Sharif Digital Repository

In this study, an arbitrary Lagrangian-Eulerian (ALE) approach is incorporated with a mixed finite-volume-element (FVE) method to establish a novel moving boundary method for simulating unsteady incompressible flow on non-stationary meshes. The method collects the advantages of both finite-volume and finite-element (FE) methods as well as the ALE approach in a unified algorithm. In this regard, the convection terms are treated at the cell faces using a physical-influence upwinding scheme, while the diffusion terms are treated using bilinear FE shape functions. On the other hand, the performance of ALE approach is improved by using the Laplace method to improve the hybrid grids, involving... 

In this study surface profiling is performed by using a scanning system and an opto-pair fiber design. In this method one fiber transmits the laser light to the target and the second one transmits back the light reflected off the target to a photodetector. The monitoring of the reflected light signal from a surface is accomplished by converting the photon light into an electric signal and measuring by a digital multimeter. By scanning an object mounted on a XYZ-translational stage the reflection signal profiles are obtained for plane and curved surfaces. Output reflection signal variations in the X-, Y-, and Z-directions are measured for different plane and cylindrical surfaces and compared.... 

Free vibration analysis of a transversely stiffened circular thin hollow cylinder made of functionally graded materials (FGMs) is analytically evaluated. Functionally graded materials are inhomogeneous composites which are usually made from a mixture of metal and ceramic. The gradient compositional variation of the constituents from one surface to the other provides an elegant solution to the problem of high transverse shear stresses induced when two dissimilar materials with large differences in material properties are bonded. In this paper, application of an FGM made of two different materials is investigated by applying Ritz method. While cylinder is assumed to be thin, strain energy... 

The equilibrium governing equations of nonlocal anisotropic thin-walled circular cylindrical shell under combined axial compressive force, torsional load, and external pressure are explicitly derived. This is accomplished by appropriately combining the equilibrium equations and the strain-displacement relations according to Flügge's shell theory and the stress-stain equations of Eringen's nonlocal elasticity theory. An analytical solution for the buckling of the shells is presented by using the complex method. This model is validated by a good agreement between the results given by the present model and available data in the literature. Furthermore, the model is utilized to elucidate the... 

As the use of MEMS-based devices and systems are continuously increasing, the understanding of their correct characteristics becomes so serious for the related researches. In this study, the supersonic rarefied gas flow over microscale hotwires is investigated using the Direct Simulation Monte Carlo (DSMC) method. Indeed, the DSMC has been accepted as a powerful method to study the rarefied gas flow especially in transitional regime. Therefore, it can be considered as a reliable method to investigate the rarefied supersonic flow over microscale objects including the microscale hotwires. In this work, we study the effective parameters, which affect the performance of these sensors at constant... 

In this study, obtaining stress intensity factors (SIFs) for functionally graded cylinders with two internal radial cracks using the weight function method has been discussed. For this purpose, reference SIFs are calculated from the results of finite element analysis, using a modified domain of the J integral. Subsequently, SIFs have been calculated for different combinations of cylinder geometry, crack depth, and material gradation by implementing the weight function method and it is shown that the results are consistent with corresponding results obtained from finite element analysis. Moreover, the effects of variation in the elastic modulus ratio on SIFs have been investigated. © 2016... 

Based on the Sanders thin shell theory, this paper presents an exact solution for the vibration of circular cylindrical shell made of two different materials. The shell is sub-divided into two segments and the state-space technique is employed to derive the homogenous differential equations. Then continuity conditions are applied where the material of the cylindrical shell changes. Shells with various combinations of end boundary conditions are analyzed by the proposed method. Finally, solving different examples, the effect of geometric parameters as well as BCs on the vibration of the bi-material shell is studied  

Underwater surface of man-made structures is quickly covered by unwanted aquatic organisms. They change the flow regime around the structure. Despite the important contributions of previous studies on the vortex induced vibration (VIV) of bluff bodies, the flow induced vibration of non-stationary cylinders covered by marine fouling appears not to have received due attentions in the literature. The current paper reports on an attempt for better understanding the marine fouling effects on the VIV of circular cylinders. A structured review of the literature related to the fluid structure interactions in marine fouled cylinders is first presented. Results of an experimental study on the VIV of... 

This paper simulates Al2O3-water nanofluid flow and forced convection around a rotating circular cylinder. The governing parameters are Reynolds number (1 ≤ Re ≤ 100), solid volume fraction of nanoparticles (0 ≤ φ ≤ 0.05) and non-dimensional rotation rate (0 ≤ α ≤ 3). The simulations are performed to study the effects of mentioned parameters on the heat transfer rate and fluid flow characteristics. The governing equations including the continuity, momentum, and energy equations are solved with a finite volume method. It is observed that the reduction of heat transfer with increase in rotation rate is in the vicinity of 6.9% and 32% for Re = 5 and 100, respectively at φ = 0.05. Furthermore,... 

A computational tool is developed to capture the interaction of solid object with two-phase flow. The full two-dimensional Navier–Stokes equations are solved on a regular structured grid to resolve the flow field. The level set and the immersed boundary methods are used to capture the free surface of a fluid and a solid object, respectively. A two-step projection method along with Multi-Processing (OpenMP) is employed to solve the flow equations. The computational tool is verified based on numerical and experimental data with three scenarios: a cylinder falling into a rectangular domain due to gravity, transient vertical oscillation of a cylinder by releasing above its equilibrium position,... 

The aero-thermo-elastic stability of layered cylindrical shells with viscoelstic cores is investigated. The Donnell's shell theory for the outer layers and the first order shear deformation theory for the viscoelastic layer are employed in conjunction with the von Karman-Donnell kinematic nonlinearity to construct the model. The pre-stresses and pre-deformations arisen from the temperature rise and static aerodynamic pressure are first determined by solving the nonlinear thermo-elastic equilibrium equations using by an exact analytical method. The results are then used in the linear aeroelastic stability equations and analyzed with the Galerkin's procedure to determine the supersonic flutter... 

In this paper, the oscillation of two spark-generated bubbles placed on a vertical column in close proximity to a confined free surface is considered. The confined free surface is accorded by the top opening of different configurations. These configurations include (i) a centrally perforated horizontal flat plate (θ = 90∘), (ii) vertically placed cylinder (θ = 0∘) and (iii) nozzle (θ > 0∘). The main objective of the present work is to study the effects of key parameters such as the nozzle geometry, the locations of the energy input (i.e., initial position of the bubbles with respect to each other and relative to the free surface) on the dynamics of the two bubbles and the free surface. It... 

The present study aims at the investigation of free vibration analysis of thin cylindrical shells surrounded by an elastic medium, which is distributed over a particular length of the shell. The Love’s shell theory is utilized along with the Winkler foundation to obtain the governing equations of motion. An exact series expansion method of solution is employed for any arbitrary boundary conditions. The excellent accuracy of the obtained results is validated by comparing to the available literature. Moreover, several case studies are performed to provide an insight into the influence of some practically important parameters on free vibrations of circular cylindrical shells, including... 

Strengthening is often a necessary measure to overcome an unsatisfactory deficient situation or where a new code requires the structure or a member of it to be modified to achieve new requirements. In the engineering practice such restraint to lateral dilation, indicated by the name of confinement, has been traditionally provided to compression members through steel transverse reinforcement in the form of spirals, circular hoops or rectangular ties. Steel and concrete jackets are other techniques for providing additional confinement for compression members, too. This paper presents the results of experimental and analytical study on the application of strapping technique for retrofitting of... 

Simulations of flow through microchannels over nano particles are widely encountered in solid particle transportation. In these simulations, the rarefaction phenomenon will affect the microflow behavior and subsequently the aerodynamics coefficients such as the drag coefficient derived for the suspended particles in the flow stream. This is why we use the Lattice Boltzmann method LBM to study the flow past a confined cylinder placed in a microchannel. The LBM is a mesoscopic method capable of solving flow in macro and micro scales. Applying the Maxwellian scattering kernel, the slip velocity is modeled on the channel and cylinder walls appropriately. To validate our formulations, we firstly... 

In this paper, free vibration of open noncircular cylinders with spiral cross section are studied under arbitrary boundary conditions. For deriving the strain energy function, Kirchhoff-Love hypotheses are employed. To obtain the solutions, Rayleigh-Ritz technique is implemented by selecting Chebyshev orthogonal polynomials of first kind as admissible displacement functions in three directions. Convergence of the proposed formulation is verified for spiral cylindrical panel and the results are compared with those of ABAQUS. Parametric study is undertaken to highlight the effect of inner radius, separation distance, subtended angle, thickness, and length of the spiral cylinders on the free... 

In the present study, a simple analytical method is introduced for determination of natural frequencies of generally laminated conical and cylindrical shells with arbitrary boundary conditions. The governing equations of motion employed are those of thin-walled shell theory of Donnell. The free-vibration equations are solved using state space method and series solution in meridional direction. The results are compared and validated with the available especial results in the literature. The effects of bending-stretching coupling, semi-vertex angle, meridional length, shell thickness, fiber directions of composite plies, and lamination sequences on the natural frequency of conical and... 

The general solution of steady-state asymmetric mechanical and thermal stresses of a hollow thick cylinder made of fluid-saturated functionally graded porous piezoelectric materials based on two-dimensional equations of thermoelasticity is considered. The general form of thermal and mechanical boundary conditions is considered on the inside and outside surfaces. A direct method is used to solve the heat conduction equation and the nonhomogeneous system of partial differential Navier equations, using the complex Fourier series and the power law functions method. The material properties are assumed to depend on the radial and circumferential variables and are expressed as power law functions... 

In this paper, the stability of whirling composite cylindrical shells partially filled with two liquid phases is studied. Using the first-order shear shell theory, the structural dynamics of the shell is modeled and based on the Navier-Stokes equations for ideal liquid, a 2D model is developed for liquid motion at each section of the cylinder. In steady state condition, liquids are supposed to locate according to mass density. In this study, the thick shells are investigated. Using boundary conditions between liquids, the model of coupled fluid-structure system is obtained. This coupled fluid-structure model is employed to determine the critical speed of the system. The effects of the main... 

Using harmonic differential quadrature method, an approach to analyze sandwich cylindrical shell panels with any sort of boundary conditions under a generally distributed static loading, undergoing elasto-plastic deformation is proposed. The faces of the sandwich shell panel are made of some isotropic materials with linear work hardening behavior while the core is assumed to be an isotropic material experiencing only elastic behavior. The faces are modeled as thin cylindrical shells obeying the Kirchhoff–Love assumptions. For the core material, it is assumed to be thick and the in-plane stresses are negligible. Upon application of an inner and outer general lateral loading, the governing...