Center for Composite Materials - University of Delaware

Research Summary

Modeling of Water Slamming for Foam Core Sandwich Composite Structures

Authors: Y. Tsuchida (PhDCE), and J.W. Gillespie, Jr.

INTRODUCTION

 Advanced composite sandwich structure is widely used as the primary hull structure of high-speed marine crafts.
 Water slamming loads on the hull structure are crucial concern from the design perspective.
 Design methods for the impulsive loads have not been established well.
 Response of the composite sandwich hull structures needs to be predicted.

FE MODELING FOR WATER SLAMMING OF RIGID STRUCTURE

 LS-DYNA (mpp971d R5.1.1) with double precision
 Symmetric problem geometry
 2-D analysis assuming a plane strain state
 Non-reflecting boundaries on Exterior surfaces of the fluid domain
 8 node solid elements for all parts : Multi-material ALE formulation for fluids, one point integration for structure.
 Coupling force is computed and distributed on the structure (Lagrangian) element surface.

PREDICTION OF SLAMMING PRESSURE

 Rigid hull structure of sandwich materials with density and elastic properties
 Constant impact velocity corresponding to Sea State 6
 No gravity effect
 FEA results for slamming pressure are compared to the analytical solution by Wagner theory.

Fig 2: Slamming Pressure Distribution at Specified Time

PREDICTION OF SLAMMING PRESSURE

 Explicit analysis to validate material model behavior in explicit time integration
 2-D analysis assuming in-plane strain state for half symmetric model
 Foam core material (CORECELL P600) model
The material behavior is defined by stress – strain relationship.
Negligible Poisson’s effect is assumed.

COMPARISON OF BEAM DEFORMATIONS

Contour of Vertical Displacement

 FEA Result (The model is reflected about the symmetric plane)
 DIC (Digital Image Correlation) Measurement

COMPARISON OF LOAD CURVES

 The TPB simulation reasonably predicts the experimental behavior.
 However, the simulation results show the stiffer behavior than the experiment. The possible reasons are:
Inertia effects,
Assuming the in-plane strain state,
Not modeling the interlayer between the facesheet and the core.

SUMMARY

 The 2-D water slamming problem is modeled by the explicit FEA.
 The fine mesh models show good agreement with the analytical solution on prediction of the slamming pressures for the rigid structure.
 The deformable sandwich structure model reasonably predicts the experimental behavior in the explicit method.
 Ongoing work is to predict the foam core response due to water slamming.

ACKNOWLEDGEMENTS

This work is supported by the Office of Naval Research through the Advanced Materials Intelligent Processing Center.

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