Sharif Digital Repository

In the present project an analytical model is proposed for the instability of spinning composite cylindrical shells partially filled with fluid. For this purpose, using the linearized Navier-Stokes equation for the incompressible flow, a 2-D model is developed for fluid motion at each section of the cylinder. The resultant pressure exerted on the cylinder wall as the result of the fluid motion, are calculated in terms of elastic displacements of the cylinder. Applying the Hamilton principle, the governing equations of motion of the cylinder are derived and then combined with the equations describing the fluid pressure to obtain the coupled-field equations of the structural-fluid motion.... 

The current study is dedicated to free vibration analysis of a thin cylindrical shell with an oblique end. To this end, governing equations of motion and the corresponding boundary conditions are derived using Hamiltonian formulations. The differential form of equations is obtained by applying by part integration to the integral form of equations of motion. Equations of motions have been solved by Galerkin method for two different kinds of boundary conditions. Convergence process for different kinds of conditions has been done and results compared with papers. The effect of different parameters such as, length of cylinder, oblique angle, thickness etc. on the fundamental frequencies has been... 

Here the differential equations of a Graphene sheet deformation is determined by making use of the most general form of first Strain Gradient Elasticity (SGE) theory. In order to derive the equations of in-plane and out-of-plane deformations, the matrix representation of Strain Gradient constitutive law is used. Vibration of the nano-plate is studied by modeling the plate based on Kirchhoff theory and application of variation of energy, therefor the in-plane and out-of-plane vibration of the nano-plate is found through Navier analytical solution. After all natural frequencies are obtained based on SGE parameters. SGE parameters are determined by calculating the potential of a representative... 

In this project, vibration and stability condition of a pipe conveying flow has been studied for use in firefighting plane. The Plane is a multi-rotor that carries the pipe to a certain height and it does the washing work there, bassed on the fluid flow from the nozzle embedded in the end of the pipe. Due to the flexibility of the pipe in this application, structure modeling is based on cable without bending stiffness. The Galerkin method is used to solve equations by considering the assumed mode shape for structure. At first, by analyzing free vibrations, different boundary conditions were considered for the pipe and the natural frequencies and natural shape modes were extracted in... 

Nanotechnology with the tools, materials and their applications in areas such as engineering mechanics, materials, electronics, computers, and machines at the nanoscale is dealing. The Fnarvy, atoms and molecules as building materials, engineering bricks counts. In mechanical engineering branch, two aspects are discussed in view of nanotechnology, nano-scale structures and analyzing the behavior of phenomena that occur at the nanoscale. In this project, methods to analyze the behavior of nanoscale materials has been studied.
The present thesis examines the natural frequencies of nano graphene sheets on elastic foundation deals. The elastic foundation modeled with two springs.At first The... 

In this study, the nonlinear vibrations of an elastic rotor that is under the elastic support and under the follower force caused by the airflow passing through the rotating plane are investigated. The elastic shaft is modeled by the Timoshenko beam theory, which is connected to a motor through a flexible coupling and the motor increases the rotational speed of the rotor by applying torque. Gibbons’ equations have been used to model the misalignment forces. First, the kinetic energy of the rotating system is calculated nonlinearly to take into account the effect of nonlinear terms due to the rotational inertia of the system, and then the potential energy and The work of external forces on... 

In this thesis, a general survey and reviewis done about the models that go beyond the standard model. Even it contains the great subjects like quantum gravity and alternative Quantum field theories. In addition to them, we concentrate on the supersymmetry that is one of the most important subjects in the beyond the standard model. Recently, the validityof supersymmetry has confronted a lot of controversy. This motivates reconsideration of many supersymmetric models. So we survey the main motivations and problems of the supersymmetry and finally we discuss some possible solutions to the problems  

This study presents the aeroelastic stability and vibration analysis of a sandwich circular cylindrical shells with a constrained viscoelastic layer. Based on the Donnell-Moshtari theory, the structural formulation of the cylinder is obtained using Lagrange method. The Rayleigh-Ritz method is implemented to solve the discretized governing equations. To describe the mechanical properties of the viscoelastic layer, the fractional order standard solid model is applied. The effects of variation of the governing parameters such as the length to radius ratio, radius to total thickness ratio and ratio of core to facing thickness on the stability margins and frequencies of sandwich cylindrical... 

In the current study, stability and nonlinear vibration of bending-torsional extensible beams conveying internal pulsatile and uniform external flow are studied. The internal and external fluid flows are assumed to be incompressible and frictionless. Applying the extensibility to the pipe along its length and using the nonlinear Euler-Bernoulli beam model and including some appropriate additional assumptions, the 3D nonlinear equations of motion of a cantilevered composite pipe is obtained. In order to derive the equations governing the fluid-structure interaction, the internal flow effect is modeled as a distributed load along the pipe which contains the inertia, Coriolis and centrifugal... 

The current study is dedicated to free vibration and buckling analysis of thick FGM conical shells conveying hot flows with the consideration of initial geometric imperfections. To this end, the higher order governing equations of motion and the corresponding boundary conditions are derived using Hamiltonian formulations. Due to the solution procedure of Frobenius series expansion, the differential form of equations is obtained by applying by part integration to the integral form of equations of motion. Radial and longitudinal temperature distributions are considered while pressure distribution and geometric imperfection variations are found to be in longitudinal direction, only. The final... 

The present study aims at investigating the stability of flexible spinning cylinders conveying flow in an external fluid Medium. Using the linearized Navier-Stokes equations for the flow, a two-dimensional model is developed governing the fluid motion. The resultant force exerted on the flexible cylinder wall due to the fluid interactions is calculated as a function of the lateral acceleration. Applying the Hamilton principle, the governing equations of flexural vibration of the rotary flexible cylinder mounted on simply supported axles are derived. Having the forces due to the conveying fluid calculated and substituting into the governing equations, a coupled field governing equations of... 

The purpose of this study is to develop the reduced order nonlinear modeling of single cell closed section thin walled composite beams. In this way, global behavior of one dimensional beam under axial load, bending and torsional moment is produced. This model is based on the classical lamination theory, and the nonlinear model is developedby usingthe von-karman strains. In this process the effects of material anisotropy and axial warping are considered. Numerical results are obtained for thin-walledcomposites box beams, addressing the effects of fiber angle and laminate stacking sequence. The nonlinear model is compared with theoretical results of homogeneous beams and the natural... 

The current study is dedicated to free vibration and Aeroelastic Stability Analysis of Truncated Conical Panels in Supersonic Flows. Governing equations of motion and the corresponding boundary conditions are derived using Hamiltonian formulations. The aeroelastic stability problem is formulated based on first-order shear deformation theory as well as classical shell theory with the linearized first-order piston theory for aerodynamic loading and solved using Galerkin method. The flutter boundaries are obtained for truncated conical shells with different semi-vertex cone angles, different subtended angles, and different thickness  

The tumor is a collection of cells (cell mass) caused by the lack or ineffectiveness of cellular proliferation inhibitors. Many types of cancers are associated with the emergence of a tumor, a tissue with specific physiological characteristics. The tumors grow very fast so researchers try to prevent their growth and eventually destroy them. Thermal ablation by MWA(microwave ablation) is a common and minimally-invasive treatment for primary and secondary liver tumors that can not be cured by surgery. During treatment, the tissue is heated by microwaves and at a temperature higher than 50 degree Celsius, destroyed by thermal ablation. In this study, two thermal models have been used to... 

Liquid droplets are a natural phenomenon with a wide applications in various fields, including food, pharmaceutical and agricultural industries. There are two regimes in the drop falling from a nozzle, dripping and jetting regimes. The size of the formed droplet and its geometry are influenced by the formation regime. One of the most challenging problems in this field is the transition from dripping regime to jetting regime. A common method of controlling of dripping to jetting transition ( DJT1 ) is the addition of surfactant. Surfactants are substances whose molecules have a hydrophobic tail and a hydrophilic head and reduce the surface tension of a liquid by adsorbing it. In this study,... 

Vibration of flexible slender structures under vortex induced vibrations is one of the important subjects in the different fields of engineering such as overhead electricity transmission cables, columns, tall towers and suspended bridges. During passes of flow around bluff bodies, in the certain range of velocity, the Von Karman vortices sheds unsynchronized from two sides of bluff bodies. When structure frequency closed to the vortex shedding frequency, resonant vibrations happen and one can observe vibrations with limited amplitude. Simulations of these phenomenons are so complicated and time consuming prosess, but there is an engineering method for simulating this phenomenon. The aim of... 

One can use the vibrational energy available in environment to harvest energy via piezoelectric materials, for various applications and this research field has received growing attention by researchers over the last years. This research motivation is, harvesting electrical energy from a fluttering plate in 2D axial flow via piezoelectric materials. For this purpose, a nonlinear Euler-Bernoulli beam model is used to model structure, an incompressible 2D vortex lattice method is used to model the aerodynamics, and coupled linear piezoelectric electro-mechanical equations is used to model piezoelectric materials. The structure is considered into axial flow, and flow speed gradually increases,... 

In the present work, the aeroelastic stability analysis for the swept taper wing and external fuel tank combination system in subsonic compressible flow are represented. The wing structure is modeled by using the Euler-Bernoulli beam theory. Fuel sloshing is modeled by using an equivalent mechanical mass-spring-damper model. Modal analysis technique is used to drive the structural equations of motion of the system. Aeorodynamic of wing is modeled by using index aerodynamic that has been dived by Marzocca and a slender body aerodynamic theory for the external fuel tank are used. For stability analysis, k-method redrived for a case that structural damping there is. The effects of the external...