GB2253641A - Underwater material transfer - Google Patents

Abstract

Riverbed or seabed materials are transferred by means of a vibrating unit (6, 23) which is lowered from a working vessel to the desired riverbed or seabed level. The vibrating unit (6, 23) agitates the materials to permit mixing with water and resulting dispersion. The vibrating unit (6, 23) may comprise one or more vibrating cylinders provided with preferably helical, vanes (9). <IMAGE>

Description

Underwater Material Transfer This invention relates to an apparatus and method for transferring riverbed or seabed materials such as deposited mud or silt, for example when dredging harbours or river channels.

Traditional dredging methods include, for example, using an excavator crane, a bucket dredger or a trailing suction hopper dredger. All these prior methods involve dredging up, transporting and dumping the spoil. Such traditional dredging methods are expensive and consequently the maintenance of harbour and river channels is costly.

It is known that it is possible to transfer riverbed and seabed materials by fluidisation and density currents. A body of bulked fluidised material may be formed and will disperse as a result of the density differential between this material and the surrounding river water or sea water. The present invention relates to a method and apparatus for achieving such a transfer of riverbed or seabed materials.

Viewed from one broad aspect the present invention provides apparatus for moving riverbed or seabed materials comprising, vibrating means and means for lowering said vibrating means to a depth corresponding to a desired riverbed or seabed level, whereby in use said vibrating means acts to agitate and fluidise said materials.

In use, the vibrating means acts to agitate the riverbed or seabed materials so as to reduce the cohesiveness and friction of such materials, and to permit water to be mixed with the materials to create a fluidised material. Such a fluidised material has a lower specific density than the original material (for example 1.15 compared to 1.3) and thus the resulting fluidised material rises to a level above the original riverbed or seabed where it then disperses as a consequence of density currents set up by the differential between the density of this fluidised material and the surrounding water. The fluidised material is dispersed until an equilibrium is established between the density differential between the surrounding water and the fluidised material, and the residual internal friction of the fluidised material.

The vibrating means may take one of a number of convenient forms. Preferably, however, the vibrating means may comprise at least one vibrating unit formed with a plurality of external vanes for agitating the riverbed or seabed material. The vibrator units may be caused to vibrate by means of, for example, an eccentric mechanism and may be powered by electric, hydraulic or pneumatic means with a power source located on an accompanying vessel.

In one embodiment the vibrating unit comprises a hollow cylindrical member disposed, in use, substantially parallel to the surface of the riverbed or seabed. The external surface of the cylindrical member is provided with a plurality of vanes arranged in a generally helical pattern. Within the cylindrical member, at the two opposed ends thereof, are provided rotatable eccentric mechanisms driven by a motor disposed therebetween. Rotation of the eccentric mechanisms causes the required vibration.

In an alternative embodiment, the vibrating means may comprise a plurality of individual vibrator units mounted on a frame, the vibrator units being disposed generally vertically with respect to the riverbed or seabed. Again, each vibrator unit is in the form of a cylindrical member with external vanes arranged in a generally helical pattern.

The vanes may be disposed in alternative arrangements, or rather than providing the vibrating units with a plurality of vanes in a helical pattern, continuously helical vanes may be provided.

The vibrating means may be lowered and suspended from the accompanying working vessel directly by means of steel wire rope or chains. Preferably, however, the vibrating means is provided at one end of an arm the other end of which is hinged to the working vessel. The angle at which the arm is hinged, and thus the depth of the vibrating means, may be adjusted by means of a cable hoist provided on the vessel and acting on the arm.

Where necessary, and especially where the vibrating means comprises a number of vibrator units disposed in a frame, means may be provided at the end of the arm to which the vibrating means is formed for adjusting the angle of the vibrating means relative to the arm so that the correct orientation of the vibrating means relative to the riverbed or seabed may be maintained at all depths.

Viewed from another broad aspect the present invention provides a method of transferring riverbed or seabed materials comprising, lowering a vibrating means to a depth corresponding to a desired riverbed or seabed level, agitating said riverbed or seabed materials by means of said vibrating means whereby said material is fluidised, and allowing said fluidised material to disperse in response to thus generated density currents.

Some embodiments of the present invention will now be described by way of example and with reference to the accompanying drawings, in which: Fig. 1 is a schematic side view showing apparatus according to a first embodiment; Fig. 2 is a perspective view of the vibrating means of the embodiment of Fig. 1; Fig. 3 illustrates the internal mechanism of the vibrating unit of Fig. 2; Fig. 4 is a sectional view through an eccentric mechanism; Fig. 5 is a perspective view showing an alternative method of suspending the vibrating unit; Fig. 6 shows an alternative vibrating unit; Fig. 7 is a view corresponding to fig. 1 of a second embodiment; Fig. 8 is a plan view of the vibrating means of the second embodiment; Fig. 9 is a perspective view of an individual vibrating unit of the second embodiment; and Fig. 10 is a side view showing the vibrating unit of the second embodiment mounted on one end of the hinge arm.

Referring firstly to Fig. 1 there is shown schematically a dredging vessel 1 for dredging a riverbed or seabed 2. The vessel 1 is provided with at least one arm 3 that is hingedly mounted at its upper end to the vessel 1. The arm 3 may be raised or lowered by means of a cable 4 that acts on the arm 3 and which is wound on drum 5 in a conventional manner.

At the end of the arm 3 remote from the vessel 1, there is provided a vibrating unit 6, shown in more detail in Figs. 2 to 4. Vibrating unit 6 is mounted to arm 3 via a flexible coupling 7, and comprises a generally cylindrical hollow member 8, the longitudinal axis of which extends at right angles to arm 3. The outer surface of cylindrical member 8 is provided with a plurality of individual vanes 9 that are arrayed about the cylindrical member 8 to define a generally helical pattern.

Figs. 3 and 4 illustrate the internal mechanism of the vibrator unit. For clarity Fig. 3 omits the external vanes. Centrally located in the interior of hollow cylindrical member 8 is an electric or hydraulic motor 10 that receives electric or hydraulic power from a power supply 11 connected ultimately to power source 12 provided on the working vessel 1. Motor 10 drives, via flexible couplings 13, two eccentric mechanisms 14 disposed at respective ends of the vibrator unit. Each eccentric mechanism 14 comprises a weight 15 eccentrically mounted on a shaft 16 supported in turn by bearings 17. Rotation of eccentric weights 15 by motor 10 causes the vibrator unit 9 to vibrate.

Returning to a consideration of Fig. 1, the operation of this embodiment will now be described.

While the working vessel 1 moves slowly in the direction of arrow A, arm 3 is lowered via cable 4 until the vibrator unit 6 is at a level 18 corresponding to the desired level of the riverbed or seabed. This level 18 is below the present level 19 of the riverbed or seabed which is caused by deposited mud and like material.

Upon operation of the vibrator unit 6, the deposited material is agitated by vanes 9, and this agitation allows surrounding water to mix with the material to create a fluidised material of lower cohesiveness and lower internal friction. The fluidised material is of a lower specific density, for example 1.15, in comparison with the specific density of the deposited riverbed or seabed material which may be as much as 1.3. The fluidised material therefore rises above the surface of the riverbed or seabed and, because the fluidised material has a greater specific density than the surrounding water, the fluidised material is dispersed because of the density currents that are set up as a result of the density differential between the fluidised material and the surrounding water. This dispersion, indicated by arrow B, continues until a density differential is established.In practice the density of the fluidised material may not quite reach the density of the surrounding water, i.e. 1, since the fluidised material will have a slight residual friction.

Fig. 5 illustrates an alternative arrangement for suspending the vibrating unit 6 from the vessel 1. In this arrangement, instead of using a hinged arm 3, the vibrating unit 6 is suspended directly by means of a pair of steel wire cables or chains 20 to which the vibrator unit 6 is fixed by brackets 21. A separate cable 22 is provided for the supply of power to the motor 10. In this arrangement the vibrator unit 6 is simply lowered directly to the desired depth.

Fig. 6 illustrates an alternative vane arrangement for the vibrator unit 6. Instead of providing the exterior surface of the vibrator unit with a plurality of relatively small individual vanes 9 disposed in a helical configuration, in this arrangement the vibrator unit 6 is provided with a series of continuous helical vanes 9'.

Figs 7-10 illustrate a second embodiment of the invention. In this embodiment the vibrating means comprises a plurality of individual vibrator units 23 mounted in a supporting framework 24. The framework 24 is designed to have a minimum resistance to upward flow of riverbed or seabed material. Fig. 9 illustrates an individual vibrator unit 23. Unlike the first embodiment, each vibrator unit is disposed with its principal longitudinal axis arranged generally vertically with respect to the riverbed or seabed. The vibrator unit 23 comprises a drive unit 25 and an extension provided with plurality of external vanes 9.

A number of rows of vanes may be provided as shown in Fig. 10. Alternatively, the vibrator unit may be provided with continuous helical vanes as in Fig. 6.

Since in this embodiment the vibrating means extends over a significant area, rather than being substantially linear as in the embodiment of Fig. 1, where the vibrating means is mounted to the end of a hinged arm 3 means must be provided for adjusting the angle of the vibrating means relative to the arm 3 to ensure that the plane of the vibrating means is parallel to the riverbed or seabed at all angles of the hinged arm 3. To this end, the vibrating means is pivotally mounted to the lowermost end of arm 3 via a pair of mounting brackets 26. As is shown particularly clearly in Fig. 10, brackets 26 are also formed with a bracket portion 27 to which is attached one end of a hydraulic actuating cylinder 28.The piston member 29 of actuating cylinder 28 is connected at the other end to a further bracket 30 which is formed on the arm 3 and to which is attached the height adjusting cable 4.

Actuating cylinder 28 thus permits the angle of the vibrating means relative to the arm 3 to be adjusted.

In particular, if arm 3 is raised to position the vibrating means at a shallower depth, the actuating cylinder 28 will be extended to reduce the angle between the plane containing the vibrating units and the arm 3.

Conversely, if arm 3 is lowered to increase the operating depth of the vibrating means, actuating cylinder 28 is retracted to increase the angle between the plane containing the vibrating units and the arm 3.

It will be appreciated that if the vibrating means is suspended directly from the working vessel in a manner corresponding to that shown in Fig. 5, then no such angle adjusting means would be necessary.

The above embodiments are by way of example only, and many other arrangements would be possible. For example, the vanes could be disposed in arrangements other than helical dispositions. Alternatively, rather than vanes, the vibrating unit(s) could be provided with a ribbed or corrugated external surface, or with some other form of protrusion, providing that the necessary agitation and fluidisation of the riverbed or seabed material is achieved.

Claims (12)

1. Apparatus for moving riverbed or seabed materials comprising, vibrating means and means for lowering said vibrating means to a depth corresponding to a desired riverbed or seabed level, whereby in use said vibrating means acts to agitate and fluidise said materials.

2. Apparatus according to claim 1 wherein said vibrating means comprises at least one vibrating unit formed with a plurality of external vanes for agitating the riverbed or seabed material.

3. Apparatus according to claim 2 wherein said vibrating unit comprises a hollow cylindrical member disposed, in use, substantially parallel to the surface of the riverbed or seabed.

4. Apparatus according to claim 3 wherein the external surface of the cylindrical member is provided with a plurality of vanes arranged in a generally helical pattern.

5. Apparatus according to claim 3 or 4 wherein within the cylindrical member, at the two opposed ends thereof, are provided rotatable eccentric mechanisms driven by a motor disposed therebetween.

6. Apparatus according to claim 1 wherein the vibrating means comprises a plurality of individual vibrator units mounted on a frame, the vibrator units being disposed generally vertically with respect to the riverbed or seabed.

7. Apparatus according to claim 6 wherein each vibrator unit is in the form of a cylindrical member with external vanes arranged in a generally helical pattern.

8. Apparatus according to any preceding claim wherein the vibrating means is provided at one end of an arm the other end of which is hinged to a working vessel.

9. Apparatus according to claim 8 wherein means are provided at the end of the arm to which the vibrating means is formed for adjusting the angle of the vibrating means relative to the arm so that the correct orientation of the vibrating means relative to the riverbed or seabed may be maintained at all depths.

10. Apparatus for moving riverbed or seabed materials substantially as hereinbefore described with reference to the accompanying drawings.

11. A method of transferring riverbed or seabed materials comprising, lowering a vibrating means to a depth corresponding to a desired riverbed or seabed level, agitating said riverbed or seabed materials by means of said vibrating means whereby said material is fluidised, and allowing said fluidised material to disperse in response to thus generated density currents.

12. A method of transferring riverbed or seabed materials substantially as hereinbefore described with reference to the accompanying drawings.