ssc-367 - Ship Structure Committee

analysis program can be used, a three-dimensional program
facilitates overall analysis effectiveness.
To analyze, the structure surface is divided into panels, much like
a finite elementmodel and the potentialflow problem is solved over
each panel and yields diffraction and radiation pressures on these
panels. While the diffractionpressuresare transformedintomember
wave loads, the radiation pressures are transformed into added mass
coefficients. Hydrodynamic drag forces on these members and both
the drag and potentialforces on smallermembers (simulatedby stick
elements) are generated using Morison’s equation. Diffraction
effects are strongly dependent on frequency, so a range of
frequenciesmust be addressed.
Mass Model
Typically the deck structural members are modeled by using
equivalent members to represent the deck structure mass and
stiffness. All other members subjectedto hydrodynamicloading are
modeled, with appropriate mass distribution. The accuracy of
structuremass and its distributiondirectly affect the accuracy of
structure motions.
Motions Model and Analysis Techniques
The mass model discussedabove allowsdeterminationofa structure’s
inertialresponseto the appliedexcitationalenvironmentalloadsby
obtaining solutions to the six-degree-of-freedom equilibrium
equations. Considering the rigid-body motions, the dynamic force
equilibrium on a structure can be expressed using the following
system of six simultaneousequations:
[ [W+[Mal1 {x}+[ [CRI+[CV] J {x}+[IfJ {X} = {FO}+{FI}+{FD,} 5-1
This equation differs from that in Section 5.3.3 in that (1) primary
damping is due to wave radiation and viscous effects, (2)
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