Songchao Zhang

Unmanned aerial vehicle (UAV) has the advantages of good repeatability and high remote sensing (RS) information acquisition efficiency, as an important supplement bridging the gap of high-altitude and ground RS platforms. A quadrotor UAV was developed for the agricultural RS application in this study. The control system consists of a main processor and a coprocessor, integrating a three-axis gyroscope, a three-axis accelerometer, an air pressure sensor and a global positioning system (GPS) module. Engineering trial method (ETM) was used to tune the parameters based on the active disturbance rejection control (ADRC) method. Also a ground control station (GCS) adapted to the quadrotor was developed realizing autonomously take-off and landing, flight route planning, data recording. To investigate the performances of the UAV, several flight tests were carried out. The test results showed that the pitch angle control accuracy error was less than 4°, the flight height control accuracy error was less than 0.86 m, the flight path control accuracy error was less than 1.5 m overall. Aerial multispectral images were acquired and processed. The reflected digital number (DN) values obtained from a height of 10-100 m with 10 m interval could be referenced to classify objects. The normalized-difference-vegetation index (NDVI) values obtained from the aerial multispectral images acquired at 15 m were compared with those obtained by the GreenSeeker (GS) and PSR-1100F. The maximum error was 20.37% while the minimum error was 1.99%, which demonstrated the developed quadrotor UAV’s satisfactions for low altitude remote sensing practice. This study provided a low-cost platform for agricultural remote sensing. Keywords: UAV, quadrotor, ADRC, agricultural remote sensing, NDVI, aerial spraying application DOI: 10.25165/j.ijabe.20191204.4641 Citation: Zhang S C, Xue X Y, Chen C, Sun Z, Sun T. Development of a low-cost quadrotor UAV based on ADRC for agricultural remote sensing. Int J Agric & Biol Eng, 2019; 12(4): 82–87.

The deformation of Carbon Fibre Reinforced Polymer (hereafter referred to as CFRP) will affect the reliability and safety of products when it is applied in the fields of aeronautics & astronautics and military, and it can provide a basis for assessing the safety performance of structures by monitoring the deformation of CFRP laminates real time. In this paper, the CFRP laminates are taken as the research object, the CFRP laminate structures model is established in the finite element analysis software ABAQUS, the load is applied, the strain value is obtained, the deflection of model is reconstructed based on the Ko displacement theory, and it is compared with the deflection obtained by the simulation. Furthermore, the test pieces of CFRP laminates are designed and prepared, the experimental system is established, the FBG sensors are used to collect the strain information, and the deflection is reconstructed based on the Ko displacement theory and compared with the measured deflection, to respectively obtain the RMS error of 0.5483 mm and 0.8515 mm between the reconstructed deflection and the measured deflection of test pieces. It is concluded that the Ko displacement theory can be applied for the deformation reconstruction of CFRP laminates.

The effective coverage and velocity of downwash are directly related to the assemblage of spraying system and spraying effect. The downwash of the unmanned agricultural helicopter (UAH) N-3 was discussed in the paper. The computational fluid dynamics (CFD) methods were used to simulate and analyze the distribution of the downwash, and a wind field measurement device had been designed to test the downwash of UAH N-3. In the tests, the UAH N-3 was raised up to 5.0 m, 6.0 m and 7.0 m from the ground, “annular-radial-distribution- point” method was introduced, 8 directions separated by an angle of 45° (the radial direction) with the intersection point of the main rotor shaft and the ground plane as the center, 0.5 m as the step length for the longitudinal (to 2.5 m) and radial (to 4.0 m) direction to set the sample points, considering the range of the rotor rotating circular area mainly. The 5 m height results of N-3 were fully discussed to describe the downwash distribution with the longitudinal altitude increased and the radial distance increased. The standard deviations of five test altitudes for eight directions were comparatively analyzed, the results showed that the total standard deviation was not greater than 0.6 m/s. The overall relative maximum margin of error calculated from the simulation and measurement data was between 0.6 and 0.7, which verified the credibility of the simulation data. High-order polynomials were used to fitting the simulation and measurement data, the fitting results showed that the polynomial coefficient of determination R2 met or exceeded 0.75 when the altitudes were more than 1 m, indicating the fit equation having the reference values. When the altitudes equal or less than 0.5 m, the polynomial coefficient of determination R2 was smaller, ranging during 0.3 to 0.7. The study would provide some foundations for the optimization of the assemblage of spraying system on the single-rotor UAH, which would promote China aviation plant protection. Keywords: unmanned agricultural helicopter, single rotor, CFD simulation, downwash distribution, spraying effect DOI: 10.25165/j.ijabe.20171005.3079 Citation: Zhang S C, Xue X Y, Sun Z, Zhou L X, Jin Y K. Downwash distribution of single-rotor unmanned agricultural helicopter on hovering state. Int J Agric & Biol Eng, 2017; 10(5): 14–24.

Droplet retention during pesticide application is a serious problem because run-off droplets flow out of the target area and pose a hazard to human health and the environment. The present study was conducted with the aim to measure the droplet retention of sprayed droplets on crop leaves in vivo using a constructed test system. In the measurement, three crop species with different surface properties (tomato, chili pepper, and winter wheat) were selected for droplet retention determination, and the variations in the time intervals of maximum retention and stable retention were determined. Contact angle and surface roughness (Ra), which are the most important surface properties of crop leaves, were used as independent variables. The Ra values of tomato, pepper, and winter wheat were 24.73 μm, 5.28 μm, and 17.59 μm, respectively, while the contact angles of tomato, pepper, and winter wheat were 97.67°, 70.07° and 131.98°, respectively. The results showed that the curves of droplet retention on sprayed tomato and wheat leaves had similar patterns over time and could be divided into four periods (rapidly increasing period, slowly increasing period, collapsing period, and stable period). The maximum droplet retention on tomato leaf surface was Rmax = 0.169 g⋅cm−2, and the stable retention was Rst = 0.134 g⋅cm−2. The maximum droplet retention on the surface of winter wheat leaf was Rmax = 0.244 g⋅cm−2, and the stable retention was Rst = 0.093 g⋅cm−2. However, droplet retention on pepper leaves was different from that on tomato and wheat leaves. The curve pattern of droplet retention on pepper leaves over time showed two peaks and two valleys. Moreover, the maximum retention, Rmax, was in the range of 0.149~0.151 g⋅cm−2, and the stable retention was Rst = 0.077 g⋅cm−2. It is expected that the obtained results can be used to characterize the properties of crop leaves and that this study can contribute to the improvement of droplet retention for effective chemical application and the reduction in the environmental pollution caused by agricultural pesticides.

The effective coverage and velocity of downwash are directly related to the assemblage of spraying system and spraying effect. The downwash of the unmanned agricultural helicopter (UAH) N-3 was discussed in the paper. The computational fluid dynamics (CFD) methods were used to simulate and analyze the distribution of the downwash, and a wind field measurement device had been designed to test the downwash of UAH N-3. In the tests, the UAH N-3 was raised up to 5.0 m, 6.0 m and 7.0 m from the ground, “annular-radial-distribution- point” method was introduced, 8 directions separated by an angle of 45° (the radial direction) with the intersection point of the main rotor shaft and the ground plane as the center, 0.5 m as the step length for the longitudinal (to 2.5 m) and radial (to 4.0 m) direction to set the sample points, considering the range of the rotor rotating circular area mainly. The 5 m height results of N-3 were fully discussed to describe the downwash distribution with the longitudinal altitude increased and the radial distance increased. The standard deviations of five test altitudes for eight directions were comparatively analyzed, the results showed that the total standard deviation was not greater than 0.6 m/s. The overall relative maximum margin of error calculated from the simulation and measurement data was between 0.6 and 0.7, which verified the credibility of the simulation data. High-order polynomials were used to fitting the simulation and measurement data, the fitting results showed that the polynomial coefficient of determination R2 met or exceeded 0.75 when the altitudes were more than 1 m, indicating the fit equation having the reference values. When the altitudes equal or less than 0.5 m, the polynomial coefficient of determination R2 was smaller, ranging during 0.3 to 0.7. The study would provide some foundations for the optimization of the assemblage of spraying system on the single-rotor UAH, which would promote China aviation plant protection. Keywords: unmanned agricultural helicopter, single rotor, CFD simulation, downwash distribution, spraying effect DOI: 10.25165/j.ijabe.20171005.3079 Citation: Zhang S C, Xue X Y, Sun Z, Zhou L X, Jin Y K. Downwash distribution of single-rotor unmanned agricultural helicopter on hovering state. Int J Agric & Biol Eng, 2017; 10(5): 14–24.