Journal of Applied and Computational MechanicsJournal of Applied and Computational Mechanics
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Feed provided by Journal of Applied and Computational Mechanics. Click to visit.Transient Natural Convection in an Enclosure with Variable Thermal Expansion Coefficient and ...
http://jacm.scu.ac.ir/article_13099_1659.html
Transient natural convection is numerically investigated in an enclosure using variable thermal conductivity, viscosity, and the thermal expansion coefficient of Al2O3-water nanofluid. The study has been conducted for a wide range of Rayleigh numbers (103≤ Ra ≤ 106), concentrations of nanoparticles (0% ≤ ϕ ≤ 7%), the enclosure aspect ratio (AR =1), and temperature differences between the cold and hot walls (∆T= 30). Transient parameters such as development time and time-average Nusselt number along the cold wall are also presented as a non-dimensional form. Increasing the Rayleigh number shortens the non-dimensional time of the initializing stage. By increasing the volume fraction of nanoparticles, the flow development time shows different behaviors for various Rayleigh numbers. The non-dimensional development time decreases by enhancing the concentration of nanoparticles.Sat, 30 Jun 2018 19:30:00 +0100Buckling Analysis of Embedded Nanosize FG Beams Based on a Refined Hyperbolic Shear Deformation ...
http://jacm.scu.ac.ir/article_13152_1659.html
In this study, the mechanical buckling response of refined hyperbolic shear deformable (FG) functionally graded nanobeams embedded in an elastic foundation is investigated based on the refined hyperbolic shear deformation theory. Material properties of the FG nanobeam change continuously in the thickness direction based on the power-law model. To capture small size effects, Eringen’s nonlocal elasticity theory is adopted. Employing Hamilton’s principle, the nonlocal governing equations of FG nanobeams embedded in the elastic foundation are obtained. To predict the buckling behavior of embedded FG nanobeams, the Navier-type analytical solution is applied to solve the governing equations. Numerical results demonstrate the influences of various parameters such as elastic foundation, power-law index, nonlocal parameter, and slenderness ratio on the critical buckling loads of size dependent FG nanobeams.Sat, 30 Jun 2018 19:30:00 +0100Differential Quadrature Method for Dynamic Buckling of Graphene Sheet Coupled by a Viscoelastic ...
http://jacm.scu.ac.ir/article_13235_1659.html
In the present study, the dynamic buckling of the graphene sheet coupled by a viscoelastic matrix was studied. In light of the simplicity of Eringen's non-local continuum theory to considering the nanoscale influences, this theory was employed. Equations of motion and boundary conditions were obtained using Mindlin plate theory by taking nonlinear strains of von Kármán and Hamilton's principle into account. On the other hand, a viscoelastic matrix was modeled as a three-parameter foundation. Furthermore, the differential quadrature method was applied by which the critical load was obtained. Finally, since there was no research available for the dynamic buckling of a nanoplate, the static buckling was taken into consideration to compare the results and explain some significant and novel findings. One of these results showed that for greater values of the nanoscale parameter, the small scale had further influences on the dynamic buckling.Sat, 30 Jun 2018 19:30:00 +0100Moving Mesh Non-standard Finite Difference Method for Non-linear Heat Transfer in a Thin Finite Rod
http://jacm.scu.ac.ir/article_13202_1659.html
In this paper, a moving mesh technique and a non-standard finite difference method are combined, and a moving mesh non-standard finite difference (MMNSFD) method is developed to solve an initial boundary value problem involving a quartic nonlinearity that arises in heat transfer with thermal radiation. In this method, the moving spatial grid is obtained by a simple geometric adaptive algorithm to preserve stability. Moreover, it uses variable time steps to protect the positivity condition of the solution. The results of this computational technique are compared with the corresponding uniform mesh non-standard finite difference scheme. The simulations show that the presented method is efficient and applicable, and approximates the solutions well, while because of producing unreal solution, the corresponding uniform mesh non-standard finite difference fails.Sat, 30 Jun 2018 19:30:00 +0100Inherent Irreversibility of Exothermic Chemical Reactive Third-Grade Poiseuille Flow of a ...
http://jacm.scu.ac.ir/article_13194_1659.html
In this study, the analysis of inherent irreversibility of chemical reactive third-grade poiseuille flow of a variable viscosity with convective cooling is investigated. The dissipative heat in a reactive exothermic chemical moves over liquid in an irreversible way and the entropy is produced unceasingly in the system within the fixed walls. The heat convective exchange with the surrounding temperature at the plate surface follows Newton’s law of cooling. The solutions of the dimensionless nonlinear equations are obtained using weighted residual method (WRM). The solutions are used to obtain the Bejan number and the entropy generation rate for the system. The influence of some pertinent parameters on the entropy generation and the Bejan number are illustrated graphically and discussed with respect to the parameters.Sat, 30 Jun 2018 19:30:00 +0100Exact Radial Free Vibration Frequencies of Power-Law Graded Spheres
http://jacm.scu.ac.ir/article_13243_1659.html
This study concentrates on the free pure radial vibrations of hollow spheres made of hypothetically functionally simple power rule graded materials having identical inhomogeneity indexes for both Young’s modulus and the density in an analytical manner. After offering the exact elements of the free vibration coefficient matrices for free-free, free-fixed, and fixed-fixed restraints, a parametric study is fulfilled to study the effects of both the aspect ratio and the inhomogeneity parameters on the natural frequencies. The outcomes are presented in both graphical and tabular forms. It was seen that the fundamental frequency is mostly affected by the inhomogeneity parameters rather than the higher ones. However, the natural frequencies except the fundamental ones are dramatically affected by the thickness of the sphere. It is also revealed that there is a linear relationship between the fundamental frequency and others in higher modes of the same sphere under all boundary conditions.Sat, 30 Jun 2018 19:30:00 +0100Bending of Shear Deformable Plates Resting on Winkler Foundations According to Trigonometric ...
http://jacm.scu.ac.ir/article_13234_1659.html
A trigonometric plate theory is assessed for the static bending analysis of plates resting on Winkler elastic foundation. The theory considers the effects of transverse shear and normal strains. The theory accounts for realistic variation of the transverse shear stress through the thickness and satisfies the traction free conditions at the top and bottom surfaces of the plate without using shear correction factors. The governing equations of equilibrium and the associated boundary conditions of the theory are obtained using the principle of virtual work. A closed-form solution is obtained using double trigonometric series. The numerical results are obtained for flexure of simply supported plates subjected to various static loadings. The displacements and stresses are obtained for three different values of foundation modulus. The numerical results are also generated using higher order shear deformation theory of Reddy, first order shear deformation theory of Mindlin, and classical plate theory for the comparison of the present results.Sat, 30 Jun 2018 19:30:00 +0100Semi-Analytical Solution for Vibration of Nonlocal Piezoelectric Kirchhoff Plates Resting on ...
http://jacm.scu.ac.ir/article_13203_1659.html
Semi-analytical solutions for vibration analysis of nonlocal piezoelectric Kirchhoff plates resting on viscoelastic foundation with arbitrary boundary conditions are derived by developing Galerkin strip distributed transfer function method. Based on the nonlocal elasticity theory for piezoelectric materials and Hamilton's principle, the governing equations of motion and boundary conditions are first obtained, where external electric voltage, viscoelastic foundation, piezoelectric effect, and nonlocal effect are considered simultaneously. Subsequently, Galerkin strip distributed transfer function method is developed to solve the governing equations for the semi-analytical solutions of natural frequencies. Numerical results from the model are also presented to show the effects of nonlocal parameter, external electric voltages, boundary conditions, viscoelastic foundation, and geometric dimensions on vibration responses of the plate. The results demonstrate the efficiency of the proposed methods for vibration analysis of nonlocal piezoelectric Kirchhoff plates resting on viscoelastic foundation.Sat, 30 Jun 2018 19:30:00 +0100The Complementary Functions Method (CFM) Solution to the Elastic Analysis of Polar Orthotropic ...
http://jacm.scu.ac.ir/article_13293_1659.html
This study primarily deals with introducing an efficient numerical technique called the Complementary Functions Method (CFM) for the solutions of the initial value problem for the linear elastic analysis of anisotropic rotating uniform discs. To bring the performance of the method to light, first, closed form formulas are derived for such discs. The governing equation of the problem at stake is solved analytically with the help of the Euler-Cauchy technique under three types of boundary conditions namely free-free, fixed-free, and fixed-guided constraints. Secondly, the CFM is applied to the same problem. It was found that both numerical and analytical results coincide with each other up to a desired numerical accuracy. Third, after verifying the results with the literature, a parametric study with CFM on the elastic behavior of discs made up of five different materials which physically exist is performed. And finally, by using hypothetically chosen anisotropy degrees from 0.3 through 5, the effects of the anisotropy on the elastic response of such structures are investigated analytically. Useful graphs are provided for readers.Sat, 30 Jun 2018 19:30:00 +0100Verification and Validation of Common Derivative Terms Approximation in Meshfree Numerical Scheme
http://jacm.scu.ac.ir/article_13292_1659.html
In order to improve the approximation of spatial derivatives without meshes, a set of meshfree numerical schemes for derivative terms is developed, which is compatible with the coordinates of Cartesian, cylindrical, and spherical. Based on the comparisons between numerical and theoretical solutions, errors and convergences are assessed by a posteriori method, which shows that the approximations for functions and derivatives are of the second accuracy order, and the scale of the support domain has some influences on numerical errors but not on accuracy orders. With a discrete scale h=0.01, the relative errors of the numerical simulation for the selected functions and their derivatives are within 0.65%.Sat, 30 Jun 2018 19:30:00 +0100Modelling of crack growth using a new fracture criteria based peridynamics
http://jacm.scu.ac.ir/article_13213_0.html
Peridynamics (PD) is a nonlocal continuum theory based on integro-differential equations without spatial derivatives. The elongation fracture criterion is implicitly incorporated in the PD theory and fracture is a natural outcome of the simulation. On the other hand, a new fracture criterion based on the crack opening displacement combine with peridynamic (PD-COD) is proposed. When the relative deformation of the PD bond between two particles reach the critical crack tip opening displacement of the fracture mechanics, we assume that the bond force vanishes. The new damage rule of fracture criteria similar to the local damage rule in conventional PD is introduced to simulate fracture. In this paper, a comparative study between XFEM and PD is presented at first. Then , four examples, i.e. a bilateral crack problem, double parallel crack, monoclinic crack and the double inclined crack are given to demonstrate the effectiveness of the new criterion.Mon, 02 Oct 2017 20:30:00 +0100Stability of a Strongly Displacement Time-Delayed Duffing Oscillator by the ...
http://jacm.scu.ac.ir/article_13341_0.html
In the current work, some perturbation methods are applied to Duffing equation having a displacement time-delayed variable to study the stability of such systems. Two approaches are considered to analyze Duffing oscillator having a strong delayed variable. The homotopy perturbation method has been applied through the frequency analysis. Nonlinear frequency is formulated as a function of all the problem’s parameters. Based on the multiple scales-homotopy-perturbation method, a uniform second-order periodic solution having a damping part has been formulated. Comparing these two approaches reveals the accuracy of using the second approaches further allowing studying the stability behavior. Numerical simulations are carried out to validate the analytical finding.Thu, 14 Dec 2017 20:30:00 +0100Cyclic and monotonic behavior of strengthened and unstrengthened square reinforced concrete columns
http://jacm.scu.ac.ir/article_13349_0.html
The use of composite materials is an effective technique to enhance the capacity of reinforced concrete columns subjected to seismic loading due to their high tensile strength. In this paper, numerical models were developed in order to predict the experimental behavior of square reinforced concrete columns strengthened with glass fiber reinforced polymer and steel bars and unstrengthened column under cyclic and monotonic loadings, respectively. Two columns were modeled in the present work. The first concerns the column without strengthening subjected to lateral monotonic loading, and the second concerns the column strengthened with glass fiber reinforced polymer and steel bars subjected to lateral cyclic loading. Comparison of the numerical modeling and the experimental laboratory tests results were performed and discussed. Good accordance between the numerical and experimental force-displacement responses was obtained. Improvement of the strength of the reinforced concrete column subjected to cyclic loading was described with comparison of the behavior of the strengthened column with the unstrengthened reference column. The results show a good improvement in the load carrying capacity and ductility of the column. The main objectives of this numerical modeling are to contribute to the comprehension of the monotonic and cyclic behavior of the square reinforced concrete columns and to compare the numerical results with the experimental ones.Wed, 20 Dec 2017 20:30:00 +0100ON THE SLIP EFFECTS FOR SQUEEZING MHD FLOW OF A CASSON FLUID BETWEEN PARALLEL DISKS
http://jacm.scu.ac.ir/article_13350_0.html
This paper considers the effects of squeezing electrically conducting Casson fluid, flowing through parallel disk under slip condition. The Nonlinear model describing the transport phenomena of the Casson fluid is analyzed adopting the homotopy perturbation method (HPM). Solutions generated from higher order non-linear equations arising from the mechanics of the fluid utilsing the HPM are used to investigate effects of rheological parameters such as squeeze and slip on fluid flow for cases of plates moving apart and coming together. Results reveal increasing velocity profile due to quantitative increase of slip parameter when plates are receding as well as collapsing, with effect more pronounced towards the upper plate. This present study provides good insights to applications such as hydraulic lifts, electric motors, nasogastric tube and syringe flow amongst other application.Wed, 20 Dec 2017 20:30:00 +0100Modeling of Self-Healing Concrete: A Review
http://jacm.scu.ac.ir/article_13355_0.html
Self-healing concrete (SHC) has received a tremendous attention due to its advanced ability of automatic crack detection and crack repairing compared to standard concrete. Two main approaches considered to-date of self-healing mechanism are autogenous and autonomous healing. In the past several years, the effort of the research has been focused on experimental works instead of numerical models to simulate the healing process. The purpose of this review is to provide comprehensive comparison from different self-healing concrete (cement based masterials) modeling approaches which are available. In this review, special attention is given to the autonomous healing model and a few of recent works of autogenous healing model are also revealed. Moreover, this review covers both of analytical and numerical simulation method of self-healing concrete model.Thu, 28 Dec 2017 20:30:00 +0100Nonlinear Dynamic Response of Functional Graded Porous Plates on Elastic Foundation Subjected ...
http://jacm.scu.ac.ir/article_13360_0.html
In this paper, the first-order shear deformation theory is used to derive theoretical formulations illustrating the nonlinear dynamic response of functionally graded porous plates under thermal and mechanical loading supported by Pasternak’s model of the elastic foundation. Two types of porosity, namely evenly distributed porosities (Porosity-I) and unevenly distributed porosities (Porosity-II), are assumed influencing effective properties of FGM plates such as Young’s modulus, the coefficient of thermal expansion and density. The strain-displacement formulations admitted Von Karman geometrical nonlinearity and general Hooke’s law are used to obtain constitutive relations. Airy stress functions with full motion equations are employed to shorten the number of governing equations, accompanying with the boundary and initial conditions lead to a system of differential equations of the nonlinear dynamic response of porous FGM plates. Considering linear parts of these equations, natural frequencies of porous FGM plates could be determined. Numerical results employed Runge-Kutta method illustrate the influence of geometrical configurations, volume faction index, porosity, elastic foundations, mechanical and thermal loads on the nonlinear dynamic response of the plates. Good agreements are obtained in comparison with other results in the literature.Sat, 06 Jan 2018 20:30:00 +0100Evaluation of fracture parameters by coupling the edge based smoothed finite element method and ...
http://jacm.scu.ac.ir/article_13372_0.html
This paper presents a technique to evaluate the fracture parameters by combining the edge based smoothed finite element method (ESFEM) and the scaled boundary finite element method (SBFEM). A semi-analytical solution is sought in the region close to the vicinity of the crack tip using the SBFEM, whilst, the ESFEM is used for the rest of the domain. As both the methods satisfy the partition of unity and the compatibility condition, the stiffness matrices obtained from both the methods can be assembled as in the conventional finite element method. The stress intensity factors (SIFs) are computed directly from their definition. Numerical examples of linear elastic bodies with cracks are solved without requiring additional post-processing technique. The SIFs computed using the proposed technique are in good agreement with the reference solutions. Crack propagation study is also carried out with minimal remeshing locally, to show the robustness of the proposed technique. The maximum circumferential stress criterion is used to predict the direction of propagation.Thu, 18 Jan 2018 20:30:00 +0100An analysis of thermal-bending stresses in a simply supported thin elliptical plate
http://jacm.scu.ac.ir/article_13400_0.html
In this paper, we consider a transient thermal stress investigation on a simply supported thin elliptical plate during sectional heating with time-dependent temperature supply. The solution of heat conduction equation with the corresponding initial and boundary conditions is obtained by employing an integral transform approach. The governing equation solution for small deflection theory is obtained and utilized to preserve the intensities of thermal bending moments, involving the Mathieu and modified functions and its derivatives. It was established that the deflection result proximately accedes with the previously given result. It is also exhibited that the temperature field in a circular solution could be resulting as a particular case from the present mathematical solution. The numerical results obtained utilizing computational implements was precise enough for practical purposes.Fri, 26 Jan 2018 20:30:00 +0100On the geometrically nonlinear analysis of composite axisymmetric shells
http://jacm.scu.ac.ir/article_13401_0.html
Composite axisymmetric shells have numerous applications; many researchers have taken advantage of the general shell element or semi-analytical formulation to analyze these structures. The present study is devoted to the nonlinear analysis of composite axisymmetric shells by using a 1D three nodded axisymmetric shell element. Both the low and higher-order shear deformations are included in the formulation. The displacement field is considered to be nonlinear function of the nodal rotations. This assumption eliminates the restriction of small rotations between two successive increments. Both Total Lagrangian Formulation and the Generalized Displacement Control Method are employed for analyzing the shells. Several numerical tests are performed to corroborate the accuracy and efficiency of the suggested approach.Fri, 26 Jan 2018 20:30:00 +0100DETERMINATION OF THE OPTIMAL REDUCTION RATIO FOR LEAST SPRINGBACK DURING COLD DRAWING OF ...
http://jacm.scu.ac.ir/article_13433_0.html
Cold drawing process is one of the most used metals forming process in industries for forming of seamless tubes. This process of plastic deformation of metals occurs below the recrystallization temperature and is generally performed at room temperature. When metal is cold worked, upon release of forming force, springback occurs. In this paper the springback effect of seamless tube that has undergone cold drawing has been studied for three different reduction ratios viz.10-15 %,15-20 % and 20-25 % with the aim to reduce it. Experiments are conducted under different reduction ratios with working conditions of die semi angles of 10 and 15 degree, die land width of 5 mm and 10 mm as well as drawing speed of 4, 6 and 8 m/min for C-45 tube material. Optimum reduction ratio is finalized using Statistical Package for Social Science (SPSS) software of data analysis using statistical tests like Kruskal-Wallis, ANOVA, Post-hoc etc. Metallurgical analysis through microstructural investigation, XRD and mechanical testing through cold draw load, hardness testing for different reduction ratios are also studied for validation purpose. The result of this research is that 10-15 % reduction ratio yields minimum springback. This can be used to help in design of tools in the metal forming industry to minimize springback and to improve the quality of the product.Wed, 07 Feb 2018 20:30:00 +0100Mixed Strong Form Representation Particle Method for Solids and Structures
http://jacm.scu.ac.ir/article_13434_0.html
In this paper, a generalized particle system (GPS) method, a general method to describe multiple strong form representation based particle methods is described. Gradient, divergence, and Laplacian operators used in various strong form based particle method such as moving particle semi-implicit (MPS) method, smooth particle hydrodynamics (SPH), and peridynamics, can be described by the GPS method with proper selection of parameters. In addition, the application of mixed formulation representation to the GPS method is described. Based on Hu-Washizu principle and Hellinger-Reissner principle, the mixed form refers to the method solving multiple primary variables such as displacement, strain and stress, simultaneously in the FEM method; however for convenience in employing FEM with particle methods, a simple representation in construction only is shown. It is usually applied to finite element method (FEM) to overcome numerical errors including locking issues. While the locking issues do not arise in strong form based particle methods, the mixed form representation in construction only concept applied to GPS method can be the first step for fostering coupling of multi-domain problems, coupling mixed form FEM andmixed form representation GPS method; however it is to be noted that the standard GPS particle method and the mixed for representation construction GPS particle method are equivalent. Two dimensional simple bar and beam problems are presented and the results from mixed form GPS method is comparable to the mixed form FEM results.Wed, 07 Feb 2018 20:30:00 +0100Further Study on Thermal Performance analysis of Porous Fin with Temperature-Dependent Thermal ...
http://jacm.scu.ac.ir/article_13473_0.html
In this present study, thermal performance analysis of porous fin with temperature-dependent thermal conductivity and internal heat generation is carried out using Galerkin’s method of weighted residual. The results of the Galerkin’s method of weighted residual show excellent agreement with the results of numerical method using shooting method coupled with Runge-Kutta method and also with the results of homotopy perturbation method. Thereafter, the developed analytical solutions are used to investigate the influences of the thermal model parameters on the thermal performance of the porous fin. It is found as the with the other model parameters that as the convective parameter increases, the rate of heat transfer from the base of the fin increases and consequently, the porous fin efficiency improves. However, increase in the nonlinear thermal conductivity parameter decreases the temperature distribution in the fin. Based on the high accuracy of the Galerkin’s method of weighted residual as displayed in this work, it is hoped that the simple analytical solutions given by the approximate analytical method will enhance the analysis of extended surfaces and also assist the designers.Sun, 18 Feb 2018 20:30:00 +0100Free convection flow of an electrically-conducting micropolar fluid between parallel porous ...
http://jacm.scu.ac.ir/article_13474_0.html
In this work, effect of temperature dependent heat sources on the fully developed free convection electrically conducting micropolar fluid between two parallel porous vertical plates in a strong cross magnetic field is analyzed. The micropolar fluid fills the space inside the porous plates when the rate of suction at one boundary is equal to the rate of injection at the other boundary. The coupled nonlinear governing differential equations are solved using differential transform method (DTM). Also the Runge-Kutta shooting method (RKSM) which is a numerical method is used for the validity of the DTM method and excellent agreement is observed between the solutions of DTM and RKSM. Trusting this validity, the effects of Hartmann number, Reynolds number, micropolar parameter and applied electric field load parameter are discussed on the velocity, microrotation velocity and temperature. The skin friction, couple stress and Nusselt numbers at the plates are shown in graphs. It is observed that the Hartmann number and micropolar parameter decreases the skin friction and couple stress at both the plates for suction and injection.Mon, 19 Feb 2018 20:30:00 +0100Evaluation of new best cross ply laminated plate theories through the axiomatic/asymptotic approach
http://jacm.scu.ac.ir/article_13516_0.html
This paper presents Best Theory Diagrams (BTDs) constructed from various non-polynomial theories for the static analysis of thick and thin symmetric and asymmetric cross ply laminated plates. The BTD is a curve that provides the minimum number of unknown variables necessary for a fixed error or vice versa. The plate theories that belong to the BTD have been obtained by means of the Axiomatic/Asymptotic Method (AAM). The different plate theories reported are implemented by using the Carrera Unified Formulation (CUF). Navier-type solutions have been obtained for the case of simply supported plates loaded by a bisinuisoidal transverse pressure with different length-to-thickness ratios. The BTDs build from non-polynomials functions are compared with BTDs using Maclaurin expansion. The results suggest that the plate models obtained from the BTD using non-polynomial terms can improve the accuracy obtained from Maclaurin expansions for a given number of unknown variables of the displacement field.Thu, 15 Mar 2018 20:30:00 +0100Study of Model Separation Flow Behaviour At High Angles of Attack Aerodynamics
http://jacm.scu.ac.ir/article_13517_0.html
This paper analyzed the aerodynamic performance and flow separation characteristics on the rectangular wing for varying Reynolds numbers. The mechanism of separation and its effect over the rectangular wing is simulated in ANSYS FLUENT using K-ω SST turbulence model. The detail analysis was performed to discuss the lift and drag force of the wing surface, surface pressure distribution around the wing surface, flow separation characteristics for different angles of attack, velocity profiles at different sections of the wing surface along the chord length, effect of wing tip vortices, etc. The simulation results show that with the increase in angles of attack, separation point moves towards the leading edge and on set of stalling it is very much closer to the leading edge. The experimental and numerical results also indicated that NACA4415 airfoil has enhanced coefficient of lift to coefficient of drag ratio at the ranges of angles of attack (AoA) 4◦-6◦ which are distinctively advantageous for the better performance of small scale wind turbine rotors. The experimental and computational results are analyzed in the context of effective change in stalling characteristics at different Reynolds numbers.Fri, 16 Mar 2018 20:30:00 +0100Extension Ability of Reduced Order Model of the Unsteady Incompressible Flows Using Combination ...
http://jacm.scu.ac.ir/article_13518_0.html
In this article, a new low-dimensional modelling approach, based on the proper orthogonal decomposition (POD) method, is presented. After projecting the governing equations of flow dynamics along POD modes, a dynamical system is obtained. Normally, the classical reduced order models do not predict accurate time variations of flow variables due to some reasons. To improve the response of the dynamical system a calibration method based on a least square optimization process, was used. The calibration polynomial can be assumed as the pressure correction term which is vanished in projecting the Navier-Stokes equations along the POD modes. The above least square procedure is a combination of POD method with solution of an optimization problem and the obtained model can predict accurate time variations of flow field with high speed. For the long time periods, the calibration term is computed using a combined form of POD and Fourier modes. This extension is a totally new extension to this procedure which has been proposed by the authors recently. The results obtained from the calibrated low-dimensional model show close agreements to the benchmark DNS data and proving high accuracy of our model.Sun, 18 Mar 2018 20:30:00 +0100Free Convection Flow and Heat Transfer of Nanofluids of Different Shapes of Nano-size particles ...
http://jacm.scu.ac.ir/article_13519_0.html
In this paper, free convection flow and heat transfer of nanofluids of different shapes nano-size particles over a vertical plate at very low and high Prandtl number are analyzed. The governing systems of nonlinear partial differential equations of the flow and heat transfer processes are converted to systems of nonlinear ordinary differential equation through similarity transformations. The resulting systems of fully coupled nonlinear ordinary differential equations are solved using differential transformation method-Padé approximant technique. The accuracies of the developed analytical methods are verified by comparing their results with the results of past works as presented in literature. Thereafter, the analytical solutions are used to investigate the effects of Prandtl number, nanoparticles volume-fraction, shape and type on the flow and heat transfer behaviour of various nanofluids over the flat plate. It is observed that the velocity and temperature of the nanofluid decreases and increases, respectively as the Prandtl number and volume-fraction of the nanoparticles in the basefluid increase. Also, the maximum decrease in velocity and maximum increase in temperature are caused lamina shaped nanoparticle and followed by platelets, cylinder, bricks and sphere shaped nanoparticles, respectively. Using a common basefluid to all the nanoparticle type, it was established that the maximum decrease in velocity and maximum increase in temperature are caused by TiO2 and followed by CuO, Al2O3 and SWCNTs nanoparticles, in that order. It is hoped that the present study will enhance the understanding of free convection boundary-layer problems as applied in various engineering processes.Mon, 19 Mar 2018 20:30:00 +0100A Comparative Analysis of TLCD Equipped Shear Buildings Under Dynamic Loads
http://jacm.scu.ac.ir/article_13520_0.html
This study targets the behavior of shear buildings equipped with tuned liquid column dampers (TLCD) which attenuates dynamic load induced vibration. TLCDs are a passive damping system used in tall buildings. This kind of damper has proven to be very efficient, being an excellent alternative to mass dampers. A dynamic analysis of the structure-damper system is made using the software DynaPy, developed in the research process. The software solves the equations of motion through numeric integration using the central differences method. The simulations results obtained with DynaPy showed that the use of TLCD can reduce the dynamic response significantly for both harmonic excitations and random excitations.Tue, 20 Mar 2018 20:30:00 +0100Free vibration analysis of quintic nonlinear beams by using the equivalent linearization method ...
http://jacm.scu.ac.ir/article_13523_0.html
In this paper, the equivalent linearization method with a weighted averaging proposed by Anh (2015) is applied to analyse the transverse vibration of quintic nonlinear Euler-Bernoulli beams subjected to the axial loads. The proposed method does not require small parameter in the equation which is difficult to be found for nonlinear problems. The approximate solutions are harmonic oscillations, which are compared with the previous analytical solutions and the exact solutions. Comparisons show the accuracy of the present solutions. The impact of nonlinear terms on dynamical behavior of beams and the effect of the initial amplitude on frequencies of beams are investigated. Futhermore, the effect of the axial force and the length of beams on frequencies are studied.Thu, 05 Apr 2018 19:30:00 +0100Wave motion and stop-bands in pipes with helical characteristics using Wave Finite Element analysis
http://jacm.scu.ac.ir/article_13555_0.html
Pipes are widely used in many industrial and mechanical applications and devices. Although there are many different constructions according to the specific application and device, these can show helical pattern, such as spiral pipes, wire-reinforced pipes/shells, spring-suspension and so on. Theoretical modelling of wave propagation provides a prediction about the dynamic behaviour, andit is fundamental in the design process of these structures/devices and in structural health monitoring techniques. However, standard approaches have limitations in terms of difficulties in modelling and impossible computational cost at higher frequencies. In this paper wave characteristics in waveguides with helical patterns are obtained using a Wave Finite Element (WFE) method. The method is described for a 1D and 2D waveguide with helical properties and it is illustrated by numerical examples. These include the optimisation of stop-bands for a fluid-filled pipe with concentrated masses and a cylindrical structure with helical orthotropy.Mon, 23 Apr 2018 19:30:00 +0100Heat Transfer in Hydro-Magnetic Nano-fluid Flow Between Non Parallel Plates Using DTM
http://jacm.scu.ac.ir/article_13563_0.html
This investigation presents a computational study on heat and flow behaviors between non parallel plates with the influence of a transverse magnetic field when the medium is filled with solid nanoparticles. The nonlinear governing equations are treated analytically via Differential Transform Method (DTM). Thereafter, obtained DTM results are validate with the help of numerical fourth order Runge-Kutta (RK4)solution. The main aim of this researchwork is to analyze the influence of varying physical parameters, in particular Reynolds number, nanofluid volume fraction and Hartmann number. It was found that the presence of solid nanoparticles in a water base liquid has a notable effect on the heat transfer improvement within convergent-divergent channels. The comparison of DTM results with numerical RK4 solution also shows the validity of the analytical DTM technique. In fact, results demonstrate that the DTM data match perfectly with numerical ones and those available in literature.Thu, 26 Apr 2018 19:30:00 +0100Clogged Impeller Diagnosis in the Centrifugal Pump using the Vibration and Motor Current Analysis
http://jacm.scu.ac.ir/article_13564_0.html
The impeller-clogging phenomenon in centrifugal pumps is such kind of the faults that leads to increase the vibration and reduce the performance of pumps. In addition, impeller-clogging could make some problems in the production process of factories. This research assigns to detection of the clogged impeller in a centrifugal pump using the vibration and motor current analysis. In this research, a test rig is set up and one of the impeller’s passageways is clogged by sealing tape. The clogging detection, based on the vibration analysis, is done using the Fast Fourier Transform (FFT). The obtained results show that the dominant frequency in the impeller-clogging phenomenon is the rotational frequency of impeller (1xRPM). The measuring vibration values in three directions (horizontal, vertical and axial) show that the clogged impeller has more effects on the axial vibration responses. Furthermore, in this case, electrical current consumption of electromotor has been reduced.Sat, 28 Apr 2018 19:30:00 +0100A note on free vibration of a double-beam system with nonlinear elastic inner layer
http://jacm.scu.ac.ir/article_13566_0.html
In this note, small amplitude free vibration of a double-beam system in presence of inner layer nonlinearity investigated. The nonlinearity is due to inner layer material and is not related to large amplitude vibration. At first, frequencies of a double-beam system with linear inner layer studied and categorized as synchronous and asynchronous frequencies, and it is revealed that inner layer does not affect higher modes significantly and mainly affects first frequency. Then, Equation of motion in presence of cubic nonlinearity in inner layer derived and transformed to the form of Duffing equation. By using analytical solution, the effect of nonlinearity is analyzed on frequency for simply-support and clamp boundary conditions. Results show the nonlinearity effect is not significant and in small amplitude free vibration analysis of a double-beam system, the material nonlinearity of inner layer could be neglected.Wed, 02 May 2018 19:30:00 +0100A Numerical Simulation of Inspiratory Airflow in Human Airways during Exercise at Sea Level and ...
http://jacm.scu.ac.ir/article_13586_0.html
At high altitudes, the air pressure is much lower than it is at sea level and contains fewer oxygen molecules and less oxygen is taken at each breath. This requires more deep and rapid breathing to get the same amount of oxygen into the blood stream as breathing in air at sea level. Exercises increase oxygen demand and make breathing more difficult at high altitude. In this study, we performed a numerical simulation of inspiratory airflow in a three-dimensional bifurcating human airways model (third to sixth generation) during exercise at sea level and at high altitude. The computational fluid dynamics (CFD) solver FLUENT is used to solve the governing equations for unsteady airflow in the model. Flow velocity, pressure and wall shear stress were obtained from the simulations with the two breathing conditions. The result of this study quantitatively showed that performing exercise with a given work rate at high altitude increases inspiratory airflow velocity, pressure and wall shear stress more than at sea level in the airway model. The ranges of the airflow fields are also higher at high altitude than at sea level. The simulation results show that there no significant differences in flowing pattern for the two breathing conditions.Sat, 12 May 2018 19:30:00 +0100SOME NEW EXISTENCE, UNIQUENESS AND CONVERGENCE RESULTS FOR FRACTIONAL VOLTERRA-FREDHOLM ...
http://jacm.scu.ac.ir/article_13592_0.html
This paper demonstrates a study on some significant latest innovations in the approximated techniques to find the approximate solutions of Caputo fractional Volterra-Fredholm integro-differential equations. To apply this, the study uses modified Adomian decomposition method (MADM) and modified variational iteration method (MVIM). A wider applicability of these techniques are based on their reliability and reduction in the size of the computational work. This study provides analytical approximate to determine the behavior of the solution. It proves the existence and uniqueness results and convergence of the solution. In addition, it brings an example to examine the validity and applicability of the proposed techniques.Mon, 14 May 2018 19:30:00 +0100Damage Identification in a Multi-DOF System under Uncertainties Using Optimization Algorithms
http://jacm.scu.ac.ir/article_13593_0.html
In this article four optimization algorithms are applied to identify damage in a multi-DOF dynamical system, composed by masses, springs and dampers. The damage is introduced artificially by choosing a lower value for the stiffness. The algorithms applied are: Nelder-Mead Simplex, BFGS Quasi-Newton, interior point, and sequential quadratic programming - SQP. In addition, some different strategies to identify damage are applied. First, a deterministic analysis is performed to identify the damage; i.e, the values of the stiffnesses. Then, random forces are considered, and after, the stiffness values are considered uncertain. The difference among the results are analyzed.Fri, 18 May 2018 19:30:00 +0100Study on free vibration and wave power reflection in functionally graded rectangular plates ...
http://jacm.scu.ac.ir/article_13595_0.html
In this paper, the wave propagation approach is presented to analyze the vibration and wave power reflection in FG rectangular plates based on first order shear deformation plate theory. Wave propagation is one of the useful methods for analyzing the vibration of structures. Wave propagation method gives the reflection and propagation matrices that are valuable for the analysis of mechanical energy transmission in devices. It is assumed that the plate has two opposite edges simply supported while the other two edges may be simply supported or clamped. It is the first time that the wave propagation method is used for functionally graded plates. In this study, firstly the matrices of reflection and propagation are derived. Then, these matrices are combined to provide an exact method for obtaining the natural frequencies. It is observed that obtained results of the wave propagation method are in good agreement with the obtained values by literature. At the end the behavior of reflection coefficients for FG plates are studied for the first time.Mon, 21 May 2018 19:30:00 +0100High order compact fnite difference schemes for solving Bratu-type equations
http://jacm.scu.ac.ir/article_13596_0.html
In this paper, we use high order compact finite difference methods to solve one-dimensional Bratu-type equations numerically. The convergence analysis of the methods are discussed and it is shown that the theoretical order of the method is consistent with its numerical rate ofconvergence. We calculate the maximum absolute errors in the solution at grid points and show that our presented methods are efficient and applicable for lower and upper solutions.Mon, 21 May 2018 19:30:00 +0100On the buckling response of axially pressurized nanotubes based on a novel nonlocal beam theory
http://jacm.scu.ac.ir/article_13600_0.html
In the current study, buckling analysis of single-walled carbon nanotubes (SWCNT) on the basis of a new refined beam theory has been analyzed. The SWCNT is modeled as an elastic beam subjected to unidirectional compressive loads. To achieve this aim, the new proposed beam theory has only one unknown variable which lead to one equation similar to Euler beam theory and also is free of any shear correction factor. The equilibrium equation has been formulated by the nonlocal elasticity theory in order to predict small-scale effects. The equation has been solved by Navier’s approach by which critical buckling loads have been obtained for simple boundary conditions. Finally, to approve the results of the new beam theory, some available well-known references have been compared.Fri, 25 May 2018 19:30:00 +0100Topology Optimization of the Thickness Profile of Bimorph Piezoelectric Energy Harvesting Devices
http://jacm.scu.ac.ir/article_13608_0.html
Due to developments in Additive Manufacturing, the production of piezoelectric materials with complex geometries is becoming viable, enabling the manufacturing of thicker harvesters. Thus, in this article a piezoelectric harvesting device is modelled as a bimorph cantilever beam with series connection, with an intermediate metallic substrate, under plain strain hypothesis. Then the thickness of the piezoelectric material of the harvester is structurally optimized using a discrete topology optimization method. Different optimization parameters are varied to study the algorithm’s convergence. The results of the optimization are displayed and analyzed, to study the influence of the harvester's geometry and its different substrate materials on the harvester’s energy conversion efficiency.Tue, 29 May 2018 19:30:00 +0100Buckling and postbuckling of concentrically stiffened piezo-composite plates on elastic foundations
http://jacm.scu.ac.ir/article_13630_0.html
This paper presents the modeling and analysis for the buckling and postbuckling behavior of sandwich plates subjected to thermal and mechanical loads. The lay-up configurations of plates are laminated composite with concentric stiffener and surface mounted piezoelectric actuators. The plates are in contact with three parameter elastic foundation with softening and/or hardening nonlinearity. Several types of grid shapes of stiffeners are studied such as ortho grid, angle grid, iso grid, and orthotropic grid. The equilibrium and compatibility equations of structures are formulated based on Kirchhoff assumptions with taking into account von-Karman nonlinear relationships. The equations are solved in two types of boundary conditions by definitions of the stress function and applying the Galerkin method. Numerical examples are well verified with available data in the literature. Several parametric investigations are conducted to examine the simultaneous effects of voltage through the thickness of piezoelectric actuators, different stiffeners, and nonlinear elastic foundations.Sat, 09 Jun 2018 19:30:00 +0100A Review of Solar Energy Collectors: Models and Applications
http://jacm.scu.ac.ir/article_13648_0.html
A current study and discussion in detail about many solar energy collectors of various types, components, classifications and configurations, through the analysis of their performance, is our aim through this review paper. The effects of the geometrical parameters of the solar air collectors as well as the functioning parameters on heat transfer and fluid flow processes were also discussed in detail. The numerical, analytical, and experimental analyses on different models of flat plate solar air collectors with various thermal transfer enhancement strategies were shown in various stages, i.e., modelling, control, measurement, and visualization of airfield, determination of heat transfer, control of friction loss and pressure drop, and evaluation of the thermal performance by the measurement of the augmentation in the temperature of the working fluid at a given solar irradiance and under given flow rate. We concluded this review by identifying the various applications possible for the solar air collectors such as heating and cooling of houses, drying agricultural food materials, and water desalination process.Fri, 15 Jun 2018 19:30:00 +0100Generalized 2-unknown’s HSDT to study isotropic and orthotropic composite plates
http://jacm.scu.ac.ir/article_13649_0.html
This paper introduces a generalized 2-unknown’s higher order shear deformation theory (HSDT) for isotropic and orthotropic plates. The well-known Shimpi’s two-unknown's HSDT is reproduced as special case. Reddy’s shear strain shape function (SSSF) can be also adapted to the present generalized theory. Results show that both Shimpi and the adapted Reddy’ HSDT are essentially the same, i.e. both present the same static results. This is due to the fact that both theories use polynomial SSSFs. This study presents a new optimized cotangential SSSF. The generalized governing equation obtained from the principle of virtual displacement is solved via the Navier closed-form solution. Results show that transverse shear stresses can be improved substantially when non-polynomial SSSFs are utilized. Finally, this theory is attractive and has potential to study other mechanical problems such as bending in nanoplates due to its reduced number of unknown’s variables.Sat, 16 Jun 2018 19:30:00 +0100Magnetohydrodynamic Free Convection Flows with Thermal Memory over a Moving Vertical Plate in ...
http://jacm.scu.ac.ir/article_13666_0.html
The unsteady hydro-magnetic free convection flow with heat transfer of a linearly viscous, incompressible, electrically conducting fluid near a moving vertical plate with constant heat is investigated. The flow domain is the porous half-space and a magnetic field of variable direction is applied. The Caputo time-fractional derivative is employed in order to introduce a thermal flux constitutive equation with a weakly memory. Exact solutions of the fractional governing differential equations for fluid temperature, Nusselt number, velocity field and skin friction are obtained by using the Laplace transform method. Numerical calculations are carried out and results are presented in graphical illustrations. The influence of the memory parameter (the fractional order of the time-derivative) on the temperature and velocity fields is analyzed and a comparison between the fluid with thermal memory and the ordinary fluid is made. It was observed that, due to evolution in time of the Caputo power-law kernel, the memory effects are stronger for the small values of the time t. Also, it is found that fluid flow is accelerated / retarded by the varying the inclination angle of the magnetic field direction.Sat, 23 Jun 2018 19:30:00 +0100Elastic-Plastic Analysis of Bending Moment – Axial Force Interaction in Metallic Beam of T-Section
http://jacm.scu.ac.ir/article_13667_0.html
This paper derives kinematic admissible bending moment – axial force (M-P) interaction relations for mild steel by considering elastic-plastic idealisations. The interaction relations can predict strains, which is not possible in a rigid, perfectly plastic idealization. The relations are obtained for all possible cases pertaining to the locations of neutral axis. One commercial rolled steel T-section has been considered for studying the characteristics of interaction curves for different models. On the basis of these interaction curves, most significant cases for the position of neutral axis which are enough for the establishment of interaction relations have been suggested.Sat, 23 Jun 2018 19:30:00 +0100Numerical investigation of the effect of bubble-bubble interaction on the power of propagated ...
http://jacm.scu.ac.ir/article_13672_0.html
The study of bubble dynamics, especially the interaction of bubbles has drawn considerable attention due to its various applications in engineering and science. Meanwhile, the study of the oscillation effect of a bubble on the emitted pressure wave of another bubble in an acoustic field has less been investigated. This issue is studied in the present paper using the coupling of Keller-Miksis and Gilmore models. The ordinary differential equations are solved using MATLAB software and Runge-Kutta forth order method with adaptive step size control. The results show the dependence of bubbles behavior and the strength of their pressure waves on two parameters of the initial radius and bubbles center-to-center distance. As the initial radius of the adjacent bubble grows, its effect on the other bubble increases and causes a reduction in the other bubble maximum radius, wall velocity, internal pressure and emitted pressure wave intensity. However, increasing the initial distance of the bubbles reduces the effect of the bubbles on each other and causes their behaviors become closer to single-bubble oscillation mode.Wed, 27 Jun 2018 19:30:00 +0100A novel approach for Korteweg-de Vries equation of fractional order
http://jacm.scu.ac.ir/article_13674_0.html
In this paper, we utilize local fractional variational iteration method (LFVIM) and local fractional series expansion method (LFSEM) to obtain approximate solutions for Korteweg-de Vries equation (KdVE) within local fractional derivative operators (LFDOs). The efficiency of the considered methods is illustrated by some examples. The results reveal that the suggested algorithms are very effective and simple and can be applied for linear and nonlinear problems in mathematical physics.Mon, 02 Jul 2018 19:30:00 +0100Experimental study of the residual stresses in girth weld of natural gas transmission pipeline
http://jacm.scu.ac.ir/article_13695_0.html
In order to achieve integrated condition in the girth welding of high pressure natural gas transmission pipelines, the weld zones and its surrounding area should have homogeneous mechanical properties as possible. Residual stresses are an important defect specially in the girth welding of pipeline. In this paper, two API X70 steel pipes (with spiral seam weld) of 56 inches outside diameter and 0.780 inch wall thickness were girth welded first. Hole drilling tests were conducted for residual stress measurement on the surfaces of the pipes. Hoop tensile residual stress on the external surface of the pipe with maximum value equal to 318-MPa was measured on the weld centerline. Hoop residual stress distributions in the internal and external surface of the pipe were approximately similar. The maximum axial residual stress was observed in the heat affected zone (a distance of approximately 30 mm from weld centerline). The maximum axial residual stress on the external surface of the pipe was tensile, equal to 137 MPa and on the internal surface of the pipe was compressive equal to 135-MPa. Axial residual stress magnitudes in the weld centerline on the internal and external surfaces of the pipe were close together. Away from the weld centerline, axial residual stresses on the internal and external surface shown opposite behavior. Thus, in the girth welding of natural gas transmission pipelines, peripheral direction on the internal surface of the pipe is the critical zone and have the highest tensile residual stresses.Thu, 12 Jul 2018 19:30:00 +0100Effect of thermal conductivity and emissivity of solid walls on time-dependent turbulent ...
http://jacm.scu.ac.ir/article_13714_0.html
Conjugate turbulent free convection with thermal surface radiation in a rectangular enclosure bounded by walls with different thermophysical characteristics in the presence of a local heater has been numerically studied. The effects of surface emissivity and wall materials on the air flow and heat transfer characteristics were the main focus of the present investigation. Conjugate convective heat transfer for the fluid (air), described in terms of linear momentum, continuity and energy equations combined with k-ε turbulence model, was predicted by using the finite difference method. Results for the isotherms, streamlines and average Nusselt numbers along the heat source are presented. The numerical experiments showed that an increase in thermal conductivity of solid walls illustrates the enhancement of heat transfer. Eventually, the main result obtained in this work provides good technical support for the development and research of energy-efficient building materials.Fri, 27 Jul 2018 19:30:00 +0100NURBS-BASED ISOGEOMETRIC ANALYSIS METHOD APPLICATION TO MIXED-MODE COMPUTATIONAL FRACTURE MECHANICS
http://jacm.scu.ac.ir/article_13715_0.html
An interaction integral method for evaluating mixed-mode stress intensity factors (SIFs) for two dimensional crack problems using NURBS-based isogeometric analysis method is investigated. The interaction integral method is based on the path independent J-integral. By introducing a known auxiliary field solution, the mixed-mode SIFs are calculated simultaneously. Among features of B-spline basis functions the possibility of enhancing a B-spline basis with discontinuities by means of knot insertion makes isogeometric analysis method a suitable candidate for modelling discrete cracks. Also repetition of two different control points between two patches can create a discontinuity and also demonstrates a singularity in the stiffness matrix. In the case of a pre-defined interface, non-uniform rational B-splines are used to obtain an efficient discretization. Various numerical simulations for edge and center cracks demonstrate the suitability of the isogeometric analysis approach to fracture mechanics.Fri, 27 Jul 2018 19:30:00 +0100Analysis of fluid dynamics and heat transfer in a rectangular duct with staggered baffles
http://jacm.scu.ac.ir/article_13717_0.html
This computational fluid dynamic analysis attempts to simulate the incompressible steady fluid flow and heat transfer in a solar air channel with wall-mounted baffles. Two ꞌSꞌ-shaped baffles, having different orientations, i.e. ꞌSꞌ-upstream and ꞌSꞌ-downstream, were inserted into the channel and fixed to the top and bottom walls of the channel, in a periodically staggered manner to develop vortices to improve the mixing and consequently the heat transfer. The analyses are conducted with the Commercial CFD software FLUENT using the finite volume method, for Reynolds number varying from 12,000 to 32,000. The numerical results are presented in terms of streamlines, velocity-magnitude, x-velocity, y-velocity, dynamic pressure coefficient, turbulent kinetic energy, turbulent viscosity, turbulent intensity, temperature field, coefficient and factor of normalized skin friction, local and average numbers of normalized Nusselt, and thermal performance factor. The insertion of the S-shaped baffles in the channel causes a much high friction loss, f/f0 = 3.319 - 32.336 but also provides a considerable increase in the thermal transfer rate in the channel, Nu/Nu0 = 1.939 - 4.582, depending on S-baffle orientations and Reynolds number. The S-upstream baffle provides higher friction loss and heat transfer rate than the S-Downstream around 56.443 %, 55.700 %, 54.972 %, 54.289 % and 53.660 %; and 25.011 %, 23.455 %, 21.977 %, 20.626 % and 19.414 % for Re = 12,000, 17,000, 22,000, 27,000 and 32,000, respectively. In addition, the result analysis shows that the optimum thermal performance factor is around 1.513 at highest Reynolds number and S-downstream.Sat, 28 Jul 2018 19:30:00 +0100