1. Field of the Invention
Various embodiments of the present invention relate to marine vehicles, and more particularly, to buoyancy controlled marine vehicles.
2. Background of Related Art
Although underwater environments are more diverse than those on land, difficulties associated with gathering underwater data has severely limited our knowledge of these habitats. In fact, many experts agree that the difficulty in assessing some underwater environments is commensurate in scope with many space missions. While space exploration has been able to rely on numerous unmanned missions, however, most oceanic monitoring and exploration is still performed by manned vehicles, and is often constrained by the limitations of these vehicles.
A variety of marine vehicles have been developed to explore underwater environments. The great majority of these vehicles are, or have evolved from, rigid-hull submersibles. The deployment and effectiveness of these vehicles has been severely limited, however, by the need to incorporate long tethered cables to a mother ship, propellers that become entangled and snarled in sea grass or debris, and rigid hulls that prevent maneuvering in close proximity to fragile ocean features, such as arctic ice or coral reefs, for fear of damaging the environment.
In addition, traditional marine vehicles are often complex machines that are mechanically propelled and require large amounts of fuel or heavy batteries to function. The use of fuel and heavy batteries for mechanical propulsion can limit the length of the vehicles' missions, as the fuel quickly runs out and the batteries quickly die. These shortcomings necessitate a different approach to oceanographic exploration.
Some researchers have developed vehicles that use buoyancy and gravity to yield locomotion, instead of fuel and batteries. In these designs, a torpedo shaped vehicle can be angled forward and downward in the water, and the buoyancy of the vehicle can be reduced. The vehicle then descends, and the forward angle causes the vehicle to move forward and downward at a given glide path. When the vehicle reaches a predetermined depth, the buoyancy can be increased, causing the vehicle to rise toward the surface of the water. A forward angle can be maintained during this ascent, again causing the vehicle to move forward in addition to upward at a given glide path. When the vehicle reaches a predetermined depth, its buoyancy can be decreased and the first forward angle reinstated, again causing the vehicle to move forward and downward. This process can be repeated until the vehicle moves a desired distance or to a desired location.
The buoyancy vehicles described above have several disadvantages. First, constant depth cannot be maintained, since depth change is necessary to impart movement. Second, side to side movement is difficult or impossible to impart without adding complex components. Third, the vehicles are heavily influenced by oceanic currents, since they generally have difficulty modifying their trajectories to compensate for the flow of the water. These disadvantages make the vehicles poorer choices for oceanic exploration, as they have very limited capabilities.
To overcome these limitations, a number of researchers have explored vehicles that are based on biomimicry of batoids, such as rays or skates. Live batoids have superior hydrodynamic characteristics and make extremely efficient use of energy. They also have excellent underwater movement capabilities. Known vehicles that imitate batoids, however, are mechanically actuated, and locomotion and maneuvering of these designs have been limited by the high complexity and power consumption of their actuators. More specifically, movement of flexible portions of the vehicles, such as their fins, has been limited by the availability and reliability of known mechanical designs as well as the amount of energy that is required to actuate these designs.
What is needed, therefore, is an efficient vehicle suitable for extended underwater missions. The vehicle can use buoyancy to effectively control its motion, but should do so in a manner that provides desirable locomotion and maneuvering capabilities. In some embodiments, the vehicle should mimic a batoid. It is to such a system that embodiments of the present invention are primarily directed.