Showing 12 results for Ziaei-Rad
Seyed Abdorahim Atashipour, Hamid Reza Mirdamadi, Rasoul Amirfattahi, Saeed Ziaei-Rad,
Volume 12, Issue 5 (1-2013)
Abstract
In this study, the structural health of a thick steel beam, made of ST-52, is inspected by ultrasonic guided wave propagation method using piezoelectric wafer active sensors that is one of the most important techniques of on-line structural health monitoring. The key parameters of the diagnostic waveform such as excitation frequency and cycle number are determined in relation to beam dimensions as well as pulse-echo configuration of PZT active sensors attached to the beam. Finite element simulations were conducted to characterize wave propagation in the beam, and the signals of wave propagation were experimentally measured. For signal processing and feature extraction, continuous wavelet transform and scaled average wavelet power technique are used. Using the extracted features, probable existing damage in the structure is detected, localized, and intensified. The acquired results are representing a higher precision of the implemented method for damage identification and characterization with respect to a previous study.
, , Saeed Ziaei-Rad,
Volume 13, Issue 9 (12-2013)
Abstract
Metals have a crystalline structure and the plastic flow in these materials occurred in the special crystalline planes and special crystalline directs that occurs in the planes. This mechanism is related to metals plastic deformation in the microscopic level. In this mechanism, non homogenous microstructure and the effect of crystalline direction play a major rule in the material behavior. Crystal plasticity constitutive equations are used for investigation of the crystalline direction effect and material texture. Voronoi method is used for simulating the non homogenous microstructure in plastic deformation. In this study, the elastic modulus parameters obtained by molecular dynamic simulations. Finally, the plastic deformation of Fe metal is simulated with finite element method that good agreement was observed with the experimental data.
Reza Tikani, Saeed Ziaei-Rad, Mohsen Esfahanian,
Volume 14, Issue 10 (1-2015)
Abstract
Hydraulic engine mounts are applied to the automotive applications to isolate the frame from the high frequency noise and vibration produced by the engine. It also designs to reduce the engine shake motions from the road distribution usually occurred at low frequencies. This implies that the stiffness and damping properties of the engine mount should be amplitude- and frequency- dependent. In the semi-active engine mounts this task will be done by changing the mount parameters such as stiffness and damping. Magneto-rheological fluids are used in the mounts to change their damping by applying the magnetic field. When the current is applied to the electromagnet and the magnetic field is present, the behavior of the magneto-rheological mount is changed by the magneto-rheological effects. In this paper, a prototype magneto-rheological mount was built and experimentally evaluated. Also, the mathematical model of the mount was developed to represent the dynamic behavior of the engine mount system. The model was numerically solved based on the prototype parameters and simulated in MATLAB. The experimental results were used to verify the model in predicting the mount characteristics.
Masoud Ziaei-Rad, Abbas Kasaeipoor,
Volume 14, Issue 14 (Second Special Issue 2015)
Abstract
This paper concerns with a similarity solution for mixed-convection boundary layer copper-water nanofluid flow over a horizontal flat plate. Appropriate similarity variables are used to convert the Governing PDEs to ODEs and the resultant equations with the nanofluid properties relations are discretized and solved simultaneously using finite-difference Keller-Box method. The effects of change in plate temperature, the volume fraction of nanoparticles, and the mixed-convection parameter, on friction coefficient, Nusselt number and velocity and temperature profiles are investigated. The results show that, the Nusselt number increases as the mixed-convection parameter and the volume fraction of nanoparticles increases. This enhancement is about 10 percent for the nanofluid with 4% volume fraction of nanoparticles, compared with the pure water. In this range, moreover, the friction coefficient parameter increases about 20 percent. However, the lower the mixed-convection parameter is, the effect of nanoparticles on the friction coefficient increment is more. The results also illustrate that the effect of the surface temperature on the increment of Nusselt number and on the reduction of friction coefficient is more considerable in higher mixed-convection parameter and volume fraction of nanoparticles. Also by increasing surface temperature, the temperature of nanofluid decreases at any surface distance.
Masoud Ziaei-Rad, Farzaneh Amani,
Volume 15, Issue 8 (10-2015)
Abstract
In this paper, the heat transfer enhancement by the nanoparticles in the film condensation of nanofluid over a cooled plate is studied numerically. Shooting method and modified-Euler scheme are employed to solve the condensation boundary layer equations. The effect of changes in the plate angle, nanofluid type, volume fraction of nanoparticles and Jacob number, on the velocity and temperature profiles and Nusselt number are investigated. Resulting graphs are compared and validated with the available theoretical results for the base fluid and nanofluid. The results show that the presence of nanoparticles in the liquid film of condensation increases the heat transfer from it. As the plate distances from the vertical position, the temperature change across the boundary layer is close to linear and thus, the heat transfer descends. Also it can be found that the average Nusselt number is almost constant up to the angle of 20o, and then reduces in a gradual manner, so that for instant, for water-TiO2nanofluid, by increasing the angle up to 60o, the temperature gradient is reduced by about 20 percent. Furthermore, it is seen that the relationship between the ratio of nanofluid to pure water Nusselt number and the nanoparticles volume fraction is linear, while the slope of the line for water-Cu and water-Ag is more than other studied nanofluids, i.e., these two nanofluids are more effective in heat transfer enhancement. The obtained results also confirm the fact that the Nusselt theory is only applicable in low Jacob numbers.
Ahmad Firouzian-Nejad, Saeed Ziaei-Rad, Masih Moor,
Volume 16, Issue 4 (6-2016)
Abstract
In this paper, thermal and vibration response of cross-ply bi-stable composite laminated plates were studied using semi-analytical, finite element and experimental method. In order to evaluate the semi-analytical and finite element results, a bi-stable composite plate was manufactured using a special procedure. Next, geometrical characteristics and displacement of different paths on the plate were measured experimentally at room temperature. In semi-analytical approach, the two stable states and the first natural frequency of cross-ply laminates are calculated based on Rayleigh–Ritz approach combined with Hamilton’s principle. In this study, a modified shape function was introduced that allows the curvatures to vary in both longitudinal and transverse directions. Using the modified shape function, the displacement of the plate in its stable configuration and the first natural frequency of the plate can be more accurately predicted in compared to the Hyer’s shape functions. The obtained results from the proposed shape function are in good agreement with the finite element and experimental data. The proposed shape functions can also be used in dynamic and vibration analysis to determine the snap-through load of the cross-ply laminates.
Masoud Karimi, Reza Tikani, Saeed Ziaei-Rad,
Volume 16, Issue 6 (8-2016)
Abstract
Harvesting energy by piezoelectric materials is nowadays an efficient way for powering low-power electric devices. Required energy for sensors which are used in condition and health monitoring of bridges and other civil infrastructures can be examples of the energy harvesters. This study aimed to improve the piezoelectric-based energy harvesting on civil infrastructures, especially on bridge structures. In this investigation, harvesting energy from the vibrations of a bridge under moving consecutivemasses is studied. Harvesting energy iscarried out through a cantilever beam with piezoelectric patch which is installed atthe middle of a simply supported bridge. Governing equations for vibration of an Euler-Bernoulli beam under moving consecutivemasses arederived. The effects of inertial, centrifugal and coriolis forces areconsidered. For verifying, the results of the numerical solution of the moving mass problem are compared to the experimental tests data of the litterature. The harvester is modelled by a cantilever beam with piezoelectric patch under base excitations which are calculated from vibrations of the bridge mid-point. The obtained equations are then solved in MATLAB environment by using the forth order Runge-Kutta method. The calculated induced voltages are compared with those obtained from experiment. A good degree of accuracy is observed.
Mohammad Mahdi Sahebifard, Alireza Shahidi, Saeed Ziaei-Rad,
Volume 17, Issue 4 (6-2017)
Abstract
This article aims to study the effect of membrane initial configuration and the membrane spontaneous curvature (local asymmetry of layers) on the shape transformation of lipid bilayer vesicles. Since the evolutionary models are considered as a generalization to the equilibrium methods, the used model is developed based on the dynamic equilibrium between the membrane bending potential and the environmental fluid friction in each domain of two-phase vesicle. The effect of membrane inertia on the dynamics of the system is ignored. Key parameters are the size of each phase and different combinations of protein distribution as the local spontaneous curvature. Assumed initial conditions are simple shapes such as dumbbell, biconcave and oblate that free vesicles are usually visible in these shapes. Previously published experimental observations are used to evaluate the numerical results. Some situations of homogeneous and multi-phase vesicles and red blood cells under the influence of the spontaneous curvature induction mechanisms (for example the composition of the membranes, membrane proteins such as albumin, environmental solution concentration changes) are simulated and the results presented in details. The possibility of the membrane deformation and the relation of membrane phenomena with the primary form and various curvature distributions are discussed.
Saeed Hayati Jafarbeigi, Mehdi Mosharaf Dehkordi, Masoud Ziaei-Rad,
Volume 18, Issue 1 (3-2018)
Abstract
In the present work, the three dimensional fluid flow inside a hydrocarbon reservoir block along with the fluid flow inside the wellbore of a production well drilled in this reservoir block is numerically simulated. To do this, the single-phase incompressible fluid flow in the hydrocarbon reservoir in terms of Darcy’s law (porous media flow) along with the fluid flow inside the wellbore in terms of Navier-Stokes equations (free flow) are simultaneously solved. The effects of boundary conditions imposed on the faces of the reservoir block, the off-centered wellbore, and the reservoir rock permeability on the fluid flow behavior inside a reservoir block are investigated. In each case, the well index is numerically approximated, using the pressure and velocity distributions in the reservoir block and the wellbore pressure, and compared with analytical well index. The numerical results indicate that the well equivalent radius and also the well index not only depend on the geometrical properties of reservoir block and well bore and the rock absolute permeability, but also depend on the boundary conditions imposed on the reservoir block faces and the well drilling location.
S.m. Zareei, M. Jamshidian, Sh. Sepehrirahnama , S. Ziaei-Rad,
Volume 19, Issue 2 (February 2019)
Abstract
Acoustofluidics, the study of acoustics in microfluidic systems, is the basis for analyzing many laboratory applications including the separation of particles, particle sorting, cleaning, and mixing multiphase systems. In this research, a three-dimensional finite element model for particle motion under acoustic radiation force in acoustic microchannels is developed and the interaction of the incident waves with a suspended particle in microchannel is investigated. Using finite element method, the first-order fields due to an applied standing wave are initially calculated and, then, the acoustic radiation force is directly calculated from the second-order perturbation equations. The simulation results for radiation force are first verified against the analytical solution in the Rayleigh limit and, then, examined beyond this limit, for which there is no explicit analytical solution. In addition, the quasi-static motion of a particle under the influence of an applied acoustic standing wave in microchannel is simulated. For simulating particle motion, the acoustic stress on particle surface is calculated and transferred as an input to the laminar flow equations. Then, the drag force is estimated based on the shear stress due to the flow around the particle. The simulation results demonstrate that the particle velocity depends on its position with respect to the wave node at the center of the microchannel. As the particle approaches to the center of microchannel, its velocity decreases until it stops at the center of microchannel.
M. Molavian Jazi, M. Ghayour , S. Ziaei-Rad , E. Maani,
Volume 19, Issue 4 (April 2019)
Abstract
The atomic force microscope (AFM) determines the topography of surfaces in nano scale based on the changes in the exited micro-cantilever’s dynamic characteristics. Therefore, it is essential to simulate and predict more accurately the dynamic behavior of cantilever beams for use in design and fabrication of AFM. Based on the experimental observations, in contrast to the classic theory, the normalized stiffness of structures is not constant with the reduction of dimensions in micro and nano scales. This change, which can be either softness or stiffness, results in size-dependent behavior, non-classic continuum theories. This paper studies the effect of size on the dynamic behavior of AFM based on modified couple stress theory, and compares the results with those obtained from classic theory. The nonlinear partial differential governing equation of the system is derived, considering intermolecular and hydrodynamic forces, based on the modified couple stress theory. By applying Galerkin projection method, partial differential equations are transformed into ordinary equations and the discrete system is extracted. It is shown that considering size effect leads to enlargement of expected working domain of AFM, and also predicted amplitude and frequency of oscillations decreases and increases, respectively. Moreover, two theories predict different start point of bi-stability region. Solution approach is verified by comparing the results with two degrees-of-freedom model and analogue equations method. Furthermore, effect of hydrodynamic forces of fluid on dynamic behaviour of AFM is investigated.
A. Firouzian-Nejad, M. Ghayour, S. Ziaei-Rad,
Volume 20, Issue 3 (March 2020)
Abstract
This study introduces a new lay-ups of bi-stable hybrid composite laminate (BHCL) which consists of 90° unidirectional composite laminas in the upper and lower layers and metallic strips distributed along with the middle layer of 0° unidirectional composite laminas in the middle layer. The static characteristics of the laminates were investigated using the finite element (FE) method and were experimentally validated. The two stable configurations of laminate have identical curvatures with opposite signs. The curvature direction of the proposed BHCLs does not change during snap-through between stable states. This feature will give the engineers more freedom to design morphing structures with desired specifications. The effect of the width, thickness, and material properties of the strips and laminate side length on the static characteristics of the laminate were numerically investigated using the finite element method through Abaqus software. Several BHCLs with different materials, lay-up and dimension were fabricated for verification of the results. The curvatures, out of plane displacement, and the static snap-through load of the laminates were determined experimentally and compared with the results of the finite element method. A good qualitative and quantitative agreement was observed between the FE and the experimental results. The results show that it is possible to adjust residual curvature and load-carrying capability by changing the width, thickness, and material of the strips and laminate geometry.
