Experimental and numerical studies on the dynamic cable tension of a subsea module during semi-submerged hoisting tests are performed. The experiments are carried out in irregular waves and the time-domain numerical simulations are conducted using the software “Simulation of Marine Operations”. The numerical formulation is validated through a comparison with experimental test measurements. The effects of the significant wave height, spectral peak period,and wave direction on the dynamic effect in the main sling and sub-slings are then investigated numerically. The relationship between the wave parameters and the dynamic effect is identified in the time and frequency domains,enabling the allowable sea states to be partially specified. The extreme dynamic effects in all slings under different wave conditions are estimated by using cumulative distribution functions of the Gumbel distribution. The results show that it is reasonable to model a complex subsea module via slender elements and depth-dependent coefficients in simulations of offshore operations. Lowering operations are safer if the wave height is 1 m and the wave period is larger than 8 s because the wave steepness is sufficient for the maximum possible dynamic effect to remain below 0.9. The dynamic tension may decrease when the wave direction is approximately 150°. It is dangerous for subsea modules to encounter lateral waves while entering the water because large overloads and underloads in the extreme dynamic tension may cause snap loads to occur and the slings to become slack.
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