Re: Midterm Question - Sort of

[brian whatcott <inet@INTELLISYS.NET>]

At 11:25 7/7/99 -0700, Leigh wrote:

> It was not the cables of the bridge that shed vortices at the bridge
> normal mode oscillation frequency, but rather the bridge deck itself.
> That is, indeed, the mechanism responsible for aeolian oscillation.
> I believe the bridge actually flexed in more than one of its normal
> modes. I won't check that just now, but maybe someone else can help
> me. I seem to have no allies in this discussion. Have I slaughtered
> a sacred cow?
>
> Leigh

The word 'Aeolian' which Leigh used is particularly a propos.
The ten or more strings of this wing-excited harp
do not in general resonate on their fundamental.

  Instead, in the delightful phrase of the EncBrit 14th,
they vibrate 'in aliquot parts'.
 This is to say, at the 2nd harmonic, which is the octave
or half string length,the third string length or  'twelfth',
 the third harmonic and so on.

If I recall the visual record, the Tacoma Narrows bed galloped
at several antinodes, in the 'Aeolian' way, helped by a 43 MPH wind
through its thin narrow (two-lane) roadway plate.



brian whatcott <inet@intellisys.net>
Altus OK