Concurrent Estimation of Ship Transfer Functions and Incoming Waves by Using Response Measurements

Estimating the incoming waves onboard is of importance to ensure effective ship operation and safety. This paper is concerned with a response-based wave estimation method, in which incoming waves are inversely estimated based on measured responses via their transfer functions (TRFs), commonly referred to as the 'Wave Buoy Analogy (WBA)'. Specifically, a phase-resolved WBA technique presented by the authors’ preceding study is referenced. The accuracy of estimated waves via the WBA is in essence contingent upon the accuracy of TRFs of the responses used. However, it is difficult to accurately estimate the TRFs onboard, as the weight distribution and operational condition would change from voyage to voyage. To address this issue, this paper proposes a novel approach to simultaneously attain estimations of ship response TRFs and incoming wave profiles, making use of measured ship responses. Specifically, parametrized TRFs are devised, and then the parameters which characterize the TRFs are identified through optimization with reference to reconstructed phase-resolved incident waves. A closed-form expression (CFE) and linear strip theory, the so-called New Strip Method (NSM) are used to parametrize the TRF, named as parametrized transfer function (P-TRF). The validity
of the present approach is validated against experimental campaigns using scaled models of a bulk carrier and container ship. It turned out that the estimation results of TRFs using the NSM-based P-TRF demonstrates a high degree of correlation with the experimental measurements, whereas the CFE-based P-TRF exhibits a notable inability to estimate the phase components of the TRFs. Estimations based on the NSM-based P-TRF are also proved to be effective to estimate incident wave profiles, particularly low frequency wave components.