1,721,084 research outputs found
River confluences: a review of recent field and numerical studies
Full text linkConfluences are common components of all riverine systems and are characterized by converging streamlines and potential mixing of separate flows. The fluid dynamics of confluences is characterized by a highly complex structure with several common types of flow features observed. Many theoretical, field, laboratory and numerical studies tried to identify and clarify the main hydrodynamics, morphodynamics and ecological features of river confluences. Those studies spanned a wide range of flow and geometrical conditions ranging from laboratory-scale studies conducted in simplified geometries to field-scale studies of large-scale confluences. In particular, the identification of the main types of coherent structures generated within the post-confluence channel and of their dynamics has led to significant progress in understanding hydrodynamics and mixing processes at natural river confluences. Still, further research is needed to fully clarify how such structures interact among themselves and with the erodible bed and channel banks, how they redistribute momentum and affect transport of heat, suspended sediment, nutrients and what is their role in creating mixing patterns of dissolved and solid matter. In addition, the role of density differences between the incoming waters has garnered increasing attention in confluence studies, while the literature about the relationship between frequently observed species richness and confluence hydrodynamics is still limited. The present paper tries to review the literature on field and numerical studies of natural river confluences with a particular focus on the case in which density contrast affects confluence hydrodynamics and mixing and on large-scale river confluences. The paper discusses some main findings based on the field studies and eddy-resolving numerical simulations conducted by the authors. The application of bioenergetics metric at two large-size concordant bed confluences is also reported. Finally, the paper identifies some directions of future research that should lead to a better understanding of flow structure, transport processes, morphodynamics as well as of the ecological role of river confluences under different conditions
The purging of a neutrally buoyant or a dense miscible contaminant from a rectangular cavity
No full text
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Fully Developed Open Channel Flow Over Clusters of Freshwater Mussels Partially Buried in a Gravel Bed
Full text linkThe present study uses results of eddy‐resolving numerical simulations to investigate the open channel flow over large clusters of freshwater mussels (Unio elongatulus) partially buried in a rough, gravel bed. The density of the mussels forming the array varies from 26 to 500 mussels/m2. The flow structure is analyzed at large distances from the leading edge of the mussel bed, where the flow can be considered fully developed. The effects of changing the mussel bed density, the filtering discharge, the burial level and the roughness of the bed surface in which mussels are burrowed, are investigated in terms of flow field, turbulent structures, drag forces, and bed shear stresses. It is found that strong interactions occur between energetic eddies generated by the larger gravels on the exposed bed surface and by the mussel shells. Simulations results show that for a burial depth close to 50% and a ratio between the average gravel size and the mussel protruding height of 0.13, the shell induced turbulence becomes dominant for mussel bed densities around 50 mussels/m2. The influence of the bed roughness becomes less relevant with increasing mussel density, as the generation of energetic eddies is mostly controlled by mussel‐to‐mussel interactions. For fixed bed roughness, burial level and filtering velocity, the mean streamwise drag force and the associated drag coefficient for the exposed part of each mussel decrease with increasing mussel density, even if strong variations are observed for individual mussels. For constant mussel bed density and burial level, the mean streamwise drag force and the mean drag coefficient decrease slightly with increasing bed roughness. Increasing the burial level decreases not only the drag forces but also the drag coefficients because of the more streamlined shape of the top of the mussels. Strong active filtering acts toward decreasing the mean streamwise force and the mean drag coefficient. The spanwise drag forces contribute significantly to the total drag force, especially for high mussel bed densities. Based on smooth bed calculations, bed‐averaged shear stresses are reduced in highly dense clusters
- …
