Modares Mechanical Engineering
Year:2020 | Volume:20 | Issue:2 |Papers Count:27

In the present study, a new combined cycle (including a two-step flash evaporation, the Kalina cycle, and a proton-exchange membrane) for simultaneous power and hydrogen generation from Sabalan geothermal wells has been proposed and analyzed from the viewpoints of energy and exergy. The effects of important parameters including separators pressure of flash evaporation, the minimum temperature difference in the pinch point, Kalian higher pressure, superheated geothermal fluid, the ratio of consumed power for hydrogen production and dead state temperature on the amount of produced hydrogen, the net generating power, thermal and exergy efficiencies of the proposed combined cycle have been studied. The results show that for the investigated case in the proposed combined cycle, the amount of the produced hydrogen, net generating power and energy, and exergy efficiency were 1536kg/hr, 12. 83MV, 11. 39% and 43. 64%, respectively. Increasing the pressure of the separators was not effective in increasing hydrogen production, while with increasing the first separator pressure, as well as, the second separator pressure to the optimum pressure, the thermal and exergy efficiency increase. With increasing the temperature of the proton membrane electrolyzer, the produced hydrogen discharge increases and while maintaining cycle net output power, thermal and exergy efficiencies increase. Also, at the optimum point for high-pressure Kalina, the maximum amount of hydrogen production is obtained. The highest amount of exergy degradation was obtained for the protonated membrane electrolyzer, evaporator and condenser 2, respectively.

In the present study, the finite element method based on the shear-lag model was used for stress analysis as well as deformation of the creep stable state of short fiber composites under axial loading. A perfect fiber/matrix interface is assumed and the steady-state creep behavior of the matrix is described by Norton numerical model. Special boundary conditions applied to the unit cell model and imaginary fiber technique has been used. Then ANSYS software is used for the calculation of all stresses and strains at the fiber/matrix interface and the outer surface of the unit cell. Then the results were verified and the values of axial and shear stresses at different points of the composite were investigated. The results show that the composite unit cell can be used as a composite representative for stress analysis. Also, the use of an imaginary fiber technique is a useful and reliable way to achieve a stress transfer model. This Model has sufficient accuracy and contrary to previous studies can predict all stresses and strains in all points.

The advantages and disadvantages of using gasoline and NG as single-fuel is a challenge for researchers in development of SI engines. Singular utilization of these fuels results in some advantages and disadvantages from economics, thermodynamics, pollution and development aspects and make it difficult to prefer one to the other. Assuming that using combination of the fuels can modify the output results, in the present research, different combinations of 100, 90, 75 and 60% gasoline and the rest of natural gas, designated as G100, G90, G75 and G60, were investigated in a SI single-cylinder engine at running at 1800rpm, 9 compression ratio and stoichiometric equivalence ratio. After collecting and processing in-cylinder experimental data in the combinations and different spark advances and their experimental data processing, consecutive cycle-to-cycle data were extracted and analyzed with engine output data. First, optimum spark advance of each combination was determined and then, the combinations were compared at their spark advances. The results revealed that increasing natural gas fraction in combination causes substantial reductions in standard deviation, σ , and coefficient of variation, COV of IMEP, so that σ and COV of G60 reduced by 51. 6% and 49. 2%, respectively, in comparison with G100. Reducing the gasoline presence in combination, the amount of CO2, NOx and HC reduced except G90 which have the higher HC and NOx, whereas, CO amount in G90 decreased to the lowest level. Also, no satisfactory performance was observed in the G90 combination.

In the present paper, the performance of a shell and tube heat exchanger in which its cold working fluid is water and its hot working fluid is flue gases from natural gas-fueled internal combustion engine with working power of 15. 4 kW was investigated. At first, with changing temperature and flow rate of inlet water, the performance of heat exchanger in both condensation and non-condensation situations was experimentally studied in the laboratory in order to have a criterion for validation of the simulations results in future. By comparing different simulation models in Aspen B-JAC software, the least error simulation model was chosen to do the other costly and impossible analyzes numerically in the laboratory environment. The study of the effect of the tube’ s inner diameter on the heat exchanger’ s performance in condensation situation showed 5. 4% increase in the heat transfer while inner diameter decreases from 7 to 6 mm. The separation of the different heat transfer stages showed 26. 4% of the latent heat transfer in the maximum discharge experiments for the inner diameter of 6 mm. Finally, the engine/heat exchanger set was assessed as micro combined heat and power and assumed that the heat exchanger is used for providing hot water for a 4-person family house in Tehran and the combustion engine is used for generating electrical power. This set was able to provide hot water during 9 warm months of a year by 1-hour work per day with 29% decrease of fuel consumption in comparison with traditional burners and at the same time, this set provides almost twice the electrical power requirements.

The focus of this paper is to investigate the possibility of consideration of grains and grain boundaries and their elastic-plastic behavior to predict the stress-strain behavior of ECAPed 7075 Al alloy using a finite element micromechanical approach. For this purpose equal channel angular pressing is performed on the alloy and hardness and tensile tests were performed in the macro mode as well as the micro-indentation test on distinct areas of microstructure. Mathematical relations were obtained for the correlate the hardness and static strength properties of the alloy using the obtained data from hardness and tensile tests. In addition to the mathematical relations, backward simulation of the micro-indentation process has been used in the Abaqus finite element software to convert the hardness in the grain and its boundary to stress-strain curves. The elastic-plastic behavior of the phases has been used in microstructural modeling. Modeling of the strain test has been performed in the finite element software for the microstructures using the microstructural image. The predicted stress-strain behavior from microstructural modeling has been compared with experimental results.

A circular hydraulic jump is a phenomenon that is shaped when a vertical fluid jet impinges on a horizontal plate, at a certain radial distance of the plate center (hydraulic jump radius). Most of the experimental and numerical studies have analyzed the circular hydraulic jump on the flat target plate and the effect of the concave plate has not been investigated yet. Therefore, in this study, using the experimental investigation and numerical simulation using Fluent software, the effect of the concave target plate on the size and shape of the hydraulic jump is investigated for the first time. In order to simulate the circular hydraulic jump, the volume of fluid method (VOF) has been applied. The continuous surface force model (CSF) has been used to investigating the surface tension. The geometric reconstruction has been used for determining the interface of the two fluids. According to the experimental results, the hydraulic jump radius is a function of the impingement jet radius, the concave target plate radius, and the volumetric flow rate. Also, based on the experimental observation, by increasing the radius of the concave target plate, the shape of these jumps change from the circular to the polygonal hydraulic jump.

In this research, the effect of square wave pulsating air on temperature distribution and film cooling effectiveness of flat plate at different frequencies and blowing ratios is experimentally and numerically investigated. Hot air is injected through the holes at an angle of 25 degrees. Square wave pulsed flow is generated at four frequencies of 2, 10, 50, 100 Hz, and five blowing ratios of 0. 5, 1, 1. 5, 2. 4 and 3. To study the film cooling, Navier-Stokes equations are solved by a Reynolds average method. The SST k-ω model was used for turbulent modeling. The results showed that the film cooling effectiveness decreases with increasing of blowing ratio along with an increase in its rate of changes. The difference of centerline film cooling effectiveness between the numerical and experimental values decreases with increasing distance from the edge of injection hole. In general, pulsating decreases film cooling effectiveness in comparison with steady-state. The lift-off of the local jet increases under pulsation. In the pulsating state, the overall film cooling effectiveness decreases by increasing the blowing ratio at a constant frequency. On the other hand, increasing the frequency increases the overall efficiency of film cooling. The maximum averaged centerline effectiveness was obtained at a frequency of 100 Hz and a blowing ratio of 0. 5 and the minimum value was obtained for a frequency of 2 Hz and a blowing ratio of 3. For pulsed flow, the maximum and minimum differences of the averaged centerline film cooling effectiveness between experimental and numerical results were 25. 55%.

In the present work, the effects of fin pitch, transverse pitch, longitudinal pitch and the number of the longitudinal pitch in a plate-fin flat tube heat exchanger were studied. The fluid flow was assumed laminar, steady, and incompressible. Continuity, momentum, and energy equations for fluid flow and conduction equation for fin were solved, using the finite volume method. Dimensionless results showed that increasing the fin pitch causes to increase of the j-Coulburn coefficient by 132. 68% and reduces the friction coefficient rate by 13. 35%. Also, increasing transverse tube pitch causes to increase of j coefficient by 203. 83% and reduces 24. 22% of the f coefficient. By increasing longitudinal tube pitch, j and f coefficients are reduced 84% and 32%, respectively. Dimensional results showed that by increasing fin pitch, heat transfer is reduced 2. 2% and thermal performance, Q/w_p, is increased by 75%. Increasing transverse tube pitch causes to increase heat transfer and thermal performance about 341% and 255%, respectively. Increasing longitudinal tube pitches result in decreasing the heat transfer and thermal performance about 71% and 79%, respectively. Increasing the number of longitudinal tube pitches, N, causes to increase of the heat transfer rate, but for N>28, no sensible increase in heat transfer rate is observed therefore, N>28 is not recommended. Maximum thermal performance is achieved at N=5 and for N>5 thermal performance is decreased.

The motion of the liquid free surface in a container (sloshing phenomenon) inserts a momentum on the container walls. This makes a great disorder in the movement of the carrier vehicle or inserts a large force and momentum on the container walls. The reason for this phenomenon is the establishment of destructive waves and hydrodynamic forces. The side effects of this phenomenon in various industries, such as ship industries carrying liquid fuels, liquid fuel rocket industries, fuel tanks or water tanks, increase the importance of predictions of the behaviors of this phenomenon. One way of controlling is to use baffles or plates in the transverse direction of the tank. In this study, the governing equations on this phenomenon have been solved using the OpenFOAM software. This software solves partial differential equations using the finite volume method, which by default considers geometry to be three dimensional. In order to solve the two-phase flow, a modified volume of the fluid model (VOF) is applied and the moving mesh model is used for the movement of the container body. In the VOF method, the phases are expressed as a fraction of one (volume fraction). To determine this parameter, based on the continuity equation, a differential equation is regulated and solved. For the turbulent flow model, a modified k-ɛ model is used by considering the effects of free-surface flows. Also, an experimental model of a real moving liquid container has been used for validation of the predictions of the presented simulation. The results show that the experimental and numerical results are in good accordance. In addition, the results show that using vertical baffles up to 50% can reduce the fluctuations caused by this phenomenon.

The application of solar energy for space cooling has been increasingly considered in Iran and other countries in the last two decades. In this study, two different configurations of a solar assisted refrigeration system have been studied. The first system is the combination of a lithium bromide vapor absorption refrigeration system and flat plate collectors. The other system is consisted of a compression refrigeration system and thermal photovoltaic panels. For this purpose, 32% of the roof area of the building has been covered with 105 flat plate collectors, each with a total area of 1. 591 m2, or 288 photovoltaic panels each with an area of 0. 556 m2. Both systems have been compared in terms of energy, exergy, and economic viewpoints. This comparison has been conducted for providing the 70 kW cooling capacity system required for an office building with an area of 500 m2. The results of this study showed that at an evaporator temperature of 5° C and the ambient temperature of 27° C, the coefficient of performance of the compression chiller is 3. 5 and the absorption chiller is 0. 71. Also, the total energy efficiency and the total exergy efficiency in the compression chiller system combined with thermal photovoltaic panels are 7. 43% and 8. 25% respectively. Those two parameters for the absorption chiller combined with flat plate collectors are 9. 16% and 6. 66%, respectively. In the economic analysis, the annual life cycle cost for the compression chiller system combined with thermal photovoltaic collectors is 9710 $ and this cost for the absorption chiller system combined with flat plate collectors is estimated 7649 $.

Increasing growth of cardiovascular disease treatment caused the occurrence of heart failure for more patients after surviving. This leads to an increase in the need for types of equipment in these patients for struggling heart failure. Ventricular assist pumps have been known as one of the main types of equipment, today. In the present study, a ventricular assist pump has been designed in which its impeller has been designed using the industrial method (pointby-point method). In this study, 7 impellers with different inlet angles (including 10, 15, 20, 30, 35, 40 and 45 degrees) and outlet angle of 25 degrees were designed and analyzed using computational fluid dynamics. The results indicate that all designed impellers in this study can fulfill the physiological requirements according to pressure difference (total head) and flow rate. Meanwhile considering hemolysis as an effective factor in the performance of ventricular assist pumps, the impeller with an inlet angle of 10 degrees is chosen due to the lowest hemolysis index, equal to 0. 0045, and complying total head and flow rate, which are equal to 108 and 5, respectively.

A horizontal axis wind turbine power generation depends upon the aerodynamic performance of its blades. Flow separation is one of the phenomena that causes power loss and consequently decreasing the wind turbine output generation. Since usually the local angle of attack in the inner and middle parts of a blade is much greater than the local angle of attack in the separation onset, the blade section encounters a highly separated flow. Hence, flow control methods are applied in order to reduce or weaken the negative effects of the separation. This paper investigates the effects of the passive flow control method for a horizontal axis wind turbine using validated three-dimensional DES (detached eddy simulation) on an S809 split airfoil. The split in the airfoil thickness causes the flow from the high-pressure zone under the lower surface is injected into the separated area over the upper surface, transporting external energy to the separated zone, hence weakening the separated area. As the result show, the overall performance of this method depends on parameters such as split locations on the airfoil pressure and suction surfaces, the direction of the jet flow with respect to the freestream wind and also the thickness of the split. In this research, two different split locations and four thickness values of 0. 5, 1, 2 and 4 percent of chord length are simulated at a range of AOA from 0 to 25 degrees. Noticeably, the results demonstrate that for an appropriate split exit location, the thickness value of 2 and 4 percent of the chord are generated more lift force. The average increase of lift coefficient for these split airfoils at a high angle of attack (17, 20, 22 and 25) are 68. 5 and 55. 8 percent respectively.

In this paper, the application of passive vibrational linear absorber on the indirect reduction of blade vibrations using its mounted on the disk-blade system is studied. The absorber receives the vibration energy of blade through a structural coupling of the disk with blade and losses it by its linear damping. Due to cyclic symmetry, the analysis of the bladed disk is reduced to the number of DOFs in a single sector. A cyclic transformation from physical to modal coordinates is used to perform this reduction. Natural frequencies and forced responses of the system are obtained by solving the characteristic and algebraic equations, respectively. The case study of a steam turbine includes 259 blades in 37 packets of 7 connected blades attached to the perimeter of the disk. Cyclic symmetric finite element analysis at 3000rpm is used to extract the natural modes and frequency diagram of the system. A two DOFs reduced-order model is identified for modeling the frequency-veering region. This region has been formed between the first and second families of natural modes and there is a strong coupling between them in this region. In addition, this region is close to the system excitation line and the possibility of resonance exists. Therefore, some linear energy absorbers are mounted on the disk for the indirect vibration reduction of blades. The initial optimal parameters were determined for the first and second modes using Den Hartog relations. These parameters reduced the system vibrations and they were used in subsequent optimization. The optimization has resulted in the improvement of absorber performance exclusively around the second mode, in compare with the tuned system by Den Hartog relations.

In this paper, the CFD-MBD numerical coupled model has been proposed for an accurate evaluation of the behavior of the partially filled railway tank wagon. The vibration response of the wagon has been obtained by the fourth-order Runge-Kutta method based on the threedimensional multibody dynamic (MBD) model with 19 degrees of freedom comprising car-body, two bogies, and four wheel-sets. The model of transient fluid sloshing inside the tank has been analyzed using the computational fluid dynamics (CFD) method combined with the volume of fluid (VOF) technique for solving the Navier-Stokes equations and tracing the fluid free surface, respectively. Validation of the numerical results has been carried out using experimental data. Then, the simultaneous interaction of the transient fluid slosh and the wagon dynamics has been considered through the development of the numerical process of coupling CFD and MBD models. The dynamic characteristics of a partially filled tank wagon have been derived in braking conditions using parametric study on the filled-volume, tank cross-section shape, and fluid viscosity. The results indicate that the filled-volume increase decreases the amplitude of the fluid’ s center of gravity coordinate. The lowest fluid slosh in the different filled-volumes has been related to the modified-oval cross-section. The fluid viscosity has a slight effect on the longitudinal fluid slosh force and the stopping distance of the railway tank wagon.

Human being has always been looking for optimal use of his surrounding materials that has been able to invent various structures through getting inspired by nature. Some of these structures are lattice structures. Due to their lower weight, high compressive strength and high stiffness, lattice structures are widely used in various applications, including energy absorbers. A new type of lattice structure is auxetic structures that have a negative Poisson’ s ratio due to their geometric structure. This characteristic has caused auxetic structures to have unique properties such as shear strength, indentation resistance, and high-energy absorption. In this study, the experimental and numerical investigation of in-plane uniaxial quasi-static loading on three auxetic structures and one non-auxetic structure have been conducted. The specimens have three different auxetic geometries including re-entrant, arrowhead and anti-tetra chiral and one honeycomb geometry that is non-auxetic. The specimens have been manufactured using additive manufacturing technology (3D printing). Experimental results were compared with finite element simulation results, which were in a good agreement. As expected, auxetic structures showed a much better performance in energy absorption compared to the honeycomb structure. So that the energy absorption of the arrowhead structure was 161% higher than the honeycomb structure.

The supersonic turbines are widely used in various industries and power generation systems, including gas turbines, space propulsion, heavy transport industries, and etc. In general, these turbines are used when a high specific work with a low fluid Mass flow is needed. It is possible to extract a high specific work from small height supersonic impulse blades in these turbines. To prevent losses due to the low blades aspect ratio, the turbine is used in partial-admission conditions; so that, the fluid flow is only fed from a part of the rotor. The degree of partialadmission and the type of blade profile are important factors that have significant effects on the turbine performance. The aim of this work is to design and investigate the effects of various types of impulse blade profiles on the turbine’ s performance. A preliminary design code is developed in order to predict turbine performance. These results are evaluated using the experimental results. In the next step, using the calculation of design code, two-dimensional profiles are created using different design methods and numerically analyzed. Finally, the profiles that were better than the original model were studied by 3D numerical analysis. It was found that the performance parameters such as efficiency, power, and torque are increased by more than 8% in the selected best model, in comparison with the original model. Moreover, the total pressure loss is 12% decreased for the selected model. In general, the results show that the selected profile would have a superior performance.

In this research, nonlinear transverse vibrations of a fluid conveying microtube under parametric magnetic axial resonance condition is studied. For this purpose, nonlinear governing equations of transverse motion of beam-like microtube are derived using Reddy’ s first-order shear deformation theory with considering the effect of fluid viscosity and fluid centripetal acceleration. In this model, nonlinear terms of Hetenyi foundation and nonlinear geometric terms of the Von-Karman theory under magnetic excitations in the presence of fluid flow beyond the flutter instability is considered. In the following, the effects of foundation parameters on the linear flutter specifications of fluid conveying magnetizable microtubes are studied. Then, the nonlinear system behavior for fluid flow velocities more than critical velocity corresponding to the coupling of the first and second vibration modes is studied using multiple scales method. Nonlinear response curves in velocities above critical velocity are obtained and effects of variations of various system parameters including flow velocity, amplitude, and frequency of the magnetic field, Hetenyi foundation stiffness constants, viscosity, and dimensions ratio on the nonlinear response of the system are investigated. Some results indicate that increasing the values of shear stiffness parameter of the Hetenyi foundation has an unstable effect so that with its increasing, the flutter instability occurs at lower frequencies.

One of the emerging methods of joining various metals is the use of laser beam welding in a variety of industries such as transportation, aerospace, radar, and marine construction, which reduces fuel consumption and thus reduces environmental pollution. In this study, the microstructure and mechanical properties of similar joints of aluminum alloy 6061 with a thickness of 2 millimeters have been investigated by the laser beam welding method with a high power of 5000 watts. Examined items include the effect of laser welding parameters such as power, frequency, and welding speed on microstructural and mechanical properties. Microstructural analysis results using an optical and scanning electron microscope show that in the process, the microstructure of the weld in the base metal to the center of the weld region changed from the dendritic column to the parallel dendritic zone and eventually reached the equiaxed dendritic area, due to the higher input temperature and consequently less cooling rate. Energy-dispersive X-ray spectroscopy (EDS) showed no significant change in the chemical composition. Investigating the mechanical properties using hardness measurement, and the tensile testing showed that the hardness in the fusion zone was lower than other base metal zones, and the optimized sample was failed in the weld zone. The tensile strength of the optimum welding sample is approximately equal to half the tensile strength of the base metal.

The torque feedback of the vehicle’ s steering wheel or driver perception of the steering wheel is one of the aspects of steering quality that has been investigated extensively in recent decades. In this paper, the driver model for sensing torque feedback or haptic interaction between the vehicle equipped with a steer-by-wire system (SWB) and the driver has been designed. The driver model consists of a preview model and a neuromuscular model. The preview driver model calculates the desired angle of the steering wheel to follow the path, and the neuromuscular driver model that can perceive real-time torque feedback determines the real angle of the steering wheel according to muscular system transfer functions to follow its desired angle. Calculating of torques on the steering wheel requires estimation of the tireroad forces. Whereas directly calculating the tire-road forces is too difficult, particularly in the lateral vehicle dynamics, suitable estimator to estimate these forces designed. The simulation results using the Carsim and Simulink software indicate that the driver model performance improved 63 % when torque feedback is enabled. So the designed driver model with torque feedback has an important role in controlling and vehicle steering in conducting double lanechange maneuvers.

In this paper, the effect of nozzle divergent section geometry on fluid flow and heat transfer within the convergent-divergent nozzle numerically and experimentally is investigated. Axisymmetric supersonic flow simulation for the converging-diverging nozzle is conducted. The flow field is a steady turbulent two-dimensional flow. The working fluid is a combustion product and is considered as a compressible ideal gas. The flow field is simulated using the commercial code FLUENT. The equations are discretized implicitly with the second order of accuracy. In this study, two convergent-divergent nozzles have been analyzed that the divergent part of one is a cone-shaped and the other is bell-shaped. The calculated parameters in the simulation have been compared with the experimental results. Based on the simulation results and the values obtained in the experimental test, the error is less than 4% that is acceptable and appropriate. According to the results, flow simulation accuracy is appropriate.

In this paper, an intelligent powerful control scheme is presented for a lower-limb rehabilitation robot. The focus of this study is on maintaining patient safety, focusing on the concept of assist as needed to improve the efficacy of robotic rehabilitation exercises and intelligent controller behavior. The proposed control scheme is consists of force field control and fuzzy logic control. Gravity compensation, friction forces, and interaction torque have been considered to the dynamic model of the system. The force field control method creates a virtual wall along the desired trajectory in the sagittal plane that can guide the patient’ s gait. Force field control parameters are selected using the fuzzy logic control rules o improve the concept of assist as needed for the rehabilitation robot in order to make a freedom of action for the patient. Therefore, the fuzzy logic control algorithm was proposed to improve the behavioral quality of the rehabilitation robot depending on the patient’ s ability in the gait process. In this regard, the proposed control scheme has been implemented for the lower-limb rehabilitation robot system. Simulation results show the efficiency of the proposed controller to improve the quality of motorized gait training.

The ball deep rolling process is used to improve the surface properties of the workpiece. In this research, the optimum state was determined using the design of the experiment to improve the properties including optimum hardness and roughness. It was determined 3 passes and the type of traditionally and ultrasonic process and proposed regression model at the speed of 1000mm/min. In this case, it showed the hardness of 131 micro vickers and also determined minimum roughness in the mean roughness of 0. 179 microns and the maximum roughness of 1. 01 microns. The microstructure and tensile tests have been investigated in the optimal sample, compared to the surface topographic reference sample. The microstructure has been shown the decreases from about 30-50 microns to about 300 nanometers in thickness at about 50 microns below the surface by scanning electron microscopy. The tensile stress and percentage increase in length were determined by 10% and 29% increase, respectively by the tensile strength test. Topography has also shown the reduction of roughness by 40%. The hardness of the subsurface was studied in the thickness of the workpiece and it was compared to the same traditional and modern optimum specimen. The result showed the effect of increasing the hardness due to the of the structure fracture and strain rate.

In this research, the effect of strain rate on the tensile behavior of the graphene/epoxy nanocomposites was investigated. The specimens were prepared for 0. 05, 0. 1, 0. 3 and 0. 5 wt. % graphene oxide and were subjected to tensile tests at different strain rates. The experimental results showed that the maximum improvements in the tensile strength, the modulus, and nanocomposite were 9%, 16%, and 0. 1 wt. %, respectively. Also, the results indicated that the epoxy and its nanocomposites were sensitive to the strain rate. The rate sensitivity decreased with the increase of the graphene weight percentages. Moreover, it was shown that by increasing the strain rate, the tensile strength and modulus for pure epoxy were improved by 15. 8% and 16. 8%, respectively. In this study, the appropriateness and applicability of the Johnson-Cook material model for describing the stress-strain relation of the nanocomposites were examined by a combined experimental-numerical-optimization technique. The numerical simulations were carried out using Abaqus commercial program and the optimizations were performed using the Surrogate modeling. The results showed that the Johnson-cook model is not accurate at very low strain rates. However, the accuracy of the model was remarkably improved by increasing the graphene weight percentage or increasing strain rate.

Superheater tubes are the most critical components of the power plant’ s boiler. These tubes are subject to degradation such as creep and overheating, due to the hard operating conditions (exposure to high temperature and pressure for a long period). Therefore, it is important to diagnose and prevent these failures. The failure report in a 320-megawatt power plant indicates that most tube ruptures are concentrated in a particular region of the platen superheater (radiative superheater). The investigation of broken tubes shows that the temperature of the tubes in this area is higher than the other platen superheater’ s regions. Three methods of metallography, oxide layer thickness measurement and thermal analysis using computational fluid dynamics were used to prove the existence of higher temperatures at the point of breakdown. All three methods provide the same results. The results of surveys confirm this significant temperature difference and show that the increase in the local temperature in the damaged tubes is due to the longer length of these tubes, which results in lower vapor mass flow rate, and absorb more heat due to the higher thermal surfaces of them.

Micro milling is widely used for producing industrial micro parts. In micromachining, approaching the depth of cut to tool cutting tip radius causes some problems in achieving desired surface quality and burr formation. It is impossible to use conventional deburring methods in micro parts due to the reduction of machining scale and the importance of high dimensional accuracy and surface quality. Therefore, it is important to comprehend micro end milling and the effect of process parameters on reducing these problems. In this study, the effect of spindle speed, feed rate and depth of cut on surface roughness and burr size during micro end milling of AISI1045 steel have been investigated using the response surface method. Two flute endmills with 0. 8 mm diameters have been used in this study. Results show that feed rate with 55. 26, 37. 53 and 44. 55 percent contribution on burr size in up milling side, down milling side and surface roughness is the most effective parameter in the micro end milling process. Selecting the maximum amount of spindle speed, feed rate, and the minimum amount of depth of cut causes minimum burr size in both up milling and down milling side. 36000RPM spindle speed, 5. 7mm/s feed rate and 0. 086 mm depth of cut causes the best surface quality in micro-milling of mentioned steel.