Microcosmic Mechanism Research On Water Skiing Of Water Strider Robot Based On Molecular Dynamic

Water striders can float and glide efficiently on water surface, attracting moreand more scholars devote themselves into the research on biomimetic water striderrobot. Currently, super-hydrophobic material is commonly used in making outprototype to study the robot’s movement. Insufficiently, these studies simply mimicthe movement of water striders in terms of super-hydrophobicity and stroke, failingto achieve the bionics in respect of the mechanism of sliding movement.Experimental studies prove that high efficiency of strider’s movement on watersurface depends on the unique nano-micro bristles regularly arranged on their legs.Starting with analyzing strider’s movement and material properties, the water skiingof strider is divided into two phases of entry and padding, referring to the NSFCproject “Research on the Water Walking Kinetics of Water Strider Robot”.Microscopic model is established to investigate the microscopic mechanism ofmovement on water surface of super-hydrophobic material on water strider robotthrough simulation. It is theoretically significant in realizing the bionics in robotmoving mechanism and improving the performance of robot moving on watersurface.Firstly, study on simulation method of super-hydrophobic material based onmolecular dynamics. For the problem of molecular dynamics simulation method ofsuper-hydrophobic material, the influence from three initial conditions of time step,equilibrium time and atom number on the simulation results is discussed separatelyto obtain desirable simulation results with both excellent accuracy and efficiencyafter equilibrium process. Criterions for determining each initial condition arepresented. The time step is selected according to contact angle deviation, timemultiplier and the product of them. The equilibrium time is determined by thecriterion of contact angle deviation and range of motion. While the atom number isdependent on the basis of contact angle variance and outline sharpness of waterdroplet. Application and effectiveness of these criterions are demonstrated byspecific simulations on super-hydrophobic material. And the required initialconditions required for adopted super-hydrophobic material is determined.Secondly, study on the microscopic mechanism of entry action of water striderrobot. The essence of leg entry action of water strider robot is super-hydrophobicmaterial coming into touch with water surface with a certain velocity. That is, themicro-mechanism of keeping Cassie state when the driving legs struck the watersurface. The microscopic analysis model is established according to moleculardynamics simulation to imitate the process of water droplet struck super-hydrophobic material surface with a range of speeds. The varying patterns ofinfiltration status, infiltration status transitions, contact angle, centroid of waterdroplet and interaction force between material and water are statistically analyzed.And then the microscopic varying pattern of critical entry velocity of the drive leg isobtained to judge the infiltration status at arbitrary striking velocity.Finally, study on the microscopic mechanism of padding process of waterstrider robot. The essence of leg padding process of water strider robot isinvestigating the microscopic mechanism of relative motion betweensuper-hydrophobic material and water surface. By dividing the padding process intothree actions, the investigation is converted into three microscopic simulationstudies: the microscopic mechanism of material maintaining super-hydrophobicityunder hydrostatic pressure, the microscopic mechanism of critical horizontalpressure of relative motion between super-hydrophobic material and water surfaceand the microscopic mechanism between driving leg and water surface whenmoving in the direction of horizontal pressure. The microscopic analysis model withvertical pressure is built up based on molecular dynamics simulation. The varyingpattern of infiltration status transitions under different vertical pressure isstatistically analyzed to achieve the critical pressure of maintainingsuper-hydrophobicity under hydrostatic pressure. The microscopic analysis modelwith both vertical pressure and horizontal driving pressure is built up based onmolecular dynamics simulation. The movement of water droplet onsuper-hydrophobic material surface under different vertical pressure and horizontaldriving pressure is statically analyzed to obtain the varying pattern of criticaldriving pressure at the beginning of relative motion between material and watersurface. The droplet velocity and viscous resistance under different vertical pressureand horizontal driving pressure are statically analyzed to gain the varying pattern ofvelocity and interaction force with relative motion between driving leg and watersurface.