Sharif Digital Repository

The present effort is the development of a multiscale modeling, simulation methodology for investigating complex phenomena arising from flowing fiber suspensions. Specific consideration was given to dynamic simulations of viscoelastic fibers in which the fluid flow is predicted by a method that is a hybrid between Direct Numerical Simulations (DNS) and Large Eddy Simulation techniques (LES), and fluid fibrous structure interactions (FSI) will be taken into account. Numerical results are presented for which focus is on fiber floc deformation by hydrodynamic forces in turbulent flows. Dynamics of simple fiber networks in a shearing flow of water in a channel flow illustrate that the... 

The use of the classical Boussinesq approximation is a straightforward strategy for taking into account the buoyancy effect in incompressible solvers. This strategy is highly effective if density variation is low. However, ignoring the importance of density variation in highly thermobuoyant flow fields can cause considerable deviation from the correct prediction of fluid flow behavior and the accurate estimation of heat transfer rate. In this study, an incompressible algorithm is suitably extended to solve high-density-variation fields caused by strong natural-convection influence. The key point in this research is the way that an ordinary incompressible algorithm is extended to... 

In this study, a real-time exible modular modeling approach to simulating the dynamic behavior of gas turbine engines based on nonlinear thermodynamic and dynamic laws is addressed. The introduced model, which is developed in the Matlab-Simulink environment, is an object-oriented high-speed real-time computer model and is capable of simulating the dynamic behavior of a broad group of gas turbine engines due to its modular structure. Moreover, a Kalman lter-based model tuning procedure is applied to decrease the modeling errors. Modeling errors are de ned as the mismatch between simulation results and available experimental data. This tuning procedure is an underdetermined estimation problem,... 

Coverage is one of the most important parameters which is always used in practice to characterize a shot peening process. At the same time however, it is the most missing parameter in the finite element simulations of this process. This study aims to relate shot peening simulation to the actual coverage that is developed during the process. Accordingly, two important models from literature are re-simulated and their capability to predict an actual coverage is assessed. Results of this study illustrate that full coverage situation is not captured by these models. Thereafter, a random finite element simulation along with a step by step examination of the treated surface is adopted in order to... 

In a multi-agent system, the number and initial position of informed agents play a major role in the convergence of uninformed agents. In this paper, three different patterns of informed agents' initial positions are studied to see how the convergence percentage can be affected by the number of informed agents. The proposed initial locations are intuitive and inferred from the collective behavior in humans. To evaluate efficiency of the proposed methods and to compare them from different points of view, large number of computer simulations is performed and results are analyzed  

In this paper we investigate the effects of social power on the evolution of opinions in model networks as well as in a number of real social networks. A continuous opinion formation model is considered and the analysis is performed through numerical simulation. Social power is given to a proportion of agents selected either randomly or based on their degrees. As artificial network structures, we consider scale-free networks constructed through preferential attachment and Watts-Strogatz networks. Numerical simulations show that scale-free networks with degree-based social power on the hub nodes have an optimal case where the largest number of the nodes reaches a consensus. However, given... 

A new approach for tracking targets in TWS systems is introduced which is based on Hough transform. The main idea is to take target's velocity and course of motion as the main tracking quantities and calculate other kinematic parameters of the target from these two main parameters. The main criteria for associating targets to tracks in Data Association (DA) step is co linearity of targets with the history of track and Hough transform is the main tool in this step. Computer simulation results are presented to compare the performance of the suggested algorithm with the conventional tracking systems  

This paper proposes an alternative method to determine the characteristic polynomial based on closed loop desired transient response. To develop the method, we have found optimal characteristic rations in simple arrangement of these parameters via performance map method. Despite its simplicity, the resulted system exhibits better transient response in comparison with the systems obtained from existing methods of determining the characteristics polynomials. Numerical simulations are used to illustrate the specifications of the proposed method  

In this work, Compressible Smooth Particles Hydrodynamics (C-SPH) is applied for numerical simulation of impulsive wave. Properties of linear and angular momentum in SPH formulation are studied. Kernel gradient of viscous term in momentum equation is corrected to ensure preservation of angular momentum. Corrected SPH method is used to simulate solitary Scott Russell wave and applied to simulate impulsive wave generated by two-dimensional under water landslide. In each of test cases, results of corrected SPH are compared with experimental results. The results of the numerical simulations and experimental works are matched and a satisfactory agreement is observed. Furthermore, vorticity... 

In this paper, we aim at an integrated approach to Dynamic Biped Walking (DBW) and Dynamic Object Manipulation (DOM) at an abstract level. To this end, we offer a unified and abstract concept with a dual interpretation as a DOM and as a DBW system. We validate the proposed approach by using a set of simulations on an illustrative case study and show how it can be used in modeling as well as design of planning and control algorithms for DOM and DBW systems. In the case study, we describe the proposed approach and show its dual interpretation by identifying the relations between 2D dynamic object manipulation of a disc using two planar manipulators and 2D dynamic object locomotion of lower... 

Modeling of the static recrystallization in deformed copper specimens with different initial grain sizes is carried out based on a previous dislocation-grain size interaction model and a Monte Carlo simulation. From the dislocation-grain size interaction model, the stored energy of the deformed copper is calculated considering the interaction of the dislocations due to the different initial grain sizes. Then, utilizing the stored energy and Monte Carlo simulation the kinetic of recrystallization and recrystallized grain sizes are obtained. The JMAK plots of the modeling results show that, in conditions of 2D modeling and site-saturated nucleation, the Avrami exponent is 2 ± 0.1. The time for... 

Fixed gain controllers for automatic generation control are designed at nominal operating conditions and fail to provide best control performance over a wide range of operating conditions. So, to keep system performance near its optimum, it is desirable to track the operating conditions and use updated parameters to compute control gains. A control scheme based on artificial neuro-fuzzy inference system (ANFIS), which is trained by the results of off-line studies obtained using particle swarm optimization, is proposed in this paper to optimize and update control gains in real-time according to load variations. Also, frequency relaxation is implemented using ANFIS. The efficiency of the... 

In this study, we explore the possibility of dynamic object manipulation of objects using a series of manipulators. Here, two three-active-link manipulators have been considered and the generality of the idea to a series of manipulator is developed easily. So without any gripper, and in an unstable grasp manner, we try to throw an object by a manipulator and catch It with another. Also we can consider the impacts generated in the moment of throwing and catching objects, as some disturbance and therefore we damp it. Finally we deal with the whole manipulation process as a system with some noise and disturbance and try to demonstrate its stability. All results have been validated with the aid... 

Order statistic (OS) CFAR processor is a powerful detector, but similar to many other CFAR detectors, suffers from clutter edge as well as interfering targets. To overcome these problems, two derivations of this detector have been developed. These are order statistic greatest of (OSGO) and order statistic smallest of (OSSO) CFAR processors. The cost, paid for this improvement, is a considerable decrease in detection probability for homogenous Weibull clutter. Furthermore, a substantial performance degradation of OSGO in interfering target (high target masking effect) and an excessive false alarm of OSSO in clutter edge, also, occur. This behavior is a result of non-soft rules used in these... 

We propose a new coded cooperation scheme for wireless communications to obtain transmit diversity in the scenarios that agents such as mobile handsets, sensor network nodes and etc., due to size, power or other constraints, cannot utilize multiple antennas. New scheme supports more than two cooperative users with a relatively low cooperation level. We evaluate the performance of the proposed scheme in a frequency nonselective slow fading channel. For two cooperative users, we provide the exact analytical analysis. However, for more than two users, as the analytical analysis is very complicated, our performance evaluation is based on computer simulations. Our numerical results show that each... 

Most of the strategies yet implemented to optimal fuel loading pattern design in nuclear power reactors, are based on maximizing the core effective multiplication factor (Keff) to extract maximum energy and lowering the local power peaking factor (Pq) from a predetermined value. However, a new optimization criterion could be of interest, aiming at maximum burn-up of the plutonium content in fuel assemblies, i.e., minimization of remaining plutonium in spent fuel at the end of cycle (EOC). In this research, we developed a new strategy for optimal fuel core loading pattern of a VVER-1000 reactor, based on multi-objective optimization: lowering the Pq, maximization of the Keff and minimization... 

Peer-to-peer streaming has recently gained attention as an effective solution to support large scale media streaming applications over the Internet. One of the main challenges of peer-to-peer video streaming is the cumulative impact of the Internet packet loss due to the decoding dependency of the compressed video frames. In this paper we study the impact of the Internet packet loss on the performance of peer-to-peer video streaming systems, and analyze the efficiency of various packet loss recovery policies in such systems. Our analytical and simulation results show how the Internet packet loss can affect the performance of peer- to-peer video streaming systems and how different packet loss... 

Elastic contact problem of a tilted shallow wedge with a half-plane is considered. The problem is solved analytically in either full slip or partial slip conditions. Closed-form expression is given for the Muskhelishvili's potential function of the contact. In the partial slip condition, the locations of the stick and slip zones were given explicitly in terms of the applied external loads and coefficient of friction. The results have been compared with finite elements modelling results. © 2007 Elsevier Ltd. All rights reserved  

The prediction of material microstructure is of great interest to the material designers since the property and performance of materials depend strongly on their microstructures. In this research the Monte Carlo method and grain growth phenomenon have been used to predict the limiting grain size in the presence of second phase particles. The results showed a good agreement with the previous published results predicted by the analytical models. It was found that the lattice orientation parameter, Q, strongly affects the kinetic of the grain growth. The experimental and theoretical results of limiting grain size predicted by Monte Carlo method showed that by decreasing the value of Q the...