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Author : Tom Allen
Results 1 - 2 of 2
Hydroelasticity in Slamming Impacts of Flexible Composite Hull Panels
Design of hulls is typically undertaken on the assumption that the pressures applied are the same as if the hull was rigid.
Understanding the effect a flexible structure has on the loads and responses during slamming events will improve the design process
for high speed marine craft. In reality the loads may vary due to fluid-structure interaction during the impact. This work characterises
the variations in both applied pressure and panel response due to hydroelasticity. Water impacts of flat panels have been undertaken
using a purpose built servo-hydraulic slam testing system with impact velocities up to 6.0 m/s and a deadrise angles of 10°. The
unsupported panel area was approx. 1000 x 500 mm with simply supported boundaries along all four edges. Clear trends between a
panel's flexibility and the total force and applied pressure have been observed. The changes in both loads and responses are largest at
the centre and chine edge of the panel. These variations can be related to the significant changes in local velocity (centre) and
deadrise angle (chine).
Polymeric foam materials are widely used as cores for sandwich composite hull structures in high performance marine vessels. Designers are faced with the challenge of selecting the most appropriate material type and density from the many different formulations of foams available on the market. Transient hydrodynamic pressures from slamming generate local regions of high transverse shear forces in the vicinity of panel boundaries and are hence a key load case for hull panel design of high-speed craft. The transient nature of the loading can generate stress rates that are high enough to affect the strength of the core material, particularly for polymeric foams. However material properties for foams are typically characterised by quasi-static, or in a few cases elevated rate, loading of coupon scale specimens, and there is very limited information available about how different polymeric cores behave in actual slamming events. The aim of this paper is to evaluate the strength of a range of polymeric core materials in controlled laboratory slam testing, and compare these to strengths measured by static and dynamic loading of coupon scale specimens. Core materials studied included Cross-linked and Linear PVC, PET and SAN Foams. This combination of materials provided a range of different levels of ductility from the low-elongation PET cores through to the high-elongation linear PVC and SAN foams. Results of the slam testing provided a quantitative ranking of the core materials, supporting empirical experience that high-elongation materials can perform better in slamming situations than predicted by their quasi-static strengths.
