JOURNAL OF MECHANICAL ENGINEERING
Year:2018 | Volume:48 | Issue:3 (84) |Papers Count:40

In this paper, an integrated biomass gasifier– SOFC– GT– ORC system for decentralized power generation application is presented. The proposed system includes a gasification unit, a gas cleaning unit, a SOFC-GT hybrid system and an organic Rankine bottoming cycle. High temperature gas cleaning system (HTGCS), were proposed for this integration. The performance of the system is evaluated using thermodynamic calculations. The results obtained indicate that for the integrated biomass gasifier– SOFC– GT– ORC power generation plant the net electrical efficiency based on lower heating value (LHV) is 55. 73%, when 2. 3 MWe power was produced. The proposed system has been modeled using Cycle-Tempo software.

Many applications of centrifugal pumps in various industries have caused that the increasing of performance in these pumps are considered. Cavitation phenomenon is one of the essential problems in centrifugal pumps function. Changing the centrifugal pumps inlet geometry could be a good solution for reducing cavitation occurrence in impeller suction. For the investigation, the flow in impeller and volute of the pump has been simulated numerically by ANSYS-CFX commercial code. Finite volume method along with K-ω SST turbulence model has been utilized for numerical analysis. Rotating and stationary frames have been used respectively to analyze flow in impeller and volute, and the results have been coupled by frozen rotor. Different inlet positions have been investigated numerically. The H-Q curve of simulated pump has been compared with factual model of 65-200 pump of Pumpiran Company. Lower numerical error has increased certainty of obtained results. Results indicate that some of the inlet geometries of pump impeller have led to improvement of pump cavitation performance with a slight reduction in pump head.

This paper investigates the influence parameters in optimum design of finite metallic plates with polygonal cutouts subjected to uniaxial loading. This objective is pursued by a particle swarm algorithm. The important features of this algorithm include flexibility, simplicity, short solution time, and the ability to avoid local optimums. The objective function used for in this algorithm seeks to minimize the value of stress concentration factor (optimum stress) around triangular, square, pentagonal and hexagonal cutouts. The novelty of this paper is determining of optimum stress around the polygonal cutouts in finite metallic plates under uniaxial loading. The method used for the calculation of stress concentration is based on analytical solution of Muskhelishvili complex variable and conformal mapping with plane stress assumption. The plate is assumed to be isotropic, linear elastic, and finite (the ratio of cutout side to plate’ s longest side in the square and triangular cutouts and the ratio of diameter of circle circumscribing other n-gonals to the plate’ s longest side are greater than 0. 2). Finite element numerical solution is employed to examine the results of present analytical solution. Numerical results are in good agreement with the results of the present analytical solution. Results show that by selecting the aforementioned parameters properly, less amounts of stress could be achieved around the polygonal cutouts leading to an increase in load-bearing capacity of the structure.

Robots, especially humanoid robot are going to be used in various fields, among them therapy fields. A new approach was emerged which utilized robots to improve the social skill, not physical skill. This approach was dealing with three challenges: firstly, autism creates a special condition that the patient dose not easily accept a therapist, so in the first step the researcher had to find a solution for interacting with autistic children, the second challenge was selecting appropriate algorithms and methods for eye tracking and head pose detection with these children who have inaccurate eye center localization as well. The third one included the treatment and research process which should not over stimulate the children. To overcome the mentioned challenges, a real time eye gaze tracking algorithm with high robustness as well as a fuzzy decision making tree for interacting the medial and engineering information were utilized during the treatment that were implemented on a humanoid robot. Whereas none of the commercial hardware used.

Most Axial compressors performance in aerodynamic applications systems are limited, due to flow instability at low mass flow rate One of these Instabilities is surge phenomena. In the present study, analysis of three-dimensional unsteady Navier-Stokes equations in multistage turbomachinery is studied by Fluent software and (k-ε ) turbulence model and SKE The results showed that this model compared with conventional types, to turbomachinery is more accurate and has faster convergence rate. And at investigate the compression system behavior when occurring phenomenon surge and changes of pressure and mass flow rate fluctuations over time, in different parts of the compressor performance is acceptable accuracy. So that the average mass flow rate calculated for the NASA Rotor 67 in the present study and the model SKE equal to 34/23 (kg /s) and laboratory data have shown the value of 34/61 (kg /s). It also became clear that under surge condition, by increasing the design round, vibration will have much decrease.

The high-speed submersion projectiles are designed to move in the supercavitation regime. In these conditions, the frictional drag decreases and the pressure drag becomes the dominant force against the projectile movement. A number of cavitation models have been suggested by researchers in order to simulate various types of cavitation flows. In the present work, by choosing a proper cavitation model, the supercavitation flow is modeled around a disk cavity. The supercavitation parameters are measured and compared with the experimental and analytical results. In this research, the supercavitating flow is simulated in different angles of attack and the drag coefficient is obtained in different cavitation numbers. The results of numerical analysis are compared with the results of quasi-empirical relations. Finally, using the results of numerical analysis, a correlation coefficient is proposed for calculating the drag coefficient at different attack angles for a range of cavitation numbers.

In this study, the energy absorption characteristics of steel end-capped conical tubes, perforated in various states, under quasi-static axial loading have been studied both experimentally and numerically. In the experimental section, steel alloy was identified after making the ready cones. In order to determine the mechanical properties, dumbbell-shaped samples cut by wire-cut from the cones and tensile test was performed, then the stress-strain curves were obtained for them. The conical structures were simulated using finite element software LS-Dyna and the results were compared with data from experimental tests. There was good agreement between experimental and numerical results. In this paper, 48 various states were investigated and collapse features were extracted and compared. These 48 states include three angles for cone edge, four thicknesses and four different modes in terms of number of holes, so in this way mechanical behavior of perforated steel end-capped conical absorber in various states were studied. Studies show that increasing the number of holes in the absorber's body reduces the maximum force and leads to an increase in crush force efficiency. According to the results, perforated conical absorbers are a good alternative for the same samples with no holes.

The active vibration control of a smart cantilever rotary beam, using dual sensor and actuator piezoelectric patches stuck on the outer surface of the beam, is studied. Motion equations are discretized by finite element method with 6 and 9 DOF elements for parts without piezoelectric patches and with them, respectively. Several types of controllers such as LQR, LQG and rate feedback controller are employed to actively control vibrations of the beam. Simulation results exhibit a better performance in terms of settling time for the LQR controller due to all states’ feedback; while rate controller is only relying on the sensor patches for feedback which is convenient in terms of cost. Also, the effect of the number of piezoelectric patches is studied.

The incremental forming is an attractive sheet forming operation. Finite element analyses specially at elevated temperatures for important alloys such as titanium Ti-6Al-4V are very affordable. In this study, warm incremental forming of Ti-6Al-4V is simulated and validated using different experimental outputs, namely forming limit diagrams, the drawing depth and the minimum thickness of the sample. Then, the effects of the process parameters on the forming forces are investigated considering heat generation during the process. It is found that the maximum amounts of the forming forces belong to the vertical component. In addition, any decrease in the initial temperature of the sheet as well as increase in the vertical pitch and/or tool diameter could cause certain increases in vertical forces. Furthermore, it is shown that the specimen geometry and the material can significantly influence the forming forces. Effective strain distributions also illustrate that the major sheet stretching occur in the centerline of the groove. Finally, the buckling and stress analyses of the tool imply that the tool instability and damage can mainly be caused by the tensile bending stresses.

The free vibration of a rotating Timoshenko nanobeam with a variable cross section on elastic foundation is investigated using the differential quadrature method. For more accuracy, the Timoshenko beam theory is applied where the effects of the shear deformation and rotary inertia are considered. First, the Eringen nonlocal elasticity theory is investigated briefly and the governing differential equations of motion of a Timoshenko nanobeam are derived considering the nonlocal scale parameter, variable cross section and rotation of the nanobeam. Then, by applying the nondimensional parameters, the equations are obtained in the nondimensional form and then, they are rewritten in the differential quadrature form. Finally, by solving these equations, the natural frequencies of the system are obtained. A number of parametric studies are conducted to assess the effects of the nonlocal scaling parameter, rotational speed, hub radius, and the stiffness coefficients of the elastic foundation on the natural frequencies of the system. By neglecting some parameters to reach a simpler model, the results are validated against those reported in the literature where a reasonably good agreement is observed.

There are many industrial applications, such as in aerospace, nuclear and petrochemical industries, that involve using metal bellows. Tube hydroforming is the major process by which the metal bellows are produced. Although many parameters may affect the final product, the fluid pressure can be regarded as the most important parameter in hydroforming a metal bellows. Low pressure may result in some defects such as wrinkling. On the other hand a high pressure may lead to a highly thinning and even rupture. In the previous researches, no theoretical criterion has been proposed to predict the allowable forming pressure. In this paper, an analytical equation is proposed for determining the allowable pressure, based on thin-walled cylindrical vessels. Neglecting the elastic deformation, Swift equation along with von-misses yield criterion was used to model tube deformation. The analytically computed pressure compared with the existing experimental results and a close agreement was observed. This evidently shows the validity of the propose model.

In this study, falling droplet in the 2-D channel is numerically studied using the lattice Boltzmann method with the pseudopotential model. Quantitative information about the flow variables such as behavior of droplet, stream line and wake of behind of droplet for two cases is investigated: a) of falling of single droplet and b) falling of two droplets in tandem arrangement. To validate the current numerical simulation, the result are compared with previous literature. The comparison shows a good agreement. The results show that wake region at the back of the droplet increases by increasing Eovos number while a reverse trend can be seen by increasing of Ohnesorge number. In the case of falling of two droplets in tandem arrangement, the droplets collide and soon after form a larger droplet with twice the diameter as the initial droplet. Eventually, the droplet breaks up due to high inertia of formed droplet.

In the present work, the effect of friction stir processing (FSP) on tribological and mechanical properties as well as the corrosion resistance of a low carbon steel (AISI 1010 (CK10)) is studied. FSP was successfully applied with different rotating speeds of 800-1600 rpm. Optimum properties was gained for the sample which was processed with the minimum rotating speed of 800 rpm. Metallographic study of this sample showed that dynamic recrystallization has decreased the average grain size to about 0. 5 μ m, while the initial value was ~10 μ m. The tensile strength of the optimal specimen increased for about 50 MPa. Also, the hardness of the processed samples was about 2. 5 times that of the raw material. As the result of grain refinement and the improvement of mechanical properties, the tribological properties of the sample were also improved such that a 28% reduction in the wear rate was observed. Finally, corrosion tests (according to ASTM G5) showed that FSP has no considerable influence on the corrosion resistance of the studied steel.

In this research, the effect of system parameters on the chaotic behavior of rotor-disk-bearing with rubbed between the disk and the stator is studied. The governing equations of motion according to Newton's second law extracting and are dimensionless. Non-linear force the oil film bearing under short bearing theory in the equation is included. Also, since the rub in the rotary axes a secondary defect, so in the equations of motion unbalance force and bow axis that the cause is rubbed between the disk and the stator is considered. At first, the dynamic behavior of the system by bifurcation diagrams, time series diagrams, phase diagram, power spectrum diagrams, Poincaré sections diagrams and maximum Lyapunov exponent is studied. Then, the influence of various parameters of system including the coefficient of friction between the disk and the stator, clearance between the disk and the stator and stiffness between the disk and stator on the behavior of chaotic system in different rotational speeds is investigated.

Electrical discharge machining (EDM) is one of the most important modern machining processes in today's industry. The tool wear in this operation, due to the nature of the process, reduces the dimensional accuracy of the manufactured parts. Therefore, efforts to reduce tool wear are one of the most important challenges in this operation. For this reason, in this research was carried out using one of the methods of severe deformation, The effect of reducing the size of the copper electrode grains on the wear of spark tools has been studied. At first, high-purity copper bars were placed under the equal channel angular pressing process (ECAP). The average of pure copper grain size was decreased homogeneously from 60. 8 to 5. 48 micrometer, through the ECAP process. Changing in grain size were determined by using electron backscatter diffraction technique (EBSD). In this study, the effect of factors including pulse on-time and spark current and electrode grain size was examined on the tool erosion. The results showed that, in high material removal rates, the tool wear decreases for 36. 8% as compared with the conventional tools. Despite of these results it was clarified that at low material removal rates the wear rate of these two tools do not show vivid differences.

Sandwich panel structures because of desirable properties such as high strength to mass ratio and damping of impact energy, have wide application in aero structures. In this article 7 alloys including stainless steel 321, stainless steel 347, Inconel 625, Inconel 718, Inconel 600 and nickel alloy 201 have been selected based on similar studies for replacing original part in aircraft horizontal tail. Yield load and damaged area determined by von-mises damage criteria based on methods in MIL-STD-401. Finally two alloys out of these seven alloys passed six parameters consist of damage onset, mechanical properties on 650 OC, density, price and environmental effects have been nominated. Results illustrated that Inconel 625 and Inconel 718 are best candidates for replacing current material of horizontal tail structure.

In this paper, an algorithm is represented to design geometry of suspension for a family of vehicles. Product platform optimization is a way to determine design variable set which not only deserves every product qualifications, but also it helps to find a set of parameters which has the most commonality features. To determine qualifications of each vehicle model, road inputs has applied to models by means of stochastic road harshness input which includes using Power Spectral density of road input as the input of vehicle geometry model. Platform based design uses optimization to maximize commonality among family besides deserving each individual constraint. In order to do this, objective functions and constraints implemented in order to find optimum designs. This algorithm optimizes ride and handling of the car besides increasing commonality among the whole family. For a numerical solution, a family of car which includes 5 products has been proposed based on Dacia-Renault platform (L90). At last, an algorithm is presented that could design geometry of vehicle suspension for a family of products.

The aim of the present paper is sensitivity of shape design analysis on thermo-elastic problems using a modified semi-analytical method. The semi-analytical method is one of the efficient methods for sensitivity analysis with respect to the design variables which combines the analytical method and finite difference method. Although this method is a powerful method, however, it is sensitive to perturbation size. Complex variables method is a new novel approach which is not sensitive to disturbance and has some potential advantages over other methods. The implementation of this method in a finite element code for sensitivities calculation is straightforward, only requiring a perturbation of the finite element mesh along the imaginary axis. This study uses the combination of analytical method and complex variables method to calculate the sensitivity of thermo-elastic problems. The proposed method has both advantages of the analytical method and the complex variables method. The advantages of this method are that it is quick, accurate and simple to implement. The obtained results are compared to other methods and it is shown that the proposed method is effective and can predict the stable and accurate sensitivity results.

In this study, an optimization technique is performed to obtain the unknown heat source distribution in order to produce the known temperature and heat flux distribution over the design surface. The medium is considered non-gray, absorber-emitter and non-scatter in radiative equilibrium. Discrete ordinate method is used for solving the radiative transfer equation. In order to consider the nongray calculations, both the spectral line-based weighted sum of gray gases approach and the gray model are implemented. The inverse problem involves the minimization of an appropriate objective function which is minimized by the conjugate gradient method. Some examples are presented to prove the ability of the approach for achieving the desired thermal conditions. Although the gray model is a low-computational-time method, the present outcomes showed that using this method results in enormous error. Compared to the gray model, accurate results could be only achieved through using the spectral line-based weighted sum of gray gases model which is a powerful and efficient method.

Electrohydraulic forming (EHF) is a high velocity sheet metal forming process in which two electrodes are positioned in a water filled chamber and a high-voltage discharge between the electrodes generates a high-pressure to form the sheet metal. In this work, extensive experimental tests are carried out (up to 3. 2 kJ) to investigate the deformation behavior of brass sheet by using EHF. To explain different aspects of sheet deformation, Smoothed Particle Hydrodynamics (SPH) formulation is coupled with Finite Element Method (FEM) in LS-DYNA and applied for simulation. In order to model the electrical discharge process, two different approaches are implemented. In the first approach, electrical discharge energy is converted to equivalent TNT mass. In the second approach electrodes gap is replaced by a plasma channel and electrical discharge energy is leaked to it. Finally, deformation history (displacement, velocity, strain and strain-rate) at different locations of sheets are presented. The results indicate that (under the conditions used in this study) the maximum of velocity and strain-rate are reached to 250 m/s and 3800/s respectively.

Friction Stir Welding is an appropriate method to connect different metals in temperatures below their melting point. In spite of this, the effect of thermal cycles causes the reduction in mechanical strength in different weldment regions. On the other hand, because of necessity of doing welding in submerged conditions like in navy industries it is of great importance to investigate and thermally modeling the submerged Friction Stir Welding. In this paper, finite element modeling of friction stir welding in the air and underwater were performed for Al6061-T6 alloys to control the thermal cycles. In addition to cooling effect, the influence of parameters such as welding speed and rotational speed on the maximum temperature in workpiece was investigated. The model results were then examined by experimental data and a reasonable agreement was observed. Results show that increasing rotational tool speed due to increasing in generating heat flux causes increasing in maximum temperature experienced by workpiece in different regions in both air and underwater welding. However, in underwater welding because of boiling water surrounding the tool, temperature drop is more greater than another one. The difference between maximum temperature in air and underwater welding is high. Reducing welding speed causes increasing the maximum temperature. This is due to reducing cumulative generated heat flux during welding. Increasing temperature during welding in air is more salient than doing welding in underwater. In the other word the effect of welding speed on maximum temperature in welding in air is more than underwater welding.

In this paper, shell-side stream flow distribution on the shell-side fluid flow of shell-tube heat exchanger by baffle space and baffle cut variation computationally was conducted. Flow distribution plays an important role to obtaining high performance in the effective operation of a shell-tube heat exchanger. Uniform flow distribution is critical to obtaining high performance and without tube vibration in shell-tube heat exchanger devices. Also Stream flow rate is a very useful to understand the heat transfer and pressure drop along a shell-tube heat exchanger with the flow distribution. So the shell-side designs of a shell-tube heat exchanger, in particular the baffle spacing and baffle cut dependencies of the stream flow rate are investigated. In the present article a novel technique base on the proposed method presented to measure the flow rates in different baffle sections. The proposed analysis method used hydraulic network principals for evaluation flow velocity distribution on a shell-tube heat exchanger has been developed. According to obtained results baffle space and baffle cut configuration significantly affect the flow field distribution. window-section flow stream have higher flow rate in the shell-side.

In order to absorb underwater acoustics waves, special coatings named “ Alberich” are used. The mechanism of these coatings is to transform the wave energy to heat by vibration through holes in them. In this study, the performance of a particular type of anechoic absorber called Alberich and made of polyurethane were evaluated by using Comsol software and the impact of various geometrical parameters were investigated, individually. The results showed that the absorption coefficient increases, while the reflection and transmission coefficients decrease, by increasing the height and radius of the air cylinders. Besides, putting cavities in the middle rows with different radii, increases the frequency range and makes the absorber wideband. Finally, the absorber was optimized to maximize the absorption coefficient. In the optimized model the cavities are in the shape of frustums with 5 degree head angle. Their radiuses in the main and middle rows are 0. 8 cm and 1. 2 cm, respectively. The Parametric study and optimization of the Alberich absorbers were done for the first time in the current research and it can be used by engineers and researchers.

In this research, an organic Rankine cycle(ORC) equipped with a regenerator and a feed fluid heater used for power production. Also a proton exchange membrane used for hydrogen production that handled by the ORC. Energy requirement of the ORC was supplied via geothermal energy. A comprehensive thermodynamic model (energy and exergy) of the integrated system was done to compare the operation of four different fluid works. The EES software was used for all of the simulations. Also, a parametric study was done to investigate the effects of the important operational parameters on the energetic and exergetic performance of the considered systems. The results showed that among the different working fluids, R245fa has the most energy and exergy efficiency with the amounts of 3. 511% and 67. 58%, respectively. After that, R114, R600 and R236fa have the best operating performance, respectively. By increasing of the geothermal fluid temperature, the amounts of power and hydrogen productions increased but the energy and exergy efficiencies decreased.

In this paper, the effect of different kind of constraints on two and three dimensional adjoint-based shape optimization of aerodynamic design in inviscid and turbulent flows has been investigated. To assess the accuracy and efficiency of the adjoint-based approach, a complete set of optimization problem is investigated: from none to fully aerodynamic and geometrical constraints. With the adjoint method, the complete gradient information needed in the design optimization can be obtained by solving the governing flow equations and the corresponding adjoint equations only once for each cost function, regardless of the number of design parameters. Drag forces was chosen to be the objective function. Hicks– Henne shape functions and free form deformation parameters are adopted for the surface geometry perturbations, for two and three dimensional geometries, respectivelyThe drag minimization results show that the adjoint equation converges well and with specifying the suitable constraints, the designed shape approaches to the most optimized level without the loss of performance.

The basic gas turbine cycle has low thermal efficiency so improved efficiency of gas turbine is important. The gas turbine power is affected by atmospheric conditions and ambient temperature. In this article, two methods including fogging and mechanical chiller for inlet air cooling to the compressor by means of energy, exergy, economic and environmental (4E) analysis are studied. The results show that cooling by mechanical chiller system decrease inlet air temperature to 28 º C and fogging system to 18 º C. Also by using mechanical chiller cooling method, the exergy destruction in compressor about 75% reduced. By using Mechanical chiller and fogging systems the gas turbine cycle efficiency increase 5% and 2% respectively. The cost of reduced carbon dioxide is 15457$ for cooling with mechanical chiller and is 7492 $ for cooling with fogging. Net present value shows for fogging and mechanical chiller the profitability begin after 4 and 5 years respectively.

Present study is a numerical solution for incompressible fluid-elastic structure interaction by use of immersed boundary method. The solid phase is an elastic filament hinged on rear of a rigid cylinder in the presence of fluid flow. The purpose of this study is investigation of interaction of flexible filament and rigid cylinder. In the immersed boundary method, solid and fluid domains are solved in separated regions. For solving the flow field and momentum equations, the lattice Boltzmann equations are employed. In present study in contrast to previous studies, the elastic filament is also modeled by a mass-spring network that provides elastic properties like young’ s and bending modulus. The mass of filament is discretized on nodes of spring network. These two solution regions are connected by applying suitable boundary conditions at each time step. Results show that the mass, geometry and location of filament behind the rigid cylinder have significant effect on the filament’ s stability and drag reduction. Indicating and analyzing a special point behind the cylinder, where the drag is minimum, is the another purpose of this study

In this paper, free vibration of the composite sandwich conical shell are investigated by using differential quadrature method (DQM). The analysis is performed for the four different types of core materials, Polyether ether ketone (PEEK), Polycarbonate (PC), Solid polypropylene (SPP) and high density polyimide foam (HDPF) and Consider a sandwich conical shell with the skin layers made of glass fabric reinforced polymer. The first-order shear deformation shell theory is adopted to formulate the theoretical model and governing equations of motion are derivated by Hamilton’ s principle. The governing equations of motion, are discretized by means of the DQM and natural frequencies are achieved. The effects of thickening, increase of length and boundary conditions on natural frequencies, are investigated. To verify the accuracy of this method, comparisons of the present results with results available in the open literature and Abaqus are performed.

Natural convection of a two-dimensional laminar incompressible fluid flow inside a square cavity with triangular roughness elements on the vertical walls has been investigated by finite element method. The present study has been carried out for different aspect ratio and various cases of position of element on the left wall singly and both left and right wall together in different Rayleigh number. Air is chosen as a working fluid. Hydrodynamic and thermal behavior of fluid in the presence of triangular roughness elements was analyzed in form of streamlines, isotherms and the average Nusselt number. Results based on this numerical study showed that the triangular elements considerably affect the hydrodynamic and thermal behavior of fluid in a square cavity. The maximum reduction in the rate of heat transfer toward the smooth cavity in case of A=0. 05, was calculated to be 26. 66% when the roughness elements were located on the hot wall in Rayleigh number equal to 106. The abstract should state briefly the purpose of the research, the principal results and major conclusions.

In order to improve vehicle lateral stability and steerability, an active rear steering strategy (ARS) using nonlinear optimal predictive control method is presented. A new reference model considering the tire/road conditions and physical limitations of real vehicle has been proposed for being tracked by the designed controller. The performance of the designed controller in tracking the proposed reference model is evaluated during a constant turning maneuver with varied coefficient of friction. Also, the effect of free parametes of controller on vehicle tracking error in the presence of uncertainty is discussued. Finally, the performance of the controller is compared with another strategy reported in literature during lane change maneuver. The simulation results show that tracking the proposed new reference model by nonlinear predictive control method improves vehicle stability and steerability, significantly.

In this paper, the effect of mass flow ratio of water to air on seawater cooling tower performance was numerically investigated. The numerical results were validated by experimental data. For mass flow ratio under one, the total heat transfer coefficient is decreased by increase of tower volume from top to bottom but for mass flow ratio above one, it is increased. For mass flow ratio under one, the most part of total heat transfer coefficient value is due to the convection heat transfer coefficient. The convection heat transfer coefficient was decreased by mass flow ratio reduction. The evaporative heat transfer coefficient was increased by mass flow ratio reduction. The required tower volume for water cooling is increased by increase of mass flow ratio. The tower volume was increased to high value in humid weather conditions. The outlet water temperature was increased by increase of mass flow ratio or atmospheric pressure reduction. By increase of mass flow ratio, the effectiveness was increased but the variation rate of the effectiveness was decreased. By increase of mass flow ratio or reduction of atmosphere pressure, the tower temperature ratio was decreased and consequently, the variation rate of it was increased.

Investigation of the air-flow in outdoor-unit of air-conditioner and study the effect of grille on exit hot air-flow characteristics has a great importance, especially in apartment complexes. In this research, the effect of two types of industrial grille (circular and square) and a suggested grille (designed with symmetrical NACA-0012 cross-section to guide the flow in desired direction) on air-throw distance and flow rate have been investigated. Numerical evaluations of flow behavior include geometrical modeling, grid generation, and flow solution within the computational domain. Flow simulation within the fan has been made using the multiple reference frame (MRF) and also the realizable k ԑ turbulence model. For outdoor-unit with a circular grille, comparison between numerical and experimental results of three high-speed averages show 6. 24 percent difference in exit flow rate. Results show that the grille of air outlet window reduces the exhaust air flow rate, increases the propeller’ s rear pressure, and increases the number of vortices. Beside, from the non-dimensional aerodynamic performance and also air-throw distance point of view, the proposed grille, and circular grille respectively have the best performance.

In the present study, effect of the using corrugated tube (modified tube) as inner tube of a double tube heat exchanger on the heat transfer rate and exergy loss is numerically investigated. Each corrugation is made of a semi-circle with various diameters of 2. 5, 5 and 7. 5 mm, and a diagonal line. The inner tube of the heat exchanger is made of copper with inner diameter of 27 mm. The outer tube with inner diameter of 54. 5 mm is considered isolated. The obtained results indicated that the use of corrugated tube as inner tube of heat exchanger had a significant effect on the heat transfer rate and exergy loss. Heat transfer in double tube heat exchangers with corrugated tubes was 1. 07 to 3. 08 times more than the transferred heat in a simple double tube heat exchanger. Furthermore, the effects of inlet hot water temperature and inlet cold water temperature on the exergy loss are studied. Based on acquired data, by increasing of the inlet hot water temperature or decreasing of the inlet cold water temperatures, exergy loss increases.

Effects of initial geometric imperfection and pre-& post-buckling deformations on vibration of isotropic rectangular plates under uniaxial compressive in-plane load have been studied. Vibration equations of a plate, using Mindlin theory and Von-Karman stressstrain relations for large deformations, have been extracted. The response of nonlinear differential equations was assumed as the summation of dynamic and static responses. Due to the large static deflection of a plate in comparison with its vibration amplitude, the differential equations have been solved in two steps. First, the static equations have been solved using the differential quadrature method and the Arc-length strategy. Next, considering small vibration amplitude about the deformed plate (the first step result) and eliminating nonlinear terms, natural frequencies have been calculated using the differential quadrature method and solving the obtained eigenvalue problem. The results for different initial geometric imperfection and different boundary conditions reflect the impact of the mentioned factors on the natural frequencies of plates.

Free vibration and static analysis of a functionally graded piezoelectric beam is carried out by the finite element method in present study. Mechanical, electrical and electromechanical properties are estimated by the power low distribution through the thickness of the beam. Governing equations are derived using Hamilton’ s principle and two dimensional theory of elasticity. Convergence of the proposed finite element method is verified by several examples in free vibration and static analysis under mechanical and electrical loads with different types of boundary conditions. After validating the model, effect of different parameters are investigated on natural frequencies and static response of functionally graded piezoelectric beam.

In this paper, the effect of various surface treatment processes and nanoclay addition on the mechanical properties of fiber metal laminates is investigated. For this purpose, the aluminum alloy 3105 was surface treated under different processes includes degreasing, mechanical abrasion, chemical etching, chromate conversion treatment and combinations of these processes. Then, the fiber metal laminates were manufactured by aluminum sheets, pure epoxy resin and modified resin with nanoclay and glass fiber using hand lay-up process. The effect of different processes of surface treatments and using nanoparticles on the flexural and impact properties of the specimens was investigated using response surface method. The results obtained indicted that the chromate conversion treatment of metal surface has a most effective role in increasing the mechanical properties of the specimens. While, among different processes of surface treatments, degreasing has a less effective role in enhancement of mechanical properties of fiber metal laminates. The result of main effects analysis also showed that despite the useful role of nanoclay in improvement of the mechanical properties of fiber metal laminates, the role of surface treatment processes is more effective than nanoparticles addition.

In this paper, experimental and numerical comparison of Baseboard radiator and Panel radiator are presented. Rated capacity of both radiators was 1200 kcal per hour. In the experimental section, at the same ambient temperature for both radiators, capacity and characteristic equation and temperature distribution in a room with dimensions of 2. 6 × 4 × 4 meter was obtained. The experimental results showed that a Uniform Temperature distribution occurs in the room for the Baseboard radiator, Temperature difference in vertical direction for center of the room for the Panel radiator in various capacities changes 3° C to 7° C, While for the Baseboard radiator at all capacities temperature difference was about 2 ° C. Temperature difference at height of 1. 5 m in horizontal direction from wall that the Panel radiator was installed to facing wall, changes 3° C to 6° C. While for the Baseboard radiator, this result was about 0. 5° C. To investigate the cause of the temperature distribution, numerical modeling was used. Numerical results and experimental results were close with 10% error. Temperature distribution curves At plane of symmetry room for both samples was drawn, Baseboard radiators were more uniform temperature distribution again. In the end, the velocity distribution diagram in the vertical plane of symmetry room was obtained which show that a strong circulation occurs in the room for the Baseboard radiator.

Nowadays, one of the most important challenges in engineering sciences is optimization of the existing designs due to the competitive industrial market. In aviation industry, weight and life of components are important criterions in their design. As an example, optimizaing the weight of main gearbox of helicopters with acceptable performance and fatigue life are major concerns. In this paper, design parameters of Agusta helicopter main gearbox has been determined by three different optimization methods: Genetic Algorithm (GA), Particle Swarm Algorithm (PSO) and the Gravitational Search Algorithm (GSA). The objective function is the weight of the gears with appropraiate constrains which are based on geometrical limitations. Alsosafety factors according to the AGMA standards are considered. The design parameters are gear width as a continuous variable and normal module as a discrete parameter. Comparison of the results show that all three optimization methods are able to minimize the weight of the gearbox in the range of 23 to 27% comparing with the existing one; but, GSA not only gives the best optimized solution it also has the highest convergence rate.

Thin walled tubes are the most efficient energy absorption systems due to their lightness, high energy absorption capacity, and large crushing distance. In this process, a primary tube can be gradually deformed in to the desired thickness and length using simple roller. In this study, mechanical joining of aluminum and steel tubes is investigated to manufacture the bilayer tubes. Mechanical locking through the plastic deformation between two layers has been investigated under specified process conditions. To create a mechanical locking, the two layers were threaded with coarse and fine threads, and then using the warm flow forming the bonding between them was enhanced. It was concluded from the shearing test that the strong bond between the two layers can be created using the flow forming process. Also crushing test of bilayer tubes prepared by pressing and flow forming, have been investigated and it was found that the pressed sample with annealed Al layer has better energy absorption. The flow formed tubes with fine threads have better crushing energy absorption.

The integrated navigation contains Inertial Navigation System (INS) and Global Positioning System (GPS) is an important method in moving vehicles such as ground, sea and aerospace vehicles navigation. This study contains the introduction of INS, the introduction of GPS, the integration method of above systems and important issues in this field. For these purposes, the most important researches of Iranian and overseas scientists are studied. Besides of issues such as using a Kalman Filter (KF), Extended Kalman Filter (EKF), Particle Filter (PF), and other methods based on KF and PF, the new approaches are also surveyed. The study results show that recently using artificial intelligence method in integration, the problem outage or block of GPS signal in integration and low-cost inertial navigation sensors have been the focus of attentions.