ARRANGEMENT FOR POSITIONING A FALL PIPE END

Description

RELATED APPLICATION

This application claims the benefit of priority from European Patent Application No. 24 165079.5, filed on Mar. 21, 2024, the entirety of which is incorporated by reference.

FIELD OF THE INVENTION

The present invention generally relates to an arrangement at a fall pipe vessel, and more specifically to a fall pipe ROV, Remotely Operated Vehicle, for positioning the end of the fall pipe during a subsea rock installation operation. In particular, a solution is presented that allows for highly qualitative and accurate subsea rock installation, while obtaining a reduced fuel consumption and increased productivity.

BACKGROUND OF THE INVENTION

Fall pipe vessels or rock installation vessels are used to install rock on subsea structures, e.g. to cover pipelines or offshore cables with rock material. For this purpose, the vessel is equipped with a fall pipe, through which rock material loaded from the deck may be deposited on the desired subsea position. To allow for rock placement with high precision, a Remotely Operated Vehicle (ROV) is arranged at the bottom end of the fall pipe. Typically, the ROV is suspended from the deck by means of hoisting cables, and the fall pipe end is fixed to the ROV or arranged inside a central channel of the ROV. The ROV is self-propelled and may be operated from the deck, thereby adjusting the position of the fall pipe end. Typically, when dumping rocks according to a desired dumping trajectory, thereby covering a pipeline or subsea cable, the fall pipe vessel moves according to a direction parallel to the dumping trajectory. The vessel position is controlled e.g. by means of a Dynamic Positioning System, while the ROV position is determined relatively to the vessel, e.g. by means of acoustic positioning beacons. The fall pipe and ROV thus roughly follow the movement of the vessel, while the ROV position is adjusted accurately by means of the ROV's own propulsion means.

Prior art fall pipe ROVs are for example disclosed in WO2012002806A1 and WO2012008829A1. In these solutions, the ROV comprises thrusters, serving as the ROV's propulsion means. A thruster is provided in each of the four faces of the ROV, thereby allowing for moving the ROV according to any vector in the horizontal plane. Typically, the ROV also comprises sensors or other types of monitoring means, like e.g. disclosed in WO2012008829A1. Such monitoring means for example serve to inspect both the state of the underwater bottom or subsea structure in front of the ROV, and the state of the installed rocks behind the ROV. For this purpose, the ROV comprises two supporting arms, provided with the monitoring means, both arms mounted at opposing sides of the ROV and being in line with one another. During the rock installation operation, the arms are directed according to the dumping trajectory, thereby allowing for the envisaged inspection. A correct orientation of the supporting arms is thus required to allow for a qualitative inspection and rock installation.

Such a correct orientation of the supporting arms may be obtained by positioning the vessel with its head in a direction parallel to the dumping trajectory. However, in such a setting the orientation of the vessel may deviate from being positioned head seas, thereby leading to an increased fuel consumption of the vessel. On the other hand, if the vessel is positioned head seas, the thrusters need to be used to rotate the ROV about its own axis, thereby obtaining the correct orientation of the inspection arms. However, this reduces the thrust available for positioning the ROV, leading to a decreased accuracy of positioning the ROV. This results in a lower rock dumping precision, and may cause interruptions during the rock installation operation, thereby decreasing productivity. Finally, rotation of the ROV by means of the thrusters requires a high amount of thrust force, thus contributing to an increased power consumption.

It is an objective of the present invention to disclose a fall pipe ROV that resolves one or more of the above-described shortcomings of the prior art solutions. More particularly, it is an objective to present a solution that allows for highly qualitative and accurate subsea rock installation, while obtaining a reduced fuel consumption and increased productivity.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention, the above identified objectives are realized by an arrangement suitable for positioning a fall pipe end during subsea rock installation from a vessel, defined by claim 1, the arrangement comprising:

• • a submersible frame adapted to be lowered towards an underwater structure, while being suspended from the vessel, the submersible frame comprising:
    • a first and a second frame structure;
    • a channel structure adapted to receive the fall pipe end or to be joined to the fall pipe end;
  • propulsion equipment adapted for moving the submersible frame in a horizontal plane, thereby controlling the position of the submersible frame independently from the vessel, the propulsion equipment being mounted to the first frame structure;
  • survey equipment adapted for subsea sensing or inspection, the survey equipment being mounted to the second frame structure;
    wherein the arrangement comprises a rotation system operable independently from the propulsion equipment, wherein:
  • the rotation system comprises an actuator, the actuator comprising a first and a second element adapted to mutually engage or interact, and the actuator being adapted to convert an energy input into a rotation of the second element when holding the first element, the rotation being about a vertical axis;
  • the second element of the actuator is connected to the second frame structure carrying the survey equipment,
    such that in suspended condition of the submersible frame, the survey equipment can be rotated about the vertical axis by energizing the actuator, without using the propulsion equipment.

Thus, the invention concerns an arrangement suitable for positioning a fall pipe end during subsea rock installation from a vessel. The vessel may be referred to as a fall pipe vessel or rock installation vessel. Rock installation refers to placing rock material at the seabed or an underwater structure. For example, rock placement is applied to cover offshore power cables and pipelines, for protection or stabilisation. It may also be used to prepare the seabed for offshore structures, or to arrange a scour protection for offshore wind turbines and platforms. Besides covering an underwater structure, the vessel may also be adapted to install rocks under a subsea structure. The rock material may comprise rocks of various sizes, stones, or other suitable aggregate material.

A fall pipe allows the rock material, stored at the deck of the vessel, to be dumped at the desired subsea position. The fall pipe may be made of a rigid material or a flexible material, or a combination thereof. For example, the fall pipe may comprise a series of cylindrical pipe elements made of a rigid material, while a flexible or resilient material is provided between adjacent pipe elements. The fall pipe has an elongated shape and extends between a top side and a bottom side. During use, the fall pipe extends downwards towards the seabed, wherein rock material is loaded at the top side the pipe, and the material leaves the pipe at the bottom side. For example, the fall pipe may extend through the hull of the vessel.

The arrangement according to the invention is suitable for positioning the fall pipe end during rock installation. The fall pipe end refers to some portion of the fall pipe at its bottom side. The arrangement thus allows to move the bottom end of the fall pipe relatively to the seabed, thereby adjusting the position at which the rock material will be deposited. The arrangement therefore serves as an underwater vehicle or comprises such underwater vehicle. The vehicle is typically remotely operatable, and may be referred to as a Remotely Operated Vehicle or ROV.

The arrangement comprises a submersible frame adapted to be lowered towards an underwater structure, while being suspended from the vessel. This implies that the arrangement comprises, or may cooperate with, a suspension system, that allows the frame to be suspended from the vessel, and the frame to be moved downwards and upwards. In this context, moving downwards or lowering refers to moving in a direction from the deck towards the seabed, while moving upwards or rising refers to a moving in a direction from the seabed to the deck of the vessel. Typically, the frame is suspended by means of hoisting cables, but other suspension means, e.g. comprising rigid rods or bars are possible too. During use, the frame is connected to the suspension means, typically at the top side of the frame, and the frame is submerged in the water.

The submersible frame comprises a channel structure adapted to receive the fall pipe end or to be joined to the fall pipe end. For example, the frame may comprise a channel, wherein during use, a portion of the fall pipe is arranged inside the channel. In this, the bottom side of the fall pipe may be extend beyond the bottom side of the submersible frame, or may be found inside the channel. In the latter case, the channel structure defines an extension of the fall pipe, wherein the rock material first passes through the fall pipe and next to a portion of the channel structure. In another embodiment, the bottom side of the fall pipe is joined to the channel structure, such that the channel defines an extension of the fall pipe. In any of the embodiments, the channel structure thus defines some space through which the rock material will pass during dumping. Due to the channel structure, the submersible frame has two openings, typically at the top side and bottom side of the frame, thereby allowing to receive rock material via the first opening, and direct it downwardly, towards the second opening. Remark that during use, a fall pipe portion arranged inside the channel structure is typically not connected to the frame; the fall pipe end is then loosely positioned inside the channel structure without being connected to it.

The arrangement comprises propulsion equipment adapted for moving the submersible frame in a horizontal plane. The propulsion equipment e.g. comprises thrusters or propellers, or any other means to propel the submersible frame. For example, the frame can be moved forward, backward and sideways, or a combination thereof, thus being movable according to any vector in the horizontal plane. Typically, at least four thrusters are available, of which one pair allows for the forward-backward movement and the other pair for the sideways movements. In this case, combined use of specific thrusters also allows for rotating the submersible frame about is own axis, i.e. rotating it in the horizontal plane. The horizontal plane is defined with respect to the submersible frame; during use, moving the submersible frame in the horizontal plane corresponds to moving the fame substantially parallel to the seabed or the vessel deck, but deviations due to interaction with the water, movements of the vessel, or the seabed not being completely flat may occur. The vertical direction of the submersible frame is the direction perpendicular to the horizontal plane. During use, the vertical direction of the frame will be substantially parallel to the direction of gravity, but deviations due to interaction with the water or movements of the vessel may occur. A vertical axis refers to an axis being parallel to the vertical direction. Remark that typically, the space defined by the channel structure of the submersible frame, extends in vertical direction. However, an angled direction deviating from vertical is also possible.

The propulsion equipment allows to control the position of the submersible frame independently from the vessel. The submersible frame therefore acts as a self-propelled vehicle, and, if operatable remotely, as a Remotely Operated Vehicle or ROV. The propulsion equipment, is mounted to, or connected to, a certain portion of the submersible frame. The latter portion is referred to as the first frame structure. The first frame structure is thus the portion of the submersible frame carrying the propulsion equipment. For example, the first frame structure comprises multiple frame parts, each of them carrying an individual thruster.

The arrangement further comprises survey equipment adapted for subsea sensing or inspection. It may also be referred to as monitoring means, inspection means, detection means, sensing means, etc. For example, the survey equipment comprises one or more sensors, wherein a sensor is a device that detects and responds to some type of input from the environment, the input e.g. being light, heat, motion, moisture, pressure or the like. For example, the survey equipment comprises one or more ultrasonic and/or optical sensors. For example, the survey equipment comprises one or more cameras, wherein a camera is a sensing device that can capture and store images. In particular, the survey equipment may be adapted to inspect the state of the underwater bottom, and/or of a subsea structure to be covered with rocks, and/or of deposited rock material. In an embodiment, the survey equipment comprises at least two inspection means, e.g. sensors, allowing for an inspection in front of the submersible frame, and an inspection behind the submersible frame, while moving the submersible frame along a dumping trajectory.

The survey equipment, is mounted to, or connected to, a certain portion of the submersible frame. The latter portion is referred to as the second frame structure. The second frame structure is thus the portion of the submersible frame carrying the survey equipment. For example, the second frame structure comprises multiple frame parts, each of them carrying an individual sensor. In an embodiment, the second frame structure may comprise one or more inspection arms, provided as elongated frame parts that each carry a sensor. For example, two such inspection arms are comprised in the second frame structure, mounted at opposing sides and being in line with one another.

The first and the second frame structure thus each refer to a particular portion of the submersible frame. Apart from the first and second frame structure, the submersible frame comprises other portions, like the channel structure, and possibly other frame parts. Typically, the channel structure is comprised in an inner structure of the submersible frame, while the first and second frame structure are comprised in an outer structure, the inner structure being adapted to surround the fall pipe and the outer structure being mounted around the inner structure. In an embodiment, the first and the second frame structure may be connected to each other, in such a way that they cannot rotate relatively to each other. The first and the second frame structure then form one unity, connected in a non-rotatable way. In such embodiment, it may be possible, however, that the second frame structure is movable or partly movable with respect to the first frame structure, e.g. due to inspection arms comprised in the second frame structure being mounted pivotably with respect to the first frame structure.

The arrangement thus comprises a self-propelled vehicle or ROV, adapted to be submerged in the water, the vehicle comprising the submersible frame, the propulsion equipment and the survey equipment. The arrangement further comprises a rotation system operable independently from the propulsion equipment. This implies that the rotation system allows to cause a rotation, but without relying on the propulsion equipment, e.g. without using the thrusters. The rotation system comprises an actuator, the actuator comprising a first and a second element adapted to mutually engage or interact. An actuator refers to a system adapted to receive energy from an energy source, and convert it into displacement, force or torque, in a controlled way. In particular, the actuator is adapted to convert an energy input into a rotation of the second element when holding the first element. The actuator may be mounted to the self-propelled vehicle, such that it is submerged during the rock installation operation, or may be positioned at the deck of the vessel.

Upon energizing the actuator, it causes a rotation of the second element relatively to the first element. For example, the second element may be a pinion, and the first element may be a curved rack provided on a slewing ring, or vice versa, the pinon and rack being adapted to engage. When holding the curved rack, the pinion may move along a trajectory along the rack, around the slewing ring, upon energizing the actuator. Energizing the actuator may e.g. happen due to a hydraulic motor comprised in the actuator, the hydraulic motor adapted to receive a pressurized fluid, and adapted to drive the pinion, i.e. rotate the pinion about its own axis. In another embodiment, another type of activation may be used, e.g. a hydraulic system wherein pistons receiving a pressurized fluid cause rotation of a slewing ring, an electrical drive, magnets, etc. The first and second element may directly engage, i.e. being in contact, or may interact without direct contact, e.g. through magnetic force, fluid jets, etc.

In any of the embodiments, the second element is the element of the actuator that is rotated upon energizing the actuator, wherein it rotates relatively to the first element. The rotation is about a vertical axis of the submersible frame. Typically, the rotation axis corresponds to the central axis of the channel structure, but another rotation axis in vertical direction is possible too. The second element of the actuator, i.e. the rotating element, is connected to the second frame structure carrying the survey equipment. On the other hand, the first element of the actuator is connected to the vessel, either directly or indirectly. In this way, in suspended condition of the submersible frame, upon energizing the actuator, the second frame structure rotates relatively to the vessel, thereby rotating the survey equipment mounted to the second frame structure. In this way, energizing the actuator allows to rotate the survey equipment about a vertical axis, relatively to the vessel or seabed, without using the propulsion equipment.

Apart from the actuator, the rotation system may comprise other components to implement the rotation, including a chain of components for providing energy from an energy source at the vessel towards the actuator. If the actuator is found at deck level, typically all components of the rotation system are positioned at the vessel, thus not being submerged during the rock installation operation. If the actuator is mounted to the submersible frame, typically not all of the components of the rotation system are mounted to the submersible frame; in this case, some components of the rotation system are submerged during the rock installation while other components may be found at the deck. For example, the rotation system may comprise a pump for feeding the actuator with pressurized fluid, the pump mounted to the submersible frame, an electrical motor for driving that pump, the electrical motor mounted to the submersible frame, an umbilical for supplying electrical energy towards the electrical motor, and a power supply at the vessel. Moreover, the rotation system may comprise bearings for enabling a relative rotation between the second and first element.

The invention goes along with multiple advantages. First, by rotating the survey equipment, the inspection or sensing means may be brought into the correct orientation during the rock installation operation, thereby allowing for a qualitative inspection and rock installation. In this, the rotation of the survey equipment may be done without using the propulsion equipment; whereas in prior art solutions four thrusters need to be energized to obtain a rotation of the ROV about its own axis, the invention allows to rotate the survey equipment by energizing the actuator, without relying on the thrusters. Consequently, the thrust available from the propulsion equipment is fully available for positioning the ROV, thereby obtaining positioning with an increased accuracy. This contributes to rock dumping at higher precision, and avoids interruptions during the rock installation operation, thereby leading to an increased productivity. Moreover, as no thrust force is required for rotating the survey equipment, this contributes to a reduced power consumption. Finally, the correct orientation of the survey equipment may be obtained even if there is a misalignment between the vessel and the submerged vehicle. Thus, the vessel may be positioned head seas during the rock installation operation, thereby contributing to a reduced fuel consumption of the vessel.

Optionally, the first element of the actuator is adapted to be connected to the vessel, via a hoisting system for suspending the submersible frame, or due to the first element being fixed directly to the deck of the vessel, thereby allowing for a rotation of the second element relatively to the first element upon energizing the actuator. In an embodiment, the first element of the actuator is connected to the vessel indirectly, e.g. due to one or more hoisting cables connecting the submersible frame to the vessel, and the first element being connected to the submersible frame. In another embodiment, the first element may be directly connected to the vessel, e.g. by being mounted at deck level. Due to the direct or indirect connection with the vessel, the first element may remain static, such that only the second element rotates upon energizing the actuator. It is also possible that the first element would slightly rotate too, e.g. due to the hoisting cables being non-rigid; in that case the second element will be rotated to a larger extent, such that still the second element rotates relatively to the first element. Due to the first element being connected to the vessel, while rotating the second element, the second frame structure carrying the survey equipment may be rotated without winding up the hoisting cables. This contributes to a more stable orientation of the survey equipment, and less required adjustments during the rock installation operation.

Optionally, the first element of the actuator is connected to the vessel via a hoisting system, and the second element of the actuator is connected to the submersible frame, such that during use, the actuator is submerged into the water together with the submersible frame. This means that the first element is indirectly connected to the vessel, e.g. by means of one or more hoisting cables. During the rock installation operation, the actuator, mounted to the submersible frame, is submerged in the water together with the frame. In other words, all the elements of the actuator make part of the self-propelled vehicle found in the water during the rock installation operation. This allows for a light, convenient construction, opposed to a rotation system wherein the first element would be found at deck level, the latter possibly leading to a more heavy and cumbersome construction.

In an embodiment, the complete channel structure may be connected to the first element of the actuator, such that the channel structure does not rotate upon rotating the survey equipment, or only to a less extent. In another embodiment, a portion of the channel structure is connected to the first element of the actuator and the other portion of the channel structure is connected to the second frame structure, such that a portion of the channel structure rotates upon rotating the survey equipment. In yet another embodiment, the complete channel structure is connected to the second frame structure, such that the complete channel structure rotates upon rotating the survey equipment.

Optionally, according to a first group of embodiments, the first frame structure carrying the propulsion equipment and the second frame structure carrying the survey equipment are joined, such that by energizing the actuator, the survey equipment and propulsion equipment are rotated together about the vertical axis. In particular, the first frame structure and the second frame structure are joined in such a way that they cannot rotate relatively to each other. In an embodiment, the first and frame structure are rigidly connected, such that both form one unity wherein not any movement between the first and second frame structure is possible. In another embodiment, the first and second frame structure may be joined, not allowing for a rotation between both structures, but still allowing that the second frame structure is moved or partly moved with respect to the first frame structure. For example, the second frame structure may comprise foldable arms, such that the arms may be pivoted with respect to the first frame structure.

Due to the first and second frame structure being joined, the survey equipment and propulsion equipment are rotated together about the vertical axis upon energizing the actuator. This has the advantage that no additional measurements faults are introduced. Indeed, typically acoustic positioning beacons are mounted to the submersible frame to know the position and orientation of the submerged vehicle relative to the vessel. As the first frame structure carrying the propulsion equipment is joined to the second frame structure carrying the survey equipment, the acoustic position beacons allow to know the position and orientation of each thruster as well as of the survey equipment. No supplementary measurement is thus needed to know the orientation of the inspection arms, in view of determining the required rotation. Conversely, in a solution wherein the second frame structure carrying the survey equipment would be rotatable with respect to the first frame structure, and the latter being rotatable on its own by means of the thrusters, such a supplementary measurement would be needed, thereby requiring additional equipment and/or introducing additional measurements faults.

Optionally, according to a another group of embodiments, the second frame structure carrying the survey equipment is mounted rotatably with respect to the first frame structure carrying the propulsion equipment, such that by energizing the actuator, the survey equipment is rotated about the vertical axis without rotating the propulsion equipment. For example, the second frame structure carrying the survey equipment may be rotated around the rest of the submersible frame, in particular around the first frame structure carrying the propulsion equipment. In this way, a double rotation option is obtained, wherein the first frame structure may be rotated on its own by means of the propulsion equipment, and the second frame structure may be rotated around the first frame structure by means of the rotation system. This has the advantage that the design of the first frame structure, channel structure and propulsion equipment may remain similar as in a prior art ROV, while the actuator and second frame structure are added as an outer structure around the existing design.

In an example within this group of embodiments, the first element of the actuator is provided as a slewing ring with toothed rack, and the second element of the actuator is provided as a pinion. In this case, the first element is connected indirectly to the vessel via the hoisting system, and upon energizing the actuator, the pinion rotates around the slewing ring. In another example, the first element of the actuator is provided as a pinion, and the second element of the actuator is provided as a slewing ring with toothed rack. In this case, the first element is connected indirectly to the vessel via the hoisting system, and upon energizing the actuator, the pinion drives the slewing ring such that the latter rotates relatively to the pinion.

Optionally, according to yet a another group of embodiments, the first element of the actuator is fixed directly to the deck of the vessel, and the second element of the actuator is connected to the submersible frame via a hoisting system, such that during use, the actuator is found at deck level and is not submerged into the water. This means that during the rock installation operation, the frame carrying the propulsion equipment and survey equipment is submerged into the water, while the actuator for enabling the rotation of the survey equipment is not submerged but is installed on the deck of the vessel. Upon energizing the actuator, the submerged frame rotates, together with the second element found at the deck. For example, the submerged frame may be fixed to the fall pipe, such that the fall pipe rotates as well. In another embodiment, a complete fall pipe system or tower may be provided, positioned on a turntable on the deck. In the latter case, the fall pipe rotates together with other components of the dumping system found at the deck.

Optionally, the second frame structure comprises one or more elongated arms, the survey equipment being mounted to the one or more elongated arms. Typically, means for inspection are provided at the bottom side of the elongated arms, thus being directed towards the seabed during the rock installation operation. In an embodiment, the one or more elongated arms are rigidly connected to the rest of the second frame structure. In another embodiment, the one or more elongated arms are collapsible with respect to the rest of the second frame structure. For example, an elongated arm, or a portion thereof, may be pivotable, thereby allowing to fold and unfold the arm with respect to the rest of the frame. Having elongated inspection arms has the advantage that during the rock installation operation, a substantial inspection range is obtained. Moreover, having collapsible or foldable inspection arms allow for a compact device in folded condition of the arms, thereby contributing to a smooth lowering and rising of the device in and out of the water, and allowing for a compact storage at the deck.

Optionally, the second frame structure comprises a set of two elongated arms, each of the arms mounted at opposite sides of the submersible frame, wherein the two elongated arms are rigidly connected to the rest of the second frame structure and are in line, or the two elongated arms are collapsible with respect to the rest of the second frame structure, and are in line in unfolded condition. This has the advantage that inspection may be done according to a straight line, thereby allowing for inspection in front of the submerged frame and behind the submerged frame. For example, the state of a subsea structure like a pipeline or cable may be inspected before dumping rocks, and the state of the deposited material may be inspected after dumping.

Optionally, the vertical rotation axis corresponds to the central axis of the channel structure, such that the survey equipment can be rotated about the central axis of the channel structure.

Optionally, the first or second element comprises a ring having a central axis extending in vertical direction. In an embodiment, the first element comprises the ring, and the actuator is adapted to move the second element along a ring-shaped trajectory coaxially with the ring, such that the second element is rotated about the central axis of the ring. For example, the ring may be provided with a toothed rack, and upon rotating a pinion about its own axis, the pinion may move along a circular trajectory around the ring, due to the pinion engaging with the toothed rack. In another embodiment, the second element comprises the ring, and the actuator is adapted to rotate the ring about its central axis. For example, the ring may be provided with a toothed rack, and upon rotating a pinion about its own axis, the ring is driven by the pinion, such that the ring rotates.

Optionally, the first or second element respectively is a slewing ring comprising a toothed rack along its circumference, and the second or first element respectively is a pinion adapted to engage with the toothed rack.

Optionally, the first element or the second element respectively comprises a slewing ring having a central axis corresponding to the vertical rotation axis, and the rotation system comprises multiple bearing assemblies distributed over the circumference of the slewing ring, each of the bearing assemblies adapted to retain the slewing ring in vertical direction with respect to the submersible frame, while allowing for a rotation of the slewing ring relatively to the second or first frame structure respectively. One bearing assembly may comprise multiple bearings, e.g. each of the bearing assemblies is a set of three bearings, namely an upper, lower and side bearing. Multiple bearing assemblies are provided along the circumference of the slewing ring. This means that instead of providing a single ring-shaped bearing that extends over the complete circumference of the slewing ring, multiple separate bearing assemblies are provided along the circumference. This has the advantage of being less prone to underwater conditions, especially due to salt water, thereby allowing for proper rotation when the actuator is submerged in the water. Also remark that such separated bearing assemblies suffice, as the occurring rotations are over an angle that is rather small; e.g. typically no rotation over 360° will occur.

Optionally, each of the bearing assemblies comprises three individual bearings, of which the first bearing engages with the upper surface of the slewing ring, the second bearing engages with the bottom surface of the slewing ring, and the third bearing engages with the side surface of the slewing ring.

Optionally, the first and second bearing each comprise a sliding interface, and the third bearing comprises a rolling element.

Optionally, the first and third bearing are integrated in a bearing block, the bearing block being tiltable with respect to the slewing ring, such that in tilted condition, the first and the third bearing do not longer engage with the upper surface respectively side surface of the slewing ring. Upon tilting the bearing blocks, a passage is created, thereby allow to mount or remove the slewing ring, and allowing for easy maintenance.

Optionally, the propulsion equipment comprises multiple thrusters, distributed along the circumference of the first frame structure.

Optionally, the thrusters are adapted to move the submersible frame according to any vector in the horizontal plane.

Optionally, the propulsion equipment comprises six thrusters, evenly distributed along the circumference of the first frame structure.

Optionally, the arrangement comprises one or more acoustic positioning beacons, mounted to the submersible frame, adapted to determine the position of the submersible frame with respect to the vessel.

Optionally, the arrangement comprises one or more hoisting cables, adapted for suspending the submersible frame from the vessel.

Optionally, the actuator comprises a hydraulic motor mounted to the submersible frame, the hydraulic motor being adapted to receive a pressurized fluid, and to drive the first or second element.

Optionally, the pressurized fluid for feeding the hydraulic motor is supplied by a pump mounted to the submersible frame, the pump being driven by an electric motor mounted to the submersible frame.

Optionally, the rotation system comprises an umbilical power cable, for supplying electric power from the vessel to the electric motor at the submersible frame.

Optionally, the umbilical power cable is integrated within a hoisting cable.

Optionally, the rotation system comprises an umbilical power cable, of which one end is fixed with respect to the second frame structure. For example, an electric motor may be connected to the second frame structure, and the end of the umbilical power cable is fixed to the electric motor. This implies that, upon rotating the second frame structure with survey equipment, the end of the power cable also rotates. This has the advantage over a dragging contact that an easier implementation and a more robust solution are obtained. On the other hand, the cable length may limit the possible range of rotation.

According to a second aspect of the present invention, there is provided a method for positioning a fall pipe end during subsea rock installation from a vessel, the method comprising:

• • providing a vessel suitable for subsea rock installation;
  • providing a fall pipe;
  • providing an arrangement according to the first aspect of the invention;
  • arranging an end portion of the fall pipe in the channel structure, or joining the fall pipe end to the channel structure;
  • lowering the submersible frame into the water, towards an underwater structure, while being suspended from the vessel;
  • operating the rotation system, by energizing the actuator, such that the second element is rotated about the vertical rotation axis relatively to the first element, thereby rotating the survey equipment about the vertical rotation axis relatively to the vessel.

According to a third aspect of the present invention, there is provided a vessel suitable for subsea rock installation, the vessel comprising:

• • an arrangement according to the first aspect of the invention;
  • a fall pipe;
  • means for suspending the submersible frame from the vessel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a fall pipe vessel during a rock installation operation, using an ROV for positioning the fall pipe end, according to a prior art solution.

FIG. 2 illustrates rotation of the ROV by means of thrusters, according to a prior art solution.

FIG. 3 illustrates rotation of the ROV by means of a rotation system, operatable independently from the thrusters, according to an embodiment of the invention.

FIG. 4 to FIG. 8 give conceptual drawings, illustrating the concept of the rotation system, according to various different embodiments of the invention. In particular, FIG. 4 illustrates an embodiment 1Aa, FIG. 5 an embodiment 1Ab, FIG. 6 an embodiment 1Ba, FIG. 7 an embodiment 1Bb, and FIG. 8 an embodiment 2A. In this, embodiments 1Aa, 1Ab, 1Ba, and 1Bb are categorized in a first class of embodiments, and embodiment 2A in a second class of embodiments. Within the first class, embodiments 1Aa and 1Ab belong to a group 1A, while embodiments 1Ba and 1Bb belong to a group 1B.

FIG. 9 to FIG. 16 illustrate a concrete implementation of the concept according to embodiment 1Aa. In particular, FIG. 9 to FIG. 11 show the ROV, wherein FIG. 10 illustrates how the ROV may be used during a rock installation operation. FIG. 12 and FIG. 13 illustrate the actuator of the rotation system, and FIG. 14 to FIG. 16 illustrate the bearing arrangement.

DETAILED DESCRIPTION OF EMBODIMENT(S)

FIG. 1 illustrates a fall pipe vessel 100 during a rock installation operation. The vessel 100 is equipped with a fall pipe 103. Rock material stored at the deck 110 is loaded into the fall pipe 103, see 109, for deposition onto the seabed 102 or a subsea structure such as a pipeline or power cable. For positioning the fall pipe end 110, a Remotely Operated Vehicle or ROV 104 is used. In FIG. 1, an ROV according to a prior art solution is illustrated, but an ROV according to an embodiment of the invention may be used in a similar way. The ROV 104 is suspended from the vessel 100 by mean of hoisting cables 106. The ROV 104 comprises thrusters 105, for propelling the ROV. For simplicity, only two thrusters 105 are shown in the figure, but typically at least four thrusters are provided on a prior art ROV. The four thrusters are arranged in four different faces, thereby allowing for forward/backward and sideways movement of the ROV, as well as rotation about its own axis. The ROV 104 comprises inspection arms 107, provided with sensors or inspection means 108 directed to the seabed 102. The inspection arms 107 allow to inspect along a straight line, in front of and behind the ROV, during the rock installation operation. In FIG. 1-3, the X-direction corresponds to the longitudinal direction of the vessel 100, and the Y-direction corresponds to the transverse direction of the vessel 100. The Z-direction corresponds to the vertical direction, also referred to as depth direction or height direction. An XY-plane is referred to as a horizontal plane.

FIG. 2 illustrates the misalignment between the vessel 100 and the inspection arms 107 of the ROV 104 when the vessel is positioned head seas. The figure shows that rock material needs to be deposited along a dumping trajectory 202. The vessel 100 is positioned head seas, see 200, and moves parallel to the dumping trajectory 202 during the rock installation operation, see 201. Therefore, initially a misalignment occurs between the inspection arms 203 and the dumping trajectory 202. To obtain a correct orientation of the inspection arms, the ROV 104 is rotated about its vertical axis, thereby obtaining an orientation 204 of the inspection arms, allowing for inspection along the dumping line 202. When using the prior art ROV 104, such rotation is obtained by means of the thrusters 105. As the ROV 104 is rotated as a whole, the points 206 where the hoisting cables 106 are connected to the ROV rotate too, see 205. As a result, the hoisting cables 106 are twisted during rotation of the ROV 104 for correctly orienting the inspection arms.

FIG. 3 illustrates how a rotation system according to the invention may be used for correctly orienting the inspection arms. Again, the vessel is positioned head seas, 200, and it moves in a direction 201 parallel to a dumping trajectory 202. Initially, the inspection arms 301 of ROV 300 are misaligned with respect to the dumping trajectory 202. By means of the rotation system, which will be further explained below, an outer structure 304 of the ROV 300 is rotated with respect to an inner structure 305. The inspection arms, mounted to the outer structure 304, are rotated too, thereby reaching the correct orientation 302. The figure also shows that the connection points 303 of the hoisting cables 106, being at the inner structure 305, do not rotate, such that the hoisting cables 106 are not twisted while rotating the inspection arms. Rotating the outer structure 304 is done by means of a rotation system, which is operated independently from the thrusters, as will further be explained below. Rotating the inspection arms towards the correct orientation may happen in an initial stage, after lowering the ROV into the water, and may happen during the rock installation operation. Typically, the operation is shortly interrupted when the orientation of the inspection arms needs to be adjusted by means of the rotation system.

FIG. 4 to FIG. 8 illustrate the concept of the rotation system, according to different embodiments of the invention. The figures are conceptual, and merely serve to illustrate the essential elements and how these may function within a particular concept of the rotation system. In practice, various designs may apply for implementing a particular concept; one such practical design, implementing the concept of FIG. 4, will be discussed in relation to FIGS. 9 to 16. FIGS. 4 to 8 illustrate the arrangement when being used during a rock installation operation, i.e. in suspended condition and with an installed fall pipe. The various concepts may be combined with the vessel 100 of FIG. 1, i.e. the ROV 104 of FIG. 1 may be replaced with one of the arrangements shown in FIGS. 4 to 8.

FIG. 4 to FIG. 7 illustrate a first class of embodiments, wherein the respective embodiments will be referred to as 1Aa, 1Ab, 1Ba and 1Bb. The concepts within this first class have in common that the actuator, for rotating the inspection arms, is mounted to the submersible frame, and is therefore submerged together with the ROV during the rock installation operation. FIG. 8 illustrates a second class of embodiments, of which the example shown in FIG. 8 is referred to as 2A. The second class comprises embodiments wherein the actuator is not mounted to the submersible frame, but is found at deck level.

FIG. 4 illustrates a first possible concept, referred to as embodiment 1Aa. The arrangement illustrated in FIG. 4 comprises a self-propelled vehicle 417 and a rotation system. The rotation system comprises an actuator 403; other components of the rotation system such as an energy source at the vessel are not shown in the figure. The self-propelled vehicle 417 may be remotely operated from the deck, and may thus be referred to as Remotely Operated Vehicle or ROV, 417. The ROV 417 is suspended from the vessel 100 by means of suspension means 416, e.g. hoisting cables, and a fall pipe 418 is arranged in a central channel of the ROV 417.

The ROV 417 comprises a submersible frame 400, propulsion equipment 415, and survey equipment 406, 407. The submersible frame 400 comprises a first frame structure 401 carrying the propulsion equipment 415, a second frame structure 402 carrying the survey equipment 406, 407, and a channel structure 410. The channel structure 410 defines a central channel, adapted for arranging the fall pipe end 414. The figure shows that the channel structure 410 makes part of an inner structure of the submersible frame 400. On the other hand, the first frame structure 401 and the second frame structure 402 make part of an outer structure, positioned around the inner structure.

The propulsion equipment 415 comprises multiple thrusters, distributed over the circumference of the vehicle 417. For simplicity, only two thrusters are shown in the figure. However, typically four thrusters are available; for example, in the implementation of FIG. 10 six thrusters are provided, distributed evenly over the hexagonal frame. The thrusters 415 allow to propel the vehicle 417 according to any direction in a horizontal XY plane. As such, by operating the thrusters 415, the fall pipe end 414 can be positioned at a desired dumping location. Remark that in FIGS. 4 to 9, the X, Y and Z direction are defined with respect to the vehicle 417; during use, these directions substantially correspond with the respective directions indicated in FIG. 1, the latter defined with respect to the vessel 100 and seabed 102.

The second frame structure 402 comprises two elongated inspection arms 404, 405, mounted at opposing sides of the frame vehicle 417. The inspection arms 404, 405 are provided with survey equipment 406, 407. E.g. a sensor, camera or other inspection means 406, 407, directed towards the seabed, is mounted to the respective arms 404, 405. During use, the inspection arms 404, 405 are in line, thereby allowing inspection along a straight line. The inspection arms 404, 405 may be collapsible or foldable, as e.g. is the case in the implementation of FIG. 9-10.

The rotation system comprises an actuator 403. The actuator 403 comprises a first element 411, a second element 412, and a drive 413, e.g. a hydraulic motor 413. The fist element 411 is provided as a circular slewing ring, on which a toothed rack is arranged. The second element 412 is provided as a pinion, engaging with the toothed rack of the slewing ring 411. In FIG. 4, the slewing ring 411 and pinion 412 are drawn in a symbolical way; a possible practical design is e.g. shown in FIG. 12-13. The slewing ring 411 has a central axis in vertical direction, corresponding to the central axis of the channel structure 410. The outer structure of the frame 400 is mounted rotatably with respect to the slewing ring 411, due to a bearing arrangement. Although FIG. 4 represents only one bearing assembly 414, multiple of such bearing assemblies 414 are provided over the circumference, as will further be discussed in relation to FIG. 14-16. As the actuator 403 is mounted to the submersible frame 400, it is submerged into the water during a rock installation operation.

FIG. 4 shows that the first element 411 of the actuator 403, i.e. the slewing ring 411, is connected indirectly to the vessel 100, namely via the hoisting cables 416. The second element 412 of the actuator 403 is connected to the second frame structure 402, the latter carrying the survey equipment 406, 407. In the shown embodiment, the actuator may be energized by suppling a pressurized fluid to the hydraulic motor 413, which will then drive the pinion 412. As the pinion 412 rotates about its own axis, it engages with the slewing ring 411, such that the pinion 412 will move along a circular trajectory around the slewing ring 411. The pinion 412 thus rotates about a vertical rotation axis 409, the latter corresponding to the central axis of the slewing ring 411 and to the central axis of the channel structure 410. As the pinion 412 is connected to the second frame structure 402, the inspection arms 404, 405 and inspection means 406, 407 are rotated about the vertical axis 409 upon energizing the actuator 403, see rotation 408. In this way, the orientation of the inspection arms 404, 405 may be adjusted, without using the thrusters 415.

FIG. 4 shows that in embodiment 1Aa, the first frame structure 401 and the second frame structure 402 are joined, thus making part of an outer structure forming one unity. This implies that upon rotating the second frame structure 402, the first frame structure 401 rotates too. The outer structure comprising the first and second frame structure 401, 402 thus rotates around the inner structure comprising the channel structure 410. Accordingly, upon energizing the actuator 403, the thrusters 415 will rotate together with the inspection arms 404, 405. This has the advantage that acoustic positioning beacons mounted to the outer structure, allow to know the position and orientation of both the thrusters 415 and the inspection arms 404, 405. No additional measurement is thus required for knowing the orientation of the inspection arms 404, 405, thereby avoiding accumulation of measurement faults.

Apart from the actuator 403, other components, not shown in the figure, may be comprised in the rotation system. For example, the rotation system may additionally comprise a pump and an electrical motor, both mounted at the submersible frame 400, a power supply at the vessel 100, and an umbilical for connecting the power supply to the electrical motor. The electrical motor allows to drive the pump, upon which the pump supplies a pressurized fluid to the hydraulic motor 413, the latter driving the pinion 412. In this case, some components of the rotation system, such as the actuator 403, the electrical motor and the pump are submerged during the operation, while other components such as the power supply are positioned at the vessel 100.

In embodiment 1Aa, shown in FIG. 4, the complete channel structure 410 is connected to the first element 411 of the actuator 413, such that the channel structure 410 does not rotate upon rotating the inspection arms 404, 405. FIG. 5 shows another embodiment, referred to as 1Ab, wherein a portion 504 of the channel structure 510 rotates upon rotating the inspection arms 404, 405. Indeed, the vehicle 517 comprises a submersible frame 500, the latter comprising a first frame structure 401, a second frame structure 402, and a channel structure 510. The channel structure 510 comprises an upper portion 503, wherein the fall pipe end is arranged, and a lower portion 504. The lower portion 504 defines a channel 505 forming an extension of the fall pipe. The upper portion 503 of the channel structure 510 is connected to the first element 411 of the actuator 413, such that it does not rotate upon rotating the inspection arms 404, 405. The lower portion 504 is connected to the second frame structure 402, and to the second element 412 of the actuator. Accordingly, the lower portion 504 of the channel structure 510 rotates together with the inspection arms 404, 405, see rotation 508. In this case, some part of the inner structure of the frame thus rotates upon energizing the actuator.

Remark that embodiments 1Aa and 1Ab, shown in FIGS. 4 and 5 respectively, have in common that the first frame structure 401 and second frame structure 402 are connected, such that the survey equipment 406, 407 is rotated together with the propulsion equipment 415 upon energizing the actuator 403. The embodiments of FIG. 4 and FIG. 5 therefore belong to the same group 1A, being a group within the first class of embodiments. Apart from embodiments 1Aa and 1Ab, other embodiments are possible within the group 1A. For example, in an embodiment 1Ac, not shown, the complete channel structure may be connected to the second frame structure 402, such that the complete channel structure rotates upon rotating the survey equipment 406, 407.

Opposed to group 1A, FIG. 6 and FIG. 7 illustrate another group 1B comprised within the first class of embodiments. In embodiments of group 1B, the second frame structure 602, 702 is not joined to the first frame structure 601, 701, but is mounted rotatably with respect to the first frame structure 601, 701.

Indeed, FIG. 6, illustrating embodiment 1Ba, shows an ROV 617, comprising a submersible frame 600. The submersible frame 600 comprises a channel structure 610, a first frame structure 601 carrying thrusters 605, and a second frame structure 602 comprising inspection arms 603, 604. The figure shows that the inspection arms 603, 604 are mounted such that they can rotate around the first frame structure 601. The actuator comprises a first element 611, provided as a slewing ring with toothed rack, and a second element 612, provided as a pinion. Upon energizing the actuator, the pinion 612 rotates around the slewing ring 611, thereby rotating the inspection arms 603, 604, see 608, just like in the previous embodiments. However, different from the previous embodiments, upon rotating the inspection arms 603, 604, the first frame structure 601 and thrusters 605 are not rotated. Accordingly, a double rotation option is obtained, wherein the first frame structure 601 may be rotated by means of the thrusters 605, and the inspection arms 603, 604 may be rotated around the first frame structure 601 by means of the actuator. Such an embodiment has the advantage that the design of the ROV, with respect to the first frame structure and channel structure, may remain similar as in a prior art ROV, while the rotation mechanism is added to this existing design.

In embodiment 1Bb, illustrated in FIG. 7, another variant withing group 1B is shown. The ROV 717 comprises a submersible frame 700. The submersible frame 700 comprises a channel structure 710, a first frame structure 701 carrying thrusters 705, and a second frame structure 702 comprising inspection arms 703, 704. The inspection arms 703, 704 are mounted such that they can rotate relatively to the first frame structure 701. The actuator comprises a second element 712, provided as a slewing ring with toothed rack, and a first element 711, provided as a pinion. The slewing ring 712 is connected to the inspection arms 703, 704, while the pinion 711 is connected indirectly to the vessel, via the hoisting cables 708. Thus, different from FIG. 6, upon energizing the actuator, the pinion 711 will drive the slewing ring 712, such that the slewing ring 712 rotates about the vertical rotation axis. As a result, the inspection arms 703, 704 are rotated, while the thrusters 705 are not rotated.

The embodiments of FIG. 4 to FIG. 7, comprised in group 1A and 1B have in common that the actuator is mounted to the submersible frame. The actuator is thus submerged during the rock installation operation. The embodiments of FIG. 4 to FIG. 7 therefore belong to a first class. Opposed to the first class, a second class of embodiments is possible, wherein the actuator is not submerged, but is installed at deck level. One example embodiment of this second class is illustrated in FIG. 8, showing an embodiment 2A.

FIG. 8 shows an ROV 817, comprising a submersible frame 800. The submersible frame 800 comprises a channel structure 810, a first frame structure 801 carrying thrusters 805, and a second frame structure 802 comprising inspection arms 803, 804. Different from the previous embodiments, the actuator 803 is not mounted to the submersible frame, but is positioned at the deck 804 of the vessel. The actuator 803 may e.g. comprises a hydraulic motor 813, a first element 811 provided as a pinion, and a second element 812 provided as a slewing ring. The ROV 817 is suspended by means of a hoisting system, wherein the submersible frame 800 is connected to the slewing ring 812. Upon energizing the actuator, the pinon 811 drives the slewing ring 812, such that the latter rotates, see 808. Accordingly, the whole suspension system and ROV 817 are rotated, thereby allowing to adjust the orientation of the inspection arms 803, 804. Remark that in this type of embodiment, all components of the rotation system, i.e. the actuator 803 as well as the chain of components for providing the actuator with energy, are installed at the vessel.

Apart from embodiment 2A, shown in FIG. 8, other embodiments are possible within the second class. For example in an embodiment 2B, not shown, a turntable may be provided at the deck 804. A complete fall pipe system or tower, comprising the fall pipe and other devices making part of the dumping installation at the deck, may be positioned onto the turntable or connected to the turntable. Moreover, the submerged ROV is connected to the fall pipe. As such, upon energizing the actuator, the whole fall pipe system rotates together with the ROV.

FIG. 9 to FIG. 16 illustrate a concrete implementation of the concept according to embodiment 1Aa, previously shown in FIG. 4.

FIGS. 9 to 11 show the ROV 417, wherein FIGS. 9 and 11 show the ROV with folded inspection arms 404, 405, e.g. when the ROV is not in use. FIG. 10 shows the ROV 417 in suspended condition, with installed fall pipe and unfolded inspection arms 404, 405, e.g. as being used during a rock installation operation. Remark that the ROV 417 can also be used with deployed inspection arms, but without a fall pipe being installed, e.g. for doing a visual inspection of the seabed. The submersible frame of the ROV 417 comprises an inner structure 902, and an outer structure 901 arranged around the inner structure 902. The inner structure 902 comprises the channel structure 410, for arranging the fall pipe end. The outer structure 902 comprises the first frame structure 401, carrying thrusters 415, and the second frame structure 402 comprising inspection arms 404, 405. The inspection arms 404, 405 are collapsible: in FIGS. 9 and 11 they are in folded condition, while in FIG. 10 they are in unfolded condition. Inspection means 406, 407 are mounted at the bottom side of the unfolded inspection arms 404, 405. In the shown embodiment, the submersible frame has an hexagonal outer circumference, and one thruster 415 is arranged at each of the six corners. The ROV can be suspended by means of hoisting cables 416, which connect to connection points 900 at the inner structure 902.

The ROV 417 comprises an actuator, arranged at the inside of the ROV. FIG. 11 indicates the location of the actuator in the ROV, see ‘A’. A more detailed view of the actuator is given in FIGS. 12 and 13. The actuator comprises a slewing ring 411 provided with a toothed rack, and a pinion 412. The slewing ring 411 is best visible in FIG. 12, wherein the pinion was taken away. FIG. 12 further shows a drive mounting plate 1200. The operation of the actuator is similar as explained above in relation to FIG. 4: upon receipt of a pressurized fluid by a hydraulic motor, the pinion 412 rotates around the slewing ring 411, thereby rotating the inspection arms 404, 405.

FIGS. 12 and 13 further show a bearing assembly 414, adapted to retain the slewing ring 411, while allowing for rotation of the outer frame structure with respect to the slewing ring. The bearing assembly 414 is shown in more detail in FIGS. 14 and 15. The bearing assembly 414 comprises three bearings: a first bearing 1501 that engages with the upper surface of the slewing ring 411, a second bearing 1502 that engages with the bottom surface of the slewing ring 411, and a third bearing 1503 that engages with the side surface of the slewing ring 411. FIG. 15 shows that the first bearing 1501 and second bearing 1502 each comprise a sliding interface, while the third bearing 1503 comprises a rolling element.

FIG. 15 further shows that the bearing assembly 414 comprises two separate portions 1500 and 1504. The second portion 1504 comprises the second bearing 1502. The first and third bearing 1501, 1503 are integrated in a bearing block 1500, corresponding to the first portion 1500 of the bearing assembly 414. The bearing block 1500 is tiltable with respect to the slewing ring 411. Upon tilting, the bearing block 1500 pivots around axis 1400, such that the first and the third bearing 1501, 1503 do not longer engage with the upper surface respectively side surface of the slewing ring 411. Upon tilting the bearing blocks, a passage is created, thereby allowing to mount or remove the slewing ring 411, and allowing for easy maintenance. It also allows to deploy the ROV without fall pipe, e.g. for doing a visual inspection of the seabed.

FIG. 16 shows that six individual bearing assemblies 414 are arranged around the slewing ring 411, distributed evenly over the circumference. Such a bearing arrangement with multiple separate bearing assemblies, has the advantage over a single circumferential bearing, that it is less prone to underwater conditions, especially due to salt water, thereby allowing for proper rotation when the actuator is submerged in the water.

Although the present invention has been illustrated by reference to specific embodiments, it will be apparent to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments, and that the present invention may be embodied with various changes and modifications without departing from the scope thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. In other words, it is contemplated to cover any and all modifications, variations or equivalents that fall within the scope of the basic underlying principles and whose essential attributes are claimed in this patent application. It will furthermore be understood by the reader of this patent application that the words “comprising” or “comprise” do not exclude other elements or steps, that the words “a” or “an” do not exclude a plurality, and that a single element, such as a computer system, a processor, or another integrated unit may fulfil the functions of several means recited in the claims. Any reference signs in the claims shall not be construed as limiting the respective claims concerned. The terms “first”, “second”, third”, “a”, “b”, “c”, and the like, when used in the description or in the claims are introduced to distinguish between similar elements or steps and are not necessarily describing a sequential or chronological order. Similarly, the terms “top”, “bottom”, “over”, “under”, and the like are introduced for descriptive purposes and not necessarily to denote relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances and embodiments of the invention are capable of operating according to the present invention in other sequences, or in orientations different from the one(s) described or illustrated above.