ssc-367 - Ship Structure Committee

5.
FATIGUE STRESS MODELS
5.1
REVIEW OF APPLICABLE MODELING STRATEGIES
The structure configuration essentially dictates the modeling
strategies and the analysis methodologies. Various strip methods
are used to determinethe wave loadingson long, slender bodies such
as ships. The strip theory can account for the effect of diffracted
and radiatedwaves. The hydrodynamicloadings on ships, aswell as
semisubmersibles,can beobtainedfromthree-dimensionaldiffraction
analysis.
Discrete systems, such as bottom-supported fixed platforms, are
substantiallydifferent from continuous systems, such as ships and
semisubmersibles, in the characteristicsof the applied loadings,
their response to these loads, and the resulting stress
distribution. Although the components of the strength model are
similar for both systems, the specifics and the related
uncertainties are different. Thus, fatigue stress models for
bottom-supported and floating marine structures are discussed
separately in Sections 5.2 and 5.3, respectively.
5.1.1 Modelinq Strategies
Analytical models are developed to determine excitational loads,
motions/response,anddeformations/stresses. The levelofdesirable
model complexity depends on many variables, including:
●
The desired level of accuracy of results.
●
Theaccuracyofvariables/assumptions input intothe analysis.
●
The effect of modeling complex
the interpretationof results.
ty on modeling errors and on
5-1