مجله مهندسی مکانیک
سال چهل و هفتم شماره 2 (پیاپی 79، تابستان 1396)

Tube bending is widely used in the aerospace and automotive industries. Of the main difficulties of this process are wrinkling, rupture and incomplete filling of the die. If the ratio of the bend radius to tube diameter (R/D) in the bending process is between 1 and 1.5, the bending cannot be performed by conventional methods. Therefore, it is important to develop a new technique in this respect. In this study, at first, closed-end seamless tubes were produced by multistage deep drawing and ironing processes. Then, the proposed hydroforming process of square cross-section tubes with the ratio of R/D=1 has been examined experimentally and by FEM. It is illustrated that the square cross section tubes with low R/D can successfully be produced by the developed technique. In addition, the effect of internal fluid pressure and die bend angle on the thickness distribution of the inner, outer and lateral walls of the bending area has been investigated. It is shown that with increasing the pressure, the thickness of the inner, outer and lateral tube walls increases. The reduction in the thickness is much greater for the external wall. The tube in the R / D = 1 was formed with multi of bending angles. The results exhibit with increasing the bending angle, the pressure of forming was decreased.

In this research, the TLP bonding of IN-738LC nickel based superalloy was studied using MBF-15 amorphous foil produced by planar flow casting process. The bonding process was performed at 1130-1170 °C for 5-60 min under vacuum atmosphere. Microstructural examinations revealed that the eutectic phases formed in non-isothermal solidified zone (ASZ) are Nickel and Chromium rich borides and Nickel silicides. Nickel silicide fine precipitates forms within γ solid solution via solid state precipitation during cooling. The blocky and acicular Cr-rich boride and carboboride precipitates were observed at diffusion affected zone (DAZ). The fraction of center zone eutectic and intermetallic phases was decreased by an increase in the bonding time. It was found that isothermal solidification was completed by performing TLP process at 1130 °C for 30 min. However, the isothermal solidification rate was decreased with increasing of TLP bonding temperature up 1170 °C. The shear strength was increased by completing of an isothermal solidification stage and elimination of brittle intermetallic particles in centerline of the bonding zone. The SEM micrographs of shear fracture surfaces of the specimens with complete isothermal solidification showed ductile and specimens with athermal solidified zone showed brittle fracture.

In this research, the direction of the magnetic field on the mixed convection heat transfer in a square cavity filled with water-copper nanofluids has been investigated numerically. In this simulation, the SIMPLE algorithm is used to solve the discrete equations. The below wall of cavity is heated and the other walls are insulated. Cooled fluid comes from entrance of channel that is above of cavity and out from the other side of channel. In this study, the effect of volume fraction, Hartmann, Reynolds, Rayleigh and Richardson numbers on Nusselt number and heat transfer are assessed. In addition, the effect of changing angle of magnetic field on various Rayleigh, Reynolds and volume friction is investigated. The results are shown that: increasing value of volume friction, Reynolds and Rayleigh causes to rising heat transfer whereas adding Hartmann number and Richardson number at constant Rayleigh number decrease heat transfer and Nusselt number. The other important conclusion is the heat transfer in the presence of horizontal magnetic field less than vertical field. Operation of magnetic fields in same direction and various angles (0˚ and 180˚) on temperature contour, stream line and heat transfer is completely similar.

In this paper, a Regenerative Organic Rankine Cycle (RORC) for micro-turbine waste heat recovery is modeled and optimized. Refrigerant mass flow rate, Micro- turbine nominal capacity, evaporator pressure, turbine outlet pressure and regenerator efficiency are considered as design parameters. Four refrigerants including R123, R134a, R245fa and R22 are selected and used as working fluids in cycle. Then, NSGA-II (Nondominated Sorting Genetic Algorithm) is used to maximize the thermal efficiency and minimize the total annual cost (including investment cost, fuel cost and environmental cost. The results of the optimal design are a set of optimum solutions, called Pareto front. The optimization results show that the best working fluid is R123 in both of economical and thermo dynamical view point. The optimum result of R123 shows the 3.70%, 18.77%, and 19.74% improvement in thermodynamic efficiency compared with R245fa, R134a, and R22, respectively. The corresponding values for the total annual cost are obtained 6.7%, 10% and 24%, respectively. Generally, it seems that fluids with zero and positive slope of vapor saturation curve have higher thermal efficiency and lower total annual cost. In addition, it is observed that micro-turbine efficiency increased by 12% by the implementation of regenerative organic rankine cycle.

In this research study, fracture behavior of Functionally Graded Materials (FGMs) is investigated. The FGM is supposed to be formed of aluminum and alumina. For experimental purposes, four point bending test was used. The results were then compared by finite element analysis. Maximum Tangential Stress (MTS), 〖(K_II)〗_min and Gradient Equivalent Stress (GES) criteria were used to estimate crack initiation angles. Stress Intensity Factors (SIF’s) were extracted from J-Integral parameters. MTS and 〖(K_II)〗_min criteria show good agreement with experimental results, however GES method does not confirm with experimental results. The numerically calculated crack direction shows good consistency with fractured specimens.

In this paper, the free vibration and divergence instability of single-walled carbon nanotubes conveying fluid with considering the effects of non-uniformity of laminar and turbulent flow velocity distribution are investigated based on nonlocal elasticity theory. The non-uniform flow velocity distribution occurs due to the viscosity of the fluids. Based on the Euler-Bernoulli beam theory, the governing equations of motion and boundary conditions are derived by using the Hamilton's principle. The centrifugal force term in the equation of motion of the nonotubes is modified for laminar and turbulent flow profiles. The differential transformation method (DTM) is used to solve the governing differential equations of motion. In vibrational analysis the effects of nonlocal parameter and non-uniform flow velocity on the vibrational properties of the carbon nanotubes with different boundary conditions are investigated. Results show that the effects of nonlocal elasticity may increase the natural frequency and critical divergence flow velocity of systems, while the non-uniform flow velocity decreases the critical divergence flow velocity and natural frequency of nanotube, compared to the uniform case. The validity of the present analysis is confirmed by comparing the results with those obtained in literature.

The purpose of this paper is to investigate the nanofluid natural convection heat transfer in a triangular enclosure with a blade heater. The Cu-water nanofluid is used. Discretization of the governing equations are achieved through a finite volume method and solved with SIMPLER algorithm. The effects of Rayleigh number, the volume fraction of nanoparticles and the size and position of the blade on the heat transfer performance of the enclosure were examined. The results show that the heat transfer rate increases with increase in solid volume fraction and Rayleigh number. The heat transfer rate increases at low Rayleigh numbers when the blade approaches to the hypotenuse but it doesn’t show the same behavior at high Rayleigh numbers. Heat transfer rate increases with the increase of the blade length. The results also show that at high Rayleigh numbers mostly heat transfer rate in the vertical blade is more than the horizontal blade, but the vertical and horizontal situation of the heater at low Rayleigh numbers has a few effects on the heat transfer rate.

In the present study, the dynamics of a red blood cell (RBC) in a simple microchannel and in a microchannel with step stenosis is simulated using combined lattice Boltzmann- immersed boundary (LB-IB) method. The RBC is considered as a deformable boundary immersed in the fluid flow. The effects of plasma viscosity on the motion and deformation of the RBC was investigated. Then the motion of a circular RBC in a Poiseuille flow was analyzed. Since the RBC is put at the centerline of the channel and the flow in the channel is axisymmetric, the lift forces acting on the top and bottom part of the RBC are in equilibrium. When passing over a step stenosis in the channel the normal RBC was found to be more deformable and take higher speed as compared to the less deformable RBC. In addition, the normal RBC experienced tank-treading motion due to its low elastic and bending coefficients whereas for the less deformable RBC the tumbling motion took place. The current results showed reasonably good agreement with the available numerical results.

Hot deformation behavior of materials is completely complex. Flow stress during hot deformation depends mainly on the strain, strain rate and temperature, and shows a complex and nonlinear relationship with them. Hot deformation characteristics of a AA2030 alloy were investigated by hot compression test over the temperature range from 350-500 ℃ and strain rate range from 0.005 to 0.5 s. Based on these experimental results, a feed-forward back propagation artificial neural network (ANN) model was developed to predict the flow behaviors of AA2030 alloy during hot deformation. The inputs of the neural network were deformation temperature, log strain rate and strain whereas flow stress was the output. This developed network consisted of one hidden layer containing 12 neurons with a tan-sigmoid activation function and Levenberg–Marquardt training algorithm. A very good correlation between experimental and predicted results has been obtained. The results show that the developed artificial neural network model presented an excellent capability to predict the flow stress level, and also the hardening and dynamic softening behavior.

In this article, cavity fluid flow is stimulated in Two-dimension. In order to model the effects of turbulence, large eddy simulation model has been used to include sub-network effects of small eddies, sub-grid Smagorinsky model was used. In this method, Smagorinsky coefficient is a constant value which should be determined by experiment. Suggested values by other researchers are in range 0.065-0.25. In this research, staggered and collocated grids have been used in analyzing lid-driven cavity flow and results were compared for different values of Smagorinsky coefficient. Furthermore, the velocity distribution was evaluated in different parts of the cavity. Comparison of numerical results shows that models presented in this research can stimulate this kind of issues with high accuracy with assigning the Smagorinsky coefficient in range of 0.5-0.7. Also, using the staggered grid in comparison with collocated grid leads to more accurate results. With increase the Reynolds number, horizontal and vertical velocity gradient in wall area increases and decreases in middle area of cavity. Also, staggered and collocated grids in low Reynolds numbers present almost similar results in predicting horizontal and vertical velocity in center of the cavity. But with the increase in Reynolds number, the gained results replaced by the staggered grid are more exact and the gradient of horizontal and vertical velocity in the collocated grid, are less moved by the staggered grid than it was supposed to do.

In this study, effect of Ti alloying element on the fatigue behavior of Hadfield steel was investigated. To do this, 3 casting samples were prepared from Hadfield steel in coreless induction furnace (without Ti addition, and with 0.5% and 1% Ti additions). Then annealing heat treatment was applied to samples at 1100ºC for 2 hours. To evaluation of the microstructures was conducted by optical metallography, and hardness of samples were measured by Vickers hardness method. Fatigue behavior examined by applying 400,500, 600 and 700 MPa loads in rotating bending fatigue test machine. After fatigue test, the fractured surfaces were observed by scanning electron microscopy. Testing results indicated that increasing Ti amount in Hadfield steel composition, improved fatigue behavior. This is due to: 1- Ti addition was increased the amount of carbides in the microstructure and was leaded to grain structure refinement. 2- Ti addition was increased the number of the grain boundaries, increased crack growth path. SEM results showed that sample without Ti had the highest fatigue crack length and sample containing 1% Ti had the lowest fatigue crack length.

In this study, the blade cross-section profile of horizontal wind turbine (NREL type) is investigated in the wind tunnel. In order to measure the velocity and turbulence intensity the hotwire anemometer is used. The tests are done in the wake of the S823 airfoil at velocities of 5, 7 and 12 m/s and at angles of attack of 0°, 7°, 10°, 13° and 15° and at stations of = , , ,1,2,3. The effects of variation of angles of attack and Reynolds numbers are investigated on velocity defect, additional flow, velocity distribution and turbulence intensity and the curves of effects of changing the downstream position on the velocity distribution are presented. The results show that the additional velocity in the near of the trailing edge of airfoil is great and increasing the angles of attack increase the additional velocity and increasing the Reynolds numbers decrease the additional velocity and also asymmetric wake of mean velocity profile and increasing region of the mean velocity profile at lager attack angle than 10° can as sign of vorticity developed at region of wake airfoil.

Nowadays due to destructive effects and the increase in cost of fossil power plants, clean and renewable energy has been considered more than ever. Renewable energies have been widely used due to the reduction of CO2 emission and environmental degradation, in recent years; The solar farm method and especially linear Fresnel reflector (LFR) has been of the interest by researchers in terms of thermodynamic performance and economical aspects. in this study by applying a thermodynamic models along with high-precision empirical correlations, a linear Fresnel solar plant with trapezium-form absorbers, consisting several absorbing pipes, is simulated. the model can be employed to investigate the effective parameters on solar plants of these types. The model is proved to have high rate of calculations and high precision. the model is applied for a specific climate conditions (Yazd, Iran) and performance of different oils are investigated. thermal efficiency, generated vapor rate, thermal dissipation and essential pumping power for each type of oil are studied in this study. at the end the most appropriate kind of oil is introduced for the considered city. furthermore, the appropriate oil type for different climate conditions regarding different seasons and different zones of the city is recommended. performance of the Fresnel Solar Plant can be simply evaluated by the proposed model.

Rotating disks function at high temperatures, thermal gradients and angular velocities in aerial or land gas turbines such as turbojets, turbofans, turboprops and turbojets. These working conditions result in reduced strength of disk material, increased amount of thermal stresses and creation of large centrifugal forces that leads to an increased level of radial and angular stresses. Therefore, thermal analysis of the disk in order to establish appropriate temperature distribution and adequate heat transfer using an effective cooling mechanism is of peculiar importance. In this paper rotating disk problem is modeled in accordance with reality. The problem which consists of a rotating disk and cavity in order to cool the disk surface is considered. After that problem is simulated by simultaneously solving flow and energy equations numerically. The results of the velocity distribution, heat transfer and temperature distribution are comprehensively explained. Furthermore, temperature distribution contours and polynomial approximation to describe the temperature of the disk in terms of its radius are derived for various flight cycles. Also, a comprehensive analysis of the parameters affecting heat transfer and temperature distribution is proposed. The polynomial approximation of temperature profiles of the disk, makes it possible to anticipate disk temperature at any rotational speed. Furthermore, based on the results of this research, outer diameter of the disk is identified as the most critical part of the disk, which is under the most severe thermal-mechanical stress.

The sound is created by gears mesh is an example of sound pollution in industries. In the present study, the sound pressure level of a pair of mesh helical gear is simulated. First stress distribution of a pair of helical gear is simulated by finite element software Abaqus. Then the results are verified and to use in later parts of the study. After the sound pressure level is simulated in mesh of helical gear teeth. To verify, the sound pressure level is achieved by pressure level equation and compared with standard noise level. In this study, the tooth profile of gear is modified to reduce the sound of mesh of helical gears with Kiss Soft software. The profile modification is done in two way tip rounding and generate cylindrical gear with hobbing cutter. The results of the study have shown tooth profile modification by tip rounding is the best result to decrease noise.

In this study, U section cold roll forming process has been analyzed by finite element (FE) method and the effect of the process parameters on the longitudinal strain and spring back has been investigated using response surface method (RSM). Then optimized range of the parameters have been determined using the contour plots. The FE model has been verified using the experimental results. Required experiments have been designed using central composite design. In this design roll diameter, linear velocity of the blank and distance and number of stands are considered as input variables and spring back and maximum plastic longitudinal strain are considered as response functions. Results show that the RSM models the effect of input parameters on the response functions with acceptable precision. According to obtained model, increasing distance the stands and rolls diameters cause to decrease of the spring back or increase the angular precision and increasing of the linear velocity of the sheet leads to increasing the spring back. Increasing stands distance and roll diameter, lead to decreasing the average plastic longitudinal strain and increasing the linear velocity the sheet leads to increasing the average plastic longitudinal strain. Also optimization results represent decreasing of the spring back and maximum plastic longitudinal strain.

A new combined system based on a biomass gasifier, gas turbine, S-CO2 cycle and an organic Rankin cycle for power generation is proposed and assessed thermodynamically. Exergy analysis is conducted to determine the irreversibilities in system components. In addition, an environmental impact assessment is performed for each of the three types of plants in the combined system. To understand the system performance more comprehensively, a parametric study is performed to investigate the effect of several important design parameters on the net power output and exergy efficiency of the system. The system performance is optimized and the optimum design parameters were determined. The results demonstrate that an increase of 300oC in the turbine inlet temperature results in 7.52% and 23.45% increases for the exergy efficiency and net power output, respectively. This temperature increase also brings about an increase of 12.98% and a nearly constant pressure ratio of the air compressor and the S-CO2 compressor in optimum working condition. In addition, compared to the gas turbine, the exergy efficiency of the combined system is 10.07% higher and the CO2 emission of the combined system is 25.82% lower.

In this study, the effect of grapheme and grapheneoxide on the mechanical properties of epoxy/Kevlar was investigated. Epoxy/Kevlar/grapheme and epoxy/Kevlar/graphene oxide nanocomposites were made as 4-layer nanocomposites with Kevlar fiber. Based on the results of tensile and bending test, addition of graphene and graphene oxide to epoxy/Kevlar increases the tensile modulus, tensile strength, flexural modulus and flexural strength. The optimum amount of graphene in the matrix was 0.5% by weight at which nanocomposites had the highest mechanical performance. In higher amounts of graphene and graphene oxide (more than 0.5% by weight), the excess amount of graphene leads to agglomerati on of matrix which causes problems in transmission of the stress. Generally, the highest elastic modulus fo rgraphene and graphene oxidecorre sponded to1% by weight and the highest ensile strength of graphene and graphene oxide reported at5% by weight. The highest flexural modulus was observed at 1% by weight of graphene and graphene oxide. The highest flexural strength in both nanocomposites was found to be at 0.5% by weight. The morphology of the samples was characterized using SEM observations. Evaluation of SEM micrographs indicated that graphene and graphene oxide agglomerate at 1% by weight which results in a weak interaction and dispersion in.

In this study, the cooling, heating and electrical energy demands of a sample residential apartment in Mashhad region (Iran) has been estimated hourly during a year. By employing a CCHP system for this apartment compared to the separate production system, hourly and monthly amounts of optimal consumption of NG as prime fuel and electrical energy imported from/sold back to grid during a year and cost saving ratio and payback ratio has been investigated. For this purpose an optimization algorithm was proposed to find the best optimized operation of the cogeneration system based on operation of the power generation unit (PGU) according to nonlinear relationship of electrical efficiency of the engine (Prime Mover) so that the cost of the energy in CCHP system, as an objective function, be least amount in each time step during a year. The results of proposed algorithm, specifying the best operation, show that PGU with 12 kW capacities has the lowest payback ratio of 3.3 years and that PGU with 5 kW capacities has the lowest energy cost saving ratio of 57%.

The 2D cascade is a simplified model which is used to reduce the grid size and consequently numerical computation time. Selection of cascade model for result validation, modeling of cascade geometry, modeling of flow domain, selection of appropriate boundary conditions, efficient grid generation and solver selection are among challenges of numerical simulation of transonic flow past 2D cascades. This challenges leads to researchers mind confusion. In this paper, these challenges and related appropriate strategies will be explained. Results show that using of coupled pressure based algorithm is an efficient way to simulate of transonic flow in turbomachines. Furthermore, need to using static pressure near peak efficiency and mass flow rate near stall as outlet boundary condition is proven. Impossibility of using periodic condition in most cascades is another results of this research.

One of the best ways to provide optimum conditions to the crop is the development of accurate greenhouse models for inside environment control. In this study a mathematical model was developed for computing transmitted total solar radiation (beam, diffused and ground reflected), for the single span greenhouse, without crops, was performed in Tabriz University. Also a dynamic model was developed to predict the all internal temperatures of the greenhouse including greenhouse inside air, soil surface and north wall temperature. The input parameters of the model were the measured meteorological conditions and the thermo-physical properties of the greenhouse components. Results showed that soil surface heat exchange has a positive contribution to the internal air temperature. Comparisons between the predicted and measured results showed close agreement for greenhouse air temperature. The correlation coefficient and mean percentage error for this model were calculated as 0.99 and -3.62%, respectively. Results also showed a considerable amount of the incident radiation was lost to outside the greenhouse by convection and radiation.

In this study, classification of various prime movers which usually used in the mCCHP systems has been investigated. Then, different parameters affecting the performance of the mCCHP systems such as primary energy saving, net efficiency, renewable energy ratio, and working time, are compared to each other. The mentioned parameters are evaluated for both compression and absorption chillers with the presence of a backup boilers. Finally, based on the consumer demands, the optimized configurations of the systems have been suggested.

In this paper DBD plasma actuator is simulated numerically and its effect on the air flow field and separation bubble domain is studied. The selected geometry to form a separation bubble is a rectangular cylinder with rounded leading edge. Present study deals with Reynolds numbers of order of 104 to 105. Flow separation exists in the leading edge of the object which is considered as a noticeable phenomenon in this flow field, that is called separation bubble. The ratio of leading edge radius to the object thickness (R/D) is one of the dimensionless parameters. For different values of R/D, the effect of plasma actuator on separation bubble domain, and re-attachment point of flow have been studied. The results show that for the geometry with sharp edge, the effect of plasma actuator is ignorable, while for the geometry with rounded edge, the plasma actuator has a noticeable effect. This effect enhances with the increase in R/D. The ratio of induced velocity to the free stream velocity is another dimensionless parameter which has an observable effect on the separation bubble domain.

Simulation of turbulent flows is one of the most important issues that engineers has forced with serious challenged about it. This type of flow simulation requires high computational cost and time. Airfoils have many applications in industry, including turbomachinery rotor blades and propeller aircraft. Two-dimensional and three-dimensional Studing flow around an airfoils that show many properties of flow is important. This article is studying about and solving the compressible flow which is density-based around two-dimensional airfoils and three-dimensional propeller by same section for the fixed two-dimensional case and rotating airfoil in the rotation condition with the velocity inlet and for three-dimensional rotation with velocity inlet for RANS method with Spalart-Allmaras,RNG,SST,RSM. For rotating airfoil added swirling equations using C programming has been to the momentum equations source term. In the two-dimensional pressure coefficint and skin friction of particular importance for the RANS methods for different angles of attack and different models for propeller three-dimensional contour speed during the formation of vortices and extracted.

In this paper, design and implementation of a new algorithm based on predictive model controller will be presented to reduce the height estimation error in vertical channel of inertial navigation system (INS). Vertical channel instability in the inertial navigation systems not only causes the measurement errors increase exponentially with altitude, but also leads to loss of precision in the state estimation process in the navigation system as well. This indicates the importance and necessity of providing accurate estimation of vertical altitude in the inertial navigation algorithms. In this paper, an integrated barometric-inertial altimeter is presented in order to reduce the vertical channel error in the INS. Designing model predictive controller, the vertical channel instability has been controlled despite of the inevitable errors in the measurement of the inertial sensors. Therefore, accurate estimate of the height will be provided. The proposed algorithm is implemented and validated by vehicular test. The experimental results show that by applying the proposed algorithm, the estimation accuracy of the vertical altitude will be enhanced.

In this paper, in order to improve the performance of lithium bromide- water absorption refrigeration system using compressor between the generator and condenser of the cycle, is analyzed and compared with a conventional absorption refrigeration cycle. In present work, the effect of changing various parameters of the systems on the operating parameters is analyzed and compared. Because of the importance of crystallization phenomena in absorption cycles with salt as a component of the operating solution, it is investigated in different operating conditions. In order to prevent this phenomenon in the cycles, at each operating condition, temperature and concentration of solution at entrance of absorber is compared with crystallization line and the range of allowable generator temperature is specified. The results show that, at low generator temperatures, absorption-recompression cycle has better performance than that of conventional cycle from the view point of first and second laws of thermodynamic. In some, operating conditions, this improvement can reach higher than 100% and 70% increment of COP and second law efficiency respectively. With higher pressure ratio of compressor, absorption-recompression cycle starts to operate at lower generator temperatures. This feature enables the absorption-recompression cycle to utilize low temperature heat sources such as waste heat, solar and geothermal.

This study aims to analyze the effects of thermal radiation on the laminar boundary layer about a flat plate in a uniform stream (Blasius flow), and about a moving plate in a stagnant fluid (Sakiadis flow) is being studied. Momentum, energy and concentration equations are solved by the similarity method. Analytical results of energy and concentration equations are validated with previous studies and showed an excellent agreement. Analytical relations for Nusselt and Sherwood numbers for the first time in the laminar boundary layer with radiation are presented and the effects of thermal radiation on the concentration boundary layer for different values of Schmidt number and the radiation parameter . The results show that with increasing the radiation parameter N and Schmidt number S, the concentration boundary layer decreases and the concentration gradient increases that these effects are more in the Sakiadis flow than the Blasius flow. And also with increasing the heat transfer parameter the concentration boundary layer and the concentration gradient increase. Keyword:

Refrigiration systems and dehumidification by desiccant are a novel method for refrigeration and air conditioning. In this method moist of air removed, and then dehumided air send to cooling unit, consequently, latent load of vapor is eliminated, and rate of usage energy is decreased. The important part of this cycle is dehumidifier of it. In this paper, parallel flow dehumidifier is compared counter flow dehumidifier. In this work, at the first, the governing equations of coupled heat and mass transfer have been written, then, these equations have solved simultaneously. Results of this study shows that, effectiveness and condensation rate in counter flow dehumidifier is more than parallel flow dehumidifier. For thirteen studed cases in this paper, the maximum difference of effectiveness is 6.45%, and the maximum of condensation rate is 0.031 g/s. It should be said that, using solution in present study is lithum chlorid (LiCl).

In the current study, the non-Newtonian blood flow in a two-dimensional stenotic vessel is simulated. Carreau-Yasuda model is used to investigate the shear-thinning behavior of fluid flow. The non- Newtonian lattice Boltzmann method is applied to numerical simulation of blood flow. Curve boundaries are modeled with two-order accuracy. Numerical results of current study are compared and successfully validated with results of non-Newtonian Carreau-Yasuda fluid in a simple two dimensional channel. Mesh grid study is conducted to show the independence of numerical method by using three different grid sizes. To investigate the effect of occlusion on different parameters affecting in blood flow such as velocity, pressure and drag coefficient, the corresponding profiles and contours are drawn. The results show that the pressure drop will be significant in the area after the stenotices. Although the blood flow is laminar and nonNewtonian, the vortex structures formed after the obstacles.

The purpose of this research is to investigate the flow thermodynamics in porous media in a channel with a rectangular obstacle, using the Lattice Boltzmann Method. Here, the Representative Elementary Volume (REV) scale with general Brinkman- Forchheimer model is used to model the heat transfer in porous media. To validate the results in porous media, the heat transfer in a channel and channel with a rectangular obstacle is modeled and results for Nusselt distribution on obstacle sides are compared with previous research. Then, the heat transfer in a fully pore channel is investigated and compared with previous data. Finally, the flow and heat transfer in a channel with a fully pore obstacle is studied and the effects of permeability and porosity are studied in different Reynolds numbers. The results show that the heat transfer is increased by increasing the permeability and the Reynolds number.

In this paper, the drawing process of sandwich sheet through wedge shaped die has been analyzed using stream function by upper bound method. The sandwich sheet has been three metal layers that thickness and materials of the outer layers are the same and are different form the inner layer. A deformation model has been introduced in which inlet and outlet shear boundaries are considered assumed to be flexible and the effect of work hardening of sheet layer materials has been considered. According to suggested stream function, velocity field, strain rates and powers have been calculated. The optimized geometry of deformation zone and required drawing force have been determined depending on the process conditions. Analytical results, including drawing force and thickness of sheets in outlet of die have been compared with the finite element results. Comparing the analytical results with the FEM simulation results show appropriate adaptation. Finally, the effect of friction factor and reduction in thickness have been investigated on drawing force and optimum die angle.

In this paper, FG circular and annular plates with stepped thickness variations is examined. Bending analysis was performed for stepped plates with various boundary conditions by using a new exact solution based on the FSDT. Stepped plates are divided into multiple constant thickness segments. Governing equations are written for each segment, individually. Then, continuity conditions of displacements and forces are imposed between various segments. Based on the presented exact solution, transverse asymmetric plates with various stepped segments may be analyzed. Loads may be imposed on arbitrary parts of plates. Mechanical properties of each segment may be different. Also, variations of properties of each segment may be determined, individually. Results of bending analyses for the stepped circular/annular plates have not been reported yet, so accuracy of the results of the proposed exact solution is verified by comparing the results with those of the three-dimensional finite element extracted from the ABAQUS software. A good agreement is noticed between present exact solution and ABAQUS results.

Nowadays, due to drying wetlands, burning fossil fuels and so on, the dust phenomenon has intensified. In addition to the consequences of environmental and technical pollution for dust, they also have psychological and social consequences. In the present study dust dispersion modeling using numerical simulation is done. The effects of changes in conditions and the architecture of the building by drawing lines and calculating the flow and pressure fields in dust concentration levels in all cases were evaluated. After reviewing the results, it was found that among the five areas identified in the first model, which areas are better places to avoid dust. The results showed a significant effect on the distribution of dust around the building with different architecture. The results also showed the more approaching to the earth surface; the more concentration of dust associated with greater fluctuations is, and differences of architecture in dust concentration at lower heights have greater effect. Furthermore, in present architectural form, for the case the building door is open, the accumulated dust is more than when the door is closed. The study is based on computational fluid dynamics and numerical model developed for commercial software ANSYS (FLUENT) is used to simulate the flow field and pollutant particles.

Functionally Graded (FG) materials are inhomogeneous composites, usually made from a mixture of metals and ceramics, providing the specific benefits of both the constituents. These materials have some unique properties such as high strength under thermomechanical stresses, lack of stress concentration and delamination. Present study is concerned with determining the alternating temperature, stress and strain fields in an FG hollow sphere subjected to cyclic thermal loading and internal pressure. The inner surface of the sphere is considered to be made of alumina grading with power law up to the outer surface made from aluminum. Duhamel's principle is utilized to calculate the temperature field in the sphere since it is appropriate in analyzing the behavior of structures with alternating boundary conditions. By considering a quasi-static condition, the governing differential equation is solved by using discretization method. The results are compared with those obtained using finite element method and good agreement is observed. The effect of frequency of the thermal load on the amplitude of the stresses is also investigated. The results show that, there is a critical range of the frequency in which the amplitude of stresses become maximum and beyond this range, the stress and strain domain vanish. It has been shown that by increasing the thickness of the sphere, the critical frequency decreases significantly.

In this paper, a meshless approach utilizing least-squares error technique and Taylor series was used to numerically solve an inviscid hypersonic flow. Second and fourth order derivatives were used as artificial dissipation terms to stabilize the solution and prevent unwanted oscillations especially around the vicinity of shockwave. In this study, chemical reactions caused by increased temperature were assumed to be in equilibrium condition and derived graphs were used to estimate the specific heat ratio. We used an explicit four-stage Runge–Kutta method for temporal discretization of governing equations, and used local time-stepping and residual smoothing techniques to accelerate the convergence process. The results obtained from meshless approach were compared with those obtained from finite-volume method with identical point distribution, and this comparison showed that using meshless approach provides better convergence and lower computation time. Result also showed that replacing ideal gas model with real gas model and applying the hot gas effects lead to precise identification of shockwave’s location, and provides a more accurate prediction of temperature and pressure distribution behind the shockwave.

The aim of this study was to investigate the effect of equivalent strain amount on evolution strength of commercially pure copper produced by equal channel angular pressing (ECAP). For this purpose, two ECAP dies with channel angle (∅) 90ᵒ and 110ᵒ, and the angle associated with the arc of curvature (ψ) ~37ᵒ were designed and manufactured. The equivalent strain at each pass of ECAP process is reduced by 25% for ECAP die with ∅ = 110ᵒ compared to ECAP die with ∅ = 90ᵒ. The cylindrical shaped commercial pure copper in the same condition undergone ECAP process at room temperature up to eight passes through two dies, and then the obtained mechanical properties using hardness and compression tests were measured and their changes reported. The obtained re-sults showed that the maximum value of strength and hardness of copper were measured about 390 MPa and 74.9 HB respectively after applying the fifth pass by using ECAP die with ∅ = 90ᵒ. On the other hand, the better mechanical properties were observed in the material produced by ECAP die with ∅ = 110ᵒ. The maximum values of hardness and strength of copper after the eighth pass by using ECAP die with ∅ = 110ᵒ was achieved about 77.5 HB (approximately 51% of the initial sample) and 424 MPa (approximate-ly 63% of the initial sample) respectively. According to obtained results for commercially pure copper produced by ECAP, it can be concluded that the more enhancement mechanical properties such as hardness and strength can be achieved by reducing the applied strain in each pass about 25% and also by increasing the ECAP-ed passes.

The TIG welding is a commercial technique in joining of dissimilar metals in oil and gas industry. The quality ofwelded jointsdependsonproper selection ofweldingparameters. Dissimilar repair welding between sheets of austenitic stainless steel and carbon steel were considered in this article. The purpose of research is selection of optimal welding parameters in order to achieve maximum mechanical strength in the joint. Electrical current, welding speed, gas flow and filler diameter have been selected as considered parameters. In experimental study design of experiments has been performed by Taguchi method. After the preparation and welding of specimens, the tensile testis carried out. Obtained data export to statistical data analysis and optimal welding condition were estimated. To validate obtained data the analysis of variance were employed. According the results welding by 110 amperes, 2.5 electrode diameters, 12.5 l/m flow rate and 190mm/min welding speed reaches to maximum tensile strength in weld metal. By selecting appropriate values of process parameters, tensile strength increased about 15 percent.

In this study metal foams are simulated by their mechanical properties with continuum mechanics model. To do so, six multi layered armors were simulated. Three armors consisted of steel/ceramic plates with different thicknesses and other armors had a layered aluminum foam between their layers. A bullet with specified velocity was collided to armors and the Johnson-Cook model was used for the steel plate and bullet and the crushable foam model was used for aluminum foam. The results of the present research showed that the multi layered armor with aluminum foam (28.4 percent overweight) reduced the stress in ceramic plate more than 50 times compared to armors without aluminum foam.

In this paper, a Sliding Mode Controller (SMC) based on Linear Quadratic Regulator (LQR) method is designed for aircraft landing control system in presence of aerodynamic disturbances. In order to obtain the control law, despite the inversion of input matrix should be calculated, in many practical systems the matrix is a non-square matrix which its inversion is not defined. To solve this problem, some approaches are developed which use pseudo inverse instead of the inversion of input matrix. A special type of transform matrix is employed for designing the proposed controller. The LQR procedure is used for calculating the transform matrix improves the performance of the control system. But in this method the external disturbances and uncertainties are not considered. Hence, the “matrix transform method" is extended for the systems with uncertainties and external disturbances. The propose controller is applied to control autonomous landing of Boeing 747. The simulation results are illustrated to show the performance of the proposed strategy.

Due to aerodynamic instabilities, their desired operation takes place in a small and limited range, so knowledge of the instabilities seems to be inevitable. In this article, aerodynamic instability of compressors are investigated analytically. For this purpose, the equations of mass, momentum and energy have been used. After a series of assumptions, the formation of a matrix related to equations and its eigenvalues are calculated, the effect of effective parameters on aerodynamic stability is evaluated. These relationships are coded in MATLAB software and by applying geometric characteristics and flow characteristics on it; the effect of important parameters on the aerodynamic stability of the engine is investigated. According to the results, it can be seen that this phenomenon occurs when the compressor is unable to produce sufficient head to overcome its lower resistance. Or, more simply, the output pressure produced by the compressor is lower than the downstream pressure. In this case, a cyclic motion will be generated in the gas stream, and the compressor's inability to overcome the disturbances that may occur around its operating point, which can cause instability in it .In the following, the effects of decreasing the mass flow through the compressor, increasing the length of the downstream duct length to the length of the lower duct, increasing the plenum volume, and increasing the cross-sectional flow of the compressor in the system stability were investigated. The results are compared with the results of previous studies and have a good correlation between the results.