مجله مهندسی مکانیک
سال پنجاه و سوم شماره 1 (پیاپی 102، بهار 1402)

In this paper, it is possible to change the alloy of the blades of the last row of steam turbine blades of Ahvaz Ramin power plant in order to increase the life with the vibration approach. After entering the geometric model into the ANSYS, dynamic analysis and stress analysis are performed on the model for steel alloy and titanium alloy, as well as crack growth in the single-blade model. In the dynamic analysis, the results showed that when we consider the material of the turbine blades as titanium alloy, we can create better vibration conditions in the turbine blades and prevent the possible occurrence of resonance phenomenon. Also in stress analysis, when titanium alloy is used in the blade, the Von Mises stress obtained is approximately equal to half the stress obtained from the steel alloy. When the blade cracks at the root, the amount of stress intensity calculated in the turbine blade is reduced by almost 50% when the blade is made of titanium alloy.

Quenching-partitioning heat treatment steels (Q-P) are among the third generation of advanced high strength steels (AHSS) that have been expanded due to having a significant set of mechanical properties including high strength along with appropriate flexibility. The principles of segmentation thermal operations are based on carbon infiltration from martensite to Return austenite (􀀃􀀄) and stabilization of 􀀃􀀄 In the present study, a high strength steel containing Ti microalloy was subjected to Q-P and Q-P-T heat treatment and compared in terms of microstructure and mechanical properties. After quenching-partitioning (Q-P) and quenching-partitioningtempering (Q-P-T) heat treatments were applied to the sheet samples, their properties were determined using scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), microhardness measurement. , tensile test and Erickson's test were evaluated. The results showed that the strength and failure strain of Q-P samples were measured as 1062 MPa and 24% and Q-P-T samples as 894 MPa and 27% respectively. Q-P samples showed more strength and less flexibility than Q-P-T samples.

Limited access to fresh water sources has raised water shortage as a crisis. Therefore, solar desalinations have received special attention today. A stepped solar desalination device which has 28 steps with a height of 30 mm, a width of 110 mm and a length of 840 mm has been designed, built and used in this research. In order to increase the daily production rate, the device has been tested and optimized in 4 different modes: first mode) simple, second mode) with phase change material (PCM), third mode) with Hybrid Nano phase change material (NPCM), fourth mode) with Hybrid NPCM under magnetic field. The phase change material and Hybrid Nano phase change material have been used as a source of thermal energy storage to continue the desalination of water when the sun sets. After conducting the tests, it was found that the fourth mode of the test, i.e. the Hybrid Nano phase change material under the magnetic field, had a 98% increase in the production rate compared to the simple mode.

One of the main methods for strengthening and increasing the hardness of the materials is the use of the severe plastic deformation (SPD) processes. Equal channel angular pressing (ECAP) method is one of the SPD methods. Two challenging issues including (1) the very high required punching force, and (2) the deflection of the punch restrict the application of the method in industry. In this paper, a new design of ECAP process is proposed, which in addition to reducing the punching force, eliminates the deflection problem. The main purpose of this paper is to investigate the effect of the process parameters including process temperature (100- 200-300) ° C, lubrication (dry and graphite) and the number of ECAP passes (1-2-3) on the hardness of 7075 aluminum material and determining their optimal levels. The Taguchi design is used for design of experiment and the S/N ratio is used to find the optimal levels of the parameters and to maximize the hardness of the material. Based on the analysis of the variance, the process temperature and the number of ECAP passes have the greatest effect on the hardness of the post ECAP samples. However, the lubrication condition has not a significant effect on the hardness of the post ECAP samples in all temperatures.

Cavity receivers are the most common design in solar dish concentrators in order to achieve high thermal performance. In the current research, in order to design the solar receiver optimally to increase the output fluid temperature, the variables of diameter and pitch of a specific type of receiver, fluid type and velocity and the flow regime have been investigated. The most suitable dimensions of the receiver and flow Reynolds are according to the parameters that lead to the highest fluid outlet temperature. In this study, a spherical concentrator with a spherical cavity receiver is considered. The results show, the most suitable diameter of the receiver tube and its corresponding pitch is 5 mm and 17 rings, the maximum temperature of the outlet fluid is obtained at Reynolds 200 and slow flow regime. Also, the temperature of the outlet fluid with the working fluid of oil and nanofluid oil with nanoparticles have been compared with each other on different days of the year. Therminol with temperature function properties has been used. Nanoparticles of copper, copper oxide and alumina in volume percentages of 0 to 5 % have been added to the oil and the temperature of the nanofluid outlet has been calculated. The results of this comparison show that by adding nanoparticles to the oil, the temperature of the output fluid will increase. The most suitable nanoparticle is copper with a concentration of 5%, which leads to an increase in the temperature of the output fluid by 118 Kelvin degrees.

In the present study, a novel tri-generation system is proposed. The system produces heat, electric power, and cooling water using concentrated solar cells alongside thermoelectric coolers. The simulation of the system is performed analytically. A zerodimensional model for thermoelectric cooler is applied and the thermal resistance network model is used for a more accurate simulation of the cooling system of the concentrated solar cells. The results indicate that the system can deliver 270 kW electrical power and 2 kg/s of cold water flow in 10℃ and 10 kg/s of hot water flow in 50℃ using 1000× CPV panels with an overall surface area of about 2 m2 which are divided into 1×1 cm pieces. The parametric study conducted on the system for different hours of the day shows that solar radiation has a minimal effect on the output cold water temperature, but it strongly affects the generated power.

In this research, for the first time, the dynamic response of a composite cylindrical shells containing fluid filled with different boundary conditions by considering the equivalent weight of the fluid and the equivalent dynamic stiffness of the shell and fluid under low-velocity impact was investigated. The first-order shear deformation theory and the two methods of Rayleigh and beam functions along with the Galerkin weight function were used to solve the governing equations and ABAQUS software was used to validate the results. The main innovation of this research is the use of equivalent dynamic stiffness of the structure containing fluid and equivalent mass of the structure-fluid with a two-degree-of-freedom model of mass and spring to calculate the impact force and interaction between the impactor and the composite shell. The results showed that the various boundary conditions were very effective on the dynamic response of the composite cylindrical shell under low-velocity impact and the presence of fluid reduced the natural frequency of the structure. The difference in the fundamental natural frequency for empty and fluid-filled cylindrical shell was calculated 78%. Parameters such as radius, length and thickness of the shell, different boundary conditions, mass and velocity of impactor are important and influential factors in the study of vibrations, impact phenomenon and structural design.

The present study aimed to investigate the effects of air inlet location and flow characteristics on the performance of a personalized ventilation system. For this purpose, a near-body personalized ventilation system is numerically simulated in an office room with the presence of a thermal manikin. Three air inlet arrangements (in front of the feet, in front of the abdomen, in front of the face) were modeled, two air temperatures (16 and 20℃) and two air velocities (1 and 2m/s) were assigned to each arrangement. Finally, airflow temperature distribution, velocity distribution, and the overall and local temperature and thermal sensation of different body segments are determined. In some cases, by changing the air inlet placement from the front of the feet to the abdomen and head, the whole-body thermal sensation is cooled by 0.54 and 0.6 units, respectively. In all cases, hands and head felt cooler than the wholebody thermal sensation, which shows that the bareness of a segment has a significant effect on its feeling in personalized ventilation systems. Unlike the foot, the head is an effective local segment for non-uniform cooling purposes in warm conditions, and due to its effect on the whole-body thermal sensation, cooling the head would be an effective way to reduce energy consumption.

Aluminum matrix composite (AMC) has many applications in the military and aerospace industries due to its improved mechanical and physical properties. In this research, "A357" aluminum base nanocomposites reinforced with clay nanoparticles with weight percentages of 0.5, 1 and 1.5 in different conditions such as different cooling rates of the melt and alloy state made using stir casting method. Numerous tests have determined and evaluated their mechanical properties such as Young's modulus, yield strength, ultimate tensile strength, stiffness, change in length during yield, change in length during failure, fracture toughness and hardness. According to the results, it was found that by adding clay nanoparticles to A357 aluminum, the mechanical properties of the resulting nanocomposite are far better than the base alloy. Among the nanocomposites made under different conditions, the best mechanical properties belong to nanocomposites reinforced with nanoclay particles a weight percentage of 1. Compared to the base alloy, the yield stress of this nanocomposite has been improved by 42%.

In this research, the transverse vibrations of the fiber glass composite plate reinforced with carbon nano particles have been investigated. For this purpose, the equations of motion of the composite plate have been written based on the third-order shear deformation theory and Glerkin method, and the linear natural frequency of the plate has been extracted. To obtain the nonlinear natural frequency, the method of multiple scales has been used. Then the sheet has been reinforced using two types of nanoparticles and the effect of these nanoparticles and their mass percentage on the linear natural frequency has been investigated. Finally, the effect of the geometrical parameters including the thickness and the ratio of the length to the width of the sheet has been studied. By reinforcing the composite plate with carbon nanoparticles and by increasing the ratio of the length to the width of the plate, the natural frequency of the plate increases, but the increase in the mass percentage of carbon nanoparticles and the increase in the thickness of the plate leads to a decrease in the natural frequency.

In the present study, two proposed designs for compressed air storage systems, one equipped with heat recovery and the other without it, are presented and their technical analysis is performed. The costs of each project are evaluated and economic analysis including Net Present Value (NPV), Internal Rate of Return (IRR), Profitability Index (PI), and Discounted Payback Period (DPBP) is performed. These analyses are presented for storage energy values of 80, 220, 360, 480, 640, and 1000 kWh and storage pressures of 50, 100, 150, 200, 250, 300, 350, 400, and 450 bar. The results of the technical and economic analysis show that these systems are more justifiable to produce higher capacities at lower storage pressures. Finally, using the results of this analysis, the optimal energy storage plan of 640 kWh with storage pressure of 50 bar is proposed. The results of this study can be used to select a suitable compressed air storage system for peak shaving during peak hours of power consumption.

In the recent years, superhydrophobic coatings have attracted considerable research atention due to their excellent properties and wide practical applications. In the present study, the surface of nickel-carbon nanotube composite coating was modified by two methods A) Increasing the roughness, and B) Modification with low-surface-energy material(Stearic Acid = SA). The morphology, wetting angle and corrosion resistance of the prepared coatings were examined by field emission scanning electron microscop (FESEM), contact angle measuring instrument and potentiostat, respectively. The results showed that the contact angle of the 4 microliter water drop on the composite coating modified with SA reached 157 degrees, which indicates the superhydrophobicity of the coating. The current density and corrosion rate of the SA modified coating showed a reduction of more than 97% compared to the highly roughness coating. It was concluded that, the presence of the SA in super hydrophobic coating can act as a barrier against the penetration of corrosive ions through the coating and consequently can reduce the corrosion rate.

In this paper, a new system is proposed for the hydrogen liquefaction based on geothermal energy, in which, the nitrogen is first converted to liquid, and then, is used as to temperature decrease the gas hydrogen, in the hydrogen liquefaction cycle. This system includes four sub-systems; an Organic Rankine Cycle (ORC), an ammonia-water absorption chiller, and two Claude cycles for hydrogen and nitrogen liquefaction. The geothermal fluid at a temperature of 200 ℃ and a mass flow rate of 100 kg/s is considered as the energy source of the system. The proposed system is assessed from the thermodynamics and economic viewpoints. Then, the effects of the compressor outlet pressure, the geothermal fluid inlet temperature, the evaporator temperature, and the generator temperature on the exergy efficiency, the cost of the produced liquid hydrogen, and the hydrogen liquefaction ratio are investigated through a parametric study. Also, increasing the compressor outlet pressure increases the power consumption of the system. Also, at the geothermal fluid temperature of 430 K, the exergy efficiency of the system is determined as 69%. Moreover, the results of the economic analysis show that the production cost of 6.629 (kg/s) liquid hydrogen will be 1.39 $/kg (7.79 $/GJ).

In the present study, a rigid viscoplastic finite element model based on Lagrangian and remeshing methods was developed to simulate the dissimilar friction stir welding of AA5083-O and AA6061-T6 aluminum alloys. Then, a combination of Cellular Automata (CA) and Laasraoui Jonas (LJ) methods was used to investigate the microstructural evolutions of materials with regard to the thermo-mechanical conditions engaged in the process. Moreover, the point tracking method was used to evaluate the flow pattern of the material around the tool and the results were compared with experiment which the elongation and movement of the material towards the upper part of the advancing side was observed for the stirring and mixing of the material. By studying the dynamic recrystallization in the simulation, the simultaneous effect of temperature and severe plastic deformation on grain refining was investigated. The results of microstructural changes showed that with increasing Zener-Hollomon (Z) parameter, grain size decreases and changes the hardness and strength of the alloys used. Also in the mechanical test, the decrease in strength at the advancing side caused the samples become fractured from this side in the tensile test.

Shoulder-fired missiles are one of the most practical tricks in the military industry and are of great importance. In this type of aerospace weapon, due to the short flight time and high maneuvers of the missile in this short duration, the high importance of the control and guidance method to achieve the goal will be determined. In these types of missiles, the speed along the longitudinal axis cannot be controlled due to the solid fuel of the missile, so directional and lateral velocities are used by flight control tools to change the direction. In this paper, first, the dynamic equations of the Shoulder-fired missiles are extracted and then the equations related to predictive control methods and PID are extracted and simulated. Finally, in order to evaluate the accuracy of the simulation results along with the control techniques, the reliability analysis was implemented on both controllers and the results of the two control models were compared. For different flight phases, the use of each controller is specified in combination or individually and the strengths and weaknesses of each controller in different phases are analyzed.

In this research, the performance of a flat-plate solar still at three slope angles of 15°, 30°, and 45° with the presence of porous material of pressed wool and heat absorbent oil in Dezful city of Iran has been investigated experimentally. The surface of the absorber plate is covered by porous material and oil circulates in the pipes connected to the absorber plate in a closed cycle. Results indicated that the energy efficiency using porous materials at slope angles of 15, 30, and 45 degrees is equal to 16.16%, 15.15% and 9.71%, respectively, and without using porous materials is equal to16.39%, 14.48% and 7.62%. In addition, the exergy efficiencies at the slope angles of 15, 30 and 45 degrees with the presence of porous materials is 1.65%, 6.65% and 4.78% respectively, and without the presence of porous materials is equal to 1.51%, 7.28% and 3.45%. The results showed that the maximum amount of distilled water produced at slope angle of 15 degree and in the state of not using porous material is equal to 3300 ml in a period of 11 hours.

The aim of this paper is to analyze the effect of combustion chamber pressure and dimensional deviations on the components force of an internal combustion engine. The internal combustion engine, as a power source of vehicles, is a complex engineering system so the analysis of dimensional and geometric tolerances of its components is very important. in this research, the effects of dimensional tolerances of components of an internal combustion engine on the force tolerance are studied. The kinetic and kinematic analysis are used to produce a suitable mathematical model to study the effect of parameters. In a case study, for a four-cylinder engine, the tolerance analysis is done and the distribution of output forces is obtained using Monte Carlo statistical method by coding in MATLAB software. The dynamic force distribution diagrams, including the effect of combustion chamber pressure and dimensional tolerances, could be used in the design of engine components using the design method based on reliability. Also, the force tolerance analysis is done by the worst-case method to compare the results.

Wheat straw is one of the wastes produced in agricultural section that is burned in the farmlands entering huge greenhouse gases into the atmosphere. The aim of this study is to evaluate thermal energy loss from external walls of a building constructed using fired clay hollow bricks filled with compacted wheat straw. Hence, fired clay hollow bricks compared to those filled with compacted wheat straw (having a density of 0.156 g cm-3) were used to build up the walls of an experimental container model outdoor and thermal energy loss throughout the walls of it were evaluated. Comparison of thermal properties of the constructed walls using non insulated fired clay hollow bricks or insulated with compacted wheat straw including: thermal conductivity, heat flow rate and heat transfer coefficient showed decreasing from 0.2 to 0.04 W m-1 ºC-1, 18.36 to 6.98 W m-2 and 1.7 to 0.41 W m-2 °C-1, respectively, for insulated walls. The results revealed a decreased thermal energy loss between 72 to 81 percent from walls of the building constructed once compacted wheat straw with the compaction degree applied.

In this paper, the energy analysis of Combined Heat and Power (CHP) generation systems of Bandar Abbas Oil Refining Company is performed. In order to investigate the importance of variables affecting the performance of CHP units, sensitivity analysis has been carried out for each of the variables. In this study, in order to facilitate the display of real-time energy efficiency on Distributed Control System (DCS) in the control rooms, the equations for calculation of efficiency have been simplified. The results show that in the case of using design data, the CHP units A, B, C, D and E have energy efficiency of 87.3, 87.3, 87.3, 83 and 75.7%, respectively. Furthermore, when operational data is used, the energy efficiency of these units is calculated as 43.67, 57.3, 57.17, 68.94 and 70.27%, respectively. The results of sensitivity analysis also show that the lower heating value of fuel with 9.74%, the steam flow of the heat recovery steam generator with 6.07% and the inlet water temperature with 4.3% have the greatest effect on efficiency.

In modern aircrafts, control allocation is one of the effective methods for executing specific maneuvers, time or energy reduction for determined operation, and compensating of actuators faults. For this purpose, the aircraft should be over-actuated in various channels. In this situation, control allocation means the distribution or division of the required control signals between aerodynamic surfaces (aerodynamic actuators) and the thrust vector control (TVC) system. Among the different approaches for control allocation, the use of methods based on soft computing is of interest. Therefore, the main goal of this article is utilization of fuzzy logic and multi-objective optimization to allocate control signals for the landing phase of the F/A-18 aircraft in the presence of elevator and TVC actuators. Therefore, flight modeling and simulation of aircraft has been done and by defining suitable fuzzy rules and specific objective functions, the ability of the developed allocation approach to converge the output variables to the expected values is demonstrated and finally, the aircraft completes the landing phase with desired accuracy and optimal control effort.