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Keyword : stress
Results 1 - 5 of 18
New Methodology of Bending Fatigue Test and Slamming Test on PVC Foam Core Sandwich with GFRP Faces
The purpose of this study is to investigate the influence of a spatially moving load and edge effects on the fatigue life of the foam-cored sandwich structures. A spatially moving load can be observed in structures subjected to slamming. A new geometry of specimen is developed to reduce the influence of edge effects in the test specimen. Numerical model results of the new geometry are presented. This study confirms that edge effects are leading to early failures and shear stress concentrations are significantly reduced near the edges, improving ASTM C393 standard.
Experimental and numerical trimming optimizations for a mainsail in upwind conditions
This paper investigates the use of meta-models for optimizing sails trimming. A Gaussian process is used to robustly approximate the dependence of the performance with the trimming parameters to be optimized. The Gaussian process construction uses a limited number of performance observations at carefully selected trimming points, potentially enabling the optimization of complex sail systems with multiple trimming parameters. We test the optimization procedure on the (two parameters) trimming of a scaled IMOCA mainsail in upwind conditions. To assess the robustness of the Gaussian process approach, in particular its sensitivity to error and noise in the performance estimation, we contrast the direct optimization of the physical system with the optimization of its numerical model. For the physical system, the optimization procedure was fed with wind tunnel measurements, while the numerical modeling relied on a fully non-linear Fluid-Structure Interaction solver. The results show a correct agreement of the optimized trimming parameters for the physical and numerical models, despite the inherent errors in the numerical model and the measurement uncertainties. In addition, the number of performance estimations was found to be affordable and comparable in the two cases, demonstrating the effectiveness of the approach.
Updated Fatigue Test Methods for Structural Foams and Sandwich Beams
Foam-cored sandwich yacht hulls are subjected to high core shear stresses during slamming events. As slamming is
repetitive by nature, failures observed on boats may be due to fatigue. This study aims to investigate possible improvements to
fatigue testing of both foam core materials and sandwich specimens. In general test set-up induces differences between the ways a
material behaves in a test coupon and in a real application. One such difference is “edge effect”, as the material behaviour can change
close to a free edge. For example, the micro-structure may have been affected by the specimen machining, which may influence
failure initiation. This is exacerbated if the test set-up induces stress concentrations close to the edge. Another difference is that in a
standard core shear fatigue testing by 4 point bending, the stress field is spatially static, when in a slamming event the stress field is
spatially variable. Does the material react differently to a static and moving stress field? This study aims to develop a core shear test
method replicating a moving stress field, free of edge effect. This paper presents the finding of the initial steps of this study: The
edge effect has been investigated using modified loading fixture. The moving stress field has been investigated with a modified 4-
point bending test using asynchronous loading. The differences in test results between the modified test methods and the relevant
standard test methods indicate that both aspects affect measured fatigue life.
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).
Singularity MAXI: A Comparison of CFD and Tank Test Results
The boat concept of Lutra 80 Singularity was to create a true dual-purpose yacht that rewards its owner with
racecourse performance and a high level of interior luxury. The hull form and underwater appendages combined with an
aggressive sail plan showed impressive results on the racecourse. This task has required a significant amount of tank and
tunnel tests. Not all the planned tests could be carried out within a limited time and with a certain constraint on the budget.
This report presents the results of a series of CFD experiments based on the OpenFOAM platform.
Marin tank test gave results which were confirmed in the real tests in the sea. The main purpose of our computations at this
stage is to reproduce the resistance (drag) curves at various heeling angles. We used different mesh sizes and configurations.
In general, we achieved a good correspondence (within 10%) between CFD and Marin tank test results. However this
correspondence is not uniform. For more accurate results, it is necessary to apply refinement of the mesh, and continue to
search for suitable regularization parameters.