Modal Model Solution Of Small Agricultural Machinery Based On Modal Synthesis And Experimental Research

There are two main methods to analyse dynamics problems of small agricultural machinery recently which have large and complex structure that is full-size test method and finite element method. Using experimental modal analysis method, modal parameters identification will be easily missed because of the complex structure and high requirements on test equipment and technology. Using finite element modal analysis method, the solving is difficult because the large and complex structure which makes the degrees of freedom so large after finite element discretization; and the accuracy is low because complex combination of various surface must be a reasonable simplifying and assumptions, it is difficult to determine the boundary conditions; costs increase because the case of constitutive model of materials is not easy to obtain which needs the material test.In this thesis, the complete modal model of small agricultural machinery is solved based on the combining with freely interface modal synthesis method of sub-structure finite element modal model and the experimental modal model, using the advantage of finite element method and experimental analysis fully, and avoiding the above-mentioned disadvantage of both methods. Normally outsourcing components used experimental modal analysis, and self-made components used finite element modal analysis which can be modified at the design stage to improve the overall dynamic characteristics. It is a superior method to solve small agricultural machinery which has complex mechanical system modal model.In this thesis, the main work and achievements are listed as follows:1. According to modal synthesis sub-structure division principle, small agricultural machinery was divided into six sub-structures that is handrails, rack, tires and frame, engines, sprocket drive components and rotary knife. Based on complexities of sub-structures determination using uniform set and rough set theory, handrails and rack should adapt the finite element modal analysis, tires and its frame, engine, transmission sprocket parts should adapt experimental modal analysis, and rotary knife group can adapt either finite element modal analysis or experimental modal analysis.2. The sub-structure modal model was solved respectively using MSC.NASTRAN and LMS Test.Lab. Accurate finite element modal model and experimental modal model were obtained.3. The dynamic model was established for the three main connection bolt connections, sockets and welding, and the processing method of various types of combination surface in modal synthesis was proposed.4. Each sub-structure was assembled using LMS Virtual.Lab, the modal model of complete machine was obtained through setting its combination surface characteristics and free interface modal synthesis.5. Machine modal model obtained by modal synthesis was tested using modal testing. First 10-order natural frequencies error were less than 6%, whole modal synthesis results were accurate, and the first-order natural frequency which is not easy to identify was obtained. This method was verified that the method has good accuracy, and overcome disadvantage of whole machine experimental modal analysis.Through small agricultural machinery modal synthesis it is found that modal data has a great impact on the results of modal synthesis. In the later research, the results of modal synthesis can be improved by improving the accuracy of sub-structure experimental modal analysis. Even more accurate results of the modal synthesis could be obtained in future.