1,720,965 research outputs found
Développement de formulations analytiques pour déterminer la réponse dynamique de plaques composites immergées soumises à des explosions sous-marines
No full textLes explosions sous-marines comprennent de nombreux phénomènes physiques complexes tels que la propagation des ondes de choc, les interactions fluide structure, la cavitation, etc. Pour modéliser ces phénomènes aussi précisément que possible, des calculs par éléments finis couplés au code ‘Underwater Shock Analysis’ (USA) sont aujourd’hui utilisés. Cependant, de telles approches nécessitent beaucoup d'efforts de modélisation et de temps de calcul. Dans ce contexte, le travail de recherche réalisé dans le cadre de cette thèse a permis de mettre au point des formulations analytiques simplifiées à la fois rapides et raisonnablement précises. Le domaine de validité des formulations proposées a été précisé en confrontant les résultats analytiques à des simulations numériques (réalisées également dans le cadre de la thèse) et des résultats expérimentaux issus de la littérature. Un outil de bureau d’étude pour l’analyse de la réponse au choc de plaques composites immergées a également été développé.Underwater explosions involve many complex physical phenomena such as shock wave propagation, fluid-structure inter actions, cavitation, etc. To model these phenomena as precisely as possible, finite element calculations coupled with the code "Underwater Shock Analysis" (USA) are used nowadays. However, such approaches require a lot of modeling effort and computation time. In this context, the research work carried out within the framework of this thesis has enabled the development of simplified analytical formulations that are both rapid and reasonably accurate. The range of validity of the proposed formulations was examined by comparing the analytical results with numerical simulations (also carried out within the framework of the thesis) and experimental results available from the literature. An office design tool for the analysis of the shock response of submerged composite plates was also developed
Application of Lagrangian Energy Approach to determine the Response of Isotropic Circular Plates subjected to Air and Underwater Blasts
No full textInternational audienceThis paper presents a simplified analytical formulation that uses Lagrangian Energy Approach to predict air and underwater blast response of air-backed simply-supported circular steel plates. Triangular and exponential pressure profiles are considered for air and underwater blast loading respectively. Calculation of the response is divided into two stages. In the first stage, maximum impulsive velocity is determined by assum-ing that the plate has negligible deformation and then by using the conservation of linear momentum for air blast and Taylor’s one-dimensional analytical model for underwater blast. In the second stage of calculation, elastic deformation is obtained by applying the initial conditions determined from the first stage, also taking into account the rotatory inertia and water-added inertia effect. The obtained analytical solutions are tested with various plate aspect ratios as well as various loading levels and the results are compared with those from non-linear finite element explicit simulations. It is found that the proposed formulations correlate well with the finite element results giving only 5–20% discrepancy provided that the plate deflections are supposed to remain small compared to its thickness. Finally, the advantages and limitations of the present method are discussed
A coupled closed-form/Doubly Asymptotic Approximation approach for the response of orthotropic plates subjected to an underwater explosion
No full textInternational audienceIn this paper, a closed-form analytical solution procedure is proposed to solve the coupled fluid-structure interaction (FSI) equations that involve the first-order Doubly Asymptotic Approximation (DAA1) formulation. An efficient method comprised of the nonstandard finite difference (NSFD) scheme is applied. First of all, analytical equations are developed to analyze the response of a rigid mass-spring oscillator in an air-backed condition when it is subjected to a plane shock exponential wave coming from a far-field underwater explosion. After validating the results with LS-DYNA/USA (DAA1), these equations are extended to determine the response of a two-dimensional, simply-supported rectangular plate, and then tested on the isotropic and orthotropic plates within a small deflection regime. Parametric studies are also performed by varying the load decay times, peak pressures, as well as the aspect ratios of the plate. Finally, the advantages and limitations of the proposed formulae are exposed along with suggestions for the future work
Application of Lagrangian Energy Approach to determine the Response of Isotropic Circular Plates subjected to Air and Underwater Blasts
No full textInternational audienceThis paper presents a simplified analytical formulation that uses Lagrangian Energy Approach to predict air and underwater blast response of air-backed simply-supported circular steel plates. Triangular and exponential pressure profiles are considered for air and underwater blast loading respectively. Calculation of the response is divided into two stages. In the first stage, maximum impulsive velocity is determined by assum-ing that the plate has negligible deformation and then by using the conservation of linear momentum for air blast and Taylor’s one-dimensional analytical model for underwater blast. In the second stage of calculation, elastic deformation is obtained by applying the initial conditions determined from the first stage, also taking into account the rotatory inertia and water-added inertia effect. The obtained analytical solutions are tested with various plate aspect ratios as well as various loading levels and the results are compared with those from non-linear finite element explicit simulations. It is found that the proposed formulations correlate well with the finite element results giving only 5–20% discrepancy provided that the plate deflections are supposed to remain small compared to its thickness. Finally, the advantages and limitations of the present method are discussed
Response of composite plates in air-backed and water-backed conditions subjected to a far-field underwater explosion
No full textInternational audienc
Development of Analytical Formulae to determine the Response of Submerged Composite Plates subjected to Underwater Explosion
No full textInternational audienceClosed-form analytical formulae are developed to analyze the bending response of submerged composite rectangular plates subjected to underwater explosions (UNDEX). These explosions are supposed to occur at a sufficiently large stand-off distance so that a uniformly distributed pressure pulse can be applied and the corresponding bubble effects can be ignored. The plate is considered in an air-backed condition. The derivation steps are divided into two main stages. In the first stage, the impulsive velocity due to the interaction of shock wave and structure is determined by using Taylor's fluid-structure interaction (FSI) formulation while supposing a negligible structural deformation. Transmission of shock waves through the thickness of the plate is considered by assuming the material under uniaxial strain. At the end of the first stage, cavita-tion is supposed to occur all over the plate. In the second stage, deformation of the plate will commence which is followed by the collapse of the cavitation zone. The corresponding mechanical response of the plate is determined by imposing a simply-supported boundary conditions and by applying Lagrangian Energy approach to derive the motion equation, taking into account the water inertial effects. The proposed method is then tested with isotropic (steel) and laminated composite (carbon-fiber/epoxy) plates to analyze for both impulsive velocity and UNDEX responses. The obtained analytical results are compared with those from non-linear finite element explicit code, LS-DYNA. Finally, the advantages and limitations of the present method are evaluated
Response of composite plates in air-backed and water-backed conditions subjected to a far-field underwater explosion
No full textInternational audienc
A coupled closed-form/Doubly-Asymptotic Approximation approach for the response of orthotropic plates subjected to an underwater explosion
No full textInternational audienceIn this paper, a closed-form analytical solution procedure is proposed to solve the coupled fluid-structure interaction (FSI) equations that involve the first-order Doubly Asymptotic Approximation (DAA1) formulation. An efficient method comprised of the nonstandard finite difference (NSFD) scheme is applied. First of all, analytical equations are developed to analyze the response of a rigid mass-spring oscillator in an air-backed condition when it is subjected to a plane shock exponential wave coming from a far-field underwater explosion. After validating the results with LS-DYNA/USA (DAA1), these equations are extended to determine the response of two-dimensional, simply-supported rectangular plate, and then tested on the isotropic and orthotropic plates within a small deflection regime. Parametric studies are also performed by varying the load decay times, peak pressures, as well as the aspect ratios of the plate. Finally, the advantages and limitations of the proposed formulae are exposed along with suggestions for the future work
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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