URaNS simulations are carried out for DTC in resistanceand self propulsion conditions with two rudder geometries, i.e.Initially equipped “twist rud.+ bulb” and reverse engineered“normal rudder”. The energy saving effect of the formerrudder is quantified in terms of comprehensive self propulsionanalysis and kinetic energy analysis. Especially in kineticenergy analysis, existing JBC results are subjected to theanalysis as a demonstrating purpose. The results show thatDTC’s “twist rud.+ bulb” is not well designed and isineffective to improve propulsive performance compared to“normal rudder”. This is revealed by both self propulsionanalysis and kinetic energy analysis. On the contrary, JBC’srecovery rate of kinetic energy for “with duct” relative to “barehull” is in the same order of magnitude to the improvementratio of propulsive efficiency between the two configurations.Diagnostics of local flow in stern region for DTC and JBCsupport each trends. Consequently, the kinetic energy can bemore “generalized” objective functions to improveperformance of ESDs by taking changes in local flow due toESDs into consideration, instead of self propulsion factors.
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