مجله مهندسی مکانیک
سال پنجاه و دوم شماره 3 (پیاپی 100، پاییز 1401)

The use of thermoelectric generators has a special place in recovering the waste heat of combustion gases. In the proposed model, a thermodynamic analysis with the effect of the thermoelectric generator module area on the performance characteristics of the device was studied. To develop the model, the properties of the thermoelectric generator were assumed to be temperature dependent. The convective heat transfer of water in the cold channel was also considered as variable. The effects of water flow regime and the module area were investigated both in the longitudinal direction and for five different values of the module rows on the functional characteristics of the device. The results showed that increasing the number of module rows and module area decreased the power and efficiency of energy and exergy and increased the rate of exergy destruction. The module area is also optimized in two different cases. One was done to achieve the maximum net power and the second to achieve the maximum ratio of maximum net power to the area module. The optimal area in the first and second cases were 0.4641m2 and 0.2207m2 , respectively.

Using Hydrogen instead of fossil fuels has grown significantly due to its high energy density and zero carbon emission during consumption. The most economical method of storing hydrogen is liquefaction. In this study, after pre-cooling by the cold energy of the PRICO and liquefied natural gas (LNG) regasification systems, hydrogen gas enters the next stage and it liquefies by a mixed refrigeration cycle. The novelty of this cycle is based on the new design of a high-efficiency hydrogen liquefaction cycle which is using the cold energy of a LNG regasification process, in turn, results in less power consumption in the compression part and also less cost of power consuming for one kilogram of liquid hydrogen compared to that for a similar cycle. Energy, exergy, and economy analyses are implemented to investigate the proposed cycle. In the proposed hydrogen liquefaction cycle with the capacity of 14 tons per hour, the specific energy consumption (SEC) 15 % and payback period 20% decreased in comparison to the similar cycle.

In this study, the effect of austempering process on the metallurgical transformations and corrosion behavior of weld metal in Hadfield manganese steel welding joints was investigated. For this 4 purpose, initially austenitized sheets with thickness 2mm prepared from Hadfield steel and then SMAW process was used for welding. Then one joint remains in welded condition and other joint were austempered at temperature 1000°C for one hour. Evaluation of the microstructures was conducted by optical microscopy. X-ray diffraction was used for the analysis of phases formed in the microstructure. For evaluation of weld metal corrosion behavior, potentiodynamic polarization and electrochemical impedance spectroscopy methods were used in the 3.5% NaCl solution. The results showed that with austempering treatment, increased corrosion resistance of the weld metal. Because the effect of austempering process, corrosion aggravating factors (amount of sediments and the number of grain boundaries) decreased in the welding joints weld metal.

Recently, two development projects for the "Sepehr and Jufair" fields and "Aban and Paydar Gharb", have been handed over to their respective contractors under the new petroleum contract type so called the IPC (Iran Petroleum Contracts). Given that these two contracts are the first of their kind in the history of Iran, many aspects of the contract still need to be examined and explained. The legal aspects of the contract have been studied by various researchers, but the technical and managerial aspects of the contract have not been considered so far. Therefore, in this study, the capacities of this type of contract to monitor technical and engineering activities in the field of technical inspection and shortcomings in this regard have been considered. This article answers the question based on financial and environmental risk criteria, whether it is essentially necessary to conduct a technical inspection of the employer in this type of contract or not? Also, the level of required client surveillance on the contractor's activities in this type of contract has been discussed.

The shape and arrangement of holes in bricks has a great effect on the rate of penetration heat transfer in the building. In the present study, a new structure has been proposed for building brick cells and the effect of the shape and dimensions of the cavities on its thermal performance has been studied using the finite element method and the surface response method (RSM). The input parameters include the geometric characteristics of the cells and the heat transfer performance is considered as the response variable. In order to minimize the heat transfer parameter, the RSM method and the finite element are used simultaneously. The threedimensional heat transfer equations are solved by considering the three mechanisms of conduction heat transfer, convection and radiation, and temperature distribution and heat transfer coefficient are obtained. The results show that by increasing the thickness of cells and the length of the cell and in general by increasing the perimeter of the cells, the thermal resistance of the blocks can be increased. The results show that among the studied designs, the best thermal performance is related to HB-10 sample with U-value equal to 1.95 which has improved 97% compared to brick without cavity.

The main objective in this study is to model the hydroforming process for Mg tube and obtain the forming limit diagram (FLD) using finite element method. In the first step, three -dimensional finite element modeling of hydroforming process of AL-7020-T6 tube was performed to plot FLD. In order to identify the appropriate criterion for the onset of necking, the hydroforming process modeling was performed by considering the four criteria including of the second derivative of minimum principal strain, maximum principal strain, thickness strain and equivalent plastic strain. Comparison between simulation and experimental results indicated that the second derivative of minimum principal strain, max principal strain and equivalent plastic strain were appropriate criteria for simulation. After validation of the hydroforming process modeling with experimental result, the FLD of the Mg tube was extracted. The results show that in the loading with different axial feeding, the necking time and the amount of stress and strain change. Therefore, various limit strains are obtained by changing the loading conditions. Also, according to the FLD, the higher ratio of axial feed to internal pressure causes the limit strain shifts to the left in FLD plane.

In this research, the buckling of moderately thick double-curved composite sandwich panel with grid-stiffened core and carbon nanotubes reinforced surface layers under axial static loading has been studied analytically for the first time. The panel core is consisted of irregular hexagonal cells. The mechanical properties of the carbon nanotubes reinforced layers with different distributions are determined by the improved rule of mixtures. The buckling equations are obtained by using of the minimum total potential energy principle and Reddy's third-order theory and solved via the Navier method for different boundary conditions .The results show that the effect of carbon nanotubes on buckling load is in the way that the buckling performance in each case depends on the geometric parameters of the grid core. By assigning the appropriate value for grid core characteristics, the maximum buckling load can be obtained by the minimum amount of carbon nanotubes. It is observed that in the FG-V distribution mode, for the smaller amount of carbon nanotubes (0.05 volume fraction), the maximum buckling load is obtained. Also, for Rx/Ry=2 and FG-V distribution mode, the maximum buckling load gains in simply support boundary condition. For Rx/Ry=2 and UD distribution mode, the maximum buckling load obtained from Simple-Clamped boundary condition. It can be noticed that, in this shell type, the maximum buckling load doesn’t belong to fully clamped boundary conditions

In recent years, the limitations of the non-renewable energy sources and the rising pollution of their overuse have led the attention to renewable and clean energy sources such as the potential energy in water resources. Because of vastly used water transportation pipelines and the existing extra pressure in these pipes, it has a high potential for generating electrical power using the in-pipe turbines. In this research, the designing, simulation, and power optimization of a particular kind of these turbines (lift type) are studied. The numerical simulation is performed by Ansys Fluent commercial package software using a 3D solver for unsteady and incompressible flow in conjunction with a proper turbulence model. After introducing the turbine's effective design parameters, the simulation of the in-pipe turbine with different geometry conditions and rotational speeds is performed and discussed. Then it is tried to enhance the generated power of the turbine using trial and error by changing the geometry conditions of the rotor. Lastly, by numerical simulation of different geometries and improving the generated power, the best turbine geometry is tested for experimental validation.

In this paper, the combination of digital image correlation and hole drilling methods has been used to investigate and measure the residual stress of polymer components. The bending stress was created by a three-point bending system and measured by the provided equipment. These stresses are considered in theory to be equivalent to the residual stresses within the component. Digital image correlation method utilized as a novel method to measuring released strain. In this regard, Plexiglas polymer materials in various thicknesses were analyzed under the different values of 3-point bending test. Finally, the obtained results from the introduced method in this paper, with the results of Finite element analysis and simulation have been compared and validated. Unlike the samples that have an unknown amount of residual stresses, the residual stresses in these specimens have a certain amount that can be compared and verified with the simulation and analytical results. Polymer materials have a higher released strain range than metals and it is possible to investigate the strain released by digital image correlation. The results show that the combination of digital image correlation and hole drilling techniques as innovations presented in this paper are capable of measuring residual stresses with a high accuracy less than 10% and also because of their major advantages. The method of using strain gauge would be a suitable alternative to the hole drilling whit strain gauge method for measuring residual stress in polymer samples.

In this study, due to the lack of gas consumption index for rural buildings, an attempt has been made for a better understanding of the rural gas consumption pattern by comparative analysis between measured consumptions and predicted values used for network design in one of the rural areas of North Khorasan province. Based on the results of this study, it was observed that using the urban buildings consumption index will cause a significant difference in predicting the consumption of rural buildings, which is about 47% and 52% in residential and religious buildings, respectively. This difference in office, medical and educational buildings, due to their much smaller dimensions compared to the corresponding urban buildings, is about 87%, 91%, and 67%, respectively. Also, the calculated difference between the predicted amount and the total hourly consumption in the study area was about 50%, which indicates a significant surplus potential ready to release in the rural sector. Finally, based on the measured data, relations to predict the maximum hourly heating consumption of rural buildings in terms of the minimum absolute ambient temperature and new consumption indexes for rural buildings were proposed.

Heat transfer enhancement from a flat plate in which a thin blade is rotating at a certain speed in the vicinity of the plate has been investigated in the present study. For this numerical study, the finite volume method was used in which the rotation of the blade was simulated by the definition of sliding mesh and interface boundary within the computational domain. The equations of mass, momentum, and energy were solved in two-dimensional and transient form for airflow with constant physical properties using Fluent commercial software and the details of the flow and thermal fields were obtained at the top of the plate. The rotational Reynolds number of the blade has been changed in the range of 1360-5460 and the dimensionless parameter of blade-end-to-plate distance to the blade length (d/D) was ranged from 0.105 to 0.420. The results indicated that heat transfer from the plate is improved by increasing the rotational speed of the blade, especially on the front side of the rotating blade, while the effect of the d/D was effective only over a limited area of the plate central section

The aim of the present study is to reduce the free vibrations of a mechanical system by optimally designing the mass ratio of a nonlinear damper called the impact damper. The impact damper contains a number of masses connected to the main system that has the ability to move in a closed enclosure and reduce the amplitude of the main system through the transmission of motion. According to research done so far, impact dampers have better performance in reducing vibrations than linear dampers. The most important factor in the optimal performance of this damper is the design of the mass ratio. Due to the complexity and high volume of calculations to analyze the behavior of an impact damper, in this study, the hybrid metaheuristic method has been applied to determine the mass ratio. By comparing the results of the presented optimization method and the conventional design, the high power and efficiency of the proposed method for damper design are evident. The optimal design of problem parameters could reduce the amplitude of system vibrations in less than 2 seconds to 5% of the initial amplitude. The application of optimal impact damper has also decreased the system energy by more than 90%

Mathematical modeling of biological systems is one of the most desirable methods for studying the behavior of these biological phenomena. The development of mathematical models has always been important for simulating, controlling, and predicting phenomena. One of the advantages of mathematical models is their application in optimization. Solving cancer therapy as an optimal control problem aims to reduce the concentration of cancer cells in the treatment period. In this solution, an important aspect that was not considered in previous studies was the optimum drug concentration that significantly affected patients' clinical health. Due to this, the present study was carried out to obtain an optimal drug-prescribing protocol to minimize the concentration of cancer cells and the drug concentration. This Multi-objective problem has been solved, for the first time, using the NSWOA algorithm, and the results were compared with the NSGA-II algorithm. Pareto front curve obtained from both algorithms offers a set of the most optimal solutions. According to the criteria of treatment choice, one of these points is chosen as the drug administration protocol.

In this research, the optimization of NASA Rotor 67 is studied to reduce the total pressure loss and conserving the mass flow rate and the flow turning angle. The blade profile is parameterized using B-splines to generate the blade camber line and the thickness distribution. the CFD solvers are utilized coupled with the genetic algorithm to improve the performance of the compressor. Finally, the optimized profiles are employed in the three-dimensional blade geometry and the flow field is solved using a 3D flow solver. In the first case, the hub and mid sections are replaced and the compressor efficiency is enhanced by 0/48%. However, the mass flow rate is decreased for this case. By applying the three optimized profiles in the hub, mid and tip sections of the Rotor 67 blade, the maximum efficiency is improved by 0/41% while the mass flow capacity of the compressor is increased as well.

Hard to cut materials such as hardened steel and super alloys are well known and popular in transportation, aerospace, marine and medical industries, due to their strength, high corrosion and fatigue resistance and high working temperature . However, their lowmachinability is one of the major problems in using them. In this article we examine machinability of the hardened CK45 steel in four processes including; conventional turning, hot turning, ultrasonic assisted turning and hot ultrasonic assisted turning as a hybrid machining. The results of these four processes are compared with each other. The heating technique is induction type which has much lower construction cost compared to other techniques such as laser beam and plasma arc. It has been illustrated in the present study that combining the heating technique with ultrasonic vibration has the most effect in improving surface quality and reducing cutting forces compared to other turning process. The chip formation under the heat and ultrasonic vibration and its influence on the surface quality have also shown that hybrid process has the most affection.

Nowadays, using wood-plastic composites has been growing in different applications as they provide special advantages. However, their application in structural parts was hindered due to poor mechanical properties. In this study, microfibrillation method was used for reinforcement, wherein the polyamide (PA) as the second phase forms microfiber morphology in the main polyethylene (PE) matrix, under special process conditions by stretching the outlet filament from the extruder orifice, . Then, in the second production step, the final parts were injection molded at the temperature below the melting temperature of the PA phase to preserve the microfiber morphology and reinforcing effect. Polyethylene (PE) was used as the main matrix and 20 wt.% of polyamide(PA) was used as the second phase. Stretching ratios were varied at three levels of 1:1, 1:3 and 1:5. Wood and carbon fibers contents were 20 wt.% and 10 wt.%, respectively. Based on the results, with increasing stretching ratio, tensile strength increases up to 20%. Also, the tensile strength of hybrid wood-plastic composite with polyamide and carbon fiber has increased by 14% compared to polyethylene-wood composite.

This paper investigated a numerical simulation of the undesirable effects of swirl inlet distortion on a low-speed axial compressor rotor and the effect of plasma actuators as an active flow control method on reducing these flow instabilities. Initially, the effect of co and counter-rotating inlet swirl distortion at angles of ±5 and ±10° on the rotor's performance and efficiency was evaluated. Then, using simulations of plasma actuators' fluid dynamics effects, the effect of this method on mitigating the destructive effects of this type of bulk swirl distortion was examined. Co-rotation swirl distortion reduces the rotor's total pressure rise coefficient, whereas counter-rotation swirl distortion reduces the stall margin. Applying plasma actuators by modifying the rotor inlet flow angle, leading to stall margin improvement. Furthermore, in the 5 degree counter rotation swirl distortion case, plasma actuators, in addition to compensating the adverse effects of swirl distortion, increased the stall margin by 1.3%

The flame fuel cell is a new type of solid oxide fuel cell in which the solid oxide fuel cell is integrated with a rich fuel flame to generate power. In this paper, a flame-assisted solid oxide fuel cell is employed to generate power, and the cell is simulated in EES. The model includes the equations of mass, energy, and chemical and electrochemical reactions. Parametric analysis of the fuel cell shows that by increasing the equivalence ratio from 1.2 to 2.8, the fuel cell efficiency changes from 4.21% to 18.23%. In this study, the supercritical Brayton carbon dioxide cycle is used to recover the waste heat of the cell. To optimize this thermal cycle, the compressor pressure ratio and flow split fraction have been considered. In the optimal pressure ratio, efficiencies for turbine inlet temperatures of 583.15 K, 823.15 K and 923.15 K have been obtained as 31.56%, 47.95% and 52.69% for the pressure ratio parameter, respectively. The results reveal that the efficiency of the integrated cycle is improved and reached from 18.23% to 26.95% for Φ = 2.8

In the present study, the natural convection heat transfer inside a corrugated U-shaped cavity studied numerically. For solving the mass equation (continuity), conservation of linear momentum equation and energy equation, the finite element method applied. The accuracy of used method investigated with the available results and a high agreement between them observed. Fluid flow is twodimensional and water is chosen as the working fluid in the cavity. Different Rayleigh numbers (103 -106 ) and corrugated walls are the variables affecting the fluid and heat transfer fields. The results expressed in terms of velocity contour, fluid flow, temperature and the average Nusselt number. The extracted results indicate that by rising the Rayleigh number, the heat transfer rate increases which the highest value of it is equal to 76.43 at Ra=106 . Also, at a fixed Rayleigh number, the smooth cavity has a highest heat transfer rate and the maximum of heat transfer’s loss occurs at cavity by corrugated on the both sides.

In this research, the stability of Khorasan Petrochemical Feed Gas Compressor (C-2102) in surge avoidance control conditions with the aim of reducing energy consumption has been studied. Surge avoidance is one of the common methods to deal with the surge phenomenon, which prevents the onset of surge condition by preventing the flow drop in the suction side of compressor. In the present paper, by examining the operating conditions and performance curves of the compressor, three types of surge avoidance systems have been designed that maintain the compressor operating point at a safe distance to the surge line by measuring the operating speed, volume flow and suction pressure to the compressor. According to the results, in case the suction flow drops to 10% as a step function, the anti-surge control system prevents approaching the surge conditions, and in case the flow drop enters as a ramp function, the control system performs better and maintains the compressor operating point in the stable zone in the event of a 40% flow drop. According to the results, if the surge avoidance control system is activated, it will be possible to increase the suction pressure of the compressor, which will reduce the compressor power consumption by 20 percent.

The most recent proposed technique for drag reduction in hypersonic flow speeds is using the exothermic coating on the blunt nose. This leads the heat addition into the flow field behind the shock wave, and increases the shock-stand-off distance. The variation of the drag force on the flying body using this technique is numerically investigated in the present study. The compressible turbulent flow is simulated around the body to compute the drag force, and to estimate the drag reduction capabilities of this technique. This quantitative analysis makes better insight to evaluate it in operational applications

In the present paper, the dynamic responses of a variable mass sled sample under the variable forces of propulsion, lift, drag and friction are investigated. First, by presenting a complete model of the various components of the sled system, the governing equations are extracted and the state space method is used. Then the variable forces applied to the designed sled model are extracted. In order to validate the results of the analytical method, the natural frequencies of the sled laboratory model are obtained experimentally. The first and second natural frequencies of the sled were 12.8 and 21.4 Hz, respectively, which were in good agreement with the analytical results. The results show that due to the disturbance applied to the sled, the dampers damped 40% of the vibrations. Also, in all cases, the oscillation rate of the rear sleeper is more than the front sleeper, this is due to the effect of the turbulence of the front sleeper on the rear sleeper. On the other hand, variable forces increase the sled displacement by 10%.

The study of materials in nanomanipulation process is done in two phases with the aim of examining the motion of the particle before and after the motion. Studies have been performed on particles such as gold in the first phase and the critical force and time for this particle has been calculated according to different environmental and geometric conditions. In order to complete the process, in this paper, gold particle manipulation in the second phase is investigated. In this research, motion modeling has been done in three dimensions and particle motion has been observed on rough and smooth surfaces. Finally, using the results of modeling and manipulation of gold particles using atomic force microscope and due to the presence of elevations and heights in the nanoscale, the results show more displacement on smooth than rough surfaces and also according to the motion study. In both x and y directions, the displacement in the y direction was greater. Other results calculated in this study include the study of surface parameters and geometry of gold particles.

In this research, semi-solid powder processing was used to fabricate Al7075-CNT nanocomposite. The effect of process variables including compression time, semi-solid temperature and the CNT percent on the sample’s hardness and microstructure was investigated. The 1%-CNT nanocomposite is observed to be superior in hardness compared to the base alloy, but the 2%-CNT sample’s hardness was between the base alloy and 1%-CNT sample. It was observed that the compression time and semi-solid temperature do not have a significant effect on the sample’s hardness. Compression for 10 minutes and forming temperature of 620 °C were selected as the suitable variables. Microstructural examination showed that in 1%-CNT alloy, the reinforcing phase is completely penetrated in the aluminum matrix and there is no CNT accumulation on the sample’s surface unlike the 2%-CNT sample. Quantitative analysis showed that a proper percentage of CNT had the greatest effect on the hardness. Increasing the temperature from 600 to 620 °C by 10% and increasing the compression time from 5 to 15 minutes by 2% increased the hardness of 1%-CNT samples compared to the base alloy.

The instability of the spacecraft and its deviation from the desired attitude is the product of the phenomenon of fluid sloshing in its tank. This is especially important while maneuvering, so that lack of attention leads to the failure of the space mission. In this paper, for the first time, a moving pulse two-ball model is used to model fuel sloshing in the semi-full tank of the spacecraft. As well as for the first time, for simultaneous control of the spacecraft and fuel sloshing, a classical controller, an LQR controller and a Lyapunov nonlinear controller have been designed. Fuel sloshing was modeled using the moving pulse two-ball model and the coupled dynamics equations of the spacecraft and the fuel masses are derived using Lagrangian equations. The results of simulations show that the proposed modeling and designed controllers to simultaneously control the fuel sloshing and attitude of the spacecraft have an acceptable.

In this study, a new desalination system, called an improved stepped solar still, is proposed to desalinate saline water using solar energy. This desalination system is created by adding a separate but integrated condenser to a standard stepped solar still. The condenser space is connected to the desalination section by two air gaps at the bottom and top of the absorber plate. Air circulation between the two parts occurs naturally (free flow). To compare and evaluate the performance of the new desalination systems, a standard stepped solar still was built with the same specifications and dimensions. The two solar stills are tested and compared in a few days of spring (June 11 and 12) and in a few days of autumn (October 10 and 11). The experimental results show that the improved stepped solar still has a better performance than the standard ones so that the freshwater produced by improved solar still is between 76 to 127% more than the freshwater produced by the standard ones. The maximum daily amount of freshwater produced by the improved solar still per square meter of occupied area of solar still area equals 4.57 liters.

System Identification is used to derive the dynamic and mathematical model of a system using experimental data. If the case study system is an aircraft, this process is called aircraft system identification, which is used to estimate the stability and control derivatives of the aircraft. The least squares method is one of the methods used in the field of time and frequency to estimate the parameters of the aircraft. In this paper, system identification and estimation of F-16 aerodynamic coefficients are performed using the least squares method and the equation error approach. Hence the main focus is on the formulation of the aerodynamic model for estimating unknown coefficients using the least squares method. In this regard, nonlinear 6-DOF of the F-16 aircraft was simulated and using its results, system identification and estimation of transfer function, force coefficients and aerodynamic moments of the aircraft lateral-directional channel using regression of least squares and the results are analyzed. The results show that the modeling and estimation of the coefficients is compatible with the experimental data and can be suitable for further studies, including control objectives.

This research presents control of a XY Nano-positioning stage using a compliant parallel mechanism with small crosstalk and yaw motion that are used in atomic force microscopes (AFM). The stage consists of two flexure displacement amplifiers driven by piezoelectric actuators. The piezoelectric actuator is explored to simultaneously reduce error of motion and fine motion tracking using controller. After identifying the system features, the Bouc–Wen hysteresis Model is established and the parameters of model are identified through particle swarm optimization (PSO) algorithm. An inverse feedforward control strategy is developed, then the PI controller is designed based on Ziegler-Nichols method. At the end, the performance of the mechanism is evaluated.

In this study, the effect of foot wearing on local and overall thermal sensation has been experimentally investigated under a personalized ventilation system in an office. Accordingly, the overall and local sensation of occupants for two arrangements of diffusers (desktop and under the desk) and two different clothing (A: conventional office clothing with thermal resistance of 0.58clo and B: similar clothing without shoes and socks) and three different inlet temperatures (16, 24 and 32°C) have been evaluated. The results showed that the feet wearing has a significant effect on the thermal sensation. In addition, the lack of coverage of the foot area increases the deviations between the sensations of various parts of the body. So, that the difference between the sensation of various segments under the conditions of using clothing A and the desktop arrangement for the diffusers is about 0.5; while this amount in the conditions of under the desk diffusers and using clothing B reaches about twice and the value of 1. Also, the results showed that if the inlet temperature is 16°C or occupants are not used the foot wearing, thermal dissatisfaction cannot be prevented.

In this paper, using different combinatorial models of carriers, the effects of basic parameters on the performance of heterogeneous organic solar cells as well as charge transfer are investigated. In order to simulate these processes, in this section, the basic parameters of P3HT: PCBM-structured organic solar cells have been studied by using the self-consistent solution of momentumdiffusion equations and Poisson equation, as well as using different recombination models by finite element method. In most of the proposed models and theoretical studies, the active region in organic solar cells is assumed to be inherent, while this assumption has drawbacks for studying and optimizing them, and the contribution of contaminating polymers should be considered for better study. To be taken. The studied structure is shown in Figure 3. This structure includes the active region with a mass structure of P3HT: PCBM with a thickness of 100 nm.

Many studies have considered the flow patterns of unmixable liquids as a significant subject of a research study. It can be due to the distinct manner of liquids with different characteristic in pipe’s setting under various operating conditions. We conducted an experiment with oil (67 cp viscosity and 0.872 g/cm3 density) and water (1 cp viscosity and 0.898 g/cm3 density) in horizontal acrylic pipe with the height of 6m and diameter of 20 mm. The Superficial velocities of water and oil were in the range of 0.18-1.2 m/s and 0.95-0.18 m/s, respectively. As a result, flow patterns were identified for two phasic flow, including Stratified, Bubbly, Dual continuous, Annular, Dispersed water in oil, and Dispersed oil in water. The identification and introduction of flow patterns and the effect of viscosity on it are the considerable aspect of this study by using high viscosity oil. The comparison of flow pattern in this study (high viscosity oil) with past ones (lower viscosity oil) is also an important result.

In this study, X70 low-alloy steel was jointed to the 2304 duplex stainless steel by tungsten-gas arc welding (GTAW) process and using ER316L filler metal. Each of the parameters of background current, maximum current, frequency and percentage of pulse on time were changed in three levels. Microstructure, mechanical properties (tensile, impact, hardness), fracture surfaces and corrosion resistance of weld metal for different samples were investigated. Based on the optical microscope observations the weld metal microstructure includes the predominant phase of austenite along with skeletal ferrite. Although in the tensile test due to the rupture of the samples from the 2304 stainless steel side the tensile properties of the samples are similar to each other, but the increase of background current, decrease of maximum current, increase of frequency and decrease of percentage of pulse on time increases the hardness and toughness of the joint. The scanning electron microscope observations of the weld metal fracture surface showed that the fracture mode is mixed (soft/brittle). The pulsed welding improves the corrosion resistance of the weld metal in comparison with the direct current.

Micromixers play a very important role in microfluidic science. These tools are widely used in various fields such as medicine, food industry, nuclear and chemical industries. Achieving high mixing quality in these mixers is very importance. There are two general methods for increasing لاthe quality of mixing in micromixers: Active methods, which use external factors such as electric and magnetic fields to increase the quality of mixing, and Passive methods, which do not use external forces and energy and only By using structural changes of micromixers, they improve the quality of mixing. Passive methods are very popular due to their low current cost and lack of use of moving parts. Creating obstacles in the path of fluid stream is one of these methods. In this paper, a micromixer with a rectangular geometry is considered, which tries to increase the mixing quality by using circular barriers. To consider these obstacles, five points have been considered, in which circular obstacles with five different diameters are placed. It is worth mentioning that the present study includes numerical modeling and due to the uncertainty in the obtained numerical results, modeling in fuzzy space can achieve more desirable results. The innovation of the work is to provide a way to optimally locate the obstacles with fuzzy data, based on which the arrangement of different obstacles in the micromixer can be achieved in such a way that the highest mixing quality is achieved. The results show that elements with diameters of 0.20, 0.15, 0.25, 0.30 and 0.10 mm should be placed in left-to-right arrangement in five designated positions. With this combination, the mixing quality increases by 467% compared to the base state.

Exosomes are the main cause of cancer so separating them from blood can be effective in the diagnosis and management of diseases. The dimensions of the exosomes are very small, so separating them is very challenging. Ultracentrifugation is generally used to manipulate exosomes. The very high spin of centrifuges eliminates the exosomes and also it is expensive and requirement of specialized equipment. One of the most popular recent methods is using induce charge electrokinetic phenomena. The present study investigated the separation of biological particles (exosome) based on Induce Charge Electrokinetice (ICEK) methods using direct current (dc). The particle size range is between 1µm to 10nm. Problem geometry is a rectangular channel with a metal rectangular obstacle inside it. The results have shown that the strength of these vortices is large enough to trap the particles. In this study, a model for simultaneous separation of 5µm and 100 nm particles from each other with 100% efficiency is presented. The model presented in this study is a rectangular channel which has a rectangular barrier and simulated in the COMSOL limited element software

In this work, a comprehensive wave propagation analysis is performed on rotating viscoelastic nanobeams resting on viscoelastic Winkler-Pasternak foundations. Here, a novel non-classical mechanical model is developed to describe accurate wave propagation behavior for viscoelastic nanobeams. In fact, to capture both hardening and softening behaviors of materials during wave propagation, general nonlocal theory (GNT) is applied to establish the governing motion of equations. Unlike Eringen’s nonlocal theory, general nonlocal theory employs two different nonlocal parameters refers to normal and shear strains. Also, Kelvin-Voigt model along with Timoshenko beam theory are considered to extract the equations and analytical solution is employed to make the results. The results are obtained for longitudinal (LA), torsional (TO) and transverse (TA) types of wave propagations. Moreover, the effects of nonlocal parameters, Kelvin-Voigt damping, foundation damping, Winkler-Pasternak coefficients and rotating velocity are illustrated and discussed in details especially for TO and TA types of wave propagation. The results show the effect of each of the mentioned parameters on the frequency for all types of wave propagation.

In the present research, the effects of thermal radiation on forced convection flow of nanofluid in a trapezoidal enclosure are investigated. This enclosure has two inclined side walls and two independent inlet and outlet ducts. For modeling the inclined walls of this enclosure, the modified blocked- off method is employed. Energy equation in this study involves all three conductive, convective and radiative heat transfer mechanisms. To calculate the impacts of radiative heat transfer mechanism in this equation, the Rosseland approximation is utilized. The nanofluid studied in this research is water-copper oxide nanofluid, which to calculate its thermo-physical properties, the effects of Brownian motion have also been considered. Interacting influences of radiative parameter and concentrations of copper oxide nanoparticles on thermal behaviors of fluid flow are investigated by plotting the dimensionless temperature profiles in the enclosure and the distributions of convective, radiative and total Nusselt numbers on its bottom wall. It is clear from the results of this research that the highest value of the total heat transfer rate on the enclosure bottom wall is related to the case of = 1 and = 0.06.

Smoke flow visualization tests in a vertical wind tunnel are carried out to investigate the flow characteristics around two infinite staggered square cylinders at a staggered angle ( = 45) for different gap distances between cylinders at Re = 750. Quantitative results like separation angle, wake width and shedding frequency were obtained for each cylinder and consequently three distinct flow regimes were recognized, namely, single body, periodic gap flow and modulated periodic flow regime. In a single body flow regime, vortex shedding occurs only from the outer layers of both cylinders and a single vortex shedding mechanism can be detected. In the periodic gap flow regime, the vortices shed from the outer shear layers of both cylinders, each with two similar frequencies. In addition, in the modulated periodic flow regime, the main features are that the frequencies of Karmann vortices and the Kelvin Helmholtz instabilities are attributed to each cylinder and not to the shear layers (the frequencies of both inner and outer layers are the same for each cylinder), however, the frequency of each cylinder is different from the other one.

Polymeric composites having high specific strength and stiffness compared to the traditional material are weak in outof-plane mechanical properties. More than above, these kinds of structures in some industrial applications are undergoing cyclic temperatures. In this manuscript, the effect of 200 thermal cycles in the range of -30 to +65 degrees Celsius on the fracture toughness of the carbon/epoxy composites is evaluated. Carbon/epoxy composite laminates are fabricated using carbon fabrics and epoxy resin in the form of the double cantilever beam (DCB), and end notched flexure (ENF) specimens. Samples are exposed to the 200 thermal cycles, and fracture tests are carried out in modes I and II. Test results revealed that the initiation fracture toughness of the samples in mode I (DCB) and mode II (ENF) are reduced 5.7 and 15.5 percent, respectively, compared to those are tested at room temperatures. Also, crack surfaces are investigated using an optical microscope and scanning electron microscope (SEM) in the specimens exposed to the thermal cycles.

In this paper, a new method is introduced to solve the inverse problems based on the repression tree (RT). To investigate the method’s efficiency to handle the nonlinear inverse heat transfer problems, two case study problems are done in this paper; first one is estimation of the free convection heat transfer coefficient of a horizontal copper cylinder and the second is estimation of the heat transfer coefficient in the surface of a quenched copper cylinder in a fluid using the cylinder temperature history. The input data were produced by solving the direct heat transfer equations of the cylinder and Churchill-chu imperial correlation and to test the method’s sensitivity to the random errors in input data, an artificial noise with normal distribution was added to the temperature results of the direct solution. The regression tree’s results were also compared with the sequential function specification (SFS) and the artificial neural network (ANN) methods. For the first case study problem, the root-mean-square error (RMSE) of RT, SFS, and ANN methods are 0.0129, 0.1231 and 0.0217, respectively, and for the second problem 8.844, 54.09 and 71.634 are the RMSE values. The comparison shows that the presented method has a good potential to solve the nonlinear inverse heat transfer problems with low error and time lag to online estimate the unknown parameter.

One of the most important topics in the context of plasticity is obtaining the material hardening properties to be used in performing numerical analysis, especially when the applied load is cyclic and its value is higher than elastic limit. In this case, investigation of the kinematic hardening, which considers bauschinger effect, is very important. Since obtaining hardening coefficients of the materials using analytical methods, not only is difficult but also it usually provides significant error in the results. Hence, a computer code is developed for calculating these coefficients. In this study, to validate the calculated coefficients, the associated parameters are obtained for SS 304LN using both numerical and analytical methods and the results are compared with the experimental data. Then, these coefficients are used to study the ratcheting behavior of a SS 304LN elbow which is subjected to constant internal pressure and cyclic bending moment The results of this case study are also compared with the experimental data provided in the literature and good agreement is obtained.