Wind Load Characteristics And Wind-Induced Interference Effects On Large Hyperbolic Cooling Towers

Large hyperbolic cooling towers are mainly used in electric power, petroleum, nuclear, mining and other industries. In recent years, with the development of chineses economy, these industries have developed rapidly, and many large cooling towers have been built.Such thin shell structure with high height, large size and light weight, wind load is one of the main domainting load in the design of the tower. Design specification provide a reference of wind loads on an isolated tower. However in practice, cooling tower are generally constructed in groups, and then the interference effects between towers cann't be ignored. In some cases, the wind load in the grouped towers is much greater than that of an isolated tower.Therefore, it is necessary to conduct relevant research.Firstly, two types of roughness element numbers and five thicknesses of element heights were used to investigate the influence of model surface roughness on wind loads of cooling towers. The technique of proper orthogonal decomposition method (POD) was employed to interpolate and reconstruct the wind pressures on the towers. The distribution of wind pressures and overall wind forces on the cooling tower were analyzed with respect to surface roughness. Then the experimental results were compared with the data of the Code, previous full-scale tests, and previous wind tunnel tests. Results show that if the surface of the tower model is smoother, the absolute value of the wind pressure on layer B (near the throat) is larger. When the number of surface roughness elements increases, the base shear coefficients of the cooling tower become larger, resulting in larger overall wind-resistant forces. The drag coefficients near the throat of the cooling tower are close to the data of the Code, whereas the drag coefficients of the top and the mid-bottom of the tower are larger than the data of the Code, in which additional attention should be paid to.Secondly, in order to study the interference effects under the situation of two towers and three towers, drag coefficients and lift coefficients on the isolated tower ,two adjacent towers, and three adjacent towers were calculated. Based on these coefficients, interference factors on distances between two towers and wind azimuths were analyzed. Results show that, for the isolated tower, the mean drag coefficients are quite large whereas the mean lift coefficients are nearly zero. However, the mean-root-squares of drag coefficients and lift coefficients on the isolated tower are comparative in the magnitude. For two adjacent towers, the interference factors of mean and dynamic drag coefficients are almost the same. Most of the interference factors of dynamic lift coefficients are bigger than 1, while the biggest value reaches 1.87. Results show that, for the situation of three adjacent towers before the wind, most of the mean base shear coefficients and most of the maxima base shear coefficients are smaller than 1,which indicate that the distribution of the three adjacent towers obstruct the passage of the wind and make the resistance of the back tower gets smaller. As in the acrosswind direction, most of the maximum base shear coefficients are bigger than 1 and the biggest value is close to 2,which includes that the fluctuation of the acrosswin directon is significant.Thirdly, this paper studys the wind load characteristics considering interaction between internal and external pressure. Results show that whether the bottom of the model has holes or not, the external pressure keep almost unchage, whereas there is significant changes for the internal pressure.The total wind pressure coefficient on the inner surface of is around -0.4 when the bottom of the model has holes, while the wind pressure coefficient is around -0.7 when the bottom of the model has no holes. Internal pressure can be considered as a uniform even pressure. It has little impact on the meridian stress and radial displacement, while it has a certain degree influence on the ring membrane stress.Finally, the mean and peak value of the interference factor of wind-induced response were investigated. Results show that interference effect of wind-induced responses is quite different with interference effect of wind loads...