| Ground machinery, regardless of ship machinery and military vehicles walking in the ground, farm machinery and the carry-scraper weapon taking the surface and the soil as the work object, the drag reduction of the soil-engaging components has been the important technical question which the domestic and foreign many scholars devote to study. Especially the adhesion and resistance of the soil (dry farmland, paddy field), the shallow seas and tidelands, the wetland, the bog, the snowy area, the desert and so on to the wheel, the caterpillar band and the work part surface's, badly influence machinery's working efficiency, the service life and the work quality, increase the energy consumption, even causes the machinery to be unable the normal operation, the work.In the biosphere, many species, especially the soil animal, has developed excellent anti-adhesion ability in the long-term evolution. The earthworm is one kind of typical soil-burrowing animals, can move in soil without soil sticking to their bodies, especially in clay. The principles of the earthworm in soil scouring mainly comprise of the effects of geometrical morphologies and shapes, chemical composition of body surfaces, liquid secretion and bioelectricity, and so on.Supported by the Specialized Research Fund for the Doctoral Program of Higher Education (No. 20050183015) and the National Natural Science Foundation of China (No.50635030), this paper mainly studies the adhesion and resistance reduction of the earthworm surface based on the biological surface structure, biological lubrication and coupling bionic theory. It may have great practical importance and broad application prospects on the anti-adhesion of the ground machinery.Eisenia foetida was used as research object, according to the movement of the earthworm, three kinds of body surface specimens were prepared, such as stretch, motionlessness and contraction. The earthworm surface feature was analyzed by using the stereo microscope and its image analysis, and then the characteristic parameters of the surface non-smooth units were extracted. Its body surface wettability was analyzed through surveying the surface angle of contact by using the angle of contact measuring instrument. It may know by analysis that the earthworm body surface appearance belongs to the typical wavy non-smooth structure: The link structure which is composed of the arthromere and the fossa between the arthromeres forms the first-level macroscopic wavy non-smooth structure, and the massive staggered lines which are distributing on the skin surface form the second-level microscopic wavy non-smooth structure. The earthworm non-smooth degree of different spot is various. The body texture is small and dense, and the non-smooth unit density is big. The forehead texture is big and thin, and the non-smooth unit density is small. The surface appearance of different condition is roughly similar, but the characteristic parameters of the non-smooth units are different. The ratio of the width and height of the non-smooth construction unit about the forehead motionless, extending and shrinking specimens were 1.65:1:0.78 and 0.23:1:1.27 respectively, while those of the body surface specimens were 1.65:1:0.81 and 0.33:1:1.28 respectively. And the density of the earthworms'non-smooth unit reduces when it is stretching, it increases when it is contracting, and it comes between when it is motionless.The earthworm body surface displays the water affinity characteristic, the static contact angle of different condition is various, which presents the following rule: contraction > motionlessness > stretch; And the contact angles of the contraction or motionlessness are approximately equal in the various spots, but the contact angle of the stretch actually has the extremely remarkable difference in the forehead and body's department.In accordance with the earthworm samples, after dehydration to exclude the interference of surface liquid, the soil adhesion test samples were prepared. Using the testing system for tiny soil adhesion based on biologic signal, the soil adhesion properties experiment of earthworm's surface specimens was conducted, direct data of the earthworm surface adhesion characteristics were obtained, and the soil adhesion behavior of earthworms'surface in different soil conditions was explored. The test results showed that the earthworm surface had the characteristic of adhesion and resistance reduction, the adhesion and resistance reduction effect of the earthworm specimen from large to small in turn was: the contraction, motionlessness, stretch. The forehead reduced the adhesion force and resistance more obvious than the body. Under the experimental conditions, compared with the steel specimen, the head contraction reduces adhesion force and resistance 75 percent and 39 percent respectively.The normal adhesion force of the earthworm body surface specimen increased with a parabola tendency along with the increase of soil moisture content, and when the soil moisture content is smaller, the adhesion reduction of the earthworm specimen is more pronounced. The sliding resistance of the earthworm body surface specimen also increased the parabola tendency along with the increase of soil moisture content, but along with water content increase, the resistance reduction reduced first, and then increased.Through orthogonal multinomial experiment, the influence of positive pressure(Z1) and unloading speed(Z2) to normal adhesion force of earthworm's non-smooth surface was explored, and regression equation was established, which is . By the same way, the influence of positive pressure(Zy? 0 =0.0143Z1?0.0000198Z12+0.242Z2?0.506(kPa)1) and sliding speed(Z2) to sliding resistance of earthworm's non-smooth surface was explored, and regression equation was established, which is . From theregressions, it is known that the positive pressure and unloading speed has the remarkable influence to the earthworm body surface's adhesion, but the positive pressure assumes two effects, the unloading speed assumes one effect, and there is no correlation between them. The positive pressure and sliding speed has the remarkable influence to the earthworm body surface's resistance, but the positive pressure assumes two effects, the sliding speed assumes one effect, and there is correlation between them. y? 0 =0.0193Z1?0.0000288Z12?0.248Z2+0.0037Z1Z2+1.391(kPa)Through experiment, the direct data about the soil adhesion characteristic of the earthworm expanding specimen were obtained for the first time. For further examining the anti-adhesion mechanism of earthworm body surface, applying discrete element method, the soil resistance, contacting force field and contacting particle number of the smooth specimen and four kinds of different forms of wavy surface specimens were compared. And then selecting a wavy surface with better resistance reduction, the speed, power, trajectory of the soil particles contacted with it were microcosmic analyzed. From the simulation, it is known that the sliding resistance of the wavy surface is composed of two parts. One is the friction force between the soil particle and the ripple surface. Another is the backward thrust force about the soil particle to the ripple. And that of the smooth surface is only the pellet friction force. Only when the sum of the friction force and the thrust force of the wavy surface is smaller than the friction force of the smooth one, it will reduce the resistance. If the backward thrust force is oversized, it can increase the resistance.When specimen advancing, the soil flowing destroys mainly occurs in the contact part and the front and rear part of the specimen. The destroys in the concave and convex are especially obvious when the wavy surface advancing, the turbulent region and the tendency all increase along with increase of the wave ridge. This mean the turbulent of the wavy surface is bigger than that of the smooth one, and the wavy surface can scour and loose soil while the resistance reduces.The sliding resistance of the wavy surface and the smooth surface all linearity increased along with the load increase. Moreover, the soil is filled in the contact interface crevice under the pressure function along with the load increase, so the pellets contacting with the wavy surface increased, and the crevice reduced. Along with the load increase, the drag reduction effect of the wavy surface is weakened.The sliding resistance slightly increased along with the increase of the advancing speed, and the growth movement of the wavy surface is smaller than that of the smooth one. Comparing with the low speed, the reduction effect of the wavy surface is more obvious when the speed is high. The ripple surface contact pellet's X direction movement is consistent with the test specimen direction of advance, the displacement assumes the linearity to increase; Y to movement approximately along with ripple surface concave-convex fluctuation periodic change, but shakes slightly to have the drop, this explained that the pellet is contacted gradually by the initial contact condition by other pellet substitution the position, thus is getting more and more far to the ripple surface, surface reason which reduces to its function.The X direction speed of the pellet contacting with the wavy surface is bigger than zero basically, and is smaller than zero only partial time interval. The pellets advance along with the specimen advancing, but its will approach the reversed direction when they interact with other pellet. Moreover, the Y direction speed is vibrated along with the wavy fluctuation.The X direction force of the pellet contacting with the wavy surface is fluctuated along with the ripple change. When meets the advancing direction of the bulge, the stress increases obviously, then contacts with the back of the bulge, it reduces. The change of the Y direction force is similar to that of the X direction, and the force size and direction are direct decided by the contacting position.The earthworm body surface is distributing many visceral foramens which can regulate automatically opens and closes. When needs lubricating or being stimulated, it will secrete the body surface fluid, which has provided a weak cutting level, forms the lubrication contact surface between the soil animal body surface and the soil level, may reduce the soil adhesion of the animal body surface. According the self-lubricating mechanism of the earthworm body surface, five bionic wetting components were designed, such as through-hole nozzle, ladder-hole nozzle, through-Chamfer-hole nozzle, bolt nozzle and complex nozzle. With water as lubricant, the wetting test of the bionic components covered with glass or plexiglass was conducted. The test results showed that the time spreading entire surface of the through-hole nozzle is longest, while that of the through-Chamfer-hole nozzle is shortest by regardless of being covered the glass or the plexiglass. Under the identical flowing speed, the distributed speed of the through-Chamfer-hole nozzle is quickest, while that of the through-hole nozzle is slowest. In the same time gap, the moist area of the bionic components from large to small in turn is: through-Chamfer-hole nozzle, bolt nozzle, complex nozzle, ladder-hole nozzle, through-hole nozzle.Finally, according to the size of the earthworm forehead contraction, selecting the through-hole nozzle, 10 kinds of bionic coupling normal adhesion samples were designed and processed. And selecting the through-Chamfer-hole nozzle, 10 kinds of bionic coupling tangential adhesion samples were designed and processed. Thereinto, No.1~6 samples were smooth surface, and No.7~10 were wavy surface. Taking the diameter, number of holes and surface morphology as factors, selecting L9 (21×34) orthogonal test table, the soil normal adhesion tests of the bionic coupling normal adhesion samples were carried out. May know by the test results, in the non-lubrication situation, compared with the No.0 sample, the bionic coupling samples can reduce adhesion, and the reduction rate of the wavy samples is bigger than that of the smooth ones. The reduction rate of No.9 was biggest, which was 20%, and that of No.3 was smallest, which was 14%. When lubricating, the normal adhesion forces of the bionic coupling samples were increased 2~4 times than that of the No.0 sample without lubricating, and the reduction rate of No.7 and No.9 were the biggest, This means that lubrication increases the normal adhesion.Taking the diameter, number of holes and surface morphology as factors, selecting L9 (21×34) orthogonal test table, the soil friction drag experiments of the bionic coupling tangential adhesion samples were carried. May know by the test results, the bionic coupling tangential adhesion samples all have the drag reduction characteristic in lubrication and non-lubrication situation, and the reduction ratio in lubrication is higher than that without lubrication. In the non-lubrication situation, compared with the No.0 sample, the soil friction resistance of the bionic coupling quadrate samples reduced 5~26%, and the reduction rate of No.7~10 specimens were bigger than that of No.1~6 specimens. In lubrication, compared with the No.0 sample without lubricating, the soil friction resistance of the bionic coupling quadrate samples reduced 50~79%. The reduction ratio of No.7 specimen was biggest, which achieved 79%, and that of No.1 specimen was smallest, which was 50%. Through range analysis, it is known that the biggest affects factor to the soil friction resistance of the bionic coupling quadrate samples is the surface morphology, next is hole quantity, and the last is hole diameter. The most superior combination is A2C3BB1, namely No. 7 specimen. It is said that No.7 specimen's drag reduction effects is most obvious.Taking the soil moisture content, the pressure, the flowing speed as well as the advancing speed as factors, selecting L9 (34) orthogonal table, the multinomial orthogonal regression experiment about No.7 specimen was carried. Through range analysis, the primary and secondary factor which affects the soil friction resistance respectively is pressure, advancing speed, soil moisture content as well as flowing speed. The most superior combination is z21z41z11z32, namely the soil friction resistance of No.7 specimen is smallest when the pressure is 100g, the advancing speed is 3mm/s, the soil moisture content is 22%, and the flowing speed is 0.19ml/s time. Through the regression analysis, it May know that the soil moisture content, the pressure, the flowing speed as well as the advancing speed all have two effects to the soil friction resistance, and along with the soil moisture content, flowing speed increase, the soil friction resistance reduces at first, and then increases.While Along with the pressure, advancing speed increase, the soil friction resistance increases at first, and then reduces.
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