Stability of Intershaft Squeeze Film Dampers

Intershaft squeeze film dampers were investigated for damping of dual rotor aircraft jet engines. It was thought that the intershaft damper would enhance the stability of the rotor-bearing system. Unfortunately, it was determined that the intershaft squeeze film damper was unstable above the engine's first critical speed. Here, a stability analysis of rotors incorporating intershaft squeeze film dampers is discussed. A rotor model consisting of two Jeffcott rotors with two intershaft squeeze film dampers was investigated. Examining the system characteristic equation for the conditions at which the roots indicate an ever-growing unstable motion results in the stability conditions. The cause of the instability is identified as the rotation of the oil in the damper clearance. Several proposed configurations of intershaft squeeze film dampers are discussed, and it is shown that the intershaft dampers are stable supercritically only with a configuration in which the oil film does not rotate

High Power, Medium Frequency, and Medium Voltage Transformer Design and Implementation

Many industrial applications that require high-power and high-voltage DC-DC conversion are emerging. Space-borne and off-shore wind farms, fleet fast electric vehicle charging stations, large data centers, and smart distribution systems are among the applications. Solid State Transformer (SST) is a promising concept for addressing these emerging applications. It replaces the traditional Low Frequency Transformer (LFT) while offering many advanced features such as VAR compensation, voltage regulation, fault isolation, and DC connectivity. Many technical challenges related to high voltage stress, efficiency, reliability, protection, and insulation must be addressed before the technology is ready for commercial deployment. Among the major challenges in the construction of SSTs are the strategies for connecting to Medium Voltage (MV) level. This issue has primarily been addressed by synthesizing multicellular SST concepts based on modules rated for a fraction of the total MV side voltage and connecting these modules in series at the input side. Silicon Carbide (SiC) semiconductor development enables the fabrication of power semiconductor devices with high blocking voltage capabilities while achieving superior switching and conduction performances. When compared to modular lower voltage converters, these higher voltage semiconductors enable the construction of single-cell SSTs by avoiding the series connection of several modules, resulting in simple, reliable, lighter mass, more power dense, higher efficiency, and cost effective converter structures. This dissertation proposes a solution to this major issue. The proposed work focuses on the development of a dual active bridge with high power, medium voltage, and medium frequency control. This architecture addresses the shortcomings of existing modular systems by providing a more power dense, cost-effective, and efficient solution. For the first time, this topology is investigated on a 700kW system connected to a 13kVdc input to generate 7.2kVdc at the output. The use of 10kV SiC modules and gate drivers in an active neutral point clamped to two level dual active bridge converter is investigated. A special emphasis will be placed on a comprehensive transformer design that employs a multi-physics approach that addresses all magnetic, electrical, insulation, and thermal aspects. The transformer is designed and tested to ensure the system’s viability

The pendulum of development: From the end of history to make poverty history

Poverty has been a central focus of development since the 1960s. Despite a marked decrease in poverty worldwide, the incidence of poverty remains high; where one in ten people live under the international poverty line of $1.90 a day. In light of the persistence of poverty, international efforts to “make poverty history” have been pursued. Neoliberalism is an economic policy characterized by state retrenchment, free trade, market liberalization, deregulation, privatization, commercialized social programs, and foreign investment. Since its triumph over communism, neoliberalism marked “the end of history.” This thesis examines poverty reduction and neoliberalism in the context of international development in order to illustrate how poverty is perpetuated through international policies of inclusive neoliberalism. Much like a pendulum, international development has oscillated between efforts to reduce poverty to the advancement of neoliberalism. The primary concern of this thesis is how poverty is sustained through international poverty reduction strategies that implicitly employ the tenets of neoliberalism in the pursuit of development. More specifically, this thesis illustrates the tension that is created when the logic of neoliberalism collides with the logic of inclusion as contained in poverty reduction strategies. There is a paradox whereby poverty reduction strategies deployed by international development institutions work against their purported aims when implicitly employing the tenets of neoliberalism. This thesis employs a Gramscian and Neo-Gramscian framework whereby the poor can be examined simultaneously alongside the overarching neoliberal hegemony that is complicit in their abject poverty. Assessing inclusive neoliberalism through a Gramscian framework offers a gateway to analyzing the determinants of existing structural global imbalances that sustain poverty. The thesis is argued through case studies of microfinance and conditional cash transfers internationally followed by a consideration of their application in Egypt. This thesis argues that, as tools of inclusive neoliberalism, these two initiatives undertaken to reduce poverty have instead reinvented ways to integrate the poor into the world market

Study of Qattara depression and its hydropower potential

The Qattara Depression is a very interesting geomorphic feature that has been suggested to be used for hydropower production. This research will investigate hydrological elements affecting the water balance of the Qattara Depression region. Climatic data obtained from weather stations surrounding the region will be used in the investigation, as climatic factors such as rain and water evaporation would affect the mass balance equation. Then environmental and economic implications of such a project will also be studied. Many schemes have been suggested in the past for the project. All these schemes are compared economically in this work for the first time as far as the author knows. And the model employed investigates elements that had not been previously investigated. The outward seepage calculation and its affect on the plant lifetime is included in the model and the economic study and also its environmental impacts are checked. The effect of the channel flow of water before reaching the lowest point of the depression as it was not previously included in the evaporation calculation, but it is investigated in this model. Also a detailed study of the effect of the salinity increase of the water in the depression is investigated. The way all this enabled is by using data from three weather stations near Qattara Depression (Siwa, Dabaa, Wadi El Natroon) and the data is used on a monthly bases to calculate the evaporation that would occur as it would be used in the mass balance equation that includes the evaporation, that is affected by the progressive salinity increase, the inward and outward seepage, the rainfall, and the inflow from the sea. Using that calculation the progressive increase in the surface level in the depression is always obtained and the best design and economic study is planned accordingly

A Study of Flooded and Rain Infiltration Relations With Surface Ponding

The non-linear partial differential equation (combination of Darcy\u27s law and continuity equation) has been used in this investigation to predict the flooded infiltration through soils possessing appreciable amount of clay and initially drier than its field capacity. One of the most important assumptions made in solving the differential equation is that the capillary conductivity-moisture content relationship is unique for each initial moisture content computation due to the different reaction of clay minerals with different initial moisture contents. Mathematical equations were also derived to predict: The rate of the wetting front advance, prior to the occurrence of surface ponding, taking into account the effect of initial soil moisture content and rate of water application. The time at which surface ponding takes place under different rain (sprinkler) intensities by utilizing the intake rate curve obtained under flooded infiltration. The derived equations enable us to estimate a definite period of time, during which a field can be sprinkled at a given application rate, beyond which if sprinkling continues runoff will take place, and to estimate the accumulative rain (sprinkler) uptake at the time of surface ponding. The theory was tested and firmly supported by the results of a multipurpose laboratory experiment conducted on samples of a Nibley silty clay loam soil packed into columns to a density of 1.25 gm/cm3

Pairwise weakly Hausdorff spaces

summary:In this paper, we introduce and investigate the notion of weakly Hausdorffness in bitopological spaces by using the convergent of nets. Several characterizations of this notion are given. Some relationships between these spaces and other spaces satisfying some separation axioms are studied

Child Labor in Egypt

Child labor is a complex worldwide problem, especially in LDCs where poverty and low educational standards are persistent. A survey of child labor worldwide finds that children are working in considerable numbers throughout many regions of the world. Each region differs in the extent of child labor and the specific sectors where children may be found working. However, the main reasons behind the work of children namely poverty and education, were common in all areas. Egypt represents a typical case where child labor exists in most of its forms, except for prostitution, traficking and child bondage, and is mainly caused by poverty. Determining the magnitude of child labor in Egypt is very difficult due to the large informal sector, the prevalence of the work of children in domestic chores and with their families in rural areas. Both international agencies and the government are attempting to solve the problem. However, it is still persistent

Development of a System for Crude Oil Classification

Crude oil is the most sought petroleum product and can be found in different places of the world. It is composed of hydrocarbon, organic compounds and small amounts of metal, this mixture can be refined to produce thousands of products that are generally called petrochemicals including gasoline, diesel oil and plastics. Crude oil can be classified according to the physical and chemical properties of the oil, such as API Gravity of the oil, viscosity, colour and specific gravity. It can also be classified as either "sweet" or "sour" crude oil based on its sulphur content. However, the API gravity classification technique is perhaps the most important because it gives good indication of the commercial value or the price of the given oil. In terms of API gravity, the crude oil is classified as light, medium, heavy and extra heavy crude oils. The classification is done in the laboratory and it’s considered as a time-consuming process. The scope of this project is to design a system that can minimize the time to classify the crude oil into two types by measuring the optical properties of the oil, applications for this system are mostly used in oil and gas field

A Theoretical Study of Infiltration into Range and Forest Soils

More than 400 rainfall simulator experiments were examined to detect which soil properties could be used to computer infiltration time relationships. Three theoretical equations were tested to determine their efficacy for calculating infiltration time relationships from soil and site characteristics. It was shown that both the modified Green and Ampt and Fletcher equations could by successfully used. Darcian type equations were developed on laboratory type samples which would show the relations between soil, solution and rainfall properties and infiltration. These latter equations have not been tested on undisturbed soils but give excellent agreement between measured and computed values for time before flooding and infiltration time relationships

Computational methods in Bioinformatics: Introduction, Review, and Challenges

Biotechnology is emerging as a new driving force for the global economy in the 21st century. An important engine for biotechnology is Bioinformatics. Bioinformatics has revolutionized biology research and drug discovery. Bioinformatics is an amalgamation of biological sciences, computer science, applied math, and systems science. The report provides a brief introduction to molecular biology for non-biologists, with focus on understanding the basic biological problems which triggered the exponentially growing research activities in the bioinformatics fields. The report provides as well a comprehensive literature review of the main challenging problems, and the current tools and algorithms. In particular, the problems of gene modeling, and gene prediction, similarity search, multiple alignments of proteins, and the protein folding problems are highlighted. The report discusses as well how such tools as dynamic programming, hidden Markov models, statistical analysis, clustering, decision trees, fuzzy theory, and neural networks have been applied in solving these problems