| Soft off-road is the carrier of agricultural vehicles.And its roughness has a close relationship with vehicle vibration.The study of the distribution characteristics of the surface morphology and its relationship with the method of farming are of great significance to the cultivation and management of the fieldit has important significance to reveal the effect of Soil texture on vibration and law through the research on the vibration transfer law in vibration system of the soft off-soil-vehicle,and the theoretical basisis provided which to reduce the vibration fatigue loss of the agricultural machinery parts,and to increase the traffic ability of agricultural machinery.Whether the soft off-soil can be used as the input stimulus of the vehicle or others?What is the relationship among the primordial roughness,effective roughness,rut roughness?In order to answer the above questions and to verify the effect of soil,tire and vehicle load on the vibration,abundant researches have been done and summarized as follows:1.The soil which on the experiment was the silt clay.The measured soil density was 1.22g/cm3 and the moisture content was 22.35%.The stress-strain test instrument was designed.According to the computed result we can know that the elasticity modulus is not the same in different process of soil compaction.The compacted stiffness of the soft off-road soil was 3.613×104?7.534×104N and of tight-road soil was 7.080×105?16.520×105 N.The restoring stiffness of the soil is about 20 times the compacted stiffness.2.A static of the roughness of soil surface was designed and manufactured-the instrument of the flat needle and rod,which ensures that the soil surface will not be influenced by the vehicle's vibration.The different soil morphology of the plough,the rotary and the harrow was measured by the instrument.The amplitude-frequency characteristics of soil primordial roughness in several kinds of farming methods were Statistical analyzed.In spatial frequency,the results show that the plough curve peaks concentrated in the 0.049?0.098m-1,the rotary curve peaks concentrated in the 0.293?0.882 m-1,the harrow curve peaks concentrated in the 0.342?0.587 m-1.From that:the biggest amplitude of the plough curve has the maximum interval span and longest wavelength.With the opposite result,the biggest amplitude of the harrow and the rotary curve has the smaller interval span and shorter wavelength.3.The 3d reconstruction model is established.The Statistical analysis of the fractal characteristics of the soil primordial roughness in several kinds of farming methods.The result showed that the surface morphology of the plough,the rotary and the harrow were significant fractal characteristics and the non-scale range is between 5?59cm.The mean value of the fractal dimension of the plough surface was 1.8322.The mean value of the fractal dimension of the rotary surface was 1.7783.The mean value of the fractal dimension of the harrow surface was 1.7968.And according to the calculated result,the fractal dimension of the plough curve was the biggest and followed by the harrow curve and the rotary curve has the smallest fractal dimension.The value of fractal dimension shows the spacevariation of the soil morphology curve.The fractal dimension of the plough is the largest,the surface morphology is the most complex,the concave and convex is the most obvious.Testing data had been detected for its measuring scale by utilizing fractal characteristics of cultivated soil,showing that scale had no effect on fractal dimension but affected the intercept of fractal curve in dual-logarithm coordinates.Then,surface morphology reconstruction was done on both two and three dimensions based on the theory mentioned above.4.Using single degree of freedom modal theory,physical and modal parameters of soil and tire were measured and computed through hammer test.The soft off-road's equivalent mass was 7.16 kg in the area of a wheel,its compacted stiffness was 4.650×104 N,and its damping coefficient was 16.08 and inherent frequency was 85.84Hz.The hard road's equivalent mass was 54.91 kg,its restored stiffness was 1.077×106N,and its damping coefficient was 2107.40 and inherent frequency was 140.07Hz.Tire has a mass around 25 kg,and its stiffness was 1.450×108N,damping was 722.61 and inherent frequency was 2408.07Hz.5.Using analysis theory of A simplified two-degrees model of vibration,the result was The natural frequencies of the forced vibrations of the tight soil-vehicle system are 116.06 Hz and 2907.10 Hz respectively.By hammering the test,the high order natural frequency is the dominant frequency of the system.Using model theory to analysis the off-road and vehicle system,the natural frequency of forced vibration system were 4.30Hz and 4505.60Hz respectively under the 2500kg of gravity load.According to the analysis of the tight soil-vehicle system,the natural frequency of forced vibration system were 20.46Hz and 1649.10Hz respectively.The vehicle's vibration frequency of the acceleration response signal was in the range of 2.58?55.64 Hz.Under the test which means the low order natural frequency was the main frequency of the vehicle vibration system.The theory analysis shows that the biggest amplitude of the tight soil-vehicle forced vibration was equal to the recovery variable of the tight soil,the sinking variable was equal to the value of compacted variable minus restored variable,also was equal to the value of the amplitude of primitive roughness minus the amplitude of Rut roughness,all leading to the soil track roughness model.Based on the construction of the frequency and amplitude of forced vibration,the model of the soil effective roughness was established.it shows on test that:the frequency in the vibration equation of the effective roughness was decided by the physical and modal parameters of the soft off-road soil in the process of vibration compaction.The amplitude was decided by the physical parameters of the tight road in the process of vibration recovery. |
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