Abstract:
Abstract: Infiltrating irrigation technology is an effective water-saving irrigation technology. As a new irrigation methods, it is getting a lot of attention. A kind of infiltrating irrigation material composed of montmorillonite (MMT) and polyacrylamide (PAM) developed recently has showed good self-adjustment property for soil moisture, and its water-absorption performance can be used to evaluate the sensitive degree that material responses to the external environment. This study aimed to simulating the water-absorption performance curve using the Laplace-transform method, which transformed a problem of solving differential equations into a problem of solving algebraic equation. Meanwhile, the model had also been used to explore the numerical relationship between water-absorbing capacity and material components. PAM and sodium montmorillonite (Na-MMT) was used as experimental material, circular material cube (4 g for each, 10 mm in height, 5 mm in radius) was for samples. Ten groups testing components of composite materials were designed including the mass proportions of MMT: PAM of 2.5:1, 5:1, 7.5:1, 10:1, 12.5:1, 15:1, 17.5:1, 20:1, 22.5:1, and 25:1. The samples made of the ratios were carried out the first and secondary water absorption performance test. In addition, another six groups with different proportions of composite materials (MMT: PAM 4:1, 14:1, 24:1, 40:1, 50:1, 60:1) were carried out the first water absorption test to verify the model. The water absorbing performance curve of composite was simulated as followed: 1) Describing the curves of water-absorption rate with algebraic equation rather than differential equation, which was to calculate the transfer function depending on the Laplace limit theorem; 2) Coding the equation in M file editor of MATLAB software; 3) Inputting the adjusted experimental values of water-absorption rate in the Matlab. Then, the system's transfer function was identified by the step response curve, and parameters of model were automatically formed, thereby the transfer function coefficients of water-absorption curves of samples during the first and second water-asborption test were obtained. Then, the water-absorption curves were simulated with the obtained parameters. The results showed that: the relative error between the simulated and measured water-absorption rate were 0.04%-7.17% and root mean square error (RMSE) was <0.0717, indicating that the water-absorption rate curves characterized by using Laplace transform is effective and accurate. Quantitative relationship between transfer function coefficient indicating the water absorbing capacity of material and material components followed exponential function. The RMSE between simulated transfer function coefficient values with the exponential function and the measured one was less than 0.5. In the validation test, the maximum relative error between the simulated and measured transfer function coefficient values was 4.01%. It suggested the reliability of the exponential function used for describing the relationship between water-absorption capacity of the compound material and its ratios. This study is valuble for design of infiltration irrigation materials and researchers on the water conductivity features of infiltration irrigation materials.