... equa- 'tions of motion are solved in the frequency domain to give the Quadratic Transfer Functions. KEY WORDS Semisubmersibles, second-order, viscous, damping, resonance, low-frequency. NOMENCLATURE A C F G G I L~x,L~y,L'xu K water plane area water line fluid force fluid moment about G centre...

... frequency dependent drag force on the line 482 h H Hs Hw) I 8 E U(w) c(w) m* q f 8 Sw) t Tz T TDl(t) TD(t) TE u(t) ut) u(t) :z,( t) w I) p water depth hOrizontal tension component Significant wavehelght complex top motion-to-line motion transfer function complex top motlon-to-tenslon transfer function...

... known linear response characteristics, placed on or around a floating structure. A model of the sea state which retains information about the amplitude, phase and direction can then be used to calculate the resulting non-'linear drift forces by means of known quadratic transfer functions. It is shown...

... (the 'near-field' or 'direct' approach). Forces and responses in irregular seas are calculated in the frequency domain, using either the full quadratic transfer function (QTF) approach, or the simplified and more approximate Newman approach. Further details of these procedures, and of the development...

.... order wave exciting forces are described by linear transfer functions in 6 degrees of freedom between force ampli- tude and wave amplitude. Transfer functions are given for a number of frequencies and directions. Time series of exciting forces are obtained by multiplying interpolated transfer func...