| dc.description.abstract | This thesis studies the response of a subsea pipeline's structure when a dropped object hits it. The pipeline and seabed were modelled using solid elements, while the container model was imported from Aker Solutions and is composed of shell elements. LS-DYNA, a finite element software, was used to conduct the analysis. The key parameters studied in this research were impact force, internal energy, and pipeline deformation. Thirteen different cases have been analysed in addition to three cases used in a mesh convergence test. The impact scenarios have been described in Table 8, Chapter 4.11 and the three mesh convergence cases have been described in Table 9, Chapter 4.11.
The thesis includes a literature study of relevant standards and previous research that has been conducted. DNVGL-RP-C204 and DNVGL-RP-F107 are the applicable standards for dropped objects in this thesis. DNVGL-RP-C204 provides essential information on calculating impact velocity, dissipation of strain energy, and force-deformation curve for tubular members. At the same time, DNVGL-RP-F107 presents information on drop probability in crane lifting operations, the hit probability onto a subsea pipeline, and various protection methods available in the industry.
A mesh convergence study was carried out to determine the optimal mesh size for the models. This involved comparing three models with the same properties, apart from the mesh size, and observing at which mesh size the outcome converged. The objective was to identify the largest feasible mesh size that would have little to no impact on the precision of the results.
A comprehensive parametric study of the subsea pipeline was conducted to analyse its response to the different cases. This involved testing for various scenarios on the pipeline under different conditions, such as altering the soil parameters, protection method, yield strength, and the impact angle of the container. The container's velocity was kept constant at 10 m/s in all the impact scenarios. The impact angle was identified as a crucial factor in the extent of damage inflicted on the pipeline. The use of concrete coating reduced the deformation and the internal energy in the pipeline. With a flexible seabed, the internal energy was reduced for the scenario with coating. However, that was not the case for the unprotected pipeline. The possible reason is explained in this thesis. By increasing the pipeline’s yield strength, the internal energy and deformation of the pipeline were significantly reduced. | |
