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Debris flow modeling: a review
ANNUAL LITERATURE SURVEY 1996
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outflow area. The periodic variation in the density structure, fo reed by wind and tides and which is clearly visible in the data, is predicted by the model. A physical interpretation of the model results is given in the absence of wind forcing. The effects ofcstuarine circulation, tidal straining and mixing on the development or breakdown of stratification are well presented by the model calculations. (Authors)
Debirs flow modeling: a review Hutter K., Svendsen B. & Rickenmann D., Continuum Mechanics & Thermodynamics, 1996, 8/1 (1-35). In English. This review begins with a survey of the literature on the physical-mathematical modeling of debris flows. We discuss the basic aspects of their phenomenology, such as dilatancy, internal friction, fluidization, and particle segregation. The basic characterization of a debris flow as a mixture motivates the application of the continuum thermodynamical theory of mixtures to formulate a model for a debris flow as a viscous fluid-granular solid mixture. A major advantage of such a formation, is that it can be used to expose and better understand the assumptions underlying existing models, as well as to derive new, more sophisticated models. Finally, we delve into the issue of how such models have been or can be implemented numerically, as well as general boundary conditions for debris flows. (from Authors) Debris flow modeling: a review Hutter K., Svendsen B. & Rickenmann D., Continuum Mechanics & Thermodynamics, 1996, 8/1 (1-35). In English. This review begins with a survey of the literature on the physical-mathematical modeling of debris flows. We discuss the basic aspects of their phenomenology, such as dilatancy, internal friction, fluidization, and particle segregation. The basic characterization of a debris flow as a mixture motivates the application of the continuum thermodynamical theory of mixtures to formulate a model for a debris flow as a viscous fluid-granular solid mixture. A major advantage of such a formation, is that it can be used to expose and better understand the assumptions underlying existing models, as well as to derive new, more sophisticated models. Finally, we delve into the issue of how such models have been or can be implemented numerically, as well as general boundary conditions for debris flows. (from Authors) The long-time evolution of the initially turbulent wake of a sphere in a stable stratification Spedding G.R., Browand F.K. & Fincham A.M., Dynamics of Atmospheres & Oceans, 1996, 23/1-4 (171-182). In English. Experiments on late wakes (Nt < 20) of towed spheres in a stably stratified fluid reveal some startling similarities and differences when compared with unstratified, 3D wakes. Predicted decay rates stemming from 3D, turbulent wake studies are unexpectedly successful in accounting for the decay in fluctuating horizontal velocity components and their spatial gradients, even at late times when the vertical velocity component is almost or exactly zero. On the other hand, the mean wake defect velocity is almost one order of magnitude higher than in the unstratified case. This is due to the increased coherence and organisation of the patches of vertical vorticity, which are stable, and persist for very long times. A correct accounting for this type of wake structure will be essential in modelling efforts for certain practical ocean applications. (Authors) Internal waves generated by a translating and oscillating sphere Dupont P. & Voisin B., Dynamics of Atmospheres & Oceans, 1996, 23/1-4 (289-298). In English. At high Reynolds and Froude numbers, lee waves owing to the horizontal motion of a body in a stratified fluid are suspended by random waves generated by its wake. The origin of these waves lies in the buoyant collapse of the large-scale coherent structures of the wake, and can be modelled as a source moving at the velocity of the body and of strength oscillating at the frequency of vortex shedding. In the presnt paper two parallel studies of the associated wavefield are described. The first of these is theoretical and considers localized and extended models of the source, while the second is experimental and involves a vertically oscillating and horizontally translating sphere. (from Authors) Some aspects of turbulence and mixing in stably stratified layers Fernando H.J.S. & Hunt J.C.R., Dynamics of Atmospheres & Oceans, 1996, 23/1-4 (35-62). In English. This paper presents a brief overview of recent work on turbulence and mixing in stably stratified flows. It is concluded (1) that the usual generalizations and 'scaling laws' of these flows need careful qualification, and (2) that the usual feature of unstratified turbulence ofhaving a single length scale for all large-scale processes may not be present, especially when mean shear and buoyancy forcing have different length scales and when there is significant wave motion (ie. the Ozmidov length scale is not the relevant macroscale). The second part of the paper reviews the modeling of motions and mixing in stable density interfaces interacting with contiguous layers of turbulence. Although the rates of mass and momentum transfer across stratified interfaces are much weaker than in unstratified turbulence, they play a crucial role in the heat and mass balances in the atmosphere and oceans. (from Authors) Efficiency of mixing by a turbulent jet in a stably stratified fluid Larson M. & Jonsson L., Dynamics of Atmospheres & Oceans, 1996, 24/1-4 (63-74). In English. Mixing in a two-layer stably stratified fluid by a turbulent jet was studied by a laboratory experiment. A nonswirling jet was discharged vertically downwards in a confined fluid system consisting initially of a top layer of fresh water and a bottom layer of salt water. A three-layer density structure developed in all cases with an intermediate layer that grew in size with time elapsed as fresh and salt water were mixed. The mixing efficiency, defined as the percentage of the supplied kinetic jet energy that is used for increasing the potential energy of the fluid system, was related to a densimetric Froude number based on the intermediate layer depth. Overall, the
93
outflow area. The periodic variation in the density structure, fo reed by wind and tides and which is clearly visible in the data, is predicted by the model. A physical interpretation of the model results is given in the absence of wind forcing. The effects ofcstuarine circulation, tidal straining and mixing on the development or breakdown of stratification are well presented by the model calculations. (Authors)
Debirs flow modeling: a review Hutter K., Svendsen B. & Rickenmann D., Continuum Mechanics & Thermodynamics, 1996, 8/1 (1-35). In English. This review begins with a survey of the literature on the physical-mathematical modeling of debris flows. We discuss the basic aspects of their phenomenology, such as dilatancy, internal friction, fluidization, and particle segregation. The basic characterization of a debris flow as a mixture motivates the application of the continuum thermodynamical theory of mixtures to formulate a model for a debris flow as a viscous fluid-granular solid mixture. A major advantage of such a formation, is that it can be used to expose and better understand the assumptions underlying existing models, as well as to derive new, more sophisticated models. Finally, we delve into the issue of how such models have been or can be implemented numerically, as well as general boundary conditions for debris flows. (from Authors) Debris flow modeling: a review Hutter K., Svendsen B. & Rickenmann D., Continuum Mechanics & Thermodynamics, 1996, 8/1 (1-35). In English. This review begins with a survey of the literature on the physical-mathematical modeling of debris flows. We discuss the basic aspects of their phenomenology, such as dilatancy, internal friction, fluidization, and particle segregation. The basic characterization of a debris flow as a mixture motivates the application of the continuum thermodynamical theory of mixtures to formulate a model for a debris flow as a viscous fluid-granular solid mixture. A major advantage of such a formation, is that it can be used to expose and better understand the assumptions underlying existing models, as well as to derive new, more sophisticated models. Finally, we delve into the issue of how such models have been or can be implemented numerically, as well as general boundary conditions for debris flows. (from Authors) The long-time evolution of the initially turbulent wake of a sphere in a stable stratification Spedding G.R., Browand F.K. & Fincham A.M., Dynamics of Atmospheres & Oceans, 1996, 23/1-4 (171-182). In English. Experiments on late wakes (Nt < 20) of towed spheres in a stably stratified fluid reveal some startling similarities and differences when compared with unstratified, 3D wakes. Predicted decay rates stemming from 3D, turbulent wake studies are unexpectedly successful in accounting for the decay in fluctuating horizontal velocity components and their spatial gradients, even at late times when the vertical velocity component is almost or exactly zero. On the other hand, the mean wake defect velocity is almost one order of magnitude higher than in the unstratified case. This is due to the increased coherence and organisation of the patches of vertical vorticity, which are stable, and persist for very long times. A correct accounting for this type of wake structure will be essential in modelling efforts for certain practical ocean applications. (Authors) Internal waves generated by a translating and oscillating sphere Dupont P. & Voisin B., Dynamics of Atmospheres & Oceans, 1996, 23/1-4 (289-298). In English. At high Reynolds and Froude numbers, lee waves owing to the horizontal motion of a body in a stratified fluid are suspended by random waves generated by its wake. The origin of these waves lies in the buoyant collapse of the large-scale coherent structures of the wake, and can be modelled as a source moving at the velocity of the body and of strength oscillating at the frequency of vortex shedding. In the presnt paper two parallel studies of the associated wavefield are described. The first of these is theoretical and considers localized and extended models of the source, while the second is experimental and involves a vertically oscillating and horizontally translating sphere. (from Authors) Some aspects of turbulence and mixing in stably stratified layers Fernando H.J.S. & Hunt J.C.R., Dynamics of Atmospheres & Oceans, 1996, 23/1-4 (35-62). In English. This paper presents a brief overview of recent work on turbulence and mixing in stably stratified flows. It is concluded (1) that the usual generalizations and 'scaling laws' of these flows need careful qualification, and (2) that the usual feature of unstratified turbulence ofhaving a single length scale for all large-scale processes may not be present, especially when mean shear and buoyancy forcing have different length scales and when there is significant wave motion (ie. the Ozmidov length scale is not the relevant macroscale). The second part of the paper reviews the modeling of motions and mixing in stable density interfaces interacting with contiguous layers of turbulence. Although the rates of mass and momentum transfer across stratified interfaces are much weaker than in unstratified turbulence, they play a crucial role in the heat and mass balances in the atmosphere and oceans. (from Authors) Efficiency of mixing by a turbulent jet in a stably stratified fluid Larson M. & Jonsson L., Dynamics of Atmospheres & Oceans, 1996, 24/1-4 (63-74). In English. Mixing in a two-layer stably stratified fluid by a turbulent jet was studied by a laboratory experiment. A nonswirling jet was discharged vertically downwards in a confined fluid system consisting initially of a top layer of fresh water and a bottom layer of salt water. A three-layer density structure developed in all cases with an intermediate layer that grew in size with time elapsed as fresh and salt water were mixed. The mixing efficiency, defined as the percentage of the supplied kinetic jet energy that is used for increasing the potential energy of the fluid system, was related to a densimetric Froude number based on the intermediate layer depth. Overall, the