مجله مهندسی مکانیک
پیاپی 152 (آذر و دی 1402)

One of the essential issues in the operation and maintenance of pipelines in industry is the line-stopping of fluid flow in the pipeline to carry out downstream repairs during incidents such as breakage or the need to make changes in the pipeline to add a new line, replacing the pipeline, installing a new valve or flange in the pipeline. Various line-stopping methods are used in drinkable and undrinkable fluid in pipelines, such as hot tap, pipe freezing, and inflatable pipe plugs. However, these methods cannot be used in all types of fluids and variable pipe diameters, and they can increase maintenance time, waste valuable fluid such as drinking water, or increase costs. In addition to explaining the different methods of line-stopping in pipelines in various industries, this paper describes the problems and limitations of using each one.

In this paper dielectric barrier discharge plasma actuator effect on flow separation of a horizontal axis wind turbine blade section were studied. Firstly, two dimensional flow simulations of plasma actuator with improved electrostatic model were performed in various operational conditions and angle of attacks. Then, an explicit response surface mathematical model was derived for the effect of variables on aerodynamic coefficients. Separation zone shrinkage was observed as a consequence of momentum injection from plasma actuation. The mathematical model has an acceptable validity and shows the significant interaction between parameters. Finally, a MATLAB code was developed to implement blade element momentum method and evaluate the mechanical output power of Tellus 100 kW wind turbine with actuator operation. The results indicate no significant effect on output power for cut-in to 10 m/s wind speeds and an increase of about 11 percent for 11 to 16 m/s speeds.

in this article, three-dimensional numerical simulation of the steady flow of a Newtonian fluid parallel to a tube assembly with regular triangular arrangements, square and hexagon, which are infinite and there are no walls around them, have been discussed. Fluid flow equations have been solved using SIMPLE method and second-order upwind approximation by Fluent software. The solution process is that first, a uniform velocity distribution is considered on the inlet face around of tubes, and with the movement of the fluid in the parallel direction of the tubes, the flow reaches the developed state. Hydrodynamic inlet length, pressure drop, friction coefficient factor and velocity distribution were investigated according to the ratio of the distance between the centers of the tubes on the diameter. To ensure the accuracy of the simulation performance, the results of the developed part of this research have been compared with the results of valid references. The results show that the length of the hydrodynamic inlet in all arrangements is less than the length of the flow inlet inside a normal circular tube with an equivalent hydraulic diameter and the ratio of this length to the equivalent hydraulic diameter decreases with the increase of the distance between the tubes. Also, by increasing the compactivity of the tubes, or in other words, reducing the distance between the tubes, the pressure drops in the 30-degree arrangement is higher than in the 45 and 60-degree situations.

In this research, the effective factors on the liner failure of the turbocharged engine (16rk215T) of the locomotive have been investigated. By preparing three liner samples from different manufacturers and sending them to the laboratory, the mechanical properties, including hardness and tensile strength, as well as the percentage of constituent elements and the difference in their values in different samples, were studied. Next, the effect of the weight percentage of different elements on the mechanical properties of gray cast iron was investigated. By preparing microscopic images at 100x magnification, the background structure was seen. Also, the shape and arrangement of lamellar-graphite in different samples were compared with each other and it effect on the fracture and crack growth in the liner was investigated. Three samples of liner, grade and material have been determined. With the appearance of eutectic phosphide in the structures of two samples A (broken liner) and B (liner with crack), as well as the high percentage of phosphorus, structural defects and the presence of dislocations in the grain cause the failure of these samples. Also, non-uniform production of lamellar-graphite in these two samples, its short length and thickness increases strength, reduces absorption and reduces energy.

In the present study, the effect of blade angle on two-phase flow (liquidsolid) distribution in a stirred tank with a pitched-blade turbine (PBT) was simulated using computational fluid dynamics (CFD). To simulate the solid-liquid two-phase flow, the standard k-ԑ turbulence model coupled with the Eulerian-Eulerian (E-E) Multi-Fluid Model was employed. The two-phase flow properties along the tank axis were computed and validated by the available data in the literature. Then, the effect of the blade angle on the fluid flow inside the tank as well as the solid phase volume fraction distribution were investigated. Results indicated that increasing the blade angle from 45 to 75 degrees at a constant speed, increased the maximum radial velocity and power consumption by 45.6% and 217%, respectively.

In this paper, aeolian vibrations of power transmission lines are studied and effects of spacers are considered. Each of the conductors is modeled as an EulerBernoulli beam and the spacer is placed as a spring and damper between them. The stiffness and damping coefficient of the spacer has been obtained using experimental tests for a spacer used in Iran's transmission lines. The equations of motion are derived using Hamilton's principle. These equations have been converted into ordinary differential equations using the Gelkerkin method and then numerically solved using the Rang-Kutta method. The effect of using the spacer on the transmission lines and the effect of different design parameters, such as the amount of mass, the stiffness and damping coefficient of the spacer, and the location of the spacer on the amplitude of the vibrations of the conductors have been studied. The results of the simulation have illustrated that the existence of the spacer is necessary to maintain the safety of the lines. However, despite our expectations, not only does a hard and heavy spacer have minimal impact on the control of vibrations but also can have adverse effects. It was also shown that increasing the mass of the spacer up to 10 times reduces the range of vibrations by 11% and the minimum stiffness equal to 2×106 (N⁄m) is needed for the spacer. Because in this value, the amplitude of vibrations decreases up to 2 times compared to lower stiffnesses.