Journal of Computational Applied MechanicsJournal of Computational Applied Mechanics
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https://jcamech.ut.ac.ir/
Feed provided by Journal of Computational Applied Mechanics. Click to visit.Dielectrophoretic effect of nonuniform electric fields on the protoplast cell
https://jcamech.ut.ac.ir/article_62115_8114.html
In recent years, dielectrophoresis based microfluidics systems have been used to manipulate colloids, inert particles, and biological microparticles, such as red blood cells, white blood cells, platelets, cancer cells, bacteria, yeast, microorganisms, proteins, DNA, etc. In the current study the governing electric potential equations have been solved in the presence of cell for the purpose of studying particle-electric field dielectrophoretic interaction. Immersed Interface Method (IIM) which is a modified finite difference method is used to solve the governing 2D elliptic electrostatic equations with irregular boundaries. A neutral particle polarizes under the application of an electric field and causes local nonuniformity in electrostatic potential distribution. So cells experience electric stresses on its surface. The electric stress on cell surface is calculated by Maxwell Stress Tensor (MST) on both sides of cell. DEP force is calculated by integrating electric stress on particle surface. In the present study calculated electric stresses is validated by DEP force calculated using EDM method and exact solution. we neglect other electrokinetic effects such as electrophoresis and electro-osmosis. Electrophoresis can be neglected if the particles are not charged. The effect of applied voltage, dielectric constants of cells and cells orientation on particle-particle interaction force has been studied.Wed, 31 May 2017 19:30:00 +0100Numerical and Economic Study of Performance of Centrifugal Pump as Turbine
https://jcamech.ut.ac.ir/article_63159_0.html
In this paper, performance of centrifugal pump as turbine (PAT) is investigated numerically. Three different specific speeds are considered and three pumps are designed using diagrams from catalogues and CFturbo V.9 software. Next, models are analyzed by Ansys CFX 16 software and results are compared with those of CFturbo software. Also, a mesh study analysis for one case is performed in order to show the effect of grid size on the solution. In addition, three different flow rates of 75%, 100%, and 125% of best efficiency point (BEP) are considered for extracting head-flow rate diagrams and comparing results of CFX and CFturbo software. In next step, using relations between pump and turbine modes (PAT formulations) and by changing boundary conditions in CFX, turbine mode is investigated and efficiency is compared with pump mode. Finally, by an economic analysis a comparison between PATs and turbines with same nominal output powers are performed to distinguish which case is more profitable. Results showed that PATs have lower payback time in comparison with turbines with equal output power (in low capacities), although they have lower efficiencies.Sun, 24 Sep 2017 20:30:00 +0100Accelerating high-order WENO schemes using two heterogeneous GPUs
https://jcamech.ut.ac.ir/article_63189_0.html
A double-GPU code is developed to accelerate WENO schemes. The test problem is a compressible viscous flow. The convective terms are discretized using third- to ninth-order WENO schemes and the viscous terms are discretized by the standard fourth-order central scheme. The code written in CUDA programming language is developed by modifying a single-GPU code. The OpenMP library is used for parallel execution of the code on both the GPUs. Data transfer between GPUs which is the main issue in developing the code, is carried out by defining halo points for numerical grids and by using a CUDA built-in function. The code is executed on a PC equipped with two heterogeneous GPUs. The computational times of different schemes are obtained and the speedups with respect to the single-GPU code are reported for different number of grid points. Furthermore, the developed code is analyzed by CUDA profiling tools. The analyze helps to further increase the code performance.Mon, 25 Sep 2017 20:30:00 +0100Transient thermoelastic analysis of FGM rotating thick cylindrical pressure vessels under ...
https://jcamech.ut.ac.ir/article_62116_8114.html
Assuming arbitrary boundary and initial conditions, a transient thermo-elastic analysis of a rotating thick cylindrical pressure vessel made of functionally graded material (FGM) subjected to axisymmetric mechanical and transient thermal loads is presented. Time-dependent thermal and mechanical boundary conditions are assumed to act on the boundaries of the vessel. Material properties of the vessel are assumed to be graded in the radial direction according to a power law function. The Poisson’s ratio is assumed to be constant. Method of separation of variables has been used to analytically calculate the time dependent temperature distribution as a function of radial direction. In a case study, the distribution of radial and hoop stresses along the thickness is derived and plotted. In order to validate the model, the analytical results have been compared with finite element method modeling results presented in literature. Any arbitrary boundary and initial conditions can be handled using the equations derived in the present research. In order to investigate the inhomogeneity effect on time dependent stress distribution and displacements, values of the parameters have been set arbitrary in the present study. To the best of the authors’ knowledge, in previous researches, transient thermo-elastic analysis of thick cylindrical FGM pressure vessels is investigated by numerical methods, while in the present research, an exact solution is derived for the same problem.Wed, 31 May 2017 19:30:00 +0100Design and Fabrication of a Portable 1-DOF Robotic Device for Indentation Tests
https://jcamech.ut.ac.ir/article_63272_0.html
There are many tactile devices for indentation examinations to measure mechanical properties of tissue. The purpose of this paper is to develop a portable indentation robotic device to show its usability for measuring the mechanical properties of a healthy abdominal tissue. These measurements will help to develop suitable mathematical models representing abdominal tissue. A 1-DOF portable robotic device has been designed to be placed on the patient’s body. The device presses sensor plate on the abdomen. Force and position sensors measure the indentation force and displacement, respectively. Due to tissue time-dependent behavior, linear viscoelastic models with three, five and seven parameters have been selected for mathematical modeling. Nonlinear Least Squares (NLS) method is adopted to fit viscoelastic models with experimental data obtained from stress relaxation tests. Using Finite Prediction Error (FPE) criterion, viscoelastic model with five parameters has been selected as the optimal model. The results of the present paper can be used in abdominal tissue simulators to facilitate teaching palpation examinations.Mon, 02 Oct 2017 20:30:00 +0100Stiffness control of a legged robot equipped with a serial manipulator in stance phase
https://jcamech.ut.ac.ir/article_62117_8114.html
The ability to perform different tasks by a serial manipulator mounted on legged robots, increases the capabilities of the robot. The position/force control problem of such a robot in the stance phase with point contacts on the ground is investigated here. A target plane with known stiffness is specified in the workspace. Active joints of the legs and serial manipulator are used to exert the desired normal force on the plane while tracking a desired trajectory on the plane. First, the equations of motion of the robot and contact forces of the feet on the ground are derived. A controller is then proposed which tracks the desired trajectory while keeping the feet contacts on the ground and prevent slipping. An optimization problem is solved in each control loop to minimize the actuation effort. This minimization is subject to position tracking for the end-effector (using inverse dynamics controller), force requirements of the feet contacts with the ground, and actuators capabilities. Simulations are conducted for the simplified model of a quadruped robot with a 2-DOF serial manipulator. To test the controller, a 20 N normal force is applied onto the target plane while moving the tip of the end-effector. It is shown that the robot can perform the task effectively without losing the ground contact and slipping.Wed, 31 May 2017 19:30:00 +0100Modeling SMA actuated systems based on Bouc-Wen hysteresis model and feed-forward neural network
https://jcamech.ut.ac.ir/article_63273_0.html
Despite the fact that shape-memory alloy (SMA) has several mechanical advantages as it continues being used as an actuator in engineering applications, using it still remains as a challenge since it shows both non-linear and hysteretic behavior. To improve the efficiency of SMA application, it is required to do research not only on modeling it, but also on control hysteresis behavior of these materials which are the fundamentals of several research opportunities in this area. Having considered these requirements, we have introduced a mathematical model to describe the hysteresis behavior of a mechanical system attached to SMA wire actuators using Bouc-Wen hysteresis model and feed-forward neural network. Due to inability of linear mass-spring-damper equations of classic Bouc-wen model to explain the hysteresis behavior of SMA actuators, in this paper we have applied changes in the mentioned equations of classic Bouc-Wen model to describe hysteresis loops of model. We also have used flexibility of the neural network systems to describe Bouc-Wen output in the main equation. Parameters of the developed model have been trained for a real mechanical system using simulation data after selecting proper configuration for the selected neural network. Finally, we have checked the accuracy of our model by applying two different series of validation data. The result shows the acceptable accuracy of the developed model.Mon, 02 Oct 2017 20:30:00 +0100Predicting Low Cycle Fatigue Life through Simulation of Crack in Cover Plate Welded Beam to ...
https://jcamech.ut.ac.ir/article_62118_8114.html
This paper presents a low cycle fatigue life curve by simulating a crack in a cover plate welded moment connection. Initiation of ductile fracture in steel is controlled by growth and coalescence of micro-voids. This research used a numerical method using finite element modeling and simulation of ductile crack initiation by a micromechanical model. Therefore, a finite element model of a cover plate welded moment connection was developed in ABAQUS software, and a FORTRAN subroutine was used in order to simulate cracking in the connection model. Thus, each crack location and the number of cycles to initiate the crack were detected. Utilizing cyclic void micromechanical model of growth analysis, which is a technique to predict fracture in a ductile material, six different cover plate connections (divided in three categories) were modeled in the steel moment frame, and then their critical points to trigger the crack were identified. Finally, for the cover plate moment connection, considering the constant amplitude of loading curves data and in order to present the low cycle fatigue life prediction, displacement versus the number of half cycles diagram is produced.Wed, 31 May 2017 19:30:00 +0100Simulation of Stresses Induced by Heat and Mass Transfer in Drying Process of Clay-like Material
https://jcamech.ut.ac.ir/article_63274_0.html
Drying represents one of the oldest unit operations employed in industrial processes. Drying is viewed as a process of simultaneous heat and mass transfer. Porous Clay-like material undergoes stresses due to non-uniform distribution of temperature and moisture induced by heat and mass transfer respectively. The aim of this work is to simulate the stresses induced by heat and mass transfer during drying. A mathematical model to simulate the convective drying of a porous material like clay has been developed. The problem investigated involves highly coupled equations considering heat, mass, and mechanical aspects. The particularity of the model is that it takes into account the strong coupling between mass transport, heat transport and mechanical behavior of the material. The variables of coupling are the solid deformation, moisture content and temperature of porous medium. A numerical solution is sought to foresee the variation of moisture content, temperature, shrinkage, heat transfer induced stresses and mass transfer induced stresses during drying. The solution developed as a model is capable of predicting the quality of the product through a failure criterion. The model is validated through the comparison of simulated and experimental data. Simulation results show that the heat transfer induced stresses are significantly less important in compression with the mass transfer induced stresses and can be neglected in modeling of drying process.Mon, 02 Oct 2017 20:30:00 +0100Multi objective optimization of the vibration analysis of composite natural gas pipelines in ...
https://jcamech.ut.ac.ir/article_62119_8114.html
The fluid-conveying pipe is a fundamental dynamical problem in the field of fluid– structure interactions. In recent years considerable attention has been given to the lateral vibrations of pipes containing by a moving fluid. In this paper, the vibration analysis of composite natural gas pipeline in the thermal and humidity environment is studied. The effect of the non-uniform magnetic field is investigated. By applying the Hamilton’s principle, the equation of motion is derived for the pipe with the effects of both linear and non-linear stress temperature cases. The differential quadrature method (DQM) has been utilized in computing the results for the pipe conveying fluid. The Bees algorithm and Genetic algorithm NSGA II for multi-objective optimization of a pipe model are used. Sample results are presented for several cases with varying values of the system parameter. Results are demonstrated for the dependence of natural frequencies on the flow velocity as well as temperature change and humidity percent. The influence of temperature change on the critical flow velocity at which buckling instability occurs is investigated. It is concluded that the effect of temperature change on the instability of conveyed fluid pipe is significant.Wed, 31 May 2017 19:30:00 +0100A new approach for nonlinear vibration analysis of thin and moderately thick rectangular plates ...
https://jcamech.ut.ac.ir/article_63295_0.html
In this study, a hybrid method is proposed to investigate the nonlinear vibrations of pre- and post-buckled rectangular plates for the first time. This is an answer to an existing need to develope a fast and precise numerical model which can handle the nonlinear vibrations of buckled plates under different boundary conditions and plate shapes. The method uses the differential quadrature element, arc-length, harmonic balance and direct iterative methods. The governing differential equations of plate vibration have been extracted considering shear deformations and the initial geometric imperfection. The solution is assumed to be the sum of the static and dynamic parts which upon inserting them into the governing equations, convert them into two sets of nonlinear differential equations for static and dynamic behaviors of the plate. First, the static solution is calculated using a combination of the differential quadrature element method and an arc-length strategy. Then, putting the first step solutions into the dynamic nonlinear differential equations, the nonlinear frequencies and modal shapes of the plate are extracted using the harmonic balance and direct iterative methods. Comparing the obtained solutions with those published in the literature confirms the accuracy and the precision of the proposed method. The results show that an increase in the nonlinear vibration amplitude increases the nonlinear frequencies.Thu, 05 Oct 2017 20:30:00 +0100Parametric study of a viscoelastic RANS turbulence model in the fully developed channel flow
https://jcamech.ut.ac.ir/article_62120_8114.html
One of the newest of viscoelastic RANS turbulence models for drag reducing channel flow with polymer additives is studied in different flow and rheological properties. In this model, finitely extensible nonlinear elastic-Peterlin (FENE-P) constitutive model is used to describe the viscoelastic effect of polymer solution and turbulence model is developed in the k-ϵ-(ν^2 ) ̅-f framework. The geometry in this study is two-dimensional channel flow and finite volume method (FVM) with a non-uniform collocated mesh is used to solve the momentum and constitutive equations. In order to evaluate this turbulence model, several cases with different parameters such as Reynolds numbers, Weissenberg number, maximum polymer extensibility and concentration of polymer are simulated and assessed against direct numerical simulation (DNS) data. The velocity profiles, shear stress profiles and the percentage of friction drag reduction predicted by this turbulence model are in good agreement with DNS data at moderate to high Reynolds numbers. However, in low Reynolds numbers, the results of model are reliable only for low 〖 L〗^2 value. Moreover, in case of high concentration of polymer, the accuracy of the model is lost.Wed, 31 May 2017 19:30:00 +0100Analysis and Optimization using Renewable Energies to Get Net-Zero Energy Building for Warm Climate
https://jcamech.ut.ac.ir/article_63296_0.html
Due to low energy price, economic optimization of consumption has no justification for users in Iran. Nowadays, the issue of ending fossil fuels, production of greenhouse gases and the main role of building in consumption of considerable amount of energy has drawn the focus of global researches to a new concept called net zero energy building. In this study, modeling, simulation and energy analysis have been used for considered building in Zahedan weather condition which has a dry and warm climate to draw the related equations and perform analysis. Multi-Objective optimization has been performed for simultaneous reduction of total energy consumption and total cost where the main decision making variables including thermal comfort, cooling, heating and lighting systems and other variables have been influential. The comparison of an ordinary optimized building and the intended optimized building which uses renewable energy resources indicates that it is possible to get to net zero energy building in addition to selling surplus 2 MWh electrical energy to electricity grid with simultaneous use of solar and wind renewable energies.Thu, 05 Oct 2017 20:30:00 +0100Updating finite element model using frequency domain decomposition method and bees algorithm
https://jcamech.ut.ac.ir/article_62121_8114.html
The following study deals with the updating the finite element model of structures using the operational modal analysis. The updating process uses an evolutionary optimization algorithm, namely bees algorithm which applies instinctive behavior of honeybees for finding food sources. To determine the uncertain updated parameters such as geometry and material properties of the structure, local and global sensitivity analyses have been performed. The sum of the squared errors between the natural frequencies obtained from operational modal analysis and the finite element method is used to define the objective function. The experimental natural frequencies are determined by frequency domain decomposition technique which is considered as an efficient operational modal analysis method. To verify the accuracy of the proposed algorithm, it is implemented on a three-story structure to update its finite element model. Moreover, to study the efficiency of bees algorithm, its results are compared with those particle swarm optimization and Nelder and Mead methods. The results show that this algorithm leads more accurate results with faster convergence. In addition, modal assurance criterion is calculated for updated finite element model and frequency domain decomposition technique. Moreover, finding the best locations of acceleration and shaker mounting in order to accurate experiments are explained.Wed, 31 May 2017 19:30:00 +0100Performance Improvements of a Centrifugal Pump with Different Impellers using Polymer Additive
https://jcamech.ut.ac.ir/article_63338_0.html
In this study, the performance of a centrifugal pump is investigated by adding polyacrylamide (PAM) polymer over the working fluid which is tap water in this case. PAM is a long chain polymer that leads to reduce the wall shear stress and drag in a turbulent fluid. Three different blade profiles including radial, straight backward and circular backward have been examined. For this purpose, a centrifugal pump test rig consists of reservoir, pump-motor, volumetric measuring tank, pressure gauges, speed control, and motor dynamometer has been used. Different concentrations of PAM polymer solution are prepared in the range of 80-240 ppm of PAM. The results show that the maximum amount of relative efficiency is approximately 3% for the radial propeller, 13% for the straight backward propeller, and 18% for the circular backward which is occurs at 160 ppm of PAM. It is found that this increase is more pronounced in the case of circular backward impeller. Moreover, in the case of radial blade profile, it is observed that in spite of efficiency increase, the head decreases at low flow rate with adding PAM.Sat, 07 Oct 2017 20:30:00 +0100Elastic analysis of functionally graded rotating thick cylindrical pressure vessels with ...
https://jcamech.ut.ac.ir/article_62122_8114.html
Based on the Frobenius series method, stresses analysis of the functionally graded rotating thick cylindrical pressure vessels (FGRTCPV) are examined. The vessel is considered in both plane stress and plane strain conditions. All of the cylindrical shell properties except the Poisson ratio are considered exponential function along the radial direction. The governing Navier equation for this problem is determined, by employing the principle of the two-dimensional elastic theories. This paper presents a closed-form analytical solution for the Navier equation of FGRTCPV as the novelty of the present paper. Moreover, a finite element (FE) model is developed for comparison with the results of the Frobenius series method. This comparison demonstrates that the results of the Frobenius series method are accurate. Finally, the effect of some parameters on stresses analysis of the FGRTCPV is examined. In order to investigate the inhomogeneity effect on the elastic analysis of functionally graded rotating thick cylindrical pressure vessels with exponentially-varying properties, values of the parameters have been set arbitrary in the present study. The presented outcomes illustrate that the inhomogeneity constant provides a major effect on the mechanical behaviors of the exponential FG thick cylindrical under pressure.Wed, 31 May 2017 19:30:00 +0100Simulation of the Mode I fracture of concrete beam with cohesive models
https://jcamech.ut.ac.ir/article_63339_0.html
Crack propagation modeling in quasi-brittle materials such as concrete is essential for improving the reliability and load-bearing capacity assessment. Crack propagation explains many failure characteristics of concrete structures using the fracture mechanics approach. This approach could better explain the softening behavior of concrete structures. A great effort has been made in developing numerical models; however, some models involve complex expressions with too many parameters, and the results are in some cases inaccurate. In this investigation, a numerical approach is developed to model the fracture process zone (FPZ). Based on the modified crack closure integral (MCCI) method, a new nonlinear spring is proposed to be placed between the interfacial node pairs to model crack propagation. A new strain energy release rates for Mode I is calculated as a function of opening in the softening part. Two benchmark beams are simulated by the ABAQUS software for the accuracy of cohesive zone model. The model decreases complexity of predicting crack propagation. It is observed that the cohesive zone model is robust, accurate and able to model the crack growth in the concrete beam. The prediction of the crack path is close to the experimental results (up to 90%). The peak loads had approximately 7.7% difference compared with the previous experimental loads. The accuracy of displacement in the present study is 15.9% compared with previously model at the same load intensity.Sat, 07 Oct 2017 20:30:00 +0100Nonlinear Vibration and Stability Analysis of Beam on the Variable Viscoelastic Foundation
https://jcamech.ut.ac.ir/article_62123_8114.html
The aim of this study is the investigation of the large amplitude deflection of an Euler-Bernoulli beam subjected to an axial load on a viscoelastic foundation with the strong damping. In order to achieve this purpose, the beam nonlinear frequency has been calculated by homotopy perturbation method (HPM) and Hamilton Approach (HA) and it was compared by the exact solutions for the different boundary conditions such as simple-simple, clamped-simple and clamped-clamped which showed a good accuracy in results. In addition, to find the deflection of the nonlinear Euler-Bernoulli beam, the problem has been solved based on homotopy perturbation method and modified differential transform method (MDTM) and finally, the results were compared by Rung-Kutta exact solutions. The derived deflection results by two mentioned methods had a good agreement with the exact RK4 solutions. By considering the paper results, buckling force is increased for each case permanently by increase in the boundary rigidity for a constant value of system amplitude (A). As a final comparison, in based on paper results, the buckling force is arisen by increasing the system amplitude for each case.Wed, 31 May 2017 19:30:00 +0100A novel computational procedure based on league championship algorithm for solving an inverse ...
https://jcamech.ut.ac.ir/article_63340_0.html
Inverse heat conduction problems, which are one of the most important groups of problems, are often ill-posed and complicated problems, and their optimization process has lots of local extrema. This paper provides a novel computational procedure based on finite differences method and league championship algorithm to solve a one-dimensional inverse heat conduction problem. At the beginning, we use the Crank-Nicolson semi-implicit finite difference scheme to discretize the problem domain and solve the direct problem which is a second-order method in time and unconditionally stable. The consistency, stability and convergence of the method are investigated. Then we employ a new optimization method known as league championship algorithm to estimate the unknown boundary condition from some measured temperature on the line. League championship algorithm is a recently proposed probabilistic algorithm for optimization in continuous environments, which tries to simulate a championship environment wherein several teams with different abilities play in an artificial league for several weeks or iterations. To confirm the efficiency and accuracy of the proposed approach, we give some examples for the engineering applications. Results show an excellent agreement between the solution of the proposed numerical algorithm and the exact solution.Sat, 07 Oct 2017 20:30:00 +0100Buckling Behavior of Composite Plates with a Pre-central Circular Delamination Defect under ...
https://jcamech.ut.ac.ir/article_62124_8114.html
Delamination is one of the most common failure modes in composite structures. In the case of in-plane compressional loading, delamination of a layered flat structure can cause a local buckling in delaminated area which subsequently affects the overall stiffness of the initial structure. This leads to an early failure of the overall structure. Moreover, with an increase in load, the delaminated area may propagate in the post-buckling mode; and consequently, to predict this behavior, a combination of failure modes will be used to predict failure. In this work, the proposed analysis will predict the delamination shape and load carrying capacity of a composite laminated plate during delamination process in post-buckling mode. For this purpose, it is assumed that the composite laminate contains an initial circular delaminated (defected) area. The analysis is performed through a numerical scheme based on finite element method. Results show that in most cases, the onset of crack growth is affected by the first opening mode while it is well probable that during the delamination growth, the effects of other modes dominate the initial primary opening mode. Consequently, during progression of any delamination which may occur as a result of further loading, a jump in failure mode which is predicted in this analysis, may occur. Moreover, the induced results show that the stacking sequence of the delaminated composite plate has a significant effect on the delamination growth and the load carrying capacity of the overall structure.Wed, 31 May 2017 19:30:00 +0100Multi-objective Optimization of web profile of railway wheel using Bi-directional Evolutionary ...
https://jcamech.ut.ac.ir/article_63341_0.html
In this paper, multi-objective optimization of railway wheel web profile using bidirectional evolutionary structural optimization (BESO) algorithm is investigated. Using a finite element software, static analysis of the wheel based on a standard load case, and its modal analysis for finding the fundamental natural frequency is performed. The von Mises stress and critical frequency as the problem objectives are combined using different weight factors in order to find the sensitivity number in the method, which specifies which elements to be omitted and which to be added. The iterative process is continued until convergence to an a priori specified material volume. The resulted web profiles show that when the stress is important, material removal is from the middle part of the web, while for frequency as the important objective, the removal is from near the rim part of the web. The suggested profile, corresponding to equal weight factor for the objectives, has a better volume and stress state compared to a standard web profile, and has a more uniform stress distribution. However, higher natural frequency, compared to that of the standard profile, are obtained for larger frequency weight factors, although with a bigger volume. In the end, considering manufacturability of the wheel, the jagged profile resulted from BESO is replaced with a fitted smooth curve and performing the finite element analysis on it. It is seen that there is an improvement in the obtained objectives for the smoothened profile, with no significant change in volume.Sat, 07 Oct 2017 20:30:00 +0100Refined plate theory for free vibration analysis of FG nanoplates using the nonlocal continuum ...
https://jcamech.ut.ac.ir/article_62125_8114.html
In this article, the free vibration behavior of nanoscale FG rectangular plates is studied within the framework of the refined plate theory (RPT) and small-scale effects are taken into account. Using the nonlocal elasticity theory, the governing equations are derived for single-layered FG nanoplate. The Navier’s method is employed to obtain closed-form solutions for rectangular nanoplates assuming that all edges are simply supported. The results are subsequently compared with valid results reported in the literature. The effects of the small scale on natural frequencies are investigated considering various parameters such as aspect ratio, thickness ratio, and mode numbers. It is shown that the RPT is an accurate and simple theory for the vibration analysis of nanoplates, which does not require a shear correction factor.Wed, 31 May 2017 19:30:00 +0100Incremental explosive analysis and its application to performance-based assessment of stiffened ...
https://jcamech.ut.ac.ir/article_63353_0.html
In this paper, the dynamic behavior of square plates with various thicknesses and stiffening configurations subjected to underwater explosion (UNDEX) are evaluated through a relatively novel approach which is called Incremental Explosive Analysis (IEA). The IEA estimates the different limit-states and deterministic assessment of plats’ behavior, considering uncertainty of loading conditions and dynamic nature of explosive loading. In this new approach, intensity parameter of explosive loading is enhanced in an incremental manner and response of the target plate is recorded for every depth-stand-off loading condition. Then, the multi IEA curves are derived from several simulation results. The fractiles method is employed to summarize large amount of IEA curves’ data in a predictive mode. In addition, some summarized damage probability indicators such as fragility curves are extracted that provide useful information for quantitative damage analysis of plates in UNDEX loading. Results show that the IEA is a promising method for performance-based assessment of marine structures subjected to UNDEX loading.Sun, 08 Oct 2017 20:30:00 +0100Evaluation of Evaporation Estimation Methods: a Case Study of Karaj Dam Lake
https://jcamech.ut.ac.ir/article_62126_8114.html
Evaporation is one of the largest water losses from most of the dam lakes in Iran. Estimating the evaporation rate enables us to apply the proper evaporation mitigation technologies. In this study, the feasibility of different evaporation estimation methods was studied to find an optimum method with a fair tradeoff between cost and accuracy. The optimum method may vary depending on the climate. We found Penman, Montieth and Unsworth (PMU) method as the optimum estimation method applicable Karaj dam lake (located north west of Tehran, Iran). For validation, we used the filed measurements for 2005. The reason is that the PMU is highly sensitive to wind velocity and only for 2005 the meteorological data contained the wind velocity. For the sky clarity, we used the 22-year average sky clarity of Karaj dam lake in augusts (i.e. 80%). The PMU model is found to provide consistent results with filed measurements (less than 2% error). For example, from 2nd to 15th of August 2005, the PMU model predicts 7.98 ± 0.83 mm/day evaporation and field measurement for the same period was 8.13 ± 0.01 mm/day.Wed, 31 May 2017 19:30:00 +0100Applications of higher order shear deformation theories on stress distribution in a five layer ...
https://jcamech.ut.ac.ir/article_63354_0.html
In this paper, layerwise theory (LT) along with the first, second and third-order shear deformation theories (FSDT, SSDT and TSDT) are used to determine the stress distribution in a simply supported square sandwich plate subjected to a uniformly distributed load. Two functionally graded (FG) face sheets encapsulate an elastomeric core while two epoxy adhesive layers adhere the core to the face sheets. The sandwich plate is assumed to be symmetric with respect to its core mid-plane. First, second and third-order shear deformation theories are used to model shear distribution in the adhesive layers as well as others. Results obtained from the three theories are compared with those of finite element solution. Results indicate that finite element analysis (FEA) and LT based on the first, second and third-order shear deformation theories give almost the same estimations on planar stresses. Moreover, the out-of-plane shear stresses obtained by FEA, are slightly different from those of LT based on FSDT. The differences are decreased on using LT based on SSDT or TSDT. Additionally, SSDT and TSDT predict almost the same distribution for the two planer stress and out-of-plane shear stress components along the face sheet thickness. Furthermore, third-order shear deformation theory seems to be more appropriate for prediction of out-of-plane shear stress at lower values of a/h ratio.Sun, 08 Oct 2017 20:30:00 +0100Elasto-plastic solution for thick-walled spherical vessels with an inner FGM layer
https://jcamech.ut.ac.ir/article_63365_0.html
Purely elastic, partially and fully plastic stress states in a thick-walled spherical pressure vessel with an inner functionally graded material (FG) coating subjected to internal and external pressures are developed analytically in this paper. The modulus of elasticity and the uniaxial yield limit of the FG coating layer are considered to vary nonlinearly through the thickness. Using Tresca’s yield criterion and ideal plastic material behavior, the plastic model is established. Under pressure loading, the scenario in which the plastic deformation starts from inner surface of FG coating layer is taken into account. Having increased the pressure loading, it is assumed that the FG coating layer becomes fully plastic and the yielding commences subsequently at the inner surface of homogenous part. Essentially, the variation of FG parameters in the radial direction is properly adjusted in order to achieve the stated yielding scenario. Furthermore, axisymmetric finite element model is performed to validate the accuracy of the analytical results. It is concluded that the elastic and plastic response of the spherical pressure vessel are influenced by grading parameters and coating behavior.Mon, 09 Oct 2017 20:30:00 +0100Effect of nano-structuration and compounding of YSZ APS TBCs with different thickness on ...
https://jcamech.ut.ac.ir/article_63368_0.html
Effect of nano-structuration and compounding of YSZ APS TBCs investigated on coating behavior in thermal shock conditions. The coatings were applied on Inconel 738 discs with three different thickness per powder. In order to harmonize the results from the samples, performance factor is defined as a criterion that in the starting of the activity has an amount of about 100 and is reduced after the damage begins. The results revealed that the growth of damage in the YSZ class is almost linear, and this behavior is observed in all samples. The thick TGO in this class shows its high oxygen permeability, and the type of damage indicates that its location is near the TGO region. The nano-structured YSZ class has a very good performance and through an interesting phenomenon, the slope of the damage growth diagrams is decreasing with time. The obvious thing about the CSZ class microstructure is the presence of horizontal and vertical cracks and its dense structure. In this class, the main location of damage is through the coating and after the beginning of damage, its curve has grown with a high rate. The best performance among all samples belongs to the nano-structured YSZ, which due to the presence of nano-zones, has a higher toughness and ability to endure more cycles.Mon, 09 Oct 2017 20:30:00 +0100On the Analysis of Laminar Flow of Viscous Fluid through a Porous Channel with ...
https://jcamech.ut.ac.ir/article_63371_0.html
The vast biological and industrial applications of laminar flow of viscous fluid through a porous channel with contracting or expanding permeable wall have attest to the importance of studying the flow process. In this paper, two-dimensional flow of viscous fluid in a porous channel through slowly expanding or contracting walls with injection or suction is analyzed using variation parameter method. From the parametric studies using the developed approximate analytical solutions, it is shown that increase in the Reynolds number of the flow process leads to decrease in the axial velocity at the center of the channel during the expansion. The axial velocity increases slightly near the surface of the channel when the wall contracts at the same rate. Also, as the wall expansion ratio increases, the velocity at the center decreases but it increases near the wall. The results of the approximate analytical solution are verified by numerical solution using shooting method coupled with Runge-Kutta method. The results of the variation parameter method are in excellent agreement with the results obtained using numerical method.Mon, 09 Oct 2017 20:30:00 +0100Analysis of Flow of Nanofluid through a Porous Channel with Expanding or Contracting Walls ...
https://jcamech.ut.ac.ir/article_63377_0.html
In this work, we applied Chebychev spectral collocation method to analyze the unsteady two-dimensional flow of nanofluid in a porous channel through expanding or contracting walls with large injection or suction. The solutions are used to study the effects of various parameters on the flow of the nanofluid in the porous channel. From the analysis, It was established that increase in expansion ratio and Reynolds number decreases the axial velocity at the center of the channel during the expansion while the axial velocity increases near the surface of the channel during contraction. Moreover, it was also established that an increase in injection rate leads to a higher axial velocity near the center and the lower axial velocity near the wall. On the verification of the results, it is shown that the results obtained from Chebychev spectral collocation method are in good agreement when compared to the results obtained using other numerical methods.Mon, 09 Oct 2017 20:30:00 +0100Prediction of Temperature distribution in Straight Fin with variable Thermal Conductivity and ...
https://jcamech.ut.ac.ir/article_63383_0.html
Due to increasing applications of extended surfaces as passive methods of cooling, study of thermal behaviors and development of mathematical solutions to nonlinear thermal models of extended surfaces have been the subjects of research in cooling technology over the years. In the thermal analysis of fin, various methods have been applied to solve the nonlinear thermal models. This paper focuses on the application of Legendre wavelet collocation method to the prediction of temperature distribution in longitudinal rectangular fin with temperature-dependent thermal conductivity and internal heat generation. The numerical approximations by the method are used to carry out parametric studies of the effects of the model parameters on the temperature distribution in the fin. The results show that the thermal performance of the fin is favoured at low values of thermogeometric parameter and internal heat generation decreases the performance of the fin. The results can serve as verification of the solutions of other methods of analysis of the component.Mon, 09 Oct 2017 20:30:00 +0100Analysis of Heat transfer in Porous Fin with Temperature-dependent Thermal Conductivity and ...
https://jcamech.ut.ac.ir/article_63384_0.html
In this work, analysis of heat transfer in porous fin with temperature-dependent thermal conductivity and internal heat generation is carried out using Chebychev spectral collocation method. The numerical solutions are used to investigate the influence of various parameters on the thermal performance of the porous fin. The results show that increase in convective parameter, porosity parameter, Nusselt, Darcy and Rayleigh numbers and thickness-length ratio of the fin, the rate of heat transfer from the base of the fin increases and consequently improve the efficiency of the fin. However, the rate of heat transfer from the base of the fin increases with decrease in thermal conductivity material. Also, from the parametric studies, an optimum value is reached beyond which further increase in porosity, Nusselt, Darcy and Rayleigh numbers, thermal conductivity ratio and thickness-length ratio has no significant influence on the rate of heat transfer. It is established that the temperature predictions in the fin using the Chebychev spectral collocation method are in excellent agreement with the results of homotopy perturbation method and that of numerical methods using Runge-Kutta coupled with shooting method.Mon, 09 Oct 2017 20:30:00 +0100Power Series -Aftertreatment Technique for Nonlinear Cubic Duffing and Double-Well Duffing ...
https://jcamech.ut.ac.ir/article_63385_0.html
Modeling of large amplitude of structures such as slender, flexible cantilever beam and fluid-structure resting on nonlinear elastic foundations or subjected to stretching effects often lead to strongly nonlinear models of Duffing equations which are not amendable to exact analytical methods. In this work, explicit analytical solutions to the large amplitude nonlinear oscillation systems of cubic Duffing and double-well Duffing oscillators are provided using power series-aftertreatment technique. The developed analytical solutions are valid for both small and large amplitudes of oscillation. The accuracy and explicitness of the analytical solutions are carried out to establish the validity of the method. Good agreements are established between the solution of the new method and established exact analytical solution. The developed analytical solutions in this work can serve as a starting point for a better understanding of the relationship between the physical quantities of the problems as it provides continuous physical insights into the problems than pure numerical or computation methods.Mon, 09 Oct 2017 20:30:00 +0100Dynamics of Nonlinear rectangular plates subjected to an orbiting mass based on shear ...
https://jcamech.ut.ac.ir/article_63386_0.html
In this paper, transverse and longitudinal vibration of nonlinear plate under exciting of orbiting mass is considered based on first-order shear deformation theory. The nonlinear governing equation of motion are discretized by the finite element method in combination with Newmark’s time integration scheme under von Karman strain-displacement assumptions. For validation of method and formulation of solution, a simply supported beam-plate under a moving force is considered and compared with existing results in the literature. The effects of nonlinearity, mass ratios, different geometric parameters, orbiting radius and angular velocity on dynamic response of plate are studied. This study present the importance of nonlinear analysis of rectangular plate under orbiting mass due to large deformation. In this paper, transverse and longitudinal vibration of nonlinear plate under exciting of orbiting mass is considered based on first-order shear deformation theory. The nonlinear governing equation of motion are discretized by the finite element method in combination with Newmark’s time integration scheme under von Karman strain-displacement assumptions. For validation of method and formulation of solution, a simply supported beam-plate under a moving force is considered and compared with existing results in the literature. The effects of nonlinearity, mass ratios, different geometric parameters, orbiting radius and angular velocity on dynamic response of plate are studied. This study present the importance of nonlinear analysis of rectangular plate under orbiting mass due to large deformation.Mon, 09 Oct 2017 20:30:00 +0100