van Genuchten(VG)方程是最常用的土壤水分特征曲线方程,其参数取值的精度直接影响到土壤水分运动方程计算的精度。该文建立了VG方程参数的优化模型,构建遗传算法与Levenberg-Marquardt算法相结合的混合遗传算法对其进行求解,并进行了...van Genuchten(VG)方程是最常用的土壤水分特征曲线方程,其参数取值的精度直接影响到土壤水分运动方程计算的精度。该文建立了VG方程参数的优化模型,构建遗传算法与Levenberg-Marquardt算法相结合的混合遗传算法对其进行求解,并进行了数值试验。结果表明采用混合遗传算法比普通遗传算法不但提高了收敛效率,而且收敛迭代次数也大大减少;采用混合遗传算法估计参数的精度比非线性单纯形法和阻尼最小二乘法要高一些,而且不需要给参数初值。因此,混合遗传算法可以作为估计VG方程参数的一种新方法。展开更多
使用随机粒子群算法拟合土壤水分特征曲线并以此求解出V an G enuch ten方程参数。通过算例与其他优化算法比较,结果表明:随机粒子群算法具有运算速度快,编程简单,初值无关性,全局收敛和计算精度高等优点,可以作为计算V an G enuch ten...使用随机粒子群算法拟合土壤水分特征曲线并以此求解出V an G enuch ten方程参数。通过算例与其他优化算法比较,结果表明:随机粒子群算法具有运算速度快,编程简单,初值无关性,全局收敛和计算精度高等优点,可以作为计算V an G enuch ten方程参数的新方法。展开更多
Van Genuchten方程是应用最广泛的土壤水分特征曲线方程,该方程的关键是4个参数的取值。为了精确地求解这些参数,引入萤火虫算法进行求解,提出了一种基于生物寄生行为的人工萤火虫优化算法(GSOPB)。该算法将萤火虫群分为寄生群和宿主群...Van Genuchten方程是应用最广泛的土壤水分特征曲线方程,该方程的关键是4个参数的取值。为了精确地求解这些参数,引入萤火虫算法进行求解,提出了一种基于生物寄生行为的人工萤火虫优化算法(GSOPB)。该算法将萤火虫群分为寄生群和宿主群两个种群,两种群间隔一定的迭代次数相互交换部分萤火虫;淘汰宿主群中适应度较差的一半萤火虫,以体现"优胜劣汰"的生物进化法则。标准测试函数的仿真结果表明了GSOPB算法的有效性;对Van Genuchten方程参数的优化结果表明,GSOPB算法的求解精度优于其他方法,可以作为求解Van方程参数的新方法。展开更多
Van Genuchten方程参数的求解属于复杂的非线性拟合问题,传统方法解决此类问题存在着诸多弊端。本文试图找到一种精确求解方程参数的有效方法,枚举法由于列出所有可能的组合,不存在陷入局部最优值,因此被本文采用求解方程参数。首先,通...Van Genuchten方程参数的求解属于复杂的非线性拟合问题,传统方法解决此类问题存在着诸多弊端。本文试图找到一种精确求解方程参数的有效方法,枚举法由于列出所有可能的组合,不存在陷入局部最优值,因此被本文采用求解方程参数。首先,通过实验对比,确定目标函数指数k的取值;然后,讨论有效数字位数对方程参数及拟合精度的影响,确定方程参数的有效数字位数;最后,将枚举法与其它方法通过实验进行比较。结果表明:在目标函数、有效数字位数等相同条件下,枚举法具有最高的拟合精度,是一种精确求解Van Genuchten方程参数的有效方法。展开更多
The hysteresis of saturation-capillary pressure(S-p) relations was investigated in a fine sandy medium under consecutive drainage-imbibition cycles,which resulted from scheduled water level fluctuations.A drainage-imb...The hysteresis of saturation-capillary pressure(S-p) relations was investigated in a fine sandy medium under consecutive drainage-imbibition cycles,which resulted from scheduled water level fluctuations.A drainage-imbibition cycle starts with a drainage process and ends with an imbibition process in sequence.The saturation and capillary pressure were measured online with time domain reflectometry(TDR) probes and T5 tensiometers,respectively.Results show that the relation between the degree of hysteresis and the number of the drainage-imbibition cycles is not obvious.However,the degree decreases with the increase of the initial water saturation of the imbibition processes in these drainage-imbibition cycles.The air-entry pressure of a sandy medium is also found to be constant,which is independent of the drainage-imbibition cycles and the initial water saturation of the drainage process.In all the imbibition processes,parameter α of the van Genuchten(VG) model decreases with the increase of the initial water saturation,which corresponds positively to the magnitude of the hysteresis.展开更多
基金Project(41072182) supported by the National Natural Science Foundation of ChinaProject(2010Z1-E101) supported by the Science and Technology Program of Guangzhou City,China+1 种基金Project(200809095) supported by the Special Funds for Environmental Nonprofit Research,ChinaProject(8151027501000008) supported by the Natural Science Foundation of Guangdong Province,China
文摘The hysteresis of saturation-capillary pressure(S-p) relations was investigated in a fine sandy medium under consecutive drainage-imbibition cycles,which resulted from scheduled water level fluctuations.A drainage-imbibition cycle starts with a drainage process and ends with an imbibition process in sequence.The saturation and capillary pressure were measured online with time domain reflectometry(TDR) probes and T5 tensiometers,respectively.Results show that the relation between the degree of hysteresis and the number of the drainage-imbibition cycles is not obvious.However,the degree decreases with the increase of the initial water saturation of the imbibition processes in these drainage-imbibition cycles.The air-entry pressure of a sandy medium is also found to be constant,which is independent of the drainage-imbibition cycles and the initial water saturation of the drainage process.In all the imbibition processes,parameter α of the van Genuchten(VG) model decreases with the increase of the initial water saturation,which corresponds positively to the magnitude of the hysteresis.