نشریه مهندسی مکانیک ایران
سال بیست و دوم شماره 3 (پیاپی 60، پاییز 1399)

Self-healing materials are a class of smart materials that have a structurally capability to recover damage caused by environmental stimuli over time. In this paper, a semi-analytic modeling is presented for predicting the mechanical behavior of a self-healing concrete beam. Along this purpose, a continuum damage-healing constitutive model is used to investigate the effect of damage and healing in stress field of concrete pressure vessels. This model use stress spectral decomposition method to model the different behavior of concrete in tensile and compressive loadings. Also, Clausius-Duhem inequality and the thermodynamics of irreversible processes are considered and conjugate forces of damage and healing are derived for a concrete beam. Gibbs potential energy is divided into three parts; elastic energy, damage energy and healing energy. In this regard, the model introduce damage and healing surfaces to detect damage and healing behaviors from elastic one. Then, two linear isotropic hardening functions are used in these surfaces for evolving of damage and healing variables. The verification of the solution is shown by solving an example for a simply supported beam having uniformly distributed the load. Finally, a result of a self-healing concrete beam is compared to elastic one to demonstrate the capability of the proposed analytical method in simulating concrete beam behavior. The results show that for the specific geometry, the self-healing concrete beam has 21% more weight tolerate, and the deflection of the entire beam up to failure load is about 27% larger than elastic solution under ultimate elastic load.

The purpose of the present work was to study the dynamic instability of a three-layered sandwich beam with flexible core and simply supported boundary conditions subjected to a periodic axial load resting on elastic foundation. A higher-order theory was used for analysis of sandwich beams. In this theory, the classical theory was used for the face sheets and quadratic and cubic functions were assumed for the core, respectively. The elastic foundation was modeled as Winkler’s type. The dynamic instability regions were investigated for simply supported conditions by Bolotin’s method. The governing equations derived by the principle of minimum potential energy. The results showed that the responses of the dynamic instability of the system were influenced by the excitation frequency, the foundation modulus and the angle of the plies. Comparison of the present results with the published results in the literature for the special case confirmed the accuracy of the proposed theory.

Due to the nonlinearity of the equations governing the satellite estimation system, linear filters are not able to estimate the precise position, and then satellite tracking is associated with several errors. In this paper, satellite motion equations are investigated then, using GPS observations, Extended Kalman filter (EKF) and Cubature Kalman filter (CKF) the satellite’s position and velocity are determined. Cubature Kalman filter is an algorithm suitable for estimating noisy high dimension nonlinear systems, which is based on the Gaussian and Kalman filter. Simulation results and RMS of the positioning errors confirm that the Cubature Kalman filter has improved accuracy and performance compared to the Extended Kalman filter. Cubature Kalman filter shows 50 percent improvement in velocity estimation in y and z directions compared to EKF. Although, relative error improvement percentage for position is less than velocity and both filters have almost similar performance. However, CKF is slightly superior and has had 10 percent, 3 and 1.5 percent improvement in relative errors of x, y and z directions, respectively.

The effect of climatic and climatic changes in different geographical areas on the types of plants, animals and objects and the importance of protecting the items has led to the study of ideas related to control of air variables in desired conditions. All of the ideas studied in this field lead to the separation of under the control area in order to reduce the effect of the environment on the control variables. This area is then modeled as a system with a defined energy and mass exchange with the environment. In the present study, thermal modeling, dynamic modeling, and control of the variables of a museum which is considered an enclosed area have been investigated. For dynamic modeling, the one-dimensional heat transfer method is used for area elements (DETECt 2.3.1 method). After dynamic modeling, temperature and humidity control have been done using model-reference and modified adaptive methods. Numerical simulation results include the behavior of the system with and without using the controller, the variation of the dynamic variables, and changes in the control signal and the adaptive gains. The results show the success of control methods in the control of temperature and humidity of the studied area.

In this paper, stress analyses by means of distributed dislocation method in a functionally graded orthotropic half-plane weakened by multiple edge cracks under anti-plane impact loading is studied. First, dislocation solution by using of Fourier and Laplace transforms, boundary conditions and continuity conditions is carried out. Then by applying inversion of Fourier transform, the fields of stress analysis in Laplace domain is calculated. Using of this solution, the integral equations for analyzing of multiple edge and internal cracks in a half-functionally graded orthotropic plane is obtained. The behavior of this equation is Cauchy singularity at the location of dislocation which is solved numerically. By applying the inversion of Laplace transform using of Stehfest’s method, the dislocation densities on the crack surface obtained which are used to determine dynamic stress intensity factors at crack tips. Finally, the effects of the isotropic or orthotropic property, non-homogeneity parameter, crack location and the interaction of multiple edge cracks on the dynamic stress intensity factors in a functionally graded orthotropic half-plane are studied.

In this paper, the problem of event-triggered robust control of half-car suspension system with parametric uncertainty is investigated. Some physical hard constraints for the system are also considered in the control design procedure. Firstly, the problem is formulated by presenting the dynamic equation of the half-car suspension system and the event-triggered mechanism for sending the sensor measured data to the controller. The parametric uncertainties are also considered in this stage. The event-triggered mechanism decreases the number of sending information from the sensors into the controller which yields a larger bandwidth of the communication network. Then, with help of the Lyapunov - Krasovskii theorem, some conditions are provided in the form of linear matrix inequalities to ensure the stability and performance of the suspension system. These linear matrix inequalities are easily solvable with standard routines. Finally, a numerical half-car suspension system is presented to show the effectiveness of the proposed method.

In this paper, numerical solution procedures are proposed for dynamic response of a functionally graded (FG) micro beam under action of a moving micro mass based on the modified couple stress theory (MCST) within the framework of Timoshenko beam theory for various boundary conditions. The governing equation and the related boundary conditions are derived by using Hamilton’s principle. Then the proposed solution for obtaining the natural frequencies and mode shapes of free vibration are presented by expressing the micro beam displacement fields in terms of the series of Legendre polynomials to find the numerical solution regardless of boundary conditions. Likewise, the computed eigenvalue of the system is developed in the modal expansion method to obtain the dynamic response. For validation purposes, the free vibration frequencies of the micro beam and the dynamic responses using the Timoshenko beam theory are compared with previously published studies and very good agreements have been observed. Furthermore, more numerical results for natural frequencies and dynamic deflection of the beam are presented and the effects of some parameters, such as material length scale parameter, thickness to length ratio of micro beam, boundary condition, the velocity of the moving load and the FG material power index are examined.

In this study, for the first time, the nonlinear bending analysis of a deep cylindrical panel reinforced with gradient carbon nanotubes under uniform load and temperature variation has been investigated. Detailed study have been done on the effect of carbon fiber distribution and the volume fraction of carbon nanotubes in bending behavior of cylindrical panels. The variation of transverse displacement component and bending moment distribution, versus uniform loading under different boundary conditions are investigated. First, the governing equations are extracted using nonlinear equations governing the deep cylindrical panel and energy relations. Regarding the complexity of the equations and the impossibility to solve them analytically, numerical methods are used to solve the equations. The bending analysis will be done using the Ritz method which is known as a semi-analytic and precise method. Based on this method, the distribution of displacement components is assumed as series functions to satisfy the essential boundary conditions. Then, these functions are placed in the Lagrangian energy equation and the governing relations are obtained by minimizing the energy relation. The most important advantage of this method is that, by satisfying the geometric boundary conditions, the natural boundary conditions governing the panel are automatically met. Finally, it is concluded that the maximum moment of bending is obtained by FG-X distribution pattern while the least by FG-Λ distribution pattern of the fibers.

In this study, low velocity impact analysis of functionally graded carbon nanotube annular plate based of finite element method is presented for the first time. The governing equations are based on first shear deformation theory and Hamilton's principle. To model the contact force between annular plate and impactor, modified contact Hertz law has been used. Results of present study is compared with previous studies, and it shows good agreement. The effect of different parameters such as distribution and volume fraction of carbon nanotubes, and also, different mass and velocity of impactor on contact force and transverse displacemet of plate have been investigated. Results denotes that by increasing the volume fraction of carbon nanotube from 11 to 17 %, the contact force 32% is increased and the contact time is notably decreased. Also, results show that, the FGX distribution of nanotubes along the thickness of plate, has the highest contact force and the lowest contact time.

Lane changing behaviors, due to the hidden aspects of factors involved, are considered as one of the most complicated behaviors in traffic flows. This paper proposes an intelligent system for discretionary lane change behaviors in the real traffic flow. The introduction presents a review of the research into the models of lane change behaviors. Then, a new method is proposed to determine the initial and final points of lane changing behavior in terms of time parameter. Hypotheses are then introduced to extract data on lane change behaviors from data recorded by NGSIM. An intelligent system is put forward using two control sub-systems based on fuzzy logic. Basically, this paper brings about innovative features by the utilization of time parameter during the execution of lane change behaviors and by the consideration of the impact of human and environmental factors through measurable data such as relative distance and relative speed in terms of time parameter. Finally, the results of the proposed intelligent system are compared with the behaviors of the driver in real situations. The framework of the result analysis employs error criteria and standard deviation (Variance). The said comparison indicates that the developed intelligent system outperforms the human behaviors in real situations.