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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

An Arbitrary Lagrangian-Eulerian Finite Element Method for Shock Wave Propagation: Validating Simulations of Underwater Explosions / En finit elementmetod med ALE för stötvågsutbredning: validering av simulerade undervattensdetonationer

Sandström, Sebastian January 2021 (has links)
Underwater explosions are often modeled with Arbitrary Lagrangian-Eulerian (ALE) Finite Element Methods. The objective of this thesis is to validate the simulation method, with respect to the propagating shock wave. A two-dimensional axisymmetric model of a spherical TNT charge submerged in water is simulated using LS-DYNA. The explosive is modeled with the Burn Fraction technique and the Jones-Wilkins-Lee equation of state. Water is modeled as a non-viscous fluid, with the Grüneisen equation of state. The convergence for different mesh resolutions, the effect of different advection methods, and varied constants in the artificial viscosity are examined. Generally, the simulations agree well with empirical results, but the maximum pressure diminishes more rapidly with distance compared to experiments. The excessive dampening is most notable in the early stages of the propagation. Also, unexpected oscillations are observed near the discontinuity. The choice of advection scheme and constants in the artificial viscosity do not resolve the issues suggesting that other numerical techniques for treating the discontinuity should be considered. / Undervattensexplosioner simuleras ofta med ALE-baserade finita elementmetoder. Detta examensarbete avser att validera simuleringsmetoden med hänsyn till stötvågens utbredning i vattnet. En tvådimensionell axisymmetrisk modell av en sfärisk TNT-laddning nedsänkt i vatten simuleras i LS-DYNA. Laddningen modelleras med hjälp av brinnfraktioner och Jones-Wilkins-Lee tillståndsekvation. Vattnet modelleras som en inviskös fluid tillsammans med Grüneisens tillståndsekvation. Nätkonvergens, val av advektionsmetod och ändring av konstanter i den artificiella viskositeten studeras. Övergripande resultat stämmer väl överens med empirisk data, men stötvågens topptryck avtar fortare än väntat. Denna dämpning är tydligast i utredningens tidiga skeden. Dessutom observeras oväntade oscillationer kring stötvågens diskontinuerliga tryckprofil. Val av advektionsmetod och konstanter tillhörande artificiella viskositeten verkar ha liten betydelse för resultaten. En alternativ numerisk metod för behandling av stötvågens diskontinuitet bör implementeras.

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