Ships – Submersible device – Having propulsion unit
Reexamination Certificate
2002-06-06
2004-03-09
Sotelo, Jesus D. (Department: 3617)
Ships
Submersible device
Having propulsion unit
C440S047000, C114S06700A
Reexamination Certificate
active
06701862
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to aquatic propulsion systems and more specifically to a propulsion system, located generally in the front and rear of a submersible device, such as a submarine or torpedo.
2. Problems in the Art
Currently, underwater vehicles, such as nuclear powered submarines, are propelled through the water using a propeller based propulsion system located only at the stern of the vehicle. Drag forces acting on the vehicle cause the water in front of, and around, the vehicle to become displaced and turbulent in nature. Propeller based propulsion systems located at the stern are forced to push the submarine against this resultant turbulent water. These drag forces lead to decreased efficiency and a lower overall thrust.
Further, these propeller-based propulsion systems cause an increase in a submarine's noise with an increase in speed. This may aid others in detecting the submarine, thereby enabling its destruction. The increase in noise is due largely to cavitation. Cavitation is the formation of noisy water vapor bubbles. Rapid propeller movement creates a vacuum-like area in the incompressible water. The vapor pressure of the water forms the bubble. Surrounding water pressure soon collapses the bubble, violently, creating noise.
As the speed of the submarine increases, the geometrically increasing wave, generated by water resistance, limits the increase in speed and contributes to cavitation (propeller noise). This wave is the main resistance to high speed in surface vessels and plays a role in submarine speed increase, albeit less when the submarine is at a depth of greater than three submarine diameters below the surface.
In addition, as submarine speed increases, surface friction from turbulence-related viscous shear stress, creates a boundary layer of retarded fluid along the surface of the moving vessel, which also causes drag. In this boundary layer, eddies of high-speed fluid contact the surface, causing deceleration and sap the watercraft's momentum. This boundary layer turbulence increases in magnitude as flow progresses rearward from the bow; thus nearly all of the vehicle's surface boundary layer is turbulent, worsening as speed increases. The friction or drag of a turbulent boundary layer is seven to ten times that of a laminar boundary layer, so the possibility of achieving significant reductions in vehicle drag, by boundary layer management, is attractive.
There have been attempts to reduce boundary layer friction on submarines. Rogers in U.S. Pat. No. 4,346,662 uses a twin hull design with extensive slots in the outer hull. These are kept open by a backflush pump in the bow at low speed. At high speeds, the bow pump is inactivated, while the main pump at the stern exhausts water that has been pulled through the slots by suction; this is the sub's main propulsion. High Reynolds numbers (friction) limited practical application.
Mayer also discusses boundary layer control in U.S. Pat. No. 3,779,199. It did not solve the boundary layer problem beyond the bow, where the problem mainly exists; the preceding Rogers patent, which followed nearly ten years later, addressed this. The Mayer patent also eliminated the conventional propeller and rudder; this loses efficiency due to poor management of the turbulent slipwater at the stern. The intake diameter did not approach the submarine diameter. The water exited through a large number of exit ports. The large numbers of parallel exit ports (slots) were arranged in a number of concentric rings at the bow; these were used for directional flow and the only source of propulsion. Due to aforementioned reasons, the Mayer patent was not utilized in a practical submarine application.
Short of significantly reducing surface resistance and wave generation by other means, submarine speed at stealth is slow, and top speed is below that of important surface ships, such as an aircraft carrier. Submarine surfaces are presently coated with rubber to make it less reflective to sonar and mute submarine noise. Stealth is the priority with submarines; it has always been the priority.
Surface water vehicles typically rely on a propeller fan, either by an inboard or outboard stern positioned engine, for propulsion. This application of power to the rear end creates an inverted pendulum, with stability problems. This stern drive requires the vehicle to be pushed through the water, which generates geometrically disproportionate wave drag resistance with any increase in speed; it is the main obstacle to increased speed for the surface water vehicle. This wave arises from displacing all of the incompressible water in front of the vehicle, to around and behind the vehicle. This frontal wave generation limits stability, efficiency and speed.
Currently, most improved water jet engines on surface crafts are placed at the stern of craft and exhaust the water outward, above the waterline. They are still subject to the preceding limitations of stern-drive only. They are a variation of the original water-jet engine that accelerates water through a curved passageway.
Attempts have been made to address these problems for water surface vehicles. U.S. Pat. No. 5,634,419 to Cymara discloses what is called a “front-drive boat” wherein a propeller propulsion system is located towards the front (bow) of the boat, which is claimed to increase stability of the boat.
U.S. Pat. No. 4,680,017 to Eller, entitled “motorboat propeller guard for improved performance”, places a propeller inside a housing, with grids configured to attempt to direct propelled water rearwardly for improved performance. It is jet-like and somewhat similar to the stern pumpjet used on modern stealth submarines, which followed earlier torpedo pumpjet designs. Cavitation (generation of noisy water vapor bubbles) was reduced in the pumpjet through pressurizing the propeller blade area and eliminating the propeller tip vortices, making higher speeds at stealth possible.
Herein incorporated by reference, U.S. Pat. No. 5,383,801 to Chas, U.S. Pat. No. 4,902,254 to Chas, U.S. Pat. No. 4,831,297 to Taylor et al., disclose propulsion systems for over the watercraft that adopt jet engine principles to attempt to increase propulsion. Another propeller based propulsion systems is U.S. Pat. No. 5,252,875 to Veronesi, et al., herein incorporated by reference. Many of the above patents resemble a jet engine in appearance and further resemble a jet engine in the manner in which they are attached to a vehicle; i.e. they hang down from the craft. They still have to push a boat through the water, causing wave displacement that increases geometrically with speed. None have twin jet accelerators in sequence. None are capable of higher stealth speed or supercavitation.
Therefore, although attempts have been made to apply jet engine principles to the above water craft, and attempts have been made to increase stability of over the water craft, submarine propulsion systems have remained relatively the same, utilizing stern drive propeller fan propulsion.
There is therefore a need for a submarine propulsion system, which avoids these and other problems in the art.
FEATURES OF THE INVENTION
A general feature of the present invention is the provision of a propulsion system for a submersible, which overcomes the problems found in the prior art.
Another feature of this invention is the provision of a propulsion system for a submersible that reduces drag caused by wave generation.
A still further feature of the present invention is the provision of a propulsion system for a submersible that reduces drag caused by surface friction.
Another feature of the present invention is the provision of a propulsion system for a submersible, which has improved stealth at higher speeds.
A further feature of the present invention is the provision of a propulsion system for a submersible that improves the speed of the submersible.
A further feature of the present invention is the provision of a propulsion system for a submersible which is c
McKee Voorhees & Sease, P.L.C.
Sotelo Jesus D.
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