Hydraulic equipment commonly is operated under complex conditions, characterized by adverse factors such as intense vibration and impact. These factors, combined with the uncertainty of structural parameters, can easily lead to pressure fluctuations in relief valves, potentially resulting in equipment failure. To address this issue, a reliability analysis model for the pressure fluctuation failure of direct‑acting relief valves is presented, considering the influence of environmental vibration and uncertainty factors. A dynamic model for the relief valve under environmental vibration is developed, and then its corresponding dynamic characteristics are analyzed. Moreover, based on the dynamic characteristics analysis of the relief valve and the released value of the national standard, a limit‑state function for pressure fluctuation failure is established. Furthermore, the reliability sensitivity analysis is performed using the Kriging model to evaluate the contribution of each parameter to the occurrence of pressure fluctuation failure. The results indicate that the vibration frequency has the most significant impact on reliability, followed by the spool mass and vibration amplitude, while the controlled chamber volume and sensitive chamber volume show a minimal contribution. The research results can provide a theoretical basis for regulating the pressure fluctuation failure of relief valves under environmental vibration.
式中:γ( x )为压力波动偏差与调定压力的比值,其值由式(1)~(5)构成的MATLAB/Simulink仿真获取,具体仿真框图见图2.图2中的5个子系统对应式(1)~(5).
对随机变量 x 的联合概率密度函数hx ( x )在失效域G( x )≤0求积分可得失效概率为[14-18]
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采用数值模拟法获取式(7)的近似解,因为其解析解通常难以计算. Monte Carlo(MC)法是精度可以接近真值的模拟法,但其计算效率低下,尤其是遇到具有隐式的复杂工程问题时.因此,MC法常作为标准法用以检验新方法的性能[14-18].近年来,代理模型因兼顾计算精度和效率而被广泛应用于可靠性领域,其中Kriging模型能够提供预测均值和方差而备受关注.故本文采用Kriging模型构建输入随机变量和响应值之间的映射关系代替实际仿真来完成计算,避免过多调用仿真计算真值,提高计算效率.
基于联合概率密度函数生成6×104个样本由MC法计算,再由Kriging模型计算,所得可靠性结果如表3所示.其中MC法计算的响应值G( x )及其频率直方图见图9和图10.由表3可知,Kriging和MC法的可靠性结果十分接近,表明基于Kriging模型的可靠性分析有效.此外,Kriging模型计算时间短,效率更高.由图10可知,在不确定性参数的影响下,压力响应不再是确定值,而是服从近似正态分布的随机值.
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