Le 14-09-16 14:39, clipka a écrit :
> Am 16.09.2014 16:24, schrieb Thomas de Groot:
>> Well, I am interested in modelling wind patterns over a reed field, or a
>> corn field. What I seem to observe are turbulent wave patterns moving
>> the stalks back and forward while going over the field.
>
> Looks quite promising for a start.
>
>> suggestions are more than welcome of course.
>
> Sure.
>
> It seems to me that you're bending any given reed with a constant radius
> along the whole length of the stalk; I suspect that the stalk should
> bend most strongly at the base, because of (a) the wind acting not only
> on the tip of the stalk, but also on lower portions, so that the wind
> force affecting the bending of any given point increases downward along
> the stalk, (b) the stalk acting as a lever, further amplifying the
> bending force exerted on any given point on the stalk based on how far
> it is from the tip, and (c) the wind force acting upon a near-vertical
> portion of the stalk being stronger than that acting upon a
> near-horizontal portion.
>
> The reeds should bend in a single direction only (albeit at different
> amplitudes) - the primary direction of the wind.
>
> As for the waves, I guess they are not from turbulences already present
> in the wind, but rather from upright reeds "shadowing" those further
> downwind causing them to rise again, while themselves being exposed to
> the wind and beginning to move downward; this effect might be initiated
> and amplified by the individual reeds also resonating in the wind due to
> (c).
>

In a field, the wind can't affect the stalks near the base because the 
other stalks up wind will shield those downwind. So, the wind only 
affect the top part as soon as you are a few meters from the wind facing 
edge.

The stalks tend to be slightly broader near the base, making them stiffer.

In most cases, there is some sort of flowering or grapes of seeds near 
the top, increasing the surface exposed to wind and adding some height 
neat the tips.

This combine in making the stalks bend in a smooth way with the maximum 
curvature somewhere near mid height.



Alain

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