Making underwater noise predictions using frequency response functions generated by the Operation Round Trip method

The Round Trip method was derived as a means to acquire frequency response functions at passive locations, where the term ‘passive’ specifies that no external known force has been applied. This allows frequency response functions to be generated at locations where the degree of freedom cannot be excited by conventional means. Sound and vibration produced by operational sources can increase signal-to-noise ratios in large complex systems and improve the quality of the measured frequency response functions, where it can be challenging to effectively excite the system by conventional experimental means. In this study, the application of a modified version of the Round Trip method that is based on transmissibility functions, termed the Operational Round Trip method, has been investigated to determine whether the forces generated by an operational source, such as an offshore wind turbine, could be utilized to predict the frequency response functions at and between passive measurement positions within a coupled mechano-acoustical system. These predicted frequency response functions have been used with the blocked forces of a vibratory source to make underwater noise predictions at remote positions, which were validated against measured underwater noise measurements.