the process within a reasonable amount of time. In this paper, using full factorial experiment design, the multiple regression equation for surface roughness in the climb milling process of DIN 1.4021 martensitic stainless steel has been obtained and then used as one of the objective functions in the Multi-objective Improved Self-Adaptive Particle Swarm Optimization (MISAPSO) algorithm. This algorithm has been used to obtain cutting parameters to achieve low surface roughness simultaneously with a high material removal rate. The relatively new algorithm MISAPSO that was developed with some changes in the common particle swarm optimization (PSO) technique, has been used in multi-objective optimization of machining processes and was shown to be able to help the process planners in selecting cutting parameters.Mon, 01 Jan 2018 20:30:00 +0100Effect of Concentrated Axial Harmonic Force on Lateral Vibration of a Mono- Disk Rotating Shaft
http://ajme.aut.ac.ir/article_2770_0.html
Articles in Press, Accepted Manuscript , Available Online from 02 January 2018<br><br>.Rotor vibrations and its control is an important subject in many industries such as power plants and gas stations. When lateral vibrations of rotors during operation exceeds allowable level, a huge damage will be occurred. Surge and stall may be some common reasons of these vibrations. This paper aims to present a simple model for surge and stall and assumes that its effect as a concentrated force acting on a rotor-disk system. This is a basic and conceptual model for future investigations in this area. Therefore, the effect of a concentrated axial force exerted on an assembled disk on a rotating shaft is investigated theoretically. Equations of motion are derived using Timoshenko beam theory. This governing equations consist of four coupled partial differential equations. Since these equations are complex, coupled and have time-varying coefficients, they are solved using a combination of Galerkin and Newmark methods. Numerical examples are analyzed as well. The accuracy of these equations is verified for a simple beam. Results indicate that the axial load has a considerable effect on the lateral vibration amplitude of the rotor and this simple proposed model can be improved for next studies in this area..Mon, 01 Jan 2018 20:30:00 +0100Nonlinear Aerothermoelastic Analysis of Functionally Graded Rectangular Plates Subjected to ...
http://ajme.aut.ac.ir/article_2786_0.html
Articles in Press, Accepted Manuscript , Available Online from 31 January 2018<br><br>In this study, the aerothermoelastic behavior of Functionally Graded (FG) plates under hypersonic airflow is investigated. The classical plate theory based on both mid-surface and the neutral surface position is used to model the structural treatment. Also, Von Karman strain-displacement relations are utilized to involve the structural nonlinearity. To consider the applied hypersonic aerodynamic loads, nonlinear (third–order) piston theory is employed to model unsteady aerodynamic pressure in hypersonic flow regime. Material properties of the FG panel is assumed to be temperature dependent and altered in the thickness direction according to a simple power law distribution. The Generalized Differential Quadrature Method (GDQM) is used to transfer the governing partial differential equation into ODE one. The onset of flutter instability, the stability boundaries and the time response analysis of a FG plate are determined by applying the fourth order Runge-Kutta method. Moreover, the effect of some important parameters such as Mach number, in-plane thermal load, plate thickness ratio and volume fraction index on the plate aerothermoelastic behavior is examined. Comparison of the obtained results with the available results in literature confirms the accuracy and reliability of the proposed approach to analyzing aerothermoelastic of FG plates in hypersonic flow.Tue, 30 Jan 2018 20:30:00 +0100ارتعاش آزاد غیرخطی نانو تیرهای مدرج تابعی کمانش ...
http://ajme.aut.ac.ir/article_2787_0.html
Articles in Press, Accepted Manuscript , Available Online from 31 January 2018<br><br>در مطالعه حاضر ارتعاش غیرخطی نانو-تیر مدرج تابعی که تحت بار حرارتی، کمانش کرده است بررسی می شود. از تئوری غیرخطی تیر غیرمحلی اولر-برنولی توام با مدهای ارتعاش خطی نانو-تیری که حول پیکربندی مد اول کمانش خود ارتعاش می کند، برای استخراج دسته معادلات دیفرانسیل معمولی حاکم بر مساله با استفاده از روش گالرکین استفاده شده است. حل نیمه تحلیلی حاکم بر فرکانسهای غیرخطی ارتعاش جانبی نانو-تیر کمانش کرده با استفاده از روش اختلال هموتوپی و روش تغییر تکرار بدست آمده است. نتایج نشان می دهد که اختلاف میان فرکانس خطی و غیرخطی با افزایش بیشترین خیز اولیه جانبی، مقدار مقیاس کوچک و شاخص قانون توانی افزایش می یابد. بررسی اثر نسبت طول به ضخامت بر اختلاف بین فرکانسهای خطی و غیرخطی نشان می دهد که نسبت منظری تاثیر چندانی بر نسبت فرکانس غیرخطی به خطی کلاسیک ندارد اما نسبت فرکانس غیرخطی به خطی غیرمحلی با افزایش نسبت منظری، کاهش می یابد. برخلاف نسبت اولین فرکانس غیرخطی به خطی که با افزایش بار محوری-فشاری کاهش می یابد، مقدار بار محوری فشاری که فراتر از بار بحرانی نانو-تیر می باشد تاثیری بر نسبت دومین فرکانس غیزخطی به خطی ندارد.Tue, 30 Jan 2018 20:30:00 +0100Surface stress size dependency in nonlinear instability of imperfect piezoelectric nanoshells ...
http://ajme.aut.ac.ir/article_2788_0.html
Articles in Press, Accepted Manuscript , Available Online from 31 January 2018<br><br>In this paper, the nonlinear instability of piezoelectric cylindrical nanoshells under the combined radial compression and electrical load including the effects of surface free energy is studied. To consider the surface effects, the Gurtin-Murdoch elasticity theory is utilized along with the classical shell theory to develop an efficient size-dependent shell model. To satisfy the balance conditions on the surfaces of nanoshells, a linear variation of normal stress is assumed through the thickness of the bulk. Electrical field is also exerted along the transverse direction. Based on the virtual work's principle, the size-dependent nonlinear governing differential equations are derived in which transverse displacement and Airy stress function are considered as independent variables. Finally, a two-stepped singular perturbation technique is employed to obtain the size-dependent critical buckling pressure and the associated postbuckling equilibrium path for alternative electrical loadings. It is revealed that the electrical load increases or decreases the critical buckling pressure and critical end-shortening of nanoshell which depends on the sign of applied voltage. Moreover, it is found that by taking surface free energy effects into account, the influence of electrical load on the postbuckling behavior of nanoshell increases.Tue, 30 Jan 2018 20:30:00 +0100