scope:

Scope and Overview of These Guidance Notes

These Guidance Notes provide the analysis procedures of air gap assessment for semi-submersibles based on either the linear analysis or the second order analysis. The theoretical background of these methods is introduced with critical parameters highlighted.

Guidance is provided on the definition of the horizontal wave impact load and the strength assessment methods for those local structural members on peripheral sides of the upper structure subject to horizontal wave impact loads. Guidance is also provided on the vertical wave impact analysis in frequency domain for semi-submersibles. The suggested method is based on the relative vertical velocities between the vessel motions and wave surface elevations using the linear diffraction-radiation analysis with consideration of wave asymmetry factors, the local wave crest enhancement, and wave run-up factors.

Section 2 describes the three-dimensional diffraction-radiation analysis used to calculate vessel motions. Both linear frequency domain and nonlinear time domain methods are addressed.

Section 3 discusses the free surface elevation induced by wave-structure interaction and addresses the wave asymmetry and wave run-up phenomenon.

Section 4 presents the linear air gap analysis procedures in frequency domain.

Section 5 demonstrates the second order air gap analysis procedures in time domain.

Section 6 presents the horizontal wave impact loads and local structural strength assessment methods for the peripheral sides of the upper structure of semi-submersibles when there are negative air gaps.

Section 7 presents the vertical wave impact loads and local structural strength assessment methods for the deck bottom or undersides of the overhanging platforms of semi-submersibles.

A diagram outlining the air gap assessment process in accordance with these Guidance Notes is given in 1/13 FIGURE 3.