GB2538974A

GB2538974A - Underwater excavation apparatus

Info

Publication number: GB2538974A
Application number: GB1509446.9A
Authority: GB
Inventors: F Whyte Alex
Original assignee: Individual
Current assignee: Individual
Priority date: 2015-06-01
Filing date: 2015-06-01
Publication date: 2016-12-07
Anticipated expiration: 2035-06-01
Also published as: GB2538974B; GB201509446D0

Abstract

An underwater excavation apparatus comprising a first chamber 13, a second chamber 15 in fluid communication with the first chamber and an impeller 7 which draws water into the first chamber via the second chamber and generates a flow out of the apparatus. The second chamber is configured to redirect water as it passes through the second chamber to counteract torque produced by the impeller. The second chamber may surround the first chamber. The second chamber may comprise one or more guides 23 located on inner and outer walls of the second chamber. The guides may comprise of elongated members which may follow a helical path. The guides may comprises one or more grooves. The guides may be oriented in an opposite sense or direction to the blades of the impeller. The second chamber may have one or more inlets 3 and outlets 21. A hydraulic motor 9 may be connected to the impeller. The impeller may draw water directly into the first chamber. Guide vanes 11 may be located between the one or more inlets to the first chamber. The apparatus may be of a modular structure and comprise a nozzle which provides an outlet from the first chamber.

Description

1 Underwater Excavation Apparatus 3 The present invention relates to the field of underwater excavation. More specifically, the 4 present invention concerns improvements to excavation apparatus that enhances the stability of such apparatus in use.

7 Background to the invention

9 Underwater excavation apparatus may be employed, for example, to create a trench or to unbury pipelines and cables by displacing material from the seabed such as sand and 11 rocks. This displacement is generally achieved by generating a high volume but low 12 pressure flow of water or conversely a low volume but high pressure flow of water, and 13 directing the flow of water at the region to be excavated. By suspending the apparatus 14 from a vessel, a trench can be created or pipelines and cables unburied by advancing the vessel while generating said water flow.

2 In some arrangements, the orientation of the apparatus may be controlled by lowering a 3 pair of clump weights on cables from the vessel, then lowering the apparatus along the 4 clump weight cables. As the ship advances, the clump weights serve to prevent the apparatus from twisting although some degree of twisting is still likely to occur due to 6 reactive torque.

8 In other arrangements, such as disclosed in US2010/043256 in the name of Rotech 9 Holdings Limited, a dual-impeller arrangement in a Y-or T-shaped body is used to overcome the reactive torque issues associated with single impeller systems. This 11 particular document also discloses that one or more thrusters can be provided to 12 counteract reactive torque in addition to steering the apparatus.

14 Another arrangement, such as disclosed in GB2297777 in the name of Hollandsche Beton Groep N.V., employs a pair of coaxial impellers which are driven in contrary rotating 16 directions such that the torque produced by one impeller tends to counteract the torque 17 produced by the other impeller.

19 Known seabed excavation apparatus rely upon complex and/or often unreliable arrangements to maintain stability and orientation during operation. Accordingly, it is an 21 object of at least one aspect of the present invention to provide an alternative underwater 22 excavation apparatus which employs a simpler and/or more reliable arrangement to 23 maintain stability and orientation during operation.

Further aims and objects of the invention will become apparent from reading the following

26 description.

1 Summary of the invention

3 According to a first aspect of the invention, there is provided an underwater excavation 4 apparatus comprising; a first chamber; 6 a second chamber in fluid communication with the first chamber; and 7 an impeller which draws water into the first chamber via the second chamber and 8 generates a water flow out of the apparatus; 9 wherein the second chamber is configured to redirect water as it passes through the second chamber to counteract reactive torque produced by the impeller.

12 The above invention provides a means to counteract torque acting on the apparatus due to 13 rotation of the impeller. By redirecting water as it passes through the second chamber, a 14 torque of the opposite sense can be imparted to the apparatus which results in at least a reduction -if not cancellation -of the net reactive torque acting on the apparatus.

17 Preferably, the first chamber may be cylindrical and the second chamber may be annular 18 and may surround the cylindrical first chamber. In this case, the first and second chamber 19 may be termed inner and outer chambers.

21 Preferably, the second chamber may comprise one or more guides. One or more guides 22 may be located on an inner wall of the second chamber. Alternatively, or additionally, one 23 or more guides may be located on an outer wall of the second chamber. Optionally, the 24 second chamber may comprise a plurality of guides.

26 Most preferably, the one or more guides may comprise one or more elongate members.

27 Preferably, the one or more elongate members may extend substantially from an upper 28 end of the second chamber to a lower end of the second chamber. Advantageously, the 29 one or more elongate members may follow a helical path within the second chamber.

Preferably, the one or more guides may comprise a plurality of elongate members which 31 may follow helical paths within the second chamber.

33 Additionally, or alternatively, the one or more guides may comprise one or more grooves.

34 Similarly, the one or more grooves may be located on an inner wall of the second 1 chamber. Alternatively, or additionally, the one or more grooves may be located on an 2 outer wall of the second chamber.

4 In any case, the one or more guides may extend radially between an inner wall of the second chamber and an outer wall of the second chamber to define flow paths through the 6 second chamber.

8 Preferably, the one or more guides are oriented in an opposite sense or direction to blades 9 of the impeller. In this case, fluid flow through the second chamber is in the same direction as through the first chamber, i.e. downwards. Alternatively, the one or more guides are 11 oriented in the same sense or direction to blades of the impeller. In this case, fluid flow 12 through the second chamber is in the opposite direction as through the first chamber, i.e. 13 upwards.

Preferably, the apparatus may comprise one or more inlets to the second chamber and 16 may comprise outlets from the second chamber to the first chamber. Preferably, the one 17 or more inlets may be provided in an outer wall of the second chamber and the one or 18 more outlets may be provided in an inner wall between the second chamber and the first 19 chamber.

21 Preferably, the one or more inlets may be located above the one or more outlets, i.e. 22 relatively higher so that the direction of water flow through the second chamber is in a net 23 downwards direction. Alternatively, the one or more inlets may be located below the one 24 or more outlets, i.e. relatively lower so that the direction of water flow through the second chamber is in a net upwards direction.

27 Optionally, the apparatus may comprise a single cast impeller. Optionally, the apparatus 28 may comprise a hydraulic motor. Optionally, the hydraulic motor is directly connected to 29 the impeller. Optionally, the apparatus comprises one or more inlets to the first chamber, which may be located towards an upper end of the apparatus, in which case the impeller 31 may also draw water directly into the first chamber. Optionally, the apparatus comprises 32 guide vanes located between the one or more inlets to the first chamber and the impeller.

34 Optionally, the apparatus further comprises one or more agitation lances which may be configured to produce high pressure water flows.

2 Preferably, the apparatus comprises a modular structure. Optionally, a module of the 3 apparatus comprises the inner wall and/or the outer wall of the second chamber and one 4 or more guides of the second chamber. Optionally, a module of the apparatus comprises a nozzle which provides an outlet from the first chamber.

7 In a preferred embodiment of the first aspect of the invention, the apparatus may comprise 8 an inner wall and may comprise an outer wall, the first chamber may be bounded by the 9 inner wall and the second chamber may be bounded by the outer wall and the inner wall, the outer wall may comprise one or more inlets to the second chamber and the inner wall 11 may comprise one or more outlets from the second chamber to the first chamber, and the 12 second chamber may comprise rifling, which may be provided by a plurality of guides 13 located in the second chamber, which may impart a helical or rotational flow component to 14 water flowing through the second chamber, which may act to counteract reactive torque which may be produced by rotation of the impeller.

17 According to a second aspect of the invention there is provided an underwater excavation 18 apparatus comprising a vortex chamber configured to redirect at least a portion of water 19 flow through the apparatus to counteract reactive torque produced by an impeller of the apparatus.

22 The vortex chamber may be configured to redirect at least a portion of water flow through 23 the apparatus in an opposite sense or direction to a flow of water generated by the 24 impeller. Preferably, the vortex chamber may be configured to redirect at least a portion of water through the apparatus in a helical manner.

27 Embodiments of the second aspect of the invention may comprise features corresponding 28 to the preferred or optional features of the first aspect of the invention or vice versa. For 29 example, the vortex chamber may comprise one or more features of the second chamber of the first aspect of the invention, or vice versa.

32 According to a third aspect of the invention there is provided a method of stabilising an 33 underwater excavation apparatus, comprising redirecting at least a portion of water flow 34 through the apparatus so as to counteract reactive torque produced by an impeller of the apparatus.

2 Embodiments of the third aspect of the invention may comprise features corresponding to 3 the preferred or optional features of the first or second aspects of the invention or vice 4 versa.

6 According to a fourth aspect of the invention there is provided a method of underwater 7 excavation or a method of using an underwater excavation apparatus, comprising 8 providing an underwater excavation apparatus according to the first aspect.

Optionally, the method comprises redirecting at least a portion of water flow through the 11 apparatus so as to counteract reactive torque produced by an impeller of the apparatus.

13 Optionally, the method may comprise lowering the apparatus towards the seabed from a 14 vessel, may also comprise generating a substantially vertical column of water to displace materials from the seabed, and may further comprise moving the vessel.

17 Optionally, the method may be employed for one or more of the following; pipeline, cable 18 and/or umbilical burial, deburial and/or freespan correction; sandwave clearance, levelling 19 and/or lowering; rock dump dispersal, inspection access and/or repairs; harbour clearance and/or maintenance; drill cuttings and/or debris burial; spud can cleaning and/or mud 21 removal; salvage for recovery and/or diver access; seabed or surface clearance, levelling 22 and/or preparation for subsea structures; and creating access for cutting manipulators 23 and/or inspection.

Embodiments of the fourth aspect of the invention may comprise features corresponding to 26 the preferred or optional features of the first, second or third aspects of the invention or 27 vice versa.

29 According to a further aspect of the invention, there is provided an underwater excavation apparatus substantially as described herein with reference to the accompanying drawings.

32 Likewise, according to another aspect of the invention, there is provided a method of using 33 an underwater excavation apparatus substantially as described herein with reference to 34 the accompanying drawings.

1 Brief description of the drawings

3 Aspects and advantages of the present invention will become apparent upon reading the 4 following detailed description and upon reference to the following drawings (like reference numerals referring to like features) in which: 7 Figure 1 illustrates an underwater excavation apparatus according to an aspect of the 8 present invention; Figure 2 illustrates an exploded view of the underwater excavation apparatus of Figure 1, 11 shown in (a) solid form and (b) partially transparent form; and 13 Figure 3 illustrates in more detail an inner component of the underwater excavation 14 apparatus of Figure 1.

1 Detailed description of preferred embodiments

3 As discussed in the background to the invention above, known underwater excavation 4 apparatus rely upon complex and often unreliable arrangements to maintain stability and orientation during operation. An embodiment of the present invention is illustrated in 6 Figures 1 to 3 and provides an alternative arrangement in an attempt to overcome these

7 problems with the prior art.

9 An underwater excavation apparatus 1 is shown in assembled view in Figure 1. Exploded views in Figure 2 show more detail of the components of the apparatus, which may be 11 assembled in a modular manner, with the partially transparent views in Figure 2(b) 12 showing additional detail. Figure 3 shows more detail of an inner component of the 13 apparatus which serves to stabilise the apparatus in use.

The apparatus 1 comprises a number of inlet ports 3 which allow water to be drawn into 16 the apparatus 1 when in use. The apparatus also comprises a nozzle having an outlet port 17 5 through which the water exits the apparatus 1. A single, cast impeller 7 is mounted 18 within the apparatus 1 with its axis of rotation coaxial with an axis through the centre of the 19 apparatus 1. The apparatus 1 generates a low pressure, high volume, vertical water column directed towards the seabed.

22 In this particular embodiment, the impeller may be rotated at a speed of 300 rpm to 23 produce a flow rate of 5600 Vs. The vertical water column exits the apparatus at 6.5 m/s.

24 The apparatus 1 may be operated at depths of between 2.5 m to over 500 m.

26 Rotation of the impeller 7 is achieved by hydraulic motor 9 which is directly connected to 27 the impeller 7. Fixed guide vanes 11 are disposed between the hydraulic motor 9 and the 28 impeller 7.

The impeller 7 and guide vanes 9 are housed within a cylindrical inner chamber 13, which 31 itself is surrounded by an annular outer chamber 15. The outer chamber 15 is bounded by 32 an inner wall 17 and an outer wall 19. The inlets 3 described above are located in the 33 outer wall 19 and act as inlets to the outer chamber 15. Outlets 21 are located in the inner 34 wall 17 (see Figure 3). The outlets 21 are located relatively lower than the inlets 3 such that flow through the outer chamber 15 is in a net downwards direction.

2 Located on the inner wall 17 (although they could equally be located on the outer wall 19, 3 both walls 17 and 19, or even free-standing) are three inlet guides 23 which are formed by 4 elongate plates which extend from the top of the inner wall 17 to the bottom of the inner wall 17. The inlet guides 23 follow a helical path along the inner wall 17. The inlet guides 6 23 extend radially from the inner wall 17 towards the outer wall 19, and are of sufficient 7 radial extent to contact or at least approach the outer wall 19. In this way, flow paths are 8 defined through the outer chamber 15. It will of course be understood that guides of lesser 9 radial extent may still influence fluid flow sufficiently to impart a useful reactive torque.

11 When the apparatus 1 is in use, the impeller 7 draws water into the apparatus through the 12 inlets 3, through the outer chamber 15, and into the inner chamber 13 through outlets 21.

13 The inlet guides 23 serve to redirect the flow of water through the outer chamber 15 in a 14 helical manner. The inlet guides 23 are oriented in the opposite direction from the blades of the impeller 7.

17 The effect of redirecting the flow of water through the outer chamber 15 in a helical 18 manner as described above is to exert a reactive torque force on the apparatus 1.

19 However, a reactive torque force is also exerted on the apparatus 1 as a result of the rotation of the impeller 7. As the inlet guides 23 are oriented in the opposite direction from 21 the blades of the impeller 7, the reactive torque forces act contrary to one another.

23 Accordingly, the provision of the outer chamber 15 acts to stabilise the excavation 24 apparatus 1 when in use. Without the outer chamber 15 and the inlet guides 23 disposed therein, the reactive torque caused by rotation of the impeller 7 would cause the apparatus 26 1 to turn in the opposite direction.

28 The outer chamber 15 may be referred to as a vortex chamber or a stabilising chamber.

29 The inlet guides 23, or the provision of such inlet guides 23, may be referred to as rifling, and the outer chamber 15 may be referred to as being rifled. It will be understood that the 31 rifling of the outer chamber may be provided by other arrangements such as grooves or 32 slots provided on an outer surface of the inner wall and/or an inner surface of the outer 33 wall. A combination of guides and slots may be provided to improve effectiveness.

34 Alternatively, while the above-described embodiment employs three inlet guides, it will be 1 appreciated that a single inlet guide which extends around the outer chamber may be 2 provided, or indeed any number of inlet guides.

4 Any such arrangement or combination of arrangements may be provided. It is however required that a helical or similar rotational flow direction is imparted to the water being 6 drawn through the chamber to counteract the reactive torque resulting from rotation of the 7 impeller.

9 Of course, the relative vertical positions of the inlets 3 and outlets 21 could be changed such that the outlets 21 are located relatively higher than the inlets 3 such that flow 11 through the chamber 15 is in a net upwards direction. In such an arrangement, the 12 orientation of the inlet guides 23 (or whichever manner of rifling is employed in the outer 13 chamber) should also be reversed such that the correct helical or rotational flow direction 14 is imparted to counteract the reactive torque resulting from rotation of the impeller.

16 In such an arrangement the inlet guides would be oriented in the same direction as the 17 blades of the impeller (as the flow through the chamber will be in the opposite direction to 18 the flow through the impeller). This arrangement may also be employed to reduce the 19 effective upthrust on the apparatus.

21 Additional inlets 33 to the inner chamber 11 are provided at an upper end of the apparatus 22 1 such that the size of the inlets 3 and outlets 21 and the capacity of the outer chamber 15 23 do not unduly restrict the volume of water which the apparatus 1 can direct towards the 24 seabed or other surface to be excavated or object to be unburied. The guide vanes 9 assist in reducing turbulence within the inner chamber 11. It will of course be understood 26 that an apparatus according to the invention may not include such additional inlets in 27 which case rather than just a portion of water flow, the entire water flow through the 28 apparatus passes through the outer chamber 15.

It will also be appreciated that while the apparatus 1 has been described as having an 31 inner chamber which houses an impeller and an outer chamber which houses a stabilising 32 arrangement, the outer chamber could house an appropriate impeller and the inner 33 chamber could house the stabilising arrangement without deviating from the scope of the 34 invention. The key consideration is the provision of a chamber in which water flow is 1 redirected in a manner which counteracts the reactive torque acting on the apparatus due 2 to rotation of the impeller.

4 As noted above, the apparatus 1 may be constructed in a modular manner. Accordingly, the component illustrated in Figure 3 may be exchanged for a similar component of a 6 different arrangement. Likewise, any other component of the apparatus 1 may be 7 exchanged for a similar component of a different arrangement. For example, a lower 8 module of the apparatus 1 comprising the outlet 5 may be exchanged for a similar module 9 having a larger or smaller outlet to alter the velocity of the vertical water column.

11 Of course, the modular approach may simply permit maintenance or replacement of 12 damaged parts as and when required without requiring construction of a completely new 13 apparatus.

The apparatus 1 is shown as including optional agitation lances 35 which provide relatively 16 high pressure water flows, for example to break up harder materials which can then be 17 removed by the water column produced through outlet port 5. The agitation lances 35 are 18 supplied with water from a top side water pump system (not shown).

An apparatus according to the invention may be used for pipeline, cable and/or umbilical 21 excavation, burial and deburial. It may also be used to prepare habitats for subsea 22 structures. Additional applications include; freespan correction of pipelines, cables and/or 23 umbilicals; sandwave clearance, levelling and lowering; rock dump dispersal, inspection 24 access and repairs; harbour clearance and maintenance; drill cuttings and debris burial; spud can cleaning and mud removal; salvage for recovery and diver access; seabed 26 preparation for jack-ups and multiple subsea structures; and seabed levelling, creating 27 access for cutting manipulators and inspection.

29 The apparatus may also be used to safely unbury unexploded ordinance for subsequent removal and/or defusing.

32 The invention provides an underwater excavation apparatus with a chamber which 33 enhances the stability of such apparatus when in use. Water is drawn through the 34 chamber and reactive torque produced by an impeller of the apparatus is counteracted by redirecting the flow of water through the chamber. The water may be redirected by one or 1 more helical members located within the chamber which imparts a resulting torque of an 2 opposite sense to that generated by the impeller. The net reactive torque acting on the 3 apparatus can therefore be reduced or eliminated.

As used herein, the terms bottom, lower, below and the like are descriptive of a feature 6 that is located towards a first end/side of an apparatus, system or component while the 7 terms top, upper, above and the like are descriptive of a feature that is located towards a 8 second, opposing end/side of the apparatus, system or component.

References to the seabed or similar shall not be construed as limiting the invention or its 11 use to subsea operations; it will be understood that the invention may find utility in any 12 underwater setting.

14 Throughout the specification, unless the context demands otherwise, the terms 'comprise' or 'include', or variations such as 'comprises' or 'comprising', 'includes' or 'including' will be 16 understood to imply the inclusion of a stated integer or group of integers, but not the 17 exclusion of any other integer or group of integers.

19 Various modifications to the above-described embodiments may be made within the scope of the invention, and the invention extends to combinations of features other than those 21 expressly described herein.