The aim of this work is to analyze bed form dynamics under the condition of imposed constraints of independent variables. The response of dunes is investigated through laboratory experiments carried out by varying sediment supply under constant water discharge or by varying water discharge under constant sediment supply. Experiments conducted in a sand bed flume allowed us to observe the behaviour of the dunes in terms of changes of the celerity, height and length, and the average slope of the bed was also observed. The experiments were conducted in simplified conditions: the flow was steady and uniform on average, the sediment was composed by almost uniform sand and the sediment transport was exclusively bed load, with a channel bed covered by two-dimensional dunes. Two types of experimental cycles were used based on whether the flow discharge or the sediment supply was kept constant: each experimental cycle starts in a state of sedimentological and hydraulic equilibrium; then a variation of the liquid flow or of the sediment supply is imposed. As a consequence to the imposed unbalance, the flow and bed geometry adjust their characteristics: bed slope, water depth, size and celerity of bed forms, until a new equilibrium condition is reached. Only data concerning the equilibrium states are considered. The analysis of experimental data highlights the role played by the dune dynamics as a response to the imposed change of liquid flow or of a sediment supply over a movable bed. A mathematical model based on the momentum conservation law is used to provide a physical interpretation of flow over dunes. Furthermore, the model was applied to give a definition of the existence conditions of the dunes and to define, the extent of the channel's potential adaptive behaviour in response to an imbalance between the sediment transport capacity of the liquid flow and the effective availability of solid material. ; Die Verformung von Transportkörpern (z.B. Dünen) durch die Strömung hat einen signifikanten Einfluss auf das ...


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    Title :

    Dune dynamics under specific constraints of flow discharge and sediment supply ; Dünendynamik bei gezielter Änderung des Durchflusses und der Sedimentzufuhr



    Publication date :

    2014-04-23



    Type of media :

    Theses


    Type of material :

    Electronic Resource


    Language :

    English



    Classification :

    DDC:    6 / 62 / 627 / 690