基于共轭梯度法的瞬态多参量导热反问题研究及在核电中的应用

发布时间：2018-06-18 12:14

本文选题：共轭梯度法 + 有限单元法　；参考：《北京化工大学》2017年博士论文

【摘要】：随着社会经济的发展我国能源需求日益增长,核电作为一种高效清洁能源正蓬勃发展起来,而核安全也成为人们关注的话题。在核电的诸多管道中,经常会遇到冷热流体汇合、热分层等温度波动情况。管道内温度波动可能诱发管道发生热疲劳失效,导致核电管道发生泄漏。以波动管热分层为例,包括中国在内的核电国家,无论是在役,还是拟建的核电站都必须完成波动管热分层分析与危害评估,足以看出热分层诱发管道热疲劳失效的重要性。由于结构完备性要求,对于核电的管道系统,不允许在管道内部或者壁面开孔来安装热电偶测量流体温度和内壁面温度,这需要探索一种间接无损的温度测量或评估方法来获得管道内流体和内壁面温度。本文提出瞬态多参量导热反问题(Transient Inverse Heat Conduction Problem with Multi-variables)来预测核电典型管道温度波动现象,亦即利用易于测量的管道外壁面温度,通过共轭梯度法对圆管的近壁面流体温度、内壁面温度及内壁面对流换热系数进行反演,同时还可获得整个管道的瞬时温度场。本文主要在以下几个方面开展研究:(1)二维和三维圆管导热正问题与瞬态多参量导热反问题研究。构建了基于有限元法的二维和三维圆管的导热正问题求解模型,进行了网格无关性验证及时间步长敏感性分析,为反问题实验台的测点布置方案及温度采集频率的确定提供了理论依据。构建了基于共轭梯度法的瞬态多参量导热反问题模型,给出了利用外壁面测量温度反演内壁面第三类边界条件的具体实施步骤。(2)瞬态多参量导热反问题实验校验及结果分析。搭建了基于热分层原理的导热反问题实验台,进行了导热反问题实验。研究利用实验结果对二维和三维导热反问题模型及反演结果进行了校验。基于校验过的导热反问题模型,研究了测点数对反演精度的影响,研究结果表明测点数越多,反演精度越高。当二维导热反问题测点数降低到2个时,平均相对误差不超过4.3%,三维导热反问题测点数降低到6个时,平均相对误差不超过6.8%。从导热反问题实验结果及反演结果可以看出:管道内壁各测点处的热边界层厚度随冷水流量的增大呈现出不同的变化规律,多数测点处的热边界层厚度随冷水流量的增大而变厚;反演的对流换热系数值随冷水流量的增大而略有增大;管壁的温度分布规律也随冷水流量的变化而发生明显改变。(3)二维瞬态多参量导热反问题反演波动管内壁面第三类边界条件。利用已校验的二维瞬态多参量导热反问题模型对核电稳压器波动管4个沿管道轴线的易发生热分层现象的典型截面进行了反演。从计算结果中可以明显看出截面所处位置的不同,其温度场分布规律不同。24D和27D截面的壁面温度最高点位于管道顶部,温度最低点位于管道底部,而20D和22D管壁温度最高点位置向右发生了偏移。这是由于管道的几何特征致使流体流动方向改变造成的。另外,四个截面得出的对流换热系数也不尽相同,处于弯管处的截面,其对流换热系数较大,但四个截面的对流换热系数值相差不大,这也说明了三维导热反问题中求解平均对流换热系数的可行性。(4)热分层三维弯管正问题数值试验及反问题结果分析。对存在热分层现象的三维弯管进行了瞬态导热正问题及多参量导热反问题研究,由抗噪性和外壁面测点数讨论得知,存在一定的“测量”误差时,该方法仍可以得到一定精度的反演结果,弯管拐角区域的测点数对反演精度影响较大,该区域的测点数越多,反演精度越高,其他区域的测点数对反演精度的影响较小。(5)三维瞬态多参量导热反问题反演热分层T型弯管温度分布。利用已校验的三维瞬态多参量导热反问题模型对存在有热分层的T型弯管的弯管段进行了反演,揭示了在湍流穿透和浮升力作用下管壁及近壁面流体在不同时刻的温度分布规律。本文所提出的一种多参量、无损、间接的温度反演方法,利用外壁面的温度信息同时求解管道内壁第三类边界条件的多个参量。经实验校验,此方法具有较高的精度。瞬态多参量导热反问题得到的结果不仅可为管道内部流场的分析提供准确的内壁面边界条件,而且可为管道的应力分析提供准确的瞬时热载荷。对于核电等结构完备性要求较高的管道系统,此方法可以为其流场分析以及热疲劳分析提供可靠的理论依据。
[Abstract]:With the development of social and economic development, nuclear power is developing vigorously as a kind of efficient clean energy, and nuclear safety has become a topic of concern. In many pipelines of nuclear power, there are often cold and hot fluid convergence, thermal stratification and other temperature fluctuations. The temperature fluctuation within the pipeline may induce pipelines to occur. Thermal fatigue failure causes leakage of nuclear power pipelines. Taking the thermal stratification of the wave tube as an example, the nuclear power countries including China, whether in service or in the proposed nuclear power plant, must complete the analysis of the thermal stratification and hazard assessment of the undulate tube, which is sufficient to see the importance of the thermal fatigue failure of the pipeline caused by thermal stratification. The pipeline system of nuclear power does not allow the internal or wall opening of the pipe to install the thermocouple to measure the temperature of the fluid and the inner wall temperature. This needs to explore an indirect and nondestructive temperature measurement or evaluation method to obtain the internal and internal temperature in the pipe. This paper proposes a transient multi parameter heat conduction inverse problem (Transient Inverse Heat Conducti). On Problem with Multi-variables) is used to predict the temperature fluctuation in the typical pipeline of nuclear power, that is to use the easily measured temperature of the outer wall of the pipe, the inversion of the near wall fluid temperature, the inner wall temperature and the inner wall facing the flow heat transfer coefficient by the conjugate gradient method, and the instantaneous temperature field of the whole pipe can be obtained at the same time. The following research should be carried out in the following aspects: (1) research on the positive and transient heat conduction problems of two-dimensional and three-dimensional tubes and transient multiparametric heat conduction problems. A finite element method for solving the positive problem of heat conduction in two-dimensional and three-dimensional tubes is constructed, and the grid independence verification and time step sensitivity analysis are carried out for the layout of the test point of the inverse problem test bench. A theoretical basis is provided for the determination of the frequency of temperature collection. A transient multi parameter heat conduction inverse problem model based on conjugate gradient method is constructed, and the concrete implementation steps for the inversion of third kinds of boundary conditions on the inner wall surface using the measuring temperature of the outer wall are given. (2) the test of the transient multi parameter heat conduction experiment and the result analysis. The experiment on the inverse heat conduction problem of the stratified principle is carried out. The experimental results are used to verify the inverse heat conduction problem model and the inverse result of the two-dimensional and three-dimensional heat conduction. Based on the checked heat conduction inverse problem model, the influence of the number of measured points on the inversion accuracy is studied. The results show that the number of points is more, the more accurate the inversion is. When the number of two dimensional heat conduction inverse problems is reduced to 2, the average relative error is not more than 4.3%, and the number of three dimensional heat conduction inverse problem points is reduced to 6. The average relative error is not more than 6.8%. from the experimental results of the heat conduction inverse problem and the inversion results can be seen that the thickness of the thermal boundary layer at the inner wall of the pipeline increases with the increase of the cold water flow. The thermal boundary layer thickness at most of the test points thickens with the increase of cold water flow. The numerical value of the inverse heat transfer system increases slightly with the increase of cold water flow, and the temperature distribution of the tube wall changes obviously with the change of the cold water flow. (3) the inversion of the two-dimensional transient multi parameter heat conduction inverse problem is in the wave tube. The third type boundary condition of the wall surface is used to inverse the typical cross section of the thermal delamination phenomenon of the nuclear power regulator's wave tube along the axis of the nuclear power regulator, using the checked two-dimensional transient multi parameter heat conduction inverse problem model. From the calculation results, it is obvious that the location of the section is different, and the distribution of temperature field is different.24D and 27D intercepts. The highest point of surface temperature is located at the top of the pipe, and the lowest temperature is located at the bottom of the pipe, while the position of the highest temperature of 20D and 22D is shifted to the right. This is caused by the change of the flow direction of the pipe because of the geometric characteristics of the pipe. In addition, the convection heat transfer coefficient of the four cross sections is not the same, at the bend of the pipe. The convective heat transfer coefficient is large, but the difference in the numerical value of the convective heat transfer system in the four cross sections is not significant. It also shows the feasibility of solving the average convection heat transfer coefficient in the three-dimensional heat conduction inverse problem. (4) the numerical test of the positive problem of the thermal stratified three-dimensional bend tube and the analysis of the inverse problem results. The problem and the inverse problem of multi parameter heat conduction are studied. From the discussion of the noise resistance and the number of exterior wall points, it is found that when there is a certain "measurement" error, the method can still get a certain precision of inversion results. The number of measuring points in the corner area has a great influence on the inversion accuracy, the more the number of the measured points in the region, the higher the inversion accuracy, the measurement of other regions. The number of points has little influence on the inversion accuracy. (5) the inversion of the thermal stratified T type pipe temperature distribution in the three-dimensional transient multi parameter heat conduction inverse problem. The inversion of the bend pipe section of the T type pipe with thermal stratification has been retrieved by using the checked three-dimensional transient multi parametric heat conduction inverse problem model, and the tube wall and the near wall surface under the effect of turbulent penetration and floating lift are revealed. The temperature distribution of fluid at different times. A multi parameter, nondestructive and indirect temperature inversion method proposed in this paper is used to use the temperature information of the outer wall to solve the multiple parameters of the third kinds of boundary conditions of the inner wall of the pipe. It is verified by experiments that the method has a high degree of precision. It can only provide accurate inner wall boundary conditions for the analysis of the internal flow field of the pipeline, and can provide accurate instantaneous thermal load for the stress analysis of the pipeline. This method can provide a reliable theoretical basis for the analysis of the flow field and the thermal fatigue analysis for the pipeline system with high completion of nuclear power and other structures.
【学位授予单位】：北京化工大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TK124;TM623

【参考文献】