Design of UAV Downwash Airflow Field Detection System Based on Strain Effect Principle.

Yalei Wu,Elizabeth M Musiu,Hao Zhang,Pei Wang,Lijun Qi,Zepeng Yang

doi:10.3390/s19112630

Abstract

Accurate measurement of the downwash flow field of plant protection unmanned aerial vehicles (UAVs) is essential for analyzing the spatial distribution of droplets. To realize on-line rapid detection of the downwash flow field of a multi-rotor UAV, a flexible polypropylene detection device based on the principle of full bridge strain effect was proposed. Its performance principle was based on the physical deformation caused by wind pressure. The Fluid Flow and Static Structural modules of ANSYS 16.0 finite element software were used to simulate one-way fluid-solid coupling interaction. The surface of the resistive strain gauge embedded in the flexible detecting structure responded well to wind speed variation, hence it was suitable for downwash airflow wind field detection. By solving the strain force on the surface of the flexible detection structure, the length and layout of the grating wire of the strain gauge on the surface of the flexible detection structure were optimized. Meanwhile at 4 m·s−1 wind speed, the output voltage at varied bridge flexible acquisition systems in the acquisition card was measured. Results indicated coefficient of variation of 3.67%, 1.63% and 1.5%, respectively, which proved the good data acquisition consistency of the system. Through calibration test, the regression equation for the relationship between output voltage and wind speed for three unique sensor signal measuring circuits was established. The determination coefficients R2 for single bridge, half bridge and full bridge circuits were 0.9885, 0.9866 and 0.9959, respectively. In conclusion, by applying the multi-rotor plant protection UAV test platform, the results indicated the maximum relative error of the wind speed at each sampling point of the system at 1.0 m altitude was below 5.61%. Simulated and measured value had an RMSE maximum error of 0.1246 m·s−1. Moreover, downwash airflow detection not only has high accuracy but also has high sensitivity. Thus, there is convenience and practicability in the plant protection offered by this approach. The rapid measurement of UAV wind field and the established two-dimensional wind field model can provide a basis for precise application of agricultural aviation.

Highlights

The multi-rotor unmanned aerial vehicle (UAV) has the advantages of high efficiency, strong droplet penetration, no need for a dedicated lifting platform, and good maneuverability
Previous studies have shown that the downwash flow field of multi-rotor plant protection UAV directly determines the movement and diffusion of droplets in space [5,6]
The measured values are taken as the reference values to calculate the root mean square error (RMSE)

Summary

Introduction

The multi-rotor unmanned aerial vehicle (UAV) has the advantages of high efficiency, strong droplet penetration, no need for a dedicated lifting platform, and good maneuverability. Sensors 2019, 19, 2630 the airborne spraying equipment converts the liquid into droplets but leaves the fuselage. At this point, the downwash flow plays an important role especially in defining how the droplets attach to the crop canopy. Previous studies have shown that the downwash flow field of multi-rotor plant protection UAV directly determines the movement and diffusion of droplets in space [5,6]. The optimization of detection technology of downwash airflow field distribution of multi-rotor plant protection UAV to curb the high cost, low efficiency and poor accuracy of field wind field measurement has become a hot research topic in this field [10]

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Results

Conclusion