[Rhodes22-list] Fluid Dynamics

[Bill Effros]

Nice Job! Ron,

Thanks --

Loved the tea leaf explanation, too.  I'd read about the "problem" but 
no one ever took the time to explain the solution.

Bill Effros

Ronald Lipton wrote:

> Bill,
>
>    In general there is a boundary layer between a solid object and
> fluid flowing around it.  Typically this is analyzed to understand the
> sources of drag on a hull, which are dependent on the relative
> velocities, the viscosity of the fluid, and whether the flow is laminar
> or turbulent.  The actual smoothness of the hull has only a minor
> effect.  The molecular layer adjacent to the hull is considered as
> moving at the hull velocity, there is then a boundary layer where the
> velocity of the the water increases to the velocity of the stream.
> For a hull moving through water at ~5 knots the boundary layer is
> a few millimeters.  It may be a bit larger in a river, but if the bed has
> few large obstacles it is hard to see how there would be a large
> enough turbulent boundary layer the tumble an anchor.  the problem
> is different if there is a bend or obstruction in the river with changes
> the direction of flow.
>
> By the way one of the nice applications of the boundary layer concept
> is the "tea leaf" problem, which analyzes the reason tea leaves 
> congregate
> at the center of a teacup after stirring in terms of boundary layer 
> effects.
>
>
> Ron
>
>
>
> On Jan 16, 2006, at 7:06 PM, Bill Effros wrote:
>
>> Here's the fluid dynamics part.  As I understand eddies, they occur 
>> because the water is not one solid mass flowing at a constant speed.  
>> I think the water can move faster at the surface than the bottom.  So 
>> if you drop an anchor it encounters turbulence which may cause it to 
>> tumble or spin on the way to the bottom, but the water may be 
>> traveling far more slowly at the bottom allowing the anchor to set at 
>> a much slower speed than the boat is moving.
>>
>> I could be completely wrong about this.
>
>
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