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ObjectiveAir-independent propulsion (AIP) submarines carry huge quantities of liquid oxygen. However, in the liquid oxygen combustion process, the cold energy is not usually recovered, and there are criticisms concerning CO2 removal in the confined space of a submarine. Aiming at the two major pain points that have long plagued AIP submarines, this paper proposes an integrated solution that organically combines the recovery and utilization of cold energy from liquid oxygen with the removal of CO2 . Method Liquid oxygen can be used as a cold energy source to process the cabin air. According to the different phase transition temperature characteristics of each air component, the CO2 in the air is frozen (condensed) and separated under normal pressure. ResultsThis study uses quantitative data analysis to show that the energy stored in liquid oxygen can basically meet the cold energy demand for freezing the CO2 produced by the crew's respiratory metabolism within the self-sustaining capacity of the submarine, and proposes a three-level workflow and implementation plan. ConclusionThe technical solution proposed in this paper can recycle 5% of cold energy from liquid oxygen, which conforms to the idea of the comprehensive integration of energy saving and noise reduction, and the full integration of overall resources. As such, it can be used for air purification and CO2 removal in confined spaces such as submarines, submersibles and deep-sea space stations powered by AIP systems.

ObjectivesThis paper investigates the influence of the span-wise stiffness of a flapping pectoral fin on its generated thrust. MethodsA scheme to fabricate a flexible pectoral fin with uniform span-wise stiffness is introduced. A series of experiments is then conducted to investigate the generated thrust and lateral force of the fabricated pectoral fin with different degrees of span-wise stiffness in the frequency range of 0.3−1.0 Hz. Combined with collected shots by a high speed camera, the impact of span-wise stiffness on generated force is analyzed. Results The experimental results show that the average propulsion force and the average lateral force generated by the flexible bionic pectoral fins are related to the size and distribution of the radial stiffness of the fin in the range of the tested flap frequency. By optimizing the spreadal stiffness of the flexible bionic pectoral fin of the robotic fish prototype (XJmanta), the maximum swimming speed can be increased by about 45%.ConclusionsThe results of this study can be used to guide the design of flapping flexible bionic pectoral fins and optimize the hydrodynamic performance of ray-like underwater robots.

ObjectivesOver millions of years of natural selection, fish have evolved various types of swimming modes with various advantages in efficiency, motility and tranquility, making them ideal biological objects on which autonomous underwater vehicles (AUVs) can be modelled. In order to develop a brand new AUV with lower noise and higher mobility, this paper puts forward a design for a myliobatid-inspired robot actuated by pairs of flexible pectoral fins.MethodsThe manufacturing process and actuating method of the prototype are illustrated in detail. In order to test the maximum speed and mobility of the prototype, a series of swimming tests is carried out.ResultsThe experimental results show that the prototype can complete a variety of maneuvers in water, including rolling, small radius steering and hovering, and its maximum swimming speed can reach 1.9 body lengths per second (about 0.73 m/s).ConclusionsThis paper outlines the preliminary design and swimming test of a myliobatid-inspired robot, giving it reference value as an indicator for the next generation of AUVs.