An elastic-plastic iceberg material model considering temperature gradient effects and its application to numerical study

Abstract

To simulate the FPSO-iceberg collision process more accurately, an elastic-plastic iceberg material model considering temperature gradient effects is proposed and applied. The model behaves linearly elastic until it reaches the ‘Tsai-Wu’ yield surfaces, which are a series of concentric elliptical curves of different sizes. Decreasing temperature results in a large yield surface. Failure criteria, based on the influence of accumulated plastic strain and hydrostatic pressure, are built into the model. Based on published experimental data on the relationship between depth and temperature in icebergs, three typical iceberg temperature profiles are proposed. According to these, ice elements located at different depths have different temperatures. The model is incorporated into LS-DYNA using a user-defined subroutine and applied to a simulation of FPSO collisions with different types of iceberg. Simulated area-pressure curves are compared with design codes to validate the iceberg model. The influence of iceberg shape and temperature on the collision process is analyzed. It is indicated that FPSO structural damage not only depends on the relative strength between the iceberg and the structure, but also depends on the local shape of the iceberg.

Keywords

iceberg material model / FPSO-iceberg collision / temperature gradient / numerical simulation / iceberg shape

References

[1] Bergan PG, Cammaert G, Skeie G, Tharigopula V. On the potential of computational methods and numerical simulation in ice mechanics. 9th World Congress on Computational Mechanics and 4th Asian Pacific Congress on Computational Mechanics, 2010

[2] Derradji-Aouat A. A unified failure envelope for isotropic fresh water ice and iceberg ice. Proc. of the ETCE/OMAE-2000 Joint Conference, Energy for the New Millennium, 2000

[3] Ding D. Introduction to engineering sea ice, 1999, Beijing: China Ocean Press, 30-31

[4] Frederking R, Timco G. Sea ice floe impacts-large scale basin experiments. Proceedings of the Tenth International Offshore and Polar Engineering Conference ISOPE'00, 2000, 640-645

[5] Gagnon RE, Gammon PH. Triaxial experiments on iceberg and glacier ice. Journal of Glaciology, 1995, 41(139): 528-540

[6] Gao Y, Hu Z, Ringsberg JW, Wang J. An elastic-plastic ice material model for ship-iceberg collision simulations. Ocean Engineering, 2015, 102: 27-39

[7] Hill B. Ship collisions with iceberg database. 7th International Conference and Exhibition on Performance of Ships and Structures in Ice, 2005, 172-178

[8] Jones SJ. A review of the strength of iceberg and other freshwater ice and the effect of temperature. Cold Regions Science & Technology, 2007, 47(3): 256-262

[9] Liu Z, Amdahl J, Løset S. Plasticity based material modelling of ice and its application to ship–iceberg impacts. Cold Regions Science and Technology, 2011, 65(3): 326-334

[10] Masterson DM, Frederking RMW, Wright B, Kerna T, Maddock WP. A revised ice pressure-area curve. 19th International Conference on Port and Ocean Engineering under Arctic Conditions, 2007, 305-314

[11] McKenna R. Iceberg shape characterization. 18th International Conference on Port and Ocean Engineering under Arctic Conditions, 2005, 555-564

[12] Michel B, Toussaint N. Mechanisms and theory of indentation of ice plates. Journal of Glaciology, 1978, 19: 285-300

[13] Schulson EM, Duval P. Creep and fracture of ice, 2009, Cambridge: Cambridge University Press, 240-241

[14] Storheim M, Kim E, Amdahl J, Ehlers S. Iceberg shape sensitivity in ship impact assessment in view of existing material models. ASME 31st International Conference on Ocean, Offshore and Arctic Engineering, 2012, 507-517

[15] Timco GW, Sudom D. Revisiting the Sanderson pressure-area curve: Defining parameters that influence ice pressure. Cold regions science and technology, 2013, 95: 53-66