New Methodology in Analysis of Physical Properties and Roll Decay with Uncertainty Estimates for Surface-Ship Model Experiments

Abstract

Physical properties and roll decay of David Taylor Model Basin (DTMB) Model 5720, a 23rd scale free running model of the research vessel (R/V) Melville, are documented with uncertainty estimates. Properties include mass, vertical center of gravity (VCG), longitudinal center of gravity (LCG), and transverse center of gravity (TCG), and moments of inertia (MOI) for roll and pitch, transverse metacentric height (GMT), and natural roll period, Tn. Previous analysis has been expanded with additional details and uncertainty estimates. Results are based on measurements with the latest technology. The significant results for model properties are as follows: length 3.3652 ±0.0010 m (±0.030 %), mass 233.21 ±0.46 kg (±0.20 %), LCG 1.6061 ±0.0011 m (±0.067 %) aft of bow, VCG 0.2640 ±0.0017 m (±0.63 %) above keel, GMT 47.76 ±0.61 mm (±1.3 %), roll radius of gyration 0.2329 ±0.0042 m (±1.8 %), and pitch radius of gyration 0.8434 ±0.0024 m (±0.28 %). The roll period in calm water was independent of the Froude number (Fr) and initial roll angle (a). At Fr = 0, 0.15, 0.22, the average roll period was 2.2298 ±0.0040 s (±0.18 %) for 76 runs, all Fr, and all initial roll angles. The initial roll angle variation was 3° to 25°. The natural roll period was 2.139 ±0.041 s (±1.9 %). The decay coefficient data were accurately approximated by a plane in three dimensions with Fr and initial roll amplitudes (a) as the independent variables. Examples are provided that show the average values for a single roll decay event from the logdecrement method are the same as the values by the curve fitting method within the uncertainty estimates.