Hydroelastic simulation of the acoustic behaviour of ship-propeller configurations with and without cavitation

Recently, noise pollution in the oceans due to ships has raised a lot of attention from the corresponding authorities. It is expected that the shipbuilding industry will have to take according actions - already at the design stage - for the sake of noise reduction, and also to comply with respective regulations that are expected in the near future.Obviously, a numerical simulation approach can be of significant help to determine the sources of noise generation and to find means to reduce them. So far, however, this topic has not yet been widely discussed in the literature. To fill this gap, we aim to start a close cooperation between the two applicants from the institutes of Ship Structural Design and Analysis and Fluid Dynamics and Ship Theory at TUHH. To this end, the proposed research project is designed to evaluate the noise generated by ship propellers, which are considered to significantly contribute to the noise pollution. In the first period, it is planned to develop reliable simulation methods which, in the second period, can be used to systematically reduce the noise level at the far-field. The far-field noise evaluation of ship propellers requires a simulation of the fluid-structure interaction (FSI) combined with an acoustic analysis. Therefore, we aim to further develop a partitioned solution procedure that makes it possible to employ specialized solvers for each involved sub-field. In this project, the fluid will be simulated by a potential theory based boundary element solver so as to avoid expensive computations. The sheet cavitation effect will be considered too, as it is one of the primary sources of noise generation in the low frequency range. On the structural side, we will consider the effect of ship propellers and also the ship hull. Ship propellers are thin-walled structures and can experience large deformations during operation. Thus, we aim to simulate them by employing novel high-order finite element methods to obtain an efficient representation of the displacements without running into the problem of locking. Regarding the aspect of efficiency, the acoustic analysis at the far-field will be performed using the Ffowcs Williams-Hawking Equation (FWHE) - an efficient and fairly new approach in naval architecture, especially in the cope of FSI. Since the involved sub-fields obey different time scales, we aim to develop staggered and parallel sub-cycling coupling procedures. Furthermore, as the FWHE depends on the results of the fluid and structure solvers at the local emission time, the effects of different sub-cycling related techniques on the acoustic results have to be investigated as well.

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