| Desertification is a serious problem facing the world today.In order to solve this problem,domestic and foreign control measures have been proposed,and the most fundamental measure is vegetation restoration.However,desertification areas are seriously deficient in water.The annual evaporation is tens to hundreds of times of annual precipitation,which makes it difficult for seedlings to survive in these areas due to lack of water.Therefore,water-saving irrigation technology is critical for solving desertification and achieving effective vegetation restoration,and the infiltration irrigation technology has become a hotspot of scholars from all over the world because of its high water use efficiency and high seedling survival rate.Aiming at the shortcomings of emitter blockage,uneven water seepage and soil salinization of traditional“hole-type”infiltration irrigation technology,a new infiltration irrigation technology based on“water bounding/water conducting”multiphase medium was developed.The survival rate of seedlings has been greatly improved by applying this technology to vegetation restoration in desertification areas.On the basis of previous work,this thesis started from the following aspects:multiphase medium design,fluid thermodynamics,fluid dynamics,fluid structure dynamics,emitter manufacturing,self-adjusting soil moisture characteristics and field application,and the water fliud dynamic theory of multiphase media was systematically studied.Furthermore,the dynamic theory was applied to actual production and field application,and remarkable effects have been obtained.The main research achievements are as follows:(1)According to the different water absorption and desorption property of polyacrylamide and montmorillonite,the multiphase medium material based on“water bounding/water conducting' was constructed and prepared,in which polyacrylamide tends to the characteristics of "water bounding”,while montmorillonite tends to the characteristics of "water conducting".The microstructure of the multiphase medium was characterized by a variety of material analysis and testing methods,and its combination mode and optimum component ratio were determined.On this basis,the characteristic parameters of the multiphase medium,such as the water characteristic curve,the hydraulic conductivity characteristic curve and the water content-distance curve,were measured and analyzed,and the dynamic equations with high fitting degree to the measured value was also obtained.(2)The water fluid thermodynamic equations of the multiphase medium were analyzed and established.It was clarified that the water potential gradient change of the multiphase medium-water system along the water-conducting fiber was the driving force for the spontaneous water conduction,and the two-phase structure of "water bonding/water conducting" was proposed.The difference between "high water content state" and "low water content state”caused by the multiphase structure was the main factor affecting the change of water potential gradient and the degree of water conduction.This conclusion was proved in both laboratory and field tests.(3)According to the structure characteristics of the water bonding/water conducting multiphase and the change of water potential gradient,the fluid dynamics equations of "high water content state" and "low water content state”were established from the two perspectives of diffusion and infiltration,respectively.In terms of water coductivity theory,the two equations had structural normality,and a unified dynamic equation was obtained.The separation of variables mothed and the finite difference method were respectively used to solve the dynamic equations of high/low water content.The results of the solution were basically consistent with the measured data,indicating the derivation and the established fluid dynamics equation of the multiphase medium-water system was correct.(4)In the aspect of structural dynamics based on water-conducting rate,the mierostructural characteristics and variation of multiphase medium in water conducting process were studied in detail.The results showed that the multiphase medium-water system had the function of structural dynamic self-adjusting.When the soil moisture was lower than the optimum soil moisture set by the multiphase medium,the "water bonding" phase polyacrylamide was dehydrated,and the“water conducting" phase montmorillonite particles were"bridged" and the water conducting rate was accelerated;on the contrary,when the soil moisture was higher than the optimum moisture of the soil set by the multiphase medium,the "water bonding" phase polyacrylamide absorbed water,and the“water conducting" phase montmorillonite pariticles were separated into the "bridge breaking" state,and the water conducting rate was lowed or even stopped.This conclusion was also consistent with the mathematical model of classical control theory established by using MATLAB software in laboratory soil test,which further proved the correctness of structural dynamics research.The kinetic study was used to the scale inoculation of Cistanche on the desertification site with remarkable results.(5)In order to better reflect the kinetic advantages of single fiber bundles for water conducting,this study proposed a complete set of new processing routes for infiltration emitter as fiber surface treatment,fiber coating,UV-curing resin mixture preparation,3D printing and post-processing.These processes had overcomed the problem of uneven fiber distribution in infiltration emitter during the process of making the water conducting composite fiber chips by casting method,and the infiltration emitter produced by the 3D printing technology had showed that the quality was stable in the application of the Cistanche inoculation in desertification areas.In summary,this thesis has deeply analyzed the infiltration irrigation fluid dynamics based on the“water bounding/water conducting”multiphase medium,and obtained the theoretical thermodynamic equations and dynamic equations that were in good agreement with the measured datas.In addition,the law of structural dynamics changes of the multiphase medium has also been revealed.The multiphase medium infiltration irrigation technology was applied to the desert Cistanche inoculation,which has increased the cistanche inoculation rate from the traditional 15%to the current over 90%,and the cistanche growth also has obvious advantages.The research work and achievements of this thesis have important theoretical and practical application value for solving the problem of low survival rate of seedlings in desertification areas. |
PDF Full Text Request