Scientia Iranica
Volume:25 Issue: 4, 2018 Jul-Aug

The time history analysis and propagation of molar concentration, temperature and displacement waves are studied in details using an analytical method. The method is applied to coupled non-Fickian diffusion-thermoelasticity analysis of a strip. The governing equations are derived using non-Fickian theory of diffusion and classic theories for coupled thermoelasticity. Molar concentration and thermoelastic wave propagations are considered to be of finite speed. The governing equations are first transferred to the frequency domain using Laplace transform technique. The unknown parameters are then obtained in analytical forms proposed by the presented method. By employing the Talbot technique, the unknown parameters are eventually determined in time domain. It can be concluded that the presented analytical method has a high capability for dynamic and transient analysis of coupled diffusion-thermoelasticity problems. The wave fronts in displacement, temperature and molar concentration fields can be tracked at various time instants employing the presented analytical method.

Currently, the HIFU (High Intensity Focused Ultrasound) therapy method is known as one of the most advanced surgical techniques in tumor ablation therapy. Simulation of the non-linear acoustic wave and tissue interaction is essential in HIFU planning to improve the usefulness and efficiency of treatment.
In this paper, linear, thermoviscous and nonlinear equations are applied using two different media, namely liver and water. Transducer power of 8.3-134 Watts with the frequency of 1.1 MHz is considered as the range of study to analyze the wave and tissue interaction. Results indicate that the maximum focal pressure of about 0.5-4.3 MPa can be achieved for transducer power of 8.3 to 134 W. Simultaneous solving of the acoustic pressure equation and Pennes’s bio-heat equation are used to determine the temperature rise at focal point and the ablated area. Finally, the linear and nonlinear simulations are compared, and the turning point of transition from linearity to nonlinearity is determined.
The simulated results provide information about the behavior of the focalized ultrasound in interaction with liver tissue. The performance of phased array HIFU transducer can be improved for treatment considering the lesion size, temperature rise in tissue and choosing best range of operational power.

An analysis is performed to study axisymmetric mixed convective boundary layer flow of a nanofluid over a vertical stretching circular cylinder in the presence of non-linear radiative heat flux. The effects of non-uniform heat source/sink and slip flow are also taken into consideration. Water as conventional base fluid containing nanoparticles of Copper (Cu) is used. By means of similarity transformations, the governing partial differential equations are reduced into highly non-linear ordinary differential equations and then solved analytically using Homotopy Analysis Method (HAM). A comparison is made with the available results in the literature and our results are in very good agreement with the known results. A parametric study of the physical parameters is made and results are presented through graphs and tables. The results indicate that, the thermal boundary layer is thicker for non-linear thermal radiation problem when compared with that of linear thermal radiation. It also found that heat transfer rate at the surface decreases with the increase in both space and time dependent heat source/sink parameters.

In this work static pull-in instability and frequency analysis of circular and annular plates in electrical field was studied. The plate is modeled based on classical plate theory with nonlinear Von Kármán strain-displacement field. The governing equation of motion and boundary conditions were obtained using Hamilton principle. For this purpose potential and kinetic energies and the work done by radial and electrostatic force are obtained. Governing partial differential equations were reduced to ordinary differential equations by Galerkin's method. Then, static pull-in instabilities of clamped circular plate and annular plate with clamped-clamped and clamped-simply boundary conditions were analyzed by arc-length continuation method. The effect of rigid core, radial load, geometric nonlinearity, inner radius and boundary conditions on pull-in instability and frequency of the plate has been studied.

The unsteady problem of impulsive stagnation-point flow on a vertical circular cylinder along with mixed convection heat transfer is solved numerically for the first time. This is because of limitations of similarity solution techniques when we encounter various physical conditions such as time-dependent states. Initially, the fluid is considered to be at rest and with a uniform temperature . At t=0 this fluid starts flowing toward a vertical cylinder at the strength rate of and the cylinder surface's temperature rises to Tw, simultaneously. The Navier-Stokes and energy equations in cylindrical coordinate system have been descritized and solved in a 2-D domain by using a SIMPLE based algorithm. The solution has been obtained in three cases. Firstly, when cylinder's wall temperature Tw is constant. Secondly, when Tw varies linearly along cylinder's axis. And thirdly, when it has parabolic variations. Considering a sample case of incompressible flow with Re=1 and , the results of Nusselt number, wall shear- stress and dimensionless velocity and temperature have been obtained at different states of cylinder's wall temperature and for some selected values of Grashof numbers. An entropy generation analysis for the case of constant wall temperature is performed which is also for the first time in this subject.

Parallel mechanisms with reduced degree of freedom (DOF) have grown in importance for industry and researchers as they o er a simpler architecture and lower manufactur- ing/operating costs with great performance. In this paper, a two degree of freedom parallel robot is proposed and analyzed. The robot with a xed base, a moving platform and three legs achieve translational and rotational motion through actuation on prismatic and revolute joints, and can be applied on pick and place applications, vehicle simulators among others. By making use of homogeneous transformation matrices and Sylvesters dialytic elimination method a closed form solution for direct kinematics is obtained for all possible assembly modes. Inverse kinematics was solved in closed form as well. This greatly decreases computational time and proposed approach is optimal. A case study was done to validate the solutions found and compared with a CAD model to corroborate results. Finally, a workspace calculation was made for di erent geometrical parameters of the robot.

The microstructure formation and mechanical properties of coiled tube CT80 grade steel was investigated with different heat treatments. Optical Microscopy (OM) and Scanning Electron Microscopy (SEM) were used to evaluate the microstructure. Acicular ferrite, polygonal and quasi-polygonal ferrite, granular bainite, martensite, pearlite, and small Martensite-Austenite (MA) islands with the banding structure were revealed in original and heat treated samples. In order to assess the effect of grain size and microstructure, mechanical properties were evaluated by hardness, charpy impact, tensile, and fatigue life tests. The best mechanical properties by tensile and fatigue test is obtained from the normalized specimen with the grain size of ASTM 13.

In this study the effect of moving pressure source and channel parameters on the generated waves in a channel was numerically investigated. Draught, angle of attack and profile shape were investigated as parameters of pressure source and water depth and blockage factor as channel parameters on wave height. Firstly, the chosen Computational Fluid Dynamics (CFD) approach was validated with the experimental data over a range of speed. Then the CFD study was conducted for further investigations. It was shown that that by enlarging draught, angle of attack and beam of the pressure source, the wave height generated will be increased. Channel study showed that it is possible to increase the wave height generated by shallowing water for a given speed as long as the depth Froude number is subcritical and the wave height generated is independent of water depth for supercritical depth Froude numbers. The blockage factor has more influence at supercritical Froude depth values, while at subcritical Froude values is negligible compare with water depth.

In this paper, we present an alternative representation of the fractional spacetime Fourier's law equation using the concept of derivative with two fractional orders and . The new de nitions are based on the concept of power law and the generalized Mittag-Leer function, where, the rst fractional order is included in the power law function and the second fractional order is the generalized Mittag-Leer function. The new approach is capable of considering media with two di erent layers, scales and properties. The generalization of this equation exhibit di erent cases of anomalous behavior and Non-Fourier heat conduction processes. Numerical solutions using an iterative scheme were obtained.

In this study, the problem of two-dimensional forced convection MHD flow and heat transfer of ferro fluids over a moving at plate with the influence of uniform heat flux and secondorder slip eff ects is considered. By applying the similarity transformation, the governing equations are reconstructed into the similarity equations and the resulting equations are solved via shooting technique. Then, we implement a stability analysis in order to verify which solutions are stable and physically realizable. The e ects of the magnetic parameter, moving parameter, mass transfer parameter, rst-order surface slip parameter, second-order surface slip parameter and volume fraction of solid ferroparticles on the dimensionless velocity, temperature, skin friction and Nusselt numbers are discussed in the form of tabular and graphical presentation. For this present study, we consider the results based on three preferred ferroparticles, namely magnetite, cobalt ferrite and Mn-Zn ferrite in water- and kerosene-based fluids. The results display the existence of dual solutions for a plate moving towards the origin in which the rst solution is stable and physically realizable, while the second solution is not. Moreover, it is demonstrated that the magnetic, moving, mass transfer and slip eff ects together with the volume fraction of ferro fluids delay the boundary layer separation.

Two Dimensional (2D) and Three Dimensional (3D) numerical simulations of an external compression supersonic ramped inlet for a free stream Mach number of 2 are presented. Comparison between numerical results and experimental data showed that multi-block structured gird using standard k-ε turbulence model gives acceptable results. The diffuser shape was then gradually varied to a circular one to encompass the Aerodynamic Interface Plane (AIP). It is observed that the 3D simulation predicted a more accurate static pressure distribution during the length of supersonic inlet and total pressure distribution at the AIP in comparison with the 2D one. Further, a better estimation of Shock Boundary Layer Interaction (SBLI), shock structure, and turbulent flow is predicted by the 3D simulation. It seems that, even though the 2D simulation scheme is widely used, it is a very weak method with low accuracy while the 3D simulation is more accurate and gives detailed flow field. Therefore; for cases where a detailed flow study along with an accurate prediction of flow parameters as well as the shock structure are required, the 3D numerical simulation must be applied.

Mixed convection heat transfer of non-Newtonian impinging slot jets was investigated numerically. The simulation was performed using a temperature dependent power-law viscosity model. The results showed that for high Richardson numbers, a recirculation zone is created in the vicinity of impingement wall which prevents the jet stream from penetration into near wall region and decreases the Nusselt number around the stagnation point. The effects of jet-to-plate spacing, inlet Peclet number and the jet inlet width on the flow structure and heat transfer characteristics of impinging jet were studied using the numerical results. By decreasing jet-to-plate spacing and jet inlet width and increasing inlet Peclet number, the flow reversal in the vicinity of heated wall was disappeared and the local Nusselt number increases as a result of deeper penetration of jet stream the near wall region. Furthermore, the results indicated that the maximum local and average Nusselt numbers belong to the shear-thinning jets with minimum inlet width and the minimum jet-to-plate spacing.

The natural frequency and the transient responses of Carbon/Epoxy layered composite plate structure have been analysed with the help of two higher-order mid-plane kinematics models in this article. The mathematical formulation of the layered composite structure is further utilised to develop a computer programme in MATLAB-15.0, to evaluate the said responses. The practical relevance of the present higher-order models has been established via comparing the present numerical results computed using suitable MATLAB computer code with the in-house experimental test data. Additionally, the fundamental frequency and the transient responses of the carbon fibre reinforced epoxy composite plate structure are simulated via finite element package (ANSYS) with the help of ANSYS parametric design language (APDL) code. The simulated frequencies are compared with those of the present experimental and MATLAB results. Finally, the significance of the proposed higher-order kinematics has been established via solving a different kind of illustrations to investigate the influence of various geometrical and material parameter on the dynamic responses of layered composite structure and discussed in detail.