Prediction of stress spectra under low-period sea states

초록

In frequency response hydrodynamic analysis, the responses based on a less fine panel can be incomplete, resulting in an inaccurate zero-order spectral moment of the stress spectrum. This paper addresses several functions to reduce this inaccuracy. Two hydrodynamic models with fine panel (FP) and normal panel (NP) sizes, which correspond to the maximum frequencies of 2.1 and 1.4 rad/s, respectively, were prepared. Hydrodynamic analyses of a full-scale 14,000 TEU container ship delivered an acceleration response amplitude operator (RAO) component and pressure RAOs. The calculated load RAOs were applied to the finite element analysis model to evaluate the stress RAOs at pre-assigned hotspots. The stress spectrum based on the FP and NP models at each hotspot revealed a significant difference at high frequencies. Four different extrapolation functions were proposed to predict the stress spectrum at the high-frequency zone (stress spectrum tails): exponential function (EF), power function (PF), rational function (RF), and logarithmic-linear function (LLF). The stress spectrum tails based on the NP model were extrapolated. In order to validate each function, the spectral moments and the fatigue damage based on the estimated stress spectrum tails were compared graphically with those based on the FP model. The LLF could predict the results with the highest accuracy.

키워드