反应堆GGR系统辅助管系稳态振动评估与振动疲劳寿命分析

根据美国机械工程师标准(ASME-OM-S/G2000)规范及法国电力公司(EDF)标准振动评估方法,提出一套用于核电站小支管振动评估及振动疲劳寿命分析的方法,应用该方法对国内某核电站汽轮机润滑顶轴盘车(GGR)系统的辅助小支管振动问题进行评估研究,并计算了小支管系统的允许有效速度.根据振动速度的测量和计算结果进行敏感性评估;采用响应谱计算方法对管座处的应力水平进行计算,并与允许振动交变应力进行比较;采用瞬态动力学方法对管座处的应力时程响应进行计算,根据Miners线性损伤累积模型对管座的振动疲劳寿命进行评估.结果表明谱响应计算得到的振动交变应力幅值高于评估准则的振动交变应力允许值,该管线属于振动敏感管线;而通过瞬态振动寿命计算得到稳态振动疲劳寿命远远高于设计寿命,有较大的安全裕量.     

基于虚拟激励的滞变支撑连接耦合结构的非一致平稳随机地震响应分析

为了得到滞变支撑连接耦合结构的非一致随机地震响应,以虚拟激励法为基础,导出系统基于多点多分量随机地震的虚拟激励与响应分析式。该方法的未知量为绝对位移,可适用于包括非一致地震在内的所有地震激励形式。数值研究表明,本文方法与基于动态相对位移的虚拟激励法和蒙特卡罗法的结果具有很好的一致性。在此基础上,开展了滞变支撑屈服力与屈服位移的参数化研究。     

反应堆吊篮在泵致脉动压力载荷下的响应研究

反应堆结构的流致振动问题一直受到核工程界的广泛关注。主泵的泵致脉动压力是一个重要激励源,其将导致反应堆吊篮等部件周期性振动,长期运行会导致结构的疲劳损坏。为研究新设计的“华龙一号”反应堆吊篮在泵致脉动压力作用下的振动响应,本文首先分析反应堆吊篮所受的泵致脉动压力,而后建立吊篮有限元模型,对其在泵致脉动压力载荷下的动力学响应进行研究,并综合考虑湍流激励,评价吊篮在堆内构件流体作用下的整体影响。应力分析表明,吊篮各位置流致振动的最大应力强度小于疲劳应力限值,结构是安全的。但对于新设计的反应堆,或反应堆冷却剂系统更换新的主泵,则反应堆吊篮及堆内构件的泵致振动需受到重视。     

多轴疲劳模型对比研究及其在核电结构热疲劳寿命预测中的应用

压水堆核电站余热排出系统冷热水混合区管道发现的热疲劳问题影响核反应堆的安全。本文通过一种采用单轴疲劳试验数据拟合疲劳寿命曲线,进而用于预测多轴疲劳寿命的分析方法,基于文献中的疲劳试验数据,对Dang Van模型、Matake模型和Fatemi-Socie模型进行了余热排出系统冷热水混合区管道材料304L不锈钢疲劳寿命预测结果的对比研究。基于余热排出系统冷热水混合区管道的三维简化有限元模型,分别应用Dang Van模型、Matake模型和Fatemi-Socie模型对管道热疲劳寿命进行了预测,并与试验结果进行了对比验证。研究结果表明,基于应变（含平均应力修正）的Fatemi-Socie模型比较适用于304L不锈钢的疲劳分析,其热疲劳寿命预测结果相对Dang Van模型、Matake模型较合理。     

核一级三通管热疲劳研究

钠冷快堆在启动和停止过程中会产生大的热应力,多次循环之后容易产生热疲劳损伤,特别是在三通管连接区域。本文将研究不同角度对三通管热疲劳性能的影响。通过ANSYS计算不同角度三通管道的热应力,确定三通管道的热疲劳寿命和疲劳损伤系数。给出了疲劳许用强度与三通管角度的函数关系。结果表明,随着角度的减小疲劳强度降低。此结果对核一级管道设计中选取三通管道的角度具有一定的参考价值。     

孔板诱发管道流致振动响应的计算方法

根据孔板诱发流体脉动压力的试验测量结果,利用ANSYS软件的随机振动分析功能对孔板扰流诱发的管道振动响应进行了计算,分析了脉动压力的相关性对管道振动响应的影响.在此基础上,提出了一种简化计算方法,并将其计算结果与详细方法的计算结果进行了对比.结果表明:该简化方法便于操作、计算时间短,计算得到的管道流致振动响应结果满足保守性要求.     

压水堆燃料棒在轴向流作用下的随机振动响应研究

基于随机振动理论,建立了在轴向流作用下压水堆燃料棒随机响应的纯理论分析方法。将流体力考虑为沿燃料棒轴向位置的脉冲随机荷载,结合模态分析技术,从功率谱分析法推导出燃料棒振动均方根响应的表达式。提供了一套不依赖燃料组件流致振动实验的纯理论分析方法,重点分析了等效流速、湍流强度、相关长度系数等几个主要流场参数对结构均方根响应的影响。结果表明,本文计算模型的精度满足工程分析要求,燃料棒响应随等效流速、湍流强度和相关长度系数的增大而增大;其中响应对于等效流速和相关长度系数的变化较为敏感,而与湍流强度呈线性变化关系;在压水堆运行中的燃料棒均方根幅值约处在μm量级。     

平板封头与筒体连接区疲劳可靠性分析

设备疲劳设计中存在诸多不确定因素,而使用概率方法可以辅助设计。为得到某平板封头连接区域疲劳可靠性,本文考虑结构几何尺寸和载荷不确定性,使用可靠性分析方法对其进行疲劳可靠性分析。计算结果表明,几何尺寸不确定因素对结构疲劳寿命不确定性影响不能忽略。同时,提出一种基于6σ概念求解载荷不确定性的疲劳可靠性计算方法,其可与几何不确定性可靠性计算方法结合使用得到综合考虑几何载荷不确定性的结果。     

输流管网流致振动特性数值模拟研究

为研究管路系统流质振动特性以优化管路设计,本文以典型输液管网系统为对象,基于Ansys Workbench平台开展了不同流体激励下的管路双向流固耦合模拟计算,获得了管路结构流致振动特性,分析讨论了激励类型、介质温度、流场结构及结构固有频率对管内流致振动特性的影响。结果表明,脉动流量激励下的管路结构振幅显著大于恒定流量激励下的结构振幅,当流体激励频率较接近管路结构固有频率时,结构和流体将趋于共振,导致结构振动加剧。通过在管道适当位置施加约束支撑,使结构固有频率远离流体激励频率,可有效减小管道的振动。此外,介质温度和流速对结构振幅有较大影响。      

基于应变与加速度响应的核电厂小支管振动评价

核电厂存在大量的仪表管、取样管、排气管等小支管,其机械振动疲劳断裂是商业运行核电厂经常出现的问题。本文以阳江核电站二号机组GRE023管线的实测振动应力对其振动疲劳寿命进行了评价,采用有限元方法以加速度时程二次积分获得的位移时程为输入对其振动疲劳寿命进行了分析,获得了小支管振动疲劳瞬态动力分析关键参数设置方法,同时也为类似结构的减振改造设计积累了经验,为核电厂小支管振动治理提供了参考。     

主回路滞流分支管振动超标的原因分析与设计优化

在某核电厂热态功能试验中,巡视发现主回路的某滞流分支管振动超标。根据实测振动随温度变化的趋势、管道固有声模态分析和模态分析等,推测管道内流体的声振动激励引发管道共振。根据滞流管三通处流体的漩涡脱落频率计算和声振动频率计算,推测漩涡脱落与滞流管内流体的固有声振动频率锁定,引发声振动激励放大。综合分析计算和实测结果,确定滞流管振动超标的原因为流声固耦合振动。对管道支架进行了优化,以错开声固耦合共振频率,在三通处倒圆角削弱漩涡脱落,以降低流声耦合的声振动幅值。优化后的分支管振动会明显降低,以保证承压边界的安全。     

Root Cause Analysis of Vibration Exceeding and Design Optimization of Stagnant Branch of Reactor Coolant Loop

During the hot function test of nuclear power plant, it was found that the vibration of a stagnant branch of reactor coolant loop (RCL) exceeded the limit. According to the natural modal analysis, acoustic modal analysis and the variation trend of measured vibration with temperature, it is inferred that the acoustic vibration of the fluid in the pipeline causes the resonance of the pipeline. According to the calculation of vortex shedding frequency and acoustic vibration frequency, it is inferred that the acoustic vibration and the vortex shedding frequency of fluid at the tee are locked, which leads to the amplification of acoustic vibration excitation. Based on the analysis result and measured data above, it is determined that the cause of the vibration exceeding is the fluid-acoustic-structure coupling vibration. The pipe supports were optimized to avoid resonance frequency of acoustic structure coupling. The fillet at the tee was used to weaken the vortex shedding, so as to reduce the amplitude of flow-excited acoustic resonance. The vibration of the optimized branch will be significantly reduced to ensure the safety of the pressure boundary.     

Thermal stress analysis for fatigue damage evaluation at a mixing tee

Fatigue cracks have been found at mixing tees where fluids of different temperature flow in. In this study, the thermal stress at a mixing tee was calculated by the finite element method using temperature transients obtained by a fluid dynamics simulation. The simulation target was an experiment for a mixing tee, in which cold water flowed into the main pipe from a branch pipe. The cold water flowed along the main pipe wall and caused a cold spot, at which the membrane stress was relatively large. Based on the evaluated thermal stress, the magnitude of the fatigue damage was assessed according to the linear damage accumulation rule and the rain-flow procedure. Precise distributions of the thermal stress and fatigue damage could be identified. Relatively large axial stress occurred downstream from the branch pipe due to the cold spot. The variation ranges of thermal stress and fatigue damage became large near the position 20° from the symmetry line in the circumferential direction. The position of the cold spot changed slowly in the circumferential direction, and this was the main cause of the fatigue damage. The fatigue damage was investigated for various differences in the temperature between the main and branch pipes. Since the magnitude of accumulated damage increased abruptly when the temperature difference exceeded the value corresponding to the fatigue limit, it was suggested that the stress amplitude should be suppressed less than the fatigue limit. In the thermal stress analysis for fatigue damage assessment, it was found that the detailed three-dimensional structural analysis was not required. Namely, for the current case, a one-dimensional simplified analysis could be used for evaluating the fatigue damage without adopting the stress enhancement factor K_t quoted in the JSME guideline. The results also suggested that, for a precise assessment of the fatigue damage at a mixing tee, the effect of multi-axial stress on the fatigue life together with the mean stress effect should be taken into account.     

Experimental study on fluid mixing phenomena in T-pipe junction with upstream elbow

Temperature fluctuation in fluid causes high cycle thermal fatigue in structure materials according to temperature distributions and time variations. A mixing tee is one of typical geometries where temperature fluctuation occurs. In the nuclear reactors and general plants, an elbow is often used near the mixing tee and it brings biased velocity distribution and also the secondary flow. In this study, influences of upstream elbow in the main pipe were studied in a water experiment of mixing tee with the elbow. Temperature distribution in the mixing tee was measured by a movable thermocouple tree and velocity field was measured by a high speed PIV. The temperature fluctuation at the mixing tee with the upstream elbow had the large component at low frequency in comparison with the straight case. The effect of the upstream elbow is significant to evaluate the high cycle thermal fatigue in the mixing tee because of larger importance of low frequency fluctuation on the point of fluid temperature-stress conversion.     

Prediction of flow-induced excitation in a pipe conveying fluid

Experimentally it is evident that the nature of the flow-induced excitation in a pipe conveying fluid is a broadband frequency excitation. It is also observed that the amplitude of excitation decreases with increase in frequency. However, there is no method to estimate such forces. The measurement of excitation force all along the length of a pipe using the pressure transducers may be difficult or perhaps impossible. Another possibility is to measure the structural responses using vibration transducers all along the pipe length and then estimate the flow-induced excitation forces (both amplitude and phase) using a finite element (FE) model of the pipe. However, the measured degree of freedoms (dofs) are always much smaller than the dofs in FE model, hence a method has been developed that uses non-linear optimization method involving the limited measured responses together with FE model to predict the excitation forces (both amplitude and phase) acting all along the pipe conveying fluid. The predicted excitation forces can then be used to perform safety related study by assessing the pipe responses at any location whether accessible or not. The theory of the proposed method and its validation has been presented in the paper through a long straight pipe conveying fluid. Typical applications of the proposed method are also discussed.     

Numerical analysis of thermal striping induced high cycle thermal fatigue in a mixing tee

Thermal striping, characterized by turbulent mixing of two flow streams of different temperatures that result in temperature fluctuations of coolant near the pipe wall, is one of the main causes of thermal fatigue failure. Coolant temperature oscillations due to thermal striping are on the order of several Hz. Thermal striping high-cycle thermal fatigue that occurs at tee junctions is one of the topics that should be addressed for the life management of light water reactor (LWR) piping systems. This study focuses on numerical analyses of the temperature fluctuations and structural response of coolant piping at a mixing tee. The coolant temperature fluctuations are obtained from Large Eddy Simulations that are validated by experimental data. For the thermal stress fatigue analysis, a model is developed to identify the relative importance of various parameters affecting fatigue-cracking failure. This study shows that the temperature difference between the hot and cold fluids of a tee junction and the enhanced heat transfer coefficient due to turbulent mixing are the dominant factors of thermal fatigue failure of a tee junction.     

Approximate calculation method for integral of mean square value of nonstationary response

The response of the structure subjected to nonstationary random vibration such as earthquake excitation is nonstationary random vibration. Calculating method for statistical characteristics of such a response is complicated. Mean square value of the response is usually used to evaluate random response. Integral of mean square value of the response corresponds to total energy of the response. In this paper, a simplified calculation method to obtain integral of mean square value of the response is proposed. As input excitation, nonstationary white noise and nonstationary filtered white noise are used. Integrals of mean square value of the response are calculated for various values of parameters. It is found that the proposed method gives exact value of integral of mean square value of the response.     

高频地震激励对核级阀门危害性分析

利用试验和修正后的集中质量有限元模型预测安装在管道中阀门在不同频率成分地震激励下的响应,研究高频地震激励对管道中质量较大核级阀门的危害性。研究结果表明：高频地震激励对核级阀门的危害在于使阀门以其自身固有振型发生共振,此时阀门顶部取代阀门与管道连接位置成为阀门中响应最大的位置,这会导致安装于阀门顶端的驱动机构遭受苛刻的地震工况。增加管道阻尼和阀门刚度能有效降低高频激励对阀门的危害,但增加阀门刚度会导致管道响应增大。利用等效静力法对阀门进行抗震鉴定时,分析结果对阀体水平部位内力估计不足,对阀体垂直部分、阀盖等阀门上部构件的内力估计结果具有较大裕度。