| The cooling tower is one of the important buildings in the thermal power generation system.The traditional cooling towers are mostly hyperbolic reinforced concrete systems.With the rapid development of steel structure systems,the application of steel cooling towers has gradually increased in recent years.However,there are also some problems in the construction process.When the hyperbolic tower type is applied to the steel structure,since the tower shell is a negative Gaussian curvature surface,the meridian curvature will change with the change of elevation,which will lead to such as increasing in the types of members and joints,reducing the regularity of the grid,increasing the difficulty of construction positioning of the main steel structure,increasing the difficulty of construction of the enclosure structure,etc.The cylinder-frustum tower type is relatively regular in contrast,which is composed of two zero-gauss curvature surfaces,a cylindrical surface and a frustum surface,which can solve or improve the above-mentioned problems.However,due to the change of the tower type,it is not clear whether the cooling performance of the cylinder-frustum cooling tower meets the process requirements,and the mechanical characteristics and failure mechanism of the structure are not clear.The fatigue performance of the envelope structure under long-term wind loads should also be considered.Therefore,in this thesis,the cylinder-frustum cooling tower is selected as the research object from the aspect that is conducive to the construction of the cooling tower.The design and application of steel cooling towers are studied from the three perspectives of cooling performance,structural behavior,and fatigue performance of the enclosure structure.Firstly,the cooling performance of the cylinder-frustum cooling tower is discussed.Secondly,the mechanical characteristics and failure mechanism of the main structure are deeply analyzed.Thirdly,the design method of the partially perforated steel cooling tower is proposed.And finally,the fatigue performance of the enclosure structure is analyzed.The main content of this thesis includes the following aspects:(1)Cooling performance of cylinder-frustum cooling towersThe cooling performance of a cooling tower is the primary indicator of its functional requirements.Therefore,the cooling performance of the tower should be studied first when the tower type is studied.Based on the thermal test of the scale model and the numerical simulation of the full-scale cylinder-frustum cooling tower models,the similarities and differences in the flow field distribution between the hyperbolic cooling tower and cylinder-frustum cooling towers with different geometric parameter values are studied.Besides,using the heat load as the measurement standard the parameter analysis of full-scale cylinder-frustum cooling tower models is carried out.The results show that the cylinder-frustum tower type can meet engineering needs.(2)Structural behavior and system optimization of cylinder-frustum cooling towersThe structural safety of the steel cooling tower is one of the basic guarantees for the normal operation of the cooling system of a power plant.It is necessary to grasp the force characteristics and failure mechanism of the structure.In this thesis,for the steel cylinderfrustum cooling tower,the structural type of Schwedler single-layer latticed shell is selected as the research object.Based on the numerical simulation method,the force mechanism and stability of steel cooling towers are analyzed,and the shell reinforcement scheme is proposed.Besides,the influence of the bottom supporting column and asymmetric wind pressure distribution on the structural bearing capacity is analyzed,and the multi-height and multi-size structural parameterization analysis is carried out.Combined with the cooling performance,the recommended value range of the special geometric parameter for the cylinder-frustum cooling tower is proposed.(3)Design method of steel cooling tower with partial openingsRegarding the design ideas of passive flow control methods for high-rise buildings and combining the separability of the main structure and envelope structure of a steel cooling tower,the design method of steel cooling towers with partial openings is proposed.Firstly,the cooling performance and wind pressure distribution characteristics of cooling towers with single holes or multi holes with different opening positions and hole sizes are studied based on numerical simulation methods.The research results show that the local opening of the cooling tower harms the cooling performance,but the effect is small,and it is beneficial to the wind pressure distribution.Based on this conclusion,the design method of partial opening for steel cooling towers is proposed.Compared with non-hole steel cooling towers,local openings can effectively reduce the total steel consumption of the structure.The above research provides new ideas for the design of steel cooling towers.(4)Wind-induced fatigue performance of enclosure structure of steel cooling towerThe envelope structure plays an important role in the formation of the structure and bears wind loads at the same time.The formed tower shell is the basis to ensure the cooling performance,thus it is necessary to ensure that the envelope structure will not fail during the service period of the steel cooling tower.Based on the test method,the fatigue failure mode of the connection form of a typical aluminum-alloy profiled plate corrugated fixed self-tapping screw connection under different load amplitudes is firstly studied,and the S-N curve is fitted.Secondly,based on the time-history analysis method,the fatigue life of enclosure structures of a steel cooling tower is evaluated using Palmgren-Miner accumulated fatigue damage rule and S-N curve. |
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