Optimal design of stiffened composite underwater hulls

International audienceThis numerical study deals with the stiffened composite underwater vessel design. The structures under investigation are laminated cylinders with rigid end-closures and inter-nal circumferential and longitudinal unidirectional composite stiffeners. Structural buckling induced by the high external hydrostatic pressure is considered as the major failure risk. An optimization design tool has been developed to obtain the reinforcement definition which maximizes the limit of stability: an analytical model of cylindrical composite shell buckling has been coupled to a genetic algorithm procedure. The numerical optimization tests carried out corroborate design tendencies validated previously by experiments

Optimized laminations for submarine composite hulls

International audienceThis work deals with the development of a numerical tool for the design of filament wound submersible composite cylinders. A genetic algorithm coupled with analytical shell models allows stacking sequences to be optimized in order to increase the buckling pressures. The examples presented concern IFREMER's current studies and characteristic lamination patterns have been obtained. FEM calculations confirm the gains corresponding to the solutions obtained. The robustness of the optimized laminations is attentively studied. The performances of the optimization procedure are also discussed.Ce travail concerne l'élaboration d'un outil numérique d'aide à Ia conception d 'enceintes sous-marines cylindriques composites réalisées par enroulement filamentaire. Un algorithme génétique couplé à des modèles analytiques des coques permet d'en optimiser Ia stratification afin d'accroître Ia limite de flambage. Les applications présentées sont liées aux travaux actuels de l'IFREMER. Les calculs d'optimisation ont conduit à l'obtention d'un type de stratification caractéristique. Les calculs MEF confirment l'intérêt des solutions optimisées. Une attention particulière est accordée à l'étude de Ia robustesse de ces solutions. De plus, les performances de Ia procédure d'optimisation sont analysées

Optimal laminations of thin underwater composite cylindrical vessels

This paper deals with the optimal design of deep submarine exploration housings and autonomous underwater vehicles. The structures under investigation are thin-walled laminated composite unstiffened vessels. Structural buckling failure due to the high external hydrostatic pressure is the dominant risk factor at exploitation conditions. The search of fiber orientations of the composite cylinders that maximize the stability limits is investigated. A genetic algorithm procedure coupled with an analytical model of shell buckling has been developed to determine numerically optimized stacking sequences. Characteristic lamination patterns have been obtained. FEM analyses have confirmed the corresponding significant increases of buckling pressures with respect to initial design solutions. Experiments on thin glass/epoxy and carbon/epoxy cylinders have been performed. The measured buckling pressures appear to be in good agreement with numerical results and demonstrate the gains due to the optimized laminations

Composite Cylinders for Deep Sea Applications: An Overview

In order to develop the knowledge base necessary to design deep sea pressure vessels it is essential to understand the full chain from design and manufacturing through NDT and characterization to long term behavior under hydrostatic pressure. This paper describes results from European and national research programs focusing on the use of composites for underwater applications over the last 20 years. Initial tests on small glass/epoxy cylinders were followed by large demonstration projects on carbon/epoxy cylinders with implosion pressures of up to 600 bar, corresponding to 6000 meter depth. Numerical modeling has enabled end closures design to be optimized for test performance. Thin and thick wall cylinders have been tested under quasi-static, and long term loading. Both thermosetting and thermoplastic matrix composites have been tested to failure, and the influence of defects and impact damage on implosion pressure has been studied. These deep sea exploitation and exploration studies were performed for oceanographic, military and offshore applications, and extensive data are available. The aim of this paper is to indicate existing results, particularly from European projects, in order to avoid costly repetition

Composite cylinders for deep sea applications, an overview

In order to develop the knowledge base necessary to design deep sea pressure vessels it is essential to understand the full chain from design and manufacturing through NDT and characterization to long term behavior under hydrostatic pressure. This paper describes results from European and national research programs focusing on the use of composites for underwater applications over the last 20 years. Initial tests on small glass/epoxy cylinders were followed by large demonstration projects on carbon/epoxy cylinders with implosion pressures of up to 600 bar, corresponding to 6000 meter depth. Numerical modeling has enabled end closures design to be optimized for test performance. Thin and thick wall cylinders have been tested under quasi-static, and long term loading. Both thermosetting and thermoplastic matrix composites have been tested to failure, and the influence of defects and impact damage on implosion pressure has been studied. These deep sea exploitation and exploration studies were performed for oceanographic, military and offshore applications, and extensive data are available. The aim of this paper is to indicate existing results, particularly from European projects, in order to avoid costly repetition