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Submarine Periscope Plume Modeling
Posted Fri July 11, 2003 @11:25AM
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Application By Paul Steer
Hydrodynamics Technology, QinetiQ, UK

A submarine is the ultimate "stealth ship". Its greatest asset is the element of surprise - the ability to remain hidden under the sea. But the security blanket of millions of tons of ocean works both ways, because it also restricts the ability of the submarine's crew to see out. Hence the need for a periscope, or "visual system mast", to see above the water while remaining submerged. In fact, modern submarines have a suite of masts that raise a variety of devices above the water surface.


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A Speck in the Distance

Even though the top of the mast is small, it can be detected by radar, and give the submarine's position away. The problem is not just the mast itself, it is also the disturbance to the water surface that produces the radar signature. Navies are therefore interested in designing masts to create as little disturbance as possible.

MacTaggart-Scott, suppliers of masts to the UK Royal Navy Astute submarines, has recently used QinetiQ's integrated fluid and radar models to reduce the need for physical modelling of these complex phenomena, and hence reduce development costs and time-scales.

Waves and Spray

To assist in periscope design, QinetiQ integrates computer models of flow and electromagnetic fields to analyse the radar signature of the mast and water plume. The flow analysis is carried out using advanced two-phase (water-air) models in the computational fluid dynamics solver.

The wave system is predicted by carefully controlling the numerical algorithms of the two-phase model, and ensuring adequate grid support for the propagating waves. The spray envelope is then calculated by evaluating the residual energy of the fluid near the surface, and ejecting spray particles with the appropriate mass and kinetic energy into the air.

Once the water plume has been predicted, the radar reflection is assessed, based on the electromagnetic properties of the surfaces of the water and mast, and the path from the radar to the periscope.

The modelling process is validated using the extensive experimental test facilities at QinetiQ's disposal. Hydrodynamic testing is conducted in the Ship Tank at Haslar Marine Technology Park, Gosport, while radar cross-section models are validated at the Funtington Radar Range.

"It was this big, and it got away..."

By integrating and validating QinetiQ tools for signature assessment with the capabilities of CFX flow modelling software, the promise of cost-effective analysis in hydrodynamics is being realized. Technology such as this will help thousands of tons of submarine to continue voyaging undetected throughout the world's oceans.

 

mast wave
Wave generated by mast, showing breaking and plume.

 

mast wave
Wave created by a representative mast.

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Related Links
  • CFX
  • MacTaggart-Scott
  • QinetiQ
  • UK Royal Navy Astute submarines
  • More on Application
  • Also by nwyman
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