Patent Publication Number: US-8523483-B2

Title: Ice break-up using artificially generated waves

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/301,076 filed Feb. 3, 2010. 
    
    
     BACKGROUND OF THE INVENTION 
     This section is intended to introduce various aspects of the art, which may be associated with exemplary embodiments of the present disclosure. This discussion is believed to assist in providing a framework to facilitate a better understanding of particular aspects of the present disclosure. Accordingly, it should be understood that this section should be read in this light, and not necessarily as admissions of prior art. 
     FIELD OF THE INVENTION 
     The present invention relates to the field of offshore operations in Arctic conditions. More specifically, the present invention relates to the break-up of ice masses in Arctic waters to prevent a collision of such ice masses with an offshore operations facility. 
     GENERAL DISCUSSION OF TECHNOLOGY 
     As the world&#39;s demand for fossil fuels increases, energy companies find themselves pursuing hydrocarbon resources in more remote areas of the world. Such pursuits sometimes take place in harsh, offshore conditions such as the North Sea. In recent years, drilling and production activities have been commenced in deepwater Arctic locations. Such areas include the Sea of Okhotsk at Sakhalin Island, as well as the U.S. and Canadian Beaufort Seas. 
     Because of the cold ambient temperatures, marine bodies in Arctic areas are frozen over during much of the year. Therefore, exploration and production operations in Arctic areas primarily take place in the summer months. Even during summer months (and the weeks immediately before and after when operations may be extended), the waters are prone to experiencing floating ice masses. Floating ice masses create hazards for equipment, support vessels, and even personnel. 
     Due to the presence of floating ice masses, it is desirable during oil and gas exploration, development, and production operations to employ ice management systems. The ice management systems would be used to reduce the ice impact loads on floating equipment. One method of ice management involves the use of ice breaking vessels to actively break large ice floes into smaller pieces. Of course, technology is already in use for mechanically breaking ice by direct contact with a ship hull. Breaking ice is generally not a case of cutting through the ice by forcing the vessel into an ice mass; rather, ice breaking occurs by the ice-strengthened ship riding up and over an ice mass, with the weight of the ship then breaking the ice. This technology is widely practiced outside the context of oil and gas exploration and production activities, such as for keeping shipping lanes open. 
     In the context of hydrocarbon development activities within an Arctic region, an ice breaking vessel has been considered for breaking large ice masses into smaller ice pieces. The smaller ice pieces may then be moved out of the path of floating equipment. Where the floating ice pieces are very small, such pieces will have only a small impact load that can readily be handled by floating equipment. Alternatively, they may be pushed aside using a tug boat or further broken by a second icebreaker. Such an active ice management method has been successfully implemented to extend the operating season somewhat beyond the summer ice-free period for seasonal production operations in the Sea of Okhotsk at Sakhalin Island as well as for exploratory drilling in the U.S. and Canadian Beaufort Sea. 
     Another technique for managing ice floes involves the use of dual ice breakers. Applicant is aware of an arctic coring expedition that was conducted near the North Pole in the summer of 2004. This was reported by K. Moran, J. Backman and J. W. Farrell, “Deepwater Drilling in the Arctic Ocean&#39;s Permanent Sea Ice,”  Proceedings of the Integrated Ocean Drilling Program , Volume 302, 2006). For this operation, two icebreakers were stationed updrift of a stationary seafloor coring vessel. The first ice breaker reportedly traveled in a circular pattern to reduce the size of large ice floes to pieces that were a maximum of 100 to 200 meters wide. The second icebreaker then broke the large ice pieces to produce smaller ice masses that were up to 20 meters wide. In this program, the coring vessel was able to maintain location for as long as nine consecutive days despite the presence of the broken ice pieces. 
     The use of active ice breaking vessels to protect floating equipment in the Arctic has several drawbacks. First, it requires maintaining at least one very robust ice breaking vessel, and preferably two. Second, where a second ice breaking vessel is used, the second ice breaking vessel may be unrealistically required to make tight circles or to maintain a position in direct coordination with the first ice breaker. Where only one ice breaking vessel is used, that vessel must not only break the large ice masses into smaller pieces, but it may also be called into duty to shepherd smaller pieces around floating equipment. In some cases, such as when a sudden change in floe direction takes place or when more than one large ice piece is approaching floating equipment simultaneously, this second responsibility may not be realistic, resulting in a need for a second icebreaker boat to prevent exposure of the floating vessel to a significant risk of collision with ice. 
     An improved method is needed for breaking up an ice mass approaching a floating operations vessel in Arctic waters. A system and improved method are also needed for clearing a floating ice mass as it approaches a hydrocarbon development platform such as a drill ship. 
     SUMMARY OF THE INVENTION 
     The methods described herein have various benefits in the conducting of oil and gas exploration and production activities in Arctic regions. First, a method is provided for clearing an approaching floating ice mass. The method, in one embodiment, includes the step of locating a hydrocarbon development platform in a marine environment. The hydrocarbon development platform may be, for example, a drill ship or a ship-shaped production platform. Alternatively, the hydrocarbon development platform may be, for example, a non-ship-shaped workover platform, a floating production, storage and offloading (“FPSO”) vessel, or an oceanographic survey vessel. Other types of vessels include a construction vessel as may be used to install subsea equipment or to lay pipe, a subsea cable installation vessel, a diver support vessel, an oil spill response vessel, or a submarine rescue vessel. 
     The marine environment comprises a large body of water. The body of water includes a water surface. The marine environment may be a bay, a sea, or an ocean in the Arctic region of the earth. The hydrocarbon development platform is optionally maintained at its location in the marine environment by a dynamic positioning system. Alternatively, a mooring system may be employed. 
     The method further includes providing an intervention vessel. The intervention vessel is preferably a ship-shaped vessel having a deck and a hull. Preferably, the intervention vessel is equipped with ice-breaking capability. 
     The intervention vessel has a water-agitating mechanism carried thereon. Various types of water-agitating mechanisms may be employed. For example, the water-agitating mechanism may comprise a gyroscopic system attached within the hull of the intervention vessel. The gyroscopic system may comprise a large spinning mass, a controller, and at least one gear for moving the large spinning mass so as to cause forced precession. The controller reciprocates the large spinning mass according to a specified frequency and amplitude. The large spinning mass is reciprocated in a direction to cause the intervention vessel to pitch, to roll, or combinations thereof. This movement of the intervention vessel, in turn, creates ice-breaking waves. 
     In another embodiment, the water-agitating mechanism comprises a plurality of air guns. The air guns are disposed below the surface of the marine environment in the body of water. The plurality of air guns may be fired substantially simultaneously at a frequency of about two seconds to five seconds (0.5 Hz to 0.2 Hz). 
     In another embodiment, the water-agitating mechanism comprises a plurality of paddles. The paddles rotate through the surface of the marine environment and into the body of water. The plurality of paddles may rotate substantially simultaneously at a frequency of about three to five seconds (0.33 Hz to 0.2 Hz). 
     In another embodiment, the water-agitating mechanism comprises at least one pair of offsetting propulsion motors. The propulsion motors operate below the surface of the marine environment and in the body of water. In one aspect, the at least one pair of offsetting propulsion motors are intermittently started and stopped in cycles to create waves having well-defined peaks and troughs. The cycles may be, for example, every two to ten seconds (0.5 Hz to 0.1 Hz). 
     In still another embodiment, the water-agitating mechanism comprises a plurality of plungers that reciprocate vertically in the body of water. In one aspect, the plurality of plungers reciprocate substantially simultaneously. 
     In one arrangement, the plurality of plungers may reciprocate according to a stroke that is about 5 to 20 feet. In this instance, the frequency of the strokes may be about every three to ten seconds (0.33 Hz to 0.1 Hz). Here, the top of the stroke is above the surface of the body of water, while the bottom of the stroke is below the surface of the body of water. 
     In another arrangement, the plurality of plungers may reciprocate according to a stroke that is about 1 to 5 feet. This is a much shorter stroke such that the plunger is in the nature of a resonance vibrator. In this instance, the frequency of the strokes is about 0.1 to 2.0 seconds (10.0 Hz to 0.5 Hz). Here, both the top and the bottom of each stroke is below the surface of the body of water. 
     The method for clearing an approaching floating ice mass also includes determining a direction from which the ice mass is approaching the hydrocarbon development platform. The method then includes positioning the intervention vessel generally between the hydrocarbon development platform and the approaching ice mass. 
     The method also includes actuating the water-agitating mechanism in order to propagate artificially generated waves. The waves travel towards a leading edge of the approaching ice mass. In one aspect, the artificially generated waves have an amplitude of about two feet to five feet. 
     The method also includes continuing to operate the water-agitating mechanism so as to fracture the ice mass along the leading edge. This causes small ice pieces to separate from the ice mass. The small ice pieces then float in the marine environment, with some tending to float towards the hydrocarbon development platform. 
     The method may optionally include continuing to further operate the water-agitating mechanism. This is for the purpose of clearing at least some of the small ice pieces from the hydrocarbon development platform. This results in a substantially ice-free zone downstream of the intervention vessel. This, in turn, allows the hydrocarbon development platform to operate without worry of ice mass collisions. As an alternative, or in addition, the hydrocarbon development platform is engineered to withstand the load caused by any impact with the small ice pieces separated from the ice mass. 
     A system for operating a development platform in an icy marine environment is also provided herein. The marine environment defines a large body of water, a water surface, and ice masses floating therein. 
     In one embodiment, the system includes a substantially stationary development platform. The development platform is preferably configured for hydrocarbon development operations. The platform is positioned in the icy marine environment. The system also includes an intervention vessel. The intervention vessel is configured to float in the marine environment. 
     The system further includes a water-agitating mechanism. The water-agitating mechanism is mechanically connected to and operates on the intervention vessel. The water-agitating mechanism is configured to propagate artificially generated waves towards a leading edge of the ice mass. In this way, the ice mass is fractured along the ice mass along its leading edge. This, in turn, causes small ice pieces to separate from the ice mass. 
     The water-agitating mechanism may be in accordance with any of the illustrative mechanisms listed above. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the present inventions can be better understood, certain drawings, charts, graphs and/or flow charts are appended hereto. It is to be noted, however, that the drawings illustrate only selected embodiments of the inventions and are therefore not to be considered limiting of scope, for the inventions may admit to other equally effective embodiments and applications. 
         FIG. 1  is a schematic view of a marine ice field wherein hydrocarbon recovery operations are taking place. A vessel having a water-agitating mechanism is provided in the marine ice field to break up ice masses and divert them around a drill ship. 
         FIG. 2A  is a cross-sectional view of an intervention vessel having a water-agitating mechanism, in a first embodiment. Here, the water-agitating mechanism is a hydro-gyroscope for inducing motion of the vessel. 
         FIG. 2B  is a plan view showing the hydro-gyroscopic system of  FIG. 2A . 
         FIG. 2C  is a side view of the hydro-gyroscope of  FIG. 2A . Here, the gear system for forced precession is seen. 
         FIG. 3  is an end view of a vessel having a water-agitating mechanism, in a second embodiment. Here, the water-agitating mechanism is a plurality of pneumatic guns. 
         FIG. 4  is a cross-sectional view of a vessel having a water-agitating mechanism in a third embodiment. Here, the water-agitating mechanism is a plurality of rotating paddles. 
         FIG. 5  is an end view of a vessel having a water-agitating mechanism, in a fourth embodiment. Here, the water-agitating mechanism is a pair of offsetting propulsion motors. 
         FIGS. 6A and 6B  are cross-sectional views of a vessel having a water-agitating mechanism, in a fifth embodiment. Here, the water-agitating mechanism is a plunger having long vertical strokes that move the plunger in and out of the water. 
         FIG. 6A  shows the plunger at the top of its stroke above the water. 
         FIG. 6B  shows the plunger at the bottom of its stroke under the surface of the water. 
         FIG. 7  is a cross-sectional view of a vessel having a water-agitating mechanism, in a sixth embodiment. Here, the water-agitating mechanism is a plunger oscillating with fast, short strokes under the water. 
         FIG. 8  is a schematic view of a marine ice field wherein hydrocarbon recovery operations are taking place, in an alternate embodiment. Here, the intervention vessel is at least one moored buoy, with each moored buoy having an attached water-agitating mechanism field to break up ice masses. 
         FIG. 9  is a flowchart showing steps for clearing an approaching floating ice mass, in one embodiment. 
     
    
    
     DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS 
     Definitions 
     As used herein, the term “hydrocarbon” refers to an organic compound that includes primarily, if not exclusively, the elements hydrogen and carbon. Hydrocarbons may also include other elements, such as, but not limited to, halogens, metallic elements, nitrogen, oxygen, and/or sulfur. Hydrocarbons generally fall into two classes: aliphatic, or straight chain hydrocarbons, and cyclic, or closed ring hydrocarbons, including cyclic terpenes. Examples of hydrocarbon-containing materials include any form of natural gas, oil, coal, and bitumen that can be used as a fuel or upgraded into a fuel. 
     As used herein, the term “hydrocarbon fluids” refers to a hydrocarbon or mixtures of hydrocarbons that are gases or liquids. For example, hydrocarbon fluids may include a hydrocarbon or mixtures of hydrocarbons that are gases or liquids at formation conditions, at processing conditions or at ambient conditions (15° C. and 1 atm pressure). Hydrocarbon fluids may include, for example, oil, natural gas, coalbed methane, shale oil, pyrolysis oil, pyrolysis gas, a pyrolysis product of coal, and other hydrocarbons that are in a gaseous or liquid state. 
     As used herein, the terms “produced fluids” and “production fluids” refer to liquids and/or gases removed from a subsurface formation, including, for example, an organic-rich rock formation. Produced fluids may include both hydrocarbon fluids and non-hydrocarbon fluids. Production fluids may include, but are not limited to, pyrolyzed shale oil, synthesis gas, a pyrolysis product of coal, carbon dioxide, hydrogen sulfide and water (including steam). 
     As used herein, the term “fluid” refers to gases, liquids, and combinations of gases and liquids, as well as to combinations of gases and solids, and combinations of liquids and solids. 
     As used herein, the term “gas” refers to a fluid that is in its vapor phase at 1 atm and 15° C. 
     As used herein, the term “oil” refers to a hydrocarbon fluid containing primarily a mixture of condensable hydrocarbons. 
     The term “Arctic” refers to any oceanographic region wherein ice features may form or traverse through and affect marine operations. The term “Arctic,” as used herein, is broad enough to include geographic regions in proximity to both the North Pole and the South Pole. 
     The term “marine environment” refers to any offshore location. The offshore location may be in shallow waters or in deep waters. The marine environment may be an ocean body, a bay, a large lake, an estuary, a sea, or a channel. 
     The term “ice mass” means a floating and moving mass of ice, floe ice, or ice berg. The term also encompasses pressure ridges of ice within ice sheets. 
     The term “platform” means a deck on which offshore operations such as drilling operations take place. The term may also encompass any connected supporting floating structure such as a conical hull. 
     Description of Selected Specific Embodiments 
     The inventions are described herein in connection with certain specific embodiments. However, to the extent that the following detailed description is specific to a particular embodiment or a particular use, such is intended to be illustrative only and is not to be construed as limiting the scope of the inventions. 
       FIG. 1  is a schematic view of a marine ice field  100 . The ice field  100  resides over a large marine body  105 . The marine body  105  is preferably a salt water body in the Arctic region of the earth. Examples of such marine areas include the U.S. Beaufort Sea, the Canadian Beaufort Sea, Baffin Bay, Hudson Bay, and the Sea of Okhotsk at Sakhalin Island. 
     The ice field  100  contains one or more large ice masses. In the arrangement of  FIG. 1 , a single ice mass is provided at  110 . The ice mass  110  is moving in a direction indicated by arrow “I.” 
     The marine ice field  100  is undergoing hydrocarbon development activities. In  FIG. 1 , a hydrocarbon development platform  120  is provided as part of the hydrocarbon development activities. In the arrangement of  FIG. 1 , the hydrocarbon development platform  120  is a drill ship. The drill ship  120  operates to drill one or more wellbores through subsurface strata. The drill ship  120  is then used to complete the wellbores in such as way as to safely and efficiently produce valuable hydrocarbons to the earth surface. 
     While a drill ship  120  is shown in  FIG. 1 , it is understood that the hydrocarbon development platform  120  may be another type of platform. For example, the hydrocarbon development platform  120  may be a production platform, a workover platform, a floating production, storage and offloading (“FPSO”) vessel, an offshore workboat, a catenary anchor leg mooring (“CALM”) buoy, or an oceanographic survey vessel. 
     The hydrocarbon development platform  120  is positioned in the ice field  100 . During warmer summer months, the marine body  105  is generally free of large ice masses such as ice mass  110 . The Arctic area may have smaller floating ice bodies, but these generally are not a threat to operations on the hydrocarbon development platform  120  as they can be quickly diverted or broken by an ice breaking vessel. However, it is desirable to extend operations on the hydrocarbon development platform  120  both earlier and later in the summer (ice-free) season. This creates a commercial risk to the hydrocarbon development platform  120 , not to mention matters of safety to operations personnel. 
     In  FIG. 1 , the hydrocarbon development platform  120  is present in the marine body  105  during a time in which a large ice mass  110  is present. It can be seen from arrow “I” that the ice mass  110  is moving towards the location of the hydrocarbon development platform  120 . Thus, the hydrocarbon development platform  120  is at risk. 
     To avoid damage to the hydrocarbon development platform  120 , an intervention vessel  130  is provided between the floating ice mass  110  and the hydrocarbon development platform  120 . The intervention vessel  130  is preferably a ship-shaped vessel capable of self-propulsion by means of propellers and propeller shafts. 
     The intervention vessel  130  is preferably equipped with integral ice-breaking capability. This means that the intervention vessel  130  preferably has a strengthened hull, a rounded, ice-clearing profile or shape, and engine power to push over ice masses within ice-covered waters. To pass through ice-covered waters, the intervention vessel  130  uses momentum and power to drive its bow up onto an ice mass. The ice is incrementally broken under the weight of the ship. Because a buildup of broken ice in front of the intervention vessel  130  can slow it down more than the breaking of ice itself, the speed of the ship is increased by having a specially designed hull to direct the broken ice around or under the vessel  130 . 
     While it is preferred that the intervention vessel  130  be an ice-breaking ship, it is within the scope of the inventions herein that the intervention vessel be moored to the ocean bottom. In this instance, the intervention vessel  130  is towed into position between the hydrocarbon development platform  120  and the direction from which any ice masses will approach. 
     In either arrangement, the intervention vessel  130  is equipped with a water-agitating mechanism. The water-agitating mechanism resides within the intervention vessel  130  or is supported by the intervention vessel  130  within the marine body  105 . The water-agitating mechanism generates artificial waves that propagate through the marine body  105  and impact the large ice mass  110 . 
     In  FIG. 1 , action of the water-agitating mechanism is immediately seen from the intervention vessel in wakes  132 . More importantly, waves created through operation of the water-agitating mechanism are seen at  135 . The waves  135  cause the ice mass  110  to be oscillated upon the surface of the marine body  105 . 
     It is known that wave action can break up ice masses. Some research has been conducted by others to study the effects of waves in order to both understand ice morphology at the leading ice edges and to understand wake impacts on the ice edges of icebreaker-maintained shipping lanes. Two such studies are reported in C. Fox. and V. A. Squire, “Strain in Shore Fast Ice Due to Incoming Waves and Swell,” Journal of Geophysical Research, Vol. 96, No. C3, pp. 4531-4547 (Mar. 15, 1991); and D. Carter, Y. Ouellet, and P. Pay, “Fracture of a Solid Ice Cover by Wind-induced or Ship-generated Waves,” Proceedings of the 6 th  International Conference on Port and Ocean Engineering under Arctic Conditions, Quebec, Canada, pp. 843-845 (1981). 
     Through research and numerical modeling, Fox and Squire found that “for 1 m [thick] ice, waves in the broad 5- to 10-second [frequency] range can break ice if their amplitude is 90 mm or more.” Fox and Squire further reported that “a 15-second wave would need to have an amplitude of 280 mm and a 20-second wave would need an amplitude of 630 mm.” Assuming the Fox and Squire analysis is of the correct magnitude, first year ice floating in an Arctic production area can be fractured using waves artificially generated at the proper frequency. 
     In  FIG. 1 , it can be seen that waves  135  artificially generated from the intervention vessel  130  have begun to fracture the ice mass  110 . First, small ice pieces  112  are formed near the ice edge along the marine body  105 . Further, large ice pieces  115  are formed interior from the ice edge. The large ice pieces  115  will be broken into smaller pieces as the waves  135  continue to be generated by the water-agitating mechanism. 
     In operation, the generation of waves  135  will cause the smaller ice pieces  112  to form and then break off from the ice mass  110 . As the smaller ice pieces  112  break away, the larger ice pieces  115  will become the new ice edge. The continued wave action from waves  135  will cause the larger ice pieces  115  (now at the ice edge) to break into new smaller ice pieces  112 . The new smaller ice pieces  112  will then break off from the ice mass  110 , thus enabling a break-up of the entire ice mass  110  over time. 
     As the smaller ice pieces  112  break away from the ice mass  110 , the smaller ice pieces  112  begin to independently float in the marine body  105 . This creates small floating ice pieces  114 . Action of the waves  135  will not only break the ice mass  110  into smaller fractured ice pieces  115 ,  112 , and small floating ice pieces  114 , but will also push the small floating ice pieces  114  away from the intervention vessel  130 . In addition, the action of the wakes  132  will urge the small floating ice pieces  114  away from the intervention vessel  130 . Of greater importance, the action of the waves  135  and the wakes  132  will keep the small floating ice pieces  114  cleared from the hydrocarbon development platform  120 . 
     A number of different mechanisms are proposed herein for propagating surface waves across a marine body. These are presented in and discussed in connection with  FIGS. 2 through 7 , below. 
     First,  FIG. 2A  provides a cross-sectional view of an intervention vessel  230  having a water-agitating mechanism, in a first embodiment. The intervention vessel  230  includes a deck  210  and a hull  212 . The water-agitating mechanism is shown within the hull  212  of the vessel  230  at  220 . 
     The vessel  230  is representative of the intervention vessel  130  of  FIG. 1 . In this respect, the vessel  230  is a ship-shaped vessel preferably having ice-breaking capabilities. In addition, the vessel  230  preferably has a large water displacement for generating substantial surface waves  135  during motion. 
     In the arrangement of  FIG. 2 , the water-agitating mechanism  220  is a gryoscopic system. Gyroscopes are commonly used in modern marine structures for providing stability to vessels deployed on the high seas. Stabilization increases passenger comfort and safety, reduces wear and tear on equipment, and increases the accuracy of warship artillery. 
     A gryoscopic system uses angular momentum and precession to counter ship oscillations. A gyroscope mounted with its gimbal axis orthogonal to the major axis of a ship serves to limit rolling motion. Further, a gyroscope mounted with the gimbal axis parallel to the major axis of the ship reduces pitching motion. Larger vessels require a larger gyroscopic system that can provide greater stabilization forces, while smaller vessels may employ a smaller gyroscopic system. 
     An early gyroscope patent is U.S. Pat. No. 1,150,311, which issued in 1915 to inventor Elmer A. Sperry. The &#39;311 patent was entitled “Ship&#39;s Gyroscope.” Mr. Sperry&#39;s gyroscope employed a large, solid spinning mass that precessed about gimbal bearings. The gimbal bearings were connected to a frame. The frame, in turn, was operatively connected to the hull of a ship. 
     Mr. Sperry&#39;s gyroscope was utilized by the U.S. Navy as an early gyro-stabilizer system. According to one publication, the gyro was installed aboard a small 700 ton destroyer, and in a submarine. Using the centrifugal motion of the spinning mass, gyrsoscopic forces were transmitted to the hulls of the naval vessels through the gimbal axis. Depending upon the orientation of the gimbal axis, the gyroscopic forces could stabilize a floating vessel either as to pitch or as to roll. 
     Mr. Sperry&#39;s gyroscope was “active” in operation, as opposed to being “passive.” In this respect, the Sperry gyroscope used a small gyroscope that sensed the onset of rolling motion. This small gyroscope was electrically connected to the switch of a motor that actuated a precessional gear mounted on a much larger gyroscope. A small gyroscope is more sensitive to rolling motion at inception than a large gyroscope. By activating the motor connected to the precessional gear of the large gyroscope, the large gyroscope was forced to precess at the moment it was needed. Further the motor can increase or decrease the angular velocity of precession to increase or decrease the stabilizing torque as needed based on the magnitude of the external torque. 
     Stabilizing torque of a gyroscope is a function of several factors. These include mass of the flywheel, or “rotor,” angular velocity of the rotor, radius of the rotor, and angular velocity of precession of the rotor when subject to an external torque. In order to provide stabilization for a large vessel such as a war ship, Mr. Sperry&#39;s ship gyroscope was required to utilize a large metal rotor having a great deal of mass. According to one publication, Mr. Sperry&#39;s gyroscope as utilized by the U.S. Navy weighed 5 tons. 
     In the present application, the gyroscopic system  220  is used not for vessel stabilization, but to actually induce side-to-side motion. The side-to-side motion may be either a rolling motion, a pitching motion, or intermittently a rolling motion and a pitching motion. The purpose is to create waves  135  that hit the ice edge and to create break-up of the ice mass  110 . To effectuate the rolling motion and the pitching motion, precession is forced upon a gear motor  255  according to a predetermined frequency and angle. 
     As seen in  FIG. 2A , the gryoscopic system  220  includes frame support members  222 . The frame support members  222  are secured to the hull  212  of the vessel  230  at an orientation that is orthogonal to the length (or major axis) of the vessel  230 . This allows the hydro-gyroscope  220  to de-stabilize the vessel  230  so that it may roll from side-to-side. If the operator desires to de-stabilize the vessel  230  as to pitch, the frame support members  222  are secured to the hull  212  of the vessel  230  at an orientation that is parallel to the length of the vessel  230 . 
     In one arrangement, a pair of vessel de-stabilizing apparatuses  220  is provided in the hull  212  of the vessel  230 , with one being positioned to de-stabilize the vessel  230  as to pitch forces, and the other being positioned to de-stabilize the vessel  230  as to roll forces. In another arrangement, a single gyroscope  220  may be employed, with the gyroscope being rotatable within the hull  212  of the vessel  230 . For example, the opposing frame support members  222  could be placed on a circular track and given rotational movability along a horizontal plane. In this way, a single gyroscope  220  (whether active or passive) may be employed to de-stabilize the vessel  230  selectively as to both pitch forces and roll forces. 
     The manufacture of gyroscopic systems is understandably expensive. In addition, the added weight of the spinning mass of a gyroscope increases the fuel consumption of the vessel  230  when in transit. Therefore, it is preferred that the gyroscopic system  220  be a “hydro-gyroscope,” meaning a gyroscopic device that employs a container that may be selectively filled with sea water, and later emptied. Such a hydro-gyroscope is disclosed in U.S. Pat. No. 7,458,329, entitled “Hydrogryo Ship Stabilizer and Method for Stabilizing a Vessel.” 
     The illustrative gyroscopic system  220  includes a spinning mass such as a liquid container  240 . The spinning liquid container has a cylindrical wall  242  that defines an internal chamber  245 . The chamber  245  provides an internal flow path in which fluid rotationally travels. Spinning movement of the liquid container  240  creates the gyroscopic forces applied to the hull  212  of the vessel  230 . 
     A means is provided for inducing rotational motion of the liquid within the inner chamber  245  of the container  240 . In the embodiment of  FIG. 2A , the means is a motor  250 . The motor  250  is a mechanical motor, and may be either electrically powered, steam powered, hydraulically powered, or powered by a hydrocarbon fuel. The motor  250  is connected to a shaft  264  and mounted to a gimbal frame  260 . This allows the liquid container  240  to precess along the major axis of the vessel  230 . 
     The gyroscopic system  220  also includes gimbal connections  224 . The gimbal connections  224  are secured between the opposing frame support members  222 . The gimbal connections  224  are connected by a shaft  225  that supports the gimbal frame  260  and that forms a gimbal axis for the liquid container  240 . Each of the gimbal connections  224  includes a bearing that provides relative rotational movement between the gimbal frame  260  and the frame support members  222 . The frame support members  222 , in turn, are secured to the hull  212  of the vessel  230 . 
     The spinning liquid container  240  (or other mass) is provided as part of a controlled gear system  270 . In this respect, the gear system  270  is neither passive nor active, but provides precessional forces in response to signals sent by a controller. A controller is seen at  280  in  FIG. 2C . 
     In the arrangement of  FIGS. 2A and 2C , the gear system  270  includes a first gear  272  connected to the gimbal axis  225 . The first gear  272  turns in response to rotational mechanical force (such as by teeth) provided from a second gear  274 . The second gear  274 , in turn, is driven by a gear motor  255 . Thus, movement by the gear motor  255  forces the gimbal frame  260  to turn, thereby creating precessional forces on the vessel  230 . 
       FIG. 2B  is a top view of the gyroscopic system  220  of  FIG. 2A . Arrow R indicates the direction of rotation of the liquid container  240 . Of course, the container  240  may be urged by the motor  250  to spin in either direction. 
     Visible in the top view of  FIG. 2B  is a bearing connector  262 . The bearing connector  262  is provided at an interface with the gimbal frame  260  and a rotational shaft  264 . The bearing connector  262  allows the liquid container  240  to rotate relative to the gimbal frame  260  around an axis that is essentially vertical to the hull  212  of the vessel  230  when the gyroscopic system  220  is not precessing. 
       FIG. 2C  is a side view of the gyroscopic system  220  of  FIG. 2A . Here, the gear system  270  is more clearly seen. The gear system  270  again includes a first gear  272  and a second gear  274 . The first gear  272  comprises a first set of teeth  271 , while the second gear  274  comprises a second set of teeth  273 . The first set of teeth  271  and the second set of teeth  273  are configured and dimensioned to interlock as is known for a gear system. 
     A controller  280  is provided as part of the gyroscopic system  220 . The controller  280  is in electrical communication with the gear motor  255  by wires  282 , and sends instructions to the gear motor  255  to turn the second gear  274  clockwise and counter-clockwise in order to provide reciprocating precessional forces to the spinning liquid container  240 . 
     In operation, the illustrative liquid container  240  serves as a hydro-gyro rotor. Preferably, the spinning liquid container  240  is filled with seawater after the intervention vessel  230  has been transported to the desired location in the marine body  105 . The container  240  filled with seawater spins about the rotational axis  264  using power from the motor  250 . The bearings  262  and shaft  225  provide lateral support for the liquid container  240  relative to the gimbal frame  260 , while allowing rotational movement of the liquid container  240 . The liquid container  240 , the gimbal frame  260 , and motor  250  are free to precess on the gimbal axis provided by the shaft  225  and frame connectors  224 . For example, when creating rolling motion in the vessel  230 , the motor  250  would swing like a pendulum into and out of the page in the view of  FIG. 2A . 
     It can be seen from  FIGS. 2A through 2C  that a unique water-agitating mechanism  220  is provided. The water-agitating mechanism  220  generates waves  135  through a ship-mounted gyroscope. The gyroscope is preferably a hydro-gyroscope, but may operate through a solid spinning mass. Other arrangements for a hydro-gyroscope are presented in U.S. Pat. No. 7,458,329, mentioned above. The &#39;329 patent is incorporated herein by reference in its entirety. 
     The gyroscope that includes a spinning mass such as fluid container  240  undergoes forced precession. The precession takes place at a desired frequency as determined by the controller  280 . The forced precession induces rocking or pitching of the vessel  230 . This rocking or pitching motion of the vessel  230 , in turn, generates a continuous train of waves  135  in the marine body  105 . The waves  135  propagate away from the vessel  230  and into the ice mass  110  to induce wave fracture. In this respect, ice break-up is caused by the brittle ice being cantilevered over or spanning across wave troughs. 
     Another means for artificially generating waves  135  within the marine body  105  involves the use of air guns. Air guns operate by containing compressed gas at high pressure (e.g., 2,000-3,000 psia) within a valve chamber. The compressed gas is ordinarily air. Air guns are commonly used as acoustic sources for marine seismic reflection and refraction surveys. Typically, one or more passages is provided in the gun to release the gas from the valve chamber and into a surrounding medium, that is, sea water. The passage remains closed while the pressure (as from a compressor on a surface vessel) is built up in the chamber. The passage is opened when the gun is “fired,” allowing the compressed gas to expand out of the chamber and into the surrounding medium. 
       FIG. 3  is a side view of an intervention vessel  330  using a water-agitating mechanism  320  in a second embodiment. The intervention vessel  330  includes a deck  310  and a hull  312 . The vessel  330  is representative of the intervention vessel  130  of  FIG. 1 . In this respect, the vessel  330  is a ship-shaped vessel preferably having ice-breaking capabilities. However, it is understood that the vessel  330  may be of any shape. For example, a non-ship-shaped vessel such as an offshore working platform may utilize the water-agitating mechanism  320 . 
     In the vessel  330  of  FIG. 3 , the water-agitating mechanism  320  comprises a plurality of pneumatic guns  322 . The pneumatic guns  322  are suspended from cables  324 . The cables  324 , in turn, are supported by cable rods  326  extending laterally from the vessel  330 . The pneumatic guns  322  extend into the marine body  105 . Alternatively, in some embodiments the pneumatic guns  322  may be extended or towed behind the vessel. 
     The pneumatic guns  322  are preferably large-diameter, cylinder-shuttle air guns. Such guns have known uses in the context of seismic exploration. A specific exemplary air gun design is disclosed in U.S. Pat. No. 5,432,757, entitled “Large-Diameter, Cylinder-Shuttle Seismic Airgun Method, Apparatus and Towing System.” This patent is incorporated herein by reference in its entirety. 
     Using the pneumatic guns  322 , powerful impulses of air may be released into the marine body  105 . Of benefit, the impulses are readily repeatable at a desired frequency. In the present application, the air guns  322  may be fired to release powerful impulses on a cycle such as every two seconds (0.5 Hz), every five seconds (0.2 Hz), every ten seconds (0.1 Hz), or other frequencies. 
     In operation, air tubes (not shown) deliver air from an air canister or air pump on the vessel  330  to the air guns  322 . The air is delivered to air chambers under pressure within the air guns  322 . A trigger mechanism is used to actuate, or “fire,” the air guns  322 . The trigger mechanism may be an electrically operated trigger valve, or solenoid valve. Upon firing, the pressurized gas is abruptly released from the air chambers and into the surrounding water medium, i.e., salt water. 
     The release of air from the plurality of air guns  322  is synchronized. In this way, wakes  132  and waves  135  are created. The waves  135  travel towards the ice mass  110  to cause ice fracture and break-up. 
     Another means for artificially generating waves  135  within the marine body  105  involves the use of large paddles. The paddles strike the surface of the marine body  105  and then stroke through the water. 
       FIG. 4  is a cross-sectional view of an intervention vessel  430  using a water-agitating mechanism  420  in a third embodiment. The intervention vessel  430  includes a deck  410  and a hull  412 . The vessel  430  is again representative of the intervention vessel  130  of  FIG. 1 . In this respect, the vessel  430  is a ship-shaped vessel preferably having ice-breaking capabilities. However, it is understood that the vessel  430  may be of any shape. 
     In the vessel  430  of  FIG. 4 , the water-agitating mechanism  420  comprises a plurality of paddles  422 . The paddles  422  are supported by oars  424 . The oars  424 , in turn, are supported by a rotating shaft  426  that extends laterally from each side of the vessel  430 . 
     In order to generate waves  135 , the shaft  426  is rotated. Rotation may be clockwise, counter-clockwise, or intermittently clockwise and counter-clockwise. Rotation of the shaft  426  is driven by a motor assembly  440 . The motor assembly  440  includes a motor  442 . The motor  442  is supported by a stand or platform  446 . The motor  442  imparts rotational movement to a drive shaft  444 . The drive shaft  444  preferably extends from each end of the motor  442 , though it may reside entirely within a housing of the motor  442 . 
     The drive shaft  444  is connected to the rotating shaft  426 . The rotating shaft  426  is supported within the hull  412  of the vessel  430  by support frames  450 . In the arrangement of  FIG. 4 , the support frames  450  are connected to the inside of the hull  412 . Opposing support frames  450  are provided on either side of the motor  442 . 
     Rotation of the drive shaft  444  causes the rotating shaft  426  to rotate. This, in turn, causes the paddles  422  to hit the surface of the marine body  105 . The paddles  422  plunge through the water within the marine body  105  and then come back out for another cycle. 
     The frequency at which the paddles  422  strike the surface of the marine body  105  and then turn through the water is a function of the speed of the motor  442 . Ideally, the paddles  422  strike the water in unison. The oars  424  and connected paddles  422  rotate at a frequency of about three to five seconds. 
     The oars  424  and connected paddles  422  are dimensioned to create waves  135  within the marine body  105 . In one aspect, the oars  424  and connected paddles  422  are about 30 to 50 feet in length. The rotating shaft  426  ideally turns at a height that is about 15 feet above the surface of the marine body  105 . This allows the paddles  422  to extend about 15 to 34 feet below the water surface  108 . 
     In the view of  FIG. 4 , only one rotating shaft  426  is shown, and only one row of paddles  422  is seen. However, the operator may choose to have more than one motor  442  so that additional rotating shafts  426  with connected oars  424  and paddles  422  may be turned. The use of multiple rows of paddles  422  would increase the amplitude of the waves  135 . This, in turn, would provide for more efficient breakage of the ice mass  110 . In one embodiment, three rotating shafts  426  with connected oars  424  and paddles  422  are turned. 
     It is understood that the movement of the paddles  422  through the water will urge the intervention vessel  430  to move across the water. It is desirable for the vessel  430  to remain substantially stationary in a position between the hydrocarbon development platform  120  and the oncoming ice mass  110 . Therefore, the vessel  430  may be moored to the bottom of the marine body  105  using anchors and catenary mooring lines (not shown). Alternatively, dynamic positioning using azimuthing propulsion motors (not shown) may be employed to counter any translation of the vessel  430  across the marine body  105 . 
     The use of azimuthing propulsion motors as suggested above may themselves create substantial artificial wave movement. This would be even without the paddles  422 . Thus, another means proposed herein for artificially generating waves  135  within the marine body  105  involves the use of azimuthing propulsion motors. 
       FIG. 5  is a cross-sectional view of an intervention vessel  530  having a water-agitating mechanism  520 , in a fourth embodiment. The intervention vessel  530  includes a deck  510  and a hull  512 . The vessel  530  is again representative of the intervention vessel  130  of  FIG. 1 . In this respect, the vessel  530  is a ship-shaped vessel preferably having ice-breaking capabilities. However, it is understood that the vessel  530  may be of any shape. 
     In the vessel  530  of  FIG. 5 , the water-agitating mechanism  520  comprises one or more pairs of propulsion motors  522 . The propulsion motors  522  operate as azimuth thrusters. Azimuth thrusters are known as a means for propelling a large ship. Azimuth thrusters have also been used as part of dynamic positioning systems for station-keeping of floating offshore platforms. 
     Generally, an azimuth thruster is a configuration of ship propellers placed in pods. The pods are typically placed underneath a ship&#39;s hull or underneath a platform for a floating offshore structure. The ship propellers can be rotated in any direction about their mounting axis. This renders the use of a rudder for steering unnecessary. In the context of a large ship, azimuth thrusters give the ship much better maneuverability than a fixed propeller and rudder system. Further, ships with azimuth thrusters do not need tugs to dock, though they may still require tugs to maneuver in tight places. 
     In  FIG. 5 , a pair of azimuth thrusters  522  is shown. Each azimuth thruster  522  is supported by the hull  512  of the vessel  530 . A support mounting is shown at  526  for each azimuth thruster  522 . The support mountings  526  enable the azimuth thrusters  522  to rotate a full 360° relative to the vessel hull  512 . 
     In the arrangement of  FIG. 5 , each azimuth thruster  522  has at least one propeller  524 . The propeller  524  is generally used to move and maneuver the intervention vessel  530  through the marine body  105 . However, upon arrival at the desired location between the hydrocarbon production platform  120  and the floating ice mass  110 , the azimuth thrusters  522  are rotated so that the propellers  524  face and act against one another. 
     The opposing disposition of the azimuth thrusters  522  creates offsetting forces that tend to keep the vessel  530  on location, although some intermittent adjustments will be required. To the extent unmanageable drift of the vessel  530  might occur, anchors may be placed on the marine bottom, or the vessel  530  maintained on location through catenary mooring lines (not shown). Alternatively, a separate set of azimuth thrusters (not shown) may be provided for dedicated station-keeping. 
     The azimuth thrusters  522  and propellers  524  preferably operate through mechanical transmission. This means that a motor (not shown) resides inside the hull  512  of the vessel  530 , with the motor being operatively connected to the propeller  524  by gearing. The motor may be diesel or diesel-electric. 
     In an alternative aspect, the azimuth thrusters  522  operate through electrical transmission. This means that an electric motor operates within the azimuth thruster  522  itself. The electric motor is connected directly to the propellers  524  without gears. The electricity needed to drive the propellers  524  and to rotate the azimuth thrusters  522  is produced by an onboard engine, usually diesel or gas turbine. 
     In order to generate waves  135 , and as shown in  FIG. 5 , a pair of azimuth thrusters  522  is positioned in opposing relation. Preferably, more than one pair of azimuth thrusters  522  is employed. Preferably, the propellers  524  are intermittently started and stopped in cycles to create waves  135  having well-defined peaks and troughs. This is in addition to the entrainment of air under the ice. The cycles may be, for example, every two to ten seconds or, more preferably, every four to eight seconds. 
     Another option offered herein for artificially generating waves  135  within the marine body  105  involves the use of subsurface plungers. The plungers strike the surface  108  of the marine body  105  and then stroke vertically down through the water and back up. Alternatively, the plungers vibrate or oscillate quickly in an up-and-down manner under the water. 
       FIGS. 6A and 6B  provide cross-sectional views of an intervention vessel  630  using a water-agitating mechanism  620 , in a fifth embodiment. The intervention vessel  630  includes a deck  610  and a hull  612 . The vessel  630  is again representative of the intervention vessel  130  of  FIG. 1 . In this respect, the vessel  630  is a ship-shaped vessel preferably having ice-breaking capabilities. However, it is understood that the vessel  630  may be of any shape or may define a floating platform. 
     In the vessel  630  of  FIGS. 6A and 6B , the water-agitating mechanism  620  comprises a plurality of plungers  620 . The plungers  622  are supported by vertical rods  624 . Each rod  624 , in turn, is supported by a reciprocating motor  632 . The reciprocating motors  632  cause the rods  624  and connected plungers  622  to reciprocate vertically, that is, up-and-down within the water body  105 . 
     In one aspect, the rods  624  are about 15 to 30 feet in length. In addition, the plungers  622  at the ends of the rods  624  are about 5 to 10 feet in length. Reciprocating motion of the rods  624  and connected plungers  622  creates wakes  132  and causes waves  135  to be propagated towards the ice masses  110 . 
     In  FIG. 6A , the plungers  622  are in their raised position. This means the plungers  622  are at the respective tops of their strokes. In this position, the plungers  622  are about 5 to 17 feet above the surface  108  of the marine body  105 . In response to movement of the vertical rods  624  by the reciprocating motor  632 , the plungers  622  are rapidly lowered into the water. The plungers  622  strike the surface  108  of the marine body  105  and then stroke vertically down through the water. 
     In  FIG. 6B , the plungers  622  are in their lowered position. This means that the plungers  622  are at the respective bottoms of their strokes. In this position, the plungers  622  are about 5 to 17 feet below the surface  108  of the marine body  105 . In response to movement of the vertical rods  624  by the reciprocating motor  632 , the plungers  622  are rapidly raised, and stroke vertically back up through the water. 
     In one embodiment, the plurality of plungers  622  reciprocate according to a stroke that is about 5 to 20 feet. The frequency of the strokes may be about every three to ten seconds (0.333 Hz to 0.1 Hz). In this instance, the top of the strokes is at or above the surface of the body of water, and the bottom of the strokes is below the surface of the body of water. 
     A final and related method for creating artificially-generated waves also involves the use of a plunger.  FIG. 7  is a cross-sectional view of a vessel  730  having a water-agitating mechanism  720 , in a sixth embodiment. Here, the water-agitating mechanism  720  is again a plunger  722 . 
     The plungers  722  are supported by vertical rods  724 . Each rod  724 , in turn, is supported by a reciprocating motor  732 . The reciprocating motors  732  cause the rods  724  and connected plungers  722  to reciprocate. Reciprocation may be vertical, that is, up-and-down, within the water body  105 , or may be lateral or circular. 
     In one aspect, the rods  724  are about 10 to 20 feet in length. In addition, the plungers  722  at the ends of the rods  724  are about 5 to 10 feet in length. Reciprocating motion of the rods  724  and connected plungers  722  creates wakes  132  and causes waves  135  to be propagated towards the ice masses  110 . It is preferred that the plurality of plungers  722  reciprocate substantially simultaneously. 
     It is noted that the plungers  722  may alternatively be shaped as paddles, such as paddles  422  of the water-agitating mechanism  420  in  FIG. 4 . In this arrangement, reciprocation or vibration by the motors  732  would preferably be more of a lateral movement than a vertical movement. In either instance, the reciprocating motors  732  provide short, fast strokes to vibrate a device under the water. 
     In the embodiment of  FIG. 7 , the plurality of plungers  722  may reciprocate according to a stroke that is about 1 to 5 feet. The frequency of the strokes may be about 0.1 to 2.0 seconds (10.0 Hz to 0.5 Hz). In this instance, both the top and the bottom of each stroke is below the surface  108  of the body of water  105 . 
     In one embodiment, the intervention vessel  130  is an azimuthal stern drive icebreaker. The icebreaker would be mounted with an ice-breaking mechanism such as the controlled gyroscopic system  220 . This has the added advantage of using its propeller wash to push ice pieces  114  out of the path of the development platform  120 . 
       FIG. 8  is a schematic view of a marine ice field  800  wherein hydrocarbon recovery operations are taking place, in an alternate embodiment. The marine ice field  800  of  FIG. 8  is the same as the marine ice field  100  of  FIG. 1 . In this respect, the ice field  100  resides over a large marine body  105 . The marine body  105  is preferably a salt water body in the Arctic region of the earth. 
     The ice field  800  contains one or more large ice masses, such as the ice mass  110 . The ice mass  110  is moving in a direction indicated by arrow “I.” 
     The marine ice field  800  is undergoing hydrocarbon development activities. In  FIG. 8 , a hydrocarbon development platform  120  is again provided as part of the hydrocarbon development activities. The depicted platform  120  is a drill ship. While a drill ship  120  is shown in  FIG. 8 , it is understood that the platform  120  may be another type of vessel. For example, the platform  120  may be a production platform, a workover platform, a floating production, storage and offloading (“FPSO”) vessel, an offshore workboat, a catenary anchor leg mooring (“CALM”) buoy, or an oceanographic survey vessel. Other types of vessels for platform  120  include a construction vessel as may be used to install subsea equipment or to lay pipe, a subsea cable installation vessel, a diver support vessel, an oil spill response vessel, or a submarine rescue vessel. 
     The hydrocarbon development platform  120  is positioned in the ice field  100 . During warmer summer months, the marine body  105  is generally free of large ice masses such as ice mass  110 . The Arctic area may have smaller floating ice bodies, but these generally are not a threat to operations on the hydrocarbon development platform  120  as they can be quickly diverted or broken by an ice breaking vessel. However, it is desirable to extend operations on the hydrocarbon development platform  120  both earlier and later in the summer (ice-free) season. This creates a commercial risk to the hydrocarbon development platform  120 , not to mention matters of safety to operations personnel. 
     In  FIG. 8 , the hydrocarbon development platform  120  is present in the marine body  105  during a time in which a large ice mass  110  is present. It can be seen from arrow “I” that the ice mass  110  is moving towards the location of the hydrocarbon development platform  120 . Thus, the hydrocarbon development platform  120  is at risk. 
     To avoid damage to the hydrocarbon development platform  120 , an intervention vessel  830  is again provided between the floating ice mass  110  and the hydrocarbon development platform  120 . In this novel arrangement, the intervention vessel  830  is a moored buoy. 
     The moored buoy  830  is dimensioned to generate waves of the desired wavelength, amplitude, and period to fracture ice that is approaching the structure  120  to be protected. Preferably, the moored buoy  830  is circular, and has a diameter substantially equivalent to the beam of a drilling vessel. The moored buoy  830  is equipped with an ice-breaking mechanism. Preferably, the ice breaking mechanism is a controlled gyroscopic system that induces precession on a predetermined cycle. Alternatively, the ice-breaking mechanism may be a motor within the buoy  830  that oscillates the buoy  830  up and down by mechanically pulling and releasing on its mooring line or lines (not shown). 
     In the embodiment shown in  FIG. 8 , the ice field  800  further includes moored buoys  832  on substantially either side of the first moored buoy  830 . These moored buoys  832  likewise have controlled gyroscopic systems or other water-agitating mechanisms attached thereon. The water-agitating mechanisms cause the buoys  830 ,  832  to oscillate in a manner that produces waves  135 . The waves  135  help to break up the ice mass  110  into smaller and still smaller pieces. The moored side buoys  832  may further help to direct smaller ice pieces such as pieces  114  away from the hydrocarbon development platform  120 . 
     It is noted in  FIG. 8  that yet a fourth moored buoy  834  is provided. Any number of moored buoys may be selected which oscillate or precess according to a desired frequency in order to generate waves  135 . In one aspect, the oscillations are substantially synchronized. 
     Each buoy  830 ,  832 ,  834  may be positioned to protect the development platform  120  from ice moving in a specific direction. In the illustrative arrangement of  FIG. 8 , four buoys are shown, with one being placed north of the platform  120 , one being placed south of the platform  120 , one being positioned east of the platform  120 , and one being placed west of the development platform  120 . 
       FIG. 9  is a flowchart showing steps for a method  900  for clearing an approaching floating ice mass, in one embodiment. The method  900  first includes the step of locating a hydrocarbon development platform in a marine environment. This step is shown at Box  910 . The hydrocarbon development platform may be a drill ship or a ship-shaped production platform. Alternatively, the hydrocarbon development platform may be a non-ship-shaped floating platform such as a workover platform, a floating production, storage and offloading (“FPSO”) vessel, an offshore workboat, a catenary anchor leg mooring (“CALM”) buoy, or an oceanographic survey vessel. 
     The hydrocarbon development platform is maintained at its location in the marine environment by a dynamic positioning system. Alternatively, a mooring system may be employed. The marine environment comprises a large body of water. The body of water includes a water surface. The marine environment may be a bay, a sea, a channel, or an ocean in the Arctic region of the earth. 
     The method  900  also includes determining a direction from which the ice mass is approaching the hydrocarbon development platform. This is represented at Box  920 . In one aspect, the floating ice mass is moving towards the hydrocarbon development platform at a speed of less than 1 meter per second. However some ice floes may travel at a faster rate. 
     The method  900  further includes providing an intervention vessel. This step is indicated at Box  930 . The intervention vessel is preferably a ship-shaped vessel having a deck and a hull. Preferably, the intervention vessel is equipped with ice-breaking capability. 
     The intervention vessel has a water-agitating mechanism carried thereon. Various types of water-agitating mechanisms may be employed, as discussed above. For example, the water-agitating mechanism may comprise a gyroscopic system attached to the hull of the intervention vessel. The gyroscopic system may comprise a large spinning mass, a controller, and at least one gear for moving the large spinning mass so as to cause forced precession. The controller reciprocates the large spinning mass according to a specified frequency and amplitude. The large spinning mass is reciprocated in a direction to cause the intervention vessel to pitch, to roll, or combinations thereof. 
     In another embodiment, the water-agitating mechanism comprises a plurality of air guns. The air guns are disposed below the surface of the marine environment in the body of water. The plurality of air guns may be fired substantially simultaneously at a frequency of about two seconds to five seconds (0.5 Hz to 0.2 Hz). 
     In another embodiment, the water-agitating mechanism comprises a plurality of paddles. The paddles rotate through the surface of the marine environment and into the body of water. The plurality of paddles may rotate substantially simultaneously at a frequency of about three to five seconds (0.33 Hz to 0.2 Hz). 
     In another embodiment, the water-agitating mechanism comprises at least one pair of offsetting propulsion motors. The propulsion motors operate below the surface of the marine environment and in the body of water. In one aspect, the at least one pair of offsetting propulsion motors are simultaneously started and stopped in cycles to create waves having well-defined peaks and troughs. The cycles may be, for example, every two to ten seconds (0.5 Hz to 0.1 Hz). 
     In another embodiment, the water-agitating mechanism comprises a plurality of plungers that reciprocate in the body of water. In one aspect, the plurality of plungers reciprocate substantially simultaneously. 
     In one arrangement, the plurality of plungers may reciprocate vertically according to a stroke that is about 5 to 20 feet. In this instance, the frequency of the strokes may be about every three to ten seconds (0.33 Hz to 0.1 Hz). Here, the top of the stroke is at or above the surface of the body of water, while the bottom of the stroke is below the surface of the body of water. 
     In another arrangement, the plurality of plungers may reciprocate according to a stroke that is about 1 to 5 feet. This is a much shorter stroke such that the plunger is in the nature of a resonance vibrator. In this instance, the frequency of the strokes is about 0.1 to 2.0 seconds (10.0 Hz to 0.5 Hz). Here, both the top and the bottom of each stroke is below the surface of the body of water. The strokes may be vertical or lateral. 
     The method  900  for clearing an approaching floating ice mass also includes positioning the intervention vessel generally between the hydrocarbon development platform and the approaching ice mass. This step is provided at Box  940 . The method  900  then includes actuating the water-agitating mechanism in order to propagate artificially generated waves. This step is provided at Box  950 . The waves travel towards a leading edge of the approaching ice mass. In one aspect, the artificially generated waves have an amplitude of about two feet to five feet. 
     The method  900  also includes continuing to operate the water-agitating mechanism so as to fracture the ice mass along the leading edge. This step is provided at Box  960 . This causes small ice pieces to separate from the ice mass. The small ice pieces then float in the marine environment, with some tending to float towards the hydrocarbon development platform. 
     The method  900  next includes continuing to further operate the water-agitating mechanism. This is shown at Box  970 . This is for the purpose of clearing at least some of the small ice pieces from the hydrocarbon development platform. This results in a substantially ice-free zone downstream of the intervention vessel. This, in turn, allows the hydrocarbon development platform to operate without worry of ice mass collisions or unwanted ice loads. 
     The method  900  protects a relatively stationary hydrocarbon development platform and utilizes the natural ice drift to break up ice using the water-agitating mechanism and then carry small ice pieces around and beyond the hydrocarbon development platform. 
     While it will be apparent that the inventions herein described are well calculated to achieve the benefits and advantages set forth above, it will be appreciated that the inventions are susceptible to modification, variation and change without departing from the spirit thereof. For example, the methods and water-agitating mechanisms disclosed herein have utility for non-hydrocarbon producing operations. Item  120  may be, for example, an ice coring ship. The ice-management system could also be used to support iceberg management in pack ice by clearing a path for an iceberg towing vessel to tow the iceberg.