Modeling of impulse loading of a liquid-filled underwater pipeline

The process of impulse loading of an underwater two-layer pipeline filled with liquid is modeled. To solve the problem, the author's software package developed for the analysis of threedimensional nonstationary processes of interaction of elastoplastic structures with compressible media is used. The algorithm is based on the improved Godunov scheme, which provides high accuracy of calculations of joint dynamics of liquids, gases and deformable bodies. The method includes an explicit Eulerian – Lagrangian realization with the definition of moving boundaries between the contacted media. Three types of computational meshes are used within one problem: surface meshes of Lagrangian type, consisting of triangular elements that define the initial geometry of objects and track their movement, as well as three-dimensional three-dimensional regular and local meshes automatically generated in the process of calculation and changed at each time step. Initiation of an impulse perturbation having an initial spherical shape is performed at some distance from the pipeline within the calculation domain. Shock waves formed as a result of the pulse perturbation initiation in the surrounding fluid interact with the underwater pipeline fragment and with the rigid bottom. The wave processes in the steel pipe, in the concrete shell weighting it, as well as in the internal fluid of the underwater pipeline are considered. Impulse loads on the underwater pipeline taking into account the influence of rigid bottom are estimated. Shape changes of pipeline shells in the areas of tensile strains formed in the places of maximum bending of the pipeline are shown. It is shown that the proximity of the bottom can significantly increase the impact of impulse loading due to the reflected shock wave from the rigid bottom. Under the action of the same impulse loading, a comparison of the shape changes of the walls of underwater pipelines, hollow inside and filled with liquid, is given. As a result of the initiated pulse loading, the wall deflections of the internally hollow subsea pipeline are observed to be larger than those of the liquidfilled subsea pipeline.