Ditching is considered as one of the important aspects of safety performances of airplanes. It is related primarily with the fluid-solid interaction, whose studies mainly depend on experiments at the present time. Num...Ditching is considered as one of the important aspects of safety performances of airplanes. It is related primarily with the fluid-solid interaction, whose studies mainly depend on experiments at the present time. Numerical and analytical methods for fluid-solid interaction by using 3-D full scale airplane＇s model will reduce the dependence on the expensive model tests. Numerical studies can be used to estimate the safety of ditching and provide a reference for the crashworthiness design. This article proposes a 3-D dynamical structural model after the real shape of an airplane and an Arbitrary Lagrange-Euler （ALE） fluid-field model, to simulate the fluid-solid interactions caused by low speed ditching. The simulation is based on interaction computational methods, within LS-DYNA nonlinear finite-element code. The results of pressure distributions and accelerating time histories of the airplane＇s subfloor are discussed in the context of the safety of ditching, and the simulation results and the analytical methods are verified.展开更多
The violent water entry of flat plates is investigated using a Riemann-arbitrary Eulerian-Lagrangian（ALE） smoothed particle hydrodynamics（SPH） model. The test conditions are of interest for problems related to air...The violent water entry of flat plates is investigated using a Riemann-arbitrary Eulerian-Lagrangian（ALE） smoothed particle hydrodynamics（SPH） model. The test conditions are of interest for problems related to aircraft and helicopter emergency landing in water. Three main parameters are considered： the horizontal velocity, the approach angle（i.e., vertical to horizontal velocity ratio） and the pitch angle, a. Regarding the latter, small angles are considered in this study. As described in the theoretical work by Zhao and Faltinsen（1993）, for small a a very thin, high-speed jet of water is formed, and the time-spatial gradients of the pressure field are extremely high. These test conditions are very challenging for numerical solvers. In the present study an enhanced SPH model is firstly tested on a purely vertical impact with deadrise angle α=4°. An in-depth validation against analytical solutions and experimental results is carried out, highlighting the several critical aspects of the numerical modelling of this kind of flow, especially when pressure peaks are to be captured. A discussion on the main difficulties when comparing to model scale experiments is also provided. Then, the more realistic case of a plate with both horizontal and vertical velocity components is discussed and compared to ditching experiments recently carried out at CNR-INSEAN. In the latter case both 2-D and 3-D simulations are considered and the importance of 3-D effects on the pressure peak is discussed for α=4° and α=10°.展开更多
基金supported by the Shanghai Key Basic Research Program of China (Grant No. 07JC14001)
文摘Ditching is considered as one of the important aspects of safety performances of airplanes. It is related primarily with the fluid-solid interaction, whose studies mainly depend on experiments at the present time. Numerical and analytical methods for fluid-solid interaction by using 3-D full scale airplane＇s model will reduce the dependence on the expensive model tests. Numerical studies can be used to estimate the safety of ditching and provide a reference for the crashworthiness design. This article proposes a 3-D dynamical structural model after the real shape of an airplane and an Arbitrary Lagrange-Euler （ALE） fluid-field model, to simulate the fluid-solid interactions caused by low speed ditching. The simulation is based on interaction computational methods, within LS-DYNA nonlinear finite-element code. The results of pressure distributions and accelerating time histories of the airplane＇s subfloor are discussed in the context of the safety of ditching, and the simulation results and the analytical methods are verified.
基金partially received funding from the European Union's Horizon 2020 Research and Innovation Programme (Grant No. 724139)
文摘The violent water entry of flat plates is investigated using a Riemann-arbitrary Eulerian-Lagrangian（ALE） smoothed particle hydrodynamics（SPH） model. The test conditions are of interest for problems related to aircraft and helicopter emergency landing in water. Three main parameters are considered： the horizontal velocity, the approach angle（i.e., vertical to horizontal velocity ratio） and the pitch angle, a. Regarding the latter, small angles are considered in this study. As described in the theoretical work by Zhao and Faltinsen（1993）, for small a a very thin, high-speed jet of water is formed, and the time-spatial gradients of the pressure field are extremely high. These test conditions are very challenging for numerical solvers. In the present study an enhanced SPH model is firstly tested on a purely vertical impact with deadrise angle α=4°. An in-depth validation against analytical solutions and experimental results is carried out, highlighting the several critical aspects of the numerical modelling of this kind of flow, especially when pressure peaks are to be captured. A discussion on the main difficulties when comparing to model scale experiments is also provided. Then, the more realistic case of a plate with both horizontal and vertical velocity components is discussed and compared to ditching experiments recently carried out at CNR-INSEAN. In the latter case both 2-D and 3-D simulations are considered and the importance of 3-D effects on the pressure peak is discussed for α=4° and α=10°.
