Journal of Applied and Computational MechanicsJournal of Applied and Computational Mechanics
http://jacm.scu.ac.ir/
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http://jacm.scu.ac.ir/
Feed provided by Journal of Applied and Computational Mechanics. Click to visit.Nonlinear Dynamic Response of Functionally Graded Porous Plates on Elastic Foundation Subjected ...
http://jacm.scu.ac.ir/article_13360_1659.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 loadings supported by Pasternak’s model of the elastic foundation. Two types of porosity including evenly distributed porosities (Porosity-I) and unevenly distributed porosities (Porosity-II) are assumed as effective properties of FGM plates such as Young’s modulus, the coefficient of thermal expansion, and density. The strain-displacement formulations using Von Karman geometrical nonlinearity and general Hooke’s law are used to obtain constitutive relations. Airy stress functions with full motion equations which is employed to shorten the number of governing equations along 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 are determined. By employing Runge-Kutta method, the numerical results illustrate the influence of geometrical configurations, volume faction index, porosity, elastic foundations, and mechanical as well as thermal loads on the nonlinear dynamic response of the plates. Good agreements are obtained in comparison with other results in the literature.Sun, 30 Sep 2018 20:30:00 +0100Stability Analysis of a Strongly Displacement Time-Delayed Duffing Oscillator Using Multiple ...
http://jacm.scu.ac.ir/article_13341_1659.html
In the present study, some perturbation methods are applied to Duffing equations 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 is applied through the frequency analysis and 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 is formulated. Comparing these two approaches reveals the accuracy of using the second approach and further allows studying the stability behavior. Numerical simulations are carried out to validate the analytical finding.Sun, 30 Sep 2018 20:30:00 +0100Determination of the Optimal Reduction Ratio for Least Springback during Cold Drawing of ...
http://jacm.scu.ac.ir/article_13433_1659.html
Cold drawing process is one of the most used metals forming processes in industries for forming 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 the release of forming force, the springback occurs. In this paper, the springback effect of the seamless tube that has undergone cold drawing is studied for three different reduction ratios viz.10-15 %,15-20 %, and 20-25 % having the aim to reduce it. Experiments are conducted under different reduction ratios with working conditions of die semi angles of 10 and 15 degrees, 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 via cold draw load, and hardness testing for different reduction ratios are also studied for validation purposes. The results of this research show that 10-15 % reduction ratio yields the minimum springback. This can be used to help designing tools in the metal forming industry to minimize springback and improve the quality of the product.Sun, 30 Sep 2018 20:30:00 +0100Free Convection Flow of an Electrically-Conducting Micropolar Fluid between Parallel Porous ...
http://jacm.scu.ac.ir/article_13474_1659.html
In the present study, the effect of temperature-dependent heat sources on the fully developed free convection flow of an electrically conducting micropolar fluid between two parallel porous vertical plates in the presence of 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 the differential transform method (DTM). Moreover, the Runge-Kutta shooting method (RKSM), which is a numerical method, is used for the validity of DTM method and an 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, the couple stress, and Nusselt numbers at the plates are shown in graphs. It is observed that the Hartmann number and the micropolar parameter decreases the skin friction and the couple stress at both plates for suction and injection.Sun, 30 Sep 2018 20:30:00 +0100An Analysis of Thermal-Bending Stresses in a Simply Supported Thin Elliptical Plate
http://jacm.scu.ac.ir/article_13400_1659.html
In this paper, a transient thermal stress investigation on a simply supported thin elliptical plate during sectional heating with time-dependent temperature supply is considered. The solution of heat conduction equation with corresponding initial and boundary conditions is obtained by employing an integral transform approach. The governing equation solution for the small deflection theory is obtained and utilized to preserve the intensities of thermal bending moments, involving the Mathieu and modified functions and its derivatives. The deflection results show an approximately good agreement with the previously given results. It is also demonstrated that the temperature field in a circular solution could be resulted in a particular case of the present mathematical solution. The obtained numerical results utilizing computational implements are precise enough for practical purposes.Sun, 30 Sep 2018 20:30:00 +0100Clogged Impeller Diagnosis in the Centrifugal Pump Using the Vibration and Motor Current Analysis
http://jacm.scu.ac.ir/article_13564_1659.html
The impeller-clogging phenomenon in centrifugal pumps is such a kind of the fault 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 the detection of 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 the 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, the electrical current consumption of electromotor is reducedSun, 30 Sep 2018 20:30:00 +0100A Study of Model Separation Flow Behavior at High Angles of Attack Aerodynamics
http://jacm.scu.ac.ir/article_13517_1659.html
This paper analyzes the aerodynamic performance and flow separation characteristics of a rectangular wing for varying Reynolds numbers. The mechanism of separation and its effect on the rectangular wing were simulated in ANSYS FLUENT using K-ω SST turbulence model. A detailed analysis was performed to discuss aspects like 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, and the effect of wing tip vortices. The simulation results showed that by increasing the angles of attack, the separation point moves towards the leading edge and the onset of stalling is very much closer to the leading edge. Also, the experimental and numerical results indicated that NACA4415 airfoil had enhanced coefficient of lift to coefficient of drag ratio at the angles of attack (AoA) ranging between 4◦ and6◦,which are distinctively advantageous for the better performance of small-scale wind turbine rotors. The experimental and computational results were analyzed in the context of effective change in stalling characteristics at different Reynolds numbers.Sun, 30 Sep 2018 20:30:00 +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 +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 +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 +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 +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 +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 +0100Evaluation of the Best New Cross-ply Laminated Plate Theories through the Axiomatic/Asymptotic ...
http://jacm.scu.ac.ir/article_13516_1659.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 built 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.Sun, 30 Sep 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_1659.html
This study presents a computational investigation 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 research work 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.Sun, 30 Sep 2018 20:30:00 +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_1659.html
In this study, four optimization algorithms are applied to identify the damage in a multi-DOF dynamical system composed of masses, springs, and dampers. The damage is introduced artificially by choosing a lower value for the stiffness. The applied algorithms include 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 finally, the stiffness values are considered uncertain and the different strategies are compared.Sun, 30 Sep 2018 20:30:00 +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_1659.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.Sun, 30 Sep 2018 20:30:00 +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 +0100Time discontinuous finite element analysis of two-dimensional elastodynamic problems using ...
http://jacm.scu.ac.ir/article_13727_0.html
This paper reformulates a time-discontinuous finite element method (TD-FEM) based on a new class of shape functions, called complex Fourier hereafter, for solving two-dimensional elastodynamic problems. These shape functions, which are derived from their corresponding radial basis functions, have some advantages such as the satisfaction of exponential and trigonometric function fields in complex space as well as the polynomial ones simultaneously, that make them a better choice than classic Lagrange shape functions, which only can satisfy polynomial function field. To investigate the validity and accuracy of the proposed method, three numerical examples are provided and the results obtained from the present method (complex Fourier-based TD-FEM) and the classic Lagrange-based TD-FEM are compared with the exact analytical solutions. According to them, using complex Fourier functions in TD-FEM leads to more accurate and stable solutions rather than those obtained from the classic TD-FEM.Tue, 21 Aug 2018 19:30:00 +0100A GENERAL RULE FOR THE INFLUENCE OF PHYSICAL DAMPING ON NUMERICAL STABILITY OF TIME INTEGRATION ...
http://jacm.scu.ac.ir/article_13728_0.html
The influence of physical damping on numerical stability of time integration analysis is an open question since decades ago. In this paper, it is shown that, under specific very general conditions, physical damping can be disregarded when studying the numerical stability. It is also shown that, provided the specific conditions, analysis of structural systems involved in extremely high linear-viscous damping are unconditionally stable. A secondary achievement is that the increase of linear-viscous damping can increase or decrease the numerical damping.Fri, 24 Aug 2018 19:30:00 +0100Experimental and Numerical Investigations on the Effect of Rectangular Openings’ Aspect Ratio ...
http://jacm.scu.ac.ir/article_13729_0.html
Up to now, a few formulas have been suggested by scholars for the amount of discharge from openings, however, the effect of opening's geometry on the amount of discharge has not addressed thoroughly. In this study, to assess the effect of rectangular openings’ aspect ratio on the discharge amount, experimental and numerical investigations have been conducted on the discharge amount from rectangular openings at the bottom of tanks. In the experimental part of the study different water depths have been considered and the amounts of discharge have been measured for openings with identical area, but different aspect ratios. In the numerical part of the study the test results have been compared to those obtained from finite-volume-based numerical simulation. The experimental and numerical results are in good agreement, and both show that there is a trend of increase in the amount of discharge with increase of the opening’s aspect ratio. The amount of this increase is from 13% to 21% for hydraulic head varying between 0.3 to 0.6 meters. On this basis, the conventional orifice formula for calculation of the rectangular opening discharge needs modification.Tue, 28 Aug 2018 19:30:00 +0100Fractional thermoelasticity model of a 2D problem of mode-I crack in a fibre-reinforced thermal ...
http://jacm.scu.ac.ir/article_13730_0.html
A model of fractional-order of thermoelasticity is applied to study a 2D problem of mode-I crack in a fibre-reinforced thermal environment. The crack is under prescribed distributions of heat and pressure. Normal mode analysis is applied to deduce exact formulae for displacements, stresses, and temperature. Variations of field quantities with axial direction are illustrated graphically. The results regarding the presence and absence of fiber reinforcement and fractional parameters will be compared. Some particular cases are also investigated via the generalized thermoelastic theory. The presented results can be applied to design different fibre-reinforced isotropic thermoelastic elements subjected to thermal load in order to meet special technical requirements.Thu, 06 Sep 2018 19:30:00 +0100Accuracy Assessment of Ultrasonic C-scan and X-ray radiography Methods for Impact Damage ...
http://jacm.scu.ac.ir/article_13731_0.html
The present study introduces two quantitative parameters for comparing the accuracy of ultrasonic C-scan testing and X-ray radiography methods in damaged area detection under low-velocity impact in polymer-based composites. For this purpose, the hand lay-up technique of composite processing was employed to prepare the composite specimen. A composite specimens consisting of glass fiber reinforced with unsaturated polyester resin was considered for this investigation. Impact tests at different energy levels were carried out on this composite specimen to create three damaged areas in it. Because the glass/polyester specimen had a transparent surface, a digital scanner was used to obtain an ideal image from the specimen for presenting the region and edge of the impacted areas in it. Two image quality factors as quantitative parameters were introduced for comparing the ultrasonic C-scan and X-ray radiography results with those of an ideal image. Our results showed that the ultrasonic C-scan is a more accurate method for inspection of the GFRP specimen.Thu, 06 Sep 2018 19:30:00 +0100Experimental Study on the surface modification by Electrical Discharge Process
http://jacm.scu.ac.ir/article_13732_0.html
The creation of modified layer on metals surfaces by the use of new methods is one of the methods in surface engineering which can improve the surface mechanical properties. Electrical discharge process is a new method that can form a modified layer on the metals surface. This paper aims to improve of pure aluminum surface properties through Electrical Discharge process with Monel 400 electrode. In order to design the experiments, pulse on time and pulse current were considered as input parameters. The SEM images indicated that the increase in pulse on time and pulse current can increase the thickness of modified layer. Based on the obtained results, the thickness of improved layer varied between 35 to 75 microns. The results of the EDX analysis indicated the diffusion of copper and nickel to the aluminum surface. Also, the results of microhardness testing of surface layer showed that after Electrical discharge process, the surface hardness has increased and the surface hardness as 35 Vickers has reached more than 400 Vickers.Thu, 06 Sep 2018 19:30:00 +0100Thermoelastic vibration of temperature-dependent nanobeams due to rectified sine wave ...
http://jacm.scu.ac.ir/article_13733_0.html
In this paper, the second type of Green and Naghdi's thermoelasticity theory is applied to present the vibration of a nanobeam subjected to rectified sine wave heating based upon the nonlocal thermoelasticity theory. Both Young's modulus and thermal conductivity are considered to be linear functions of the temperature. Laplace transform domain is adopted to solve the governing partial differential equations using the state space approach. Numerical computations are carried out using the inverse of Laplace transforms. Effects of nonlocal parameter and angular frequency on thermal vibration quantities are discussed. Results of all quantities are illustrated graphically and investigated.Sun, 09 Sep 2018 19:30:00 +0100Bending and free vibration analysis of functionally graded plates via optimized non-polynomial ...
http://jacm.scu.ac.ir/article_13739_0.html
Optimization concept in the context of shear deformation theories was born for the development of accurate models to study the bending problem of structures. The present paper seeks to extend such approach to the dynamic analysis of plates. A compact and unified formulation with non-polynomial shear strain shape functions (SSSFs) is employed to develop a static and free vibration analysis of simply supported functionally graded plates. In this context, three new non-polynomial displacement fields are proposed using trigonometric and hyperbolic SSSFs. Then, the non-polynomial SSSFs are optimized varying the arguments of the trigonometric and hyperbolic functions. Additionally, the Mori-Tanaka approach is used to estimate the effective properties of the functionally graded plates. Principle of Virtual Displacement (PVD) and Hamilton’s Principle along with the Navier closed-form solution technique are used in order to obtain exact results. The obtained numerical results are in good agreement with 3D and 2D higher order shear deformation theory solutions available in the literature.Thu, 13 Sep 2018 19:30:00 +0100A New Quasi-3D Model for Functionally Graded Plates
http://jacm.scu.ac.ir/article_13807_0.html
This article investigates the static behaviour of functionally graded plate under mechanical loads using a new quasi 3D model. The theory is designated as fifth-order shear and normal deformation theory (FOSNDT). Properties of functionally graded material are graded across the transverse direction using rule of mixture i.e. power law. The effect of thickness stretching is considered to develop the present theory. In this theory, axial and transverse displacement components involve fifth-order and fourth order shape functions respectively to evaluate shear and normal strains. The theory involves nine unknowns. Zero transverse shear stress conditions are satisfied using constitutive relations. Analytical solutions are obtained using double Fourier series technique. The results predicted by the FOSNDT are compared with existing results. It is pointed out that the present theory is helpful for accurate structural analysis of isotropic and functionally graded plates compared to other plate models.Sun, 30 Sep 2018 20:30:00 +0100On The Use of Acoustic Emission and Digital Image Correlation for Welded Joints Damage ...
http://jacm.scu.ac.ir/article_13822_0.html
A series of tests has been conducted to investigate fatigue damage characterisation in corroded welded steel plates using structural health monitoring (SHM) techniques. AE is a non-destructive testing (NDT) technique with potential applications for locating and monitoring fatigue cracks in service. In the present work, AE was used to characterise damage during crack evolution based on the relationship between RA value (the rise time divided by the amplitude) and the average frequency of the recorded data. Results were confirmed by visual observation of the crack geometry at the end of the test and by Digital Image Correlation (DIC) measurements. The results obtained allowed a more detailed understanding of such damage mechanisms, enabling an early warning against final failure and hence ensuring the safety and integrity of the structures.Sat, 06 Oct 2018 20:30:00 +0100Effect of exponentially variable viscosity and permeability on Blasius flow of Carreu nanofluid ...
http://jacm.scu.ac.ir/article_13834_0.html
The present investigation brings attention regarding the effect of exponential variable viscosity modeled by Vogel and variable permeability on stagnation point flow of Carreu nanofluid over an electromagnetic plate through a porous medium. Brownian motion and thermophoretic diffusion mechanism are taken into consideration. An efficient fourth order R K method along with shooting technique is used to obtain the required solution of the non-dimensional modeled equations. The contribution of the present study is that augmented electromagnetic field strength due to suitable arrangement of the plate and that of porosity parameter yield an accelerated motion while that of viscosity parameter produces retarded motion of shear thickening fluid, however, contrary to shear thinning fluid. At the same time it brings about an outcome that inclusion of porous matrix controls the thermal as well as concentration boundary layers while enhanced Brownian motion exhibits diametrically opposite trend for them in response to shear thickening fluid.Sun, 07 Oct 2018 20:30:00 +0100ISOGEOMETRIC TOPOLOGY OPTIMISATION OF CONTINUUM STRUCTURES USING EVOLUTIONARY ALGORITHM
http://jacm.scu.ac.ir/article_13835_0.html
Topology optimization has been an interesting area of research in the recent years. The main focus of this paper is to use evolutionary swarm intelligence algorithm to perform Isogeometric Topology optimization of continuum structures. A two dimensional plate is analysed statically and the nodal displacements are calculated. The nodal displacements using Isogeometric analysis were found to be in good agreement with the nodal displacements obtained using standard finite element analysis. The sizing optimization of the beam is then performed. The formulation to determine the stress at any point in the beam is presented. The optimal cross section dimensions by performing Isogeometric analysis are obtained and verified with the cross section dimensions obtained by using bending stress and shear stress criteria as well. The topology optimization of a two dimensional simply supported plate continuum and a problem on three dimensional continuum are optimized and presented. The results show that the minimum weight obtained by applying Isogeometric topology optimization gives better results over traditional finite element analysis.Sun, 07 Oct 2018 20:30:00 +0100Electro-magneto-hydrodynamics flows of Burgers fluids in cylindrical domains with time ...
http://jacm.scu.ac.ir/article_13836_0.html
This paper investigates the axial unsteady flow of a generalized Burgers’ fluid with fractional constitutive equation in a circular micro-tube, in presence of a time-dependent pressure gradient and an electric field parallel to flow direction and a magnetic field perpendicular on the flow direction. The mathematical model used in this work is based on a time-nonlocal constitutive equation for shear stress with time-fractional Caputo-Fabrizio derivatives; therefore, the histories of the velocity gradient will influence the shear stress and fluid motion. Thermal transport is considered in the hypothesis that the temperature of the cylindrical surface is constant. Analytical solutions for the fractional differential momentum equation and energy equation are obtained by employing the Laplace transform with respect to the time variable t and the finite Hankel transform with respect to the radial coordinate r. It is important to note that the analytical solutions for many particular models such as, ordinary/fractional Burgers fluids, ordinary/fractional Oldryd-B fluids, ordinary/fractional Maxwell fluids and Newtonian fluids, can be obtained from the solutions for the generalized fractional Burgers' fluid by particularizing the material coefficients and fractional parameters. By using the obtained analytical solutions and the Mathcad software, we have carried out numerical calculations in order to analyze the influence of the memory parameters and magnetic parameter on the fluid velocity and temperature. Numerical results are presented in graphical illustrations. It is found that ordinary generalized Burgers’ fluids flow faster than the fractional generalized Burgers’ fluids.Thu, 11 Oct 2018 20:30:00 +0100Transient MHD convective flow of fractional nanofluid between vertical plates
http://jacm.scu.ac.ir/article_13837_0.html
Effects of the uniform transverse magnetic field on the transient free convective flowsof a nanofluid with generalized thermal transport between two vertical parallel plates have beenanalyzed. The fluid temperature is described by a time-fractional differential equation withCaputo derivatives. Closed form of the temperature field is obtained by using the Laplacetransform and fractional derivatives of the Wright’s functions. A semi-analytical solution for thevelocity field is obtained by using the Laplace transform coupled with the numerical algorithmsfor the inverse Laplace transform elaborated by Stehfest and Tzou. Effects of the derivativefractional order and physical parameters on the nanofluid flow and heat transfer are graphicallyinvestigated.Thu, 11 Oct 2018 20:30:00 +0100Residual power series method for solving time-fractional model of vibration equation of large ...
http://jacm.scu.ac.ir/article_13838_0.html
The primary aim of this manuscript is to present the approximate analytical solutions of the time fractional order Vibration Equation (VE) of large membranes with the use of aniterative technique namely Residual Power Series Method (RPSM). The fractional derivative isdefined in Caputo sense. Example problems have been solved to demonstrate the efficacy of the present method and the results obtained are verified graphically. The convergence analysis of the proposed method has also been included in this article. It is seen that the present method is found to be reliable, very effective and easy to implement for various kinds of fractional differential equations used in science and engineering.Thu, 11 Oct 2018 20:30:00 +0100The solar air channels: Comparative analysis, introduction of arc-shaped fins to improve the ...
http://jacm.scu.ac.ir/article_13839_0.html
The problem under investigation contains a computational simulation of a specific heat exchanger with complex geometry fins. The problem solved is potentially interesting for researchers and engineers working on solar collectors and aerospace industry. It is known that heat transfer enhancement can be achieved by creating longitudinal vortices in the flow. These vortices can be generated by arc-shaped fins, and a computational analysis of such solar air channels is not a simple task. Therefore, we used a present-day commercial CFD code to solve the problem. The mathematical problem including the main equations and their explanation, as well as the numerical procedure was presented. The impact of arc-fins’ spacings on streamlines and temperature distributions was completely investigated, as well as the heat transfer rate, pressure drop and thermal enhancement factor. The Nusselt number (Nu) and friction loss (f) values of the solar air channel at AR = 1.321 (aspect ratio of channel width-to-height) and S = Pi/2 are found to be around 11.963 % and 26.006 %; 21.645 % and 40.789 %; 26.196 % and 50.314 %; and 30.322 % and 58.355 % higher than that with S = 3Pi/4, Pi, 5Pi/4 and 3Pi/2, respectively. Importantly, the arc-fins with Re = 12,000 at S = Pi/2 showed higher thermal enhancement performance than the one at S = 3Pi/4, Pi, 5Pi/4 and 3Pi/2 around 2.530 %, 6.576 %, 6.615 % and 6.762 %, respectively. This study contains the information which seems to be important for practical engineers.Thu, 11 Oct 2018 20:30:00 +0100Modified multi-level residue harmonic balance method for solving nonlinear vibration problem of ...
http://jacm.scu.ac.ir/article_13841_0.html
Nonlinear vibration behavior of beam is an important issue of structural engineering. In this study, a mathematical modeling of a forced nonlinear vibration of Euler-Bernoulli beam rest on nonlinear elastic foundation is presented and the nonlinear vibration behavior of the beam is investigated by using a modified multi-level residue harmonic balance method. The main advantage of the method is that only one nonlinear algebraic equation is generated at each solution level. The computational time of using the new method is much less than that spent on solving the set nonlinear algebraic equations generated in the classical harmonic balance method. Besides the new method can generate higher-level nonlinear solutions neglected by previous multi-level residue harmonic balance methods. The results obtained from the proposed method compared with the results obtained by a classical harmonic balance method to verify the accuracy of the method which shows good agreement between the proposed and classical harmonic balance method. Besides, the effect of various parameters such as excitation magnitude, linear and nonlinear foundation stiffness, shearing stiffness etc. on the nonlinear vibration behaviors are examined.Sat, 13 Oct 2018 20:30:00 +0100Traveling Waves of Some Symmetric Planar Flows of Non-Newtonian Fluids
http://jacm.scu.ac.ir/article_13842_0.html
We present some variants of Burgers-type equations for incompressible and isothermal planar flow of viscous non-Newtonian fluids based on the Cross, the Carreau, the Power-law rheology models, and a symmetry assumption on the flow. We numerically solve the associated traveling wave equations by using industrial data and prove existence and uniqueness of solutions to the equations for validation of the models. We also provide numerical estimates of the shock thickness as well as maximum strain associated with the traveling waves.Sat, 13 Oct 2018 20:30:00 +0100Axial and torsional free vibrations of elastic nano-beams by stress-driven two-phase elasticity
http://jacm.scu.ac.ir/article_13843_0.html
Size-dependent longitudinal and torsional vibrations of nano-beams are examined by two-phase mixture integral elasticity. A new and efficient elastodynamic model is conceived by convexly combining the local phase with strain- and stress-driven purely nonlocal phases. The proposed stress-driven nonlocal integral mixture leads to well-posed structural problems for any value of the scale parameter. Effectiveness of stress-driven mixture is illustrated by analyzing axial and torsional free vibrations of cantilever and doubly clamped nano-beams. The local/nonlocal integral mixture is conveniently replaced with an equivalent differential law equipped with higher-order constitutive boundary conditions. Exact solutions of fundamental natural frequencies associated with strain- and stress-driven mixtures are evaluated and compared with counterpart results obtained by strain gradient elasticity theory. The provided new numerical benchmarks can be effectively employed for modelling and design of Nano-Electro-Mechanical-Systems (NEMS).Mon, 15 Oct 2018 20:30:00 +0100