水力瞬变中动态摩阻的改进加权类模型

有压输水管道系统中,由于阀门的启闭或水力元件的不当操作等因素常会发生水锤现象,从而可能会影响水力系统的正常运行甚至发生危险事故.因此,针对上述管道水锤现象进行有效的数值模拟预测具有重要意义.在管道水力瞬变过程模拟计算中,Zielke提出的加权动态摩阻模型可以较好地模拟压力波动过程,是一维水锤模拟中计算结果最接近试验值的数学模型.由于加权函数与历史流速及历史加速度相关,模型计算时需保存每一时步的流速值,占用计算机内存大,故计算效率较低.为提高模型计算效率,尝试利用Matlab 的LSQNONLIN函数模块对Zielke加权函数进行3个指数函数之和型式的近似拟合,得到新的近似加权函数的各系数值,并通过与Zielke加权函数曲线及已有的改进加权函数曲线对比验证新函数的优越性,以及利用试验数据验证新模型的准确性和高效性.结果表明,模型在一定程度上提高了加权类动态摩阻模型的计算效率.

Improved weight-function model of unsteady friction in hydraulic transients

In pressurized water conveyance pipeline system,water hammer phenomenon often occurs due to the opening and closing of valves or improper operation of hydraulic components,affecting the normal operation of hydraulic system and even causing dangerous accidents.Therefore,it is of great significance to carry out effective numerical simulation prediction for the above water hammer phenomenon.In the simulation of pipeline hydraulic transient process,the weight-function unsteady friction model proposed by Zielke,which is considered to be the most accurate mathematical model in one-dimensional water hammer simulation,can accurately simulate the pressure fluctuation process.Since the weighting function is related to the historical velocity and acceleration,the velocity value of each step needs to be saved in the model calculation,which occupies a large amount of computer memory.So,the calculation efficiency is low.In order to improve the model′s computational efficiency,therefore,Matlab LSQNONLIN function module is tried to use to approximately fit the Zielke weighting function with a new function,which is the form of the sum of three exponential functions,gets the coefficients of new approximation weighting function,as well as the new function′s superiority by comparing Zielke weighting function curve and existing improved weighting function curves,as well as the new model′s accuracy and efficiency against experimental data.The results show that the model improves the calculation efficiency of the weight-function unsteady friction model to some extent.