Wind motions

Wind Energy Energy present in wind motion that can be converted to mechanical energy for driving pumps, mills and electric power generators. Wind... 

The author estimates that in any one day during the great droughts of the late 1930 s in the United States as much as 107 tons of fine particles remained suspended in the air and were moved to areas far removed from the Dust Bowl of their origin. In the Dust Bowl itself, the estimated movement within a few inches of the surface probably ranged from 0.2 to 0.5 ton per yd per hr across the direction of wind motion. Samples of settled dust taken in the Dust Bowl and analyzed as to composition and size frequency indicated a sharp differentiation as to the size of... 

Cyclones are large-scale storms characterized by low pressure in the center surrounded by circular wind motion. The United States National Weather Service technical definition of a tropical cyclone (National... 

See p. 23 above al-Mas udi, Kifaya, f 124 cf. Jahdn-i danish, 75-76. Ibn al-Haytham s treatise on winding motion is lost. He also wrote another work on the subject, in which he responded to problems raised by a contemporary against certain views of Ptolemy (published as Rail shukuk harakat ai-iitifdf). On these works, see Sabra, Configuring the Universe , 298 ff. Hashed, Celestial Kinematics , gff. 

Gup and Vane Anemometers. A number of flow meter designs use a rotating element kept in motion by the kinetic energy of the flowing stream such that the speed is a measure of fluid velocity. In general, these meters, if used to measure wind velocity, are called anemometers if used for open-channel Hquids, current meters and if used for closed pipes, turbine flow meters. 

Wind speed has velocity components in all directions so that there are vertical motions as well as horizontal ones. These random motions of widely different scales and periods are essentially responsible for the movement and diffusion of pollutants about the mean downwind path. These motions can be considered atmospheric turbulence. If the scale of a turbulent motion (i.e., the size of an eddy) is larger than the size of the pollutant plume in its vicinity, the eddy will move that portion of the plume. If an eddy is smaller than the plume, its effect will be to difhise or spread out the plume. This diffusion caused by eddy motion is widely variable in the atmosphere, blit even when the effect of this diffusion is least, it is in the vicinity of three orders of magnitude greater than diffusion by molecular action alone. 

The atmosphere is nearly always in motion. The scales and magnitude of these motions extend over a wide range. Although vertical motions certainly occur in the atmosphere and are important to both weather processes and the movement of pollutants, it is convenient to consider wind as only the horizontal component of velocity. 

Turbulence is highly irregular motion of the wind. The atmosphere does not flow smoothly but has seemingly random, rapidly varying erratic motions. This uneven flow superimposed on the mean flow has swirls or... 

The NACA 65 blade profiles were tested in a systematie manner by Herrig, Emery, and Erwin. The easeade tests were earried out in a easeade wind tunnel with boundary-layer suetion at the end walls. Tip effeets were studied in a speeially designed water easeade tunnel with relative motion between wall and blades. 

In the case of the ship shown in Figure 1.3, the rudder and engines are the control inputs, whose values can be adjusted to control certain outputs, for example heading and forward velocity. The wind, waves and current are disturbance inputs and will induce errors in the outputs (called controlled variables) of position, heading and forward velocity. In addition, the disturbances will introduce increased ship motion (roll, pitch and heave) which again is not desirable. 

In Gaussian plume computations the change in wind velocity with height is a function both of the terrain and of the time of day. We model the air flow as turbulent flow, with turbulence represented by eddy motion. The effect of eddy motion is important in diluting concentrations of pollutants. If a parcel of air is displaced from one level to another, it can carry momentum and thermal energy with it. It also carries whatever has been placed in it from pollution sources. Eddies exist in different sizes in the atmosphere, and these turbulent eddies are most effective in dispersing the plume. 

The airflow in the center of the roof tends to be downward. The downward motions in the downstream cavity wake are also more intense for winds approaching from an angle. ... 

Transport of outdoor contaminants is controlled by both the mean motion of winds and dispersal by turbulence. Since airflow around buildings has... 

Furthermore, winds at an angle to the building side will have downward air motions above the roof and downwind of the building, which also will increase rooftop concentrations. 

Wind Air motion relative to the earth s surface caused by thermal forces and the earth s rotation. 

Turbulence is generated by wind shear in the surface layer and in the wake of obstacles and structures present on the earth s surface. Another powerful source of turbulent motion is an unstable temperature stratification in the atmosphere. The earth s surface, heated by sunshine, may generate buoyant motion of very large scale (thermals). 

After a fragment has attained a certain initial velocity, the forces acting upon it during flight are those of gravity and fluid dynamics. Fluid-dynamic forces are subdivided into drag and lift components. The effects of these forces depend on the fragment s shape and direction of motion relative to the wind. 

The force of aerodynamic drag opposing foiward motion of the vehicle depends on its drag coefficient (Cj), its frontal area (A,), the air density (p), and the velocity of the wind with respect to the vehicle. In still air, this velocity is simply the vehicle velocity (V.). If driving into a headwind of velocity V , however, the wind velocity with respect to the vehicle is the sum of these two. Multiplying the aerodynamic drag force by vehicle velocity provides the aerodynamic power requirement (PJ. 

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