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Climate Analysis
Published in Kjell Anderson, Design Energy Simulation for Architects, 2014
Wind speed increases at increasing elevations above the surrounding terrain according to a function called the wind gradient. Wind speeds at airports are typically measured at 33’ above the ground, so wind speeds from weather files will over-predict wind speeds for ground-level buildings and under-predict for taller buildings. Generally, a few hundred yards above the surface of the Earth (above the boundary layer), wind flows at much higher speeds, without interacting significantly with the terrain below. These wind patterns circulate warm and cold air across the globe.
Distributions for two-point statistics of scattered signals with variable scattering strength
Published in Waves in Random and Complex Media, 2023
James G. Ronan, D. Keith Wilson, Vladimir E. Ostashev
The PE calculations were performed at frequencies of 100 Hz, 200 Hz, and 400 Hz, in both the downwind and upwind directions. For each of these frequencies and directions, calculations were performed with 4096 random realizations of the turbulence fields and (for the cases with uncertainty) refractive profiles. Example realizations are shown in Figure 4. In the downwind direction (indicated in this article as positive values on the range axis), a positive vertical wind gradient generally leads to ducting and multipath interference, although random turbulent scattering substantially weakens the duct. In the upwind direction (indicated as negative ranges), a negative vertical wind gradient leads to a refractive shadow zone into which sound energy is randomly scattered by turbulence.
The effect of yaw speed and delay time on power generation and stress of a wind turbine
Published in International Journal of Green Energy, 2023
Jianwei Zhang, Jianwen Wang, Sijia Yan
The process of the yaw motion of the wind turbine in the experiment is shown in Figure 5. The process is illustrated for a 30° wind direction. The wind turbine is controlled using the rotating platform. It starts at 0° (facing the wind direction) and stops at 30°. This simulates a wind-direction change. The wind-direction change represents the change during extreme wind shear (wind gradient) in agreement with the IEC61400 standard. This change is 30° in 6s, i.e., the angular speed associated with the wind-direction change is 5°/s. When the wind-direction change angle is 30°, a yaw delay occurs, that is, the time to stay at the angle after the wind direction changes a certain angle. This experiment used two types (no delay, 30-seconds delay), after which the yaw movement toward the wind started, the yaw angle was then decreased to 0° (facing the wind). The experiment was done with four different yaw speeds (0.5°/s, 1.0°/s, 1.5°/s, 2.0°/s).
Fluid-structure interaction analysis of a lightweight sandwich composite structure for solar central receiver heliostats
Published in Mechanics Based Design of Structures and Machines, 2023
Sulaiman O. Fadlallah, Timothy N. Anderson, Roy J. Nates
When flow is perpendicular to the heliostat’s reflective surface, i.e., 90° tilt angle and 0° wind incidence angle (Figure 12), the high stress regions are located at the upper and lower ends of the interface between the steel attachments and the back surface of the panel, with higher stresses seen at the upper ends. The heliostat panel is subjected to a wind gradient (the wind strength increases with height above ground). This explains the higher stresses at the upper ends of the interface compared to the lower ends.