سال:1391 | دوره: | شماره: |تعداد مقالات:11

Flocking through leader following structures in mobile networks raises attractive control problems. Due to limited sensing radii, leaders locally influence a network of agents. In this paper, we consider the problem of real-time maximization of flocking velocity. By using local information and a Particle-Swarm-Optimization (PSO) algorithm, a Leader Agent (LA) actively motivates flocking at high speed. The LA manages topology of the network in its neighborhood and increases flocking velocity. PSO output quality and calculation costs show that the proposed optimization algorithm is practically feasible. A case-study is also presented.

A three dimensional numerical study of unsteady turbulent cavitating flows around a circular disk and a cone cavitator. Cavitating flows which can occur in a variety of practical cases can be modeled with a wide range of methods. The RANS (Reynolds Average Navier Stokes) equations and an additional transport equation for liquid volume fraction are solved by using finite volume approach through the SIMPLE algorithm. In this simulation, a truncated Rayleigh-Plesset equation is applied for bubble dynamic. Also specific numerical modifications are used in a finite volume approach to promote robust solution when cavitation is present. Moreover, the VOF method is adopted to track the interface between the liquid and the vapor phases. For implementation of turbulent flow, the shear stress transport, k-w model is selected. The main characteristics of the cavity are analyzed and compared with experimental data. The present results for both cases are in good agreement with experimental data and analytical relations. These agreements confirm the authority of this simulation to be implemented in more complicated shapes.

In the present study, the motion of Newtonian and non-Newtonian liquid drops has been investigated experimentally. In order to investigate the effect of bulk fluid on drops, we have used water and air, as two fluids with different properties, and various industrial and biological applications. Image processing is utilized to analyze the images obtained by a high speed camera. The research has been separated into two parts. The first part has been devoted to the experiments in which air is the bulk fluid, and the second is related to the experiment carried out in water. The range of Reynolds number is, approximately, 50<Re<500. The major concern of the present study is the size variation of drops and its effect on the drag coefficient. It is proved that the period of size variation of a drop does not vary with properties. Rheological aspects of the problem have also been considered. In air with small density and viscosity, addition of non-Newtonian characteristics to the fluid causes the behavior of the drop to undergo dramatic changes. However, in water, a denser and more viscous bulk fluid, the behavior of Newtonian and non-Newtonian drops (at least for shear thinning fluids) looks the same.

This paper proposes combined regenerative Brayton and two parallel inverse Brayton cycles with regeneration before the inverse cycles. Performance analysis and optimization for the combined cycle are performed based on the first law. The analytical formulae of thermal efficiency and specific work are derived. The performance analysis and optimization of thermal efficiency and specific work are carried out by adjusting the compressor pressure ratios of the bottom cycles. The influences of the effectiveness of the regenerator and other parameters on the optimal thermal efficiency and the optimal specific work are analyzed by numerical examples. It is found that the combined regenerative cycle can obtain higher thermal efficiency than that of the base cycle but with smaller specific work. It is revealed that if the effectiveness of regenerator equals to 0.9, the combined cycles will attain an optimal thermal efficiency of 51.2%.

In this paper, the results of using a Coarse Grained Molecular Dynamics (CGMD) model to simulate the process of manipulation of nano clusters with a flexible tip are reported, and the reasons for some failures are discussed. After comparison of these results with those from a macro model, some failures of the nano manipulation process, due to damage, fracture, or crushing of tip, substrate, and nano cluster, are examined. At the end, after a parametric study of nano cluster deformations, the use of the tip cluster, ep-SP diagram, for optimal selection of the tip material, is discussed.

In this paper, the differential quadrature (DQ) method is employed to solve some nonlinear chaotic systems of ordinary differential equations (ODEs). Here, the method is applied to chaotic Lorenz, Chen, Genesio and Rossler systems. The first three chaotic systems are described by three-dimensional systems of ODEs while the last hyperchaotic system is a four-dimensional system of ODEs. It is found that the DQ method is unconditionally stable in solving first-order ODEs. But, care should be taken to choose a time step when applying the DQ method to nonlinear chaotic systems. Similar to all conventional unconditionally stable time integration schemes, the unconditionally stable DQ time integration scheme may also be possible to produce inaccurate results for nonlinear chaotic systems with an inappropriately too large time step sizes. Numerical comparisons are made between the DQ method and the conventional fourth-order Runge-Kutta method (RK4). It is revealed that the DQ method can produce better accuracy than the RK4 using larger time step sizes.

Accurate prediction of static and dynamic response of nano structures under external excitations has been one of the interests of scientists in the last decade. Several applications of nano machines make it necessary to analyze their components, such as nano bearing, precisely. In this paper, the static and vibrational behavior of a fullerene as a sensitive part of nano bearing under external forces is simulated by a newly designed spherical super element.This super element is designed in such a way that the user can select as many numbers of nodes as desired, so that it can be implemented in different desired precisions. In this study, a 228-node super element, which is similar to a hollow sphere (114 nodes on each inner and outer surface), is used, and the formulation of shape functions are introduced. Also, the mechanical properties of fullerene and the boundary conditions of nano ball bearings are presented. Two strategies are utilized to validate the results, the super element and conventional elements. Findings indicate that applying one super element for simulation of the fullerene leads to the same results as implementing 154764 conventional elements. Infinitesimal relative errors show the accuracy of calculations and shape functions of the super element.

Biodiesel is one of the major renewable energy sources, produced from vegetable oils. Jatropha curcas L. is considered as a promising energy crop for biodiesel production in Thailand. This study is about continuous biodiesel production from jatropha oil by transesterification in a flow process with microwave heating. Sodium methoxide was used as a catalyst at concentrations between 0.25%-1.5%, with microwave power of 800 W, irradiation time between 10-40 s, and oil to methanol molar ratio of 1: 3-1: 9, respectively. Results showed that jatropha oil can be converted to biodiesel (96.5%) within 30 s under oil/methanol molar ratio of 1: 6 and 1.0% catalyst. The findings indicated that this method can offer alternative means to produce biodiesel continuously.

The mechanical properties of Red Blood Cells (RBCs) are influenced by invasion and occupation of Plasmodium falciparum (Pf). The corresponding variation results from the stiffening of RBCs and their ability to adhere to endothelial cells. In this study, the transient deformation of Plasmodium falciparum-parasitized red blood cell (Pf -RBC) has been studied numerically. The cell is modeled as deformable liquid capsule enclosed by neo-Hookean elastic membrane. The effect of shear elasticity is included, but bending stiffness is neglected. The numerical model is based on the immersed boundary-lattice Boltzmann method (IB-LBM). The LBM is used to simulate fixed grid while the IBM is utilized to incorporate the fluid-membrane interaction in a Lagrangian manner by a set of moving grids for membrane. The results investigate the significance of elastic shear modulus and initial shape on hematocrit ratio and deformation of Pf -RBC at different stages. The Pf -RBC at trophozoite and schizont stages obtain the lower hematocrit ratio, as they become near-circular. The results are in good agreement with experiments and previous studies. It appears, therefore, that the IB-LBM can be used to predict in vitro and in vivo studies of malaria.

An advanced model of irreversible thermoelectric generator with a generalized heat transfer law is established based on finite time thermodynamics. The generalized heat transfer law represents a class of heat transfer laws including Newtonian heat transfer law, linear phenomenological heat transfer law, radiative heat transfer law, Dulong-Petit heat transfer law, generalized convective heat transfer law and generalized radiative heat transfer law. The inner effects including Seebeck effect, Fourier effect, Joule effect and Thomson effect, and external heat transfer are taken into account in the model. The Euler-Lagrange functions at maximum power output and maximum efficiency are established. Applying the model to a practical example in engineering, it is found that the external heat transfer law does affect the characteristics and optimal performance of the thermoelectric device, and the maximum power output and maximum efficiency with Newtonian heat transfer law are the maximum among the several typical heat transfer laws. The results can offer principles for the power and efficiency optimization of practical thermoelectric generators at various external heat transfer conditions.

Nowadays, designing a reliable controller for an Atomic Force Microscope (AFM) during the manipulation process is a main issue, since the tip can jump over the target nanoparticle and, thus, the process can fail. This study aims to design a Sliding Mode Controller (SMC) as a robust chattering-free controller to push nano-particles on the substrate. The first control purpose is positioning the micro cantilever tip at a desired trajectory by the control input force, which can be exerted on the micro cantilever in the Y direction by an actuator located at its base. The second control target is the micro-positioning stage in X, Y directions. The simulation results indicate that not only are the proposed controllers robust to external disturbances and nonlinearities, such as deflection of the AFM tip, but are chattering free SMC laws that are able to make the desired variable state to track a specified trajectory during a nano-scale manipulation.