INFLUENCES OF THE FUNDAMENTAL FREQUENCY ON THE WIND DYNAMIC EFFECTS OF A HYPERBOLIC COOLING TOWER

Studies were initiated for clear interpretation of the influence of the fundamental frequency, f₀, on the wind dynamic effects of hyperbolic cooling towers (HCTs). Based on the preceding wind dynamic calculation in time domain and the features of dynamic effects, a new method was proposed to adjust f₀ and brought into the following operation. In this new method, the material elastic modulus E was changed to get different f₀'s and corresponding wind dynamic effects, especially the resonance component,σ_R. The advantages of this method are also presented. The results show that the coupling effect between the resonance and background components, σ_R and σ_B, obtained in time domain is negligible no matter what value the f₀ takes.σ_R increases with the decrease of f₀, especially when f₀ is less than 0.7 Hz. However, the total gust response,σ_T, increases more slowly with the decrease of f₀ because the significant contribution of σ_B and σ_B does not change with f₀. Therefore,σ_T shows quick increase only if f₀ is less than 0.5 Hz. There are two reasons for the increase of σ_R when f₀ decreases: 1) the wind spectrum increases with the decrease of frequency and 2) more resonant modes would be excited. A parameter Rp=(1/f₀×(1/f₀-1/2)), which could cover the above two reasons, was proposed for convenient evaluation of σ_R. A linear relationship is found between σ_R of all responses and the parameter RP.