Parameter Optimization and Experimental Study on Alfalfa Stem Flattening Process Based on DEM–MBD

To address issues such as uneven flattening and high stem breakage rate in post-harvest alfalfa field conditioning operations, an adjustable-clearance flattening and modulating device was designed. The device incorporates a dual-spring floating pressure mechanism and preload adjustment mechanism to ensure the adaptive performance of conditioning rollers during alfalfa stem flattening. Based on the biological characteristics of alfalfa stems, a rigid–flexible coupling model between stems and the flattening and modulating device was established. Using the Discrete Element Method (DEM) and Multibody Dynamics (MBD) co-simulation technology, experiments were conducted with feeding amount, roller speed, and buffer spring preload force as test factors, while stem crushing rate and bonding key fracture rate served as evaluation indices. Box–Behnken experimental design was employed to simulate the dynamic conditioning process, followed by regression analysis of the simulation results. The findings revealed optimal parameter combinations as follows: feeding amount of 5.10 kg/s, modulation roller speed of 686.87 r/min, and buffer spring preload force of 670.02 N. According to the optimal combination of parameters to carry out field tests, the average flattening rate of stem and stem crushing rate were 95.71% and 1.73%, respectively, which showed small relative error with the predicted value and met the requirements of alfalfa steam flattening and modulation operation. These research findings provide theoretical basis and technical support for the design and optimization of alfalfa flattening and modulating devices.