Scientia Iranica
Volume:25 Issue: 1, Jan - Feb 2018

In this study, a homotopy analysis method was used to obtain analytic solutions to predict dynamic pull-in instability of an electrostatically-actuated microbeam. The nonlinear describing equation of a microbeam affected by an electric field including the fringing field effect, based on strain gradient elasticity, couple stress and classical theory was obtained. Influences of different parameters on dynamic pull-in instability were investigated. The equation of motion of a double-clamped microbeam was discretized and solved by using Galerkin’s method via mode summation. The resulting non-linear differential equation was also solved by using the homotopy analysis method (HAM). The influence of HAM parameters on accuracy was studied specifically in the vicinity of the pull-in voltage. Comparison of the results for pull-in voltage indicated at low voltages good agreement existed between numerical and semi-analytical methods while at high voltages HAM results deviated from those of numerical methods. Findings indicate that considering strain gradient and couple stress effects results in a stiffer microbeam than with classical theory. Effects of an auxiliary parameter on convergence were also studied. Convergence domains were determined at different voltages and orders of HAM approximation

Recently, electrode-based Dielectrophoresis (eDEP) has been used for particle manipulation by means of triangular electrodes. In this theoretical and numerical study, a microchannel with quarter-of-ellipse electrodes is presented and a detailed comparison with triangular electrodes is made. Electric field, resultant DEP force, and particle trajectories for each microchannel are evaluated by means of COMSOL Multiphysics 4.4. Afterwards focusing and separation efficiencies of the systems are assessed and compared. Finally, our proposed model’s separation efficiency of live and dead cells is compared with our previous model published in the literature [1]. It is demonstrated that our proposed model have higher lateral DEP force, responsible for cell separation, compared to the previous triangular-electrode model. This feature is reflected in the 96% focusing efficiency for 10-micron particles and 100% separation efficiency for live and dead mammalian cells.

The use of artificial neural network in conjunction with artificial bee colony algorithm is proposed as a method for performance and emissions optimization of an SI engine. The case study here involves the oxygen enriched combustion of an SI engine fueled with hydrous ethanol and gasoline. In this study, the engine is considered as a black box and its performance and emissions were extracted experimentally at different intake air oxygen concentrations, hydrous ethanol injection rates, and ethanol concentration in the hydrous ethanol mixture. Then the simultaneous injection of hydrous ethanol and oxygen enriched combustion was investigated to maximize the fuel conversion efficiency and minimize the CO and NOx emissions. Therefore, an objective function consisting of both the emission and performance parameters was optimized using the Artificial Bee Colony algorithm. The engine model used in this optimization process was obtained from an Artificial Neural Network trained with experimental engine data. For operating speed of 3000 rpm, the optimization results indicated 1.21% improvement in fuel conversion efficiency and 31.11% and 13.94% reduction in CO and NOx emissions, respectively. At the speed of 2000 rpm, fuel conversion efficiency improved by 4.11% and CO emission decreased 18.73%, while NOx concentration increased 28.35%.

Forced convection fluid flow and heat transfer is investigated in a porous channel with expanding or contracting walls with which is filled Al2O3-Cu/water micropolar hybrid nanofluid in the presence of magnetic field. In order to solve the governing equations analytically, the least square method is employed. The hot bottom wall is cooled by the coolant fluid which is injected into the channel from the top wall. The range of nanoparticles volume fraction (90% Al2O3 and 10% Cu by volume) is between 0% and 2%. The effects of consequential parameters such as Reynolds number, Hartmann number, micro rotation factor and nanoparticles volume fraction on velocity and temperature profiles are examined. The results show that with increasing Reynolds number, the values of temperature and micro rotation profiles decrease. Furthermore, when the hybrid nanofluid is used compared to common nanofluid, the heat transfer coefficient will increase significantly. It is also observed that when the Hartmann number increases, Nusselt number increases, too.

In this paper, by combining the computational fluid dynamics (CFD) and NSGA II algorithm, the forced convective heat transfer flow in a stack of horizontal parallel plates has been multi-objectively optimized. In the optimization process, the distance between the plates in the set of parallel channels has been changed so as to simultaneously optimize the amount of heat transfer between the plates and fluid and the pressure drop of the fluid (maximization of heat transfer and minimization of pressure drop). The Pareto front, which illustrate the changes of the heat transfer from the plates and the pressure drop of fluid simultaneously, have been presented in the results section. This result contains important information regarding the thermal designing of stack of channels subjected to forced convective heat transfer. The Pareto front have been obtained for four different fluids that have different Prandtl (Pr) numbers (mercury, air, water and oil), and the results related to each fluid have been discussed. Finally, the multi-objective optimization results obtained in this paper have been compared with the results of the asymptotic analysis method (which is a single-objective method aimed at increasing the amount of heat transfer from plates) for internal fluid flows; and useful information has been obtained.

The control of flexible cable-driven parallel robots usually requires not only the feedback from the joints, but the feedback from the end-effector pose or cable tension. This paper presents a new approach for reducing the vibration of flexible cable-suspended robots, using only the feedback from the joints. First, the dynamic equations of a 6DOF cable-suspended parallel robot with elastic cables were derived by Gibbs-Appel formulation. Subsequently, three different control approaches were investigated based on the computation load and required sensors. As a result, a feedback linearization method based on the rigid model of the system was selected. In order to reduce the vibration, a robust input shaping method was employed to prevent excitation of natural modes. Simulation results revealed that the proposed approach leads to a noticeable vibration and settling time reduction in cases of low and high cable stiffness, respectively. Moreover, another simulation compares the presented approach with a composite controller, which uses the feedbacks from the end-effector and actuators. Thereafter, the performance of the approach in vibration reduction is quantitatively shown. Finally, experimental validation of the approach was accomplished by frequency analysis of the vibration obtained from the IMU sensor, attached to the end-effector.

The performance of a HTPB/N2O hybrid motor was experimentally investigated. A hybrid motor was designed and manufactured in a laboratory with the purpose of studying the effects of various parameters on the motor’s performance, including fuel regression rate and specific impulse. A series of tests were conducted to find a correlation between the fuel regression rate and the oxidizer’s mass flux. The effects of chamber’s pressure on the regression rate as well as other performance parameters were investigated. While the burning rate did not change dramatically, both the efficiency and ISP of the motor were increased. The local fuel regression rate and the fuel port were also calculated. In addition, instantaneous regression rate was calculated using a special technique.

Analytical relation for slow motion thin liquid films bounded by a fixed wall and free surface for Newtonian and non-Newtonian fluids are obtained in this work. Assuming long-wave approximation, the momentum and continuity equations for thin liquid films of power-law fluids are simplified and solved analytically to derive the evolution equation of thin liquid films. The evolution equation is derived for two- and three-dimensional cases. A relation for evolution of thin films is obtained for a simple case in which the liquid film is supported from below by a solid surface and subjected to gravity and constant surface tension forces. This evolution equation of thin film has been solved numerically in order to compare the behavior of Newtonian and non-Newtonian liquids for different Bond numbers. It is shown that the power-law model at low and high strain rates is invalid and it affects the results. The Rayleigh-Taylor instability is another subject that is studied in this work. This interesting phenomena is investigated by solving the evolution equation numerically for different Bond numbers. The results show that the evolution of the free surface thin film for pseudo plastic fluids is different from that of Newtonian and dilatant fluids

In this research, the feasibility of solar assisted desiccant evaporative cooling system for office buildings was studied. An office building in Chabahar, Iran, as a high cooling load demanding region was considered as the case study. Different configurations as the desiccant based cooling systems were examined to determine the most appropriate configuration in terms of established indoor air conditions and required cooling energy. The configurations were simulated hourly and the monthly mean values were determined. TRNSYS software was used for this purpose. The results indicated that the desiccant based cooling system operating in the recirculation cycle with pre-cooling, Config. E has the potential to keep the indoor air conditions within the standard recommendations. In addition, it was shown that Config. E is the superior configuration in terms of the energy performance and could meet the cooling energy requirements of the space.
The potential of providing the desiccant regeneration heat by the solar energy was also investigated. Three standard solar thermal panels were explored to propose the most proper array plant. The study showed that an array of solar panels consists of two rows of four unglazed solar thermal collectors could meet the heat energy requirement by the regenerating process.

The paper aims to develop a harmonic identification scheme for a hydraulic shaking table’s sinusoidal acceleration response. Nonlinearities are inherent in a hydraulic shaking table. Some of them are dead zone of servo valve, backlash and friction between joints, and friction in actuator. Nonlinearities cause harmonic distortion of the system shaking response when it correspondsto a sinusoidal excitation. This lowers the system control performance. An efficient, time-domain acceleration harmonic identification is developed by using Hopfield neural network. Due to the introduction of energy function used to optimize the computation for the identification harmonic method, the fully connected, single layer feedback neural network does not require training in advance and is able to identifyharmonic amplitudes and phase angles. Each harmonic,as well asthe fundamental response,can be directly obtained.Simulations and experiments show very promising results that the proposed scheme is really applicable to identify harmonicswith high precision and good convergence. Comparisons between the presented method and other method are carried out to further demonstrate its efficiency.

This paper presents a model reference controller (MRC) of mode shift that intends to decrease the vehicle jerk and the clutch frictional loss for a dual-mode power-split hybrid electric vehicle (HEV). To design a model-based control system in this paper, simplified dynamic equations capturing mode shift dynamics of the dual-mode power-split HEV are derived. To simplify the complicated dynamic characteristics of mode shift, switched system theory is applied to partition the state space of mode shift into domains and facilitate the controller design. To deal with the friction-induced discontinuity of the clutch torque during mode shift, a MRC is proposed that coordinately manages the engine torque, the motor-generator torque and the clutch friction torque. In addition, because the control system is overactuated by three control variables (three torques) and two output variables (two angular speeds), the controller parameter selections that involves selecting the combination of the control variables and the feedback-feedforward parameters are comparatively analyzed. The simulation and the experimental results demonstrate that the proposed MRC in this paper can simultaneously reduce the vehicle jerk and the clutch frictional loss, thereby improving the shift quality, when compared with the conventional controller.

This work deals with asymptotic periodicity and compactness for a class of composite fractional relaxation equation. Some difficulties arises when the effect of different kinds of nonhomogeneous terms are taken into consideration. To overcome these we use methods coming from regularized families and fixed point techniques, which are an important tool to study of nonlinear phenomena. We can cover a large class of nonlinearities.