Indirect Wave Load Estimates Using Operational Modal Analysis: Preliminary Findings

Wave loading on offshore structures has proven difficult to quantify through direct full-scale measurements. Therefore, engineers rely on codes and guidelines, numerical simulations, and scaled experiments in the design and as-built evaluation process. In this paper, it is shown that by monitoring the response of the structure and utilizing Operational Modal Analysis (OMA) it is possible to indirectly identify loads, occurring in actual conditions.

A method employing modal parameters to establish a response function, which is used to back-calculate the hydrodynamic wave loading of a structure is presented. The process of inverting the system matrices is stabilized by merging the model with linear wave theory and hence constraining the solution to a scaling function of a predefined load distribution.

The method is validated through a numerical case study and by wave flume experiments. Both cases are constituted as two-dimensional loading on a semi submerged cantilever cylinder.