مجله مکانیک سازه ها و شاره ها
سال چهارم شماره 1 (بهار 1393)

This paper presents the design and implementation of fuzzy control for a robotic camera in tracking an object. The robotic camera which consists of a robotic arm and a camera، locates the moving object on the center of the image frame. The proposed controller uses the voltage control strategy and transforms the task-space tracking error to the joint-space tracking error using fuzzy systems. This control approach which has been implemented for the first time، is free from the dynamical model of the arm and robust against image uncertainties. Compared with the conventional control of robot that is based on the torque control strategy، it is simpler and computationally more efficient. In addition، it employs the blob tracking algorithm and centroid tracking algorithm for tracking the object in image frame. The experimental results provided by a two-link robotic camera driven by permanent magnet dc motors confirm that the proposed control approach is superior to the proportional-derivative control.

This paper deals with the issue of analysis and examination of the factors contributing to rapidness of response time in non-linear model of electro-hydrostatic actuator. In this relation، the design and simulation of an electro-hydrostatic actuation system referred to as EHA using multidisciplinary modeling method is presented. For linear models، the bandwidth is a criteria of rapidness of response، but EHA has a non-linear model. Due to the non-linear behavior of EHA، a new method for analyzing of rapidness of response is developed and influencing factors is investigated. In this method، the ability to track a reference in special frequency shows rapidness of response of actuator. Results show the external load has a significant impact on the rapidness of response of actuator. Finally، hydraulic circuit equipment capacity influence on rapidness of response of actuator are evaluated. Changing accumulator size and pump displacement have minor effect on rapidness of response of actuator. However، results show changing cylinder capacity has a major effect on rapidness of response of actuator.

In this study، dynamic buckling of a metallic plate with external electrorheological (ER) damper is investigated using the finite element method. The stability region and load carrying capacity of the metallic plate is improved by applying an external ER damper to the plate. The post yield behavior of the ER fluid (nonlinear behavior) is considered for modelling the ER damper. ER fluids are a class of smart fluids that their mechanical behavior is changed considerably in miliseconds by applying the electric field. In another word، applying the electric field increases the viscosity of the smart fluid. This behavior lead to an increase in the damping of the structure. Consequently، the stability of the system increases. Different parameters such as the intensity of the applied electric field and the geometric properties of the external ER damper can affect the stability regions of the structure. The effect of these parameters on the stability of the metallic plate is investigated in the present study.

In this research، the optimization of laminated cylindrical shells with composite ring stiffeners is implemented by the Genetic Algorithm (GA). The objectives seek the maximum general buckling pressure and minimum weight of laminated stiffened shells. The buckling pressure is evaluated using Love’s First-order Shear Deformation Theory (FSDT) and solved using the Rayleigh-Ritz energy method. The research introduces a strain energy formulation for laminated ring stiffeners، in which each ring stiffener may be treated individually and the geometrical dimensions and material properties of the stiffeners may be different from one another. Furthermore، the formulation enables the analyst to optimize the material properties of the stiffeners different from those of the parent shell. The results show that the effect of the material and geometrical properties of the shell and stiffeners on the stiffened shell’s buckling capacity is larger than its weight. Also، the buckling optimization has much greater efficiency than the buckling-weight and weight optimizations.

In this research، effects of section geometry and metallic foam filler on mechanical behavior of thin-walled tubes under axial quasi-static loads are studied both experimentally and numerically. Three types of Al-1200 thin-walled geometries، circular، square and hexagonal in the forms of hollow and foam-filled tubes are subjected to quasi-static loads and their energy absorption characteristics including maximum load، mean crushing load، absorbed energy and deformation modes are studied and compared. Instron 8305 model machine is used to axial quasi-static loading of the samples. Results of the research show that circular section has the greatest values of mean crushing load and absorbed energy; metallic foam filler increases the mean crushing load and energy absorption capacity; foam-filling does not affect the number of folds in general and finally، absorbed energy for foam-filled tube is larger than sum of energies absorbed by the tube and foam when are loaded separately. Furthermore، numerical results are in good agreement with the experimental data.

This article presents an elastic analysis and a closed form analytical solution for rotating functionally graded thick-walled hollow cylindrical shells subjected to constant internal and/or external pressure. Regarding the problem which could not be solved through elasticity theory، the solution based on the higher-order shear deformation theory (HSDT) is suggested. The material is assumed to be isotropic heterogeneous with constant Poisson’s ratio and radially varying elastic modulus and density continuously along the thickness with a power function. Based on HSDT، and the virtual work principle، the general governing differential equations of axisymmetric rotating pressurized thick cylindrical shells made up of functionally graded materials (FGM) have been derived. Following that، the set of non-homogenous linear differential equations with constant coefficients for the cylinder with clamped-clamped ends was solved analytically، and the effect of loading and inhomogeneity on the stresses and displacements was investigated. The results are compared with the findings of both shear deformation theory (SDT) and finite element method (FEM). Finally the effects of higher-order approximations on the stresses and displacements have been studied.

In this paper، a new mathematical model is developed to represent the interaction between healthy and cancer cells in the human body، focusing on the role of input on the dynamics of the cancer. For this purpose، the effect of input on the dynamics of a system is investigated. The question is whether an input implemented only for a limited duration can change the characteristics of a dynamic system such that the behavior of the free system، after eliminating the input، differs from that before acting the input? It is shown that nonlinearity is a necessary condition for a system in order that its dynamical properties change due to a limited duration acted input. Then، based on this new approach، the radiotherapy protocols are evaluated and the best protocol، which has the lowest fraction of normal cell kill (FN) and shorter time for the tumor removal، is extracted. According to the results، the accelerated fractionation is the best protocol. Also، after removing the radiotherapy the patient becomes healthy and the cancer do not relapse due to change in the dynamics of the cancer. So، the present analysis suggests that a proper treatment method should change the dynamics of the cancer instead of only reducing the population of cancer cells.

In this paper، the nonlinear method، “wavelet sliding-mode control with varying boundary layer via time-variant sliding function” for the pitch autopilot controlling EMRAAT missle، based on steering logic BTT is employed. Time-variant sliding surface filters all un-modeled frequencies. The adjustable boundary layer width، break-frequency bandwidth and the consequent parameters in neural wavelet approximation are tuned، to reduce the effects of the system uncertainties، un-modeled frequencies،. The chattering phenomenon do not occur and control cost is lower than other methods. The tracking operation is time optimal operation. Three theorems and one lemma، which facilitate design of the employed controller، are presented. To investigation the operation of the employed method، the Mexican Hat wavelet function as wavelet basis function is selected. This method is implemented for a couple of examples، pitch autopilot control systemand invert pendulum، to illustrate adventages of the proposed method. Keywords: Break frequency bandwidth، Rejection regulator، Sliding Mode Control، Missle، Autopilot، Wavelet Varying Boundary Layer، Wavelet networks

In the current study، the phenomenon of free convection around a metal cylindrical with uniform heat flux is experimentally investigated using PIV technique. The experimental tests are performed in a qubic container that contains liquid water with free surface which a metal rod horizontally passes through it. To create a two-dimensional flow، two parallel planes are inserted in the container and then، the metal rod is passed though it. The tests are performed for different heights of water and their results are compared with each other. To measure flow velocity in a specified region، the PIV technique is used. The tests are implemented by using a 200 mW laser and a CCD camera of 25 fps. In the experiments، the particles having the same density of water are tracked through the container in a specified time interval to calculate the flow field around the rod. sequence analyses of flow field during the different moments obtains the unsteady flow field. Although removing the 3D effects of flow، the results show that the flow field is strongly oscillatory and unsteady.

Drying is one of the main processes during manufacturing ceramic products. The part shrinks as the water content evaporates. Shrinkage phenomenon during the drying of ceramic materials can cause defects such as crack and deformation as a result. Since many parameters influence the ceramics drying & drying shrinkage، the experimental investigation of all of them is time consuming and expensive. Numerical simulation for drying process can be an appropriate method so as to control and improve the defects mentioned above، and it can also be as a tool for mold and ceramic parts design in reverse engineering. The objective of the current research is to study the drying of a ceramic material with known chemical composition and to analyses the process using Finite Element Analysis method. Deformation values were experimentally measured using machine vision and image processing techniques. Strain vectors were determined based on which a comparison could be performed between analytical and experimental model. The drying model developed was verified by experiments.

The measurement of hydrodynamic forces on underwater bodies is one of the principal uses for water tunnels. For this type of work an accurate force balance is necessary. This paper describes the design of a new six-component force-moment strain gauge balance with bending beams for measuring forces and moments simultaneously and directly on cavitating and Non-cavitating models in water tunnel. This balance is a complex structural spring element، which provides high-precision measurements of the hydrodynamic loads exerted on the water tunnel model، by measuring strain within its flexural elements. This measured strain is then converted into an electrical signal. Electrically measured strain as a function of an externally applied load forms. The main idea of the new balance design is to translate all desired forces and moments in such a way that they yield bending strain at selected strain-gauge station. This is done by using bending balance geometry. A strain gauge balance is a complicated structure with a very large number of dimensions. So the balance design cannot be achieved as an analytical solution from the external dimensions and the required component ranges. The dimensions of the «optimum» section and the likely deflection of the balance under load were determined using finite-element analysis. Hydrodynamic loads on typical water tunnel models were calculated، and the results were used to determine the strain level required to obtain the desired sensitivity. The size of the cantilever beams was carefully planned in order to determine the appropriate strain gauges needed for the experiment.