弹性安装条件下机械设备自由振速测量方法

提出了一种弹性安装条件下机械设备自由振速的测量方法。首先,采用阻抗分析法建立了单层耦合隔振系统的动力学方程;其次,利用有效点导纳将多输入多输出系统转化为单输入单输出系统,理论分析了隔振系统对自由振速的影响因素,进而提出了一种自由振速的获取方法;最后,对该方法进行了误差分析,并给出了适用频率范围。通过有限元模拟和实验验证了该方法的正确性。本研究对于自由振速的获取提供了理论参考,具有一定的工程应用价值。

全柔性浮筏隔振系统建模与隔振性能分析

建立了一种包含设备、隔振器、筏架和基础的全柔性浮筏隔振系统的动力学模型。首先,将设备自由振速引入到浮筏隔振系统建模中,提高了模型精度;然后,利用四端参数模型的思想,将筏架的点到点导纳矩阵表示为四端参数网络模型;最后,采用阻抗综合法完成总系统动力学方程,该模型简洁且通用性强。通过数值算例验证了本模型的正确性和有效性,并分别讨论了筏架刚性与柔性以及隔振器参数对隔振效果的影响。所提出的方法对浮筏系统隔振效果的工程计算和设计具有较为重要的理论价值。

船舶设备激励源载荷转换方法及应用

设备激励源是分析船舶振动噪声特性的输入条件,对其获取方法研究具有重要价值。介绍以自由振速为桥梁的不同安装环境下船舶设备激励源特性转换关系,建立利用台架试验数据估算实船安装环境下设备激励源特性的工程应用方法,并给出应用流程。通过典型船用设备激励源特性测试和计算,提出振动测点布置原则和数据测试要求。设备机脚和基座的振动速度计算结果和实船测试结果吻合良好,表明所采用的船舶设备激励源特性转换方法可应用于船舶振动噪声工程问题分析。

Numerical study on the correlation of transonic single-degree-of-freedom flutter and buffet

Transonic single-degree-of-freedom(SDOF) flutter and transonic buffet are the typical and complex aeroelastic phenomena in the transonic flow. In this study, transonic aeroelastic issues of an elastic airfoil are investigated using Unsteady Reynolds-Averaged Navier-Stokes(URANS) equations. The airfoil is free to vibrate in SDOF of pitching. It is found that, the coupling system may be unstable and SDOF self-excited pitching oscillations occur in pre-buffet flow condition, where the free-stream angle of attack(AOA) is lower than the buffet onset of a stationary airfoil. In the theory of classical aeroelasticity, this unstable phenomenon is defined as flutter. However, this transonic SDOF flutter is closely related to transonic buffet(unstable aerodynamic models) due to the following reasons. Firstly, the SDOF flutter occurs only when the free-stream AOA of the spring suspended airfoil is slightly lower than that of buffet onset, and the ratio of the structural characteristic frequency to the buffet frequency is within a limited range. Secondly, the response characteristics show a high correlation between the SDOF flutter and buffet. A similar "lock-in" phenomenon exists, when the coupling frequency follows the structural characteristic frequency. Finally, there is no sudden change of the response characteristics in the vicinity of buffet onset, that is, the curve of response amplitude with the free-stream AOA is nearly smooth. Therefore, transonic SDOF flutter is often interwoven with transonic buffet and shows some complex characteristics of response, which is different from the traditional flutter.

Experimental investigation of vortex-induced vibrations of long free spans near seabed

There are many experimental studies dedicated to determining the effect of the proximity of a plane boundary on the vortex-induced vibration (VIV) of submarine pipeline spans, but they all only concerned the first mode VIV motion of the pipe. In this paper, a pipe model, 16 mm in diameter, 2.6 m in length and with a mass ratio (mass/displaced mass) of 4.30, was tested in a current tank. The reduced velocity was in the range of 0-16.7 and gap ratios at the pipe ends were 4.0, 6.0 and 8.0. The response of the model was measured using optical fiber strain gauges. Results of response amplitude and frequency were presented and the transition from the first dominant mode to the second one was shown. In the tests, it was found that the response amplitude experienced a continuous transition between the two modes, but the dramatic increase in the response frequency appeared with the shift in dominant mode from the first mode to the second one as the flow velocity increased. As the gap ratio decreased, the shift in the dominant mode took place at a higher reduced velocity.