Sharif Digital Repository

Due to the shrinkage defects, casting parts is sometimes unusable; as a result, researchers is tackling porosity removal problem, so that they would be able to cast parts in a way that have the least porosity. Nowadays, simulation is used to predict the location of the porosity. The design and the elimination of defects, which leads to additional costs, can reduce the overall costs in the projects.
In this thesis, we focus on shrinkage defects. The main cause of porosity is the drop of pressure. As a matter of fact, the thermal agitation of the molecules is weaker than the strong intermolecular forces that would pull the molecules; therefore, the molten metals’ density will be increased... 

A fully coupled numerical model is developed for the modeling of the cracks in porous media with flow of two fluids using the extended finite element method.The governing equations of two-phase fluid flow in deformable porous media, which account for the coupling between various physical phenomena, are derived within the framework of the generalized Biot theory. The solid phase displacement, the wetting phase pressure and the capillary pressure are taken as the primary variables of the formulation. The other variables are incorporated into the model via the experimentally determined functions that specify the relationship between the hydraulic properties of the porous medium, i.e.... 

This thesis is concerned with the modeling and simulation of twelve degrees of freedom parafoil-payload system, as a multibody aircraft configuration. This 12-DOF dynamic model represents three degrees of freedom each for rotational motion of the parafoil (including suspension lines and canopy) and payload, and three degrees of freedom for translational motion of the parafoil, and one degree of freedom for relative translational motion of the payload, also two degrees of freedom for rotation of the canopy frame respect to the parafoil frame.
For evaluation of the flight dynamic behavior of parafoil-payload system, the nonlinear differential equations of the system have been derived and... 

In this project, modeling and control of grasping phase of flight is investigated inspired by birds’ aerial hunting. For this purpose, grasping mechanism and its challenges in flight is studied. In the following, an explanation about gripper, its design and its performance in flight is given. Both 1-DOF and 2-DOF gripper is modeled. Then, the simulation is evaluated during different test cases. After modeling, optimum trajectory for an air-vehicle in grasping phase is studied and analyzed. When using a 2-DOF gripper instead of a 1-DOF gripper, the vehicle is capable of grasping in different positions and attitudes. Therefore, the results of trajectory generation show more chances of grasping... 

In this work, nanoparticle production via microemulsion method has been investigated from theoretical and experimental points of view. Population balance approach has been used to model nanoparticle formation in an inverse microemulsion system. The study of nanoparticle formation in the inverse microemulsion system of Marlipal O13/40-cyclohexane-water reveals that in low reactants concentrations, the coagulation phenomenon has an important effect on the formation of particles. In this regard, the population balance equations has been developed to consider the coagulation phenomenon in the inverse microemulsion system. The kernel of coagulation has been calculated based on attractive and... 

Network coding, as a promising method for data exchange in wireless communication network, is investigated by many researchers. However, the random nature of packet generation and transmission as well as the collision among transmitted packets have not been fully addressed in network codingrelated literature. In this dissertation, we analyze the network coding-based wireless network from this point of view. In order to achieve this goal, we apply mathematical tools such as probability theory and queuing theory. In the first part of this dissertation, we address the interaction between MAC and network coding. In this respect, we consider a multihop tandem wireless network, where each node is... 

The appearance of water in pipe lines of the natural gas transportation would cause several problems. In this regard, disparate methods have been developed to produce and refine of the natural gas, and one of the most common method is adsorption process. In this study, modeling and simulation of the adsorption process in the packed bed of zeolite 4A has been done. This research includes four steps, first, adsorption process and all types of adsorbent were investigated. Second, using rigorous solution method, equations of mass and energy balance derived. Third, using the collocation method and MATLAB programing, system equations of mass and energy was solved. Finally, accuracy of simulation... 

Tehran air quality is facing a real crisis. Reports of pertinent organizations show air quality is deteriorating in recent years and unhealthy days are increasing. As a result, study and planning in order to change this trend and moving toward improving air quality is a necessity. On the other hand, in order to make proper decisions and choosing effective approaches considering cost-effective attribute and legal, temporal and budget restrictions, selecting the right tool is essential. Air quality models are the tools which in a cost saving manner and reasonable time can provide the required results for researchers, decision makers and legislators. An applicable model correspondent with urban... 

Nowadays, in many of industrial processes, it’s necessary to measure acceleration of a moving object. Among the different type of accelerometers, the piezoelectric type are most useful and the most widely used. These sensors come in various configurations.
In the past, analytical and semi-empirical models have been used to design piezoelectric accelerometers. In these methods, based on some assumptions, the accelerometer nonlinear model is replaced with a linear model and the equivalent circuit model has been used to model accelerometer behavior. In these methods, the behavior of accelerometer become different from the expected one.
Recently, with the invention of efficient computing... 

In this article, the problem of mixed convection in vertical rectangular microchannels for both regular fluids and nanofluids have been solved, using the CFD technique in the entrance regions of momentum and heat transfer taking in account the influences of viscous heating, inertial force and sleep conditions. In case of nanofluid flow, both the Brownian and thermophoresis molecular transfer mechanisms were considered.The predicted results were validated using fully developed distributions of velocity and temperature. Furthermore, the influences of mixed convection parameter (Gr/Re) and Kn number values on distributions of velocity and temperature through the entrance and fully-developed... 

Nowadays, using smart buildings to improve performance and welfare of residents is of interest. Usually, these systems consist of safety systems that provide safety and security for residents. For example, fire detection system, sound the alarm and activating sprinkler in the building. For different types of critical events that can occur, variety of safety systems has been designed. Response time of these systems should be less than the deadline and the correct operation must be compeleted. As a result, analyzing and checking out the real-time and logical features of safety systems are the issues that we treat and investigate in this thesis.
In general, these systems are either... 

Nowadays, modeling the deformation behavior of materials is an indispensable tool to describe the evolutions of microstructure and mechanical properties of materials during deformation. As previous investigations have shown, the dislocation density is the most appropriate parameter for investigating the deformation behaviour of materials. In present research, considering the effect of stacking fault energy (SFE), the deformation behavior is investigated. In this regard, at first a thermodynamics based modeling of deformation is presented. Previous studies have shown that due to heterogeneous distribution of dislocations during severe plastic deformation, it is needed to use multi-variable... 

Tire is one component of the suspension system and has beneficial effects on reducing vibrations caused to the vehicle. This study aims to determine the factors affecting the damping and stiffness of the tire is carried out. The modeling of factors were identified. For testing the modeling effort is to be made to the instruments used to measure the damping and stiffness of the tires. To make the structural static analysis, dynamic and modal was to have sufficient structural strength and the displacements and stresses are sensibly placed. Factors that have influence on the hardness of the ring diameter, the outer diameter of the tire, tire pressure, tire tread depth, tire wall thickness,... 

Based on special properties of metal dampers such as high energy dissipation, stable hysteric cycles and simple application, low cost, insensitivity to changes of temperature and ability to be substituted after occurring of earthquakes, they are being used for structures control. ADAS and SSD are two kinds of metal dampers which are connected to top of the chevron braces and under the middle of beams. When shear forces are applied, these dampers yield and enter the plastic zone. In Endurance Time (ET) method gradually intensifying acceleration functions are created in a manner that the linear and nonlinear response spectra of them, while being proportional to average of real earthquakes... 

In this research, the amount of partitioning Invertase to be evaluated in nine systems, these systems contain Peg 2000,Peg 4000 & Peg 6000 with three different salt.In first, Binodal curve for nine systems to be drown by cloudy point method, then five point be selected in each system such as sample feed. Invertase in every systems to be solved in constant weight fraction. The analysis of every phasesto be achieved by Merchuk method. For correlation data of this method to be used by Othmer-Tobias method and then using equation Mrchvk ensure the accuracy of phase analysis , analysis of the results obtained with the UV method was studied.Accuracy of UV analysis was studied by using lattice... 

We present a model for noise in Ring Oscillator in order to improve their phase noise. Each Ring Oscillator consists of some nonlinear blocks. We study effect of these blocks on phase noise. In this study, noise behavior of each block is analyzed and a design guide for improvement of noise characteristic is presented.
It is essential for phase noise improvement to obtain insight about operation mechanism of oscillator. A comprehensive model is presented to get this insight. In this model, we show how a noise current produces phase noise also, a formula for phase noise is derived.
In second step, phase noise of Ring oscillator is improved by using the model. Active inductor is used in... 

To investigate the accurate performance of a structure, the knowledge of the way its connections function, is of great importance. Moreover, cognition of the actual behavior of connections which is often semi-rigid can lead to better apprehension of the actual and more accurate behavior of structures, whilst it is often considered to be pinned or fully-rigid.Therefore, in this study a new semi-rigid steel connection of beam to column will be introduced, and its behavior will be investigated using commercial finite element packages along with mathematical approximate modeling methods. One of the features of this connection is that its behavior mainly depends uponfolding of top and bottom... 

Pedestrian accidents involve most of traffic accidents mainly happen in urban intersections (signalized or non-signalized). The present research is to identify and evaluate the factors influencing the pedestrian decision while crossing the street at signalized intersections. The data used in this study are captured by recording the behavior of 596 pedestrians while crossing 2 signalized intersections in Karaj. To better identify the variables affecting the behavior of pedestrians, such as age, education, etc., 394 people have been interviewed in person. The factors affecting the pedestrian behavior are divided into two general groups: 1- Social, demographic, economic, family, and other... 

The objective of the present research, for the first time, was to configure a novel dynamic model to be applied in a general manner to simulate bioelectrochemical systems including microbial fuel cell and microbial electrolysis cell. Biochemical reactions engaged in organic substances degradation in both anolyte and biofilm were described by two anaerobic digestion models; Bernard’s anaerobic digestion model and ADM1. In addition, the bioelectrogenesis and electron transfer were modeled based on the direct electron transfer mechanism across the conductive biofilm. The biofilm simulation was established upon the one-dimensional distributions of substrates and microorganisms. In this study,... 

Low back pains (LBP) are prevalent and costly. One of the important factors causing LBP is excessive axial compression and shear forces that are applied on the intervertebral discs during different activities. Due to lack of direct in vivo measurement methods for estimating these loads, musculoskeletal biomechanical models have been emerged as indispensable tools under various activities. Different biomechanical models have been suggested to estimate muscle forces and spinal loads base on optimization, EMG and hybrid (EMG assisted optimization, EMGAO) methods. Although there have been a number of studies on the differences between various optimization and EMG-based methods, there has been no...