| Nuclear reactor coolant pump(RCP),also called the nuclear main pump,plays a vital role of driving the coolant flow in the primary circuit system,and thus is referred to as the"heart" of nuclear power station.To ensure supplying sufficient coolant flow for a period in case of sudden power outage to the pump,RCP flywheel is designed and installed on the pump motor shaft to store kinetic energy at normal working condition.During the pump coast-down process,the stored energy will keep the shaft still rotating for an expected long time so as to transport the residual heat generated in the reactor core to prevent from nuclear accident due to overheating.Apparently,the energy storage performance and safety operation of the RCP flywheel has a great impact on the safety operation of the whole nuclear power station.Nevertheless,due to the severe working environment of high temperature,high pressure,nuclear radiation and etc.,the design spaces of material selection,working speed and structure dimension are strictly limited,which makes a contradiction between flywheel design requirements of pursuing high stored energy,low weight,long lifetime and high reliability.Aiming at this problem,based on finite element analysis(FEA)and structural optimization methods,this dissertation is dedicated to the shape optimization of the radial cross-section and topology optimization of the axial rotation-plane with respect to traditional RCP flywheel comprised of solid disk with the objective to enhance the energy density(kinetic energy stored in unit mass).Moreover,structural analysis and size optimization of the multi-ring packed flywheel with tungsten alloy layer developed in the third generation nuclear power technology are carried out to reveal the mechanical principle in the segment and gap design of the tungsten alloy layer.The main content is as follows:In chapter 1,the development history of international nuclear power technology,current situation of international nuclear power industry,and the status of nuclear power technology in China are firstly summarized.Secondly,the working principles,structural characteristics and design requirements of several typical RCP flywheels in the shaft seal and canned motor pumps are introduced.The corresponding design difficulties in pursuing large rotational inertia and high energy density are also presented.Finally,based on research status of the RCP flywheel,the necessity and feasibility for the structural optimization of flywheel are analyzed.The urgent scientific and technical problems to be solved in the multi-ring packed flywheel with tungsten alloy layer developed in the third generation nuclear power technology are discussed.In chapter 2,regarding to the solid disk flywheel with low energy density,shape optimization of the flywheel radial cross-section is carried out with the objective to enhance the energy density.Using curve fitting method with control points to describe the axial thickness distribution along radius and employing ANSYS and ISIGHT to establish the FEA model and the shape optimization model,shape optimizations of the radial cross-sections of an integrated flywheel and an interference fit assembly flywheel are carried out.The optimization results under stress constraint and constant mass constraint are obtained.It is found that,optimal shapes of the two flywheel radial cross-sections show the same characteristic of "thin middle and thick ends".With respect to the interference fit flywheel,shape optimization not only significantly increases the energy density,but also improves the stress concentration in the ends of fitting surface due to interference fit assembly and reduces the stress amplitude during flywheel start-stop cycle resulting great improvement on the fatigue life.In chapter 3,with respect to the traditional design of solid disk flywheel,topology optimization of the flywheel rotation-plane is carried out with the objective to improve the energy density.Based on variable density method in OptiStruct,topology optimization model of the flywheel rotation-plane is established.Firstly,the flywheel rotation-plane is divided into three regions,called inner ring,middle ring and outer ring respectively.The inner ring and outer ring are fixed to keep the structural integrity of flywheel boundary and the middle ring is defined as design domain.Then,through topology optimization,the material with low utilization rate to rotational inertia in the middle ring(design domain)will be removed to achieve the goal of enhancing flywheel energy density.Finally,topology optimization results under minimum member size(MMS)control,rotational symmetry constraint,stress constraint and volume fraction constraint are obtained,and the corresponding influence rules of these control and constraints on flywheel topological design are revealed.This work may provide valuable guidance for the topological design of energy storage flywheel in engineering.In chapter 4,regarding to the novel design of the multi-ring packed flywheel with tungsten alloy layer,the mechanical principle in the segment and gap design of tungsten alloy layer is studied.Based on FEA method,the stress under interference fit assembly force,centrifugal force and thermal loading of the flywheel comprised of inner hub,tungsten alloy layer and outer ring in the canned motor pump is determined,and the stress characteristics of two flywheels with integrated tungsten alloy layer and tungsten alloy segments are compared respectively.Results show that,under high temperature working condition,mismatch of the thermal expansion coefficients between the stainless steel and tungsten alloy causes thermal stress in flywheel,and particularly gives rise to a large circumferential tensile stress in the tungsten alloy layer.It is also found that,segment design of the tungsten alloy layer can efficiently relieve the thermal stress.Subsequently,the optimal number for tungsten alloy segments and the optimal gap dimension between segments are obtained.The work in this chapter reveals the mechanical principle in the multi-ring packed flywheel with tungsten alloy layer,and provides theoretical foundation for the digestion of foreign technology and the proposal of our own innovative flywheel design.In chapter 5,aiming to enhance the energy storage performance of the multi-ring packed flywheel with tungsten alloy layer,optimization design of the radial dimensions of flywheel layers and the initial magnitude of interference fit assembly is studied.Through the design of experiment(DOE)method and the radial basis function(RBF)approximation model,optimization design process of the radial dimensions of the flywheel layers and the magnitude of interference fit between the tungsten alloy layer and the outer retainer meeting the requirements of structural strength safety and sufficient contact pressure is carried out.Finally,the optimal range of the magnitude of interference fit and the optimal dimensions of the flywheel layers are obtained with the objectives of maximizing energy density and rotational inertia respectively.According to the optimization designs of the multi-ring packed flywheel,the energy density is increased by 11.6%and the rotational inertia is increased by 80.8%compared with the traditional design of solid disk flywheel.This chapter may provide guidance for the structural optimization on energyˇstorage performance of the multi-ring packed flywheel with tungsten alloy layer. |
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