Wind force

The science of building aerodynamics considers the influence of wind forces over buildings and the associated mechanics of fluids these are complex in nature and are not considered here. It is sufficient to briefly consider Fig. 9.21, which shows how wind passing over a building produces a positive pressure on one side and a negative pressure on the other side. It is this pressure difference that produces airflow through openings. The combined wind and stack effects vary with the seasons. 

Air infiltration The uncontrolled air interchange through structural imperfections and other openings into a space, due to natural convection, rising currents, or wind forces over a building. 

Beaufort scale The scale used for estimating and reporting wind forces, in which 0 is calm (velocity less than 0.5 m s" ) and 12 is a hurricane. 

Infiltration The leakage of air through the imperfections in a building structure, due to thermal or wind forces. 

Natural ventilation Ventilation achieved by means of wind forces or density differences or a combination of the two, as opposed to mechanical ventilation, which depends on a rotodynamic device. 

Natural ventilation system Ventilation of a space by the influence of thermal forces and wind forces over and around a building. Under certain conditions only one of these applies, however, in the majority of cases it is assumed that both apply. 

Through ventilation Ventilation that takes place through a space due to wind forces, normally resulting in poor mixing of the room air due to short circuiting. 

Ventilation, natural Air movement created by wind forces, thermal forces, or a combination of both. 

Table 6.10 presents some damage effects. It may give the impression that damage is related only to a blast wave s peak overpressure, but this is not the case. For certain types of structures, impulse and dynamic pressure (wind force), rather than overpressure, determine the extent of damage. Table 6.10 was prepared for blast waves of nuclear explosions, and generally provides conservative predictions for other types of explosions. More information on the damage caused by blast waves can be found in Appendix B. 

It will be shown that a more elegant and more easily applicable solution of the problem is given by choosing another reference system. Both the dilute alloy and the unperturbed host can be described with respect to a common reference system, which consists of the unperturbed part of the alloy system and for obvious reasons is called void system. This void system allows for a single-site evaluation of the matrix element describing the wind force in electromigration and the t-matrix element required for the calculation of the residual resistivity due to a saddle-point defect. 

The formalism described above will be used to calculate the wind valence in different systems. The wind force on an atom is proportional to the applied electric field... 

Figure 4 The wind valence in A1 along the migration path. The initial and saddle point positions are at the origin and at 0.5 respectively. The lower curve is for Cu, the upper curves are for self-electromigration. The dashed and the dotted curve show the influence of a Cu atom at positions 1 and 2 of Fig. 3 respectively, on the wind force in pure A1 (thick curve).

Wind forces shall be applied to the entire structure. The wind directions that result in the highest stresses for each component of the structure must be determined and considered. Wind forces for the various wind speeds shall be calculated according to... 

The supports for a tall chimney must be designed to withstand a 120 mph wind. If the chimney is 10 ft in diameter and 40 ft high, what is the wind force on the chimney at this speed T = 50°F. 

For a building with a flat roof (pitch less than 10°) it is normally assumed that reflection does not occur when the blast wave travels horizontally. Consequently, the roof will experience the side-on overpressure combined with the dynamic wind pressure, the same as the side walls. The dynamic wind force on the roof acts in the opposite direction to the overpressure (upward). Also, consideration should be given to variation of the blast wave with distance and time as it travels across a roof element. The resulting roof loading, as shown in Figure 3.8, depends on the ratio of blast wave length to the span of the roof element and on its orientation relative to the direction of the blast wave. The effective peak overpressure for the roof elements are calculated using Equation 3.11 similar to the side wall. 

EWEA (European Wind Energy Association) and Greenpeace (2003). Wind Force 12. www.ewea.org/fileadmin/ewea documents/documents/publications/reports/ wfl2-2005.pdf. 

Model 4-Tropics, Small Response of Production Rate to Trade Wind Forcing... 

If the bullet is spun clockwi se by the rifling, the wind force tending to push the nose up induces a precession, and the nose of the bullet is turned to the right of the trajectory as viewed from die gun. This in tum produces a further precession, and the nose rises... 

Krahmann G. and Visbeck M. (2003). Arctic sea ice response to Northern Annual Mode wind forcing. Geophysical Research Abstracts, 5, 13830. 

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