Scientia Iranica
Volume:29 Issue: 2, Mar & Apr 2022

The work-rolls of the hot ring rolling process are subjected to various damages due to the contact with hot metal. Thermo-mechanical fatigue is one of these damages. In order to predict failure due to the thermo-mechanical stress in the work-rolls, the developed code in ABAQUS has been used. The comparison between three- and two-dimensional models and, also, thermal and thermo-mechanical response of work-rolls with variable boundary conditions has been investigated. The results have shown that by applying mechanical and thermal loads separately or simultaneously, the response of work-rolls is completely different. In the mandrel, the location of the maximum equivalent stress is on the surface, while the location of equivalent maximum stress is in the subsurface of the main-roll. By making use of cumulative damage rules and the stress life method, the thermo-mechanical fatigue life was estimated. The cumulated damage in the mandrel’s surface was higher than subsurface regions. In contrast to the mandrel, the cumulated damage in the main-roll’s subsurface was higher than surface regions. In hot ring rolling machines, these locations are prone to crack initiation as a result of the thermo-mechanical fatigue in the work-rolls.

Combined bearing, which consists of spherical roller bearing and thrust spherical roller bearing, is an important support in various low-speed and heavy load institutions and the stability of its running state is a strong guarantee for the normal operation of the supporting mechanism. Basing on the wellbore trajectory control tool, the loading distribution of combined bearing under pure radial and axial forces is studied theoretically. Two kinds of limit state of rolling elements movement named "Odd press" state and "Even press" state is considered and the Hertzian line elastic contact model is used to deal with the contact between roller and raceway. The calculation results of contact stress and radial displacement are very close to the analysis results, and the accuracy of the analysis results is verified by the radial displacement experiment. The results show that the radial load will lead to the radial displacement of the combined bearing axis, which is about 5.81×10-3 mm. The radial displacement can affect the guiding accuracy of the tool to a certain extent. The radial displacement can be reduced by adjusting the bearing structure design parameters .This research can be used to design SRB and TSRB combined Bearing in actual engineering problem.

Flow and thermal characteristics of mixed convection in a nanofluid filled wavy conduit was numerically investigated in this study. The conduit was considered to contain a pair of rotating cylinders. It was heated and cooled from its lower and upper wavy surface, respectively. The rotating cylinders were placed along the centerline of the wavy conduit. It was also permeated by an external magnetic field. Finite element method was implemented to simulate the conservation equations. Based on the current investigation, a new model was developed for improving thermal conductivity of nanofluids inside a wavy conduit. In addition, a detailed parametric study was presented to visualize the effects of governing parameters on the flow structure and temperature field in the conduit. The numerical results indicated that the physical parameters noticeably influenced both fluid flow in terms of streamlines, velocity profiles and temperature distributions in terms of isotherms, average Nusselt number. The rotating cylinders, wavy surfaces and the inclined magnetic field were found to have the most significant effect on the heat transfer mechanism. Maximum heat transfer occurred as the magnetic field was placed at an angle of 90o.

The purpose of this paper is to develop an analytical solution for free vibration analysis of smart functionally graded (FG) plates by the Levy solution in conjunction with the state-space approach. The FG substrate is sandwiched between two piezoelectric layers. The rectangular structure has two simply-supported opposite edges while the boundary conditions of the other two edges are arbitrary. Based on the simple but efficient four-variable refined plate theory, the governing equations are extracted employing Maxwell’s equation and Hamilton’s principle. The achieved fourth-order partial differential equations are transformed to first-order ordinary ones using the Levy solution along with the state-space approach and then, they are solved by applying the eigenvalue method. Meanwhile, an iterative algorithm is proposed to obtain the natural frequencies of the structure with various boundary conditions. A comparison is made between the obtained results and those available in the literature which verifies the accuracy of the solution method and numerical algorithm proposed in this study. Finally, the effect of several parameters such as type of boundary conditions, aspect ratio, power-law index, piezoelectric layer thickness, and thickness-to-side ratio is examined on the obtained results.

In the friction stir welding process, preferred joint property is vastly reliant on the selection of optimal welding conditions. The present study aims at the application of the Taguchi approach to finding out the optimal process conditions to get superior ultimate tensile strength in the friction stir welded aluminium matrix composite (AMC) joints. AMC reinforced with rutile particles which have a potential application in the aerospace, automotive, and marine industries are used in the present work. Taguchi parametric design technique was used to identify the influence of rotational speed, tool traverse speed, and tool geometry on joint strength. Taguchi approach confines the optimum level of process variables and optimization of these variables was performed based on this study. Investigation reveals that the parameters within the chosen range of values, critically affect the output. The predicted value of the output response is 155.48 MPa which was validated by conducting further trials with optimum process variables. ANOVA results indicated that the UTS of the composite joint is mainly affected by the tool traverse speed followed by rotational speed, and tool geometry. The microstructural study unveiled that grain size is dependent on process variables and finer grains offer better joint properties.

Although industrial robots are common, a higher degree of manipulability might be required to expand the applications of manipulators in the field of medicine. Modifying the mechanical design of a robot as per the workspace can be perceived as an optimization problem. Hence, a novel spatial manipulator is designed for a diagnostic apparatus using different optimization algorithms. Standard Genetic Algorithm (SGA) and GA (Genetic Algorithm) with hybrid functions like pattern search (PS) and fmincon are proposed to optimize the link lengths of a 3degrees of freedom (DOF), 6-DOF, and novel 9-DOF hybrid redundant manipulator. A 9-DOF robot is designed to manipulate a needle in CT machine environment. The fitness function for all the manipulators is formulated using forward kinematic equations according to their workspace. Limits and constraints of each link are decided beforehand. A comparative study between all the hybrid GA functions is performed. MATLAB is used to solve and train the proposed GA method for optimizing the link lengths. Results show that GA with PS provide better-optimized link lengths for a 3-DOF and 9-DOF manipulator while fmincon is well suited for a 6-DOF robot manipulator. Workspace and dead zone analysis is also performed using the optimized link lengths obtained.

A generalized finite element approach, for the free vibration analysis of an axially functionally graded (AFG) beam, having non-uniform thickness, has been presented in the current analysis. The use of non-uniform beam element and the way of assembling the same, make the finite element model, a generalized one. The current approach can be used for beams of both uniform and non-uniform thickness, with any of the homogenous and inhomogeneous material variation. The governing equation for free vibration of beam has been derived considering Euler-Bernoulli beam theory and by using Euler-Lagrange's equation. The cross-section of the of the beam is decreasing along the length depending upon the exponential function considered for variation in thickness. The material inhomogeneity is as per the Power and Exponential law of material variation along the axial direction, taken from the literature. Mathematical modelling of geometric non-uniformity, material inhomogeneity and finite element analysis of the AFG beam, have been performed using MATLAB. The effect of geometric non-uniformity and material gradient parameters on the fundamental frequencies of vibration in different classical boundary conditions have been investigated. The efficacy of the current method has been ascertained by comparing the result of available literature.

An asymmetric numerical study has been performed to investigate the effect of utilizing circular porous fins on heat convection inside of an annulus enclosure. The walls are considered to be at a constant temperature. The porous fins are installed on the outer wall, and other walls are insulated. Governing equations discretized using the FVM based on the second-order upwind scheme. The effect of different parameters on heat transfer enhancement inside the annulus, such as annulus inclination angle, annulus aspect ratio, Darcy number, Rayleigh number, thermal conductivity, the position of fins, number, and length of fins, has been investigated. Results declared that increasing Darcy number from a certain value would enhance the average Nusselt number dramatically at both aspect ratios, even though annulus with an aspect ratio of 3:1 has a higher value of average Nusselt number compared to the aspect ratio of 2:1. It has been illustrated utilizing low relative solid to fluid phase thermal conductivity nullify the effect of the increasing number of porous fins on heat transfer enhancement but, by increasing relative thermal conductivity to Ke=100, installing four porous fins on the inner cylinder increases the average Nusselt number by 7 percent compared to using only one fin.

The study of the flow and convective heat transfer from rotary sphere in fluid mechanics, astrophysics and astronaut subjects are important. Today, porous mediums use has become widespread because of the heat transfer characteristics as well as their lightweight and low volume. Many numerical studies in heat transfer and fluid mechanics have been done regarding rotary sphere. The present project studies the phenomena of flow and heat transfer due to the rotation of the sphere at a constant temperature around itself in a porous medium, assuming a laminar, steady and incompressible flow. Analytical solution of equations used are based on power series and the porosity coefficient is assumed between 0 to 1in this problem. In the spherical coordinate system used here, changes in azimuthal angle direction are ignored and the body force and pressure gradient for the problem are considered zero. The presence of porous medium is expected to increase thermal parameters.

During an impulsive orbital maneuver, thrust vector misalignment from the center of mass (C.M) generates a large exogenous disturbance torque that results in attitude deviation. This paper aims not to use the reaction control system (RCS) for the spacecraft attitude control. In order to reject the large disturbance very fast, a new control system is proposed. In this method, the large disturbance torque is rejected quickly while the RCS is not employed. The control system is based on one degree of freedom (1DoF) gimbaled-thruster, spin-stabilization, and two control moment gyros (CMG). The nonlinear two-body dynamics of the mentioned spacecraft is formulated. Because RCS is not used, this method is an efficient and implementable method for attitude control of small spacecraft. Numerical simulation shows that thrust vector deviation converges to zero despite disturbance torques. By this method, the disturbance is rejected very fast; thus an accurate orbital velocity change can be obtained. This method can eliminate the initial attitude deviation easily in addition to disturbance rejection. The results show the good performance and superiority of the proposed method compared to some other thrusting maneuver methods.