GB2053303A

GB2053303A - Elastic Tie Member

Info

Publication number: GB2053303A
Application number: GB8023510A
Authority: GB
Original assignee: Platts M J
Current assignee: Platts M J
Priority date: 1979-07-20
Filing date: 1980-07-18
Publication date: 1981-02-04
Also published as: GB2053303B

Abstract

A tie member comprising an elongate elastomeric body 22 reinforced with co-axial layers 24, 25, 26, 27 of helically wound relatively inelastic filaments 23. Adjacent pairs of layers 24, 25, 26, 27 are spaced by the elastomeric material and have their filaments 23 wound in opposite- handed helical relationship. The tie member may be used as a mooring line 18. <IMAGE>

Description

SPECIFICATION Improvements in or Relating to Tie Members This invention relates to a tie member, and more particularly but not exclusively, to a tie member for use as a mooring iine.

According to the present invention, there is provided a tie member comprising an elongate body of elastomeric material, and relatively inelastic filaments incorporated in the body so as to reinforce the body and helically extending along the length of the body in at least two layers thereof radially displaced with respect to each other by the elastomeric material, the filaments in a said layer extending in opposite-handed helical relationship with respect to the filaments in an adjacent said layer.

Preferably, the filaments are wound at a helix angle with the longitudinal axis of the tie member of between 400 to 55 .

Desirably, at least one electrically conductive filament is incroporated in the tie member for monitoring the integrity of the body by a nondestructive testing method.

The elongate elastomeric body may be of hollow form, and means may be provided for passing a fluid through said hollow elongate body, for example to cool said body.

The elongate body may comprise natural rubber or synthetic rubber, and the filaments may comprise steel, glass fibres, carbon fibres, or plastics materials such as nylon.

In one application of the invention, the filaments may be disposed in several substantially co-axial layers, and such that the filaments in adjacent said layers are in opposite-handed helical relationship.

Desirably, the elongate body is of circular form in transverse cross-section.

The invention will now be further described by way of example only with reference to the accompanying drawings in which: Figure 1 shows a diagrammatic side representation of a Cockerell raft wave energy converter; Figure 2 shows a diagrammatic representation in the direction of arrow 'A' in Figure 1; Figure 3 shows to an enlarged scale and in part section a fragmentary view on the line Ill-Ill of Figure 1; Figure 3a shows to an enlarged scale a view on the line Illa--llla of Figure 3; Figure 4 shows to an enlarged scale a fragmentary sectional representation on the line IV-lV of Figure 1; Figure 4a shows a sectional view on the line IVa-IVa of Figure 4; Figure 4b shows a modification of the sectional view of Figure 4;; Figure 4c shows a sectional view on the line IVc-lVc of Figure 4b; Figure 5 shows to an enlarged scale a fragmentary sectional representation on the line V-V of Figure 1; and Figure 5a shows a modification of the sectional view of Figure 5.

In the above Figures, like parts have like numerals.

Referring now to Figure 1 and Figure 2, the wave energy converter shown is in the form of a Cockerell Raft 10 which has been described for example in British Patent Specification No.

1448204 and co-pending patent application Nos.

7938465 and 7938464 to which reference should be made for further detailed information.

Briefly, the Cockerell raft 10 shown comprises a forward pontoon 11 and an aft pontoon 12 which are hingedly connected together at 13, and are shown floating in a liquid 14 such as the sea.

Relative motion between the forward pontoon 11 and the aft pontoon 12 in response to waves is used to perform useful work, e.g. actuate a piston in a hydraulic cylinder (not shown) which is connected by a hydraulic circuit (not shown) to a turbine (not shown). The Cockerell Raft 10 is moored to the sea bed by four mooring lines 18 each attached to a respective anchor 1 9.

Each mooring line 18 as shown in Figures 3 and 3a comprises an elongate body 22 of an elastomeric material such as natural rubber reinforced with glass fibre filaments 23 arranged in four concentric circular layers 24, 25, 26 and 27 respectively, the layers 24-27 being separated by the natural rubber of the elongate body 22. The filaments 23 extend in a helical manner along the length of the elongate body 22 but such that adjacent layers 24--27 27 have filaments 23 extending in opposite-handed relationship, for example, the filaments 23 in the layers 24 and 26 extending in right hand helices and the filaments 23 in the layers 25 and 27 extending in left hand helices.

Referring now to Figures 4 and 4a, the upper end of each elongste body 22 has been stretched and subsequently clamped by a split clamp end member 30 having a flange 43 secured to threaded spigots 45 extending from the Cockerell Raft 10. In order to improve the grip of the end member 30 about the elongate body 22, the inside surface of the end member 30 is serrated at 48.

At the lower end of each elongate body 22 as shown in Figure 5 to which reference is made, the elongate body 22 is held by an end member 30 identical to that fitted at the upper end of the elongate body 22. The flange 43 of the end member 30 is secured to a hollow cylindrical casing 59 having a central aperture 62 through which a shaft 63 of the anchor 19 extends and is retained in the casing 59 by an end flange 65.

In operation, the elasticity of the mooring lines 1 8 allows the Cockerell Raft 10 to ride or yield to the waves as it extracts energy therefrom, thus considerably reducing the axial loads on the mooring lines 1 8 in comparison with the loads to which a conventional chain or cable would be subjected under the same conditions.

Under the effect of the varying load on each mooring line 18, the respective mooring line 1 8 elastically varies in length, and these variations are accompanied by consequent straightening and subsequent relaxing of the helically wound relatively inelastic filaments 23 as they take and relax from the load on the mooring line 18, the elastomer between the layers 24-27 being in shear and providing the elasticity of the mooring line 18.

The invention enables a tie member such as the mooring line 18 to be provided with a designed elasticity, the variables which effect the elasticity being 1) the radial thickness of the elastomeric material between the layers of filaments 2) the number of layers and the number of filaments in the layers 3) the helix angle at which the individual filaments are wound and 4) the mechanical properties of the elastomeric material and of the filaments.

The filaments are desirably wound at a helix angle with the longitudinal axis of the tie member of between 400 to 550 but other such helix angles may be used.

Suitable filaments include steel, carbon fibres, glass fibres, or plastics materials such as nylon. It will be understood that the filaments may themselves have elastic properties, but in comparison with the elastic properties of the elastomeric material of the tie member the filaments should be relatively inelastic in extending considerably less than the elastomeric material under the effect of the same load.

Natural rubber is the preferred elastomeric material but other suitable elastomers may be used, for example synthetic rubbers such as Neoprene.

Although the invention has been described in relation to a solid tie member, it may also be incorporated in a hollow tie member for example, to provide a bore through which a fluid (e.g.

seawater) may be circulated to dissipate heat generated by the varying strain to which the tie member is subjected. Such an arrangement is shown in Figures 4b and 4c to which reference is made. In Figures 4b and 4c, the upper end of a mooring line 1 8 is shown having a tubular elongate body 22a with a bore 21 and reinforced with three concentric circular layers 24a, 25a and 26a of filaments 23 (not shown in Figure 4b) helically wound in a similar manner to that described in relation to the elongate body 22 of Figure 3 so that the filaments 23 in adjacent layers 24a, 25a, or 26a are in opposite-handed relationship.The upper end of the tubular elongate body 22a is joined to the Cockerell Raft 10 by an end member 30 identical to that shown in Figure 4, and a tubular metal insert 31 is provided in the bore 21 and at the end of the tubular elongate body 22a to prevent the collapse of the tubular elongate body 22a under the effect of the radial pressure exerted by the end member 30, the tubular insert 31 having a flange 32 to which a fluid circulating system (not shown) may be joined. At the lower end of the tubular elongate body 22a as shown in Figure 5a, in the bore 21 thereof, a tubular metal insert 67 is provided for a similar purpose as that of the tubular insert 31 to resist the radial pressure of the end member 30 and to provide a port for seawater, apertures 61 being provided in the side of the casing 59 for the flow therethrough of the seawater.

In order to assist in monitoring the integrity of the mooring line 18, several conductive filaments may be incorporated in the mooring line 18 for connection to conventional non-destructive testing equipment, examples of such filaments being copper, aluminium or steel.

It will be understood that a tubular tie member of the invention may incorporate several radially directed fins in the bore thereof to resist radial collapse of the tie member. Furthermore, the tie member of the invention may be of non-circular crosssection.

Although the invention has been described in relation to the use of three or four radially displaced layers of filaments, alternative combinations of layers may be selected, for example two layers or five layers or more.

It is important that the filaments be wound so that pairs of layers have the filaments thereof in opposite-handed relationship. An additional advantage of the radial displacement of the layers is that chafing of adjacent filaments is minimised.

The tie member may have alternative end connections to those aforedescribed, for example, the use of semi-circular or quarter shell taper wedges in an internally tapered collar, of if desired the ends of the tie member may be bound with a suitable filament.

Claims

1. A tie member comprising an elongate body of elastomeric material, and relatively inelastic filaments incorporated in the body so as to reinforce the body and helically extending along the length of the body in at least two layers thereof radially displaced with respect to each other by the elastomeric material, the filaments in a said layer extending in opposite-handed helical relationship with respect to the filaments in an adjacent said layer.

2. A tie member as claimed in Claim 1, wherein the body is reinforced with a plurality of said layers of the filaments, the filaments in adjacent said layers helically extending in opposite-handed relationship with respect to each other.

3. A tie member as claimed in Claim 1, wherein the body is reinforced with a plurality of the layers, and pairs of said layers have the filaments thereof extending in opposite-handed relationship.

4. A tie member as claimed in any one of the preceding Claims, wherein the filaments extend at a helix angle of between 400 to 55 .

5. A tie member as claimed in any one of the preceding Claims, wherein the body defines a bore therethrough for the passage of a cooling fluid through the bore.

6. A tie member as claimed in Claim 5, including several radially directed fins in the bore to resist radial collapse of the tie member.

7. A tie member as claimed in any one of the preceding Claims, including a clamp member one at each end of the tie member and shaped to provide a respective end connection for the tie member.

8. A tie member as claimed in Claim 7, including a respective tubular metal insert in the bore at each end of the body for resisting collapse of the body.

9. A tie member as claimed in any one of the preceding Claims, including at least one electrically conductive filament incorporated in the body for monitoring the integrity of the body by a non-destructive testing method.

10. A tie member as claimed in any one of the preceding Claims, wherein the tie member is of circular form in transverse cross-section.

11. A tie member substantially as hereinbefore described with reference to Figures 1 to 4a and Figure 5 of the accompanying drawings.

12. A tie member substantially as hereinbefore described with reference to Figures 1 to 3, and Figures 4b, 4c, and 5a of the accompanying drawings.