| As the scale development of corn cultivation and the expanded application of large tractors in recent years,here come the new requirements of planting machines:the max width and high speed.Most of the domestic planting machines in market are small and medium-sized tractors and the common case is that a seed-metering device is assigned to a single line.It's necessary to increase the quantity of seed-metering devices whenever the width is extended.The excessive seed-metering devices will cause that the seeding machine has the bloated and large structure and bring in inconvenience to the site transportation and quality guarantee.Therefore,it's available for the centralized seeding system which has high efficiency in seeding and simplified structure to accomplish the seeding task with a seed-metering device assigned to several lines.The planting machine with max width will greatly reduce the quantity of seed-metering devices and simplify the structure of the seeding machine.The centralized seeding system has become the development trend in recent years.On the basis of domestic and International research,this essay has presented the one-step centralized pneumatic seeding system.It has optimized the structure of seeding system and amended the design calculation by applying the method of CFD-DEM coupled numerical model.Moreover,it has made the prototype of one-step centralized pneumatic seeding system,established the test bed to do research on the seeding performance of one-step centralized pneumatic seeding system and concluded the optimized parameter of seeding performance.The main research contents of this essay are as shown as below:(1)According to the relative references,it has concluded the planting requirement of wheat.It's requested to fix the plan of the one-step centralized pneumatic seeding system,explain the structure and operating principle in detail and calculate the parameter of system work and critical components.(2)It has created the numerical simulation model and arranged the coupling calculation by referring to the parameter of centralized seeding system.Meanwhile,it has indicated that the model astringency performs excellently and verified the model reliability.Though the speed of seed removal from system reaches 2m/s,there is not any blocking.The one-step centralized pneumatic seeding system has worked out.Plus,the seeding speed is 15.6kg/min and the coefficient of variation is 4.7%.In this case,it'll meet the requirement of seeding in high speed.(3)By going through the relative references,it has arranged the simulation experiment on the PB test of parameter design which makes influence on the seeding performance of centralized seeding system and concluded that the length of mixing chamber,ratio of the elbow&pipe diameter and length of gusseted tube are the most critical influences.What's more,it has arranged the rotary quadratic combination design to do simulation experiment and concluded the influence rule on seeding performance by the length of mixing chamber,ratio of the elbow&pipe diameter and length of gusseted tube.The conclusion after analysis is that the variable coefficient of the consistency will be 3%-5%under the following conditions:the length of mixing chamber is 200mm,ratio of elbow&pipe diameter is 5 and the length of pressure inlet is 300mm.The prototype of seeding system is produced by referring to the optimized structure parameter by stimulation experiment.The consistency of the seeding quantity in all lines gets close to 5%.The test results seem bigger but similar as each other.It has verified that the result of the simulation experiment is reliable.The reason why the data is big is that there is tolerance during installation&production and the test condition fails to meet the requirement of ideal boundary of model.(4)It has arranged the single factor experiment which is about the seeding performance impacted by air velocity and feeding speed.The conclusion is that when the feeding speed is 260g/s,air velocity is 40m/s,then the variable coefficient of the consistency will be 6.8%at the lowest and when the feeding speed is 300g/s,air velocity is 40m/s,then the variable coefficient of the consistency will be 6.1%at the lowest.After that,it has introduced in the orthogonal experiment and the test result is that the variable coefficient of the consistency will become smaller under the following conditions:air velocity is 50m/s,the ratio of elbow&pipe diameter is 5 and the feeding speed is 260g/s.(5)It has done some research on the seeding impact caused by the structure andoperating parameter on the basis of the design of the centralized pneumatic seeding system,so as to provide the parameter reference and theoretical basis for the engineering design and further study. |
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