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Session 3

Numerical Simulation of the Ice-Structure Interaction in LS-DYNA
Design of offshore structures in Arctic waters is strongly dependent on local and global ice loads. These loadings are, in general, contact forces transmitted to the structures during interaction with ice floes, ice ridges or icebergs. The prediction of ice forces on structures relies heavily on a thorough understanding of mechanical behavior of sea ice as well as on in-depth knowledge of interaction between ice features and structures. Sloping, or conical shaped structures are commonly used structures for arctic oil and gas exploration and production due to the fact that these structural shapes induce ice bending failure on the structure slope, so that the horizontal ice loads on the structure can be reduced compared to a crushing type of failure, which occurs when ice floes interacting with vertical structures. As an ice sheet advances toward a conical or sloping structure, the ice load increases until the drifting ice sheet fails by bending and forms ice blocks. Following the failure of the ice cover, the failed ice blocks are pushed up the sloping structure or forms ice rubble in front of the structure. Predicting the correct failure modes (crushing, bending, and splitting or combined modes of failure) is desirable as well as the global force on the structure. However, this is not straightforward due to the complexity of the mechanical behavior of ice. It is facing some challenges such as, anisotropy (ice can be considered as a transversally isotropic material), inhomogeneity, and strain rate and pressure dependent response. Some of these key behaviors are considered on this study as a preliminary start for the further investigations as a part of the ColdTech project.
Analysis of a single stage compressed gas launcher behaviour : from breech opening to sabot separation
Single stage compressed gas guns are used in Shock Physics laboratory to perform characterization experiments and ballistic events. The main advantage of this kind of launcher is that impact conditions are well defined (impact obliquity, impact velocity). In order to achieve high quality in ballistic performance, it is essential to understand the behaviour of the projectile in the barrel of the gun. This paper is devoted to the simulation of the whole behaviour of a laboratory gun, from breech opening up to the muzzle blast sabot separation due to air drag forces. LSDYNA was used as a numerical tool for the improvement of the launched package behaviour which consists in sabots and projectile. The simulation needs to reproduce the in-bore operations of a launcher taking into account gases which act on both sides of the projectile: very high pressures release at the base as well as pressure built-up and the gas thrown out from the tube at the front. There is also a need to predict perfectly the sabots behaviour when the projectile is released from the tube so as to control the impact conditions on the target. The Fluid / Stucture Interaction (FSI) capability of LSDYNA is used as a numerical tool to increase the knowledge in this field. The challenge is to obtain a simulation recreating the effect of gases on the projectile at both high pressures and high velocities. High speed and ultra high speed video cameras set up in our facility allow us to make correlation between calculations and experiments and so validate the simulation. This work gives to our Laboratory a real tool for optimizing the sabots design in terms of material, shape, dimensions and thus increases the quality and reliability of ballistic experiments.
imulation of the flow around a Vertical Axis Wind Turbine : LS-DYNA v980
The future 980 version of LS-DYNA® will include Computational Fluid Dynamics (CFD) solvers. The main objective of these new solvers will be to perform fluid structure interactions by directly solving the Navier-Stokes equations and by using any LS-DYNA® Lagrangian model for the solid part. In the process of evaluating the new possibilities offered by these new solvers, in particular concerning fluid structure interaction, AS+ has worked in partnership with both industrial and academic clients on the case of a vertical axe wind turbine which was used in the French around the world boat race “Vendée Globe”. The final objective of these simulations is to test various turbine shapes and airfoils in order to determine which one would offer the best aerodynamic behavior without any compromise to its structural behavior. Tests were therefore first conducted on static or oscillating airfoils. Then, 2D simulations of various turbine shapes were performed before aiming for the complete 3D simulation of the problem. This paper aims to highlight the main features of the new incompressible solver by presenting the results obtained on one of the first industrial cases that use the new v980 version.
Numerical Simulation of Consequences of Passenger Aircraft Tyre Damage
All new-designed passenger aircrafts have to meet strict national and international safety requirements in accidents. One of the accidents is pneumatic tyre failure (a tyre burst). Because of that the tyre can be fragmented. An air stream from the tyre and some tyre pieces under the air stream can impact on vitally important aircraft system elements in the landing gear box and disable or break them. In this case a designer has to provide a documentary evidence of system assembly reliability in possible accident cases considered. The problem solution by means of direct full-scale tests is too much expensive. Therefore the experimental-numerical method based on the optimal combination of a detailed computer simulation and model experiments for the computer simulation verification can be used. Numerical simulation and some experimental results of dynamic elastic-plastic deformation researches of some aircraft system subjected to the air flow pressure and the tyre piece impact are presented in the paper. The numerical investigations are performed by means of gas-dynamics and structural strength conjugate problem solution on the basis of STAR-CCM+ and LS-DYNA® software.