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Keyword : slamming
Results 1 - 5 of 9
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.
There are many factors critical to the success of a Whitbread Round The World Race™ campaign. One of the most significant is the design, construction, and selection of an individual leg inventory of offwind sails. As a result of the technical challenges to the experimental and computational analysis of offwind sails, shape development for this class of sails has historically relied upon empirical efforts. An added element for any advanced, state-of-the-art, sail development program is the extensive reliance upon wind tunnel results to guide sail shape improvement and leg inventory selection of offwind sails. Lessons regarding improved offwind sail shapes, construction techniques, use of exotic materials, and sail trim learned or reinforced during the 1997-98 Whitbread Round the World Race sail development program for Swedish Match, are described with particular emphasis placed on the role of wind tunnel testing.
Current methods for assessing slamming of ships in head seas are generally based on constant-velocity wedge impact results for each hull section. A 2D Smoothed Particle Hydrodynamics (SPH) method is described for calculating slamming loads on realistic hull section shapes and impact velocity profiles. SPH is a particle-based method that is mesh-free and is therefore able to accurately simulate large free surface deformations such as jets and splashes, which are an important factor in slamming events. It is shown that large slamming pressures are predicted on wedge shaped hull sections and the concave part of flared monohull sections. Similarly, cross-deck slamming of catam aran hulls can produce large slamming pressures at the top of the arches. The nature of relative vertical velocity profiles during slam events is also discussed. Hull sections with varying velocity profiles are modelled using SPH to show the effect on slamming pressures as compared to the commonly used constant velocity profile.
Slotted Headsail Luff Support System - the development of these systems has proceeded at an extremely rapid rate. Starting with the Sea Stay and proceeding through the Stream Stay, Head Foil, Sail Leda, and Micro Foil, etc. Some of the new systems replace the headstay entirely while others fit on over (around, etc.) the existing headstay. This report establishes a framework for analysing these systems and reports on certain physical features of the more prominent ones.
Wind tunnel test results of a winglet keel model are presented. Results including force measurements and wake surveys for several winglet pitch angles and two winglet longitudinal positions are shown. The measured trends as well as the absolute values of the forces and the wake fields can be used for validating CFD codes.
An aerodynamic numerical optimisation procedure for an AC72 rigid wing sail was developed. The core of the method is the geometric parameterisation strategy based on a mesh morphing technique. The morphing action, which uses radial basis functions, is integrated within the Reynolds-averaged Navier-Stokes solver and provides an efficient parametric sail aerodynamic nanalysis method which is integrated in an optimisation environment based on a velocity prediction program. A hydrodynamic model is coupled to the parametric numerical solver in an iterative procedure. The shape modifiers operate on angle of attack and twist of nthe fore and aft wing element. For each true wind condition, the velocity of the boat is maximised by iterating between the solution of the velocity prediction program and the solution of the fluid dynamic solver. The effectiveness of the proposed method is demonstrated testing a range of wind speeds.
Experimental Study of the Hydro-Impact of Slamming in a Modern Racing Sailboat
The hydrodynamic impact, or hydro-impact, phenomenon caused by slamming on racing yachts and the local structure’s response is studied experimentally. Pressure transducers and a special measurement system named ‘Slam Patch’ have been designed and implemented to measure the hydro-impact pressure and/or the local structure’s response. The measurement systems were installed on a 1/7-scale model of an Open 60 yacht. Modal, rotational drop, and seakeeping-slamming tests are carried out. The measured hydro-impact pressure was processed statistically. A methodology to scale up the test results to prototype is mentioned. At the same time, the transient response of a simple structure under half-sine impulse is calculated using a commercial finite element analysis program to study the effect of the relationship between impulse duration and natural frequency of the structure.
An Investigation of Slam Events in Two Dimensions Using Smoothed Particle Hydrodynamics
Smoothed Particle Hydrodynamics (SPH) is a mesh-free Lagrangian computational method suited to modelling fluids with a freely deforming surface. In the present work, SPH has been applied to the problem of slamming, focusing particularly on the impact of two dimensional wedge forms on a free surface contained in a hydrostatic tank. Results from the wedge simulations have shown good agreement with previous experimental studies, paving the way for the work to be extended to mono-hull and catamaran hull forms. The completed validation of the SPH algorithm as applied to the two-dimensional dam beak test case is also discussed.