In this work, structural response (Vertical Shear
Force, SFZ, and Lateral Bending Moment, BMY) to irregular seas
for a 7440 DWT and 112-m lbp tanker is calculated for three
loading conditions, traveling at constant speed. SCORES computer
program was used to linearly calculate the response on regular
waves, obtaining the Response Amplitude Operators (RAO) of the
Internal forces for different wave lengths and angles of incidence.
To calculate Internal Forces at irregular waves, Short and Long
Term load prediction methods were implemented. In both cases
Spectra of the internal forces were calculated using Bretschneider
formulation to represent the surfave elevation. For the first
approach, navigation was considered in stationary conditions in
three sea states: 5, 6 and 7 of the Beaufort scale, and with
probabilities of exceedance of 10-7, 10-8 and 10-9. For the Long
term approach, it was considered 20 years of navigation for a
constant route between South America and Western Europe, and
calculations were performed with a probability of exceedence of 10-
8 and 10-9. These calculations were performed using Weibull
distribution, including a simple process to estimate its parameters.
Finally, these results from probabilistic Short and Long Term
approaches were compared with formulas from DNV classification
society, and with results from classic quasistatic approach,
obtaining acceptable differences.
Keywords—Structural Random response, Small tanker,
irregular seas.
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