离岸直升机起落甲板设计指南 OFFSHORE HELIDECK DESIGN GUIDELINES 2(8)

曝光台 注意防骗 网曝天猫店富美金盛家居专营店坑蒙拐骗欺诈消费者

It is recommended that the overhang should be such that the centre of the helideck is vertically above, or outboard of, the corner of the installation superstructure (see Figure 10.2.
10.4.4 Helideck Height and Air Gap under the Helideck
The height of the helideck, and the presence of an air gap between the helideck and the supporting module, are the most important factors in determining wind flow characteristics.  The helideck should ideally be located at a height above, or at least equal to, all significant surrounding structures.  This will minimise the occurrence of turbulence and downdraft downwind of adjacent structures.
An air gap, separating the helideck from superstructure beneath it, promotes beneficial wind flow over the helideck. If there is not an air gap under the helideck, then wind conditions above are likely to be severe, particularly if the helideck is mounted on top of a large multi-story accommodation block.  It is the distortion of the wind flow around the bulk of the platform that is the cause.

Based on previous research work [Ref: 41] it is recommended that the air gap on production platforms should be in the range 3m – 5m.  Helidecks mounted on very tall accommodation blocks require the largest clearance, whilst those on smaller blocks and with very large helideck overhangs tend to require less.  For shallow superstructures of three stories or less, such as often found on semi-submersible drilling vessels, a 1m gap may be sufficient.  
In combination with an appropriate overhang (see Section 10.4.3), the air gap encourages the disturbed airflow to pass under the deck leaving a relatively linear and clean flow over the top (see Figure 10.3).
It is essential that the air gap is preserved throughout installation operational life, and does not become a storage area for bulky items that might obstruct the free flow of the air through the gap.  
NOTE:  However, it should be noted that CAP 437 recommends that the helideck height should not exceed 60m above sea level.  Above this height the regularity of helicopter operations may be affected by low cloud base conditions.
10.4.5 Proximity to Tall Structures
Offshore installations topsides tend to include a number of tall structures (drilling derricks, flare towers, cranes, gas turbine exhaust stacks etc.), and it is usually impractical to mount the helideck at a higher elevation.  All such tall structures will cause areas of turbulent, sheared or downdraft flow downwind that may potentially pose a hazard to the helicopter.  The severity of the disturbances is greater the bluffer the shape, and the broader the obstruction to the flow.  It is reduced the greater the distance downwind.
It should be noted that the location and configuration of drilling derricks can vary during the field life. The derrick position over the well slots can change, and temporary work-over rigs may be installed from time to time.  The assessment of the helideck location should take into account the various derrick configurations that are expected to occur during the life of the installation.
　
中国航空网 www.aero.cn
航空翻译 www.aviation.cn
本文链接地址：离岸直升机起落甲板设计指南 OFFSHORE HELIDECK DESIGN GUIDELINES 2(8)