IRREGULAR-FREQUENCY-FREE CALCULATIONS OF ADDED MASSES AND DAMPING OF TWO-DIMENSIONAL CYLINDERS: EXAMPLES

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Authors
  1. Ando, S.
Corporate Authors
Defence Research Establishment Atlantic, Dartmouth NS (CAN)
Abstract
The crux of ship-motion and wave-load predictions lies in the calculation of added-mass and damping coefficients in the equations of motion. Yet the theoretical model most commonly used for calculating these coefficients inevitably breaks down at certain frequencies of oscillation called irregular frequencies. In this study, added-mass and damping coefficients for hull-shaped two-dimensional cylinders have been calculated using DREA's computer program AMADIFF so as show to what extent the lid method (or the extended-boundary method) might be expected to be effective in suppressing irregular frequencies. Added-mass and damping coefficients for two-dimensional cylinders predicted by the lid method or the extended-boundary method for suppressing irregular frequencies as implemented in DREA's computer program AMADIFF were found to be free of irregular frequencies up to omega (B/2g greater than or less than 3.15, approximately, irrespective of cross section, whre omega is the angular frequency, B the waterline breadth and g the gravitational acceleration. For ships of the Canadian Navy's Halifax-class and comparative size, for example, this means that AMADIFF will ensure stable calculations of ship motions and wave loads for frequencies at least up to 3.68 rad/s, well beyond the frequency of practical importance insofar as ship motions and wave loads are concerned. TRUNCATED
Keywords
Added mass;Irregular frequencies;Ship motions;Wave loads;Green's function;Close-fit method
Report Number
DREA-TM-98-230 — Technical Memorandum
Date of publication
01 Oct 1998
Number of Pages
87
DSTKIM No
99-00854
CANDIS No
510766
Format(s):
Hardcopy;Document Image stored on Optical Disk

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