Despite the shadow zone of overlap, the distinction is there.
These are placed on the top of the barrier in order to reduce sound diffracted into the shadow zone.
The method makes it possible to predictLATat the receiver, located beyond the shadow zone that is caused by upward refraction.
Improved noise control in the shadow zone of a barrier is achieved by the use of two control sources and angular orientation as mentioned above.
Moving downward, away from the drift, the shadow zone asymptotically re-equilibrates to the undisturbed flow conditions due to capillary forces.
Specifically, we measured the effective shadow zone by using sand traps designed for this purpose and found a linear relationship between the shadow zone and the wind shear velocity, consistent with Sharp's hypothesis.
Nonetheless, the shadow zone can be one of the major mechanisms contributing to the linear increase of the ripple wavelength with wind speed at the nonlinear growth stage of the ripples where merging events between small ripples take place.
However, contrary to what Sharp assumed, we found that the shadow zone is not completely screened from particle impacts, which as indicated by numerical simulations is due to the wide distribution of impact angles.
Second, it is shown that the method can be applied to design outdoor sound barriers in order to reduce the sound level in the shadow zone behind the barrier.
Particular angular orientations, with respect to the center of the barrier top, and spacings of the linear arrays of control sources and error sensors result in moderate to significant additional reduction of the acoustic pressure in the shadow zone.
It has been found that the flow causes a modification and displacement of the lobes of the directivity pattern and the shadow zone of the scattered field, which can be important at Mach numbers greater than 0·2.
