Scientia Iranica
Volume:25 Issue: 2, Mar - Apr 2018

In this paper, we study static bending and free vibration behavior of Bernoulli–Euler micro-beams with a single delamination using the modified couple stress theory. The delaminated beam is modeled by four interconnected sub-beams using the delamination zone as their boundaries. The free and constrained mode theories have been utilized to model the interaction of delamination surfaces in the damaged area. The continuity as well as compatibility conditions are satisfied between the neighboring sub-beams. After verification of the results for some case studies with available solutions, the effect of various parameters such as spanwise and thicknesswise locations of the delamination, material length scale parameter, and boundary conditions on the static bending and free vibration characteristics of the size-dependent micro-beam have been investigated in detail.

The purpose of this work is to analyze two dimensional rectangular porous radiant burners for investigating the thermal characteristics of this type of burners in starting time period. Since, the solid and gas phases are not in thermal equilibrium, two separate energy equations for these two phases are solved numerically with alternative direction implicit scheme. The gas is considered non-radiative medium and for computation of radiative heat flux through the solid phase, the radiative transfer equation (RTE) is employed and solved with the discrete ordinates method (DOM). It is obtained that due to the dominant radiation effects, the required time to reach the steady gas temperature is very low. Furthermore, the effects of optical thickness and scattering albedo on the performance of porous radiant burner (PRB) are investigated.

Biological cell studies have many applications in biology, cell manipulation and diagnosis of diseases such as cancer and malaria. In this study, inverse finite element method (IFEM) combined with Levenberg-Marquardt optimization algorithm has been used to extract and characterize material properties of mouse oocyte and embryo cells at large deformations. Then, the simulation results have been validated using data from experimental works. In this study, it is assumed cell material is hyperelastic, isotropic, homogenous and axisymmetric. For inverse analysis, FEM model of cell injection experiment which implemented in Abaqus software has been coupled with Levenberg-Marquardt optimization algorithm written in Matlab; based on this coupling the optimum hyperelastic coefficients which give the best match between experimental and simulated forces are extracted. Results show that among different hyperelastic material models, Ogden material is well suitable for characterization of mouse oocyte cell and Mooney-Rivlin or polynomial are suitable for characterization of mouse embryo cell. Moreover the evaluated Poisson ratio of the cell is obtained to be equal to 0.5, which indicates the structural material of mouse oocyte and embryo, are compressible.

One of the methods of force/moment exertion to micro beams is utilizing piezoelectric actuators. In this paper the problem of vibration boundary control of a clamped-free Timoshenko micro-cantilever considering effects of the piezoelectric actuator to achieve asymptotic stability is addressed. To achieve this purpose, the dynamic equations of the beam actuated by a piezoelectric layer laminated on one side of the beam are extracted. The control law has been made to decay vibrations of the beam. This control law is achieved from the feedback of time derivatives of boundary states of the beam. The obtained control is applied in the form of voltage of the piezoelectric. To illustrate the impact of the proposed controller to the micro beam, the finite element method and Timoshenko beam element have been used and then the simulation has been performed. The simulation shows that not only does this control voltage decay the vibration of the beam, but also the mathematical proofs proposed in this article are precise and implementable.

An experimental comparison of water productivity between a conventional single slope, solar still and a modified one is introduced in this work. The modified solar still is incorporated with a new heating technique on the saline water surface using finned cover with holes. These fins are used to increase the heat transfer area between the cover and saline water meanwhile, holes are used to allow evaporated water to go through. These experiments are held under the outdoor conditions of Tanta, Egypt. The performance of the two solar stills has been tested at a water depth of 0.05 m and a quantity of saline water of 50 L. The results indicated that the productivity of water per square meter per day for the modified design still is higher than the conventional still by about 30.6%.

In this paper, free vibration analysis of rotating annular disc made of functionally graded material (FGM) with variable thickness is presented. Elasticity modulus, density and thickness of the disc are assumed to vary radially according to a power low function. The natural frequencies and critical speeds of the rotating FG annular disc of variable thickness with two types of boundary conditions are obtained employing the numerical generalized differential quadrature method (GDQM). The boundary conditions considered in the analysis is the both edges clamped (C-C) and the inner edge clamped and the outer edge free (C-F).The influence of the graded index, thickness variation, geometric parameters and angular velocity on the dimensionless natural frequencies and critical speeds are demonstrated. It is shown that using a plate with a convergent thickness profile, we have a higher critical speed and natural frequency and using a divergent thickness profile, we can lower the critical speed. It is found that increase in the ratio of inner-outer radii could increase the critical speed of the FG annular disk. The results of the present work could improve the design of the rotating FG annular disk in order to avoid resonance condition

Primary aim of current attempt is to analyze the peristaltic flow of non-Newtonian material in a curved channel subject to two salient features namely the Soret and Dufour and radial magnetic field. Channel walls are of compliant characteristics. Problem formulations for constitutive equations of Jeffrey fluid are made. Lubrication approach is implemented for the simplification of mathematical analysis. Dimensionless problems of stream function, temperature and concentration are computed numerically. Characteristics of distinct variables on the velocity, temperature, coefficient of heat transfer and concentration are examined. Besides this graphical results indicates that velocity profile enhances significantly for compliant wall parameters however due to the resistance characteristics of Lorentz force velocity profile decays. Furthermore it is noted that temperature profile enhances for larger Dufour number however reverse behavior is noticed in the concentration profile when Soret and Schmidt numbers are increased.

Inlet Performance has an important role in the operation of air-breathing propulsion systems. In this study, performance of a supersonic axisymmetric mixed-compression inlet in the supercritical operating condition is numerically studied. The effects of free-stream Mach number and engine-face pressure on performance parameters, including mass flow ratio, drag coefficient, total pressure recovery, and flow distortion are investigated. To this sake, a multi-block density-based finite volume CFD code is developed and Reynolds-averaged Navier-Stokes equations with Spalart-Allmaras one-equation turbulence model is employed. The code is validated by comparing numerical results against other computational results and experimental data for two test cases of inviscid flow in a two-dimensional mixed-compression inlet and flow in an external compression inlet. Finally, the code is utilized for investigation of a specific supersonic mixed-compression inlet with the design Mach number of 2.0 and length to diameter ratio of 3.4. Results revealed that the increment of free-stream Mach number leads to decrease in total pressure recovery and drag coefficient, while mass flow ratio and flow distortion increase. The effects of engine-face pressure on performance parameters showed that by increasing the engine-face pressure, mass flow ratio and drag coefficient remain constant while total pressure recovery increases and flow distortion decreases.

Monolithic titanium, Ti–1 wt% B4C, Ti–2.5 wt% TiB2 were spark plasma sintered at 1050 ºC for 5 min under 50 MPa. The effect of B4C and TiB2 additions on densification process, microstructural development and mechanical properties of titanium was investigated. The results revealed that relative density of undoped, B4C- and TiB2-doped Ti samples reached ~98-99%. X-ray diffraction patterns, thermodynamic assessments, and microstructural investigations verified the in-situ formation of TiB whiskers in both composite samples as well as appearance of TiC spheres in Ti–B4C composite. However, trace unreacted TiB2 and B4C additives were remained in the composites as a result of incomplete chemical reactions due to short-time SPS process. Compared to undoped Ti sample, grain growth was hindered when the sample was doped by B4C or TiB2. Elongation, ultimate tensile strength and Vickers hardness of B4C- or TiB2-doped samples were higher than those of monolithic titanium but bending strength of ceramic-doped samples significantly lower, compared to undoped titanium. These outcomes were discussed in detail and related to presence/formation of several ceramic phases with different morphologies in Ti matrix.

This paper presents a time saving methodology for design and sizing the magnetic gear sets. Some new design parameters similar to mechanical gears are defined to calculate the torque capacity based on these. Finite element analysis is extensively used to calculate the variation of gear set torque capacity due to changes in different geometric parameters of a set. Different design curves are obtained by which the design and sizing of the gears can routinely be accomplished. Optimal performance of magnetic gear wasn’t the main target of this research and just this method helps gear designers to decide on parameters such as scale of gears, magnet thickness, stack length and pole pair numbers and come up with a close to optimum geometry design

Linear stability of a thixotropic fluid obeying the Moore model is investigated in pipe flow using a temporal stability analysis in which infinitesimally-small perturbations, represented by normal modes, are superimposed on the base flow and their evolution in time is monitored in order to detect the onset of instability. An eigenvalue problem is obtained which is solved numerically using the pseudo-spectral Chebyshev-based collocation method. The neutral instability curve is plotted as a function of the thixotropy number of the Moore model. Based on the results obtained in this work, it is concluded that the thixotropic behavior of the Moore fluid has a destabilizing effect on pipe flow

In this article, an analytical solution to the moderately large amplitude transverse vibration of thin functionally graded micro-plates (FGMPs) is presented based on a practical approach. The size-dependent nonlinear governing equation is obtained in conjunction with the Kirchhoff’s plate and modified couple stress theories. The material properties of functionally graded (FG) micro-plates are varied according to the Reddy’s model. The employed non-classical theory contains one material length scale parameter to capture the size effects. The highly nonlinear governing equation is solved by means of homotopy analysis method to obtain accurate analytic approximations. The both of simply supported and clamped micro-plates with immovable edges are considered. Comparison of the present results with earlier studies wherever possible confirms the reliability and effectiveness of the present formulation for the design purpose. Furthermore, the effects of different parameters such as material gradient index, length scale parameter, and aspect ratio on the nonlinear frequency ratio are investigated.

This paper presents finite element formulation for dynamic analysis of orthotropic plates using two-variable refined plate theory (RPT). Hamilton's principle is employed to obtain the governing equations and the semi-discrete approach is utilized for solving the equations. After constructing spatial weak form equations, a 4-node rectangular plate element with six degrees of freedom (DOFs) per node is introduced for discretization of the domain. An unconditionally stable implicit Newmark scheme is used for temporal discretization. A MATLAB code with capability of modeling both static and dynamic plate problems with various boundary conditions is generated. Several numerical problems are solved and the obtained displacements and stresses are compared with the existing results in the literature. The results demonstrate the accuracy, simplicity and efficiency of present method in dynamic analysis of plate problems.

In this study using ductile fracture criterion defined fracture energy, determining the critical damage value of normalized Cockcroft –Latham. True stress-strain value and materials properties were obtained from the tensile tests of zirconium alloy 702 and finite element analysis. It was observed that specimen fracture the maximum value occurred in the central area of the cross section, the highest critical damage value equal to 0.649. In this paper, through the inverse analysis method of the FEA to explore on rarely research data zirconium alloys. The results proposed to evaluate the forgeability, expect the present study could be used as a basis of designing and developing zirconium alloy.