Scientia Iranica
Volume:25 Issue: 5, Sep - Oct 2018

In this work, for better understanding of microvessels disorders, mass transfer at a stenotic and the straight capillary wall in the presence of RBC motion is investigated. The immersed boundary- lattice Boltzmann method is used for this purpose. The erythrocyte is considered as an immersed biconcave shaped tissue around the capillary as a porous media. The gamma function for input concentration, which is close to the actual stenosis brain capillary, is used. The simulated results obtained for both stenosis and straight capillaries are compared. It is shown that while the RBC motion has negligibly small effects on wall mass transfer in straight capillaries, its effect is not negligible at stenosis capillaries.

In this paper, the mode III crack problem of a non-homogenous layer bonded to an elastic half-plane is considered. It is assumed that the half plane is homogeneous and the layer is non-homogeneous in which the elastic properties are continuous throughout the layer. The stress field in a non-homogeneous layer and in an elastic half plane with Volterra type screw dislocation is obtained. Fourier transforms was applied to governing equations to derive a system of singular integral equations with simple Cauchy kernel. Then, the integral equations are solved numerically by converting to a system of linear algebraic equations and by using a collocation technique. The results given include the effect of the non-homogeneity parameters, interaction between the multiple cracks and distance of the cracks on the stress intensity factors for the purpose of gaining better understanding of the mechanical behavior of non-homogenous coating.

The collocation nite element method is applied to obtain solitary wave solutions to Korteweg-de Vries equation with power law nonlinearity. The stability and error analysises are also carried out for these waves. Additionally, conservation laws are studied numerically.

In this paper, free vibration of the micro-cylinder made by functionally graded material that is stiffened in circumferential direction, has been investigated based on the modified couple stress and first order shear deformation theories. Modified couple stress theory (MCST) has been used to catch size effects in micro scales. By using first order shear deformation theory and Hamilton principle, general equations of motion and corresponding boundary conditions have been derived. Free vibration of the structure has been investigated by implementing simply supported boundary condition as a common case. The effects of different parameters such as dimensionless length scale parameter, distribution of FGM properties, number of stiffeners, thickness and length on the natural frequencies were calculated and compared with classical continuum theory. Results show that effects of the size are considerable and also using stiffeners lead to increase in natural frequencies which is because of increase in stiffness of the cylinder.

In this paper, a new mechanism with unique and prominent feature for helical swimmer robot has been presented. “Double Helices Propulsion Mechanism”, consists of two parallel helices with single axis which rotate in the same direction. The outer helix acts as the main propulsion component and the inner helix, which is made of a shape memory alloy (SMA), controls the forward velocity during swimming. This mechanism by varying the geometrical parameters of its helical tail can change the forward velocity of the helical swimmer robot that is required by its predefined missions. In order to study the effects of geometric parameters on the forward velocity in the single helical swimmer, a hydrodynamic model based on Slender Body Theory (SBT) are implemented. Moreover, in order to validate the predicted results, a scaled-up macro-dimension prototype with a single helical tail and Reynolds number of less than one, is built. Finally the performance of the double helices system is estimated by modeling the dynamics of the motion in different tail lengths. This comparison indicates that, this mechanism increases the forward velocity and the efficiency of swimmer robot and it can be produce the variable forward velocities at each frequency.

A nonlinear robust adaptive sliding mode admittance controller is proposed for exoskeleton rehabilitation robots. The proposed controller has robustness against uncertainties of dynamic parameters using an adaptation law. Furthermore, an adaptive Sliding Mode Control (SMC) scheme is employed in the control law to provide robustness against disturbances (non-parametric uncertainties) with unknown bounds. For this purpose, another adaptation law is defined for the variation of the SMC gain. The proposed scheme is augmented with an admittance control method to provide compliance for the patient during interaction with the rehabilitation robot. The stability of the proposed controller and the tracking performance of the system are proven using the Lyapunov stability theorem. To verify the effectiveness of the proposed control method, some simulations are conducted for a nonlinear lower-limb exoskeleton robot interacting with a patient leg via some braces. Based on the obtained results, the controller is able to provide a flexibility for the patient and appropriately respond to his/her non-compliant interaction torques. Moreover, the proposed controller significantly reduces the chattering of the input torques in comparison with a previous adaptive control method with a constant SMC gain, while it maintains a similar tracking performance.

This paper investigates the double–diffusive natural convection in partially layered square cavity. The cavity composed of porous layer on the left and fluid layer on the right. A conductive solid body is included inside the cavity to control the natural convection. The left wall is kept at constant high temperature and adjusted with high concentration, while the right wall is kept at low temperature and low concentration. The horizontal walls are thermally insulated. The 2-dimensional governing equations have been solved using up-wind scheme finite difference method. The Parndtl number and buoyancy ratio are fixed at 6.26 and 1, respectively. The problem has been governed by five parameters namely, Lewis number (Le = 1–50), Rayleigh number Ra (103-106), Darcy number (10-9-1), aspect ratio of the body relative to the cavity A (0.3, 0.5) and the position of the body. The results have showed that locating the solid body close to the mid height of the left wall gives maximum convective heat transfer, while minimum heat transfer is associated when the solid body is located at the cavity center. It is also found that the Nusselt and Sherwood numbers behave contradictory with the location of the solid body.

In the present study, a layerwise finite element method is utilized to solve the coupled elasticity and piezoelectricity equations to study a functionally graded shell panel integrated with piezoelectric layers under electromechanical loading. The system of equations is reduced to ordinary differential equations with variable coefficients by means of trigonometric function expansion in circumferential and longitudinal directions satisfying mechanical and electrical boundary conditions. These equations are solved using the Galerkin FEM and Newmark method. The results of stress, displacement and electrical potential are presented and the effect of panel thickness and applied voltage on the structural behavior is investigated.

Most of the biped robots are controlled using pre-computed trajectories methods or methods based on the multibody dynamics models. The pre-computed trajectory based methods are simple but the system gets highly vulnerable to the external disturbances. In contrast, the dynamically based methods make the system acts faster, but they need extensive knowledge about the kinematics and dynamics of the system. This fact gave rise to the main purpose of this study, i.e., developing a controller for a biped robot to take advantages of the simplicity and computational eciency of trajectory-based methods and the robustness of the dynamic-based approach. To do so, this paper presents a twolayer hierarchical control framework for an under-actuated, planar, 5-link biped robot model. The upper layer contains a centralized dynamic-based controller and uses all system sensory data to generate stable walking. The lower layer in this structure is a decentralized trajectory-based controller network which learns to control the system based on the upper layer controller output. When the lower controller fails to control the system, upper layer controller takes action and makes the system stable. Then, when the lower layer controller gets ready, the control of the system will be handed to this layer.

The aerodynamic loads and energy losses for a typical 600 KW wind turbine with S816 airfoil blade under two different icing conditions, have been studied. Three sections at different radial positions are considered for estimation of the icing effect along the blade. Ice accretion simulations in wet and dry regimes are performed, using the NASA LEWICE 3.2 computer program. The airflow simulations are carried out with CFD methods and implementing the SST k-ω turbulence model. The results of these simulations including; streamlines, surface pressure, skin friction, lift, and drag coefficients are inspected for both clean and iced-airfoils. In the case of wet iced-airfoil, a separation bubble is created in the leading edge due to a horn shaped ice and further downstream, the airflow is reattached. Ice-induced separation bubbles dominate the flow field and the aerodynamic performance of the wind turbine. In order to assess the production losses, the Blade Element Momentum (BEM) theory is used to calculate the power curves for clean and iced wind turbine blades. In the case of dry regime, the performance deterioration is about 30% and in another case, the turbine fails to produce any power at all.

In this article, the acoustic radiation responses of the layered composite flat panel in an infinite rigid baffle under the influence of harmonic point load and various support conditions are investigated numerically. The laminated composite flat panel responses have been computed using the ANSYS parametric design language code. The natural frequencies obtained using the current simulation model are matched with the earlier published values as well as in-house experimental results. The eigenvectors corresponding to the validated eigenvalues are extracted and utilised for the computation of the acoustic properties numerically by solving through Rayleigh integral scheme. The first radiation mode’s amplitudes for the vibrating plate have been computed and validated with the results available in open literature. Further, the self-radiation efficiency and radiated sound power are obtained based on the structure dependent radiation modes and all the radiation modes are also included to evaluate the exact radiated sound power. Finally, the effect of the different composite (Carbon/Epoxy and Glass/Epoxy) properties, constraint conditions and the location of point load on the displacement and velocity responses, radiation efficiency and the radiated acoustic power level of the layered flat panel have been investigated and discussed in detail.

The bending responses of nanotube-reinforced curved sandwich shell panel structure are studied under the influence of the thermomechanical loading. Further, the temperature dependent material properties of the sandwich structure are assumed to evaluate the exact responses. In addition, the face sheets of the sandwich construction are modeled using different grading pattern through the panel thickness. The final form of the equilibrium equation of the deflected sandwich structure obtained by minimising the total potential energy functional. Now, the equation is solved computationally via a suitable computer code (MATLAB) using the novel higher-order kinematics including the finite element method. The constancy and the accuracy of the current finite element solutions are verified by solving a different kind of numerical examples as same as the published examples. The effect of parameters associated with structural stiffness and the flexural behaviour of the nanotube-reinforced curved sandwich structural panel are examined together with the unlike temperature distributions (uniform and linear) and discussed the final conclusions in detail.

Transport pipes have been widely used for their several advantages including their cost-effectiveness and simplicity of installation. These pipes are constantly in contact with the flowing fluid and therefore pipe’s material properties may degrade due to the diffusion of the fluid into the material system. These conditions are exacerbated as a result of high pressure and temperature of the transported fluid. Therefore, to simulate the behaviour of such pipes, three interactive phenomena of mechanical stress, heat transfer and mass diffusion need to be investigated. This study considers the three mechanisms simultaneously and provides an analytical solution to the corresponding coupled governing equations. The results of this work are in good agreement with the results of double coupled physics available in the literature and therefore can be used to predict the material behaviour under complicated environmental conditions.