Study On Influence Of Openings On Tornado Load Of Nuclear Power Conventional Island

Tornadoes are the strongest vortex phenomenon in the atmosphere.They have the characteristics of small influence,rapid birth and disappearance,indefinite track,and strong destructiveness.Due to its relatively low probability of occurrence,our country's load code for the design of building structures has not included the design standard of anti-tornadoes for common structures.However,for certain facilities with serious consequences,such as nuclear power plants,thermal power plants,etc.,the impact of tornado load must be taken into account in designing to ensure that it is sufficiently resistant to tornadoes.The enveloping structure of the nuclear power plant in the conventional island main building,especially the roof structure,requires not only the effect of external pressure but also the combination of internal and external pressures effect.The destruction of most envelope structures(such as roof overturning and wall collapse)is caused by the combined effect of internal and external pressures,especially under extreme environmental conditions(such as tornadoes).A reasonable estimate and the distribution characteristics of the tornado load on each surface of the structure after opening are obtained,so that targeted reinforcement measures are carried out to help improve the anti-tornado performance of important civil structures such as nuclear power plants and reduce economic losses under bad environmental conditions.Firstly,numerical model of the tornado field was established and the numerical simulation results were analyzed.The study found that the change law of tangential wind speed and the pressure drop varied with radius of the numerical tornado wind field are in good agreement with the 2D Rankine vortex theoretical model,which verifies the reliability of the numerical simulation results.Subsequently,the effect of swirl ratio on the structure and characteristic parameters of the tornado field was analyzed.The results showed that with the increase of swirl ratio,the absolute value of pressure drop and the maximum tangential wind speed in the tornado field gradually decrease,and the corresponding core radius increases gradually.Under low swirl ratios,the change rate of tornado tangential wind speed and pressure drop is significantly higher than that under high swirl ratios.When the swirl ratio S=1.0,the tornado is transformed from single vortex core structure to multi-vortex core structure,and the wind field structure tends to be unstable.Secondly,based on the tornado numerical model,the continuous destruction of the envelope structure at the core radius of the tornado was analyzed.The study showed that,at the core radius of the tornado,the max negative wind pressure was at the edge of the structural roof near the windward surface.The roof was firstly toppled and damaged.At this time,the wind pressure at various points of inner surface was nearly equal and had high consistency.Due to the joint action of internal and external pressures,the windward surface,leeward surface and surface near vortex damaged in sequence.The surface far away from vortex was not damaged.Among them,the destruction rate on the windward surface was the highest,reaching 22.2%.Finally,the influence of the openings on the distribution characteristics of structual wind pressure was studied by using CFD numerical simulation technology.The main plant structure of nuclear power conventional island was placed at the core radius of the tornado field.The distribution characteristics of structural wind pressure with different opening area,opening position and number of openings were analyzed,which was compared with the result of wind-induced mean internal pressure theoretical formula.As for structures with complex openings,it is impossible to directly judge the inlet and outlet positions of the air flow.Complicated trial calculations are required when calculating the average internal pressure of the structure according to the wind-induced internal pressure theoretical estimation formula.For this purpose,the wind-induced internal pressure theoretical estimation formula was combined with numerical simulation techniques to provide a solution for the wind-induced average internal pressure estimation under complex opening conditions.