Ships – Floating platform – Float assembly
Reexamination Certificate
1998-11-16
2001-03-06
Swinehart, Ed (Department: 3617)
Ships
Floating platform
Float assembly
C114S261000
Reexamination Certificate
active
06196151
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to floating platforms on a body of water or other liquid. More particularly, the present invention relates to water-borne crafts which can form a long, continuous surface such as a runway capable of handling the takeoff and landing requirements of large fixed-wing aircraft.
Military and civilian aircraft operations in the world today often require landing facilities in areas remote and distant from land-based airfields, particularly in flights conducted over large bodies of water. Although military ships like aircraft carriers serve in some extent to fill these needs, these monolithic hulled ships are typically only 1000 feet in length and only capable of servicing the landing requirements of smaller single seat or multi-seat airplanes. Larger cargo aircraft such as the C-17 or the smaller C-130 would likely require runways on the order of about 5000 feet, and ships capable of servicing such aircraft do not currently exist.
The theoretical solution of building a large floating platform for landing airplanes like transport aircraft faces practical difficulties related to deploying such a large structure at sea. Wave and weather conditions, in sea states where these platforms would be needed, place enormous stress on the structural integrity of such a platform. The lack of such a floating platform in the world today can be attributed in part to the technical challenges presented by the inclimate conditions encountered at sea.
Earlier attempts to design a suitable ocean-going platform proposed a conventional monolithic floating structure. In these cases, tests revealed that the vertical plane bending moment caused by waves was beyond the limits of the rigidly formed monolithic hull. The monolithic hull was too long to handle tumultuous wave conditions. Its transverse bending and torsional resonant periods in the zone of wave periods and its wave induced bending and torsional moments were not acceptable.
Other prior designs attempted to address this problem by de-coupling the modules in one degree of freedom, such as using hinges between modules to decouple the pitch degree of freedom. However, none of the remaining five degrees of freedom at the module interfaces were de-coupled. These designs were technically infeasible due to excessive transverse bending and torsional loads, and a transverse bending resonant period in the region of the exciting wave periods. While there is merit in the concept for pitch-axis stability, the concept was unsatisfactory as it lacks structural integrity in both transverse bending and torsion (i.e. yaw and roll). Sea states within which the platform operates would likely produce waves that would destroy such a structure.
Further design concepts proposed the use of universal joints to eliminate the large moments and resonant periods. However, the shear loads in the connectors are excessive, 10 to 100 times larger than typical in the design of floating oil field equipment. Structural elements capable of resisting the huge loads would be impractical to build. As mechanical loads under design wave conditions are far too great for connections between the modules can withstand, a practical concept for an inter-module connector that fixedly attaches modules that could mechanically stabilize the structure in all three axes is infeasible.
Accordingly, it is desired to design a floating platform capable of withstanding torsion and transverse bending loads/resonant dynamics encountered in unstable, high seas. It would further be desirable if the floating platform were included a runway capable of handling the operational takeoff and landing needs of large, fixed-wing cargo aircraft.
SUMMARY OF THE INVENTION
The present invention is directed towards a floating structure of sufficient size to handle the needs of nearly all aircraft which uses positioning devices that can withstand the wave conditions encountered at sea. The present invention contemplates a much larger floating structure able to handle multi-ton transport aircraft and civilian airliners. In the exemplary embodiment, the present invention would have a runway 5000 feet in length. A preferred conceptual design would provide for an aircraft runway to be connected between modules or Sub Base Units (SBUs) which are independently positioned while having runway bridges allowing for six degrees of freedom between each module. The independent module concept solves the high connector load problems exhibited in previous designs by substantially eliminating load-bearing connectors between modules. The runway bridge is not a connector, in the traditional sense, as it transfers almost no load between the modules for module positioning purposes. The concept preferably solves the strength and dynamic response issues by subdividing the platform into a sufficient number of smaller more feasible independent modules comprising relative position keeping elements and bridges for providing substantially continuous runway surfaces.
In one aspect, the present invention provides a floating platform comprising a plurality of floating modules having positioning thrusters adapted to position the modules to define a substantially continuous runway across at least two of the modules. One of the modules typically has an extension or bridge in slidable, releasable contact with an adjacent module when the runway is in a continuous configuration. The bridge is usually adapted to allow for six degrees of motion between adjacent modules so as to minimize the stress on the extension. Preferably, the positioning of the modules to maintain the substantially continuous runway will be accomplished by the positioning thrusters. More preferably, the bridge or extension has an upper surface allowing for aircraft to roll from the end of one module to an adjacent end of another module when the modules are moving in all six degrees of freedom. The runway bridge will preferably not hold the modules together. In a specific embodiment, the runway connectors may be viewed as retractable and articulated ramps. The runway bridge may have an end surface maintained substantially in alignment and contact with an module end surface.
In another aspect, the present invention provides a floating platform comprising a donor module and a receiver module. The modules have dynamic positioning elements and a connecting bridge spanning an operational distance between the modules. A first portion of the connecting bridge extends from the donor module and a second portion extends from the receiver module. A sliding interface may be defined between the first portion and the second portion. Specifically, the first portion defines a first connecting surface and the second portion has a second connecting surface where the connecting surfaces remain in substantial contact with one another. The first portion from the donor module preferably contacts a landing region on the receiving module. This advantageously allows the connector to rest on the receiver module. The second portion usually has a spring damper system pushing against the first portion.
In a still further aspect, the present invention provides a connection assembly for spanning an operational distance between adjacent floating modules. The assembly includes a bridge element mountable on one of the modules, a yaw compensation assembly, and a gap closure assembly. The bridge element and assemblies form a substantially continuous surface between adjacent modules when the connection assembly spans the operation distance. Preferably, the connection assembly is configured to allow for six degrees of relative motion between modules while maintaining a continuous surface between modules. In some embodiments, the gap closure assembly is mounted on a receiver module, the yaw compensation assembly mounted adjacent the gap closure assembly, and the bridge element is pivotally mounted on a donor module and having first and second positions. The bridge element is typically releasably connected to yaw compensation assembly on the receiving module when in t
Dolan Daniel K.
Grant Robert G.
Lundberg Richard C.
Bechtel Group Inc.
Swinehart Ed
Townsend and Townsend / and Crew LLP
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