ebrahim shirani

Frostbite is severest form of cold injury that can have serious consequences on limbs such as digits, ears, cheek and nose which are far from the heart. Therefore, in this article, it has been tried to simulate the temperature distribution and find the starting time of frostbite in a human finger as a member that is sensitive to cold stress with a realistic approach. In this research, anatomical data has been extracted from MR images which approximate bone, soft tissues and vessels volume independently. The approach that is presented for converting the MR images to a 3-D finite element model is one of the novelties of this research. A coupled thermo-fluid model is applied to simulate a finger exposed to cold weather. The effect of heat conduction, metabolic heat generation, heat transport by blood perfusion, heat exchange between tissues and large vessels are considered in energy balance equations. Environmental situations such as ambient temperature and wind speed and also glove thermal resistance have been investigated and compared to each other.

In this paper, flow past a single Dissipative Particle Dynamics (DPD) particle with low Reynolds number is investigated and it is inquired that whether a single DPD particle immersed in a fluid, has an intrinsic size. Then a minimum length scale is determined such that the hydrodynamic behavior based on standard DPD formulation is modeled correctly. Almost all of the previous studies assume the DPD particles as point centers of repulsion with no intrinsic size. Hence to prescribe the size of a simulating sphere, a structure of frozen DPD particles is created. In this paper two effective radii, Stokes-Einstein radius and a radius based on the Stokes law, for DPD particles are introduced. For small Reynolds numbers; it is proved that the two radii approach each other. Finally in spite of the typical simulations which assume DPD particles as point centers of repulsion, it is concluded that each of the individual DPD particles interact with other particles as a sphere with non-zero radius. It results the reduction of the required number of particles and eventuates more economical simulations. Moreover contemplating the radius of the particles is necessary for the new Low-Dimensional model which is derived based on the DPD method.

Expanding and appropriate planning in higher education is one of the criteria for economic and cultural development of the country. The higher the education of the society, especially the youth of the country, the higher would be the public culture and potential for better quality work. On the other hand, the heterogeneous, disproportionate, uncounted and ongoing expansion of higher education without providing the requirements will lead to reduction in the quality of education, increase in the unemployment, and the emergence of social and cultural problems. During the ten-year interval, 1384-94 of the two five-year of economic, social, and cultural development programs of the Islamic Republic of Iran, there have been widespread changes in higher education in the country. Specifically, a significant increase in the number of students, in the number of universities and institutes, and in the number of graduate students are among the characteristics of this era. In this paper, analyze is made on the statistics and information related to factors such as the number of students, the number of universities, the ratio of students to faculty members, with emphasis on engineering discipline during the fourth and fifth development plans.  The problems and issues arising from such a large change in higher education are discussed and examined. Ultimately, approaches to overcome such difficulties are presented.

Analytical relation for slow motion thin liquid films bounded by a fixed wall and free surface for Newtonian and non-Newtonian fluids are obtained in this work. Assuming long-wave approximation, the momentum and continuity equations for thin liquid films of power-law fluids are simplified and solved analytically to derive the evolution equation of thin liquid films. The evolution equation is derived for two- and three-dimensional cases. A relation for evolution of thin films is obtained for a simple case in which the liquid film is supported from below by a solid surface and subjected to gravity and constant surface tension forces. This evolution equation of thin film has been solved numerically in order to compare the behavior of Newtonian and non-Newtonian liquids for different Bond numbers. It is shown that the power-law model at low and high strain rates is invalid and it affects the results. The Rayleigh-Taylor instability is another subject that is studied in this work. This interesting phenomena is investigated by solving the evolution equation numerically for different Bond numbers. The results show that the evolution of the free surface thin film for pseudo plastic fluids is different from that of Newtonian and dilatant fluids

The radios of particles in Dissipative Particle Dynamics (DPD) method is investigated numerically taking into account size and type of conservative force. In the most of previous studies, the DPD particles have been considered as a point center of repulsion with zero radios and hence sphere size is prescribed by the creation of a structure of frozen DPD particles. Although only in ideal gas state or zero conservative force the DPD point particle is meaningful and with conservative force the DPD particles have an intrinsic size which is assigned by the spherical impenetrable domain occupied by each particle when immersed in a sea of other particles. At first the appropriate method should be define to calculate the size of DPD particle. Different methods including Stokes-Einstein relation, Stokes law and radial distribution function (RDF) are studied and it is concluded that according to limitation of Stokes-Einstein and Stokes relations the RDF is the best method for evaluation of DPD particle size. In the following, the trend of DPD particle size changing and their distribution in the system with linear and exponential conservative force examined. At the end we demonstrate that the employing of exponential conservative forces for the colloid-colloid and colloid-solvent interactions but keep the conventional linear force for the solvent-solvent interactions achieve a well-dispersed suspension with different particle sizes without extra computation

In this study, the optimal distribution of Wall Shear Stress (WSS) in a bifurcation and its effect on the morphology of blood vessels were investigated. The optimal WSS was obtained through minimization of energy loss due to friction and metabolic consumption. It was shown that the optimal WSS is a function of metabolic rate, fluid properties, diameter, and flow regime. For fully developed laminar and turbulent flows different patterns of WSS were observed. For laminar flows WSS is constant but for turbulent flows WSS is a function of diameter such that the exponent of diameter varies by tube relative roughness. Based on the optimal WSS and conservation of mass, the optimal relationship between diameters of mother and daughters’ vessels was obtained for different flow regimes. Also, it was theoretically shown that the optimal distribution of WSS in a bifurcation minimizes flow resistance as well as energy loss. In addition, it was demonstrated that the specific relationship between the length and diameters of a blood vessel and optimal relationship between diameters lead to optimal WSS distribution. Finally, the numerical simulation was used to investigate the effect of Reynolds number on the optimal WSS and flow resistance, and to verify the theoretical formula predictions, obtained in this work.

In order to simulate the heat transfer process from wall to fluid in nanochannel numerically, extensive range of spring constants with regard to wall material is used. In this paper, the effect of variation in wall spring constant on the heat transfer and distribution of the macroscopic properties of fluid has investigated. In this regard, heat transfer in argon gas between two stationary walls of a 5.4 nm nanochannel with Knudsen number 10 has simulated using the molecular dynamic method. Comparison between the results shows that by reducing the wall spring constant, the amplitude of wall atoms vibration increased so it makes the gas atoms to become closer to the wall surface that results in an increase in the heat flux and thermal conductivity coefficient of the gas. Evaluating the result reveals that while the spring constant reduces from k_s=1100εσ^(-2) to k_s=100εσ^(-2), the thermal conductivity coefficient of the gas changes from 0.11 mW⁄(m-K) to 0.27 mW⁄(m-K). Furthermore, the reduced distance between the gas atoms and wall surface results in a decrease in the temperature jump on the wall so it increases the gas density near the cold wall while it decreases near warm wall. Comparison between temperature, density and pressure profiles in the nanochannel height shows that regardless to the amount of spring constant variation, the maximum of these properties has occurred at σ⁄2 from the walls.

In this paper heat transfer through argon gas between two stationary walls of a nano sized channel, is investigated by the use of molecular dynamic method. Comparison between two and three-dimensional solutions shows that for accurate modeling of wall force filed on heat transfer, the accuracy of two-dimensional molecular dynamic solution is inadequate. Two-dimensional solution predicts the value for density and temperature less than the value of three-dimensional solution near each wall. Considering the effect of domain size on accuracy of thermal solution shows that domain size should be extended at least for one mean free path in periodic direction to have domain independent results. Distribution of fluid properties in the width of the channel shows that independent of implemented temperature difference, presence of the wall force field changes the temperature and density profile in one nanometer from each wall drastically. In addition to variation in density due to the wall force filed, temperature difference between the walls cause additional variation in density profile near walls. Increasing the temperature difference between the walls to value more than 20 degree, make a notable density variation to more than 5 percent in comparison with gas density distribution in isothermal walls case. Variation in density near walls due to temperature differences leads to mismatch between the non-dimensional temperature profiles and calculated thermal conductivity coefficient of the gas for various temperature differences.

In this paper, the results obtained from experimental measurements of average and turbulence quantities of a turbulent rectangular impinging jet hitting a fixed wall is reported using the laser doppler anemometry (LDA) method. The nozzle to plate distance is 10 times the nozzle width, and the tests are repeated for three different Reynolds numbers, namely Re=3000, 6000 and 9000. The aim of the current research was to investigate and comparise of flow in different Re and also to determine the two effective experimental errors on average velocities, namely data sampling and residence time in measurement volume. The results reveal that the previous stated correlation for prediction of the number of data required for ensuring independence of the average flow variables on the number of the sampled data is not sufficient by itself, and depending on the turbulence intensity of the flow, this correlation could become ineffective. Further, in the present study, the residence time is used for calculation of average velocities, and the results are compared with those obtained by particle image velocimetry (PIV) method. The comparison shows good agreement between the results from LDA and PIV when considering effect of residence time within the avaraging equations in the former method. The results show that the behavior and quantity of the dimensionless average velocities for various Reynolds numbers are identical at most cross sections of the flow domain while the dimensionless turbulent stresses have different quantities at different values of the Reynolds number.

The variation of wall shear stress (WSS) in the microvessels may damage the endothelial layers. It also changes the mass diffusion and sediment and may be considered as an important factor in the formation of the fatty plaques and causing heart disease. According to the importance of the issue, the aim of this paper is to study the effective parameters on the wall shear stress in microvessels. In this paper, the hybrid method, combined lattice Boltzmann and immersed boundary methods is used to simulate the red blood cell (RBC) motion in the plasma flow. It should be mentioned that red blood cell has significant effect on WSS, in this regard; the present results show that the blood rheological behavior has the important effect on WSS. The results also demonstrate the effect of stenosis severity and RBC location in different regions on wall shear stress and consequently causing heart, coronary disease. It should be noted that the presented results have been evaluated by previous numerical results for microvessels and the results show the ability of lattice Boltzmann method to simulate complex problems especially for modeling the deformable solid objects suspended in the fluid.

In the present study, the hydrodynamic behaviours of the Couette Taylor flow in different flow regimes were investigated, experimentally and numerically.In this research, the effects of Taylor number on wavelength of the flow, which are two important hydrodynamic charactristics of the Couette Taylor flow, are investigated both experimentally and numerically in order to study the stability of the flow and formation of vortices. In addition, the velocity and pressure variation of the the flow between two cylinders were considered and compared for different Taylor numbers to understand the behaviuor of the flow.

A 3D numerical simulation using large eddy simulation (LES) method is performed for a submerged turbulent water slot jet impinging normally on a flat plate with a nozzle-to-plate distance of 10 jet width and a Reynolds number of 16000 and the results are compared with the existing experimental data. The numerical platform is an open source CFD code based on the field operation and manipulation C class library for continuum mechanics (OpenFOAM) and is used to simulate the flow and represent the mean and instantaneous flow field characteristics. Also, simulations are performed with two different subgrid-scale (SGS) models, one-equation based subgrid-scale model and localized dynamic smagorinsky model. Evaluating the different subgrid-scale (SGS) models, a priori and a posteriori test is done. Comparison between results obtained using the SGS models and experimental data shows that the simulation results using localized dynamic Smagorinsky model are more compatible with the experimental data compared with those that obtained from the kinetic energy one-equation model especially in regions close to the impingement wall and in free jet region.

The purpose of this paper is to investigate theLow-Density Lipoproteins (LDL) mass transfer in vessel walls using the Lattice Boltzmann Method (LBM). High Schmidt number of LDL leads to numerical instability of LBM.In order to solve this problem, LBM and finite volume method (FVM) are combined.In this hybrid method, the blood velocity field is solved by LBM using the single relaxation time, SRT, model and FVM has been used for LDL concentration equation. LBM is able to simulate flow and mass transfer for the Schmidt number, Sc, up to 3000 only if the time consuming multi relaxation time is used. However, the purposed hybrid method suggested in this article can be used to solve the problem for Sc as high as 107. Good agreement between our results obtained from the hybrid simulation and the available results in the literature and noticeable decrease in CPU time compared with when the LBM is used for both flow and mass transfer, indicates the ability of the hybrid method.Finally, the hybrid methodis used to simulate the mass transfer of LDL particles and investigate the effective factors for increasing the surface concentration, such as the size of LDL particles, wall suction velocity, wall shear stress, Newtonian and non-Newtonian fluids behavior and change of concentration boundary layer with various Schmidt number.

Electroosmosis is the predominant mechanism for flow generation in lab-on-chip devices. Since most biofluids encountered in these devices reveal non-Newtonian behavior, a special understanding of the fundamental physics of the relevant transport phenomena seems vital for an accurate design of such miniaturized devices. In this study, a numerical analysis is presented to explore transport characteristics of typical non-Newtonian biofluids through annular microchannels under combined action of pressure and electrokinetic forces. The flow is considered steady and hydrodynamically fully developed. A finite difference method is used to solve the Poisson-Boltzmann and Cauchy momentum equations, while the classical boundary condition of no velocity-slip for the flow field is applied. The Poisson-Boltzmann equation is solved in the exact form without using the Debye-Hückel approximation. After numerically solving the governing equations, role of the key parameters in hydrodynamic behavior of the flow is analyzed and discussed.

In this research an inverse design algorithm, called ball-spine algorithm (BSA) is developed on a 90-degree bend duct between the radial and axial diffuser of a centrifugal compressor with viscous swirling inflow to bend duct. The shape modification process integrates inverse design algorithm and a quasi-3D analysis code. For this purpose, Ansys CFX software, is used as flow solver and inverse design algorithm is written as a code inside it. Shape modification is accomplished for viscous and inviscid flow to check the effect of viscosity on convergence rate. Also, the effect of swirl velocity in shape modification process is investigated, by considering increased pressure as the target parameter. The algorithm reliability for swirling flow is verified by choosing different initial geometries. Finally, aerodynamic design of the bend duct with BSA is accomplished to reduce losses in 90-degree bend. Shape modification process is carried out by improving the current wall pressure distribution and applying it to the inverse design algorithm. Results show that convergence rate and stability of BSA are favorable for designing ducts with swirling viscous flow. So that, the pressure recovery coefficient of the 90-degree bend duct is 4%increased.

Neurological diseases such as cancer damage blood brain barrier and consequently cause more permeability in tissues. Generally, if there is damage to the brain tissues the contrast agent used in MRI diffuses outside the capillaries and the MRI picture brightness changes. The purpose of this paper is to show the effects of different parameters on the contrast agent diffusion in the brain capillary. In this study, the lattice Boltzmann method with multi-relaxation time (MRT) is used to simulate the flow in the capillary and porous media around it. The results show that the porosity in extravascular tissues (it shows the tissue damage), the kind of contrast agent and capillaries curvature have an impact on the contrast agent diffusion in the tissues. The presented results show the effects of curvature on shear stress and thus on mass transfer in the capillary. It should be noted that the presented results have been evaluated by previous statistical and analytical results for flow in the damaged brain capillary with different permeability. It has been shown that the lattice Boltzmann method is able to simulate the complex problems, especially in porous media.

In this study, slip-flow heat transfer in a laminar, steady state, two-dimensional incompressible flow between parallel plates micro-channel is investigated numerically. A new method based on perturbation expansion for modeling of slip micro-flows is presented. Navier-stokes equations are developed by using perturbation expansions of velocity, pressure and temperature fields. Different orders of equations depending on the magnitude of Knudsen number are obtained and each set of the equations are solved. The computations are performed for micro-channels with Constant Wall Heat Flux (CWHF) and Constant Wall Temperature (CWT) boundary conditions to obtain heat transfer characteristics of gaseous flow in slip regime. The effects of compressibility and viscous dissipation are neglected in this study. The numerical methodology is based on Semi-Implicit Method for Pressure-Linked Equations (SIMPLE) method. The effects of Knudsen number and thermal creep flow on Nusselt number are numerically investigated.This study confirms that the perturbation method with different orders of Knudsen number can predict the velocity and temperature fields with good accuracy. The obtained solutions are compared with both available numerical and analytical results and good agreement is obtained.

The effects of driving voltage waveform and frequencies on the performance of piezoelectrically actuated micropump are investigated in details. A full three-dimensional piezoelectric micropump was modeled numerically and tri electro-mechanical-fluidic coupling effects have been taken into account on its interface boundaries. Standard excitation waveforms including sinusoidal, triangle, sawtooth and square shapes were implemented and the results were compared with each other. The real time pump flow behavior was studied in each case for different membrane positions. The analysis predicts that the more sharp jump in the wave form, the more pump flow can be attained at the outlet. Square shape excitation with the sharpest instantaneous slope has the most notable overall flow rate compared to the other types in the examined range of frequencies. The behavior can be explained by considering the generated vortices in the flow. Due to sudden jump in membrane position, the flow forms strong vortices which magnify the diodicty of valves.

In the present work, for the first time, the application of a Multi-Relaxation-Time Lattice Boltzmann (MRT-LB) model for large-eddy simulation (LES) of turbulent thermally driven flows on non-uniform grids is considered. A Taylor series expansion and Least square based Lattice Boltzamnn method (TLLBM) has been implemented in order to use a nonuniform mesh. It permits to reduce the required mesh size and consequently the computational cost to simulate the turbulent buoyant flow fields. The implementation is discussed in the context of a MRT-LB model in conjunction with both Smagorinsky and mixed scale viscosity sub-grid models. At first, to validate the code, a multi-relaxation–time lattice Boltmann method on non-uniform grid is utilized to simulate a lid-driven cavity flow. Then large eddy simulation of this model is applied to simulate a turbulent Rayleigh-Bénard convection at different Rayleigh numbers in ranging 104 to 1015 for Prantdl number of 0.71. The simulation results show that lattice Boltzmann method is capable to simulate turbulent convection flow problems at high Rayleigh numbers.

In this study، the effect of number of stages on Tesla microvalve performance has been studied. To do this، different layouts including one to four-stage microvalves are investigated numerically. The main criterion is used for evaluation of valves performance is diodicity. Two-dimensional and steady state computations of the fluid flow have been utilized that reveal a strong dependence of diodicity on Reynolds number and the pressure drop. The results showed that for the same flow condition، the diodicity average of the two-stage microvalve is approximately 1. 32 times of that of one-stage. Additional stages increase the complexity and they do not change the diodicity considerably. It is concluded that two-stage layout of Tesla type valve is the best option between the studied layouts. A two-stage layout of this valve in valveless micropump besides being compact، has the adaptability of the various functions. Also، the two-stage valve performance in three different sizes is compared with nozzle - diffuser type valve. Comparisons which are performed based on calculation of diodicity for applicable range of Reynolds numbers show that the diodicity is function of Reynolds number and is independent of the valve size. Also، the superiority of the Tesla type valve for higher Reynolds number and its weakness at lower Reynolds number are shown.

The trend of evolution and takeover of new industries, as well as emerging new sciences and technologies, will bring deep and radical changes in industries and daily life of mankind. Responding to the today's and tomorrow's need of industries by Mechanical Engineers requires different tools and knowledge that are typically used today and parallel to the above mentioned changes, Mechanical Engineering Education needs to be changed. In this paper, a brief history of engineering education in general and mechanical engineering education in particular, will be discussed first and the trend of changes in this regard will be reviewed. The necessity of putting the emphasis on the applied problems and "engineering education" rather than "engineering sciences" is mentioned without undermining the importance of theoretical and basic subject-materials typically offered in the mechanical engineering curriculum. Paying more attention on research in mechanical engineering education in Iran is another matter which is recommended in this paper. Here, the necessary changes in the mechanical engineering curriculum are categorized in the four cases: 1) issues related to the learning environment, 2) issues related to the mechanics of the learning process, 3) issues related to the partnership with industry and other institutions and 4) issues related to the content of mechanical engineering education (especially the latter), due to the emerging novel technologies and the role of the mechanical engineers in these matters are given. Such new technologies are: micro/nano technology, biotechnology, information technology, and ecology/energy. Finally, a list of actions necessary to take in mechanical engineering education is listed.