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May 16, 2005: Pylon airflow

Sometimes you never know when your past will catch up with you. When I first came to MUSC, our outsourced IT support folks could not execute within my frame of reference - Internet-centric learning. So I formed the Information Technology Laboratory, aptly named the IT Lab by Nafees BinZafar, one of my first. The IT Lab was set up to give me the freedom to execute within the web world and I can honestly say that I have learned more from them than they from me. I simply ignited their curiosity fuse and then got out of their way. One of the few rules in the IT Lab was that you cannot resign - only graduate.

Nafees and Nathan are two of my graduates that now work for Digital Domain - doing systems and animation infrastructure - and they continue to contribute back to our IT Lab. Today Nafees wrote and confessed of being confused by the design of the tops of the east and west pylons. Being a well trained graduate of my IT Lab, he did a simulation to explore two different alternatives.

In his words

Hi Frank.  I've been looking at your cooper river bridge pictures.  
And I wondered why the tops of the towers were indented, and not flat.  
I guessed it had to be for aerodynamic reasons, but I couldn't find anything 
on the web about the exact reasons.  So I ran a simulation.  I couldn't 
find the exact dimensions for the tops, so I eyeballed it from your 
pictures.  For comparison I modelled a tower with a flat top.  
I suppose I should have done one with a pointed top also.

I'm attaching movies of the top view and the side view of the simulations.  
The wind is blowing in at about 22 mph.  The massless tracer smoke is 
generated by 2 sources; 1 on top, and 1 on the leeward side.  The sims 
didn't really show anything numerically conclusive.  My simulation 
resolution is much too low for that.  The vortex shedding frequency seems 
a little bit higher in the "flat-top" configuration, and downstream 
the flow is more turbulent.  Also, there is a very substantial pressure 
drop in the indented region.  So I suspect that you will have some 
really good photo-ops of condensation trails on a cold and windy day. 

Here are the two videos (avi and mpg format). As with any collaborative effort, there are issues. In this case, the avi or mpg files may require some care when displaying. We are exploring alternative formats.

Sept. 22, 2008:. Nafees has done well at Digital Domain, winning an Oscar for his work in fluid simultion. Check out the writeup from the Bangladesh perspective

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