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Keyword : slamming loads
Results 1 - 5 of 15
Hull - Furniture Interaction in the Primary Response to Global Loads of a Sailing Yacht
The aim of this work is to investigate the contribution of those “non-structural” components to the hull strength in order to evaluate their effect on the stress and deformation distribution of a large sailing yacht. Two different finite element models of a 94 ft sailing yacht, with and without “non structural components”, have been carried out with a very high level of detail in order to evaluate the outfit and furniture contribution to the primary hull response.
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).
Slamming Induced Loads on a Rigid Cylinder and Comparison with Rigid Wedges
Slamming is a pervasive issue for marine vehicles, few of which are composed entirely of flat panels. Experimental and numerical data from flat panels and wedges are often extrapolated to handle other shapes because much previous work has focused on flat panels and wedges. Though correction factors and other strategies have been employed to achieve satisfactory correlation, curved shapes behave in a fundamentally different way. The current work seeks to investigate the effect of curvature on slamming loads through the use of constant velocity experimental testing and coupled Finite Element-Smoothed Particle Hydrodynamics numerical simulations. Experiments and numerical modelling conducted in the current work show that curved bodies experience a much higher initial loading than rigid wedges, which then abates to a quasi-constant residual load. This load profile varies significantly from that found in flat panels. Peak impact force and impulse plots generated from simulating a range of geometries indicate rigid cylinder slamming represents a more severe load case than rigid wedge slamming. Correlation between experiments and simulations is evaluated by comparison of the time-frequency domain representations of the respective transient signals which results in a single goodness of fit value. Once correlated, numerical simulation techniques can be used to further investigate the influence of curvature on slamming loads. Understanding this relationship between curvature and slamming loads has the potential to increase design optimization resulting in more failure resistant structures.
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.
A combined strip theory and Smoothed Particle Hydrodynamics approach for estimating slamming loads on a ship in head seas
Smoothed Particle Hydrodynamics (SPH) is a mesh-free Lagrangian numerical method suited to modelling fluids with a freely deforming surface. A two-dimensional SPH algorithm has been developed and applied to the problem of ship keel and bow-flare slamming. Freely decelerating drop tests of a model flared hull section were used as a basis for an initial validation of the SPH model. Relative vertical velocity profiles measured during tow tank experiments were then imposed on two-dimensional SPH models and reasonable agreement between the experimental and numerical slamming pressures was found. Finally, relative vertical velocity profiles calculated using SEAWAY software were implemented in the SPH algorithm, so as to simulate slamming on a typical V-form hull model.