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Near free surface behaviour of a submarine

Ling, XW, Leong, ZQ ORCID: 0000-0002-0644-1822, Duffy, J ORCID: 0000-0003-3484-1345, Chin, C ORCID: 0000-0002-3070-731X and Woodward, M ORCID: 0000-0003-3622-9459 2022 , 'Near free surface behaviour of a submarine', paper presented at the IMC 2022 International Maritime Conference, 10 - 12 May 2022, International Convention Centre, Sydney, Australia.

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A well-known but poorly understood issue with submarines operating at small submergence depths is the effect of the free surface on its hydrodynamic and manoeuvring characteristics. Generally, submarines are designed only to be marginally stable for ease of manoeuvrability with the assumption that most of their operations take place while deeply submerged. Thus, off-design operations such as high speeds at small submergence depths can make them unstable. When deeply submerged, the flow field of the submarine is assumed to be unaffected by boundary effects and this greatly simplifies stability and control requirements. However, travelling near the free surface invalidates this assumption. Submarines operating near the free surface experience a submergence depth and speed dependent heave force and pitch moment, which can significantly impact the stability of the submarine.Small changes in submergence depth combined with the effects of speed can cause significant increases in the free surface induced forces and moments. This condition warrants further study as the resulting hydrodynamic forces can overwhelm the control system in maintaining the desired trim and depth. Hence, this paper presents an evaluation of the effects of the free surface on the hydrodynamics of the bare hull geometry of a submarine. The work was carried out using Computational Fluid Dynamics (CFD) simulation models validated against experimental data for selected conditions. The investigation covers a range of speeds, submergence depths, and length-to-diameter ratios. The results show that the effects of the free surface vary with speed and diminish rapidly with submergence depth.

Item Type: Conference or Workshop Item (Paper)
Authors/Creators:Ling, XW and Leong, ZQ and Duffy, J and Chin, C and Woodward, M
Keywords: free surface, SUBOFF, CFD, length-to-diameter ratio, submergence depth
Journal or Publication Title: Proceedings of the 2022 International Maritime Conference
Publisher: AMDA Foundation Limited
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