Sharif Digital Repository

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... 

This paper presents efficient denoising and lossy compression schemes for electrocardiogram (ECG) signals based on a modified extended Kalman filter (EKF) structure. We have used a previously introduced two-dimensional EKF structure and modified its governing equations to be extended to a 17-dimensional case. The new EKF structure is used not only for denoising, but also for compression, since it provides estimation for each of the new 15 model parameters. Using these specific parameters, the signal is reconstructed with regard to the dynamical equations of the model. The performances of the proposed method are evaluated using standard denoising and compression efficiency measures. For... 

This paper investigates the free vibrations of a shell made of n cone segments joined together. The governing equations of the conical shell were obtained by applying the Sanders shell theory and the Hamilton principle. Then, these governing equations are solved by using the power series method and considering a displacement field which is harmonic function about the time and the circumferential coordinate. Using the boundary conditions of the two ends of the shell and the continuity conditions at the interface section of shell segments, and solving the eigenvalue problem, the natural frequencies and the mode shapes are obtained. Very good agreements exist between the analytical results of... 

The aim of this study is to investigate the free vibration of a rotating joined cylindrical-conical shell in the presence of the centrifugal and Coriolis forces as well as the initial hoop tension resulting from rotation of the shell. Based on the equations of general rotating shells of revolution, the equations of motion of rotating cylindrical and rotating conical shells are derived, and then these governing equations were solved by employing the power series method. For validation and comparison purposes, the results of the special cases of the studied problem were compared with the results reported in the literatures. Another comparison study was also conducted by the results of finite... 

The nonlinearity of a nonlinear transmission line (NLTL) may have a variety of forms. The Korteweg-de Vries (KdV) equation is the governing equation of a highly specific category of NLTLs having a C - V characteristic as C(V) = C0 (1-bV), but works as an approximate model in a general NLTL having any other kinds of nonlinearities. Here, the soliton response of a varactor-loaded NLTL is studied analytically. The presented analysis gives the exact nonlinear partial differential equation (PDE) governing these networks. It is shown that the obtained PDE, being different from the KdV equation, has soliton solutions showing the well-known properties of the KdV solitons. These obtained solitons... 

Meshless methods are a relatively new type of numerical methods that have attracted the attention of many researchers over the past years. So far, a number of meshless methods have been developed and applied to solve problems in various fields of engineering, including solid mechanics and geotechnical problems. The Element-Free Galerkin (EFG) method is adopted in this study for solving the governing partial differential equations of equilibrium and continuity of pore fluid flow for numerical simulation of coupled hydro-mechanical problems. For this purpose, the weak form of the governing equations is derived by applying the weighted residual method and Galerkin technique. The penalty method... 

Bridge behavior under passing traffic loads has been studied for the past 50 years. This paper presents how to model congestion on bridges and how the maximum dynamic stress of bridges change during the passing of moving vehicles. Most current research is based on mid-span dynamic effects due to traffic load and most bridge codes define a factor called the dynamic load allowance (DLA), which is applied to the maximum static moment under static loading. This paper presents an algorithm to solve the governing equation of the bridge as well as the equations of motions of two real European trucks with different speeds, simultaneously. It will be shown, considering congestion in eight case... 

A moving vehicle, owing to its vibration and mass inertia, has significant effects on the dynamic response of structures. Most bridge codes define a factor called the dynamic load allowance, which is applied to the maximum static moment under static loading due to traffic load. This paper presents how to model an actual truck on bridges and how the maximum dynamic stresses of bridges change during the passage of moving vehicles. Furthermore, an algorithm to solve the governing equation of the bridge simultaneous with the equations of motion of an actual European truck is presented. Subsequently, 32 dynamic analyses of different bridges with different spans, road profiles and boundary... 

One of the most important problems facing structural engineers is the analysis of dynamic behavior of bridges subjected to moving vehicles. In addition, viscoelastic supports under bridges change their dynamic behavior under passing traffic loads. This paper presents how to model a bridge with viscoelastic supports and how the maximum dynamic stress of bridges changes during the passing of moving vehicles. Furthermore, this paper presents an algorithm to solve the governing equation of the bridge with viscoelastic supports as well as the equation of motion of a real European truck with different speeds, simultaneously. Using viscoelastic supports with appropriate characteristics can make a... 

Droplet-based microfluidics technologies hold great attention in a wide range of applications, including chemical analysis, drug screening, and food industries. This work aimed to describe the effects of different physical properties of the two immiscible phases on droplet formation in a flow-focusing microfluidic device and determining proper flow rates to form a droplet within the desired size range. A numerical model was developed to solve the governing equations of two-phase flow and the results were validated with previous experimental results. The results demonstrate different types of droplet formation regimes from dripping to jetting and different production rates of droplets as a... 

In this study, we investigate the limitations and influence of various factors on the performance of trolling mode atomic force microscopy (TR-AFM). For this purpose, at first, based on the governing equations of motion and using a conventional control method, a simulation tool capable of correctly simulating the imaging procedure in TR-AFM is developed. Then based on the developed simulation tool, imaging of different surfaces is performed, and the effect of different factors on the image quality is analyzed. The flexibility of nanoneedle in TR-AFM has unpredictable effects on dynamics of system as well as imaging performance. One problem in imaging is due to coexistence of two stable... 

Recently a great attention has been given to the oscillatory flow modeling in the pulse tube cryocoolers. In this paper multi dimensioning effects of the fluid flow in the pulse tube are investigated. A complete system of governing equations is solved to report the flow field, friction coefficient and Nusselt number in the pulse tube. Harmonic approximation technique is employed to derive an analytical solution. In this respect, mass, momentum and energy balance equations as well as the equation of state for ideal gas are transformed by implementing the harmonic approximation technique. The present model is able to predict the behavior of the two dimensional compressible oscillatory flow in... 

We describe and discuss the recent progress in the study of propagation and localization of acoustic and elastic waves in heterogeneous media. The heterogeneity is represented by a spatial distribution of the local elastic moduli. Both randomly distributed elastic moduli as well as those with long-range correlations with a nondecaying power-law correlation function, are considered. The motivation for the study is twofold. One is that recent analysis of experimental data for the spatial distribution of the elastic moduli of rock indicated that the distribution is characterized by the type of long-range correlations that we consider in this study. The second motivation for the problem is to... 

In this work, cavitation during creep in AA7075-T76 was simulated employing a probabilistic cellular automata scheme. Two-dimensional cellular automata coupled with the governing equations for cavity growth were utilized to define the size and distribution of cavities during creep. Both diffusion and strain-controlled mechanisms were taken into account while the first and second neighboring cells were considered for determination of the cavity growth as well as to generate the initial microstructure. Moreover, uni-axial creep experiments on AA7075-T76 were carried out under different temperatures and applied stresses including 170 MPa at 150 °C and 150 MPa at 160 °C. The microstructural... 

Gravity drainage is known to be one of the most effective methods for oil recovery in fractured reservoirs. In this study, both free fall and controlled gravity drainage processes were studied using a transparent fractured experimental model, followed by modelling using commercial CFD software. The governing equations were employed based on the Darcy and mass conservation laws and partial pressure formulation. Comprehensive examination was done on variables such as fluid saturation, velocity, and pressure distribution in the matrix and fracture, as well as fluid front level and production rate. Additionally, effects of the model parameters on the gravity drainage performance were... 

The fully developed longitudinal slip-flow mixed convection between a periodic bunch of vertical microcylinders arrangedin regular arraysis investigated inthe present work. The two axially constant heat flux boundary conditions of H1 and H2 are considered in the analysis. The rarefaction effects are taken into consideration using first-order slip velocity and temperature jump boundary conditions. The method considered is mainly analytical, in that the governing equations and three of the boundary conditions are exactly satisfied. The remaining symmetry condition on the right-hand boundary of the typical element is applied to the solution through the point-matching technique. The results... 

In this paper, strain gradient thermo-elasticity formulation for Functionally Graded (FG) thick-walled cylinders is presented. Elastic strain energy density function is considered to be a function of gradient of strain tensor in addition to the strain tensor. The material properties are assumed to vary according to power law in radial direction. Using the constitutive equations and equation of equilibrium in the cylindrical coordinates, fourth order non-homogenous governing equation for thermo-elastic analysis of thick-walled FG cylinders subjected to thermal and mechanical loadings is obtained and solved numerically. Results show that the intrinsic length parameter affects the stress... 

The present work reports the outcome of a comprehensive parametric study on mixed electroosmotically and pressure-driven flow in slit microchannels with constant wall heat fluxes. Special attention is given to disclose the applicability ranges of usual assumptions in simplified analyses. The governing equations for fully developed conditions are first made dimensionless and then solved by means of an implicit finite difference method. The results reveal that the assumption of constant thermophysical properties does not leadto significant errors in practical applications. Although the Debye-Huckel linearization may successfully be used to evaluate velocity profiles up to the zeta potentials... 

Because of technological restrictions, it is actually impossible to fabricate smooth microchannels. Therefore, exploring the roughness effects on the flow characteristics at microscale is of great importance for scientific communities. The present investigation deals with the effects of corrugated roughness on the fully developed slip flow forced convection in micropipes. The governing equations subject to first-order slip boundary conditions are solved by means of the straightforward perturbation method. Closed-form expressions are obtained for the dimensionless velocity and temperature distributions, for the friction coefficient and pressure drop, and finally for the Nusselt number. The... 

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...