Nonlinear dynamic response of catenary mooring cables: FPM modelling and flume validation

Catenary mooring cables are critical for the station keeping of floating offshore structures, yet their dynamic response under coupled wave-excitation loading remains insufficiently understood. This study develops an FPM cable model and validates it against laboratory-scale flume tests on 3, 4, and 5 mm mooring cables under periodic-wave, top-end-excitation, and coupled loading. For selected representative validation cases, the predictions agree well with measurements, with RMSE values ranging from 0.0134 to 0.1413 N, the Pearson correlation coefficients ranged from 0.853 to 0.925, and peak-tension errors of 0.02% to 1.92%. The results show that (i) cable diameter primarily governs the mean tension level under periodic-wave loading, whereas wave period has a stronger influence on tension fluctuations; (ii) top-end excitation has limited influence on mean tension but significantly enhances tension fluctuations at higher excitation frequencies; (iii) under coupled loading, the dominant tension response gradually shifts from wave-controlled variation to excitation-controlled high-frequency oscillation; and (iv) larger cable diameters generally produce higher mean tension and greater absolute tension fluctuations. The proposed FPM framework provides an alternative approach for predicting the dynamic tension response of catenary mooring systems under combined wave and platform-motion loading.