Journal of Computational Applied Mechanics
Volume:49 Issue: 1, Jun 2018

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.