Principles of creating numerical models for studying the impact of impulse loads on underground structures

Summary. The current situation in Ukraine has led to new geotechnical challenges, the solution of which is aimed at protecting critical infrastructure facilities from the effects of explosive shock waves. Protective structures that are buried in the soil environment are built to protect critical infrastructure facilities. A necessary condition to ensure their safe operation is the assessment of the stress-strain state of the system “soil environment-shelter building”. It is important to choose an adequate phenomenological model of the behavior of the materials of the protective structure and the soil environment, which describes the work of materials under the impulse impacts. The paper analyses four methods of constructing numerical models for calculating the impact of impulse loads, namely: Lagrange mesh. Euler's mesh. Arbitrary Lagrangian-Eulerian (ALE). Smooth Particle Hydrodynamics (SPH). Each of the methods has its advantages and disadvantages. The Lagrangian mesh enables to easily track the boundary between materials of different structures, both before and after the calculation, and it does not require much computational time. However, this method is not practical in cases of significant model deformations with rapid changes in time. The Euler and Arbitrary Lagrange-Euler methods allow to model the problems with a large distortion of the model, such as an underground or underwater explosion. Their disadvantage is the size of the computational domain and the considerable labour intensity for the model setup. Smooth Particle Hydrodynamics is a meshless Lagrangian method. The advantage of this method is the ability to work with large model deformations. The disadvantage is labour intensity and calculation time. All of these methods of building a numerical model are available in the LS-Dyna software package. During the analysis of calculations in LS-Dyna, we found that it is advisable to use the Lagrange mesh to create a model of a structure made of reinforced concrete or steel due to their high stiffness. The Euler and ALE methods are preferable for soil, they enable a strong change in the geometry of the model under the influence of the blast. Different methods are combined to achieve adequate model performance and to obtain correct results that will closely match the actual behavior of structures, facilities and materials under impulse loads.