| Hydraulic transmission is a kind of fluid transmission which is the core transmission form of walking machinery and high energy ratio industrial machinery.Its effects extending all over industries,especially the field of national security.In the next 20 years,the goal of the development of hydraulic transmission is "green,compact,efficient,intelligent,and long life",which is also the main problem faced by the hydraulic transmission currently.In nature,there are hydraulic systems in spiders.They achieve efficient driving with low internal pressure,and demonstrate the advantages of no pollution,compact structure,high efficiency and power quality ratio,coordinated motion control,stability and reliability.Spiders have achieved extraordinary biological functions by hydraulic transmission,natural long term evolution has contributed to its efficient hydraulic transmission components and integrated systems.Through the study on the operating mechanism and energy transfer process of the hydraulic system of biological high performance,it can inspire us to find the new driving mode and new energy conversion devices,providing a new reference for the development of the hydraulic system.Under the support of the National Natural Science Fund(51675219),this paper takes large predator spider as the research object,from the study of the internal characteristics of the spider's leg,The driving mechanism and the energy transfer process were investigated based on the CFD calculation results of internal flow and the fluid-solid coupling characteristics between hemolymph and exoskeleton.The main research work and the related conclusions are as follows:1.The 3D model of the outer contour of spider and the establishment of the internal fluid transmission channel in the legA portable 3D laser scanner was used to scan the sample surface,and the 3D reconstruction of the whole outline of the spider appearance was finished through smoothing,modifying and post-processing.In view of the fact that the internal transmission channel of spider leg is coupled with exoskeleton,muscle,blood vessel and nerve cells,the structure is very complicated.A variety of experimental methods were tried: The tissue section experiment showed that the tibia segment was almost full of muscles;the micromorphology of the muscles in different parts had a large difference.Scanning electron microscopy(SEM)confirmed the results of tissue slices.The MicroCT experiment showed that the end of the Metatarsus segment was closed.Based on the manual construction method of using UG software combined with micro-CT images,the geometric model of the distal hydraulic joint and the 3D model of the internal flow path of the spider leg were finally completed,which provided a solution model for the subsequent simulation.2.CFD numerical simulation of the internal flow of a spider's legFor CFD numerical simulation of the inner flow field of the leg which has only import,two types of boundary conditions are set up during the calculation process: one is the pressure inlet boundary condition,the other is the control inlet velocity boundary condition.By comparing the mass flow rate with the theoretical value under the two boundary conditions,it is determined that the calculated results under the condition of velocity inlet boundary are more reasonable.3.Test of the biomechanical properties of a spider's legBecause there are many factors affecting the mechanical properties of the leg shell,here we chose the outer layer of the spider's leg shell after drying to carry out nanoindentation measurement.The test parameters were set as follows: the Poisson ratio of the sample was 0.25,the strain rate was 0.1 s^-1,the pressed depth was 2000 nm,the holding time was 20 s,and the thermal drift rate was 0.1nm/s.The average elastic modulus and hardness of the outer shell of the metatarsus and tibia segments were obtained through the data processing of five test points in different parts of the sample: The average elastic modulus of the outer shell of metatarsus segment is E=4.154 GPa,and the tibia segment is E=5.187 GPa,and parameters of the material mechanical properties needed for the nexr fluid-solid interaction calculation are obtained.4.The unidirectional fluid-solid coupling calculation between haemolymph and outer shell of a spider's legThe unidirectional fluid-solid coupling calculation between the inner fluid and the shell is carried out by using ANSYS Workbench.The connection between the tibia and metatarsus segments of the spider leg is an elastic folding membrane.In order to accurately simulate the effect of the fluid-solid coupling,the model of the leg shell is divided into three parts.The rigid outer shell of both sides is simplified as homogeneous isotropic material,and the density is approximated by the density of the crust of the arthropod;the mechanical parameters of the elastic vessel wall is selected as an approximation of the performance parameters of the elastic film in the middle part.5.Study and analysis of the hydraulic driving mechanism of a spider's legIn this paper,CFD numerical simulation and fluid-solid coupling calculation of spider's leg are analyzed in detail.Based on the flow field characteristics and the fluidsolid coupling characteristics,the driving mechanism is described as follows: the flow field nephogram shows that the velocity of fluid at the end of metatarsus segment is close to zero,and the pressure is negative pressure,the pressure difference between the metatarsus terminal and the inlet makes the fluid flow smoothly to the end.However,due to the end closure,the increase of fluid starts to cause expansion.The mechanical properties of the structural materials are different,making the junction of the middle thin film expand obviously,which is just like the result of the fluid-solid coupling deformation,and the expansion continues to increase,triggering the rotation of the joint to realize the movement of the leg.According to the trajectory of hemolymph in the flow channel obtained from the processing data of CFD calculation,a set of bionic hydraulic system is designed in this paper.The hydraulic circuit proposed in this paper is not only consistent with the existing literature,but also is further developed and closer to the hydraulic system in the sense of engineering,thus providing a new way of thinking for the design and performance improvement of the hydraulic system. |
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