Journal of Computational Applied MechanicsJournal of Computational Applied Mechanics
https://jcamech.ut.ac.ir/
Mon, 10 Dec 2018 02:59:23 +0100FeedCreatorJournal of Computational Applied Mechanics
https://jcamech.ut.ac.ir/
Feed provided by Journal of Computational Applied Mechanics. Click to visit.On The Effect of Nanofluid Flow and Heat Transfer with Injection through an Expanding or ...
https://jcamech.ut.ac.ir/article_65910_8741.html
The studies of the behavior of fluid on the nano-level has shown to be an important means of influencing the characteristic of fluid must especially in the area of thermal conductivity. Giving relevance in numerous fields such as biomedicine, manufacturing, fuel cells and soon on. This article considers flow and heat transfer of viscous fluid conveying Gold nanoparticles through expanding or contracting porous channel with injection. The nanofluid is described by the high order coupled nonlinear equations of the fourth order which is analyzed utilizing the regular perturbation method whose analytical solutions is adopted in describing the effect of various thermal-fluidic parameters such as Reynolds number and temperature power index. Where results reveals that increasing Reynolds causes an increasing velocity distribution while increasing temperature power index demonstrates decreasing temperature effect. Also comparison of obtained analytical solution against numerical solution shows satisfactory agreement. Study provides good advancement to applications such as fluid transport, power plant operations and manufacturing amongst others.Thu, 31 May 2018 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_8741.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.Thu, 31 May 2018 19:30:00 +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_8741.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.Thu, 31 May 2018 19:30:00 +0100Dynamics of nonlinear rectangular plates subjected to an orbiting mass based on shear ...
https://jcamech.ut.ac.ir/article_63386_8741.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.Thu, 31 May 2018 19:30:00 +0100Performance, Thermal Stability and Optimum Design Analyses of Rectangular Fin with ...
https://jcamech.ut.ac.ir/article_64209_8741.html
In this study, we analysed the thermal performance, thermal stability and optimum design analyses of a longitudinal, rectangular fin with temperature-dependent, thermal properties and internal heat generation under multi-boiling heat transfer using Haar wavelet collocation method. The effects of the key and controlling parameters on the thermal performance of the fin are investigated. The thermal stability criteria and optimum design parameter were established. From the investigation, the study reveals that the performance of the fin is enhanced as the boiling condition parameter or the exponent decreases. It is also established that the optimum fin length (at which Q/ζ reaches a maximum value) increases as the non-linear thermal conductivity term β, increases. Furthermore, the study shows that the optimum value of M can be obtained based on the value of the non-linear term. The computational results obtained in this study were compared with established numerical solutions and is found to be in good agreement with the standard numerical solutions.Thu, 31 May 2018 19:30:00 +0100Nonlinear free vibration of viscoelastic nanoplates based on modified couple stress theory
https://jcamech.ut.ac.ir/article_66135_8741.html
In this paper, a new viscoelastic size-depended model developed based on a modiﬁed couple stress theory and the for nonlinear viscoelastic material in order to vibration analysis of a viscoelastic nanoplate. The material of the nanoplate is assumed to obey the Leaderman nonlinear constitutive relation and the von Kármán plate theory is employed to model the system. The viscous parts of the classical and nonclassical stress tensors are obtained based on the Leaderman integral and the corresponding work terms are calculated. The viscous work equations are balanced by the terms of size-dependent potential energy, kinetic energy. Then the equations of motion are derived from Hamilton’s principle. The governing nonlinear integro-differential equations with coupled terms are solved by using the fourth-order Runge-Kutta method and Galerkin approach. The results are validated by carrying out the comparison with existing results in the literature when our model is reduced into an elastic case. In order to explore the vibrational characteristics, the inﬂuences of the thickness ratio, relaxation coefficient, and aspect ratio on the frequency and damping ratio were also examined. The results revealed that the frequency, vibration amplitude and damping ratio of viscoelastic nanoplate were signiﬁcantly inﬂuenced by the relaxation coefficient of nanoplate material, and length scale parameter. Also, it was found that with increasing (h/l) the vibration frequency decreases and its amplitude and damping ratio increase.Thu, 31 May 2018 19:30:00 +0100Transverse Sensing of Simply Supported Truncated Conical Shells
https://jcamech.ut.ac.ir/article_64204_0.html
Modal signals of transverse sensing of truncated conical shells with simply supported boundary condition at both ends are investigated. The embedded piezoelectric layer on the surface of conical shell is used as sensors and output voltages of them in considered modes are calculated. The Governing sensing signal displacement equations are derived based on the Kirchhoff theory, thin-shell assumption, piezoelectric direct effect, the Gauss theory and the open circuit assumption. A conical shell with fully covered piezoelectric layer is considered as a case study and the layer is segmented into 400 patches. Modal voltages of the considered model are calculated and evaluated. The ideal locations for sensor patches are in the middle of conical shell surface in the longitudinal direction and locations near the ends of the conical shell are not recommended. The longitudinal membrane strain signal has a leading role on the total signal in comparison with other strain signal components. The output signals of the sensor can be used as a controller input for later active vibration control or structural health monitoring.Tue, 19 Dec 2017 20:30:00 +0100An Investigation on the Effects of Optimum Forming Parameters in Hydromechanical Deep Drawing ...
https://jcamech.ut.ac.ir/article_64678_8741.html
The present research work is concerned with the effects of optimum process variables in elevated temperature hydro-mechanical deep drawing of 5052 aluminum alloy. Punch-workpiece and die-workpiece friction coefficients together with the initial gap between the blank holder and matrix were considered as the process variables which, in optimization terminology, are called design parameters. Since both the maximum reduction in sheet thickness and the final product uniformity (thickness variation) are important in the hydro-mechanical deep drawing, they are selected as the objective functions for optimization. After conducting 27 finite-element simulations of the operation and validation of the numerical results, a neural network was trained and combined with the genetic algorithm to obtain the optimum design parameters. The outcomes of this investigation have shown that these optimized process variables simultaneously resulted in the best values for both the objective functions, in comparison with all the conducted finite-element analyses.Thu, 31 May 2018 19:30:00 +0100Numerical and Neural Network Modeling and control of an Aircraft Propeller
https://jcamech.ut.ac.ir/article_64203_8741.html
In this paper, parametric and numerical model of the DC motor, connected to aircraft propellers are extracted. This model is required for controlling trust and velocity of the propellers, and consequently, an aircraft. As a result, both of torque and speed of the propeller can be controlled simultaneously which increases the kinematic and kinetic performance of the aircraft. Parametric model of the motor is derived by conducting standard tests such as locked rotor test and step and sine wave input one. In order to derive a neural network and numerical model, a set of sinusoidal, triangular, and random step signals are applied as the input to the motor and its speed is recorded as an output. Neural network of the motor is extracted by using these datasets and considering a multilayer perceptron (MLP) neural network structure with Levenberg-Marquardt training method. Results of the numerical model and parametric model are compared and validated by experimental implementations. The superiority of the proposed method is also shown respect to traditional PID algorithm.Thu, 31 May 2018 19:30:00 +0100On the Thermal Conductivity of Carbon Nanotube/Polypropylene Nanocomposites by Finite Element Method
https://jcamech.ut.ac.ir/article_64210_8741.html
In this paper, finite element method is used to obtain thermal conductivity coefficients of single-walled carbon nanotube reinforced polypropylene. For this purpose, the two-dimensional representative volume elements are modeled. The effect of different parameters such as nanotube dispersion pattern, nanotube volume percentage in polymer matrix, interphase thickness between nanotube and surrounded matrix and nanotube aspect ratio on the thermal conductivity coefficient of nanotube/polypropylene nanocomposite are investigated. For the dispersion pattern, three different algorithms, including random dispersion, regular dispersion along the temperature difference and regular dispersion perpendicular to the temperature difference are employed. Furthermore, the temperature is considered in the range of 0°C to 200°C. The nanotube volume percentage in the polymer matrix is selected as 1%, 3% and 5%. It is shown that the polypropylene matrix reinforced by the regular distribution of nanotubes directed parallel to the temperature difference leads to the largest thermal conductivity coefficients. Besides, the nanocomposites with larger volume percentages of carbon nanotubes possess larger thermal conductivity coefficients.Thu, 31 May 2018 19:30:00 +0100Heat Transfer Study of Convective-Radiative Fin under the influence of Magnetic Field using ...
https://jcamech.ut.ac.ir/article_64207_0.html
The development and production of high performance equipment necessitate the use of passive cooling technology. In this paper, heat transfer study of convective-radiative straight fin with temperature-dependent thermal conductivity under the influence of magnetic field is carried out using Legendre wavelet collocation method. The numerical solution is used to investigate the effects of magnetic, convective and radiative parameters on the thermal performance of the fin. From the results, it is established that increase in magnetic, convective and radiative parameters increase the rate of heat transfer from the fin and consequently improve the thermal performance of the fin. The results obtained are compared with the results established results in literature and good agreements are found. The analysis can help in enhancing the understanding and analysis of the problem. Also, they can provide platform for improvement in the design of extended surfaces in heat transfer equipment under the influence of magnetic field.Tue, 19 Dec 2017 20:30:00 +0100Free Vibration Analysis of Nanoplates Made of Functionally Graded Materials Based On Nonlocal ...
https://jcamech.ut.ac.ir/article_65214_8741.html
In this paper, an analysis of free vibration in functionally graded nanoplate is presented. Third-order shear deformation plate theory is used to reach more accuracy in results. Small-scale effects are investigated using Eringen`s nonlocal theory. The governing equations of motion are obtained by Hamilton`s principle. It is assumed that the properties of nanoplates vary through their thicknesses according to a volume fraction power law distribution. The finite element method (FEM) is presented to model the functionally graded nanoplate and solve mathematical equations accurately. The finite element formulation for HSDT nanoplate is also presented. Natural frequencies of FG nanoplate with various boundary conditions are compared with available results in the literature. At the end some numerical results are presented to evaluate the influence of different parameters, such as power law index, nonlocal parameter, aspect ratio and aspect of length to thickness of nanoplate. In addition, all combinations of simply supported and clamped boundary conditions are considered.Thu, 31 May 2018 19:30:00 +0100Investigation on Instability of Rayleigh-Benard Convection Using Lattice Boltzmann Method with ...
https://jcamech.ut.ac.ir/article_64208_0.html
In this study, the effects of Prandtl number on the primary and secondary instability of the Rayleigh-Benard convection problem has been investigated using the lattice Boltzmann method. Two different cases as Pr=5.8 and 0.7 representing the fluid in liquid and gas conditions are examined. A body forces scheme of the lattice Boltzmann method was presented. Two types of boundary conditions in the presence of body forces are analyzed by the moment method and applied to a Poiseuille flow. Characteristic velocity was set in such a way that the compressibility effects are negligible. The calculations show that the increment of Prandtl number from 0.7 to 5.8 causes to create a secondary instability and onset of the oscillation in the flow field. Results show that at Pr=5.8, when the Rayleigh number is increased, a periodic solution appeared at Ra=48,000. It is observed that the dimensionless frequency ratio for Ra= 105 with Pr=5.8 is around 0.0065. The maximum Nusselt number for Ra = 105 with Pr=5.8 are estimated to be 5.4942.Tue, 19 Dec 2017 20:30:00 +0100Free vibration and buckling analysis of third-order shear deformation plate theory using exact ...
https://jcamech.ut.ac.ir/article_64679_8741.html
In this paper, wave propagation approach is used to analysis the free vibration and buckling analysis of the thick rectangular plates based on higher order shear deformation plate theory. From wave viewpoint, vibrations can be considered as traveling waves along structures. Waves propagate in a waveguide and reflect at the boundaries. It is assumed that the plate has two opposite edge 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 thick plates. In this study, firstly the matrices of propagation and reflection are derived and by combining them, the characteristic equation of the plate is obtained. Comprehensive results on dimensionless natural frequencies and dimensionless buckling loads of rectangular thick plates with different boundary conditions for various values of aspect ratio and thickness to length ratio are presented. It is observed that obtained results of wave propagation method with considerable accuracy are so close to obtained values by literature.Thu, 31 May 2018 19:30:00 +0100Variation of Parameters Method for Thermal Analysis of Straight Convective- Radiative Fins with ...
https://jcamech.ut.ac.ir/article_65076_8741.html
In this study, thermal performance across straight convecting- radiating fin with temperature dependent thermal conductivity is considered. The variation of parameters (VPM) is adopted to analyze the nonlinear higher order differential equations arising due to thermal conductivity and heat transfer coefficient on temperature distribution. Pertinent parameters such as thermo geometric and radiation parameters effect on temperature profile are investigated. Result obtained illustrates that quantitative increase of thermo geometric parameter causes a significant increase in temperature distribution due to increase in ratio of convective to conduction heat transfer which influence is significant toward fin base while increasing radiation parameter leads to decrease in temperature distribution due to increasing heat transfer from fins surface to ambient environment . Comparative analysis of result obtained in study against literature proves to be in satisfactory agreement. Therefore study provides useful insight to fins operational performance in applications such as radiators, boilers, refrigeration devices, oil pipelines amongst others.Thu, 31 May 2018 19:30:00 +0100Strongly stable multi-time stepping method with the option of controlling amplitude decay in ...
https://jcamech.ut.ac.ir/article_64206_8741.html
Recently, multi-time stepping methods have become very popular among scientist due to their high stability in problems with critical conditions. One important shortcoming of these methods backs to their high amount of uncontrolled amplitude decay. This study proposes a new multi-time stepping method in which the time step is split into two sub-steps. The first sub-step is solved using the well-known Newmark method and for the second sub-step an extended version of Newmark method is applied. In fact, similarity in basic formulas of the mentioned methods makes it available to control the amount of amplitude decay in responses obtained by the proposed method; in other words, the amplitude decay in the proposed method is controlled through constant parameters of the two methods applied on each sub-step. The precision assessment of the proposed method is performed using numerical approaches and revealed the minor period elongation error of the proposed method in comparison with other existing methods. In addition to this, the unconditional stability region of constant parameters is also determined through computation of spectral radius of the proposed method. Finally, practical assessment of the proposed method is performed through several numerical examples.Thu, 31 May 2018 19:30:00 +0100Investigation of energy consumption reduction in multistage compression process and its solutions
https://jcamech.ut.ac.ir/article_64489_0.html
During hot seasons the inlet temperature of Nitrogen increases, as a result compressor consumes more power for compressing a specific mass ratio of fluid and consequently total energy consumption of the compressor increases as well. In this research, a three stage centrifugal compressor with intercooler was modeled thermodynamically in order to decreases the energy consumption of the compressor. In each compressor, isentropic efficiency, outlet temperature of the Nitrogen gas and power compression was investigated. The effect of inlet Nitrogen temperature and cooling water temperature on intercoolers’ efficiency were investigated. In this study, Nitrogen gas is considered as an ideal gas. It is found that, in each compressor any growth in inlet temperature of the Nitrogen gas will result in linear increase in the outlet temperature of the Nitrogen gas and power compression furthermore, it is observed that increasing the temperature of Nitrogen gas has the most negative effect on efficiency and power compression of the first compressor in comparison to the second and the third compressor consequently, it will result in a 10 percent decrease in special power compression specially during summer time. According to the results, it is figured out that any growth in inlet Nitrogen temperature causes a smooth decline in isentropic and Power Compression of the first, second and third compressors besides increasing the temperature of the Nitrogen gas increases the isentropic efficiency up to 3 Percent and increasing the cooling water temperature decreases the intercooler efficiency up to 7 Percent.Mon, 08 Jan 2018 20:30:00 +0100Effect of the asymmetrical rolling process on the micro hardness and microstructure of brass wire
https://jcamech.ut.ac.ir/article_64550_8741.html
Current experimental investigation deals with the effects of asymmetrical rolling parameters on the inhomogeneity, microstructure, mechanical, and geometrical properties of rolled brass wire. Toward this end, a roll machine with three different roll radii ratios was set up. The asymmetrical conditions are arranged using three different sets of rolls with different diameters that result into different reductions. Investigating the effects of the inhomogeneous structure of unrolled brass wire on the output radius, total width, and width of the rolled part (in the z direction) are the aim of this study. Furthermore, the influences of three unlike roll radius ratios on the grain size, inhomogeneity and mechanical properties of the rolled brass wire are considered. In addition, the micro-Vickers measurements on the rolled brass wire are performed. It is shown that the regions near to faster roll with greater strain quantities have higher values of hardness compared to the other areas.Thu, 31 May 2018 19:30:00 +0100Modelling of the Dynamics of an immersed body in a microchannel with stenosis using the ...
https://jcamech.ut.ac.ir/article_64549_0.html
In the present study, the combination of lattice Boltzmann and immersed boundary methods is used to simulate the motion and deformation of a flexible body. Deformation of the body is studied in microchannel with stenosis and the effect of the flexibility changes on its deformation is investigated. The obtained results in the present manuscript show that by increasing the elasticity modulus, the deformation of the body and its speed decrease. In this case, the flow pressure around the body increase. When the body is initially located outside the microchannel center, tank-treading motion occurs due to the difference in velocity of the shear layers. In addition, with a decrease in the size of microchannel stenosis, the body is less deformed and goes faster and reaches to the end of the microchannel in less time. The faster or slower movement of the biological membranes than the normal state causes the proper exchange of materials between the membrane wall and the surrounding flow and that disturbs its most important duty i.e. the exchange of materials with tissues. The analysis in this study shows that the results of the simulation are in good agreement with the available results and demonstrates the efficiency of the combination of lattice Boltzmann and immersed boundary methods to simulate the dynamic behavior of biological membranes, red blood cells and deformable particles inside the flow.Wed, 10 Jan 2018 20:30:00 +0100Modelling of Suddenly Expanded Flow Process in Supersonic Mach Regime using Design of ...
https://jcamech.ut.ac.ir/article_64593_8741.html
The present work is an attempt to model, analyze, and control the flow at the base of an abruptly expanded circular duct by using design of experiments (DOE) and response surface methodology (RSM). Tiny-jets in the form of orifice were positioned at an interval of 900, 6.5 mm from the primary axis of the main jet of the nozzle. Experiments were conducted to measure two responses namely, base pressure without the use of micro jets or active control (WoC) and base pressure with the use of micro jets or active control (WC). Mach number (M), nozzle pressure ratio (NPR), area ratio (AR) and length to diameter ratio (L/D) were considered as input variables (parameters), which control the outputs (i.e. base pressure). Non-linear regression models based on central composite design (CCD) and Box-Behnken design (BBD) have been developed in order to facilitate the input-output relationships. Moreover, the significance of main, square and interaction terms of the developed models have been tested by performing analysis of variance (ANOVA). The ANOVA and significance test results and their respective correlation coefficient values indicate that both the CCD and BBD regression models are statistically adequate for both the base pressure responses of without control and with control respectively. The performances of the nonlinear models have been validated for accuracy prediction by use of 15 test cases. The performance of BBD model is found to be better in forecasting base pressure for both cases of without control and with control when compared to the CCD model.Thu, 31 May 2018 19:30:00 +0100A Genetic Algorithm based Optimization Method in 3D Solid Reconstruction from 2D Multi-View ...
https://jcamech.ut.ac.ir/article_66039_8741.html
There are mainly two categories for a 3D reconstruction from 2D drawings: B-Rep and CSG that both these methods have serious weaknesses despite being useful. B-Rep method which has been older and have wider function range is problematic because of high volume of calculations and vagueness in answers and CSG method has problem in terms of very limited range of volumes and drawings that it can analyze. Proposed method in this paper is an innovative method based on B-Rep in which optimization of genetic algorithm has been used to identify the relationship among the components of various views in 2D drawings. Using genetic algorithm that is a stochastic algorithm contributes that high volume of calculation that is one of main weaknesses of B-Rep method is solved. Moreover, considering correspondence condition of one to one among response in this method has caused that vagueness problem which is another weakness of B-Rep method to be almost solved so it can be said in addition to having wide range, present method doesn’t have common problems of B-Rep method and it even turns it to an effective method.Thu, 31 May 2018 19:30:00 +0100Surface hardness improvement in high efficiency deep grinding process by optimization of ...
https://jcamech.ut.ac.ir/article_64205_8741.html
The grinding is one of the most important methods that directly affects tolerances in dimensions, quality and finished surface of products. One of the major problems in the material removal processes specially grinding is the heat generation during the process and the residual tensile stress in the surfaces of product. Therefore, optimization of High Efficiency Deep Grinding (HEDG) process is the main goal of this study to reduce the generated heat and residual tensile stress and increase strength and surface hardness of AISI1045 annealed steel. To this end, the effects of main parameters e.g. depth of cut, wheel speed, workpiece speed and cross feed on surface hardness has been investigated. The experimental results demonstrated the reduction in surface temperature and increase in hardness as optimum conditions are applied to the grinding process. Moreover, the experimental results were validated by comparing with other experimental results and analyzing of surface microhardness, surface temperature and normal and tangential forces.Thu, 31 May 2018 19:30:00 +0100Design and Fabrication of a Portable 1-DOF Robotic Device for Indentation Tests
https://jcamech.ut.ac.ir/article_63272_8741.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.Thu, 31 May 2018 19:30:00 +0100Finite Element Investigation and comparing different models of wrist prosthesis
https://jcamech.ut.ac.ir/article_64655_0.html
Joint replacement surgery in the wrist is less common than other replacement, but can be an option if you have painful arthritis that does not respond to other treatments. In wrist joint replacement surgery, the damaged parts of the wrist bones are removed and replaced with artificial components, called a wrist prosthesis. If the cartilage is worn away or damaged by injury, infection, or disease, the bones themselves will rub against each other, wearing out the ends of the bones. This causes a painful, arthritic condition. Osteoarthritis, the most common form of arthritis, results from a gradual wearing away of the cartilage covering on bones. Rheumatoid arthritis is a chronic inflammatory disease of the joints that results in pain, stiffness and swelling. Rheumatoid arthritis usually affects several joints on both the right and left sides of the body. Both forms of arthritis may affect the strength of the fingers and hand, making it difficult to grip or pinch.Wed, 17 Jan 2018 20:30:00 +0100Impeller and volute design and optimization of the centrifugal pump with low specific speed in ...
https://jcamech.ut.ac.ir/article_64656_0.html
Now a day centrifugal pumps are vital components of industries. Certainly, one of the most important specifications of centrifugal pumps are the performance curves. In the present work, performance curves of a centrifugal pumps are obtained by Computational fluid dynamics (CFD) and as an outcome, CFD results compare by practical curves. At the first step impeller and volute are designed with two standards and at the end former design completed by automatic design process using CFturbo software. For this purpose, full 3D-RANS equations in coupled with SST turbulence model are solved for several flow rate between 20% and 140% of the operation condition by means of a commercial code, CFX. This simulation is defined by means of the multi-reference frame technique in which the impeller is situated in the rotating reference frame, and the volute is in the fixed reference frame. Proposed simulation is based on a steady state flow, non-Newtonian, incompressible and constant property condition. Operation point is simulated to get the total head and then non-operation points are simulated to obtain performance curves. Practical curves and numerical ones are in good agreement, so numerical approach could be a perfect way to make centrifugal pump design better and easier. Indeed pump simulation with CFD approach can increase our knowledge about pump behavior such as consumption energy, trimming process and saving energy before we have any activities on the pump so the predictions have bettering and excise about any process on the pump.Wed, 17 Jan 2018 20:30:00 +0100Comparison between the frequencies of FML and composite cylindrical shells using beam modal ...
https://jcamech.ut.ac.ir/article_64657_0.html
A comparison between the vibration of fiber-metal laminate (FML) and composite cylindrical shells has been studied in this manuscript. Love’s first approximation shell theory has been applied to obtain Strain-displacement relations. In addition, beam modal function model has been used to analyze the cylindrical shell with different boundary conditions. In this manuscript, the frequencies of FML and composite cylindrical shells have been compared to each other for different materials, lay-ups, boundary conditions, axial and circumferential wave numbers. The most commercially available FMLs are CARALL (carbon reinforced aluminium laminate), and GLARE (glass reinforced aluminium laminate), which are studied in this research. The results showed although the frequencies of carbon/epoxy are greater than glass/epoxy for all of the n, this process is not constant for FML. Also, with increasing the n, the frequencies of FML cylindrical shells are converged more faster than the composite one. Moreover, the frequencies of both boundary conditions are converged with increasing n for both FML and composite cylindrical shells.Wed, 17 Jan 2018 20:30:00 +0100Modification of exponential based hyperelastic strain energy to consider free stress initial ...
https://jcamech.ut.ac.ir/article_64739_8741.html
In this research, the exponential stretched based hyperelastic strain energy was modified to provide the unstressed initial configuration. To this end, as the first step, the model was calibrated by the experimental data to find the best material parameters. The fitting results indicated material stability in large deformations and basic loading modes. In the second step, the initial pseudo stress value (ISV) was eliminated from the hyperelastic strain energy using a function of the determinant of the deformation gradient. The modified and unmodified models were implemented in ABAQUS/VUMAT user subroutine and the deformation behavior of the natural rubber and the thermoplastic elastomer was predicted. The results obtained from the modified model represented a better agreement with the experimental data, in comparison to those gained by the unmodified model. In order to present the significance of the unstressed initial configuration in engineering applications, the stenting phenomenon in the atherosclerosis human artery was investigated. It was revealed that a uniform stress distribution could be achieved in the artery using the modified model, thereby reducing the possibility of tearing and restenosis.Thu, 31 May 2018 19:30:00 +0100Numerical simulation of the effect of particle size on the erosion damage in ball valves of ...
https://jcamech.ut.ac.ir/article_64776_0.html
Ball valve is one of valves that have many applications in industry especially in gas delivery systems. This kind of valve is categorized in the on - off flow control valve. This study aims to investigate unusual application of ball valve to control fluid flow in industry and its destructive effect including erosion of ball and body of valve. Simulation of industrial ball valve is done using ANSYS Fluent software and effect of erosion on it is investigated in different working conditions. In this article, working condition is performed regarding 2 different concentrations for suspended particles as well as four positions of ball in different angles. We assess the effect of increased particle diameter on the rate of erosion for three diameters (3.86e-6 m , 267.45e-6 m and 531.03e-6 m) in four conditions of valve (25%, 50%, 75% and 100%) and two different concentrations of particle (3% and 6%). It is shown that rate of erosion is increased with increased particle diameters in 25%, 50% and 75% open state of valve. On the contrary, the results show that opposite rule governs complete open state. Furthermore, it is demonstrated that increase in particle diameter decreases the area of erosion in four conditions of valve.Fri, 26 Jan 2018 20:30:00 +0100Size-dependent on vibration and flexural sensitivity of atomic force microscope
https://jcamech.ut.ac.ir/article_65215_0.html
In this paper, the free vibration behaviors and the flexural sensitivity of atomic force microscope cantilevers with small-scale effects are investigated. To study the small-scale effects on natural frequencies and flexural sensitivity, the consistent couple stress theory is applied. In this theory, the couple stress is assumed skew-symmetric. Unlike the classical beam theory, the new model contains a material-length-scale parameter and can capture the size effect. For this purpose, the Euler–Bernoulli beam theory is used to develop the AFM cantilever. The tip interacts with the sample that is modeled by a spring with constant of k. The equation of motion is obtained through a variational formulation based on Hamilton’s principle. In addition, the analytical expressions for the natural frequency and sensitivity are also derived. At the end, some numerical results are selected to study the effects of material-length scale parameter and dimensionless thickness on the natural frequency and flexural sensitivity.Thu, 15 Feb 2018 20:30:00 +0100Evaluation of Thermo-mechanical stress in work rolls of ring rolling mill under thermal and ...
https://jcamech.ut.ac.ir/article_65484_0.html
The defect in work rolls directly influence the forming cost and the final shape of the product. The researchers tend to investigate the thermo-mechanical stress in work roll of rolling machines. These stresses may reduce the roll life. Since the investigation of the thermo-mechanical stress in work roll with real-conditions is complex, comprehensive studies by means of numerical methods are available in numerous literature. However, simulating the thermo-mechanical stress is time-consuming. So, most researchers desire to simplify the geometry and boundary conditions in order to reduce simulation cost. This paper proposes an integrated finite element model to study the thermo-mechanical behavior of work rolls during hot ring rolling process. Various methods were simulated and advantages and disadvantages of each method were discussed. Due to complexities of ring rolling process, the presented model was used in flat rolling in order to verify model integrity. After that work rolls of ring rolling mill subjected to partial boundary conditions are investigated. The results of thermal and thermo-mechanical simulations show stresses in the contact region of work rolls are rather different. However, they expressed the same results in other regions. Based on the obtained results, it is revealed that the effect of mechanical loads in the equivalent stresses should be considered and the location of equivalent maximum stress is below the surface.Wed, 28 Feb 2018 20:30:00 +0100Prediction and optimization of load and torque in ring rolling process through development of ...
https://jcamech.ut.ac.ir/article_65485_0.html
Developing artificial neural network (ANN), a model to make a correct prediction of required force and torque in ring rolling process is developed for the first time. Moreover, an optimal state of process for specific range of input parameters is obtained using Genetic Algorithm (GA) and Particle Swarm Optimization (PSO) methods. Radii of main roll and mandrel, rotational speed of main roll, pressing velocity of mandrel and blank size are considered as input parameters. Furthermore, the required load and torque in ring rolling process are taken into account as process outputs. Various three dimensional finite element simulations are performed for different sets of process variables to achieve preliminary data for training and validation of the neural network. Besides, the finite element model is approved via comparison with the experimental results of the other investigators. The Back Propagation (BP) algorithm is considered to develop Levenberg–Marquardt feed-forward network. Additionally, Model responses analysis is carried out to improve the understanding of the behavior of the ANN model. It is concluded that results of ANN predictions have an appropriate conformity with those from simulation and experiments. Moreover, GA and PSO methods have been implemented to obtain the optimal state of process while their outcomes have been also compared.Tue, 06 Mar 2018 20:30:00 +0100Numerical Simulation of the Effect of Valve Opening and Particle Concentration on the Erosion ...
https://jcamech.ut.ac.ir/article_65701_0.html
Ball valve is one of valves that have many applications in industry especially in gas delivery systems. This kind of valve is categorized in the on- off flow control valve. This study aims to investigate unusual application of ball valve to control fluid flow in the oil and gas industry and its destructive effect including erosion of ball and body of valve. Simulation of industrial ball valve is done using ANSYS Fluent software and effect of erosion on it is investigated in different working conditions. In this study, working condition is performed regarding 3 different concentrations for suspended particles as well as four positions of ball in different angles. It is shown that rate of erosion for 25% open state of valve is increased to about 15000 times of complete open state of valve, and rate of erosion is increased to about 3500 times for half open state (50% open state); and rate of erosion is increased to about 220 times for 75% open state of valve.Tue, 24 Apr 2018 19:30:00 +0100Hydrodynamic investigation of multiple rising bubbles using lattice Boltzmann method
https://jcamech.ut.ac.ir/article_65702_0.html
Hydrodynamics of multiple rising bubbles as a fundamental two-phase phenomenon is studied numerically by lattice Boltzmann method and using Lee two-phase model. Lee model based on Cahn-Hilliard diffuse interface approach uses potential form of intermolecular forces and isotropic finite difference discretization. This approach is able to avoid parasitic currents and leads to a stable procedure to simulate two-phase flows. Deformation and coalescence of bubbles depend on a balance between surface tension forces, gravity forces, inertia forces and viscous forces. A simulation code is developed and validated by analysis of some basic problems such as bubble relaxation, merging bubbles, merging droplets and single rising bubble. Also, the results of two rising bubbles as the simplest interaction problem of rising bubbles have been calculated and presented. As the main results, square and lozenge initial configuration of nine rising bubbles are studied at Eotvos numbers of 2, 10 and 50. Two-phase flow behavior of multiple rising bubbles at same configurations is discussed and the effect of Eotvos number is also presented. Finally, velocity field of nine rising bubbles is presented and discussed with details.Tue, 24 Apr 2018 19:30:00 +0100Solving Single Phase Fluid Flow Instability Equations Using Chebyshev Tau- QZ Polynomial
https://jcamech.ut.ac.ir/article_65771_0.html
In this article the instability of single phase flow in a circular pipe from laminar to turbulence regime has been investigated. To this end, after finding boundary conditions and equation related to instability of flow in cylindrical coordination system, which is called eigenvalue Orr Sommerfeld equation, the solution method for these equation has been investigated. In this article Chebyshev polynomial Tau-QZ algorithm has been selected for the solution technique to solve the Orr Sommerfeld equation because in this method some of complex terms in the instability equation in cylindrical coordination will be appeared. After finding Orr Sommerfeld parameters related to Chebyshev polynomial Tau-QZ algorithm the solution have been done for Re=5000 and Re=1000, then the results had been compared with the results of valid references where other methods had been used in them. It have been observed that the use of Chebyshev Tau-QZ algorithm has higher accuracy concerning the results and it also has a higher accurate technique to solve the Orr Sommerfeld instability equations in cylindrical coordination system.Fri, 27 Apr 2018 19:30:00 +0100Thermal simulation of two-phase flow in under-balanced drilling operation with oil and gas ...
https://jcamech.ut.ac.ir/article_65810_0.html
The accurate prediction of wellbore temperature distribution helps to accurately estimate well pressure profile and bottom-hole pressure (BHP) which is important in the under-balanced drilling (UBD) operation. In this paper effect of temperature variation due to heat transfer of drilling fluid with the formation and also oil and gas production from the reservoir into the annulus in under-balanced drilling condition were investigated. Gas-liquid two-phase flow model considering thermal interaction with the formation is used to numerically simulate a well with real dimensions. Based on drilling fluids flow and heat transfer characteristics in wells, conservations of mass and momentum and energy equations have been developed to compute BHP and wellbore temperature and pressure profile. After temperature and pressure validation of the numerical model, the effect of heat transfer between drilling fluid inside the well and the formation was considered on the pressure distribution and bottom-hole pressure. The results of two-phase flow, considering thermal effect gives better results compared to two-phase flow with geothermal temperature distribution analysis and better accuracy in comparison with other models.Sat, 05 May 2018 19:30:00 +0100Fatigue and Anisotropic behaviours of cold rolled AA1200 Aluminium Alloy
https://jcamech.ut.ac.ir/article_65822_0.html
This study examines the fatigue and anisotropy behaviour of cold rolled AA1200 aluminium alloy for light weight automotive connecting rod application. Aluminium (Al) 1200 ingots were melted at temperature of 680 0C (after one hour of heating) cast in sand mould and cast samples homogenized for 6 hrs at 480 0C. The cold rolling process was carried out after homogenisation for 10, 20, 30, 40 and 50% thickness reductions. The samples were characterised in 00, 150, 300, 450, 600, 750 and 900 to the rolling direction. The results show that degree of deformation increase linearly with mean stress, stress range, stress ratio, stress amplitude, thickness and area ratio for all the reductions and directions examined. Area and thickness ratio increases linearly with deformation at higher inclination (> 150). The fatigue life obtained in this work shows life cycles at different degrees of deformation: 7.5 x 104 cycles at 10% reduction, 1.3 x105 cycles at 20% reduction, 4.3 x 104 cycles at 30% reduction; 2.6 x 105 cycles at 40% reduction and 1.09 x 105 cycles at 50% reduction). The results of this study provide evidence that systemic controlled cold deformation can potentially be used to significantly enhance the fatigue life of AA1200 aluminium alloy components subjected to cyclic loadings.Sun, 06 May 2018 19:30:00 +0100Attractor Based Analysis of Centrally Cracked Plate Subjected to Chaotic Excitation
https://jcamech.ut.ac.ir/article_66038_0.html
The presence of part-through cracks with limited length is one of the prevalent defects in the plate structures. Due to the slight effect of this type of damages on the frequency response of the plates, conventional vibration-based damage assessment could be a challenging task. In this study for the first time, a recently developed state-space method which is based on the chaotic excitation is implemented and nonlinear prediction error (NPE) is proposed as a geometrical feature to analyze the chaotic attractor of a centrally cracked plate. For this purpose using line spring method (LSM) a nonlinear multi-degree of freedom model of part through cracked rectangular plate is developed. Tuning of Lorenz type chaotic signal is conducted by crossing of the Lyapunov exponents’ spectrums of nonlinear model of the plate and chaotic signal and in the next step by varying the tuning parameter to find a span in which a tangible sensitivity in the NPE could be observable. Damage characteristics such as length, depth and angle of crack are altered and variation of proposed feature is scrutinized. Results show that by implementation of the tuned chaotic signal, tangible sensitivity and also near to monotonic behavior of NPE versus damage intensity are achievable. Finally, the superiority of the proposed method is examined through the comparison with the frequency-based method.Thu, 22 Feb 2018 20:30:00 +0100A wave-based computational method for free vibration and buckling analysis of rectangular Reddy ...
https://jcamech.ut.ac.ir/article_66040_0.html
In this paper, the wave propagation method is combined with nonlocal elasticity theory to analyze the buckling and free vibration of rectangular Reddy nanoplate. Wave propagation is one of the powerful methods for analyzing the vibration and buckling of structures. 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 thick nanoplates. In this study, firstly the matrices of propagation and reflection are derived. Then, these matrices are combined to provide an exact method for obtaining the natural frequencies and critical buckling loads which can be useful for future studies. 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 obtained results are presented to evaluate the influence of different parameters such as nonlocal parameter, aspect ratio and thickness to length ratio of nanoplate.Tue, 22 May 2018 19:30:00 +0100Minimization of Entransy Dissipations of a Finned Shell and Tube Heat Exchanger
https://jcamech.ut.ac.ir/article_66041_0.html
Improving heat transfer and performance in a radial, finned, shell and tube heat exchanger is studied in this study. According to the second law of thermodynamics, the most irreversibilities of convective heat transfer processes are due to fluid friction and heat transfer via finite temperature difference. Entransy dissipations are due to the irreversibilities of convective heat transfer. Therefore, the number of entrancy dissipation is considered as the optimization objective. Thirteen optimization variables are considered, such as the number of tubes, tube diameter, tube length, fin height, fin thickness, the number of fins per inch length of tube and baffle spacing ratio. The “Delaware modified” technique is used to determine heat transfer coefficients and the shell-side pressure drop. In this technique, the baffle cut is 20 percent. The results show that using genetic algorithm the optimization can be improve the heat transfer by 13 percent and performance of heat exchanger increased by 18 percent. In order to show the accuracy of the algorithm the results compared to the particle swarm optimization.Tue, 22 May 2018 19:30:00 +0100Effects of Casting Speed and Runner Angle on Macrosegregation of Aluminium-Copper Alloy.
https://jcamech.ut.ac.ir/article_66042_0.html
Abstract During the solidification of binary metal alloys, chemical heterogeneities at product scale over a long distance range (1cm-1m) develop and this has detrimental effect on the resulting mechanical properties of cast products. Macrosegregation is of great concern to alloy manufacturers and end users as this problem persist. In this study, the use of process parameters namely casting speed and runner angle to reduce macro-segregation in aluminum-copper-zinc binary alloy solidification is reported. The results from optical microscope, scanning electron microscope and energy dispersive spectrometry show that these parameters significantly influenced the development, size and volume of macro-segregation. The combination of parameters namely the pouring height between 96 mm/s, 100mm/s, and runner angles between 1200, 1500 produced less segregations with improved mechanical properties within standard specification. The tensile strength (110 MPa), modulus of elasticity (6800 MPa) and 2.5 % elongation obtained in this study are within standard (88- 124 MPa), 7100 MPa and (1-25 %) respectively for this class of alloy.Wed, 23 May 2018 19:30:00 +0100A review of size-dependent elasticity for nanostructures
https://jcamech.ut.ac.ir/article_66097_8741.html
Nanotechnology is one of the pillars of human life in the future. This technology is growing fast and many scientists work in this field. The behavior of materials in nano size varies with that in macro dimension. Therefore scientists have presented various theories for examining the behavior of materials in nano-scale. Accordingly, mechanical behavior of nano-plates, nanotubes nano-beams and nano-rodes are being investigated by Non-classical elasticity theories. This review includes the last researches on bending, buckling, and vibration of nano-plates, nano-beams, nanorods, and nanotubes which were investigated by non-local elasticity theory and nonlocal strain gradient theory. Great scholars have written valuable reviews in the field of nanomechanics. Therefore, given a large number of researches and the prevention of repetition, the articles in the past year are reviewed. Thu, 31 May 2018 19:30:00 +0100Static and dynamic axial crushing of prismatic thin-walled metal columns
https://jcamech.ut.ac.ir/article_67381_0.html
In this paper, a novel approach is proposed to investigate the progressive collapse damage of prismatic thin walled metal columns with different regular cross sections, under the action of axial quasi-static and impact loads. The present work mainly focuses on implementation of some important factors which have been neglected in other studies. These factors include the effect of reducing impactor velocity and inertia effect during collapse, a mixed collapse mode for crushing mechanism, and consideration of a realistic elasto-plastic model for material. Taking all these factors into account, the analysis led to some parametric algebraic equations without a possible general solution in terms of collapse variables. Consequently, a new theoretical approach was proposed based on previously offered Super Folding Element (SFE) theory, to obtain the closed form explicit relations for the static and dynamic mean crushing forces and collapse variables. The proposed approach considers an analytic-numeric discretization procedure to solve these equations. To evaluate the results, a detailed finite element analysis on square mild steel models was conducted under an axial impact load, using LS-DYNA and ANSYS software programs. Comparison of the experimental results that are available in the literature with those of finite element analysis, shows the applicability of this approach in predicting the collapse behavior in such structures.Sun, 02 Sep 2018 19:30:00 +0100Free Vibration Analysis of BNNT with Different Cross-Sections via Nonlocal FEM
https://jcamech.ut.ac.ir/article_68033_0.html
In the present study, free vibration behaviors of of carbon nanotube (CNT) and boron nitride nanotube (BNNT) have been investigated via Eringen’s nonlocal continuum theory. Size effect has been considered via nonlocal continuum theory. Nanotubes have become popular in the world of science thanks to their characteristic properties. In this study, free vibrations of Boron Nitride Nanotube (BNNT) and Carbon Nanotube (CNT) are calculated using the Nonlocal Elasticity Theory. Frequency values are found via both analytical and finite element method (FEM). Galerkin weighted residual method is used to obtain the finite element equations. BNNT and CNT are modeled as Euler - Bernoulli Beam and solutions are gained by using four different cross-section geometries with three boundary conditions. Selected geometries are circle, rectangle, triangle, and square. Frequency values are given in tables and graphs. The effect of cross-section, boundary conditions and length scale parameter on frequencies has been investigated in detail for BNNT.Sun, 14 Oct 2018 20:30:00 +0100A preconditioned solver for sharp resolution of multiphase flows at all Mach numbers
https://jcamech.ut.ac.ir/article_68327_0.html
A preconditioned five-equation two-phase model coupled with an interface sharpening technique is introduced for simulation of a wide range of multiphase flows with both high and low Mach regimes. Harten-Lax-van Leer-Contact (HLLC) Riemann solver is implemented for solving the discretized equations while tangent of hyperbola for interface capturing (THINC) interface sharpening method is applied to reduce the excessive diffusion of the method at the interface. In this work, preconditioning technique is used in a system of equations including viscous and capillary effects. Several one- and two-dimensional test cases are used to evaluate the performance and accuracy of this method. Numerical results demonstrate the efficiency of preconditioning in low Mach number flows. Comparisons between results of preconditioned and conventional system highlight the necessity of using preconditioning technique to reproduce main characteristics of low-speed flow regimes. Additionally, preconditioned systems transform to the conventional systems at high Mach number flows thus exhibiting the same level of accuracy as the standard flow solver. Therefore, the preconditioned compressible two-phase method can be used as an all-speed two-phase flow solver accounting for capillary and viscous stresses.Tue, 13 Nov 2018 20:30:00 +0100The effect of boundary conditions on the accuracy and stability of the numerical solution of ...
https://jcamech.ut.ac.ir/article_68329_0.html
The aim of this study is to investigate the effect of boundary conditions on the accuracy and stability of the numerical solution of fluid flows in the context of single relaxation time Lattice Boltzmann method (SRT-LBM). The fluid flows are simulated using regularized, no-slip, Zou-He and bounce back boundary conditions for straight surfaces in a lid driven cavity and the two-dimensional flow in a channel. The solutions for all types of the boundary conditions show good agreement with numerical references and exact solutions. The cavity pressure contours at low relaxation time show drastic perturbations for Zou-He boundary condition, whereas, the perturbation is ignorable for regularized boundary condition. At High Reynolds number, severe velocity gradients are major reason for numerical instabilities. Therefore, regularized boundary condition, which considers the velocity gradient in its calculation, has better numerical stability comparing the Zou-He boundary condition. Overall, the selection of appropriate boundary condition depends on the flow regime and Geometry. The proper boundary conditions at low Reynolds numbers are Zou-He and bounce back boundary conditions, and at high Reynolds numbers, regularized and no-slip boundary conditions are recommended.Tue, 13 Nov 2018 20:30:00 +0100Internal heat source in a temperature dependent thermoelastic half space with microtemperatures
https://jcamech.ut.ac.ir/article_68652_0.html
A two dimensional deformation due to internal heat source in a thermoelastic solid with microtemperatures under the dependence of modulus of elasticity and thermal conductivity on reference temperature has been studied. A mechanical force of constant magnitude is applied at the free surface of thermoelastic half space. The normal modes technique has been applied to obtain the exact expressions for the components of normal displacement, microtemperature, normal force stress, temperature distribution, heat flux moment tensor and tangential couple stress for thermoelastic solid with microtemperatures. The effect of internal heat source, thermal conductivity and microrotation on the derived components have been derived analytically. The graphical results are shown in the presence and absence of thermal conductivity and microrotation to show the appreciable effect of rotation and temperature on the quantities. The problem may also be extended to show the effect of different types of mechanical and thermal sources applied in the medium.Thu, 06 Dec 2018 20:30:00 +0100A two dimensional Simulation of crack propagation using Adaptive Finite Element Analysis
https://jcamech.ut.ac.ir/article_68653_0.html
Finite element method (FEM) is one of the most famous methods which has many applications in varies studies such as the study of crack propagation in engineering structures. However, unless extremely fine meshes are employed, problem arises in accurately modelling the singular stress field in the singular element area around the crack tip. In the present study, the crack growth simulation has been numerically simulated by using the dens mesh finite element source code program using Visual FORTRAN language. This code includes the mesh generator based on the advancing front method as well as all the pre and post process for the crack growth simulation under linear elastic fracture mechanics theory. The stress state at a crack tip has been described by the stress intensity factor which is related to the rate of crack growth. The displacement extrapolation technique is employed to obtain crack tip singular stresses and the stress intensity factors values. The crack direction is predicted using the maximum circumferential theory. Verification of the predicted stress intensity factors and crack path direction are validated with relevant experimental data and numerical results obtained by other researchers with good agreements.Thu, 06 Dec 2018 20:30:00 +0100ON MAXWELL'S STRESS FUNCTIONS FOR SOLVING THREE DIMENSIONAL ELASTICITY PROBLEMS IN THE THEORY ...
https://jcamech.ut.ac.ir/article_68654_0.html
The governing equations of three dimensional elasticity problems include the six Beltrami-Michell stress compatibility equations, the three differential equations of equilibrium, and the six material constitutive relations; and these are usually solved subject to the boundary conditions. The system of fifteen differential equations is usually difficult to solve, and simplified methods are usually used to achieve a solution. Stress-based formulation and displacement-based formulation methods are two common simplified methods for solving elasticity problems.This work adopted a stress-based formulation for a three dimensional elasticity problem. In this work, the Maxwell's stress functions for solving three dimensional problems of elasticity theory were derived from fundamental principles. It was shown that the three Maxwell stress functions identically satisfy all the three differential equations of static equilibrium when body forces were ignored. It was further shown that the three Maxwell stress functions are solutions to the six Beltrami-Michell stress compatibility equations if the Maxwell stress functions are potential functions. It was also shown that the Airy's stress functions for two dimensional elasticity problems are special cases of the Maxwell stress functions.Thu, 06 Dec 2018 20:30:00 +0100Nonlinear stability of rotating two superposed magnetized fluids with the technique of the ...
https://jcamech.ut.ac.ir/article_68655_0.html
In the present work, the Rayleigh-Taylor instability of two rotating superposed magnetized fluids within the presence of a vertical or a horizontal magnetic flux has been investigated. The nonlinear theory is applied, by solving the equation of motion and uses the acceptable nonlinear boundary conditions. However, the nonlinear characteristic equation within the elevation parameter is obtained. This equation features a transcendental integro-Duffing kind. The homotopy perturbation technique has been applied by exploitation the parameter growth technique that results in constructing the nonlinear frequency. Stability conditions are derived from the frequency equation. It's illustrated that the rotation parameter plays a helpful result. It's shown that the stability behavior within the extremely uniform rotating fluids equivalents to the system while not rotation. A periodic solution for the elevation function has been performed. Numerical calculations area unit created for linear analysis furthermore the nonlinear scope. Moreover, the elevation function has been premeditated versus the time parameter. The strategy adopted here is vital and powerful for solving nonlinear generator systems with a really high nonlinearity arising in nonlinear science and engineering.Thu, 06 Dec 2018 20:30:00 +0100Longitudinal Magnetic Field Effect on Torsional Vibration of Carbon Nanotubes
https://jcamech.ut.ac.ir/article_68656_0.html
Torsional dynamic analysis of carbon nanotubes under the effect of longitudinal magnetic field is carried out in the present study. Torque effect of an axial magnetic field on a carbon nanotube has been defined using Maxwell’s relation. Nonlocal governing equation and boundary conditions for carbon nanotubes are obtained by using Hamilton’s minimum energy principle. Eringen’s nonlocal stress gradient elasticity theory is used in the formulation. Fourth order nonlocal equation of motion is solved by utilizing differential quadrature method. Clamped-clamped and clamped-free nonlocal boundary conditions are considered. Nonlocal and axial magnetic field effects on torsional vibration of carbon nanotubes are investigated. The magnetic field has significant effects on the dynamics of carbon nanotubes and may lead to torsional buckling. Critical torsional buckling load reduces with nonlocal effects. Nonlocality shows softening effect on carbon nanotube’s lattice structure. Present results can be used in the design and analysis of nanoelectromechanical products like nano-motors.Sun, 25 Nov 2018 20:30:00 +0100