Numerical Simulation Of Soil Water Movement In Moistube Irrigation

This paper is based on consulting and summarizing the domestic and international moistube irrigation theory and technology,the technical route involved laboratory experiment,theoretical analysis and numerical simulation,which numerical simulation and experimental verification is the main route.Indoor experiments were carried out to study the flow characteristics of moistubes in the air and provide the necessary basis for moistube irrigation.Through the indoor experiment and numerical simulation,to research moistube irrigation the influence of soil water movement characteristics in different facters without the condition of vegetation on soil texture,which soil texture,specific discharge,initial moisture content and buried depth and so on,analysis of different irrigation technology elements combination under moistube irrigation wet body moisture distribution and soil infiltration characteristics,to establish the moistube irrigation soil wetting front transport distance and cumulative infiltration amount and irrigation time prediction model.Based on the theory of unsaturated soil water movement,the establishment of moistube irrigation,the mathematical model of soil water movement was established,the determination of soil hydraulic characteristic parameters,and the SWMS-2D software are applied to solve the model.under different irrigation technology elements,quantitative get the space distribution features of soil moisture and water infiltration characteristics,for moistube irrigation system and actual operation to provide technical basis.The infiltration law of soil water under different influencing factors was analyzed,and the following results were obtained:(1)The flow of moistube accords with Darc's law,and there is a clear linear positive correlation between the flow rate and the pressure water head.Under the same water pressure head,the specific discharge of moistube increases with the increase of the angle and has a liner relationship with the inclination of sine,while the moistube angle can be converted into equivalent head.The calculation formula of moistube specific discharge including angle and pressure head is put forward.(2)When the moistube was buried horizontally,measured values of moistube infiltration in per unit length revealed there is a difference between the simulation result and measurement values and the relative error average of the absolute value is 11.7% in the beginning of infiltration.In the late of infiltration,the simulation result agreed well with measurement values and the relative error average of the absolute value is 4.7%.On the whole,the results of numerical calculation are well matched with the measured data.The model can truly reflect soil water movement under the way of moistube standard of laying.(3)When the moistube was buried horizontally,the soil wetting front is a cylindrical distribution along the microtube,the wetting vertical downward distance>horizontal migration distance>vertical upward distance.The simulated values of each time period are basically consistent with the measured values,and the mean relative error of the absolute value is 7.38%.The relative error of soil moisture volume simulation and measured value decreases with the increase of infiltration time,and shows that the longer the irrigation time.It is fit that with soil wetting volumes between the simulation result and measurement values.The contour of soil moisture content is the concentric circle around the moistube.With the increase of the radius of the wetted soil,the soil moisture content of the soil is the largest at the pipe wall of moistube,but the saturation moisture content was not reached.(4)The level of moistube irrigation conditions,soil wetting front distance follows the trends of vertical downward distance> horizontal migration distance> vertical upward distance,the contour line of water content and ratio flow all have a remarkable effect on pipe as it's axle centre,the law of soil texture,initial moisture content,than the flow has nothing to do with buried depth in different influencing factors.The soil texture,initial water content and ratio flow all have a Remarkable effect on characters of wetted soil,the greater the soil is more sticky,the more slowly the wetting front rate is,the different thus of all the directions and volume of soil wetting front become smaller,moistube embellish pipe near the moisture content is higher,the soil moisture content contour more dense;The wetting front migration distance and the volume of wetting body were positively correlated with the initial moisture content and the ratio of the flow rate.The buried depth have no influence on the wetting front distance,while it has obviously effect on the distribution localization of soil wetting front,the soil wetting front moved downward with the downward of buried depth.(5)The relationship between the soil wetting front moved and infiltration time of each direction in the control area of the moistube fluidic tube can be expressed by power function.Through numerical simulation,the simulation results show that the infiltration coefficient is related to soil bulk density,and the change of infiltration index does not have much effect on the migration distance of wetting front.Through indoor test and the existing literature,validation of moistube irrigation the soil wetting front moved prediction model,comparison results show that the established moistube embellish irrigation model can more accurately reflect the characteristics of soil water infiltration.