Sharif Digital Repository

Dissipative particle dynamics (DPD) is an emerging mesoscopic computational method in which the interparticle forces arise because of coarse-graining at the molecular level. In the asymptotic limit of large length scales, the governing equations of continuum are reproduced, as demonstrated in this work. This method of simulation has the capability of simulating larger order of time and space in compare with dynamic molecular method. One of the important applications of DPD is simulating the dilute polymer solution. In this project, we developed a general code to simulate dilute polymer behavior which consists of polymeric forces and different types of usual DPD boundary conditions. This code... 

The railroad blocking problem emerges as an important issue at the tactical level of planning in freight rail transportation. This problem consists of determining the paths of each shipment which minimize the total cost subject to the key constraints such as limitation on travel time, limitation on number of dispatched trains, and limitation on the number of cars classified at each station. The multi-path railroad blocking model is developed and then a new heuristic algorithm based on the Lagrangian relaxation technique to solve the realistic rail network is introduced.To consider the uncertainty which is inherent in the demand and travel time (as a supply indicator of rail system), a... 

Knee pain and injuries are very common in athletes. Anterior cruciate ligament (ACL) injury is one of the most important reason of knee acute and chronic pains. As ACL plays a significant role in knee stability and due to amount of reported ACL related injuries, much effort has been placed on finding proper and on time diagnosis and treatment of these injuries. Arthrometric methods are the most non-invasive reliable diagnosis option; however they are not fully capable of separating partial injuries from intact joint. This weakness can be investigated by quantifying the tests using computer simulations; so far few studies have been conducted toward this goal. In this study a two dimensional... 

Physical and mechanical properties of cast alloys is partly a function of the morphology and volume fraction of phases from freezing. The microstructure of the eutectic solidification is function of physical properties (especially mobility and surface tension) and the volume fraction of phases involved in the evolution. The prediction of solidification microstructures will be very helpful for improving the mechanical properties of casting alloys and designing of new families of alloys. The theoretical study of the formation of eutectic microstructures is very difficult and almost impossible in general cases and empirical studies are expensive. The purpose of this study is to predict the... 

We carry out computer simulations in the hope of understanding the properties of assemblies of molecules in terms of their structure and the microscopic interactions between them. This serves as a complement to conventional experiments, enabling us to learn something new, something that cannot be found out in other ways. One of the main families of simulation technique are molecular dynamics (MD). Over the last decade , nanoscience and nanotechnology have emerged as two of the pillars of the research that will lead us to the next industrial revolution. The fundamental entities of interest to nanoscience and nanotechnology are the isolated individual nanostructures and their assemblies. Nano... 

Nowadays internal combustion engines play an important role in the power generation as well as transportation fields all over the world. By using the turbocharger in internal combustion engine, more power is obtained in compare with aspirated engine having the same size, which is limited for gasoline engines. In this research, by a three-zone computer simulation code and experimental tests, the power boost limitations of the gasoline turbocharged engine are investigated. The results of single cylinder aspirated gasoline engine tests are used for validation the natural aspirated part of the code. For validating the turbocharged engine simulation, the results of a four cylinders gasoline... 

The production of agricultural products is one of the most important human economic activities. The issue of mechanized and optimal use of pesticides is vital for human health and the environment, and the use of helicopters makes this possible. Although spray-based systems in helicopters are one of the most effective ways to produce agricultural products, it is still unclear how droplet movement in aerial spraying is affected by the complex downwash flow created by rotors. Modeling agricultural air spray to identify the spray trend of droplets in the air stream, downwash flows, and consequent vortices has attracted more attention as a result of the development of computational fluid... 

The following thesis is concerned with the control of automated irrigation channel using model predictive control in order to eliminate upstream transient error propagation and amplification phenomenon. It is illustrated in the literature that one way of dealing with this phenomenon is to solve a constrained optimization problem at each receding horizon. However, this problem becomes infeasible for automated irrigation channels. Several methods in the literature have been proposed that exploit terminal constraints to guarantee the feasibility of this problem. Finding these constraints, however, is extremely time-consuming as well as impractical for large-scale automated irrigation channels.... 

Increasing of industrial society's need to refinery's product, high consuming energy in distillation process and pollution product in it cause to researchers investigate about the alternative process for crude oil refinery. At this time, supercritical fluid extraction was regard as a less energy consuming process. The aim of this work was prepare to a computerized model for simulating of crude oil refinery's process. In this work effects of temperature and pressure on the supercritical extraction were investigated. The experiment was done at four temperatures (35, 40, 45, 50°C) and four pressures (100, 120, 140, 160 bar) by supercritical carbon dioxide and obtained samples were analyzed by... 

In order to respond to the concerns of safety and productivity of construction operations, in this research, the model based on discrete event simulation has been proposed. In this model, with simulation of different scenarios of construction operation in planning and designing phases, before starting construction operation, the level of safety and productivity of each scenario evaluates concurrently. The Scenario that best meets the safety and productivity concerns concurrently has been selected for operation. In order to evaluate the feasibility of the model in construction operation, the model has been implemented in a fabrical example. The operation of installing tiles on the sloping...