Journal of Applied and Computational Sciences in Mechanics
Year:2016 | Volume:27 | Issue:2 (14)|Papers Count:12

Piezoelectric layers have significant effect on the vibration behavior and buckling capacity of the structures. For optimum usage of piezoelectric materials, it is possible to use the piezoelectric patches instead of the piezoelectric layers. In this paper, the effects of piezoelectric patches and boundary conditions on the buckling and vibration behaviors of Euler-Bernoulli beams is investigated. The piezoelectric stress resultants are introduced in terms of Heaviside discontinuity functions and the characteristics equation is obtained via Galerkin method. The effects of variation of location, length of the piezoelectric patches and the applied voltages on the natural frequencies and critical buckling loads of beam with different boundary conditions are investigated. Results show that the natural frequencies and critical buckling load are dependent on the voltage, length and location of the piezoelectric patches and the axial load. Also, patches have a considerable effect if they placed at the beam center.

In this research, the flapping amplitude effect and flexible shell on the MAV (Micro Air Vehicle) aerodynamic performance in hovering flight are experimentally investigated. For this purpose, a flapping membrane wing mechanism and an experimental measurement setup for measuring generated thrust were designed and constructed. In these tests, for two wings with different flexibility, generated thrust and power usage were measured in the range of flapping frequency and amplitude. In general, flapping wing generated thrust increases with raising flapping amplitude. Values of the propulsion force are different for these two wings.

In this study, the effect of fatigue loading on the redistribution of mechanical residual stresses in compact tension specimens has been investigated. Fatigue crack growth experimental tests were conducted in accordance with E647 standard for specimens with and without initial residual stress. To investigate the crack tip plastic zone and fracture mechanics parameters finite element analysis using ABAQUS was used. The results showed that the initial residual stress redistributed after a few cycles of fatigue loading. Redistribution depends on the amplitude of cyclic loading. Near crack tip plastic zone area also decrease after a few cycles and reaches a stable value. In experimental tests, the fatigue life of specimens with mechanical residual stresses was lower than specimen having no residual stresses.

In this paper, linear accelerated turbulent pipe flow has been simulated at various Reynolds numbers using five common turbulence models. The models considered are the Baldwin-Lomax algebraic model, the Spalart-Allmaras one-equation model, theκ-e model with wall correction of Lam and Bremhorst, theκ-ω model and the κ-ε-ν2 model. The goal is to evaluate the performance and precision of these models for prediction of the wall shear stress, Reynolds stress, turbulence viscosity, delay time in response and mean velocity. Factors such as changes in pipe diameter, fluid type, initial Reynolds number of acceleration and rate of acceleration and its effect on the above parameters has examined carefully. In order to verify the results, the experimental and numerical results (turbulence modeling and Large Eddy Simulation) of other researchers have been compared with the present results. The results show the desired accuracy of the one-dimensional modeling of accelerated turbulent pipe flow in comparison with Large Eddy Simulation results (three-dimensional). The response of delay time, simulated by the models (except BL model) shows relatively good agreement with experimental data. Comparing the distribution of mean velocity, turbulent kinetic energy and turbulent viscosity shows  k-e-ν2 model leads to a better accuracy compared with the other models.

Continuum Damage Mechanics (CDM) is a powerful tool to solve problems such as large plastic deformation, Where the fracture mechanics is unable to analysis of its effects. Continuum damage mechanics in terms of the internal variable theory of thermodynamics is derived and based on the experimental results on material properties is developed. As regards, Aluminum has an important role in designing and construction of aerospace structures and devices, since its density and strength are suitable to aerospace applications. Al 5083 is one of the most widely used materials in the construction of missiles, space vehicles and sounding rocket structure. In this paper, the continuum damage mechanics principles are studied. Nucleation, development and propagation of damage in Al 5083 are investigated based on Bonora model as a non-linear model. FE simulation of material behavior during failures is carried out by ABAQUS software package and USDFLD subroutine. The results are validated with experimental tests. This comparison shows that the simulation results are agree with that of experimental tests, also the Bonora model can be used of damage modeling of AL 5083.

This paper deals with heat transfer in jet impingement of nanofluids. Attention is focused to compare single-phase and two-phase nanofluid models and to study separate behaviors of the base fluid and the nanoparticles through the Eulerian-Eulerian two-phase model. For this purpose, jet impingement of Al2O3/water nanofluid in different conditions is simulated adopting the single-phase, two-phase mixture and Eulerian-Eulerian models and the corresponding results are discussed. For the solution of the governing equations of the three models, the control-volume approach is used. The accuracy of the current simulations is demonstrated by comparing the obtained results with those of open literature. The results indicate that in all of the approaches, increase in the Reynolds number as well as nanoparticle fraction leads to heat transfer improvement. During the current computations, the two-phase models predict higher heat transfer as compared to the single-phase model. Closer scrutiny of the two-phase approaches indicates that heat transfer of the Eulerian-Eulerian model is higher than the mixture model. However, it is found that with increase in the Reynolds number and decrease in the nanoparticle fraction, results of the two approaches become closer. Finally, the Eulerian-Eulerian model demonstrates that temperature distribution in the base fluid and the nanoparticles are similar but the corresponding velocity distributions are distinct.

This paper discusses the effect of the horizontal movement of impinging jets on the convective heat transfer from a cylindrical concave surface. In this way, the averaged Navier-Stokes equations for turbulent incompressible flow in a steady state considering two prevalent turbulence models and a Low- Re model with the Yap correction in the 3D computational space were solved. Results indicate that the Yap correction significantly improves the over-prediction of Nusselt number in the impingement zone. The results show that the decrease in the distance of the center of the jets to the outlet edge of the concave surface leads to the transfer of the maximum amount of the Nusselt number to the upstream flow, and the approach of the main flow of the jet to the recirculation region formed in the upstream flow results in the increase in the turbulent kinetic energy of this area and the Nusselt number in the stagnation point.

Torsional micro-actuators have found variety of applications in optical switches, displays, interferometry, spectroscopy, abbreviation correction and biomedical imaging. In order to improve the performance of these systems, it is usually desirable to maximize their operating angle amplitude and their switching frequency. To reach this, the overshoot and the settling time of the system in following desired outputs should be minimized. The objective of this paper is to propose an optimal fuzzy controller to stabilize the angle of a torsion micro-actuator beyond its pull-in range. To do so, a dynamic model considering both rotational and translational degrees of freedom is considered. Using Lagrange equations, the differential equations of motion are derived. In the next step, the static behavior of the system is briefly reviewed. Also the effects of applied voltage and damping coefficient on both degrees of freedom are studied briefly. Based on the resulting understanding from the system, the required linguistic IF-THEN rules are derived. Using the famous combination of singleton fuzzifier, product inference engine and center average defuzzifier along with the fuzzy IF-THEN rules as the heart of the fuzzy system, a fuzzy controller is designed and simulated. The results show that the use of the designed controller and the closed-loop system can perfectly follow the commands either within or beyond the pull-in range with an acceptable overshoot and small settling time. It is expected that the designed controller be successfully utilized in analysis and optimization of torsional micro-actuators for better dynamic performance.

In this paper, using thin wall beam theory, at first the deflection of an arbitrary point of a horizontal wind turbine has been determined. Then, calculating potential and kinetic energy of wind turbine structure and using Lagrange equations, the equations of motion have been derived. Also, forced vibration of structures under various excitation such as aerodynamic forces, centrifugal effects, weight of elements and base excitation have been investigated. Finally, the effects of lengths, material and angular velocity of blades and wind speed on dynamic behavior of structure have been investigated. For validation, the tower of turbine has been modeled and analyzed in ANSYS software and good agreement between the obtained results and the proposed method has been observed.

In this study, Given the importance of Bandar Abbas steam power plant in terms of Location and its electricity generating, it has been considered for applying the repowering method. After reference cycle modeling and assessing results accuracy, the applied repowering method has been implemented and it’s results reported in four main scenarios. Exergy efficiency and electricity generation cost (per kWh) have been considered as objective functions. Based on the six independent variables and four different scenario multi objective optimization has been done. The final reported results can be implemented by the energy managements for making the best decision and choosing the adequate option. Multi objective optimization of proposed combined cycles with single and double pressure heat recovery boilers indicate that the exergy efficiency upgrades up to 46%.