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Patent Searching and Data


Title:
WAVE SUPPRESSION APPARATUS AND METHOD
Document Type and Number:
WIPO Patent Application WO/2003/062534
Kind Code:
A1
Abstract:
A method and apparatus for suppressing waves at the surface of a body of liquid is disclosed. The apparatus comprises discharging means for discharging gas into the body of liquid. One or more parameters of the system are dynamically configurable by a control signal to allow optimal operation of the system.

Inventors:
Evett, Alan John (Birsemohr Lodge, Birse Aboyne, Aberdeenshire AB34 5ES, GB)
Graves, Leslie John (Dungreggan, Slug Road, Stonehaven AB34 2DU, GB)
Cook, Peter Andrew (Rock Cottage, Brownshill Stroud, Gloucestershire GL6 8AQ, GB)
Application Number:
PCT/GB2003/000275
Publication Date:
July 31, 2003
Filing Date:
January 24, 2003
Export Citation:
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Assignee:
CALASH LIMITED (Birsemohr Lodge, Birse Aboyne, Aberdeenshire AB34 5ES, GB)
Evett, Alan John (Birsemohr Lodge, Birse Aboyne, Aberdeenshire AB34 5ES, GB)
Graves, Leslie John (Dungreggan, Slug Road, Stonehaven AB34 2DU, GB)
Cook, Peter Andrew (Rock Cottage, Brownshill Stroud, Gloucestershire GL6 8AQ, GB)
International Classes:
B63B39/10; E02B1/00; (IPC1-7): E02B1/00; B63B39/10
Domestic Patent References:
WO1999025609A11999-05-27
Foreign References:
US3822555A1974-07-09
US3068655A1962-12-18
Other References:
PATENT ABSTRACTS OF JAPAN vol. 009, no. 014 (M - 352) 22 January 1985 (1985-01-22)
PATENT ABSTRACTS OF JAPAN vol. 014, no. 243 (M - 0977) 23 May 1990 (1990-05-23)
Attorney, Agent or Firm:
KENNEDYS PATENT AGENCY LIMITED (Floor 5 Queens House, 29 St Vincent Place, Glasgow G1 2DT, GB)
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Claims:
Claims
1. Apparatus for suppressing waves at the surface of a body of liquid, comprising discharging means for discharging gas into the body of liquid, said discharging means having one or more parameters dynamically configurable by a control signal.
2. Apparatus as claimed in Claim 1 further comprising means for detecting a condition at or near the surface of the body of liquid and providing a detection signal to a processing module, said control signal being activated in response to said detection signal.
3. Apparatus as claimed in Claim 2 wherein the processing module incorporates means for communicating information on the surface condition to an operator.
4. Apparatus as claimed in any preceding Claim wherein means is provided for allowing manual activation of the control signal by an operator.
5. Apparatus as claimed in any of Claims 2 to 4 wherein the processing module is hardware capable of running a computer program, and the control signal is generated by the computer program.
6. Apparatus as claimed in Claim 5 wherein the computer program includes an optimisation function for optimising the condition detected at or near the surface of the body of liquid.
7. Apparatus as claimed in any preceding Claim further comprising means for inputting data corresponding to a required wave suppression effect.
8. Apparatus as claimed in any preceding Claim including means for manually overriding the control signal.
9. Apparatus as claimed in any preceding Claim wherein the discharge means comprises a central manifold and a plurality of gas distributors.
10. Apparatus as claimed in any preceding Claim wherein the position of the discharge means is dynamically configurable.
11. Apparatus as claimed in any preceding Claim wherein the discharge volume of gas is dynamically configurable.
12. Apparatus as claimed in any preceding Claim wherein the depth of one or more gas distributors is dynamically configurable.
13. Apparatus as claimed in any preceding Claim wherein the position of one or more gas distributors in a horizontal plane is dynamically configurable.
14. Apparatus as claimed in any preceding claim wherein energy consumption of the discharging means is minimised.
15. Apparatus as claimed in any preceding claim wherein a wave suppression effect provided is the minimum effect required for a particular operation.
16. Apparatus as claimed in any preceding Claim wherein the depth below the surface of the discharging means is greater than 10m.
17. A method of suppressing waves at the surface of a body of liquid, the method comprising the steps of: discharging gas into the body of liquid from a discharging means, and; dynamically configuring one or more parameters of said discharging means by a control signal.
18. The method as claimed in Claim 17 further comprising the steps of: detecting a condition at or near the surface of the body of liquid and providing a detection signal to a processing module; activating said control signal in response to said detection signal received by said processing module.
19. The method as claimed in Claim 18 wherein the detected condition is selected from the group comprising: pitch, roll, yaw, attitude, upward/downward velocity, heave (measured in terms of distance and offset), wind direction, amplitude of oscillation.
20. The method as claimed in Claim 18 or 19 wherein the processing module is hardware capable of running a computer program, and the control signal is generated by the computer program.
21. The method as claimed in any of Claims 17 to 20 wherein the control signal is capable of being overridden.
22. The method as claimed in any of Claims 18 to 21 further comprising the step of communicating information on the surface condition to an operator.
23. The method as claimed in any of Claims 17 to 22 wherein the control signal is capable of being activated manually by the operator.
24. The method as claimed in any of Claims 18 to 23 comprising the additional step of optimising the condition detected at or near the surface of the body of liquid.
25. The method as claimed in any of Claims 17 to 24 wherein the position of one or more gas distributors is configured.
26. The method as claimed in any of Claims 17 to 25 wherein the volume of gas discharged at one or more gas distributors is configured.
27. The method as claimed in any of Claims 17 to 26 further comprising the step of inputting data corresponding to a required wave suppression effect.
28. The method as claimed in any of Claims 17 to 27 wherein energy consumption of the discharging means is minimised.
29. The method as claimed in any of Claims 17 to 28 wherein a wave suppression effect provided is the minimum effect required for a particular operation.
30. The method as claimed in any of Claims 17 to 29 wherein the depth below the surface of the discharging means is greater than 10m.
Description:
Wave suppression apparatus and method The present invention relates to the field of wave suppression, and in particular to the suppression of waves by discharging gas into a liquid.

In the context of this description, the term wave should be interpreted broadly to cover waves, swell, wakes generated by passing vessels, billows, turbulence, or any other type of disruption at the surface of a body of water.

It is well known in the field of hydraulic engineering that it is possible to affect the mechanical properties of a body of liquid by discharging gas below the surface.

Such systems have proposed, albeit without practical verification, to create calm surface regions in a body of water, thus allowing various weather sensitive operations to take place in conditions that would otherwise be more difficult to achieve.

For example, it can be seen that applications could exist in marine construction. The installation of subsea or

topside structures for the oil or gas industries, subsea maintenance or intervention operations, or the construction of towers in the offshore wind farm industry requires the lifting and manoeuvring of heavy equipment on marine vessels. Such heavy lifts may ordinarily only be conducted in very calm conditions, or with vessels having specifically designed or modified compensated cranes.

In addition, the prior art describes the use of pneumatic breakwaters, which may be created around harbours or jetties allowing calmer conditions to be achieved for the manoeuvring and docking of vessels. Applications also exist for these techniques for offshore facilities and structures.

Further applications exist in affecting the wave conditions in order to control the flow of oil slicks or other chemical spills around environmentally sensitive areas.

WO 99/25609 Al discloses a system for modifying the mechanical properties of a body of water, by dispersing bubbles below the surface. However, this document does not adequately deal with issues relating to the volumes of gas used, or the depths at which the gas is discharged. Furthermore, the document does not disclose a system that may be configured to provide a wave dispersal effect to suit different conditions.

In general, the prior art systems have limitations in their effectiveness when used in real-life situations.

They lack the versatility and adaptability required in

order to perform in the wide variety of weather conditions that arise in marine environment.

The systems suggested in the prior art do not give appropriate consideration to the complex relationship between depth, volume of gas discharge and diffuser design. The prior art arrangements take a simplistic approach that does not adequately deal with each of these factors when configuring the system. Consequently, the arrangements do not operate optimally.

A key deficiency of the prior art is a lack of efficiency. If the gas is not discharged at the correct depth, large volumes of gas are required in order to provide an adequate suppression effect. This can make the systems impractical to operate, as they require large amounts of energy in order to run the compressors. This problem is exacerbated by the fact that the prior art machines fail to offer the dynamic variation necessary to run the devices at optimal efficiency, providing just enough gas discharge to create the desired degree of wave suppression.

It would therefore be desirable to provide a wave suppression system that obviated, or at least mitigated one or more drawbacks of the prior art.

It is one object of the invention to provide a wave suppression system that is capable of being adapted to suit the particular weather conditions.

It is another to provide controlled suppression of the surface waves irrespective of water depth and seabed topography.

It is yet another object of the invention to provide a wave suppression system that is efficient in its operation.

It is a further aim of the invention to provide a wave suppression system that is capable of providing a wave suppression effect for a particular task with optimal efficiency.

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

According to a first aspect of the invention, there is provided apparatus for suppressing waves at the surface of a body of liquid, comprising at least one gas distributor having an outlet through which gas is discharged into the body of liquid, said gas distributor having at least one parameter dynamically configurable by a control signal.

In the context of this description, the term"dynamically configurable"is used to reflect the ability to adjust or readjust the system during use. The adjustment or readjustment may be effected automatically in response to a monitoring system, or the adjustment may be a manual intervention by an operator. For example, in a partially automated system, the adjustment may be effected by the operation of controls at a control interface. However, in a simpler implementation, the manual intervention

could be a physical adjustment of operative components of the system themselves.

According to a second aspect of the invention there is provided method of suppressing waves at the surface of a body of liquid, comprising the steps of: - discharging gas into the body of liquid through an outlet of at least one gas distributor, and; - dynamically configuring one or more parameters of said gas distributors by a control signal.

The method may further comprise the steps of: - detecting a condition at or near the surface of the body of liquid and providing a detection signal to a processing unit; - activating said control signal in response to said detection signal received by said processing unit.

According to a third aspect of the invention there is provided apparatus for suppressing waves at the surface of a body of liquid, comprising discharging means for discharging gas into the body of liquid, said discharging means having one or more parameters dynamically configurable by a control signal.

According to a fourth aspect of the invention there is provided a method of suppressing waves at the surface of a body of liquid, comprising the steps of: - discharging gas into the body of liquid from a discharging means, and ; - dynamically configuring one or more parameters of said discharging means by a control signal.

According to a fifth aspect of the invention there is provided apparatus for suppressing waves at the surface of a body of liquid, comprising discharging means for discharging gas into the body of liquid, said discharging means having a depth dynamically configurable by a control signal, the depth below the surface being greater than 10m.

According to a sixth aspect of the invention there is provided a method of suppressing waves at the surface of a body of liquid, comprising the steps of: - discharging gas into the body of liquid through an outlet of at least one gas distributor, and; - dynamically configuring the depth below the water surface of said gas distributors by a control signal, wherein the depth below the surface is greater than 10m.

Preferably, the position of the discharging means is configurable in X, Y and Z axes. More preferably, the discharge volume of the gas is configurable.

The apparatus may further comprise means for detecting a condition at or near the surface of the body of liquid and providing a detection signal to a processing unit, said control signal being activated in response to said detection signal.

The processing unit may incorporate means for communicating information on the surface condition to an operator.

Optionally, the operator manually activates the control signal.

The processing unit may be hardware capable of running a computational fluid dynamics model (or similar software), the control signal being generated by the computational fluid dynamics model. The control signal may include means for manually overriding the control signal.

Optionally, the computational fluid dynamics model includes an optimisation function for optimising the condition detected at or near the surface of the body of liquid.

The apparatus may further comprise an interface for inputting data corresponding to a required wave suppression effect.

The discharge means may comprise a central manifold and a plurality of gas distributors.

Preferably, the depth of one or more gas distributors is configurable. Optionally, the position of one or more gas distributors in a horizontal plane is configurable.

Each gas distributor may be connected to the central manifold via a hose, and the central manifold may include a control valve for controlling the volume of gas entering the hose.

One or more gas distributors may comprise a plurality of electrical thrusters for imparting movement to the gas distributor. Alternatively, or in addition, one or more

gas distributors may be attached, via a cable, to a winch for imparting movement to the gas distributor.

The winch attached to the seabed preferably has a hydrostatic control mechanism which allows the depth of the control distributor to be controlled irrespective of water depth.

The detected condition may be a condition of a vessel located in the body of liquid.

Alternatively, the detected condition may be a condition of a buoy located in the body of liquid.

Preferably, the detected condition is selected from the group comprising: pitch, roll, yaw, attitude, upward/downward velocity, heave (measured in terms of distance and offset), wind direction, amplitude of oscillation.

The method may further comprise the steps of: - detecting a condition at or near the surface of the body of liquid and providing a detection signal to a processing unit; - activating said control signal in response to said detection signal received by said processing unit.

The processing unit may run a computational fluid dynamics model, the control signal being generated by the computational fluid dynamics model or similar software.

The computational fluid dynamics model may include an optimisation function for optimising the condition detected at or near the surface of the body of liquid.

The detected condition may be optimised by configuring the position of one or more gas distributors.

Alternatively, or in addition, the detected condition may be optimised by configuring the volume of gas discharged at one or more gas distributors.

Various embodiments of the invention will now be described by way of example only, and with reference to the following figures in which: Figure 1 schematically illustrates a first embodiment of the invention ; Figure 2 schematically illustrates an alternative embodiment of the invention; Figures 3A and 3B schematically illustrate an alternative embodiment of the invention Figure 4 schematically illustrates a further embodiment of the invention ; Figure 5 schematically illustrates the embodiment of Figure 4 as applied to a harbour; Figure 6a schematically shows an example embodiment of the invention ;

Figure 6b schematically shows an example embodiment of the invention, including an interface and a display.

Figure 1 shows wave suppression apparatus generally depicted at 10, positioned within a body of liquid 11, which in this case is a marine environment. The apparatus includes central manifold 12 and gas distributor 14 connected to the central manifold via hose 13. The central manifold and gas distributor are connected to the seabed via cables 15.

Each cable 15 is attached to a controllable winch 16 that is fixed to the seabed. The central manifold 12 and the gas distributor 14 are provided with buoyancy aids, imparting an upward force, which is countered by the cable when at its full extent. Thus the depths of the central manifold 12 and the gas distributor 14 may be controlled by the cable and the winch which irrespective of depth, pays out until the distributor is at the required distance below the water surface. The buoyancy aids may be air bags, foams, or any other acceptable buoyancy system.

The gas distributor 14 is provided with a hydrostatic head for calculating the water pressure. The hydrostatic head is therefore able to provide information on the depth of the distributor below the water surface. This method of measuring the depth is preferable to measuring the length of cable administered from the winch at the seabed, so that the depth remains constant irrespective of variations in seabed topography. Alternative methods of measuring the depth of the gas distributors may be employed, for example Sonar.

In this embodiment, conduit 17 provides air to the central manifold from a vessel 18 floating on the water.

In use, air is compressed at the surface and pumped in the direction of the arrow to the central manifold 12.

Central manifold includes a control valve 19 for controlling the passage of air into the hose 13, and thus to the gas distributor 14. Air is discharged from the gas distributor 14, and the density gradient causes the air bubbles to rise to the surface. As the gas rises, it expands to create areas of aerated water on the water surface. Waves entering the aerated region are severely damped by the bubbles. Consequently, an area of calm 20 is created in the lee of the prevailing weather directions (illustrated by arrow 21).

Typically, the gas discharge means will operate at depths greater than 10m below the water surface. These depths allow an effective level of wave suppression even for relatively low volumes of gas discharged. For example, for a 3 percent by volume aeration (in a region just below the surface), gas discharge at 4 metres requires twenty times the volume of gas discharged than when the distributors are at a depth of 60 metres.

The extent of the wave dampening effect is a function of the volume of gas discharged, and the depth of the gas distributor 14. The present system is configurable with respect to both of these parameters to provide a highly adaptable wave suppression effect at increased efficiency.

Included within the apparatus is a processing unit for controlling the depth of the gas distributor 14 and the volume of the gas discharged. The processing unit may be positioned on the vessel at 22, and communicates with the central manifold via conduit 17. Alternatively, there may be a wireless, or acoustic communication link between the vessel 18 and the central manifold 12. Another possibility is that the processing unit is positioned within the central manifold 12.

The processing unit runs a computational fluid dynamic (CFD) model which calculates the suppression effect of the bubble flume 22 on the surface waves for a given gas discharge volume and gas distributor depth. The CFD predetermines values for these parameters, based on the sea state obtained by the model. However in this embodiment, the vessel is provided with means for measuring a number of factors characteristic of the vessel movement. These include vessel pitch, roll, attitude, upward/downward velocity, heave (measured in terms of distance and offset), amplitude of oscillation, wind direction, wave height, and yaw. The measurements can be made using gyroscopic techniques known in the art or by any other suitable means.

By monitoring the above parameters of vessel movement, the apparatus makes a direct measurement of the affect of the bubble plume on the vessel. This data is fed back into the CFD model and utilised in order to provide an improved wave suppression effect as follows.

The CFD incorporates an optimisation function for optimising the detected conditions of vessel movement.

Control signals generated by the processing unit in response to the CFD model are sent to the central manifold to alter one or more of gas discharge volume and gas distributor depth. For example, to increase the suppression effect, the gas discharge volume may be increased, or the depth of the distributor increased by shortening the cable.

The effect of the parameter change is re-evaluated by the CFD model by measuring the detected motion in the vessel.

If the detected conditions do not fall within acceptable limits, associated for example with a required stability level, the gas discharge volume or gas distributor position may be adjusted again in order to adapt the wave calming effect further.

In this manner, the apparatus provides a wave suppression effect that is self-monitored by virtue of the feedback mechanism from the waterborne vessel. The CFD model is able to improve and develop itself by including data detected at the water surface when calculating predictive suppression effects.

Thus, in addition to the regular monitoring and adjustment of the gas discharge parameters provided by the feedback loop, the CFD model is able to"learn"the most appropriate characteristics for given weather conditions.

Figure 6a is a schematic representation useful for demonstrating how the apparatus is dynamically configured.

Linked to a processing unit 60 is a detector 64 and gas distributor 64. The detector 62 monitors the wave suppression effect produced by the gas distributor 64, and provides a detection signal 61 to the processing unit 60. The processing unit, in accordance with software running on the unit, generates a control signal 63 to configure the depth, position, and/or gas discharge volume of the gas distributor, in order to optimise the wave suppression effect produced..

It is envisaged that the system could have a number of preset modes of operation, with successive modes providing successively greater wave-suppression effects.

The mode can be selected before an operation is commenced, according to the requirements of that operation. This approach allows the system to be tailored to the needs of the users quickly and easily, and avoids the consumption of excessive amounts of energy during relatively low sensitivity operations.

In an alternative arrangement, the feedback loop has an element of manual control. The parameters of vessel movement are monitored by gyroscopic sensors, and data is displayed to a system operator. Such a display could, for example, be a computer monitor showing data in graphical form. The operator can review the effect of the apparatus on the vessel movement, and adjust the parameters of volume and or position depending on the extent of wave suppression required.

Yet simpler systems may include an instruction to an operator that he or she should increase or decrease the

wave suppression effect. Alternatively, the system may require a greater degree of operator judgement.

An arrangement with manual control is shown in Figure 6b.

The apparatus is additionally provided with a display 66 and an interface 67, which may be a keyboard. In this example, the processing unit displays data in response to the detection signal 61. An operator of the system is therefore able to monitor the effect of the gas discharge on the surface conditions. Interface 67 allows the operator to adjust the position and/or the discharge volume of gas if the display indicates that it is required. In addition, the interface allows the operator to override a control signal that is generated automatically by the processing unit or intervene in some other manner.

Figure 2 shows an alternative embodiment of the invention having a plurality of gas distributors 14a to 14d. Each gas distributor is attached via a hose to central manifold 12, and each hose is provided with a control valve (not shown) proximal with respect to the central manifold 12.

The plurality of gas distributors allows waves to be suppressed over an increased area 20 at the surface of the body of water. In addition, each gas distributor is attached to the seabed via a cable and winch. Thus, the height of each gas distributor is independently adjustable according to the seabed topography and the conditions at the water surface. As before, the volume discharged through each distributor can be controlled at the central manifold.

Figure 2 shows conduit 17 supplying compressed air through the central manifold. This air may be supplied from a vessel floating at the surface of the water, as shown in Figure 1. Alternatively, the compressed air may be supplied from another source, such as a pump situated on a permanent or semi-permanent structure protruding through the water surface. A further alternative is to provide compressed air from storage cylinders positioned above or below the surface of the water.

In this embodiment the CFD model initially calculates the most appropriate positions and gas discharge volumes for each gas distributor in accordance with predicted surface state. As before, by measuring characteristics pertaining to the movement of vessel in the wave suppressed area, the parameters of gas discharge volume and distributor position can be adjusted in order to optimise the wave suppression effects.

It is envisaged that if the system was to be deployed in extreme depths, each gas distributor could be provided with a free-swimming remotely operable vehicle (ROV) to allow manoeuvrability in 3-dimensions.

It should be noted that when multiple gas distributors are used, it is necessary to avoid preferential flow of the gas. That is, for two gas distributors at differing depths, supplied by a single gas supply, the gas will preferentially follow the path of least resistance. This will result in a greater discharge of gas through the highest positioned distributor (lower pressure), and a

lesser amount through the distributor at the greater depth (higher pressure).

This problem can be compensated for in a number of ways.

Firstly, the depth of each distributor can be controlled such that they all remain at the same depth. The ROVs/winches are used to adjust the positions of the distributors to ensure that they are each working efficiently.

Alternatively, giving each distributor its own supply, at an independently controlled pressure and volume can negate the above need. A further option is to provide the apparatus with control release valves so the distributors only discharge gas at predetermined pressures/depths.

The present invention also allows preferential flow to be utilised in the wave suppression technique. For example, the balance of gas discharge between two distributors can be shifted by raising or lowering one or other of the distributors.

The arrangement shown in Figure 2 is extremely flexible with regard to the suppression effect provided at the surface.

In addition, a further function of the cable arrangement is to allow the manifold and gas distributors to be stored close to the seabed until they are required.

An alternative embodiment is shown in Figures 3a and 3b.

Figure 3a shows waterborne vessel 18 being connected to

gas discharging means 13 via conduit 17. Fixed to the gas discharging means is remotely operated vehicle (ROV) 32 also connected to the vessel via umbilical 33.

ROV 32 is manoeuvrable via a group of electrical thrusters located on the ROV. These thrusters then control the depth of the gas discharging means in addition to the position in a horizontal plane, and therefore the gas distributor can be manoeuvred in three dimensions.

The Figure shows the gas distributor located such that the bubble plume is created windward of the vessel, and the artificially calm area of water is positioned"up- weather"of the vessel. Once again, the apparatus contains a processing unit for running a CFD model. The CFD model is able to optimise the vessel conditions by carefully controlling the position and depth in X, Y and Z axes of the ROV and the volume of gas discharged.

Figure 3B illustrates an embodiment of the invention in use. In this example, the body of water has a fast flowing current in direction 34, and the position of the gas distributor is offset accordingly. The plume of bubbles 35 begins at a point distanced from the vessel, and the current 34 tends to deflect the plume towards the vessel so that the wave suppressed area is located close to the vessel. As before, a feedback mechanism and optimisation function can be utilised to maintain the position of the distributor in the ideal location.

Figure 4 shows a further embodiment of the invention. In this embodiment, a buoy is utilised in the wave-

suppressed area. The buoy contains means for measuring a number of factors characteristic of its motion, such as pitch, roll, attitude, upward/downward velocity, amplitude of oscillation, wind direction, wave height, and yaw. The data is used in the CFD model to monitor the effectiveness of the gas discharging means, and if required, a control signal configures the parameters of the apparatus.

Figure 4 shows an alternative type of gas discharging means to the type used in earlier embodiments. In this case, the gas discharging means is a permanent or semi- permanent structure 42 fixed to the seabed. Clearly, the position of this apparatus is not as readily adjustable.

However, the wave suppression effect can be adapted by controlling the gas discharge rate in accordance with the CFD model.

The embodiment described with reference to Figure 4 may be utilised in situations where a high degree of positional variation is not required. Such an example is in a harbour, where it is desirable to provide a wave- suppressed area in a fixed location.

Figure 5 illustrates the embodiment of Figure 4, as applied to a harbour. Figure 4 shows an existing breakwater 50 defining one wall of a harbour. Positioned under the surface is a conduit 52 fixed to the seabed.

The conduit contains a series of distributors for discharging gas into the body of liquid.

The conduit and distributors are positioned such that bubble plumes 54 create a wave-suppressed region along

the mouth of the harbour. Thus the waves in the vicinity of the harbour area 53 are attenuated as they pass into the harbour. This creates a calm region 55 within the harbour area.

As in the case for Figure 4, the apparatus is provided with a wave-rider buoy, equipped to measure various surface conditions. By transmitting the data to a processing unit contained elsewhere within the apparatus, a feedback loop is created. This allows the gas discharge volume to be controlled in order to optimise the wave suppression effect.

The present invention discloses an improved wave suppression system with high configurability.

A further benefit of the system, in at least one of its aspects, is that it is mobile, easily moved from location to location and capable of providing protection where water depth and seabed topography are variable. In addition, the technique can easily be adapted where and when variable surface conditions require different levels of suppression for a given task.

The key to at least one aspect of the invention is in providing discharging means with a number of configurable parameters. In all of the described embodiments, the apparatus allows the wave suppression effect to be controlled by a CFD model in order to optimise the surface conditions. However, it is envisaged that where necessary, the CFD model can be overridden by a manual control signal activated by an operator. This may necessary where an unusually high degree of wave

suppression is required, for example when conducting a particularly sensitive operation.

Likewise, the invention may be used to provide a lesser degree of wave suppression when required. One of the problems associated with the prior art devices is that they are effectively two-state devices, being either"on" or"off".

In contrast, the present system is dynamically variable, and may be used to provide varying degrees of wave suppression, according to the particular task in hand.

Thus, for relatively straightforward operations, the apparatus could discharge less gas, using less energy than required for a maximum suppression effect.

Furthermore, the present system can be used in order to provide different types of suppression effect during different stages of an operation.

As well as varying the output of the system according to the weather sensitivity of the operation in hand, the effect can be altered according to the sensitivity of the particular vessel. Larger vessels will, in general, be less susceptible to adverse conditions than smaller vessels. The present system is able to cater for the vessel size, and expend the minimum amount of energy in achieving the required suppression effect.

Additionally, deploying the system at increased depths below the water surface provides further economical benefits by reducing the volume of gas required to be discharged.

It will be evident to one skilled in the art that the communication between the various components of the apparatus can be accomplished in a variety of ways. For example, data characteristic of surface conditions, detected by either the buoy or a vessel, can be communicated to the processing unit by wiring or by a wireless transmitter/receiver arrangement. Likewise, the control signal from the processing unit to the central manifold of the discharging means may be transmitted via suitable cables or by wireless means.

Further, different spatial configurations of conduits and distributors may be used other than those described above. For example, if a wave suppression effect is required over a large area, it may be desirable to provide a two-dimensional array of gas distributors.

Various modifications and improvements may be incorporated within the scope of the invention.