مجله مهندسی مکانیک
سال پنجاه و یکم شماره 4 (پیاپی 97، زمستان 1400)

Laser interferometry is one of the novel methods for performing nondestructive testing for composites and polymer materials. In this method, probable defects are investigated by measuring the very small surface displacement gradients. One of the major advantages of this method is the examination of a wide range of body surfaces simultaneously. Despite the major advantages of this method in performing non-destructive industrial tests, especially for composites and polymer materials, the implementation of this method requires identifying effective parameters and how to select and control them in order to achieve optimal results. Among the effective parameters in this method, the shear amount and loading value can be mentioned. In this paper, after introducing the principles of laser interferometry, the quantitative effect of these parameters on the detection of plate defects in polymer materials has been investigated. For this purpose, after examining the proper operation of the shearography system, samples of polymer with different size of plate defects are tested. By discussing the results, the appropriate load value and proper shear amount for determining the defects would be investigated. Investigations show that the best results are obtained when the shear amont is within the range of the defect size of the plate.

The present study aimed to introduce two novel power-refrigeration combined cycles into optimal usage of LNG cryogenic energy and reducing exergy losses due to high-temperature difference in the heat transfer process. The combined cycles include a compression-ejector refrigeration cycle and two low and high-pressure Rankine cycles in which the power required to operate the compression-ejector refrigeration cycle’s compressor is provided by the power generated by the two-cycle Rankin turbines. Increasing the cooling energy compared to direct LNG evaporation is considered as the benefits of the novel combined cycles. A thermodynamic analysis, along with optimizing both novel combined power-refrigeration cycles, was performed through the first and second thermodynamics laws and the fixed surface model assumption for the ejector. Analyzing the design parameters demonstrated that the maximum thermal and exergy efficiency and maximum refrigeration increasing ratio in both novel combined power-refrigeration cycles increase as the pump discharge pressure increases and the output pressure of Rankine cycle turbine reduces. The maximum thermal and exergy efficiency in cycle (І) were 77.31% and 23.69%, and 87.49% and 23.95% in cycle (ІІ), respectively through performing optimization in the boundaries set for the design parameters. Finally, the highest refrigeration increasing ratio to direct evaporation of LNG for cycle І and ІІ was 63.37% and 73.9%, respectively.

In the present study, the effect of the uniform electric field on the hydrodynamic of salt-water drops in crude oil is studied. For this approach, COMSOL Multiphysics software is used, which is based on the finite element method. The obtained results are compared and validated with the available numerical and analytical results and good agreement is observed. The effect of different parameters including the electric Capillary number, the Reynolds number, direction of the electric field, and the relative permittivity of fluid, on the movement of a single drop of saltwater in crude oil under the electric field, is investigated. The results reveal that electric stresses at the interface cause drop deformation and elongation in the direction of the electric field. The magnitude of this deformation increased with increasing the ratio of electric force to surface tension (electric capillary number). Also, the motion process of drop takes longer time in vertical electric field compared with the horizontal electric field in the same condition. Therefore, a uniform external electric field can be used for non-contact controlling of a dropping movement.

In this study, our main objective is to evaluate heat convection and pressure drop simultaneously to obtain optimum properties of Nano-fluid and porous media contribution for high cooling efficiency. In fact, the main contribution of this study is to simulate Nano-fluid flow effects on cooling process of heating resources located inside channels that are completely surrounded by parallel walls. To do this, porous materials are located on predefined blocks in the channel to increase heat transfer and then determine the effect of porous materials on quality of heat transfer. One of the most significant goal of this study is to use various geometries of porous blocks on this process. For various porous media geometry, the rate of heat transfers along with pressure drop have been evaluated to obtain best geometry. To do this, the fluent software is employed to study the effect of different parameters including Re number, Nu number and pressure reduction on optimal conditions of heat transfer, temperature distribution and fluid flow stream lines respectively. It is expected that, investigating different geometries can give us enough opportunity to identify the most appropriate geometry of porous blocks. This achievement enables us to define the best possible mode of conducting the highest heat volume while the amount of pressure reduction is minimized concurrently. Results show that the amount of heat transfers from heat resources will increased when the porous media along with Nano-fluid are used simultaneously.

The phenomenon of cavitation is one of the most important issues in the pumping industry. Occurrence of this phenomenon in the pump, in addition to damaging the pump impeller and reducing its life, causes vibration and noise, which in the long run causes the pump to fail. This phenomenon occurs when the NPSHa (net positive suction head at the station) is less than the NPSHr (net positive suction head required by the pump). The purpose of this paper is to design a suitable inductor for centrifugal pump type OH1 150-500 at the inlet of the pump in order to prevent cavitation to reduce the amount of NPSHr and increase the reliability. To model the turbulence, the K-Omega SST turbulence model with a standard wall function is used. Also, the finite volume numerical method is used in this paper. The obtained numerical results are compared with the experimental results and provide acceptable agreement. The results show that the presence of an inductor at the pump inlet increases the difference in NPSH from a number less than 1 m to more than 2 m and thus causes it to be further away from the cavitation point.

According to recent achievements in multi-agent systems, the use of cooperative arrangement of the multi-agent systems like robots and UAVs such as rescuing, aerial mapping, aerial photography, and goods delivery missions is growing as fast as possible. Implementation a cooperative mission involves two Characteristic: Assigning tasks to each agent in optimally way and path planning of agents to their related tasks. In this article, a hierarchical approach based on linear programming algorithm is developed in order to solve task assignment problem with moving targets and multiple tasks on each target, which has a non-linear structure. Dynamic targets, which have variable position and their position change in every stage of algorithm as a time varying parameter, are considered. All the timing and non-timing constraint with the consideration of flight endurance time, priorities and the moving states of each agent and target will be satisfied. The most part of forming this hierarchical approach is assuming variable position for each target and solving the dynamic task assignment by linearization and discretization of time variables and using time windows for solving stage by stage.

Identification of unstable systems always has been a challenging issue in the field of controller design. The purpose of this study is to provide a new way to identify and design the control of unstable systems in the loop. For this purpose, after stabilizing the system with a simple controller (Inner Controller), the Inner Loop is identified and then an accurate controller (Outer Controller) will be designed for this loop. For validation, this method is simulated on an inverted pendulum and also implemented on a laboratory system. Because the multi-rotor is unstable, the Inner controller is designed and simulated on a low-precision model. After implementing the Inner controller on the real system and data gathering, the dynamic model of the Inner Loop is identified and finally, with the exact model of the inner loop, the design of the Outer controller is done to Improve stability and performance. The simulation and test results show the interesting and very good performance of this method.

In this study, commercial pure copper was subjected to a combined forming process. For this purpose, a twist extrusion die with an outlet channel narrowed was used. In this technique, by applying radial and longitudinal strains, different shear sliding systems were activated which leads to a change in mechanical and physical properties of the sample. The results showed that the microstructure of the sample was changed via passing through the twist extrusion die and a very fine gain size was obtained.The grain size was further decreased by passing through the outlet channel and applying direct extrusion, and more homogeneous grains were achieved. The compressive yielding strength was increased from 115 to 167 MPa and the average hardness value was raised from 80 to 127 Vickers by applying the twist extrusion process to the copper. After applying the direct extrusion process to the sample, these values reached 192 MPa and 140 Vickers, respectively. The results also showed that by applying twist and direct extrusion to the copper, its surface electrical resistance increased about 7 %, compared with the reference sample.

In this paper, the characteristics of the ventilated cavitation around an axi-symmetric body with a cone nose at different water velocities and injection rates have been investigated experimentally. The experiments are done in an open loop water tunnel with a maximum water flow of 40 m/s. The main purpose of this research is to study the rate of air injection and the flow velocity on the coefficient of drag and the relevant super-cavity shape. The effect of air injection rates from end of the cone nose of the body on two phases fluid flow characteristics was studied for different water velocities within the tunnel. For each case of input conditions, the variations of the drag force and pressure distribution profiles along the length of the body and the length of the super-cavity are measured. The results of the present study show that increasing of the injection rate to an optimal value has a significant effect on the reduction of the drag force and after that the reduction of the drag force is negligible.

In recent years, because of expanding human-robot interaction, especially in collaborative robots, safety in collision between a human and a robot has drawn much attention. A safe manipulator can be equipped with either active or passive system. A safe manipulator with a passive system usually consists of a mechanical elements, such as a spring which can absorb the collision force and reduce it. These joints are composed of a spring-loaded mechanism which is capable of acting as soon as a torque is dealt with, and by absorbing force from the spring causing the torque to fall to a safety limit. But for a torque lower than a limit, the rigid behavior of the manipulator which is necessary for the accurately is guaranteed. In this paper, design of revolute joint with nonlinear spring system is considered by a four-bar mechanism with a linear torsion spring so that it can be stiff for high values of an input torque for normal operation, but immediately after collision the torque will drop to its safety limit. We also show that the singularities of the four-bar mechanism can be used to design a secure joint so that the different behavior of the joint can be expected in different situations.

In this research, the energy absorption capacity of hollow and filled foam thick-wall aluminum tubes under axial loading with a variety of damage models has been investigated empirically and numerically. Experiments to determine the mechanical properties of the specimens and to apply compressive loads on them were performed using a Zwick servohydraulic testing machine. Numerical simulations were performed using the Abaqus finite element software and the results were compared with the results of the experiments. In numerical analysis, three damage models, Johnson-Cook, Gurson-Tvergaard-Needleman (GTN) and modified Rousselier were used. Eventually it turned out that the modified Rousselier model has the least error. The Johnson-Cook damage model is available in Abaqus software but the Gurson-Tvergaard-Needleman and the modified Rousselier damage models were created through programming in Abaqus software. Also, in this research, the effect of thickness and foam injection on the energy absorption capacity of aluminum pipes was investigated and it becomes clear that increasing the thickness of absorber increases the absorbed energy and ultimate crushing force.

In this work, a reliable mathematical model for numerical modeling of co-current and counter-current spontaneous imbibition in 1D and 2D modes is presented using MATLAB software and validated. Then, several studies are conducted on the effect of boundary conditions on the imbibition process. Results show that the oil recovery in co-current imbibition was 1.5 times greater than counter-current imbibition after 20 days. The results also show that in blocks with different heights, oil recovery is different. Investigation of the counter-current spontaneous imbibition in 2D mode in a large matrix block fully immersed in water indicated the effect of the gravity force in doubling the oil recovery after 120 days. Moreover, reducing the matrix block-water contact results in a decrease in the performance of imbibition process in the oil production so that the amount of the counter-current imbibition oil recovery decreased from 49% (four faces in contact with water) to 30% (one face in contact with water) after 10 days. The results show the increase of the water-contacted boundaries improves the spontaneous imbibition process efficiency.

The knowledge of the thermal properties of Spacer fabrics is important with regard to their vast applications in most industries such as the automotive industry, mattresses, etc. Thermal properties, are as one of the physical features of a textile, are influenced by its structural parameters such as thickness, density, and so on. This paper aims at the measurement of thermal properties, heat distribution and the relation between thermal transmission and parameters of the spacer fabric. For this purpose, an image processing method was used to produce clustered images based on the k-means clustering algorithm to determine the sample temperature and heat distribution.The 3D thermal distribution of fabric and the results of image processing with the clustering technique showed that the heat transfer rate and heat distribution of fabrics depended on the thickness and density of the fabrics, so that dense samples have more uniform heat distribution. At the relationship between heat transfer and the fabric parameters, the results showed that thermal conductivity increases as the thickness and density of the spacer fabric increases. Image processing technique is proposed as an accurate method to determining the heat distribution in three-dimensional objects.

The forming of tailor machined blanks due to the different thicknesses is more complex than the monolithic sheets. The presence of two sections with different thicknesses leads to different formability behaviors and consequently their different spring-backs. Therefore, it is important to examine the spring-back in the thin and thick sections of tailor machined blanks in order to minimize the spring-back value. In this paper, an adaptive neural-fuzzy inference system is used to model the effect of important parameters to predict the percent of spring-back corresponding to the thin and thick sections on the creep age formed tailor machined blanks. In addition, the obtained model is used to optimize the creep forming process using particle swarm optimization algorithm. In order to model the process behavior, some experiments have been performed on the creep forming of tailor machined blanks. The accuracy of the obtained model is investigated using different figures as well as by the specific criteria , , , and .

In this research, 3-D numerical simulation based on Eulerian-Lagrangian approach was performed on solid-liquid two-phase flow in a convergent-divergent 200 μm microchannel. The size of particles used in this research is 20, 40 and 60 μm with density of 1.05 gr/cm3. Results include velocity domain of the particle at the channel cross section, Reynolds No. effect on particle velocity, particle diameter effect on particle velocity, and the effect of top-down and side walls on particle velocity. The numerical results show that in addition to the top-down walls, the side walls also reduce the velocity of the particles in the direct microchannel up to 42%. Compared with similar studies, the effect of channel convergence on particle deposition is investigated in this study. The results show that the convergent-divergent part of the microchannel reduces particles sedimentation up to occurs 45% comparing with direct part of the microchannel due to particle acceleration, which is one of the benefits of convergent-divergent microchannels.

In this study, operating parameters of a diesel engine including engine power, torque and specific fuel consumption, with the oil fish biofuel were investigated under the effect of nanoparticles of silver (Ag) and carbon nanotubes (CNT). Biodiesel was produced from fish oil using trans-esterification reaction. Then, the blend was prepared as volume ratio of %20 biodiesel and %80 diesel (B20). According to past research results, the blend of B20 was used due to its optimal parameters than the other blends. Nanoparticles of silver (Ag) and carbon nanotubes (CNT) with concentrations of 30, 60 and 90 ppm were applied for blending with biodiesel fuel to investigate the impact of Nano fuels on performance of the diesel engine under test. Mean comparison of mixed fuels and engine speed using Duncan was analyzed on their main effect and interactions of measured parameters (power, torque, specific fuel consumption). The experiments were carried out on a single-cylinder diesel engine at engine speed levels of 1800, 2100, 2400 and 2700 rpm, under full load conditions. The results showed that increasing concentrations of nanoparticles using Nano fuel and biodiesel fuel (B20) at all engine speeds, power and torque was increased and specific fuel consumption was decreased compared to biodiesel. Power and torque of the engine were increased with fuel of BD+CNT90 at 2400 rpm as %17.29 and %17.08, respectively.

Design of the bearings with different geometric structures and using additives along with lubricants are among the proposed solutions to improve the dynamic stability of the hydrodynamic journal bearings. It is inevitable to apply new analytical models for evaluating the performance of non-Newtonian lubricants compared to Navier-Stokes equations. Couple stress fluid is a sample of these models, which is employed in this study to investigate the stability of noncircular 3-lobe bearings. To do so, the modified Reynolds equation is first derived based on the couple stress theory. Then, the dynamic pressure components and equivalent stiffness and damping coefficients of the lubricant are calculated by assuming a linear model for the rotor disturbances as limit cycle oscillations (LCOs). Finally, the critical mass parameter and whirl frequency ratio are obtained to determine the bearing stability range by simultaneously examining the Reynolds and rotor motion equations. The results show the bearing stability and lubricant damping ability improve by increasing the couple stress parameter. Also, the effects of upgrading lubricant characteristics on bearing performance significantly enhance with increasing the amount of 3-lobe bearing noncircularity.

The aim of this study was mold design for batch type casting and selection of optimal pouring process, especially for low-alloy steel slabs production with dimensions and the simulation for validation of mentioned process. For this purpose, initially a metallic mold (water cooled copper) with dimensions 4000 × 2000 × 150-300 mm was designed. Then, batch type mold design and pouring optimization process were simulated by ProCAST casting software. It is noteworthy that for the slab casting process simulation, thicknesses of 150 and 300 mm were considered. Also for high-alloy steels family, AISI 5132 steel were considered. The results showed that the use of copper mold for steel slabs casting of low-alloy steels provided satisfactory results. The results showed that by increasing the thickness of low- alloy steels slabs from 150 mm to 300 mm, amount of gas and contraction cavities, solidification time, melt turbulence, the number of slab hot spots and the time necessary to achieve the melt to solidus line all increased and in contrast, the solidification rate decreased.

The dynamic features of flow field in three models of the unidirectional and bidirectional grooves of the dry gas seal of a centrifugal compressor are simulated using computational fluid dynamics. The computational domain is the gas film between two rotating and stationary rings and inside the grooves. The seal performance is investigated under different thicknesses. The continuum and Navier-Stokes equations are solved by assuming the ideal gas fluid by using structural and hexagonal cells. The flow is considered laminar. the results include pressure distribution, opening force, leakage, and stiffness of the gas film. First, the unidirectional seal is modeled and the results are compared with the experimental results. The results show that the effects of turbulence can be ignored. In the following, two different geometrical models of the bidirectional grooves are used and the results are compared. The results show that the opening force and stiffness of the gas film in two bidirectional groove models are higher than the unidirectional groove. Also, the leakage values in these two models are reduced compared to the unidirectional groove.

Axial flow compressors are subject to two distinct aerodynamic instabilities, rotating stall and surge, which can severely limit the compressor performance. These instabilities are disruption of the normal operating condition and can severely lower the compressor performance. One of the famous models of predicting these instabilities is the Moore-Greitzer Model. This theory has been used extensively in stall and surge analysis. In this study a mathematical algorithm is used to convert the system of three simultaneous non-linear third order partial differential equations (PDE) to a system of three simultaneous ordinary differential equations (ODE), and then to solve this system through applying a third order polynomial introduced as the characteristic curve proposed for axial compressors. a control parameter called “B-Greitzer” is also used to predict the performance of the compressor. Results shows that the amplitude of disturbances are periodically increased as B > 0.3, and converges to a constant limit for values of B < 0.3. Moreover, it is observed the domain of stream function and pressure ratio are totally extended as the value of B-Greitzer is increased, and the turns of perturbation cycles are also increased. Finally, it is found that the value of B = 0.26 can be considered as a critical point to prevent the axial compressor from operating in rotating stall and surge modes.

As the energy generation with photovoltaic systems is exponentially growing, the need for prediction of generation power is much more important than ever. In this paper, based on the experimental data of the solar site along one-year, the photovoltaic systems of monocrystalline and polycrystalline panels for 2.5 kW solar power plant at Vali-e-Asr University of Rafsanjan, has been modelled with artificial neural network. To obtain the optimal model for the desired panels, different variables have been considered as the input and output of the model, while all variables are: panel temperature, direct radiation, the output power and the kind of panels (monocrystalline and polycrystalline). Also sensitivity analysis has been performed for different input and output parameters as well as for the number of different layers of neurons and functions. The results show that the model with the input of temperature and radiation and the output of the power of monocrystalline and polycrystalline panel is the most accurate model with lowest error.

The present study aims at investigating a couple stress ferro-fluid lubricant effects on the performance of a squeezed film once a uniform external magnetic field is applied. For this purpose, Shliomis ferro-hydrodynamic and couple stress fluid models are employed. The considered geometry is parallel elliptical plates. The effects of couple stress, volume concentration, Langevin parameters and aspect ratio on squeeze film characteristics including time vs. height and load carrying capacity are investigated. According to the results, employing couple stress ferro-fluid lubricant in the presence of the magnetic field leads to an increased performance of the squeeze film. On the other hand, variation of aspect ratio leads to significant effects on the squeeze film characteristics. The present study aims at investigating a couple stress ferro-fluid lubricant effects on the performance of a squeezed film once a uniform external magnetic field is applied. For this purpose, Shliomis ferro-hydrodynamic and couple stress fluid models are employed. The considered geometry is parallel elliptical plates. The effects of couple stress, volume concentration, Langevin parameters and aspect ratio on squeeze film characteristics including time vs. height and load carrying capacity are investigated. According to the results, employing couple stress ferro-fluid lubricant in the presence of the magnetic field leads to an increased performance of the squeeze film. On the other hand, variation of aspect ratio leads to significant effects on the squeeze film characteristics.

Nowadays, one of the suitable technologies in terms of power generation and saving energy with high efficiency is using the multigeneration systems that renewable fuels are used as an alternative to fossil fuels. In the present study, a multigeneration system including biogas fired gas turbine, Organic Rankine Cycle (ORC), domestic water heater, Reverse Osmosis (RO) unit and Proton Exchange Membrane (PEM) electrolyzer. The proposed multigeneration system is assessed from energy and exergy viewpoints. After that, a comprehensive parametric study is carried out to show the effects of some key parameters (including pressure ratio of compressor, condenser pressure, evaporator temperature, preheater temperature and inlet temperature of gas turbine) on main performance criteria of the multigeneration system. Finally, the multi generation system is optimized from thermal efficiency point of view. The optimization results indicate that the thermal efficiency has optimum values for evaporator temperature and pressure ratio of compressor. Also, results show that the values of generated power, produced fresh water, thermal efficiency, exergy efficiency, produced hydrogen and total exergy destruction are calculated as 1192 kW, 5.584 kg/s, 55.74%, 30.56%, 1.455 kg/hr and 2827 kW, respectively.

This study presented a new method to accurate design of shell and tube heat exchanger network. It’s considered some parameters as decision variables such as the design of determined the flow path of each fluids, number of required shell side, allowable velocity and pressure drop, number of tubes, number of passes in shell and tube sides, length of tube, layouts of tubes, size and percentage of baffle cut, shell diameter, tube diameter, tube pitch and experimental equations to calculate pressure drop and heat transfer coefficients in shell and tube side heat exchanger units. It has been used whale algorithm to achieve optimum total annual cost for heat exchanger unit. The total annual cost is as objective function that included capital and energy costs. The results showed in two cases studies including four and ten streams in shell and tube heat exchanger networks. The total annual cost reduced almost 20.55% and 14.40% compared with others for two case study.

Motion of drops in microchannels is encountered in a wide range of applications, such as encapsulation, DNA analysis, and drug delivery. In this study, the formation of drops in a Y-junction microchannel is numerically investigated. To this approach, the Ansys Fluent software is used. To verify the simulation, results are compared to the previous experimental data. The comparison depicts that the current simulation has a deviation of less than 10% with previous experimental results. Effect of change in the flow rate ratio (0.6≤Q≤25.2) on the flow pattern, size of drops, the distance between them, and the breakup time are studied for the four junction angles of the microchannel (45, 90, 135 and 180 °) in details. Three flow regimes are observed: parallel, squeezing and dripping flow. Results reveal that the junction angle of 135° is the optimum angle for the formation of the smallest drops in the microchannel. It is also observed that, at the optimum angle, increasing the flow rate ratio from 0.6 to 25.2 decreases the size and time of drop formation by factors of 3.83 and 3.33, respectively. However, it has an adverse effect on the distance between the drops which results in 4.33 time larger distance between formed drops.

In this study, the thermal performance of inner groove oscillating heat pipes (IGOHP) with deionized water as a working fluid has been experimentally investigated. The results showed that in the filling ratio, 60% of the IGOHP has the lowest thermal resistance and the highest thermal conductivity. Then at the best filling ratio (60%) the IGOHP was investigated at different heating powers and also at different inclination angles. The achieved results indicated that in heating power of less than about 75 watts in 70° and 90°, thermal resistance is higher than angles of 5°, 15° and 30°, and among them, the angle of 15° had the lowest thermal resistance, but in heating power of more than 100 watts The performance of the IGOHP at 90° was better than the other angles, Also, the start-up of the IGOHP at an inclination angle of 15° occurred earlier than the vertical position. In this research more remarkable result is that at heating power above 200 watts, the thermal resistance of the IGOHP at an angle 15° is approximately equal to the angle of 90°, which in turn is a point for the IGOHP, which can promise to solve the problem of oscillating heat pipes at angles close to the horizon.

In the present study, a combined Lattice Boltzmann method-smoothed profile method is used for simulation of a liquid-solid fluidized bed with non-Newtonian Power-law fluids. The geometry is contained circular monodisperse particles in a cylindrical channel. The hydrodynamic model of the flow is based on the Bhatnagar–Gross–Krook Lattice Boltzmann method and the smoothed profile method is adopted to enforce the no-slip boundary condition at the liquid-solid interface. A numerical instance of a fluidized bed involving 416 particles is presented to demonstrate the capability of the combined scheme. The results for both Newtonian and non-Newtonian liquids have compared with the experimental results of other researchers. Porosity and bed height results of Newtonian fluid (water) compared with the Richardson-Zaki equation which was showed good correspondence. Non-Newtonian fluid results compared with the Yu equation for estimating minimum fluidization velocity and the Machač-Ulbrichová equation for porosity and bed height, yet by considering uncertainty in non-Newtonian equations results of comparisons are acceptable.

In this research, the entropy generation by steady two-dimensional boundary layer flow of a hybrid nanofluid on a porous vertical flat plate with the magnetic field is studied. The governing equations by using of similarity solution transformed to nonlinear ordinary differential equations and also effect of buoyancy, magnetic, the volume fraction of nanofluid are investigated particularly on speed, temperature, and dimensionless entropy generation. The results showed that in entropy generation with an increase of similarity parameter, the thermal profile and absolute value of thermal gradient are decreased and therefore dimensional thermal entropy generation is decreased and trends to zero and after a certain amount thermal boundary layer is disappeared and just the entropy of fraction loss and magnetic field are produced. Also, the investigation shows with increasing density of nano particles, the speed of nanofluid decreases by about 30 percent and increases the thermal profile about 40 percent. The results also show with increase the magnetics, the speed of nanofluid decreases about 15 percent and decreases thermal profile about 10 percent.

This paper presents a model predictive control algorithm for path following of an autonomous vehicle in a curvilinear path. To define vehicles’, motion a nonlinear bicycle model of vehicle with 6 degrees of freedom is employed. Some kinematic constraints imposed to the state and control variables, as well as constraints on vehicle acceleration and braking deceleration for desired path following of the vehicle. Then, an appropriate prediction horizon and a quadratic optimization model is formulated and employed for minimizing the path following error and control variable’s variation of the vehicle. In the optimization computation process suitable weight coefficient for all state and control variables are considered. Finally, a simulation study is performed to analyze the capability and efficiency of the presented algorithm for following the desired path. The simulation results show that the presented path following algorithm is acceptably able to follow the desired path with acceptable accuracy and desirable speed.

In this study, thermal modeling and optimization of combined production of cooling, heating, power (CCHP) and desalinated water system are carried out. In the cogeneration system, the desalination system is coupled with the CCHP plant which is supplied its required energy by the prime mover and an auxiliary boiler to meet the cooling, heating, electricity, and freshwater needs of a hotel. In the traditional system, the hotel demands are met separately, by each of the equipment of the cogeneration system. Coupling the two systems together will reduce environmental pollution and annual costs compared to the traditional system. The results show that the annual cost and penalty of pollutant emissions for the cogeneration system decreased by 39.34% and 40.65%, respectively, compared to the traditional system. Also, the increase in energy consumption of equipment with their performance and efficiency in optimal partial load compared to the maximum performance and efficiency in a particular partial load has been calculated, the maximum of which in the eighth month for absorption and electrical chillers by 91% and 94% and per month Twelfth for backup boiler and diesel engine at 45% and 6%, respectively.

In the present paper, the effect of addition of a functionalized graphene oxide (FGO) on the mechanical properties of an epoxy adhesive was investigated. GO was first prepared by oxidation of graphite using Modified Hummers’ method. Then silane coupling agents 3-aminopropyltriethoxysilane (APTES) was used for surface modification of GO. The solution mixing method is used for dispersing 0.1 wt%, 0.2 wt% and 0.3 wt% amine-modified graphene oxide (GO-NH2) in the epoxy adhesive to investigate the tensile and shear properties of the nano-composite. The tensile and shear properties of the neat and GO-NH2 reinforced epoxy adhesives were determined using the bulk and the thick adherend shear test (TAST) specimens, respectively. Significant improvements in the mechanical properties have been observed by the addition of nano-fillers in epoxy adhesive. The highest improvement in strength was obtained by 0.1 wt% loading of GO-NH2. So that, the addition of 0.1 wt% of FGO increases the Young’s modulus, tensile strength, toughness and shear modulus by 35% , 44%, 53% and 34%, respectively.

The flow of micronutrients into micro channels and the manufacture of micro fluidic devices has been an important topic in recent decades and has been applied to various industries and sciences including biological sciences, pharmaceutical, food, water and wastewater, minerals and more. Many scholars and researchers today are looking for techniques to model two-phase currents of this type. The research method in this paper is based on experimental and numerical methods. Experimental experiments were carried out on a rectangular micro channel with a height of 200 μm. Due to the dilution of the coupling current under investigation, the particle size used is 20, 31.7 and 51.7 microns with a density of 1.05 g / cm3 and a refractive index of 1.59. Also, the studied regime of Stokes with Reynolds number is lower than one and laminar and thus ignores the turbulence effects of the current.As the Reynolds number increases, particle settling decreases

In this paper, a cascade solar water sweetening still with the capability of installing latent heat thermal energy storage system (LHTESS) was fabricated, and the Glauber salt as a phase change material (PCM) was used in the thermal reservoir for thermal energy storage. Application of weir on the cascade edge leads to force water flow on the absorption sheet and increases the residence time in the apparatus. Thermal performance of the still with (LHTESS) and without thermal energy storage system (WLHTESS) were analyzed at different days. Results showed that the amount of sweet water productivity in WLHTESS is higher than that of LHTESS at the sunny days. However, after the sunset, the amount of produced sweet water in the LHTESS is considerably greater than of the WLHTESS. Furthermore, results showed that increasing the flow rate of sour water from 50 to 150 ml/min for the WLHTESS decreased the sweet water production from 423 to 252 ml/m2 day and for LHTESS from 396 to 235 ml/m2 day.

In the current study using the enthalpy-porosity method, natural convection heat transfer in the melting process of Carreau non-Newtonian PCM was investigated in porous media within the space between two co-centric vertical cylinders. First, continuity, momentum and energy equations were developed for the non-Newtonian fluid melting process. Then to obtain a general pattern for  modeling the melting process, the aforementioned equations in the dimensionless mode were presented. To assure the accuracy of calculation, this study also controlled for the independency grid of the geometric model. To check for the validity, the results of this study were compared with prior studies. The results were expressed in the form of graphs of changes in melting volume fraction according to the change in Stephan number, Carreau index and porosity coefficient. The results showed that by increasing the aspect ratio from 0.5 to 2, Nusselt number and velocity increase but the velocity of melting decreases. The melting rate also increases with increasing Stefan number as well as decreasing porosity parameter. In addition, in a porous medium a change in the carreau index has no effect on the melting process rate.

Today, the use of fossil fuels is worrying due to the excessive increase of greenhouse gases, especially CO2. This issue has negative and irreversible effects on human health, the environment and the economy. The methane bi-reforming process which is a combination of steam reforming and dry reforming of methane, is a new and promising method to reduce CO2 emissions in synthesis gas production. In this study, CO2 inhibition and determining the appropriate ratio of hydrogen to carbon monoxide was investigated. The range of the operating temperature and pressure was 525-850°C and 12-18 bar according to the literature. The location of the recycle flow for economic savings and prevent wastage of methane gas, as well as the suitable ratio of steam to feed for high-efficiency reforming reactions were also investigated. The thermodynamic model selected in this study is very well adapted to industrial data with a maximum deviation of 10%. The simulation results showed that the suitable operating conditions for CO2 inhibition are temperature range of 550-650°C and pressure of 15.4 bar. Also, the appropriate ratio of steam to feed of process was considered as three. Water-gas shift reactor was a suitable location for recycle flow entry. Under these conditions, CO2 inhibition is well performed and the appropriate ratio of hydrogen to carbon monoxide (2.29) is produced as a suitable feed for the alcohol industry.

In the present study, the energy performance of a villa building in Isfahan was studied during a year using DesignBuilder (Ver. 6.1) and the results were evaluated with energy bills including both gas and electricity consumptions. After identifying the energy performance weaknesses of the building, the skin was enhanced in two scenarios to meet the requirements of code No 19 and ASHRAE 90.2. It is found that the energy required for cooling and heating of the existing building can be saved by 63% and 70%, respectively, in compliance with the requirements of code No 19 of and ASHRAE 90.2. The results also show that despite all the weaknesses of code No 19, the energy intensity of the building's sector in Iran can be saved considerably only by following the regulation. The role of green roofs in terms of the energy saving in these two scenarios was also studied. In addition to other benefits of green roofing from architectural and environmental perspectives, an extra reduction in energy consumption by 9.5% and 4% can be achieved by a typical green-roof in a building based on code No 19 and the requirements of ASHRAE 90.2.

In this paper, asymmetric rolling process of metal sheets is investigated by method of upper bound. In analyses, the contact arches of the rolls are replaced by their chords. The material under deformation is divided into upper and lower regions separated by a line parallel to the midline of the sheet at exit. The intersection points of the chords with the mentioned line, boundary of the upper and lower regions, are selected as the origins of the cylindrical coordinate systems. Each region is divided into three deformation zones and based on the proposed velocity field presented, shear, friction, internal deformation and the total power terms are calculated. The total power is optimized with respect to the positions of the origins of the cylindrical coordinates systems and the positions of the neutral points. The results of the analysis including the required torque, rolling force and the curvature of the sheet at the exit, are compared with the analytical and experimental results of other researchers, as well as numerical simulation results obtained from Deform software. Finally, the effects of the asymmetric factors of the process, on the required torque, the rolling force and the curvature of the deformed sheet have been investigated.

In this study, a method for uncertainty analysis of laminated rectangular plate made of glass/epoxy with interlaminar crack (delamination) in loading mode I, II and I/II is performed using energy criterion. Limit state functions have been obtained to analyze the reliability of delamination growth in each loading mode according to the concepts of fracture mechanics and energy release rate. By using random variables and limit state functions according to energy criterion, uncertainty assessment will be performed using Response Surface Methodology (RSM). The main idea of the response surface methodology is to approximate the implicit response surface function using an explicit mathematical equation with random variables involved in the limit state function. Since the approximation of the limit state function is explicit, the first/second order reliability method can be used to estimate the probability of failure. It was indicated that in all modes the probability of delamination growth calculated by the surface response method has the highest value. Finally, the effects of initial delamination, laminate layer and loading in different modes on the delamination growth are obtained from the perspective of the reliability of composites laminates.

The fine-grained metals and alloys produced in various ways have good mechanical properties such as high strength, high toughness and proper formability and have certain applications. In recent years, studies of different methods of producing and improving the mechanical properties of specimens have been the subject of much research. Recently, the processing of this type of material using severe plastic deformation has received considerable attention from researchers. In this study, in order to modify the conventional ECAP method, The copper specimen was subjected to severe plastic deformation by means of a new die named combined die. In order to compare the mechanical properties of the produced specimens with this method and ECAP, the experimental tests were performed. By investigation the hardness values at different points from the cross-section of the specimens as well as the determination of strength and grain size in the created microstructures, it was found that after performing the present method, a finer grain structure with a higher degree of hardness, yield strength and Ultimate tensile Strength could be obtained compared to the ECAP method

Todays, the discussion of the droplets interaction with fluid is one of the most challenging topics in multi-phase (liquid-liquid) flow. In the present work, an experimental study was done to investigate the oil droplet rising through a stagnant fluid water and crossing the water-oil interface. Thus, an image recording and processing have been used. The employed oil in the experiments is a heavy crude oil extracted from an Iranian oil reservoir and the drop diameter is controlled in the range of 2 to 3mm. Firstly, the range of the obtained dimensionless numbers was compared and validated with the experimental data of the other works. The results showed that in the applied conditions, the drop shape is ellipse-like and the Weber number decreased by increasing aspect ratio. Moreover, residence time versus drop diameter did not follow a uniform procedure. Finally, the best correlation was introduced to predict the residence time of oil droplets by comparing the experimental results with the presented empirical equations

In the last years, Ni-W coatings attracted a lot of attention because of high hardness and excellent corrosion resistance. At the current study, Ni-W coatings with different amounts of tungstate ion concentration and with the current density of 10-70 mA/cm2 were plated by pulse method on the copper substrates. The morphology and chemical composition of coatings were characterized by Scanning Electron Microscopy (SEM) and, Energy Dispersive X-Ray Analysis (EDS). Grain size calculations was conducted by means of X-ray diffraction (XRD). The hardness of coatings was analyzed by Vicker’s micro hardness tester. Tafel Polarization and electrochemical Impedance methods were used to evaluate the corrosion resistance behavior of the coatings in M3.5% NaCl solution. The results displayed that coatings were obtained from the bath with 60 g/l tungstate concentration, current density of 70 mA/cm2 and duty cycle of 20% showed highest microhardness (719 HV) and maximum corrosion resistance (7.39 KΩ.cm2). Also with decreasing the current density from 70 to 10 mA/cm2, microhardness decreased to (570 HV) and the corrosion resistance declined to 2.78 KΩ.cm2.

Tip Leakage vortex in axial compressor is source of unsteadiness and loss in flow field, so it is very important to investigate its controlling method. The aim of this article is numerical simulation of plasma actuator effect on tip leakage vortex in low speed axial compressor rotor. By applying linear distribution of body force at upstream of rotor on casing, effects of plasma actuator on tip leakage vortex have been investigated. Numerical simulation confirm that plasma actuator at blade tip region boost the flow momentum and in addition to decreasing the size of tip leakage vortex and reduces blockage due to the flow separation from blade surface, leads to decreasing loss in tip region. In addition, Plasma actuator can eliminate leading edge spillage and Trailing edge backflow in tip clearance region. Furthermore, the results show that plasma actuator caused the stall margin of the rotor blade row to increase by 5.2%.

In this research, the thermal-hydraulic performance for non circular tube with louvered and flat fin in cross flow of the air at 70 ≤ ReH ≤ 350 were numerically investigated. The comparison of the thermal-hydraulic performance between louver fin and flat fin having cam-shaped tube has been carried out. Geometrical parameters of louvered fin such as louver length and louver angle and louver pitch are investigated. The results indicate that in the range of Reynolds testing, the thermal-hydraulic performance of cam-shaped tube with louvered fin 18.99 to 26% is more than circular tube with louvered fin. Investigation the geometrical parameters of louver fin reveal that by increasing the louver angle (15 to 25o) or louver length (6 to 12 mm), the thermal-hydraulic performance increases by about 1 to 8 percent. However, increasing the number of congresses (4 to 5) has a small effect on the thermal-hydraulic performance of the cam-shaped.

In the present paper, CFD simulation and simultaneous exergy analysis of parsian gas refinery 104 unit furnace is done in order to decrease thermal wastes and fuel consumption optimization. This furnace has six burner, 29 meter height and 5.35 meter diameter in the combustion chamber and using in order to heat natural gas and refresh the molecular screening. Simulations were performed using species transport model in combustion with turbulence and radiation. Numerical results have been compared with experimental data and a good agreement has been seen between these results and the maximum relative error is 3.91%. Numerical results show that decreasing excess air from 20% to 5%, leading to decrease 28% of outlet thermal wastes and preheating the combustion air temperature from 308.15 kelvin to 458.15 kelvin, leading to decrease 20% of outlet thermal wastes. In the optimum operation of furnace, it’s exergy efficiency increasing from 20% to 31.34% and it’s thermal efficiency increasing from 71.11% to 78.9%.

In this paper, the hydrodynamic and thermal behavior of〖 Fe〗_3 O_4ferrofluid flow in a horizontal U-shaped copper tube on a surface, is studied experimentally under the effect of a variable magnetic field. The ferrofluid flowed at a low Reynolds value through a U-shaped tube under the thermal boundary conditions of the tube with uniform heat flux affected by magnetic field in some regions. The purpose of the study was the empirical investigation of the effects of using nanofluid, volume percentage of nanoparticles, and frequency on variable magnetic field, and the effect of constant magnetic field on ferrofluid behavior in three regions of the tube, namely straight inlet, curvature, and straight outlet sections. Analysis of the percentage of impact of each parameter in different sections showed that the variable magnetic field had the greatest impact by increasing the volume percentage of nanoparticles in the straight inlet section of the tube by 8.8 % at a frequency of 50 Hz.

To improve the performance of photovoltaic-thermal (PV/T) system through thermal management, the effects of four different ‎geometry of cooling pipes including circular direct pipe (CDP), circular sinusoidal pipe (CSP), rectangular zigzag duct (RZD), ‎and rectangular step duct (RSD), type of refrigerant, and flow rate are investigated on the temperature distribution, thermal, and ‎electrical efficiencies through numerical modeling in this paper. The results show that RSD has the best performance, so that the ‎thermal and electrical efficiencies have been improved by 15.2% and 2.2%, respectively. On the other hand, the fluid head loss ‎in RSD is increased by about 2.6 times compared to that of CDP. The results also indicate that microencapsulated phase change ‎material (MPCM) fluid leads to an increase in the thermal efficiency of about 40% respect to the water, however, Ag nano-fluid ‎just improves the thermal efficiency by 28%. Increasing the flow rate of refrigerant also caused to enhance the heat transfer ‎coefficient and leads to a decrease in the average surface temperature of the PV panel by 6.4oC and 7.5oC in CDP and RSD, ‎respectively.‎

The study on the fatigue cracks growth of the carbonized bolts of the cylinder head in the gasoline engine was performed in two experimental and numerical sections. The experimental section of the study included chemical composition determination, tensile properties, hardness, microstructure, and fractography. Scanning electron microscope (SEM) observations of the fracture surface identified fatigue as the main cause of premature bolts failure with an approximate fatigue life of 1.44×10^8 cycles. The crack initiates from the carbonized surface layer of the bolts, where impurities of oxide compounds and cavities help to propagate the crack until final faracture. The numerical section of the study included stress analysis and fatigue crack growth. Stress analysis showed that the maximum stress created in the bolts is about 4% more than the standard value. High-stress concentration in the threaded zone is one of the factors in crack initiation that the cyclical force of combustion pressure has caused the propagation of fatigue cracks. Numerical analysis of fatigue also showed that the presence of cracks to a depth of 0.12 mm is the origin of premature failure. Comparison of the two experimental and numerical sections showed that the calculated crack depths are consistently consistent with the observations of the oxide layer of optical and scanning electron microscopes.

In this study, management of the electronic board temperature using an aluminum heat sink with9 fins containing phase change material (PCM) was investigated, experimentally. The critical temperature of the electronic board was 85 ° C and according to this temperature, stearic acid was selected as PCM for temperature management of the system. Experiments were performed in the wide power range and in different volume fractions of PCM. Using PCM at 11% volume fractions at power of 4 W significantly increased 20 minutes the operating time of the electronic board. Increasing the volume fraction of PCM from 11% to 50% at the power of 6 W, increased PCM melting range by 878 seconds and increased the operating time by 14 minutes. Experiments with alternative power (10 minutes on and 80 minutes off) in several consecutive heating-cooling cycles and at high powers (10, 15 and 18 watts) showed that the sensitivity of heat sink performance to PCM volume percentage at high powers is more than in low powers.

Heat management of fuel cell is necessary to maintain the cell temperature in an appropriate temperature range (60-80℃) and to make a uniform temperature distribution in the cell, because the temperature control has a significant impact on the performance, efficiency and life cycle of a polymer membrane fuel cell. One of the passive cooling methods is to use phase change process. The heat pipe facilitates a uniform temperature control of the cell without consumption of electric power. In this paper, a heat pipe for cooling a low-power 200-watt fuel cell is proposed, and the two-phase and transient flow of a heat pipe with water as working fluid is modeled. In order to investigate the performance of the heat pipe, the volume of fluid model and the porous medium model have been used. Simultaneous modeling of evaporation and condensation processes in the heat pipe is performed using a user defined function in the ANSYS Fluent software. The results show that utilization of thermal pipe leads to maintain the temperature of the evaporator section at 69℃, which is equal to the temperature of the bipolar plates of the cell, and it is in the appropriate range of the operating temperature. In fact, the heat pipe is able to dissipate the heat of the cell properly and to maintain a relatively uniform temperature distribution inside the cell, simultaneously. The low values calculated for the thermal resistance of the heat pipe indicate an improvement in the performance of the fuel cell cooling system.

In this paper, a tempering glass furnace is numerically analyzed and multi-objectively optimized for energy performance investigation. In order to manufacture high-strength tempered glass, the glass must be heated inside the furnace at above 700 °C. Numerical modeling is simulated using computational fluid dynamics and temperature distribution in the furnace is obtained by studying the radiation model. Numerical analysis results are validated with experimental data. The multi–objective optimization is performed to reduce the furnace energy consumption and the primary cost of constructing the furnace, coupled the production of high quality glass tempered. The effects of several design variables are investigated based on genetic algorithm. In optimization, the effects of several important design variables are investigated, which are: the distance between the torches and the pieces of glass inside the furnace, the distance between the torches with each other, the furnace length, the furnace width, the furnace height and ect. The results show that the variation in the value of the design variables leads to reduction in the cost of manufacturing and consumption of fuel, coupled the production of tempered glass with the appropriate standard.

In this paper, the low-velocity impact response on fiber metal laminate (FML) plates is investigated using three new models. The boundary conditions are considered as simply supported and the behavior of the material is linear elastic. The relationships are based on classical plate theory and the Navier method is used to solve the governing equations. The mass of the impactor is considered to be large and therefore the impact response is categorized as quasi-static. In the first impact model, the contact force history is first considered as a half-sine and then the maximum contact force and contact duration are calculated. In the second model, a two-degree-of-freedom (TDOF) spring-mass system is expressed by calculating the effective contact stiffness using a fast iterative scheme. In the third model, which is expressed for the first time in this paper, the plate is considered as a series of masses and springs constructing a multi-degree-of-freedom (MDOF) spring-mass system and the applied force on the last spring is introduced as the contact force. Validation of these models is done by comparing the results with the analytical and experimental results and shows good agreement. Results show that the new MDOF sprin-mass sysem is more accuracte for calculating the deflection of the plate at the impact point rather than the TDOF sprin-mass system.

The collision of deformable drops in the flow between two opposite moving plates (shear flow) has been studied numerically by solving the Navier-Stokes equations completely. The numerical finite difference/front tracking method is used. This method is a mixed of capturing and drop tracking methods. For a fluid bulk, a structured fixed, cubic and staggered grid would be used, but the drop is tracked using a separate grid triangle irregular and moving grid with a lower dimension than channel fluid grid. The surface tension effects are accounted for by adding appropriate source terms into the governing equations. The results showed that as the computational domain increases, the droplets are more affected by the vortex created by the intermittent reaction of the walls, and their crossing themselves motion path turns to return path. Also, by increasing the effects of inertia due to the increase in Reynolds number, the droplets make a reciprocating motion in the larger channel. As the capillary number increases, the droplets move further towards each other.

The heat control subsystem of each satellite is responsible for providing the allowable temperature of the equipment of that satellite. Naturally, if this subsystem of the satellite is not designed properly, the satellite mission will not be performed properly. In the present work, small-scale satellite heat control subsystems have been designed by using Thermal desktop and Sinda softwares. This simulation is based on two cold and hot critical states and the results are compared with the available experimental data in the literature, which has about 9% difference. According to studies conducted in this research, the most suitable heat control equipment are paints, coatings, insulators and heaters. According to the analysis, the cargo subsystem experiences the temperature about -19 to 28 degrees Celsius before applying the proposed thermal scheme, which using AMJ-700-IBU paint, its temperature is in the range of -10 to 47 degrees Celsius that is within the allowable temperature range.

Thermal motors are used to generate mechanical energy using heated water produced by different equipment, without environmental pollutions. In this paper, a thermal engine is first designed and manufactured using Nitinol wires. Then, the effects of different parameters on angular velocity, output torque and engine rotation time are investigated. The results show that increasing hot-water temperature and decreasing cold-water temperature increase the angular velocity. However, as long as transformations get completed, these parameters have a neglectable effect on the torque. In addition, increasing the wires’ diameter and number and using the friction-reducer beads, increase the output torque and angular velocity. It is also observed that decreasing the transformation temperature increases the duration of rotation and angular velocity of the engine. The maximum angular velocity is related to a certain position of the fixed constraints. The maximum torque and angular velocity are calculated to be about 20.601 N.mm and 58 rpm respectively.

In this paper, Isogeometric analysis (IGA) based on nonuniform rational B-splines (NURBS) is developed to study the free vibration analysis of the perforated plates with different open hole shapes and hole patterns. In this way, the governing equilibrium equations of perforated plate and strain-displacement relations are obtained using the first-order shear-deformable plate theory. The optimal number of control points and the order of the NURBS basis functions are determined to perform physical geometry related to perforated plate geometry. The eigenvalue equations with linear stiffness are established using the weak form of motion equations, energy method and Hamilton principle. The vibrational frequencies and corresponding mode shapes of the perforated plate is derived from governing eigenvalue equations. The results of linear vibrations of plate with central hole are validated considering the previously reported data and finite element analysis, which showed a good agreement. Thereafter, the influence of hole size and shape are explored on the linear vibrations of the plate with hole in same hole area ratio. Further, the effect of the triangular and rectangular pattern under the fully clamped and simply boundary conditions is presented.

High-speed flying objects are subjected to temperature variation caused by aerodynamic heat, which reduces flight performance due to instability. Due to high tensile force generated by increasing temperature, Shape Memory Alloys (SMA) may be used to reinforce these structures. In this study, the axial buckling of composite cylindrical shells reinforced with SMA fibers made of Nitinol is studied. Properties of SMA fibers are determined using the Brinson's constitutive model. Governing equations are derived using classical shell theory with the Von-Karman type of geometrical non-linear in conjunction with Love's first approximate accompanied with the static mode of virtual displacement principle. To solve the governing equations generalized differential squares method are used in longitudinal direction. The effect of pre-strain, volume fraction and position of SMA fibers on the critical load of the cylindrical shells are investigated. Results show that shell reinforcement with small percentage of pre-strained SMA fibers significantly increases the critical load. Also, the use of SMA fibers in the longitudinal direction and in the layer close to the inner surface of the cylinder has a favorable result in increasing the critical load.

In the present work, by using the concept of fuzzy derivative, an effective method is presented for analyzing the uncertainty of temperature distribution in a straight thermal fin. In the present study, all sources of uncertainty are considered simultaneously by triangular fuzzy numbers. The proposed method has the advantage of involving the experiences and opinions of the expert about the input parameters through the concept of membership degree. As one of the main results, it has been shown that the use of strongly generalized Hukuhara derivative leads to invalid solutions, while the granular derivative, as a newfound fuzzy derivative, provides reasonable results that are consistent with the physics of the problem. Another result of the present work is a relation that explicitly states the effects of all uncertain parameters on the temperature distribution along the thermal fin. The effect of two parameters including fin length and fin root temperature has been studied in detail. The results of the present work have been compared with the results of the classical Monte Carlo method showing good agreement.

Air intakes play an important role in the operation of aircrafts, so their optimal performance can have a significant effect on the performance of the propulsion system. The purpose of this study was to design and optimize an axisymmetric air intake for a mass flow rate of 10 kg / sec in a free-stream Mach number of 2.5 at sea-level conditions. In the present study, pressure recovery and flow distortion coefficients are selected as functional parameters for optimization. Initially, the parametric design of the intake and the selection of geometric parameters were dealt with, and then the interval of the parameter changes was determined. In this research, the NSGA-II multi-objective genetic algorithm was used as an optimization algorithm; artificial neural network was used to predict intake performance in the optimization loop; for training neural networks 243 Initial geometry has been designed and numerically solved. The genetic algorithm that used has 20 population per generation and 1000 generations. After 1000 generations, the resulting population is selected as optimal geometries. At the end of the optimization, the pressure recovery and flow distortion were improved by 4.4% and 49%, which indicates the efficiency of the optimization process.

In this paper, the mixing efficiency of the ejector in the ejector expansion refrigeration cycle with condenser outlet split using R134a as refrigerant is investigated. Considering the effects of non-equilibrium expansion of the flow in the primary nozzle, a correlation has been derived with the aid of available experimental results to correct the mass flow rate resulted from the homogeneous equilibrium model. Two thermodynamic models, one based on the mixing pressure correction and the other based on the secondary flow velocity correction, have been compared. According to the experimental results, in the model based on the mixing pressure correction, mixing efficiency is in the range of 0.09 to 0.32 and in the model based on the secondary flow velocity correction, mixing efficiency is in the range of 0.03 to 0.3. However, in thermodynamic analysis of the ejector expansion refrigeration cycle, the mixing efficiency is considered in the range of 0.7 to 0.9. The results of thermodynamic analysis based on the mixing efficiency obtained from the experimental data showed that there are temperature ranges for condenser, low-temperature evaporator and high-temperature evaporator in which the ejector is not able to supply secondary flow. However, in the same temperature ranges, thermodynamic analysis with mixing efficiencies in the range of 0.7 to 0.9 shows that the ejector has the ability to supply secondary flow.

In this paper, the performance of a closed-loop dynamical system is investigated in the presence of controller, actuator and sensor. Usually, in analysis, the dynamics of sensor and actuator are assumed to be ideal and they are ignored however these components have dynamic practically. Since, the function speed of the sensor and the actuator must be more than the speed of dynamic system, it is reasonable to separate the equations of the closed-loop system, in the presence of the actuator and sensor, into slow equations (the dynamical system’s equations) and fast equations (equations of actuator and sensor). This paper focuses on this issue and the modeling of the closed-loop system in the structure of singular perturbation systems with the breakdown of fast and slow operating modes. Some theorems in the area of stability analysis and stabilization of the closed-loop system are given. Finally, simulations have been carried out for a mechanical example and it has been shown that the dynamics of the actuator and sensor should be faster than the dynamic system to achieve the desired results.

The efficiency of an exhaust manifold in a CI internal combustion engine is affected by its geometrical parameters and hot gases flow parameters. In this study, the geometry of an exhaust manifold with 〖90〗^° bend in its runners is modeled. The effects of plenum diameter and runner diameter on the flow and heat transfer characteristics are numerically simulated. The numerical simulations are done by the finite element method in the Comsol Multiphysics software package. After generating an appropriate grid having an appropriate number of elements distributed smoothly in the model, the Navier-Stokes and heat transfer equations are discretized by a second-order scheme. Since the flow in the exhaust manifold is turbulent, the standard k-ε turbulence model is applied. After validating the simulations via comparing the results with experimental data available in the literature, the diagrams of velocity, pressure, and Nusselt number are plotted and then interpreted. The results show that as the plenum diameter and runner diameter increase, the exhaust velocity of hot gases decreases and the backpressure increases while the Nusselt number at the outlet of the exhaust manifold decreases.

Nowadays, the use of lasers in welding titanium alloys has special applications in high-tech industries. This study aims to extract the statistical model showing the effect of changes in the diameter of laser beam diameter and distance in line thickness welding temperature. At first, For establishing this model, the required experiments were designed by the Taguchi method and then evaluated using the finite element method. The surface response method is used to extract the statistical model based on the variation of laser beam diameter and distance through the workpiece thickness. By the analysis of the variance, the statistical model error was evaluated in an acceptable range. According to the evaluated results, the influence percent of the distance along with the workpiece thickness and the laser beam diameter is 76.67 and 97 %, respectively, on the welding temperature. By increasing the diameter of the laser beam, the amount of the welding temperature is significantly reduced. For laser welding of Ti6Al4V, the best laser beam diameter is between 0.2 and 0.24mm.

In this paper, the fin profile of heat exchangers change effect on the heat transfer and fluid flow pattern has been investigated. In order to best model presentation to the user by comparing the various models results. For numerical simulation and discretization of governing equations, the finite volume method and for coupling the velocity and pressure fields, the SIMPLEC method have been used. The inlet fluid to heat exchanger is Newtonian; the fluid is steady, incompressible and according to Reynolds number range, is turbulent; the no-slip condition has been applied on the walls.Also the inlet fluid temperature is 573K and the heat exchanger walls have constant temperature equal to 353K. The numerical results have been compared with valid data which illustrated good agreement. The average Nusselt number on the wall, pressure drop, output temperature, and velocity variation have been analyzed in different models with more details for two mass flow rates. The results show that the heat exchanger with 6 fins and m ̇=0.04 kg⁄s has best performance and presented the high nusselt and PI and also low pressure drop.

The ability of baffles in increasing the hydrodynamic damping of sloshing in circular cylindrical containers is investigated in this study by analytic, numerical, and experimental methods. Baffles as separate components are installed in tanks containing fluid and can change various aspects of dynamic characteristics of sloshing. The primary objectives of this study is to examine the relative effectiveness of baffle arrangements to provide experimental data for the verification of the numerical models and to recommend a practical baffle arrangement that would be effective over a range of frequencies. The results show that the proposed baffle arrangement has a very effective effect on the damping and sloshing frequencies, and satisfies the anticipated design requirements optimally. The results also display that at liquid height close to the bottom of the container, the theoretical curve predicts that the fundamental frequency of the sloshing will decrease, while the experimental frequency not only decreases but also shows an increasing average. In addition, the results of finite element method and finite volume method in calculation of sloshing frequency and damping are highly consistent with experimental results.

The use of sunshades is one of the methods that is sometimes recommended to improve the performance of direct evaporative coolers. So far, limited research has been done on the role of sunshades in reducing water consumption and increasing the efficiency of swamp air coolers. In this paper, a simplified practical model is presented to simulate the performance of direct evaporative air coolers under non-adiabatic conditions. The performance of the proposed model is validated against experimental data in conditions where the air cooler is affected by solar radiation. The results showed that by eliminating the effect of solar radiation, the cooling efficiency of the cooler will be improved by about 5% and water consumption will be reduced up to 6.5%. Finally, the effectiveness of four different common sunshades was evaluated and compared. Results indicated that the use of sunshades of the same size as the roof of the cooler has a negligible effect. It was also found that the sunshades with dimensions twice the size of the cooler roof and with a diagonal edge have a relatively good performance.

Modeling of processes and systems is very essential step in control engineering. This paper considers a two-degree-of-freedom launcher which can move in Azimuth and Elevation directions and presents a model of the system. In this model, the relationships between inputs and outputs of the system and their interactions are carefully derived. In addition to the effect of controlled inputs, all other effective factors such as friction and backlash on the behavior of the system are considered. For this purpose, two types of Viscous and Coulomb frictions have been considered in different parts of the launcher, and a model of them is presented. Furthermore, in order to use this modeling in control procedure, a single-input single-output approach (SISO) is presented. In other words, using this view, both Azimuth and Elevation direction of the launcher are considered independent of each other, and the interferences between these two directions are considered as disturbance inputs.

In this paper, the buckling of rectangular sheets with variable thickness under in-plane loads is investigated. Each sheet structure under compressive load may buckle at a certain level of load and lose its stability. In analyzing the stability of a low-thickness structure, determining the buckling load is important and necessary. The buckling load depends on some parameters such as geometric features, boundary conditions and type of loading. In this paper, the amount of buckling load was obtained for changes in sheet thickness with different patterns and different boundary conditions. For thickness changes, various modes such as how the changes, starting location, and intensity of the changes are examined. The buckling load was calculated using the Galerkin method as well as numerical methods and compared with the available results. The results showed that the amplitude of thickness changes is the most important parameter affecting the reduction of buckling load. For sheets with trapped edges, the effect of these parameters is more noticeable. Also, asymmetric thickness changes will have a significant effect on the buckling load.

Generally, microstructural changes have been neglected for the material models used for simulation of chip formation process. This event leads to limitation in precision of numerical results compared to what happens in reality. For this purpose, in the present study the effect of microstructure changes in machining process of Inconel 718 super alloy was taken into account by development of multi-step user-subroutine in Finite Element Model (FEM). Firstly, microstructure change was modeled using the Dynamic Recrystallization (DRX) and critical strain criterion. After that, a modified material model was presented and grain size variation was incorporated into the material model for each step and each element during the simulation. At the end, effectiveness and performance of the new material model was successfully evaluated by comparison with corresponding experiments at the different machining conditions. The results indicate that, implementation of microstructure changes in material model plays effective role for simulation of more realistic behavior of material and consequently improvement of numerical results machining.

Maintenance is one of the most important elements in any industry. Next to manufacturing, it probably has utmost importance in the production of industrialgoods.It has even higher priority when rotary machines are used. Having an appropriate algorithm for maintenance can prevent human and financial problems in such industries. In recent times, various methods of remaining useful life (RUL) prognosis have been proposed for rotary machines, but there is not a comprehensive review article that can well differentiate different methods. Herein, after describing the meaning of remaining useful life, the three most commonly used prognosis methods, including data-driven approach, model-based approach and hybrid prognostics approach, are elaborated upon. Subsequent to that, concept and mathematics of RUL in rotary machines for each method, have been discussed. Toward the end, there are constructive suggestions for researchers in this field in terms of dealing with RUL and PHM.