You can try the following:

Chitrapu, A.S. and Ertekin, R.C. (1992), "Effect of Nonlinear Drag Forces on the Low- and High-Frequency Response of Floating Platforms," Proc. 11th Int. Conf. on Offshore Mechanics and Arctic Engineering, OMAE '92, ASME, June 7-11, Calgary, Vol. I, Part A, pp. 97-104.

Chitrapu, A.S. and Ertekin, R.C. (1995),"Time-Domain Simulation of Large-Amplitude Response of Floating Platforms," Ocean Engineering, Vol. 22, No. 4, pp. 367-386.