| As an important structure for circulating cooling water in power plants to save water,large cooling towers are widely used in large thermal power plants and nuclear power plants.The hyperbola reinforced concrete cooling tower is one of the most traditional structural forms,and the cylinder-conic section steel cooling towers are a new type of cooling towers after hyperbolic reinforced concrete cooling towers.Most of China’s thermal power plants are located in windy northern areas.The super-high and thin-wall characteristics of large cooling towers make them very sensitive to wind loads,and make the cylinder-conic section steel cooling towers inevitably suffer from wind-induced fatigue damage.Moreover,the existing specifications do not clearly give the wind pressure distribution characteristics of the outer surface of the unique shape of the cylinder-conic section steel cooling towers.Therefore,it is necessary to analyze the flow field characteristics,wind vibration response characteristics and fatigue damage.The cylinder-conic section indirect steel cooling tower controls the bottom ventilation rate through the louvers at the bottom of the structure.Therefore,the RANS method is used in Fluent software to simulate the numerical wind tunnel of the cylinderconic section steel cooling tower under different bottom ventilation rates.The influence of the change of the bottom ventilation rate on the steel cooling tower structure is analyzed from the three aspects of flow field wind velocity,structural surface wind pressure and structural shape coefficient of wind load.According to the wind pressure coefficient formula in the specification,the shape coefficient on the surface of the cooling tower is fitted.The results show that it is necessary to consider the influence of the bottom ventilation rate on the structure when designing the cylinder-conic rigid cooling structure.Based on the region where the cylinder-conic section cooling tower project is located,the local annual wind speed distribution is obtained using a two-parameter Weibull distribution model and wind speed discretization is carried out.Then the external surface wind speed and wind pressure load of the cooling tower under different wind speeds are generated by the AR model of the linear filtering method.In ABAQUS finite element analysis software,the internal main structure model of cylinder-conic section steel cooling tower is established.The stress and displacement responses of steel cooling tower based on different bottom ventilation rates under different wind speeds and wind loads are analyzed.The results of wind-induced vibration response analysis show that the maximum stress of the cylinder-conic section steel cooling tower is located at the 0 °bottom column and the 0 ° top wind-resistant truss of the structure,and the maximum displacement is located at the 0 ° and 90 ° top of the structure.Based on stress amplitude in the analysis results,three fatigue dangerous parts,namely,0 ° bottom column base node,the 0 ° wind resistant truss high-strength bolt node at the height of 0.26 in the cone section aspect ratio and 270 ° compressed steel plate screw node at the air inlet.Based on Miner’s linear cumulative damage theory,fatigue life curve or strain life curve,the fatigue calculation of key nodes of cylinder-conic section steel cooling towers is carried out,and the damage situation of each fatigue hazardous area is analyzed.For the 0 ° bottom column base node of the structure and the 270 ° compressed steel plate screw node of the air inlet,select the appropriate S-N curve to calculate fatigue damage and estimate fatigue life.For the 0 ° wind resistant truss high-strength bolt nodes at a height of 0.26 in the aspect ratio of the cone section,combined with the fatigue performance parameters of the material,fatigue damage calculation and fatigue life estimation are carried out using the Brown Miller combined shear strain and normal strain methods with Morrow average stress correction in FE-SAFE software.The analysis results show that the most prone to fatigue damage of the structure is the compression steel plate screw node at the 270 ° air inlet,followed by the 0 ° wind resistant truss highstrength bolt node at the height of the structural cone section with a height to diameter ratio of 0.26. |
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