A method and system for predicting soil moisture uniformity of a fixed sprinkler irrigation system based on dimensional analysis

Abstract

The present invention discloses a method and system for predicting the soil moisture uniformity of a fixed sprinkler irrigation system based on dimensional analysis, including: selecting several physical quantities from the hydraulic performance indexes of sprinklers and the soil hydraulic parameters; based on the physical quantities, using the π theorem method of dimensional analysis to obtain several dimensionless π terms; establishing a functional relationship between the soil moisture uniformity and the hydraulic performance indexes of sprinklers and the soil hydraulic parameters; constructing a numerical model for soil moisture movement in a fixed sprinkler irrigation system; designing an orthogonal experiment to quantitatively obtain the soil moisture content under various sprinkler irrigation conditions through the numerical model; conducting a multiple non-linear regression of the soil moisture uniformity and the physical quantities to obtain the empirical coefficients and the fitting indexes of each item, and determining the prediction model of the sprinkler irrigation soil moisture uniformity; and predicting the sprinkler irrigation soil moisture uniformity based on the prediction model. The present invention realizes the goal of simulating the sprinkler irrigation soil moisture uniformity through common soil hydraulic parameters and the hydraulic performance indexes of sprinklers.

Description

Technical Field

[0001] The present invention belongs to the technical field of soil water movement in sprinkler irrigation, and particularly relates to a method and system for predicting the soil water uniformity of a fixed sprinkler irrigation system based on dimensional analysis. Background Technique

[0002] The uniformity of a fixed sprinkler irrigation system is measured by arranging rain gauges in the sprinkling area. The rain gauges mainly collect the surface water volume, and the calculated uniformity represents the uniformity of the surface water volume distribution. However, crops mainly absorb water from the soil through their roots, and their growth and development processes are more directly affected by the distribution of subsurface water volume. Therefore, it is more important to explore the distribution of subsurface water volume in sprinkler irrigation than the distribution of surface water volume.

[0003] Previous studies have found that even when the surface uniformity is less than 70%, the soil water uniformity can exceed 90%, indicating that the soil water distribution under sprinkler irrigation is indeed more uniform than the surface water volume distribution. However, in actual engineering design, the redistribution ability of sprinkler water in the soil is rarely considered, and only the water volume distribution uniformity on the ground is used to judge whether the sprinkler irrigation system is qualified, resulting in a serious underestimation of the actual irrigation effect of the sprinkler irrigation project and an unnecessary increase in the system investment cost. The reason is that previous studies were all based on the inference and qualitative analysis of experimental results, and did not give the quantitative relationship between the surface water volume distribution and the subsurface water volume distribution in sprinkler irrigation.

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

[0005] Aiming at the deficiencies of the prior art, the present invention proposes a method and system for predicting the soil water uniformity of a fixed sprinkler irrigation system based on dimensional analysis, realizing the goal of simulating the soil water uniformity in sprinkler irrigation through common soil hydraulic parameters and nozzle hydraulic performance indicators, and solving the problems of inconvenient manual measurement and high cost of arranging sensor experiments.

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

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

[0008] Select several physical quantities from the nozzle 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 of the sprinkling area, irrigation time t i , water movement time t m , sprinkler surface uniformity CUg ;

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

[0010] Based on the dimensionless π terms, a functional relationship between the sprinkler irrigation soil moisture uniformity CU s and the sprinkler hydraulic performance index and soil hydraulic parameters is established;

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

[0012] An orthogonal experiment is designed, and the soil moisture content under various sprinkler irrigation conditions is quantitatively obtained through the three-dimensional numerical model of soil moisture movement in a fixed sprinkler irrigation system;

[0013] Based on the soil moisture content under the various sprinkler irrigation conditions, a multiple nonlinear regression of the sprinkler irrigation soil moisture uniformity CU s with the soil matrix potential |Ψ|, saturated hydraulic conductivity K s , total flow rate Q of the spraying area, irrigation time t i , moisture movement time t m and sprinkler irrigation ground uniformity CU g is carried out to obtain the empirical coefficient and the fitting index of each item, and to determine the prediction model of the sprinkler irrigation soil moisture uniformity CU s in the fixed sprinkler irrigation system;

[0014] Based on the prediction model, the sprinkler irrigation soil moisture uniformity CU s in the fixed sprinkler irrigation system is predicted.

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

[0016] π1 = CU s , π5 = CU g

[0017] where CU s is the sprinkler irrigation soil moisture uniformity.

[0018] Preferably, the method for establishing a functional relationship between the sprinkler irrigation soil moisture uniformity CU s and the sprinkler hydraulic performance index and soil hydraulic parameters includes:

[0019]

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

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

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

[0023] A sixth-degree polynomial based on the least squares method is used to fit the numerical values of the sprinkler irrigation intensity along the range direction to obtain the radial water distribution curve of the sprinkler.

[0024] The radial water distribution curve is imported into Surfer software to obtain the grid-like water distribution within the superimposed 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, which is a non-uniform precipitation boundary and evaporation boundary that does not change with time during irrigation, and only evaporation exists at the upper surface boundary during non-irrigation periods.

[0027] The bottom boundary is set as a free drainage boundary, and the side boundaries are set as zero-flux boundaries.

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

[0029] The designed simulation duration is 72 h, and the time step is 1 h.

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

[0031] Preferably, the prediction model is:

[0032] R 2 = 0.855;

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

[0034] The present invention also provides a prediction system for the soil moisture uniformity of a fixed sprinkler irrigation system based on dimensional analysis, which is characterized by comprising: 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 a number of physical quantities from the nozzle hydraulic performance indexes and soil hydraulic parameters, where the physical quantities include: soil matrix potential |Ψ|, saturated hydraulic conductivity K s , total flow rate Q of the spraying area, irrigation time t i , moisture migration time t m , sprinkler irrigation ground uniformity CU g ;

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

[0037] The first construction module is used to establish a functional relationship between the sprinkler irrigation soil moisture uniformity CU s and the nozzle hydraulic performance indexes and soil hydraulic parameters;

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

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

[0040] The third construction module is used to conduct a multiple non-linear regression of the sprinkler irrigation soil moisture uniformity CU s with the soil matrix potential |Ψ|, saturated hydraulic conductivity K s , total flow rate Q of the spraying area, irrigation time t i , moisture migration time t m and sprinkler irrigation ground uniformity CU g to obtain the empirical coefficients and the fitting indexes of each item, and determine the prediction model of the sprinkler irrigation soil moisture uniformity CU s in the fixed sprinkler irrigation system;

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

[0042] Compared with the prior art, the beneficial effects of the present invention are as follows:

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

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

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

[0046] In order to more clearly illustrate the technical solutions of the present invention, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

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

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

[0049] Figure 3 It is the CU of an embodiment of the present invention s Comparison diagram of measured values (COMSOL-3D simulation) and CU s predicted values (dimensional analysis model). DETAILED DESCRIPTION OF THE EMBODIMENTS

[0050] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0051] In order to make the above objects, features, and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below with reference to the drawings and specific embodiments.

[0052] Example 1

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

[0054] S1. Determine the parameter to be predicted as the sprinkler irrigation soil moisture uniformity CU s , and select 6 physical quantities from the nozzle hydraulic performance indicators and soil hydraulic parameters. The 6 physical quantities are, respectively, the soil matrix potential |Ψ|, the saturated hydraulic conductivity K s , the total flow rate Q of the spraying area, the irrigation time t i , the water movement time t m and the sprinkler irrigation ground uniformity CU g . List the solution equation of CU s as shown in Equation (1);

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

[0056] S2. Select 2 basic dimensions: the soil matrix potential |Ψ| and the saturated hydraulic conductivity K s , |Ψ| and K s are respectively quantities of geometry and kinematics, and their dimensions are [L] and [L·T -1 ;

[0057] S3. According to the π theorem method of dimensional analysis, obtain 5 dimensionless π terms: π1 = CU s , and π5 = CU g (CU s and CU g are dimensionless and are used as π1 and π5 respectively);

[0058] S4. Establish the functional relationship between the soil moisture uniformity CU s and the nozzle hydraulic performance indicators and soil hydraulic parameters as shown in Equation (2),

[0059]

[0060] where λ is an empirical coefficient; η1, η2... η4 are fitting exponents;

[0061] S5. Build a three-dimensional numerical model of soil moisture movement in a fixed sprinkler irrigation system based on the COMSOL 6.1 software;

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

[0063] S7. Conduct CU s with |Ψ|, K s , Q, t i , t m and CU g for multiple nonlinear regression to obtain the empirical coefficient λ and the fitting indices (η1, η2... η8) of each item, and determine that the prediction model of CU s in the fixed sprinkler irrigation system is Equation (3),

[0064]

[0065] After simplification, Equation (4) can be obtained,

[0066]

[0067] where R 2 is the goodness of fit of Equation (3).

[0068] In this embodiment, in step S1, the units and dimensions of the sprinkler irrigation hydraulic performance index and the soil hydraulic parameters are as follows: |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, in step S2, the saturated hydraulic conductivity K s involves three types of soil, and the physical properties and hydraulic parameters of the soil are shown in Table 1.

[0070] Table 1

[0071]

[0072]

[0073] In this embodiment, in step S5, for the three-dimensional numerical model of soil moisture movement in the fixed sprinkler irrigation system, the nozzles are arranged in a square pattern, the depth of the simulation area is 1 m, and the side length is The installation height of the nozzle is 1.7 m. The rain gauges are arranged radially on three rays extending from the nozzle. The distance between adjacent rain gauges is 0.5 m, and the included angle between the radial lines is 30°. After the test, the average value of the water volumes measured by the rain gauges at the same distance from the nozzle is taken, and the sprinkler irrigation intensity in the direction of the range is calculated by Equation (5).

[0074]

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

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

[0077] The irrigation time is set by a step function.

[0078]

[0079] The upper surface boundary condition is set as the atmospheric boundary, which is a non-uniform precipitation boundary and an evaporation boundary that do not change with time during irrigation, and only evaporation exists on the upper surface boundary during non-irrigation. The bottom boundary is set as a free drainage boundary, and the side boundary is set as a zero-flux boundary. A free tetrahedral mesh is used to set the numerical calculation domain, and local mesh refinement is performed in the area near the geometric vertices. The mesh size is "extremely refined", and the average mesh size is 1.4×10 -3 m. The designed simulation duration is 72 h, and the time step is 1 h. Refer to Figure 2 .

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

[0081] Table 2

[0082]

[0083] The six sprinkler irrigation uniformities mentioned above 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 mentioned above are different expression forms of the same physical quantity. In the field of soil infiltration, the initial soil moisture content can be converted into soil matrix potential through the following formula, and the obtained results are shown in Table 2.

[0087]

[0088]

[0089] where θ(h) is the volumetric water content function related to the soil suction value, cm 3 ·cm -3 ; h is the soil matrix potential, m; θ is the soil volumetric water content, cm 3 ·cm -3 ; θ r is the soil residual water content, cm 3 ·cm -3 ; θ s is the soil saturated water content, cm 3 ·cm -3 ; α is an empirical parameter, equal to the reciprocal of the air entry suction value, cm -1 , n and m are the shape coefficients of the V-G curve; S e is the soil available water content, 0 < S e < 1; l is the pore connectivity parameter, generally taken as 0.5; K(h) is the soil unsaturated hydraulic conductivity, mm / h.

[0090] The irrigation time t mentioned above i is calculated through the following formula, and the obtained results are shown in Table 2.

[0091] W = γ·h w ·A·(θ max - θ0)

[0092]

[0093] where W is the sprinkler irrigation water volume, m 3 ; γ is the soil bulk density, kg·m -3 ; h is the planned wetting layer depth, 0.8 m; A is the sprinkling area, m 2 ; θ maxThe upper limit of the suitable water content, %, is taken as 85% θ f ; θ f is the field water holding capacity, %; θ0 is the initial water content, %; is the average sprinkler irrigation intensity, mm·h -1 .

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

[0095]

[0096] The water movement time t m is calculated starting from the end of irrigation. The infiltration duration is uniformly set to 48 h, and CU is calculated every 12 h s .

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

[0098] Example Two

[0099] The present invention also provides a prediction system for the soil water uniformity of a fixed sprinkler irrigation system based on dimensional analysis, which is characterized in that it includes: 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 nozzle hydraulic performance indexes and soil hydraulic parameters, and the physical quantities include: soil matrix potential |Ψ|, saturated hydraulic conductivity K s , the total flow rate Q of the spraying area, irrigation time t i , water movement time t m , sprinkler irrigation ground uniformity CU g ;

[0101] The first calculation module is used to obtain several dimensionless π terms based on the physical quantities by using the π theorem method of dimensional analysis;

[0102] The first construction module is used to establish the sprinkler irrigation soil water uniformity CU based on the dimensionless π terms sThe functional relationship between the hydraulic performance indexes of the sprinkler head and the soil hydraulic parameters;

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

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

[0105] The third construction module is used to carry out the sprinkler irrigation soil water uniformity CU s with the soil matrix potential |Ψ|, saturated hydraulic conductivity K s , total flow rate Q of the spraying area, irrigation time t i , water movement time t m and sprinkler irrigation ground uniformity CU g for multiple non-linear regression to obtain the empirical coefficients and the fitting indexes of each item, and determine the prediction model of the sprinkler irrigation soil water uniformity CU s in the fixed sprinkler irrigation system;

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

[0107] The above embodiments are only descriptions of the preferred embodiments of the present invention, and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall 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; Determine the parameter to be predicted as the sprinkler irrigation 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 CU s The solution equation is: F(CU s ,|ψ|,K s ,Q,t i ,t m ,CU g )=0; Choose 2 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 ]; 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; 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; 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 design simulation duration is 72 h, and the time step is 1 h; The orthogonal test 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; three initial soil moisture contents: 55%, 65% and 75% of field water holding capacity; The prediction model is: Among them, R 2 is the degree of fit.

2. A soil moisture uniformity prediction system for a fixed sprinkler irrigation system based on dimensional analysis, the system being used to implement the soil moisture uniformity prediction method for a fixed sprinkler irrigation system based on dimensional analysis as claimed in claim 1, 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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