Sharif Digital Repository

The phenomenon of lateral spreading occurs as a consequence of earthquakes induced liquefaction in grounds with mild slopes or ending to an opening. This phenomenon has caused many damages to deep foundations and associated structures. Therefore, it is necessary to study and estimate the forces which may be induced by lateral spreading to these structures. Due to the complex mechanism of the effect of lateral spreading on the piles, various tests have been carried out in the form of shaking table as well as centrifuge tests. According to the results of these tests, the forces applied to the piles are significant and can cause crucial damages to deep foundations. On the other hand, because... 

Lateral spreading is defined as finite lateral displacement of mildly sloping grounds or those ending in free faces induced by liquefaction. Severe damages of pile groups due to lateral spreading in past earthquakes has been reported. Since earthquake is unavoidable, it is necessary to study the response of piles, especially pile groups, to liquefaction induced lateral spreading. Until now, a number of methods have been developed by researchers for design of deep foundations against lateral spreading, but reported failure of piles in last earthquakes indicates that these methods are associated with high uncertainties. This is due to the lack of laboratory and experimental data to evaluate... 

Natural gas liquefaction is a gas refrigeration technology, which enables the export of natural gas worldwide, in liquids formed and stored at very low temperatures. In this project, a plate-fin type of heat exchanger, which is used for liquefaction of natural gas (mainly methane) at very low temperatures, has been investigated. The most important and effective part of this gas refrigeration cycle is the cold box heat exchanger. The cold box consists of two or more floors in which some sorts of fins are installed in each floor. In this simulation, the three-sream heat exchanger is designed in such a way that the input temperature of the natural gas is about 200 K and the output is 145 K at a... 

Natural gas liquefaction is an enabling technology which could make natural gas resources globally accessible. Nonetheless, the design and operation of LNG processes is highly complex, and is subject to multiple criteria including energetic, environmental and safety performance. Moreover, such processes must be flexible enough to operate under different feed conditions. The present research applies integrated process and product design framework to enhance simultaneously energy efficiency, environmental benignness, and inherent safety of a small-scale LNG process. The challenge is that the current group contribution methods applied for the estimation of the thermophysical properties, suffer... 

Cryogenic is the study of physical phenomena at temperatures below 123 Kelvin. One of the applications of cryogenic science is the liquefaction of gases. In the liquefaction cycles of gases, such as helium liquefaction, fluidization occurs in the pressure reducing valve but temperature of the gas should be greatly reduced before it enters the pressure reducing valve. For this purpose, high-performance heat exchangers should be used. Spiral Wound is one of the heat exchangers that has ability to achieve over 90% efficiency due to its structure. Researchs in the field of design and simulation of spiral heat exchangers are limited and are done with a lot of simple assumptions such as constant... 

A numerical framework is proposed to estimate the liquefaction-induced settlement of the fully saturated sandy layers in the free fields due to earthquake excitation and the results of the proposed method are compared with those of the empirical or probabilistic methods suggested by the previous researchers. Liquefaction is a sudden transformation of saturated sandy soil into a viscous fluid which is caused by the increase in the pore pressure and decrease in the effective stress and results in the reduction of the shear strength of the soil. One of the most important consequences of liquefaction is the liquefaction induced settlement which has caused severe damages in many places in the... 

Gas liquefaction is one of the main applications of Cryogenics science. Due to the unique properties of Helium, it is a strategic product in the world. Therefore, appropriate and applicable analysis should be used to investigate and optimize the Helium liquefaction cycles. In the current study, the goal is to find the optimal point with the help of energy and exergy analysis based on economic criterion, for the various parameters of Collins’ cycle. In order to simulate the cycle, a computer code is developed. First, sensitivity analysis of different parameters affecting the exergy efficiency and liquid fraction of the cycle has been done. Then, Artificial Neural Network and Genetic Algorithm... 

Liquefaction of gases is one of the applications of cryogenic science. Among the gases, Helium has the lowest boiling point, which at a pressure of 1atm is approximately 4.2K. Liquid helium can be used to cool superconductors in transportation equipment, military radars, and medical imaging equipment. For helium liquefaction, various cycles are used; these cycles have different parameters in their structure such as of input mass fraction to expanders, heat exchanger effectiveness, expander arrangement and ... which their analysis for improving the performance of the cycle is important. In this research, the aim is to study 2, 3 and 4 expander cycle with various parameters and structure. For... 

Heat exchangers are one of the most important components used in liquefaction cycles and overall efficiency of the cycle mainly depends on the heat exchangers effectiveness. It has been shown that the effectiveness of these equipments should be high enough to be able to liquefy a gas. Spiral heat exchangers are used frequently in cryogenic industry and specially in Helium liquefaction industry due to their specific characteristics, however according to literature review it turns out that little study is done in the field of simulation and geometrical parameter investigation of these kind of heat exchangers, so in this study the design and simulation of these cryogenics heat exchangers are... 

Soil liquefaction occurring in loose saturated sand deposits during seismic loadings is one of the most destructive earthquake-induced phenomena in the field of earthquake geotechnical engineering. Catastrophic destructions due to this phenomenon that have been observed in the earthquakes such as Kobe (1995), Chi-Chi (1999), etc. has led to extensive studies in this field. In case of soil slopes prone to liquefaction hazard, detailed analysis of this phenomenon requires considering soil-related factors (e.g. shear strength, relative density, permeability, slope geometry) on the one hand, and earthquake-related characteristics (e.g. amplitude, frequency, duration) on the other. Numerical... 

In recent earthquakes piles have been severely damaged due to liquefaction-induced lateral spreading. Liquefaction causes lateral spreading in gently sloped saturated soft granular soils, leading to significant damage in structures and deep foundations. Although in recent years many studies have focused on different aspects of this phenomenon, the complex nature of the dynamic interaction between piles and liquefied soil is not yet fully understood. This potential damages are of high degree of importance in southern and northern coastal areas of Iran where several ports and critical facilities are located. The present study focuses on the behavior of a 2x2 pile group against lateral loads... 

Softening and liquefaction of granular soils due to earthquakes have been a major cause for much destruction in preceding decades. This phenomenon mostly occurs in sandy soils, yet its occurrence has also been reported in gravelly soils in the last three decades. Despite the numerous researches which have investigated the undrained cyclic behavior of gravelly soils during earthquakes, there are still some aspects that need further study.This research investigates the effect of initial static shear stress on undrained cyclic resistance of a well graded, medium dense gravelly soil by conducting a series of cyclic triaxial tests. The 23 performed tests are categorized into 5 groups with... 

Liquefaction is an important phenomenon in geotechnical engineering which can cause severe damages to structures. Liquefaction-induced lateral spreading is defined as the lateral displacement in mild slopes or level grounds ending in free faces (such as quay walls) triggered by liquefaction in subsurface soil layers. During recent years, extensive studies have been conducted around the world documenting liquefaction induced lateral spreading and its effects on deep foundations. In the present study, a series of shaking table experiments which were previously conducted at Sharif University of Technology are numerically simulated using the three dimensional finite difference based program,... 

Gas liquefication in low temperatures is one of the most challenging fields in engineering due to complexity of its thermodynamic analisys and fabrication of equipments. Heat Exchangers are one of the most important equipments in these prosseces. High prices of Heat Exchangers in these facilities makes their Optimal and cost effective design, of crucial importance. In this thesis three dimensional model of a Plate Fin Heat Exchanger is thoroughly investigated. Fistly, by means of Aspen Heat Exchanger design Software a counter flow Heat Exchanger is designed. This HX is to be placed in Collins cycle, so, working fluid in both hot and cold streams is Helium Gas. The HX then by means of ANSYS... 

One of the main geotechnical phenomena that causes severe damage during earthquake is liquefaction. This incident occurs due to the undrained behavior of loose sandy soils. In this occurrence, the interaction between the solid and liquid phases in a cyclic motion leads to an increase in pore water pressure and a decrease in interactive forces (effective forces) between grains in the solid grains. Therefore, shear strength decreases. Different aspects of the aforementioned phenomenon is investigated, namely, field, laboratory, and numerical; nevertheless, the study is largely focused on the numerical modelling. Most studies in this field are carried out on a one-layer saturated sand. However,... 

Study on gravelly soils is one of the topics that Geotechnical Engineering researches have been concentrated on. Although several researches have enlightened the way to understand the behavior of gravelly soils, yet, there are some shortage of information about the dynamic behavior of this kind of soil in undrained condition. In this research, a series of cyclic triaxial tests have been performed using cyclic triaxial apparatus of Advanced Soil Mechanics Laboratory of Sharif University of Technology to study the effect of anisotropic consolidation (initial static shear stress) on dynamic behavior of a kind of gravel. The performed tests were divided into four groups with different initial... 

Liquefaction-induced lateral spreading has imposed severe damages to many important structures supported on pile foundations during past earthquakes. As a result, evaluation of pile response to lateral spreading is an important step towards safe and resistant design of pile foundations against this destructive phenomenon. The boundary conditions for physical modeling in problems of earthquake geotechnical engineering have significant influence on the test results. In order to reduce the undesirable effects of boundaries on the model responses, the flexible containers are used. The flexible containers are those in which the shear stiffness of the walls is proportional to the soil inside. A... 

Using appropriate box as an artificial boundary condition is one of the critical tasks in geotechnical physical modeling of the soil mass especially under cyclic loading such as earthquakes. In general there are two types of boxes which can simulate boundary conditions of scaled models as rigid or flexible conditions. Main purpose of this study is design and construction of a flexible box in a way that effects of boundary condition have been minimized during tests. Construction of this box is the first step of an investigation project which concern to evaluate the effect of lateral spreading as a result of liquefaction on deep foundations of bridges, piers, harbors by using shake table test... 

Lateral spreading due to liquefaction and resulting destruction of buildings is important in Iran because of high seismicity and important infrastructure near south and north coasts of Iran. Lateral spreading is vast lateral movement of sloping ground or level ground ending in an opening like river which is caused by earthquake inducedliquefaction. For considering the effects of lateral spreading during design of deep foundations of structures in a susceptible area, one needs to determine the lateral loads on piles under lateral spreading. Present study investigates the behavior of a 3x3 pile group against lateral loads due to lateral spreading with numerical methods using OpenSees software.... 

Settlement and tilt of structures due to liquefaction of subsoil layers is a major cause of damage during earthquake. Among different soil profile type, two layered soil is very common which was reported many times in differen earthquakes. Settlement of structures was measured by means of empirical methods before which were not viable because they do not consider different effective parameters. Consequently, different experimental studies performed to shed light on different aspects of liquefaction phenomena. In these studies, researchers consider some of the main parameters which have effect on the soil, otherwise, they neglected some important factors. So, numerical procedure is more...