Lower bounds to irregular frequencies in wave-ship interactions for engineering applications

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Authors
  1. Ando, S.
Corporate Authors
Defence Research Establishment Atlantic, Dartmouth NS (CAN)
Abstract
An analytical method has been developed to separate the frequency domain for calculations of ship motions and wave loads into two regimes. One is free of irregular frequencies and for which the well-established and well-validated ordinary integral equation method is appropriate. The other includes irregular frequencies and for which an alternative method for suppressing irregular frequencies is required. This dichotomy of the frequency range was achieved by obtaining sharp estimates of lower bounds to the irregular frequencies inherent to the integral-equation method. This work was motivated by the practical need to ensure the efficiency as well as accuracy of the calculations of ship motions and wave loads. Knowledge of two frequency regimes enables one to incorporate a "switch" in the computer codes so as to activate any one of the time-consuming, and often numerically unstable, alternative methods for suppressing irregular frequencies only when it is truly needed. In most cases, however, the need for the latter method would arise only rarely. Theoretically, the present method is based on the monotone relation between the magnitudes of the fundamental eigenvalue and the domain of the interior boundary-value problem associated with the given exterior problem for wave-body interactions, which is derived in this report.

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Keywords
Irregular waves;Irregular frequencies;Integral equations;Source-distribution method;Variational methods
Report Number
DREA-TM-2001-192 — Technical Memorandum
Date of publication
01 Jan 2002
Number of Pages
43
DSTKIM No
CA020573
CANDIS No
517274
Format(s):
Hardcopy;Document Image stored on Optical Disk

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