Numerical modelling of waves and current acting on piles

Abstract

Calculating the applied forces of pile structures exposed to waves and currents is an important issue in the offshore industry. Because these constructs are costly, they must be carefully analyzed before evaluating all results. For designers, physical models can be cost and time constraining while helping them optimize their designs. Therefore, the use of numerical models provides a significant advantage. While numerical models offer flexibility in the design of complex structures, their accuracy must be compatible with physical experiments. In this study, the effects of a pile on a flat ground subjected to waves were numerically modeled. These numerical models were solved using the open-source computational fluid dynamics code called REEF3D. In addition, a mesh-convergence study was performed to determine the optimal mesh size. Numerical models of wave and current study samples were constructed using the optimal mesh size and the results were compared with experimental data and analytical results. It was observed that the numerical model was compatible with the experimental results in pile structures affected by waves and currents. First, two test scenarios were created for validation. In the first of these scenarios, only current effects were observed. These current effects were compared with the results of previous physical experiments. Some observation points were used in this comparison. These observation points were placed at certain distances from the single pile perpendicular to the base. The velocity information obtained from the observation points was compared with the numerical model results modeled with REEF3D and velocity profiles were obtained. These velocity profiles were found to be compatible with the results of the physical experiment and the numerical model. In the second verification scenario, only wave effects were observed. Wave forces acting on a fixed diameter cylinder were investigated. Numerical models were established and the results were obtained. These results were compared with the Morison equation results and the results were found to be consistent. After both verification scenarios were made, it was revealed that both wave and current forces can be modeled correctly with the REEF3D program. After this step, the forces acting on four different pile types in eight different scenarios were examined. To understand the diffraction effects, half of the eight scenarios were constructed with parameters where diffraction effects were considered important. At the beginning of these parameters is the change of the pile diameter. In the first of four different piles in eight scenarios, a pile diameter with a constant diameter and such that diffraction effects can be ignored was chosen. A new pile of this diameter was then created to create a cone of appropriate proportions. Wave and current forces acting on this new cone-shaped pile were calculated. The forces acting on both the fixed diameter pile and the cone shaped pile were compared with the results of the Morison and Beji equations and it was seen that reasonable results were obtained. On the other hand, pile scenarios with relatively larger diameters were created and fixed diameter and cone-shaped piles were remodeled in these pile scenarios. Evaluation of all results was re-evaluated and reasonable results were found. A separate mesh-convergence study was performed for all cases. For the mesh convergence study, a coarse mesh size was chosen and gradually reduced. It was desired to see whether it converged to such a value or not. The mesh created by the meshconvergence study were optimized and it was predicted that it could yield reasonable results. At the end of the studies, the compared results were presented both in tabular form and graphically. These results, obtained thanks to open-source tools, showed that we can produce solutions to engineering problems with REEF3D. In the final case, the forces generated by different waves and currents acting on the pile placed on a flat base were analyzed. Thanks to this study, wave or current forces acting on the piles were calculated, and further studies revealed that both wave and current forces could be calculated by computational fluid dynamics method. The use of numerical models has been a turning point in the analysis of pile structures exposed to waves and currents. Due to the limitations and costs of traditional physical experiments, the flexibility and cost-effectiveness of numerical models provide a great advantage. Open-source computational fluid dynamics codes such as REEF3D allow engineers to further examine the behavior of pile structures. This study demonstrates the potential of REEF3D for the analysis of pile structures exposed to waves and currents. It has been shown that the forces acting on the pile structures can be accurately calculated using numerical models. This helps designers make better decisions about the safety and durability of piles. In addition, the validation scenarios and analyzes performed in the study showed that the numerical models are compatible with the experimental data and analytical results. This supports the reliability and accuracy of the numerical models. The results of the study emphasize that numerical models are an important tool in the design of pile structures exposed to waves and currents. Using these models, designers can better understand, optimize, and safely design the behavior of piles. In the future, more advanced numerical models are expected to be developed and used for the analysis of more complex pile structures and different environmental conditions. Moreover, it will be possible to obtain more comprehensive and accurate results by integrating different open-source tools and computational methods.