Intensive study has been carried out in respect of the outstanding swimming skill of some marine animals such as dolphin and tuna in the recent 20 years. Focusing on their prime propulsion device, i.e. their caudal fin, the researchers has preliminarily found out the locomotion of body-caudal fin and hydrodynamic principle [5] [6]. Parameter range has even been worked out to achieve optimum kinematics of caudal fin flipping by conducting modeling, simulation calculation and model experiment in the pool [7][8][9][10]. The results of these researches have facilitated the birth of the Prototype of mission-scale biorobotics autonomous undersea vehicle. Low speed maneuverability, lower noise and high efficiency have become hot issues [11]. Anderson et al. developed the Vorticity Control Unmanned Undersea Vehicle. The 2.4m -long VCUUV follows the morphology and kinematics of a yellow fin tuna and adopt hydraulic-power 4 joints tail drive structure. It attained a speed of

1.2 m/s, and a yaw rate of 75°/s. [12-13]. Nakashima et al. developed a two joints dolphin robot, which is 1.75 m long. The robot attained a propulsive speed of 1.2 m/ s and a propulsive efficiency of 0.35. [14-16]

Yet all of these achievements are not convincing enough to talk the chief designer of autonomous undersea vehicle into adopting bionic propulsion technology in his AUV project in the near future. Tangible proofs need to be put forward to show that biorobotics propulsion has remarkable advantages in some respects. At the same time, other factors also require consideration such as payloads, endurance and stability, so as not to lose too much performance of the vehicle.

Biorobotic autonomous undersea vehicle SPC-III, developed by Robotics institute, BeiHang University, is a prototype of mission-scale autonomous submersible vehicle. According to its displacement tonnage, it can be classed as portable UUV [17]. The purpose is to develop an available biorobotics propulsion device on the basis of the understanding of the mechanism of caudal fin in itinerant state as well as the current mature engineering technology. The said biorobotics propulsion device should not only improve maneuverability and reduce noise of the conventional propulsion UUV but also have acceptable speed, propulsion efficiency or endurance. Researches on SPC series biorobotics unmanned undersea vehicle started from 2001. SPC-I is a prototype used to study what impact navigation stability and yaw may have on tail fin propulsion [18]. SPC-II is a prototype used to study hovering and turning maneuverability. It achieved a yaw rate of 30o/s and a turning diameter about its body length. In 2004 it was applied in an attempt to the mission of Underwater Archaeology in Dongshan Island of Fujian undertaken by the Underwater Archaeological Team of the National Museum of China [19-20]. SPC-III has the same torpedo shape with the conventional UUV. Its two joints caudal fin thruster can be easily replaced with screw propeller. Since the hydrodynamic shape of the two are almost the same, preliminary results of the performance of various propellers has been achieved, which are used to evaluate the feasibility of applying the designed biorobotics unmanned undersea vehicle to probe commission.

The rest parts of this article are arranged as: Part 2 is a detailed description of Biorobotic autonomous undersea vehicle SPC-III, especially the realization of two joints caudal fin thruster; Part 3 presents the comparison result between propulsion power, turning radius as well as rate and screw propeller; Part 4 is a description of the result of the long-distance probe test carrying Water Quality Multiprobes; Part 5 discusses the performance and problems of SPC-III; Part 6 is the conclusion of this paper and the prospect for the future.

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