Sharif Digital Repository

Dynamic instabilities are quite common in planing crafts. This study deals with the elimination of one type of dynamic instabilities known as porpoising. The controller device is a pneumatically driven trim tab that applied to the transom of the boat. The governing dynamic equations of the planing craft and the pneumatically driven system are derived. The stability analysis of the system is carried out and porpoising instability is shown under some conditions. A dual control scheme consisting of the actuator control subsystem (inner control subsystem) and the planing craft (outer control subsystem) is proposed in order to control the planing craft from porpoising instability. Since the... 

Buckling and post-buckling behaviors of geometrically imperfect annular sector plates made from nanoparticle reinforced composites have been investigated. Two types of nanoparticles are considered including graphene oxide powders (GOPs) and silicone oxide (SiO2). Nanoparticles are considered to have uniform and functionally graded distributions within the matrix and the material properties are derived using Halpin-Tsai procedure. Annular sector plate is formulated based upon thin shell theory considering geometric nonlinearity and imperfectness. After solving the governing equations via Galerkin’s technique, it is showed that the post-buckling curves of annular sector plates rely on the... 

In this paper, a method for modeling of elastic-plastic hardening materials under large deformations is proposed. In this model the generalized strain rate tensor is used. Such a tensor is obtained on the basis of the method which was introduced by the authors. Based on the generalized strain rate tensor, a flow rule, a Prager-type kinematic hardening equation and a kinematic decomposition is proposed and the governing equations for such materials are obtained. As an application, the governing equations for the simple shear problem are solved and some results are compared with those in the literature. Copyright © 2008 by ASME  

In this paper, a thorough investigation of response of a composite Timoshenko simply-supported beam with actuating layers, under the motion of a partially distributed mass is studied and a control system based on the feedback of beam's deflection velocity is applied to alleviate and suppress the vibration of the beam in either case when the mass is still traveling on the beam or departed the beam. The actuating layers are made up of Terfenol-D smart material which are sensitive to magnetic field (magnetostrictive materials) and this trait makes them very suitable to be used for vibration control. They introduce damping to the system through which the energy of system dissipates. The response... 

In this paper dynamic analysis of multi-span bridges subjected to a moving vehicle is investigated. Finite element method is used to model the problem, and the Newmark technique is used for direct integration of the governing equations. In this regard, the moving node technique is applied to represent the dynamic responses of the multi-span bridge, and the vehicle is idealized as a sprung-mass system. Results indicate that the maximum vertical deflection of the multi-span bridge occurs at the span under the vehicle. It was found that the mid-span vertical deflection of spans for dynamic and static loading are not the same, and the position of the vehicle for maximum deflection for dynamic... 

In the present study, the effect of using magnetorheological elastomer materials and a magnetic field on the dynamic stability of a sandwich beam under a follower force has been investigated for various boundary conditions. The considered sandwich beam consists of a magnetorheological elastomer core constrained by elastic layers. The structural governing equations are derived using Hamilton’s principle and solved by the finite element method. The validity of the result is examined by comparison with those in the literature. The effects of variation in the parameters such as magnetic field intensity and the thickness of the layers on the stability of the sandwich beam are studied. Finally,... 

In this contribution, we have investigated the effects of magnetoelastic loads on free vibration characteristics of the magnetorheological-based sandwich beam. The considered sandwich beam consists of a magnetorheological core with elastic top and base layers. For these means, the structural governing equations are derived using the Hamilton principle and solved by the finite element method. The results are validated in comparison with the existing results in the literature. The effects of variation in the parameters such as magnetic field intensity and the thickness of the core and top layers on the deviation of the first natural frequency and the corresponding loss factor are studied as... 

In this article, the effects of the changes in the mass of the floating wind turbine (as a multi-body system) on its nonlinear vertical vibrations are investigated. The fluctuations of the hydrodynamic added mass of the floating platform and the mass of the vibration absorbers, which added to the structure to mitigate the lateral vibrations, change the mass and consequently the dynamics of the vertical vibrations. In this regard, first, the governing equations of the vertical vibrations of the floating wind turbine are derived. The FAST code is used to validate the proposed model of the dynamics of the vertical vibrations through numerical simulations. Then, derived equations are solved... 

This is the first research on the frequency analysis of a graphene nanoplatelet composite circular microplate in the framework of a numerical-based generalized differential quadrature method. Stresses and strains are obtained using the higher order shear deformation theory. The microstructure is surrounded by a viscoelastic foundation. Rule of the mixture is used to obtain varying mass density and Poisson’s ratio, whereas the module of elasticity is computed by a modified Halpin–Tsai model. Governing equations and boundary conditions of the graphene nanoplatelet composite circular microplate are obtained by implementing Hamilton’s principle. The results show that outer to inner radius ratio... 

Purpose: The purpose of this study is to present a comprehensive hydrothermal analysis on an inclined mini-channel using numerical and experimental techniques. The fin array acts as heat source within the channel, and a wavy wall located at the top of the channel is heat sink. The side walls are insulated with curved profiles. Also, the channel is inclined with four known inclination angles. To solve the governing equations, the dual-multi-relaxation-time lattice Boltzmann method with D2Q9 and D2Q5 lattice models for flow and temperature fields is used, respectively. Also, the channel is filled with SiO2-glycol nanofluid. Design/methodology/approach: Identifying the behavior of a thermal... 

This article investigates the basis for pressure sensor application based on the magnetic shape memory effect in membranes. Von Karmans nonlinear terms are considered in strain–displacement relationships of thin films, and a new method is presented for solution of large deflections of thin films with arbitrary boundary condition. In this study, the equations of motion of magnetic shape memory alloys are extended. In pressurized membranes, the complex distribution of mechanical stress can cause the martensitic reorientation, which is the underlying mechanism for sensing applications in magnetic shape memory alloys. To examine the obtained model, the governing equations of magnetic shape... 

Recently, eliminating the gap between design and formability analysis of sheet metal parts has been studied to simulate sheet metal stamping processes. In this regard, a transfer-based inverse isogeometric formulation has been proposed. This method has various advantages such as solving the governing equations in two-dimensional networks without any concern about the convergence; however, it neglects the bending effect which is a major contributor in die/punch profile radii. The present work aims to consider the bending effects by introducing a bending-dependent inverse isogeometric formulation. The developed model deals with the minimization of potential energy, deformation theory of... 

In this research, electrically characteristics of a graphene nanoplatelet (GPL)-reinforced composite (GPLRC) microdisk are explored using generalized differential quadrature method. Also, the current microstructure is coupled with a piezoelectric actuator (PIAC). The extended form of Halpin–Tsai micromechanics is used to acquire the elasticity of the structure, whereas the variation of thermal expansion, Poisson’s ratio, and density through the thickness direction is determined by the rule of mixtures. Hamilton’s principle is implemented to establish governing equations and associated boundary conditions of the GPLRC microdisk joint with PIAC. The compatibility conditions are satisfied by... 

In this study, the existence of a sinusoidal splitter on the formation and distribution of hydrogen and air co-jets are investigated in a dual-combustion ramjet engine. The main scope of this research is to analyze the comprehensive flow structure and flame features directly downstream of the sinusoidal splitter. In this work, shockwave/shear-layer interactions behind the sinusoidal splitter are thoroughly studied through a computational fluid dynamic approach. Two different splitter profiles are compared with a simple splitter to demonstrate the main effects of multi shock wave interactions on fuel distribution and penetrations. To simulate co-air jet, Reynolds Average Navier-Stocks... 

This article is the first attempt to employ deep learning to estimate the frequency performance of the rotating multi-layer nanodisks. The optimum values of the parameters involved in the mechanism of the fully connected neural network are determined through the momentum-based optimizer. The strength of the method applied in this survey comes from the high accuracy besides lower epochs needed to train the multi-layered network. It should be mentioned that the current nanostructure is modeled as a nanodisk on the viscoelastic substrate. Due to rotation, the centrifugal and Coriolis effects are considered. Hamilton’s principle and generalized differential quadrature method (GDQM) are presented... 

In this article, wave propagation characteristics of a size-dependent laminated composite nanostructure coupled with a piezoelectric actuator (PA) is investigated. In order to consider the effects of small scale, the governing equations of the laminated composite nanostructure coupled with PA are derived using Hamilton’s principle based on the nonlocal strain gradient theory (NSGT). The differential equations of motion are solved with the assistance of the analytical method. Afterward, a parametric study is carried out to investigate the effects of the PA thickness, wave number, angular velocity and the ply angle on the value of phase velocity. The results show that the ply angle plays an... 

In this paper, boundary control (BC) laws are designed to find a BC solution for a single-link nonlinear vertical manipulator to suppress the link’s transverse vibrations and control the rigid body nonlinear large rotating motion. The governing equations of motions and boundary conditions, which all consist of a set of PDEs and ODEs have been derived based on the Hamilton principle. It is desired to regulate large angular orientation, suppress the flexible link’s transverse vibrations and compensate the boundary disturbance simultaneously. The amount of elastic boundary vibration has remained within the constraint range. By considering novel Barrier-Integral Lyapunov functional in order to... 

In this paper, the nonlinear dynamic responses of an inclined pinned-pinned Euler-Bernoulli beam with a constant cross section and finite length subjected to a concentrated vertical force traveling with constant velocity is investigated by using the mode summation method. Frequency analysis of the PDE's governing equations of motion for steady-state response is studied by applying multiple scales method. The nonlinear dynamic deflections of the beam are obtained by solving two coupled nonlinear PDE's governing equations of planar motion for both longitudinal and transverse oscillations of the beam. The dynamic magnification factor and normalized time histories of mid-point of the beam are... 

In this paper, an analytical solution is presented for free vibration and dynamic behavior of doubly curved laminated shell consisting of a functionally graded core layer and surface attached functionally graded piezoelectric layers. Shell through-thickness kinematics is based on higher order shear deformation theory of shells, whereas a quadratic variation is assumed for electric potential. Using Hamilton's principle and Maxwell's equation, the governing equations of motion under mechanical loads are derived as seven highly coupled partial differential equations. Implementing Laplace transformation, doing few mathematical operations and using Laplace inverse method, time dependencies of... 

The nonlinear dynamic and static deflection of a micro/nano gyroscope under DC voltages and base rotation are investigated. The gyroscope undertakes two coupled bending motions along the drive and sense directions and subjected to electrostatic actuations and intermolecular forces. The nonlinear governing equations of motion for the system with the effect of electrostatic force, intermolecular tractions and base rotation are derived using extended Hamilton principle. Under constant voltage, the gyroscope finds the preformed shape. First, the deflection of the micro/nano gyroscope under electrostatic forces is obtained by static and dynamic analyses. Furthermore, the static and dynamic...