The unsteady hydromagnetic flow due to torsional oscillations of a rotating disc in a viscous incompressible electrically conducting fluid which is also rotating is studied taking the effects of the Hall current and ion-slip into consideration. The governing equations are solved analytically. The results show that the inclusion of the Hall current and ion slip have important effects on the velocity distributions as well as shear stresses at the disc. The flow is characterized by two opposite circularly polarized waves, travelling with different velocities. It is found that there is a formation of two-deck boundary layers, thicknesses of which increase with increase in either Hall parameter or ion-slip parameter. The radial velocity increases with an increase in Hall parameter and the azimuthal velocity increases with an increase in either Hall parameter or ion-slip parameter. Further, it is found that the amplitude of the transverse shear stress at the disc decreases with an increase in either Hall parameter or ion-slip parameter.

This paper provides a closed form solution for degenerate scale problem of the Joukowcki thin airfoil configuration in antiplane elasticity. The solution depends on a conformal mapping function for the Joukowcki thin airfoil configuration.

In this article a two dimensional incompressible viscous flow past a square cylinder oscillating in cross flow with zero and 45 degree angles of attack is numerically studied by a Characteristics Based Splitter (CBS) finite element method. The solver is coupled to a mesh movement scheme using the Arbitrary Lagrangian-Eulerian (ALE) formulation to account for the body motion in the flow field. First, the accuracy of the numerical code is tested by comparing the numerical results obtained for the flow over the stationary square cylinder at the three different Reynolds numbers (Re = 100, 200, and 300) with the experimental data available. Then, the numerical results for the square cylinder undergoing transverse oscillations in the two angles of attack at different values of frequency and amplitude are investigated to determine the lock-on region. The results indicate physical similarity between circular and square cylinders concerning lock-on regions. Also the effect of lock-on phenomenon on the flow field pattern and time-averaged drag coefficient is investigated.

In this research, thermal buckling analysis of circular functionally graded plates with Actuator/Actuator piezoelectric layers (FGPs) is studied based on neutral plane, classical and first order shear deformation plate theories. Mechanical properties of the plate are considered as those of Reddy Model. Plate is assumed to be under thermal loading. Nonlinear temperature rises through the thickness and boundary conditions are considered clamped. Equilibrium and stability equations have been derived using calculus of variations and application of Euler equations. Finally, critical buckling temperature changes are studied based on the mentioned theories for a sample plate. An appropriate agreement is seen among the present results and the results of other researches.

In this study, the fictitious time integration method (FTIM) is applied to investigate wave propagation over an arbitrary bathymetry with measured uncertainty. The FTIM is used to convert the higher-order elliptic mild-slope equation (EMSE) into a FTIM like EMSE (FTIMEMSE). It has the advantage to describe wave transformation from deep water to shallow water region in a large coastal area with numerical efficiency. The validity of the noise resistance for the measured uncertainty of the bathymetry is also studied. In addition, typical examples for waves propagating over an elliptic shoal rest on a horizontal and sloping bottom is presented. It is concluded that the FTIM is robust in the numerical stability and capable of against the noise of the measurement.

The unsteady hydromagnetic flow of a viscous incompressible electrically conducting fluid between two parallel disks rotating with the same angular velocity initially about non-coincident axes, which are suddenly made coincident, has been studied. An analytical solution describing the flow at large and small times after the start is obtained by the use of Laplace transform technique. The physical interpretations for the emerging parameters are discussed with the help of graphs. The shear stresses obtained from the general solution and from the solution for small time are compared.

This paper presents a two dimensional asymptotic model of counterflow diffusion flame in the presence of radiation heat loss. The fuel and oxidizer, respectively, are injected from left and right hand side of the flame. The effects of burning rate, Lewis and Damkohler number on the structure and extinction of the flame is studied using perturbation method. To do so, the structure of the flame is considered to be composed of reaction zone with a thickness of O(ε) and radiation heat loss zone, of O(δ) thickness, that sandwiches the reaction zone. The effect of burning rate is illustrated by burning pre-exponential parameter, B. It is found that with the increase of the parameter, the flame temperature is also increased, and flame location moves toward the fuel side. In addition, the variation of Lewis number of fuel and oxidizer has a significant effect on the location and temperature of the flame.

In this paper, Laplace transformation method is used to solve the velocity profile and pressure gradient of the unsteady unidirectional flow of Bingham fluid. Between the parallel microgap plates, the flow motion is induced by a prescribed arbitrary inlet volume flow rate which varies with time. Due to the rarefaction, the wall slip condition is existed; therefore, the complexity of solution is also increased. In order to understand the flow behavior of Bingham fluid, there are two basic flow situations are solved. One is a suddenly started flow and the other is constant acceleration flow. Furthermore, linear acceleration and oscillatory flow are also considered. The result indicates when the yield stress τ0 is zero; the solution of the problem reduces to Newtonian fluid.

A non-linear analysis has been made to study the unsteady hydromagnetic boundary layer flow and heat transfer of a micropolar fluid over a stretching sheet embedded in a porous medium. The effects of thermal radiation in the boundary layer flow over a stretching sheet have also been investigated. The system of governing partial differential equations in the boundary layer have reduced to a system of non-linear ordinary differential equations using a suitable similarity transformation. The resulting non-linear coupled ordinary differential equations are solved numerically by using an implicit finite difference scheme. The numerical results concern with the axial velocity, micro-rotation component and temperature profiles as well as local skin-friction coefficient and the rate of heat transfer at the sheet. The study reveals that the unsteady parameter S has an increasing effect on the flow and heat transfer characteristics.

Accuracy of numerical analysis is always important but it is much more important in failure analysis of ductile materials. In ductile materials, the process of removing the effects of necking to obtain stress-strain curve usually need reverse identification methods which are based on iterative finite element analysis. Moreover, triaxiality factor and Lode angle (two parameters that control failure of ductile materials) are obtained from finite element analysis.

In this article based on some experiments, the effect of triaxiality factor and Lode angle on the failure strain of X100 pipeline steel is studied. In order to gain a better understanding of the response of triaxiality and Lode angle to deviations of stress, a sensitivity analysis is done on these two parameters before the start of finite elements (FE) analysis. This sensitivity analysis shows that the two parameters are really sensitive to stress deviations in some areas. Three geometries are selected and their FE analysis shows that it is necessary to reduce the element size lower than what is reported in literature in order to get convergence in triaxiality factor and Lode angle in critical areas.

A method to simulate contact between two boundaries of structures which are not aligned to predefined axes when using Comsol Multi-physics (v3.3, Comsol Ltd, Cambridge, UK) is presented. This method was developed because of limitations in the existing default contact modelling. Some of these limitations were recently addressed in a separate study; however, the method exploited symmetry across an axis of the coordinate system. The method presented here enables contact modelling with arbitrarily aligned structures within such a coordinate system. The contact method presented is then applied to a simple model with two deformable structures that come into contact, and compared over a range of positions. Results show a minimal variation in peak stress and contact pressure with model orientation, demonstrating that results are independent of orientation. Therefore, the contact method enables contact simulations in Comsol Multi-physics without assuming symmetry about an axis for contract. The method is compatible with the true transient contact method defined.

In this paper, the modified collocation Trefftz method (MCTM) and the exponentially convergent scalar homotopy algorithm (ECSHA) are adopted to analyze the inverse boundary determination problem governed by the biharmonic equation. The position for part of the boundary with given boundary condition is unknown and the position for the rest of the boundary with overspecified Cauchy boundary conditions is given a priori. Since the spatial position for portion of boundary is not given a priori, it is extremely difficult to solve such a boundary determination problem by any numerical scheme. In order to stably solve the boundary determination problem, the MCTM will be adopted in this study owing to that it can avoid the generation of mesh grid and numerical integration. When this problem is modeled by MCTM, a system of nonlinear algebraic equations will be formed and then be solved by ECSHA. Some numerical examples will be provided to demonstrate the ability and accuracy of the proposed scheme. In addition, the stability of the proposed meshless method will be tested by adding some noise into the prescribed boundary conditions and then to see how does that affect the numerical results.

High noise levels in a multi-noise plant can be harmful to workers and can lead to both psychological and physiological problems. Consequently, noise control work on equipment such as acoustic hoods becomes vital. However, research work of shape optimization on space-constrained close-fitting acoustic hoods has been neglected.

In this paper, a sound insertion loss used for evaluating the acoustic performance of an acoustical hood will be adopted. A numerical case for depressing the noise levels at the receiving points along the boundary of three kinds of multi-equipment plants by optimally designing a shaped one-layer close-fitting acoustic hood and reallocating the equipment within a constrained space will also be introduced. Moreover, an artificial immune method (AIM) is adopted and coupled with the equations of sound attenuation and minimal variation square in conjunction with a twelve-point monitoring system.

Consequently, this paper provides a quick and effective method for reducing the noise impact around a plant by optimally designing a shaped one-layer close-fitting acoustic hood and reallocating equipment within the AIM searching technique.

In clinical practice, cam-out failure at the recess-screwdriver interfaces may occur when tightening or removing a bone screw. For titanium-based periarticular fixation, the literature reports have revealed that cold welding at the plate-screw interfaces makes the screw recess especially prone to cam-out failure during screw removal. In this study, the effects of the four recess shapes (cross, hexagon, star, and crest), three torque value (0.8, 1.0, and 1.2N-m), and the three interfacial misfits (0.00, 0.05, and 0.10mm) on the cam-out failure were numerically evaluated. The free-rotation angle, torque-recess angle, slippage-resisting length, and interfacial stress distribution were defined and chosen as comparison indices for the twelve recess-misfit variations. The results revealed that the interfacial slippage, torque transfer, and stress distribution are highly related to both recess shape and interfacial misfit. The stresses of all recesses and screwdrivers consistently initiate at the contact sites. However, the recess profile significantly affects the stress propagation. The stress patterns of the recess and screwdriver are quite different between the cross-star and hexagon-crest groups. The cross-star group is superior to the hexagon-crest group in terms of the torque-recess angle and slippage-resisting length over. This makes the recess of the cross-star group less stressed than its counterpart. However, the volumes of the cross and the star screwdriver are more highly stressed than the hexagon due to the irregular shape and the thinner flange, respectively. The greater torque and misfit increase the performance difference between the four recess designs. In conclusion, the geometry of the cross and star groups provide the better performance of the screw recess in terms of torque-transferring efficiency and slippage-resisting ability. If the screwdriver material is properly strengthened and the stress-concentrating corners are modified, the cross and star groups would be the optimal designs that protects and extends the lifetime of both recess and reused screwdriver.

In this paper, free vibration analysis of functionally graded rectangular plate is investigated based on the first order shear deformation theory and the effect of in-plane displacements on the natural frequencies of such plate is studied. The governing equations of motion are obtained, which are five coupled partial differential equations, without any simplification. Some mathematical manipulation leads us to decouple the equations. The decoupled equations are solved by the Levy's method for various boundary conditions. As the results show, in some boundary conditions the in-plane displacements cause a drastic change of frequencies. In other words, neglecting the in-plane displacement, which is assumed in some papers, is not proper for these boundary conditions. However, in the other boundary conditions, the natural frequencies are not significantly affected by the in-plane displacements. The results for various boundary conditions are discussed in detail and some interpretations for these differences are provided. Besides to the comparisons, the accurate natural frequencies of the plate for six different boundary conditions with several aspect ratios, thickness-length ratios and power law indices are presented. The natural frequencies of Mindlin functionally graded rectangular plates with considering the in-plane displacements are reported for the first time and can be used as benchmark.

This research experimentally investigates the rotor aerodynamics of horizontal-axis, micro-wind turbines. Specifically, the aerodynamic characteristics of large-tip, non-twisted blades are studied. The study is conducted in a wind tunnel system to obtain the relations between the power coefficient (CP) and tip speed ratio (TSR), the torque coefficient (CT) and TSR. Effects of rotor position inside a flanged diffuser, rotor solidity and blade number on rotor performance are investigated. The blade cross-section is NACA4415 airfoil. The pitch angle of the blades is fixed at 30°, and the chord length ratio between the blade root and tip (Cr / Ct) is fixed at 0.3. Results show that larger power output is obtained when the rotor placed closer to the diffuser inlet. The 60%-solidity rotor, in general, achieves better power and torque outputs among the test rotor solidities. The higher the blade number is, the larger the power output is, but the difference is small. Comparisons between the present and previous relatively short-tip blades (Cr / Ct = 0.5) show that the present blades have better power and torque outputs at lower rotor rotational speed. These results suggest that the large-tip blades are suitable for micro-wind turbine applications, and make rotor-generator matching more flexible.