Mechanical characteristic analysis of rice seedlings under water wave stress

Machine transplanting as an advanced technology in rice cultivation has been widely adopted. Nevertheless, under extreme wind conditions, transplanted rice seedlings can float and then die off due to external forces generated by wind and water waves. Studying the mechanical characteristics of these seedlings is essential for understanding the underlying mechanisms of rice seedling floating. In this study, the Volume of Fluid (VOF) method is applied to study the flow mechanisms of water waves around rice seedlings. It is found that the pressure differential between the windward and leeward wave sides of the rice seedlings changes during wave diffraction, resulting in unsteady drag forces. The drag force reaches its maximum value when the wave crest propagates to the rice seedlings. Under the condition where waves do not break, increasing wave height does not alter the fluctuation pattern of drag force but leads to a larger drag force amplitude. When the wave height increases sufficiently to cause wave breaking, additional loads are generated, resulting in a significant increase in drag amplitude and exciting new high-frequency disturbances. Increasing wavelength reduces the drag force amplitude but raises its fundamental fluctuation frequency and introduces new low-frequency pulsations. As the rice seedlings tilt, the altered flow mechanism has an uncertain effect on the variation in drag force amplitude and generates new excitations with other frequencies. It indicates that increased wave height, decreased wavelength, and rice seedling inclination may all elevate the risk of rice seedlings lodging. These results could provide valuable references for the prevention of floating rice seedlings.