مجله مهندسی مکانیک
سال پنجاه و سوم شماره 3 (پیاپی 104، پاییز 1402)

Todays, the use of small satellites for communication, research and military purposes is expanding. One of the main problems of these satellites is the design and construction of the propulsion system. The propulsion system used in two cases. One is to provide power to leave the earth and the second one is to provide power to stabilize, correct or transfer the orbit of satellite. The main purpose of this article is design and manufacture of a butane storage tank made of stainless steel under 10 bar explosion pressure for a micro size satellite. For this purpose, the required diameter and length of tank determined then thickness of tank calculated based on the theoretical method, according to the ASTM standard. In order to ensure the optimal performance of the tank, finite element simulation performed in ABAQUS software. Simulation done in 12 different cases. Simulation done in several other thicknesses to obtain the minimum working thickness of tank. According to all the analysis, the appropriate thickness was determined to be 1.5 mm. Then, proper propulsion management system designed in zero gravity condition to separate liquid phase from gas. For this purpose, compressed metal meshes used as a porous material. Finally, the tank was manufacture and inspected according to the design. 

Humidification of polymer membrane fuel cell (PEMFC) reactant gases is necessary for keeping the membrane humidified. Planar membrane humidifiers are widely used for reactant gas humidification due to their proper performance, simple structure, and long life span. In this study performance of a planar membrane humidifier with symmetrical L-shaped obstacles in both channels is investigated numerically by ANSYS fluent and its performance is compared with a simple planar humidifier. The Effects of geometrical parameters are studied by 3D numerical modeling. Accordingly, two parameters of water recovery ratio (WRR) and dew point temperature at the dry channel outlet are considered the main performance criteria. Results show performance decreases with the increase of the gasses mass flow rates. Dry gas outlet temperature noticeably increases by the L-shaped obstacles insertion which indicates better heat transfer. The effect of four geometrical parameters of the obstacle consisting of obstacle length, height, the distance between the obstacles and the top and bottom of the channels, and their relative distance are investigated. Three values are considered for each geometrical variable, and the distance between the obstacles and the membrane exhibits more influence on the performance of the humidifier. The geometrical study improves the performance of the obstacles and raises the WRR and the dew point temperature by about 3% and 3.5 degrees, respectively.

The insect flight mill is a device that used for studying insect flight. With this tool, the main parameters of flight such as distance, speed and duration can be calculated and analyzed. In addition to the aerospace field, which focuses on improving and optimizing existing flying devices and can be inspiring for the construction of micro air vehicle (MAV), it is also used in agriculture to combat pets and increase the quantity and quality of agriculture products. This article discusses the design and construction of a sample insect flight mill device that provides researchers with valuable and extensive information on insect flight performance while being simple. After a brief explanation of the various exiting methods in insect flight research and the introduction of insect tethered flight device, the governing equations of the device are presented. Then, the construction method and testing procedure are described, followed by an analysis and comparison of the obtained data with similar and upgraded devices. Finally, the advantages and disadvantages of the device are discussed.

Nowadays, the economic, environmental, and technical advantages are a suitable approach for multigeneration systems, and the approach of using waste heat for these systems shows its value more than ever. In this study, a multigeneration system consists of a supercritical carbon dioxide (S-CO2) Brayton, Organic Rankine Cycle (ORC), Proton Exchange Membrane (PEM) electrolyzer, and Reverse Osmosis (RO) system. First, energy and exergy analysis has been done on the proposed system, then a parametric study has been performed on this proposed system and finally, it has been optimized from maximum output power viewpoint. The optimization results also show that 252366 kW, 43.1%, 58.37%, 12.13 kg/hr, and 55.52 kg/s, respectively, are calculated for the values of generated power, thermal and exergy efficiencies, hydrogen production, and produced fresh water. Moreover, the new multi-generation system that uses supercritical CO2 in Bryton has better thermal efficiency compared to the previous study.

Investigating the flow pattern developed whitin spaces with relatively large scales that can be caused by forced or natural convection is of particular importance based on which, one can comment on the spread of polluting particles, temperature distribution and thermal comfort conditions. Calculating the developed flow field whitin such spaces using numerical methods, requires relatively large memory and long calculation time. Whereas, suitable zonal methods can predict accurate flow patterns with a very small amount of calculations. In the present research, equations similar to that of one-dimensional flow passing through an orifice, which is known as the zonal power law method, were used to predict the flow between the adjacent cells. These equations along with the mass conservation equation defined for each cell of the domain were solved using an innovative numerical method and the velocity distribution was specified. The 2-D sample domain had 1 m height and two different lengths of 0.5 and 2 m where the air inlet and outlet were considered at different positions. The air velocity at the inlet was 2 m/s. In order to make a better match with the experimental results, variable loss coefficients between the cells were used and significant improvement was found in the results. Despite the comformity made in the velocity distribution, the existence of recirculating flows predicted by the numerical methods could not be obtained using the employed method even with the variable coefficients.

In this research, a spectrum variety of AUSM-family, including AUSM+, AUSM+UP, SLAU, and AUSM+M, in a numerical framework, based on the finite volume method to solve preconditioned two-dimensional Eulerian equations, was developed in an unstructured grid and the performance of this family has been investigated in incompressible flow. Where fluid velocity is low, convergence rate of density base solvers is distorted. Turkle's preconditioning method based on the conservation variable has been utilized to remedy the poor convergence at low speeds flows. In addition, at low speeds, the imbalance between the elements in this family's convective and pressure fluxes results in a deterioration of accuracy. Therefore, the necessary mathematical literature has been developed to solve the imbalance problem raised at the low speeds of the AUSM family. In addition, to further accelerate the convergence rate and reduce the stiffness of the equations at low speeds, the time part of the equations has been discretized utilizing the modified second-order Bashforth-Moulton method. To investigate the accuracy and efficiency of the developed AUSM family, steady two-dimensional inviscid tests around the NACA0012 airfoil, three-element 30P-30N airfoil, and half-cylindrical have been constructed for a wide range of low and highly- low Mach numbers. The results show no optimal trade-off between convergence rate and accuracy improvement within AUSM family. The accuracy improvement is not accompanied by reduced convergence time necessarily in low velocity flow field.

Present research investigates the feasibility of using hydropower in water transfer canals of Gavshan dam to generate distributed electricity with hydrokinetic turbines which operate at water velocity of less than 2 m/s. The reason for this is the high potential for power generation in this type of currents. For this purpose, first the hydraulic characteristics of water flow were extracted. Then, the turbine blade profiles were first calculated by Schmitz theory, then by modeling in SolidWorks and analysis in ANSYS-FLUENT, the amount of power is obtained. The results were validated and a turbine was designed for each canal/tunnel. The results show that the efficiency of hydroturbines will be about 90%. By using a hydrokinetic turbine with a diameter of 4 m and a water velocity of 2 m/s, the electricity demand of a village near the tunnel would by supplied and annually 39366 kWh of electricity can be sold to the public grid. Furthermore, the payback period is 3.4 years and the net present value of the project is highly positive. The reduction in carbon dioxide production is 109 tons/year.

In many impact-contact events we face the problem of wave propagation on a composite rod. In this type of problem, there is a possibility of developing a gap and re-collision between the object and the rod, which requires defining a boundary condition capable of modeling this complex process. Also, a numerical method that can provide accurate modeling of the stress wave propagation process is very critical. Using the wave element method with boundary conditions related to impact-contact problems, we have been able to model stress waves propagating in multi-layer rods. It includes repeated contact and short-term rebound at different points on the body and at various time instants. In the present research, the wave element method and the impact-contact boundary condition have been used to model wave propagation in multi-layer rods. The results obtained from this method are compared with the analytical solution presented for simpler problems, and then problems with the nature of complex stress wave propagation are modeled. It has been shown that the introduced method has the ability to analyze problems with good accuracy.

Tensegrity systems are lightweight spatial grid structures that are composed of compression and tension elements that can be used in adjustable structures. The primary stability of these structures is achieved by creating pretension conditions between the elements. These systems have low structural damping, which makes them vulnerable to dynamic loads. As a result, it is essential to predict the behavior and extract the dynamic characteristics of these structures to achieve a safe design. This article presents the vibration analysis of a one to four stage tensegrity structure with a square cross-sectional area. A Lagrangian approach and the finite element method were used to extract the nonlinear dynamic equations of the system based on the coordinates of the nodes. For one to fourstage tensegrity systems with fixed cross-sections and heights, the force density method is used as an initial form finding method. Each element's cross-section is designed to have a minimum mass, and dynamic modeling allows for observing elastic/plastic deformations under various boundary conditions, as well as static and dynamic loading on each node, taking gravity stiffness into account. Dynamic simulations in the form of comparative studies have been conducted to investigate natural frequencies, mode shapes, time responses of nodal displacements, elements deformations, and internal forces for one to four-stage tensegrity structures.

Preparing composites before welding and using nanocomposites is one of the new methods of joining. In this research, the mechanical strength of thermosetting composites surface prepared by chemical etching using polyvinyl chloride (PVC) polymer in the presence of aluminum oxide nanoparticles has been investigated. Thermal analysis of PVC containing different weight percentages of aluminum oxide nanoparticles shows a 45% increase in thermal conductivity. A regression model based on the response surface methodology using the effective parameters of welding time, weight percentage of nanoparticles and thermal conductivity obtained from variance analysis was developed to predict the maximum force and displacement of joint failure. The results show the maximum breaking strength and strain of 59 MPa and 0.04 of the welded sample, respectively, in the presence of 1% by weight of aluminum oxide nanoparticles. The increase of 1.3 and 1.2 times of the maximum tensile strength and breaking strain of the joint, respectively, in comparison with pure PVC samples, indicates the improvement of mechanical properties. Examining the microstructure with SEM shows that a uniform connection has been established along the weld line.

Surge is a dynamic instability in the compressor that is determined by limit cycle fluctuations and leads to large-amplitude distortions in flow rate and pressure. This mode is an unstable mode of operation of the compressor system that occurs in low flows and not only limits the performance and efficiency of the compressor, but also leads to damage to the compressor and accessories due to large thermal and mechanical loads. Today the use of active control methods to increase the operating range of the compressor has received much attention. Given the need for available surge controllers to be fully aware of the characteristic curve of the compressor system, presence of uncertainties and disturbances can deteriorate the performance of the controller. In this paper a finite time backstopping sliding mode controller is designed for overcome surge instability in the presence unknown uncertainties. An adaptive control rule is proposed which does not need knowledge of upper limit of disturbances or uncertainties. Lyoponov theory is used to stability analysis. The proposed controller can cover the effects of uncertainty and uncertainty on the compressor and throttle characteristics and unmodified dynamics, and in addition is resistant to time-varying disturbances in the flow and pressure applied to the system. The simulation results performed in MATLAB, indicate that the proposed regression controller, in addition to being robust, is able to ensure the stability of the system in the presence of turbulence and uncertainty.

In this research, by using the combined lattice Boltzmann and smooth profile method, for power law non-Newtonian fluidized bed, the effect of changing the geometric and fluid on the expansion behavior of the bed has been studied. Investigations have been carried out for 7 different geometries and 4 Newtonian and non-Newtonian fluids with a power law index of 0.8 to 1. The results of the bed with Newtonian fluid show more porosity than the bed with non-Newtonian fluid. Also, increasing the index of the power law caused an increase in the porosity of the bed, and the porosity of the non-Newtonian bed decreased with an increase in the density of solid particles and the initial height of the bed. Investigating the porosity ratio in the non-Newtonian bed showed that with the increase in the diameter of the solid particles, this ratio decreases and increases with the increase in the diameter of the fluid bed. In addition, comparing the results of the bed with carboxymethyl cellulose 0.1% solution as fluid showed that the effect of reducing the particle diameter in the bed, to increase the porosity ratio is 2 times more than the effect of increasing the diameter of the bed. Finally, the output of the model showed that the porosity ratio for the bed containing solid particles with different diameters is lower than the bed containing particles with equal diameters.

One of the challenging issues in all types of cars is cooling and heat transfer. This issue requires its own unique design in cars with special use. In this article, the cooling system of the heavy-duty vehicle is designed and its various characteristics are investigated. First, with the help of a 1D model in GT-SUITE software, the temperature of the engine coolant is calculated based on the performance of the heat exchanger and the flow rates of the radiator coolant, and then this 1D model is coupled with a 3D- CFD model to examine the air flow patterns through the underhood. With the help of the cooling system design algorithm presented in this paper, it is possible to check the effect of the geometry characteristics of the air inlet channel on the performance of the cooling system. Using fan frame, radiator frame and inlet and outlet grill increases the flow rate by 20% and using the angle of the inlet grill at 70 degrees instead of the initial 35 degrees increases the flow rate of air passing through the radiator by 21.74%. 

In this research, the evolution of damage and martensitic transformation of AISI 304, 316 and 321 stainless steels have been studied experimentally and numerically at room temperature. At first stage, the standard tensile tests have been performed and in the second stage the XRD has been tested and the available phases and the volume fraction of martensite have been obtained. The tensile tests have been performed for a variety of loading-unloading elongation. Damage is obtained using this loading-unloading slop. The graph of force-deformation has been achieved. The samples were cut by water jet machine and the X-ray diffraction tests have been performed on the stretched samples to obtain the volume fraction of martensite. Numerical simulations have been performed by the implementing the UMAT code in ABAQUS. In the simulations, the properties achieved from experimental tests are employed. The numerical simulations have two separated sections: damage-plastic and martensitic phase transformation. In this research, these two phenomena are considered simultaneously. This model can explain both phenomena at ambient temperature. The verifications have been compared simulation results with experimental data.

Liquid hydrogen is a solution for storing and transmitting electricity that is produced by renewable energy sources such as geothermal energy. In this paper, a Rankine cycle with a proton exchange membrane electrolyzer, an ammonia absorption refrigeration cycle, and a hydrogen liquefaction cycle are simulated and analyzed for storing geothermal energy as liquid hydrogen. The power generated by the Rankine cycle is used to produce hydrogen gas in the electrolyzer. Additionally, the cooling obtained from the absorption refrigeration cycle is used to pre-cool the hydrogen gas to a temperature of -9.26 ℃, and then the hydrogen is liquefied at -253 ℃ by a mixed refrigeration cycle. The innovation of this study is based on using the cold energy obtained from the absorption refrigeration cycle in the liquid hydrogen production cycle and integrating the liquid hydrogen production process with the geothermal energy system. By using energy, exergy, and economic analysis, the final cycle efficiency was improved compared to the initial system. The special energy consumption of the liquefaction unit is 81.8 kWh per kilogram of hydrogen. In a three-year payback period, using economic analysis, the minimum selling price is calculated to be $2.11, which is lower than a similar liquid hydrogen production cycle presented in the past.

Today, nanotechnology is used in various fields. One of the practical tools of this new technology is the Atomic Force Microscope (AFM). AFM is used in imaging, making microscale equipment, extracting the properties of biological tissues and manipulation. Manipulation of particles using AFM is considered in two phases. The first phase is before the movement of the target particle and the second phase is during the movement of the target particle. Determining the exact path of the particle in the second phase of nanomanipulation is of great importance. One of the important parameters in the simulation of the second phase is the friction model used. In this research, for the first time, three exact friction models of LuGrr, Leuvn and Greenwood-Williamson have been used to investigate the 3D second phase of nanomanipulation. The target particle under investigation is a gold nanoparticle, whose dimensions and geometry were obtained experimentally by imaging with an AFM. The obtained results have shown that the LuGre model predicts the lowest amount of displacement and the Greenwood-Williamson model predicts the highest amount of displacement.

 Solar collectors and photovoltaic panels are usually exposed to the sun at a fixed angle relative to the horizon. The optimal angle has a significant effect on receiving maximum energy. Since there is not a comprehensive study to determine the optimal angle in Khuzestan province, in this research, the centers of counties in Khuzestan province, including twenty-six cities, were considered. The energy received on an inclined surface was calculated based on the average of 16 years of solar radiation data and the isotropic and non-isotropic models (HDKR model). Different angles from -20 to 90 degrees with a step of 0.1 were examined using Fortran codes, and the angle corresponding to the maximum received energy was determined as an optimal angle. Comparing the obtained results with previous studies showed that the HDKR model has better performance, and the average optimal angle of the cities of Khuzestan province was approximately 26 degrees with a standard deviation of 0.8 degrees.

In this paper, governing equation of pressurized axisymmetric cylinders made of homogeneous and isotropic materials with large deformations is derived using the Nonlinear Plane Elasticity Theory (NPET). Because of large deformations along the radial direction and hence existence of nonlinear terms in kinematic equations, the governing equation is a nonlinear second-order equation with variable coefficients, which is solved in plane stress and plane stress states using perturbation theory. According to the equilibrium equation, boundary conditions and different end conditions of the cylinder; radial and circumferential normal stresses and radial displacement in cylindrical shells are calculated analytically. The effect of thickness, material and boundary conditions on stresses and displacement in cylindrical shell is studied by the results obtained from analytical solution. For investigating the accuracy of the results obtained from the analytical solution, the numerical finite element modeling of mentioned cylinder is done with ABAQUS software and the results of the two methods are compared. This research reveals that the obtained results by the mentioned analytical solution procedure have good accuracy for cylindrical shells under pressure loading.

SARS-CoV-2 which caused to Covid-19 was reported as an epidemic by the World Health Organization (WHO). In this virus, one of the essential cysteine proteases, which is called the main protease, can be used as a drug target for many herbal and chemical inhibitors. One of the factors in the effectiveness of drugs inhibitory is the binding affinity of them to main protease. In this paper, the comparison of the binding affinity of herbal compounds (Nigelidine, from black seed and Liquiritigenin from licorice plant) with Remdesivir on the main protease from SARS-CoV-2 has been investigated using steered molecular dynamics simulation. The results showed that Nigelidine has the highest rupture force among herbal ligands. Despite of the fact that Remdesivir has the highest rupture force compared to herbal inhibitors. Also, the electrostatic and van der Waals energy for Remdesivir and main protease shows a more negative value than other herbal inhibitors. Therefore, despite of the high dock score of the compounds of black seed and licorice, Remdesivir as a chemical compound shows more binding affinity.

In order to improve the efficiency of hydraulic circuits, it is necessary to change the displacement volume of the pump and its output flow based on the load on the actuator. The use of a displacement control valve next to a variable flow pump makes it possible for the pump output oil flow to adapt to the load on the hydraulic actuators. In this paper, first of all, the mathematical relationships governing the variable flow pump with the displacement control valve are presented. Then, in order to determine the variables of the hydraulic pump in steady-state conditions, the mathematical relations governing it are solved in three working positions of the pump displacement control valve. Also, the effect of the load on the hydraulic motor shaft and the cross-sectional area of the flow control valve between the pump and the motor on the circuit state variables was investigated. The appropriate closeness of the experimental results with the results of solving mathematical relations in steady-state conditions and different working conditions of the displacement control valve confirmed the correctness of the mathematical relations governing the hydraulic circuit including variable displacement pump with control valve and variable displacement motor.