Water Impact Test and Simulation of a Composite Energy Absorbing Fuselage Section

A 25‐ft/s vertical drop test of a composite fuselage section was conducted onto water. The purpose of the test was to obtain experimental data characterizing the structural response of the fuselage section during water impact for comparison with two previous drop tests that were performed onto a rigid surface and soft soil. For the drop test, the fuselage section was configured with ten 100 lb. lead masses, five per side, that were attached to seat rails mounted to the floor. The fuselage section was raised to a height of 10 ft. and dropped vertically into a 15 ft. diameter pool filled to a depth of 3.5 ft. with water. Approximately 70 channels of data were collected during the drop test at a 10 kHz sampling rate. The test data were used to validate crash simulations of the water impact that were developed using the nonlinear, explicit transient dynamic codes, MSC.Dytran and LS‐DYNA. The fuselage structure was modeled using shell and solid elements with a Lagrangian mesh, and the water was modeled with both Eulerian and Lagrangian techniques. The fluid‐structure interactions were executed using the “fast” general coupling in MSC.Dytran and the Arbitrary Lagrange‐Euler (ALE) coupling in LS‐DYNA. Additionally, the smooth particle hydrodynamics (SPH) meshless Lagrangian technique was used in LS‐DYNA to represent the fluid. The simulation results were correlated with the test data to validate the modeling approach. Additional simulation studies were performed to determine how changes in mesh density, mesh uniformity, fluid viscosity, and failure strain influence the test‐analysis correlation.