hamidreza mirdamadi

In the present paper, electromechanical finite element modelling of a smart adaptive composite beam is presented. The model is formulated based on linear electromechanics and electrokinematics assumptions. The proposed model is a three layers piezoelectric composite beam that acts as transversely actuator. elastic material of core is isotropic whereas the outer piezoelectric layers is orthotropic. The accuracy of analytic and numerical models is demonstrated by examining the simulation of the two principles of mechanical and electrical energy conservation in a finite element program and also comparing its results with the ANSYS numerical model. In the numerical simulation of the finite element model, there are three mesh including 10, 50, and 100 elements. Parametric simulation consists of three mechanical, electrical and electromechanical static loading sets. By comparing the results of modeling in the finite element programming and ANSYS, and verifying the principle of electromechanical energy conservation, it can be concluded that the proposed finite element model is efficiently and accurately.

Respect to the concept of the control structures, the author of this study recently suggested a novel hysteresis damper with named nested-eccentric-cylindrical shells damper (NESD) for increasing the damping in structures.According to the greater ability of the shell structures versus the plate structures, the NESD is designed based on the shell structures. The configuration of the shells in the NESD is designed in such a way that it can be increasing the performance and stability of the device. These members are as well as the multi-springs with the combination of series and parallel form. Also, the configuration of this device is designed by the simple form and with an easy way to install in structures. However, to evaluate the seismic performance of the proposed damper, the NESD used into the structures with various heights with four, eight, and twelve floors and analyzed by dynamic nonlinear time history. The seismic analyses are run with eleven records by particular geography characteristics of seismic hazard zone. In this evaluation, the efficiency of this damper in damping seismic energy and reducing the displacement and base shear responses is approved. In the seismic analysis, Therefore, by modeling this damper in structures, it was found that by using this damper in structures could be a damping of up to 35% of the seismic energy in the structures and reduce an average of 50% in displacement and could cause a reduction of 7 to 27% in the base shear for the structures. However, it was found that the NESD could be better behavior for reducing the response of mid-rise structures.

Dynamic behavior of biological membranes is involved in many processes within the cells and organelles like transport in the Golgi apparatus, endoplasmic reticulum and mechanisms of shaping used by cytoskeleton. Among different dynamic procedures and shape transformations of membranes, formation of tubular structures called tether is well-known. Tethers are involved in many cellular processes such as inter, intracellular transport and cell-cell adhesion. Tubular networks are also observed in the Golgi apparatus, the smooth part of the Endoplasmic reticulum and the inner membrane of the Mitochondrion. Membrane tubes can be formed by in vitro experiments. Tethers are also extracted from synthetic vesicles using different techniques such as optical tweezer and hydrodynamic flow. In this paper, the dynamic behavior of a bilayer membrane in tether extension process is studied using a mathematical model based on the mechanical properties of the bilayer membrane. A fluid bilayer membrane is utilized in this model consisting of two monolayers sliding on each other. The bending and stretching energies in addition to dissipations due to the fluidity of each monolayer and the inter-monolayer drag are defined for the bilayer membrane. The dynamic behavior of the bilayer membranes in the tether extension process is studied. The tether is extruded by a constant pulling rate and the dynamic pulling force is measured. The effect of the pulling rate and the surface tension on the dynamic pulling force is investigated. These two parameters have a great effect on the dynamic pulling force and the steady state of the process.

By the concept of control structures a new shell configuration for a steel energy dissipative device designed for earthquake protection of structures is proposed in this study. This device is named a nested-eccentric-shells damper (NESD). This device is made of a large cylindrical shell that surrounded three small cylindrical shells. The conventional methods of welding or metal casting can be applied in constructing this damper. The configuration of the shell-type components is designed in such a way that to be able as a combination of series and parallel springs. To assess the performance of this damper, numerical analysis and full-scale testing are run. Hysteretic loops obtained from the analysis with highly ductile performance are applied to determine the behavior of this proposed damper. The results indicate that the nested-eccentric-shells damper is of a stable behavior in hysteretic loops, and can provide appropriate damped energy subject to cyclic loading. However, in order to improve the performance and interaction of the internal members of this damper, a thickness ratio is proposed for the inner shells and the usefulness of using this modification in numerical analysis has been proven in this study.

Structural health monitoring (SHM) systems operate online and test different materials using ultrasonic guided waves and piezoelectric smart materials. These systems are permanently installed on the structures and display information on the monitor screen. The user informs the engineers of the existing damage after observing signal loss which appears after damage is caused. In this paper health monitoring is done for plate shaped structures made of ST-37 steel. After conducting the experimental tests, the stored signals by the multi-layer artificial neural network algorithm is processed and the damage caused in the plate is detected. By analyzing the graphs, it becomes clear that after causing damage the signal amplitude decreases. In the experimental test two piezoelectric discs are used on a steel plate which have been installed using a strong adhesive. Using a strong adhesive improves wave, propagation in the structure. Developing innovative testing methods for the SHM system has caused better control in structures after assembly.

Bistable and multistable plates are types of smart composite structures that have two or more static equilibrium. In this paper, a bistable hybrid composite plate with an external metal layer is studied. The difference between these plates and conventional bistable composite plates and bistable hybrid composite plate with an inner layer of metal is the deformation of them. In other words, unlike the conventional bistable composite plates, in both stable state, transverse curvatures that they have the same size and sign and but twisted curvature is the considerable. The analytical method for studying the behavior of the plate is Rayleigh- Ritz method and minimization of potential energy and finite element used. In order to increase the accuracy of the Rayleigh – Ritz method, out of the plane displacement using is guessed Legendre polynomial. At the frist, states of equilibrium and stable states are determined. To understand better the difference between a bistable hybrid plate with an external metal layer and a CFRP bistable composite plate, a comparison between deform at room temperature, curvature and out of plane displacement are done. In the next part, the moment required to snap through between stable states is achieved. Also, the effect of metal layer thickness on out of plane displacement and stability boundary is investigated. Comparing the results of the proposed shape function and Hyer shape function compared to experimental results and the results of finite element analysis show that the results of the proposed shape function is more accurate.

In this article, vibration analysis of an Euler-Bernoulli beam resting on a Pasternak-type foundation is studied. The governing equation is solved by using a spectral finite element model (SFEM). The solution involves calculating wave and time responses of the beam. The Fast Fourier Transform function is used for temporal discretization of the governing partial differential equation into a set of ordinary differential equations. Then, the interpolating function for an element is derived from the exact solution of governing differential equation in the frequency domain. Inverse Fourier Transform is performed to rebuild the solution in the time domain. The foremost advantages of the SFEM are enormous high accuracy, smallness of the problem size and the degrees of freedom, low computational cost and high efficiency to deal with dynamic problems and digitized data. Moreover, it is very easy to execute the inverse problems by using this method. The influences of foundation stiffness, shear layer stiffness and axial tensile (or compressive) forces on the dynamic characteristic and divergence instability of the beam are investigated. The accuracy of the present SFEM is validated by comparing its results with those of classical finite element method (FEM). The results show the ascendency of SFEM with respect to FEM in reducing elements and computational effort, concurrently increasing the numerical accuracy.

Piezoelectric actuators and sensors have been broadly used for design of smart structures over the last two decades.
Different theoretical assumptions have been considered in order to model these structures by the researchers. In this paper, an enhanced piezolaminated sandwich beam finite element model is presented. The facing layers follow the Euler-Bernoulli assumption while the core layers are modeled with the third-order shear deformation theory (TSDT). To refine the model, the displacement-strain relationships are developed by using von Karman's nonlinear displacement-strain relation. It will be shown that this assumption generates some additional terms on the electric fields and also introduces some electromechanical potential and non-conservative work terms for the extension piezoelectric sub-layers. A variational formulation of the problem is presented. In order to develop an electromechanically coupled finite element model of the extension/shear piezolaminated beam, the electric DoFs as well as the mechanical DoFs are considered. For computing the natural frequencies, the governing equation is linearized around a static equilibrium position. Comparing natural frequencies, the effect of nonlinear terms is studied for some examples.

In this paper، a novel four-variable refined theory of plate، called RPT، has been proposed for free vibration of composite laminated plates، using a hyperbolic sine function، for calculating out-of-plane shear strains. It is one of the properties of this theory that the boundary condition of zero shear stress is satisfied over upper layer and under lower layer of plate، with no reference to Timoshenko shape factor. In contrast to other higher-order shear deformation theories، in RPT theory، equations of motion are coupled dynamically only in inertial terms، while elastic energy terms are not coupled for the variables used. From this viewpoint، RPT theory is similar to classical plate theory (CLPT). Some of the objectives of this paper are the investigation of effect of influential parameters on fundamental frequency، such as modulus ratio، angle of plies، and plate length-to-thickness ratio. The results of this proposed version of RPT are compared and validated with those of first-order shear deformation theory (FSDT)، higher-order shear deformation theory (HSDT)، and the original version of RPT.

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.