| Along with the further adjustment of rural economic structure,and the agricultural sector of China attaches great importance to characteristic agricultural products,the lotus root planting area increased year by year.Its planting and management link is simple,and it has high economic benefit,but lotus root growing under mud long mainly rely on artificial digging,so greater labor intensity,bad working environment,low production efficiency,serious lotus root injury,poor product quality problem have become the bottleneck of restricting the lotus root production.To solve the above problems,in view of higher cost of the existing digging lotus root equipment,the tedious operating process,some certain experience required to master digging technology of defects,put forward a new kind of jetting spin type digging lotus root machine.Combined with the mechanism of hydraulic digging lotus root,the self-rotating pipeline was designed to simplify the whole structure and enlarge the operation width.It is easy to dig lotus root by manpower or vehicle pushing the machine forward,and the operation is simple,the manufacturing cost is low.In the paper,based on the systematic analysis and summarization of the research on both domestic and abroad digging lotus root machine and jetting theory,aiming at the characteristics of the digging lotus root in China’s lotus root field and the demand for digging lotus root machinery,adopting the method of combining theory with experiment,the research and exploration of jetting spin type digging lotus root machine had carried.The main research contents are as follows:(1)according to the related literature and material characteristic test standard,using the image processing,ring knife method,moisture content measurement instrument,soil compactness measuring instrument,respectively measured mud parameters.Accumulation angle of mud is 42 °,volume density is 1714 kg/m3,moisture content is 46.7%,and maximum compactness of mud of 0.4 m depth is 1.63 MPa.The compressive strength of lotus root is 2.32 MPa and the ultimate bending moment is 6 N·m with universal material testing machine.The volume density of lotus root was determined by the drainage method.The volume density of lotus root is 0.93x10-3 kg/m3,and it is calculated that the thrust of lotus root is 1.4 N in the water,the floating up time of lotus root under 0.4 m depth mud is 1 s.(2)Combined with discrete element method and finite element method,fluid-solid coupling technology of EDEM-Fluent was used to analyze the action mechanism of jet flowbreaking and digging mud,and the influence rule of nozzle parameters on digging depth and digging width was researched.1 The digging depth decreases with the increase of jetting angle and increases with the increase of jetting velocity.The digging width increases with the increase of jetting angle and jetting velocity.When the jetting velocity is 20 m/s,the digging depth of 0.43 m can be reached to meet the requirements of the depth of digging lotus root.Through the analysis of the pressure condition of the particle body,when the jetting velocity is 20 m/s,it will not damage or break the lotus root.2 The velocity vector diagram of mud particles was obtained by studying the particle motion analysis in the coupling simulation process.Change rules of the maximum velocity of mud particles between time and the total volume of particles between time and the maximum pressure of particles between time were obtained.And the action mechanism of jetting impact mud is analyzed.3 Comparing digging depth and digging width of the simulation test with the bench test,the average error is 9.5% and 9.2% respectively,It shows that the model of fluid-solid coupling simulation has high reliability.This method can effectively analyze the effect of nozzle parameters on digging mud.It is also indicated that the coupling simulation of discrete element and fem fluid dynamics is feasible in the study of the interaction mechanism between jet flow and mud.However,in the process of simulation,when the simulation time arrived at around 0.4 s,digging depth have already been to 0.43 m.It is different to the bench test about the relationship between digging time and digging depth.Therefore,the simulation time cannot be used as the analysis data of digging speed.(3)By means of fluid dynamics analysis of jet flow field structure,the influence mechanism of jetting impact range is determined by jet flow theory,and the mathematical model of jetting impact range is established.Under the condition of jetting angle of 45°,the flow field of different length-diameter ratio nozzle is analyzed by CFD simulation: The flow field structure of different nozzle diameter is similar.And the dynamic pressure generated by the 17 mm nozzle with the largest diameter decays much slower than others,which is consistent with the theory of flow field structure analysis.The approximate radius of the jet flow of 17 mm nozzle is 0.05 m by measuring the velocity distribution range in the flow field.In addition,using CFD fluid dynamics simulation to analyze the flow resistance and the flow field of straight motion of rotating pipeline in the water.Established the resistance coefficientmodel of linear motion of the rotating pipeline in the water,and the resistance coefficient is calculated by Origin2017 data analysis and processing software as 14.95 kg/m.(4)According to the theory of fluid mechanics and the simulation analysis of EDEM-Fluent,the structure of the rotating pipeline and the structure parameters of the nozzle were optimized.The jetting pressure of the minimum diameter of 17 mm nozzle on the surface of the lotus root is 0.20 MPa and the jetting force is 97.22 N which will not damage lotus root.Based on the buoyancy check of floating ring and the calculation of Maple engineering mathematics,the design has a universal frame structure,which can adapt to the operation demand of the lotus toot field with a depth of 0.3-0.5 m.(5)Using mechanics analysis method combined with CFD analysis of flow field and fluid dynamics analysis,through the calculation of MATLAB software to solve mathematic model of the pipeline rotating speed in the water,confirmed the influence law of various structural parameters on the rotating pipeline speed.Using kinematics analysis method,the mathematical model of the impact frequency and time of the single point of the jet was established,and the factors that restrict the advance speed of the machine were obtained.On the basis of ensuring the digging depth and the quality of lotus root,the operation efficiency of digging lotus root could be improved.Based on CFD flow field analysis and dynamic analysis method,the mathematical model of the loss power and the rotation speed of the rotating pipeline was established.With the comprehensive analysis,the mathematical model of the speed of the moving forward and the time of the single point impact mud and the rotation speed of the rotating pipe was obtained,which provided the theoretical basis for the adjustment of operation parameters of the machine.(6)Based on the theoretical analysis of the working mechanism and the mathematical model of the relevant parameters,the bench test and field experiment were carried out to obtain the optimum structural parameters of the nozzle,and the rationality of the theoretical design was verified by orthogonal test:1 The digging depth is negatively correlated with the jetting angle through the two-factor test,and is positively correlated with the jetting velocity.The digging width is positively correlated with jetting angle and jetting velocity.When the jetting angle is 30°,the digging depth is largest,and floating rate is higher.But the digging width is lower,it is not conducive to improving the efficiency of digging lotus root.When the nozzle diameter is 17 mm and jetting angle is 45°,the digging depth enough to dig up lotus root under 0.4 m depth mud,so the parameters are the optimal nozzle structure parameters.2 Through single factor test,the influence rule of nozzle installation angle on digging depth,digging width and rotation speed of pipeline is analyzed.When installation angle outward slant 60°,it has the largest digging width of 1.42 m,the maximum digging depth of 0.419 m and the actual rotation speed of 43 r/min which is the lowest rotation speed compared to the response from other angles,and the loss power is calculated to be 0.085 k W.3 Under the condition of optimal structure parameters of nozzle,the single point digging time of digging 0.4 m depth is 1.52 s.Replace the optimal nozzle diameter of 17 mm,the outward slant installation angle of 60°,jetting angle of 45°and single point digging time of 1.52 s into the mathematical model of machine forward speed,the forward speed is0.1 m/s by calculated.4 The effect of each factor on the response index is analyzed by orthogonal test,and the conclusion is consistent with the theoretical analysis.The order of affecting digging depth is jetting angle > nozzle diameter > installation angle;The order of affecting digging width is jetting angle > installation angle > nozzle diameter.The optimal parameter combination is analyzed under different mud compactness conditions.When the mud compactness is greater than 1.6 MPa,jetting angle of 30°is better to improve the digging depth;When the mud compactness is less than 1.6 MPa,jetting angle of 60°is better to improve the digging width.5 The optimal structure parameter combination and working parameters of the jetting spin type digging lotus root machine are confirmed by the improvement of the prototype and the field experiment.Through the actual measurement and calculation,it is concluded that the operation efficiency of the machine is 432 m2/h. |
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