Hydraulic Analysis And Optimal Design Of Microirrigation Field Pipe Network

Hydraulic design is the precondition and foundation of the installation and operation of the microirrigation systems,which directly effect the capital cost,running fees,irrigation quality and reliability of the micro-irrigation systems.In this dissertation,the hydraulic analysis and optimal design of the micro-irrigation system in sloping field were chosen as the study objects,the currently existing problems were concluded based on the summary of published literature home and abroad.Design theory and methods about microirrigation field network were studied using the microirrigation pipe hydraulics and mathematical method.Hydraulic analytical models of the microirrigation lateral and submit unit laid on the uniform sloped ground as well as the microirrigation lateral laid on the non-uniform sloped ground were built.Consequently,the simplified design methods of the sloped microirrigation network were proposed,which the corresponding programs were wrote by using Equation Solver and VBA language in Microsoft Excel.In addition,several design examples were analyzed and verified.The main conclusions of this dissertation were shown as follows:(1)Based on the energy gradient line method,the hydraulic model of the single inlet microirrigation lateral laid on uniform sloped ground is supplemented and perfected by modifying the friction coefficient considering water temperature.By proposing a new formula of the best inlet position parameter for the paired laterals,the new hydraulic models for the paired laterals laid on the uniform sloped ground were established.All equations of the design parameters were regression analyzed by the least square method with the specific velocity exponent and the pressure loss ratio of a single downhill lateral with the same length as the paired laterals.The simplified and efficiently progresses for the hydraulic design of microirrigation laterals were illustrated by designing examples without using any softwares.Besides,the simplified optimal procedures for designing the single inlet lateral and paired laterals were separately proposed when the operating pressure head were known.The study showed that the length of the uphill part of the paired laterals decreases with the increases of the pressure loss ratio parameter,and increases with the velocity exponent.(2)By analyzing the influence of lateral layouts on the working pressure head and water application uniformity,the selection standards of lateral layouts for the uniform sloped microirrigation lateral were put forward.When the pressure loss ratio parameter varies from 0~1,the appropriate lateral layout was proposed as the paired layout,otherwise,the lateral should use the single layout.On this basis,the hydraulic analysis models of the lateral using the appropriate layout were derived.Then,the simplified formulations of the designed diameter and length of the uniformly sloping lateral were separately developed by using the pressure loss ratio parameter as the indepent variable.By changing the design formula of the water application uniformity indexes affected by the hydraulic factors,the dimensionless design parameters of the diameter and length corresponding to each water application uniformity index were defined respectively.The relationships between the diameter design parameters and the pressure loss ratio and the relationships between the length design parameters and the pressure loss ratio were developed and drawn.The value ranges of the designed diameter and length were also analyzed corresponding to the different values of diameter design parameter and length design parameter.The regression equations of the pressure loss ratio parameters with the specific velocity exponent were regression analyzed by the least square method according to the diameter design parameters and the length design parameters.The design formula of the lateral working pressure head were furtherly simplified.Finally,the simplified optimal design methods of the diameter and length of the uniformly sloping microirrigation lateral which satisfy the design standard of the microirrigation system were proposed.The study shows that the proposed quantitative criterion of the pressure loss ratio parameter could be used for optimal selecting the appropriate layout much more reliable than the traditional design experience.On the other hand,there were 1,2 or more design values of the diameter or length of the lateral to meet the requirements of water application uniformity and emitter flow.(3)The hydraulic analysis model of the uniformly sloping microirrigation subunit with the different combinations of single and paired layouts of the lateral and submain were developed.The simplified optimal procedures for desiging the uniformly sloping microirrigation subunit were proposed with the known pipe layouts and the unknown and known inlet working pressure head.By designing the practical cases to analyze the difference of design parameters of the microirrigation subunit under difference pipe layouts by designing the practical cases,the appropriate selective criteria of the appropriate pipe layouts were proposed.When the pressure loss ratio of the lateral or submain varies from 0~1,the lateral or submain should use the paired layout,otherwise,the single layout should be used.On this basis,the hydraulic analysis model of the uniformly sloping microirrigation subunits using the appropriate layout were developed.By taking the microirrigation subunit as a whole and using the design water application uniformity and emitter flow as the known design parameters,the optimal procedures were proposed for designing the maximum irrigation areas and minimum one-time investment.(4)According to the probability theory,the average and standard deviation of measured elevation data were used to quantitatively describe the characteristics of non-uniformly sloping topography.By the hydraulic analysis,the formula for calculating the coefficient of variation of emitters’ flow only affected by the hydraulic factors of the microirrigation lateral laid on the non-uniformly sloped ground condition were deduced.Furthermore,the hydraulic analysis model of non-uniformly sloping single inlet and paired laterals were developed,respectively.On this basis,the simplified optimal procedures for designing the non-uniformly sloping microirrigation single and paired laterals were proposed under the conditions that the inlet working pressure head is known or unknown.(5)According to the hydraulic analysis model of the uniformly sloped microirrigation laterals and subunits,the design cases illustrated the rapid design progresses of the microirrigation laterals.The simple computation sheets for designing the uniformly sloping lateral and subunit with the known inlet working pressure head were compiled in Microsoft Excel 2013.By using the Equation Solver in Microsoft Excel,the trial computations in the design processes could be realized quickly and easily.According to the simplified design procedures of the design diameter and length of the pipe,the lateral diameter and length could be quickly and easily designed with the selection of the appropriate pipe layouts.Based on the proposed simple design procedures of the uniformly sloping microirrigation subunit and non-uniformly sloping microirrigation lateral with the unknown inlet working pressure head,the corresponding computation sheets were compiled in Microsoft Excel 2013,the corresponding “macro modules” were programmed by VBA language,then the trial computation could be quickly and easily achieved while ensuring the optimal layout of the pipe network.(6)By designing several practical engineering cases,the accuracy and reliability of the hydraulic analytical models and the proposed methods were verified by comparing the results of the proposed methods with those of other methods or the experiment data.The results showed that the accuracy of the model can satisfy the design requirements of microirrigation system,and the design procedures were simple,direct and easily adaptable for using by ordinary engineers.All the proposed procedures could be directly using in the practical microirrigation engineering,which could improve the design efficiency.