离岸直升机起落甲板设计指南 OFFSHORE HELIDECK DESIGN GUIDELINES 2(13)

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The limitations that currently exist apply to both the vertical linear motion (heave) and the angular motions (roll and pitch).  Large accelerations can cause the helicopter to slide across the deck or tip over (though these do not at present form part of the limitations applied).  
The angle of roll and pitch experienced is the same for all points on the vessel or structure, but the amount of heave, sway or surge motion experienced can vary considerably, depending on the location of the helideck on the vessel.
The severity of the helideck motions and the operational limitations will depend on:
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The wave environment (e.g. more severe West of Shetland than in the Southern North Sea)

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The size of the vessel (a small vessel generally tends to exhibit larger and faster motions than a large vessel)

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The vessel’s motion characteristics (certain hull forms exhibit larger wave motions than others, or are sensitive to particular sea conditions)

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Whether the vessel is moored, underway or under tow

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The location of the helideck (vertical motions tend to be greater at the bow and stern of a ship than at midships, and sway motions due to roll tend to increase with helideck height)

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The design of the helicopter itself (different motion limits apply to different helicopter types)

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The time of day (more onerous motion limits are applied to helidecks on smaller ships in the hours of darkness due to the degraded visual cues available to the pilot).

NOTE:  A new helideck motion criterion is currently under development (see Section 10.12.1).
10.5.3 Sea State Characterisation
Sea states are usually characterised in terms of the significant wave height, an associated wave period (usually either the mean zero up-crossing period or peak spectral period) and a wave energy spectrum.  Standard wave spectral formulae, such as the JONSWAP or Pierson-Moskowitz spectrum, are commonly used in design to define the way in which wave energy is distributed across the wave frequency range. Wave spectra may be defined as either uni-directional or multi-directional, the latter describing the proportion of wave energy coming from each direction by means of a directional spreading function.
10.5.4  Vessel Motions and Helideck Downtime
The motions of a vessel or floating installation generally become larger as the significant wave height and period increase, but may be especially severe at certain wave periods (e.g. at natural roll or pitch periods), and may be sensitive to the frequency content of the wave spectrum.  The motion characteristics of a vessel or floating platform may be reliably predicted by recourse to well-established computer models, or to physical model testing.
Helideck downtime will occur whenever the motions of the vessel exceed the criteria (see Section 10.13 for an outline of a method to estimate the downtime.)
　
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