Modelling and simulation of surface ship wake signatures

Tools for numerical analysis of fenomena causing signatures in the wake of surface ships are evaluated and discussed. The addressed signatures are wave patternson the water surface, detectable by optical means or surface aperture radar (SAR), and small air bubbles entrained in the water. The latter being readily detected by active sonar scan, due to the high target strength when the sonar frequency coincides with the bubble resonance frequency. The method used for surface wave simulation is described and validated against experimental and analytical data from two test cases: A submerged Rankinebody and a Wigley hull form. The validation effort includes a brief grid dependency study and the simulation results are in good agreement with experimental and analytical data. Bubble dynamics and aspects of the bubbly wake are addressed and simplified models are presented for estimation of relevant bubble sizes, resonance frequencies, bubble distribution in the ship wake and bubble residence times. Available methods to include air bubbles in CFD simulations are reviewed, but not yet applied.