Sharif Digital Repository

This work presents a method to find the exact solutions for the free vibration analysis of a delaminated beam based on the Timoshenko type with different boundary conditions. The solutions are obtained by the method of Lagrange multipliers in which the free vibration problem is posed as a constrained variational problem. The Legendre orthogonal polynomials are used as the beam eigenfunctions. Natural frequencies and mode shapes of various Timoshenko beams are presented to demonstrate the efficiency of the methodology  

Quality and continuity of electrical power to sensitive loads especially in power plants and industrial sectors is of great importance. For this reason, bus transfer is used. During the bus transfer interval, sensitive loads especially motors will be interrupted, and may encounter difficulties. So, it is used reactive power compensator and custom power devices to mitigate stress in motors and improve power quality indices. This paper presents the effect of reactive power compensator and custom power devices paralleling with motor in process of bus transfer which is done in two methods: EMTS and STS. Also, it is investigated dynamic performance of induction motor and spin-down curves in... 

This paper presents a novel Gait Pattern Generator ((IPC) developed for the "Alice" social humanoid robot, which up to now lacked an appropriate walking pattern. Due to t he limitations of this robot, the proposed gate pattern generator was formulated based on a nine-mass model to decrease the modeling errors and t he inverse kinematics of the whole lower-body was solved in such a way that the robot remained statically stable during t he movements. The main challenge of this work was to solve t he inverse kinematics of a 7-link chain with 12 degrees of freedom. For this purpose, a new graphical-numerical technique has been provided using the definition of the kinematic equations of the robot... 

This paper presents a novel Gait Pattern Generator ((IPC) developed for the "Alice" social humanoid robot, which up to now lacked an appropriate walking pattern. Due to t he limitations of this robot, the proposed gate pattern generator was formulated based on a nine-mass model to decrease the modeling errors and t he inverse kinematics of the whole lower-body was solved in such a way that the robot remained statically stable during t he movements. The main challenge of this work was to solve t he inverse kinematics of a 7-link chain with 12 degrees of freedom. For this purpose, a new graphical-numerical technique has been provided using the definition of the kinematic equations of the robot... 

The acoustical system of car was analyzed using finite element method (FEM) and identification of the system. The acoustical model of a vehicle was proposed and by using FEM modal analysis, acoustic modal analysis, structural modal analysis, and coupling modal analysis was performed successfully. The influence of the acoustic system on the driver ears to understand these effects were also shown. The methods and results can be applied to a vehicle design procedure for conformability of the human being when riding  

Sound in the interior cabin of cars has been of the great importance nowadays. The automotive industry has long been fiercely competitive with different vendors attempting to produce vehicles with better performance, handling and fuel efficiency. The competition of the automotive industries today is directed on the reduction of noise in the cars cabin. This paper proposes a new method for noise studies in the cabin, which frequencies of excitation are lower than 200 Hz. The topics, which are covered in the paper, include the computation of the structural and acoustic mode shapes, resonant frequencies of the passenger compartment, coupling between structure and acoustic effects, and forced... 

Numerical analysis has been conducted to simulate and capture Buzz phenomenon in a supersonic mixed compression air intake. Buzz is an unsteady self-sustained phenomenon occurred in supersonic intakes, especially when operating its subcritical condition, during which the system of compression and shock waves oscillate and move upstream and downstream along the intake. An axisymmetric and unsteady numerical simulation was used to solve Navier-Stokes equations in combination with URANS SST k-ω turbulence model The simulations were performed at M=2.0 and at a specific subcritical point of the intake operation where buzz was detected experimentally. Results are compared with experimental... 

Infill walls are realized to affect the nonlinear response of infilled frames. Yet, due to modeling and analysis complexities, infill walls are usually neglected in the modeling and analysis phase. In this paper, the nonlinear behavior of infilled steel braced frames is investigated using the Endurance Time (ET) method. The ET method is a novel and straightforward approach for the nonlinear analysis of structures under dynamic excitations. Two 2D braced frames, one concentrically braced frame and one eccentrically braced frame, with unreinforced masonry clay brick walls as infills, are considered. The infill panels are macro-modeled using equivalent compressive struts, with appropriate... 

The geometry structures of hexa-coordinated [NiLX]X complexes (X = Cl -, Br-, I-) {L = 8,9,18,19-tetrahydro-7H,17H- dibenzo[f,o] [1,5,9,13]dioxadiaza cyclohexadecine-8,18-diol} are optimized by density functional theory (DFT) using B3LYP/LANL2DZ. The calculated geometric parameters are in good agreement with the corresponding experimental values. Calculation results about these complexes show that dipole moment decreases, and the energy levels of HOMOs descend from iodo-complex to chloro-complex. The energy levels of HOMOs descend gently from iodo-complex to chloro-complex, while the energy levels of LUMOs in the present complexes are almost similar; therefore the energy gapes between HOMOs... 

A rather new semi-analytical method towards investigating the free vibration analysis of generally laminated composite beam (LCB) with a delamination is presented. For the first time the combined effects of material couplings (bending-tension, bending-twist, and tension-twist couplings) with the effects of shear deformation, rotary inertia and Poisson's effect are taken into account. The semi-analytical solution for the natural frequencies and mode shapes are presented by incorporating the constraint conditions using the method of Lagrange multipliers. To verify the validity and the accuracy of the obtained results, they were compared with the results from other available references. Very... 

In this paper, the free vibration analysis of generally laminated composite beam (LCB) based on Timoshenko beam theory are presented using the method of Lagrange multipliers where in the free vibration problem is posed as a constrained variational problem. The effect of material couplings (bending-tension, bending-twist, and tension-twist couplings) with the effects of shear deformation, rotary inertia and Poisson's effect are taken into account. Analytical expression for the natural frequencies and mode shapes are presented. The calculated natural frequencies are verified against some available results in the literature and very good agreement is observed. Furthermore, the effects of some... 

The objective of this study is to present a brief survey on the geometrically nonlinear free vibrations of the Bernoulli-Euler, the Rayleigh, shear, and the Timoshenko beams with simple end conditions using the Homotopy Analysis Method (HAM). Expressions for the natural frequencies, the transverse deflection, postbuckling load-deflection relation to, and critical buckling load are presented. The results of nonlinear analysis are validated with the published results, and excellent agreement is observed. The effects of some parameters, such as slender ratio, the rotary inertia, and the shear deformation, are examined as other parameters are fixed. Copyright  

The aim of this paper is to present analytical and exact expressions for the frequency and buckling of large amplitude vibration of the symmetrical laminated composite beam (LCB) with simple and clamped end conditions. The equations of motion are derived by using Hamilton's principle. The influences of axial force, Poisson effect, shear deformation, and rotary inertia are taken into account in the formulation. First, the geometric nonlinearity based on the von Karman's assumptions is incorporated in the formulation while retaining the linear behavior for the material. Then, the displacement fields used for the analysis are coupled using the equilibrium equations of the composite beam.... 

The free vibration analysis of generally laminated composite beam (LCB) with a delamination is presented using the finite element method (FEM). The effect of material couplings (bending-tension, bending-twist, and tension-twist couplings) with the effects of shear deformation, rotary inertia, and Poisson's effect are taken into account. To verify the validity and the accuracy of this study, the numerical solutions are presented and compared with the results from available references and very good agreement observed. Furthermore, the effects of some parameters such as slenderness ratio, the rotary inertia, the shear deformation, material anisotropy, ply configuration, and delamination... 

In this study, the dynamic response of the laminated composite beam with arbitrary lay-ups has been investigated within the framework of the third-order shear deformation theory using the finite element method. A new three-nodded finite element compliant with the theory is introduced next. To deal with the dynamic contact between the delaminated segments, unilateral contact constraints are employed in conjunction with Lagrange multiplier method. Furthermore, the Poisson's effect is incorporated in the formulation of the beam constitutive equation. Also, the higher-order inertia effects and material couplings (flexure-tensile, flexure-twist and tensile-twist couplings) are considered in the... 

A hot gas generator is a compact heat exchanger that produces high temperature or enthalpy gases. This paper presents two methods for controlling the system. The first one is an adaptive sliding mode controller that is a Lyapunov based method and proposed to confront the dynamic modeling deficiencies and system uncertainties. The second one is a linear adaptive controller that gives a new attractive ability to the system which can track a complicated requested path. Each of the presented controllers has some capabilities that may be preferred to other. In this paper, these methods are extensively compared by several transient inputs. On the other hand, since heat exchangers are typically... 

In the present work, nanostructured aluminum titanate (Al2TiO5 or AT) was synthesized by the sol-gel method and potential effects of mechanical strain on its phase analysis, morphology, and thermal stability were investigated in some details for the first time, because the thermal instability of AT is beneficial to the fabrication of in-situ aluminum matrix composites. To characterize the particle distribution, microstructure and thermal durability of AT after the strain induction, field-emission scanning electron microscope (FE-SEM), differential scanning calorimetry (DSC), and x-ray diffraction analysis (XRD) were utilized. The experimental results showed that a 3-h ball milling process... 

In this study, plasmonic properties of transition metal atoms (Sc-Zn, Pd, Pt) adsorbed on various sites of graphene sheets were investigated before and after CO adsorption by density functional theory (DFT). To this aim, Electron Energy Loss Spectroscopy (EELS) of these systems were obtained by periodic DFT. The results indicated that the highest in-plane plasmon peaks undergo blue shifts after CO adsorption, in such a way that Co–graphene system demonstrates the highest blue shift of 2.42 eV from Visible to UV region. Also, out-of-plane plasmons do not exhibit significant sensitivity to CO adsorption. For deeper understanding of electronic structure of metal-graphene systems, appropriate... 

This paper deals with the dynamic analysis of a delaminated Bernoulli-Euler beam with constrained model under the action of an external moving force. The beam is analyzed as four interconnected sub-beams using the delamination as their boundaries. The continuity and compatibility conditions are satisfied between adjoining beams. An analytical solution is presented in a basis of the series expansion of the unknown deflection. The delaminated beam response differences with the healthy beam have been investigated. Effect of the parameters like the moving speed of the force and the size, depth and spanwise location of the delamination on the dynamic response of the beam has been studied.... 

This paper presents a novel approach for evaluating LBP in various settings. The proposed system uses cost-effective inertial sensors, in conjunction with pattern recognition techniques, for identifying sensitive classifiers towards discriminate identification of LB patients. 24 healthy individuals and 28 low back pain patients performed trunk motion tasks in five different directions for validation. Four combinations of these motions were selected based on literature, and the corresponding kinematic data was collected. Upon filtering (4th order, low pass Butterworth filter) and normalizing the data, Principal Component Analysis was used for feature extraction, while Support Vector Machine...