Sharif Digital Repository

With rising oil prices and predictions about the future of hydrocarbon reserves, issues of enhanced oil recovery and optimal production of existing reservoirs are of particular importance. In this study, molecular dynamics simulation was used to study the absorption of silica nanoparticles with surface groups at the interface of water and decane. The effect of surface chemistry of silica nanoparticles on the interface properties of water-decane with changing the surface groups was simulated. The initial surface factor of nanoparticle is hydroxyl (OH), which is called a hydrophilic surface agent. Nanoparticles were modified by methyl and ethyl surface agents to increase the hydrophobicity and... 

Video communications over mobile ad hoc networks is increasingly deployable as these networks become deployed in various applications such as disaster recovery. Error-prone nature of the mobile ad hoc networks and the vulnerability of compressed video to packet losses have brought many challenges to realize video transmission over MANETs. In this thesis, it is tried to achieve a good quality of service by resilient video coding and multipath transmission over mobile ad hoc networks. To generate error resilient video, a hybrid method is used by combining scalable video coding and multiple description video coding techniques. First, the video sequence is coded to two layers and then each layer... 

The business model is very important, as many researchers in this field believe that the success or failure of a business is highly dependent on right design and application of this model. In most recent innovation studies, application of innovation in business models or developing an innovative business model itself is one of the main factors to enable an organization to have stable status in the competitive market. This is unlike the traditional believes, which technology and process were the main motivators behind organization to stand out in competitive market. Designing a proper business model requires a system thinking approach, which considers both internal interactions factors, and... 

Conventional defects in GTAW welding of Aluminum 5052 alloy are the decrease in weld zone strength because of grain growth, formation of columnar grains in the fusion line, solidification cracks and porosities. In this work, effect of strong field electromagnetic stirring on solidification structure of 5052 alloy and elimination of GTAW defects have been investigated. For arc welding processes (especially tungsten inert gas welding), a process called magnetic stirring was proposed, patented, and investigated in the 1970s. The essential aim was to improve weld quality and they indicated that the the Lurentz force is cause of weld stirring. In the earlier researches, alternating magnetic field... 

Analysis of hydrodynamic model of sea wave problems has very good conformity with boundary element method (BEM). Because, the governing equation of many sea wave problems is potential equation which is the base of BEM. In this research, after some explanation about BEM and its application in fluid mechanics, a new composition of elements on the discretized boundary is introduced in favor of increasing the precision. In this method, the constant elements are used in corner elements and the linear elements are used in other elements. This issue is validated by comparing with analytical solution. In addition, free surface flow with porous medium in the fluid is investigated in sloshing 2D... 

Dependency of human life to supplying of electricity energy, leads to different challenges for power system operators and planners. Demand growth and development of renewable energy sources have caused heavy investment costs to the transmission system. High price of construction of new transmission lines make planners to investigate effective factors on transmission expansion planning in order to make better decisions. On the other hand, the different amount of energy consumption during a day and the uncertainty of renewable energy result in transmission line congestion which cause electricity price gap between peak hours and off-peak hours. This price gap, also, necessitate the development... 

The main goal of this thesis is the design and development of a rehabilitation device for helping patients “to improve blood circulation” & retain and recover their abilities if possible that were lost during the stroke or a accident like that (my research in karaj/iran shows that it is possible by just movement of the specific body part). The focus is on hand in this thesis because Injuries to the hand are common and can be very debilitating since our hands are our primary means for interacting with our world. For rehabilitation in case of human hand there are several practices that should be done for patients either in home or in a rehabilitation center, time and money that is supposed to... 

In the past few decades, shaking tables are widely used to evaluate system response of structures under seismic excitations. These devices are used without any fundamental research performed on a shaking table system as an entity model. In most of these studies for simplicity, it is assumed that there exist no considerable vibration and displacement around the shaking tables, and no attention is paid to the peripheral substances such as soil settled under the foundation.
In this thesis, result of ambient vibration test on shaking table system (solid deck, concrete foundation and soil layer) has been presented. Precise sensors known as low frequency and high accuracy accelerometers have... 

Out of several ground improvement techniques available, stone columns have been widely used. This technique has been successfully applied to increase the bearing capacity and to reduce the settlement for foundation of structures like liquid storage tanks, earthen embankments, raft foundations, etc., where a relatively large settlement is permissible. This technique has, generally, been proven successful in increasing the stiffness of weak soils, upgrading their safe bearing capacity, and reducing their total and differential settlements, as well as speeding up their consolidation process. The beneficial effects of stone column installation in weak deposits is manifested in the form of... 

Laminar forced convection flow through a channel partially filled with a porous material was numerically studied in this thesis. The Navier-Stokes and Brinkman-Forchheimer equations were used to model the fluid flow in the free and porous regions, respectively. Coupling of the pressure and velocity fields was resolved using the SIMPLEC algorithm. The local thermal equilibrium was adopted in the energy equation. The effects of the thermal conductivity ratio, Darcy number, porosity, Reynolds number and height of the porous insert on velocity and temperature field were investigated. The results show that the flow behavior and its associated heat transfer are susceptible to the variation of the... 

In the present study, a new version of haptic devices is presented in which user’s hand is in contact with the device just while collision with virtual surface. In this system, the position of user’s finger can be traced by using a camera and the haptic device follows user’s finger at the distance of about two centimeters. While the haptic device approaches to the virtual surface, gradually reduces its speed and stops about two centimeters distant of virtual plane. Then user’s hand collides with the haptic device which is static. Greater fidelity, transparency, more stability and also no need to large actuators are of the advantages of this system. In this project, first we present a new... 

In this thesis we try to find optimized parameters for imaging and manipulation of a biosample with AFM. For this we have prepared a numerous Molecular Dynamics simulation and find some reliable result. So, first we have focused on imaging process in Non contact mode (the less harmful mode). Then we headed into the manipulation process. The main problem about manipulating a biosample is the environment. In imaging section, the process of imaging a biomolecule by AFM is modeled using molecular dynamics simulations. Since the large normal force exerted by the tip on the biosample in contact and tapping modes may damage the sample structure and produce irreversible deformation, the non-contact... 

Results of previous studies on silt and clay indicated that variations in the small strain shear modulus, Gmax, during drying had a non-linear increasing trend with matric suction with greater values upon wetting. However, due to different material properties and inter-particle forces, different behaviour in Gmax is expected for sand. Although considerable research has been devoted in recent years to characterize the behaviour of Gmax of sand during drying, rather less attention has been paid to the effect of hydraulic hysteresis on Gmax and its variations during wetting. In the study presented herein, an effort was made to characterize the variation of Gmax for specimens of sand during...