Hydrodynamic loadings acting on submerged bodies advancing in waves — an assessment of accuracy

Abstract

Two numerical methods have been reviewed to predict hydrodynamic loadings on the submerged cylinders advancing in waves. The velocity potentials in these methods are calculated by the discrete source distribution technique and the direct solution by the classical integral equation method. These methods have been modified to improve the numerical accuracy of the hydrodynamic forces on submerged cylindrical bodies. This has been done by solving the logarithmic part of the Green's function analytically. The numerical accuracy of the damping coefficients predicted by both modified approaches is extensively investigated. This accuracy check is done by calculating the damping coefficients by the energy flux consideration in the fluid domain and by direct pressure integration on the body boundary contour. The accuracy check is also performed by varying the number of the elements and for different depths of immersion. The errors in the estimation of the damping coefficients are found to be less than 0·5% and the computation time has also decreased considerably. For the twin cylinders case the accuracy is also checked by varying the number of dipole images. In practical computation the infinite series are truncated to a certain number of mirror images. Calculations are also performed on the number of terms required to be taken for convergence of the series. The accuracy of wave excitation forces and the second-order forces is investigated. The numerical results of the second-order horizontal and vertical forces by both near field and far field approaches are studied and discussed. The accuracy check of the damping coefficient of the 3D surface piercing ellipsoid for the zero speed case is also presented.