Sharif Digital Repository

In this thesis, a fully coupled numerical model is developed for the modeling of dynamic cohesive crack propagation and hydraulic fracture in saturated porous media using extended finite element method. Many engineering structures like concrete or soil dams and buildings foundation are built with porous materials like concrete, rock and soil. Behavior of these materials in which void among the solid particles are filled with one or more fluids are so complicated rather than single solid phase. Dynamic analysis of porous mediums containing a discontinuity has many applications in various civil engineering fields including structure, earthquake, hydraulic structures, etc. For instance... 

Considerable research work has been dedicated to the development of structural control systems to improve the performance of structures and reduce the casualties resulting from earthquakes. It is generally accepted that semi-active control systems result in better structural performance compared to what can be achieved using passive systems. However, it has been observed that the majority of the performance improvement obtained from semi-active control systems stems from the reduction of brace flexibility effects, rather than the control algorithm used. In this study, it is attempted to utilize this fact to improve the performance of passive control systems, or develop simple semi-active... 

In this thesis, a fully coupled numerical model is developed for the modeling of the cohesive crack propagation and hydraulic fracturing in porous media using the extended finite element method in conjunction with the cohesive crack model. The governing equations, 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 three-phase formulation. The other variables are incorporated into the model via the experimentally determined functions that specify the relationship between the hydraulic... 

Local scouring at the downstream of sluice gates in the erosive beds is one of the main concerns of hydraulic engineers because of the significant damage that it can cause to the hydraulic structures. It is important to control the local scour depth at downstream of hydraulic structures to ensure safety operation of these systems. Many researchers have conducted various studies to predict the maximum depth and diameter of scour hole and develop new methods in order to control this phenomenon. One way to overcome this problem is the use of apron, or non-erosive bed. In order to shorten the apron length or decrease the effect of the... 

Membrane bioreactors can replace the activated sludge process and the final clarification step in municipal wastewater treatment. The combination of bioreactor and crossflow microfiltration allows for a high chemical oxygen demand (COD) reduction of synthetic wastewater. In this study, experimental data from a laboratory scale membrane bioreactor are presented. In order to investigate the influence of various operating parameters such as hydraulic retention time (HRT), biomass concentration and organic loading rate on organic pollutant removal, the pilot scale submerged membrane bioreactor (SMBR) with a Polyvinylidene Fluoride (PVDF) hollow fiber membrane module was conducted using synthetic... 

Local scour downstream of sluice gates in the erosive bed is one of the main concerns of hydraulic engineers, since it can cause serious damage to the structure. One of the ways to overcome this problem is the use of apron, or non-erosive bed. In order to shorten the apron or decrease the effect of the turbulence flow, different measures can be used. These approaches can be divided into two main branches, "Energy dissipating" and "bed reinforcement" measures. This study has investigated the scour phenomenon under the different conditions of the bed material gradation and bed reinforcement using vertical buried plates. The effect of sediment non-uniformity, unlike uniform sediment, has a... 

Two phase slug flow often happens in culvert and water tunnels conveying water from dams and weirs. Having complicated hydraulic properties, little is known about different hydraulic properties of this kind of flow, while most of the previous studies deal with other liquids than water and air, mostly dealing with chemical and mechanical engineering problems. In this paper, the results from experimental study of air/water slug flow due to changing in slope of the conduit from horizontal to 2, 3 and 4% are presented. The conduit has rectangular cross section with dimension cm of Plexiglas material and inclined part. Air is added to the system upstream of the conduit using an air discharge.... 

Geotextiles are one of the most widely used materials in filtration and drainage applications. Since geotextiles are exposed to different stresses and hydraulic gradients, thier hydraulic behavior in real situations is of great importance. In this study, filtration and drainage of several nonwoven needle-punched geotextiles with different properties and unit masses per area of 200g/m2, 400g/m2, 500g/m2 and 800g/m2 under various confined stresses and hydraulic gradients are investigated. To get to these aims, permittivity and transmissivity apparatuses were designed and built in the course of this investigation. Then samples which were emerged for at least 24 hours were tested under different... 

In the oil industry, after drilling an oil well and laying pipes, it is time for the hydraulic fracturing process. In the process of hydraulic fracturing, a fracture must be created in the casing pipe of the well. The reason for this is that the oil from the existing reservoir enters the well so that it can be extracted. The end of the well must be blocked to cause a fracture in the well body. The reason is that after creating a fracture in the casing pipe, proppant particles are pumped together with water inside the well to keep it open. For the proppant particles to be placed inside the cracks, it is necessary to create pressure in the fracture area. To create pressure in the fracture area... 

Total knee replacement surgery is the most common joint replacement in the world. Considering the increasing rate of this procedure and costs and difficulties of the repeated operation, many efforts have been made to improve the performance and lifetime of implants. The Polyethylene component of the implant is the most prone component to fail due to wear. To evaluate new knee prosthesis designs, it is necessary to have a wear test simulator. Objective of this project is to detail design a knee prosthesis wear simulator according to ISO 14243 in order to investigate the performance of prosthesises in long term and under in-vivo conditions. During this project, studies have been made to get... 

Microfluidics with the ability to control Nano-to-Pico meter volumes have caused the revolution in the systems of analytical biology and chemistry. However, the most Lab-On-Chip technologies (LOCs) depend on external control elements, so a lab is required to operate a chip. Bubble or drop logic through the bubble (drop) can control the flow internally and intrinsically digitally without utilizing of off-chip or moving components. Non-linearity is applied by using mutual drop-drop' effects on reversible linear flow in low Reynolds. for the proper exploitation of microfluidic systems, It is necessary to control droplet generation systems in one chip appropriately. The most crucial part of the... 

Motion simulators have been highly sought after by the growth of the aerospace industry. In the meantime, the Stewart mechanism, or the so-called Hexapads, is a robot that, in addition to being used in machining tools, is mainly used to simulate the flight. The Stewart-Gaph mechanism was created and introduced in 1954 and 1965, and since then dynamics and control have been widely addressed in the mechanical engineering literature. The robot is considering the project to test parts and equipment installed in marine vessels under sea movements and waves. Therefore, according to information obtained through relevant organs, the purpose of this project is to design and implement a hexapad... 

Reducing noise, vibration and damage to the vehicle's passenger compartment was always a problem that has been investigatedin many researches. Here engine mounts as connecting members between engine and chassis play a big role. Because both of engine and road vibration put on it. Many studies have been done to optimize the engine mounts. As a result, many of hydraulic engine mounts with different variety of system control. But a few researches did about optimization of location and orientation of engine mounts. Therefore this project is to provide a process to optimize the location and orientation of engine mounts. The optimization process is First the dynamic equations of dynamic system are... 

According to high nominal pressure and controllable flow, variable displacement axial piston pumps are used widely in hydraulic industry. However, there still exist many problems and limitations in the areas of design, controllers and performance. To solve the problems without wasting time and money in making prototypes, an accurate dynamic model of the pump is required which predicts pump behavior under various control signals and loads. The lack of simple and practical methods of measuring describing parameters of pump dynamics, makes investigation and verification of such a model very challenging. In this thesis, literature review is presented in a wide range. After investigating of... 

With the production from the reservoirs, the amount of in-situ oil storage has decreased and there is a need to increase oil recovery (EOR) from the reservoir. Increased oil recovery (EOR) includes operations such as acidizing and hydraulic fracturing. Considering the economic and high operational costs and geomechanical complexities, as well as the technical progress of hydraulic fracturing and its future; It is necessary to manage hydraulic fracturing operations optimally. This research is about hydraulic fracturing and its main goal is to optimize the parameters of the fracture or the geometry of the fracture. The research study was carried out on the Bangistan Reservoir located in the... 

Hydraulic fracturing, as an industry-leading technology, has proven to be very efficient in increasing the productivity of oil and gas wells. Therefore, this technology has been taken into attention in recent years and the number of hydraulic fracturing operations has been increasing. In order to enhance the efficiency of this technology, the final transmissibility of the fracture needs to be at the maximum possible value. To do so, proppant injection is the most common way to maintain a fracture open. To achieve a successful hydraulic fracture operation, detailed knowledge of the particle's transport and distribution inside the fracture is needed.In this study, a static fracture geometry... 

One of the most important challenges in drilling horizontal and directional wells is the optimization of hydraulics and hole cleaning and ECD management. In these wells, poor hole cleaning can lead to formation of cutting bed on the low side of the annulus and cause problems such as stuck pipe or increase in torque and drag. Also poor hydraulic design can lead to decrease in rate of penetration and thus, increase in costs. Mud weight should be placed inside the range of mud window (more than pore pressure and less than formation fracture pressure) in order to prevent kick of reservoir fluid or mud loss.In this thesis, the main goal is to optimize hydraulics and hole cleaning and manage ECD... 

Discharging treated or raw waste water in to surface water may cause lots of serious problems, including growth of algae, as a result of the presence of nutrients in waste water.algae decrease the concentration of dissolve oxygen in water.phosphorus removal from waste water is of absolute necessity. according to the standards set by the environmental organization, discharge the untreated waster water in to the surface water is not allowed. on the other hand, given manager facilities of deprived area,effort is channeled to reach the desired result through designing the simplest treatment systems. anaerobic-aerobic systems have remarkably been used for many years in the treatment of urban and... 

To have a deeper understanding of Hydraulic fracturing operation, in this study four important parts in this field was developed and simulated. In the first part, continuity and momentum equations for a single phase flow in a propagating penny-shaped fracture inside an impermeable matrix was revisited based on a fixed coordinate system. Its correctness was validated against experimental data and its features were compared with the well-known lubrication theory in analytical form. The new derived continuity equation caused the fracture tip to have a positive and finite pressure while, the conventional model predicted negative infinity for that. In the second part, Finite Volume method was... 

In this thesis was investigated the effect of solid retention time (SRT), Hydraulic retention time (HRT), activated carbon and suspended carrier on styrene and ethylbenzene biological removal and also on membrane fouling. In addition to the typical analysis (COD, MLSS, MLVSS, and SVI), the flocculation ability, sludge particle size distribution (PSD), FTIR analysis, excitation-emission matrix (EEM) fluorescence spectroscopy, soluble microbial product (SMP), extracellular polymeric substance (EPS), microscopic observations, microbial activities, microorganism population, and filamentous bacteria are considered to determine sludge characteristics. This study was done in five sections: in the...