To address the limitations of the current discrete element model of rice plants in terms of accurately reflecting structural differences and threshing characteristics, this study proposes a whole-rice-plant modeling method based on segmented hollow stalks and establishes a whole-rice-plant model that accurately represents the bending and threshing characteristics of the actual rice plant. Initially, based on the characteristics of the rice plant, the rice stalk was segmented into three sections of hollow stalks with distinct structures—namely, the primary stalk, the secondary stalk, and the tertiary stalk—ensuring that the model closely resembles actual rice plants. Secondly, the mechanical and contact parameters for each structure of the rice plant were measured and calibrated through mechanical and contact tests. Subsequently, utilizing the Hertz–Mindlin contact model, a multi-dimensional element particle arrangement method was employed to establish a discrete element model of the entire rice plant. The bending characteristics of the stalk and the threshing characteristics of the rice were calibrated using three-point bending tests and impact threshing tests. The results indicated calibration errors in the bending resistance force of 4.46%, 3.95%, and 2.51% for the three-section stalk model, and the calibration error for the rice model’s threshing rate was 1.86%, which can accurately simulate the bending characteristics of the stalk and the threshing characteristics of the rice plant. Finally, the contact characteristics of the model were validated through a stack angle verification test, which revealed that the relative error of the stacking angle did not exceed 7.52%, confirming the accuracy of the contact characteristics of the rice plant model. The findings of this study provide foundational models and a theoretical basis for the simulation of and analytical applications related to rice threshing and cleaning.

Rice seed production is a critical step in breeding high-quality varieties. To ensure seed purity, it is essential that no residual grains or broken ears remain in the harvester header after harvesting each variety, thus preventing cross-contamination. This study addresses the issue of seed retention in existing rice harvesters, which lack efficient self-cleaning or other cleaning mechanisms and cannot be cleaned rapidly. A self-cleaning device for the harvester header was designed to enable one-click cleaning after harvesting a single variety. A novel cleaning nozzle was developed as the key component of the device, with its structure optimized through single-factor and orthogonal combination experiments. The number of nozzles was determined based on their spray width and the header width. A header-cleaning airflow simulation model based on Fluent–EDEM coupling was constructed to investigate the effects of nozzle inlet pressure, airflow incident angle, and nozzle outlet height on the self-cleaning rate. Optimal cleaning parameters were identified to maximize the self-cleaning rate, and the simulation results were validated. The study revealed that the nozzle’s expansion section length, throat diameter, and contraction section length significantly affect the spray width. When the expansion section length was 10 mm, the throat diameter was 8 mm, and the contraction section length was 8 mm, the nozzle achieved the largest jet angle, measuring 50.3 cm. Further analysis indicated that inlet air pressure had the greatest influence on the self-cleaning rate, followed by airflow incident angle and nozzle outlet height. The optimal parameter combination was identified as an inlet air pressure of 0.6 Mpa, an airflow incident angle of 118.25°, and a nozzle outlet height of 2.64 mm, achieving a maximum self-cleaning rate of 99.63%. A one-click cleaning system was designed using an STM32 microcontroller and hardware circuits. Field experiments under optimal parameters demonstrated a self-cleaning rate of 97.68% with a cleaning duration of 10 s per cycle. The findings provide theoretical guidance for the design and optimization of self-cleaning headers for rice seed production.

In this paper, a low-damage flexible drum-shaped threshing element is designed to address the stringent requirements for seed harvesting, specifically targeting the issues of high seed breakage rates, low threshing rates, and elevated entrainment loss rates during the mechanized harvesting process of rice seed propagation. Initially, a mathematical model was developed to determine the maximum normal impact force exerted by the threshing elements on rice seeds throughout the threshing process, derived from a comprehensive mechanical analysis. Subsequently, experimental research was conducted to investigate the physical properties of rice, leading to the establishment of a flexible, multi-level hollow stem discrete element rice model. This model facilitated an examination of the normal and tangential threshing forces from a microscopic perspective, thereby validating the performance of the flexible drum-shaped threshing element. Optimization simulation tests were then performed, with drum speed, feeding amount, and threshing gap serving as test factors, while the crushing rate and loss rate were used as test indexes. The results indicate that, under the optimal structural parameters of the threshing element, the ideal configuration includes a drum speed of 900 rmp, a feeding amount of 3.734 kg/s, and a threshing gap of 23.214 mm, resulting in a normal force of 18.05 N and a tangential force of 12.96 N, with a loss rate of 0.929%. Finally, a field harvest verification test was conducted based on these optimization results. Under identical working parameters, the breakage rate of the newly designed flexible threshing element was reduced by 55.9% compared to the traditional steel nail teeth, while the loss rate decreased by 15.3%, thereby fulfilling the high-quality harvesting requirements for rice seeds.