Eighteenth Symposium on Naval Hydrodynamics (1991) / Chapter Skim
Currently Skimming:
A Stochastic Analysis of Nonlinear Roling in a Narrow Band Sea
A Stochastic Analysis of Nonlinear Roling in a Narrow Band Sea
Pages 141-148
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 141... ...
This is for example the case when the rudder is released in the attempt to recover from an excessive heeling in manoeuvering, non properly adjusted antirolling tanks are employed to reduce excessive rolling, a route change is adopted to avoid the beam or quartering action of wave trains; - structural failure with consequent opening of holes in the hull and flooding of some compartment; - effect of additional heeling moments due to water loading on deck and through the deck openings caused by the large amplitude rolling or
|
From page 142... ...
To this end, the probability density function of the response levels should be computed by means of approximate analytical methods in the following three cases of interest: - bifurcation between the anti- and the resonant oscillation in the main resonance region in stochastic beam sea; - bifurcation between non resonant and subharmonic in the first subharmonic region in stochastic beam sea; - bifurcation between zero amplitude (or negligible one) and parametric suharmonic rolling in stochastic following or quartering sea.
|
From page 143... ...
This procedure applied to normalized standard wave height spectra Sly using IMSL library routine RNLIN, provided the following values [1 13: - ITTC So=.35 cof-1.16 ~=.50 is= 0 143 - JONSWAP with sharpness magnification factor equal to 7 (maximum value) So=.13 c~=1.01 y=.14 The transformation of wave heights into inclining moments actually broadens a little the spectrum.
|
From page 144... ...
In particular, in the considered cases, the most sharp JONSWAP is not far from the higher limit of values of That gives multiple regime of oscillations. In the sinusoidal case, in the frequency region where three states are possible, only the two extreme represent stable oscillations and the bifurcation involves them.
|
From page 145... ...
3.0 35 Of/Oo 40 Fig. 3 Variance os of the subharmonic component, excitation threshold CIfth for subharmonic oscillation onset and variance aQ of the out of resonance component as a function of tuning ratio cl)
|
From page 146... ...
4 Variance as of the subharmonic component, excitation threshold Fifth for subharmonic oscillation onset and variance aQ of the out of resonance component as a function of tuning ratio Of/Coo. The following values have been used for the parameters: a3=-1.75., p=.005, 6f=.1414, y=.01.
|
From page 147... ...
AllTHORS' REPLY Actually, the frequency dependence of the hydrodynamic coefficients is not included in the model. This is not due only to the obvious overcomplications involved, but to the necessity of a better clarification of the exact meaning of frequency in presence of a stochastic excitation with the possibility of multiple regime of oscillation and of the techniques for transfering this frequency der~endence when doing time domain simulation with nonlinear - -r v models.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.