مجله مهندسی مکانیک امیرکبیر
سال پنجاه و دوم شماره 1 (فروردین 1399)

In this paper, using modified couple stress theory, dynamic stability of a cantilevered micro-tube embedded in several types of elastic media has been studied. The governing equation for lateral vibrations of the micro-tube conveying fluid is derived using the extended Hamilton’s principle. The numerical results are obtained by employing the extended Galerkin’s method. For validation purposes, the obtained results for simple cases are compared and findings indicate a very good agreement with those available in the literature. The stability maps of different configurations with different flow velocities are studied and the influences of various parameters such as material length scale, external diameter and different elastic properties on the stability of the system are considered. Results indicate that elastic environments may enlarge the stability regions significantly at larger values of mass ratio parameter while decrease it for smaller values of mass ratio parameter. Moreover, using elastic media mathematically defined by series functions provides the capability to simulate almost any real time operational environment the micro-tube embedded in and results in an optimal stability state of the micro-structure carrying fluid flow.

The battery pack is one of the main components in electric vehicles which is usually composed of many cells connected in series. Battery state of charge estimation is one of the most important functions of the battery management system in electric vehicles. Due to the different manufacturing and operational conditions, all of the cells in a battery pack do not have the same states of charge and therefore, the cell and pack states of charge are not the same. This paper presents a method for battery pack state of charge estimation which benefits rather low computational cost as well as the high precision. First, the coulomb counting method and the open circuit voltage graph, which is obtained from the experimental results, are used simultaneously to estimate the pack average state of charge. Then, the extended Kalman filter method is used to estimate the difference between the pack average state of charge with those of the cells. The proposed method has been evaluated and verified using an experimental test bench for three series-connected lithium cells. Experimental test results indicate good performance of the proposed method in estimating the lithium battery pack state of charge.

So far, variety of complicated and impractical algorithms have been presented to identify the suspension system faults. In this research, a new effective and practical method, based on model and dynamic behavior of the vehicle for accurate and fast fault diagnose of the suspension system has been presented. In this method, it is not necessary to use special equipment and tests to diagnosis the fault, in the event of a fault, during the passage of the vehicle from obstacles with the necessary excitation threshold such as speed bumper, the alert is given to the user and its position and size are determined. Designing the suitable structure and using neural-fuzzy networks to identify faults plays an important role in reducing the error of fault diagnosis. Reducing the number and type of sensors (using only the accelerometer) and not relying on high sample rates are other advantages of the proposed method, and make it easy to use and low-cost. After study the effectiveness of different conditions and factors and selection the appropriate parameters in the process of fault diagnosis, verification of fault diagnosis system performance and the ability to implement it by designing and doing experiments and obtaining experimental results is confirmed.

In this paper, a method is proposed which allows computing the position of the end-effector base on neural networks approach by considering external forces applied to the end-effector. As in under-constrained robots kinematics and statics are intrinsically coupled together, and they simultaneously should be considered, the forward kinematic problem of the robot converts to an optimization problem. Solving the optimization problem is time consuming and not suitable for practical purposes. So, in order to solve the forward kinematics problem a SimMechanics model base on the robots geometry and dynamic designed and presented. By means of this method, the forward kinematic problem is solved offline and used online. Moreover, an analysis of workspace is performed which reveals that the solution of the forward kinematic problem of the under-constrained cable robots can be calculated uniquely. By means of neural network method A position control is performed and the proposed method is validated. The comparison of operated and desired path is shown for a helical trajectory. Maximum error in the assumed workspace is 0.4 percent. Finally the proposed method was implemented experimentally and the results confirm the efficiency of the foregoing method.

In this paper, design, modeling and control of a grip-based planar climbing robot is performed which is consist of a triangular plate and three actuating legs. This robot is extremely applicable for many applications in which a human operator should climb through a truss infrastructure and implement some manipulations on the relevant installations. The proposed robot in this paper can be substituted and decrease the death danger and increase the safety of operation. In this paper however, a grip-based climbing robot is designed which is able to perform manipulating tasks. Overall kinematics and kinetics of the robot is modeled and its manipulation is controlled using Feedback Linearization for operational phase. All of the modeling are verified by conducting some analytic simulation scenarios in the MATLAB and the results are also compared with the results of the robot which is modeled and simulated in ADAMS software to investigate the correctness of modeling and simulations. It is shown that by the aid of the proposed and designed climbing robot, it is possible to climb and perform a complete operational task through trusses and infrastructures with the best status of safety and accuracy.

this paper discussed and introduced a new path-planning algorithm, based on improved potential field and Lyapunov guidance vector field. According to the requirements of the unmanned aerial vehicle for tracking and avoidance obstacle mission, a real-time method is proposed by combining the Lyapunov guidance vector field and improved potential flow field, eventually, the proposed method used for coordinated tracking and obstacle avoidance application. The features of this newly introduced algorithm are real-time, fast computing and obstacle avoidance capability which causes the algorithm to perform well in complex environments and applications like coordinated tracking of unmanned aerial vehicles. Improved potential flow field (IPFF) primarily provides avoidance obstacle feature and Lyapunov guidance vector field provides tracking feature for this newly introduced algorithm. To achieve the mission of tracking the target and avoid the obstacle at the same time, the guidance vector field by LGVF is taken as the original vector field of IPFF. The results prove that the new hybrid and combined method are applicable to complex environments and complex application like coordinate tracking of moving target can be used in real-time applications.

Aircraft flexibility causes problems and difficulties which this problems even might endanger health and safety of the aircraft. This phenomena changes dynamic response of aircraft to surface control and gust. Also it has diverse effect on flight quality and handling. then considering flexibility effects on dynamics response of aircraft is significant which requires that coupled dynamic and viberational equations of aircraft. In this paper, dynamics of a wide body aircraft has been developed on base of a six degree of freedom model witch includes two rigid and four flexible degree of freedom. Quasi steady aerodynamics has been used to describe interaction between solid and fluid. The characteristics of this model enhance perdition of dynamic response to gust and other external disturbances because of its development of elastic modes. the characteristics of this external disturbances causes more flexible modes to be exited and strain energy ratio in general dynamics of aircraft increases. In this simulation different parameters like stiffness ,gust length and its profile has been studied and a comparison between different length gust has been done .

In this paper, feedback control algorithms to tracking a desired path of a piezoelectric size dependent cantilever nanobeam as a nano-actuator are developed. In size dependent piezoelectric nanobeam, the governing Partial Differential Equation (PDE) of motion is obtained based on the non-classical continuum mechanics which introduces material length scale parameters. Nonlinear formulation of isotropic piezoelectric Euler-Bernoulli nanobeam is derived based on consistent size-dependent piezoelectricity theory. By considering geometrically nonlinear and axial displacement of the centroid of nanobeam section, basic nonlinear equations are obtained by Hamilton’s principle and variational approach. In order to reduce the governing partial differential equations into a set of ordinary differential equations (ODEs) the Galerkin method is applied. By introducing the new set of variables the state space model of nanobeam is derived. The control algorithms are employed to achieve an output tracking control based on the state space model of the nanobeam, for the supply voltage as a control input. The effectiveness of the proposed control algorithms and input voltage are illustrated by some numerical simulations.

In this paper, free vibration analysis of the rotating thin-walled composite beams with embedded shape memory alloy (SMA) wires is represented. Pre-strained SMA wires are embedded in the middle of the cross section of thin-wall composite beam, symmetrically. The one-dimensional thermo-mechanical constitutive law suggested by Liang-Rogers is applied to model the thermomechanical behavior of SMA wires. The differential governing equations are extracted by using the extended Hamilton’s principle based on first-order shear deformation theory. By heating the thin-walled beam, strain recovery operation will produce a tensile force along the longitudinal thin-walled beam. In order to solve the governing equations, the extended Galerkin method (EGM) is used. The result investigated the effect of rotational speed, recoverable strain limit, pre-twist angle, number of SMA wire and temperature difference on the natural frequency in temperature above the austenite finish are illustrated. It is found that the natural frequencies of rotating thin-walled beam increase as the number of SMA wires and compressive pre-strained SMA wires increases. In addition, results are in good agreement with those obtained in the literature.

Vibrations of a continuous rotor with uniform circular cross section supported by two tilting-pad journal bearings (TPJB) at both ends are analyzed. Since the shaft is slender, shear deformation is neglected, but, gyroscopic effect is considered (Rayleigh beam theory). In addition, geometric nonlinearity due to large deformation of the rotor is considered. Based on short bearing assumption, an analytical model of a TPJB with laminar and turbulence flow has been derived. Galerkin method is applied to discretize differential equations of motion. On mode (the first mode) is used for discretization. By solving discrete rotor-bearing system equations, the response is obtained. For further investigation, responses of rotor-bearing system in different situations are presented. Comparing the responses of the linear and nonlinear rotor with two TPJB at both ends shows that the nonlinear rotor has less amplitude than linear rotor and nonlinear rotor is closer to reality. In addition, nonlinear model has a larger natural frequency in comparison to the linear rotor. Using turbulence flow makes the bearing stiffer and have less amplitude than laminar flow. Reducing viscosity of lubricant leads to increase of amplitude of response and shows that higher viscosity make the bearing stiffer.

The multimodal free vibration of a beam with a breathing crack excited by arbitrary initial conditions is investigated. Taking the initial conditions to be arbitrary makes more than one mode of the beam to be excited simultaneously. By considering the bending moment at the crack position, a multi-harmonic function describing the instantaneous opening and closing of the crack is extracted. Since the modal stiffnesses of the beam are dependent on the crack parameters, the extracted crack breathing function will appear in the equations of motion and makes them to be coupled. These equations are solved using the perturbation method. Then, the free response of the beam is extracted under three cases of initial conditions: excitation of the first mode, simultaneous excitation of the first and second modes, and simultaneous excitation of the first three modes. The results show that by exciting the first mode solely, the harmonic components of the response offer very limited information about the crack, however, by exciting the first several modes simultaneously, many other harmonic components appears at the frequency response curves which are more sensitive to the crack and contain more comprehensive information about the crack parameters.

In this paper, free and forced vibration of viscoelastic nanoplate on the Pasternak viscoelastic foundation will be studied. In this study, due to the inability of classical theories to describe the behavior of nano-dimensional structures, the non-classical modified couple stress theory has been used for express the size effect. By using the Galerkin semi-analytic method, free vibrations analysis for six different boundary conditions are discussed; also, forced vibration of rectangular viscoelastic nanoplate is studied by using the Navier method for simply supported boundary condition. Kelvin-Voigt model are used to simulate the behavior of viscoelastic nanoplate. In the results analysis section, the effect of small-scale factor, structural viscoelastic coefficient, linear elastic coefficient of foundation, external damping coefficient of foundation and shear coefficient of foundation on the natural frequency, maximum dynamic deflection and resonance phenomenon are presented. The obtained results show that considering length scale parameter leads to increasing the natural frequency of nanoplate and occurring the resonance phenomena in the higher frequencies. On the other hand linear elastic and shear coefficients of foundation result in occurring the resonance in the lower frequencies.

In this paper, nonlinear finite element modeling has been presented to conduct a parametric study of disc properties on biomechanical behavior of lumbar spine. This model includes vertebra (cancellous bone and cortical bone), disc (nucleus, annulus fibrosus, and collagen fibers), end plates, and ligaments. Medical image processing software package of Mimics (Materialise Inc., Leuven, Belgium) has been used in the current study to create a more realistic geometrical model of lumber spine. HyperMesh software (Altair, Troy, MI, USA) has then been employed to provide a better meshing of different parts of lumbar spine. Following applying loads and boundary conditions to the model, finite element analysis has been conducted in ABAQUS (ABAQUS Inc., Providence, RI, USA). Experimental tests available in literature indicate that lumbar spine shows a nonlinear mechanical behavior; hence, to consider this nonlinear behavior in this work, ligaments and annulus fibers have been modeled as nonlinear springs. The obtained results of the current study, which include intradiscal pressure and intervertebral rotation, have been compared with previous experimental as well as numerical data. The results of this work show that increasing of hyperelastic material constants of disc leads to decreasing of disc intervertebral rotation for each case study considered.

This study consider the impact of transient flow around an annular fin on the development of thermal stress and strain. The finite volume method was used to solve the flow equations and the finite element method to solve the thermal stress equations in the solid. The fin thermal stress results were solved for two general cases with and without flow around the fin. Moreover, two scenarios were considered for the case with the flow. First, the fin was analysed in free flow and then, to be more practical, the problem of flow around one fin among a group of fins was considered. The free flow results were compared to the case with no flow. The investigations are suggestive that the thermal stresses developing in the fin are initially similar in the two cases . Furthermore, the results show that the maximum tangential stress takes place at the same location in the two cases but it is exacerbated. In addition, the tangential is not symmetrical in the case with the flow and the maximum stress, although at the base of the fin, is located in the flow front. Moreover, in the case with the flow, the two-dimensional temperature distribution results in a considerable asymmetrical thermal strain and consequently, asymmetrical thermal stress none of which are observed in the case with no flow. A careful analysis of the flow around the fin shows radial temperature distribution information to be insufficient to determine the maximum effective stress.

Due to unique properties, grid-stiffened composite plates are used extensively in aviation, marine and automotive industry. In recent decades, several studies are done to predict the critical buckling load of grid-stiffened composite plates without breakdown or failure. One of the most important non-destructive methods, is Vibration Correlation Technique (VCT). The aim of this research is the prediction of the critical buckling load of grid-stiffened composite plates using VCT. For this purpose, nonlinear vibration analysis of grid-stiffened composite plates are firstly performed in different compressive loads using finite element software ABAQUS. In the next step, critical buckling load of grid stiffened composite cylinder shells is predicted using VCT. To validate the results of VCT, three grid-stiffened composite plates are fabricated using filament winding and hand lay-up method with same conditions and was placed under axial compression test. Finally, the critical buckling load is measured experimentally. The results show that the difference between the critical buckling load of VCT with experimental buckling load is less than 5%. This subject implies that VCT is suitable for prediction of critical buckling load of grid-stiffened composite plates with very high accuracy.

In this article, a nonlinear elastic Bernoulli–Euler beam model is presented to investigate the chaotic behavior and primary and superharminic resonance of single walled carbon nanotubes embedded in a visco-elastic medium at an elevated temperature. Using the Galerkin method and fourth-order Runge-Kutta method the governing equation is solved. The bifurcation diagram and largest Lyapunov exponent are employed to detect the critical amplitude of external force of periodic and chaotic response of single walled carbon. Having known the critical values, phase portrait and Poincare maps are presented to observe the periodic and chaotic behavior of the system. Moreover, the amplitude–frequency response for the primary superharmonic resonance of system is derived with the multiple scale method to investigate the feasibility of jump phenomenon. The sensitivity of jump phenomenon are studied for the selected viscoelastic foundation parameters, detuning parameter and external amplitude load. The results show that the amplitude of external force, viscoelastic foundation parameters, detuning parameter and temperature change in the cases of high and low temperature have a significant effect on the frequency response with jump phenomenon of system. In addition, the chaotic vibration of CNT can be controlled by changing of amplitude of external force.

Topology optimization of structures, seeking the best distribution of mass in the design space to improve the performance and weight of a structure, is one of the most comprehensive issues raised in the field of structural optimization. In addition to the structure stiffness as the most common objective function, frequency optimization is of great importance in industries achieved by maximizing the fundamental frequency or the gap between two consecutive eigenfrequencies. The phenomenon of multiple frequencies, mesh dependency of topology responses, checkerboarding, geometric symmetry constraint, and occurrence of artificial localized vibration modes in low density regions are the most important challenges faced by the designer in stiffness and frequency optimization problems which influence the manufacturability of the design too. In this paper, BESO method is applied for a frequency and stiffness problem separately via creating a software package including a Matlab code and Abaqus FE solver. Also, in this paper the effect of geometric symmetry constraint is considered on resulted topologies from stiffness and frequency problems. So the BESO method is applied for modeling a 2D beam and its stiffness and frequency optimization and finally the optimization results of both objective functions will be compared with initial structure.

In this research, the evolution of ductile damage and strain-induced martensitic transformation of AISI 304 stainless steel have been obtained from experimental tests at first. Each test contains two stages. The first stage is the tensile testing of floating test piece in liquid nitrogen and the second is performing XRD to obtain the phase of the test piece. First of all, the tensile tests have been performed for a verity of elongation on the AISI 304 stainless steel test pieces at cryogenic temperature. Therefore, the cryogenic chamber has been designed and crafted. So, the graph of force-deformation has been achieved. Then, this test pieces have been tested with XRD and the available phases and the volume fraction of martensite for the variety of elongation, has been obtained from this test. Numerical simulation has been performed by the implementing the UMAT code in ABAQUS. In the simulation, the properties achieved from experimental tests are employed. The numerical simulation has two separated sections: damage-plastic and martensitic phase transformation. . In this research, by considering the experimental test data, the final model has been calibrated in monotonic tensile loading and the coefficients has been obtained.