| Harvesting machinery is a typical off-road vehicle,which is exposed to vibrations caused by soil,machine and plant in complex operating excitation environment and condition.Harvester vibration characteristics have playing an important influence on not only harvester structure's lifetime and working precision,but also influence on driver's comfort and grain loss.Therefore,vibration and noise have become bottlenecks increasingly in high reliability and comfort of harvester compared with similar product overseas.The excitation of complex field environment of soil,machine and plant interaction causes the failure of cracking and deformation of weld,tearing of bolt hole which happened on the frame structure of corn harvester(frame,header,etc.).It is difficult to describe the vibration characteristics and modal parameters accurately of corn harvester in complex excitation operating environment,which only relies on the traditional methods of vibration modeling or theoretical modal analysis,for there are many simplifications in vibration modeling or theoretical modal analysis.Accordingly,the study of vibration characteristics and modal parameter identification methods based on complex operation environment plays an important role in vibration suppression and optimization design.At present,vibration modal test and verification methods based on measured field data are attracting more and more attention of researchers.In order to obtain accurate and effective vibration characteristics and modal parameters of harvester frame structure under complex environmental excitation,combined with theoretical analysis and numerical simulation,a vibration and modal test system which considers synchronous sampling of the clock was established,and a method of identification of operating modal parameters is proposed,which consider the time variation of the mass.Based on the requirement of practical engineering problems,research on vibration and characteristics and modal parameters is carried out.Research works of this dissertation includes:(1)The vertical vibration model of 2 degree freedom was established for corn harvester machine frame-wheel,which corn harvester without suspension damping measures(rigid connection between working parts and frame),and natural frequency and mode shape of the vibration differential equation are obtained by analytical method,at the same time,differential equation in the modal coordinates is derived.Taking a domestic 3 rows corn harvester(4YZP-3XH)as the test object,and the hardware test system,which including NI USB-6216 signal acquisition card,constant current source conditioning module,switching power supply and amplifier,has been built.The vibration test acquisition program is compiled by using LabWindows/CVI interactive C language,the vibration test of harvester frame structure was carried out effectively.Using field vibration test and resonance analysis method,the resonance frequency of corn harvester was determined,and verified the theory model,it shows that theoretical modeling and natural frequency calculation with high accuracy.(2)Theoretical basis of time domain method(ERA algorithm)and frequency domain method(PolyMax algorithm)are derived.The modal test of frame structure for harvester was studied based on multiple-input and multiple(MIMO)out method,based on the excitation and vibration response data,modal parameters of header frame were identified by using ERA and PolyMax algorithm,and verified the correlation of modal parameter identification results,comparing with the difference results of 2 modal parameter identification algorithms,Furthermore,the modal tests are used to verify the results of finite element free mode,and the constraint modal values were obtained which more consistent with the actual operating condition.Finally,the vibration test scheme of header frame was studied and the test system was built.The vibration time domain characteristics and vibration frequency distribution of different operating conditions were obtained,and the corresponding law between vibration frequency and mode shape of header frame is pointed out.(3)By means of cascading multiple test acquisition devices,a test system for phase synchronization of each channel's vibration was built,the confusion of modal data caused by phase information is solved.The boundary information of soil and crop was measured,and the operating modal test considering the mass which is time-varying was completed.A modal parameter identification method for harvesting machinery based mass time-varying is proposed,the vibration modal parameters(natural frequency and damping ratio)of the harvested mechanical frame are identified based on time domain SSI and frequency domain EFDD algorithm by using vibration response data under the field harvest operation.Furthermore,the vibration mode and operating deformation characteristics of harvester are further studied and analyzed.In addition,Fourier transform method,SSI and EFDD method were used to determine vibration frequency,it shows that the results are credible.(4)Schematic mechanism and mathematical descriptions of 4 different kinds of spot weld models,including Rbe2(rigid bar element 2),RBAR,CWELD and ACM2(area contact model 2)models were studied and corresponding finite element models were established to conduct two kinds of numerical simulation mode including static analysis and modal analysis.The numerical simulation model is verified by strain test,an applicability analysis and optimum seeking of spot weld method on numerical simulation of modal analysis for corn harvester are proposed.On this basis,applicability criterion of modal and stress-strain mode were put forward,influence on different welding spot models on the accuracy of the finite element calculation of harvesting machine frame was investigated.(5)Studied the influence of discontinuous change of interval of frame wall thickness and stiffness on the frequency and mode,to improve the first-order frequency based on the fundamental frequency optimization method,an topological optimization model of frame structure is established,a optimization design method of harvester frame structure with vibration suppression as the goal is put forward,after optimizatibn of vibration,the first order vibration frequency of frame was improved,and modal displacement and deformation were reduced,the durability test shows that the failure rate of optimized frame is reduced,and the mean time without failure increase from 20h to 60h. |
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