Scientia Iranica
Volume:19 Issue: 1, 2012

In the present study, mixed convection of a fluid in the fully developed region in a horizontal concentric cylindrical annulus with different uniform wall temperatures, is numerically investigated in both steady and unsteady states in the presence of radial MHD force, as well as in consideration of heat generation due to viscous dissipation. Also, cylinder length is assumed to be infinite. Moreover, radiation heat transfer from the hot surface is assumed to be negligible. Buoyancy effects are also considered, along with Boussinesq approximation. The forced flow is induced by the cold rotating outer cylinder at slow constant angular velocity, with its axis at the center of the annulus. Investigations are made for various combinations of non-dimensional group numbers; Reynolds number (Re), Rayleigh number (Ra), Hartmann number (Ha), Eckert number (Eck) and annulus gap width ratio (σ0). These dimensionless parameters used in the present study will be investigated over a wide range to present the basic flow patterns and isotherms in a concentric cylindrical annulus. A finite volume scheme, consisting of the Tri-Diagonal Matrix Algorithm (TDMA), is used to solve governing equations, which are continuity, two-dimensional momentum and energy, by the SIMPLE algorithm. The numerical results reveal that the flow and heat transfer are suppressed more effectively by imposing an external magnetic field. Furthermore, it is found that the external magnetic field causes the fluid velocity and temperature to be suppressed more effectively. Moreover, it will be shown that viscous dissipation terms have significant effects in situations with high values of Eckert and Prandtl number and low values of Reynolds number.

The frequency response behavior of Atomic Force Microscopy (AFM) cantilevers in liquids is completely different from that in air, due to changes in the applied hydrodynamic forces and squeeze forces. In this paper, a finite-element method is used to explore the dynamic behavior of AFM cantilevers in air and in liquids. Furthermore, the frequency response of the tapping mode AFM under acoustic excitation force is studied. In the theoretical model, hydrodynamic forces exerted by the liquid on the AFM cantilever are approximated by additional mass and hydrodynamic damping. The results show that the microcantilever operating in liquids is an intensively damped system, with a relatively large shift in its resonant frequencies from its natural frequencies, along with a considerable reduction in vibration amplitudes. The simulation results are compared with experimental results, showing very good agreement between the two. In addition, the effects of liquid viscosity and liquid density on the frequency response function are studied. Finally, the dynamic behavior of the AFM cantilever under tip-sample interactions is analysed in both repulsive and attractive regimes. The paper shows further that the frequency response in liquid environments close to the surface depends on two important parameters: squeeze force and tip-sample interaction.

Red Blood Cells (RBCs) are the main cells in human blood, with a main role in the mechanical properties of blood as a fluid. Several methods have been improved to simulate the mechanical behavior of RBC in micro-capillaries. Since, in microscopic scales, using discrete models is more preferred than continuum methods, the Moving Particle Semi-Implicit method (MPS), which is a recent innovative particle based method, can simulate micro-fluidic flows based on Navier–Stokes equations. Although, by recent developments, the MPS method has turned into a considerable tool for modeling blood flow in micro meter dimensions, some problems, such as a commitment to use small time step sizes, still restrict the method for large models and also for long time simulations. A new modified semi-implicit algorithm is developed and implemented on RBC motion through microvessels, in order to reduce calculation time by more than a factor of twenty, while the error of position and velocity remains constant. A two-dimensional, parallel plate, fluid flow is simulated based on the proposed method, and the effect of the calculation time decrement is evaluated. Findings indicate a reduction of 90 percent in simulation time compared to previous studies with the same results. This significant developed method could be applied to RBC interaction within micro-capillaries and constricted zones in blood flow.

Hemodynamic factors, such as Wall Shear Stress (WSS), play a substantial role in arterial diseases. In the larger arteries, such as the carotid artery, interaction between the vessel wall and blood flow affects the distribution of hemodynamic factors. In the present study, both rigid-wall and deformable-wall models are developed in a 3D numerical simulation to assess the effectiveness of arterial rigidity on worsening hemodynamics, especially WSS. Two different rheological models (Newtonian and Carreau–Yasuda) have been employed to evaluate the influence of blood, non-Newtonian properties, as well. The importance of vessel wall deformability was compared with the rheological model of blood. Although the deformability changes hemodynamic factors under the steady state boundary condition, or at the last two phases of the cardiac cycle (when the blood flow in carotid looks like a steady condition), WSS distribution is mostly affected by the blood rheological model. In other words, the influence of shear-thinning behavior at the end-diastolic phase of the cardiac cycle is undeniable unlike the deferability. However, the effects of deformability, like the rheology of blood on WSS could not be neglected at the first two phases of the cardiac cycle when pressure reaches its highest values.

The longitudinal and shear velocities of ultrasonic waves in glass systems are influenced by the microstructural properties and compositions of the chemical constituents. The relationship between them is highly non-linear and very complex. Artificial Neural Networks (ANN) are adaptive and parallel information processing systems that have the potential to learn by examples and capture the non-linear as well as complex relationships between its inputs and outputs. Neural networks are invaluable where formal analysis would be difficult or impossible. An attempt has been made to predict the ultrasonic velocities in tricomponent oxide glass systems, using the microstructural properties of the constituents as inputs to the ANN.

A novel and robust intelligent scheme is proposed to control a highly non-linear 3-RRR (revolute-revolute-revolute) planar parallel robotic manipulator, via an Active Force Control (AFC) strategy that is embedded into the classic Proportional-Integral-Derivative (PID) control loop. A PID-type Iterative Learning (IL) algorithm, with randomized initial conditions, is incorporated into the AFC loop to approximate the estimated inertia matrices of the manipulator adaptively while the manipulator is tracking a prescribed pulsating trajectory in the presence of harmonic disturbances. The IL algorithm employs a stopping criterion, which is based on tracking error, to stop the learning process when the desired error goal of the system is reached, to signify a favorable controlled condition. A numerical simulation study was performed to verify the robustness of the proposed methodology in rejecting disturbances, based on given loading and operating environments. The results of the study reveal the superiority of the proposed system, in terms of its excellent tracking performance compared to the AFC, with crude approximation techniques, and Proportional-Integral-Derivative (PID) counterparts.

The purpose of this study is to create a three dimensional parametric model of the lower cervical spine and to validate it by examining the model with some experimental data and other similar studies Bonivtch et al. (2006) [1], Panjabi (1979) [2], Panjabi et al. (1998) [3], Panjabi (2001) [4]. The first step is to create a master model with the capability of simply changing parameters, which can be extracted from CT-scan images. By implementation of these parameters to the model, it would be updated for each case. The next step is the mesh-generating of the model, and, thus the material properties for each part of the model have been implemented. In this model, the vertebra, endplate and facet have been considered as simple elastic solids, and the nucleus, annulus and ligaments have been considered as incompressible solid, hyper-elastic solid, and non-linear springs, respectively. After finalizing the modeling procedure, analysis of the model for each case is done. The results have been compared with some references, and after validation of the model, the model could be used for extended similar studies.