GB2199919A - Landing device - Google Patents

Abstract

A landing device for controlling landing of one unit upon another, eg in a sub-sea system, comprises a plunger (12) slidably retained in a housing (10) and biased by resilient biasing means (32) to project from the housing (10). The plunger (12) and resilient biasing means (32) are arranged such that the resilient biasing means (32) absorbs a substantial portion of the initial impact resulting from landing. After the initial impact, hydraulic fluid can be admitted to chamber (46) to move ring (42) to hold plunger (12) retracted (position shown in the Fig.) and further retraction can be controlled by releasing fluid from an initially filled chamber (24). <IMAGE>

Description

Title:- Landing Device The present invention provides a landing device which finds particular but non-limiting application to sub-sea systems where one unit is lowered onto another unit which is already in position.

Conventionally, sub-sea systems have been established from relatively stable semi-submersible vessels.

Consequently, it has been possible to lower one sub-sea unit onto another with considerable precision so as to avoid any significant impact when one unit lands on the other.

For various reasons, not the least of which is cost, it has become desirable to establish and operate sub-sea systems from non-submersible vessels such as barges. A major problem associated with such a change in established procedure is that non-submersible vessels are susceptible to heave caused by wave action. Such movement of the surface vessel can produce relatively violent impact between a unit being lowered and the unit to which it is intended to be connected. This can severely damage the units, especially if they carry hydraulic and electrical connectors. The problem can be particularly acute for smaller vessels which often represent the optimum commercial requirements.

With a view to mitigating this problem, the present invention provides a landing device for controlling the landing of one unit upon another, comprising a plunger slidably retained in a housing and biased by resilient biasing means to project from the housing, the plunger and resilient biasing means being arranged such that the resilient biasing means absorbs a substantial portion of the initial impact resulting from landing of one unit upon another.

Advantageously, the plunger is also arranged to effect alignment between the two units.

Preferably, the landing device includes means for controlling further retraction of the plunger into the housing subsequent to absorption of the initial impact.

Beneficially, a mechanism is provided to suppress the action of the resilient biasing means prior to said controlled further retraction of the plunger into the housing.

An embodiment of the invention will now be described by way of example only and with reference to the accompanying drawing, figure 1, which shows a sectional view through a device embodying the invention.

The landing device shown in figure 1 includes a two part housing 10 and a plunger 12. Housing 10 comprises an end cap 14 and a hollow cylindrical body or housing section 16. Body 16 and end cap 14 are secured together by a thread arrangement 18. A piston 20 is housed within end cap 14 and is slidable longitudinally therein. Piston 20 is retained in end cap 14 by body 16 which has an internal diameter smaller than that of end cap 14. Cylindrical body 16 also has a radially inward projecting lip 50 which forms a narrow annular end face against which piston 20 abuts at one limit of its travel. Seals 22 are provided between the piston 20 and the internal cylindrical surface of end cap 14 so as to define a fluid tight chamber 24 within the cap 14. Flow of fluid into and out of chamber 24 is effected by a port 26 which passes through cap 14.

Plunger 12 is a cylindrical body closed by a head 13 at one end and having a large internal bore 28 open to the other end- thereof. The end face to which internal bore 28 opens incorporates a radially outward projecting lip 30. Two compression springs 32 extend into internal bore 28 and, with the device assembled. springs 32 act between piston 20 and plunger 12. A hollow rod 34 is secured to the head 13 of plunger 12 so as to extend centrally within bore 28 for substantially the whole of the length of the bore. Rod 34 thereby provides a guide which extends longitudinally through the centre of helical compression springs 32. A further hollow rod 36 is attached concentrically with piston 20 and extends within cylindrical body 16. The external diameter of rod 36 is less than the internal diameter of rod 34 such that rod 36 slides freely within rod 34.

The open end of housing 10 threadedly receives an annular stop ring 38. The external cylindrical surface of plunger 12 is in sliding contact with the inner periphery of stop ring 38 and fluid tight seals 40 are provided between the two. Plunger 12 is retained within housing 10 since the peripheral lip 30 of the plunger 12 is radially more extensive than the central aperture of stop ring 38. However, peripheral lip 30 does not contact stop ring 38 due to the provision of an annular ring 42 positioned between lip 30 and stop ring 38.

Ring 42 slidably engages both the inner cylindrical surface of housing section 16 and the outer cylindrical surface of plunger 12. Seals 44 provide fluid tight contact between ring 42 and the cylindrical surfaces over which it slides. Consequently, a fluid tight annular chamber 46 is established between rings 38 and 42. Fluid flow into and out of chamber 46 is effected by one or more ports 48 which pass radially through housing section 16 adjacent the inner end of stop ring 38.

Rim 50 of housing body 16 has a relatively small radial extent and its longitudinal extending face defines a circular aperture having a diameter just slightly larger than the maximum diameter of lip 30.

The end of plunger 12 which projects from housing 10 is terminated by an end face 52 having a central recess 54 provided therein. Recess 54 has an outer portion of tapered profile 56 which reduces to a cylindrical bore 58. The recess 54 enables the landing device to also provide alignment, by mating of the cylindrical bore 58 with a correspondingly configured stud (not shown). The landing device and stud are provided on respective units which are to be brought into contact. The tapered profile 56 guides the plunger onto the stud.

The intended operation of the landing device is as follows. Hydraulic pressure is initially established in chamber 22 via port 26 so that piston 20 is forced into contact with the internal rim SO of housing section 16, as shown in the drawing. However, there is initially an absence of hydraulic pressure in chamber 46 so that, unlike the condition shown in figure 1. ring 42 abuts against ring 38 and is maintained in that position by lip 30 under the action of compression springs 32.

Thus, the plunger 12 is fully extended from housing 10.

The landing device is provided on one or other of two units to be brought into contact with each other and upon initial contact plunger 12 is forced back into housing 10 against the action of springs 32. Springs 32 absorb a substantial portion of the initial impact. The hydraulic pressure established in chamber 24 is such that there is little, if any, movement of piston 20 within end cap 14 at this stage.

After initial impact. plunger 12 will have been forced back into housing 10 to an extent determined by the forces acting to bring the two units into contact and by the strength of springs 32. This may or may not result in plunger 12 having been brought into contact with piston 20. In any event, it is undesirable for the relatively uncontrolled biasing force of springs 32 to influence significantly the final mating of the two units. Thus, hydraulic pressure is established in chamber 46 via port 48 resulting in ring 42 moving longitudinally towards end cap 14. Sufficient hydraulic pressure is applied to cause ring 42 to abut against inner rim 50 of housing section 16, at which position lip 30 of plunger 12 is held opposite rim 50 closely adjacent piston 20. Plunger 12 is thus restrained against moving back out of housing 10, even if there is any reduction in the overall force tending to bring the two units into contact. This is the condition shown in the drawing. Subsequently, the hydraulic pressure is released from the chamber 24 via port 26 such that plunger 12 is retracted into housing 10 in a controlled manner. The device can be arranged such that plunger 12 is sufficiently retracted within housing 10 so that its end face 52 is flush with the interface between the two units thus does not interfere with the connection therebetween.

One embodiment of the invention has been described with reference to the accompanying drawing but it will be readily apparent to those skilled in the art that various modifications can be made without departing from the scope of the present invention.

Claims (7)

CLAIMS:

1. A landing device for controlling the landing of one unit upon another, comprising a plunger slidably retained in a housing and biased by resilient biasing means to project from the housing, the plunger and resilient biasing means being arranged such that the resilient biasing means absorbs a substantial portion of the initial impact resulting from landing of one unit upon another.

2. A landing device as claimed in claim 1, including means for controlling further retraction of the plunger into the housing subsequent to absorption of the initial impact.

3. A landing device as claimed in claim 1 or 2, including a mechanism which suppresses the action of the resilient biasing means subsequent to the said absorption of a substantial portion of the initial impact.

4. A landing device as claimed in claim 2, wherein the means for controlling further retraction of the plunger comprises a hydraulically controlled piston against which the said resilient biasing means acts.

5. A landing device as claimed in claim 3, wherein the said mechanism comprises an annular ring slidably located between the plunger and the housing and a radially outward extending lip provided. on the plunger and against which the said annular ring acts.

6. A landing device as claimed in any preceding claim wherein the plunger is configured so as to effect alignment between the two units.

7. A landing device substantially as hereinbefore described with reference to and as ii lustrated in the accompanying drawing.