Dissertations / Theses: 'Underwater explosions'

1

Ogilvy, Iver. "Fluid dynamics of underwater explosions." Thesis, University of Birmingham, 2010. http://etheses.bham.ac.uk//id/eprint/8840/.

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The detonation of an explosive in water leads to a complex set of chemical and physical phenomena. When the detonation wave reaches the surface of the explosive it reacts violently with the water, producing a shock wave propagating outwards and also a nearly spherical gaseous bubble of detonation products. The fact that the characteristic time scales of these two phenomena differ by approximately two orders of magnitude has often been exploited by utilising independent models to describe the shock and the bubble. In this thesis both the shock and the bubble are examined using a range of methods from a differential equation solver approach through to full hydrocode simulation. With the increasing use of the hydrocode approach for the underwater explosion (UNDEX) problem and the subsequent loading of a structure, then a verification and validation process is required to ensure its accuracy. In this study the capability of the hydrocode to model the shock and the bubble and also their interaction with a rigid structure and with a flexible structure, has been assessed. This has been done computationally, by using faster running purpose built codes, and also by comparison with experimental data. A familiarisation work-up of the boundary integral code for the incompressible bubble flow, which included incorporating modifications into the code in order to investigate the pathlines swept out by the particles in the fluid during the expansion and collapse of the bubble. The boundary integral code was also used to provide a comparison with the Kelvin impulse method with respect to the computation of the zones of explosion bubble collapse direction in a shallow water environment. The validation and verification work carried out and the comparisons of the various computational approaches, make this multifaceted study a useful reference for research workers in the field of UNDEX phenomena.

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Krueger, Seth R. "Simulation of cylinder implosion initiated by an underwater explosion." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2006. http://library.nps.navy.mil/uhtbin/hyperion/06Jun%5FKrueger.pdf.

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Thesis (M.S. in Mechanical Engineering)--Naval Postgraduate School, June 2006.
Thesis Advisor(s): Young S. Shin. "June 2006." Includes bibliographical references (p. 99-100). Also available in print.

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Hart, David T. "Ship shock trial simulation of USS Winston S. Churchill (DDG-81) : surrounding fluid effect /." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2003. http://library.nps.navy.mil/uhtbin/hyperion-image/03Mar%5FHart.pdf.

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Roux, André. "Protection of electronics in submerged enclosures against underwater explosions." Master's thesis, University of Cape Town, 2007. http://hdl.handle.net/11427/5476.

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Includes bibliographical references (leaves 185-187).
In the milieu of military sea mine design, it is often necessary to design mines that are to be placed at small distances from each other. A possible tactical purpose may require that each mine be set to explode at controlled instances in time without disturbing the operation of the other mines in the field or causing sympathetically detonated reactions. Thus two problems (on face value) are prevalent when reliable operation of two mines in close proximity is to be considered. The first problem is sympathetic detonation. The second problem is reliability failure.

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Schneider, Nathan A. "Prediction of surface ship response to severe underwater explosions using a virtual underwater shock environment." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2003. http://library.nps.navy.mil/uhtbin/hyperion-image/03Jun%5FSchneider.pdf.

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Thesis (Mechanical Engineer and M.S. in Mechanical Engineering)--Naval Postgraduate School, June 2003.
Thesis advisor(s): Young S. Shin. Includes bibliographical references (p. 161-162). Also available online.

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6

Ucar, Hakan. "Dynamic response of a catamaran-hull ship subjected to underwater explosions." Thesis, Monterey, Calif. : Naval Postgraduate School, 2006. http://bosun.nps.edu/uhtbin/hyperion.exe/06Dec%5FUcar.pdf.

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Thesis (M.S. in Mechanical Engineering)--Naval Postgraduate School, December 2006.
Thesis Advisor(s): Young S. Shin, Jarema M. Didoszak. "December 2006." Includes bibliographical references (p. 137-138). Also available in print.

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7

Hammond, Lloyd Charles 1961. "The structural response of submerged air-backed plates to underwater explosions." Monash University, Dept. of Civil Engineering, 2000. http://arrow.monash.edu.au/hdl/1959.1/9244.

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8

Fox, Padraic K. Kwon Young W. "The dynamic response of cylindrical shells subjected to side-on underwater explosions." Monterey, Calif. : Springfield, Va. : Naval Postgraduate School; Available from the National Technical Information Service, 1993. http://handle.dtic.mil/100.2/252856.

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Thesis (M.S. in Mechanical Engineering and Mechanical Engineer) Naval Postgraduate School, March 1992.
Thesis advisor, Young W. Kwon. Cover title: Nonlinear ... to underwater side-on explosions. AD-A252 856. Includes bibliographical references. Also available online.

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9

Fox, Padraic K., and Young W. Kwon. "The dynamic response of cylindrical shells subjected to side-on underwater explosions." Thesis, Monterey, California: Naval Postgraduate School, 1993. http://hdl.handle.net/10945/24152.

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10

Elder, David James, and d. elder@crc-acs com au. "Optimisation of parametric equations for shock transmission through surface ships from underwater explosions." RMIT University. Aerospace, Mechanical and Manufacturing Engineering, 2006. http://adt.lib.rmit.edu.au/adt/public/adt-VIT20080212.105012.

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Currently shock effects on surface ships can be determined by full scale shock trials, Finite Element Analysis or semi empirical methods that reduce the analytical problem to a limited number of degrees of freedom and include hull configurations, construction methods and materials in an empirical way to determine any debilitating effects that an explosion may have on the ship. This research has been undertaken to better understand the effect of hull shape on surface ships' shock response to external underwater explosions (UNDEX). The study is within the semi empirical method category of computations. A set of simple closed-form equations has been developed that accurately predicts the magnitude of dynamic excitation of different 2- D rigid-hull shapes subject to far-field UNDEX events. This research was primarily focused on the affects of 2-D rigid hull shapes and their contribution to global ship motions. A section of the thesis,

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11

Nassor, Alice. "Domain decomposition method for acoustic-elastic coupled problems in time-domain. Application to underwater explosions." Electronic Thesis or Diss., Institut polytechnique de Paris, 2023. http://www.theses.fr/2023IPPAE015.

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Ce travail étudie les approches globales en temps de décomposition de domaine pour résoudre des problèmes transitoires d'interaction fluide-structure. Afin de déterminer un algorithme optimal, nous étudions dans un premier temps la solvabilité des problèmes élastodynamiques et acoustiques transitoires avec des conditions aux frontières de type Robin et de Neumann. Nous énonçons des résultats de solvabilité, en soulignant les différentes régularités espace-temps des solutions. Nous étudions également la solvabilité du problème couplé élastodynamique-acoustique transitoire. Puis en nous basant sur ces résultats mathématiques, nous proposons ensuite un algorithme itératif global en temps basé sur les conditions aux limites de type Robin pour le problème couplé et prouvons sa convergence.Ces résultats sont ensuite mis en oeuvre pour coupler deux méthodes numériques efficaces. La réponse du fluide en temps discret est obtenue à l'aide d'une approche Z-BEM qui combine (i) une méthode d'éléments de frontière (BEM) accélérée par la méthode des matrices hiérarchiques dans le domaine de Laplace et (ii) une quadrature de convolution. La réponse de la structure est modélisée à l'aide de la méthode des éléments finis. Nous développons de cette manière une méthode numérique de couplage itérative globale en temps à convergence garantie, permettant en outre d'utiliser deux méthodes numériques distinctes de manière non intrusive.Plusieurs améliorations sont ensuite proposées: une méthode d'accélération de convergence est mise en œuvre et une approximation à haute fréquence est proposée pour améliorer l'efficacité de la Z-BEM. On propose ensuite un deuxième couplage itératif global-en-temps basé sur une interface acoustique-acoustique, dont la convergence est également démontrée. Ce couplage permet ensuite d'introduire des effets non linéaires dus au phénomène de cavitation pour préciser le modèle fluide. La Z-BEM est enfin adaptée en utilisant la méthode des images pour permettre la prise en compte d'une surface libre.Cette méthode est appliquées à des problèmes à dynamique rapide de dispersion d'ondes de choc acoustiques par des structures élastiques immergées et permet de simuler des configurations réalistes rencontrées dans l'industrie navale
This work addresses global-in-time domain decomposition approaches for the numerical solution of transient fluid-structure interaction problems. To determine an optimal algorithm, we first study the solvability for the transient acoustic and elastodynamic problems with Robin and Neumann boundary conditions. We state solvability results along with the different space-time regularities of the solutions. We also study the solvability for the transient coupled elastodynamic-acoustic problem. Using on these mathematical results we then propose a global-in-time iterative algorithm based on Robin boundary conditions for the coupled elastodynamicacoustic problem and we prove its convergence.These results are leveraged to design a computational methodology by coupling two efficient numerical methods. The fluid response is formulated in the discrete-time domain, using a Z-BEM approach that combines (i) a boundary element method (BEM) accelerated with hierarchical matrix implemented in the Laplace domain and (ii) a convolution quadrature method. The structure response is modelled using the finite elements method. We thus propose a global-in-time iterative coupling with guaranteed convergence, which enables the use of two distinct numerical methods in a non-intrusive manner.Several improvements are then explored: an acceleration method is implemented and a high-frequency approximation is proposed to improved the Z-BEM efficiency. A second iterative global-in-time coupling based on an acoustic-acoustic interface is then proposed and its convergence is also proved. This coupling enables the addition of non linear effects due to the cavitation phenomenon to derive a more realistic fluid model. The Z-BEM is lastly adapted using the method of images to take a free surface into account.This method is applied on fast-time problems of acoustic shock wave scattering by submerged elastic structures and enables to simulate realistic configurations from naval industry

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12

Didoszak, Jarema M. "Parametric studies of DDG-81 ship shock trial simulations." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2004. http://library.nps.navy.mil/uhtbin/hyperion/04Mar%5FDidoszak.pdf.

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13

Petrusa, Douglas C. "Evaluation and analysis of DDG-81 simulated athwartship shock response." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2004. http://library.nps.navy.mil/uhtbin/hyperion/04Jun%5FPetrusa.pdf.

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14

Avachat, Siddharth. "Experimental and numerical analyses of dynamic deformation and failure in marine structures subjected to underwater impulsive loads." Thesis, Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/44904.

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The need to protect marine structures from the high-intensity impulsive loads created by underwater explosions has stimulated renewed interest in the mechanical response of sandwich structures. The objective of this combined numerical and experimental study is to analyze the dynamic response of composite sandwich structures and develop material-structure-property relations and design criteria for improving the blast-resistance of marine structures. Configurations analyzed include polymer foam core structures with planar geometries. A novel experimental facility to generate high-intensity underwater impulsive loads and carry out in-situ measurements of dynamic deformations in marine structures is developed. Experiments are supported by fully dynamic finite-element simulations which account for the effects of fluid-structure interaction, and the constitutive and damage response of E-glass/polyester composites and PVC foams. Results indicate that the core-density has a significant influence on dynamic deformations and failure modes. Polymeric foams experience considerable rate-effects and exhibit extensive shear cracking and collapse under high-magnitude multi-axial underwater impulsive loads. In structures with identical masses, low-density foam cores consistently outperform high-density foam cores, undergoing lesser deflections and transmitting smaller impulses. Calculations reveal a significant difference between the response of air-backed and water-backed structures. Water-backed structures undergo much greater damage and consequently need to absorb a much larger amount of energy than air-backed structures. The impulses transmitted through water-backed structures have significant implications for structural design. The thickness of the facesheets is varied under the conditions of constant material properties and core dimensions. The results reveal an optimal thickness of the facesheets which maximizes energy absorption in the core and minimizes the overall deflection of the structure.

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15

Smith, Paul R. "Underwater Explosion Energy Dissipation Near Waterborne Infrastructure." UKnowledge, 2016. http://uknowledge.uky.edu/ce_etds/35.

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Underwater explosions pose a significant threat to waterborne infrastructure though destructive pressure waves that can travel significant distances through the water. However, the use of bubble screens can attenuate the peak pressure and energy flux created by explosions to safe levels. This study investigates the prediction of pressure wave characteristics based on accumulated data, the damage potential of underwater explosions based on applied loads and effective material strength, and the bubble screen parameters required to prevent damage. The results were compiled to form a procedure for the design and implementation of a bubble screen the protection of waterborne infrastructure.

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16

Miller, William Earl. "Simulation of the underwater nuclear explosion and its effects." Thesis, Monterey, California. Naval Postgraduate School, 1992. http://hdl.handle.net/10945/24037.

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17

Matsumoto, Kazuhiro. "Boundary curvature effects on gas bubble oscillations in underwater explosion." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1996. http://handle.dtic.mil/100.2/ADA308087.

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18

Oglesby, Douglas B. "Human male and female biodynamic response to underwater explosion events." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1998. http://handle.dtic.mil/100.2/ADA350567.

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Thesis (Degree in Mechanical Engineer and M.S. in Mechanical Engineering) Naval Postgraduate School, June 1998.
Thesis advisor, Young S. Shin. "June 1998." Includes bibliographical references (p. 139-141). Also available online.

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19

Boticario, Luis A. "Dynamic response of cylindrical shells to underwater end-on explosion." Thesis, Monterey, California. Naval Postgraduate School, 1991. http://hdl.handle.net/10945/28133.

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Cunningham, Richard E. "Simplified finite element modeling of stiffened cylinders subjected to underwater explosion." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1996. http://handle.dtic.mil/100.2/ADA310376.

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21

Hooker, Donald T. "Effect of initial imperfections of the response of cylinders to underwater explosion." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1993. http://handle.dtic.mil/100.2/ADA276428.

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Thesis (M.S. in Mechanical Engineering and Mechanical Engineer) Naval Postgraduate School, December 1993.
Thesis advisor(s): Young S. Shin. "December 1993." Bibliography: p. 96. Also available online.

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Nelson, Kurt W. "Dynamic response and failure analysis of aluminum cylinders subjected to underwater explosion." Thesis, Monterey, California. Naval Postgraduate School, 1992. http://hdl.handle.net/10945/23645.

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Approved for public release; distribution is unlimited
An underwater explosion test was conducted on two closed aluminum cylinders to provide physical results from a dynamic collapse. Axial and side-on attack geometries were investigated in this study. Both cylinders displayed numerous fractures and significant plastic deformation. Finite element models of the cylinders were developed to aid in physical understanding of the dynamic response. Sensitivity analysis of the model parameters were conducted to determine the optimum modeling method. A computer model with failure prediction capability was utilized to investigate the dynamic failure mechanism.

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Mavaleix-Marchessoux, Damien. "Modelling the fluid-structure coupling caused by a far-field underwater explosion." Electronic Thesis or Diss., Institut polytechnique de Paris, 2020. http://www.theses.fr/2020IPPAE012.

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Les sous-marins militaires doivent résister aux sollicitations induites par une explosion sous-marine. Pour s'en assurer, la simulation numérique est d'une importance capitale, compte tenu du coût très élevé des campagnes expérimentales. Une explosion sous-marine lointaine est un événement complexe qui a deux effets distincts : elle libère une onde de choc, puis crée une bulle de gaz oscillante qui pousse une grande quantité d'eau plus lentement. Les deux phénomènes ont des caractéristiques et des échelles de temps assez différentes. Dans ce travail, nous supposons que l'explosion est suffisamment éloignée pour (i) que la présence du navire affecte peu l'explosion, et (ii) permettre une séparation temporelle des deux phénomènes, tels que perçus par le navire. Dans ces conditions, notre objectif est de concevoir, implémenter (dans le cadre du calcul haute performance) puis valider une méthodologie de simulation numérique pour le problème d'interaction fluide-structure prenant en compte les deux phénomènes. Pour ce faire, nous commençons par étudier les deux perturbations en l'absence du sous-marin, pour déduire une modélisation et des méthodes numériques adaptées. Nous développons ensuite une procédure éléments de frontière (BEM) accélérée, basée sur une combinaison de la méthode de quadrature de convolution avec une approximation haute fréquence empirique originale. Plus largement, cette procédure permet de simuler efficacement des problèmes transitoires rapides 3D de propagation d'ondes en milieu non-borné, et offre une complexité très favorable : O(1) par rapport à la discrétisation temporelle et O(N log N) par rapport à la discrétisation spatiale. Enfin, nous mettons en place des stratégies performantes de couplage éléments finis/éléments de frontière (FEM/BEM) pour la phase d'interaction fluide-structure de l'onde de choc (acoustique linéaire) et celle de la bulle de gaz (écoulements incompressibles). La procédure globale, validée sur des problèmes académiques, fournit des résultats très prometteurs sur des cas industriels réalistes
Submarines must withstand the effects of rapid dynamic loads induced by underwater explosions. Due to the very high cost of experimental campaigns, numerical simulations are very important. A remote underwater explosion is a complex event that has two distinct effects: it sends a shock wave, then creates an oscillating gas bubble that sets water in slower motion. The two phenomena have quite different characteristics and time scales. In this work, we consider remote enough underwater explosions so that (i) the presence of the submarine only marginally affects the explosion, and (ii) there is a temporal separation of the two phenomena, as experienced by the ship. Under these conditions, our overall goal is to design, implement (in the context of high performance computing) then validate a computational methodology for the fluid-structure interaction problem, taking into account both phenomena. With this aim, we first study the two perturbations without considering the submarine, to propose appropriate modelling and numerical methods. Then, we design a fast boundary element (BEM) procedure, based on the combination of the convolution quadrature method and an original empirical high frequency approximation. The procedure allows to efficiently simulate 3D rapid transient wave propagation problems set in an unbounded domain, and shows advantageous complexity: O(1) in regards to the time discretisation and O(N log N) for the spatial discretisation. Finally, we implement adequate finite element/boundary element (FEM/BEM) coupling strategies for the shock wave fluid-structure interaction phase (linear acoustics) and that of the gas bubble (incompressible flow). The overall procedure, validated on academic problems, provides very promising results when applied on realistic industrial cases

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Klenow, Bradley A. "Assesment of LS-DYNA and Underwater Shock Analysis (USA) Tools for Modeling Far-Field Underwater Explosion Effects on Ships." Thesis, Virginia Tech, 2006. http://hdl.handle.net/10919/42786.

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This thesis investigates the use of the numerical modeling tools LS-DYNA and USA in modeling general far-field underwater explosions (UNDEX) by modeling a three-dimensional box barge that is subjected to a far-field underwater explosion. Past UNDEX models using these tools have not been validated by experiment and most are limited to very specific problems because of the simplifying assumptions they make. USA is a boundary element code that requires only the structural model of the box barge. LS-DYNA is a dynamic finite element code and requires both the structural model and the surrounding fluid model, which is modeled with acoustic pressure elements.

Analysis of the box barge problem results finds that the program USA is a valid tool for modeling the initial shock response of surface ships when cavitation effects are not considered. LS-DYNA models are found to be very dependent on the accuracy of the fluid mesh. The accuracy of the fluid mesh is determined by the ability of the mesh to adequately capture the peak pressure and discontinuity of the shock wave. The peak pressure captured by the model also determines the accuracy of the cavitation region captured in the fluid model. Assumptions made in the formulation of the fluid model causes potential inaccurate fluid-structure interaction and boundary condition problems cause further inaccuracies in the box barge model. These findings provide a base of knowledge for the current capabilities of UNDEX modeling in USA and LS-DYNA from which they can be improved in future work.
Master of Science

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Maines, Geoffrey C. "Underwater Pressure Pulses Generated by Mechanically Alloyed Intermolecular Composites." Thèse, Université d'Ottawa / University of Ottawa, 2014. http://hdl.handle.net/10393/30708.

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Recently, the use of thermite-based pressure waves for applications in cellular transfection and drug delivery have shown significant improvements over previous technologies. In the present study, a new technique for producing thermite-generated pressure pulses using fully-dense nano-scale thermite mixtures was evaluated. This was accomplished by evaluation of a stoichiometric mixture of aluminium (Al) and copper(II)-oxide (CuO) prepared by mechanical alloying. Flame propagation speeds, constant-volume pressure characteristics and underwater pressure characteristics of both a micron-scale and mechanically alloyed mixture were measured experimentally and compared with conventional nano-scale thermites. It was determined that mechanically alloyed mixtures are capable of attaining flame propagation speeds on the same order as nano-scale mixtures, with flame speeds reaching as high as approximately 100 m/s. Constant-volume pressure experiments indicated that mechanically alloyed mixtures result in lower pressurization rates compared with conventional nano-scale mixtures, however, an improvement by as much as an order of magnitude was achieved compared with micron-scale mixtures. Thermochemical equilibrium predictions for pressures observed in constant-volume reactions were found to capture relatively well the equilibrium pressure for both low and high values of relative density. Generally, the predictions over-estimated the measured pressures by approximately 60%. Results from underwater experiments indicated that the mechanically alloyed samples produced peak shock pressures and waveforms similar to those for a nano-scale Al-Bi2O3 mixture reported by Apperson et al. (2008). In an effort to model the pressure signal obtained from the underwater reaction, calculations were performed based on the rate of expansion of the high pressure gas sphere. Predicted pressures were found to agree fairly well in terms of both the peak pressure and pressurization rate. The present study has thus identified the ability for mechanically alloyed thermite mixtures to produce underwater pressure profiles that may be conducive for applications in cellular transfection and drug delivery. Récemment, l'utilisation d'ondes de pression produite par des mélanges de thermite pour des applications dans la transfection cellulaire et l'administration de médicaments ont démontré des améliorations importantes par rapport aux technologies précédentes. Dans l'étude ci jointe, une nouvelle technique pour produire des impulsions de pression générée par un mélange thermite, soumit a de l'alliage mécanique, a été évaluée. Ceci a été accompli par l'évaluation d'un mélange stoechiométrique d' aluminium (Al) et de l'oxyde de cuivre(II) (CuO), préparé par mécanosynthèse. Les vitesses de propagation de la flamme, les caractéristiques de pression pour la combustion à volume constant et les caractéristiques de pression pour la combustion sous l'eau ont été mesurées expérimentalement et comparés avec les thermites conventionnel à l'échelle nano. Nous avons déterminé que les mélanges alliés mécaniquement sont capables d'atteindre des vitesses de propagation de flamme du même ordre que les mélanges à l'échelle nanométrique, atteignant jusqu'à environ 100 m/s. Les expériences de combusition à volume constant, indique que les mélanges alliés mécaniquement induit des taux de pressurisation inférieures à celles des mélanges de nano-échelle conventionnel, cependant, une amélioration de près d'un ordre de grandeur a été atteint par rapport aux mélanges d'échelle micronique. Prédictions thermochimiques des pression de compbustion se sont révélés capable de relativement bien saisir les valeurs observées dans les expériences à volume constant. En règle générale, les prévisions sur-estimé les pressions mesurées par environ 60%. Les résultats des expériences sous-marines ont indiqué que les échantillons alliés mécaniquement ont produit des pressions et des profils d'onde similaires à celles produit par un mélange de Al-Bi2O3 de nano-échelle, comme indiqué par Apperson et al. (2008). Pour modéliser les pressions obtenues dans les expériences sous-marines, des calculs basés sur le taux d'expansion de la bulle de gaz à haute pression ont été obtenus. Les pressions prédites ont été trouvés d'être relativement en accord avec la pression maximale et le taux de pressurisation observé. Cette étude a ainsi identifié la possibilité pour l'utilisation des mélanges de thermites alliés mécaniquement pour produire des profils de pression sous l'eau propices pour des applications de transfection cellulaire et l'administration de médicaments.

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Mathew, Ajai Kurian. "Modeling Underwater Explosion (UNDEX) Shock Effects for Vulnerability Assessment in Early Stage Ship Design." Thesis, Virginia Tech, 2018. http://hdl.handle.net/10919/82531.

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This thesis describes and assesses a simplified tool for modeling underwater explosion shock effects during early naval ship concept design. A simplified fluid model using Taylor flat-plate theory is incorporated directly into the OpenFSI module code in Nastran and used to interface with the structural solver in Nastran to simulate a far-field shockwave impacting the hull. The kick-off velocities and the shock spectra captured in this computationally efficient module is compared to results from a high-fidelity CASE (Cavitating Acoustic Spectral Element) fluid model implemented with the ABAQUS/Nastran structural solver to validate the simplified framework and assess the sufficiency of this very simple but, fast approach for early stage ship design.
Master of Science

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Brainard, Benjamin Chase V. "An Underwater Explosion-Induced Ship Whipping Analysis Method for use in Early-Stage Ship Design." Thesis, Virginia Tech, 2016. http://hdl.handle.net/10919/64508.

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This thesis presents an analysis method for determining the whipping response of a hull girder to underwater explosion (UNDEX) bubble pulse loading. A potential flow-based UNDEX bubble model capable of calculating the behavior of a migrating bubble for up to three pulses is developed. An approximate vertical plane ship vibration model is derived using fundamental beam theory by representing the ship as a free-free beam with varying cross-sectional properties along its length. The fluid-structure interaction is approximated using strip theory and the distant flow assumption. The most severe predicted whipping load conditions are applied to a MAESTRO finite element model of the ship as a quasi-static load case to determine the response of the structure to the whipping loads. The calculated hull girder bending moments are compared to the ultimate bending strength of the hull girder to determine if the girder will collapse. The analysis method is found to be a useful method for determining preliminary UNDEX-induced whipping design load cases for early-stage ship design. However, more detailed and accurate data is needed to validate and verify the predicted whipping responses. It is found that the most severe whipping loads occur as the result of an UNDEX event that occurs under the keel near midship and produces a bubble with a pulsation frequency similar to the natural vibration frequency of the ship in its third mode. Significant damage to the ship structure and hull girder collapse is possible as a result of these loads.
Master of Science

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28

Wood, Steven L. "Cavitation effects on a ship-like box structure subjected to an underwater explosion." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1998. http://handle.dtic.mil/100.2/ADA354937.

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Thesis (M.S. in Mechanical Engineering) Naval Postgraduate School, September 1998.
"September 1998." Thesis advisor(s): Young S. Shin. Includes bibliographical references (p. 115-116). Also Available online.

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Trevino, Theodore. "Applications of Arbitrary Lagrangian-Eulerian (ALE) analysis approach to underwater and air explosion problems." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2000. http://handle.dtic.mil/100.2/ADA384983.

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Thesis (M.S. in Mechanical Engineering)--Naval Postgraduate School, Sept. 2000.
Thesis advisor(s): YShin, Young S. "September 2000." Includes bibliographical references (p. 175-177). Also available in print.

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30

Lu, Zhaokuan. "Computationally-effective Modeling of Far-field Underwater Explosion for Early-stage Surface Ship Design." Diss., Virginia Tech, 2020. http://hdl.handle.net/10919/104996.

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The vulnerability of a ship to the impact of underwater explosions (UNDEX) and how to incorporate this factor into early-stage ship design is an important aspect in the ship survivability study. In this dissertation, attention is focused on the cost-efficient simulation of the ship response to a far-field UNDEX which involves fluid shock waves, cavitation, and fluid-structural interaction. Traditional fluid numerical simulation approaches using the Finite Element Method to track wave propagation and cavitation requires a high-level of mesh refinement to prevent numerical dispersion from discontinuities. Computation also becomes quite expensive for full ship-related problems due to the large fluid domain necessary to envelop the ship. The burden is aggravated by the need to generate a fluid mesh around the irregular ship hull geometry, which typically requires significant manual intervention. To accelerate the design process and enable the consideration of far-field UNDEX vulnerability, several contributions are made in this dissertation to make the simulation more efficient. First, a Cavitating Acoustic Spectral Element approach which has shown computational advantages in UNDEX problems, but not systematically assessed in total ship application, is used to model the fluid. The use of spectral elements shows greater structural response accuracy and lower computational cost than the traditional FEM. Second, a novel fully automatic all-hexahedral mesh generation scheme is applied to generate the fluid mesh. Along with the spectral element, the all-hex mesh shows greater accuracy than the all-tetrahedral finite element mesh which is typically used. This new meshing approach significantly saves time for mesh generation and allows the spectral element, which is confined to the hexahedral element, to be applied in practical ship problems. A further contribution of this dissertation is the development of a surrogate non-numerical approach to predict structural peak responses based on the shock factor concept. The regression analysis reveals a reasonably strong linear relationship between the structural peak response and the shock factor. The shock factor can be conveniently employed in the design aspects where the peak response is sufficient, using much less computational resources than numerical solvers.
Doctor of Philosophy
The vulnerability of a ship to the impact of underwater explosions (UNDEX) and how to incorporate this factor into early-stage ship design is an important aspect in the ship survivability study. In this dissertation, attention is focused on the cost-efficient simulation of the ship response to a far-field UNDEX which involves fluid shock waves, cavitation, and fluid-structural interaction. Traditional fluid numerical simulation approaches using the Finite Element Method to track wave propagation and cavitation requires a highly refined mesh to deal with large numerical errors. Computation also becomes quite expensive for full ship-related problems due to the large fluid domain necessary to envelop the ship. The burden is aggravated by the need to generate a fluid mesh around the irregular ship hull geometry, which typically requires significant manual intervention. To accelerate the design process and enable the consideration of far-field UNDEX vulnerability, several contributions are made in this dissertation to make the simulation more efficient. First, a Cavitating Acoustic Spectral Element approach, which has shown computational advantages in UNDEX problems but not systematically assessed in total ship application, is used to model the fluid. The use of spectral elements shows greater structural response accuracy and lower computational cost than the traditional FEM. Second, a novel fully automatic all-hexahedral mesh generation scheme is applied to generate the fluid mesh. Along with the spectral element, the all-hex mesh shows greater accuracy than the all-tetrahedral finite element mesh which is typically used. A further contribution of this dissertation is the development of a non-numerical approach which can approximate peak structural responses comparable to the numerical solution with far less computational effort.

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Klenow, Bradley. "Finite and Spectral Element Methods for Modeling Far-Field Underwater Explosion Effects on Ships." Diss., Virginia Tech, 2009. http://hdl.handle.net/10919/37648.

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The far-field underwater explosion (UNDEX) problem is a complicated problem dominated by two phenomena: the shock wave traveling through the fluid and the cavitation in the fluid. Both of these phenomena have a significant effect on the loading of ship structures subjected to UNDEX. An approach to numerically modeling these effects in the fluid and coupling to a structural model is using cavitating acoustic finite elements (CAFE) and more recently cavitating acoustic spectral elements (CASE). The use of spectral elements in CASE has shown to offer the greater accuracy and reduced computational expense when compared to traditional finite elements. However, spectral elements also increase spurious oscillations in both the fluid and structural response. This dissertation investigates the application of CAFE, CASE, and a possible improvement to CAFE in the form of a finite element flux-corrected transport algorithm, to the far-field UNDEX problem by solving a set of simplified UNDEX problems. Specifically we examine the effect of increased oscillations on structural response and the effect of errors in cavitation capture on the structural response which have not been thoroughly explored in previous work. The main contributions of this work are a demonstration of the problem dependency of increased oscillations in the structural response when applying the CASE methodology, the demonstration of how the sensitivity of errors in the structural response changes with changes in the structural model, a detailed explanation of how error in cavitation capture influences the structural response, and a demonstration of the need to accurately capture the shape and magnitude of cavitation regions in the fluid in order to obtain accurate structural response results.
Ph. D.

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Santiago, Leonard D. "Fluid-interaction and cavitation effects on a surface ship model due to an underwater explosion." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1996. http://handle.dtic.mil/100.2/ADA320830.

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Beiter, Keith A. "The effect of stiffener smearing in a ship-like box structure subjected to an underwater explosion." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1998. http://handle.dtic.mil/100.2/ADA353271.

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Kaufman, Robert E. "Effects of geometric and material imperfections on the dynamic response of cylindrical shells subjected to underwater explosion." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1995. http://handle.dtic.mil/100.2/ADA299939.

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Thesis (M.S. in Mechanical Engineering and Mechanical Engineer) Naval Postgraduate School, June 1995.
Thesis advisor(s): Young S. Shin. "June 1995." Bibliography: p. 101-102. Also available online.

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Hawkins, Darrin L. Van Leuvan Barbara C. "An XML-based mission command language for autonomous underwater vehicles (AUVs) /." Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2003. http://library.nps.navy.mil/uhtbin/hyperion-image/03Jun%5FHawkins.pdf.

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Oesterreich, Mark H. "Transient response analysis of the 72 Inch TAC-4 ruggedized shipboard rack subjected to an underwater explosion event." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1998. http://handle.dtic.mil/100.2/ADA354298.

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Thesis (Degree of Mechanical Engineer and M.S. in Mechanical Engineering) Naval Postgraduate School, June 1998.
"June 1998." Thesis advisor(s): Young S. Shin. Includes bibliographical references (p. 97). Also available online.

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Stettler, Jeffrey W. "Damping mechanisms and their effects on the whipping response of a submerged submarine subjected to an underwater explosion." Thesis, Monterey, California. Naval Postgraduate School, 1995. http://hdl.handle.net/10945/25799.

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Stettler, Jeffrey W. (Jeffrey Wayne). "Damping mechanisms and their effects on the whipping response of a submerged submarine subjected to an underwater explosion." Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/11085.

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Thesis (Nav. E.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering, 1995, and Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1995.
Includes bibliographical references (leaves 102-107).
by Jeffrey W. Stettler.
M.S.
Nav.E.

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Nusom, F. Allen. "Application of the systems engineering process to the explosive ordnance disposal requirement for an underwater system." Master's thesis, This resource online, 1990. http://scholar.lib.vt.edu/theses/available/etd-12232009-020010/.

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Smith, James R. "Effect of fluid mesh truncation on the response of a Floating Shock Platform (FSP) subjected to an Underwater Explosion (UNDEX)." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1999. http://handle.dtic.mil/100.2/ADA371731.

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Thesis (M.S. in Mechanical Engineering) Naval Postgraduate School, September 1999.
"September 1999:. Thesis advisor(s): Young S. Shin. Includes bibliographical references (p. 71-72). Also Available online.

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Park, Jinwon. "A Runge Kutta Discontinuous Galerkin-Direct Ghost Fluid (RKDG-DGF) Method to Near-field Early-time Underwater Explosion (UNDEX) Simulations." Diss., Virginia Tech, 2008. http://hdl.handle.net/10919/28905.

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A coupled solution approach is presented for numerically simulating a near-field underwater explosion (UNDEX). An UNDEX consists of a complicated sequence of events over a wide range of time scales. Due to the complex physics, separate simulations for near/far-field and early/late-time are common in practice. This work focuses on near-field early-time UNDEX simulations. Using the assumption of compressible, inviscid and adiabatic flow, the fluid flow is governed by a set of Euler fluid equations. In practical simulations, we often encounter computational difficulties that include large displacements, shocks, multi-fluid flows with cavitation, spurious waves reflecting from boundaries and fluid-structure coupling. Existing methods and codes are not able to simultaneously consider all of these characteristics. A robust numerical method that is capable of treating large displacements, capturing shocks, handling two-fluid flows with cavitation, imposing non-reflecting boundary conditions (NRBC) and allowing the movement of fluid grids is required. This method is developed by combining numerical techniques that include a high-order accurate numerical method with a shock capturing scheme, a multi-fluid method to handle explosive gas-water flows and cavitating flows, and an Arbitrary Lagrangian Eulerian (ALE) deformable fluid mesh. These combined approaches are unique for numerically simulating various near-field UNDEX phenomena within a robust single framework. A review of the literature indicates that a fully coupled methodology with all of these characteristics for near-field UNDEX phenomena has not yet been developed. A set of governing equations in the ALE description is discretized by a Runge Kutta Discontinuous Galerkin (RKDG) method. For multi-fluid flows, a Direct Ghost Fluid (DGF) Method coupled with the Level Set (LS) interface method is incorporated in the RKDG framework. The combination of RKDG and DGF methods (RKDG-DGF) is the main contribution of this work which improves the quality and stability of near-field UNDEX flow simulations. Unlike other methods, this method is simpler to apply for various UNDEX applications and easier to extend to multi-dimensions.
Ph. D.

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Webster, Keith Gordon. "Investigation of Close Proximity Underwater Explosion Effects on a Ship-Like Structure Using the Multi-Material Arbitrary Lagrangian Eulerian Finite Element Method." Thesis, Virginia Tech, 2007. http://hdl.handle.net/10919/31077.

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This thesis investigates the characteristics of a close proximity underwater explosion and its effect on a ship-like structure. Finite element model tests are conducted to verify and validate the propagation of a pressure wave generated by an underwater explosion through a fluid medium, and the transmission of the pressure wave in the fluid to a structure using the Multi-Material Arbitrary Lagrangian/Eulerian method. A one dimensional case modeling the detonation of a spherical TNT charge underwater is investigated. Three dimensional cases modeling the detonation of an underwater spherical TNT charge, and US Navy Blast Test cases modeling a shape charge and a circular steel plate, and a shape charge and a Sandwich Plate System (SPS) are also investigated. This thesis provides evidence that existing tools and methodologies have some capability for predicting early-time/close proximity underwater explosion effects, but are insufficient for analyses beyond the arrival of the initial shock wave. This thesis shows that a true infinite boundary condition, a modified Gruneisen equation of state near the charge, and the ability to capture shock without a very small element size is needed in order to provide a sufficient means for predicting early-time/close proximity underwater explosion effects beyond the arrival of the initial shock wave.
Master of Science

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Brochard, Kévin. "Modélisation analytique de la réponse d’un cylindre immergé à une explosion sous-marine." Thesis, Ecole centrale de Nantes, 2018. http://www.theses.fr/2018ECDN0019/document.

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La conception d’une coque de sous-marin est cruciale pour son opérabilité et la sécurité de l’équipage, mais également complexe. En effet, les ingénieurs doivent prendre en compte à la fois la légèreté, la discrétion acoustique et la résistance de la coque à la pression d’immersion et aux attaques extérieures. Les explosions sous-marines représentent une menace de premier ordre pour l’intégrité de la coque, dont le comportement doit être correctement analysé. Les travaux présentés dans cette thèse portent sur le développement d’une méthode simplifiée, basée sur des formulations analytiques, pour étudier la réponse mécanique d’un cylindre profondément immergé à une explosion sous-marine. Le but de cette méthode est de fournir aux ingénieurs une estimation rapide des dommages subis par la coque cylindrique, leur permettant de simuler un grand nombre de scénarios d’explosion. Dans ce travail de thèse, le modèle de la corde plastique sur fondation plastique est repris et adapté à l’étude d’un cylindre immergé soumis à un chargement explosif, pour lequel les effets de pression d’immersion et d’interaction fluide-structure sont à prendre en compte. Une modélisation simplifiée de l’interaction fluide-structure est couplée avec le modèle de corde plastique sur fondation plastique, en considérant d’une part les effets de la pression d’immersion et d’autre part le raidissage circonférentiel du cylindre. Des expressions analytiques sont développées pour calculer l’enfoncement de la coque ainsi que son énergie de déformation plastique. Les résultats obtenus sont comparés à des résultats d’essais et de simulations numériques, ce qui permet de valider progressivement la méthode simplifiée, mais aussi de mettre en évidence ses limitations
The design of a hull of submarine is crucial for its operability and the safety of the crew, but also complex. Indeed, the engineers have to take into account at the same time lightness, acoustic discretion and resistance of the hull to immersion pressure and to environmental attacks. Underwater explosions represent a first-rate threat to the integrity of the hull, whose behavior needs to be properly analyzed. The works presented in this thesis concern the development of a simplified method, based on analytical formulations, to study the mechanical behavior of a cylinder deeply immersed subjected to an underwater explosion. The purpose of this method is to give engineers a fast estimation of the damage undergone by the cylindrical shell, allowing them to compute a large number of scenarios of explosion.In the scope of this thesis, the model of the plastic string on plastic foundation is picked up and adapted to the study of an immersed cylinder subjected to an explosive load, for which the effects of immersion pressure and fluid-structure interaction are to be taken into account. This simplified model of the fluid structure interaction is coupled with the model of a plastic string resting on plastic foundation, by considering on one hand the effects of the immersion pressure and on the other hand the circumferential stiffening of the cylinder. Analytical expressions are derived in order to calculate the final deflection of the shell as well as its energy of plastic deformation. The obtained results are compared with results obtained with numerical simulations, which allows to validate gradually the simplified method, but also to highlight its limitations

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Van, Leuvan Barbara C., and Darrin L. Hawkins. "An XML-based mission command language for autonomous underwater vehicles (AUVs)." Thesis, Monterey, California. Naval Postgraduate School, 2003. http://hdl.handle.net/10945/975.

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Approved for public release, distribution is unlimited
Autonomous Underwater Vehicles (AUVs) are now being introduced into the fleet to improve Mine Warfare capabilities. Several AUVs are under government-contracted development. Mission planning and data reporting vary between vehicles and systems. This variance does not pose an immediate problem, as only one AUV is currently in production. However, as more AUVs are put into production, commands will begin to get multiple AUVs. Without a single mission command language, multiple systems will require familiarity with multiple languages. Extensible Markup Language (XML) and related technologies may be used to facilitate interoperability between dissimilar AUVs and extract and integrate mission data into Navy C4I systems. XML makes archive maintenance easier, XML documents can be accessed via an http server, and, in root form, XML is transferable on the fly by stylesheet. This thesis presents an XML-based mission command for the command and control of AUVs. In addition, this thesis discusses XML technology and how XML is a viable means of achieving interoperability. Furthermore, this thesis provides an example mission file using existing software, and demonstrates the future of XML in AUV technology. Finally, this work ends with a compelling argument for the use of an XML-based mission command language to command all AUVs.
Ensign, United States Navy
Captain, United States Air Force

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Phaneuf, Matthew D. "Experiments with the REMUS AUV." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2004. http://library.nps.navy.mil/uhtbin/hyperion/04Jun%5FPhaneuf.pdf.

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Tartière, Jérémie. "Prediction of deformation and residual stress in the high explosive hydroforming process using numerical simulation." Electronic Thesis or Diss., Brest, École nationale supérieure de techniques avancées Bretagne, 2022. http://www.theses.fr/2022ENTA0008.

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Avant la pandémie de COVID-19, Airbus recevait de plus en plus de commandes d'aéronefs, et espérait, via l’hydroformage par explosif, pouvoir répondre à davantage de demandes. Pour éviter des coûts supplémentaires pour le développement d’une nouvelle technique, la simulation numérique est utilisée. Toutefois, le temps nécessaire, que ce soit de calcul ou ingénieur, est trop important et la précision parfois insuffisante pour permettre une intégration facile au sein des différents projets concernés. De plus, la viabilité du procédé en vue d’une industrialisation doit être considérée. Pour répondre à ce besoin, dans un premier temps, les différentes étapes liées à l'hydroformage par explosif sont identifiées. En premier lieu, la détonation est étudiée pour permettre une meilleure compréhension de la source d'énergie agissant lors du formage par explosif. Ensuite, la propagation du choc issue de l’explosion sous-marine est évaluée ainsi que l’interaction fluide-structure dans le cas du formage par explosif tel que défini au sein d’Airbus. A partir de ces considérations, un outil « FSILoad », basé sur une approche semi-analytique, permettant l’application d’une pression équivalente à la détonation de cordeaux explosifs est créée. Pour s’assurer la bonne définition de l’alliage d’aluminium dont est fait la pièce, cet alliage est caractérisé via des essais de traction quasi-statiques uni-axial, des essais dynamiques via les barres d’Hopkinson et le choc laser. Un modèle numérique est réalisé à l'aide de ces nouvelles données d'entrée. Lors de l'hydroformage par explosif, les contraintes résiduelles issues de la simulation sont comparées à l’expérience et un modèle analytique est défini pour permettre l’identification de paramètres influents. Finalement, les paramètres susceptibles d’affecter la déformation finale en simulation sont identifiés, la viabilité de l’outil FSILoad quantifié et la répétabilité du procédé pour répondre à un besoin industriel évaluée
Before the COVID-19 pandemic, Airbus was receiving more and more orders from aircraft, and was hoping, through high explosive hydroforming, to be able to meet more demands. To avoid additional costs for the development of a new technique, numerical simulation is used. However, the time required for calculation and engineering is too long and the accuracy is sometimes insufficient to allow easy integration into the various projects concerned. In addition, the viability of the process for industrialisation must be considered. To meet this need, the various steps related to High Explosive HydroForming are first identified. Firstly, the detonation is studied to allow a better understanding of the energy source acting during explosive forming. Next, the propagation of the shock wave from the underwater explosion is evaluated as well as the fluid-structure interaction in the case of explosive forming as defined within Airbus. Based on these considerations, a «FSILoad» tool, based on a semi-analytical approach, allowing the application of a pressure equivalent to the detonation of explosive cords is created. To ensure the correct definition of the aluminium alloy of which the part is made, this alloy is characterised by quasi-static uni-axial tensile tests, dynamic tests via Hopkinson bars and laser shock. A digital model is created using this new input data. During high explosive hydroforming, the residual stresses resulting from the simulation are compared to the experiment and an analytical model is defined to allow the identification of influential parameters. Finally, the parameters likely to affect the final deformation in simulation are identified, the viability of the FSILoad tool quantified and the repeatability of the process to meet an evaluated industrial need

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Nico, Thibaut. "Étude et développement de solutions de relocalisation d'objets sous-marins par des véhicules sous-marins hétérogènes." Thesis, Brest, École nationale supérieure de techniques avancées Bretagne, 2019. http://www.theses.fr/2019ENTA0005.

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Dans le contexte de guerre des mines (MCM), il est important de revisiter les objets potentiellement dangereux afin de les identifier et les neutraliser s’il s’agit effectivement de mines. Cette dangereuse tâche était habituellement réalisée par des plongeurs démineurs qui sont petit à petit remplacés par des drones sous-marins. Le design « low cost » des robots de revisite/destruction de mines ne permet en général pas de garantir la revisite d’une cible géolocalisée en allant droit dessus. De plus, le robot pourrait commencer sa mission sous-marine à une distance éloignée et l’absence de positionnement GPS en environnement sous-marin imposent l’élaboration d’une stratégie afin de garantir la revisite de la cible. En se basant sur des informations a priori de l’environnement et notamment la présence de points de repère (amers), le problème est résolu par la planification d’une stratégie à suivre en prenant en compte les incertitudes de déplacement inhérentes en milieu sous-marin. Dans un contexte d’erreurs bornées, une approche ensembliste est proposée. Premièrement, en se basant sur la position et la forme des amers, ainsi que la zone visible du capteur embarqué, les cartes de recalages sont construites afin de définir les poses du robot qui permettent de détecter les différents amers afin de réduire l’incertitude de position du robot.Deuxièmement, en se basant sur un modèle paramétrique de déplacement avec des paramètres incertains, une stratégie haut-niveau est proposée à travers l’optimisation d’un graphe. La stratégie consiste à naviguer entre les cartes de recalage afin de réduire l’incertitude de position du robot et finalement garantir la revisite de la cible souhaitée
In the Mine Counter Measure (MCM) context in the underwater environment, it is vital to revisit some potentially dangerous objects to identify and neutralize them if they are actually mines. This dangerous task was usually performed by humandivers but more and more it is conducted by unmanned underwater robots. Due to the low cost design of the revisit/mine-killer robot, going straightforward to the geolocalized suspicious object does not guarantee that the robot will redetect it.Moreover the robot may dive at a far position from the target and the lack of absolute positioning system in underwater environment demands a strategy to follow to guarantee the revisit of this target. Based on a priori information in the working area and especially the presence of geolocalized landmarks, the problem is solved as a motion planning problem considering uncertainties due to the increasing error when navigating underwater. In the context of bounded errors, the problem is solved in a set-membership manner. Firstly, based on the location and the shape of the landmarks, and on the visibility area of the sensor embedded, the registration maps are computed indicating the sets of robot poses to detect the different landmarks considered in order to reduce the uncertainty on the robot position. Secondly, based on a parametric motion model with uncertain parameters, an high level strategy is provided through a raph optimization. The strategy consists in navigating between the registration maps toreduce each times the uncertainty in position of therobot and finally to guarantee the reachability of agoal area corresponding to the redetection of the target

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Elbergui, Ayda. "Amélioration des techniques de reconnaissance automatique de mines marines par analyse de l'écho à partir d'images sonar haute résolution." Thesis, Brest, 2013. http://www.theses.fr/2013BRES0042/document.

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La classification des cibles sous-marines est principalement basée sur l'analyse de l'ombre acoustique. La nouvelle génération des sonars d'imagerie fournit une description plus précise de la rétrodiffusion de l'onde acoustique par les cibles. Par conséquent, la combinaison de l'analyse de l'ombre et de l'écho est une voie prometteuse pour améliorer la classification automatique des cibles. Quelques systèmes performants de classification automatique des cibles s'appuient sur un modèle pour faire l'apprentissage au lieu d'utiliser uniquement des réponses expérimentales ou simulées de cibles pour entraîner le classificateur. Avec une approche basée modèle, un bon niveau de performance en classification peut être obtenu si la modélisation de la réponse acoustique de la cible est suffisamment précise. La mise en œuvre de la méthode de classification a nécessité de modéliser avec précision la réponse acoustique des cibles. Le résultat de cette modélisation est un simulateur d'images sonar (SIS). Comme les sonars d'imagerie fonctionnent à haute et très haute fréquence le modèle est basé sur le lancer de rayons acoustiques. Plusieurs phénomènes sont pris en compte pour augmenter le réalisme de la réponse acoustique (les effets des trajets multiples, l'interaction avec le fond marin, la diffraction, etc.). La première phase du classificateur utilise une approche basée sur un modèle. L'information utile dans la signature acoustique de la cible est nommée « A-scan ». Dans la pratique, l'A-scan de la cible détectée est comparé à un ensemble d'A-scans générés par SIS dans les mêmes conditions opérationnelles. Ces gabarits (A-scans) sont créés en modélisant des objets manufacturés de formes simples et complexes (mines ou non mines). Cette phase intègre un module de filtrage adapté pour permettre un résultat de classification plus souple capable de fournir un degré d'appartenance en fonction du maximum de corrélation obtenu. Avec cette approche, l'ensemble d'apprentissage peut être enrichi afin d'améliorer la classification lorsque les classes sont fortement corrélées. Si la différence entre les coefficients de corrélation de l'ensemble de classes les plus probables n'est pas suffisante, le résultat est considéré ambigu. Une deuxième phase est proposée afin de distinguer ces classes en ajoutant de nouveaux descripteurs et/ou en ajoutant davantage d'A-scans dans la base d'apprentissage et ce, dans de nouvelles configurations proches des configurations ambiguës. Ce processus de classification est principalement évalué sur des données simulées et sur un jeu limité de données réelles. L'utilisation de l'A-scan a permis d'atteindre des bonnes performances de classification en mono-vue et a amélioré le résultat de classification pour certaines ambiguïtés récurrentes avec des méthodes basées uniquement sur l'analyse d'ombre
Underwater target classification is mainly based on the analysis of the acoustic shadows. The new generation of imaging sonar provides a more accurate description of the acoustic wave scattered by the targets. Therefore, combining the analysis of shadows and echoes is a promising way to improve automated target classification. Some reliable schemes for automated target classification rely on model based learning instead of only using experimental samples of target acoustic response to train the classifier. With this approach, a good performance level in classification can be obtained if the modeling of the target acoustic response is accurate enough. The implementation of the classification method first consists in precisely modeling the acoustic response of the targets. The result of the modeling process is a simulator called SIS (Sonar Image Simulator). As imaging sonars operate at high or very high frequency the core of the model is based on acoustical ray-tracing. Several phenomena have been considered to increase the realism of the acoustic response (multi-path propagation, interaction with the surrounding seabed, edge diffraction, etc.). The first step of the classifier consists of a model-based approach. The classification method uses the highlight information of the acoustic signature of the target called « A-scan ». This method consists in comparing the A-scan of the detected target with a set of simulated A-scans generated by SIS in the same operational conditions. To train the classifier, a Template base (A-scans) is created by modeling manmade objects of simple and complex shapes (Mine Like Objects or not). It is based on matched filtering in order to allow more flexible result by introducing a degree of match related to the maximum of correlation coefficient. With this approach the training set can be extended increasingly to improve classification when classes are strongly correlated. If the difference between the correlation coefficients of the most likely classes is not sufficient the result is considered ambiguous. A second stage is proposed in order to discriminate these classes by adding new features and/or extending the initial training data set by including more A-scans in new configurations derived from the ambiguous ones. This classification process is mainly assessed on simulated side scan sonar data but also on a limited data set of real data. The use of A-scans have achieved good classification performances in a mono-view configuration and can improve the result of classification for some remaining confusions using methods only based on shadow analysis

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CHEN, BO-GAO, and 陳柏高. "GRP Surface Ship Subjected to Underwater Explosions." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/qn7qgn.

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碩士
國立高雄科技大學
造船及海洋工程系
107
The anti-shocking capability of the ship is one of the important conditions to suit the mission. This paper takes the reaction of the GRP monocoque (frameless) construction ship under the underwater explosion as the research object. First using MSC.Dytran to establish a simulation model of TNT in underwater explosions, verify the relevant parameters settings; then establish ship model, analyze its response of various parts under underwater explosion, and use Tsai-Wu damage criterion to check material’s failure. The result of the underwater explosion simulation are mainly divided into un-destruction(should be), destruction and un-destruction(improved). It is hoped that the result of this paper can be used as a reference to help ship designer or relative researcher shorten the exploration time in simulation of the response of GRP ship subjected to underwater explosions.

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H, Liu T., and 劉子豪. "A Study of the Effects of Underwater Explosions." Thesis, 2004. http://ndltd.ncl.edu.tw/handle/28194276205298377471.

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Abstract:

碩士
大葉大學
機械工程研究所碩士班
92
The detonation of a condensed high explosive underwater produces two pressure pluses which is a shock then followed by a bubble pulse associated with the expansion of the products of detonation. The purpose of this paper is largely the result of published research on underwater explosions carried out by past literatures such as Roop(1943), Cole(1948), Aron(1949), Keil(1961), Smith(1994) and M kinen(1998). Much of the present knowledge and understanding of this field was acquired became of the demands and the few available discussions of the subject have become inadequate on obsolete. This paper is an attempt to supply a reasonable comprehensive account which will be for use both workers in the field of underwater explosions and others interested in the basic physical processes involved. Numerical studies of underwater explosions including shock wave pressure, bubble pulse and water plume are also investigated in details using MSC.Dytran finite element software, and compared with existing experimental data and empirical methodologies.

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Dissertations / Theses on the topic 'Underwater explosions'

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