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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Linear stability analyses of Poiseuille flows of viscoelastic liquids

Palmer, Alison January 2007 (has links)
The linear stability of the Giesekus and linear Phan-Thien Tanner (PTT) fluid models is investigated for a number of planar Poiseuille flows in single, double and triple layered configurations. The Giesekus and PTT models involve parameters that can be used to fit shear and extensional data, thus making them suitable for describing both polymer solutions and melts. The base flow is determined using a Chebyshev-tau method. The linear stability equations are also discretized using Chebyshev approximations to furnish a generalized eigenvalue problem which is then solved using the QZ-algorithm. The eigenspectra are shown to comprise of continuous parts and discrete parts. The theoretical and numerical results are validated for the Oldroyd-B model, which is a simplified case of the Giesekus and PTT models, by comparing with results in the literature. The continuous and discrete parts of the eigenspectra are determined using a purely numerical scheme to solve the discretized eigenvalue problem. The continuous spectra are then more accurately determined using a semi-analytical scheme which uses an analytical solution of the Orr-Sommerfeld equation alongside a numerical solution for the base flow. A comprehensive survey of the effect of each shear thinning and extensional fluid parameter is undertaken and an instability is found for particular parameter values for the Giesekus fluid. A preliminary investigation of this instability is undertaken whereby the unstable discrete eigenvalue is investigated using an Orthonormal Runge-Kutta scheme within a shooting method which uses the results from the Chebyshev-QZ scheme as a starting point. The linear PTT fluid is found to be stable to infinitesimal disturbances within the range of shear-thinning and extensional parameters considered. The computational e ciency and accuracy of the numerical methods are also investigated.
2

Soil characteristics, cropping patterns, and use of organic resources in the coastal sandy area of Thua Thien Hue province, Central Vietnam

Hoang Thi Thai, Hoa 25 November 2008 (has links)
Sandy soils make up more than 205,000 ha in the coastal area of the North Central region of Vietnam. Thua Thien Hue province lying in the south of this region has predominantly sandy soils that cover almost 47,000 ha out of the 84,000 ha of cultivated land. Most of the population lives in the coastal area and people’s livelihoods are largely dependent on crop farming in these inherently poor soils. The objectives of this study were to provide extensive information on the soil and organic resources (including agricultural and aquatic sources) in the coastal area of Thua Thien Hue province, to assess the fertilization capacity of various organic materials when applied at different rates to soils for different crops and to make a diagnosis of the balance of main plant nutrients within the farms to assess possible risks of depletion in soils or of release to the environment. Soil characteristics were measured from a survey of 300 cultivated plots in seven villages scattered in the coastal area. All these light-textured soils are acidic and are very poor in organic C. Consequently, the cation exchange capacity is very low. Soil properties are linked significantly to the different cropping patterns. Farmers in the studied area use wide diversify of organic materials for various purposes. Very large variations in the content of major elements (C, N, P, K, Ca, and Mg) are observed in the organic samples. Crop yield and soil fertility increased following the rate of farmyard manure and organic amendment application. Organic amendments brought higher profit for rice and peanut growers in coastal sandy area. The highest fertilization efficiency was observed for pig manure in case of growing rice and peanut and goat manure for sweet potato. The most frequently used species of aquatic plants by local farmers are Najas indica, Vallisneria spiralis, Potamogeton malaianus plus various algae species. Najas Indica and Hydrilla verticillata showed the highest fertilization capacity. At farm level, the N, P, K balances in 10 studied farms were positive. More detailed N-P-K balances in 9 field plots indicated that N balance was largely positive for rice and sweet potato plots. P imports exceeded P exports in all studied plots, whereas K balance was always negative in 4 cropping systems.
3

ベトナムにおける洪水対策ガバナンス -Thua Thien Hue省のBo川流域を事例として-

望月, 聡之 24 September 2021 (has links)
京都大学 / 新制・課程博士 / 博士(地球環境学) / 甲第23560号 / 地環博第217号 / 新制||地環||42(附属図書館) / 京都大学大学院地球環境学舎環境マネジメント専攻 / (主査)教授 佐野 亘, 教授 西前 出, 教授 宇佐美 誠 / 学位規則第4条第1項該当 / Doctor of Global Environmental Studies / Kyoto University / DGAM

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