Sloshing induced damping across Froude numbers in a harmonically vertically excited system

An investigation was performed to measure sloshing motion and damping during harmonic forced vertical motion of a rectangular tank containing fluid, with a particular focus on the amplitude dependent transition between lateral sloshing and turbulent, vertical slamming. Qualitative and quantitative explanations are provided for the damping saturation point and dissipation effects, together with metrics to distinguish the different sloshing regimes, and a ballistic-harmonic analytical model is presented capable of reproducing the physical trends. Image processing tools were used to analyse experimental high-speed video footage, illustrating potential routes to increased damping in vertically oscillating structures, and correlating well with measured fluid forces and flow regimes. Keywords: Damping, Sloshing, Loads Alleviation, Parametric excitatio

Analysis of Damping From Vertical Sloshing in a SDOF System

The effect of the sloshing motion of liquid in a tank on the vertical transient motion of a single degree of freedom system is investigated. Step release tests of a vertically vibrating structure, including a tank containing liquid, demonstrate that added damping from the sloshing motion depends upon the amount of fluid in the tank and the maximum acceleration. The maximum amount of damping was observed at a 50% fill level and the system showed three distinct response regimes during the transient decay, all related to different motions of the fluid. The first response regime, immediately at the start of the transient, is considered to be the most important to exploit for aircraft gust loads alleviation due to its dominant role in the overall energy dissipation balance. Further, to advance the understanding of the modelling and predictive capabilities, coupled fluid-structure models of two opposing levels of fidelity were developed and evaluated. Namely, smoothed particle hydrodynamics (SPH) and an equivalent mechanical model (EMM) based on a bouncing ball model were considered to represent the fluid motion in the tank during the experiment. Both models are shown to provide good predictive capability in the initial impacting sloshing mode while the subsequent flow regime can be predicted with the SPH model only. The findings in this paper open routes towards improved coupled fluid-structure models and their use in improved aeroelastic wing design

Nonlinear Identification of Transient Tank Vertical Sloshing Motions

In an effort to reduce the fuel burn of commercial jet aircraft, much effort is currently being devoted towards reducing the loads that aircraft experience in-flight due to gusts and turbulence using a range of passive and active methodologies. The EU H2020 SLOW-D project is undertaking a series of fundamental experiments to gain an understanding of vertical sloshing and the added damping that these motions provide, and to apply them for future aircraft wing designs. Recent transient and harmonic experiments undertaken as part of SLOW-D have shown that the added damping from the vertical sloshing motion is a function of the motion amplitude, filling level and excitation frequency. Further, the transient tests have shown that the added damping to a single DOF system comprises three different physical sloshing regimes, whereas the harmonic tests show the importance of the Froude number. In this paper, a selection of the experimental transient data sets from vertical sloshing experiments are analysed using nonlinear identification techniques based upon NAR and NARX models. It is shown how a continuous time model can be identified that accurately predicts the variation of the damping with amplitude and frequency. Surrogate models of identified parameters are developed to enable parametric studies

Effect of Fuel Sloshing on the Damping of a Scaled Wing Model – Experimental Testing and Numerical Simulations

Vertical sloshing of liquid-filled tanks has been shown to induce substantial dissipative effects. Building upon these previous results obtained on simpler sloshing systems, a scaled wing prototype is presented here, equipped with a fuel tank that allows the observation of liquid sloshing and quantification of induced dynamic effects. Based on experiments conducted at a 50% filling level for a baffled wing fuel tank model, substantial additional damping effects were demonstrated with liquid inside the tank regardless of the vertical acceleration amplitude. A numerical model based on a finite element wing structural model and a surrogate 1DOF fluid model was explored, with numerical simulations showing good agreement compared to experiments throughout the decaying motion of the system