Monday, February 14, 2005

What's your Strouhal Number?

I was hoping to do some moderately original research in this area (completely outside my current fields of expertise), but I have not been able to find any data with which to do the research. Specificly, I need high quality digital video (preferrably with time markers) of multiple world-class runners covering a known distance. I also need to know the the length of their strides while doing that running.

Why? I think it would be worth it to compute a Strouhal number for an efficient (world-class) human. Don't some people seem to look like they are moving efficiently, while others seem to move rather inefficiently? Perhaps this could explain why. It also might help the world of robotics. Hmm... as I type this, I'm wondering if I can't do a fair amount of the research on myself.

What is a Strouhal number? This page does a good job of describing it:
For an animal or insect in flight, the Strouhal number is determined by the frequency (f ) of wing strokes, multiplied by the amplitude (A) of the wing, divided by the animal’s forward speed (U) through the air. The Strouhal number is equal to f A/U.
Note that the amplitude (A), also known as wingtip excursion, of the stroke is the vertical distance traveled by the tip of the wing during the flapping stroke (from highest point to lowest point). For a human, this would be the horizontal distance of the stride.

Nature magazine did an article on this topic and included a graph which shows that flying and swimming animals all have Strouhal numbers that fall into a range of 0.2 to 0.4.  Additional analysis was done at Oxford.

Biomechanics may come into play here, in which case, papers like this one and this one would be of interest for topics on the human stride. So would this discussion of the scaling of walking speed.
Perhaps someone has done some research on this with regard to humans now.  By the way, did you know everyone converts from walking to running between 2 and 3 m/s?

Speaking of efficiency (warning: drastic change of subject ahead)... here is a man after my own heart. Some might suggest that I need better organization skills... maybe I do, maybe I don't. Either way, this is an example of stuff to keep in mind.


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