Development Of Monitoring Device For Vibration Process After Raindrops Hit Plant Leaves And Characteristics Of Leaf Motion Energy Dissipation

Rainfall is the key factor that causes soil erosion and surface runoff turbulence.Plant leaves,as the direct contact surface of rainwater,will bend,twist and produce certain vibration under the action of raindrop kinetic energy.Through vibration,the raindrop falling kinetic energy is gradually dissipated to slow down the direct erosion of rainfall on soil surface.The process of raindrop impacting leaves is affected by many factors,and the complexity is far beyond the direct study of ordinary solid or liquid surfaces.The simplified model represented by cantilever beam is difficult to fully reflect the real process of leaf vibration due to the great difference between its properties and the characteristics of the plant surface.However,there are relatively few device systems directly used to monitor the vibration of leaves,which results in insufficient research on the kinetic energy dissipation process related to a series of processes such as impact,sputtering,rebound,detachment and storage after raindrops contact the leaf surface,limiting the understanding of the functional mechanism of vegetation soil and water conservation.In order to study the vibration process and energy change of plant leaves when they are hit by raindrops,a set of raindrop kinetic energy measurement device system is developed based on the characteristics of PVDF piezoelectric film sensor that can effectively detect vibration and combined with the knowledge of signal and system.The thin film sensing can convert the vibration signal of the leaf into an electrical signal for output.Through the simulation experiments in the laboratory,a dissipation model for evaluating the kinetic energy dissipation capability of the leaf to raindrops is analyzed and summarized.Finally,the device and model are used to observe the energy change characteristics and dissipation of single raindrops and continuous raindrops hitting the leaves.The results showed that:1.The raindrop kinetic energy measurement device system consists of three modules: the thin film sensing system,the monitoring and capturing of blade vibration and the raindrop generating device.The accuracy of the thin film sensing system is0.01953 V,and the measurement range is-2.000～3.000 V.The output voltage signal under the excitation of raindrops has obvious waveform,which shows the trend of oscillation attenuation.The natural frequency of the system is 34.50～48.50 Hz.The minimum value of peak-peak variation coefficient of voltage signal is 0.513%.The accuracy and stability of the measurement results of the film sensing system meet the requirements of capturing blade vibration.2.The deformation of the film sensor in the direction of the polarization axis is the result of the combined effect of blade bending and surface vibration,and the captured voltage signal actually reflects the deformation caused by the first impact of raindrops on the blade surface.During the impact process,the energy conversion experienced a process from raindrop kinetic energy to leaf bending energy to PVDF bending energy.The vibration signal energy obtained by the sensor is essentially a part of the kinetic energy of raindrops converted into the bending energy of blades.3.With the increase of kinetic energy of raindrops,the maximum upper peak voltage of the same species showed a significant increase trend.Taking Platanus acerifolia as an example,the difference of the maximum upper peak voltage under five kinds of kinetic energy was 12.71 times.The size of the leaf area plays an important role in the dissipation of raindrop energy,which is expressed as Populus tomentosa had the strongest kinetic energy dissipation capacity for raindrops less than 150 μJ,and the leaf with large leaf area of Platanus acerifolia showed more prominent kinetic energy dissipation capacity for raindrops greater than 150 μJ.The storage bending energy of Ligustrum lucidum leaf was the lowest under all kinetic energy of raindrops.The bending energy stored in leaves of each species is quite different.4.The voltage-time curve of continuous raindrop impact is similar to that of single raindrop impact,showing a trend of oscillation attenuation.The oscillation curve between the two impact points on the same curve is clear and does not overlap.With the increase of raindrop frequency,the impact degree of leaves increases.The time domain index analysis shows that the overall energy increases,and the raindrop frequencies of4.33 Hz and 2.07 Hz are identified in the low frequency band of vibration spectrum.The bending energy stored in leaves increased step by step in continuous rainfall.The total kinetic energy stored in the same leaf was affected by the frequency of raindrops and the kinetic energy of single raindrop.The relationship between blade mass,blade area and the diameter of the middle of the petiole is complicated with the vibration energy and dissipation of the blade.