VibrationMaster 发表于 2012-5-20 09:58

Flutter is a self-feeding and potentially destructive vibration where aerodynamic forces on an object couple with a structure's natural mode of vibration to produce rapid periodic motion. Flutter can occur in any object within a strong fluid flow, under the conditions that a positive feedback occurs between the structure's natural vibration and the aerodynamic forces. That is, the vibrational movement of the object increases an aerodynamic load, which in turn drives the object to move further. If the energy input by the aerodynamic excitation in a cycle is larger than that dissipated by the damping in the system, the amplitude of vibration will increase, resulting in self-exciting oscillation. The amplitude can thus build up and is only limited when the energy dissipated by aerodynamic and mechanical damping matches the energy input, which can result in large amplitude vibration and potentially lead to rapid failure. Because of this, structures exposed to aerodynamic forces — including wings and aerofoils, but also chimneys and bridges — are designed carefully within known parameters to avoid flutter. In complex structures where both the aerodynamics and the mechanical properties of the structure are not fully understood, flutter can only be discounted through detailed testing. Even changing the mass distribution of an aircraft or the stiffness of one component can induce flutter in an apparently unrelated aerodynamic component. At its mildest this can appear as a "buzz" in the aircraft structure, but at its most violent it can develop uncontrollably with great speed and cause serious damage to or lead to the destruction of the aircraft, as in Braniff Flight 542.

ChaChing 发表于 2012-5-20 11:32

本帖最后由 ChaChing 于 2012-5-20 11:35 编辑

yyxt007 发表于 2012-5-17 08:38 http://www.chinavib.com/static/image/common/back.gif
回复 10 # ChaChing 的帖子

颤振"从外界吸收能量"这个确实没有说清楚,应该是从外界吸收的能量大于系统本身 ...

个人水平有限, 也是不知该如何表述较好! 试著说明如下, 大家讨论帮忙修订下:@)
结构体不断从气动力吸收能量, 当该吸收能量大于系统阻尼(结构体&气动)消耗的能量时, 即发生系统动态发散现象(颤振)
或说成, 系统间一种能量的转移, 对系统而言并无所谓输出或输入能量

ChaChing 发表于 2012-5-20 11:55

SZCLGZQ 发表于 2012-5-20 08:57 static/image/common/back.gif
谢谢指导,那么请问颤振有可能是共振吗

这个问法可能没问清楚!?
或许应该问, 针对一个振动现象, 如何判断其为颤振或共振?

如yyxt007所说颤振和共振不是一回事!
共振时所显现的频率为结构固有频率, 但当考虑气动效应时, 系统的固有频率已经不同於原有结构固有频率了! 当然发生颤振时, 其表徵频率也不同於原有结构固有频率了

yyxt007 发表于 2012-5-20 18:40

本帖最后由 yyxt007 于 2012-5-20 18:42 编辑

看大家对颤振还挺有兴趣的,今天特地把当年所用的教材翻了一遍,现在把其中的一些关键词汇的理解摘抄如下:
颤振:弹性系统在均匀气流中的自激振动,是系统的动不稳定性问题;
颤振特点:颤振是一种自激振动;颤振是几个自由度之间耦合作用的结果,不同自由度运动之间的相位差也是引发颤振的一个重要原因。
自激振动(来源于非线性振动):系统在常能源作用下,依靠自身各部分之间的相互耦合作用而产生的稳态周期运动。
自激振动例子:

sees 发表于 2012-5-21 12:53

ChaChing 发表于 2012-5-20 02:24 static/image/common/back.gif
回复 12 # sees 的帖子

可能个人表达不清!?


非常感谢!

//bow

看图中公式没有阻尼项,应该像楼上大侠所说,在颤振情况下,阻尼为0或者负值。

那对于小变形情况,我还是想不出来,怎么会有这个情况,不知能否举例说明。

对于第二个问题,弄清楚了,再谢!

ChaChing 发表于 2012-5-22 00:58

本帖最后由 ChaChing 于 2012-5-22 00:58 编辑

回复 20 # sees 的帖子

抱歉, 真的没表达清楚
应该说许多地方在方便求解时, 是做了小变形的假设
13F给的图, 主要是为了简单说明aerodynamic forces induced by the structural deformation Fa及external forces Fe两者的差异, 更严谨的话, Fa不一定仅为位移的函数
另外结构是可以考虑结构阻尼项的, 如19F所示

cxmnpu 发表于 2012-5-22 16:07

ChaChing 发表于 2012-5-20 02:24 static/image/common/back.gif
回复 12 # sees 的帖子

可能个人表达不清!?


专业。。。。学习了。
有些液压阀上听说有颤振。

lcbaoqi 发表于 2012-5-23 15:45

受教了。。谢谢

tiger0004 发表于 2012-6-18 13:33

颤振和共振的区别简单来说就是:共振时,系统只靠自身阻尼来平衡外力,弹簧力和惯性力相互抵消了。而颤振时一般阻尼是负的,其从一种能量消耗机制变成了能量输入机制,其输入的能量维持了系统周期性的振荡,并且在总体上说由于没有能量耗散,往往会损坏机械。

卖薪沽酒 发表于 2013-8-5 17:23

学习了,谢谢。
最近正在做壁板颤振的相关问题,也对问下中提到的颤振概念很迷茫,论坛上的解释虽然还是没有理解透彻,但是比以前理解的要深刻多了~再次谢谢这个伟大的论坛~

mxlzhenzhu 发表于 2013-8-5 20:10

http://www.cfd-online.com/Forums/cfx/70304-fsi-flutter.html

402144999 发表于 2014-7-26 12:19

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查看完整版本: 关于颤振的具体含义!!!