When a semi-infinite body of homogeneous fluid initially at rest behind a vertical retaining wall is suddenly released by the removal of the barrier the resulting flow over a horizontal or sloping bed is referred to as a dam-break flow. When resistance to the flow is neglected the exact solution, in the case of a stable horizontal bed with or without `tail water', may be obtained on the basis of shallow-water theory via the method of characteristics and the results are well known. Discrepancies between these shallow-water based solutions and experiments have been partially accounted for by the introduction of flow resistance in the form of basal friction. This added friction significantly modifies the wave speed and flow profile near the head of the wave so that the simple exact solutions no longer apply and various asymptotic or numerical approaches must be implemented to solve these frictionally modified depth-averaged shallow-water equations. When the bed is no longer stable so that solid particles may be exchanged between the bed and the water column the dynamics of the flow becomes highly complex as the buoyancy forces vary in space and time according to the competing rates of erosion and deposition. Furthermore, when the Froude number of the flow is close to unity perturbations in the height and velocity profiles grow into N-waves and the bed below develops ripples which act to sustain the N-waves in the fluid above. It is our intention here to study dam-break flows over erodible sloping beds as agents of sediment transport taking into account basal friction as well as the effects of particle concentrations on flow dynamics including both erosion and deposition. We shall consider shallow flows over initially dry beds and investigate the effects of changes in the depositional and erosional models employed as well as in the nature of the drag acting on the flow and the slope of the bed. These models include effects hitherto neglected in such studies and offer insights into the transport of sediment in the worst case scenario of the complete and instantaneous collapse of a dam. / Mathematics

When a semi-infinite body of homogeneous fluid initially at rest behind a vertical retaining wall is suddenly released by the removal of the barrier the resulting flow over a horizontal or sloping bed is referred to as a dam-break flow. When resistance to the flow is neglected the exact solution, in the case of a stable horizontal bed with or without `tail water', may be obtained on the basis of shallow-water theory via the method of characteristics and the results are well known. Discrepancies between these shallow-water based solutions and experiments have been partially accounted for by the introduction of flow resistance in the form of basal friction. This added friction significantly modifies the wave speed and flow profile near the head of the wave so that the simple exact solutions no longer apply and various asymptotic or numerical approaches must be implemented to solve these frictionally modified depth-averaged shallow-water equations. When the bed is no longer stable so that solid particles may be exchanged between the bed and the water column the dynamics of the flow becomes highly complex as the buoyancy forces vary in space and time according to the competing rates of erosion and deposition. Furthermore, when the Froude number of the flow is close to unity perturbations in the height and velocity profiles grow into N-waves and the bed below develops ripples which act to sustain the N-waves in the fluid above. It is our intention here to study dam-break flows over erodible sloping beds as agents of sediment transport taking into account basal friction as well as the effects of particle concentrations on flow dynamics including both erosion and deposition. We shall consider shallow flows over initially dry beds and investigate the effects of changes in the depositional and erosional models employed as well as in the nature of the drag acting on the flow and the slope of the bed. These models include effects hitherto neglected in such studies and offer insights into the transport of sediment in the worst case scenario of the complete and instantaneous collapse of a dam. / Mathematics

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Dam failure mechanism produces the rapidly varied unsteady flow situation and the appropriate analysis to determine the flow condition is necessary. Over the world, more than 80,000 dams were constructed. There have been more than 200 distinguished dam failures occurred within the twentieth century. The history of dam construction exists together with the probability of dam failure causing casualties and catastrophic situations. As climate change effect has caused the change in flow situations, the safety concern in the dam is also necessary. Casualties and damages due to dam break events depend upon the depth, flow velocity, population distribution as per geography and warning time related to the time to reach the peak flow to the downstream areas. Prediction of actual breaching scenario is not certain and is related to the geographical and geological features of the site, embankment type, type of breach, reservoir storage and flow conditions. Estimating the accurate breaching scenarios and modeling of the dam break situation to characterize the hydrodynamic risk is necessary. Among the numerous techniques of modeling dam break situation, this study focused on the use of HEC-RAS for analyzing the dam break situation. Most of the simulation of a dam break situation used one-dimensional analysis to solve flow conditions after the break of the dam. The Latest development of HEC-RAS 2D capabilities is also used in conjunction with 1D HEC-RAS dam break analysis to compare and explore both analysis capabilities of HEC-RAS. The effect of HEC-RAS simulation altering the breaching conditions is analyzed for the dam failure case of Big Bay dam located in Lamar County, Mississippi. The study area is chosen to obtain the simulation of piping dam failure, which was the real cause of the dam failure event. In addition, the overtopping failure parameters established by the different breaching regression equations were analyzed. Results obtained with both one- dimensional and two- dimensional analysis is compared along with the modeling procedure and concept of analysis. From the analysis, it is found that the time of peak water surface elevation and its magnitude is responsible in determining the extent of vulnerable areas to the dam break scenarios. The present study showed the variation in peak flow condition between different breach parameters. Breach bottom width found to be more sensitive parameters in dam failure events. HEC-RAS analysis is found to be suitable to predict the uncertain hydraulic behavior of dam break situation.

Made available in DSpace on 2018-08-02T00:02:59Z (GMT). No. of bitstreams: 1 tese_11317_ALAN VICTOR FERREIRA MODOLO .pdf: 4918358 bytes, checksum: 4f9210c521179af173132f3ad0f9737f (MD5) Previous issue date: 2017-03-24 / Ao longo do último século, o Dam Break Flow vem sendo estudado por muitos autores. A compreensão deste tipo de fenômeno é de grande relevância, uma vez que envolve aplicações em barragens que oferecem múltiplos benefícios para a humanidade. Porém, o rompimento de uma dessas barragens pode trazer consequências indesejáveis e imensuráveis para a sociedade e para o setor de mineração, por exemplo. Neste trabalho estamos interessados em entender como o número de Froude e as propriedades não-newtonianas, particularmente a viscoplasticidade, afetam o perfil de interface do escoamento e a distância alcançada pelo material após o Dam Break Flow. Tais resultados são comparados com o deslocamento de um fluido newtoniano. Através de uma simples abordagem experimental, uma solução de material viscoplástico ou newtoniana incialmente armazenada em um reservatório é instantaneamente liberada. As imagens do escoamento são capturadas durante o teste de duas maneiras diferentes. Uma é feita utilizando uma câmera CCD e a outra é através da Velocimetria por Imagem de Partícula. A partir das imagens obtidas pela câmera CCD, obtém-se um mapa do escoamento, com as suas respectivas velocidades, nível de líquido, formato das interfaces ar-líquido e distância percorrida pelo material são observadas. Já os resultados obtidos com o PIV, são para determinar o campo de velocidade dos momentos iniciais do Dam Break Flow para os diferentes tipos de materiais estudados. Neste trabalho, é mostrado que a plasticidade do material tem total influência sobre a distância alcançada pelo escoamento e também resultam em instabilidades ao longo do mesmo. Foi ainda identificado que o fluido viscoplástico alcança velocidades iniciais maiores que o caso newtoniano. Porém, no decorrer do escoamento, decrescem rapidamente. Quando analisado o caso viscoplástico para um leito com rugosidade, nota-se que para uma superfície lisa, há deslizamento do material de forma significativa para altos valores de plasticidade. Através da análise com PIV, foi constatado que a velocidade de frente de onda é um pouco menor do que a velocidade máxima obtida pelo escoamento. Palavras chave: Dam Break Flow, material viscoplástico, PIV, plasticidade, deslizamento.

Until recently, research has been scarce in the field of physical modelling of dam breaching. Over the past few years, teams from the University of Ottawa, Canada, Delft University of Technology, Netherlands, and HR Wallingford, United Kingdom have worked on several physical models to help determine how various dam breaching characteristics vary due to changes in dam geometry and geotechnical properties. The purpose of this project is to use these new experimental data sets to compare and validate the applicability range of two existing pieces of software, MIKE11-DB and BREACH developed by the Danish Hydraulic Institute and National Weather Service, respectively. Several breaching characteristics such as the outflow hydrograph, peak flow, lag time, breaching time, breach width, and water level are considered in the present study. A sensitivity analysis is also performed on the model’s main input parameters and their sensitivity and performance is ranked accordingly.

Until recently, research has been scarce in the field of physical modelling of dam breaching. Over the past few years, teams from the University of Ottawa, Canada, Delft University of Technology, Netherlands, and HR Wallingford, United Kingdom have worked on several physical models to help determine how various dam breaching characteristics vary due to changes in dam geometry and geotechnical properties. The purpose of this project is to use these new experimental data sets to compare and validate the applicability range of two existing pieces of software, MIKE11-DB and BREACH developed by the Danish Hydraulic Institute and National Weather Service, respectively. Several breaching characteristics such as the outflow hydrograph, peak flow, lag time, breaching time, breach width, and water level are considered in the present study. A sensitivity analysis is also performed on the model’s main input parameters and their sensitivity and performance is ranked accordingly.

Numerical dam break analyses of Kirazlik&ouml / pr&uuml / Dam are performed under various hydraulic scenarios. Kirazlik&ouml / pr&uuml / Dam is located on the G&ouml / kirmak River near the city of Bartin. The objective of these analyses is to investigate adverse effects of such dam break failure on the regions downstream of the dam. The numerical model used in the simulations is FLDWAV, which is developed by the National Weather Service (NWS) in the United States. It appears that most adversely effected regions are those that are closest to the dam location. The results of these simulations can be used sufficiently to prepare emergency action plans in case of possible failures.

Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第15344号 / 工博第3223号 / 新制||工||1485(附属図書館) / 27822 / 京都大学大学院工学研究科都市社会工学専攻 / (主査)教授 細田 尚, 教授 後藤 仁志, 准教授 米山 望 / 学位規則第4条第1項該当

Until recently, research has been scarce in the field of physical modelling of dam breaching. Over the past few years, teams from the University of Ottawa, Canada, Delft University of Technology, Netherlands, and HR Wallingford, United Kingdom have worked on several physical models to help determine how various dam breaching characteristics vary due to changes in dam geometry and geotechnical properties. The purpose of this project is to use these new experimental data sets to compare and validate the applicability range of two existing pieces of software, MIKE11-DB and BREACH developed by the Danish Hydraulic Institute and National Weather Service, respectively. Several breaching characteristics such as the outflow hydrograph, peak flow, lag time, breaching time, breach width, and water level are considered in the present study. A sensitivity analysis is also performed on the model’s main input parameters and their sensitivity and performance is ranked accordingly.