The nonlinear forced vibrations of a cantilevered pipe conveying fluid under base excitations are explored by means of the full nonlinear equation of motion, and the fourth- order Runge-Kutta integration algorithm is ...The nonlinear forced vibrations of a cantilevered pipe conveying fluid under base excitations are explored by means of the full nonlinear equation of motion, and the fourth- order Runge-Kutta integration algorithm is used as a numerical tool to solve the discretized equations. The self-excited vibration is briefly discussed first, focusing on the effect of flow velocity on the stability and post-flutter dynamical behavior of the pipe system with parameters close to those in previous experiments. Then, the nonlinear forced vibrations are examined using several concrete examples by means of frequency response diagrams and phase-plane plots. It shows that, at low flow velocity, the resonant amplitude near the first-mode natural frequency is larger than its counterpart near the second-mode natural frequency. The second-mode frequency response curve clearly displays a softening-type behavior with hysteresis phenomenon, while the first-mode frequency response curve almost maintains its neutrality. At moderate flow velocity, interestingly, the first-mode resonance response diminishes and the hysteresis phenomenon of the second-mode response disappears. At high flow velocity beyond the flutter threshold, the frequency response curve would exhibit a quenching-like behavior. When the excitation frequency is increased through the quenching point, the response of the pipe may shift from quasiperiodic to periodic. The results obtained in the present work highlight the dramatic influence of internal fluid flow on the nonlinear forced vibrations of slender Pipes.展开更多
空间熔盐堆运行过程中,反应性控制起到十分重要的作用,目前陆地上常采用的主动反应性控制方式存在出现故障的概率等问题。空间熔盐堆需要一种非能动反应性控制方式,在无需外源及人为操控情况下,对反应性实施自动控制,降低事故发生风险...空间熔盐堆运行过程中,反应性控制起到十分重要的作用,目前陆地上常采用的主动反应性控制方式存在出现故障的概率等问题。空间熔盐堆需要一种非能动反应性控制方式,在无需外源及人为操控情况下,对反应性实施自动控制,降低事故发生风险。本文针对热管式液态燃料空间熔盐堆,利用液态燃料的热胀冷缩机制,当堆芯处在正常运行工况下温度发生变化时,提出并设计一种液态燃料移出移入非能动反应性控制系统(Liquid Fuel in/out Transfer in a Passive Reactivity Control System,LFT-PRCS),并对含有该系统的堆芯进行在正常运行工况下物理特性分析,以及该系统结构参数与反应性补偿能力分析。结果表明:正常运行工况下,含有LFT-PRCS的堆芯具有更负的反应性,且堆芯物理特性未发生明显变化;LFT-PRCS中毛细管道较佳结构参数为:高度为10 cm、内层半径为0.2 cm、外层半径为0.4 cm;LFT-PRCS在寿期初、寿期末温度发生2 K波动时,可向堆芯引入约20 pcm的反应性。上述结果表明,LFT-PRCS可提高堆芯固有安全性,一定程度上补偿燃耗造成的反应性损失。展开更多
基金supported by the National Natural Science Foundation of China (Nos. 11622216 and 51409134)
文摘The nonlinear forced vibrations of a cantilevered pipe conveying fluid under base excitations are explored by means of the full nonlinear equation of motion, and the fourth- order Runge-Kutta integration algorithm is used as a numerical tool to solve the discretized equations. The self-excited vibration is briefly discussed first, focusing on the effect of flow velocity on the stability and post-flutter dynamical behavior of the pipe system with parameters close to those in previous experiments. Then, the nonlinear forced vibrations are examined using several concrete examples by means of frequency response diagrams and phase-plane plots. It shows that, at low flow velocity, the resonant amplitude near the first-mode natural frequency is larger than its counterpart near the second-mode natural frequency. The second-mode frequency response curve clearly displays a softening-type behavior with hysteresis phenomenon, while the first-mode frequency response curve almost maintains its neutrality. At moderate flow velocity, interestingly, the first-mode resonance response diminishes and the hysteresis phenomenon of the second-mode response disappears. At high flow velocity beyond the flutter threshold, the frequency response curve would exhibit a quenching-like behavior. When the excitation frequency is increased through the quenching point, the response of the pipe may shift from quasiperiodic to periodic. The results obtained in the present work highlight the dramatic influence of internal fluid flow on the nonlinear forced vibrations of slender Pipes.
文摘空间熔盐堆运行过程中,反应性控制起到十分重要的作用,目前陆地上常采用的主动反应性控制方式存在出现故障的概率等问题。空间熔盐堆需要一种非能动反应性控制方式,在无需外源及人为操控情况下,对反应性实施自动控制,降低事故发生风险。本文针对热管式液态燃料空间熔盐堆,利用液态燃料的热胀冷缩机制,当堆芯处在正常运行工况下温度发生变化时,提出并设计一种液态燃料移出移入非能动反应性控制系统(Liquid Fuel in/out Transfer in a Passive Reactivity Control System,LFT-PRCS),并对含有该系统的堆芯进行在正常运行工况下物理特性分析,以及该系统结构参数与反应性补偿能力分析。结果表明:正常运行工况下,含有LFT-PRCS的堆芯具有更负的反应性,且堆芯物理特性未发生明显变化;LFT-PRCS中毛细管道较佳结构参数为:高度为10 cm、内层半径为0.2 cm、外层半径为0.4 cm;LFT-PRCS在寿期初、寿期末温度发生2 K波动时,可向堆芯引入约20 pcm的反应性。上述结果表明,LFT-PRCS可提高堆芯固有安全性,一定程度上补偿燃耗造成的反应性损失。
