Flow-induced Vibration Response And Its Uncertainty Analysis Methods And Applications For Nuclear Fuel Structure

Nuclear fuel assembly is the core and key component of nuclear power plant reactors.With the continuous increase of domestic nuclear power units,nuclear power accounts for an increasing proportion in domestic energy resources.Independent nuclear fuel research and development play a very important role in ensuring the safety of domestic nuclear fuel supply and the oversea development policy of "going out".The fretting wear of the grid and fuel rods caused by flow-induced vibration is the main cause of the Pressurized Water Reactor(PWR)fuel rod damage in recent decades.Flow-induced vibration is one of the key technical issues in independnent nuclear fuel research and development,and in-depth research must be carried out.Besides,there are also flow-induced vibration problems in many engineering fields.From a disciplinary perspective,the in-depth study of nuclear fuel structure flow-induced vibration problems also has important scientific and engineering significance.Focus on the flow-induced vibration response and flow-induced vibration response uncertainty of nuclear fuel structures,this dissertation carries out theoretical analysis,numerical calculation and experimental research to guide-independnent nuclear fuel research and development and design,and may lay a theoretical foundation for subsequent engineering applications and independent numerical software development.The research content is as follows:(1)Based on the continuous beam method and the potential flow theory,a computational model for the free vibration characteristics and added mass of the multi-constrained fuel rod structure is established.In order to realize the multi-span interaction simulation in the fuel rod structure,a multi-span continuous beam is used to simulate the multi-constrained fuel rod,of which vibration control equation in the air is established,and the overall stiffness matrix and mass matrix of the structure are given.Furthermore,through the potential flow theory,considering the influence of fluid axial flow and boundary conditions,the added mass matrix of axial flow is obtained,and the calculation models of the free vibration characteristics and added mass of the multi-constrained fuel rod structure are established.The natural frequencies and modes of free vibration of PWR fuel rods in air and axial flow are calculated,and the influence of fluid added mass,spring stiffness and spans between grids on vibration characteristics is discussed.(2)Based on the response power spectral density method,a computational model for the flow-induced vibration response of the multi-constrained fuel rod structure is established,and the flow-induced vibration response of the PWR fuel rod is numerically analyzed.Taking the axial flow force on the fuel rod as a random pulse load distributed along the axis of the fuel rod,the load power spectrum of the axial flow is given.Based on the vibration modes of the fuel rod structure free vibration in the axial flow,the power spectrum analysis method and the coupling integral method are used to establish the flow-induced vibration response computational model of the fuel rods.The flow-induced vibration response of the PWR fuel rods is numerically solved,and the influence law of the grid spans and the axial flow velocity are studied and analyzed.(3)The flow-induced vibration response of fuel-related assembly rods in axial flow is numerically calculated,and the analysis method of flow-induced vibration response is verified through experiments.Using the analysis method of fuel rod flow-induced vibration response,the vibration control equation of fuel-related assembly rods in air is established,and the added mass of axial flow is considered,and the numerical calculation results of the flow-induced vibration response of fuel-related assembly rods in axial flow are obtained.The influence of axial flow velocity on the vibration frequencies,vibration modes and flow-induced vibration responses of fuel-related assembly rods are analyzed.The correctness of the analysis method of the flow-induced vibration response is verified by the experiment results of the flow-induced vibration response of the cylindrical structure.(4)A non-contact visualization experiment for the flow-induced vibration response of nuclear fuel structures is designed,and the flow-induced vibration response of fuel-related assembly rods is obtained through the experiment.A visualization experiment program was proposed to measure the flow-induced vibration response of nuclear fuel structures,and a high-definition camera was used to record the flow-induced vibration response,and the data analysis method for the flow-induced vibration response video data was determined.Through visualization experiment,the one-dimensional and two-dimensional flow-induced vibration displacement responses of fuel-related assembly rod in the guide tube and its variation rules are obtained.The free-interference and real-time measurement of the flow-induced vibration for fuel-related assembly rod in the guide tube is achieved.The flow-induced vibration stability of fuel-related assembly rod is researched by analyzing the power spectrum density measured in the experiment.(5)A numerical scheme for the uncertainty evaluation of the flow-induced vibration response of nuclear fuel structures is established based on the interval analysis method.There are many uncertainties in the flow-induced vibration response.In order to consider the impact of uncertainty,the Chebyshev polynomial proxy model is used to construct the interval expansion function.A calculation strategy of positive and inverse analysis for the flow-induced vibration response uncertainty in nuclear fuel structures is proposed.Using interval positive analysis,the influencing factors of flow-induced vibration response uncertainty and input parameter interval are identified,and the influence law of input parameter interval on response uncertainty is determined.Based on this,the interval analysis of the inverse problem is transformed into two types of deterministic inverse problems for solution.By comparing the flow-induced vibration responses measured in the experiment with the flow-induced vibration responses predicted by analysis model,an objective function related to the input parameters is constructed,and the input parameter interval is obtained by solving the extreme value method for the objective fuction with L-M algorithm.Finally,the research work of this dissertation is summarized and prospected,and some research focuses of follow-up work are pointed out.