A new approach to low-frequency QTF and its application in predicting slow drift force

In this paper, the classical free surface integral formula is examined by an analysis based on the development of the free surface forcing term in a power expansion with respect to Δω. The zero order contribution to the infinite integration which produces the corresponding load of first order Δω is formulated. Then a novel approach which can be easily implemented for predicting the low-frequency QTF is proposed. By applying higher order BEM and adaptive method in element integration, a numerical program is developed. The developed program is tested on simple geometric bodies and offshore platforms. The results from the present study agree well with the results of available exact solutions. Time domain simulation and spectral analyses of the slow drift force are performed for typical kinds of platforms. Extensive discussions and comparisons of the results based on the present method, Teng's exact method and widely used Newman's approximation are presented. The effectiveness of the proposed novel method is further demonstrated by these comparisons.

► A novel approach which is effective and can be easily implemented for predicting the low-frequency QTF is proposed.
► Compared with results of exact variation-frequency wave QTF solutions, computation in present study agrees well with them.
► Based on the difference-frequency wave force QTF time-series simulation.
► Spectral analyses of the slow drift force are performed for typical kinds of platforms in random seas.
► General and comparison of simulated fight on present method, Teng's exact method and usually used Newman's estimate are existing.