Gust Response Factor Research Articles

Wind Effects on Cooling-Tower Shells

The design of natural-draft cooling towers is dominated by wind action. With respect to the response of the structure the wind load may be divided into a static, a quasistatic, and a resonant part. The effect of surface roughness of the shell and of wind profile on the static load is discussed. The quasistatic load may be described by the variance of the pressure fluctuations and their circumferential and meridional correlations. The high-frequency end of the pressure spectra and of the coherence functions are used for the analysis of the resonant response. In general, the resonant response is small even for very high towers. It increases overlinearly with wind velocity. Equivalent static loads may be defined using appropriate gust-response factors. These loads produce an approximation of the behavior of the structure and in general are sufficiently accurate.

Gust Factors for Hyperbolic Cooling Towers

The wind pressure distribution and dynamic behavior of hyperbolic cooling towers are significantly different from those of simple slender structures. Therefore, the gust response factors developed for design of these simple structures may not be applicable to cooling towers. A method which considers the dynamic interaction of the wind and tower is presented to obtain the gust factors for cooling tower design. Wind pressure distribution measurements made on model towers in wind tunnels are used. Simplifying assumptions are made concerning the correlation characteristics of wind pressure on a tower surface. Effect of change in wind and tower parameters on gust factors is examined.

Gust Factors and Alongwind Pressure Correlations

An expression for gust response factors for tall buildings is derived using an analysis, based on first principles, of three-dimensional structures subjected to random loading. The expression permits an evaluation of the effect of the alongwind pressure correlations, with regard to which differences exist between various methods presently in use. It is found that depending on the assumptions to which they resort in order to take this effect into account, some methods overestimate, while other methods underestimate, gust factor values by as much as 15 to 30%. The expression derived offers, in addition, the potential for obtaining more economical gust factors by incorporating in their structure a more realistic model of the pressure in the wake.

Improved Methods of Atmospheric Turbulence Prediction for Aircraft Design and Operation J

New atmospheric turbulence prediction techniques have been developed to define the existence and magnitude of turbulence. These empirical methods were developed from the vast amount of recorded atmospheric turbulence data in several forms. Early data from aircraft response to turbulence was collected, primarily by NACA, with recorders on board civil transport aircraft. Recently, the gust probe method has been used in several programs to define atmospheric turbulence magnitudes under a variety of conditions. These atmospheric turbulence environment data, used in empirical prediction techniques, provide potential improvement in gust design criteria and in avoidance planning of high-risk flight regions. Nomenclature A = gust response factor, <JY/VGW AA = average terrain route altitude, ft a — inverse slope parameters for response distribution, 0.791 ay b ~ inverse slope parameters for gust distributions (derived equivalent or true gust velocity peaks), 0.791 cr C = gust response parameter, &nz/Ude, #/fps e =2.718 FA = airplane flight altitude, ft

Gust Response Factors

The gust response factor is a measure of the effective wind loading on a structure and is intended to translate the dynamic response phenomena due to gust loading into relatively simpler static design criteria. The calculation involves a power spectrum analysis of dynamic structural response of a linear, single-degree-of-freedom system with viscous damping and utilizes reported measurements of wind gust spectra and gust correlation coefficients. Calculated results of this method are presented in the form of charts which permit the direct determination of gust response factors. A rational method of transferring long-term Weather Bureau wind records to rough and obstructed exposures is presented. The effect of gusts on the design and serviceability of buildings is discussed. For large structures, the results of this paper suggest that the use of fastest mile pressures could overestimate the true wind loading on such structures.