نشریه یافته های نوین کاربردی و محاسباتی در سیستم های مکانیکی
سال سوم شماره 2 (تابستان 1402)

This research aims to model the nonlinear dynamics of the space propulsion system equipped with an electro-pump. For modeling, this system includes the combustion chamber, fuel and oxidizer tanks, and the corresponding pressurization system. A set of governing equations has been modeled in the Simulink of MATLAB software. The results of the modeling including changes in the angular velocity versus the time, changes in combustion chamber pressure versus the time, and changes in the mass flow rate of the fuel and oxidizer to the combustion chamber versus the time, are presented. In the end, the obtained results are compared with the results of the available engine and in addition to validating the results, it is possible to confirm and validate the performance of the electro-pump in a liquid fuel engine. The results showed that the angular velocity rate, the average acceleration rate of the combustion chamber, the average flow rate of the oxidizer to the combustion chamber and the average flow rate of the fuel to the combustion chamber obtained from the simulation and the available reference have a maximum error of 20%. The amount of difference in the conceptual design stage is free of problems. In addition, the trend of the graphs is similar.

In the present research, an autonomous wheeled seven-degree-of-freedom robot with an adaptation mechanism to a passive diameter pipe was designed with the help of Adams software, and after checking the correctness of its movement, by designing a fuzzy controller in the Simulink section of the software, the dynamic simulation of its movement in various geometric conditions such as straight and vertical pipes, elbows, pipes with reducers, deposits and corrosion were investigated. A fuzzy controller was designed to guide this robot inside the tube, and its control system was implemented using direct current motors for each of the robot's wheels. The ability of the fuzzy controller of the robot to follow the desired input speed and its response characteristics in the steady state were investigated, and the presented results showed that the fuzzy controller performs better in following high speeds and has a better transient response at these speeds. Using the optimal torque distribution system, the robot control system is improved and the output signal of the fuzzy controller can be sent to the robot wheels in a targeted way. Therefore, the application of this method caused a significant reduction in the power consumption of the robot and optimization of its energy consumption. This designed robot has a high potential for making an accurate sample, commercialization and responding to the current needs of the country's oil and gas industry due to its less expensive mechanism compared to similar ones.

In this study, the effect of limited inclination angle on two-phase flow in a vertical pipe was investigated, focusing on the formation of liquid film thickness using image recording and processing techniques. To generate annular flow patterns, non-homogeneous air-water flow was utilized in three transparent pipes with diameters ranging from 25 to 75 millimeters. After analyzing the flow pattern results for various superficial gas and liquid velocities, Reynolds numbers, and different pipe diameters, both the maximum and minimum liquid film thicknesses were calculated and presented, along with their ratios. Additionally, the dimensionless equivalent liquid film thicknesses for inclined pipes were provided concerning the uniform film thickness in the fully vertical condition. The results indicated an increase in the ratio of maximum to minimum film thickness with a change in inclination angle from 90 to 85 degrees. Furthermore, the dimensionless equivalent liquid film thickness decreased with inclination angle, consistent with prior research findings. The uncertainty analysis revealed a maximum uncertainty of 4.9 percent in the experimental assessment of the liquid film thickness, which falls within an acceptable range.

In order to convert mechanical vibrations into useful electrical energy, is one of the goals of many researchers in today's science, and for this purpose, harvesting equipment with piezoelectric components has been used. To check the performance of this system, knowledge of the behavior and output of the vibration system, and the effect of different parameters of that system is of great importance. In the current research, it is tried to investigate the effects of different parameters on the performance of the harvester by modeling the vibration system as a two-degree-of-freedom model, in two different configurations. To check more closely and find a result closer to reality, using the theory of linear random vibrations, the stimulation in question was white noise type. In the mathematical modeling, two two-degree-of-freedom states have been investigated, in the first state, the piezoelectric between the base and the first mass, and in the second state, the piezoelectric between the base and the second mass has been assumed. After extracting the governing equations in each configuration and applying the input to the system with random excitation, the effect of all identified and introduced parameters in the system is studied, and the configuration with higher efficiency, in terms of the average energy harvester, is introduced and the results are expressed graphically.

In this project, a three-dimensional investigation of the fluid flow inside a stirred tank inside an industrial reactor has been done to investigate the velocity distribution and heat transfer. To model the stirred tanks and its blades, first the geometry structure was carefully studied, then the geometry modeling was done using SOLIDWORKS software, then the generated geometry was entered into the Ansys Space claim or Ansys Design Modeler software. After that, meshing is done with Ansys Meshing software, and then appropriate boundary conditions are applied on the stirred tank and its blades. In this project , SST , k-ω turbulence model is used. For meshing, unorganized mesh generation was used, and the average mesh quality, aspect ratio, and elongation for the computational mesh of the tank with an anchor agitator were 0.84, 1.84, and 0.22, and also the flow field inside an agitator tank with a baffle was For the angular speeds of 60 , 120 and 180 rpm , it was simulated for two types of stirrers. By increasing the angular speed of the propeller, the performance of mixers improves and better mixing takes place. Examining the velocity vectors showed that four strong wake regions were formed near the impeller, and two rings were formed on each side, one at the bottom and the other at the top of the stirrer. The first jet circulates to the bottom of the tank and then returns to the propeller area. The second fluid jet also circulates in the upward direction. In the new mixer, there are more high-speed areas in the distance between the bottom of the tank and the impeller compared to the anchor mixer. In fact, the speed is almost twice that of the anchor stirrer. Therefore, the new agitator has a much better performance than the anchor agitator in the bottom areas of the tank. So, the new mixer has a better performance for mixing solid materials that have the possibility of sedimentation. At distances farther from the bottom of the tank, the tank with the anchor stirrer has better mixing than the new stirrer , and this anchor stirrer has more high-velocity areas than the new stirrer. In the new high-speed mixer, the distance between the bottom of the tank and the propeller is greater than that of the anchor mixer. In fact, the speed is almost 2 times that of the anchor stirrer. Therefore, the new stirrer is much better than the anchor stirrer in the bottom areas of the tank. So, the new mixer has a better performance for mixing solid materials that have the possibility of sedimentation. At distances farther from the bottom of the tank, the tank with the anchor stirrer has better mixing than the new stirrer, and in these areas the anchor stirrer has a higher speed than the new stirrer. At a height of y = 0.880 m meters of fluid is divided into four symmetrical jets and the rest of the fluid flows upwards and reaches the free surface , and the speed increases with the height until reaching the height y = 1.330 m , where the length of the vortices decreases and circulates from the impeller to the impeller shaft due to the pumping effect . The speed of the fluid flow in the tank that is stirred by the new propeller is much higher than that of the anchor propeller , so the mixing time with the new propeller is less than that of the anchor propeller.