Numerical Prediction of Ship Hydrodynamic Derivatives in Close Proximity to a Vertical Bank and Maneuvering Stability Analysis

As bank effect has a remarkable influence on the maneuverability of a ship proceeding close to a vertical bank, the assessment of ship maneuvering stability is of great importance. The hydrodynamic derivatives of a ship can reflect the change of the ship’s maneuverability and they are determined with the method of planar motion mechanism (PMM) tests. This paper presents a numerical way to simulate the PMM captive model tests for the ship KVLCC2. A general purpose viscous flow solver was adopted to solve unsteady Reynolds averaged Navier Stokes (RANS) equations in conjunction with a RNG k-ε turbulence model. A hybrid dynamic mesh technique is developed to update the mesh volume around the ship hull when the ship is undertaking pure yaw motions and it turns out efficient and effective to solve the limitation of small ship-bank distance to the mesh configuration and remeshing.. The numerical simulations and the accuracy of the numerical method was validated in comparison with the results of PMM tests in a circulating water channel. Then a series of distances between ship and bank together with different water depths were set for simulating the PMM tests of the KVLCC2 model in proximity to a vertical bank. The first order hydrodynamic derivatives of the ship were analyzed from the time history of lateral force and yaw moment according to the multiple-run simulating procedure. The values of derivatives in different lateral proximities to the bank and variant water depths were compared and it showed some favorable trends for predicting the ship’s maneuverability in the restricted waterways. For example, the influence of velocity derivatives on lateral force reduces while that of velocity derivatives on yaw moment strengthens and this is partly due to the suction force and bow-out moment caused by bank wall effect. The straight line stability and directional stability in terms of the calculated hydrodynamic derivatives were also discussed based on the MMG model for ship maneuvering. Results indicate that the ship is inherently unstable without control and the enhancement of bank effect makes the condition even worse. Moreover, a stable or unstable zone of PD controller parameters focusing on the directional stability was illustrated and setting the values of controller parameters in the range of “Control with high sensitivity” is recommended for cases of the ship navigating in very close proximity to a bank.