The Role of Curvature and Structural Compliance on Water Impact Loading of Composite Structures

Abstract

The widespread use of composite sandwich structures in offshore racing yachts and the nature of competitive racing have led to the development of lighter and stiffer structures designed increasingly closer to expected loads. Unfortunately, “What loads are to be expected?” is an open question, especially for ocean going yachts where hull slamming, also known as water impact, is a critical design case. Water impact has been a topic of research since the early 1900’s initially in relation to sea plane landing but much work, both experimental and analytical, has been carried out on bodies of different shapes though the main focus has been on water impact of wedge shaped bodies. This work focuses first on the effect of curvature on constant velocity rigid body water impact loads, and then on the structural response of corresponding deformable composite sandwich panels subjected to water impact. Specimens were subjected to constant velocity water impact via a servo-hydraulically controlled constant velocity panel impact system. The physical testing of specimens ranging in radius from 0.300 to 5.00m at impact velocities of 1-5 m/s was conducted in parallel with a Smoothed Particle hydrodynamics (SPH) based study using the LSDYNA solver. A novel application of a time-frequency based goodness of fit tool was used in order to quantitatively compare the intricate time histories from experiments and simulations with promising results. Curvature was found to significantly affect the loads experienced by rigid specimens with peak impact force increasing with specimen radius. Reasonable correlation of peak impact force with existing analytical and empirical models found in literature was observed. Rigid specimens did not obey linear or Froude based scaling rules proposed in literature but a modification to existing scaling methods is proposed which significantly improves correlation with experimental data. Deformable specimens were found to experience reduced loads and pressures in comparison to rigid specimens. Specimens with little curvature were found to experience an unstable loading region due to snap-through instability where consistent loads produce varied specimen response.