Abstract:
There is disclosed a floating barrier for installation in deep oceans for dampening winds, waves, and currents, and for containing oil spills. Applications of this invention include tsunami wave alleviation, storm protection, and oil spill containment.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation-In-Part of, and claims priority of, U.S. patent application Ser. No. 13/104,082, filed on May 10, 2011, which is a Continuation-In-Part of U.S. patent application Ser. No. 13/084,788, filed on Apr. 12, 2011 now abandoned. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to floating barrier methods and apparatus and, more particularly, to open ocean floating barriers used to protect ocean installations, harbors, and coastlines by dampening the forces of winds, waves, water currents, and containing oil spills. 
     BACKGROUND OF THE INVENTION 
     An ocean installation, such as an offshore platform for exploration and production of carbon hydrates, may experience high winds, large waves, and strong currents in its service life. This activity can also cause an oil spill. Coastal areas of continents are under the threat of tsunamis (as a result of an earthquake or a volcano eruption, e.g.), especially those regions surrounding the Pacific Ocean and the Indian Ocean. Harbors and low lying areas on coasts are prone to storm surge, such as the cities of New Orleans and Galveston in the United States. Man-made structures are used to mitigate the forces of the nature in some of the examples enumerated above. 
     Breakwaters, installed in shallow water and close to the coastal areas, are used to reduce the intensity of wave action, and therefore to reduce coastal erosion. Levees are used to prevent floods from, e.g., a storm surge. Oil booms have been used at a large scale, to contain oil spills. 
     Wave dampers are used to alleviate the strength of the wave forces in laboratories. In a wave basin, the wave dampers, consisting of layers of porous screens and located at one end, absorb the waves generated by wave makers at the opposite end. This way, the progressive waves generated at one end will reach the other with minimum reflection, so that ocean waves can be more realistically simulated. A study by Thomson indicated that with two layers of porous screens, 80% of wave transmission can be eliminated. Molin and Fourest studied the quantitative relation between wave absorption and the number of screens. 
     In an open ocean, winds, waves, and currents often act simultaneously. The wave dampers used in a laboratory, if installed offshore, can dampen the forces from all these disturbances. These dampers can also be designed to act as barriers to contain crude oil on the sea surface, in case of an oil spill. The issue is to have a support structure, in shallow and in deep water, on which the barriers can be mounted. The support structures must have minimum motions themselves in winds, waves, and currents. 
     If the water is not deep, say, less than 500 feet, a fixed platform concept can be used to support the barriers. However, very often there is a need to use barriers in a deep ocean, where the water depth is over 1,000 feet. One example is to dampen the tsunami waves, which have a smaller wave height in deepwater (about 3 to 6 feet), while these waves can reach over 30 feet or greater when they land on shore. Another example is the need to protect deepwater oil platforms, which are regularly operating at a water depth of over 5,000 feet. Floating barriers, if installed surrounding these platforms, can alleviate the environmental loads and barricade an oil spill, should it occur. 
     Over the past 40 years, floating structures at great ocean depth have been installed to explore and to produce carbon hydrates. New floating structure concepts also emerge. One of them is the fully constrained platform abbreviated as FCP shown and described in my copending U.S. patent application Ser. No. 13/084,788, which is hereby incorporated herein in its entirety. Referring now to  FIG. 1  for the fully constrained platform concept hereinafter abbreviated as “FCP”, a buoyant, surface structure FCP is constrained with a tether system  12  vertically and angularly. The tethers  12  are anchored on the seabed. The buoyancy generated by the buoyant surface structure FCP is larger than its weight. The excessive lift force is taken by the tether system  12 , which will compensate for the payloads. A key feature of a FCP is that its motion is constrained in all six degrees of freedom, namely, surge, sway, heave, roll, pitch, and yaw, so that it will have minimal motion under environmental loads. 
     No known floating barriers have been permanently installed in deep oceans at a large scale. There is clearly a need in the art to alleviate winds, waves, and currents in an open ocean, in a gulf or in a bay, or to barricade an oil spill. The present invention discloses methods and apparatus for such a purpose. 
     SUMMARY OF THE INVENTION 
     The present invention is directed toward a floating barrier for applications in deep oceans, to dampen forces from winds, waves, and currents, and to contain an oil spill. The present floating barriers can also be used to protect ocean installations, harbors, and coastlines. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side elevation view showing, somewhat schematically, a fully constrained platform, 
         FIG. 2  is a side elevation view showing, somewhat schematically, a fully constrained platform having screens attached thereto. 
         FIG. 3  is a side elevation view showing, somewhat schematically, elongate screens supported by two fully constrained platforms. 
         FIG. 4  is a schematic top plan view showing an elongate chainlike floating barrier. 
         FIG. 5  is an end view of the chainlike floating barrier of  FIG. 4 . 
         FIGS. 6A and 6B  are elevation views showing, somewhat schematically, a buoyant floating surface structure before and after installation of a net and tethers, respectively. 
         FIGS. 7A ,  7 B, and  7 C are schematic illustrations of several configurations of a single tether having multiple attachment legs. 
         FIG. 8  is an elevation view of a screen having a plurality of perforations. 
         FIG. 9  is an elevation view of various shapes of perforations. 
         FIGS. 10A and 10B  are partial cross sectional views showing a one-sided screen and a two-sided screen, respectively. 
         FIG. 11  is an elevation view of a screen having upper, middle, and lower portions for different purposes. 
         FIG. 12  is an elevation view of the screen of  FIG. 11 , showing a perforated upper portion for dampening winds and waves, a middle portion having no perforations for containing an oil spill, and a perforated lower portion for dampening ocean currents 
         FIGS. 13A and 13B  are a side elevation and a top plan view, respectively, showing a weight for use with the tethers. 
         FIG. 14  is a schematic top plan view illustrating layers of floating barriers offshore of a coastline. 
         FIG. 15  is a schematic top plan view illustrating floating barriers surrounding an offshore oil and gas production platform. 
         FIG. 16  is a schematic top plan view illustrating floating barriers offshore of the coastal states of the Gulf of Mexico. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention is based upon a concept termed as “fully constrained platform” hereinafter abbreviated as FCP shown and described in my copending U.S. patent application Ser. No. 13/084,788, which is hereby incorporated herein in its entirety. As shown in  FIG. 1 , in a FCP, the buoyant, surface structure  10  is constrained by both vertical and angular tethers  12 . Since a motion in any of the six degrees of freedom will stretch the tethers  12  and thus will be resisted by its axial stiffness, the buoyant, surface structure  10  is fully constrained. In oceans, there are many disturbances which can offset a buoyant, surface structure, such as the winds, currents, swells, and surface and internal waves. The wind, current, swell, and internal wave forces are mainly static or quasi-static in nature (meaning changing at a very low rate), while the surface waves are oscillatory. When a structure is subjected to steady loads, its motion is controlled by its stiffness. The greater the stiffness a structure has, the smaller the motion it experiences. Therefore, for a properly sized FCP, the steady motion can be a minimum. 
     For the dynamic forces from the oscillatory waves, the FCP system will respond with a dynamic amplification factor. In this case, the key to minimize responses of a FCP is to avoid resonance: the coincidence of the system natural frequencies and the excitation frequencies of waves. A structure in oceans can be sized by modifying its mass or stiffness to shift its natural frequencies away from the significant wave frequency zone. Since the payloads on a FCP are small, especially if the surface structure and/or the barriers are fabricated with light, non-metallic materials, such as polyesters or high density polyethylene (abbreviated as HDPE) or Glass Reinforced Epoxy (abbreviated as GRE), it is entirely feasible for the structures to avoid resonance. 
     The FCPs can therefore be used to support the barriers in deep oceans, for dampening the forces from winds, waves, and currents, and to contain an oil spill. The buoyant, surface structure  10  of a FCP can be partitioned into a plurality of tanks. When one of the tanks is damaged and flooded, the entire structure will still have sufficient buoyancy such that the normal function is not compromised. The buoyant, surface structure  10  is so designed that when the tethers  12  fail, the structure will still be stable. To eliminate the possibility of becoming a floating hazard in case the screens (described hereinafter) are detached from the buoyant, surface structure  10 , their weights are designed to be heavier than that of the seawater. Once completely separated from their support structures, the screens will sink. Hooks embedded in the screen structures will aid in their recovery if needed. 
     Referring now to  FIG. 2 , in one embodiment, the buoyant, surface structure  10  of a FCP supports layers of porous screens  14 , which are mounted on the left, right and bottom sides of the surface structure. The screens  14  on the left and right sides have inclinations, while at the bottom they are leveled. Truss sub-structures  15  and  16  are used to aid the mounting of the screens  14  at the bottom and at the top sides of the structure  10 , respectively. As shown in  FIG. 2 , the buoyant, surface structure  10  is water surface piercing at the water line WL. Alternatively, it can also be fully submerged. 
     The configuration described above is for the screens  14  supported by two closely positioned FCPs. In this case, the screens  14  do not need intermediate supports. Referring now to  FIG. 3  for a larger view, the screens  14  are supported by one FCP at one end and by a second FCP at the other end. 
     Referring now to  FIG. 4 , there is shown, an elongate chainlike embodiment of the buoyant, surface structure  10 A with the screens  14  attached and moored by tethers  12  attached at one end along its longitudinal direction sides. The other ends of tethers  12  are anchored onto the sea floor. As seen from one end in  FIG. 5 , the flat top surface  10 B of the buoyant, surface structure  10 A can be used as a passage for vehicles, to reach out to the entire route to perform routine maintenance work, such as removing the debris trapped by the screens. The buoyant, surface structure  10 A may also be provide with wind turbines and solar panels along with batteries to provide electricity needed for maritime signals and lighting, etc, and thus can be self-sufficient. 
     As shown in  FIGS. 6A and 6B , to minimize the motion of the buoyant, surface structure  10  in winds, waves, and currents, the tethers  12  can be integrated into a net  20 , made from wire ropes and covering a portion of the surface structure. As seen in  FIG. 6B , the lower part of the buoyant, surface structure  10  is constrained by the net  20  and the tethers  12 . Screens  14  are attached to the buoyant surface structure  10 . 
     Referring now to  FIGS. 7A ,  7 B, and  7 C, a single tether  12  can also have multiple attachment legs  12 A which are connected to the net at various positions to further increase the stability of the surface structure, and to reduce the number of tethers.  FIGS. 7A and 7B  illustrate various configurations of this single tether, multiple attachment leg system.  FIG. 7C  illustrates the single tether, multiple attachment leg system attached to a net  20  which covers a buoyant, surface structure  10 . The tether joint  12 B (from which the legs are coming out) is represented by a double circle. This tether joint  12 B can be inside or outside of the water. The length of each attachment leg  12 A can vary to accommodate the distance from the tether joint  12 B to the net  20 . The net  20  can be pre-assembled on the buoyant, surface structure  10 , or alternatively, the net and the tethers may be connected before securing the buoyant, surface structure. The single tether, multiple attachment leg configuration can also cascade. 
     Referring now to  FIG. 8 , the screens of the floating barriers consist of plate sheets with perforations  18 . These perforations  18  do not line up, from one screen to the adjacent screens, when layers of screens are used. The shape of the perforations can be a square, a circle, etc, as is illustrated in  FIG. 9 . Referring now to  FIG. 10A , if the direction of the flow, indicated by the arrow, is known and is always in a particular direction, such as those used to protect a harbor, one-sided screens  14  having tapered perforations  18 A are preferred, in order to relieve the pressure downstream. Otherwise, two-sided screens having straight perforations  18 B should be used. 
     In regions where there are offshore drilling and production activities, the screens can be designed based on the concept illustrated in  FIG. 11 . The upper part  14 A of the screen  14  is for dampening the winds and waves (the height of this portion will depend on the local wave height and the size of the object intended to protect). The middle part  14 B of the screen  14  is for oil spill containment (the height of this portion is typically 3 to 6 feet, with the waterline centered approximately in the middle). The lower portion  14 C of the screen  14  is for dampening the waves and currents. The height of this portion can be as large as a few dozens to one or two hundred feet. 
     In one embodiment of this screen design (referring additionally to  FIG. 12 ), the height of the screen  14  is divided into three zones: zone  14 A, with perforations, is for winds and waves, zone  14 B, with no perforations, is for crude oil, and zone  14 C, with perforations, is for waves and currents. Screens for other purposes can also be designed, such as those for the fishery industry. 
     Referring now to  FIGS. 13A and 13B , the anchors  30  for tethers  12  are such that the entire system can be quickly installed. The preferred type of anchor  30  is a gravity based anchor. In one embodiment, the anchor consists of a cone-shaped weight, preferably made from steel and with a plurality of hook eyes  31  welded on its flat surface. The tether lines  12  can be attached to the hook eyes  31 . 
     The entire floating barriers can be fast quickly installed, segment by segment, following the method below. 
     (a) drop the weight anchor, which connects to one end of the tethers, from the installation boat, 
     (b) use small buoys to float the upper end of the tethers and/or nets, 
     (c) place the buoyant, surface structure in water, 
     (d) secure the said surface structure with the tethers and/or nets, 
     (e) attach screens if they are not already installed, and 
     (f) repeat steps (a) through (e) for each floating barrier segment. 
     Referring now to  FIG. 14 , two or more layers of floating barriers formed of elongate screens  14  supported by FCPs, as shown in  FIG. 3 , are placed along the coast line  40 , each being a few miles apart to act as barriers to prevent the buildup of waves of tsunamis or storms when they approach the shorelines, as represented by arrows  50 . One particular application, with some urgency, is the preparedness for the consequences of earthquakes and volcanic eruptions in the “Pacific ring of fire”. The protective barriers can be strategically placed, along the coast lines and surrounding the islands in the Pacific Ocean, to alleviate the tsunami waves. 
     As illustrated in  FIG. 15 , the floating barriers formed of the FCPs and screens  14  can also be installed around an important offshore structure, such as an offshore oil and gas production platform  60 , to protect them from storm damages and to contain potential oil spills. A similar floating barrier system to that shown in  FIG. 15  can be used to protect the shorelines of the states surrounding the Gulf of Mexico, as shown in heavy dashed line in  FIG. 16 . At certain positions along the route of the floating barriers, passages can be made to allow the traffic of ships and boats. These floating barriers are installed far from the shore and will not obstruct the views of the ocean.