Yes / Local scour around submarine pipelines can affect the stability of the pipeline. The accurate estimation of the scour around submarine pipelines has been a hot topic of research among marine engineers. This paper presents results from a numerical study of clear-water scour depth below a submarine pipeline for a range of the steady flow conditions. The flow field around the pipeline under scour equilibrium condition is numerically simulated by solving the Reynolds-Averaged Navier-Stokes (RANS) equations with the standard k-ε turbulence closure. The flow discharge through the scour hole for various flow conditions is investigated. The results are used to establish the relationship between the flow discharge and the maximum scour depth. Incorporated with the Colebrook-White equation, the bed shear stress is obtained and an iterative method is proposed to predict the scour depth around the submarine pipeline. The calculated scour depths using the present method agree well with the laboratory measurements, with the average absolute relative error being smaller than that using previous methods, indicating that the proposed method can be used to predict the clear-water scour around the submarine pipeline with satisfactory accuracy. / National Nature Science Fund of China (Grant No.50879084, 51279189), the Open Fund from the State Key Laboratory of Hydraulics and Mountain River Engineering, Sichuan University (SKHL1302),China Scholarship Council, Public Projects of Zhejiang Province (2016C33095) and the Natural Science Fund of Zhejiang Province (LQ16E090004).

Yes / This paper presents the results of laboratory experiments and numerical simulations to investigate the effect of different piggyback pipeline configuration on the morphology of local seabed scour subject to steady currents. Piggyback pipeline configuration investigated includes the commonly used piggyback pipeline, namely a small pipe attached on the top of large pipe and new form of piggyback pipeline proposed in this study in which a small pipe is attached to the large pipe on the upstream and downstream side, respectively. Pressure gradient, drag coefficient, lift coefficient and scour extent around pipelines are measured and analyzed for a range of pipelines and current conditions. Results show that the vortex strength downstream of the commonly used piggyback pipeline is larger than that for a single as well as the new piggyback pipeline under the same condition. This new type piggyback pipeline can effectively reduce the depth and width of the scour hole. In particular, when the ratio of the small pipe diameter over the large pipe diameter is greater than 0.3, little scour under this new type piggyback pipeline occurs for the test conditions. The bed topography downstream of the pipe has also been altered to favor the backfill. / National Natural Science Foundation of China (No. 51279189).

Nesta dissertação estão apresentados os principais conceitos teóricos envolvidos na ação dos jatos formados em dissipadores tipo salto esqui sobre fossa de erosão pré-escavada, desde o trajeto do jato em sua fase aérea e em sua fase submersa, dando especial ênfase às pressões hidrodinâmicas e sua caraterização junto ao fundo da bacia. Para estudar experimentalmente a ação dos jatos nas bacias de dissipação, utilizou-se de um modelo físico de escala 1:100 construído no Laboratório de Obras Hidráulicas do IPH/UFRGS com ensaios de diferentes vazões e diferentes profundidades de fossas pré-escavadas. Os dados foram extraídos dos ensaios no modelo físico através de vasta instrumentação, utilizando-se comportas, pontas linimétricas, piezômetros, sensores de pressão, imagens e outros equipamentos. Foi realizada uma análise criteriosa dos dados gerados no modelo físico a partir das imagens do jato na sua trajetória aérea e no escoamento do jato em sua fase submersa, comparando os dados do modelo aos resultados obtidos por métodos tradicionais de cálculo. Também foram analisados os dados de pressão gerados durante os ensaios, sendo apresentados os resultados relativos às pressões médias e às pressões dinâmicas. As pressões dinâmicas observadas no modelo físico foram comparadas com as calculadas por meio de metodologia teórica abordada na bibliografia com a finalidade de avaliar a qualidade dessa metodologia para aplicação em projetos de engenharia, onde se observou grandes diferenças de magnitude da pressão quando em colchões rasos, e diferenças de distribuição de pressão ao longo do fundo da bacia de dissipação, principalmente quando em colchões profundos. No sentido de ajustar a metodologia aplicada, foi proposta a variação de parâmetros que regulam a forma do bulbo de pressões e a aplicação de um coeficiente de amortecimento de pressões, sendo que assim foi possível melhorar significativamente a distribuição e a magnitude das pressões calculadas devido à ação dos jatos no fundo da bacia de dissipação. Os resultados se mostram satisfatórios até determinada distância após o pico de pressão provocado pelo jato, sendo que após este ponto os efeitos de ressalto hidráulico prevalecem e devem ser pesquisados em estudos futuros. / In this dissertation are presented the main theorical concepts involved in the action of the jets formed in ski jump spillways on stilling basins type pre-excavated scour hole, from the path of the jet in its air stage and in his submerged phase, with particular emphasis on hydrodynamic pressures and its characterization by the bottom of the basin. To experimentally study the action of the jets in stilling basins, was used a physical model in scale 1:100 built in Hydraulic Works Laboratory of IPH/UFRGS with experiments of different flow rates and different depths of pre-excavated scour hole. The data were extracted from experiments on the physical model through extensive instrumentation, using gates, piezometers, pressure sensors, images and other equipment. A careful analysis of the data generated in the physical model from the jet images in your path through the air was performed and the flow of the jet in its submerged phase, comparing the model data to the results obtained by traditional methods of calculation. The pressure data generated during the tests and presented the results for the mean pressures and dynamic pressures were also analyzed. Dynamic pressures observed in the physical model were compared with those calculated by means of theoretical methods for the purpose of evaluating the quality of this methodology for use in engineering projects, where we observed large differences in magnitude of pressure when in shallow water beds, and diferences in pressure distribution over the stilling basin bottom, especially when in deep water beds. In order to adjust the applied methodology, it was proposed to change parameters governing the shape of the pressure bulb and the application of a pressure damping coefficient, and thus was possible to significantly improved the distribution and magnitude of the calculated pressures due to action of the jets in the stilling basin bottom. The results have been satisfactory up to a certain distance after the peak pressure caused by the jet, and after this point the hydraulic jump effects prevail and should be investigated in future studies.

Nesta dissertação estão apresentados os principais conceitos teóricos envolvidos na ação dos jatos formados em dissipadores tipo salto esqui sobre fossa de erosão pré-escavada, desde o trajeto do jato em sua fase aérea e em sua fase submersa, dando especial ênfase às pressões hidrodinâmicas e sua caraterização junto ao fundo da bacia. Para estudar experimentalmente a ação dos jatos nas bacias de dissipação, utilizou-se de um modelo físico de escala 1:100 construído no Laboratório de Obras Hidráulicas do IPH/UFRGS com ensaios de diferentes vazões e diferentes profundidades de fossas pré-escavadas. Os dados foram extraídos dos ensaios no modelo físico através de vasta instrumentação, utilizando-se comportas, pontas linimétricas, piezômetros, sensores de pressão, imagens e outros equipamentos. Foi realizada uma análise criteriosa dos dados gerados no modelo físico a partir das imagens do jato na sua trajetória aérea e no escoamento do jato em sua fase submersa, comparando os dados do modelo aos resultados obtidos por métodos tradicionais de cálculo. Também foram analisados os dados de pressão gerados durante os ensaios, sendo apresentados os resultados relativos às pressões médias e às pressões dinâmicas. As pressões dinâmicas observadas no modelo físico foram comparadas com as calculadas por meio de metodologia teórica abordada na bibliografia com a finalidade de avaliar a qualidade dessa metodologia para aplicação em projetos de engenharia, onde se observou grandes diferenças de magnitude da pressão quando em colchões rasos, e diferenças de distribuição de pressão ao longo do fundo da bacia de dissipação, principalmente quando em colchões profundos. No sentido de ajustar a metodologia aplicada, foi proposta a variação de parâmetros que regulam a forma do bulbo de pressões e a aplicação de um coeficiente de amortecimento de pressões, sendo que assim foi possível melhorar significativamente a distribuição e a magnitude das pressões calculadas devido à ação dos jatos no fundo da bacia de dissipação. Os resultados se mostram satisfatórios até determinada distância após o pico de pressão provocado pelo jato, sendo que após este ponto os efeitos de ressalto hidráulico prevalecem e devem ser pesquisados em estudos futuros. / In this dissertation are presented the main theorical concepts involved in the action of the jets formed in ski jump spillways on stilling basins type pre-excavated scour hole, from the path of the jet in its air stage and in his submerged phase, with particular emphasis on hydrodynamic pressures and its characterization by the bottom of the basin. To experimentally study the action of the jets in stilling basins, was used a physical model in scale 1:100 built in Hydraulic Works Laboratory of IPH/UFRGS with experiments of different flow rates and different depths of pre-excavated scour hole. The data were extracted from experiments on the physical model through extensive instrumentation, using gates, piezometers, pressure sensors, images and other equipment. A careful analysis of the data generated in the physical model from the jet images in your path through the air was performed and the flow of the jet in its submerged phase, comparing the model data to the results obtained by traditional methods of calculation. The pressure data generated during the tests and presented the results for the mean pressures and dynamic pressures were also analyzed. Dynamic pressures observed in the physical model were compared with those calculated by means of theoretical methods for the purpose of evaluating the quality of this methodology for use in engineering projects, where we observed large differences in magnitude of pressure when in shallow water beds, and diferences in pressure distribution over the stilling basin bottom, especially when in deep water beds. In order to adjust the applied methodology, it was proposed to change parameters governing the shape of the pressure bulb and the application of a pressure damping coefficient, and thus was possible to significantly improved the distribution and magnitude of the calculated pressures due to action of the jets in the stilling basin bottom. The results have been satisfactory up to a certain distance after the peak pressure caused by the jet, and after this point the hydraulic jump effects prevail and should be investigated in future studies.

Nesta dissertação estão apresentados os principais conceitos teóricos envolvidos na ação dos jatos formados em dissipadores tipo salto esqui sobre fossa de erosão pré-escavada, desde o trajeto do jato em sua fase aérea e em sua fase submersa, dando especial ênfase às pressões hidrodinâmicas e sua caraterização junto ao fundo da bacia. Para estudar experimentalmente a ação dos jatos nas bacias de dissipação, utilizou-se de um modelo físico de escala 1:100 construído no Laboratório de Obras Hidráulicas do IPH/UFRGS com ensaios de diferentes vazões e diferentes profundidades de fossas pré-escavadas. Os dados foram extraídos dos ensaios no modelo físico através de vasta instrumentação, utilizando-se comportas, pontas linimétricas, piezômetros, sensores de pressão, imagens e outros equipamentos. Foi realizada uma análise criteriosa dos dados gerados no modelo físico a partir das imagens do jato na sua trajetória aérea e no escoamento do jato em sua fase submersa, comparando os dados do modelo aos resultados obtidos por métodos tradicionais de cálculo. Também foram analisados os dados de pressão gerados durante os ensaios, sendo apresentados os resultados relativos às pressões médias e às pressões dinâmicas. As pressões dinâmicas observadas no modelo físico foram comparadas com as calculadas por meio de metodologia teórica abordada na bibliografia com a finalidade de avaliar a qualidade dessa metodologia para aplicação em projetos de engenharia, onde se observou grandes diferenças de magnitude da pressão quando em colchões rasos, e diferenças de distribuição de pressão ao longo do fundo da bacia de dissipação, principalmente quando em colchões profundos. No sentido de ajustar a metodologia aplicada, foi proposta a variação de parâmetros que regulam a forma do bulbo de pressões e a aplicação de um coeficiente de amortecimento de pressões, sendo que assim foi possível melhorar significativamente a distribuição e a magnitude das pressões calculadas devido à ação dos jatos no fundo da bacia de dissipação. Os resultados se mostram satisfatórios até determinada distância após o pico de pressão provocado pelo jato, sendo que após este ponto os efeitos de ressalto hidráulico prevalecem e devem ser pesquisados em estudos futuros. / In this dissertation are presented the main theorical concepts involved in the action of the jets formed in ski jump spillways on stilling basins type pre-excavated scour hole, from the path of the jet in its air stage and in his submerged phase, with particular emphasis on hydrodynamic pressures and its characterization by the bottom of the basin. To experimentally study the action of the jets in stilling basins, was used a physical model in scale 1:100 built in Hydraulic Works Laboratory of IPH/UFRGS with experiments of different flow rates and different depths of pre-excavated scour hole. The data were extracted from experiments on the physical model through extensive instrumentation, using gates, piezometers, pressure sensors, images and other equipment. A careful analysis of the data generated in the physical model from the jet images in your path through the air was performed and the flow of the jet in its submerged phase, comparing the model data to the results obtained by traditional methods of calculation. The pressure data generated during the tests and presented the results for the mean pressures and dynamic pressures were also analyzed. Dynamic pressures observed in the physical model were compared with those calculated by means of theoretical methods for the purpose of evaluating the quality of this methodology for use in engineering projects, where we observed large differences in magnitude of pressure when in shallow water beds, and diferences in pressure distribution over the stilling basin bottom, especially when in deep water beds. In order to adjust the applied methodology, it was proposed to change parameters governing the shape of the pressure bulb and the application of a pressure damping coefficient, and thus was possible to significantly improved the distribution and magnitude of the calculated pressures due to action of the jets in the stilling basin bottom. The results have been satisfactory up to a certain distance after the peak pressure caused by the jet, and after this point the hydraulic jump effects prevail and should be investigated in future studies.

This thesis reports on investigations carried out to study of the effect of horizontal wall jets on rough, fixed and mobile beds in open channel flow. Experimental tests were carried out, using fixed and mobile sediment beds. Computer simulation models for the flow within the jet and resulting sediment transport were developed and their results analysed in this study. In the experimental phase, tests were carried out with both fixed and mobile sediment beds. The shape of the water surface, numerous point velocity measurements and measurements of the evolving scour hole shape were made. Detailed descriptions of the turbulent flow field over a fixed rough bed and for scour holes at equilibrium were obtained for a range of initial jet conditions. Fully turbulent, multiphase flow was modelled using the Fluent Computational Fluid Dynamics software. This was used to analyze the flow caused by a jet in a rectangle open-channel with a rough bed, and also the flow pattern in a channel with a local scour hole. The volume of fluid (VOF) multiphase method and K- model was used to model the fluid flow in both cases. The model predictions of velocity and shear stress were compared against experimental observations. The experimental data was used to develop new empirical relationships to describe the pattern of boundary shear stress caused by a wall jet over fixed beds and in equilibrium scour holes. These relationships were linked with existing bed-load transport rate models in order to predict the temporal evolution of scour holes. An analytical model describing the relationship between the wall jet flow and the development of a local scour hole shape was reported and its predictions compared with experimental data.

This thesis reports on investigations carried out to study of the effect of horizontal wall jets on rough, fixed and mobile beds in open channel flow. Experimental tests were carried out, using fixed and mobile sediment beds. Computer simulation models for the flow within the jet and resulting sediment transport were developed and their results analysed in this study. In the experimental phase, tests were carried out with both fixed and mobile sediment beds. The shape of the water surface, numerous point velocity measurements and measurements of the evolving scour hole shape were made. Detailed descriptions of the turbulent flow field over a fixed rough bed and for scour holes at equilibrium were obtained for a range of initial jet conditions. Fully turbulent, multiphase flow was modelled using the Fluent Computational Fluid Dynamics software. This was used to analyze the flow caused by a jet in a rectangle open-channel with a rough bed, and also the flow pattern in a channel with a local scour hole. The volume of fluid (VOF) multiphase method and K- model was used to model the fluid flow in both cases. The model predictions of velocity and shear stress were compared against experimental observations. The experimental data was used to develop new empirical relationships to describe the pattern of boundary shear stress caused by a wall jet over fixed beds and in equilibrium scour holes. These relationships were linked with existing bed-load transport rate models in order to predict the temporal evolution of scour holes. An analytical model describing the relationship between the wall jet flow and the development of a local scour hole shape was reported and its predictions compared with experimental data.

In this study, the effects of submergence on local scour in a uniform cohesionless sediment bed by a plane turbulent wall jet and the resulting flow field were investigated experimentally. Here, submergence is defined as the ratio of the tailwater depth to the thickness of the jet at its origin. The main focus was to determine scour dimensions at an asymptotic state, examine whether there was similarity in the velocity profiles for the flow in the scour hole, and to determine the growth of the length scales and decay of the maximum velocity of the jet. Also examined were the relationships between the scales for the velocity field in the scour hole and the scour hole size.<p>In the experiments, the range of submergence was varied from 3-17.5, whereas the range of densimetric Froude number and the ratio of the boundary roughness to the gate opening (relative boundary roughness) were varied from 4.4-6.9 and 0.085-0.137 respectively. The velocity field in the scour hole at asymptotic state was measured using a SonTek 16-MHz MicroADV. Time development of the characteristic dimensions of the scour hole was also measured.<p>The dimensions of the scour hole were found to increase with increasing submergence for all experiments with a bed-jet flow regime. In the bed-jet flow regime, the jet remains near the bed throughout the scouring process. Further, the time development of the scour hole dimensions were observed to increase approximately linearly with the logarithm of time up to a certain time before the beginning of asymptotic state for experiments with either the bed-jet or surface-jet flow regimes.<p> The flow field results showed that the velocity profiles in the region of forward flow and the recirculating region above the jet were similar in shape up to about the location of the maximum scour depth. Relationships describing this velocity profile, including its velocity and length scales, were formulated. The decay rate of the maximum velocity, the growth of the jet half-width, and the boundary layer thickness were also studied. The decay and the growth rate of the jet length scales were found to be influenced by the submergence ratio, densimetric Froude number, and the relative boundary roughness.<p>Two distinct stages in the decay of the maximum streamwise velocity, with distance along the direction of flow, were observed for the jet flows having a bed-jet flow regime. The first stage of velocity decay was characterized by a curvilinear decay of velocity, which followed that of a wall jet on a smooth, rigid bed for streamwise distance approximately equal to 2L. For the surface-jet flow regime, the decay of velocity was observed to be similar to that of a free-jump on a smooth, rigid bed for a streamwise distance approximately equal to L. Here, L is defined as the streamwise distance measured from the end of the rigid apron to where the maximum streamwise velocity in the jet is half the velocity of the jet at the end of apron. The streamwise maximum velocity of the jet was then seen to increase in what was called the recovery zone.<p>A relationship for the streamwise decay of the maximum velocity within the scour hole is proposed. Moreover, other scales representing the flow inside the scour hole such as the streamwise distance from the end of the apron to where the streamwise maximum velocity starts to deviate from curvilinear to linear decay and the streamwise distance to where maximum streamwise velocity starts to increase are suggested. Some new results on the velocity distribution for the reverse flow for a bed-jet flow regime are also presented. Finally, some dimensionless empirical equations describing the relationship between the jet scales for the jet flow in a scour hole and the scour hole size are given.

In this study, the effects of submergence on local scour in a uniform cohesionless sediment bed by a plane turbulent wall jet and the resulting flow field were investigated experimentally. Here, submergence is defined as the ratio of the tailwater depth to the thickness of the jet at its origin. The main focus was to determine scour dimensions at an asymptotic state, examine whether there was similarity in the velocity profiles for the flow in the scour hole, and to determine the growth of the length scales and decay of the maximum velocity of the jet. Also examined were the relationships between the scales for the velocity field in the scour hole and the scour hole size.<p>In the experiments, the range of submergence was varied from 3-17.5, whereas the range of densimetric Froude number and the ratio of the boundary roughness to the gate opening (relative boundary roughness) were varied from 4.4-6.9 and 0.085-0.137 respectively. The velocity field in the scour hole at asymptotic state was measured using a SonTek 16-MHz MicroADV. Time development of the characteristic dimensions of the scour hole was also measured.<p>The dimensions of the scour hole were found to increase with increasing submergence for all experiments with a bed-jet flow regime. In the bed-jet flow regime, the jet remains near the bed throughout the scouring process. Further, the time development of the scour hole dimensions were observed to increase approximately linearly with the logarithm of time up to a certain time before the beginning of asymptotic state for experiments with either the bed-jet or surface-jet flow regimes.<p> The flow field results showed that the velocity profiles in the region of forward flow and the recirculating region above the jet were similar in shape up to about the location of the maximum scour depth. Relationships describing this velocity profile, including its velocity and length scales, were formulated. The decay rate of the maximum velocity, the growth of the jet half-width, and the boundary layer thickness were also studied. The decay and the growth rate of the jet length scales were found to be influenced by the submergence ratio, densimetric Froude number, and the relative boundary roughness.<p>Two distinct stages in the decay of the maximum streamwise velocity, with distance along the direction of flow, were observed for the jet flows having a bed-jet flow regime. The first stage of velocity decay was characterized by a curvilinear decay of velocity, which followed that of a wall jet on a smooth, rigid bed for streamwise distance approximately equal to 2L. For the surface-jet flow regime, the decay of velocity was observed to be similar to that of a free-jump on a smooth, rigid bed for a streamwise distance approximately equal to L. Here, L is defined as the streamwise distance measured from the end of the rigid apron to where the maximum streamwise velocity in the jet is half the velocity of the jet at the end of apron. The streamwise maximum velocity of the jet was then seen to increase in what was called the recovery zone.<p>A relationship for the streamwise decay of the maximum velocity within the scour hole is proposed. Moreover, other scales representing the flow inside the scour hole such as the streamwise distance from the end of the apron to where the streamwise maximum velocity starts to deviate from curvilinear to linear decay and the streamwise distance to where maximum streamwise velocity starts to increase are suggested. Some new results on the velocity distribution for the reverse flow for a bed-jet flow regime are also presented. Finally, some dimensionless empirical equations describing the relationship between the jet scales for the jet flow in a scour hole and the scour hole size are given.

Scour is a process of removing soils around foundations by currents and waves. For the pile-supported marine structures such as the monopile-supported offshore wind turbines (OWTs) and the pile-supported bridges, scour can decrease the pile capacities and alter the dynamic responses of the structures. At present, there is not a widely accepted method to estimate pile axial or lateral capacity under scoured conditions. For example, different recommendations are used among the existing design standards for estimation of the vertical effective stress and the resulting capacities for single piles under different scour conditions. None of the existing standards or design practice has even considered the scour effects on the behavior of pile groups. Furthermore, the investigation into the responses of piles under multiple hazards of scour and earthquakes is rarely reported. To address the foregoing limitations, this study first introduces an analytical solution to determining the vertical effective stress of soils around single isolated piles under scoured conditions and uses it to examine the limitations of the existing standards in estimation of pile tensile capacity (Chapter 1). The effect of soil-pile interface friction is highlighted. Next, the study proposes new approaches to investigating the combined effects of scour and earthquakes on the lateral responses of the monopile-supported OWTs in sand (Chapter 2) and soft clay (Chapter 3). Lastly, simple and practical methods are developed based on the p-y curve framework for analyzing the lateral responses of pile groups in sand (Chapter 4) and soft clay (Chapter 5) subjected to static lateral loading. The proposed methods in this study were encoded into a series of open-source computer scripts for engineering practice. They were verified with the 3D continuum finite element (FE) analyses. Using the proposed methods, standard methods, and 3D FE method, parametric analyses were conducted to investigate the scour effects on the lateral behavior of the monopile-supported OWTs under crustal earthquakes and that of the pile groups under static loading. The factors considered in the parametric study included effects of scour-hole dimensions, soil stress history, soil density, soil-pile interface behavior, soil liquefaction potential, pile group configurations, etc. Through the parametric analyses, the standard methods were critically assessed by comparing the results to those calculated by the proposed methods and 3D FE methods, and some design-related issues were also discussed. / Graduate