نشریه مهندسی مکانیک ایران
سال بیست و یکم شماره 3 (پیاپی 56، پاییز 1398)

The problem of the Segway robot and wheeled inverse pendulum is one of the most important classic issue and well-known example of nonlinear control problem in engineering control. The main purpose of the control in this paper is achieving the cart body to the desired angle and the speed of the body as quickly as demanded velocity by controlling of the applied torque. This paper presents an intelligent control method for Segway robot, in which the downstream fuzzy controller using the calculated error from the plant output, provides the proper input to the dynamic system. But, there is a learning mechanism in the upstream controller that compares the output of the controller VS the reference model and then improves it using fuzzy inverse controller. it makes method more robust and efficient. Dynamic equations of the system are extracted by the Kane method. The design of the fuzzy controller, based on the experience of the expert human for such a system, can perfectly overcome the instability and nonlinear nature of the system. Therefore, the use of the superviser controller, due to automatic and intelligent adjustment, can help simpler design of this controller. The performance of the proposed control algorithm on Segway robot case study is evaluated and demonstrated by simulation in MATLAB. Also, considering the system's uncertainty in design and disturbances, the controllers are robust against the uncertainties and disturbances in the problem. Figures and results are evidence of this issue.

Rutting is one of the most critical distresses influenced the asphalt pavement performance and its service life. Due to the complexity of the mechanical asphalt pavement responses, to study the mechanical behavior of this material under applying loads, a thermodynamically consistent visco- elastic visco- plastic visco- damage constitutive model has been presented in the implicit time discrete form to predict their mechanical responses within the framework pf the finite element method in software ABAQUS- Standard. It is worthy to mention that employing an implicit time discretization technique reduces the computational cost and a more stable solution is found. In this work, rutting phenomenon and prediction of the asphalt pavement service life has been investigated under three types of moving loading regimes, which forty percent of rutting difference has been obtained by comparing the pulse and equivalent loadings under moving load that would cause erroneous predictions in asphalt pavement service life.

In this paper, the linear buckling analysis of double – bonded micro - beam was carried out based on the Reddy-Levinson model and the modified strain gradient theory. The studied system consists of an isotropic micro - beam and a magneto-electro-elastic composite micro beam. The beams are connected by an enclosing elastic medium and were simulated according to the both Winkler and Pasternak models. In order to verify the outcomes, they were compared with the available published data. The comparison shows that the results are in a good agreement with other research outcomes.The results show that as the Winkler and Pasternak constants increase, the critical buckling load decreases along the ratio of the thickness to the material length scale parameter. Moreover, the results confirm that the addition of a magneto-electro-elastic composite micro beam of the system, including anisotropic micro - beam lead to the reduction of the critical buckling load.

In this work, thermo – elastic analysis for functionally graded thick – walled cylinder with temperature - dependent material properties at steady condition is investigated. The length of cylinder is infinite and loading is consist of internal hydrostatic pressure and temperature gradient. All of physical and mechanical properties expect the Poisson's ratio are considered as multiplied an exponential function of temperature and power function of radius. With these assumptions, the nonlinear differential equations for temperature distribution at cylindrical coordinate is obtained. Temperature distribution is achieved by solving this equation using classical perturbation method. With considering strain – displacement, stress – strain and equilibrium relations and temperature distribution that producted pervious the constitutive differential equations for cylinder is obtained. By employing mechanical boundary condition the radial displacement is yield. With having radial displacement, stresses distribution along the thickness are achieved. The results of this work show that by increasing the order of temperature perturbation series the convergence at curves is occurred and also dimensionless radial stress decrease and other stresses with dimensionless radial displacement increase.

In this article, the vibrational behavior of sandwich beams with stiff and flexible core and face sheets reinforced with carbon nanotubes has been investigated. Carbon nanotubes are used as materials that their properties change along the thickness. In this research for modelling the sandwich beam an extended high order sandwich theory is used. In order to model the behavior of faces the Timoshenko beam’s theory is employed and also for modeling the behavior of the core, three-degree displacement field is used considering the axial stresses and also compatibility conditions of the core. The equations of motion are derived using the variations of energy and the Ritz method is used to solve the equations of motion. The obtained results are compared with available results that show the high accuracy of the present modelling. The results for different distributions of carbon nanotubes and different boundary conditions have been investigated. In this research new results are presented for different boundary conditions in terms of different length to thickness ratio. One of the important result of this research is that, generally it cannot be say that what distribution of CNT leads to maximum or minimum natural frequency of the structure and this problem is strongly depended on the length to thickness ratio of the bam and also stiffness or flexibility of the core.

To reduce the damage caused by sudden collisions, energy absorbers are used. Energy absorbers, with their large deformation and folding, cause a large amount of collision energy to be absorbed, thus preventing damage to critical components. In the present research, the effect of geometric parameters of bi-tubular conical tubes and effect under axial loading on energy absorption is investigated by experimental and numerical methods. Then, the effect of foam is also studied to absorb more energy. In the experimental section, firstly, conical tubes made of aluminum with empty and filled with polyurethane foam were prepared, and then the samples are experimentally tested and the displacement-force diagram is obtained in each test. In the numerical section, the simulation of the axial deformation phenomenon of the thin-walled conical tubes is carried out with the ABAQUS software. The comparison of experimental and numerical results show that the proposed model is a suitable method for studying its collapse and amount of energy absorbed in the energy absorber system. Finally, the effect of the main system parameters, such as difference of inner and outer tube diameter, tube length, wall thickness, type of tube material, and the filling of foam, is studied on the energy absorption in thin-walled bi-tubular conical tubes absorber using numerical methods.

Due to the different application of the beam-attached mass structures, and also increment of the importance of nanocomposite materials, in this paper, the study on nonlinear vibrations of composite cantilever beam with tip mass under the harmonic excitation is presented. The equations of motion are derived using a geometrically exact formulation based on the Cosserat theory for rods. The Muri-Tanaka model is implemented to formulate the mechanical properties of carbon nanotube reinforced beam. The Galerkin approach is implemented to derive the linear natural frequencies and corresponding mode shapes of the mentioned beam with tip mass. The extracted mode shapes are employed to discretize the equation of motion. The discretized equations of motion, which includes geometrical and inertial non-linearitites, are solved using the method of multiple scales and the frequency response is extracted. The effect of attached mass, carbon nanotube volume fraction and the excitation force amplitude on the frequency response of the system is investigated.

In this study aeroelastic instability of laminated beam-plates with two overlapping delaminations with equal length that is subjected to supersonic ‎flow is investigated analytically. The classical laminate plate theory with small deflection assumptions with quasi-steady aerodynamic theory is ‎utilized to derive the governing equations of the system. Additionally, it is assumed that the delaminations parts are forced to vibrate with each other. ‎In this case to predict critical flutter pressure, the delaminated composite beam-plates are divided into five parts. The boundary conditions at the ‎ends of beam-plates and at the ends of each delamination region are employed to predict flutter pressure. The effect of different parameters such as ‎delaminations length, axial position, their position through thickness of delaminated beam-plate and different stacking sequence are considered on ‎flutter pressure of beam-plate with two overlapping delaminations. According to the results, flutter pressure of delaminated beam-plate with two ‎overlapping, equal length delaminations in comparison to beam-plate with single delamination is reduced 20 through 40 percentages approximately. ‎Additionally, it has been shown, as far as two delaminations are closer to the mid-plane of the beam-plate, the aeroelastic behavior will change ‎further. ‎

In this paper, buckling analysis of an Euler-Bernoulli nanotube with simply support boundary condion is investigated using modified nonlocal elasticity theory considering the surface elasticity, surface tension effect and nonlocal parameter. Using Hamilton principle in conjuctre with modified nonlocal elasticity theory considering surface effect the governing dynamic equations of motion for nanotube has been derived. Th critical buckling load for nanotube considerng surface tension effect is analytically obtained based on Navier’s series soltion. Then, rearrenging of serie solution for nanotube buckling load to eliminate effect of recocnized terms of soltion, the modofied governing equations are rewritten and derived. Effect of changes of various parameters such as mode coefficent of buckling, nanotube length and diameter, surface tension and nonlocal paprameter on the critical buckling load are all investigated. finally, the obtained results for critical bucklinf load from modified nonlocal theory of elasticity are compared with those from nonlocal and classic beam theories.

In the present study, the asymptotic stress distribution related to the mode I loading has been calculated by using the complex potential functions method for the key-hole notch. The new solution is an extension to the previous study of Zappalorto and Lazzarin [1] and has been developed to derive the components of stress field in the series expansion. Moreover, the displacement fields around the keyhole notch have been derived in both Cartesian and polar coordinate systems. Then, the over-deterministic method is utilized to calculate the coefficients of the series. According to the over-deterministic method the asymptotic stress or displacement field will be fitted to a large number of data points and the coefficients of the series will be derived based on the least square sense. Finally, to evaluate the derived coefficients, the truncated stress series have been compared with its relevant finite element values. The results show that considering the singular terms alone will generate large amounts of errors in calculations.