Sharif Digital Repository

A new approach for PID tuning, based on GA (Genetic algorithm) and Internal Model Control (IMC) technique, is presented in this paper. PID tuning is based on using Method. The IMC technique reduces the number of parameters that must be tuned for a multivariable system using PID controller. The algorithm uses GA for optimal determination of IMC variables. Simulation results present the good performance of the proposed method. © 2007 IEEE  

We present N-body simulations of unstable spiral modes in a dynamically cool collisionless disc. We show that spiral modes grow in a thin collisionless disk in accordance with the analytical perturbation theory. We use the particle-mesh code SUPERBOX with nested grids to follow the evolution of unstable spirals that emerge from an unstable equilibrium state. We use a large number of particles (up to N = 40 & 106) and high-resolution spatial grids in our simulations (1283 cells). These allow us to trace the dynamics of the unstable spiral modes until their wave amplitudes are saturated due to nonlinear effects. In general, the results of our simulations are in agreement with the analytical... 

In this paper, capabilities of switched-current (SI) circuits are utilized to design a high-speed A/D converter. New methods to improve the performance of the SI circuits are introduced. An 8-bit 300MS/s pipeline ADC is design in 0.18um CMOS technology and an ENOB of 7.3b is obtained from simulations. The ADC consumes 40mW from a 1.8V supply. © 2007 IEEE  

In this paper the performance characteristics of turbocharger twin-entry radial inflow gas turbine with unsymmetrical volute and rotor tip diameter of 73.6 mm in steady state and under full and partial admission conditions are investigated. The employed method is based on one dimensional performance prediction which is developed for partial admission conditions. Furthermore this method is developed for unsymmetrical volute of the turbine considering flow specifications. Experimental investigation of the research carried out on special test facility under full and partial admission conditions for a wide range of speed. The comparison of experimental and modeling results shows good agreements.... 

In this work, a comprehensive study of radial forging process is presented through 2-D axisymmetric and 3-D finite element simulations while considering internal tube profile. The tube used in this investigation has four internal helical grooves along its length. The material is modeled with the elastic-plastic behavior, and sliding-sticking friction model is utilized to model the die-workpiece and mandrel-workpiece contacts. The numerical results in the 2-D case are compared with available experimental data. Residual stresses in the forged product, stress concentration around the grooves, pressure distribution on the hammers and mandrel and maximum forging load are studied. The effects of... 

In this work we assume that there is an agent in an unknown environment (domain). This agent has some predefined actions and it can perceive its current state in the environment completely. The mission of this agent is to fulfill the tasks (goals) that are often assigned to it as fast as it can. Acting has lots of cost, and usually planning and simulating the environment can reduce this cost. In this paper we address a new approach for incremental induction of probabilistic planning operators, from this environment while the agent tries to reach to its current goals. It should be noted that there have been some works related to incremental induction of deterministic planning operators and... 

A communication protocol consists of a sequence of messages used by peer entities to communicate. Each entity in a network is equipped by at least one protocol stack. Due to the need for on-the-fly reconfiguration of protocol stack in future communication and computation devices, formalizing substitutability and compatibility of protocol entities are important in correctness assessment of dynamic reconfiguration. In this paper, we extend Constraint Automata and propose I/O-Constraint Automata to model behavior of protocols and propose enough formalism for substitutability and compatibility relations between protocols. We introduce input-blocking property of communication protocols, and show... 

Various attempts have been made to derive linearized, reduced order models of induction generators. Due to the fact that there is usually numerous number of these machines in wind power plants, these models provide great facilities in calculations, and therefore are used widely in power system transient stability studies. In this paper, some of these methods are discussed and compared and then a method known as "balanced realizations" is used to reduce the dynamic order of the machine. Computer simulation shows that the last method markedly improves the accuracy of the resulting reduced order model. The improvement is demonstrated by comparing the response characteristics predicted by each... 

In this paper a new technique called switched-resistor is used as an alternative to switched-capacitor circuits in a low-voltage low-power high-speed A/D converter. Simulation results for an 8-bit 150MS/s pipeline ADC are presented. This converter consumes 20mW from a 1.8V supply and provides an ENOB of 7.5bit. © 2007 IEEE  

One important point in microflow study is the correct consideration of the Knudsen layer. In addition to the many complexities behind numerical simulation of the Knudsen layer near the solid walls, there are serious uncertainties at the microchannel inlet (the point at which the flow enters the microdomain). One major difficulty is the appearance of two singularities at the two corners of the inlet section. They seriously affect the solution in the entrance region of microchannels in which the lengths are comparable with the lengths of their hydrodynamic developing zones. Although the macro inlet flow problem has been largely investigated, there has been little attempt to study the issue in... 

Traditionally, solid-liquid mixing has always been regarded as an empirical technology with many aspects of mixing, dispersing and contacting where related to power draw. One important application of solid-liquid mixing is the preparation of brine from sodium formate. This material has been widely used as a drilling and completion fluid in challenging environments such as in the Barents Sea. In this paper large-eddy simulations, of a turbulent flow in a solid-liquid, baffled, cylindrical mixing vessel with a large number of solid particles, are performed to obtain insight into the fundamental aspects of a mixing tank. The impeller-induced flow at the blade tip radius is modeled by using the... 

With the increasing use of pervasive computing environments (PCEs), developing dynamic reconfigurable software in such environments becomes an important issue. The ability to change software components in running systems has advantages such as building adaptive, long-life, and self-reconfigurable software as well as increasing invisibility in PCEs. As dynamic reconfiguration is performed in error-prone wireless mobile systems frequently, it can threaten system safety. Therefore, a mechanism to support assured dynamic reconfiguration at run-time for PCEs is required. In this paper, we propose an Assured Dynamic Reconfiguration Framework (ADRF) with emphasis on assurance analysis. The... 

Although several analytical models have been proposed in the literature for different interconnection networks with different routing algorithms, there is only one work dealing with partially adaptive routing algorithms. This paper proposes an accurate analytical model to predict message latency in wormhole-routed hypercube based networks using the partially adaptive routing algorithm. The results obtained from simulation experiments confirm that the proposed model exhibits a good accuracy for various network sizes and under different operating conditions. © 2006 IEEE  

Due to advantages of tubular polymerization reactors, a tubular reactor was used as the postpolymerizer for thermal bulk polymerization of styrene. By solving the mathematical model, static and dynamic simulations were carried out to study the reactor's behavior. In order to have a desired product regarding the monomer conversion and polydispersity at the reactor outlet, a specific temperature profile must be kept along the reactor's length. Based on the desired profile and using the system model, a trajectory for the jacket temperature was obtained. To apply the desired jacket temperature, the jacket is divided into three zones. The set-point of each zone has been obtained by discretizing... 

The main attempt of this paper is to present a new methodology to model a generic low-level flight close to terrain, which guarantees terrain collision avoidance. Benefiting the advantages of high-speed computer technology, this method uses satellite elevation maps to generate so called 'Quad-tree forms'. The latter is then used to find the optimal trajectories for low-level flights. The novelty of this approach, entitled the 'cost map', lies in the integration of aircraft dynamics into the segmented map. This procedure results in some near-optimal trajectories with respect to aircraft dynamics that could easily be used for minimization of flight path together with pilot effort. Different... 

Density current is a dense fluid, which is continuously released from a source and spreads down a sloping surface inside a lighter, motionless fluid. A low-Reynolds number k-ε model (Launder and Sharma, 1974) has been used to simulate the behavior of 3-D density currents. Density current with a uniform velocity and concentration enters the channel via a sluice gate into a lighter ambient fluid and moves forward down-slope. The model has been verified with the experimental data sets. Although the k-ε Launder and Sharma model is applied here to a conservative density current, it seems the analysis is valid in general for turbidity current laden with fine particles. Copyright © 2006 by ASME  

In this research a phase change micropump as a novel type of non-mechanical micropumps has been investigated. A one dimensional model has been developed to describe the pumping mechanism and assess the working characteristics of the micropump. Conservation of mass, momentum and energy have been employed to obtain an algebraic equation for the flow rate which depends on seven non-dimensional numbers. The governing equation has been solved to study the effect of various operating parameters on the micropump performance. To verify the analytical approach, an experimental set up has been constructed. The results show that the theoretical model is in reasonable agreement with the experimental... 

This paper studies and compares three nonadaptive (bidirectional, unidirectional, and sliding mode) and two adaptive (active control and backstepping) synchronization methods on the synchronizing of four pairs of identical chaotic systems (Chua's circuit, Rössler system, Lorenz system, and Lü system). Results from computer simulations are presented in order to illustrate the effectiveness of the methods and to compare them based on different criteria. © 2005 Elsevier Ltd. All rights reserved  

We study the sample complexity of learning a high-dimensional simplex from a set of points uniformly sampled from its interior. Learning of simplices is a long studied problem in computer science and has applications in computational biology and remote sensing, mostly under the name of “spectral unmixing.” We theoretically show that a sufficient sample complexity for reliable learning of a K-dimensional simplex up to a total-variation error of ε is O(Kε2 log Kε ), which yields a substantial improvement over existing bounds. Based on our new theoretical framework, we also propose a heuristic approach for the inference of simplices. Experimental results on synthetic and real-world datasets... 

In this work, numerical simulation is used to study the stability enhancement of high speed supercavitating Shkval missile. Although supercavitation is known as one of the most effective methods for drag reduction, producing the cavity, either by ventilation or by cavitator at front of the body, may cause some instabilities on cavity surface and thus on the projectile's motion. Therefore removing these instabilities comes as an important point of discussion. First of all, we calculate the sources of instabilities and measure respective forces and then present some approaches that significantly reduce these instabilities. One of these methods that could produce more stable supercavities is...