Sharif Digital Repository

The dependence of undrained behavior of silty sand on initial state of stress and direction of principal stresses with respect to vertical (ff) is assessed under generalized loading paths using hollow cylinder apparatus. During applying shear load, value of intermediate principal stress parameter (b) is held constant and ff value is increased from zero to the aimed value and held constant. Specimens are consolidated, both, isotropically and anisotropically to evaluate the effect anisotropic consolidation on the behavior of these soils. The wet tamping method was selected to prepare specimen. Shear loading was carried out under strain-controlled condition to capture post-peak strain-softening... 

In this paper, employing an analytical method, optimum design of multi-layer compound cylinders is investigated. To this end, considering Tresca criterion, maximum shear stress in each layer is minimized. Analytical relations for optimum values of a layer dimension, residual pressures and radial interferences are derived. A technique for shrink-fitting of layers is also proposed and relationships for radial interferences, residual pressures and required temperature differences during the shrink-fitting process are derived. Three different examples are presented to show the effectiveness of the proposed method. It is shown that increasing the number of layers makes shear stress distribution... 

One of the main subjects in automotive industries is to enhance the efficiency of internal combustion engines. Wear between cylinder and ring is one of the major parameters reducing the engine performance. So many parameters are affecting the wear losses. Temperature plays a key role on the severity of wear condition in internal combustion engines. In conventional cast iron cylinders, it is not possible to increase the temperature from a defined level, as it causes excessive wear in contact area between cylinder liner and piston ring. One of the major benefits of using ceramic coating is their ability to withstand in higher temperatures, while having adequate hardness to improve wear rate... 

In this article, a constitutive model in the framework of continuum damage mechanics is proposed to simulate the elastic behavior of concrete in tension and compression states. We assume two parts for Gibbs potential energy function: elastic and damage parts. In order to obtain the elastic-damage constitutive relation with the internal variables, two damage thermodynamic release rates in tension and compression derived from the elastic part of Gibbs potential energy are introduced. Also, two anisotropic damage tensors (tension and compression) are defined which characterize the tensile and compressive behaviors of concrete. Furthermore, two different linear hardening rules for tension and... 

The dynamics and stability of rotating circular cylindrical shells partially filled with ideal liquid is analyzed. The structural dynamics of the shell is modeled by using the first-order shear deformable shell theory and the flow inside the cylinder is simulated by a quasi 2D model based on the NavierStokes equations for ideal liquid. The fluid and structural models are combined using the nonpenetration condition of the flow on the wetted surface of the cylinder and the fluid pressure on the flexible shell. The obtained fluidstructure model is employed for the determination of the stable regions of the spinning frequency of the cylinder. A series of case studies are performed on the... 

In this paper, the nonlinear oscillation of a pendulum wrapping and unwrapping on two cylindrical bases is studied, and an analytical solution is obtained using the multiple scales method. The equation of motion is derived based on an energy conservation technique. By applying the perturbation method to the differential equation, the nonlinear natural frequency of the system is calculated, along with its time response. Analytical results are compared with numerical findings and good agreement is found. The effect of large amplitude and radius of cylinders on system frequency is evaluated. The results indicate that as the radius of the cylinder increases, the system frequency is increased.... 

A finite element formulation is derived for the structural analysis of functionally graded hollow cylinders. The power-law distribution model is used for the composition of the constituent material in the thickness direction. According to property variation in FG cylinders, it is difficult to analyze them using the conventional element formulation. In order to facilitate the process of modeling and analyzing the FG cylinders, the finite element formulation is based on a newly designed cylindrical element. The new cylindrical element allows for property variations along the thickness, which results in considerable reduction of the required elements and eliminates the need to mesh the cross... 

In this paper, strain gradient elasticity formulation for analysis of FG (functionally graded) micro-cylinders is presented. The material properties are assumed to obey a power law in radial direction. The governing differential equation is derived as a fourth order ODE. A power series solution for stresses and displacements in FG micro-cylinders subjected to internal and external pressures is obtained. Numerical examples are presented to study the effect of the characteristic length parameter and FG power index on the displacement field and stress distribution in FG cylinders. It is observed that the characteristic length parameter has a considerable effect on the stress distribution of FG... 

A three-dimensional elasticity solution for the analysis of functionally graded rotating cylinders with variable thickness profile is proposed. The axisymmetric structure has been divided in several divisions in the radial direction. Constant mechanical properties and thickness profile are assumed within each division. The solution is considered for four different thickness profiles, namely constant, linear, concave, and convex. It is shown that the linear, concave, and convex thickness profiles have smaller stress values compared to a constant thickness profile. The effects of various grading indices as well as different boundary conditions, namely solid, free-free hollow and fixed-free... 

In this paper, free vibration of a fiber reinforced composite cylinder in which volume fraction of its fibers vary longitudinally, is studied using a semi-analytical method. The distribution of volume fraction of fiber in base matrix is based on power law model. A micromechanical model is employed to represent its mechanical properties including elastic and physical properties of this composite cylinder. In addition, kinematically the first order shear deformation shell theory is employed for strain field. Then, weak form formulation and spatial approximations of variables are utilized to discretize the equations of motion. Different problems are solved in which primarily the validity of the... 

In this paper, the buckling analysis of a multilayered composite cylindrical shell which volume fraction of its fiber varies according to power law in longitudinal direction, due to applied compressive axial load is studied. Rule of mixture model and reverse of that are employed to represent elastic properties of this fiber reinforced functionally graded composite. Strain displacement relations employed are based on Reissner-Naghdi-Berry's shell theory. The displacement finite element model of the equilibrium equations is derived by employing weak form formulation. The Lagrangian shape function for in-plane displacements and Hermitian shape function for displacement in normal direction to... 

There are hundreds models of reticulated structures including the squared reticulated cylindrical shells. It is considered as comprising of a number of circumferential and longitudinal rods. Analytical governing equation for natural frequencies has been derived for this type of structures and to verify the validity of solutions, Finite Element Method (FEM) is used. The comparison of results demonstrate close agreement between analytical and FE solutions. Also a comparison is preformed between a reticulated and equivalent solid hollow cylinder shell. The equivalent solid hollow cylinder has equal weight, length and outer diameter with the squared reticulated cylindrical shell. This comparison... 

Object handover as continually tracking an object across disjoint-view cameras is a necessary part of video-based monitoring systems. While having nonoverlapping cameras is a requirement for monitoring a wide area, there is no common 3D location that can be used to detect multiple views of the same object, in contrast with overlapping cameras. Appearance features play an important role for object handover in such camera networks. This paper focuses on modeling appearance features of moving vehicles by a new major color representation called codebook representation. Toward this end, in each frame, the k-means algorithm is used to cluster major colors of an object. In the subsequent frames, a... 

In this paper, nonlinear oscillation of a pendulum wrapping and unwrapping around two cylindrical bases is studied and an analytical solution is obtained using multiple scales method. Equations of motion are derived based on energy conservation technique. Applying perturbation method on the equations, nonlinear natural frequency of the system is calculated along with its time response. Analytical results are compared with numerical findings and good agreement is found. Effect of nonlinearity due to large amplitude and radius of cylinders on the system frequency is evaluated. Results indicate that as the radius of cylinder is increased, nonlinear frequency is enhanced. Initial amplitude plays... 

In this study, two physical properties of simply supported hollow cylinders made of functionally graded materials are investigated. These two properties are mass and first natural frequency which is desirable to be minimized and maximized respectively in mechanical applications. The functionally graded material properties are assumed to vary continuously through the thickness of the cylinder. In this multi-objective optimization problem the first natural frequency of the FGM cylinders as well as its mass are formulated in terms of the volume fraction of the constituents, then by using Genetic algorithm optimization method the continuous volume fraction function of the constituents has been... 

A series of experimental and numerical investigations on two tandem cylinders wake have been studied. The velocity profile and turbulence intensity have been acquired by a single one dimensional Hot Wire anemometer. The two cylinders were mounted in a tandem manner in the horizontal mid plane of the working section. The effect of the upstream cylinder diameter, Reynolds number and the distance between the cylinders on the wake profile and turbulence intensity on the downstream cylinder was investigated, while the Reynolds number ranged between1.5× (10)∧4 ∼ 3×(10)∧4. The upstream cylinder diameter (d) was 10, 20 and 25 mm, while the downstream cylinder diameter (D) was 25 mm, corresponding to... 

In this article, an analytical elastic-plastic solution for thick-walled cylinders made of Functionally Graded Materials (FGMs) subjected to internal pressure and thermal loading is presented. Based on the experimental results, a mathematical model to predict the yielding through the thickness of FG AlA359/SiCp cylinder is developed. It is shown that under the temperature gradient loading, there is a point in the cylinder where the circumferential stress changes from compressive to tensile. The position of this point depends on the geometry and material properties of the FG cylinder and is independent of the temperature gradient  

A body insonified by a sound field is known to experience a steady force that is called the acoustic radiation force. In this paper, the method of wave function expansion is adopted to study the scattering and the radiation force function caused by a plane normal harmonic acoustic wave incident upon an arbitrarily thick-walled functionally graded cylindrical shell submerged in and filled with compressible ideal fluids. A laminate approximate model and the so-called state space formulation in conjunction with the classical transfer matrix (T-matrix) approach are employed to present an analytical solution based on the two-dimensional exact equations of elasticity. Two typical models,... 

Purpose - The purpose of this paper is to analyze a squared lattice cylindrical shell under compressive axial load and to optimize the geometric parameters to achieve the maximum buckling load. Also a comparison between buckling loads of a squared lattice cylinder and a solid hollow cylinder with equal weight, length and outer diameter is performed to reveal the superior performance of the squared lattice cylindrical shells. Design/methodology/ approach - A cylindrical lattice shell includes circumferential and longitudinal rods with geometric parameters such as crosssection areas of the rods, distances and angles between them. In this study, the governing differential equation for buckling... 

Since it is quite difficult to analytically optimize hollow-core Bragg fibers to have minimum confinement loss without using the Floquet theorem, which does not hold for cylindrical structures, the cylindrical Bragg mirror is approximated by its planar counterpart. For this reason, first, the optimum planar waveguide formed by sandwiching a hollow layer between 1-D Bragg mirrors is found in this paper. The optimization for the dominant transverse-electric mode is analytically performed by using the pointwise wavenumber closely related to the wave admittance. A closed-form expression is then found to relate the propagation constant of this waveguide to the thickness of the hollow layer. This...