Patent Grant
9272756
The present invention pertains generally to buoys. More specifically, the present invention pertains to the buoys which can have variable buoyancy for ease of deployment and power savings as the buoys are deployed.
Moored buoys are well known in the prior art for use in various purposes, including marking navigational hazards, aids to navigation channels, etc. A moored surface buoy must have a relatively high net buoyancy to limit overtopping in higher sea states. In the case of high surface current, the high net buoyancy is needed to prevent the buoy from being drug under by the tension in the mooring.
In some instances, buoys are deployed from a ship. In other instances, it may be desired to deploy a buoy from a stowage configuration that is already underwater. Reasons for such stowage can include preventing (or at least slowing) the growth of marine growths such as kelp on the outer hull of the buoy. For these cases, a buoy could be required to ascend a water column for deployment, and descend in the water column during retraction and re-stowage. During the retraction phase, a large relative force may be required to bring it back down to the stowage structure. By adding a pressure sensitive variable buoyancy, the buoy can have the advantage of relatively large excess buoyancy at the surface, while having a significantly decreased net buoyancy at depth; thus, saving energy during descent.
In view of the above, it is an object of the present invention to provide a variable buoyancy buoy having variable buoyancy, which can be protected inside a flooded area inside the main floatation portion of the buoy. Another object of the present invention is to provide a variable buoyancy buoy that inhibits formation of marine growth on the buoy and maintains a kelp shedding aspect for the buoy. Still another object of the present invention is to provide a variable buoyancy buoy that decrease in buoyancy with increase depth in the water. Yet another object of the present invention is to provide a variable buoyancy buoy that can require decreased power to retract the buoy when the buoy is stowed underwater. Another objective of the present invention is to provide a variable buoyancy buoy, which is easy to manufacture and use in a cost-effective manner.
A variable buoyancy buoy and method for deployment therefor can include a fixed buoyancy portion formed with an enclosure and a variable buoyancy portion that can be inserted into the enclosure. The fixed buoyancy portion can be formed with at least one opening to establish a path of fluid communication between the exterior of the buoy and the variable buoyancy portion. The fixed buoyancy portion can further be formed with a cavity. A pressure vessel body containing electronics or other materials can be located within the cavity. The fixed buoyancy portion can have a spar buoy configuration or a marker buoy configuration, according to the needs of the user.
The buoy can have variable buoyancy, which can vary from maximum buoyancy at atmospheric pressure to minimum buoyancy, which can occur at stowage depth for the buoy. The variable buoyancy portion can have a variable volume, which can change from a maximum volume at the surface of the water (atmospheric pressure) to a minimum volume when the buoy is at stowage depth. To do this, the variable buoyancy portion can be a compressible bladder, or compressible foam. The variable buoyancy can facilitate the retraction of the buoy with a winch which can be located at the floor of the water body. As the winch retracts the buoy, the buoyancy can decrease as the buoy descends into the water, which can decrease the power required to retract the buoy.
The novel features of the present invention will be best understood from the accompanying drawings, taken in conjunction with the accompanying description, in which similarly-referenced characters refer to similarly-referenced parts, and in which:
In brief overview, a moored surface buoy must have a relatively high net buoyancy to limit overtopping in higher sea states. In the case of high surface current, high net buoyancy is required to prevent the buoy from being drug under by the tension in the mooring. Thus, a buoy that is required to ascend and descend in a water column would require a large relative force to bring it back down. Additionally, the buoy can have a low profile, to maximize kelp shedding properties for the buoy (kelp shedding can be taken to refer to the ability of the buoy to move through an existing kelp forest as it ascends and descends through the water column). By incorporating pressure sensitive variable buoyancy into a buoy, the buoy can have the advantage of relatively large excess buoyancy at the surface, while having significantly decreased net buoyancy at depth; thus, saving energy during descent. This disclosure describes two passive methods that can solve this problem while keeping the outer hull of the buoy static and smooth for kelp shedding (i.e., marine growth on the buoy hull).
Referring now to
As shown in
In still other embodiments, and as mentioned above, variable buoyancy portion 18 can be made of low density contracting closed cell foam which is resistant to compression set. It can be shown that an appropriate closed cell foam can survive the depths without becoming waterlogged or losing its uncompressed shape once the variable buoyancy portion 18 is returned to the surface. Thus, it can increase the buoyancy of the buoy at the surface and will then lose its volume as it is compressed at depth and repeat the cycle irrespective of soak time or number of cycles. Other methods of variable buoyancy can include active expansion of a chamber via regulated pressure or mechanical sliding of a pressure vessel with relative vacuum.
As shown in
Referring now to
When buoy 10 is on the surface 34 of the water, the variable buoyancy portion has a maximum volume Vmax and buoy 10 has corresponding maximum buoyancy Bmax. Once the desired mission of the buoy 10 has been accomplished, the operator can selectively retract buoy 10 using a winch (not shown in
Based on depth, the buoy will change net buoyancy. Because of the variable buoyancy (due to compressible volume and displacement by water) of variable buoyancy portion 18, the buoy net buoyancy B can decrease with depth making the net force required to retract the buoy 10 (i.e., the tension force on tether 30) decrease.
As an illustrative case of the above, and given a bladder or closed cell foam is used, the buoy will decrease its variable buoyancy by half every time the external pressure doubles to an increase in depth of the buoy 10, for example:
Surface (1 atmosphere, ATM)=6 lb variable buoyancy; total buoyancy=12 lb
33 ft (2 ATM)=3 lb variable buoyancy; total buoyancy=9 lb
100 ft (4 ATM)=1.5 lb variable buoyancy; total buoyancy=7.5 lb
233 ft (8 ATM)=0.75 lb variable buoyancy; total buoyancy=6.75 lb
500 ft (16 ATM)=0.37 lb variable buoyancy; total buoyancy=6.37 lb
Given the net buoyancy of a buoy is 12 lb at the surface (Bmax=12 lb), and 6 lbs of that buoyancy is variable, as buoy 10 descends it will decrease in net buoyancy as the variable buoyancy is compressed and the net buoyancy approaches the fixed buoyancy (Bmin), which in this case is 6 lb. The available change in buoyancy can be based on the depth at which the buoy 10 will be stowed and the available compressible volume V of variable buoyancy portion 18 which can be displaced by water/seawater.
Form the above, it can be seen that the force required for retraction of the buoy can decrease significantly which in turn can save energy for the winch. Since the retraction mechanism power is typically provided by batteries, this can be extremely desirable, as the retraction mechanism can often be at depth (in the example above, at 500 ft) that can make it extremely difficult to replace the batteries. Thus, power needed to deploy the variable buoyancy buoy is decreased, and reliability of the system is increase (typically batteries) in a retractable buoy system. The excess buoyancy is thus greatest on the surface where it is needed for wave following and stability concerns. The fixed buoyancy is reserved as a minimum for what the buoy would need to overcome stowed forces, and maintain its shape for shedding possible obstacles such as seaweed, and to avoid the situation where the buoy does not reach the surface given the line weight or due to water current blow down.
The advantage of this invention according to several embodiments can be its simple and passive nature. Either embodiment of variable buoyancy portion 18, whether foam or bladder, is capable of compressing and re-expanding reliably without any activation or electronics overhead. Since variable buoyancy portion 18 is simply constructed and occupies a flooded pocket (enclosure 14) in the hull of the buoy, it can be unlikely to become fouled or damaged by obstacles normally encountered by the buoy during its ascent or descent. However, it is conceivable that the variable buoyancy portion 18 can be external, such as a float ring, if kelp is not an issue. Finally, because there is no seal to leak, they are well suited for long term use and a high number of cycles.
This invention can further be envisioned for use with Unmanned Underwater Vehicles (UUV's) that require surface operation as part of their mission. The variable buoyancy portion 18 would become more buoyant near the surface, thus allowing for RF or other communications without requiring the UUV to be actively driving upward to maintain surface operation. Once the UUV is finished, and it dives to a specified depth, it can then become near neutral again so it would not expend extra energy to maintain its depth. Thus the UUV could have a hybrid operation (spending part of its mission as a buoy and part as a roaming vehicle, more efficiently. Also, surfacing for pickup, if it is required, would be made easier as more of the vehicle would be visibly out of the water and sit higher for attaching an arresting hook or other method of capture.
Referring now to
As shown in
The use of the terms “a” and “an” and “the” and similar references in the context of describing the invention (especially in the context of the following claims) is to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.
Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.
The United States Government has ownership rights in this invention. Licensing inquiries may be directed to Office of Research and Technical Applications, Space and Naval Warfare Systems Center, Pacific, Code 72120, San Diego, Calif., 92152; telephone (619) 553-5118; referencing NC 102678.
| Number | Name | Date | Kind |
|---|---|---|---|
| 4054104 | Haselton | Oct 1977 | A |
| 4788925 | Simon et al. | Dec 1988 | A |
| 6321676 | Kohnen et al. | Nov 2001 | B1 |
