| Lotus root is an important aquatic vegetable in China,which is loved by our people for its delicious and nutritious taste.It has high edible medicinal value and broad market prospect.The development of lotus root industry is limited by the low degree of mechanized harvesting in the process of mechanization of the whole lotus root production.At present,lotus root harvesting mainly relies on human labor aided by means of jet streams.Since lotus root harvesting is concentrated from October to April,the cold operating environment and heavy workload make root diggers one of the toughest professions.Therefore,there is an urgent need for a machine that can effectively complete the harvesting of lotus roots and break the bottleneck of lotus root industry development.To address the problem of lotus root harvesting in cohesive soil,this paper designs a jet excavation device based on a crawler float type root digger chassis developed by the group.The device adopts a combination of mechanical excavation and hydro-jet flushing.The key components are optimized through 3D structural design,computer simulation,bench testing and field testing.The main research contents of the full paper are as follows.(1)Jet excavation device was designed.The structural parameters and operating principle of the jet excavation device were determined by the growing environment and characteristics of lotus roots.The mechanical model of the excavation process of the shovel teeth was established,and the dynamic equilibrium relationship between the frictional resistance moment,the resistance moment of the lotus root soil mixture and the active moment was analyzed.Referring to the resistance analysis of excavator backhoe digging,the resistance of a single shovel tooth reaching the maximum digging depth of0.5m was calculated to be about 177.715N.The full process of shovel tooth excavation was strength calibrated by Ansys transient dynamics analysis module.(2)Hydraulic jet system was designed and selected with theoretical calculations.The hydraulic jet system is composed of a water suction device,a water delivery device and a jet device.According to the overall design plan of the jet system,the parts are designed and selected.The water suction device is composed of 2.5 inch check valve filter and 2.5inch steel wire hose.The airtightness of the suction link is ensured by using clamps for each joint to be tightly connected.The BJ-16C water pump is used as the power source to pressurize the water stored in the root field.The water flow is conveyed to each nozzle on the jet excavation shovel through a 2.5-inch to 4-point water divider.The smallest unit of the jet device is a 4-point female tee threaded with a 90-degree elbow,equipped with 1,2,and 3-point specification nozzles.The hydrodynamic modeling of the jet system was carried out to determine the source of energy loss and calculate it.The results show that the hydraulic jet system has a head loss of 37.51m,and the pump flow and head can meet the operational requirements.Adams software was used to simulate the kinematics of the flexible body of the pipeline,to obtain the required margin of the pipeline at each joint and to carry out a reasonable arrangement of the pipeline.(3)Coupled simulation analysis of the sub-mud jet mechanism was conducted.CFD-DEM fluid-solid coupling method is used to analyze the soil disturbance effect of the jet under the nozzle mud,and to study the influence law of the jet parameters on the soil disturbance effect.The simulation test results show that the nozzle diameter,angle and burial depth have a significant effect on the soil disturbance effect,and the interaction of nozzle diameter and nozzle angle has a significant effect on the index.When the nozzle diameter decreases,the angle increases and the burial depth decreases,the disturbance effect of the water jet on the soil tends to increase.Among the test groups,the nozzle inner diameter of 1 minute,the angle of 45 degrees,burial depth of 350 mm has the best effect on the soil disturbance,reaching 29.743%.Nozzle diameter has a significant effect on the soil flushing height.The height of soil lift by 6mm,8mm and 10mm nozzles is578.4mm,450.5mm and 370.5mm respectively.The height of soil lift by small diameter nozzles is high.In the two-nozzle jet test,the nozzle spacing directly affects the superposition effect of the flow field,which in turn affects the effect of soil disturbance.The height of nozzle flushing to the soil decreases with increasing nozzle spacing.When the nozzle spacing is large enough,it can be seen as a translation of the effect of a single nozzle on soil disturbance.(4)Resistive moment bench test for lotus root excavation process was designed.The mathematical-physical model of the bench was developed,and the whole process of digging the lotus root by analyzing the shovel teeth.The optimal jet parameters for the actual working conditions were determined by designing the bench structure and conducting bench tests.A two-factor three-level test was designed with the nozzle inner diameter and the number of nozzles.The results showed that the nozzle inner diameter had a significant effect on the digging resistance moment(P<0.05),and the number of nozzles had a highly significant effect on the digging resistance moment(P<0.01).The maximum excavation resistance moment of the control group without jet treatment was85.509N·m,and the maximum excavation resistance moment of the test groups with jet treatment was concentrated between 40N·m and 70N·m.The minimum excavation resistance moment of the shovel teeth on the root-soil mixture was 40.195N·m when the number of nozzles was 4 and the inner diameter of the nozzles was 10mm.The results show that the soil disturbance by jet treatment can effectively reduce the excavation resistance moment.It is suitable for lotus root excavation under cohesive soil.(5)Field trial of jet digging lotus root harvester was conducted.The operational performance of the jet digging root excavator was tested by field trials.Soil parameters and lotus root growth depth of the lotus root field were counted.The data showed that the lotus root growth depth was concentrated at 15 cm to 35 cm below the mud.The field efficiency of the lotus root digger was 50.4m~2/h,with an operating width of 1.4m.The net digging rate of lotus root reached 89.74%,the quality damage rate was 11.17%and the quantity damage rate was 13.82%.The machine operated normally in the field test.The adaptability and working reliability of the machine to the water field were verified. |
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