Scientia Iranica
Volume:23 Issue: 3, 2016

Numerous experiments were conducted on a section of a 660kw wind turbine blade in a subsonic wind tunnel. The selected airfoil was tested with a clean and distributed contamination roughness surface, also with high and low tunnel turbulence intensity. Surface contamination was simulated by applying 0.5 mm height roughness over the entire upper surface of the airfoil. The surface pressure distribution is measured in the steady and unsteady condition at three Reynolds numbers, 0.43, 0.85, and 1.3 million, and over a range of angles of attack, AOA=7o-19o. Unsteady data were acquired by both pitch and plunge-type oscillation of the model about its quarter chord at a reduced frequency of 0.07. Results show that the surface roughness reduces section aerodynamic efficiency and the lift coefficient, but increases the drag coefficient for all the Reynolds numbers. The application of roughness reduces upper surface pressure coefficient and extends a separation region at high angles of attack. Increasing the tunnel turbulence intensity resulted in delay of the stall, an increase of maximum lift coefficient, and smoothness of the stall behavior. However, the drag coefficient increased significantly. Furthermore, turbulence intensity affected the predicted power output of the blade.

The aim of this study is to simulate the self-assembly of the surfactant molecules with special chemical structure and bending stiffness into bilayer membranes using a mesoscopic Dissipative Particle Dynamics (DPD) method. Thesurfactants are modeled with special chemical structure and bending stiffness. To confirm that the novel model is physical, we determine the interaction parameters based on matching the compressibility and solubility of the DPD system with real physics of the fluid. To match the mutual solubility for binary fluids, we use the relation between DPD parameters and -parameters in Flory-Huggins-type models. Unsaturated bonds can change the stiffness of a lipid membrane which is modeled by introducing a bond bending potential. To verify our model we investigate the effect of surfactant structure like chain length and stiffness of those molecules on the properties of the modeled membrane as area per surfactant. To validate our results, we also compare them with the theoretical calculations as well as with the experimental and other existing simulations results. We show that there is a good coincidence between all of the results.

The present numerical study aims to investigate the e ects of uncertainties of di erent conductivity models on mixed convection fluid ow and heat transfer in a square cavity lled with Al2O3-water nano uid. The left and right vertical sides of enclosure are maintained at high and low constant temperatures, respectively, while the bottom and top horizontal sides of the enclosure are kept insulated. Furthermore, the right wall moves from down to up with a constant velocity, Vp. To approximate the nano fluid e ective thermal conductivity, ve most commonly used models, namely, Maxwell, Khanafer and Vafai, Corcione, Chon et al., and Patel et al., are employed. Finite volume method and SIMPLER algorithm are used in order to discretize the governing equations. Simulations are performed for nanoparticles volume fraction ranging from 0 to 0.05 and Richardson number ranging between 0.01 and 100. The results indicate that there are signi cant di erences between the average Nusselt numbers predicted by the ve employed conductivity models.

This paper aims to establish a control strategy for parallel hybrid electric vehicles equipped with full-toroidal Continuously Variable Transmission (CVT). First, the advantages of CVT are elucidated. Afterwards, a modi ed control strategy on the base of Baseline static Control Strategy (BCS) is proposed. Employing this strategy, in some moments, the engine operates in its fuel-optimal point to decrease the vehicle Fuel Consumption (FC). It is demonstrated that the modi cations in BCS are applicable using a CVT as the power train. In order to investigate the implemented modi cation, an optimization on the proposed control strategy and BCS in SC03 driving cycle is accomplished and then, the optimized control strategies are compared. It will be demonstrated that the proposed method is superior to BCS in terms of FC in SC03 driving cycle. Finally, in order to examine generality of the comparison, the optimized control strategies are compared in other driving cycles. It is revealed.

It is well recognized that size-e ect often plays a signi cant role in the mechanical performance of nano-structures. Herein, strain gradient continuum elasticity is employed to investigate the size dependent pull-in instability of the cantilever nanoactuators immersed in ionic liquid electrolyte. The presence of dispersion forces, i.e. Casimir and van der Waals eld, is considered in the theoretical model as well as the double-layer electrochemical attraction. To solve the non-linear constitutive equation of the system, two approaches, i.e. the Rayleigh Ritz Method (RRM) and the numerical solution method, are employed. Impact of the size dependency and dispersion forces on the instability characteristics are discussed as well as the e ect of ion concentration in liquid.

Charcoal is becoming an alternative source of energy to traditional fossil fuels such as coal and coke. In theoretical studies, some types of biomass have been identi ed as alternative sources of fuel to coke. The use of charcoal for sintering applications has been evaluated in separate experiments in the world. These experiments indicate that charcoal can replace a portion of the coke breeze (approximately 20-30%). The aim of this thermodynamic study was to evaluate the possibilities of charcoal utilization in iron-ore sintering process. Thermodynamic analysis has shown that the main factors determining the composition and properties of sinter are chemical composition of input materials (including fuels), thermodynamics of fuels burning, and oxidation potential of the gaseous phase (CO2/CO ratio). The main objective of this work was to determine the e ects of coke substitution by charcoal in the laboratory sintering process with respect to combustion eciency and sinter quality. The coke substitution and energy requirement provided by charcoal was in range of 8 to 86%. The use of charcoal fuel resulted in a decrease in sintering time and the replacement of coke with charcoal may lead to increase in sinter productivity. Overall, the results from the laboratory scale tests suggest that replacement of coke breeze energy with an equivalent amount of energy from charcoal in the iron-ore sintering process is possible and has no negative influence on technological and ecological parameters.

Due to the increasing number of people su ering from physical disabilities in the elbow and wrist, developing an assistive wearable robot seems crucial. These disabilities are mostly common in elderly people and people who are su ering from spinal injury or stroke. In this paper, a wearable assistive robot for rehabilitation of the wrist and elbow is developed. The mechanism has 3 Degree of Freedom (DoF); two active DoF for assisting the flexion/extension of the elbow and wrist, and a passive one in order to have unconstrained supination/pronation of the forearm. The motors and sensors were chosen based on kinematic constraints governing the motion of arms and wrists. Finally, with the intention of evaluating the performance of the robot, some preliminary experiments were conducted using a prototype of the designed wearable robot. Experimental results showed that the proposed assistive robot meets its design goals and can assist patient motion in the desired DoF.

The area of the exit and throat region of a nozzle play a crucial role in its design. This paper is a report of numerical simulations carried out to investigate the influence of these parameters on the performance factors of an axisymmetric cold gas nozzle of micron-size throat diameter. It was assumed that the deviations of the flow behavior from that of a continuum flow can be taken care of by applying the rst-order slip boundary conditions at the wall. The solution methodology includes a nite-volume-based numerical procedure based on structured quadrilateral grids. A parametric study reveals that to reach the highest values of the thrust and speci c impulse, one should choose a nozzle with the highest possible throat diameter. However, by increasing the outlet diameter, the thrust initially reaches a maximum and then decreases. In these conditions, the speci c impulse is always a decreasing function of the outlet diameter of the micronozzle. It is also observed that the mass flow rate is an increasing function of both the throat and outlet diameters. In addition, the comparison of the results with and without slip velocity shows that the amounts of the mass flow rate, thrust force, and speci c impulse are higher when the rarefaction e ects are taken into account. Nevertheless, no fundamental di erence is observed in flow physics with and without slip velocity.

Three di erent adaptive methods are presented for meshless calculation of steady and unsteady ows. Two approaches of point re nement/coarsening and point movement have their ground in the mesh-based methods that, in the present work, are extended for meshless calculations. However, the third approach is a new concept, socalled adaptive neighboring scheme, that concerns the optimum selection of the neighbors for each point in the meshless framework. This means that the selection of the neighboring region for each particular point is a ected by the flow features in the domain. In this paper, an explicit meshless method based on the least square scheme is used. The results are presented for di erent steady and unsteady flows and the eciency of the methods in terms of computational cost and accuracy is investigated. It is observed that using these adaptive approaches decrease the computational cost of the method by about 60% as compared with the un-adapted results while improving the accuracy of results at the same time.

Mixed convection heat transfer in a lid-driven square cavity with sinusoidal boundary temperature at the bottom wall in the presence of magnetic eld is investigated, numerically. The top wall is preserved at a lower temperature. The left and right sidewalls of the cavity are thermally insulated. Finite volume method is used to solve the mass, momentum, and energy equations. The heat transfer rate is examined by varying the dimensionless parameters of Richardson number and Hartmann number. The fluid flow and the heat transfer rate are strongly a ected inside the cavity by the presence of magnetic field.

In order to improve the performance of thin lm devices, it is necessary to characterize their mechanical, as well as electrical, properties. In this work, a model is developed for analysis of the mechanical and electrical properties and the prediction of residual stresses in thin lms of silver nanoparticles deposited on silicon substrates. The model is based on inter-particle di usion modeling and nite element analysis. Through simulation of the sintering process, it is shown how the geometry, density, and electrical resistance of the thin lm layers are changed by sintering conditions. The model is also used to approximate the values of Young''s modulus and the generated residual stresses in the thin lm in the absence and presence of cracks in the lm. The results are validated through comparing them with available experimental data.

In this paper, we employ a sub-equation method to nd the exact solutions to the fractional (1 1) and (2 1) regularized long-wave equations which arise in several physical applications, including ion sound waves in plasma, by using a new de nition of fractional derivative called conformable fractional derivative. The presented method is more e ective, powerful, and straightforward and can be used for many other nonlinear partial fractional di erential equations.

Loss of lower extremities has been one of the main problems in human life. Although most of the available knee devices are aesthetically acceptable, there is a necessity for lighter and more compact mechanisms, especially for younger amputees. This problem can be solved by the combining compliant mechanism design with traditional mechanism design methods. In this study, one group of the prosthetics that is known as the compliant knee mechanisms« is evaluated. At rst, the di erent knee mechanisms, such as fourand six-bar knee linkages are investigated to calculate the values of the control moments (actuator torque). Then, the suitable location (where the actuator torque is to be exerted) is determined to reduce the knee control moment. Finally, the compliant joints are employed to provide the improved designs. Furthermore, an optimization method is employed to determine the optimum values of sti ness instead of using an experimental technique. The obtained results show that use of the compliant joints in the knee mechanisms reduces the values of the control moments, signi cantly. In fact, the compliant members decrease the peak torques during the stance phase. Therefore, by applying a compliant joint, a higher energy eciency and lighter knee mechanism can be achieved for ambulation.

In this paper, decentralized control of formation of a special category of leaderfollower networks on bounded velocity trajectories is addressed. The network of the agents in this study is supposed to have a directed graph with a spanning tree rooted at the leader agent. Moreover, follower agents do not receive online or have oine velocity of the desired trajectory, such as in tracking problem of trajectories which are not prede ned or when the total bandwidth is narrow. Furthermore, the leader does not receive any information from any agent and its control is fully centralized. In the present study, formation problem is considered a consensus problem. The controller is designed for integrator and doubleintegrator agents via backstepping. Furthermore, suitable condition of the robustness of the controller against the changes of the communication topology of the network is derived. Simulations verify the capability and robustness of the designed control law. In a simulation, formation keeping error reduction by tuning a gain of the controller, as claimed in the design procedure, is demonstrated.