This presentation was made at the NAFEMS Seminar "Exploring Explicit Dynamics - Impact, Shock & Crash" held on the 13-14 April 2021.

Explicit Dynamics Finite Element Analysis has been used by industry and academia for many years. With advanced techniques such as particle methods, Arbitrary Lagrangian-Eulerian and advance failure methods becoming more prevalent in general purpose simulation packages, simulation engineers have never had such capabilities at their fingertips.

Modelling impact, shock & crash phenomenon is inherently difficult. The process is highly non-linear, materials are strain rate dependant, damage has to be realistically represented in order to capture the response of the product. The aim of this seminar was to present and discuss the challenges, and solutions in this field, using real engineering examples.

Resource Abstract

Reinforced concrete is an inherently non-linear material with non-linear compressive behaviour. Concrete cracking and reinforcement yielding alter the stiffness and cause redistribution of forces within statically indeterminate structures. The concrete gravity substructure for the West White Rose Offshore Platform is subject to extreme, often dynamic loads such as wind, wave, hydrostatic and impact from icebergs and ice-class vessels. Because the structure is being constructed on dry land and towed out to sea, it is also important to optimise the design for weight and floating stability. These design and material constraints require the use of an explicit solver code which can predict material nonlinearities in such detail that they can be accepted as part of the design, since it would be impossible to keep the structure entirely crack- and yield-free throughout its design life.



In this presentation, a practical design approach is described which involves explicit modelling of concrete and reinforcement components, material non-linearities, and impact type loadcases. The approach uses the MAT_WINFRITH material model within the LS-DYNA finite element software which is used extensively during the detailed engineering design of the concrete gravity substructure which will be installed off the east coast of Newfoundland, Canada.



The structural design is discussed considering these constraints and with reference to the various tools available as part of the LS-DYNA package. Though the structure was designed for many different loadcases, one – the ship impact loadcase - is presented in detail to demonstrate how LS-DYNA predicted that the recovery of elastic deformation in the steel reinforcement closed cracks upon ship rebound. This analysis meant that some level of damage from through-thickness cracking was accepted. Such precise conclusions, and the acceptance of such damage, would not have been possible without the tools and material models available in LS-DYNA.