基于混合变邻域的自动化滴灌轮灌分组算法

    Division algorithm of the rotation irrigation group for automated drip irrigation based on hybrid variable neighborhood

    • 摘要: 为了解决自动化滴灌轮灌分组手工计算效率低的问题。该研究分析比较自动化滴灌与手工控制滴灌问题特征和划分原则,构建以轮灌组流量均衡为目标的数学模型,模型以流量标准差最小为目标函数,以流量差、压力差和离散度指标等为约束条件,以支管数量、流量大小和轮灌组数为决策变量,并提出一种基于混合变邻域的GSRV-GA算法进行模型求解。算法通过设计罚函数以及子代修复算法来解决工程约束以及交叉变异产生的非法解问题,然后将选择算子结合模拟退火机制以避免优化解陷入局部最优。为了提高算法搜索精度,设计基于流量和位置调整的2种邻域结构,通过变邻域搜索来强化遗传算法的搜索能力。对新疆某团场灌区工程进行实例优化分析,求解的最小标准差为10.03 m3/h,算法在350代左右实现收敛,求解时间为2 504.53 s。在3组不同规模的案例中求解最小标准差分别为15.18、13.93和7.52 m3/h,在1~5个支管堵塞抖动试验中离散度指标均达到1。该模型和算法可为后续挖掘自动化滴灌节水技术提供研究基础。

       

      Abstract: Drip irrigation has been one of the most effective water-conserving irrigation technologies in the arid and semiarid areas. Among them, the rotational irrigation mode has been the mainstream application in Xinjiang, Western China. The Rotation Irrigation Groups (RIGs) have been widely designed to deal with the water shortage in the farmlands irrigation. However, the RIGs arrangement can often be taken several days to calculate in large-scale projects, according to the experience or EXCEL software. Furthermore, these traditional approaches cannot acquire the reasonable solution. Therefore, a single-objective model was previously proposed to verify the feasibility of the intelligent algorithm on the manual drip irrigation. In this study, a mathematical model was proposed to determine the minimum flow standard deviation using a gravitational search algorithm (GSRV) and Genetic Algorithm (GA) with the hybrid variable neighborhood. A systematic analysis was made to clarify the differences between the automated and manual drip irrigation, particularly for the high calculation efficiency under the intelligent algorithm. The chromosome coding and population initialization were also established to acquire the problem characteristics of automated drip irrigation, according to the dividing and dispersion index. An offspring repair algorithm was also designed to reduce the constraint and illegal solutions from the crossover and variation using the penalty function method. The selection of operator was also combined with a simulated annealing mechanism to avoid the optimization process falling into the local optimum. Since the classical GA presented the global solid search but the weak local search, two neighborhood structures were constructed using the flow and location adjustment, while a search algorithm was designed using Variable Neighborhoods Search (VNS), further to enhance the GA searchability and accuracy. As such, the different neighborhood operators were selected for the VNS to jump out of the local minima. The shaking procedure and the Local Search (LS) procedure were iteratively alternated until a predefined stop condition, thereby to escape from local optimal solutions. The specific search procedure was as follows. 1) The parameters were first initialized to calculate the population fitness, then to select the coding bit with the probability for the dynamic performance of variable neighborhood search. The next step was check the constraints to calculate the fitness value and update the population for the subsequent search. Finally, the population encoding was output until the population traversal was completed or the algorithm iterations reached. The experimental results show that the improved model was effective and universality in this case. Specifically, the minimum standard deviation of the solution was 10.03 m3/h. The solution was also converged in about 350 generations, where the branch pipes were dispersed in the different sub-main pipes. The GSRV-GA demonstrated an excellent convergence and search accuracy, which verified the effectiveness of the proposed algorithm. Three groups of cases with different sizes were selected to carry out the verification of model universality, also indicating an excellent performance. The minimum standard deviations were 15.18, 13.93, and 7.52 m3/h, respectively. The average standard deviations of shaking experiment simulating the blockage of 1-5 branch pipes were 10.50, 11.09, 11.47, 12.15, and 12.81 m3/h, respectively. The jitter simulation experiment showed the influence of branch blockage on the flow equalization of the irrigation group, indicating the robustness of the model. At the same time, the approximate standard deviations of the flow rate were no more than 1%, and the dispersion values were 1 and 0.73 for the improved model and the previous one in the actual case, respectively. It infers that the different grouping requirements of rotation irrigation group were realized in the design. Consequently, the feasibility was achieved for the RIG division of automatic drip irrigation, thereby to fully meet the hydraulic calculation and engineering requirements in modern agriculture. The finding can provide the research foundation for the subsequent mining of water-saving technology in automatic drip irrigation.

       

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