Method and system for predicting soil moisture uniformity of fixed sprinkling irrigation system based on dimensional analysis

Abstract

The invention discloses a method and a system for predicting the soil moisture uniformity of a fixed sprinkling irrigation system based on dimensional analysis. The method comprises the following steps: selecting a plurality of physical quantities from nozzle hydraulic performance indexes and soil hydraulic parameters; based on the physical quantity, a plurality of dimensionless pi terms are obtained by using a pi theorem method of dimensional analysis; establishing a function relationship between the soil moisture uniformity and the nozzle hydraulic performance index and the soil hydraulic parameter; constructing a soil moisture migration numerical model of the fixed sprinkling irrigation system; designing an orthogonal test, and quantitatively obtaining the soil moisture content under various sprinkling irrigation working conditions through a numerical model; carrying out multivariate nonlinear regression of the soil moisture uniformity and the physical quantity to obtain empirical coefficients and fitting indexes of all items, and determining a prediction model of the spray irrigation soil moisture uniformity; and predicting the moisture uniformity of the spray irrigation soil based on the prediction model. According to the invention, the water uniformity of the spray irrigation soil can be simulated through common soil hydraulic parameters and nozzle hydraulic performance indexes.

Description

Technical Field

[0001] The invention belongs to the technical field of soil moisture migration in sprinkler irrigation, and in particular relates to a method and system for predicting soil moisture uniformity in a fixed sprinkler irrigation system based on dimensional analysis. Background Art

[0002] The uniformity of a fixed sprinkler irrigation system is measured by placing rain gauges in the spraying area. Rain gauges mainly collect ground water, and the calculated uniformity represents the uniformity of ground water distribution. Crops mainly rely on their roots to absorb water from the soil, and their growth and development process is more directly affected by groundwater distribution. Therefore, it is more important to explore the groundwater distribution of sprinkler irrigation than the surface water distribution.

[0003] Previous studies have found that even if the ground uniformity is less than 70%, the soil moisture uniformity can exceed 90%, indicating that the soil moisture distribution under sprinkler irrigation conditions is indeed more uniform than the surface water distribution. However, in actual engineering design, the redistribution capacity of sprinkler irrigation water in the soil is rarely considered. The qualification of the sprinkler irrigation system is judged only based on the uniformity of the ground water distribution, resulting in the actual irrigation effect of the sprinkler irrigation project being seriously underestimated, which unnecessarily increases the system investment cost. The reason is that previous studies were all based on reasoning and qualitative analysis of test results, and did not give a quantitative relationship between the sprinkler surface water distribution and the groundwater distribution.

[0004] Therefore, it is of great engineering significance to construct a soil moisture uniformity prediction method for a fixed sprinkler irrigation system based on dimensional analysis and accurately calculate the sprinkler soil moisture uniformity through known sprinkler hydraulic performance parameters and soil hydraulic parameters. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention proposes a soil moisture uniformity prediction method and system for a fixed sprinkler irrigation system based on dimensional analysis, which achieves the goal of simulating the uniformity of soil moisture in sprinkler irrigation through common soil hydraulic parameters and sprinkler hydraulic performance indicators, and solves the problems of inconvenience of manual measurement and high cost of arranging sensor tests.

[0006] To achieve the above object, the present invention provides the following solutions:

[0007] A method for predicting soil moisture uniformity of a fixed sprinkler irrigation system based on dimensional analysis comprises the following steps:

[0008] Select several physical quantities from the sprinkler hydraulic performance index and soil hydraulic parameters, where the physical quantities include: soil matrix potential |Ψ|, saturated hydraulic conductivity K s , total flow rate Q in the spraying area, irrigation time t i , water migration time t m , sprinkler irrigation ground uniformity CUg ;

[0009] Based on the physical quantity, using the π theorem method of dimensional analysis, several dimensionless π terms are obtained;

[0010] Based on the dimensionless π term, the sprinkler irrigation soil moisture uniformity CU is established s Functional relationship with sprinkler hydraulic performance index and soil hydraulic parameters;

[0011] Based on the functional relationship, a three-dimensional numerical model of soil moisture migration in a fixed sprinkler irrigation system is constructed;

[0012] Design an orthogonal experiment to quantitatively obtain soil moisture content under various sprinkler irrigation conditions through a three-dimensional numerical model of soil moisture migration in a fixed sprinkler irrigation system;

[0013] Based on the soil moisture content under various sprinkler irrigation conditions, the sprinkler irrigation soil moisture uniformity CU was carried out. s and soil matrix potential |Ψ|, saturated hydraulic conductivity K s , total flow rate Q in the spraying area, irrigation time t i , water migration time t m and sprinkler irrigation ground uniformity CU g The multivariate nonlinear regression was used to obtain the empirical coefficients and the fitting index of each item, and the uniformity of soil moisture CU in the fixed sprinkler irrigation system was determined. s prediction models;

[0014] Based on the prediction model, the soil moisture uniformity CU of the fixed sprinkler irrigation system is calculated. s Make predictions.

[0015] Preferably, based on the physical quantity, using the π theorem of dimensional analysis, a method for obtaining several dimensionless π terms includes:

[0016] π1=CU s , π5=CU g

[0017] Among them, CU s Soil moisture uniformity for sprinkler irrigation.

[0018] Preferably, based on the dimensionless π term, the sprinkler irrigation soil moisture uniformity CU is established s Methods for functional relationships between sprinkler hydraulic performance indicators and soil hydraulic parameters include:

[0019]

[0020] Among them, λ is the empirical coefficient; η1, η2…η4 are fitting indexes.

[0021] Preferably, based on the functional relationship, the method for constructing a three-dimensional numerical model of soil moisture migration in a fixed sprinkler irrigation system includes:

[0022] The sprinklers are arranged in a square shape, with a simulated area depth of 1m and a side length of The installation height of the sprinkler is 1.7m. The rain gauges are arranged radially on three rays drawn from the sprinkler. The distance between adjacent rain gauges is 0.5m, and the angle between radial lines is 30°. After the test, the water volume measured by the rain gauges at the same distance from the sprinkler is averaged to calculate the sprinkler irrigation intensity along the range direction.

[0023] The sixth-order polynomial based on the least square method is used to fit the sprinkler intensity value along the range direction to obtain the radial water distribution curve of the sprinkler head.

[0024] Import the radial water distribution curve into Surfer software to obtain the grid-shaped water distribution in the superposition area;

[0025] Based on the grid-like water distribution, the irrigation time is set through a step function;

[0026] The upper surface boundary condition is set as the atmospheric boundary, and during the irrigation period, it is a non-uniform precipitation boundary and an evaporation boundary that does not change with time. During the non-irrigation period, only evaporation exists on the upper surface boundary.

[0027] Set the bottom boundary to a free drainage boundary and the side boundaries to zero flux boundaries;

[0028] The free tetrahedral mesh is used to set the numerical calculation domain, and the local mesh is encrypted in the area near the geometric vertices. The mesh size is "extremely fine" and the average mesh size is 1.4×10 -3 m;

[0029] The designed simulation duration is 72 hours and the time step is 1 hour.

[0030] Preferably, the orthogonal test includes three factors: spraying uniformity, soil texture and initial soil moisture content, and 6 spraying uniformities are set: 46.3%, 81.9%, 35.2%, 57.1%, 65.2% and 74.0%, 3 soil textures: clay loam, silty clay and loam; 3 initial soil moisture contents: 55%, 65% and 75% of field water holding capacity.

[0031] Preferably, the prediction model is:

[0032] R 2 =0.855;

[0033] Among them, R 2 is the degree of fit.

[0034] The present invention also provides a soil moisture uniformity prediction system for a fixed sprinkler irrigation system based on dimensional analysis, characterized in that it comprises: a selection module, a first calculation module, a first construction module, a second construction module, a second calculation module, a third construction module and a prediction module;

[0035] The selection module is used to select several physical quantities from the sprinkler hydraulic performance index and soil hydraulic parameters, wherein the physical quantities include: soil matrix potential |Ψ|, saturated hydraulic conductivity K s , total flow rate Q in the spraying area, irrigation time t i , water migration time t m , sprinkler irrigation ground uniformity CU g ;

[0036] The first calculation module is used to obtain a plurality of dimensionless π terms based on the physical quantity using the π theorem of dimensional analysis;

[0037] The first building block is used to establish the sprinkler irrigation soil moisture uniformity CU based on the dimensionless π term. s Functional relationship with sprinkler hydraulic performance index and soil hydraulic parameters;

[0038] The second construction module is used to construct a three-dimensional numerical model of soil moisture migration in a fixed sprinkler irrigation system based on the functional relationship;

[0039] The second calculation module is used to design an orthogonal experiment to quantitatively obtain the soil moisture content under various sprinkler irrigation conditions through a three-dimensional numerical model of soil moisture migration in a fixed sprinkler irrigation system;

[0040] The third building block is used to carry out sprinkler irrigation soil moisture uniformity CU based on the soil moisture content under the multiple sprinkler irrigation conditions. s and soil matrix potential |Ψ|, saturated hydraulic conductivity K s , total flow rate Q in the spraying area, irrigation time t i , water migration time t m and sprinkler irrigation ground uniformity CU g The multivariate nonlinear regression was used to obtain the empirical coefficients and the fitting index of each item, and the uniformity of soil moisture CU in the fixed sprinkler irrigation system was determined. s prediction models;

[0041] The prediction module is used to predict the soil moisture uniformity CU in the fixed sprinkler irrigation system based on the prediction model. s Make predictions.

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] 1. The present invention proposes a method for predicting soil moisture uniformity of a fixed sprinkler irrigation system based on dimensional analysis. The method can calculate the uniformity of soil moisture in sprinkler irrigation through sprinkler irrigation hydraulic performance indicators and soil hydraulic parameters, and clarify the redistribution of soil moisture.

[0044] 2. Soil moisture uniformity CU in the fixed sprinkler irrigation system proposed by the present invention s The prediction model can quantitatively analyze the effects of soil texture, initial soil moisture content, irrigation duration, water migration duration and sprinkler surface uniformity on sprinkler soil moisture uniformity, providing a basis for engineering design.

[0045] 3. Compared with the existing methods for obtaining soil moisture uniformity: most of them are obtained through soil moisture sensors or manual measurement, which are costly and inconvenient to promote; the present invention is based on dimensional analysis, realizes the accurate simulation of sprinkler soil moisture uniformity, and greatly reduces the test cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] In order to more clearly illustrate the technical solution of the present invention, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0047] Figure 1 This is a flow chart of a method for predicting soil moisture uniformity of a fixed sprinkler irrigation system based on dimensional analysis according to an embodiment of the present invention;

[0048] Figure 2 A schematic diagram of a COMSOL-3D numerical model of an embodiment of the present invention;

[0049] Figure 3 CU of the embodiment of the present invention s Measured value (COMSOL-3D simulation) and CU s Comparison chart of predicted values ​​(dimensional analysis model). DETAILED DESCRIPTION

[0050] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0051] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0052] Embodiment 1

[0053] like Figure 1 As shown, this embodiment proposes a method for predicting soil moisture uniformity of a fixed sprinkler irrigation system based on dimensional analysis, comprising the following steps:

[0054] S1, determine the parameter to be predicted as the sprinkler soil moisture uniformity CU s , six physical quantities are selected from the sprinkler hydraulic performance indicators and soil hydraulic parameters, the six physical quantities are soil matrix potential |Ψ|, saturated hydraulic conductivity K s , total flow rate Q in the spraying area, irrigation time t i , water migration time t m and sprinkler irrigation ground uniformity CU g . List CU s The solution equation is shown in formula (1);

[0055] F(CU s ,ψ,K s ,Q,t i ,t m ,CU g )=0 (1)

[0056] S2, select two basic dimensions: soil matrix potential |Ψ| and saturated hydraulic conductivity K s , |Ψ| and K s are geometric and kinematic quantities, respectively, with dimensions [L] and [L·T -1 ];

[0057] S3, according to the π theorem of dimensional analysis, we get 5 dimensionless π terms: π1=CU s , and π5=CU g (CU s and CU g dimensionless, as π1 and π5 respectively);

[0058] S4, establish soil moisture uniformity CU s The functional relationship between the sprinkler hydraulic performance index and soil hydraulic parameters is shown in formula (2):

[0059]

[0060] Among them, λ is the empirical coefficient; η1, η2…η4 are fitting indexes;

[0061] S5, construct a three-dimensional numerical model of soil water movement in a fixed sprinkler irrigation system based on COMSOL 6.1 software;

[0062] S6, design an orthogonal experiment to quantitatively obtain the soil moisture content under various sprinkler irrigation conditions through a three-dimensional numerical model of soil moisture migration in a fixed sprinkler irrigation system;

[0063] S7, CU was carried out using SPSS25.0 s and |Ψ|, K s , Q, t i ,t m and CU g The multivariate nonlinear regression was used to obtain the empirical coefficient λ and the fitting index (η1, η2…η8) of each item to determine the CU in the fixed sprinkler irrigation system. s The prediction model is as follows:

[0064]

[0065] Simplifying formula (4),

[0066]

[0067] Among them, R 2 is the fitting degree of formula (3).

[0068] In this embodiment, in step S1, the units and dimensions of the sprinkler irrigation hydraulic performance index and the soil hydraulic parameter are respectively |Ψ| (unit m, dimension [L]), K s (Unit: mm·h -1 , dimension [L·T -1 ]), Q (unit: m 3 ·h -1 , dimension [L 3 ·T -1 ]),t i (unit h, dimension [T]), t m (unit h, dimension [T]) and CU g (Unit: %, dimensionless).

[0069] In this embodiment, the saturated hydraulic conductivity K involved in step S2 s Three types of soil are involved, and the soil physical properties and hydraulic parameters are shown in Table 1.

[0070] Table 1

[0071]

[0072]

[0073] In this embodiment, in step S5, the three-dimensional numerical model of soil moisture migration in the fixed sprinkler irrigation system is arranged in a square, the simulation area depth is 1m, and the side length is The installation height of the sprinkler is 1.7m. The rain gauges are arranged radially on three rays drawn from the sprinkler. The distance between adjacent rain gauges is 0.5m, and the angle between radial lines is 30°. After the test, the water volume measured by the rain gauges at the same distance from the sprinkler is averaged, and the sprinkler irrigation intensity along the range direction of the sprinkler is calculated by formula (5).

[0074]

[0075] I RG is the sprinkler irrigation intensity of a single rain gauge, mm / h; The average water volume of three rain gauges at the same distance from the sprinkler head, cm 3 ; A RG is the water receiving area of ​​a single rain gauge, cm 2 ; t is the spraying time of the nozzle, h.

[0076] The sixth-order polynomial based on the least squares method is used to fit the sprinkler intensity values ​​along the range direction to obtain the radial water distribution curve of the sprinkler. The radial water distribution curve is imported into the Surfer software to obtain the grid-shaped water distribution P(x, y, H, d, t) in the superposition area. Among them, P(x, y, H, d, t) is the sprinkler intensity at any point (x, y) in the superposition area at time t under different working pressures H and nozzle diameters d, mm / h.

[0077] Set the watering time via a step function.

[0078]

[0079] The upper surface boundary condition is set as the atmospheric boundary. During the irrigation period, it is a non-uniform precipitation boundary and an evaporation boundary that does not change with time. During the non-irrigation period, only evaporation exists on the upper surface boundary. The bottom boundary is set as a free drainage boundary, and the side boundary is set as a zero flux boundary. The free tetrahedral mesh is used to set the numerical calculation domain. The local mesh is encrypted in the area near the geometric vertices. The mesh size is "very fine" and the average mesh size is 1.4×10 -3 m. The design simulation duration is 72 hours and the time step is 1 hour. Figure 2 .

[0080] In this embodiment, in step S6, the orthogonal test includes three factors: spraying uniformity, soil texture, and initial soil moisture content. Six types of sprinkler uniformity (46.3%, 81.9%, 35.2%, 57.1%, 65.2%, and 74.0%), three types of soil texture (clay loam, silty clay, and loam), and three types of initial soil moisture content (55, 65, and 75% of field water holding capacity) are set respectively. The 18 groups of orthogonal test simulation parameters are shown in Table 2.

[0081] Table 2

[0082]

[0083] The six types of sprinkler irrigation uniformity are generated by three types of sprinkler heads under different working conditions. The working conditions of each group of sprinkler heads are shown in Table 3.

[0084] Table 3

[0085]

[0086] The initial soil moisture content and soil matrix potential are different expressions of the same physical quantity. In the field of soil infiltration, the initial soil moisture content can be converted into soil matrix potential by the following formula. The results are shown in Table 2.

[0087]

[0088]

[0089] Where θ(h) is the volumetric water content function related to soil suction value, cm 3 cm -3 ; h is soil matrix potential, m; θ is soil volume water content, cm 3 cm -3 θ r is the residual moisture content of soil, cm 3 cm -3 θ s is the saturated moisture content of soil, cm 3 cm -3 ; α is an empirical parameter, equal to the inverse of the intake suction value, cm -1 , n and m are the shape coefficients of the VG curve; S e is the effective soil moisture content, 0 e <1; l is the porosity correlation parameter, which is generally taken as 0.5; K(h) is the unsaturated hydraulic conductivity of soil, mm / h.

[0090] The irrigation time t i The results are shown in Table 2.

[0091] W=γ·h w ·A·(θ max -θ0)

[0092]

[0093] Where W is the amount of sprinkler irrigation water, m 3 ; γ is soil bulk density, kg·m -3 ; h is the planned wet layer depth, 0.8m; A is the spraying area, m 2 θ max ​The upper limit of suitable moisture content is %, which is taken as 85%θ f θ f is the field water holding capacity, %; θ0 is the initial water content, %; is the average sprinkler intensity, mm·h -1 .

[0094] The total flow rate (irrigation volume) Q of the spraying area is calculated by the following formula.

[0095]

[0096] The water migration time t m The calculation starts from the end of irrigation, the infiltration time is uniformly set to 48 hours, and CU is calculated every 12 hours. s .

[0097] Finally, through the above steps S1 to S7, the predicted value of soil moisture uniformity of the fixed sprinkler irrigation system based on dimensional analysis is obtained, see Figure 3 The NSE between the predicted value and the measured value is 0.886, MAE is 2.774, NRMSE is 0.040, and RMSE is 3.277%. From the perspective of confidence band width, as CU s The increase of Figure 3 The discreteness of the data points in the model first decreases and then increases. However, in general, all data points are roughly evenly distributed near the 1:1 line, and the simulated values ​​are close to the measured values, indicating that the model has a good prediction effect.

[0098] Embodiment 2

[0099] The present invention also provides a soil moisture uniformity prediction system for a fixed sprinkler irrigation system based on dimensional analysis, characterized in that it comprises: a selection module, a first calculation module, a first construction module, a second construction module, a second calculation module, a third construction module and a prediction module;

[0100] The selection module is used to select several physical quantities from the sprinkler hydraulic performance indicators and soil hydraulic parameters, where the physical quantities include: soil matrix potential |Ψ|, saturated hydraulic conductivity K s , total flow rate Q in the spraying area, irrigation time t i , water migration time t m , sprinkler irrigation ground uniformity CU g ;

[0101] The first calculation module is used to obtain a plurality of dimensionless π terms based on the physical quantity using the π theorem of dimensional analysis;

[0102] The first building block is used to establish the sprinkler irrigation soil moisture uniformity CU based on the dimensionless π term sFunctional relationship with sprinkler hydraulic performance index and soil hydraulic parameters;

[0103] The second construction module is used to construct a three-dimensional numerical model of soil moisture migration in a fixed sprinkler irrigation system based on the functional relationship;

[0104] The second calculation module is used to design orthogonal experiments and quantitatively obtain soil moisture content under various sprinkler irrigation conditions through a three-dimensional numerical model of soil moisture migration in a fixed sprinkler irrigation system;

[0105] The third building block is used to carry out the sprinkler irrigation soil moisture uniformity CU based on the soil moisture content under the multiple sprinkler irrigation conditions. s and soil matrix potential |Ψ|, saturated hydraulic conductivity K s , total flow rate Q in the spraying area, irrigation time t i , water migration time t m and sprinkler irrigation ground uniformity CU g The multivariate nonlinear regression was used to obtain the empirical coefficients and the fitting index of each item, and the uniformity of soil moisture CU in the fixed sprinkler irrigation system was determined. s prediction models;

[0106] The prediction module is used to predict the soil moisture uniformity CU in the fixed sprinkler irrigation system based on the prediction model. s Make predictions.

[0107] The embodiments described above are only descriptions of the preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for predicting soil moisture uniformity in a fixed sprinkler irrigation system based on dimensional analysis, characterized in that: The following steps are involved: Select several physical quantities from the sprinkler hydraulic performance index and soil hydraulic parameters, where the physical quantities include: soil matrix potential |Ψ|, saturated hydraulic conductivity K s , total flow rate Q in the spraying area, irrigation time t i , water migration time t m , sprinkler irrigation ground uniformity CU g ; Based on the physical quantity, using the π theorem method of dimensional analysis, several dimensionless π terms are obtained; Based on the dimensionless π term, the sprinkler irrigation soil moisture uniformity CU is established s Functional relationship with sprinkler hydraulic performance index and soil hydraulic parameters; Based on the functional relationship, a three-dimensional numerical model of soil moisture migration in a fixed sprinkler irrigation system is constructed; Design an orthogonal experiment to quantitatively obtain soil moisture content under various sprinkler irrigation conditions through a three-dimensional numerical model of soil moisture migration in a fixed sprinkler irrigation system; Based on the soil moisture content under various sprinkler irrigation conditions, the sprinkler irrigation soil moisture uniformity CU was carried out. s and soil matrix potential |Ψ|, saturated hydraulic conductivity K s , total flow rate Q in the spraying area, irrigation time t i , water migration time t m and sprinkler irrigation ground uniformity CU g The multivariate nonlinear regression was used to obtain the empirical coefficients and the fitting index of each item, and the uniformity of soil moisture CU in the fixed sprinkler irrigation system was determined. s prediction models; Based on the prediction model, the soil moisture uniformity CU of the fixed sprinkler irrigation system is calculated. s Make predictions.

2. The method for predicting soil moisture uniformity of a fixed sprinkler irrigation system based on dimensional analysis according to claim 1 is characterized in that: Based on the physical quantity, using the π theorem of dimensional analysis, methods for obtaining several dimensionless π terms include: Among them, CU s Soil moisture uniformity for sprinkler irrigation.

3. The method for predicting soil moisture uniformity of a fixed sprinkler irrigation system based on dimensional analysis according to claim 1 is characterized in that: Based on the dimensionless π term, the sprinkler irrigation soil moisture uniformity CU is established s Methods for functional relationships between sprinkler hydraulic performance indicators and soil hydraulic parameters include: Among them, λ is the empirical coefficient; η1, η2…η4 are fitting indexes.

4. The method for predicting soil moisture uniformity of a fixed sprinkler irrigation system based on dimensional analysis according to claim 1, characterized in that: Based on the functional relationship, the method for constructing a three-dimensional numerical model of soil moisture migration in a fixed sprinkler irrigation system includes: The sprinklers are arranged in a square shape, with a simulated area depth of 1m and a side length of The installation height of the sprinkler is 1.7m. The rain gauges are arranged radially on three rays drawn from the sprinkler. The distance between adjacent rain gauges is 0.5m, and the angle between radial lines is 30°. After the test, the water volume measured by the rain gauges at the same distance from the sprinkler is averaged to calculate the sprinkler irrigation intensity along the range direction. The sixth-order polynomial based on the least square method is used to fit the sprinkler intensity value along the range direction to obtain the radial water distribution curve of the sprinkler head. Import the radial water distribution curve into Surfer software to obtain the grid-shaped water distribution in the superposition area; Based on the grid-like water distribution, the irrigation time is set through a step function; The upper surface boundary condition is set as the atmospheric boundary, and during the irrigation period, it is a non-uniform precipitation boundary and an evaporation boundary that does not change with time. During the non-irrigation period, only evaporation exists on the upper surface boundary. Set the bottom boundary to a free drainage boundary and the side boundaries to zero flux boundaries; The free tetrahedron mesh is used to set the numerical calculation domain, and the local mesh is encrypted in the area near the geometric vertices. The mesh size is "extremely fine" and the average mesh size is 1.4×10 -3 m; The designed simulation duration is 72 hours and the time step is 1 hour.

5. The method for predicting soil moisture uniformity of a fixed sprinkler irrigation system based on dimensional analysis according to claim 1, characterized in that: The orthogonal experiment includes three factors: spraying uniformity, soil texture and initial soil moisture content. Six spraying uniformities are set: 46.3%, 81.9%, 35.2%, 57.1%, 65.2% and 74.0%, three soil textures: clay loam, silty clay and loam; and three initial soil moisture contents: 55%, 65% and 75% of field water holding capacity.

6. The method for predicting soil moisture uniformity of a fixed sprinkler irrigation system based on dimensional analysis according to claim 1, characterized in that: The prediction model is: Among them, R 2 is the degree of fit.

7. A soil moisture uniformity prediction system for a fixed sprinkler irrigation system based on dimensional analysis, characterized in that: include: A selection module, a first calculation module, a first construction module, a second construction module, a second calculation module, a third construction module and a prediction module; The selection module is used to select several physical quantities from the sprinkler hydraulic performance index and soil hydraulic parameters, wherein the physical quantities include: soil matrix potential |Ψ|, saturated hydraulic conductivity K s , total flow rate Q in the spraying area, irrigation time t i , water migration time t m , sprinkler irrigation ground uniformity CU g ; The first calculation module is used to obtain a plurality of dimensionless π terms based on the physical quantity using the π theorem of dimensional analysis; The first building block is used to establish the sprinkler irrigation soil moisture uniformity CU based on the dimensionless π term. s Functional relationship with sprinkler hydraulic performance index and soil hydraulic parameters; The second construction module is used to construct a three-dimensional numerical model of soil moisture migration in a fixed sprinkler irrigation system based on the functional relationship; The second calculation module is used to design an orthogonal experiment to quantitatively obtain the soil moisture content under various sprinkler irrigation conditions through a three-dimensional numerical model of soil moisture migration in a fixed sprinkler irrigation system; The third building block is used to carry out sprinkler irrigation soil moisture uniformity CU based on the soil moisture content under the multiple sprinkler irrigation conditions. s and soil matrix potential |Ψ|, saturated hydraulic conductivity K s , total flow rate Q in the spraying area, irrigation time t i , water migration time t m and sprinkler irrigation ground uniformity CU g The multivariate nonlinear regression was used to obtain the empirical coefficients and the fitting index of each item, and the uniformity of soil moisture CU in the fixed sprinkler irrigation system was determined. s prediction models; The prediction module is used to predict the soil moisture uniformity CU in the fixed sprinkler irrigation system based on the prediction model. s Make predictions.

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