مجله مهندسی مکانیک
سال چهل و هشتم شماره 1 (پیاپی 82، بهار 1397)

Today's energy needs are increasing very fast and this is while the energy resources are very limit. In this paper by using numerical methods and investigation absorption coefficient of different colors, the most appropriate color to reduce energy consumption in all seasons has been selected for external wall of a building in Mashhad. Modeling of building has been done and meshed by using Gambit software as a three dimensions model. The simulation of falling solar radiation to building which is the main objective of this study, has been done by Fluent software based on building’s location and in turbulent flow. The results of this research indicate that by selecting the most appropriate color, in total during of the year by 1.5°C temperature decrease in warm days and about 1°C increase in cold days, we have significantly reduce energy consumption in electricity and gas. Finally according to the results of this research and by investigating absorption coefficient of different colors, gray color has been chosen as the most suitable criteria in order to reduce building energy consumption.

In this paper, a new inverse hyperbolic shear deformation theory is proposed, formulated and validated for a variety of numerical examples of laminated composite beam for the static responses. The proposed theory based upon shear strain shape function yields nonlinear distribution of transverse shear stresses and also satisfies traction free boundary conditions. Principle of virtual work is employed to develop the governing differential equations. A Levy type closed form solution methodology is also proposed for crossply simply supported beams which limits applicability. However, it provides accurate solution which is free from any numerical /computational error. It is observed that the present theory can be more accurately applied for the modeling of laminated composite beams at the same computational cost as that of other shear deformation theories.

Grid composite structures are a new generation of composite materials which due to their unique design (consist of network of stiffeners which have been located upon a skin) possess high specific strength and stiffness, as well as excellent energy absorption. In this study, the effect of addition of multi walled carbon nanotubes in various weight percentages (0, 0.1, 0.25 and 0.4) on the high-velocity impact properties of grid composite plates was investigated. Multi-walled carbon nanotubes by using mechanical stirrer and ultrasonic waves were dispersed into the polymeric matrix. Grid composite plates with hexagonal geometry were fabricated by hand lay-up method and then high velocity impact test by cylindrical projectile with conical nose was performed on these plates. Experimental results showed that the presence of network of ribs which reinforced with carbon fibers restricts the damaged area and increases the energy absorption. For grid composite plates, the best high-velocity impact behavior was obtained with the addition of 0.4 wt. % of carbon nanotubes which in this case, the ballistic limit velocity and absorbed energy during highvelocity impact was increased by 11 and 22%, respectively. Also with the addition of multi walled carbon nanotubes, the damage size of grid composite plates was decreased.

In this paper, the conjugate gradient method, coupled with the adjoint problem, is used in order to solve the inverse heat conduction problem and estimation of the time-dependent heat flux, using temperature distribution at a point in a non homogenous geometry. Also, the effect of noisy data on the final solution is studied. The numerical solution of the governing equations is obtained by employing a finite-difference technique. For solving this problem, the general coordinate method and body fitted coordinate method are used. The irregular region in the physical domain (r,z) is transformed into a rectangle in the computational domain (ξ,η). The present formulation is general and can be applied to the solution of boundary inverse heat conduction problems over any region that can be mapped into a rectangle. The obtained results show the good accuracy of the presented method. Also, the solutions have good stability even if the input data includes noise. The problem is solved in an axisymmetric case. Applications of this model is in the thermal protect systems (t.p.s.).

In this research a low velocity impact analysis of a sandwich plate with multilayered composite face-sheets and flexible core under thermal conditions is investigated. In this regard, thermal effects and temperature dependent properties of the core are considered. In this study, equations of motion are derived based on a hybrid LW/ESL finite element formulation considering the thermal effects by which the number of unknowns is independent on the number of layers. This new formulation is in the framework of Carrera’s Unified Formulation (CUF). The CUF unify many theories in a unified form such that can be differed by the order of expansion and definition of the variables in the thickness direction. In order to satisfy the interlaminar continuity of transverse stresses between the layers the Reissner Mixed Variational Theorem (RMVT) is employed. In this paper for considering the thermal effects, the nonlinear strains are used. In this research in order to modeling the low velocity impact a new modified spring-mass model is proposed using the two degree spring–mass model and also Choi linearaized law. Results of this formulation are compared with experimental results which show the high accuracy of the proposed formulation. Results show that with increasing the temperature, the impact force decreases and also impact time duration increases significantly. In this study, some new results are presented for different thermal conditions, aspect ratios, face thickness ratios and also different initial energy of impactor.

Increasing energy consumption nowadays has caused consideration of renewable energies, in particular solar energy, using photovoltaic systems to be brought into attention. Using concentrating systems in order to increase radiation intensity on solar cells would cause increasing the power and hence decreasing the cost. Of these, systems with concentrating ratio of less than 10 are of great importance due to the usage of normal mono crystal solar cells with no complicated cooling systems. In this paper, the performance of a solar cell was stated by three models; ideal, mono diode and two diodes versions and the validity and the accuracy of models were evaluated by experimental results. Among three alternatives, the two-diode version showed more accurate results. Then, effect of concentrating sunlight on mono crystal solar cells were investigated experimentally. A mono crystal solar panel was modeled and variations in open circuit voltage, short circuit current and output power with changes in radiation intensity and panel temperature were simulated. The experimental results by a concentrating system were then compared with those of simulations. In these experiments, where concentrating of sun lights was achieved by using mirrors, radiation intensity and cell’s temperature, changed. By using a concentrator system, output power of solar panel has increased up to 1.9 times in comparison with standard conditions.

The In this research, aerodynamics forces and lambda wing flow physics with a sharp leading edge and leading edge sweep angles of 54.9° and 29.5° have been investigated in the ground effect region numerical method. At Mach number 0.2, angle of attack from 0° through 8°, with clearance free stream through 0.05 is varying. The equations is solved based on the finite volume method. Two equation k- SST model is used for turbulence modeling. The drag, lift, nose up moment, aerodynamics efficiency, parasitic drag increase with decreasing flight height, and decrease the induced drag. The coefficients variations percentage relative to free stream increases with height decreasing and angle of attack, and most variation percentage are at clearance from 0.3 to 0.05.The study flow physics at angle of attack 8° is exhibited with the flight height decreasing, the flow between the ground and the windward side is blocked to decrease dynamic pressure and increase static pressure. Also, suction on the leeward side increase and the strengthened primary vortex. With the flight height decreasing, wing kink location vortex is weakened and vortex breakdown is transferred to the upstream flow.

In this study , to examine the effect of different parameters on stress analysis of infinite plates with central quasi-square cutout using imperialist competitive algorithm and also to introduce general optimum parameters in order to achieve the minimum amount of stress concentration around this type of cutout on orthotropic plates are purposed. Basis of the presented method is expansion of analytical method conducted by Lekhnitskii for circular and elliptical cutouts. Design variables in this study include fiber angle, load angle, curvature radius of the corner of the cutout, rotation angle of the cutout and at last material of the plate. Imperialist competitive algorithm is the mathematical model and the computer simulation of human social evolution. Finite element numerical solution is employed to examine the results of present analytical solution. Overlap of the results of the two methods confirms the validity of the presented solution. Results ae showed that by selecting the aforementioned parameters properly, less amounts of stress could be achieved around the cutout leading to an increase in load-bearing capacity of the structure.

Engineers need the equation of states to simulate refinery processes in order to respond to their needs. In the present study the Perturbed-chain Statistical associating fluid theory (PC-SAFT) Equation of State are used to predict thermodynamic properties of hydrocarbon fluids. PC-SAFT is able to predict the thermodynamic properties of associating fluids such as hydrocarbons. The thermodynamic relationships are derived analytically with MATLAB. The numerical values of the thermodynamic properties of hydrocarbons, such as density, entropy, enthalpy, in thermal energy, heat capacity of hydrocarbons are obtained by MATLAB as well. By comparing the results with experimental results, the author found that PC-SAFT entails accurate predictions about the properties of hydrocarbons and also can predict thermodynamic properties of hydrocarbons at high pressures and low temperature. The calculated results from PC-SAFT minimum error for pure hydrocarbon and the maximum error for mixed hydrocarbons. Furthermore, the maximum calculated average absolute are 1.18% for density, 2.5% for enthalpy, 0.77% for internal energy, 3.33% for constant volume heat capacity and 4% for constant pressure heat capacity. Therefore, very low level of errors indicates the appropriateness of PC-SAFT performance to predict thermodynamic properties of materials.

Present paper introduces a novel floor heating system which provides its heat by the Sun. This integrated system incorporates the advantages of both floor heating and free energy supply simultaneously. It is examined for a special building under different climate conditions. Based on the obtained results for very cold climate conditions the new system’s performance is significantly low. This is mainly due to the working fluid’s high temperature limit which causes the supporting solar system to be too much bigger than the normal one which is sufficient to heat up the building. The most significant advantages of the proposed design is for moderate climate conditions where the inlet temperature limit does not impose an extra area and, hence, cost for the solar system. For this condition the integrated system has superior advantages to the traditional ones.

In the present research work, flow behavior in a centrifugal compressor has been experimentally investigated at various operating conditions from far to near surge and different compressor rotational speeds. Having introduced the experimental set-ups, results of velocity fluctuations at compressor inlet, as a surge precursor, have been presented. Hot-wire anemometry of high frequency response was used to measure these fluctuations at three compressor rotational speeds of 9000, 10000 and 13000 rpm and three operating conditions of maximum flow coefficient, near design point and surge conditions. Experimental results showed that reduction from maximum flow coefficient towards the surge point can increase fluctuations of instantaneous velocity signals at aforementioned rotational speeds by the factor of 2.6, 1.9 and 1.57, respectively. In addition, increase of compressor rotational speed increases fluctuation of instantaneous velocity signals at surge condition by an average factor of 1.17. Finally, analysis of frequency spectrums of velocity fluctuations, showed a dominant frequency of surge at about 30 percent of the blade passing frequency.

In this study non-Newtonian fluid flow in two-dimensional channel with a circular obstacle has been studied using lattice Boltzmann method. The Carreau-Yasuda non-Newtonian model is used to simulate the non-Newtonian fluid behavior. The exponential model with different temperature-thinning coefficients is utilized to investigate the temperature-dependent viscosity of non-Newtonian fluid. Regarding to the local properties of the lattice Boltzmann method, the shear-dependent and temperature-dependent properties of Carreau-Yasuda non-Newtonian fluid are easily modeled with two-order accuracy. The validation of results for fluid flow and heat transfer parameters are completed, successfully. Results show a reduction in the power index of Carreau-Yasuda non- Newtonian model leads to growth of average Nusselt number, especially in high Reynolds numbers. Simulations show an increasing in the Carreau number causes to increase of wakes formed behind the cylinder. The results of drag coefficient versus temperaturethinning coefficient shows that the temperature-dependent viscosity has a significant effect on the flow field; in a way that a growth in the temperature-thinning coefficient leads to increase and decrease of drag coefficient and size of the vortices, respectively.

Today, the great vehicle companies use of computational simulation of vehicle crash and different software to avoid spending too much time and cost. In this investigation first, applying the Johnson-Cook ductile damage criterion in the ABAQUS explicit code, crash of a few important components of Pride vehicle such as fender, hood, door, and rear trunk which are most at risk of crash to barrier are simulated. Speed boundary conditions, barrier shape, and impact angle are adopted from the real accidents and implemented into the software. Carrying out the simulations, the results of deformation and damage in any of the above mentioned parts are predicted, maximum damage zones and near to failure are identified. Then, simulation results are compared with the results of the actual samples, to evaluate the Johnson-Cook damage criterion and material properties. Comparison of the numerical and real results reveal that the Johnson-Cook damage criterion can well predict the deformations and strength of different parts of the car through the crashing to barrier.

Fatigue failure occurring in most engineering components, generally is related to multiaxial loadings. Variation in principal axes of stresses and strains in multiaxial loading causes additional hardening and this is assumed as the main reason of fatigue life decrease. The origin of multiaxiality may have diverse reasons and may arise from multiaxial loading, complicated geometry or residual stresses. In the present study various multiaxial fatigue criteria were applied for predicting fatigue life of an alloy and by using the finite element method a hollow cylindrical specimen made of alloy GH4169 was simulated under strain controlled multi-axial loading at high temperature. Hysteresis loops derived from simulation results and estimated life have been validated and compared with reference sample experimental results. The results shows that approaches considering simultaneous effect of stress, strain and additional hardening, especially at high temperature loading condition, could better predict the life. Among the presented criteria, Fatemi-Kurath, Fatemi-Socie and energy criteria have closest predictions to experimental results.

A cold room assisted vapor-compression refrigeration cycle is dynamically modelled and optimized. The design parameters are evaporator pressure, condenser pressure, length, wall’ thickness and height of cold room, mass flow rate of refrigerant as well as the value of superheating/subcooling in evaporator/condenser. To find the optimum value of design parameters Multi Objective Genetic Algorithm (MOGA) is applied. Moreover three refrigerants included R22, R134a and R407c are used as working refrigerant in this system. Total annual cost (TACO) and coefficient of performance (COP) are selected as two objective functions. The optimum solutions show that R407c is the best refrigerant in both thermo dynamical and economical view points with 9148.2 $/year as total annual cost and 6.12 for COP. The optimum result of R407c showed the total annual cost improved 50.74%, and 8.68% in comparison with R134a and R22 respectively. Furthermore, COP improved 9.97% and 13.72% in comparison with R134a and R22, respectively. It is worth mentioning the optimum results reveal the compatible between two objectives, the coefficient of performance and the total annual cost (in maximum point of COP have minimum point of TACO). However by using R407c as refrigerant of system have the minimum area of cold room, the refrigerants R134a and R22 are in the next ranking, respectively.

In recent years, because of need to energy production at low cost, using micro hydro turbines has been very attractive. The low construction costs, easy installation and maintenance, low head and flow requirements, small size, no need for the extensive power network and decentralization of hydro power are some of the unique characteristics of Micro hydro turbines. Hydrocoil turbine as a new, efficient and affordable axial flow turbine is one of the best options for distributed generation of electricity. Although Hydrocoil’s design is mainly inspired by Archimedes screw turbine, there are differences in their blade’s pitch and installing angle. In this work, two different samples of hydrocoil turbine with constant and variable pitches have been studied numerically under identical conditions to study the effect of pitch changes on operating point at constant head and five different rotational speeds. The results indicate that efficiency and power of variable pitch turbine are 30 to 40 percent more than constant pitch turbine. These results provide necessary background to build optimized variable pitch hydrocoil for the first time in Iran.

Graphene without defect exhibits extraordinary mechanical properties. However, it suffers from defects such as Stone-Wales of atoms. Also, graphene, generally completed by thermodynamic conditions, is not smooth and this can change its behavior. In this paper, the stretching stiffness of a rippled graphene containing Stone-Wales defect under uniaxial tensile load is studied. The corrugated surface of the rippled graphene is modeled by a random function using MATLAB software and the flat and rippled graphene sheets are compared. In order to investigate the effect of Stone-Wales defect on the strength of graphene, the molecular dynamics simulation is used and the AIREBO potential function is utilized to model the covalence bonding of the carbon atoms. Also, the Nose-Hoover thermostat is used to control the temperature of the system. The results show that the existence of Stone- Wales defect considerably reduces the strength of armchair graphene, but less effect on strength in zigzag direction. Also, rippling causes an increasing strength in zigzag direction.

In this investigation, performance enhancement of direct evaporative cooling system using storage reservoir of cold water has been studied. The water in the reservoir is aimed to store the cold energy overnight and use it during daytime to reduce the temperature of exhaust air from cooler. In this paper, at first stage, the governing equation of above mentioned hybrid direct evaporative cooler is extracted and then, the effect of water storage reservoir mass on the temperature of exhaust air from cooler is investigated. Take a typical summer day in Tehran for example; the results indicate that the use of storage reservoir containing water with a mass of three times larger than the mass of dry air passed through cooler per hour decreases the temperature of the cooled air by 2.02℃ at 14:00 clock. The major advantages of this system are shifting the hours for the maximum and minimum cooled air temperatures towards other hours of a day (e.g., from 05:00 and 14:00 to 06:00 and 18:00, respectively) as well as reducing the cooled air temperature range from 6 to 3.5℃.

Since solar energy is known as one of the most important and renewable energy resources, increasing the absorption of solar energy plays significant roles in the effectiveness of thermal collector systems. This research aims to analyze empirically the function of direct absorption solar collectors with the use of graphene oxide nanoplatelets /deionized water. Weight percent’s of the graphene oxide in the deionized water are selected 0.005, 0.015 and 0.045. Collectors have been examined according to EN 12975-2 standard in various intern fluid temperature and with flow rates of 0.0075, 0.015 and 0.0225. Results show by increasing the weight percent of Nanofluid, collector’s performance is increased. Moreover, the maximum efficiencies of collector with the flow rate of 0.045 are determined 63.28%, 72.59% and 75.07%. This amount for the normal fluid is 58.25%.

Artificial vessel graft is one of most common procedures. In order to prevent damaging the blood hemodynamic’s, mechanical behavior of this prosthesis should be close to the natural blood vessel. The main goal of this study is to develop an adequate model for artificial blood vessel analysis and to use that model to design a good artificial vessel with functionally graded material. In this study, geometry, three layer structure and pressure conditions of blood in ascending part of aorta have been modeled, and radial displacement versus time, radial displacement versus length, circumferential and von-mises stress have been obtained. After validating this simulation, two common materials for artificial blood vessel were used to design functionally graded materials with different heterogeneous indexes. After FSI simulation of artificial vessel made of parabolic functionally graded material and natural vessel, response parameters for different heterogeneous indexes were calculated and compared with the natural vessel behavior. Results of this study suggest that using a functionally graded material made of Dacron, Teflon and Polyurethane with intermediate heterogeneous index shows a close behavior to the natural blood vessel.

The size and the axial/radial velocity distributions of electrically controlled droplets generated from Taylor cone operating in the stable cone-jet regime are simulated by numerical modeling of electrosprays. To achieve these goals, a numerical code in FORTRAN is developed. Electrospray droplet dynamics considered the diluted two-phase flow and used Lagrangian method for tracking of a single drop and in the simulation the effect of still air around drops is taking to account in one direction. Also, a new model is used to determine the primary breakup process of jet to calculate the initial droplet diameter and breakup space. A model is formulated as function of liquid flow rate, needle-to-counter electrode distance, applied voltage, and electrical conductivity and surface tension of the liquid in a DC electric field is presented with a 2D electrohydrodynamic model. The droplet size reduction can be explained by evaporation and/or Coulomb explosion. Results show that moving downstream, the average velocity of droplets decreases monotonically. This paper reports a numerical study of the effects of an externally applied electric field on the dynamics of drop formation from a vertical metal capillary. The fluid issuing out of the capillary is a viscous liquid, the surrounding ambient fluid is air, and the electric field is generated by establishing a potential difference between the capillary and a horizontal, electrode placed downstream of the capillary outlet. The Primary jet Break-up and droplet transport and evaporation of electrohydrodynamic sprays is investigated by modeling of droplet size and velocity distribution in spray cones and a series of drop migrations under the influence of an electric field were carried out and the results are in good agreement with other theoretical and experimental studies.

One of the important factors in the poultry industry is the cost of fossil fuel and electricity consumption. These costs directly affect the price of all products such as poultry meat and eggs, as major products. The ventilation rate is one of the crucial factors in the consumption of fuel and energy. The need for adequate ventilation is determined by the age of poultries and more specifically by taking account of live weights. The amount of air which is determined for the ventilation is around 4-7 cubic meters per hour per kilogram of body weight. In this study, by management of ventilation system which is include opening a certain number of inlet for air, is tried to fuel consumption to be reduced. The results show that in a poultry house with 20000 number usage of this method reduces fuel consumption by 5 to 80 percent is due to different ambient temperatures range in winter. Also this method for poultry industries which use diesel fuel (natural gas) as fuel for heating will save 2500 liter in a year which is mean%11 reduction in fuel consumption. For warm seasons, as well as to reduce cooling costs using all the inlet potentials is recommended.

The main process that occurs in the CNG refueling station is filling fast process. The main objective of the present study is to apply a more accurate thermodynamic analysis of fast filling process than previous works. By using the thermodynamic analysis, a CNG refueling station with the cascade system, has been simulated. Comparing real and ideal gas models, it can be realized that the temperature profiles are highly different and temperature rise is much more for ideal gas model. the lack of Joule-Thompson cooling effect is the most important factor for this different. The results indicated that there is a temperature rise in order 50 K for real gas and 80 K for the case of ideal gas. The results of the present work have been validated against the experimental data and previous studies. The AGA8 Equation of State has been used to calculate the thermodynamic properties of CNG. The results show that the energy consumed by the compressor for a cycle is equal to 55.1 kWh and the average energy consumption is equal to 1.6 kWh for a vehicle.

Interference fitting widely uses in industry. These joints manufacturing are always associated with limitations and high precision. To reduce manufacturing costs, it is essential to study the influence of form defects on the assembly strength. Standards are limited to simple cylindrical parts. But, variation in interference are common in manufacturing process of these parts. In this article, it has been tried to predict strength of interference joints successfully, by proposing of new definition of mean interference for parts with form defects. Then, strength of interference joints were calculated using traditional Lame approach and mean interference value. Also, real model of interference fit with form defects were analyzed by finite element method. Theoretical results were compared with experimental results for validation. Theoretical results correlate well with those obtained through experiments. Results show that for defected interference fit joints, mean interference can be considered as reliable criterion for evaluation of joint strength.

Nonlinear vibration analysis of the reaction wheel based on rotating shaft/disk model with elastic bearings which subjected to temperature changes is investigated. The rotating shaft has been modeled by the Timoshenko beam theory and elastic bearing model consists of a nonlinear spring and linear damping characteristics. Gyroscopic effects and disk imbalance forces, as well as the couplings associated with the shear deformation have been considered in the equation of motion. Temperature changes (increase or decrease) is appeared in system as an axially load when the supports of the rotor do not allow the shaft to move in axial direction. The method of multiple scales has been applied directly to solve nonlinear mathematical model and hence obtain the nonlinear dynamic response of the rotor system. Numerical simulations are based on a real reaction wheel parameters. The resonant curves have been plotted in time and frequency domain and discussed w/wo temperature changes. It has been shown that temperature changes significantly affects the dynamic behavior of the rotor system leading to resonant hard spring type curves.

In this paper, by employing the Computational Fluid Dynamics (CFD) and applying the NSGA II algorithm, the geometry of devotee plate of high pressure heaters in Shazand thermal power plant is multi-objectively optimized. In the optimization process, three geometrical design variables are changed so as to simultaneously minimize the maximum velocity in heater and minimize the force applied to the devotee plate. The three design variables are: inlet diameter of devote plate, thickness of straight part and thickness of indirect part. In the results section, the Pareto front will be presented, and it will be demonstrated that the Pareto front conveys very important results for the designing of the shape of devotee plates. Such important optimal principles would not have been obtained without the use of both CFD modeling and the multi-objective Pareto optimization approach. It should be mentioned that the MOO is performed two times. One for the case that the thickness of devotee plate is fixed and equal to 25 mm and the second times which the thickness of devotee plate can varied and is one of the design variables.

In this study a two-dimensional combustion chamber was simulated to investigate the effect of oscillating inlet air in turbulent Methane-Air diffusion flame. In this study, the velocity of inlet air to combustion chamber was oscillated in form of sinusoidal with amplitude about half of the inlet velocity in steady state and 20 Hz frequencies. The time step in numerical analysis was considered as 1/8 time in per cycle. According to considered frequency, the time step was 0.00625s and the results was investigated after 100 and 200 complete cycles. The PDF model was used for estimate the turbulence-combustion interaction and the turbulent behavior of streams is predicted via the standard k−ε model. The modeling of thermal formation of NOx was adopted the extended Zeldovich mechanism. The temperature distribution from PDF model has a better agreement with experimental results than Eddy dissipation model. Also the results show that using of oscillating inlet air, in addition to increasing temperature, will cause increasing in NOx from the combustion and changing of the frequency to 50 and 100 Hz have an insignificant effects on temperature distributions.

In this paper a new combined flash-binary cycle is proposed for power generation from geothermal wells of Sabalan region in Iran, considering the temperature and pressure differences of wells. Using the real data of these wells, the proposed cycle is analyzed from the viewpoints of the first and second law and the optimum pressure values are calculated for two flash chambers. The results indicate that for R141b, as the best working fluid for the binary cycle the net output power, energy and exergy efficiencies of the proposed cycle are calculated as 17.11 MW, 14.35% and 53.38% respectively. The results of exergy analysis show that the condenser of binary cycle has the highest value of exergy destruction. The performance of the proposed cycle in the present work is compared with the previously proposed system for geothermal sources of Sabalan, and the results show that the net output power, energy and exergy efficiencies of the proposed cycle in this paper is 26.3 %, 31.8% and 23% higher than the corresponding values obtained for the previously proposed system.

In this study, physical/mechanical properties of transparent nanocomposite coats based on polyurethane with different weight fractions of alumina nanoparticles was studied. Physical/mechanical properties was studying employing impact, bending, tensile tests and dynamic mechanical thermal analysis (DMTA). The state of nanoparticles spreading in coats was studied using of a field emission scanning electron microscopy (FESEM). It was observed that by increasing nanoparticles up to 2 wt. % tensile strength and energy at break point and up to 4 wt. % cross bond density and storage modulus of the coats improves. It was also seen that impact and bending strength of nanocomposites didn’t decrease because of good flexibility of polyurethane in low weight fractions. Improving physical/mechanical properties of nanocomposites was related to the good spreading of nanoparticles in coats and their high modulus. Nanoparticels could also dissipate the exerted energy in interface of coat/nanoparticles and improve the strength of the samples.

In this paper, the preconditioned nonlinear multigrid algorithm is used with aim of improving convergence rates,reducing CPUtime for solving compressible flow equations. MultiGrid (MG) methods are a group of algorithms that are used for acceleratingconvergence of differential equations using a series of discretizations. This method is based upon the principle that explains whenthe global (low-frequency) error of a fine mesh is represented on a coarse mesh, it retains the same characteristics as of the local(high-frequency) error, thus the same method for removing high frequency errors is also applicable in such situation. When thenonlinear multigrid algorithm drives the external iterations, the choice of smoother on each grid level plays an important role in theperformance. In this research, a preconditioning method has been used to reduce instabilities of the linear system that arise in eachiteration. Some important results of this research are: choosing the best preconditioning scheme to be coupled with MG method,assessment of MG method performance in equations of turbulence, laminar,inviscid flows,analysis of different cyclingschemes.

Failure of parts may happened under the influence of four parameters, design, materials, production process and improper use or combination of these. Therefore, the goal of studying the cause of parts failure is to specify any those parameters and avoid repeating them. Crank shaft is an important component of internal combustion engine that experiences a large number of load cycle during its service life. Crank shaft is subjected to several forces which vary in magnitude and direction. Most of crank shaft fails in cause of fatigue in fillet areas due to bending load. In this research, the failure causes of a train crank shaft were studied using chemical analysis, macroscopic and microscopic investigations by optical and scanning electron microscopes, measurement of journals surface roughness and radius of fillet and mechanical properties. It was found that the cause of failure is fatigue, but a lot of inclusions and probably high roughness and partial decarburizing due to machining have been decreased the fatigue strength.

In this research, thermal effect on the natural frequency of axisymmetric free vibration of a thin nano circular plate made of functionally graded material will be studied. Thermal distribution has been assumed uniform and properties of the materials are changing through the thickness of the plate. The modified couple stress theory has been used for considering the length scale parameter and the governing equation of motion and boundary conditions are obtained using the Hamilton’s principle and based on the classical plate theory. The analytical solution for the clamped and simply supported boundary conditions are established utilizing the Bessel functions. The results show that by increasing the temperature changes, ratio of the thickness to length scale parameter, ratio of radius to thickness and power-law index, the natural frequency decreases at both boundary conditions. The effect of increasing ratio of the thickness to length scale parameter in clamped boundary condition is more than simply supported boundary condition but for higher ratios, this effect decreases at both boundary conditions. The effect of increasing temperature changes in simply supported boundary condition is more than clamped boundary condition such a way that the lower temperature changes lead to the nonlinear behavior of the plate.

The unsteady nature of solar energy is one of its major drawbacks. In this regard, an efficient thermal energy storage system can enhance the performance of a solar power plant, effectively. In this paper, different configurations of a steam super-heater heat exchanger based on phase change materials for thermal energy storage are simulated numerically, and analyzed based on the second law of thermodynamics to identify the best configuration. Also, the performance of a concrete energy storage system is compared with other configurations. The results indicate that by increasing the storage modules of phase change materials from one to three, the thermodynamic irreversibility decreases and the system efficiency increases from one to three percent. The results indicates that increase of steam flow rate and inlet steam temperature leads to decrease of exergy efficiency. By increase of inlet steam flow rate by five times and increase of steam temperature by twenty degree in charging mode, the system efficiency decreases by almost five percent.

An analytical method for free vibration analysis of a cylindrical FG shell integrated by two thin piezoelectric layers is presented in this paper. The piezoelectric layers on inner and outer surfaces of the core could be considered as sensor and actuator used in controlling the characteristic vibration of the system. One of the innovations of this paper is that the piezoelectric layers considered as functionally graded materials. The First order shear deformation theory is used in order to model the electromechanical system. Nonlinear Equations of motion are derived by considering Von Karman nonlinear strain-displacement relations using Hamilton’s principle. The equations of motion are discretized by Navier method. Numerical simulation after linearization is performed to investigate the effect of different parameters of structure on the characteristic vibration of the system. Results of this study show that natural frequency of system would decrease by increasing FGM index of the core. Also increasing the thickness of core cause increasing the natural frequency of system.

Trains on the move create disturbances in the surrounding air that provides the flow over the entire length of the moving vehicles. With the ever-increasing speed of the trains, this issue has become more imperative. When a high-speed train passes near the structures such as the tunnels, bridges, etc. interaction between the moving train and the structures generates noise flow around the train that is in turn responsible for the creation of pressure waves. Such pressure waves can cause detrimental effects on the trains and the track wayside equipment and endanger safety and wellbeing of people that either live or work near the tracks. In this research, with the review and evaluation of the trains' aerodynamic standards the issue of the effects of the crosswinds on the running safety of the high-speed trains is studied. By simulating the effects of the crosswinds on the aerodynamic behavior of the high-speed trains in the speed range of 160-300 km/hr, some of the parameters that are vital for the train dynamic safety are considered. Also, some propositions for increasing the train running safety and improving its ride and dynamic behavior are suggested. When the flow of wind is perpendicular to the direction of the train travel, it can cause deterioration of the train travel safety. Such issues are investigated in this research and some practical technical remedies are offered. It needs to be reminded that the high-speed trains do not operate in Iran. Therefore, these types of studies have never been performed. However, within the countries that already have the high-speed train systems, such studies, in the past and present, are quite common.

Mixing plays an important role in many micro devices; therefore, increasing of mixing in micro devices is important. In this paper, the physics of mixing due to non-linear induced-charge electrokinetic flow in a rectangular microchannel with embedded conducting hurdles is studied. Since most previous studies have focused on non-conductive objects with fixed charges, in the present study, mixing with conductive hurdles and induced charges is investigated. Numerical results show flow circulation near the conductive hurdles which leads to an increase in the mixing. The vortices are generated due to non-uniform distribution of zeta potential on the hurdles. The Mixing efficiency is also reported based on hurdles location, ratio of hurdles height to the channel height and angle of triangular hurdles. When location and angles of the hurdles are fixed, by increasing the ratio of hurdles height to channel height, the mixing efficiency is increased. In addition, with increasing of the angle, the mixing efficiency is decreased. Finally, effect of electric field on mixing is completely analyzed.

In this paper, the response of simply supported flexible core sandwich beam with piezoelectric patch, under uniform harmonic loading with and without the control is analyzed. Sandwich beam is modeled using three-layer sandwich beam theory. Governing equations of motion are obtained using Hamilton’s principle, based on Euler–Bernoulli beam theory for face-sheets and linear displacement field theory for soft core. By defining suitable state variables in time domain and using Galerkin’s method, the state space equations of system are derived from governing equations of motion. Controller is designed using LQR technique. Dynamic response and frequency response of beam in open and closed loop configuration are obtained and the effect of flexible core on the control of dynamic response is investigated. The obtained results show that the controller can play an important role toward damping out the vibration of the sandwich beam. Also, it is shown that the %18 difference between vibration amplitudes of top and bottom face sheets, because of the flexibility of the core, affects the position of piezo actuator and sensor.

In this study, the use of Genetic Algorithm in the optimal sizing of the radiation recuperators with counter flow arrangement is presented toachieve minimum cost of construction,operation. The radiation recuperators are extensively used to heat recovery,air preheating in hightemperature industrial furnaces. In this paper, the thermal calculations of recuperator are done with regard to radiation,based on thelogarithmic mean temperature difference method. The total annual cost which is the sum of the capital cost of the device,the operating cost asthe objective function is used to determine the optimal geometric dimensions of the radiation recupeartors for given a heat duty. The optimalgeometric dimensions of recuperator are determined by using genetic algorithm based on evolutionary optimization methods which the total costis minimized. To confirm the results found in this study, the methodology is applied to some case studies .The results show that the proposedmethod can be implemented as a more efficient method of traditional trial,error process in the economic optimal design of the radiationrecuperators with specific heat duty.

The wear, as a result of contacting of spindle surface with bearings, can be caused the inefficiency of spindle and drop quality of produced parts. According to obtained information from factories operating in the field of machine tools, the axis of spindles made from 16MnCr5 steel. In the current work, the effects of different surface heat treatments involving; carburizing, carbonitriding, nitrocarburizing and first carburizing then nitriding (as an empirical method) on wear behavior of 16MnCr5 have been investigated to increase the spindle service life. The used wear test type was block on ring. In addition, Scanning Electron Microscopy (SEM), microhardness test and metallography have been used for further analysis of results. The wear results showed that, the samples treated by carbonitriding, has a good wear resistance compared with the other samples. Also, the analysis images from the SEM show that surface treatments has not had significant effect on the fracture mode of the samples.

In this paper, the thermal buckling of a thick circular plate made of functionally graded material (FGM) with actuator/actuator piezoelectric layers based on first order shear deformation plate theory under uniform and non-uniform thermal loads is studied. The clamped boundary condition are assumed. The material properties through the thickness are assumed to be power functions of the thickness. Equilibrium and stability equations are derived by using the calculus of variations method and applying Euler equations on total potential energy. Then, the analysis of the thermal buckling of the circular plate under two types of the thermal loadings are presented by solving the equations. In the following, to investigation of the several parameters effects on critical buckling temperatures, the results are displayed by tables and graphs. Finally, the results of this study are compared with results of other works. Results show that the piezoelectric layers increase the critical buckling temperatures and this increase for homogenous plate is more than FGM plate. Also, the critical buckling temperature increases by increasing plate and piezoelectric layer thickness to plate thickness ratios.