Wind speed profiles

If one is studying the transport of material through the tree canopy of a forest, it is most desirable to disturb the natural environment as little as possible in making a wind measurement in the canopy. An extremely sensitive wind system is necessary because one would expect the winds to be extremely light. Also, it may be necessary to make supporting measurements both above and below the canopy, so that a wind speed profile is obtained. 

Wind has a highly turbulent and gusting character. In addition, a time-mean speed varies with the height from the ground and the roughness of the terrain over which the wind passes. The time-mean wind speed profile can be determined using the following expression ... 

The Britter-McQuaid model is a dimensional analysis technique, based on a correlation developed from experimental data. However, the model is based only on data from flat rural terrain and is applicable only to these types of releases. The model is also unable to account for the effects of parameters such as release height, ground roughness, and wind speed profiles. 

Although a logarithmic wind speed profile did not exist in our chamber, the measured wind speed was adjusted to an artificial wind speed of 2.21 m/s at 10 cm height using Equation 7. 

Figure 10. Average wind speed profiles (shaded area) and standard deviations (vertical bars) when wind was blowing from a clearcut into a 27 m Douglas fir forest.

Here, kgj is in (kmol/m2/s), Ps is the ambient pressure in (Pa), T is the liquid pool surface temperature (K), w is a 10 meter wind speed in (m/s), and n is an exponent that depends on atmospheric stability and surface roughness. Typical values for n range between 0.25 and 1. When n is equal to 0.25, the wind speed profile implied by the correlation is a 1/7 power law profile. For n = 0.25, equation (3-5) reduces to... 

Plants exert a frictional drag on moving air masses (e.g., Fig. 7-5) and thereby modify the local wind patterns. The frictional interaction between trees and wind is different from that of a flexible crop such as wheat, which leads to different form drag (Eq. 7.9) and different wind patterns in the overlying turbulent air. Topographical features such as canyons or cliffs also affect the local wind speed profile above the vegetation. 

Within the surface layer the mean wind-speed profile is commonly described by logarithmic expressions. For situations when stratification has only a minor influence a modified logarithmic law has been proposed ... 

Log Law - In reference to a wind energy conversion system, the wind speed profile in which wind speeds increase with the logarithmic of the height of the wind turbine above the ground. 

Windpower Profile - The change in the power available in the wind due to changes in the windspeed or velocity profile the windpower profile is proportional to the cube of the wind speed profile. 

Wind Speed Profile - A profile of how the wind speed changes with height above the surface of the ground or water. 

The program reads the information on the building and its location for every policy in the insurance portfolio and then assigns a wind speed profile to it based on its location. Next the algorithm calculates the number of comer and middle units per floor. At the same time the vulnerability curves for all types of apartment units and the corresponding components physical vulnerability curves are selected. 

TABLE V Values of zo and u. for Use in Vertical Wind Speed Profiles... 

The models discussed up to this section are an idealized picture where the wind-speed profile is uniform, the... 

Wind data are normally quoted on the basis of 10 m height. Wind speeds are reduced substantially within a few meters of groimd due to frictional effects. As many smaller discharges of dense materials remain near ground level, wind data should be corrected from 10 m to that relevant for the actual release. An equation for the wind speed profile is given for near-neutral and stable wind profiles in API (1996) and AIChE/CCPS (1996a) ... 

More detailed dense gas models require additional inputs. These could include groimd roughness, physical properties of the spilled material (molecular weight, atmospheric boiling temperature, latent heat of vaporization), wind speed profiles, and the physical properties of the ground (heat capacity, porosity, thermal conductivity). 

FIGURE 16.8 Sample wind speed profile over ripped slag at a smelter site, (a) Linear z (b) logz. 

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