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The development and applications of remotely operated and autonomous underwater vehicles have significantly increased in recent years. As these vehicles operate in the harsh underwater environment, demanding requirements for their design usually reflect in a high cost of underwater systems. However, with more readily available inexpensive electronics and powering systems, lower cost developments have been initiated. In the present work, several modifications of a low-cost remotely operated underwater platform are described. One is a construction of a two-degree-of-freedom arm for manipulating underwater objects. The second is an improvement of the propulsion control on the vehicle to allow for gradual variation of thrust forces instead of the original on/off mode. The third enhancement is a computer vision system for identifying underwater objects of interest that is applied for automated steering of the vehicle. Initial tests with these elements in a laboratory tank are presented and discussed. They include (1) autonomous detection of a target and maneuvering towards it, (2) grabbing and moving an object with manual remote control, and (3) the combined test with autonomous identification, grabbing, and moving of a target. The reported developments and test results can help other researchers pursuing low-cost developments of underwater vehicles. 

Practically all marine vessels have fixed-geometry hulls. This limits their capabilities and high-performance regimes to a limited set of operational conditions. Having a transformable or adaptive hull structure can help maximize ship’s operational performance for various scenarios. In this work, a transformable concept boat is conceived that can change its configuration from monohull to twin-hulled configuration. A catamaran is desirable for carrying volumetric cargo or creating a large deck space that can serve, for example, as a launch pad for aircraft, while more compact monohulls can be more easily stored or operated in restricted environments. A monohull and a catamaran also have different stability, hydrodynamic, maneuvering and seakeeping characteristics. In the present effort, a small-scale model boat has been constructed with two hulls that can be brought together or separated using an expansion mechanism driven by a servo motor. This model setup has been equipped with propulsors, batteries, and control and communication modules for radio-controlled operations. In addition, a remote data acquisition system was assembled for measuring boat’s kinematic and powering characteristics. Results of initial tests with the small-scale transformable boat in an open water reservoir are reported and discussed in this paper. 

An effective method to reduce ship drag is to supply air under specially profiled bottom with the purpose to decrease wetted surface area of the hull and thus its water resistance. Although such systems have been installed on some vessels, the broad implementation of this technique has not yet occurred. A major problem is how to sustain air lubrication in rough water. Modeling of air-ventilated flows is challenging, but modern computational fluid dynamics tools can provide valuable insight. In this study, a wide-beam, shallow-draft hull with a bottom air cavity is considered. This hull imitates a semi-planing boat that can be used for fast transportation of cargo from large marine vessels to shallow shores. To simulate fluid flow around this hull in calm water and head waves, as well as heave and pitch motions of the boat, CFD software Star-CCM+ has been employed. It is found that the air cavity effectiveness decreases in waves; vertical accelerations exhibit high-frequency oscillations; and heave, pitch and vertical accelerations increase, while time-averaged heave, pitch and added drag show non-monotonic behavior with increasing wave amplitude. The air-cavity hull also demonstrates substantially lower vertical accelerations in waves in comparison with a similar solid hull without bottom recess. Time histories of kinematic parameters and distributions of flow field variables presented in this paper can be insightful for developers of air-cavity hulls. 

Hydrodynamic performance of ships can be greatly improved by the formation of air cavities under ship bottom with the purpose to decrease water friction on the hull surface. The air-cavity ships using this type of drag reduction are usually designed for and typically effective only in a relatively narrow range of speeds and hull attitudes and sufficient rates of air supply to the cavity. To investigate the behavior of a small-scale air-cavity boat operating under both favorable and detrimental loading and speed conditions, a remotely controlled model hull was equipped with a data acquisition system, video camera and onboard sensors to measure air-cavity characteristics, air supply rate and the boat speed, thrust and trim in operations on open-water reservoirs. These measurements were captured by a data logger and also wirelessly transmitted to a ground station and video monitor. The experimental air-cavity boat was tested in a range of speeds corresponding to length Froude numbers between 0.17 and 0.5 under three loading conditions, resulting in near zero trim and significant bow-up and bow-down trim angles at rest. Reduced cavity size and significantly increased drag occurred when operating at higher speeds, especially in the bow-up trim condition. The other objective of this study was to determine whether computational fluid dynamics simulations can adequately capture the recorded behavior of the boat and air cavity. A computational software Star-CCM+ was utilized with the VOF method employed for multi-phase flow, RANS approach for turbulence modeling, and economical mesh settings with refinements in the cavity region and near free surface. Upon conducting the mesh verification study, several experimental conditions were simulated, and approximate agreement with measured test data was found. Adaptive mesh refinement and time step controls were also applied to compare results with those obtained on the user-generated mesh. Adaptive controls improved resolution of complex shedding patterns from the air cavity but had little impact on overall results. The presented here experimental approach and obtained results indicate that both outdoor experimentation and computationally inexpensive modeling can be used in the process of developing air-cavity systems for ship hulls.