The work presents an experimental investigation into the motion of and hydrodynamic forces along a single flexible stem in regular waves. The experiment covers a large range in relevant non-dimensional parameters: the drag-to-stiffness ratio, the inertia-to-stiffness ratio, the Keulegan-Carpenter number and the Reynolds number. The two first parameters relate to the response of the stem in waves and thus account for material properties, while the two last parameters are relevant for hydrodynamic forces on the stem. The displacement of the stem was captured with a digital video camera and the displacement along the stem was captured for every 2.5 mm at 25 Hz. This unique laboratory data set allowed for the following analyses: (i) Determination of the relevant non-dimensional parameter to predict the stem motion and shape. (ii) A direct comparison between the measured force for mimics of two lengths (0.15 m and 0.30 m) illustrating the force reduction potential for flexible mimics. (iii) Direct evaluation of the average force coefficients (drag) and (inertia) for the flexible stems. (iv) The distributed external hydrodynamic loading and the internal shear forces were estimated from the laboratory experiments. The distribution of the shear force helped to understand the breakage mechanisms of flexible stems. (v) A linkage between phase lags and internal shear forces was suggested. The data set is considered valuable as validation material for numerical models of stem motion in waves.@en

This study presents a detailed comparison between the k-. e(open) and k-. τ turbulence models. It is demonstrated that the numerical accuracy of the k-. e(open) turbulence model can be improved in geophysical and environmental high Reynolds number boundary layer flows. This is achieved by transforming the k-. e(open) model to the k-. τ model, so that both models use the same physical parametrisation. The models therefore only differ in numerical aspects. A comparison between the two models is carried out using four idealised one-dimensional vertical (1DV) test cases. The advantage of a 1DV model is that it is feasible to carry out convergence tests with grids containing 5 to several thousands of vertical layers. It is shown hat the k-. τ model is more accurate than the k-. e(open) model in stratified and non-stratified boundary layer flows for grid resolutions between 10 and 100 layers. The k-. τ model also shows a more monotonous convergence behaviour than the k-. e(open) model. The price for the improved accuracy is about 20% more computational time for the k-. τ model, which is due to additional terms in the model equations. The improved performance of the k-. τ model is explained by the linearity of τ in the boundary layer and the better defined boundary condition.

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