Structural Analysis Department (D²S) DCNS Research

Structural Analysis Department (D²S) – DCNS researchA team of R&D engineers geared toward researches in naval shipbuildingDCNS research is the Research and Technological Centre of the French naval shipbuilderDCNS, Fig. 0. Within DCNS Research the Structural Analysis Department (D²S) is a contributor inthe development and the validation of numerical methods for the simulation of fluid-structureinteraction problems, with applications to naval shipbuilding. Gathering 5 R&D Engineers withdifferent fields of expertise, and complemented with 5 PhD Students, the team is involved invarious scientific collaborations ; it aims at bridging the gap between fundamental research in thefield of computational mechanics and industrial applications of innovative numerical methods forship design.It is active within a network of experts and scientists originating from Industry (eg. BUREAUVERITAS, CEA, CNIM, EDF, STX) or Academia (eg. CNRS, ENSTA Paris, ENSTA Bretagne,Université de la Rochelle, Université de Nantes, Ecole Centrale de Nantes, INSA Lyon, IReNav),as well as from gouvernemental agencies (eg. Office of Naval Research, Centre National de laRecherche Scientifique, Délégation Générale pour l’Armement), Professional Associations (eg.Association Française de Mécanique, American Society of Mechanical Engineers) or numericalcode developers and editors (eg. ANSYS, CD-ADAPCO, EDF R&D, SIMULIA). Engineers from theD²S team are also major contributors in collaborative R&D projects in the context of regional ornational initiatives, such as IRT Jules VERNE in Pays de la Loire.Fig. 0 – DCNS Research is the R&T Centrer of French Naval shipbuilder DCNS. It is a unique structurewhich hosts some 125 experts, engineers, researchers and PhD students. DCNS offers a wide range ofsolutions, from R&T studies (such as those presented in the paper) to services (such as testing, nondestructive controls and expertise) and products (such as submarine auto-pilots and unmanned surfacevehicles).

The team has conducted researches with more than 15 PhD students over the past ten years andhas contributed to the publication of some 45 papers in scientific journals and 65 communicationsin national and international conferences.Members of the team are R&D engineers with a high level of technical and scientific skills.Bruno LEBLE is an expert in numerical techniques for strongly non-linear problems, with anemphasis on underwater explosions, non-linear behaviour of materials and systems; he is also thetechnical manager of R&D programs.Cédric LEBLOND, PhD, develops mathematical models applied to fluid-structure interaction,mainly based on reduced-order-modelling and low rank approximations (using such techniques asProper Generalised Decomposition).Florent BRIDIER, PhD, investigates numerical techniques for solving multi-physic problems,including the numerical simulation of welding, in order to assess the lifetime issues of marinestructures.Romain FARGERE, PhD, develops numerical tools to assess the dynamic behaviour of variousmechanical systems, with fluid-structure interaction modelling (for instance for journal bearings).Jean-François SIGRIST, PhD, is the head of the D²S team; he co-supervises researchesperformed by PhD students within the team; he is also the technical manager of collaborativeprojects.Researches in fluid-structure interaction modellingFluid-structure interaction is related to the dynamic behaviour of structures coupled to a fluidand therefore stands as major concern in naval shipbuilding. Contribution of the D²S team in thedevelopment of numerical methods aims at tackling the variety of situations of engineeringrelevance in shipbuilding, among which the following.oVibroacousticsThe team is involved in the development of finite-element based method to account for the vibroacoustic behaviour of complex immersed structures. Complexity may stem from geometry anddesign, for instance with multi-material structures (combining composites and metallic subparts, ormaterial with visco-elastic properties). Reduced-order modelling are developed and investigated;the proposed numerical strategies allows for a drastic reduction in computational cost, whileembedding the complex physics at stake. Such strategies pave way for uncertainty managementand optimisation-oriented design.(a) Finite element model of a compleximmersed structure(b) Computation of frequency response with parametervariabilityFig. 1 – From 2012 and on, a dedicated algorithm has been developed to compute the frequency responseof immersed structures composed of multi-materials. The algorithm is shown to be accurate over anextended frequency range. It is besides designed in order to take into account the variability of various

material properties, thus providing a set of data needed for an optimal design. Its numerical efficiency is alsounderlined: data produced by the proposed algorithm in one calculation would require some millioncalculations with a “classical” finite element resolution, being out of reach with existing computer resources.oHydrodynamicsResearches in the fields of hydrodynamics and fluid-structure interaction aim at taking into accountthe influence of structural deformations on the hydrodynamic performances of propellers (forinstance in terms of efficiency, or cavitation inception), by combining both experimental andnumerical approaches. Numerical techniques based on co-simulation strategies are developed inorder to describe detailed physics, such as involved in the vibration/cavitation couplingmechanisms. Such methodology is now made available to mechanical engineers for theoptimisation of hydrodynamic profiles.(a) Fluid flow around a deformable hydrofoil incavitating condition (experimental and numerical)(b) Hydrodynamic performance of a deformablepropellerFig. 2 – From 2006 to 2014, numerical strategies based on coupling structural and fluid codes have beenextensively investigated and validated on various configurations. Influence of fluid-structure interaction on thehydrodynamic performance of lifting profiles in cavitating/non-cavitating conditions has been evidenced. Thenumerical methods are now accessible for large industrial applications in propulsion, sea-keeping or energyharvesting.oSafety assessmentModelling fluid-structure interactions allows for a more detailed physics to be accounted for in thesimulations of the dynamics behaviour of critical systems. In some cases, for instance whenstructures are subjected to severe loading conditions (eg. impact on water, response to underwaterexplosions), a too crude simplification of the physics at stake might lead to misleading resultswhich are not acceptable when safety is at stake. Simulations embedding a more detailed physicsallow for a more accurate description of the system behaviour, thus guaranteeing accuracy of thecalculation.

(a) Impact of ship bow on water (‘slamming’)(b) Response of a submerged cylindrical shell toan underwater explosionFig. 3 – From 2005 to 2011, dedicated numerical methods have been developed and applied to tackle thephysics at stake in the case of impact on water of a ship bow (a) or the stress-state of a submerged shellsubjected to an underwater explosion (b). In both examples, the simulation strategy is a unique combinationof numerical and semi-analytical methods aimed at enhancing the physical accuracy of the simulations.From R&T to industrial applicationsThese researches are geared toward industrial applications; to name but a few, they are ofengineering relevance in the following instances:osafety of critical installations (such a compact nuclear propulsion reactor in exceptionalconditions) [2];ooptimisation of marine energy harvesting devices, such as tidal turbines or thermal energy,Fig. 4;oreduction of noise radiated by structures, at global (eg. a ship) or local scale (eg. apropeller), Fig. 4;ocontrol of structural vibrations, such as shaft lines and geared transmission;odurability of structures in marine environment, such as lifting devices.The researches have contributed to enhance the design process of complex naval structures sincesome of the proposed innovations in computational mechanics have been implemented in thenumerical tools made available to the practitioner.

(a) Finite element model of a surface ship at full scale(b) Finite volume model of a tidalturbineFig. 4 – The industrial applications of the researches in finite element-based methods cover a widerange in naval shipbuilding. Over the past years, the calculations performed within the designprocess of naval structures have benefited from researches in fluid-structure interaction modelling.As a result, a better understanding of complex phenomena is accessible to the practitioner,resulting in optimisation of structures and enhancement of their performances.Selected referencesJ.F. SIGRIST, S. GARREAU. Dynamic Analysis of Fluid-Structure Interaction Problems with Spectral MethodUsing Pressure-Based Finite Elements. Finite Element Analysis in Design, 43, 287-300, 2007.J.F. SIGRIST, D. BROC. Fluid-Structure Interaction Modeling for the Modal Analysis of a Steam GeneratorTube Bundle. Journal of Pressure Vessel Technology, Paper n 031302, 131, 2009.A. DUCOIN, F. DENISET, J.A. ASTOLFI, J.F. SIGRIST. An Experimental and Numerial Investigation of Flow Over aHydrofoil in Transient Pitching Motion. European Journal of Mechanics. B/Fluids, 28, 728-743, 2009.C. LEBLOND, J.F. SIGRIST. A Versatile Approach to the Study of Submerged Two-Dimensionnal Thin ShellTransient Response. Journal of Sound and Vibration, 329, 56-71, 2010.A. TASSIN, N. JACQUES, A. NÊME , A. EL MALKI ALAOUI, B. LEBLÉ, Assessment and Comparison of SeveralAnalytical Models of Water Impact, The International Journal of Multiphysics, 4, 125-140, 2010.A. DUCOIN, F. DENISET, J.A. ASTOLFI, J.F. SIGRIST. Numerical and Experimental Investigation ofHydrodynamics Characteristics of Deformable Foils. Journal of Ship Research, 53, 214-226, 2009.L. ROULEAU, J.F. DEÜ, A. LEGAY, J.F. SIGRIST. Vibro-Acoustic Study of a Viscoelastic Sandwich RingImmersed in Water. Journal of Sound and Vibration, 331, 522-539, 2012.A. DUCOIN, J.A. ASTOLFI, J.F. SIGRIST. An Experimental Analysis of Fluid-Structure Interaction on a FlexibleHydrofoil in Various Flow Regimes Including Cavitating Flow. European Journal of Mechanics. B/Fluids, 36,63-74, 2012.A. TASSIN, N. JACQUES, A. NEME, A. EL MALKI ALAOUI, B. LEBLE. Hydrodynamic loads during water impact ofthree-dimensional solids: Modelling and experiments, Journal of Fluids and Structures, 28, 211-231, 2012.S. IAKOVLEV, C. SEATON, J.F. SIGRIST. Submerged Cylindrical Shell Subjected to Two Consecutive ShockWaves: Resonance-like Phenomena. Journal of Fluids and Structures, 42, 70-87, 2013.J.F. SIGRIST, D. BROC. Modelling Inertial Effects in Periodic Fluid-Structure Systems with an HomogenisationApproach: Application Seismic Analysis of Tube Bundles. Journal of Fluids and Structures, 49, 73-90, 2014.