Jianan Xu

Analysis and experiment research of the turtle forelimb's hydrofoil propulsion method

Based on agility, stationarity, low-noise, and special methods of pose control about sea turtle swimming, the bionic turtle forelimbs hydrofoil propulsion principle was researched. Taking a ripe green-turtle as the biological prototype, utilizing the real-time monitor experiment platform of turtle movement, its skeleton configuration characters were analyzed, the hydrofoil motion parameters were extracted, and the forelimbs hydrofoil propulsion principle was researched from the point of dynamic and static state respectively. Secondly, established the two DOF motion model of turtle hydrofoil, analyzed its kinematics and dynamics characteristics, and confirmed that the model physical parameters and movement parameters as the influential factors for the bio-mechanism motion. Finally, in point of function bionics, the hydrofoil motion bio-mechanism was designed. By using of not only the performance test experiments of azimuth spin and stroke spin, but also the mechanism loading experiments under multimode, the control elements of bio-mechanism motion control was obtained. At the same time, the reliability and rationality of the design was validated by the experiments, enriching the underwater propulsion theories.

Fluid dynamics analysis of passive oscillating hydrofoils for tidal current energy extracting

A passive oscillating hydrofoil energy extracting technology that imitates the tail swinging of aquatic organisms to extract energy from flow field is presented in this paper, as an alternative to conventional rotating blades turbine. On the basis of analysis of the relationship between the movement characteristics of oscillating hydrofoil and the parameters including power coefficient, efficiency and reduced frequency, the device based on passive oscillating hydrofoil to extract tidal current energy is designed. The investigation is undertaken over a wide range of kinematic parameters including pitching amplitudes, heaving amplitudes and reduced frequency. The results reveal that the power extracted from the oncoming flow mainly comes from the heaving motion and the energy contribution from pitching motion is quite limited. Detailed examination of the motion parameters indicates that when the heaving amplitude reaches one chord length, the pitching amplitude reaches 70° and the reduced frequency reaches 0.11, the highest power extraction efficiency can reach 34.7%.

Bionic hydrofoil propulsion experiments research

In order to discuss hydrofoil propulsion method, the experimental research of bionic turtle hydrofoil propulsion was carried out. Based on the analysis of living prototype motion principle, the bionic hydrofoil propulsion experimental sample was developed including bio-hydrofoil motion machine, bio-palmiped motion machine and centralized control module. Then, the direct navigation and yawing performance test experiments of bionic sample in the pool were taken out, validating the influence that change of motion parameters effects on the longitudinal component force and plane yawing torque of bionic sample. The experiments results indicated that, the angular velocity of hydrofoil stroke spin ω1 had a descending acceleration direct proportion to the direct navigation speed and yawing velocity of sample; the double hydrofoils contrary phase differential yawing had merely increased the motion efficiency about 60% rather than mono-limb yawing because of the much more vortex resistance; following the augment of ω1, the propulsion efficiency of right hydrofoil had a from high to low decline trend comparing to the left. These experimental researches had provided significant references to the study on control strategies for the sample.

Analysis of bionic hydrofoil propulsive performance

Combined with the motion characteristics of turtles, a 2 degree-of-freedom periodic moving method is proposed for the single hydrofoil model of a hydrofoil propelled prototype. According to the hydrofoil hydrodynamic calculation formula, factors and motion parameters that affect thrust force produced by the hydrofoil are concluded. Changes of factors related in different profiles of stroke spin angular velocity are analyzed. Effects of different profiles of stroke spin angular velocity to the hydrofoil propulsive performance are predicted. Taking the average thrust force produced by the hydrofoil in periodic motion as the yardstick of the hydrofoil propulsive performance, three kinds of profiles of stroke spin angular velocity are adopted in calculation respectively, relationships between the average thrust force and the azimuth spin amplitude as well as the angular frequency are obtained. Taking the physical parameter limitations of the hydrofoil model into consideration, the optimal comprehensive propulsive properties of the hydrofoil is achieved using the trigonometric function profile stroke spin angular velocity with the same motion parameters.