ssc-367 - Ship Structure Committee

their function, selecting appropriate element aspect ratios (less
than 1:2) will contribute both to better accuracy and a better
model.
5.2.2
Stationary Marine Structures
Determination of Loads
Stationarymarine structureshavevariousconfigurationsand exhibit
a wide range of compliancy. A substantial effort is desirable to
minimize the fatigue loadings on stationary structures. For a
moored tanker FPSO the smallestfunctionalsize exhibitinga minimum
silhouette is desirable. For structures composed of columns and
pontoons, the column spacing,column water plane area, displacement
of pontoons affecting overall center of buoyancy and the total
displacement are some of the interactingparameters that affect not
only the magnitude and characterof the applied loading but also the
response of the structureto applied loading (see Reference 5.6 for
structure configurationoptimization).
While the hydrodynamic forces on a slender stationary body can be
determined based on strip method or diffraction theory, a structure
made up of columns and pontoons can be determined either by
Morison’s equation or by diffraction theory. As discussed in
Section 5.1, large diameters disturb the flow, leading to
diffraction which is highly frequency dependent. There are two
benefits of using diffraction theory:
●
Diffraction usually causes a reduction in the wave loads,
●
Viscosity can be ignored and thus, treating the flow as
irrotational,potential flow theory may be used.
The hydrodynamicloads actingon astructure are typically generated
using a combination of three-dimensionaldiffraction theory, i.e.,
a source-sink distributed potential theory (Reference 5.7) and a
conventional Morison’s equation. Although a two-dimensional
5-1o
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