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- Ge, Muye, 1991, et al.
(författare)
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Investigations on prediction of ship noise using the FWH acoustic analogy with incompressible flow input
- 2022
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Ingår i: Ocean Engineering. - : Elsevier BV. - 0029-8018. ; 257
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Tidskriftsartikel (refereegranskat)abstract
- Ship noise predictions using FWH acoustic analogy with incompressible flow solution inputs are investigated for a model scale container vessel with a cavitating propeller. Numerical predictions of cavitation and hull pressure pulse predictions are validated first, comparing simulations performed for the tunnel test section and experimental measurements inside a large-size cavitation tunnel. The predictions agree well including the sheet cavitation development, tip vortex cavitation (TVC) bursting, convex shaped sheet cavitation closure line and the traveling re-entrant jet underneath the sheet cavity triggers the TVC bursting behavior. Noise predictions are performed within a large open simulation domain instead of the cavitation tunnel test section. With incompressible solutions, noise levels are predicted based on two different placements of Permeable/Porous Data Surfaces (PDS) where one encloses the cavitating propeller, rudder and downstream wake (PDS−L1) and one encloses the whole ship as a rectangular box (PDS−L2). The FWH noise predictions with impermeable surfaces (S−FWH) are also studied. Differences between predictions using PDS−L1, PDS−L2, and S−FWH are discussed. To compare calculated noise source level (Ls) at different noise receivers at varying distances, normalization assuming spherical spreading acoustic wave is used. In certain combinations of receiver point and method of acoustic computation, the predicted Ls agreed well comparing to experimental measurements, including the prediction with PDS−L2 and receiver close to the PDS and direct probed incompressible hydrodynamic pressure at similar receiver locations. However, with increasing distance to the receiver, the predicted Ls increases for higher frequencies and levels out at unrealistically high levels. To study this phenomenon, a free-field monopole representing the cavity structure dynamics is tested with different combination of PDS and receiver placements, using both incompressible and compressible input. This analysis gives a clear indication that the origin of this erroneous effect is the combination of the FWH acoustic analogy with an incompressible solver.
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| 2. |
- Vikström, Marko, et al.
(författare)
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The Effect of Porous Data Surface Shape and Size on Ship Noise Prediction using the FWH Acoustic Analogy with Incompressible Solver for a Cavitating Propeller
- 2022
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Ingår i: Proceedings of the seventh International Symposium on Marine Propulsors - smp'22. - 2414-6129. - 9788269112030 ; , s. 166-173
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Konferensbidrag (refereegranskat)abstract
- Using Ffowcs-Williams and Hawkings (FWH) acoustic analogy with an incompressible solver has become a rather common approach for ship noise prediction. Here the method is studied for a model scale container vessel. The numerical study includes both the ship hull and a rotating propeller, using the sliding mesh approach. The simulations are performed for a condition with cavitation around the tip of the propeller blades to study the propeller induced noise including the contribution from cavitation. To complement this study, e.g., to exclude any wall reflections and rotating sources, an additional pure monopole source case study was performed with both incompressible and compressible methodology. Since cavitation is a volume source acoustic term there is a need to use a Porous Data Surface (PDS) in combination with the FWH acoustic analogy. The choice of PDS shape and size using FWH is studied both for the model scale container vessel as well as for the pure monopole source case. The results show that when using different PDS shapes, a directionality effect is evident when using the incompressible solver. The Sound Pressure Level (SPL) is dependent on the receiver angular location in relation to the PDS. The directionality effect is largest for a PDS shape where there is a large variation in distance from the source to the PDS faces, e.g. box. Furthermore, there is also a receiver distance discrepancy for the incompressible solver with FWH. The SPL curves for different receiver distance do not coincide for higher frequencies. Using a compressible solver and FWH, the shape effect and receiver distance discrepancy is not present.
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