Underwater sediment management
The present invention relates to underwater sediment management. In particular, we will describe dredging and scouring apparatus for removing sand, silt, clay and like materials from sea or river beds. There is described an apparatus comprising a body (10) having a bottom face (13, 14) and comprising an outlet flow path (28) in which is mounted propeller thrust means (29) to direct, in use, a swirling jet of water downwards towards an area of sea or river bed or the like, orientation means (48, 49) to connect said apparatus, in use, to a support means to orientate said apparatus with respect to the sea or river bed, and at least one inlet flow path (30) through which water is supplied, in use, to the propeller thrust means (29); characterised in that the inlet (30) and outlet (28) flow paths are provided with respective openings in the bottom face (13, 14) or the body. In the preferred embodiments, the inlet and outlet flow paths are parallel, but of opposite directions.
The present invention comprises to an apparatus for carrying out controlled excavation and movement of loose bed material in marine, river, lake and similar underwater environments. Modifying the underwater bed topography, by selective removal of bed material from one area and deposition in another, comes under the ambit of sediment management. The present apparatus is designed for sediment management operations, primarily, in shallow water (1-50 m water-depth).
The herein-described apparatus incorporates an embodiment of a means for dredging, scouring, excavation and cleaning, described more particularly in PCT/GB2003/005030. In the latter document the embodiment, namely a ducted-propeller, is described in more detail, together with various alternative modes of operation and means of deployment. The herein-described apparatus can be seen as providing a suspended underwater vehicle deployment means, for bring to bear the operation of the ducted-propeller.
As such, the present invention is deployable in a similar manner to the Wing Dredger described in U.S. Pat. No. 6,125,560, in terms of deployment from a floating vessel by means of suspension wires for the purpose of controlling the direction of the propeller jet(s) relative to the bed. A further similarity exists with the Wing Dredger in the design of the propeller and the duct, and in having the propeller mounted at the outlet end of the duct. However, the present invention differs from the Wing Dredger in being designed specifically for use in shallow water, in being more versatile in terms of single- and multiple-jet operation and in embracing a wholly new and novel approach to propeller jetting.
This new approach recognises and takes advantage of the fact that the jet created by the said ducted-propeller, is not simply a thrust means. Rather, it is a complex swirling flow, which includes a number of embedded vortical flow elements. The various ways in which the said swirling jet can be modified and can be used for excavation and controlled movement of bed material are described, more particularly, in PCT/GB2003/005030. Suffice it to say, swirl imbues the jet with certain behavioural characteristics, which when properly directed can be highly beneficial for a range of sediment management operations.
In its broadest sense, the present invention provides an apparatus comprising a body having a bottom face and comprising an outlet flow path in which is mounted thrust means to direct, in use, a wash of water downwards towards an area of sea or river bed or the like, orientation means to connect said apparatus, in use, to a support means to orientate said apparatus with respect to the sea or river bed, and at least one inlet flow path through which water is supplied, in use, to the thrust means; characterised in that the inlet and outlet flow paths are provided with respective openings in the bottom face of the body; in that at least a portion of the outlet flow path comprises a duct; and in that the thrust means comprises a propeller mounted within the duct.
Preferably, the inlet and outlet flow paths are parallel, but of opposite directions.
Preferably, the duct is formed with an outlet in the undersurface of a central section of the body.
Suitably, an adjustable flow regulator is provided adjacent the inlet of the inlet flow path. Typically, the flow regulator comprises a louvre assembly.
In one particular embodiment, the body is in the form of a wing having an angled face at at least one of leading and trailing edges thereof. Such face or faces may be provided by means of an additional wing profile attachment to the body.
Suitably, the apparatus is of simple box-like construction, being made from steel plate, with one ducted propeller unit per apparatus. The design is preferably such that two or more units can be easily coupled together in different configurations for multiple jetting operations. In order to be able to operate in very shallow water and yet maintain a reasonable distance from the bed, the apparatus is designed with intakes on the underside that face downwards. Provided the apparatus is initially filled with water (primed) it can continue to operate when lifted partway above the waterline, since water will continue to siphon through the body of the apparatus and into the propeller duct. Adjustable opening louvre plates over the intakes provide protection from ingress of debris and also a means for preventing rotation of the apparatus (countering the propeller torque) when operating in single-jetting mode. More importantly, they also provide a means for controlling the rate of water flow through the propeller duct.
The propeller is driven by a high-pressure hydraulic motor, which is located axially within the duct. The use of a hydraulic motor is an integral part of the overall design of the apparatus, since it enables a very compact and light-weight construction (compared to the aforementioned Wing Dredger) and also provides for variable speed and direction control over propeller rotation. The apparatus can also be more easily fitted with the means to modify the behaviour of the jet: to create a straight-sided or wide-angle jet, as required.
The above and other aspects of the present invention will now be described by way of example only and with reference to the accompanying drawings, in which:
FIGS. 10 to 13 shows various ways in which the apparatus can be suspended from a vessel and various ways in which multiple units can be coupled together.
To provide added stiffness to the construction, as shown in
Reference to
Various attachment points are provided on the outside of the tank, as indicated in
Referring to
Also on the top of the tank and attached to top plate 13 by means of multiple bolts, is a circular plate 25. Circular plate 25, when removed, gives access to the inside of the tank for the purpose of removing the propeller duct unit. The circular opening in top plate 13 that is covered by circular plate 25 is, therefore, slightly larger in diameter than the widest lateral dimension of the propeller duct. Circular plate 25 is fitted with a rubber gasket designed to effect an air-tight seal.
Also formed centrally in circular plate 25 are three circular openings set out in triangular fashion, which provide penetrations for the three hydraulic hoses that connect to the motor (two high-pressure power hoses and one low-pressure casing drain hose). Split flanges 26, formed of rigid plastic, and bolted to circular plate 25 over each opening, encircle each hose and provide an air-tight seal where the hoses enter the tank. Split flanges 26 also serve to secure the hoses at the point of entry to the tank, thus preventing any risk of chaffing of the hoses against metal edges. Split flanges 26 can be more clearly seen in
Completing the appurtenances on the top of the tank, as shown in
Referring to
Located either side of the propeller duct outlet 28, are two water intakes 30. These are rectangular in shape and are of such a size that one on its own would provide for unhindered flow of water into the propeller duct, when the propeller is rotating at full speed. Attached to the bottom plate 14 and extending vertically over each opening are three thick metal grill plates 31. These are designed to prevent large items of debris, or obstructions sticking up from the seabed, from penetrating the intakes. They are also designed to take the weight of the apparatus when the latter is placed on-deck or onto a hard-standing surface. If the apparatus were to be placed on a soft surface, wooden sleepers would be used to prevent the grill plates from penetrating into the surface.
Referring to
When the louvre plates are lying flat (
It should be noted that the louvre plates are set in such a way that they face in opposing directions over each intake. While this is of little consequence when the plates are fully closed or fully open, it will be appreciated that with the louvre plates at intermediate positions (
Lastly, in referring to
Reference to
Motor 37 is supported axially within the duct by means of collar 40 to which the motor is secured by a ring of axial bolts, and the collar is secured to the inside of the duct by means of angled fin plates 41. The fin plates are vertically set in order to present a limited surface area to the direction of flow and their edges are also chamfered to further minimise flow obstruction There are five supporting fin plates 41, equally spaced; this number being purposely chosen to provide both a rigid axial support to the motor and an non-equal or non-multiple of the propeller blade number (four-bladed propeller): the latter being good engineering practise in terms of ducted propeller design. The arrangement of the fin plates can be better seen in horizontal section, in
The motor can be seen to taper downward at its front end, forming a smooth transition with the hub of the propeller 29. The smooth profile of the motor and propeller hub matches the shape of the duct, giving a uniform width of annulus between the motor and the duct.
The duct, complete with motor, can be detached from the tank and removed through the top of the tank. The duct has three rings 42 welded around its outer circumference. These are designed, partly, to maintain the ovality of the duct both during and following fabrication. The uppermost ring also gives added stiffness to the duct at the point of fixity of the angled motor support fin plates, while the lowermost ring also acts as a seating flange when the duct is installed into the tank. This lowermost ring has two holes drilled into it that act as stabbing guides for pegs 43 (indicated by small arrows) that stick up from a landing flange 44 on the bottom of the tank. The two upper rings also have holes drilled in them to enable the duct to be rigidly secured on either side to the central vertical bulkhead plate 45. Angled brackets 46, in pairs, provide the means for bolting the propeller duct to the bulkhead plate and can be seen in
Also visible in
Lastly, in referring to
The workings of the apparatus will now be briefly described by reference to
Since all other points of ingress for water into the tank are sealed, the louvre plates provide an effective means for regulating (i.e. reducing) the flow of water through the propeller duct for any given speed of rotation of the propeller. The main reason for wanting to reduce the flow of water through the propeller duct is that the axial velocity of the jet is reduced compared to its swirl velocity and so the Jet Swirl Number is increased (see PCT/GB2003/005030 for a more detailed description of Jet Swirl Number). In propeller design parlance, a decrease in flow through the propeller disc is referred to as a reduction in propeller advance coefficient (J). One of the significant effects of this (as described more particularly in PCT/GB2003/005030) is that the behaviour of the jet is changed, making it more susceptible to breakdown.
When starting the apparatus in very shallow water an initial priming action may be necessary, which is illustrated in
Normal jetting, once established, can continue even with much of the tank out of the water, because the propeller creates sufficient suction head for water to siphon into the propeller duct. The fact that the intakes are placed on the underside of the tank also means that there is less likelihood of air being sucked in via a drain-hole vortex. Clearly, for this siphonic action to work effectively the emergent top of the tank has to be fully air-tight.
For most operations, where simple jetting of the bed is required, the apparatus would be suspended by one or two pairs of wires from a crane, or A-frame, mounted on a support vessel. FIGS. 10 to 13 show a number of possible support options, together with various ways in which several single-jet units can be coupled together to form multiple units. In
Single unit operation is intended primarily for pipeline (or cable) jetting work. For instance, where a pipeline laid on the seabed is required to be lowered below the bed for the purpose of increased protection. The ability to tilt the apparatus sideways is important, since by directing the tilted jet just under the pipe as the unit traverses along and adjacent to the line of the pipe, material can be displaced to the far side of the pipe to form a levee stockpile. The same material can then be used to backfill the trench by jetting from the opposite side with the jet tilted towards the stockpile and the trench. Note that a significant advantage of this jetting equipment over conventional pipeline ploughing equipment is that there is no mechanical contact with the pipe.
In
A double in-line unit (or indeed a triple in-line unit, as shown in
Finally,
Advantages of the apparatus for the present invention include:
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- 1. An improved ability (compared to U.S. Pat. No. 6,125,560) to operate in shallow water for the purposes of carrying out underwater jetting excavation and movement of bed material. Said ability being achieved by means of a short propeller duct, housed inside an air-tight tank, with the primary water intakes on the underside of the tank and with the ability to carry out an initial priming operation wherein the propeller is reversed to induce filling of the tank.
- 2. An improved ability and greater versatility to operate in single- and multiple-jetting configurations, by coupling single jetting units together.
- 3. An improved ability to control and regulate the velocity of flow through the propeller duct and at its outlet end for the purpose of modifying the behaviour of the jet. Said control being-exercised by adjusting the degree of opening of the louvre plates, which function like one-way valves.
- 4. An ability, stemming from point 3 and the use of various attachments (as discussed in PCT/GB2003/005030), to carry out very rapid excavation in a wide range of loose bed materials, with the attendant directional movement of the excavated material over long distances (100 m's).
- 5. An ability, also stemming from point 3 and the use of various attachments (as discussed in PCT/GB2003/005030), to carry out excavation (albeit at a slower rate) in stiff clay materials that are otherwise not amenable to excavation by means of low-pressure water jetting.
- 6. An ability, equal with U.S. Pat. No. 6,125,560 to operate the apparatus from a support vessel by means of a wire suspension system wherein the attitude of the apparatus can be adjusted in terms of both pitch and roll. Said capability being used for the purpose of sideways displacement of material (such as for pipeline jetting) and for forward displacement of material (such as for pre-sweeping and sediment management operations).
- 7. An added benefit, further to point 3, that the said louvre plates also provide a means for preventing access of debris into the propeller duct.
- 8. An added benefit, further to point 3 and point 7, that the said louvre plates when half open also provide a means for preventing rotation of the apparatus by countering the turning moment induced by the propeller.
- 9. The added benefit, further to point 7, wherein thick grill plates over the intakes protect from ingress of coarse debris and penetration of seabed obstructions. Said grill plates also provide a means for supporting the apparatus when not in use.
- 10. A simple body shape that is strong, light-weight and functional (in terms of forming an air-tight sealed tank), that is, in effect, self-cleaning by having a hopper-like base form, that has attachment points strategically placed to enable the body to be suspended from wires and chains and coupled to like bodies in different configurations for the purpose of multiple jetting.
- 11. A simple means for installing and removing the propeller duct, i.e. for maintenance purposes, and to enable said propeller duct to be used in other propeller jetting embodiments (as described in PCT/GB2003/005030).
- 12. The added benefit, further to the self-cleaning ability noted in claim 10, of using the priming action, noted in point 1, as a further means for cleaning (back-washing) the inside of the tank.
Claims
1. An apparatus comprising a body having a bottom face and comprising an outlet flow path in which is mounted thrust means to direct, in use, a wash of water downwards towards an area of sea or river bed or the like, orientation means to connect said apparatus, in use, to a support means to orientate said apparatus with respect to the sea or river bed, and at least one inlet flow path through which water is supplied, in use, to the thrust means; characterised in that the inlet flow path and outlet flow path are provided with respective openings in the bottom face of the body; in that at least a portion of the outlet flow path comprises a duct; and in that the thrust means comprises a propeller mounted within the duct.
2. An apparatus as claimed in claim 1 wherein the inlet and outlet flow paths are parallel, but of opposite directions.
3. An apparatus as claimed in claim 1 wherein the duct is formed with an outlet in the undersurface of a central section of the body.
4. An apparatus as claimed in claim 1 wherein an adjustable flow regulator is provided adjacent the inlet of the inlet flow path.
5. A apparatus as claimed in claim 4 wherein the flow regulator comprises a louvre assembly.
6. An apparatus as claimed in claim 1 wherein the body is in the form of a wing having an angled face at at least one of the leading and trailing edges thereof.
Type: Application
Filed: Jan 26, 2004
Publication Date: Jul 13, 2006
Inventor: John Redding (Lamberhurst)
Application Number: 10/542,710
International Classification: E02F 3/88 (20060101);