Sharif Digital Repository

The shear modulus of soils is a key material quantity which is frequently used in the evaluation of wave propagation through soil layers in dynamic response analyses for many geotechnical systems. The shear modulus, G, is defined as the slope of the shear stress-strain hysteresis loop and is significantly influenced by the shear strain amplitude induced in a soil specimen. Of particular interest in geotechnical engineering, the value of shear modulus for strains less than 10-6 defined as the small strain shear modulus, Gmax. The early experimental studies on the shear modulus of water-saturated or dry soil showed that shear modulus is highly dependent on mean effective sress, p´, and void... 

Groundwater is the most important freshwater resource in the coastal zones. There are some factors contaminate fresh groundwaters. Sea water intrusion (SWI) is one of the most important components of groundwater salinization. Also Submarine groundwater discharge (SGD) occurs when hydraulic gradient is from landside to seaside in coastal aquifers. There are many factors intensify SWI and SGD. In this research at the first part, coastline shape effect on SWI and SGD is investigated. For to this 4 different aquifers with different coastline shapes as stepped coastline, vertical coastline, steep slope coastline, and mild slope coastline are simulated with the same hydraulic parameters and... 

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... 

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... 

Unconventional fracturing applications such as long-term waterflooding at fracturing pressure, produced water re-injection and waterfracs, etc., are characterized by very high fluid leakoff velocity, long operation time and significant changes in stress, pore pressure, and/or permeability and porosity, affecting possibly large regions around the wellbore and/or fracture. These special characteristics make fracturing modeling methods developed for conventional fracturing applications inadequate. Some of the problems encountered include grid effects resulting in oscillation of fracture growth with time (limiting the stability of conventional fracture modeling models), singularity of material... 

In the last decades, Hydraulic Fracturing has been found widespread applications. One of its main applications is fracture producing in hydrocarbon reservoirs and increasing the outflow of oil and gas. Thus, control and prediction of crack path is really necessary. One of the major parts in any model is an appropriate crack propagation criteria. Many criterion has been proposed in literature. These models often assume some simplifying assumptions. They often consider isotropic media. In fact, this assumption is not applicable in geo-mechanics. In other words, there are many inhomogenities such as micro-cracks and microdefects. These appear in the flow characteristics (e.g. permeability) and... 

Shear modulus and confined modulus are important parameters for static and dynamic analysis in geotechnical applications. Elastoplastic and nonlinear constitutive models has been formulized by these parameters. Cyclic simple shear apparatus had been developed by mounting bender element and ultrasonic sensor to measure continuous shear wave and pressure wave velocities for determination of G_max and M.For this purpose two new pedestals have been fabricated on which HAE ceramic disc and sensors were mounted. A pressure control panel and a hanging column system have been designed to apply high and low matric suction with high accuracy.At first two small strain tests were conducted for... 

Analysis of neutronic and thermal-hydraulics fluctuations has various applications in calculation or measurement of the core dynamical parameters (temperature reactivity coefficients) furthermore it is applicable in thermal-hydraulics surveillance and diagnostics. Experience of the Fukushima Dai-ichi plant and the lessons learned from the European stress tests, demonstrated that alternative and various tools and methods are needed for the reactor's condition identification. In this paper the feasibility of development of an alternative accident monitoring via eminent coupling of neutron and thermal-hydraulics noise is proposed. and it is programming a simple simulator for calculating... 

Due to nuclear power plants’ growing roll in providing energy, analyzing probable accidents and their prevention is of vital importance. The thermal-hydraulic shock accident which happened in Bushehr nuclear power plant deaerator has been simulated in this study. Steam bubble collapsing which takes place in two phase medium by mixing steam and subcooled water leads to this kind of shock causing financial and physical irreparable damage in nuclear power plants. For carrying out this simulation, first an steady state model of the deaerator was run using RELAP5 code and then using this model and other plant’s data such as the ropert of the accident and plant’s Final Safety Analysis Report... 

Results of an advanced suction controlled triaxial test device in an attempt to define the constitutive relationship between suction stress and matric suction (Suction Stress Characteristic Curve, SSCC) for unsaturated sand was presented. The suction stress is a macroscopic stress that incorporates the effects of capillary van der Waals forces cementation, and electrical double-layer repulsion into the definition of effective stress for unsaturated soils. Results of previous studies on silt and clay indicated that variations in the suction stress, during drying path had a non-linear increasing trend with matric suction with greater values upon wetting. However, due to different material... 

One of the most important parameters in dynamic analysis is small-strain shear modulus of soils (Gmax). Additionally, due to the seasonal variations and traffic loading, determination of constraint modulus (M) of subragde soils is of great importance. Seasonal Variations such as evaporation, evapotranspiration and precipitation causes subgrade soils to be on unsaturated state. Therefore, there is an extending need to study the influence of matric suction and degree of saturation on maximum shear modulus and constraint modulus in the design and analysis of earthen structures.In this study, we employed a dynamic simple shear apparatus in order to fully understand variations of Gmax and M with... 

The main concept of this thesis is to simulate, develop, and analyze the performance of force control method by applying to a Unimate MK-II hydraulic manipulator. In this investigation, simulation studies are based on the concept of impedance control technique. Position-based formulation of impedance control is employed. First in this research, a PID controller is employed and is shown to be capable of performing position control task precisely despite the fact that inertia, joint stiction, valve deadband and other nonlinearities are presented. Although trajectory tracking is performed well after several investigations, we have concluded that the impedance control cannot perform a desirable... 

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... 

Evaluation of the seismic-induced settlement of an unsaturated soil layer depends on several variables, among which the small strain shear modulus, Gmax, and soil’s state of stress have been demonstrated to be of particular significance. Recent interpretation of trends in Gmax revealed considerable effects of the degree of saturation and hydraulic hysteresis on the shear stiffness of soils in unsaturated states. Accordingly, the soil layer is expected to experience different settlement behaviors depending on the soil saturation and seasonal weathering conditions. In this study, a semi-empirical formulation was adapted to extend an existing Gmax model to infer hysteretic effects along... 

Given the broad role of oil and gas playing in the world economy, finding the hydrocarbon reservoir that economically is affordable is quite significant. Some of the unconventional oil and gas reservoirs are important from the economic point of view since they produce insufficient hydrocarbon due to either low permeability or damage during drilling and production. Hydraulic fracturing is one of the most significant methods for improving the productivity of wells and reservoirs. Hydraulic fracturing acts by affecting on reservoir rock physic. In the current century, this approach has an essential effect in enhancing the permeability and production of reservoirs by creating, extending and... 

The exploitation of oil and gas were changed dramatically with the advent of hydraulic fracturing. By using enhanced oil recovery methods in unconventional reservoirs, USA could raise the rate of production in comparison with the rate of consumption. Hydraulic fracturing is one of the enhanced oil recovery methods.The purpose of this research is the study of the effects of geomechanical parameters in the characteristics of the cracks induced by hydraulic fracturing in unconventional oil reservoirs. The minimum in-situ stress and tensile stress of rock can be overcome by injecting fluid and thus the rock will be cracked. Changes in geomechanical parameters such as modulus of elasticity,... 

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... 

The core behaviour of a nuclear reactor might be fluctuated (deviations from the normal operating conditions) in operating conditions due to various reasons. Control rod vibrations and the alterations of coolant temperature and velocity could be the main reasons for the fluctuations. These fluctuations lead to neutronic flux noise and subsequently power noise. The main objective of the current thesis was to study the thermal-hydraulic noise of the PWRs in two-phase with the emphasis on VVER-1000, which is similar to the Bushehr-1 nuclear reactor. By considering the possibility of existing two-phase flow (maximum allowable quality is about 14%) in hot channel of the PWRs, thermal-hydraulic... 

Many natural and engineering materials have a heterogeneous structure at a certain level of observation. These materials are often referred to as composite materials or multi-phase materials or heterogeneous materials. It has been widely recognized that many macroscopic phenomena originate from the mechanics of the microstructural constituents, such as inclusions, cracks, voids, etc. The size, shape, spatial distribution, volume fraction and properties of the microstructural constituents have a significant impact on the behavior of the material observed at the macroscale. The nature of hydrocarbon reservoirs as multi-phase porous media are known for heterogeneous media at various multiple...