基于导热正反问题耦合解法的汽包疲劳寿命分析

发布时间：2018-09-17 12:28

【摘要】：汽包是锅炉最大的高温厚壁承压部件,在启、停过程中承受着温度分布不均引起的热应力和内部压力引起的机械应力,频繁的应力变化将引起汽包的疲劳寿命损耗。因此研究汽包的疲劳寿命,对汽包疲劳寿命进行在线监测,控制启停过程中温度变化率在允许范围之内,减小疲劳寿命损耗,对提高锅炉运行的安全性、经济性具有重要意义。如何在提高汽包温度场和应力场计算精度的同时又能保证较高的计算效率,是汽包寿命研究的关键。本文针对增压锅炉汽包外壁受热的特点,提出了基于导热正反问题耦合解法的汽包瞬态温度场计算方法。首先根据外壁受热与否,分区域分别采用导热正反问题求解温度,两部分交接耦合区域采用边界耦合方式,将反问题解法求得的交界温度值赋值给正问题解法作为已知边界条件,从而实现正反问题耦合,得到整个汽包的温度场。然后在此基础之上,运用有限元方法,采用平面八节点等参单元,按照平面应变问题对汽包截面的瞬态应力进行求解分析。最后,基于雨流计数法,采用Miner线性累加疲劳损伤原理,对汽包疲劳寿命进行计算,得到汽包的寿命损耗,指导锅炉安全经济运行。
[Abstract]:Drum is the largest high-temperature and thick-wall pressure part in boiler. During the process of starting and stopping, it bears thermal stress caused by uneven temperature distribution and mechanical stress caused by internal pressure. Frequent stress changes will cause fatigue life loss of steam drum. Therefore, it is of great significance to study the fatigue life of the drum, monitor the fatigue life of the drum on line, control the temperature change rate within the allowable range during the start and stop process, reduce the fatigue life loss, and improve the safety and economy of boiler operation. How to improve the accuracy of the calculation of the temperature field and the stress field of the drum and at the same time ensure the higher calculation efficiency is the key to the study of the life of the drum. In view of the heating characteristics of the outer wall of a turbocharged boiler, this paper presents a method for calculating the transient temperature field of the drum based on the coupling solution of the heat conduction forward and negative problems. Firstly, according to whether the outer wall is heated or not, the temperature is solved by the positive and negative problem of heat conduction in the sub-region, and the boundary coupling method is used in the coupling region of the two parts. The boundary temperature value obtained by the inverse problem solution is assigned to the forward problem solution as the known boundary condition, so that the forward and negative problems can be coupled and the temperature field of the whole drum can be obtained. On the basis of this, the transient stress of the drum section is solved by using the finite element method and the isoparametric element with eight points in the plane, according to the plane strain problem. Finally, based on the rain flow counting method and the principle of Miner linear cumulative fatigue damage, the fatigue life of the drum is calculated, and the life loss of the drum is obtained, which guides the safe and economical operation of the boiler.
【学位授予单位】：华北电力大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TK223.13

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