In this study, continuous contact problem in the functionally graded (FG) layer loaded with two rigid flat blocks resting on the elastic semi-infinite plane was analyzed by the finite element method. The two-dimensional numerical model of the FG layer was made with the software added to the ANSYS program. This software can be adapted to all contact problem types by making minor changes. The accuracy check of the program was performed by comparing with the analytical solution of the problem by homogeneous layer and its solution by the finite element method. So, fast and practical solutions can be obtained by the developed finite element method on many applications such as; automotive, aviation and space industry applications. The comparisons made showed that the proposed solution gave good results at acceptable levels. In the problem, it was thought that all surfaces were frictionless. The external loads P and Q were transmitted to the FG layer via two flat rigid blocks. Normal stresses between the FG layer and the elastic plane, initial separation loads, initial separation distances and contact stresses under the blocks were investigated for various dimensionless quantities.

It is of practical significance to develop a constitutive model which is able to predict the thermomechanical behaviors of the shape memory effect occurring in a shape memory polymer (SMP) accurately. The mechanism of shape memory effect of SMP is explained based on the assumption that SMP is composed by two phases, reversible phase and stationary phase. Especially the different flow elements are respectively added to the reversible phase and stationary phase in order to express the plastic behavior of SMP. There are two springs in series, one dashpot and one flow element in the reversible phase. There are two springs in parallel, one dashpot and one flow element in the stationary phase. A constitutive equation is developed to express the thermo-mechanical behaviors of shape memory effect in the SMP based on viscous-elastic mechanics and plastic theory. An internal variable, frozen ratio, is defined to follow the shape memory process in SMP, and the material properties are described as the functions of frozen ratio based on phase transition theorem. The developed constitutive model, which includes above constitutive equation and material parameter functions, is used to numerically simulate the thermo-mechanical behaviors of SMP under various load cycles. Results show that the developed constitutive model can not only predict the shape memory process of SMP accurately, but also express the rate-dependent behaviors of SMP effectively.

Inhomogeneous materials (the ones exhibiting spatial variations in their, all or specific, material properties) present a great deal of interest for scientists and engineers in both academia and industry. For over a hundred years, the mechanical behavior of inhomogeneous materials excites numerous attempts in mathematical modeling and development of methods for proper analysis and verification. With this concern, the reach experience was gained by scientists of different scientific schools in many countries. Despite numerous significant achievements, some results, unfortunately, remain unnoticed by the wide scientific community. On the other hand, one can observe a growing number of publications which repeatedly publish the solutions reported years ago or deal with the similar problems with slight modifications. The main objective of this paper is to: i) present a brief survey of the development history of the elastic analysis of inhomogeneous solids and ii) characterize some dominant analytical and semi-analytical methods. It was not our intent here to provide a comprehensive list of references on the topic, which is nearly impossible to make in view of rapidly growing number of publications and other restrictions, but to emphasize some important, in our opinion, stages of the development, methods and results.

Origami, the ancient paper folding art has inspired the engineering equipment and design for decades. The basic concept of origami is very general, which leads to applications ranging from small scale to large scale. Recently, researchers are interested in being able to create self-folding structures. Such a structure enables kinematic manipulation by external forces or moments without folding and/or unfolding operations. This is a beneficial application for many fields including aerospace systems, robots, small devices and self-assembly systems. In this paper, the investigation and analyses of the previous literatures on the key driving force of the actuation structure, including the heat, light, electricity, gas and other actuation methods. The aims are to provide researchers and practitioners with the support to systematically understand the latest technologies in this important and evolving field, with inspiration and direction for follow-up.

Temperature resulting from the joule heating power and the turn-on and turn-off dissipation of high-power, high-frequency applications is the root cause of their thermal instability, electrical performance degradation, and even thermal-fatigue failure. Thus, the study presents thermal and electrical characterizations of the power MOSFET module packaged in SOT-227 under natural convection and forced convection through three-dimensional (3D) thermal-electric (TE) coupled field analysis. In addition, the influences of some key parameters like electric loads, ambient conditions, thermal management considerations (heat sink, heat spreader) and operation conditions (duty cycle and switching frequency) on the power loss and thermal performance of the power module are addressed. The study starts from a suitable estimation of the power losses, where the conduction losses are calculated using the temperature- and gate-voltage-dependent on-state resistance and drain current through the device, and the switching losses are predicted based on the ideal switching waveforms of the power MOSFETs applied. The effectiveness of the theoretical predictions in terms of device’s power losses and temperatures is demonstrated through comparison with the results of circuit simulation and thermal experiment.

The present article deals with the influence of the induced magnetic field on an unsteady two dimensional incompressible free convective chemically reacting slip flow of Jeffrey fluid between two parallel plates under the influence of the thermal radiation, Soret and Dufour. It is assumed that the flow is generated due to periodic suction/injection and the non-uniform temperature and concentrations are varying periodically with time at the plates. The governing partial differential equations are reduced into nonlinear ordinary differential equations by using similarity transformations and solved by shooting method along with Rung-Kutta 4th order scheme. The results are analyzed for various flows, heat and mass transfer characteristics with respect to various prominent parameters such as the ratio of relaxation to retardation times, Deborah number, magnetic Reynold’s number, Strommer’s number, radiation parameter, chemical reaction parameter, Soret and Dufour numbers in details through graphs and tables. It is observed that the temperature of the fluid is enhanced with Soret and Dufour whereas the concentration is decreased. Also the mass transfer rate of the fluid is enhanced with Strommer’s number, whereas the heat transfer rate decreases with increasing of the Jeffery fluid parameter. The present results have good agreement with published work for Newtonian case.

In the present paper, a general analytical solution is proposed for anisotropic heat conduction through truncated composite spherical shells. The solution is so important in designing the spherical vessels which are usually used to store the CNG, LNG, LPG and other petroleum condensates. Herein, it is supposed that the fiber angle of composite laminate is in range of zero to 90 degrees. Heat convection with ambient flow, an external heat radiation, and a possible internal heat generation are modeled within the heat transfer equation. The exact solution is derived using the complex finite Fourier transform method. The particular solution of transferred equation is found based on the Green’s function and Sturm-Liouville theories. Finally, an inverse integral transformation is applied to form the final analytical solution in physical space. Defining four materials differing in the value of conductivity coefficient in fiber direction, the effects of used composite material and fiber angle on temperature distribution of the spherical shell are investigated in detail.

The two-phase flow pattern of a flow mixing nozzle plays an important role in jet breakup and atomization. However, the flow pattern of this nozzle and its transformation characteristics are still unclear. A diesel-air injection simulation model of a flow mixing nozzle is established. Then the two-phase flow pattern and transformation characteristics of the flow mixing nozzle is studied using a numerical simulation method. The effect of the air-diesel velocity ratio, ratio of the distance between the tube orifice and nozzle hole and the tube diameter (H/D), and the diesel inlet velocity was studied in terms of the jet breakup diameter (jet diameter at the breakup position) and jet breakup length (length of the diesel jet from the breakup position to the nozzle outlet). The results show that the jet breakup diameter decreases with the decrease in H/D or the increase in the air-diesel velocity ratio and diesel inlet velocity. The jet breakup length increases first and then decreases with the increase in H/D and air-diesel velocity ratio; the trend of the diesel inlet velocity is complicated. In addition, a change in the working conditions also causes some morphological changes that cannot be quantitatively analyzed in the diesel-air flow pattern. The transition characteristics of the flow pattern are analyzed, and it is found that the main reason for the change in the flow pattern is the change in the inertial force of the air, surface tension force, and viscous force of diesel (non-dimensional Reynolds number and Weber number describe the transition characteristics in this paper). The surface tension force of diesel decreases and the viscous force of diesel and inertial force of air increase when the air-diesel velocity ratio increases or H/D decreases. However, the effects of the diesel surface tension force and viscous force effect are much smaller than that of the air inertial force, which changes the diesel-air flow pattern from a drop pattern to a vibration jet pattern, broken jet pattern, and then a chaotic jet pattern.

The problem of unsteady boundary layer flow of a nanofluid over a stretching surface is studied. Heat transfer due to melting is analyzed. Using a similarity transformation the governing coupled nonlinear partial differential equations of the model are reduced to a system of nonlinear ordinary differential equations, and then solved numerically by a Runge-Kutta method with a shooting technique. Dual solutions are observed numerically and their characteristics are analyzed. The effects of the pertinent parameters such as the acceleration parameter, the Brownian motion parameter, the thermophoresis parameter, the Prandtl number and the Lewis number on the velocity, temperature and concentration fields are discussed. Also the effects of these parameters on the skin friction coefficient, the Nusselt number and the Sherwood number are analyzed through graphs. It is observed that the melting phenomenon has a significant effect on the flow, heat and mass transfer characteristics.

Present study explores stagnation point flow of nanofluid towards a nonlinear stretching sheet of variable thickness in the presence of electromagnetic field and convective heating. The effect of viscous dissipation and Joule heating are also taken into consideration. Novel concept of non-linear radiative heat flux is also considered. The nanofluid is inspired by Lorentz force which is instigated from the interaction of magnetic and electric fields. Using similarity transformation, the governing partial differential equations are transformed into a system of coupled nonlinear ordinary differential equations and then solved numerically by fourth order Runge-Kutta method along with shooting technique. The velocity, temperature and nanoparticle concentration profiles are plotted and analysed corresponding to various pertinent flow parameters. Also, the skin friction and rate of heat and mass transfers at the surface are computed and explained in detail. It is observed that higher wall thickness parameter results in the reduction of velocity, temperature and nanoparticle concentration when velocity power index is less than unity and opposite effect is observed when velocity power index is greater than unity. Due to intensification of electric field, nanofluid velocity is getting retarded and thereby resulting in enhancement of fluid temperature and nanoparticle concentration.

Effects of geometric parameters of diffuser vanes as well as impeller micro grooves depth on the performance of a vertically suspended centrifugal pump have been studied. Different diffuser vanes height,leading angles, trailing angles, wrapping angles and furthermore, impeller micro grooves depths have been analyzed thoroughly. Numerical results have been verified by comparing experimental data. Results, without considering cavitation, reveal that diffuser vanes height has the profound impact on the vertically suspended centrifugal pump performance followed by vanes wrapping angle. Additionally, it is observed that delivered head and efficiency of micro-grooved impellers reduce more by flow rate enhancing rather than that of the original impeller.

In the current study, for the first time, a semi-analytical technique is used for solving eigenvalue problem arising from linear hydrodynamics stability of fluid flow through the curved rectangular ducts at different curvature ratios and aspect ratios. To this accomplishment, symmetric disturbances are assumed and the Homotopy perturbation method (HPM) is applied to solve our eigenvalue problem for curvature ratios ranging from 0.01 to 0.8 and aspect ratios ranging from 0.05 to 20. Our semi-analytical results are validated through the existing numerical and experimental data, showing good agreement. The semi-analytical results indicate that, as the curvature ratio increases the critical Dean number (Dnc) is increased and the flow becomes more stable, especially for aspect ratios lower than 1.Moreover, for all intended curvature ratios, irregular behavior in variation of Dnc is detected by an increase in the aspect ratio. So that, the Dnc is decreased when the aspect ratio increases from 0.05 up to 1 and the fluid flow becomes unstable. When the aspect ratio is increased from 1 to 5, it causes to increase the Dnc and fluid flow becomes stable. Furthermore, when the aspect ratio increases from 5 to 20, the Dnc is decreased again. In addition, Dnc and eigenvalues of critical complex wave number corresponding to Dnc for the onset of Dean flow instability is reported under different curvature ratios and aspect ratios.

In this study, the pull-in phenomenon of a Nano-actuator is investigated employing a nonlocal Bernoulli-Euler beam model with clamped-clamped conditions. The model accounts for viscous damping, residual stresses, the van der Waals (vdW) force and electrostatic forces with nonlocal effects. The hybrid differential transformation/finite difference method (HDTFDM) is used to analyze the nonlocal effects on a graphene sheet nanobeam, which is electrostatically actuated under the influence of the coupling effect, the von Kármán nonlinear strains and the fringing field effect. The pull-in voltage as calculated by the presented model deviates by no more than 0.29% from previous literature, verifying the validity of the HDTFDM. Furthermore, the nonlocal nonlinear behavior of the electrostatically actuated nanobeam is investigated, and the effects of viscous damping, residual stresses, and length-gap ratio are examined in detail. Overall, the results reveal that small scale effects significantly influence the characteristics of the graphene sheet nanobeam actuator.