Research On Key Technologies Of Hydraulic-Driven Bionic Propeller Inspired By Undulating Fins

Underwater bionic propulsion technology has gained much attention around the world, especially the bionic undulating propulsion in MPF(Median and/or Pair Fin) mode with special structure and outstanding propelling characteristics. However, as is restricted by the development of undulation mechanism and engineering technology, most of the bionic undulating propellers (BUPs) are designed and implemented with rigid transmission chain. Such a rigid chain is consisted of rotational motors and motion-changing frameworks, which make the general propulsion performance far away from that expected, say nothing of comparing to the swimming ability of nature fish. Obviously, research on BUP with flexible structure and propelling character is of significance in near future practical applications.This work is supported by the Basic Science Foundation of National Defense. After a detailed consult on the conventional BUPs. and considering about the special structure and unique acting rules of hydraulic transmission, a newly-designed BUP driven by Valve-Pump controlled hydraulic system (HBUP) is presented with a novel structure and flexible power driven-chain in this dissertation. Then some research has been carried out on the mechanism and structure design, kinematics and dynamics, together with hydrodynamic characters. The main work can be summarized as follows:1. A novel scheme of BUP's hydraulic driven structure and driven-chain is proposed in this dissertation, and the hydraulic driven system in HBUP is designed, including the structures of the rotational direction valve, hydraulic swinging unit, and the HBUP's comprehensive structure. The peculiarity of fluid transmission makes each hydraulic swinging unit swings independently, so that rigid transmission shafts are no longer necessary. The HBUP's structure could fit underwater robots" shape and produce bionic undulation with a changeable amplitude on the structure during starting and stopping processes. Meanwhile, the HBUP system could carry complex fluid load passively and keep the whole structure with a best load capacity. While the hydraulic system doesn't work, the bionic undulating fin will recover to the original balance state automatically, so as to reduce the fluid resistance during cruising.2. The uniform flux equation of the rotational direction valve's ports and transfer function of the hydraulic swinging unit are presented and developed. Within these equations, the acting rules and characters of the hydraulic system in HUBT are studied. Referring to the analyzing method of common hydraulic direction valve, this uniform equation of the rotational direction valve's ports is built up to analyze the flux between different ports Then effects of hydrodynamic force and torque caused by the shaft rotation is also considered. The hydraulic swinging unit system performance, in terms of stability, balance and position holding ability, are respectively studied with the established transfer function, according to the analyzing means of valve-controlled symmetrical cylinder. Simulations of the hydraulic system model show that it could drive the HBUP consisted of several hydraulic swinging units to produce a bionic motion from a flat shape to an undulating shape and vice versa.3. The ruled-surface kinematics model of the HUBP is brought forward, so is the multi-rigid-body dynamic model. Then the extensibility of the niled-surface, and effects of structure parameters to bionic undulating fins are theoretically analyzed. The Lagrange equation is introduced to build multi-rigid-body dynamic model of swinging poles in HBUP. and then a prototype model of the multi-rigid-body system in HBUP is developed as well. With these models, effects of different spring rigidities, different damp coefficients and different hydraulic forces on the multi-rigid-body system are explored, one by one. The results reveal that the restoration springs are of importance since the balance position of the HBUP is ensured stable, and the swinging poles could be driven into undulation effectively and rapidly. The bionic undulation in starting and stopping processes exhibits flexibility and auto-stability characters.4. The computational hydrodynamic model of the HBUP is proposed and developed. In detail, the ruled-surface kinematics equation is used to design the changing mle of the dynamic mesh in computational fluid dynamics (CFD) method, which is used to compute the hydrodynamic force and torque, as well as the fluid pressure distributing characters. The results show that the hydrodynamic force and torque change periodically in evidence, and some of them present doubled-frequency character. The doubled-frequency character can be summarized as follows: the changing frequencies of the propelling force, lifting force and pitching torque are twice of the bionic undulation frequency respecitvely. the values of yawing force, rolling torque and yawing torque are nearly zero in average. At last, the load adaptability of the HBUP is proposed, and hereafter, the reasons and effects are studied as well.5. The testbed of HBUP is constructed, and some function-verifying experiments are carried out as well as propelling tests. With the testbed, the flux-distributing function of the rotational direction valve is verifid, and the swinging character of hydraulic swinging unit is also tested and compared, with spring and no spring structure, under different hydraulic system parameters. Then the flexible starting character and load adaptability are verified. The propelling tests of the HUBT are also brought out under different hydraulic system parameters. The results show that bionic fin of HBUP could form a valid undulation shape to produce propelling force, so as to make the prototype moving, its propelling force and direction could be easily controlled by adjusting the rotation velocity and direction of the shaft in the rotational direction valve. The experiments have verified the conclusions and meet the expected objectives.