Abstract:
An improved underwater excavation apparatus achieves efficiency and control of movement through provision of a hollow body having at least one inlet and at least one outlet, at least one pair of impellers coaxially displaced one from the other and rotatably mounted in the hollow body, and a mechanism for driving the impellers in contrary rotating directions. The underwater excavation apparatus comprises a pair of horizontally opposed inlets communicating with a single outlet, the outlet being disposed vertically downwards substantially midway between the two inlets, in use. The excavation apparatus may, therefore, be substantially “T” or “Y” shaped. The mechanism for driving the impellers may include at least one drilling motor.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to an improved excavation apparatus, and in particular to an improved underwater excavation apparatus. 
     Underwater excavation apparatus are known, eg, from GB 2 240 568 (CONSORTIUM RESOURCE et al). In that disclosure there is described. an underwater excavation apparatus comprising a hollow body with an inlet to receive water and an outlet for discharge of water. A propeller is rotatably mounted in the hollow body to draw water through the inlet and deliver a flow 6f water through the outlet. Water jets on the propeller tips rotate the propeller when water is supplied to the jets. 
     Such rotation causes water to be drawn into the body through the inlet and expelled from the body as a flow through the outlet. The flow can be used to displace material on the seabed. 
     Known prior art underwater excavation apparatus suffer from a number of problems/disadvantages, for example: 
     (a) Low energy efficiency due to e.g. hydrodynamic limitations of fluid jets, thus requiring extremely large and power hungry pumps to drive the system); 
     (b) tendency of apparatus to rotate in reaction to rotation of the propeller; 
     (c) difficulty in steering and positioning of the apparatus. 
     SUMMARY OF THE INVENTION 
     It is an object of at least some of the aspects of the present invention to seek to obviate or mitigate one or more of the aforementioned problems in the prior art. 
     According to a first aspect of the present invention there is provided an underwater excavation apparatus comprising a hollow body having at least one inlet and at least one outlet, at least one pair of impellers rotatably mounted in the hollow body and means for driving the impellers. 
     Advantageously, the driving means cause the impellers to be driven in contrary rotating directions, in use. 
     The at least one inlet may be inclined at an angle to an axis along which the at least one outlet is provided. 
     Preferably, there is provided at least one pair of inlets. 
     Preferably, the at least one pair of inlets are substantially symmetrically disposed around an axis extending from the outlet. 
     In one embodiment the underwater excavation apparatus comprises a pair of horizontally opposed inlets communicating with a single outlet, the outlet being disposed vertically downwards substantially midway between the two inlets, in use. In this case, the excavation apparatus is, therefore, substantially “T” shaped in profile. 
     In an alternative embodiment the underwater excavation apparatus comprises a pair of inlets communicating with a single outlet, the inlets being substantially symmetrically disposed around an axis extending from the outlet, the outlet being disposed vertically downwards substantially midway between the two inlets, in use. In this case, the excavation apparatus is, therefore, substantially “Y” shaped in profile. 
     Advantageously, the outlets are each spaced/inclined substantially 45° from the axis extending from the outlet. 
     At least one impeller may be provided within/adjacent each inlet. 
     The means for driving the/each impeller(s) may include at least one drilling motor. 
     The at least one drilling motor may comprise a stator and a rotor rotatably mounted in the stator, the stator being provided with a rod recess and an exhaust port, the rotor being provided with a rotor channel and at least one channel for conducting motive fluid from the rotor channel to a chamber between the rotor and the stator, the rod recess being provided with a rod which, in use, forms a seal between the stator and the rotor. 
     Although not essential it is highly desirable that the rotor be provided with a seal for engagement with the stator. 
     Preferably, the seal is made from a material selected from the group consisting of plastics materials, polyethylethylketone, metal, copper alloys and stainless steel. 
     Advantageously, the rod is made from a material selected from the group consisting of plastics materials, polyethylethylketone, metal, copper alloys and stainless steel. 
     Preferably, the stator is provided with two rod recesses which are disposed opposite one another, and two exhaust ports which are disposed opposite one another, each of the rod recesses being provided with a respective rod, the rotor having two seals which are disposed opposite one another. 
     The drilling motor may advantageously comprise two drilling motors arranged with their respective rotors connected together each motor comprising a stator and a rotor rotatably mounted in the stator, the stator being provided with a rod recess and an exhaust port, the rotor being provided with a rotor channel and at least one channel for conducting motive fluid from the rotor channel to a chamber between the rotor and the stator, the rod recess being provided with a rod which, in use, forms a seal between the stator and the rotor. 
     Preferably, the drilling motors are connected in parallel, although they could be connected in series if desired. 
     Advantageously, the drilling motors are arranged so that, in use, one drilling motor operates out of phase with the other. Thus, in a preferred embodiment each drilling motor has two chambers and the chambers in the first drilling motor are 90° out of phase with the chambers in the second drilling motor. Similarly, in an embodiment in which each drilling motor has four chambers, the chambers in the first drilling motor would preferably be 45° out of phase with the chambers on the second drilling motor. This arrangement helps ensure a smooth power output and inhibits stalling. 
     Alternatively, the at least one drilling motor may be a “Moineau”, hydraulic or a suitably adapted electric motor. 
     The impellers may be driven by means of a gearbox or by exploitation of the opposing reactive torque on a drive body of the motor. 
     When the reactive torque upon the motor body is utilised, at least one impeller may be connected to an output shaft of said motor, while at least one other impeller may be connected to the motor body. 
     Alternatively the impellers may be driven by a pair of motors operating in opposite directions. In such case said motors and impellers are balanced and equal. 
     The underwater excavation apparatus may further comprise an agitator device having mechanical disturbance means and fluid flow disturbance means. 
     The underwater excavation apparatus may, in use, be suspended from a surface vessel or mounted upon a sled of the type currently known for use in subsea excavation operations. 
     According to a second aspect of the present invention there is provided an underwater apparatus comprising a hollow body having a pair of inlets communicating with an outlet, at least one pair of impellers rotatably mounted in the hollow body and means for driving the impellers, the inlets being substantially symmetrically disposed around an axis extending from the outlet, wherein the inlets are not horizontally opposed to one another. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: 
     FIG. 1 shows a cross-sectional side view of a first embodiment of an excavation apparatus according to the present invention; 
     FIG. 2 shows a longitudinal cross-sectional view of one embodiment of a drilling apparatus for use in the excavation apparatus in FIG. 1 according to the present invention; 
     FIGS. 3A-3D are cross-sectional views along line A—A of FIG. 2 showing a rotor of the motor in four different positions; and 
     FIGS. 4A-4D are cross-sectional views along line B—B of FIG. 2 showing the rotor in four different positions. 
     FIG. 5 shows a cross-sectional side view of a second embodiment of an excavation apparatus according to the present invention; 
     FIG. 6 shows a cross-sectional side view of a third embodiment of an excavation apparatus according to the present invention. 
    
    
     DETAILED DESCRIPTION OF INVENTION 
     Referring to FIG. 1, there is shown a first embodiment of an underwater excavation apparatus  300   a  according to the present invention. The apparatus  300   a  comprises a hollow body  370   a  formed from a pair of horizontally opposed inlet ducts  371   a  and an outlet duct  373   a , a drive motor  310   a  and a pair of impellers  335   a ,  340   a.    
     The apparatus  300   a  is further provided with deflection baffles  302   a  within the hollow body  370   a , suspension brackets  306   a  to enable the apparatus  300   a  to be suspended from a surface vessel, guide vanes  386   a  to regulate the flow of fluid past the impellers  335   a ,  340   a , and safety grids  385   a  to seek to prevent the ingress of solid matter which may damage the impellers  335   a ,  340   a.    
     In this first embodiment, the drive motor  310   a  is provided along an axis common to the horizontally opposed inlet ducts  371   a  and impellers  335   a ,  340   a . An output shaft  330   a  of the motor  310   a  is connected to a first impeller  335   a  while the second impeller  340   a  is attached to a shaft  342   a  connected via a swivel  325   a  to an outer housing of the drive motor  310   a.    
     In use, motive fluid is supplied to the motor  310   a  via fluid inlet  308   a  which in turn causes the output shaft  330   a  and impeller  335   a  to rotate. Reactive torque from this rotation causes the outer housing of the drive motor  310   a  to rotate in a direction opposite to that of the output shaft  330   a . This in turn results in the rotation of the second impeller  340   a . The impellers  335   a ,  340   a  are configured such that, despite rotating in opposite directions, they each provide an equal flow rate of water into the hollow body  370   a . Water drawn into the hollow body  370   a  thus is directed via the deflection baffles  302   a  through the outlet duct  373   a  and towards the seabed  400   a.    
     The shaft  342   a  and swivel  325   a  may, in an alternative embodiment, be replaced by a second motor which directly drives the impeller  340   a , as hereinbefore described with reference to FIG.  5 . 
     The excavation device  300   a  may be suspended, for example, from the bow or stern of a surface vessel, or through a moonpool of a dedicated subsea operations vessel. 
     In an alternative embodiment the device  300   a  may be provided upon a sled (not shown) of the type currently used for subsea operations. The excavation apparatus  300   a  may further be provided with an agitator device (not shown) having mechanical disturbance means and fluid flow disturbance means. 
     In an advantageous embodiment the motor  310  comprises a drilling motor, such as that disclosed in WO95/19488, the content of which is incorporated herein by reference. 
     The drilling motor  310  may comprise a first motor  20  and a second motor  50 . 
     The first motor  20  comprises a stator  21  and a rotor  23 . A top portion  22  of the rotor  23  extends through an upper bearing assembly  24  which comprises a thrust bearing  26  and seals  25 . 
     Motive fluid, e.g. water, drilling mud or gas under pressure, flows down through a central sub channel  12  into a central rotor channel  27 , and then out through rotor flow channels  28  into action chambers  31  and  32 . 
     Following a motor power stroke, the motive fluid flows through exhaust ports  33  in stator  21 , and then downwardly through an annular channel circumjacent the stator  21  and flow channels  35  in a lower bearing assembly  34 . A portion  36  of the rotor  23  extends through the lower bearing assembly  34  which comprises a thrust bearing  37  and seals  38 . 
     The ends of the stator  21  are castellated and the castellations engage in recesses in the respective upper bearing assembly  24  and lower bearing assembly  34  respectively to inhibit rotation of the stator  21 . The upper bearing assembly  24  and lower bearing assembly  34  are a tight fit in an outer tubular member  14  and are held against rotation by compression between threaded sleeves  16  and  84 . 
     A splined union  39  joins a splined end of the rotor  23  to a splined end of a rotor  53  of the second motor  50 . The second motor  50  has a stator  51 . 
     A top portion  52  of the rotor  53  extends through an upper bearing assembly  54 . Seals  55  are disposed between the upper bearing assembly  54  and the exterior of the top portion  52  of the rotor  53 . The rotor  53  moves on thrust bearings  56  with respect to the upper bearing assembly  54 . 
     Motive fluid flows into a central rotor channel  57  from the central rotor channel  27  and then out through rotor flow channels  58  into action chambers  61  and  62 . Following a motor power stroke, the motive fluid flows through exhaust ports  63  in stator  51 , and then downwardly through an annular channel circumjacent the stator  51  and flow channels  65  in a lower bearing assembly  64 . A portion  66  of the rotor  53  extends through a lower bearing assembly  64 . The rotor  53  moves on thrust bearings  67  with respect to the lower bearing assembly  64  and seals  68  seal the rotor-bearing assembly interface. Also motive fluid which flowed through the flow channels  35  in the lower bearing assembly  34 , flows downwardly through channels  79  in the upper bearing assembly  54 , past stator  51  and through flow channels  65  in the lower bearing assembly  64 . 
     The upper bearing assembly  54  and lower bearing assembly  64  are a tight fit in an outer tubular member  18  and are held against rotation by compression between threaded sleeve  84  and a lower threaded sleeve (not shown). 
     FIGS. 2A-2D and  3 A- 3 D depict a typical cycle for the first and second motors  20  and  50  respectively, and show the status of the two motors with respect to each other at various times in the cycle. For example, FIG. 2C shows an exhaust period for the first motor  20  while FIG. 3C, at that same moment, shows a power period for the second motor  50 . 
     As shown in FIG. 2A, motive fluid flowing through the rotor flow channels  28  enters the action chambers  31  and  32 . Due to the geometry of the chambers (as discussed below) and the resultant forces, the motive fluid moves the rotor in a clockwise direction as seen in FIG.  2 B. The action chamber  31  is sealed at one end by a rolling vane rod  71  which abuts an exterior surface  72  of the rotor  23  and a portion  74  of a rod recess  75 . 
     At the other end of the action chamber  31 , a seal  76  on a lobe  77  of the rotor  23  sealingly abuts an interior surface of the stator  21 . 
     As shown in FIG. 2B, the rotor  23  has moved to a point near the end of a power period. 
     As shown in FIG. 2C, motive fluid starts exhausting at this point in the motor cycle through the exhaust ports  33 . 
     As shown in FIG. 2D, the rolling vane rods  71  and seals  76  have sealed off the action chambers and motive fluids flowing thereinto will rotate the rotor  23  until the seals  76  again move past the exhaust ports  33 . 
     The second motor  50  operates as does the first motor  20 ; but, as preferred, and as shown in FIGS. 3A-3D, the two motors are out of phase by 90° so that as one motor is exhausting motive fluid the other is providing power. 
     The seals  76  are, in one embodiment, made of polyethylethylketone (PEEK). The rolling vane rods  71  are also made from PEEK. The rotors ( 23 ,  25 ) and stators ( 21 ,  51 ) are preferably made from corrosion resistant materials such as stainless steel. 
     When a seal  76  in the first motor  20  rotates past an exhaust port  33 , the motive fluid that caused the turning exits and flows downward, then through the channels  79 , past the exhaust ports  63  and the flow channels  65 . 
     It should be appreciated that although in the disclosed embodiment the drilling motor  310  comprises two motors  20 ,  50 , with suitable adaptation, the drilling motor  310  may comprise only one motor  20  or  50 . 
     Referring now to FIG. 5, there is shown a second embodiment of an underwater excavation apparatus  300   b  according to the present invention. Like parts of the apparatus  300   a  are identified by numerals used to identify parts of the apparatus  300   a  of FIG. 1, except subscripted with “b” rather than “a”. 
     The apparatus  300   b  differs from the apparatus  300   a  in that the shaft  342   a  and swivel  325   a  are replaced by a second motor  310 ′ b  and a T-coupling  326   b . Thus in this embodiment the impellers  335   b ,  340   b  are driven by respective motors  310   b ,  310 ′ b . In use, motive fluid is supplied to motors  310   b ,  310 ′ b  via fluid inlet  308   b  and T-coupling  326   b.    
     Referring now to FIG. 6, there is shown a second embodiment of an underwater excavation apparatus  300   c  according to the present invention. Like parts of the apparatus  300   b  are identified by numerals used to identify parts of the apparatus  300   b  of FIG. 5, except subscripted with “c” rather than “b”. 
     The apparatus  300   c  differs from the apparatus  300   b  in that whereas in apparatus  300   b  the inlets  371   b  are horizontally opposed, in apparatus  300   c  the inlets are substantially symmetrically disposed around an axis extending from outlet  373   c , such that the apparatus  300   c  is substantially “Y” shaped. In this embodiment there is, therefore, provided a Y-coupling  326   c.    
     The embodiments of the invention hereinbefore described are given by way of example only, and are not meant to limit the scope of the invention in any way. It should be particularly appreciated that the drilling motor  310  is suitable for use in any of the disclosed embodiments.