结构基频对冷却塔风振效应的影响

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

为明确结构基频f0对冷却塔风振效应的影响,以某大型冷却塔为例,在风振响应时程计算和风振效应特征分析的基础上,通过调整材料弹性模量E实现对f0的改变,以单独分析f0对风振效应尤其是共振分量?R的影响,并阐述了该方法的优点。结果表明,根据共振与背景分量?R、?B在时域内的分离方法,不管f0如何变化,?R与?B之间的耦合分量始终可以忽略。各响应?R随f0的降低而增加,并在f0小于0.7 Hz以后急剧增加,但因?B在总脉动响应?T中贡献较高,故?T和阵风响应因子GRF仅在f0小于0.5 Hz以后才有较明显的增加。各响应?R随f0的降低而增加的原因在于风谱能量随频率的降低而增加,且结构f0越小其共振参与模态越多。为方便评价共振响应?R随f0的变化,提出参数RP=(1/f0×(1/f0?1/2))综合考虑以上两种因素作为?R的评价指标,且各响应的?R与RP均呈线性变化。

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,σR. The advantages of this method are also presented. The results show that the coupling effect between the resonance and background components,σR and σB, obtained in time domain is negligible no matter what value the f0 takes.σR increases with the decrease of f0, especially when f0 is less than 0.7 Hz. However, the total gust response,σT, increases more slowly with the decrease of f0 because the significant contribution of σB and σB does not change with f0. Therefore,σT shows quick increase only if f0 is less than 0.5 Hz. There are two reasons for the increase of σR 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 σR. A linear relationship is found between σR of all responses and the parameter RP.