Sharif Digital Repository

In this investigation a mathematical model has been developed for simulation of the incompressible flow with free surface during mould filling. The simulation 3D melt flow with free surface is based on the SOLA-VOF technique. In the model the effects of variations parameters including heat and mass transfer as well as influences of backpressure, and friction have been considered. The solid and free boundary conditions have been modified and a new algorithm has been developed to calculate the effect of wall-slip ratio, during mold filling. In this algorithm, the effect of wall-slip ratio on the filling pattern has been modeled with an experimental function. In order to verify the... 

2D minerals are among key elements of advanced systems, but the need for understanding their interactions/reactions with materials and systems in which they are involved necessitates tracking their molecular and atomic monitoring. Zeolitic structures are microporous materials formed in the nature through volcanic activities or synthesis. Because of their outstanding physicochemical properties like cation exchange capacity and excellent adsorption properties, zeolites have found application in diverse chemical processes, e.g., gas adsorption, water purification, and wastewater treatment. Prediction of zeolite performance for a targeted application saves time and expense as such projection... 

This paper presents an analytical approach to estimate the speedup in a simulation-emulation cooperation environment. The speedup of this approach as compared with the speedup of a pure simulation is analyzed. Also, an analysis of the speedup is given when different types of application instructions are utilized. The analysis is based on using both Verilog and VHDL. The results show that when only the simulation part of the simulation-emulation co-operation is used, the speedup is higher, than when the pure simulation is used. The total speedup is also depended on the type of application instructions and the communication cycle time between the simulator and the emulator. © 2002 IEEE  

Nanoparticles (NP) have capability to adsorb proteins from biological fluids and form protein layer, which is called protein corona. As the cell sees corona coated NPs, the protein corona can dictate biological response to NPs. The composition of protein corona is varied by physicochemical properties of NPs including size, shape, surface chemistry. Processing of protein adsorption is dynamic phenomena; to that end, a protein may desorb or leave a surface vacancy that is rapidly filled by another protein and cause changes in the corona composition mainly by the Vroman effect. In this review, we discuss the interaction between NP and proteins and the available techniques for identification of... 

Computer networks courses are hard to teach as there are many details in the protocols and techniques involved that are difficult to grasp. Employing programming assignments as part of the course helps students to obtain a better understanding and gain further insight into the theoretical lectures. In this paper, the Partov simulation engine and experience using this engine in a computer networks course are discussed. Since 2009, various programming assignments based on the Partov system have been set to help students in their learning process. Student feedback has been very good; this has been quantified in two surveys in which a majority of students expressed their satisfaction with this... 

Simulation is perhaps the most cost-effective tool to evaluate the operation of a system under design. A flexible, easy to extend, fully object-oriented, and multilayered simulator for interconnection networks can be a very useful tool for multicomputer designers and researchers. It is so desirable to attach newly designed components to the existing models and to exploit detailed results. This paper presents XMulator, an object-oriented listener-based simulation environment for evaluating multicomputer interconnection networks. The simulator involves a toolbox of various network topologies, routing algorithms, switching techniques, and flexible router models. This work introduces a... 

Ducted fan aerial vehicles have drawn many attentions in the world because of their successful involvement in non-traditional reconnaissance and surveillance missions. However, due to inherent dynamic uncertainties as well as inconsistent responses, significant control challenges are still to be addressed. In this study, a non-linear dynamic model for ducted fan is firstly proposed to be employed for control design. This model is then validated by performing a series of standard simulation scenarios. Afterwards, an adaptive control method, named as model reference is utilized to design perfect controllers in hover as well as vertical flight. The capability of the adaptive laws to update the... 

In this study two-dimensional finite element models of Al/SiC metal matrix composites (MMC) by using of ABAQUS Explicit software are investigated. Chip formations and machining forces for three types of MMC with 5, 15 and 20% of SiC reinforcement particles were studied and compared with experimental data. The resulted chips in simulation and the generated chips in experiments have both continuous and saw tooth in appearance. On the other hand, the variation of the cutting forces with the cutting time in simulation and experiment have fluctuating diagram. This is due to the interaction between cutting tool and SiC particles during chip formation. ABAQUS explicit software was used for... 

In this paper, the application of neural networks for simulation and optimization of the cogeneration systems has been presented. CGAM problem, a benchmark in cogeneration systems, is chosen as a case study. Thermodynamic model includes precise modeling of the whole plant. For simulation of the steady sate behavior, the static neural network is applied. Then using dynamic neural network, plant is optimized thermodynamically. Multi- layer feed forward neural networks is chosen as static net and recurrent neural networks as dynamic net. The steady state behavior of Excellent CGAM problem is simulated by MFNN. Subsequently, it is optimized by dynamic net. Results of static net have excellent... 

The outcome of the classic percolation approach is several power-law curves with some universal (critical) exponents. Here, the universality means that these power laws as well as their critical exponents, which control the global properties of a system, are independent of its details. Classic percolation considers the connectivity between two lines and two faces at opposite sides of a system in 2- and 3D problems, respectively; whereas, in practice (e.g. hydrocarbon formations), production and injection wells are represented by points (in 2D areal models) and lines (in 3D models). This study presents the results of Monte Carlo simulations of a 2D percolation model wherein the connection... 

We introduce a new robust simulation optimization method in which the probability of occurrence of uncertain parameters is considered. It is assumed that the probability distributions are unknown but historical data are on hand and using φ-divergence functionality the uncertainty region for the uncertain probability vector is defined. We propose two approaches to formulate the robust counterpart problem for the objective function estimated by Kriging. The first method is a minimax problem and the second method is based on the chance constraint definition. To illustrate the methods and assess their performance, numerical experiments are conducted. Results show that the second method obtains... 

In the aftermath of earthquakes, hospitals serve the critical role of treating casualties. In many cases, the key components of a hospital (i.e., the building, staff, medicine inventory, technical systems, and medical equipment) are affected by an earthquake. To handle the demand surge, affected hospitals should recover in an effective manner. Hospital recovery is a complex and dynamic process because each component requires specific types and amount of resources to recover. Furthermore, the recovery of each component not only affects its performance but also plays a role in the overall hospital recovery. Hospital administrators need to model the complex recovery process after a future... 

Access to clean water is one of the challenges of the 21st century. Thus water purification is inevitable. One method of water treatment is purification by magnetic particles in the presence of magnetic field. The contaminants are attached to the magnetic particles and then by applying a magnetic field, magnetic particles and, thus, the pollutants can be collected. For the optimal design of a water treatment system, the effect of important parameters in the design, such as magnetic fields, particle size, and Reynolds number are determined numerically by modeling and simulating the water treatment process. Two methods are used to create the magnetic field: permanent magnet and coils. It is... 

Molecular dynamics (MD) simulation was used to study of mechanical properties of NiTiCu with different content of copper. It was shown that the percent composition of copper are significantly affects the stress-strain curves curve. The results showed that as the Cu content increased, the Yield Strength and Young's modulus decreased. © 2017 Elsevier Ltd  

The architecture of a hardwired simulator for implementation of a discrete event-driven simulation of digital systems at the logic level is presented. In the design of this system, attempts have been made to utilize techniques of high performance computing to have a system capable of simulating the digital circuits rapidly. The centralized event-driven simulation algorithm chosen here, has the advantages of being efficient and conceptually straightforward. The high reliability of the simulator has been taken care of through a collection of handshake signals between each two of the three main modules. © Sharif University of Technology, December 2007  

In this study a Monte Carlo simulation was used to investigate the effect of cell reactivities and particle diffusivities in the cells and matrix on the diffusion and reaction rate constants in gel-immobilized cell systems with different spatial cell configurations. A variety of conditions were examined ranging from instantaneous to very slow reactions with reaction probabilities equal to or less than one, and diffusivity ratios bigger or smaller than one in a spherical domain. In the case of high reactivity (diffusion-limited), the simulation results indicated a decrease in the reaction rate constants when heterogeneity in the cell distribution was increased. In the case of low reactivity... 

In this investigation, we have studied the kinetics and mechanism of photocatalytic conversion of methane into methanol reaction over the MoO 3(010) surface using a computer simulation method. Methane and oxygen as the reactants are used at room temperature and atmospheric pressure under UV photoirradiation of the catalyst. According to our data analysis, the order of methanol formation reaction with respect to CH4 and O 2 was determined to be l = 0.30 and m = -1.03, respectively. The highest methanol formation rate (TOF) value was obtained at about 0.05 molecule/s.site in a range of 25-35 W/cm2 incident light intensity with energy hv ≥ Eg. The selectivity of CH3OH was increased with... 

In this investigation, we have studied the kinetics and mechanism of formation and desorption of H2S on the Pt(111) surface using a kinetic random walk model. The effect of temperature on the H2S formation was studied in the range of 85-150 K. It was observed that a maximum amount of H2S is formed at 90 K and the amount is reduced at higher temperatures. H2S production yield as a function of time at different initial sulfur coverage ranging from 0.02 to 0.33 ML (1 ML ≃ 1 x 1015 atoms/cm2) was also examined. It was obvious that as the initial S coverage increases, the rate of H2S formation rapidly increases and reaches a maximum value and then declines gradually. Furthermore, according to our... 

Computation of the acoustic disturbances generated by unsteady low-speed flow fields including vortices and shear layers is considered. The equations governing the generation and propagation of acoustic fluctuations are derived from a two-step acoustic/viscous splitting technique. An optimized high order dispersion-relation-preserving scheme is used for the solution of the acoustic field. The acoustic field generated by a corotating vortex pair is obtained using the above technique. The computed sound field is compared with the existing analytic solution. Results are in good agreement with the analytic solution except near the centre of the vortices where the acoustic pressure becomes... 

This paper presents a new method to solve the problem of finding the best configuration of fuel assemblies in a pressurized water reactor (PWR) core. Finding the optimum solution requires a huge amount of calculations in classical methods. It has been shown that the application of continuous Hopfield neural network accompanied by simulated annealing method to this problem not only reduces the amount of calculations, but also guarantees finding the best solution. In this study flattening of neutron flux inside the reactor core of Bushehr NPP is considered as the objective function. The result is the optimum configuration which is in agreement with the pattern proposed by the designer. © 2001...