Prediction And Reconstruction Of Soil Surface Effective Roughness Under The Interaction Of Soil And Wheel

Effective roughness is the displacement excitation of the wheel in the form of a certain roughness when the wheel interacts with the soft road surface.The acquisition of effective roughness is the precondition for the research of vehicle vibration.Study and analysis of the mechanism of effective roughness is of great significance for the vehicle ride comfort.In order to acquire effective roughness,numerical analysis method and DEM modeling&simulation are used in this thesis.Based on original roughness data,the effective roughness curves of the soil were derived and calculated respectively when the wheels interacted with the soil.The curves were interpolated by using iterated function and improved random midpoint displacement fractal interpolation method respectively after tested and verified.Finally,detailed and effective roughness data are obtained.The major research work and results are summarized as following:1.Roughness laser tester was developed from aspects of overall design,hardware design and software design.Developed roughness tester mainly included motor&drive system and roughness data acquisition system,the tester has been tested and verified,who meet the overall design requirements well,could test data accurately.The correlation between the measured object shape and the standard shape was greater than 0.994 and precise.2.Based on original roughness data,rutting roughness data,wheel vertical displacement,tire stiffness and pavement stiffness,the dynamic analysis of the enveloping effect between tire and soil was carried out from the aspects of static load and dynamic load,and the effective roughness curves of soil surface under static load and dynamic load were derived by numerical method.Through comparative analysis,the effective roughness data obtained by static load analysis was smaller than the original roughness value,and the curve was smoother and gentle,indicating that the high-frequency part of the original roughness has been filtered when the tire interacts with the road surface.The basic shape of the effective roughness curve obtained by dynamic load analysis was similar to the effective roughness obtained by static load,but the dynamic effective roughness curve is much sharper.3.The relative theories of contact modeling were analyzed,including linear complementarity problem,static and dynamic friction model,set-valued mapping theory of mechanical model,nonsmooth generalized-α method for solving nonsmooth multibody dynamic equation.In order to measure the shear deformation modulus of soil,triaxial experiment was used to test the internal friction angle and internal cohesion of soil.Based on the theory of modeling,absolute node coordinates(ANCF)and the reference node(ANCF-RN)method were used to establish a wheel model,discrete element method was adopted to establish the model of soil surface,and then a model of dynamic equation was built,which nonsmooth generalized-α and Verlet method was used to solve the equation.The matlab software was used to solve the program,and a steel ball numerical example was demonstrated its the validity;The motion parameters of wheels and each soil particle were derived by using the solver program,and then the effective roughness curve was obtained.The relationship between the curve and the wheel’s velocity and load was analyzed,and the following conclusions included:(1)The model was verified by using the example of the free-falling rigid sphere.It was observed that when the rigid sphere collided with the ground,the nearby ground particles would be crushed to form a depression,and the bounce-back would occur and the ground particles would keep in contact with each other.The simulation results were reasonable.(2)The hub reference node of the wheel moved in free fall firstly,and then oscillated up and down in Y direction.When the elastic runout was weakened,the track of the wheel rolled smoothly,indicating that the simulation process was reasonable.(3)After the wheel rolls stably,the effective roughness value decreased with the increase of load,but the effective roughness difference under different loads was very small(only about 10-6m).(4)The higher the torque was,the higher the wheel speed was,and the more obvious the fluctuation of effective roughness was.(5)After the introduction of the original roughness curve,the uneven soil surface caused the wheel to jump correspondingly.that was,the motion trajectory of the hub center was consistent with the trend of the original roughness curve,which was more consistent with the reality,indicating that the introduction of the roughness data in the wheel-soil coupling simulation analysis would make the simulation results more accurate.4.Based on the soil bin testing platform,a project of the coupling between the wheel and soil was designed.Considering the speed of the car,tire pressure and load,a total of 27 kinds of state.The original roughness,rut roughness,effective roughness were tested,calculated and analyzed,and the relationship between the soil subsidence quantity and effective roughness and the three factors.The following conclusions included:(1)When the velocity increased,the subsidence decreases.With the increase of load,the soil subsidence increases,and the impact of tire pressure on the subsidence was small.(2)For low-speed agricultural vehicles,the relationship between wheel runout and speed was not obvious,and the change of load within a certain range has little impact on wheel runout.For soft soil,tire pressure has little effect on wheel runout.(3)For the same original roughness,the same speed range and the same load,the effective roughness curve tested basically coincides with the effective roughness obtained by the two methods,indicating that the effective roughness acquisition method is correct and effective.5.A 3D fractal interpolation system based on the iterative function method and the improved random midpoint displacement method was developed,both of which can accurately reconstruct the soil surface.After interpolation,the statistical characteristics of the two systems remain within±5%before interpolation.The former has more interpolation points but lower efficiency.The latter generates far fewer data points than the iterative function method,and the reconstruction efficiency was good.Two algorithms were used to reconstruct the effective roughness obtained by the two methods,and more detailed effective roughness data was obtained.