液力—磁耦合传动岩屑清洁装置的磁扭矩数值优化

钻井过程中水平井段岩屑携带困难、易形成岩屑床,因而研发了一种新型液力—磁耦合传动岩屑清洁工具,但对其磁扭矩传动影响机制、最佳磁路结构及磁铁配置等尚不清楚。为此,应用有限元数值模拟方法分析了磁路结构和永磁铁几何尺寸对磁扭矩的影响规律,数值模拟和室内实验的结果表明:(1)通过提高气隙磁通密度,降低磁路磁阻,增加静磁能的储积等方式可以提高磁扭矩的传递效率;(2)磁扭矩随磁偶对数的增加呈先增大后减小的趋势,12对磁偶的磁扭矩达到最大值;(3)对工具有效断面磁铁覆盖面积和磁体厚度这两种因素制约下的磁铁用量的耦合,得到永磁铁厚度为8.4 mm、工具有效断面上磁铁覆盖面积为71%时,单位体积磁铁产生的磁扭矩为最高;(4)室内实验结果与数值模拟计算结果绝对误差小于17%,能够满足工程计算对精度的要求。结论认为,所建立的数值模拟模型较为合理,可作为该工具结构优化分析的技术手段。

A magnetic torque optimization method for a hydraulic–magnetic coupling-drive cuttings cleaning tool

In the process of well drilling, cuttings carrying is difficult in the horizontal section, and cuttings beds tend to form easily. In view of this, a hydraulic–magnetic coupling-drive cuttings cleaning tool is newly developed, but its magnetic torque transmission mechanism, optimum magnetic circuit structure and magnet layout are rarely researched. In this paper, the influence laws of magnetic circuit structure and permanent magnet dimension on the magnetic torque were analyzed by using finite-element numerical simulation method. And the following research results were obtained on the basis of numerical simulation and experimental study. First, the transmission efficiency of magnetic torque can be enhanced by increasing the magnetic flux density in the air gap, decreasing the magnetic circuit reluctance or increasing the magnetostatic energy. Second, the magnetic torque increases first and then decreases as the number of pole-pair increases. And it reaches the maximum value when the number of pole-pair is 12. Third, based on the coupling of the magnet volume under two constraints, i.e., the coverage area of permanent magnet on the tool's effective cross section and the magnet thickness, the thickness of permanent magnet is 8.4 mm. And the magnetic torque on the unit volume of magnet reaches the maximum value when the coverage area of permanent magnet on the tool’s effective cross section is 71%. Fourth, the absolute error between the experimental result and the numerical simulation result is less than 17%. It is indicated that the numerical simulation model can satisfy the required engineering calculation accuracy. In conclusion, the numerical simulation model established in this paper is rational and can be used as a technical method for optimizing the structure of this newly-developed tool.