Sharif Digital Repository

Thermopneumatic micropump is one type of positive displacement micropumps, which has many applications due to its relatively large stroke volume, low working voltage, and simple fabrication in microscale. In this paper, a numerical study of heat transfer and fluid flow in a valveless thermopneumatically driven micropump is presented. For rectifying the bidirectional flow, a nozzle and a diffuser are used as the inlet and outlet of the chamber. Since the fluid flow is induced by the motion of a diaphragm, the numerical simulation includes fluid structure interaction, which requires applying a dynamic mesh. The domain of solution is divided into two sections; the actuator unit, which contains... 

One of the problems associated with lean premixed combustion is their stability. Low swirl flame is a modern technology for reducing NOx emissions and increasing stability.In this thesis, first, the effect of geometric parameters on the flame stability was investigated. This study was carried out in high fuel and oxidizer mixture flow rate. Having find, the most stable burner, two other burners with the same geometrical parameters were built. Stability of these three burners were analyzed. Second, they were located in a ring together in three different relative positions. In each configuration stability and NOx emissions of the burners were determined.The study shows that NOx and CO... 

Unique properties of Gold at nanoscale have made it one of the most popular substances used in nanotechnology. The interaction of Gold and Thiolates is one of the most favorite fields of research. Extensive studies about this interaction have revealed the importance and usage of this system in future technology. Due to difficulties of experimentationat nanoscale, computer simulations arevery important. Although interatomic potentials lead to higher computational speeds, they have deficiencies in precise simulation of some phenomena. Ab-initio methods, such as density functional theory, provide powerful tools to increase the accuracy. In this research, the interaction of gold and thiolates... 

Special geometrical sections, known as “duct”, which can be installed on merchant vessels stern in order to improve propulsion system and propeller performance, today have evolved considerably. The force which produces by the propeller depends on efficiency of propulsion system. In the way of improving the efficiency of propulsion systems, by using these special geometrical sections, to much research have been done from the mid-twentieth century. The Wake Equalizing Ducts (WEDs) in addition to conduct the more uniform fluid flow to the propeller disk (which causes to improve the propeller operation), affect on flow separation in ship stern zone and will decrease the separated flow zone.... 

In this project, we examine the stability or sustainability issue in unions, in other words we want to know whether integration in European Union is stable? Countries have positive attitude toward unions and being member in unions is at special priorities. The main reason for countires is improve economy and national Security.
The main question in this research is modeling European Union with Axiomatic Design Theory and analysis of sustainability based on this theory. This study has attempted to push Axiomatic Design Theroy in the new field of Systems Engineering and also it gives a new and differnet approach to stability.
 

In recent years, introduction of new technologies has highlighted the need to more data rate in mobile networks. Classical methods of resource allocation in mobile networks cannot respond to this huge demand for data rate because of their limitations. Resource allocation, as one of the operators’ tasks, plays a key role in the network efficiency and users’ data rate. Opportunistic resource allocation and scheduling have gained attention in recent years. On the other, using single-channel (frequency reuse-1) networks is also one of the methods to improve data rate in mobile networks. It is expected that the use of opportunistic scheduling in single-channel networks can repond to the huge... 

In this thesis, employing the definition of an effective configuration in the Continuum Damage-Healing Mechanics (CDHM), mechanical responses of elf-healing materials are investigated. Firstly, a constitutive model is proposed to investigate damage and healing phenomena in concrete materials. In order to consider the different behavior of concretes in tension and compression, a spectral decomposition of the stress is utilized. In addition, employing the Clausius-Duhem inequality and considering the irreversible thermodynamics, conjugate forces of the damage and healing are expressed. The Gibbs potential energy is decomposed into three parts; elastic, damage and healing. In the next section,... 

In this paper, we introduce a new dataset for SAD and evaluate certain common methods such as GMM, ANN, and RNN on it. We have collected our dataset in a semi-supervised approach, using subtitled movies, with a labeling accuracy of 95%. This semi-automatic method can help us collect huge amounts of labeled audio data with very high diversity in language, speaker, and channel. We model the problem of SAD as a classification task to two classes of speech and non-speech. When using GMM for this problem, we use two separate mixtures to model speech and non-speech. In the case of neural networks, we use a softmax layer at the end of the network, with two neurons which represent speech and... 

The gas-liquid interaction is one of the most important and common phenomenons in chemical, biochemical and mineral industries which is generally observed as liquid in a gas stream (droplet) or gas in a liquid stream (bubble). Although bubbles produced in the industrial applications are in the form of a group of bubbles, understanding the hydrodynamics of a single bubble in a quiescent liquid provides a starting point for studying bubble groups. It should be noted that changes in the velocity and drag coefficient of the bubbles in various fluids are essential parameters for designing gas-liquid systems. In the present research, in order to examine the effect of system parameters and... 

When the fluid passes through the microchannel, some energy is lost due to drag force and pressure drop. One of the methods used in the last few decades to optimize energy consumption is creating superhydrophobic surfaces in microchannels. These surfaces, with their features such as increasing the contact angle and reducing the contact angle hysteresis, can reduce energy loss, which is due to the presence of unevenness on the surface, and by trapping air and creating a two-phase flow, they reduce the drag force. On the other hand, the air trapped inside these irregularities will also affect the heat transfer of the passing fluid in the microchannel, which by creating resistance in the... 

Lean premixed combustion is highly susceptible to thermoacoustic instabilities. Such instabilities are compounded in low swirl flames by the fact that low swirl flames are stabilized aerodynamically at a relatively considerable distance downstream of the burner rim, such stabilization mechanism makes the flame more prone to both vertical and acoustic perturbations. The main objective of the present thesis is to evaluate effects of acoustic and hydrodynamic perturbations on low swirl flame features. To such aim, first, low swirl flame characteristics and stabilization mechanism are studied using large eddy simulations along with thickened flame combustion model. The obtained results show that... 

An environmentally friendly heterogeneous ternary carbon dots (CDs)/MIL-88B (Fe)/Bi2S3 nanocomposite was synthesized by a multistep method. In this study, we have studied low-temperature calcination with relatively inexpensive reactants. Fabricated nanocomposite structures were characterized by FT-IR, XRD, EIS, SEM, BET, and TGA techniques, demonstrating the decoration of the Bi2S3 on the CDs/MIL-88B (Fe) nanocomposite surface. MOF templating has been chosen as a systemic method for limited size CD formation inside MIL-88B (Fe) pores. The CD arrays also revealed an excellent efficacy for catalytic and photocatalytic applications. According to the experimental results, CDs/MIL-88B (Fe)/Bi2S3... 

Thermal piles represent a novel technology in engineering for harnessing clean, cost-effective, and renewable surface geothermal energy. Due to their composite nature, they have a lower initial construction cost compared to other similar systems. However, their dual thermal-mechanical performance presents challenges in analyzing their interaction behavior and designing them safely and efficiently, necessitating further research and studies.The main objective of this research is to investigate the thermo-hydro-mechanical behavior of single geothermal energy piles (GEPs) in unsaturated soils. By physically modeling these systems under gravitational acceleration conditions (g1), this study aims... 

In this study, the transient liquid phase bonding of the nickel-based superalloy GTD-111 was investigated using a 75 μm thick MBF-30 interlayer. Bonding was carried out at 1150 °C for durations of 10, 60, 240, and 480 minutes, and the relationship between microstructural evolution and solidification behavior at the joint region was examined as a function of bonding time. Results indicated that, with increasing bonding time, the eutectic structure composed of γ and Ni₃B phases formed at the joint center gradually diminished, and complete isothermal solidification was achieved at 480 minutes. As bonding time increased and isothermal solidification occurred, the maximum hardness—over 1000... 

The purpose of this study is to estimate the temperature distribution of the internal body organs using electromagnetic waves. When the external electromagnetic field propagates in biological tissues under a process like microwave hyperthermia, the temperature of the tissue at the field concentration area increases. Due to temperature and frequency dependence of the tissue dielectric, the tissue permittivity changes; thus, the electric field scattered by the tissue changes. Therefore, by measuring the field scattered from the object, dielectric changes of the tissue structure can be calculated. Since the biological tissues’ dielectric coefficient at frequencies lower than 2GHz is linear,...