SACS - Morison Drag Linearisation for Frequency Domain Analysis

Dear Sir,

I have a question about Wave Force based on Morison Equation using for Frequency Domain Analysis.

As you know that wave force based on Morison equation is 'Nonlinear Behaviour on Drag term' which is square of wave particle velocity.

This is complicated situation when it is used in Frequency Domain analysis which is based on Fourier series i.e. linear superposition of sin, cos wave.

I am curious about 'SACS wave force calculation used for transfer function based on Morison equation'.

Is SACS make some linearisation in the drag term when generating transfer function? And How?

Is it based on the procedure recommended in "Borgman (1967)  Ocean Wave Simulation for Engineering Design"

I cannot found anything about this issue in SACS manual.

It is much appreciate, if you can explain some background of SACs calculation.

Regards,

Kasiphon