Chao Chen

In sprinkler irrigation systems in hilly areas, pressure-regulating devices can improve the uneven pressure distribution on branch pipes and consequently improve the irrigation uniformity. A pressure-regulating device for sprinkler irrigation systems was developed; the variation characteristics of the internal pressure field and velocity field distribution over time, variation law of the elastic diaphragm of the pressure-regulating device with respect to the inlet pressure, and pressure-regulating and flow stabilizing mechanisms were assessed. The results show that the pressure regulation and flow stabilization of the pressure-regulating device were affected by the deformation of the elastic diaphragm. When the elastic diaphragm deforms, the main factors of pressure regulation and flow stabilization in the pressure regulation device gradually shift from the side channel and compensation chamber to the side channel and secondary channel. The channel structure plays a crucial role in the entire fluid system. A comparison and analysis of the changes in cross-sectional pressure and flow velocity of the flow channel under different inlet pressures revealed that increasing the height of the side flow channel baffle and auxiliary flow channel effectively improved the pressure-regulating and flow-stabilizing performance of the pressure-regulating device. The results can be useful to optimize the structure of pressure regulation devices and to solve the problem of excessive pressure deviation in sprinkler irrigation systems in hilly areas.

Multistage pumps are essential in emergency water supply, irrigation, and other systems undergoing unavoidable hydraulic transitions like pump startup and valve operations. These transitions cause rapid changes in impeller speed, flow rate, and pressure, destabilizing the internal flow field and impacting system reliability. To study transient flow characteristics, a numerical analysis of a three-stage pump was conducted, focusing on vortex identification, entropy production, and time–frequency pressure pulsation. Using the SST turbulence model, the simulation analyzed different start times and flow rate variations. Findings revealed that shorter startup times intensified transient effects, with the head increasing rapidly initially and then stabilizing. Vortex structures showed periodic development and dissipation. Entropy production rose with impeller speed, peaking higher with shorter startups. Blade passing frequency dominated pressure pulsations, with increased low-frequency pulsations as speed rose. During valve opening, flow stabilization accelerated with increasing flow rates, reducing amplitude and eliminating low-frequency components. This research aids the reliable operation of high-pressure pumping systems in energy storage.

To solve the problem of non-destructive crop water content of detection under outdoor conditions, we propose a method to predict lettuce canopy water content by collecting outdoor hyperspectral images of potted lettuce plants and combining spectral analysis techniques and model training methods. Firstly, background noise was removed by correlation segmentation, proposed in this paper, whereby light intensity correction is performed on the segmented lettuce canopy images. We then chose the first derivative combined with mean centering (MC) to preprocess the raw spectral data. Hereafter, feature bands were screened by a combination of Monte Carlo uninformative variable elimination (MCUVE) and competitive adaptive reweighting sampling (CARS) to eliminate redundant information. Finally, a lettuce canopy moisture prediction model was constructed by combining partial least squares (PLS). The correlation coefficient between model predicted and measured values was used as the main model performance evaluation index, and the modeling set correlation coefficient R_c was 82.71%, while the prediction set correlation coefficient R_P was 84.67%. The water content of each lettuce canopy pixel was calculated by the constructed model, and the visualized lettuce water distribution map was generated by pseudo-color image processing, which finally revealed a visualization of the water content of the lettuce canopy leaves under outdoor conditions. This study extends the hyperspectral image prediction possibilities of lettuce canopy water content under outdoor conditions.

The frequency and duration of drive spoon–dispersed water jet directly influence the water distribution pattern and, further, affect water distribution uniformity. A mathematical model for calculating the duration was established, and an experiment was carried out to verify the accuracy of the theory by using high-speed photography (HSP) technique. Another important component of the investigation was the influence of frequency and duration on the water distribution pattern and water distribution uniformity. The results showed that the frequency of drive spoon–dispersed water jet increased and the duration time decreased with increased working pressure and decreased distance between counterweight-installed position and rotation axis. The calculated values of the theory were greater than the measured values. Differences between the measured and predicted values decreased with increased working pressure, and the average difference decreased to 2.98% when the working pressure increased to 0.40 MPa. The application rates within 1–13 m improved and increased about 50% by decreasing the distance from 135 mm to 80 mm. The maximum application rates decreased from 10.3 to 9.2 mm h⁻¹, 9.5 to 8.8 mm h⁻¹, and 8.4 to 7.9 mm h⁻¹ with a working pressure of 0.30, 0.35, and 0.40 MPa, respectively. The Christiansen’s uniformity coefficient (CU) values decreased by increasing the distance between the counterweight and the rotation axis. The maximum CU values were obtained at the spacing coefficient of 1.2, 1.2, and 1.1 for 0.30, 0.35, and 0.40 MPa, respectively. By decreasing the distance from 135 mm to 80 mm, the maximum CU values increased from 58.96% to 75.1%, 68.85% to 80.1%, and 72.46% to 82.17% for 0.30, 0.35, and 0.40 MPa, respectively.

To overcome the problem of poor uniformity of solid-fertilizer-dissolving devices due to lag of fertilizer dissolution, a closed-loop control system based on fuzzy proportional-integral-derivative (PID) was designed and tested. A fertilizer concentration regulation model was then established according to the results. In this system, the control core was an STM32 used to feed back the fertilization concentration by detecting the electrical conductivity. For real-time adjustment of the fertilizer flow rate and water flow rate, a fuzzy PID control algorithm was utilized to compare the detected concentrations with the set concentrations. The linear relationships between quantities such as the fertilizer rate and PWM frequency, water flow rate and PWM duty ratio of the direct-current pump, and fertilizer concentration and electrical conductivity were all established to calibrate the system. The influence of the fertilizer flow rate and water flow rate on fertilizer concentration was determined by the control variable test method. The results showed a positive linear relationship between fertilizer concentration and fertilizer flow rate, while a reverse linear relationship was established between fertilizer concentration and water flow rate. After the introduction of the control system into the self-developed solid-fertilizer-dissolving device, the fertilizer concentration fluctuated near the set concentration in a range of no more than 1 g/L. After the disturbance of the fertilization device, the control system fine-tuned the device with a steady-state error of about 0.55 g/L after the system reached stability. The control system designed in this study was shown to run normally with good stability, speed, and accuracy, and with improved fertilization uniformity of the solid-fertilizer-dissolving device. This study lays the foundation for further study of fertilization control systems. It also provides a reference for the development of precise and intelligent fertigation.

The pressurized irrigation network aims to deliver water to consumption nodes at an appropriate pressure and discharge. The traditional pipe network optimization minimizes the annual operating cost or investment per unit area. The present work establishes the traditional pipe diameter and operating frequency optimization models based on flattish terrain. It proposes a new synchronization optimization method of pipe diameter and operation frequency to find the best match point for pipe diameter and operating frequency in the branched network system. The irrigation costs of the above three models, including the energy and pipe network costs, are compared with the original irrigation network system. Based on the results of optimizing the typical experimental field, the operation frequency optimization model and the pipe diameter optimization model can save about 1.4% and 10.6% in irrigation cost, respectively. Furthermore, the synchronous optimization model can significantly reduce the irrigation cost to about 19.3%, including a 26.6% reduction in the pipe network cost and a 21.9% increase in the energy cost. Compared with pipe diameter optimization, synchronous optimization can further reduce network costs while generating lower energy costs. The results of this research can be used for the design of the network system in flattish terrain to reduce the irrigation cost.

The time and position that fertilizer takes to uniformly mix with water in an irrigation system significantly affects the development of a fertilization strategy. A pipe irrigation system was used to study the fertilizer–water mixing law in irrigation pipes using numerical simulation and experiments. The effect of the diameter of the water pipe and fertilizer pipe, water and fertilizer flow rates, concentration and viscosity of fertilizer, frequency of fertilizer injection on the mixing speed, and uniform mixing length indicated that the frequency of fertilizer injection did not affect the mixing process. The increase in the water pipe diameter and fertilizer flow rate or the decrease in fertilizer pipe and water flow rate diameter result in the increase of the speed of fertilizer solution mixing with water along the radial direction of the mixing pipe. The uniform mixing length was directly proportional to the fertilizer pipe diameter, water pipe diameter, water flow rate, and fertilizer viscosity, while it was inversely proportional to the flow rate and concentration of fertilizer. The relationship between the uniform mixing length and six influencing factors was fitted, the fitting was highly accurate, and the fitting equation can be used to predict the uniform mixing length under other conditions.

Injectors are key pieces of equipment for chemigation systems, and their hydraulic performance has a significant effect on chemigation systems and crops. In order to investigate the influence of different working parameters on hydraulic performance for a water-powered proportional injector (PI), three key parameters of inlet and injection flow rate were researched using a one-factor experimental design method. The regression equations between different factors and response variables were established through a response surface method based on one-factor experimental results. Lastly, a mathematical model of the actual injection ratio was established. Some experiments under different, randomly selected parameter combinations were carried out to verify the prediction precision of the mathematical mode. The results showed that the injection flow rate increased first within the differential pressure of 0.05 to 0.10 MPa and then tended towards stability with increasing differential pressure. The injection flow rate decreased by increasing the viscosity and the change in the injection flow rate was small enough when the viscosity was greater than 500 mPa·s. The impact factors, in order of significance, for inlet flow rate were differential pressure, viscosity of injection liquid and setting injection ratio. The impact factors, in order of significance, for injection flow rate were viscosity of injection liquid, setting injection ratio and differential pressure. The regressive model for predicting the actual injection ratio was validated using an experiment and the relative deviation between calculated value and tested value was less than 5.98%, which indicated that the mathematical model had high credibility.

Solid fertilizers, which have a low operating cost, are widely applied in Chinese crop fields. In order to distribute solid fertilizer through fertigation, an innovative device with a simple structure was designed, which can feed, dissolve, and distribute fertilizer simultaneously. The parameters of the outlet pipe and fertilizer-feeding component were designed, and a preliminary equation for calculating the fertilizer-feeding flowrate was established. Then experiments were conducted to optimize the established equation. Obtained results showed that the deviation between the measured and the calculated feeding flowrate through the optimized equation was about 5%. This ensured that the fertilizer-feeding flowrate can be adjusted accurately. Experiments were also conducted to explore the effect of the working parameters on the fertilization uniformity of the designed device. It was found that as the fertilization time and inlet water flowrate increases, the fertilization uniformity increases but fertilizer concentration decreases. Based on the obtained results, it is concluded that the designed fertigation device outperforms the conventional pressure differential tank that is normally applied to distribute solid fertilizers.