Hydroelastic effects during the fast lifting of a disc from a water surface

Abstract

Here we report the results of an experimental study where we measure the hydrodynamic force acting on a plate which is lifted from a water surface, suddently starting to move upwards with an acceleration much larger than gravity. Our work focuses on the early stage of the plate motion, when the hydrodynamic suction forces due to the liquid inertia are the most relevant ones. Besides the force, we measure as well the acceleration at the center of the plate and the time evolution of the wetted area. The results of this study show that, at very early stages, the hydrodynamic force can be estimated by a simple extension to the linear exit theory by Korobkin (2013), which incorporates an added mass to the body dynamics. However, at longer times, the measured acceleration decays even though the applied external force continues to increase. Moreover, high-speed recordings of the disc displacement and the radius of the wetted area reveal that the latter does not change before the disc acceleration reaches its maximum value. We show in this paper that these phenomena are caused by the elastic deflection of the disc during the initial transient stage of water exit. We present a linearised model of water exit that accounts for the elastic behaviour of the lifted body. The results obtained with this new model agree fairly well with the experimental results.

Experimental investigation of the water entry and/or exit of axisymmetric bodies

“…Evolution of as a function of the non-dimensional elevation during the water exit of the disc for different values of . The plots denoted by , , and correspond to four experimental results obtained by Vega-Martínez et al (2019) with a 10.8 cm radius circular disc.…”

“…

Figure 29.Evolution of as a function of the non-dimensional elevation during the water exit of the disc for different values of . The plots denoted by , , and correspond to four experimental results obtained by Vega-Martínez et al (2019) with a 10.8 cm radius circular disc.

Figure 30.Evolution of as a function of the non-dimensional elevation during the water exit of the cone for different values of .

Figure 31.Evolution of as a function of the non-dimensional elevation during the water exit of the sphere for different values of .

…”

“…The results obtained for the disc, the cone and the sphere are plotted in figures 29, 30 and 31, respectively. The experimental results of Vega-Martínez et al (2019) corresponding to the water exit of an elastic circular disc are also shown for comparison in figure 29, but note that their experimental results are limited to c(t)/c 0 > 0.9. Two important conclusions can be drawn from these observations.…”

“…Reis et al (2010) conducted their experiments at very low scale on circular discs and without measuring the hydrodynamic force or the evolution of the wetted surface. More recently, Vega-Martínez et al (2019) published experimental results on the water exit of a circular disc, but the elasticity of the disc had a large effect on the results and the measurement of the wetted surface was restricted to the very beginning of the water exit ().…”

Hydroelastic effects during the fast lifting of a disc from a water surface – CORRIGENDUM

“…In figure 6 of our paper (Vega-Martínez et al. 2019), incorrect values of the plate lifted height, , were used for the horizontal axis. These values correspond to correct measurements of the plate height, but at later times, due to a mistake in the frame rate of one of the videos that was introduced in the image processing algorithm.…”