间歇和连续喷灌下土壤水分运动特征COMSOL数值模拟与验证

为探明间歇喷灌和连续喷灌条件下的土壤水分运动规律，建立喷灌随时间变化的非均匀灌水边界下的土壤水分二维运动模型，借助COMSOL数值模拟软件，实现模型的求解，并通过土箱试验对模型进行验证，分析不同喷灌模式下土壤水分运动特征，评估喷灌均匀性和喷灌模式对土壤含水率均匀性的影响。结果表明，土壤含水率和土壤湿润峰模拟值与实测值之间的一致性较好。喷灌模式对土壤水分运动过程和含水率均匀度影响不大。随着间歇次数和间歇时长的增加，喷灌结束时表层土壤含水率减小、水分入渗深度增加。喷灌条件下，土壤含水率均匀度高于地表测得的喷灌均匀度。当喷灌均匀度为39.77%～80.15%时，土壤含水率均匀度为88.57%～94.47%。当喷灌均匀度较低、点喷灌强度较高、总灌水量较大时，采用间歇喷灌、增加间隙次数和总间歇时长，可以一定程度降低地表径流和深层渗漏风险、改善土壤含水率均匀性。研究可为喷灌系统设计均匀度合理取值和高效运行提供理论基础。

COMSOL numerical simulations and experiments of soil water movement under intermittent and continuous sprinkler irrigation

Soil water movement can greatly contribute to the water flow with the soil profile in the engineering of sprinkler irrigation. In this study, a numerical simulation was proposed to explore the soil water movement under intermittent and continuous sprinkler irrigation using COMSOL software. The time variable and non-uniform infiltration boundary conditions were also utilized in the sprinkler irrigation. A series of experiments on soil tanks were conducted to validate the accuracy of the simulation. A comparison was made on the simulated and measured parameters, including the soil water content and downward vertical wetting front. Finally, a systematic investigation was applied to evaluate the effects of sprinkler irrigation and irrigation uniformity on soil wetting and soil water content. Sprinkler irrigation was verified by four patterns (continuous, intermittent 1, 2, and 3) and three uniformity coefficients of sprinkler irrigation (39.77%, 59.87% and 80.15%). The results showed that the COMSOL simulation was used to accurately simulate the soil wetting patterns in sprinkler irrigation. The root mean square error and the coefficient of residual mean square error values were less than 0.014 and 0.017 cm³/cm³, respectively, between the calculated and measured soil water contents at 72 h after the sprinkler irrigation. The coefficient of determination R² value was higher than 0.961. There were higher movement speeds of the soil wetting front and the soil water contents of the wetted zone from 0 to 12 h after the irrigation, indicating the slow-down trending, as time passed. There were no significant effects of sprinkler irrigation patterns on soil water movement and soil water content uniformity. The water content of surface soil decreased, as the intermittent frequency and duration increased, while the water infiltration depth increased after the sprinkler irrigation. Meanwhile, the soil water content decreased with the increasing intermittent frequency and duration at 72 h after the end of irrigation. Christiansen uniformity coefficient was used to evaluate the uniformity of soil water content after simulation. The soil water content uniformity coefficient was higher than the uniformity coefficients of sprinkler irrigation, according to the initial surface-measured distribution. The soil water content uniformity coefficient of shallow-layer soil increased, as time passed, while that of the deeper-layer soil decreased. The soil water content uniformity coefficient at the soil depth of 10 cm was selected to represent the uniformity of soil water content. The soil water content uniformity coefficient increased with the increasing uniformity coefficients of sprinkler irrigation. Furthermore, the soil water content uniformity coefficient values were 88%-90% under the continuous and three intermittent sprinkler irrigations, when the uniformity coefficients of sprinkler irrigation ranged from 40% to 60%. Once the uniformity coefficients of sprinkler irrigation increased to 80%, the soil water content uniformity coefficient values increased higher than 94%. The research space was provided to reasonably reduce the design uniformity coefficients of sprinkler irrigation in sprinkler irrigation. In the low uniformity of sprinkler irrigation, there were high rates of peak water application and a large total irrigation amount using intermittent sprinkler irrigation. The intermittent frequency and duration can be expected to reduce the risk of surface runoff and deep percolation, thus improving the uniformity of soil water content.