加劲式压力钢管临界外压数值计算方法

Numerical Calculation Method of Stiffened Penstock’s Critical External Pressure

压力钢管是水利水电工程中常见的衬砌类型,其外压稳定性至关重要。为构建加劲式压力钢管临界外压有限元准确计算方法,提出多环建模、分段约束的数值求解模型,将计算结果与Mises理论公式、规范公式展开对比讨论;考虑复杂外部约束环境,全面探究加劲环位置不同约束方案对钢管抗外压能力的影响,并基于数值求解方案研究加劲环对钢管管壁临界外压的增强作用及其有效约束长度,结合光面管的屈曲临界外压公式进一步提炼一种加劲式压力钢管管壁临界外压快速计算方法。结果表明:有限元软件ABAQUS中的特征值屈曲计算具有较高的准确度,与Mises公式计算结果保持较好的一致性,而规范采用的简化式计算结果会随着钢管屈曲波数的变化与Mises公式存在不同程度的差异;针对不同径厚比的加劲式压力钢管,其管壁临界外压随着加劲环位置约束作用的提高而增大,随着加劲环间距、钢管半径与钢管厚度比值的增大而逐渐减小,且当加劲环间距大于20 m后不再发生明显的波动现象,逐渐失去约束作用;本文提出的加劲式压力钢管管壁临界外压快速计算方法可同时应用于光面管和加劲环管,与相关Mises理论公式、规范公式相比,具有准确性高、计算简单、方便使用的特点,可为实际工程中钢管管壁临界外压计算提供一种新的选择。

Penstock is a common type of lining in water conservancy and hydropower projects,and its stability under external pressure is very important.In order to establish an accurate finite element method for calculating the critical external pressure of stiffened penstock,a reliable numerical model with multiple rings was proposed in the paper,and the results were compared with those calculated by the von Mises theoretical formula and the simplified formula used by design specification for steel penstocks.Considering the complex external environment,the influence of different constraint schemes of stiffening ring under the external pressure of penstock was comprehensively investigated.Based on the proposed numerical solution under particular constraint scheme,the effect of stiffening ring on the critical external pressure of penstock and its effective constraint length were studied.A new fast method for calculating the critical external pressure of stiffened penstock was developed based on the buckling critical external pressure formula of plain penstock.The results show that the eigenvalue buckling analysis in ABAQUS has high accuracy and is in good agreement with the results of the von Mises formula.However,the results of the simplified formula used in the specification differ from the von Mises formula to some extent with the change of the bending wave.For stiffened penstocks with different diameter-thickness ratios,the critical external pressure of the stiffened penstock increases with the increase of the constraints,and it decreases with the increase of the spacing and the ratio of the penstock. When the distance between the stiffening rings is greater than 20 m, no obvious fluctuation occurs. The fast calculation method for the critical external pressure of penstock presented in this paper can be applied to both plain penstock and stiffened pen-stock, which is accurate, simple and convenient, and can serve as an alternative method for the critical external pressure calculation in practical engineering.