Drag Force Parameters of Flexible Elements and Vegetation

Wednesday, 17 December 2014
John Allan Chapman1, Bruce N Wilson2 and John S Gulliver1, (1)University of Minnesota Twin Cities, Minneapolis, MN, United States, (2)Univ Minnesota, Saint Paul, MN, United States
This presentation evaluates parameters that characterize flow resistance and drag resulting from vegetation flexibility. Drag forces have been measured in a flume for simple cylindrical obstructions of the same shape and size but with different flexibility under several flow conditions. This data set is used to fit drag parameters and to relate their value to flexibility, Cauchy Number, and elastic modulus. A formulation is presented where the drag coefficient is evaluated as a function of the relative velocity and the elastic modulus of the obstruction. While a Vogel exponent and reference velocity can be used to provide a similar predicted response, the new formulation provides more insight to the physical behaviour occurring in the element.