Rigid-Flexible Coupling Fatigue Life Reliability Study on Bonic Fish Driving Shaft

12 Due to the complex loads on a bionic robotic fish operating underwater, the reliability of its working mechanism has an important effect on its 13 overall performance. By establishing a virtual prototype model for the rigid – flexible coupling of a bionic robotic fish, we obtained the instan- 14 taneous load on the caudal fin of the robotic fish based on the flapping-wing propulsion theory with MATLAB. A rigid – flexible coupled virtual 15 prototype model for the caudal fin drive as a flexible member of the bionic robotic fish was established, and dynamic simulations were con- 16 ducted on the model. The simulations revealed the weak links in the drive shaft and established a damage level indicator and fatigue reliability 17 analysis method based on damage theory. The behavior of fatigue reliability for different stress cycles was established, and a dynamic reliability 18 design method with great engineering application value was proposed for virtual prototypes of rigid – flexible coupled underwater bionic robots 19 by combining the virtual prototype technology of rigid – flexible coupling with the theory of flapping wing propulsion and the theory of random 20 load fatigue reliability. proposed a design method for the dynamic reliability of rigid – flexible coupled virtual prototypes for bionic robots in underwater applications. This research provides definitive data support and new methods for the design and development of underwater bionic robots and possesses significant engineering application value.


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Bionic robotic fish play an important role in marine development and scientific investigation. Bionic killer whales feature 25 the characteristics of nimble movement flexibility, high transmission efficiency, and low noise. [1] The propulsion mechanism of 26 the bionic killer whale-that is, the tail fin-consists of components that are susceptible to failure due to complex and variable 27 impact loads. A recent study on the virtual prototyping of bionic robotic fish includes the design of the tail fin propulsion 28 mechanism with two degrees of freedom and the mechanical structure of the pectoral fin with a single degree of freedom based on 29 the bionic study of the swimming mechanism of Caranjidae model fish conducted by Zhu. [2] This study also presents the hy-30 drodynamic analysis of tail and pectoral fin propulsion. [2] Using virtual prototype technology, Fan [3] conducted dynamic per-31 formance analysis of a multijointed robotic fish driven by a synchronous belt tandem epicyclic gear and obtained dynamic data of 32 the torque and power of the drive shaft. These data served as important references in the model selection, mechanical structural 33 optimization, and motion control of the mechanical fish. Lin [4] built a virtual prototype model for the swing mechanism of a 34 three-node robotic crocodile tail with ADAMS and analyzed the relationship curves between the displacement, speed, and time 35 for each section of the tail as well as the relationship curves between the driving speed and the speed of each section of the tail.

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Zhang [5] used ADAMS to conduct a dynamic simulation analysis of Caranjidae robotic fish. By driving the robotic fish in dif-37 ferent modes with tandem rudders, Zhang obtained the bulk wave amplitude envelope curves of the robotic fish in each swim 38 mode and identified the most practical drive mode of the robotic fish.

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While operating underwater, the bionic robotic fish experiences nonlinear, time-varying, and strongly coupled loads. The  The power source of the bionic killer whale is the propulsion generated by the flapping of wings. Before modeling the 48 instantaneous load, one needs to analyze the forces and establish a mathematical model for the propulsion force. The tail fin of the 49 bionic killer whale may be defined as a flapping wing with a single degree of freedom. [6][7][8] Figure 1 shows the analysis of the 50 forces of the flapping wing.  Figure 1 shows a flapping wing movement mechanism, and Figure 2 shows the angle  of the vibration, calculated as where t  is the offset, A is the amplitude of the flapping wing,  is the frequency, and i  is the phase angle.
where yt  is the density of the liquid, wq A is the projected area of the flapping wing on the XOY coordinate plane, C sl is 61 the lift coefficient, and R e is the Reynolds number.

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The additional mass force fj F can be calculated as follows: where c and b are the chord length and the extension of the flapping wing, respectively. In Figure 1, the total thrust zs F 65 generated by the flapping wing is the sum of the lift force sl F and the additional mass force fj F .

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The direction of the resistive force zl where zl C is the drag coefficient.         The results in Figures 9-13 show that the force experienced by the drive mechanism of the tail fin of the bionic killer whale [ , ]    , as shown in Figure 15.