The effects of variable viscosity and thermal conductivity on the natural convection heat transfer over a vertical plate embedded in a porous medium saturated by a nanofluid are investigated. In the nanofluid model, a gradient of nanoparticles concentration because of Brownian motion and thermophoresis forces is taken into account. The nanofluid viscosity and the thermal conductivity are assumed as a function of local nanoparticles volume fraction. The appropriate similarity variables are used to convert the governing partial differential equations into a set of highly coupled nonlinear ordinary differential equations, and then, they numerically solved using the Runge-Kutta-Fehlberg method. The practical range of non- dimensional parameters is discussed. The results show that the range of Lewis number as well as Brownian motion and thermophoresis parameters which were used in previous studies should be reconsidered. The effect of non-dimensional parameters on the boundary layer is examined. The results show that the reduced Nusselt number would increase with increase of viscosity parameter and would decrease with increase of thermal conductivity parameter.

A numerical study has been carried out to analyze the constant heat flux, internal heat generation, variable viscosity and thermal radiation effects on the flow and heat transfer of a Newtonian fluid over an exponentially stretching porous sheet. Using a similarity transformation, the governing partial differential equations are transformed into coupled, non-linear ordinary differential equations with variable coefficients. Numerical solutions to these equations subject to appropriate boundary conditions are obtained by using an efficient Chebyshev spectral method. The effects of various physical parameters such as viscosity parameter, the suction parameter, the radiation parameter, internal heat generation or absorption parameter and the Prandtl number on velocity and temperature are discussed by using graphical approach. Moreover, numerical results indicate that in the presence of constant heat flux, the skin-friction coefficient as well as Nusselt number is strongly affected by the viscosity parameter, suction parameter, radiation parameter and the internal heat generation parameter.

The paper is devoted to a study of steady hydromagnetic fluid flow with heat and mass transfer over an inclined nonlinear shrinking porous sheet in the presence of thermophoresis and heat generation. The problem is formulated as a non-linear boundary value problem. A numerical method is developed to solve the problem. The surface velocity of the shrinking sheet and the applied transverse magnetic field are considered as power functions of the distance from the origin. The viscosity and thermal conductivity of the fluid are considered temperature-dependent. The viscosity is taken to be an inverse function of temperature, while the thermal conductivity is supposed to vary linearly with temperature. By using suitable transformation, the equations governing the flow, temperature and concentration fields are reduced to a system of coupled non-linear ordinary differential equations, which are solved numerically by developing an appropriate numerical method. Velocity, temperature and concentration profiles as well as the skin-friction coefficient and wall heat transfer are studied with particular emphasis. Their variations with different parameters are investigated. The computed numerical results are presented graphically.

For economizing the space of equipment and increasing the throughput of product, a vertical transportation is usually used for manufacturing a large and thin glass substrate. Due to the fragile characteristic of the large and thin glass substrate, investigation of a method for maintaining the glass substrate stably and safely on a supporting frame during manufacturing processes becomes an important subject. This subject belongs to a kind of moving boundary problem and the method of Arbitrary Lagrangian Eulerian (ALE) with a finite element scheme is suitably used to solve it. Also, related methods of the generalized minimal residual method (GMRES) and pressure convection diffusion method are adopted to calculate pneumatic pressures distributed on the glass substrate. The results show that under a low frequency of the vertical transportation the glass substrate stably lies on the supporting frame, oppositely under a high frequency of the vertical transportation the glass substrate has possibility to depart from the supporting frame. The later situation is disadvantageous to the glass substrate and should be avoided as much as possible.

The unsteady MHD free convection and mass transfer boundary layer flow of an incompressible electrically conducting fluid past an accelerated infinite vertical flat plate embedded in porous medium with ramped wall temperature is considered here. It is assumed that the plate accelerates in its own plane in the presence of thermal radiation incorporating first order chemical reaction. The governing equations are solved analytically using the Laplace transformation technique. The flow phenomenon has been characterized with the help of flow parameters such as permeability parameter, Hartmann number, phenomenon has been characterized with the help of flow parameters such as permeability parameter, Hartmann number, thermal radiation parameter etc. The influences of these parameters on the velocity, temperature field and concentration distribution have been studied and the results are presented graphically and discussed quantitatively. Also, the effects of the various parameters on the skin friction coefficient, the rate of heat and mass transfer at the surface are discussed.

In the present work, a recently developed in-house 2D CFD code is used to study the effect of gas turbine stator blade roughness on various performance parameters of a two-dimensional blade cascade. The 2D CFD model is based on a high resolution flux difference splitting scheme of Roe (1981). The Reynolds Averaged Navier-Stokes (RANS) equations are closed using the zero-equation turbulence model of Baldwin-Lomax (1978) and two-equation Shear Stress Transport (SST) turbulence model. For the smooth blade, results are compared with experimental data to validate the model. Finally, a correlation between roughness Reynolds number and loss coefficient for both turbulence models is presented and tested for three other roughness heights. The results of 2D turbine blade cascades can be used for one-dimensional models such as mean line analysis or quasi-three-dimensional models e.g. streamline curvature method.

Although the numerical properties of a step-by-step integration method can be evaluated based on the currently available techniques, there is still lack of a technique for evaluating its capability to capture dynamic loading. In this work, the amplitude error caused by the step discretization error is identified and the correlation between the relative amplitude error and relative step discretization error is analytically established. As a result, it is thoroughly confirmed that the asymptotic constant of the discretization error amplification factor for the displacement response to a cosine loading can be considered as an indicator of the capability to capture dynamic loading for a general step-by-step integration method.

This paper studies the buckling analysis for a ring-stiffened cylindrical shell consisted of functionally graded material (FGM) subjected to hydrostatic pressure and thermal loads. Material properties of the ring-stiffened FGM cylindrical shell are assumed to be temperature-dependent, and vary smoothly through the thickness direction of the structure according to a volume exponent. Based on the Donnell assumptions, buckling loads of the ring-stiffened FGM cylindrical shell are presented by utilizing the Galerkin method. Numerical results reveal that thermal loads, volume exponent and geometric parameters have significant effects on the buckling behavior of the ring-stiffened cylindrical shell.

In this article, the analyses of the natural frequency and buckling of orthotopic nanoplates, such as single-layered graphene sheets, resting on Pasternak's elastic foundations with various boundary conditions are presented. New functions for midplane displacements are suggested to satisfy the different boundary conditions. These functions are examined by comparing their results with the results obtained by using the functions suggested by Reddy (Reddy JN. Mechanics of Composite Materials and Structures: Theory and Analysis. Boca Raton, FL: CRC Press; 1997). Moreover, these functions are very simple comparing with Reddy's functions, leading to ease of calculations. The equations of motion of the nonlocal model are derived using the sinusoidal shear deformation plate theory (SPT) in conjunction with the nonlocal elasticity theory. The present SPT are compared with other plate theories. Explicit solution for buckling loads and vibration are obtained for single-layered graphene sheets with isotropic and orthotropic properties; and under biaxial loads. The formulation and the method of the solution are firstly validated by executing the comparison studies for the isotropic nanoplates with the results being in literature. Then, the influences of nonlocal parameter and the other parameters on the buckling and vibration frequencies are investigated.

The Lie group transformation method is applied for solving the problem of mixed convection flow with mass transfer over a permeable stretching surface with Soret and Dufour effects. The application of Lie group method reduces the number of independent variables by one and consequently the system of governing partial differential equations reduces to a system of ordinary differential equations with appropriate boundary conditions. Further, the reduced non-linear ordinary differential equations are solved numerically by using the shooting method. The effects of various parameters governing the flow and heat transfer are shown through graphs and discussed. Our aim is to detect new similarity variables which transform our system of partial differential equations to a system of ordinary differential equations. In this work a special attention is given to investigate the effect of the Soret and Dufour numbers on the velocity, temperature and concentration fields above the sheet.

In this paper, mixed convection stagnation point flow of nanofluids over a stretching/shrinking surface is studied numerically in the presence of thermal radiation and viscous dissipation. The governing boundary layer equations are transformed into a system of nonlinear ordinary differential equations, by using a similarity transformation, which are then solved numerically using a fifth-order Runge-Kutta-Fehlberg method with shooting technique. The effects of various physical parameters are analyzed and discussed. Computed results are presented in graphical and tabular forms. It is found that the Richardson number, thermal radiation and internal heat generation/absorption have interesting and significant effects on skin-friction and local Nusselt number for all the three types of nanofluids.

The peristaltic flow of nanofluids under the effect of slip conditions was theoretically investigated. The mathematical model was governed by a system of linear and non-linear partial differential equations with prescribed boundary conditions. Then, the exact solutions were successfully obtained and reported for the first time in the present work. These exact solutions were then used for studying the effects of the slip, thermophoresis, Brownian motion parameters and many others on the pressure rise, velocity profiles, temperature distribution, nanoparticle concentration and pressure gradient. In addition, it is proved that the obtained exact solutions are reduced to the literature results in the special cases.

In the general case, it was found that on comparing the current solutions with the approximate ones obtained using the homotopy perturbation method in literature, remarkable differences have been detected for behaviour of the pressure rise, velocity profiles, temperature distribution, nanoparticle concentration and finally the pressure gradient. An example of these differences is about effect of the Brownian motion parameter on the velocity profile; where it was shown in this paper that the small values of this parameter have not a significant effect on the velocity, while this situation was completely different in the published work. Many other significant differences have been also discussed. Therefore, these observed differences recommend the necessity of including the convergence issue when applying the homotopy perturbation method or any other series solution method to solve a physical model. In conclusion. The current results may be considered as a base for any future analysis and/or comparisons.

The present work studies the torsional instability of an elastic structure due to hydrodynamic loads into the water current. The structure applied here is a rectangular flat plate with an elastic axis in its mid-chord length. The elasticity in the structure is provided by torsion spring. The flat plate has only one degree of freedom which is rotation in pure yaw about its axis. Through the free vibration experiments, it is observed that as the current speed exceeds a critical velocity, the flat plate becomes unstable. Two different chord lengths are tested and the instability occurs for a chord base range of Reynolds number, 0.75 × 105 < Rec < 1.5 × 105. As a result of the instability, the flat plate begins to yaw about the elastic axis. The hydrodynamic moment acting on the flat plate is modeled by means of the flutter derivatives. As an identification technique to extract flutter derivatives, a curve fitting scheme called General Least-Square (GLS) theory is applied on the results of the free vibration experiments. The results confirm that the structure becomes dynamically unstable due to the hydrodynamic moment applied on it beyond the critical velocity. The super-critical Hopf bifurcation is also discussed in the light of the analysis.

With the increasing use of plastic gears in substitution of conventional steel ones, a plastic involute helical gear has been introduced to engage with a steel involute worm thus forming a novel plastic-steel worm-gear pair. The geometry and kinematics of this kind of worm-gear pair has been established first to derive its meshing properties which have been further verified by the finite element simulation. And it turns out that the contact area of this worm-gear pair is a point or an ellipse instead of a line. Further, a discrete dynamic model has been applied to investigate the dynamic transmission of motion and power of this worm-gear pair through the dynamic mesh force and the driven plastic involute helical gear. And the effects of angular and distance assembling errors have also been included.

A new type of large semi-rigid solar array structure with a new structural concept of rigid-flexible combination has developed for space application. Due to the good features of large scale and lightweight, such structure can well satisfy to the large power requirements of spacecraft and thus has drawn increasing attention recently. However, its structural weakness of inherently flexibility makes low frequency vibrations happen much easier. It is highly required to obtain an accurate dynamic model for predicting the dynamic characteristics of this kind of semi-rigid space structure. Because this structure is composed of different components that have quite different stiffness properties respectively, it is very difficult to build up an accurate dynamic model of this complex structure. In this paper, a novel analytical dynamic model is developed for solving this problem. To validate the correctness of the proposed model, experiment studies are conducted. By comparing the simulation results with experimental results, it can be concluded that this dynamic modeling method presented in the paper is credible. The present study is significant for the structural construction and application of this special structure.

This study adopted the distinct element method (DEM) to explore the key influencing factors on the variations of lateral earth pressure, including packing type, interior friction angle, particle stiffness and particle size. The reference parameters for the DEM model were retrieved from direct shear tests of a rod assembly. Based on the reference parameters, the evolution of lateral earth pressure is further simulated, and a parametric study was conducted. The results showed that: (1) the analysis model could effectively capture the variation of lateral earth pressure under both active and passive conditions, and the simulated failure patterns were consistent with those from the sandbox tests; (2) the greater interior friction angle ϕinterior decreased the active coefficient Ka and increased the passive coefficient Kp; (3) increasing particle stiffness decreased the active coefficient Ka and increased the passive coefficient Kp; (4) larger particle sizes led to a larger active coefficient Ka and a smaller passive coefficient Kp; and (5) when the particle assembly was arranged in order, its lateral pressure was much larger than that of the randomly packed assembly.

In the present study, the instability of laminar flow of two immiscible fluids is investigated. The theory of energy gradient is employed for the analysis. The distributions of energy gradient for various viscosity ratios, i.e., ratios of lower viscosity to higher one, are obtained and the results for the onset of instability are compared with the available experimental data. The comparison of the results shows excellent agreement with the existing experimental data. It will be also demonstrated that as the viscosity ratio decreases the flow becomes more stable even at high Reynolds numbers.

This paper explores the design space of centimeter-scale micro wind turbines to power wireless sensors through an experimentally validated modeling and simulation environment. A stochastic optimizer is used to obtain a functional relationship between the minimum wind velocity required to find a feasible design and multiple constraints relevant to turbine designers, such as the maximum turbine radius, electrical power required, minimum voltage required and available generators. This relationship is created from an optimization formulation that uses knowledge from the underlying physics and previous optimizations. It is shown that the design space of micro wind turbines is significantly different than large wind turbines due to the low Reynolds number regime. Also, a strong coupling exists between the choice of generator and optimal wind turbine geometry to minimize the wind required to meet the requirements. Smaller generators are more appropriate for micro wind turbines only if a constraint is applied on the maximum radius of the turbine and if no minimum voltage is required for a fixed power output.

The imaginary part of the Clausius-Mossotti factor, Ki, is crucial for quantitative particle/cell manipulation and characterization using travelling wave dielectrophoresis (twDEP) and electrorotation (ER). It can be measured rather easily using twDEP instead of using ER, as numerical calculation of the electric field and complicated devices are not needed for evaluating Ki using twDEP. However, the current single frequency twDEP method works only for particles/cells exhibiting negative dielectrophoresis (DEP), which is in general the case when cells are manipulated in physiological strength buffers with conductivity of order of 1S/m. In order to remove such a restriction, a modified twDEP method is proposed using dual frequency operation here capable of measuring the Ki spectra of particles/cells for the entire range of medium conductivity, irrespectively of whether the particles/cells exhibit positive or negative DEP. The success of the modified method relies on the adequate design of force balance between various forces in a designed micro channel, which was discussed in details. The method was validated, and demonstrated by measuring Ki spectra of three human cancer cells for medium conductivity from 0.01 ~ 1.2S/m. Both the method and the cell result find biomedical and other industrial applications.

Contact between hot objects and liquids occurs in many industries, such as nuclear reactors, metal casting industries and paper production. In such cases growth of vapour film leads to steam explosion that may cause human and financial damages. It is obvious that possibility of these phenomena can be judged by comparing vapour film radius growth and pressure inside vapour film. In this paper vapour film growth and pressure inside the vapour film formed, on hot sphere interaction with water, are investigated. The numerical simulation of problem is obtained and then validated using experimental test and other available results. The effects of the variations of different parameters such as hot sphere diameter, temperature, immersion depth into water and bulk water temperature are investigated on the vapour film radius, vapour pressure inside vapour film and the saturation temperature of phase interface surface. Finally, the overall results show that the effect of hot sphere interaction with water would be the same pressure inside vapour film suddenly increases up to 5 times more than initial pressure which would lead to hazard and put the safety of the system at risk.