Sharif Digital Repository

This paper presents dynamic response of a delaminated composite beam under the action of moving oscillatory mass. The Poisson's effect, shear deformation and rotary inertia have been considered in this analysis. We have used the constrained mode model to simulate the behavior between the delaminated surfaces. Based on this model, eigen-solution technique is used to obtain the natural frequencies and their corresponding mode shapes for the delaminated beam. Then, the forced response is determined by employing the modal series expansion technique. The obtained results for the free and forced vibrations of beams are verified against reported similar results in the literature. Moreover, the... 

Thermal transport characteristics of electroosmotic flow of power-law fluids in the presence of pressure gradient through a slit microchannel are studied in this paper. Considering a fully developed flow with a constant wall heat flux as the boundary condition, the governing equations are numerically solved by means of the finite difference method. A complete parametric study is done in order to investigate the effects of different flow parameters on the thermal behaviors of the flow. The results show that the non-Newtonian characteristic of the fluid can influence the thermal behaviors of the flow by affecting the rate of heat convection and viscous dissipation; however, its influence... 

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... 

Bolted Column Base Plate (BCBP) connections are widely used to connect steel columns to the concrete foundations. This paper conducts a parametric study on the initial stiffness of bolted base plate with Square Hollow Section (SHS) column connection, through an extended 3-D Finite Element Modeling (FEM). Different features of the connection such as material behavior, geometric details, typical contact phenomena and large displacements are also considered in the modeling. A comparison between experimental test and FEM is carried out to illustrate the ability of the numerical method to simulate the connection behavior. An analytical explanation on the initial stiffness of the connection is... 

The governing differential equation of motion of a thin rectangular plate excited by a moving mass is considered. The moving mass is traversing on the plate's surface at arbitrary trajectories. Eigenfunction expansion method is employed to solve the constitutive equation of motion for various boundary conditions. Approximate and exact expressions of the inertial effects are adopted for the problem formulation. In the approximate formulation, only the vertical acceleration component of the moving mass is considered while in the exact formulation all the convective acceleration components are included in the problem formulation as well. Parametric studies are carried out to investigate the... 

A friction damper device (FDD) is used for vibration control of an existing steel jacket platform under seismic excitation. First, the damping is presented for vibration mitigation of structures located in seismically active zones. A new method for quick design of friction or yielding damping devices is presented. The effectiveness of the damping system employing such FDDs in a jacket platform is evaluated numerically. The influence of key parameters of the damping system on the vibration suppression of the offshore structure is studied in detail. To examine the vibration control effectiveness of the FDD for the jacket platform, performance of the controlled structure under the seismic... 

This paper presents a precise solution to predict the behavior of steel fiber reinforced concrete (SFRC) under the four point bending test (FPBT). All the force components at the beam section (before and after cracking) are formulated by applying these assumptions: a realistic stress-strain model is used for concrete behavior in compression, a linear response is considered for the uncracked tension region in a concrete constitutive model, and an exponential relationship is proposed as a stress-crack opening in the crack region which requires two parameters. Then the moment capacity of the critical cracked section is calculated by using these forces and satisfying equilibrium law at the... 

During the recent decade, high induction diffusers have become more appealing in applications which require relatively high ventilation airflow rates, such as clean rooms. In this research, the effect of geometric parameters on the performance of a specific type of swirling air diffuser is investigated numerically. The results show that although the diffuser slots geometry, namely their angle and aspect ratio, is impressive on the diffuser performance, it is not as important as the swirling blade angle and the performance is almost constant in a wide range of slots specifications. The results also demonstrate that the diffuser performance and the resultant indoor airflow distribution highly... 

In this paper, the coupled three-dimensional flexural vibration of micro-rotors is investigated by taking into account the small-scale effects utilizing the strain gradient theory, which is a powerful nonclassical continuum theory in capturing small-scale effects. A micro-rotor consists mainly of a flexible micro-rotating shaft and a disk. With the aid of Hamilton's principle, governing equations of motion are derived and then transformed to the complex form. By implementing the Galerkin's method, a coupled ordinary differential equation is attained for the system. Expressions for the first two natural frequencies of the spinning micro-rotors are obtained with truncated two-term equation.... 

Although Alkaline-Surfactant-Polymer (ASP) flooding is proved to be efficient for heavy oil recovery, the displacement mechanisms/efficiency of this process should be discussed further in fractured porous media especially in typical waterflood geometrical configurations such as five-spot injection-production pattern. In this study, several ASP flooding tests were conducted in fractured glass-etched micromodels which were initially saturated with heavy oil. The ASP flooding tests were conducted at constant injection flow rates and different fracture geometrical characteristics were used. The ASP solutions constituted of five polymers, two surfactants and three alkaline types. The results... 

In this paper, compressive strength of carbon fiber reinforced polymer (CFRP) confined concrete cylinders is formulated using a hybrid method coupling genetic programming (GP) and simulated annealing (SA), called GP/SA, and a robust variant of GP, namely multi expression programming (MEP). Straightforward GP/SA and MEP-based prediction equations are derived for the compressive strength of CFRP-wrapped concrete cylinders. The models are constructed using two sets of predictor variables. The first set comprises diameter of concrete cylinder, unconfined concrete strength, tensile strength of CFRP laminate, and total thickness of CFRP layer. The most widely used parameters of unconfined concrete... 

Grinding is widely used for manufacturing of components that require fine surface finish and good dimensional accuracy. In this study a thermo-mechanical finite element analysis is conducted to find out how grinding parameters can affect temperature and residual stress distribution in the workpiece. Results of parametric study presented in this work indicate, by carefully selecting the grinding parameters, minimum thermal and mechanical damage can be achieved. Higher workpiece velocities produce higher surface residual stress. By increasing depths of cut, depth of tensile residual stresses increases. Convection heat coefficient does not have any considerable effect on surface residual stress... 

Nonlinear vibration of a three-dimensional moving gantry crane carrying a trolley hoisting a swinging object is studied in this paper.A finite element method is used to solve nonlinear coupled governing equations of the structure. A combinational technique (Newmark-Runge-Kutta) is employed for direct integration procedure. To develop a comprehensive parametric study and sensitivity analysis of the coupled nonlinear system, sequence of numerical simulations are carried out. Parametric study is directed to find out how different parameters like speed and acceleration of the trolley and gantry crane as well as the mass of the moving trolley and swinging object may affect the linear and... 

Pore network modeling of porous media has this advantage that can consider the pore structure incorporating any desired details, but it has not been studied sufficiently. In addition, most studies are limited to mathematical modeling only which need validation. In the present study, this approach was applied to hydrogen separation from syngas by nanoporous ceramic membrane to predict the membrane permeance theoretically based on its pore structure. Gas transport through nanoporous membrane was modeled with the aim of a 2D network model. A dusty gas model was used for gas transport in the individual pores. Model validation showed that the model predictions are in good agreement with the... 

Tapered composite beams are increasingly being used in various engineering applications such as helicopter yoke, robot arms, and turbine blades. In the present work, the buckling analysis of laminated tapered composite beams is conducted using a higher order finite element formulation. In tapered laminates, the material and geometric discontinuities at ply drop-off locations lead to significant discontinuities in stress distributions. Higher order formulation ensures the continuity of the stress distribution through the thickness of a laminate as well as across the element interfaces, which is very important for the analysis of tapered laminates. In addition, higher order finite element... 

In this study, residual stress distributions in autofrettaged homogenous spherical pressure vessels subjected to different autofrettage pressures are evaluated. Results are obtained by developing an extension of variable material properties (VMP) method. The modification makes VMP method applicable for analyses of spherical vessels based on actual material behavior both in loading and unloading and considering variable Bauschinger effect. The residual stresses determined by employing finite element method are compared with VMP results and it is demonstrated that the using of simplified material models can cause significant error in estimation of hoop residual stress, especially near the... 

In the conceptual design phase of a turbocharger, where emphasis is mainly on parametric studies, before manufacturing and tests, a generalized and robust model that applies over a wide range properly, is unavoidable. 12The critical inputs such as turbine maps are not available during the conceptual design phase. Hence, generalized turbine models use alternate methods that work without any supplementary tests and can operate over wide ranges. One of the common and applicable modeling methods in design process is 'Dimensionless Modeling' using the constant coefficient scaling (CCS). This method can almost predict the turbine characteristics at the design point. However, at off-design... 

The effects of insulated and isothermal thin baffles on pseudosteady-state natural convection within spherical containers were studied computationally. The computations are based on an iterative, finite-volume numerical procedure using primitive dependent variables. Natural convection effect is modeled via the Boussinesq approximation. Parametric studies were performed for a Prandtl number of 0.7. For Rayleigh numbers of 104, 105, 106, and 107, baffles with three lengths positioned at five different locations were investigated (120 cases). The fluid that is heated adjacent to the sphere rises replacing the colder fluid, which sinks downward through the stratified stable thermal layer. For... 

Occurrence of liquefaction in saturated sand deposits underlying foundation of structure can cause a wide range of structural damages starting from minor settlement, and ending to general failure due to loss of bearing capacity. If the bearing capacity failure is not the problem, reliable estimation of the liquefaction-induced settlement will be of prime importance in assessment of the overall performance of the structure. Currently, there are few procedures with limited application in practice for estimation of settlement of foundations on liquefied ground. Therefore, development of a general relationship is important from the practical viewpoint. In this paper, the dynamic response of... 

In the conceptual design phase of a turbocharger, where emphasis is mainly on parametric studies, before manufacturing and tests, a generalized and robust model that implies over a wide range properly, is unavoidable. The critical inputs such as compressor maps are not available during the conceptual design phase. Hence, generalized compressor models use alternate methods that work without any supplementary tests and can operate on wide range. One of the common and applicable modeling methods in design process is the 'Dimensionless Modeling' using the constant coefficient scaling (CCS). This method almost can predict the compressor characteristics at design point. However, at off design...