GB2467345A

GB2467345A - Mooring limb

Info

Publication number: GB2467345A
Application number: GB0901529A
Authority: GB
Inventors: David Parish
Original assignee: University of Exeter
Current assignee: University of Exeter
Priority date: 2009-01-30
Filing date: 2009-01-30
Publication date: 2010-08-04
Also published as: WO2010086666A3; GB0901529D0; WO2010086666A2

Abstract

A mooring limb for use in a fluid comprises at least one substantially impervious sleeve 150 defining at least one chamber. The shape of the at least one chamber is variable and the device includes at least one orifice 80 for allowing a fluid into and/or out of the at least one chamber. The mooring limb may act as a pump and/or as a damping device. Also disclosed is a method of mooring a floating object (20, Fig 1) comprising attaching one end of the limb to the floating object and the other end to a fixed object (30, Fig 1). A method of damping the movement of a floating object is also disclosed in which the mooring limb is connected between the floating object and a fixed object and the flow of fluid in and out of the limb is controlled, to damp the change in the length of the limb due to the movement of the floating object with respect to the fixed object.

Description

Mooring Limb The present invention relates to a mooring limb, a method of mooring an object and a method of damping the movement of an object. In particular, although not exclusively, the invention relates to a damping mooring limb.

Mooring limbs, legs, tethers, or lines, are required for mooring objects, such as ships, pontoons, and buoys so that they do not move too much relative to the land beneath the surface of the water. To more closely limit the movement of such an object it is known to use more than one limb, possibly at either end of a ship, for instance.

Known mooring limbs typically comprise ropes or chains. There are two principal kinds of mooring limbs. The first are taught in use, and the second are slack in use.

The present invention may be either taught and/or slack in use.

To allow for the rise and fall of the water level on which a moored object is floating due to, for instance, tides or waves, a certain amount of slack must be provided in the length of a slack-type limb. However, this allows for the object to move "off station" when the water level is lower than the highest level catered for by the slack.

Although this is not a problem for most applications, it can cause problems for objects, such as pontoons or wave energy converters, which need to remain substantially "on station" and yet be able to rise and fall with, for instance, the tides.

A known system which overcomes this problem is provided in the form of a resilient limb comprising rubber-type materials. These limbs allow for an extension and contraction of its longitudinal length whilst maintaining tension therein. This allows for the object to rise and fall with the tides, waves and other movements of the water whilst remaining on station.

The present invention provides an alternative system for mooring substantially floating objects which also allows for the damping, with controllable frequency response, of the oscillations often induced in such a system.

In one aspect, the invention provides a mooring limb for use in a fluid comprising at least one substantially impervious sleeve defining at least one chamber, wherein the shape of the at least one chamber is variable, the device including at least one orifice for allowing a fluid into and/or out of the at least one chamber.

I

The shape of the at least one impervious sleeve may be variable and the variability of the shape of the at least one chamber may be proportional to the variability of the shape of the at least one impervious sleeve.

In other words, the shape of the at least one chamber may be variable by virtue of the shape of the impervious sleeve being variable without an additional body entering or exiting the chamber. In one embodiment, the impervious sleeve may be flexible.

The at least one chamber may have a longitudinal axis and a radial axis, wherein the longitudinal length measured along the longitudinal axis may be substantially greater than the radial width measured along the radial axis. Alternatively, the at least one chamber may be substantially spherical.

The at least one chamber may be fluid-tight, apart from the at least one orifice.

The shape of the at least one impervious sleeve may be substantially cylindrical with end pieces closing the chamber. Alternatively, the at least one impervious sleeve may be gathered at each longitudinal end such that the radial width reduces at each end. The at least one impervious sleeve may comprise hyperlon.

The fluid may he sea water, fresh water, or may comprise other fluids such as the tailings from industrial processes. The fluid may act as a damping medium.

In an initial state the at least one chamber may be completely filled with the fluid. As the length of the sleeve increases due to a force provided on it, by the movement of the object to which it is attached, the volume of the at least one chamber will decrease as the cross-sectional area, measured radially, decreases. Fluid within the at least one chamber will thus be forced out of, or expelled from, the orifice. Conversely, as the longitudinal length of the limb decreases the volume of the chamber will increase as the cross-sectional area, measured radially, increases. Fluid will thus be sucked into the at least one chamber through the orifice.

The mooring limb may be a damping mooring limb for damping oscillations induced in the limb, and/or the object to which it is attached, in use. Moreover, the mooring limb may include frequency control means for variably adjusting the damping frequency response of the limb to the oscillations induced in the limb, and/or the object to which it is attached, in use. For instance, the oscillation of the object, to which the limb is attached, may be caused by more than one factor such as waves and tides. Each factor may have a different frequency. The overall frequency of the oscillation of the object may thus be a result of the combination of the various factors. The mooring limb may be tuned to damp an individual frequency of one of the factors, or to damp the resultant frequency on the mooring limb, and/or the object to which it is attacied, or any other frequency as required.

The frequency control means may comprise the at least one orifice.

The at least one orifice may include flow rate control means for controlling the flow of the fluid into and/or out of the at least one chamber so as to limit and/or van the rate of change of the shape of the limb. For instance, valves may be employed in association with the orifice. The valves may be non-return (one-way), or two-way. The volume flow rate through the orifices may be variable, for instance by adjusting the cross-sectional area of the inlet/outlet. The orifices may be completely sealable to prohibit flow through them. This variation may be manual and/or may be achieved remotely via, for instance, the use of motors and/or hydraulic/pneumatic controls. The volume flow rates and other characteristics of the orifices may be pre-set prior to installation, in anticipation of the specific requirement of each installation.

In this way, the rate at which the shape, and thus the length, of the limb changes may be controllable. For example, it may be slowed such that the length of the limb increases and/or decreases, and thus its shape changes, at a controlled rate. Also, if the valves are closed then further extension of the limb may be prevented since fluid will not be able to leave the at least one chamber. In this way, the frequency of the oscillations induced in the limb, and/or object to which it is attached, may be controilably damped.

Moreover, the rate of change of the volume flow rate of the fluid entering and/or exiting the at least one chamber may be non-linear. This is because the volume of the at least one chamber may change non-linearly with respect to the change in length of the at least one chamber.

As the forces acting on the limb may also vary non-linearly due to the oscillations induced in the system the limb may be tuned so as to be more, or less, effective at damping those oscillations. This may be effected by adjusting the volume flow rate of fluid entering and/or exiting the at least one chamber by means of the flow rate control means.

The limb may include a resilient sleeve. The resilient sleeve may be braided. The resilient sleeve may be of stainless steel and/or of textile. The resilient sleeve may be resilient in the longitudinal direction of the limb. In this regard, the term "longitudinal direction" means the axis of the limb between the two points at which it is attached to the land surface beneath the fluid and the moored object. Additionally, or alternatively, it may be resilient in the radial direction of the limb. In this regard, the term "radial direction" means either of the axes perpendicular to the longitudinal direction of the limb. The resilience may be achieved by the braiding comprising a criss-crossing arrangement of braids in a similar manner to stents known in the medical field. It is contemplated that instead of the limb being attached, or connected, directly or indirectly to a land surface it may be attached to another object in the fluid, such as another moored object.

The resilience may allow for the longitudinal length, and thus the shape, of the limb to be varied while stiLl providing strength and protection to the impervious sleeve.

The resilient sleeve may be located radially outward of the at least one impervious sleeve. It is also possible that this sleeve is located radially inward of the at least one impervious sleeve. It is also possible that this sleeve is integral with the at least one impervious sleeve and/or be provided within the at least one impervious sleeve. It may be linked to the impervious sleeve in some way so that the change in its length and diameter directly influence the change in the length and diameter of the impervious sleeve. For instance, some of the braids may pass through loops or straps provided on the inner or outer surface of the impervious sleeve so as to help pull, or push, the impervious sleeve back into shape after it has been squashed by the braided sleeve, in use.

The resilience of the resilient sleeve may urge the limb to retain a defined shape such that when the shape is changed due to a force provided on it by the moored object the resilient sleeve urges the limb to regain its original shape. The resilient sleeve may also provide tension along the length of the limb.

The rate of change of the shape of the limb due to the resilience of the resilient sleeve may be non-linear. This non-linearity may be controllable by varying certain qualities of the resilient sleeve, such as the types of materials and its shape. This non-linearity may be exploited as well as, or instead of, the non-linearity discussed above with regard to the volume flow rate through the at least one orifice so as to provide an additional way of tuning the limb to damp induced oscillations.

Means of attaching the limb to a fixed object, such as an anchor point provided on the land surface beneath the fluid, and to the object to be moored may be provided.

These means may be connected to the at least one impervious sleeve and/or the resilient sleeve.

The limb may include a first resilient means, being resilient in the radial direction, located radially inward of the impervious sleeve for providing a force in a substantially radially outward direction. These means may comprise one or more scroll-type springs. The axis about which they are wound may lie parallel to the longitudinal axis of the limb. They may lie such that they press against the inside of the at least one impervious sleeve. In use, as the longitudinal length of the limb increases and the radial dimension decreases the springs may become compressed, or further wound, such that their outer dimension (measured in the radial plane of the limb) decreases. The pressure exerted on the inside of the impervious sleeve may help to maintain its overall shape and help the at least one impervious sleeve, and thus the limb, to re-establish its original shape when the force pulling on the limb reduces. Other means of providing this resilience are contemplated such as coils springs arranged substantially across the radial axis.

The first resilient means could be located radially outward of the at least one impervious sleeve, and/or could be incorporated within the at least one impervious sleeve.

The mooring limb may include a second resilient means, being resilient in the longitudinal direction, located radially inward of the at least one impervious sleeve. This second resilient means may be an elastic member comprised of rubber-type materials. It may extend along the entire length of the limb. Its ends may project through the at least one impervious sleeve and connect with the means of attachment discussed above for connection to the external anchor/mooring points. Alternatively, or additionally, they may connect with the resilient sleeve and/or the at least one impervious sleeve.

In use, this second resilient means provides tension in the limb to aid the re-establishment of the original shape of the at least one impervious sleeve, and thus the limb, after its shape has been changed due to the external forces provided on it.

It is contemplated that this second resilient means may be located radially outward of the at least one impervious sleeve and/or could be incorporated within the at least one impervious sleeve and/or first resilient means. Moreover, there may be more than one second resilient means.

The rate of change of the shape of the limb due to the resilience of the second resilient means may be non-linear. This non-linearity may be controllable by varying certain qualities of these means, such as the types of materials and its shape. This non-linearity may be exploited as well as, or instead of, the non-linearity discussed above with regard to the volume flow rate through the at least one orifice, and/or the resilient sleeve, so as to provide additional ways of tuning the limb to damp induced oscillations.

Although several different means of re-establishing the original shape of the limb have been discussed it is also possible that the at least one impervious sleeve itself is resilient in the radial and/or axial directions. This may be due to additional resilient means embedded within, or attached to its walls, or could be by virtue of the characteristics of the material(s) used in the at least one impervious sleeve's composition. Either way, the limb may be arranged such that the at least one impervious sleeve will collapse, and thus be collapsible, possibly in a concertina fashion, if its overall longitudinal length is less than its relaxed/unstressed length. This may be effected by any one or more of the resilient means discussed above reducing the longitudinal length of the limb.

The rate of change of the shape of the limb due to the resilience of the at least 011e impervious sleeve may be non-linear. This non-linearity may be controllable by varying certain qualities of the at least one impervious sleeve, such as the types of materials and its shape. This non-linearity may be exploited as well as, or instead of, the non-linearity discussed above with regard to the volume flow rate through the at least one orifice, and/or the resilient sleeve, and/or the second resilient means, so as to provide additional ways of tuning the limb to damp induced oscillations.

The mooring load may be carried by any one or more of the at least one impervious sleeve, the resilient sleeve, first resilient means and second resilient means.

The mooring limb, may be a pumping mooring limb for pumping the fluid to a predetermined destination. The fluid may be the fluid in which it is situated in use. In this regard the limb may be used as a pump as well as, or instead of a damping or a mooring limb. In one embodiment, the limb may include means for directing the fluid, as it leaves the at least one chamber, to an energy conversion apparatus. For instance, pipes or other conduits may be used, possibly with appropriate valve arrangements, to direct any fluid forced out of the at least one chamber.

In another aspect, the invention provides a method of mooring an object substantially floating in a fluid using at least one mooring limb, as described above and/or as recited in any of claims I to 13 herein, comprising the steps of; directly or indirectly attaching one axial end of the device to the object and directly or indirectly attaching the other axial end to a substantially fixed object.

In this regard the term "axial ends" may refer to the ends located at either end of the longitudinal length of the device. If the at least one chamber is substantially spherical then the axial ends may be located at opposite points around its outer surface.

However, the attachment points do not necessarily have to be directly connected to the sphere as other possibilities described herein are contemplated.

The method may include the step of directing the fluid, as it leaves the at least one chamber, to a predetermined destination. This may be an energy conversion apparatus.

In a different aspect, the invention provides a method of damping the movement of an object substantially floating in a fluid, comprising the steps of directly or indirectly attaching one axial end of at least one mooring limb, as described above and/or as recited in any of claims I to 15 herein, to the object; directly or indirectly attaching the other axial end of the at least one limb to a substantially fixed object; controlling the flow of the fluid into and/or out of the at least one chamber to damp the change in the longitudinal length of the limb caused by movement of the object relative to the substantially fixed object.

The term "change in the longitudinal length" may be replaced by the term "change in the shape".

The method may further comprise the step of directing the fluid, as it leaves the at least one chamber, to a predetermined destination. This may be an energy conversion apparatus.

The limb may comprise more than one chamber. Some or all of these chambers may be fluidly interconnected by means of suitable conduits. The flow through the conduits may be controlled by valves or other such flow regulators. Some or all of these chambers may also be connected by physical means to provide tension in the device.

For instance, cables, wires or chains may be used to interconnect them. It is also possible that the second resilient means may interconnect the chambers as well as, or instead of, the cables, \vires or chains. It is also possible that the limb comprises more than one chamber of varying sizes and shapes. For instance, at one end the limb may comprise a substantially spherical, followed by a substantially cylindrical chamber, followed by another substantially spherical chamber. One resilient sleeve may be provided around all three chambers. Alternatively, more than one resilient sleeve may be provided around one or more chambers, the one or more resilient sleeves possibly being interconnected.

The limb according to the invention may be only a relatively short length of the overall mooring limb. For instance, the overall mooring limb may comprise a mooring limb according to the invention, attached to the land beneath the fluid (or shore) at one end, and to the object to be moored at the other end, by means of chains, ropes or wires, wherein the combined lengths of the chains, ropes or wires are much longer than the length of the limb according to the invention. In this regard, the mooring limb according to the invention may be called a "mooring component".

The above and other characteristics, features and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. This description is given for the sake of example only, without limiting the scope of the invention. The reference figures quoted below refer to the attached drawings.

Figure 1 is an elevational side view of a general arrangement of one embodiment of the invention in use; Figure 2 is a perspective view of the embodiment of Figure 1; Figure 3 is a radial cross-sectional view of another embodiment of the invention having a first longitudinal length; Figure 4 is a longitudinal cross-sectional view of the embodiment of Figure 3; Figure 5 is a radial cross-sectional view of the embodiment of Figures 3 and 4 having a second longitudinal length; and Figure 6 is a longitudinal cross-sectional view of the embodiment of Figure 5.

The present invention will be described with respect to particular embodiments and with reference to certain drawings but the invention is not limited thereto but only by the claims. The drawings described are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn to scale for illustrative purposes. The dimensions and the relative dimensions do not correspond to actual reductions to practice of the invention.

Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequence, either temporally, spatially, in ranking or in any other manner. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein.

Moreover, the terms top, bottom, over, under and the like in the description and the claims are used for descriptive purposes and not necessarily for describing relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other orientations than described or illustrated herein.

It is to be noticed that the term "comprising", used in the claims, should not be interpreted as being restricted to the means listed thereafter; it does not exclude other elements or steps. It is thus to be interpreted as specifying the presence of the stated features, integers, steps or components as referred to, but does not preclude the presence or addition of one or more other features, integers, steps or components, or groups thereof. Thus, the scope of the expression "a device comprising means A and B" should not be limited to devices consisting only of components A and B. It means that with respect to the present invention, the only relevant components of the device are A and B. Similarly, it is to be noticed that the term "connected", used in the description, should not be interpreted as being restricted to direct connections only. Thus, the scope of the expression "a member A connected to a member B" should not be limited to devices or systems wherein an output of device A is directly connected to an input of device B. It means that there exists a path between an output of A and an input of B which may be a path including other devices or means. "Connected" may mean that two or more elements are either in direct physical or electrical contact, or that two or more elements are not in direct contact with each other but yet still co-operate or interact with each other.

Reference throughout this specification to "one embodiment" or "an embodiment" means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment, but may refer to different embodiments.

Furthermore, the particular features, structures or characteristics may be combined in any suitable manner, as would be apparent to one of ordinary skill in the art from this

disclosure, in one or more embodiments.

Similarly it should be appreciated that in the description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the claims following the detailed description are hereby expressly incorporated into this detailed description, with each claim standing on its own as a separate embodiment of this 111V entlon.

Furthermore, while some embodiments described herein include some but not other features included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the invention, and form different embodiments, as would be understood by those skilled in the art. For example, in the following claims, any of the claimed embodiments can he used in any combination.

In the description provided herein, numerous specific details are set forth.

However, it is understood that embodiments of the invention may be practised without these specific details. In other instances, well-known methods, structures and techniques have not been shown in detail in order not to obscure an understanding of

this description.

The invention \vill now be described by a detailed description of several embodiments of the invention. It is clear that other embodiments of the invention can be configured according to the knowledge of persons skilled in the art without departing from the true spirit or technical teaching of the invention, the invention being limited only by the terms of the appended claims.

In Figure 1 the limb is referenced "10". It is shown mooring an object 20 which is floating at the surface 25 of a body of fluid to a fixed point 30, which in this case is a concrete block resting on the land surface (sea bed) 35 beneath the fluid. The fixed point 30 and the object 20 include anchor points 40 between which the limb is arranged.

The limb 10 itself comprises an impervious sleeve 50 at each end of which are arranged connectors 60, which are simple loops in the present case. Standard chains or ropes 70 are used to connect the anchor points 40 to the connectors 60. Although the length of the limb 10 is shown as approximately equal in length to the sum of the two lengths of chains or ropes 70, it might be substantially less than this summed length such that it forms only a relatively short part of the overali length of the mooring member (comprising the limb 10 and chains or ropes 70).

Although only one limb 10 is shown it is contemplated that more than one may be used with the same floating object 20 and the same, or one or more other, fixed points 30 such that the object 20 is maintained "on station".

One embodiment of the limb 10 is shown in more detail in Figure 2. It comprises the impervious sleeve 50 and an inlet/outlet means 80 provided on its surface. The inlet/outlet means includes a valve 90. Although shown as a single inlet/outlet, it is contemplated that tlie inlet and outiet may be separate from one another. The inlet/outiet 80 may be located on the ends or the sides of the substantially cylindrical impervious sleeve 50.

The limb 10 also includes connectors 60 provided at each longitudinal end thereof. These connectors 60 comprise relatively short lengths of rope, chain, cable etc. attached at one end to the limb 10 and having loops or shackles at the other end.

Figure 3 shows an alternative embodiment of the limb 110. The view is a radial cross-section along the longitudinal axis of the limb 110. The impervious sleeve is referenced 150. Radially outward of the impervious sleeve 150 a braided outer sleeve is provided. Only a few of the wires forming this braided outer sleeve 155, as discussed below, are shown for the sake of clarity. Radially inward of the impervious sleeve 150 an inner resilient member 180 is provided substantialiy along the longitudinal axis of the limb 110. An additional resilient member 170 is also provided radialiy inward of the impervious sleeve.

The inner resilient member 170 may be a substantially cyhndrical length of rubber-type material or other such elastic/resilient material. Cross-sectional shapes other than circles are contemplated for this inner resilient member, such as square.

Moreover, although the overall shape of the cross-sectional view of the limb is shown as circular, other shapes are contemplated such as hexagonal, square, triangular, etc. The additional resilient member 170 is shown as a coil having an overlap of only approximately 100 degrees. However, the overlap may be more or less, for instance, 10 -180 degrees. Other overlapping dimensions are possible. Furthermore, it may be possible not to have an overlap.

The view in Figure 3 is one of the limb 110 in a relaxed state having an original unstressed and unchanged shape.

In Figure 4, a longitudinal cross-sectional view is shown of the same limb 110 as Figure 3. The entire length of the limb 110 is visible. It comprises the impervious sleeve 150 which is a substantially cylindrical "sausage" shape. The impervious sleeve is surrounded by the braided outer sleeve 155. This takes the form of a criss-cross arrangement of wires which lie circumferentially around the impervious sleeve 150 and at two different angles to the radial plane of the limb 150. A first set of wires are arranged at one angle (approximately 45 degrees clockwise from the radial plane) and a second set are arranged at another angle (approximately 45 degrees anticlockwise from the radial plane). The sleeve 155 is reduced in diameter at each end as it is "throttied down" or "gathered in" to be received in a ferrule 165.

Within the impervious sleeve 150 a resilient means 180 is provided along the longitudinal axis of the limb 110. It extends between the t\vo longitudinal ends of the limb 110. The resilient means 180 is connected to the ferrules 165 at each end thereof The resilient means 180 may be linked to the impervious sleeve 150 such that its length changes correspondingly with a change in length of the impervious sleeve 150.

Alternatively, the resilient means 180 may, relatively freely, pass through the ends of the impervious sleeve 150 such that the change in length of the resilient means 180 is partially, or completely, independent of the change in length of the impervious sleeve 150. This may be necessary where a non-resilient (in a lengthwise direction) impervious sleeve is provided. In the embodiment shown in Figures 4 and 6 the impervious sleeve is non-resilient (in a lengthwise direction) and accordingly, the length of the resilient means 180 is independent of the length of the impervious sleeve 150.

The ferrules 165 are also connected to the braided outer sleeve 155.

Also within the impervious sleeve 150 are arranged three additional resilient means 170. One is located proximate one ferrule 165, one is arranged proximate the other, opposite, ferrule 165 and one is arranged substantially at the mid-point of the longitudinal length of the limb 110. Other arrangements are possible. Also, the number of these additional resilient means 170 may be different from three.

Inlet and outlet means 80 are provided through the impervious sleeve 150 to allow fluid to ingress and egress into and out of the inner chamber formed by the impervious sleeve 150.

Connectors 160 are provided at each longitudinal end of the limb 110 connected to the ferrules 165, such that any tension imposed on the limb 110 is transmitted via the connectors 160, to the ferrules 165 and thus the resilient sleeve 155 and the resilient means 180.

In Figure 5, a radial cross-sectional view is provided of the same limb 110 as in Figures 3 and 4. However, in this view the radial cross-sectional area of the limb 110 has decreased due to the longitudinal length thereof having been increased.

Accordingly, the additional resilient means 170 has become further wound such that the overlap is now approximately 260 degrees. However, other overlaps are contemplated, for instance, in the range 180 to 360 degrees.

The effect of the increase in the longitudinal length of the limb 110 is shown in more detail in Figure 6. In particular, the resilient member 180 has become narrower in the radial direction and longer in the longitudinal direction as it has become stretched.

Furthermore, the braided outer sleeve 155 has altered in shape such that its longitudinal length has increased commensurate with the increase in longitudinal length of the limb 110, and its radial dimension has decreased commensurate with the decrease in the radial dimension of the limb 110. The length of the impervious sleeve 150 has remain unchanged. However, its radial dimension (or diameter) has been reduced. This has been effected by the braided sleeve 155 pressing radially inward against the impervious sleeve 150. Accordingly, the volume of the chamber defined by the impervious sleeve 150 has decreased.

The two sets of braids discussed above have also altered their angles relative to the radial plane. The first set now lies at an angle approximately 60 degrees clockwise from the radial plane and the second set now lies at an angle approximately 60 degrees anticlockwise from the radial plane.

Other features such as the ferrules 165 and connectors 160 remain the same as in Figure 4.

Once the tension exerted on the limb 110 has reduced either, or both, of the resilient means 155 and 170 urge the impervious sleeve 150 back to its original shape as shown in Figures 3 and 4 such that the volume of the chamber defined by the impervious sleeve 150 increases and fluid is sucked into the chamber defined by the impervious sleeve 150 via inlet 80.

The overall longitudinal length of the limb may lie in the range I metre to 20 metres. The radial dimension of the limb may lie in the range 15 cm to 200 cm.

Claims

Claims 1. A mooring limb for use in a fluid comprising at least one substantially impervious sleeve defining at least one chamber, wherein the shape of the at least one chamber is variable, the device including at least one orifice for allowing a fluid into and/or out of the at least one chamber.
2. The mooring limb according to claim 1, wherein the shape of the at least one impervious sleeve is variable and the variability of the shape of the at least one chamber is proportional to the variability of the shape of the at least one impervious sleeve.
3. The mooring limb of either one of claims I and 2 being a damping mooring limb for damping oscillations induced in the limb, and/or the object to which it is attached, in use.
4. The mooring limb of claim 3, including frequency control means for variably adjusting the damping frequency response of tile limb to the oscillations induced in the limb, and/or the object to which it is attached, in use.
5. The mooring limb of claim 4, wherein the frequency control means comprises the at least one orifice.
6. The mooring limb of any preceding claim, wherein the at least one orifice includes flow rate control means for controlling the flow of the fluid into and/or out of the at least one chamber so as to limit and/or vary the rate of change of the shape of the at least one chamber.
7. The mooring limb of any preceding claim, including a resilient sleeve.
8. The mooring limb of claim 7, wherein the resilient sleeve is braided.
9. The mooring limb of either one of rlsirn5 7 and 8, wherein the resilient sleeve is resilient in a longitudinal direction of the limb.
10. The mooring limb of any one of daitnc 7 to 9, wherein the resilient sleeve is resilient in a radial direction of the limb.
11. The mooring limb of any preceding daini, including a first resilient means, being resilient in a radial direction.
12. The mooring limb of any preceding dnirn, including a second resilient means being resilient in a longitudinal direction.
13. The mooring limb of any preceding rlsitn, wherein the at least one impervious sleeve is resilient in a radial and/or axial direction.
14. The mooring limb of any preceding daini, being a pumping mooring limb for pumping the fluid to a predetermined destination, in use.
15. The mooring limb of any preceding dahn including means for directing the fluid, as it leaves the at least one chamber, to an ener conversion apparatu&
16. A method of mooring an object substantially floating in a fluid using at least one mooring limb of any preceding rlsitn, comprising the steps o4 directly or indirectly attaching one axial end of the device to the object and directly or indirectly attaching the other axial end to a substantially fixed object.
17. A method of mooring an object according to daini 16, further comprising the step of directing the fluid, as it leaves the at least one chamber, to a predetermined destination.
18. A method of clamping the movement of an object substantially floating in a fluid, comprising the steps o4 directly or indirectly attaching one axial end of at least one mooring limb, according to any preceding claim, to the object; directly or indirectly attaching the other axial end of the at least one limb to a substantially fixed object; controlling the flow of the fluid into and/or out of the at least one chamber to damp the change in the longitudinal length of the limb caused by movement of the object relative to the substantially fixed object.
19. A method of damping the movement of an object according to claim 19, further comprising the step of directing the fluid, as it leaves the at least one chamber, to a predetermined destination.
20. The method of either one of claims 17 and 19, wherein the predetermined destination is an energy conversion apparatus.
21. A mooring limb substantially as hereinbefore described with reference to the accompanying drawings.
22. A method of mooring an object substantially floating in a fluid substantially as hereinbefore described with reference to the accompanying drawings.
23. A method of damping the movement of an object substantially floating in a fluid substantially as hereinbefore described with reference to the accompanying drawings.