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Improved Solver for coupled fluid-structure interaction and particle simulations

Drilling is essential for the recovery and storage of sub-surface energy, such as oil, gas and geothermal heat. It typically accounts for large parts of the project costs. For optimal drilling operations it is required to achieve an efficient transport of cuttings from the drill-bit to the surface. As drilling often reaches several thousand meters below the surface, in-situ measurements of drilling parameters are very challenging. Therefore, limited field knowledge about the underlying phenomena exists and many investigations rely on simplified laboratory setups and detailed software-based simulations. Beside technical challenges, drilling projects are always very costly, e.g. in case of deep geothermal wells only the drilling costs account for at least 50% of the total project costs. Large shares of these costs are caused by non-productive time during the drilling process caused by damages to underground equipment or borehole integrity issues. These can cause days for pulling out and tripping in again the drill string or re-conditioning of the borehole. Particular importance in these fatigue processes are lateral vibrations of the drill string. Previous work already analyzed different factors influencing the damping of drill string vibrations, e.g. drilling mud, fluid flows, rotation. Based on the work from the presentation at the OpenFOAM workshop 2019, the software setup was shifted from fluid solid interaction toolkit published for foam-extend-4.0 to the new solids4foam library. Using this new approach future phenomena can be simulated in the coupled code. The existing solver was therefore implemented as a new fluid solver within the framework of solids4foam. Additionally, the coupling between the particle solver and the fluid solver was improved to use the existing functionality within the codebase instead of exchanging data via custom data files. Besides speed improvements, it is also expected that the temporary data produced by the solver is largely decreased. The paper closes with a brief simulation study which demonstrates the correct execution of the new proposed solver and initial results from a validation study.