Optimal flight parameters of unmanned helicopter for tea plantation frost protection

To determine proper flight parameters of an unmanned helicopter for tea plantation frost protection,field experiments were conducted to study the impact of flight height,speed and interval on airflow disturbance and temperature rise around tea canopies based on the analysis and simulation of frost protection with a certain helicopter.The relationship between temperature rise after flight and the above flight parameters was established through a regression orthogonal experiment,based on which the optimal combination of flight parameters was obtained through the single-factor golden section method.The results showed that wind speed around tea canopies decreased with the increase of flight height when flight speed was constant.There was a multivariate linear relationship between temperature rise and flight parameters,and the sequence of flight parameters’influence on frost protection effect was flight interval,flight height,flight speed.The optimal combination of flight parameters were flight height of 4.0 m,flight speed of 6.0 m/s and flight interval of 20 min.After the flight with the above parameters air temperature around tea canopies increased 1.6℃ when background thermal inversion strength was 3.8℃.

Optimal design of wind machine impeller for frost protection based on CFD and its field test on airflow disturbance

Wind machines have been increasingly applied to prevent frost damage through airflow disturbance in tea fields and orchards.An impeller is the most important component of the machine.However,there are few studies on customized impeller design or airflow disturbance performance.The objective of this study was to design a new impeller for frost protection wind machines based on reverse engineering and CFD simulation.The characteristic parameters of an impeller include blade cross-section shape,installation angle,sweep angle,hub ratio and blade number.The optimal combination of the above parameters was obtained through the simulation of the impeller’s aerodynamic performance.Field tests were conducted in a tea field to evaluate airflow disturbance performance of the designed impeller.The result shows that at a certain rotation speed and rotation diameter,the optimal combination of impeller parameters was:single arc cross-section ofϕ2400 mm,installation angle of 15°,sweep angle of 87°,hub ratio of 0.3 and blade number of 4,of which the impeller could achieve the highest usage of 0.56,the least consumed power of 1.363 kW and more uniform distribution of surface pressure on the windward side.Compared with other commercial frost protection wind machines,the maximum airflow velocity of the developed impeller was higher at 12 m in front of it.The probability of airflow velocity above 3.0 m/s within 30 min was the highest(71.7%),indicating its improvement of airflow stability.Without swing the new impeller could cover an effective area of 300 m2,which was similar to that of the commercial ones.

Small RNAs in pollen

In plants, each pollen mother cell undergoes two rounds of cell divisions to form a mature pollen grain, which contains a vegetative cell(VC) and two sperm cells(SC). As a companion cell, the VC carries the SCs to an ovule by germinating a pollen tube. In-depth sequencing analyses of mature pollen showed that micro RNAs(mi RNAs) and short interfering RNAs(si RNAs) are present in both the VC and SCs. Additionally, epigenetically-regulated transposable elements(TEs) are reactivated in the VC and these TE m RNAs are further processed into 21-nt epigenetically reactivated si RNA(easiR NA) in SCs, which prevent 24-nt si RNA accumulation and sequester mi RNA loading. Small RNAs are thought to move from the VC to SCs, where they regulate gene expression and reinforce TE silencing. Here, we summarize current knowledge of the biogenesis and function of mi RNAs, si RNAs, and easi RNAs in pollen, emphasizing how these different small RNAs coordinately contribute to sperm cell formation and TE silencing.

Comparative experiments and effectiveness evaluation on vertical blowing fans(VBF)for frost protection

Experiments were conducted to evaluate the performance of vertical blowing fans(VBF)for frost protection in a vineyard on a steep slope near Napa Valley in Northern California,USA,and a tea plantation located on undulating terrain in Zhenjiang,China.Minimum temperature comparisons from within the grape vineyard on nights with and without VBF operation with control station minimum temperatures exhibited no temperature benefit.Profile measurements from the test in China indicated that there was an increase in temperature when the VBF was first started,but that benefit was lost over time.No clear benefit from using the VBF was observed.Observation of frost deposition and thermal imagery also showed no benefit except for within about 5 m of the VBF.Based on this work,the effectiveness of the VBF for frost protection was not validated.

Control system of a performance test-bed for frost protection wind machines

To test the performance and optimize operational parameters of various frost protection wind machines,a control system of performance test-bed was designed and developed based on Programmable Logic Controller(PLC)and touch screen.The system realized automatic control of operational parameters including hydraulic platform height,impeller rotation speed,depression angle,rotation range and cycle.Field case study results shows that the control accuracy of all the parameters was achieved with the average errors of 2.11 cm for height,9.5 r/min for impeller rotation speed,0.83°for pan-tilt rotation range and 0.061 min for rotation cycle.With the control of the test-bed,the performances of various wind machines,such as the distribution of airflow and temperature,and frost protection effect,could be tested under various working conditions,which provide experiment supports for developing wind machines adapted to different conditions with higher frost protection effect.