مجله مهندسی مکانیک امیرکبیر
سال پنجاه و پنجم شماره 6 (شهریور 1402)

To prevent safety issues such as thermal runaway, lithium-ion batteries must be constantly monitored. Most thermal management methods are based on designing suitable cooling systems. Also, since the surface temperature is measurable through a sensor, it is considered the main criterion of thermal management. However, in extremely fast charge-discharge operations, the core temperature can be significantly higher than the surface temperature, so the cooling system may not be able to solely maintain the core temperature in the safe range. The objective of this paper is to combine electrical and thermal management and set the core temperature as the main criterion. To achieve that, model predictive control (MPC) is implemented to control the supplied or drawn current of the battery cell and Sigma point Kalman filter (SPKF) is used to estimate model states. The simulation and experimental results indicate that incorporating MPC and nonlinear Kalman filter Estimators can be a novel strategy to simultaneously manage electrical and thermal states. It is also expected that controlling the core temperature in fast charge-discharge operations, may increase the safety and lifetime of the cell.

One of the most important analyses in the design of various structures, especially pressure vessels and their safety is the fracture mechanics. One of the important parameters in fracture mechanics is the study of the stress intensity factor of cracks in the tank wall. In the present study, the behavior of a semi-elliptical crack in a spherical pressure vessel made of functionally graded materials has been studied using Abaqus finite element software. The effects of parameters such as crack geometry, simultaneous internal and external cracks, pressure distribution, thermal load distribution, changes in the properties of the functionally graded material, and support conditions on the value of the stress intensity factor have been investigated. In order to model and analyze the stress intensity factor in this type of tank, various power, exponential and linear functions were used in the form of MATLAB code as well as a subroutine code. The results showed that with increasing pressure, the stress intensity factor increases. Crack geometry is also an important factor that has a significant effect on the stress intensity factor. So with the increase of the a/c value, the stress intensity factor also increases. Also, the examination of the support conditions shows that with the increase in the number of foundations, the stress intensity factor also increases.

Endplates are one of the most important components of polymer electrolyte membrane (PEM) fuel cell that must apply uniform contact pressure distribution on the membrane electrode assembly (MEA). For this reason, these plates must have good bending rigidity. In this research, the bending behavior of composite sandwich plates has been investigated numerically in order to achieve a composite structure with high bending stiffness for use in the endplates of PEM fuel cells. For this purpose, the bending strength of composite sandwich panels with grid core was evaluated based on the type of material and relevant standards through numerical simulation. Numerical simulation has been performed in Abaqus software using finite element method. The effect of different angles of fibers in and three different geometries of square, triangular and diamond grid core for C/Sic and E-Glass Epoxy materials on the bending behavior of composite sandwich panels were analyzed. The obtained results indicate the better performance of C/Sic materials in the stress test, as well as the more suitable bending behavior of triangular mesh geometry with fiber angles (0-45-90).

The drill-string is exposed to strong vibration due to its long length and the dynamic forces caused by the bit-rock interactions. The Anti Stick-Slip Tool which is located at the end of the drill-string and inside the bottom hole assembly prevents occurrence of the stick-slip. In this research, a new model for investigation of this tool is presented, which covers the limitations of previous models for analyses of the drill-string along with Anti Stick-Slip Tool. The system is modelled with two degrees-of-freedom in non-activated state and behaves like a rigid body. By activation of the tool, a degree-of-freedom is added to the system based on kinematic constraint of the tool and the system becomes three degrees-of-freedom. Based on the proposed model and determined conditions, the tool switches between the non-activated state with two degrees-of-freedom and the active state with three-degrees-of-freedom. The results obtained by simulating the dynamics of the tool represent a sensible behavior of the tool in presence of the external forces and torques on two parts of the tool. The proposed model precisely demonstrates the effect of weight on bit and weight on hook on the activation of the tool. The non-linear behavior of the tool caused by the switch between two set of linear equations has been discussed by using the presented model in a certain operational condition.

Due to its buckling resistance, the spherical shell is an ideal geometry for use in pressure vessels under uniform external pressure. The collapse pressure of these types of shells is much lower than its theoretical value due to the high sensitivity to imperfections and the yield stress of the material. Unlike cylindrical shells, the collapse pressure of spherical shells is not only dependent on the size of the imperfection, but is also dependent on the shape of the imperfection. Since the imperfection depends on the sheet metal forming method, it is necessary to investigate the effect of the fabrication method on the collapse pressure. This article is focused on experimental and numerical study of buckling of hemispherical shell made by spinning forming method. The most important problem of this method is the lack of control over the thickness. In this method, the imperfections are axially symmetrical, which is one of the advantages of this method. In this article, buckling analysis due to both diameter and thickness variations are done separately and simultaneously. It has been shown that thickness variations in rotational forming should be considered in the analysis of shell collapse. Also, by comparing the numerical and experimental results shown with the help of quadratic volume elements, thickness changes and boundary conditions can be applied with higher reliability compared to the shell element.

is In this research, the microstructure and wear behavior of high-strength AISI 4340 low-alloy steel coated using austenitic stainless steels ER309, ER312 and cobalt base steel stellite 6 were investigated by tungsten-gas arc welding method. Microstructural investigations were carried out by optical microscope and scanning electron microscope equipped with X-ray energy diffraction spectroscopy system.Hardness measurement was done by Vickers method with a load of 30kgf on the surfaces and Vickers microhardness in the transverse sections of the welds in zigzag form. Also, in order to evaluate the wear behavior, the wear test of the pin on the disc was used to identify the wear mechanism. By reducing the intensity of the current in the second layer and also by increasing the number of welding layers, the dilution and mixing of the sub-layer decreased and the hardness increased, and the highest hardness was 565 (HV) for stellite6. The results of the wear test showed that the highest friction coefficient was related to ER 309 weld metal has an average value of 0.68 and the lowest friction coefficient is related to stellite 6 weld metal with an average value of 0.53.