GHS Wind-Heeling-Moment Options
GHS offers several ways to represent wind-heeling moments using the vessel geometry:
- HM upright x Cos(heel) - Upright heeling moment multiplied by the cosine of the heel angle.
- HM LPL(heel) - Heeling moment from component Lateral Plane projections as a function of heel.
- HM Bands(heel) - Heeling moment from lateral plane sampled in horizontal Bands.
Variations are also available. For example, in the first case listed above, the function multiplying the upright heeling moment could be cosine squared, cosine to an intermediate power or simply 1.0 for a constant heeling moment. Cosine+Sine combinations are also possible.
Basically there are two mechanisms for deriving wind force from the vessel geometry.
(1) The classical method, which adds the lateral projection of each Component in the model.
(2) The newer Band method, which projects the lateral plane of all components of each Part onto a common set of horizontal bands. This has the advantage of accounting for the shielding when one component is masked by another.
The contributions from individual Parts in the model can either be added without regard to shielding between them or they can be combined into a common set of bands which assumes inter-component shielding regardless of Part divisions.
Because of its shielding, the Band method is much better suited for use at heel angles beyond upright.
The Band method also has the advantage of sampling the wind pressure at closer height intervals since each band gets its own pressure from the wind height profile. Band widths are typically set at 0.1 meter; other band widths may be selected by the user.
Another important advantage of the Band method is that it can be used with any wind direction. The clasical lateral plane method is restricted to strictly lateral projections and therefore is useful only for beam winds.
The Band method works for any wind direction. This is particularly useful for
and other floating structures where stability about more than one heeling axis is of concern.
When only the upright wind-heeling-moment calculation is desired (i.e. where the variation with heel is to be represented by a standard function), either the classical lateral plane method or the Band method can be used.
The method of obtaining the lateral center of resistance from the underwater portion of the vessel model is the same as the method being used to obtain the wind area and center.
See some Test Cases.
Motor Yacht example
See individual Righting-Arm / Heeling-Arm plots:
Bands, superstructure separate
Copyright © 1997 , Creative Systems, Inc.