Development of a Potential Flow Program for the Hydrodynamic Problems of Multiple Bodies at Zero or Nonzero Forward Speed and its Applications
MetadataShow full item record
The configuration of multiple floaters is of growing interest in offshore operations. An in-house program, MDLMultiDYN, is developed to evaluate the hydrodynamics of the multiple bodies. The fully nonlinear problem in potential theory is decomposed into 1st order and 2nd order problems. Applying the Green function method, the source formula is adopted to solve for the 1st order problem for multiple bodies with zero or nonzero speed. The added mass and damping for an asymmetric case are derived. The theory to simplify the boundary condition is discussed. To capture the physical resonance, the irregular frequencies must be removed. The theory to ensure the uniqueness of the solution is reviewed and improved. Four methods are proposed to evaluate the log singularity at the internal free surface, which is a necessary step in the extended boundary condition method. The jump conditions are discussed and the effective formula to remove the irregular frequencies is presented. The 2nd order problem is also discussed. The formula of the 2nd order force and moment for a general case are presented. The importance of removing the irregular frequency effect is discussed. Additionally, improvement is made to accurately calculate the wave elevation around the waterline of the floater. The wave elevation can be calculated in an approximately analytical way. The problem of two box barges side-by-side is investigated in both the CFD approach and the potential method. The results are validated against the experimental data. Excellent agreement between the CFD results and the experimental data is achieved. The discrepancy between the results from the potential method and the CFD approach is contributed by the friction effect of the ship hull at the selected wave frequency. Finally, the current artificial damping methods are discussed and an alternative wall damping method is proposed. The effectiveness of the method is discussed by comparison against the experimental data. The study provides a complete and comprehensive study in the potential theory to evaluate the hydrodynamic loads and responses of multiple floaters. By comparisons against CFD results and experimental data, we gain a deeper understanding of the interaction phenomenon.
irregular frequency removal
Liu, Yujie (2018). Development of a Potential Flow Program for the Hydrodynamic Problems of Multiple Bodies at Zero or Nonzero Forward Speed and its Applications. Doctoral dissertation, Texas A & M University. Available electronically from