A Galerkin Numerical Method for the Pipe Conveying Supercritical Fluid Under Forced Vibration
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摘要: 当流速超过临界值,输液管的直线平衡位形会发生失稳,但是系统会重新稳定在新的曲线平衡位置.通过引入坐标变换的方法,动力学模型转变为含有变系数的偏微分控制方程.采用4阶Galerkin截断的方法,使控制方程转变为常微分方程.给出具体的数值算例,发现4阶截断的固有频率要比2阶截断的固有频率更精确.同时,计算出前两阶固有频率出现可公度的情况,从而激发2∶1内共振现象.利用Runge-Kutta数值模拟的方法,在发生内共振流速范围的特定区域进行大量数值运算,结果表明高维系统的条件下,管道的不同径向坐标点的横向位置处,均出现软硬特性,而在内外共振完全调谐时,出现双跳跃现象.
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关键词:
- 超临界 /
- Galerkin方法 /
- 内共振 /
- 软硬特性 /
- 双跳跃
Abstract: For the pipe conveying fluid, as the flow rate increased over a critical value, the equilibrium configuration was found to get unstable and bifurcate into curved equilibrium patterns. The nonlinear dynamic model for the simply-supported pipe was built and converted to variable-coefficient partial differential control equations through coordinate transformation. The 4-term Galerkin truncation procedure was then applied and the control equations of motion were transformed to 2nd-order ordinary differential equations to be solved with numerical techniques. The natural frequencies of the simply-supported pipe conveying fluid were calculated, and the result comparison was made between the 2-term and 4-term Galerkin truncation methods to give that the latter had higher accuracy. For specific system parameters, the 2nd-order natural frequency was approximately two times of the 1st-order one within a certain range of flow velocity, and the 2-to-1 internal resonance occurred. Massive computation of the amplitude-frequency responses of the pipe conveying fluid before and after internal resonance was conducted with the Runge-Kutta numerical technique. The results show that, as the flow rate and tuning parameter vary, the softening, hardening and double jumping phenomena will be respectively identified by the amplitude-frequency responses of the pipe.-
Key words:
- supercritical fluid /
- Galerkin procedure /
- internal resonance /
- softening and hardening /
- double jumping
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