The disclosure relates generally to a directions control system for submersible vehicles such as Remotely Operated Vehicles (ROV) or Autonomous Underwater Vehicles (AUV) that may be operated by umbilical tether, radio control, optical control or acoustical control. More specifically, the disclosure relates to a control system for submersible vehicles that can achieve six degrees of freedom in positional and motion control by employing two thrusters with no need for external control planes. The instant disclosure can achieve the aforementioned functionality while improving vehicle inherent stability and other desirable vehicle control abilities.
The current designs for submersible vehicles, such as autonomous underwater vehicles (AUV) and remotely operated vehicles (ROV), are propelled through the water column using a single thruster assembly. The thruster assembly usually consists of any one of various types of electric or fuel motor that provide power to a drive shaft that, in turn rotates a propeller mounted thereto. There are various types of shrouds, ducts or exposed propeller assemblies that direct the thrust generated by the propellor along the fixed earth coordinate system X-axis to provide forward or reverse movement. Directional control of these vehicles is typically achieved using three, or more, exposed external control surfaces. These exposed external control surfaces or “control planes” operate independently, or in concert with each other. The movement of the planes causes water resistance against the movement of the vehicle body in the water column, thereby forcing the vehicle to change direction giving the vehicle three degrees of freedom via yaw (vehicle moves left or right on the X axis), pitch (vehicle moves up or down on the Y axis), and roll (vehicle rotation angle off centerline on the X axis), as shown in
The presently used control systems for submersible vehicles suffer from many design flaws and disadvantages. For example, while various AUVs use this basic design method to control AUV movement and directional control in water, the design fails to address multiple environmental and desired position control issues that can arise during marine surveys.
In general, all submersible vehicles that are thrust from, and/or positionally controlled from, the aft section of the vehicle body are inherently unstable and require constant adjustments by the positional control system to keep them on a desired course. Further, any body shape other than a sphere generates a moment when the submersible vehicle is inclined in an inviscid flow. The d′Alembert's paradox predicts zero net force, but not necessarily a zero moment. This, so-called, Munk moment arises because of asymmetric location of the stagnation points, where pressure is highest on the front of the body (decelerating flow) and lowest on the back (accelerating flow). The Munk moment is always destabilizing, in the sense that it acts to turn the vehicle perpendicular to the flow. This effect can be countered by vehicle designs that utilize forward (bow) section control planes, forward thrusters that can apply thrust counter to the Munk Moment or a combination of these design elements. The longer the vehicle and the wider the cross section of the vehicle, the more pronounced the Munk Moment force against the vehicle, requiring the control system to exert increased effort to maintain desired position. To account for the Munk Moment force, some submersible vehicles utilize a combination of five or more thrusters and two sets of control planes to achieve six degrees of freedom control. The addition of forward (bow) section control planes can be used to minimize Monk Moment on the hull to help stabilize forward motion along the X axis.
Geo positional control of these submersible vehicle design types require a minimum forward or reverse movement (speed) along the vehicle's X axis to generate flow over the control planes in order for the vehicle to maintain the desired geo position along all three axis of control. Depending on multiple factors, such as the individual vehicle mass and shape in relation to the size and type of control planes, water resistance, ocean currents or other dynamic force that can affect the vehicle position such as surface waves, surface wind etc., the vehicle must maintain a certain minimum forward motion in order to maintain geo positional control. Once the vehicles forward motion falls below this minimum the vehicle will suffer loss of positional control and will drift off the desired course or position or suffer other unwanted movement such as loss of pitch, roll, yaw. Avoiding these loss of control conditions is critical for accurate geo positional control of the vehicle as well as being able to maintain vehicle stability to assure a stable platform for whatever data collecting sensors or instruments payloads are being utilized during the survey.
In addition, when a submersible vehicle of this design type encounters ocean currents along the X (surge), Y (sway), or Z (heave) axis, these vehicle designs are poorly suited to counter these forces to maintain geo positional control, such as when a submersible vehicle is transiting down current along the X axis, and the ocean current exceeds the vehicles minimum required forward motion to maintain directional control. If a vehicle's optimal forward programmed survey speed is 4 km per hour and the vehicle requires a minimum forward speed of 3 km per hour to maintain positional control, an ocean current of 2 km per hour would produce a vehicle speed over ground of 6 km per hour. The vehicle will try to slow down forward motion to maintain the programed survey speed of 4 km per hour over ground. As a result of the reduction in forward motion, the vehicle will be moving down current at 4 km per hour over ground but only moving 2 km per hour through the water column, resulting in the vehicle not having enough forward movement to achieve the minimum 3 km per hour through the water column to maintain positional control of the vehicle.
In another example, a submersible vehicle can be moving up current along the X axis. If the ocean current exceeds the vehicles maximum forward motion capabilities it will fail to maintain directional control. If the vehicles maximum forward survey speed is 4 km per hour, the minimum positional control speed is 3 km per hour and the ocean current is 2 km per hour, the vehicle will not be able to achieve minimum forward motion of 3 km per hour to meet survey speed and may lose the ability to maintain directional control.
Further still, if a submersible vehicle is moving along X axis at survey speed but encounters ocean currents along the Y axis and if the ocean current exceeds the vehicles ability to maintain heading positional control along the X axis; then, the vehicle can fail to maintain geo position along the X axis or cause the vehicle to excessively yaw into the current to maintain X axis position causing degradation of survey data, loss of movement efficiency or possibly loss of positional control.
Moreover, the current submersible vehicle designs are incapable of performing several desirable positional control maneuvers. Those desirable positional control maneuvers can include:
(1) Maintaining positional control along the X axis in both directions from 0 km per hour to maximum vehicle speed.
(2) Maintaining positional control along the Y axis in both directions from 0 km per hour to the maximum vehicle speed.
(3) Maintaining positional control along the Z axis in both from 0 km per hour to the maximum vehicle speed.
(4) Maintaining positional control along the Z axis in both directions from 0 km per hour to maximum vehicle speed at any desired degree of pitch.
The ability of subsea marine vehicles such as AUVs to maintain 0 km per hour in all three axis and maintaining any desired position in six degrees of freedom along the three axis of positional control in dynamic environment is typically referred to as “station keeping” or “Parking.” Current submersible vehicles are not capable of station keeping positional control along all three axis with positional control of the vehicle in six degrees of freedom with designs utilizing any less than five thrusters to maintain position. Current designs of submersible vehicles utilizing five, or more, thrusters can include:
(1) An AUV utilizing twelve distinct thrusters to achieve six degrees of freedom positional control
(2) An AUV utilizing eight thrusters and articulating vehicle body segments to achieve six degrees of freedom positional control;
(3) A hovering autonomous underwater vehicle (HAUV) utilizing five thrusters to achieve six degrees of freedom positional control; and
(4) An AUV utilizing a combination of five thrusters and two sets of control planes to achieve six degrees of freedom control. The forward (bow) section control planes can be used to minimize Monk Moment on the hull to help stabilize forward motion along the X axis
The foregoing attempts in the prior art fail to meet the needs of the industry. There exists significant industry demand, for a submersible vehicle propulsion and system that can achieve six degrees of freedom utilizing a combination of as few thrusters as possible to improve power efficiency, simplify control, and with no external control planes.
The present disclosure preserves the advantages of prior art while proving an improved submersible vehicle propulsion and positional control system that can achieve six degrees of freedom positional control utilizing a combination of only two thrusters in conjunction with two thrust vectoring control assemblies, with no external control planes.
One objective of the present disclosure is to improve the inherent stability of a submersible vehicle by directly countering Munk moment via vehicle thrust and positional control on both the bow (forward section) and stern (after section) simultaneously.
Another objective of the present disclosure includes improving other desirable vehicle control abilities with better positional control of the bow section of the vehicle while transiting on the surface in all sea states, which provides for more stable vehicle control of the vehicle while on the surface. This also optimizes the vehicle position for visual location and communications with the vehicle while on the surface.
A further objective of the present disclosure includes providing for redundant positional control for vehicle self-rescue in case of failure of one of the thrusters or positional control assemblies as either the bow or stern thruster and positional control sections can control the vehicle independently of one another.
Yet another objective of the present disclosure can include reducing, or in some cases eliminating, protrusions that are typical on other submersible vehicle designs such as external control planes and exposed or partially exposed thruster assemblies or propellers to reduce drag, increase propulsion efficiency and reduce potential for the vehicle to become entangled in debris, structures, or marine organics or on these surfaces.
A still further objective of the present disclosure can include the elimination of external control planes and exposed or partially exposed thruster propellers to reduce the chances of damage to the vehicle during survey operations, launch and recovery from a support vessel, fixed platform or shore, or during routine vehicle handling.
Other objectives of the present disclosure will be discussed in detail throughout the present disclosure, figures, and claims.
The novel features which are characteristic of the present disclosure are set forth in the appended claims. However, the disclosure's preferred embodiments, together with further objects and attendant advantages, will be best understood by reference to the following detailed description taken in connection with the accompanying drawings in which:
Certain exemplary embodiments will now be described to provide an overall understanding of the principles of the structure, function, manufacture, and use of the device and methods disclosed herein. One or more examples of these embodiments are illustrated in the accompanying drawings. Those skilled in the art will understand that the devices and methods specifically described herein and illustrated in the accompanying drawings are non-limiting exemplary embodiments and that the scope of the present disclosure is defined solely by the claims. The features illustrated or described in connection with one exemplary embodiment may be combined with the features of other embodiments. Such modifications and variations are intended to be included within the scope of the present disclosure. Further, in the present disclosure, like-numbered components of the embodiments generally have similar features, and thus within a particular embodiment each feature of each like-numbered component is not necessarily fully elaborated upon. Additionally, to the extent that linear or circular dimensions are used in the description of the disclosed systems, devices, and methods, such dimensions are not intended to limit the types of shapes that can be used in conjunction with such systems, devices, and methods. A person skilled in the art will recognize that an equivalent to such linear and circular dimensions can easily be determined for any geometric shape. Further, to the extent that directional terms like top, bottom, up, or down are used, they are not intended to limit the systems, devices, and methods disclosed herein. A person skilled in the art will recognize that these terms are merely relative to the system and device being discussed and are not universal. While reference is made with respect to autonomous underwater vehicles, it will be appreciated to those skilled in the art that the present disclosure can be used in other underwater vehicles or aquatic vehicles generally. Moreover, while reference is made to water, it will be appreciated to those skilled in the art that the vehicles discussed herein may be used in other fluids.
The present disclosure is generally shown and illustrated in
In general, as shown in
Turning now to
At
A detailed view of the vector control shroud 24 is provided at
In the illustrated embodiment, as described above in
A mast 46 may be provided for remote communications with the submersible vehicle. The mast 46 may serve as a radio antenna or a connection point for an umbilical tether allowing electronic interconnectivity for control and data transfer between the submersible vehicle and the remote-control center. The mast 46 may be fixed or retractable to allow a reduction of turbulence when the submersible vehicle is operating below the water surface. For example, the mast/antenna 46 is preferably pivotally connected to the body 12 about a pivot point 47, as seen in
Importantly, by regulating the flow of water, or the thrust, via the damper assembly the position of the vehicle can be controlled in all three fixed frame coordinates in one direction. Notably, each of the respective discharge ducts include a respective damper assembly. For example, the bow section positional direction and speed of vehicle can be controlled while moving forward if the two dampers on the upper side of the assembly (45° and 315° thruster outlets) are partially closed to reduce the flow and thrust, then the vehicle will pitch up. In a further example, if the two bow dampers on the underside of the assembly (135° and 225° thruster outlets) are partially closed to reduce the flow and thrust, then the vehicle will pitch down. Changes in the position of the respective dampers, with respect to the ducts, can affect both the volume and velocity of the water discharged from the respective duct thus affecting the amount of measurable thrust that duct produces. The relative orientation of the respective dampers, for example how far it is opened or closed, can increase or decrease thrusting force on the submersible vehicle affecting both positional direction and or speed through the water column.
In another example of use, if the two dampers on the port side of the assembly (45° and 135° thruster outlets) are partially closed to reducing the flow and thrust, then the vehicle will yaw to port. Similarly, if the two dampers on the starboard side of the assembly (225° and 315° thruster outlets) partially close reducing the flow and thrust the vehicle will yaw to starboard. In this example, the bow dampers can be partially closed while the stern dampers can be fully open if the stern thruster is providing thrust in the same direction as the bow. Alternatively, the bow dampers can be fully closed and not in use for this particular control maneuver.
The submersible vehicle can function in several modes. 1. Bow section only forward movement: in this mode the forward movement thrust along the X axis and positional control is only three axis of directional control, with the stern section not being utilized. 2. Bow section with stern section forward movement: in this mode the movement thrust along the X axis is produced by both the bow and stern sections (the stern section can take water into the control dampers in an open position and eject the water out of the assembly “intake” to provide thrust in the same direction along the X axis as the bow assembly) while the bow section provides three axis of directional control. 3. Bow and stern section six axis of control: In this mode, both bow and stern assemblies take in water from the thruster inlets and eject the water via the dampers allowing for the thrust to be used to hold the submersible vehicle in “Parking” position or move the submersible vehicle in any of the 6 axis of control. The bow and stern assemblies can thrust against each other to maintain desired position, if the bow section reduces thrust via reducing volume of water from the thruster motor (reduce motor rpm) without changing bow damper positions the submersible vehicle would move in the direction of the stern along the X axis as the stern section is now producing more thrust than the bow section etc. 4. Stern section reverse movement: In this mode, the stern section can provide thrust and three axis of directional control along the X axis in reverse submersible vehicle direction. This mode could be used for self-rescue if the bow section fails, the submersible vehicle gets stuck in an artifact or rock formation and need to reverse along the X axis, maneuver in reverse along the X axis on the surface during submersible vehicle recovery or to avoid collision etc.
Forward motion of the submersible vehicle along the X axis can be controlled via closing or opening all four dampers of the bow section synchronously while matching the proportion of each damper is open or closed. Additionally, forward motion can be controlled by varying water volume/velocity via changing thruster motor rotation rpm.
By installing two of the vector control assemblies on a submersible vehicle, one on the bow and one on the stern, disposed in opposing directions, as shown in
In addition, the direction of the flow of the water through the stern vector control assembly can be reversed making the thruster outlets the water inlet and the inlet the thruster outlet to give all positional control of the vehicle to the bow vector control assembly, while using the stern vector control assembly only for forward motion thrust giving the vehicle three axis control in one direction, as shown in
The rim thruster designs have several advantages for marine use, as no watertight shaft seals are needed, they are crush proof and can work at any water depth, they produce more torque (force on the water) at lower RPMs than conventional shaft driven motors etc. As rim thrusters do not utilize a shaft armature/drive shaft assembly they are less likely to be fouled with debris such as fishing line and seaweed etc. As described above and shown in the figures, the rim thruster is shown being used to provide water propulsion for the vector control assembly. Other more conventional motor/propeller types could be used in conjunction with the damper assemblies, but the illustrated embodiment uses rim thruster for the advantages described above.
It would be appreciated by those skilled in the art that various changes and modifications can be made to the illustrated embodiments without departing from the spirit of the present disclosure. All such modifications and changes are intended to be covered by the appended claims.
This application is related to and claims priority from earlier filed U.S. Provisional Patent Application No. 63/246,325, filed Sep. 21, 2021, the entire contents of the foregoing is incorporated herein by reference.
Number | Date | Country | |
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63246325 | Sep 2021 | US |