GB2304353A

GB2304353A - Underwater excavation apparatus

Info

Publication number: GB2304353A
Application number: GB9516738A
Authority: GB
Inventors: George John Stroud
Original assignee: Individual
Current assignee: Individual
Priority date: 1995-08-16
Filing date: 1995-08-16
Publication date: 1997-03-19
Anticipated expiration: 2015-08-16
Also published as: GB2304353B; GB9516738D0

Abstract

An underwater excavation apparatus comprises a housing having water inlet means and water outlet means, and a propeller mounted for rotation within the housing and having a plurality of blades 7 and a hollow annular sleeve 9 which is joined to and encircles the blades. At least one of the blades 7 has a passage 10 in communication with an annular channel 19 in the annular sleeve 9, and nozzles 12 are provided on the annular sleeve 9. Fluid is supplied under pressure to the passage 10 which, in turn, supplies fluid to the nozzles 12 via the annular channel 19 to create fluid jets which cause the propeller to rotate so as to draw water into the inlet means and deliver a controlled flow of water through the outlet means for dispersing materials such as soil, sediment or rocks, or drilling muds.

Description

UNDERWATER EXCAVATION APPARATUS The present invention relates to underwater excavation apparatus and, in particular, underwater excavation apparatus suitable for use in soil removal and/or dispersing of sediments from the seabed.

Underwater excavation apparatus is used in a wide range of soil removal applications in the offshore engineering and salvage industries. Such apparatus effects soil removal by the generation of a large downward flow of water, at a controlled velocity, several metres above the seabed. The apparatus is normally deployed on a drill string from a dredging vessel or alternatively can be suspended over the seabed from a crane on board such a vessel.

Such an apparatus is known from British Patent No. 2 240 568 which describes an underwater excavation apparatus incorporating a propeller mounted for rotation in a hollow body into which sea water is drawn in through an inlet and delivered in a stream through an outlet. In this apparatus water jet means are provided in the form of nozzles on the tips of blades of the propeller, water being supplied to the nozzles at high pressure through passages in the propeller blades in order to cause the propeller to rotate due to reaction of the resulting water jets against vanes or walls which surround the propeller. In one illustrated embodiment the tips of the propeller blades having the nozzles protrude into an annular chamber surrounding the rotating propeller.

Discharge vents connect this chamber directly to the surrounding sea water in which the apparatus operates and consequently much power is lost in overcoming the frictional force of sea water surrounding the blade tips in order to rotate the propeller by means of the jet means provided on the blade tips. Consequently fluid must be supplied under very high pressure to the jet means. Moreover, the discharge vents can get blocked with debris e.g. fluidised soil, leading to increased fluid pressure around the jets resulting in increased drag forces on the propeller.

In another embodiment described in GB 2 240 568, the tips of the propeller blades are joined by a solid annular sleeve which surrounds the propeller blades, the water jet means on each blade tip protruding through the annular sleeve and vanes are distributed on the inside of the hollow body, around the propeller, on which vanes the water jets act to cause rotation of the propeller.

Although the annular sleeve minimises energy lost through frictional resistance on the propeller blade tips as the propeller rotates, this design has several disadvantages. One disadvantage is that water supplied under pressure to the nozzles is expelled directly into the hollow body causing water in the hollow body to become turbulent. This, in turn, causes drag resistance on the propeller. This occurs as water is drawn down into the hollow body from the inlet above the propeller, as the propeller rotates, into the annular region between the propeller sleeve and the interior of the hollow body and there meets the water expelled from the nozzles on the blade tips.These different fluid flows cause turbulence in the annular region between the propeller sleeve and the hollow body causing flow restrictions on jet flows dispersing from the nozzles and drag resistance on the propeller which, in turn, affects the performance of the excavation apparatus.

Again, water must be supplied to the jet means at a very high pressure in an attempt to overcome these effects, although this may contribute further to turbulence effects. Movement of the apparatus through the surrounding fluid generally perpendicularly to the generated vertical fluid outflow at the rate of for example, one metre per minute, can further contribute significantly to turbulence effects acting on the propeller.

Additionally, problems will be experienced with both the embodiments described in GB 2 240 568 if any of the jet nozzles or any of the passages in the propeller blades become blocked by debris such as fluidised soil and seabed materials. This results in an initial drop in system performance. When this happens, more fluid is supplied to the other nozzles at increased pressure.

This can render the propeller unbalanced and also cause unnecessary loading on the other nozzles, both of which effects past experience has shown can lead to extensive system damage and consequential system "down time".

It is an object of the present invention to provide an underwater excavation apparatus which overcomes one or more of the aforementioned disdavantages.

According to the present invention an underwater excavation apparatus comprises a housing having water inlet means and water outlet means, which inlet and outlet means are in communication with a first chamber provided in said housing, and a propeller mounted for rotation within the housing so as to draw water into the first chamber though the inlet means and to generate a controlled flow of water out of the first chamber through the outlet means, wherein the propeller comprises a plurality of blades and a hollow annular sleeve which is joined to and encircles the blades, at least one of said blades having passage means in communication with an annular channel defined within said hollow annular sleeve, a plurality of fluid jet means being provided on said hollow sleeve, preferably between adjacent blades, and fluid supply means being provided for supplying fluid under pressure to said passage means which, in turn, supply fluid to said jet means via said annular channel to cause the propeller to rotate so as to draw water into said inlet means and deliver a controlled flow of water through said outlet means for dispersing material located in the path of said flow of water.

One advantage of the apparatus according to the invention is that should any of the plurality of fluid jet means become blocked, the flow of fluid under pressure to the other jet means remains largely unchanged due to the jet means being located on the hollow annular sleeve, between the propeller blades.

Fluid supplied under pressure through the passage means in the blade(s) is able to continue flowing round the annular channel defined within the sleeve even if one or more of the jet means become blocked. Where more than one propeller blade has said passage means then, similarly, a blockage in one of the passage means does not affect the supply of fluid to the jet means.

Preferably, said fluid jet means protrude into a second chamber which is defined by said hollow annular sleeve and said housing such that fluid from said jet means exhausts into said second chamber.

Said hollow annular sleeve preferably has an outer annular groove in each of an upper and a lower rim of said sleeve. Said outer grooves may inter-engage with protruding annular lips provided on said housing. In use, the inter-engaging lips and grooves form fluid seals between said first chamber wherein water flows generally vertically between the inlet and outlet means and said second chamber into which said fluid jet means protrude.

An advantage of this arrangement is that water flowing into the first chamber is kept separate from fluid flow from the jet means on the hollow annular sleeve. Thus, there is no opportunity for turbulence to arise in fluid surrounding the propeller blades and/or the annular sleeve, thereby avoiding undesirable drag resistance on the propeller as it rotates. This, in turn, makes the apparatus more energy efficient than the described known prior art apparatus as there are less frictional or drag losses to overcome.

Said housing is preferably provided with discharge means in communication with said second chamber and said outlet means such that fluid in said second chamber is discharged into the flow of water which is delivered through said outlet means.

By discharging fluid from the second chamber,which has been exhausted thereinto by the jet means, into the flow of water passing to the outlet means, rather than directly into the environment surrounding the excavation apparatus, it is less likely for the discharge means to become blocked by debris such as fluidised soil surrounding the apparatus, thus ensuring that efficient jet flow into the second chamber and discharge therefrom is maintained. Moreover fluid from the jets is discharged to the outlet means, where it contributes to the controlled fluid flow delivered therefrom, thus making maximum use of the pressurised fluid supplied to the propeller.

As the second chamber is not subjected to water pressure outside the apparatus, or in the first chamber, it is therefore possible to supply fluid to the propeller at relatively high or relatively low pressures, since it is not necessary to overcome surrounding water pressure on the propeller blade tips and/or the annular sleeve in order to cause the propeller to rotate. Much greater control and a larger range of outflow velocities can thus be achieved with the apparatus of the present invention, than with the known prior art apparatus.

This in turn enables greater energy efficiency and faster rates of excavation/soil removal to be achieved.

Said plurality of fluid jet means may comprise a plurality of nozzles. Preferably, said nozzles are removeable. A series of nozzles having various diameters may be provided for use with the apparatus.

Blanking caps may be provided for replacing one or more of said nozzles so as to reduce the total number of fluid jets provided on the hollow annular sleeve. The apparatus can thus be powered by a high flow rate, low pressure fluid supply or a low flow rate, high pressure supply. This enables further control over the operating speed of the propeller and the fluid outflow velocity to be achieved. Said nozzles may also be provided with streamlined shrouds.

The propeller may be mounted on a shaft and the apparatus may further comprise upper and lower bearing assemblies which support the shaft above and below the propeller respectively.

The upper and lower bearing assemblies each preferably comprise load and thrust taper bearings. These counteract forces of load and thrust acting on the rotating propeller so as to balance, and thereby, prevent oscillation of, the propeller. The upper and lower bearing assemblies may thereby enable the apparatus to be operated with the propeller shaft and housing tilted at any desired angle to the horizontal.

This makes the apparatus more versatile, enabling it to be used in a broader range of applications.

The housing may be provided with outer structural braces which strengthen the housing and protect the apparatus from impact damage. Preferably, the outer surface of the housing, incorporating said braces, has a substantially flush finish. This can help to prevent rotational "rocking" motion exhibited by known prior art systems which utilise braces in the form of fins disposed on the outer surface of the housing.

The pressurised fluid supplied to the nozzles may conveniently be freshwater or sea water, or alternatively it is conceivable that drilling mud could be used.

The high energy efficiency, fast outflow velocities and versatility of the apparatus according to the invention make it particularly suited not only to the dispersement of seabed sediments and soils on the seafloor, but also numerous additional applications for which the described prior art apparatus would be unsuitable. These include the removal of crushed rock piled on the seafloor, dispersement or removal of the fine, sandy/silt moraine sediments found at the mouths of river estuaries, as well as the agitation of drilling fluid and the shearing of drilling muds.

An embodiment of the underwater excavation apparatus according to the present invention will now be described by way of example only and with reference to the accompanying drawings in which: Fig. 1 is a cross-sectional side view of an underwater excavation apparatus according to the present invention in which blades of a propeller are shown partly exposed; Fig. 2 is a schematic cross-sectional view of the apparatus taken along line 2-2' of Fig. 1, and Fig. 3 is a magnified view of the ringed portion A of the apparatus of Fig. 1, the propeller having rotated by approximately forty-five degrees.

Figure 1 shows an underwater excavation apparatus 1 comprising a housing 2 in which a propeller 3 is mounted for rotation on a shaft 11 which extends into the housing 1. A first chamber 6 is defined within the housing 1. The housing comprises three sections, an upper section 13, lower section 15 and middle section 14 which is bolted to each of the upper and lower sections and through all of which sections the first chamber 6 extends. A series of water inlets is provided in the upper section 13 and outlets 5 are provided in the lower section 15, both the inlets and outlets opening into the first chamber 6. The propeller 3 has four blades 7 adjacent ones of which are spaced by substantially 90".

Each blade 7 incorporates an inner passage 10 which extends from the centre of the propeller 3 to the tip of the blade. An annular sleeve 9 of generally cylindrical form encloses the blades 7 as illustrated in Figures 1 and 2. The sleeve 9 is joined to the tips of the blades 7 and is hollow, defining an inner annular channel 19 in the sleeve 9. The channel 19 is integral with the passage 10 at each propeller blade tip. A nozzle 12 is provided on the annular sleeve 9 between each two adjacent propeller blades where a respective opening is provided in the sleeve. The nozzles are removeable and are each provided with screw fittings 28 for their attachment to the annular sleeve 9. Each nozzle has a streamlined shroud 17. Caps (not shown) may also be provided for blocking off one or more of the openings provided in the sleeve 9 for the nozzles 12 where the respective nozzles have been removed.

A second chamber 8 is located between the hollow sleeve 9 and the middle section 14 of the housing 2. The sleeve 9 has upper and lower ends 9a, 9b which are each provided with an outer annular groove 22, 24. The upper section 13 of the housing 2 has a downwardly extending lip 23 which engages with the annular groove 22 on the upper end 9a of the sleeve 9 and the lower section 15 of the housing has an upwardly extending lip 25 which engages with the annular groove 24 on the lower end 9b of the sleeve, as shown in Fig. 3. The three housing sections 13, 14, 15 and the exterior of hollow sleeve 9 thus defines the second chamber 8. The nozzles 12 project into the second chamber 8. A discharge port 20 located in the second chamber opens into a passage which extends through the housing 2 and into a lower region of the first chamber 6, below the propeller 3.

An upper bearing assembly 16 comprising thrust and taper bearings is disposed around a portion of the shaft 11 located above the propeller 3 in the upper housing section 13 and a similar lower bearing assembly 18 is disposed around a portion of the shaft 11 located below the propeller 3, in the lower housing section 15, within the first chamber 6. Outer bracing 30 may be provided on the housing 2 and the outer surface of the housing is formed to have a generally flush appearance.

In use, the apparatus is submerged and an upper end of the shaft 11 is connected to a drill string or other fluid supply means through which water is pumped, under pressure, down into the centre of the propeller, along the passages 10 in the propeller blades and into the annular channel 19 in the sleeve 9 so as to form a ring of fluid, as illustrated by Fig. 2. Water enters the nozzles 12 and is expelled therefrom, as jets of water, into the second chamber 8 where the jets wash against the inner surface of an annular wall of the middle section 14 of the housing 2 so as to cause the propeller 3 to rotate. This in turn draws water into the first chamber 6 through the inlets 4 (not shown in detail) in the upper section of the housing.The rotating propeller blades 7 generate a high velocity stream of water which is directed downwards and out of the housing 2 through the outlet 5 where the flow of water disperses material in its path, such as sediments on the sea or river bed.

The water in the first chamber 6 forms fluid seals where the lips 23, 25 engage with the grooves 22, 24 of the hollow sleeve 9. The second chamber 8 is thus completely sealed and separate from the first chamber 6 such that the vertical fluid flow through the first chamber does not meet with the water jets from the sleeve 9.

Water in the second chamber 8 is discharged through the discharge port 20 into the lower region of the first chamber 6 where it joins the high velocity stream of water discharged downwardly from the housing. Thus power expended in pumping water down into the propeller 3 is not wasted.

Larger and/or smaller diameter nozzles may be utilised and/or caps may be used to replace, for example, two of the nozzles, so as to operate the apparatus with either low pressure and high flow rates, or high pressure and low flow rates, of fluid supplied to the nozzles. Fresh or sea water may be supplied to the nozzles at a fluid weight of between 8.3 and 8.9 p.p.g. Alternatively, drilling mud could be used.

The upper and lower bearing assemblies 16, 18 of thrust and taper bearings act to balance the rotating propeller 3 and enable the apparatus to be tilted between 900 and 0 to the horizontal and retained in this position during operation. The bearings also act to prevent unwanted oscillation of the propeller during operation.

Claims

1. Underwater excavation apparatus comprising a housing having water inlet means and water outlet means, which inlet and outlet means are in communication with a first chamber provided in said housing, and a propeller mounted for rotation within the housing so as to draw water into the first chamber through the inlet means and to generate a controlled flow of water out of the first chamber through the outlet means, wherein the propeller comprises a plurality of blades and a hollow annular sleeve which is joined to and encircles the blades, at least one of said blades having passage means in communication with an annular channel defined within said hollow annular sleeve, a plurality of fluid jet means being provided on said hollow sleeve, and fluid supply means being provided for supplying fluid under pressure to said passage means which, in turn, supply fluid to said jet means via said annular channel to cause the propeller to rotate so as to draw water into said inlet means and deliver a controlled flow of water through said outlet means for dispersing material located in the path of said flow of water.

2. Underwater excavation apparatus according to claim 1, wherein said fluid jet means are provided between adjacent blades of the propeller.

3. Underwater excavation apparatus according to claim 1 or claim 2, wherein said fluid jet means protrude into a second chamber which is defined by said hollow annular sleeve and said housing such that fluid from said jet means exhausts into said second chamber.

4. Underwater excavation apparatus according to claim 3, wherein said housing is provided with discharge means in communication with said second chamber and said outlet means such that fluid in said second chamber is discharged into the flow of water which is delivered through said outlet means.

5. Underwater excavation apparatus according to any preceding claim, wherein said hollow annular sleeve has an outer annular groove in each of an upper and a lower rim of said sleeve.

6. Underwater excavation apparatus according to claim 5, wherein said housing is provided with protruding annular lips for inter-engagement with said outer annular grooves of said hollow annular sleeve.

7. Underwater excavation apparatus according to any preceding claim, wherein said plurality of fluid jet means comprises a plurality of nozzles.

8. Underwater excavation apparatus according to claim 7, wherein one nozzle is provided between each two adjacent propeller blades where a respective opening is provided in the hollow annular sleeve.

9. Underwater excavation apparatus according to claim 7 or claim 8, wherein each nozzle has a streamlined shroud.

10. Underwater excavation apparatus according to any of claims 7 to 9, wherein said nozzles are formed and arranged so as to be removable.

11. Underwater excavation apparatus according to claim 10, wherein a series of interchangeable nozzles having various different diameters is provided for use with the apparatus.

12. Underwater excavation apparatus according to claim 10 or claim 11, wherein one or more blanking caps are provided for replacing one or more of said nozzles so as to reduce the total number of fluid jet means provided on the hollow annular sleeve.

13. Underwater excavation apparatus according to any preceding claim, wherein the propeller is mounted on a shaft and the apparatus further comprises upper and lower bearing assemblies which support the shaft above and below the propeller respectively.

14. Underwater excavation apparatus according to claim 13, wherein said upper and lower bearing assemblies each comprise load and thrust taper bearings.

15. Underwater excavation apparatus according to any preceding claim, wherein the housing is provided with outer structural braces for strengthening the housing.

16. Underwater excavation apparatus according to claim 15, wherein the outer surface of the housing has a substantially flush finish.

17. Underwater excavation apparatus substantially as herein described and with reference to Figs. 1 to 3 of the accompanying drawings.