Sharif Digital Repository

Pipe freezing has become well established in industry as a method of short-termisolation in order to carry out maintenance or repairs. It is often necessary to repair system components without plant shutdown or drainage of system having many piping structures which may have hazardous or expensive fluid. Therefore, a series of tests has been arranged to investigate the ice plug formation in two standard pipes with different diameter size. The freeze zone on the pipe has been created by means of an aluminum jacket which liquid nitrogen flows in it. In the tests the freezing time, amount of liquid nitrogen usage andthe pressure tolerance of ice plug have been determined. Moreover, the numerical... 

In modern era, standpoints about atrium design have been revolutionized. In modern architecture, atrium not only designed for illuminating purposes but also designed by natural ventilation and passive cooling policies. Numerous parameters are making role in thermal efficiency of Atrium. A couple of these parameters are Atrium shape and openings area. In high rise atria the lower level rooms enjoy the advantage of buoyancy-driven ventilation while the upper level rooms suffer from its lack or weak presence. One strategy to solve this problem is designing building with various opening area in different heights but manipulating the opening size is restricted by some facts. Excessive Opening’s... 

Subfloor heating and cooling systems in residential and commercial buildings present advantages from the point of view of comfort conditions and energy saving. In the present work a two dimensional and a three dimensional model for subfloor heating and a two dimensional model for subfloor cooling, using the Fluent software based on the finite volume method were developed. From the point of view of exergy destruction as we may have lower temperature difference between the heating medium and space, we come up with less exergy destruction. To determinate the optimum working conditions of these systems, a numerical model for subfloor heating and cooling is presented. Different methods of... 

Cleanrooms have a broad scope of applications from electronics, pharmacy, biotechnology to hospital industries, and are susceptible to fine and ultra-fine particles. In this work operating room in the category of hospital applications is chosen. Airborne particles in the operating room depends on many factors such as room geometry, inlet and outlet design, air displacement rate, obstacles, etc. Surgical light is one of the most critical obstacles in the operating room as it is upstream to the surgery zone. The study presented in this thesis aimed to numerically investigate the influence of radiation emitted from the medical lamps on the indoor airflow quality in operating room environment.... 

The structural behavior of deep beams is different with usual beams as a result of the low span-to-height ratio. Shear failure load is less for deep beams. Implementation of externally bonded reinforcement such as fiber reinforced polymers (FRP) is a unique method for shear strengthening of deep beams. In this study, the effects of FRP layers on the web of the reinforced concrete deep beam have been investigated by a nonlinear finite element program. Five beams four of which were strengthened with FRP laminates were numerically modeled and the results were compared with experimental results. The effect of some governing parameters such as compressive strength of concrete, orientation of... 

In this thesis the performance of anew energy dissipative device, slit steel damper (SSD) is investigated. The slit steel damper is manufactured with I-shaped, wide flange H-shaped profiles with a number of slits cut from the web. The device is installed between beam and chevron brace and fastened by four bolts on each side, which enables the replacement of the device due to strong earthquake.A numerical study is conducted to studythe nonlinear behavior of the SSD systems by using a nonlinear FE program. It is found that the numerical modeling results have a good agreement with the existing test results.In the next step a parametric study is performed to study the effects of the number of... 

The present research illustrate the finite element modeling of contact between solid bodies, with a special emphasis on the imposing the contact constraints and modification of contact properties on surface in the case of frictional slip. A new approach for both two-dimensional and three-dimensional formulation of contact constraint that allows for a simple and unified treatment of all potential contact scenarios in the presence of large deformations in static case, is presented. The most important outstanding issue in this approach is symmetrical contact stiffness matrix which reduces computational efforts. Based on the observation of numerical results and comparison by experimental models,... 

Bubble collapse is a two-phase problem whose numerical simulation has many important applications in science and technology. In hydrodynamics systems (pumps, ship propellers, …), bubbles form due to cavitation. These bubbles grow and collapse These bubbles grow and collapse farther downstream and their energy destroys the surrounding walls. In medical sciences, the shear force caused by collapse of a bubble can be used to destroy adipose tissues in arteries. The small scales time in this phenomenon, as well as the compressibility of the flow in bubble collapse, are interesting challenges researchers face. The present thesis targets are two-dimensional numerical simulation of bubble collapse... 

In the current study, first, the presence history of dielectric barrier discharge (DBD) plasma actuator in flow control usages has been investigated. After recognizing the importance of plasma actuator in this branch of engineering, this active controller was modeled relying on computational fluid dynamics (CFD) knowledge to control flow separation. In order to model this actuator, physics based model called spilt-potential model and modifications done to improve it, were used. Using this model and solving two elliptic equations, electrical field and plasma charge density distribution are obtained in range of solution domain and body force from plasma actuator modeling in all computational... 

Radiation evaluation in non-gray gaseous media is a very complicated issue. Previous researches have shown that the radiation properties of non-gray gases would strongly depend on the wavelengths. The gray gas assumption is the simplest model to calculate the radiation properties. Dispite simplicity, it is widely used in various industrial applications. In this model the gas radiation properties are assumed no to chang across all wavelengths. Evidently this would results in an inaccurate radiation modeling. Using the Spectral Line-based Weighted-sum-of-gray-gases model, SLW, the spectral behavior of radiation properties of gas is almost taken into account in computations. So the use of this... 

Here we have used CFD to simulate the flow field around a DBD plasma active controller for flow control. Enhanced Electrostatic model is applied to model the plasma actuator, by solution of two elliptic equations to find electric field and charge density in whole flow field. So, it provided the body force by neglecting the magnetic forces in Lorentz equation. The body force is added to the momentum equation as a source term. A commercial software FLUENT is used for this simulation. To validate the algorithm, flow over a flat plate using DBD actuator is solved and results are compared with experimental and numerical results. Flow control around a cylinder with Reynolds number of 18,000 is... 

Troposphere layer includes complex flows which their effects in acoustic sensors are indicated as acoustic wave noise.It is essential to analyze these complex flows to recognize how to reduce the noise. In this thesis we have perused and modeled the sound wave propagation in troposphere layer.Given data are some thermal and velocity profiles of atmospheric flowsthe assumptions are: 1- gravity waves are negligible, 2- air density depends only on altitude, 3- sound waves parabolic equation assumptions are applied. Our goal Is to find the sound pressure level originated from a sound source in troposphere layer.This thesis emphasizes on analysis, recognition and modeling of the problem. Main... 

Flameless combustion in combustion technology is an innovative method with low nox production that few years provided it passes. In this paper the effects of various parameters on flameless combustion chamber with separate fuel and air jets, has been modeled numerically with the help of Fluent 6.3 software. Differences between traditional combustion and flameless combustion were determined and the flame structure has been studied in different scenarios. In numerical modeling, approach were used to modeling turbulence and eddy dissipation concept (EDC) approach use to modeling combustion and turbulence interaction effects. A global Two-step reaction mechanism for propane and a global... 

A global rotating atmosphere with polar vortex and super rotation is simulated using a simplified Venus General Circulation Model (GCM). The polar vortex is maintained strongly by meridional circulation develops in the form of a simple Hadley cell, extending from the equator to the pole in both hemispheres and rotation terrestrial planet. Venus Total Polar Vortex Parameter (PVP) was defined like globally integrated super-rotation but at polar skullcaps (60-90 deg). Venus Polar Vortex Parameter is PVP=1.5 that’s qualitatively similar to observed polar vortex. Then with study in terrestrial planet and Titan modeling, we appointed the Polar Vortex Parameter and critical limit of Polar Vortex... 

Here, we have simulated isothermal vacuum assisted resin transfer moulding (VARTM) using a control volume/finite element scheme. Two dimensional and dimensional (shell geometries) spatial discretization is used. Resin motion through fibers is enforced by vacuum negative pressure in downstream. The governing equations are mass conservation and well known Darcy equation. Using an unstructured triangular grid, complex geometries could be modelled. Application of a quasi-steady algorithm results in a system of linear equation for pressure distribution. This system must be solved in each time step. The point successive over-relaxation (PSOR) scheme is used to solve the system of linear... 

Coastal groundwater aquifers are among the prime resources for providing fresh water for coastal cities that are in danger of intensified seawater intrusion due to climate change and excessive pumping. These coastal aquifers extensively exist in different cities around the world, for example, in the south and north of Iran, and due to their complex inherent, they have yet to receive enough attention among scholars. The prime objective of this research is to simulate seawater intrusion by considering preferential path flows using COMSOL Multiphysics. Based on numerical approaches merits, this study aims to simulate seawater intrusion in karst aquifers. It explores the effects of conduits'... 

This study aims to numerical modeling of piezocone penetration test (CPTu) in saturated clayey soils under undrained conditions using FLAC-2D software. According to the available studies, measuring excess pore water pressure during the piezocone penetration test can play an important role in determining the characteristics and engineering parameters of clayey soils. In many geotechnical problems, the initial state of existing stresses in the ground and are an important parameter that must be known for designs and analysis. The relationship between vertical and horizontal effective stress under zero lateral deformation is usually expressed by the coefficient of lateral earth pressure at... 

Shallow geothermal energy is a renewable and sustainable form of energy that has the potential to help alleviate the growing climate and energy crisis. The most common system used to extract shallow geothermal energy is the ground source heat pump (GSHP) system. The concept of using underground structures in exploiting shallow geothermal energy for space heating and cooling has received increasing attention. This study focuses on the use of geothermal tunnels as a means of extracting shallow geothermal energy.This research examines the effects of different heat transfer mechanisms, and highlights the effects of this phenomenon by focusing on the effects of natural convection around the... 

Ordinary structures absorb a large amount of input energy by structural elements whereas failure in these elements causes a huge loss in structure and it’s really difficult to repair or unrepairable. Nowadays a wide range of metallic dampers is used in structures as fuse elements. this research evaluates the response of structures that are equipped with a novel steel damper named Telescopic Lead Yield Damper (TLYD) which was introduced by Eskandari in 2018. As TLYD has a different yielding plateau it can tolerate large deformations. In this research firstly this novel damper was introduced and the performance of the damper under cyclic loading was demonstrated. Then a numerical model of 6,... 

Landslide is a natural hazard associated with economic losses and fatalities. The geometric of the slope, the soil properties, hydrological factors, and groundwater are important factors that affect the stability of a slope. The landslide investigation is important due to the identification and prevention of damages. Thus, more researchers studies on this subject. The new questions in this field are “how can simulate the vegetation effects in slope stability analysis?” and “what effects do precipitation and infiltration have on landslide triggering?”. Although the classic methods of slope stability analysis provide the initial information for the design, they have limitations in answering...