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Keyword : composite materials
Results 1 - 5 of 51
Impact of Composite Layup on Hydrodynamic Performances of a Surface Pierc- ing Hydrofoil
Composite materials are good candidates for hydrofoils manufacturing, ensuring a good balance between strength and weight. In the high performances sailing yacht domain, hydrofoils are thin structures, highly loaded that experience sig- nificant displacements. This study investigates experimentally and numerically the influence of the laminate layup on the hydrodynamic performances of a surface piercing hydrofoil. Four hydrofoils with a constant chord, geometrically identical with different composite layups are mechanically characterized and tested in a hydrodynamic flume. The foils are designed to have a significant tip displacement of 5 to 10% of the span. Experimental results highlight a bending-twisting effect that leads to significant change in the hydrodynamic performances of the structures. Two different FSI numerical approach: from a potential code coupled with beam theory to the full coupling of a shell structural code and a VOF hydro model with free surface are presented and the first one is compared to the experiments with great results. The two approaches are two com- plementary bricks in the design process to compute the effect of passive deformation on hydrodynamic performances of the foils and therefore the yacht stability.
An Analytical Approach to Estimate the Compressive Strength of Carbon Fibre Reinforced Plastics
This study deals with the estimation of the compressive strength of carbon fibre reinforced plastics composites used in yacht racing. This property is one the key design parameters in marine engineering. The mechanism of fibre micro-buckling as well as a structural effect including the neighbouring plies of the unidirectional ply and the deformation gradient linked to the the mechanical loading are taken into account to propose an analytical model for estimating this property. The parameters involved require a number of experiments to characterise the microstructure at the level of components (fibre, matrix, ply) and the mechanical behaviour (elastoplasticity). Some of them can be estimated using a micro-mechanical approach. It is shown that estimations and experiments show good agreement on two cases: one with a constant deformation gradient, the other one in pure compression. The paramount influence of the initial misalignment of the fibre is highlighted.
Fully Integrated Fluid-Structural Analysis for the Design and Performance Optimisation of Fibre Reinforced Sails
This paper presents an advanced and accurate integrated
system for the design and performance optimisation of
fibre reinforced sails, commonly named string sails,
developed by SMAR Azure. This integrated design system
allows sail designers not only to design sail shapes and the
reinforcing fibre paths, but also to validate the performance
of the flying sail shape and have accurate production
details including the overall sail weight, material used,
which means costs, and length of the fibre paths, which
means production time.
The SMAR Azure design and analysis method,
extensively validated and used to optimise several racing
and super-yacht sailing plans, includes a computationally
efficient structural analysis method coupled with a
modified vortex lattice method, with wake relaxation, to
enable a proper aeroelastic simulation of sails in upwind
conditions. The structural analysis method takes into
account the geometric non-linearity and wrinkling
behaviour of membrane structures, such as sails, the fibre
layout, the influence of battens, trimming loads and
interaction with rigging elements, e.g. luff sag calculation
on a headstay, in a timely manner.
Specifically, this paper presents an optimisation of a real
fibre reinforced membrane sailplan of an aluminium super
yacht, carried out in collaboration with Paolo Semeraro
(Banks Sails Europe). The optimisation process of the fibre
layouts led to a sensible reduction in maximum stress,
strain and displacement compared to the initial designs,
keeping the same fibre weight or slightly increasing it. The
results have been confirmed in the sailing tests, although no
exact measurements have been performed.
Sailing Yacht Transom Sterns - A Systematic CFD Investigation
The question adressed in this project is whether modern hull lines with wide, box-shaped transoms, that seem
to originate from extreme racing machines, are also beneficial for modern performance cruisers from a hydrodynamic
performance point of view. A new 41 ft (12.3 m) hull was designed as an average of contemporary performance hulls in
the 40 ft segment. The aft part of the hull was stretched stepwise and cut at constant length overall in order to
systematically increase the transom size. Six hull variations with box shaped transoms were created in this way. To
investigate the influence of the transom shape, the six hull variants were redesigned with a more rounded transom. The
resistance was calculated for all twelve hulls in the upright and heeled conditions at Froude numbers 0.35 and 0.60. The
computations were carried out using a Reynolds-Averaged Navier-Stokes (RANS) solver with a Volume of Fluid (VOF)
representation of the free surface. The solver was validated against several hulls in the Delft Systematic Yacht Hull
Series (DSYHS). Very different optima are found for the low and high speed cases. In an upwind-downwind race the
round transoms performed best for the three fastest transom sizes. The fastest hull around the course has an immersed
transom area to midship area ratio of 0.16 and it has a rounded shape. It is 1.9 % faster than a more box like transom.
Overall the round transoms are faster around the race course.
Characterisation of the Processing Properties of Out-of-Autoclave Prepregs
Out-of-autoclave prepregs are the construction material of choice for high performance marine craft, due to their high
material properties, and relatively low processing costs compared to traditional autoclave prepregs. Because of the low compaction
pressure, voids are not collapsed by external pressure; therefore air must be removed from the laminate prior to cure to ensure a low
void-content, high quality laminate is produced. This work presents the development of experimental techniques to accurately
measure the as-laminated void content, compaction response and in-plane and through thickness air permeability of two prepreg
materials. The material models developed were implemented into an air removal model, and compared against experiments.
Excellent correlation was observed for the cloth material, whereas the unidirectional material exhibited complete closing of air
pathways, which was not captured well by the current model.