Experimental investigation of the fluid-structure interaction during the water impact of thin aluminium plates at high horizontal speed

Spinosa, Emanuele; Iafrati, Alessandro

doi:10.1016/j.ijimpeng.2020.103673

Cited by 16 publications

(5 citation statements)

References 35 publications

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“…The objective of these experiments is to provide an estimate of the forces acting on the fuselage during a guided water landing, thus to retrieve essential information on the aircraft dynamics in this critical phase. Whereas an accurate reproduction of the hydrodynamic phenomena and of the fluid-structure interaction aspects occurring in the ditching phase necessarily needs full scale tests on sample specimens [40,3,41,42], the investigation of the aircraft dynamics at ditching can be only conducted with small-scale free-flight tests [43,44,45]. The difficulties in achieving a precise control of the attitude of the aircraft when it touches the water, together with the strong non-linearity of the loading associated to the water impact, make such kind of tests not very useful neither for the verification of the final design, nor for the validation of computational model used in the design phase.…”

Section: Experimental Setup and Datamentioning

confidence: 99%

A noise reduction method for force measurements in water entry experiments based on the Ensemble Empirical Mode Decomposition

Spinosa,

Iafrati

2021

Preprint

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In this paper a denoising strategy based on the EEMD (Ensemble Empirical Mode Decomposition) is used to reduce the background noise in non-stationary signals, which represent the forces measured in scaled model testing of the emergency water landing of aircraft, generally referred to as ditching. Ditching tests are performed at a constant horizontal speed of 12 m/s with a controlled vertical motion, resulting in a vertical velocity at the beginning of the impact of 0.45 m/s. The measured data are affected by a large amplitude broadband noise, which has both mechanical and electronic origin. Noise sources cannot be easily avoided or removed, since they are associated with the vibrations of the structure of the towing carriage and to the interaction of the measuring chain with the electromagnetic fields. The EEMD noise reduction method is based on the decomposition of the signal into modes and on its partial reconstruction using the residue, the signal-dominant modes and some further modes treated with a thresholding technique, which helps to retain some of the sharp features of the signal. The strategy is developed and tested first on a synthetic signal with a superimposed and known background noise. The method is then verified on the measurement of the inertial force acting on the fuselage when it is moving in air, as in this case the denoised force should equal the product of the mass by the acceleration, both of them being known. Finally, the procedure is applied to denoise the forces measured during the actual ditching experiment. The results look superior to the application of classical filtering methods, such as a moving average filter and a low-pass FIR filter, particularly due to the enhanced capabilities of the EEMD-denoising strategy here developed to preserve the sharp features of the signals and to reduce the residual low-frequency oscillations of spurious origin.

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Section: Experimental Setup and Datamentioning

confidence: 99%

A noise reduction method for force measurements in water entry experiments based on the Ensemble Empirical Mode Decomposition

Spinosa,

Iafrati

2021

Preprint

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“…In a computational study on the 2-D oblique impact of an elastic plate (beam) with free-free boundary condition at both ends on a thin liquid layer, Khabakhpasheva & Korobkin (2020) also show the possibility of air entrainment as a consequence of plate deformation and rotational motion. Spinosa & Iafrati (2021) conducted an experimental study of the water impact of aluminum plates at large horizontal speed and it is pointed out that the structural deformation causes a reduction in peak pressure and an increase in the total load. Faltinsen (1999) proposed an orthotropic plate theory for the coupled analysis of the structural dynamics and the flow motion during the vertical water entry of a ship panel.…”

Section: Introductionmentioning

confidence: 99%

The controlled impact of elastic plates on a quiescent water surface

Wang

Wong

et al. 2022

J. Fluid Mech.

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The impact of flexible rectangular aluminum plates on a quiescent water surface is studied experimentally. The plates are mounted via pinned supports at the leading and trailing edges to an instrument carriage that drives the plates at constant velocity and various angles relative to horizontal into the water surface. Time-resolved measurements of the hydrodynamic normal force ( $F_n$ ) and transverse moment ( $M_{to}$ ), the spray root position ( $\xi _r$ ) and the plate deflection ( $\delta$ ) are collected during plate impacts at 25 experimental conditions for each plate. These conditions comprise a matrix of impact Froude numbers ${Fr} = V_n(gL)^{-0.5}$ , plate stiffness ratios $R_D= \rho _w V_n^2 L^3D^{-1}$ and submergence time ratios $R_T= T_sT_{1w}^{-1}$ . It is found that $R_D$ is the primary dimensionless ratio controlling the role of flexibility during the impact. At conditions with low $R_D$ , maximum plate deflections on the order of $1$ mm occur and the records of the dimensionless form of $F_n$ , $M_{to}$ , $\xi _r$ and $\delta _c$ are nearly identical when plotted vs $tT_s^{-1}$ . In these cases, the impact occurs over time scales substantially greater than the plate's natural period, and a quasi-static response ensues with the maximum deflection occurring approximately midway through the impact. For conditions with higher $R_D$ ( $\gtrsim 1.0$ ), the above-mentioned dimensionless quantities depend strongly on $R_D$ . These response features indicate a dynamic plate response and a two-way fluid–structure interaction in which the deformation of the plate causes significant changes in the hydrodynamic force and moment.

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“…More recently, water entry tests on flat plate ditching at high horizontal speed were performed in Iafrati et al (2015) and in Iafrati (2016). Particular attention was also paid to the analysis of the structural deformations, see Spinosa and Iafrati (2021). The study was further extended to double curvature specimens, for which hydrodynamic phenomena such as cavitation and ventilation have been observed to be important (see Iafrati and Grizzi (2019); Iafrati et al (2020)).…”

Section: Introductionmentioning

confidence: 99%

“…These works have shown that during the impact phase a localised high pressure area develops on the submerged part of the aircraft at the spray root (Climent et al (2006); Seddon and Moatamedi (2006)). The large pressure areas result in very large hydrodynamic loads, which can lead to a possible structural damage of the fuselage and to fluid-structure interaction phenomena (Groenenboom and Cartwright (2010); Cheng et al (2011); Hughes et al (2013); Groenenboom and Siemann (2015); Spinosa and Iafrati (2021)).…”

Section: Introductionmentioning

confidence: 99%

Hydrodynamic analysis of the water landing phase of aircraft fuselages at constant speed and fixed attitude

Spinosa¹,

Broglia²,

Iafrati³

2022

Preprint

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In this paper the hydrodynamics of fuselage models representing the main body of three different types of aircraft, moving in water at constant speed and fixed attitude is investigated using the Unsteady Reynolds-Averaged Navier-Stokes (URANS) level-set flow solver χnavis. The objective of the CFD study is to give insight into the water landing phase of the aircraft emergency ditching. The pressure variations over the wetted surface and the features of the free surface are analysed in detail, showing a marked difference among the three shapes in terms of the configuration of the thin spray generated at the front. Such a difference is a consequence of the different transverse curvature of the fuselage bodies. Furthermore, it is observed that at the rear, where a change of longitudinal curvature occurs, a region of negative pressure (i.e. below the atmospheric value) develops. This generates a suction (downward) force of pure hydrodynamic origin. In order to better understand the role played by the longitudinal curvature change on the loads, a fourth fuselage shape truncated at the rear is also considered in the study. The forces acting on the fuselage models are considered as composed of three terms: the viscous, the hydrodynamic and the buoyancy contributions. For validation purposes the forces derived from the numerical simulations are compared with experimental data.

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Experimental investigation of the fluid-structure interaction during the water impact of thin aluminium plates at high horizontal speed

Cited by 16 publications

References 35 publications

A noise reduction method for force measurements in water entry experiments based on the Ensemble Empirical Mode Decomposition

A noise reduction method for force measurements in water entry experiments based on the Ensemble Empirical Mode Decomposition

The controlled impact of elastic plates on a quiescent water surface

Hydrodynamic analysis of the water landing phase of aircraft fuselages at constant speed and fixed attitude

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