Risk-based assessment of seaway-induced dynamic loads of ship structures

Load assumptions in class society rules are partly founded on empirical experience and quasi-static load application. This may cause big uncertainties for the structural dimensioning of new and/or unconventional designs. Moreover, the implemented safety level is hardly quantifiable, and assumed to be inconsistent for the ship structure. Nowadays, it is common sense that dynamic amplification of structural loads due to interaction of the ship structure with the surrounding water flow (e.g. whipping and springing) makes an important contribution to the life-cycle loads.

The stochastic and highly nonlinear natures of both seaway-induced excitation and dynamic structural responses, however, complicate the establishment of design loads based on the direct numerical assessment of life-cycle loads.

The project aim is to develop a procedure to numerically compute design loads for ship structures using first-principle approaches and long-term statistics. The procedure shall comprise all relevant aspects of seaway-induced structural loads, and shall provide measures to assess the uncertainty of the analysis. Existing numerical tools will be applied to determine long-term statistical spectra of structural loads relevant for structural design. Where necessary, these methods will be improved.

Tools for fluid-structure coupling based on RANSE methods will be further developed to improve numerical efficiency and fitness for the intended application, i.e. accurate simulation of life-cycle extreme events.

Furthermore, existing statistical methods will be adopted and used to identify wave sequences that cause load excitations corresponding with a defined probability of exceedance.

The project is sponsored by GL (Germanischer Lloyd SE)

By applying the developed procedure to different ships in a given wave climate, it is possible to compare the effective implemented safety levels of their structures. This in turn helps to harmonise the rule requirements and promote a rationally established safety level requirement.